JP2013065381A - Magnetic recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium for high density recording, the medium having excellent electromagnetic conversion characteristics.SOLUTION: The magnetic recording medium has a nonmagnetic layer containing a nonmagnetic powder and a binder, and a magnetic layer containing a ferromagnetic powder and a binder, in this order on a nonmagnetic support body. The magnetic layer further contains a compound expressed by general formula A. In general formula A, Ar represents an aryl group optionally having a substituent; X represents a divalent connecting group; and Rand Reach independently represent a hydrogen atom or a substituent. The ferromagnetic powder is a hexagonal ferrite powder. The binder in the magnetic layer is a mixture of a vinyl chloride copolymer, a polyurethane resin and polyisocyanate. The polyurethane resin has a glass transition temperature in the range from 90 to 130°C and a storage modulus of 2.5 to 5.0 GPa at 80°C. The nonmagnetic layer is a radiation cured layer obtained by curing a radiation curable composition containing a nonmagnetic powder and a binder component with radiation. The binder component comprises a radiation-curable vinyl chloride copolymer and a radiation-curable polyurethane resin. Both of the radiation-curable vinyl chloride copolymer and the radiation-curable polyurethane resin have a glass transition temperature in the range from 30 to 100°C.

Description

  The present invention relates to a magnetic recording medium and a manufacturing method thereof, and more particularly to a magnetic recording medium for high density recording having excellent electromagnetic conversion characteristics and a manufacturing method thereof.

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

  In order to obtain good electromagnetic conversion characteristics in a high-density recording region, it is effective to use a fine particle magnetic material and to disperse the fine particle magnetic material highly to improve the smoothness of the magnetic layer surface.

As a means for improving the dispersibility of the magnetic material, for example, as described in Patent Document 1, a method of incorporating a polar group such as an SO ₃ Na group into a binder is widely used. Various compounds have been proposed as additives for imparting a dispersion effect. Among them, phenylphosphonic acid described in Patent Document 2 is widely used as a dispersant in magnetic recording media.

Japanese Patent Laid-Open No. 2003-132931 JP 2007-257713 A

In recent years, there is a tendency for magnetic materials to become finer and finer for higher density recording. Conventionally, a ferromagnetic metal powder has been mainly used for the magnetic layer of a magnetic recording medium. However, in a magnetic recording medium for high density recording including a fine particle magnetic material, a hexagonal ferrite powder is used rather than a ferromagnetic metal powder. It is advantageous. Because hexagonal ferrite powder has high crystal magnetic anisotropy derived from the crystal structure and excellent thermal stability, it can maintain excellent magnetic properties suitable for magnetic recording even when miniaturized. In addition, a magnetic recording medium using hexagonal ferrite powder for the magnetic layer is excellent in high density characteristics due to its perpendicular component.
Further, as described above, in order to obtain good electromagnetic conversion characteristics in the high-density recording region, the fine particle magnetic material should be used and the fine particle magnetic material should be highly dispersed. As a means for improving the dispersibility of the ultrafine particle magnetic material, it is an effective means to introduce a polar group into the binder as described in Patent Document 1, but when the amount of the polar group in the binder becomes excessive, Conversely, dispersibility may be reduced.
Therefore, the present inventor has improved the dispersibility of the hexagonal ferrite powder by using the hexagonal ferrite powder advantageous for high-density recording together with phenylphosphonic acid, which has been used as a dispersant having a high effect of improving dispersibility. Although it was thought that excellent electromagnetic conversion characteristics could be obtained in the high-density recording area, it was contrary to expectations and dispersibility and electromagnetic conversion characteristics could not be improved.

  An object of the present invention is to provide a magnetic recording medium for high-density recording having excellent electromagnetic conversion characteristics.

As a result of intensive studies to achieve the above object, the present inventor has obtained the following new knowledge.
(1) Ferromagnetic metal powders and hexagonal ferrite powders are widely used as ferromagnetic powders in magnetic recording media, but dispersants that exhibit good dispersibility in ferromagnetic metal powders are hexagonal ferrite powders. Similarly, it does not always show good dispersibility. For example, the above-described phenylphosphonic acid is insufficient as a dispersant for hexagonal ferrite powder in a magnetic recording medium for high density recording that requires high dispersibility. Therefore, in order to enhance electromagnetic conversion characteristics in a magnetic recording medium for high-density recording using hexagonal ferrite powder, a dispersant suitable for hexagonal ferrite powder should be selected and used.
(2) In a high-density recording area in which an ultrafine particle magnetic material is used, fine head deposits that have not been a problem in the past cause a decrease in output, thereby reducing electromagnetic conversion characteristics.
Therefore, the present inventor has repeatedly studied a compound that functions as a dispersant capable of highly improving the dispersibility of the hexagonal ferrite powder as a countermeasure to the above (1), and has developed a carboxyl group represented by the general formula A described later. It has been found that the contained compound has excellent properties meeting the above requirements.
Furthermore, according to the examination of the inventor regarding the above (2),
A small amount of scraping on the surface of the magnetic layer during travel (coating material destruction) is the cause of head deposits, and
Using a polyurethane resin with a high glass transition temperature and a high storage elastic modulus in a high temperature region as a binder component of the magnetic layer will be a countermeasure against head deposits,
Became clear.
This point will be described in more detail. By using a polyurethane resin having a high glass transition temperature (high Tg) as a binder component of the magnetic layer, it is possible to improve the running durability by increasing the coating film strength, for example. -319011, etc. However, as a result of investigations by the present inventors, merely using a high Tg polyurethane resin is insufficient for measures against head deposits. Therefore, the present inventor has evaluated the thermal characteristics of the polyurethane resin in detail, and found that the storage elastic modulus E ′ in the high temperature region is reversed from Tg. Even if the polyurethane resin has a high Tg, it is stored in the high temperature region. When the elastic modulus E ′ is low, a conclusion is reached that a small amount of scraped material on the surface of the magnetic layer cannot be sufficiently suppressed. The relationship between the surface scraped material, Tg, and storage elastic modulus can be explained as follows. Since the storage elastic modulus is greatly reduced at a temperature of Tg or higher, the polymer has a reduced strength. Polyurethanes are generally composed of multiple types of monomers for a variety of purposes such as Tg and solubility. However, when high Tg / low Tg monomers are used in combination, Tg is affected by high Tg monomers. Although it becomes high, storage elastic modulus falls from the temperature lower than Tg under the influence of a low Tg monomer. For this reason, even if the same Tg is exhibited, the storage elastic modulus in the high temperature region does not become an equivalent value, and therefore it is necessary to define the storage elastic modulus in the high temperature region together with Tg.
However, on the other hand, a magnetic layer formed using a binder having a high glass transition temperature and a high storage elastic modulus at high temperature cannot obtain sufficient surface smoothness and still obtain excellent electromagnetic conversion characteristics. It turned out to be difficult. In this regard, the inventor considered that the nonmagnetic layer located below the magnetic layer contributed to the decrease in surface smoothness of the magnetic layer, and further studied. As a result, it has been newly found that the surface smoothness of the magnetic layer can be enhanced by forming the nonmagnetic layer from a radiation curable resin having a low Tg. This is because the nonmagnetic layer can be a radiation-cured layer to suppress interfacial mixing between the nonmagnetic layer and the magnetic layer, and the lower layer is composed of a low Tg binder to ensure flexibility of the lower layer in the calendar temperature range. This is because the calendar formability is improved.
The present invention has been completed based on the above findings.

That is, the above object has been achieved by the following means.
[1] A magnetic recording medium having a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder in this order on a nonmagnetic support,
The magnetic layer has the following general formula A:
[In General Formula A, Ar represents an aryl group which may have a substituent, X represents a divalent linking group, and R ¹¹ and R ¹² each independently represent a hydrogen atom or a substituent. ]
A compound represented by the formula:
The ferromagnetic powder is a hexagonal ferrite powder,
The binder of the magnetic layer is a mixture of a vinyl chloride copolymer, a polyurethane resin and a polyisocyanate, and the polyurethane resin has a glass transition temperature in the range of 90 to 130 ° C. and a storage elastic modulus at 80 ° C. of 2. In the range of 5 to 5.0 GPa
The nonmagnetic layer is a radiation curable layer obtained by radiation curing a radiation curable composition containing a nonmagnetic powder and a binder component, and the binder component is a radiation curable vinyl chloride copolymer. And a radiation curable polyurethane resin, and both the radiation curable vinyl chloride copolymer and the radiation curable polyurethane resin have a glass transition temperature in the range of 30 to 100 ° C. .
[2] The magnetic recording medium according to [1], wherein the hexagonal ferrite powder has an average plate diameter of 40 nm or less.
[3] The compound represented by the general formula A is represented by the following general formula A1:
[In General Formula A1, Z is a hydrogen atom or a hydroxyl group, and R ¹¹ , R ¹² , and X have the same meanings as those in General Formula A, respectively. ]
The magnetic recording medium according to [1] or [2], which is a compound represented by:
[4] The compound represented by the general formula A is selected from the group consisting of N-phenylglycine, N- (4-hydroxyphenyl) glycine, phenoxyacetic acid, 2-phenoxypropionic acid and 3-phenylpropionic acid [ The magnetic recording medium according to any one of [1] to [3].
[5] The radiation curable vinyl chloride copolymer according to [1] to [4], wherein the radiation curable vinyl chloride copolymer is a radiation curable vinyl chloride copolymer including a structural unit represented by the following general formula (1). Magnetic recording medium.
[In General Formula (1), R ¹ represents a hydrogen atom or a methyl group, and L ¹ represents a divalent linking group represented by the following Formula (2), Formula (3), or the following General Formula (4). . ]
[In General Formula (4), R ⁴¹ represents a hydrogen atom or a methyl group. ]
[6] The radiation curable polyurethane resin is a radiation curable polyurethane resin obtained from a sulfonic acid (salt) group-containing polyol compound represented by the following general formula (2) as a raw material [1] to [5]. A magnetic recording medium according to any one of the above.
[In General Formula (2), X represents a divalent linking group, and R ¹⁰¹ and R ¹⁰² each independently represents an alkyl group having 2 or more carbon atoms having at least one hydroxyl group or carbon having at least one hydroxyl group. It represents an aralkyl group having a number of 8 or more, and M ¹ represents a hydrogen atom or a cation. ]
[7] The magnetic recording medium according to any one of [1] to [6], wherein the polyurethane resin contained in the binder of the magnetic layer is a polyester polyurethane resin.
[8] The magnetic recording medium according to any one of [1] to [7], wherein the binder of the magnetic layer includes 10 to 100 parts by mass of polyisocyanate with respect to 100 parts by mass of the vinyl chloride copolymer.
[9] The magnetic layer according to any one of [1] to [8], wherein the magnetic layer contains the compound represented by the general formula A in an amount of 1.5 to 10 parts by mass per 100 parts by mass of the hexagonal ferrite powder. recoding media.
[10] A method of manufacturing a magnetic recording medium according to any one of [1] to [9],
After the application and radiation curing of the radiation curable composition, a magnetic layer is formed on the formed radiation cured layer, and then a calendar treatment is performed at a calendar temperature equal to or higher than the glass transition temperature of the radiation cured layer. The manufacturing method.

  According to the present invention, it is possible to provide a magnetic recording medium for high-density recording that can exhibit excellent electromagnetic conversion characteristics over a long period of time.

The present invention relates to a magnetic recording medium having a nonmagnetic layer containing nonmagnetic powder and a binder and a magnetic layer containing ferromagnetic powder and a binder in this order on a nonmagnetic support. The magnetic recording medium of the present invention is
(1) The magnetic layer contains the compound represented by the general formula A together with the hexagonal ferrite powder.
(2) The binder of the magnetic layer is a mixture of a vinyl chloride copolymer, a polyurethane resin and a polyisocyanate, and the polyurethane resin has a glass transition temperature in the range of 90 to 130 ° C and a storage elasticity at 80 ° C. The rate ranges from 2.5 to 5.0 GPa,
(3) The nonmagnetic layer is a radiation curable layer obtained by radiation curing a radiation curable composition containing a nonmagnetic powder and a binder component, and the binder component is a radiation curable vinyl chloride type. A copolymer and a radiation-curable polyurethane resin are included, and (4) the radiation-curable vinyl chloride copolymer and the radiation-curable polyurethane resin both have a glass transition temperature in the range of 30 to 100 ° C.
As described above, the magnetic recording medium of the present invention can exhibit excellent electromagnetic conversion characteristics over a long period of time by combining the above (1) to (4).
Hereinafter, the magnetic recording medium of the present invention will be described in more detail.

Magnetic layer
(i) Binder In the magnetic recording medium of the present invention, the binder of the magnetic layer is a mixture of vinyl chloride copolymer, polyurethane resin and polyisocyanate. This is because it is difficult to obtain the appropriate flexibility required for a magnetic recording medium with a vinyl chloride resin alone, and when using a magnetic material finely divided for high density recording with a polyurethane resin alone, This is because it is difficult to disperse well. In the magnetic recording medium of the present invention, the polyurethane resin used for imparting appropriate flexibility to the magnetic layer has a glass transition temperature in the range of 90 to 130 ° C. and a storage elastic modulus at 80 ° C. (hereinafter simply referred to as “ A material having a storage elastic modulus) of 2.5 to 5.0 GPa is used. When the polyurethane resin has a glass transition temperature of 90 ° C. or higher and a storage elastic modulus at 80 ° C. of 2.5 GPa or higher, the occurrence of head stains due to scraping of the magnetic layer surface (coating material destruction) during running Can be suppressed. On the other hand, when the glass transition temperature of the polyurethane resin exceeds 130 ° C. and the storage elastic modulus at 80 ° C. exceeds 5.0 GPa, the polymer becomes too rigid and it is difficult to ensure solvent solubility. From the viewpoint of achieving both suppression of head contamination and solvent solubility, the storage modulus of the polyurethane resin at 80 ° C. is preferably in the range of 2.5 to 3.0 GPa. The glass transition temperature and the storage elastic modulus in the present invention are both values determined by dynamic viscoelasticity measurement. For specific measurement methods, the description of Examples described later can be referred to.
As will be described later, in the present invention, the nonmagnetic layer is a radiation-cured layer, but the magnetic layer may be formed by either heat curing or radiation curing. In the case of thermosetting, it is more preferable because the Tg and storage elastic modulus of the coating film (magnetic layer) are further improved by the generated urethane bond. That is, in the magnetic layer, the polyurethane resin, the vinyl chloride copolymer, and the polyisocyanate may react with each other in the mixture to form a reaction product.

  Polyurethane resins having a glass transition temperature and a storage elastic modulus within the above ranges can be synthesized by known methods, and some are commercially available. In general, a polyurethane resin not containing a polyether component, for example, a polyester polyurethane resin has a high glass transition temperature and a high storage elastic modulus at a high temperature, and is preferable as a polyurethane resin used in the magnetic layer in the present invention. For such polyurethane resin, reference can be made to, for example, paragraphs [0004] to [0019] of Japanese Patent No. 3085408, paragraphs [0012] to [0025] of JP-A-2005-293769, and examples thereof.

  The binder constituting the magnetic layer of the magnetic recording medium of the present invention is a mixture of the polyurethane resin having the above thermal characteristics, a vinyl chloride copolymer and polyisocyanate. From the viewpoint of achieving both suppression of occurrence of surface scraping and dispersibility, the mixing ratio of the polyurethane resin and the vinyl chloride copolymer is polyurethane resin: vinyl chloride resin = 20: 80 to 60:40 (mass ratio). It is preferable to set it as the range.

  As the vinyl chloride copolymer used in combination with the polyurethane resin, it is preferable to use a vinyl chloride copolymer that can favorably maintain the properties of the coating film (magnetic layer) provided by the polyurethane resin. From this point of view, a preferable vinyl chloride copolymer includes a vinyl chloride copolymer having a sulfonic acid (salt) group, a hydroxyl group and an epoxy group in the molecule, as described in, for example, JP-B-1-26627. Coalescence can be mentioned. A vinyl chloride copolymer having a sulfonic acid (salt) group in the molecule is preferred in order to further improve the dispersibility of the magnetic substance.

The polyurethane resin and vinyl chloride resin described above have a number average molecular weight (polystyrene conversion value measured by GPC method) of, for example, 1,000 to 200,000, preferably 10,000 to 100,000. As for the polyurethane resin and vinyl chloride resin, in order to obtain a more excellent dispersibility and durability, if _{necessary, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) ₂ , -O-P = O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, SH, CN, It is also possible to introduce at least one polar group selected from the above by copolymerization or addition reaction. The amount of such a polar group can be, for example, 10 ⁻¹ to 10 ⁻⁸ mol / g, and preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  Usually, the magnetic layer component includes a so-called curing agent (or a crosslinking agent) capable of forming a crosslinked structure with the binder resin in order to increase the coating strength. In the present invention, the “binder” includes such a curing agent. In the present invention, polyisocyanate is used as the curing agent in the magnetic layer. By using a polyisocyanate together with a polyurethane resin and a vinyl chloride copolymer, it is possible to improve the thermal characteristics of the magnetic layer and to suppress the occurrence of surface scrapings. From the viewpoint of controlling the glass transition temperature as a magnetic layer and the storage elastic modulus at 80 ° C., the preferred amount of polyisocyanate used is in the range of 10 to 100 parts by mass with respect to 100 parts by mass of the vinyl chloride copolymer. More preferably, it is the range of 10-60 mass parts. The amount of binder in the magnetic layer is preferably 10 to 25 parts by mass with respect to 100 parts by mass of the ferromagnetic powder including the curing agent. In the present invention, the glass transition temperature and the storage elastic modulus at 80 ° C. of the binder (mixture of binder components) used for forming the magnetic layer are controlled by suppressing the abrasion of the magnetic layer surface during running and calendering properties. From the viewpoint of achieving both, it is preferable that the glass transition temperature is in the range of 80 to 130 ° C, and the storage elastic modulus at 80 ° C is in the range of 1.5 to 3.0 GPa.

  Examples of polyisocyanates include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate and the like. Moreover, the product of these isocyanates and polyalcohol, the polyisocyanate produced | generated by condensation of isocyanate, etc. can be used. Curing agents can be used alone or in combination of two or more utilizing the difference in curing reactivity. Among these, trifunctional or higher polyisocyanates are more preferable because they can be three-dimensionally crosslinked. Any of the polyisocyanates used in the present invention is commercially available.

(ii) Ferromagnetic powder As described above, in the present invention, hexagonal ferrite powder suitable for high density recording is used as the ferromagnetic powder. In order to achieve high density recording, it is preferable to use a hexagonal ferrite powder contained in the magnetic layer having an average plate diameter of 40 nm or less. The average plate diameter is preferably 10 nm or more from the viewpoint of obtaining stable magnetization without thermal fluctuation. From the viewpoint of achieving both magnetization stability and high density recording, the average plate diameter is more preferably in the range of 10 to 35 nm.

The average plate diameter of the hexagonal ferrite powder can be measured by the following method.
The particles of hexagonal ferrite powder are photographed using a Hitachi transmission electron microscope H-9000 type, and the particles are photographed at a photographing magnification of 100,000. The target magnetic material is selected from the particle photograph, the outline of the powder is traced with a digitizer, and the particle size is measured with the image analysis software KS-400 manufactured by Carl Zeiss. The plate diameter of 500 particles is measured. Let the average value of the plate diameter measured by the said method be an average plate diameter of hexagonal ferrite powder.

In the present invention, the sizes of various powders (hereinafter referred to as “powder size”) are as follows: (1) The shape of the powder is needle-like, spindle-like, or columnar (however, the height is greater than the maximum major axis of the bottom surface). In the case of large), it is represented by the length of the long axis constituting the powder, that is, the length of the long axis. Is smaller than the maximum longest diameter of the bottom surface), and is represented by the maximum longest diameter of the plate surface or bottom surface. (3) The shape of the powder is spherical, polyhedral, unspecified, etc., and the powder is composed of the shape. When the major axis to be identified cannot be specified, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by carrying out the measurement as described above for 500 primary particles. Primary particles refer to an independent powder without aggregation.

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

From the viewpoint of high density recording, the BET specific surface area of the hexagonal ferrite powder is preferably 10 m ² / g or more and 200 m ² / g or less. Regarding other details of the hexagonal ferrite powder, paragraphs [0105] and [0107] to [0109] of JP-A-2009-96798 can be referred to.

(iii) Compound represented by general formula A
The compound represented by the general formula A (hereinafter, also referred to as “compound A”) can exhibit a high dispersibility improving effect on the hexagonal ferrite powder. By using the compound represented by the general formula A together with the hexagonal ferrite powder, a magnetic recording medium having high surface smoothness and exhibiting excellent electromagnetic conversion characteristics can be obtained.

[In General Formula A, Ar represents an aryl group which may have a substituent, X represents a divalent linking group, and R ¹¹ and R ¹² each independently represent a hydrogen atom or a substituent. ]

  Hereinafter, Formula A will be described in more detail.

In general formula A, X represents a divalent linking group, for example, one or a group selected from the group consisting of — (CH═CH) —, —O—, —NR ^a —, and — (CR ^b R ^c ) — It is a divalent linking group comprising a combination of two or more. Here, R ^a , R ^b and R ^c are each independently a hydrogen atom or an alkyl group. When R ^a , R ^b , and R ^c are alkyl groups, the alkyl group may be linear or branched, and is preferably an alkyl group having 1 to 5 carbon atoms, such as a methyl group, an ethyl group, or a propyl group. And more preferably a methyl group.

In compound A, the carboxyl group which is an adsorbing functional group is linked to the aryl group via —X—CR ¹¹ R ¹² —, so that it is adsorbed on the hexagonal ferrite particle surface by the carboxyl group, It is considered that the high dispersibility improvement effect can be exerted on the hexagonal ferrite powder because it is possible to hydrophobize a wide range and interact with the binder in a larger volume. In addition, since compound A has excellent compatibility with the binder, the affinity between the hexagonal ferrite particles and the binder is increased by being adsorbed on the surface of the hexagonal ferrite particles by the carboxyl group which is an adsorption functional group. be able to. On the other hand, a compound having only a phenolic hydroxyl group as an adsorptive functional group, such as 4-t-butylphenol used in a comparative example described later, has poor adsorptivity to the hexagonal ferrite particle surface, and a partially free compound is formed on the coating film. This may cause a decrease in durability. In addition, since the carboxyl group and the hexagonal ferrite particles are adsorbed by an acid-base interaction, the adsorptivity to the magnetic substance increases as the acidity of the carboxyl group increases. In this regard, when the divalent linking group represented by X contains an oxygen atom or a nitrogen atom (hereinafter referred to as “hetero atom”), the acidity of the carboxyl group is affected by the effect of the −I effect. This is preferable because the degree becomes high. Moreover, when X consists of one or a combination of two or more of — (CH═CH) —, the electron withdrawing effect of the aryl group can be propagated to the carboxyl group due to the influence of the resonance effect, and thus the effect of increasing the acidity of the carboxyl group From the viewpoint of. When X does not contain-(CH = CH)-, if the number of carbons in the main chain portion of the divalent linking group represented by X is 2 or less, it is affected by the -I effect of the aryl group. Since the acidity of a carboxyl group is large compared with normal aliphatic carboxylic acid, it is preferable.

  In the case where the divalent linking group represented by X does not contain a heteroatom, and in the case where it contains a heteroatom, the divalent linking group represented by X is selected from the viewpoint of the stability of the compound and the acidity of the carboxyl group. The number of carbon atoms is preferably 1 or more and 3 or less. If the carbon number is 1 or more, the effect of hydrophobizing a wider range on the magnetic material can be satisfactorily exhibited. If it is 3 or less, the distance between the aryl group and the carboxyl group is appropriate, and the aryl group It is preferable since the acidity of the carboxyl group is increased due to the electron withdrawing effect and the adsorptivity to the hexagonal ferrite particles is increased. Since the hetero atom is a hydrophilic atom as compared with the carbon atom, from the viewpoint of hydrophobizing the hexagonal ferrite particle, it is preferable that X contains one hetero atom.

  In general formula A, Ar represents an aryl group. The aryl group represented by Ar may have a substituent or may be unsubstituted. Examples of the substituent include an alkyl group (for example, an alkyl group having 1 to 6 carbon atoms), a hydroxyl group, an alkoxyl group (for example, an alkoxyl group having 1 to 6 carbon atoms), a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom) and the like. Can be mentioned. Here, the “carbon number” in the case of having a substituent means the carbon number of a portion not including the substituent. Further, in the present invention, “to” indicates a range including numerical values described before and after that as a minimum value and a maximum value, respectively. The aryl group represented by Ar is preferably a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, for example, a phenyl group, a hydroxyphenyl group, a naphthyl group, or a hydroxynaphthyl group, from the viewpoint of the effect of improving dispersibility. More preferred are a phenyl group and a hydroxyphenyl group.

In General Formula A, R ¹¹ and R ¹² each independently represent a hydrogen atom or a substituent. Examples of the substituent include various substituents exemplified above. From the viewpoint of improving dispersibility, an alkyl group is preferable, an alkyl group having 1 to 6 carbon atoms is more preferable, and an alkyl group having 1 to 3 carbon atoms is preferable. Alkyl groups are even more preferred, and methyl groups are particularly preferred.

As a preferable aspect of the compound A demonstrated above, following general formula A1:
[In General Formula A1, Z is a hydrogen atom or a hydroxyl group, and R ¹¹ , R ¹² , and X have the same meanings as those in General Formula A, respectively. ]
Preferred examples of the compound include N-phenylglycine, N- (4-hydroxyphenyl) glycine, phenoxyacetic acid, 2-phenoxypropionic acid and 3-phenylpropionic acid. Can do.

Further, the compound represented by the general formula A is preferably not a polymer compound used as a binder. This is not desirable from the viewpoint of high-density recording because the filling rate of the magnetic material decreases as the additive component used in the magnetic layer increases. This is because addition is required. In order to obtain an excellent dispersibility improvement effect with a small addition amount, the compound A preferably has a molecular weight of 1000 or less, more preferably 500 or less, and even more preferably 200 or less. Further, the lower limit of the molecular weight of Compound A is not particularly limited, but considering the molecular weight of each part of Ar, X, R ¹¹ , R ¹² , and carboxyl group contained in the structure, the lower limit is, for example, 100 or more, Or it can be 150 or more.

  The magnetic recording medium of the present invention preferably contains compound A in the magnetic layer in an amount of 1.5 parts by mass or more per 100 parts by mass of hexagonal ferrite powder from the viewpoint of improving dispersibility. As described above, since it is desirable to increase the filling rate of the ferromagnetic powder from the viewpoint of high density recording, it is preferable to reduce the additive amount within a range in which the effect can be exhibited. From the above viewpoint, the content of the compound A in the magnetic layer is preferably 10 parts by mass or less per 100 parts by mass of the hexagonal ferrite powder. From the viewpoint of achieving both the dispersibility and the filling rate of the hexagonal ferrite powder, the content of the compound A in the magnetic layer is more preferably 3 to 10 parts by mass per 100 parts by mass of the hexagonal ferrite powder.

  When preparing the magnetic layer coating solution, compound A and other magnetic layer components such as hexagonal ferrite powder and binder may be mixed at the same time or may be added separately in two or more steps. . For example, a method of simultaneously adding Compound A, hexagonal ferrite powder and binder, a method of mixing and dispersing Compound A and hexagonal ferrite powder in advance, and then mixing with the binder can be taken. Either method can be adopted.

(iv) Additives Additives other than the dispersant can be added to the magnetic layer as necessary. Examples of additives include abrasives, lubricants, dispersion aids, antifungal agents, antistatic agents, antioxidants, and solvents. For details of specific examples and the like of the above additives, reference can be made, for example, to paragraphs [0111] to [0115] of JP2009-96798A.

  Carbon black can be added to the magnetic layer as necessary. JP, 2011-102372, A paragraph [0116] can be referred to for details of carbon black which can be used for a magnetic layer.

  These additives used in the present invention can be properly used in the magnetic layer and further in the nonmagnetic layer described later as needed. All or a part of the additives used in the present invention may be added in any step during the production of the coating liquid for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, when adding at a kneading step with a ferromagnetic powder, a binder and a solvent, when adding at a dispersing step, when adding after dispersing, when adding just before coating, etc. There is.

Nonmagnetic Layer The magnetic recording medium of the present invention has a nonmagnetic layer that is a radiation-cured layer obtained by radiation-curing a radiation-curable composition containing a non-magnetic powder and a binder component. For example, a non-magnetic layer (radiation-cured layer) is applied to the surface of a non-magnetic support under running by applying a non-magnetic layer coating solution (radiation curable composition) to a predetermined thickness and radiation curing. The magnetic recording medium of the present invention can be obtained by forming the magnetic layer and then applying the magnetic layer coating liquid so as to have a predetermined film thickness to form the magnetic layer. In general, when a lower non-magnetic layer coating solution and an upper magnetic layer coating solution are sequentially applied in multiple layers, the non-magnetic layer may partially dissolve in the solvent contained in the magnetic layer coating solution. Here, if the non-magnetic layer is a radiation-cured layer formed from a radiation-curable composition, the binder component is polymerized and crosslinked in the non-magnetic layer by irradiation, resulting in a high molecular weight. Dissolution in the solvent contained can be suppressed or reduced. This makes it possible to improve the surface smoothness of the magnetic layer located in the upper layer.

In the present invention, as the binder component contained in the radiation curable composition, a radiation curable vinyl chloride copolymer and a radiation curable polyurethane resin having a glass transition temperature in the range of 30 to 100 ° C. are used. To do. When the glass transition temperature is 100 ° C. or lower, the flexibility of the lower layer can be increased, and therefore, the cushioning property of the lower layer can be increased, thereby improving the calendar moldability. In the magnetic recording medium of the present invention, the magnetic layer has the above-described configuration in order to suppress the abrasion of the surface of the magnetic layer during traveling as described above, but this reduces the calendar moldability of the magnetic layer itself. Therefore, in the present invention, by providing flexibility to the nonmagnetic layer, that is, by using a binder component having a glass transition temperature of 100 ° C. or less, the reduction in calenderability of the magnetic layer is compensated. Can do. However, if the glass transition temperature is less than 30 ° C., the nonmagnetic layer is too flexible and the running stability is lowered, so the lower limit is set to 30 ° C. From the viewpoint of achieving both running stability and calendar moldability, the glass transition temperature is preferably 55 to 100 ° C.
In addition, the glass transition temperature of the nonmagnetic layer formed from the binder component is preferably in the range of 30 ° C to 85 ° C from the viewpoint of achieving both running stability and calendar moldability, The range is more preferable, and the range of 65 to 85 ° C. is even more preferable.

The radiation curable vinyl chloride copolymer and radiation curable polyurethane resin used as the binder component of the nonmagnetic layer are not particularly limited as long as they have a glass transition temperature in the above range. For example, the radiation curable vinyl chloride copolymer and polyurethane resin described in JP-A No. 2004-352804 can be used, and details thereof are described in paragraphs [0012] to [0019] of the same publication and the implementation thereof. See examples.
Among them, as a radiation curable vinyl chloride copolymer preferable as a binder component of the nonmagnetic layer in the present invention, a radiation curable vinyl chloride copolymer containing a structural unit represented by the following general formula (1) ( The radiation curable polyurethane resin is a radiation obtained from a sulfonic acid (salt) group-containing polyol compound represented by the following general formula (2) as a raw material. A curable polyurethane resin (hereinafter referred to as “polyurethane resin B”) can be exemplified.
Hereinafter, the copolymer A and the polyurethane resin B will be described.

(i) Copolymer A
The copolymer A includes a structural unit represented by the following general formula (1).

[In General Formula (1), R ¹ represents a hydrogen atom or a methyl group, and L ¹ represents a divalent linking group represented by the following Formula (2), Formula (3), or the following General Formula (4). . ]
[In General Formula (4), R ⁴¹ represents a hydrogen atom or a methyl group. ]

  The copolymer A containing the structural unit represented by the general formula (1) has high curability by irradiation, and this reduces the surface smoothness of the magnetic layer due to dissolution of the nonmagnetic layer in the magnetic layer coating solution. It is thought that it contributes to suppressing more effectively. This high curability is considered to be due to the high reactivity of the radiation-curable functional group contained therein and the appropriate flexibility of the structure. That is, in the structure represented by the following general formula (1), the (meth) acryloyloxy group surrounded by a round frame line is a group having particularly high reactivity among the radiation curable functional groups, and a square frame line. It is presumed that the reason why the copolymer A exhibits high curability upon irradiation with radiation is that the connecting portion with the main chain surrounded by (ii) has sufficient flexibility to form a crosslinked structure. On the other hand, even if a resin having a highly reactive radiation curable functional group is introduced, if the structure is rigid, the radiation curable functional groups cannot be sufficiently close to each other. It is considered difficult to form a crosslinked structure.

[Details of the general formula (1) will be described later. ]

The copolymer A is a vinyl chloride copolymer having a radiation curable functional group capable of causing a curing reaction (crosslinking reaction) upon irradiation with radiation, and at least one of the radiation curable functional groups is represented by the following general formula (1). (Meth) acryloyloxy group contained in the structural unit represented by As described above, the copolymer A is high at the time of radiation irradiation because the (meth) acryloyloxy group having high reactivity is bonded to the main chain via a linking portion having appropriate flexibility. It is assumed that curability can be exhibited.
In the present invention, “(meth) acryloyloxy group” includes a methacryloyloxy group and acryloyloxy group, and “(meth) acrylate” includes methacrylate and acrylate.
Moreover, the copolymer A can also contain groups other than a (meth) acryloyloxy group as a radiation-curable functional group. Such a radiation curable functional group is preferably a radical polymerizable carbon-carbon double bond group, and more preferably an acrylic double bond group from the viewpoint of reactivity. Here, the acrylic double bond group means residues such as acrylic acid, acrylic acid ester, acrylic acid amide, methacrylic acid, methacrylic acid ester, and methacrylic acid amide.

  Hereinafter, Formula (1) will be described in more detail.

In general formula (1), R ¹ represents a hydrogen atom or a methyl group. High curability can be obtained regardless of whether R ¹ is a hydrogen atom or a methyl group, but R ¹ is preferably a methyl group from the viewpoint of availability.

In General Formula (1), L ¹ represents a divalent linking group represented by the following Formula (2), Formula (3), or the following General Formula (4). In the general formula (4), R ⁴¹ represents a hydrogen atom or a methyl group, and R ⁴¹ is preferably a hydrogen atom from the viewpoint of availability. In general, from the viewpoint of curability, a divalent linking group represented by formula (3) or general formula (4) is preferable, and from the viewpoint of cost, formula (2) or The divalent linking group represented by (3) is preferred.

  From the viewpoint of further enhancing the curability during radiation irradiation, the copolymer A preferably contains 1 mol% or more of the structural unit represented by the general formula (1) with 100 mol% of all polymerized units. Although the upper limit of the content rate of the structural unit represented by the general formula (1) in the copolymer A is not particularly limited, for example, even if it is about 5 mol% or less, the effect can be sufficiently exhibited. . The copolymer A can contain the structural unit represented by the general formula (1), preferably 1 mol% or more and 50 mol% or less per 100 mol% of all the polymerization units. The copolymer A can exhibit even higher curability by including the structural unit represented by the general formula (1) at the above content.

  Since copolymer A is a vinyl chloride copolymer, it contains a structural unit derived from vinyl chloride (the following structural unit) together with the structural unit represented by general formula (1).

  Although the content rate of the structural unit derived from the vinyl chloride in the copolymer A is not particularly limited, it is preferably about 50 to 99 mol% based on 100 mol% of all polymerized units.

  The copolymer A can also contain the structural unit represented by the following general formula (5). The inclusion of a structural unit represented by the following general formula (5) is effective for further enhancing the curability. Moreover, since the copolymer containing the structural unit represented by following General formula (5) is easy to synthesize | combine, it is preferable also on synthetic | combination suitability.

  Hereinafter, the general formula (5) will be described.

In General Formula (5), R ⁵¹ and R ⁵² each independently represent a hydrogen atom or a methyl group. R ⁵¹ and R ⁵² is a hydrogen atom, can be obtained a high curability be any of methyl group, from the viewpoint of feedability is preferably R ^51, R ⁵² is a methyl group. Further, in the general formula ^{(5), L 51} represents a divalent linking group represented by the formula (2), the formula (3) or general formula (4).

In general formula (5), L ⁵² represents a divalent linking group. The divalent linking group represented by L ⁵² is preferably an alkylene group or alkyleneoxy group having 1 to 25 carbon atoms, more preferably an alkylene group or alkyleneoxy group having 1 to 20 carbon atoms, a methylene group or an ethylene group. , Propylene group, butylene group, ethyleneoxy group, diethyleneoxy group, and triethyleneoxy group are particularly preferable. These groups may have a substituent. In that case, the carbon number refers to the carbon number of the portion not containing the substituent.

Substituents which may be included in the ^{L 52} is preferably an alkyl group having 1 to 20 carbon atoms, among them, preferably an alkyl group having 1 to 15 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, carbon An alkyl group having 1 to 7 is particularly preferable. Specific examples of the substituent include a methyl group, an ethyl group, a branched or linear propyl group, a branched or linear butyl group, a branched or linear pentyl group, a branched A straight chain hexyl group is most preferred.

  The copolymer A can contain, for example, 1 mol% or more and 45 mol% or less of the structural unit represented by the general formula (5) per 100 mol% of all the polymerization units. The copolymer A can exhibit even higher curability by including the structural unit represented by the general formula (5) at the above content.

  Copolymer A can also contain a cyclic ether structure. The inclusion of a cyclic ether structure is effective in enhancing the stability during copolymer synthesis and curability under various conditions. The cyclic ether structure is also effective as a functional group for introducing a polar group into the copolymer. The cyclic ether structure is preferably an oxirane ring, oxetane ring, tetrahydrofuran ring, tetrahydropyran ring or crown ether, more preferably an oxirane ring, oxetane ring, tetrahydrofuran ring or tetrahydropyran ring, and an oxirane ring, oxetane ring or tetrahydrofuran ring. Particularly preferred. The said cyclic ether structure is contained in the side chain part of a copolymer, for example. As an example of the preferable aspect, what contains a cyclic ether structure in the structural unit represented by following General formula (8) can be mentioned.

In the general formula (8), L ⁸ represents a divalent linking group, for example, an oxyalkylene group such as —CH ₂ OCH ₂ —. R ⁸ represents a cyclic ether structure, the details of which are as described above.

  From the viewpoint of improving curability, the copolymer A preferably contains 1 to 100 cyclic ether structures per molecule. Moreover, as content rate of the structural unit represented by the said General formula (8), 1 mol% or more and 45 mol% or less are preferable per 100 mol% of all the polymerization units.

By the way, in order to improve the dispersibility of magnetic powder, nonmagnetic powder, etc., binders for magnetic recording media are widely introduced with polar groups. Therefore, from the viewpoint of suitability as a binder for magnetic recording media, the copolymer A also preferably has a polar group for improving dispersibility. Examples of the polar group include a hydroxyalkyl group, a carboxylic acid (salt) group, a sulfonic acid (salt) group, a sulfuric acid (salt) group, and a phosphoric acid (salt) group. In the present invention, the “sulfonic acid (salt) group” is a substituent in which a in the following general formula (A) is 0, and includes a sulfonic acid group (—SO ₃ H), —SO ₃ Na, — And sulfonate groups such as SO ₃ Li and —SO ₃ K. In addition, the “sulfuric acid (salt) group” is a substituent in which a in the following general formula (A) is 1, and includes a sulfate group and a sulfate group in the same manner as described above. The same applies to carboxylic acid (salt) groups, phosphoric acid (salt) groups, and the like.

In the general formula (A), M represents a hydrogen atom or a cation, and ^* represents a bonding position. a is 0 or 1, and when a = 0 as described above, the substituent represented by the general formula (A) is a sulfonic acid (salt) group, and when a = 1, in the general formula (A) The represented substituent is a sulfuric acid (salt) group.
The cation may be an inorganic cation or an organic cation. The cation has the general formula (A) in the ^- (O) _a SO ₃ - is intended to electrically neutralize, is not limited to monovalent cations, be a divalent or higher cation You can also. The cation represented by M is preferably a monovalent cation. When an n-valent cation is used, it means (1 / n) mole of cation with respect to the substituent represented by the general formula (A).

The inorganic cation is not particularly limited, but is preferably an alkali metal ion or an alkaline earth metal ion, more preferably an alkali metal ion, and further preferably Li ⁺ , Na ⁺ or K ⁺ .
Examples of organic cations include ammonium ions, quaternary ammonium ions, pyridinium ions, and the like.

The M is preferably a hydrogen atom, an alkali metal ion, a quaternary ammonium ion or a pyridinium ion, more preferably a hydrogen atom, Li ⁺ , Na ⁺ , K ⁺ , a tetraalkylammonium ion or a pyridinium ion. , K ⁺ , tetraalkylammonium ion or pyridinium ion are particularly preferred.

  As one aspect of the copolymer A containing a sulfuric acid (salt) group, a structural unit represented by the following general formula (6) in which a structural unit represented by the general formula (1) is substituted with a sulfuric acid (salt) group Can be mentioned.

  In general formula (6), M represents a hydrogen atom or a cation, and the details thereof are as described above for M in general formula (A).

In General Formula (6), R ⁶ represents a hydrogen atom or a methyl group, and L ⁶ represents a divalent linking group represented by Formula (2), Formula (3), or General Formula (4). Details of R ⁶ and L ^{6 in} the general formula (6) are as described for R ¹ and L ¹ in the general formula (1).

  The copolymer A can contain a sulfonic acid (salt) group in the structural unit represented by the following general formula (7), for example.

In General Formula (7), R ⁷ represents a hydrogen atom or a methyl group, L ⁷ represents a divalent linking group, and preferably represents a C 1-7 alkylene group which may be branched. The alkylene group may have a substituent. More substituents are as set forth above for substituents that may be included in L ^2.

  In general formula (7), M represents a hydrogen atom or a cation, and the details thereof are as described above for M in general formula (A).

  However, the copolymer A is not limited to those having the structural unit (6) or (7), and polar groups such as a sulfonic acid (salt) group and a sulfuric acid (salt) group can be added at any position. Can be included. The polar group content of the copolymer A will be described later.

  JP, 2011-102372, A paragraphs [0048]-[0067] can be referred to for the synthesis method of copolymer A.

  Next, various physical properties of the copolymer A will be described.

(A) Average molecular weight, molecular weight distribution The copolymer A has a mass average molecular weight of 10,000 to 500,000 (in the present invention, "10,000 to 500,000" is also described as "10,000 to 500,000") The same shall apply hereinafter.), Preferably 10,000 to 400,000, more preferably 10,000 to 300,000. A mass average molecular weight of 10,000 or more is preferable because the storage stability of the coating layer formed using the copolymer A as a binder is good. A mass average molecular weight of 500,000 or less is preferable because good dispersibility can be obtained.

  The molecular weight distribution (mass average molecular weight Mw / number average molecular weight Mn) of the copolymer A is preferably 1.00 to 5.50. More preferably, it is 1.01 to 5.40. A molecular weight distribution of 5.50 or less is preferable because the composition distribution is small and good dispersibility can be obtained. In addition, before and after the reaction for introducing a radiation curable functional group and / or a polar group into the vinyl chloride copolymer, the mass average molecular weight and the molecular weight distribution (Mw / Mn) usually hardly change or change little.

(B) Glass transition temperature As mentioned above, the glass transition temperature (Tg) of the copolymer A is 30 degreeC-100 degreeC, and it is preferable that it is 55 degreeC-100 degreeC.

(C) Polar group content It is preferable that the copolymer A contains a polar group as described above. The polar group content in the copolymer A is preferably 1.0 mmol / kg to 3500 mmol / kg, more preferably 1.0 mmol / kg to 3000 mmol / kg, and 1.0 mmol / kg to More preferably, it is 2500 mmol / kg.
If the content of the polar group is 1.0 mmol / kg or more, a sufficient adsorptive power to a powder such as a nonmagnetic powder can be obtained, and the dispersibility is good, which is preferable. Moreover, if it is 3500 mmol / kg or less, since the favorable solubility to a solvent is obtained, it is preferable. As described above, the polar group is preferably a sulfonic acid (salt) group or a sulfuric acid (salt) group represented by the general formula (A). The content of the polar group selected from the group consisting of a sulfonic acid (salt) group and a sulfuric acid (salt) group is preferably 10 mmol / kg or more and 2000 mmol / kg or less from the viewpoint of achieving both dispersibility and solvent solubility.

(D) Hydroxyl content The copolymer A may contain a hydroxyl group (OH group). The number of OH groups contained is preferably 1 to 100,000 per molecule and more preferably 1 to 10,000. When the number of OH groups is within the above range, the solubility in the solvent is improved, and the dispersibility is good.

(E) Radiation-curable functional group content Copolymer A contains a (meth) acryloyloxy group that is a radiation-curable functional group in the structural unit represented by the general formula (1). In addition, various radiation-curable functional groups can be contained. Details of these radiation-curable functional groups are as described above. The content of the radiation curable functional group in the copolymer A is preferably 1.0 mmol / kg to 4000 mmol / kg, more preferably 1.0 mmol / kg to 3000 mmol / kg, 1.0 mmol More preferably, it is / kg-2000 mmol / kg. If the content of the radiation curable functional group is 1.0 mmol / kg, a coating film having high strength can be formed by radiation curing, which is preferable. Further, if the content of the radiation curable functional group is 4000 mmol / kg or less, it is preferable because a calendering property is good even when calendering is performed after radiation curing, and a magnetic recording medium having good electromagnetic conversion characteristics can be obtained. .

  Specific examples of the copolymer A include exemplified ponomers (1) to (10) described in [0076] and [0077] of JP2011-102372A.

Polyurethane resin B
The polyurethane resin B is obtained using a sulfonic acid (salt) group-containing polyol compound represented by the following general formula (2) as a raw material.

[In General Formula (2), X represents a divalent linking group, and R ¹⁰¹ and R ¹⁰² each independently represents an alkyl group having 2 or more carbon atoms having at least one hydroxyl group or carbon having at least one hydroxyl group. It represents an aralkyl group having a number of 8 or more, and M ¹ represents a hydrogen atom or a cation. ]

The usual polyurethane synthesis reaction is carried out in an organic solvent, whereas the sulfonic acid (salt) group-containing polyol compound is generally poorly soluble in an organic solvent and therefore has a poor reactivity and a desired amount of sulfonic acid (salt) group. The problem is that it is difficult to obtain a polyurethane resin into which is introduced. On the other hand, since the sulfonic acid (salt) group-containing polyol compound exhibits high solubility in an organic solvent, a polyurethane resin in which a desired amount of sulfonic acid (salt) group is uniformly introduced can be easily obtained. it can. Therefore, according to the polyurethane resin B, the dispersibility of the powder component in the nonmagnetic layer can be increased, thereby increasing the surface smoothness of the nonmagnetic layer and, in turn, further increasing the surface smoothness of the magnetic layer above it. be able to.
Hereinafter, the polyurethane resin B will be described in more detail.

X in the general formula (2) represents a divalent linking group, preferably has 2 to 20 carbon atoms from the viewpoint of solubility in an organic solvent, and is preferably a divalent hydrocarbon group. An alkylene group, an arylene group, or a combination of two or more of these is more preferable, an alkylene group or an arylene group is more preferable, an ethylene group or a phenylene group is particularly preferable, and an ethylene group Most preferably.
Examples of the phenylene group include an o-phenylene group, an m-phenylene group, and a p-phenylene group, preferably an o-phenylene group or an m-phenylene group, and an m-phenylene group. It is more preferable that

  The alkylene group preferably has 2 to 20 carbon atoms, more preferably 2 to 4 carbon atoms, and even more preferably 2. The alkylene group may be a linear alkylene group or a branched alkylene group, but is preferably a linear alkylene group.

  The arylene group preferably has 6 to 20 carbon atoms, more preferably 6 to 10 carbon atoms, and still more preferably 6.

The alkylene group and the arylene group may have a substituent shown below, but are preferably a group consisting of only a carbon atom and a hydrogen atom.
Examples of the substituent that the alkylene group may have include an aryl group, a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), an alkoxy group, an aryloxy group, and an alkyl group.
Examples of the substituent that the arylene group may have include an alkyl group, a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), an alkoxy group, an aryloxy group, and an aryl group.

R ¹⁰¹ and R ¹⁰² in the general formula (2) each independently represent an alkyl group having 2 or more carbon atoms having at least one hydroxyl group or an aralkyl group having 8 or more carbon atoms having at least one hydroxyl group, The aralkyl group may have a substituent.
Examples of the substituent that the alkyl group and aralkyl group may have other than a hydroxyl group include an alkoxy group, an aryloxy group, a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), a sulfonyl group, and a silyl group Examples are groups. Among these, an alkoxy group or an aryloxy group is preferable, an alkoxy group having 1 to 20 carbon atoms or an aryloxy group having 6 to 20 carbon atoms is more preferable, and an alkoxy group having 1 to 4 carbon atoms or More preferred is a phenoxy group.
Further, the alkyl group and the aralkyl group may be linear or branched.

The number of hydroxyl groups in R ¹⁰¹ and R ¹⁰² is 1 or more, preferably 1 or 2, and particularly preferably 1. That is, the sulfonic acid (salt) group-containing polyol compound represented by the general formula (1) is particularly preferably a sulfonic acid diol compound.

The number of carbon atoms of the alkyl group in R ¹⁰¹ and R ¹⁰² is 2 or more from the viewpoints of solubility in an organic solvent, raw material procurement, cost, etc., preferably 2 to 22, and preferably 3 to 22. More preferably, it is 4-22, still more preferably 4-8.

The number of carbon atoms of the aralkyl group in R ¹⁰¹ and R ¹⁰² is 8 or more from the viewpoint of solubility in an organic solvent, raw material availability, cost, etc., preferably 8 to 22, and preferably 8 to 12. More preferably, 8 is even more preferable.
In the aralkyl group in R ¹⁰¹ and R ¹⁰² , the α-position and the β-position of the nitrogen atom are preferably saturated hydrocarbon chains. In that case, the nitrogen atom may have a hydroxyl group at the β-position.
R ¹⁰¹ and R ¹⁰² preferably have no hydroxyl group at the α-position of the nitrogen atom, more preferably at least one hydroxyl group at the β-position of the nitrogen atom, and only the β-position of the nitrogen atom. It is particularly preferable to have one hydroxyl group. By having a hydroxyl group at the β-position of the nitrogen atom, the synthesis is facilitated and the solubility in an organic solvent can be further enhanced.

R ¹⁰¹ and R ¹⁰² are each independently an alkyl group having 2 to 22 carbon atoms having at least one hydroxyl group, an aralkyl group having 8 to 22 carbon atoms having at least one hydroxyl group, and a carbon number having at least one hydroxyl group. It is preferably an alkoxyalkyl group having 3 to 22 or an aryloxyalkyl group having 9 to 22 carbon atoms having at least one hydroxyl group, and an alkyl group having 2 to 20 carbon atoms having at least one hydroxyl group, at least one It is an aralkyl group having 8 to 20 carbon atoms having a hydroxyl group, an alkoxyalkyl group having 3 to 20 carbon atoms having at least one hydroxyl group, or an aryloxyalkyl group having 9 to 20 carbon atoms having at least one hydroxyl group. More preferred.

  Specific examples of the alkyl group having 2 or more carbon atoms having at least one hydroxyl group include 2-hydroxyethyl group, 2-hydroxypropyl group, 2-hydroxybutyl group, 2-hydroxypentyl group, 2-hydroxyhexyl group, 2-hydroxyoctyl group, 2-hydroxy-3-methoxypropyl group, 2-hydroxy-3-ethoxypropyl group, 2-hydroxy-3-butoxypropyl group, 2-hydroxy-3-phenoxypropyl group, 2-hydroxy- 3-methoxy-butyl group, 2-hydroxy-3-methoxy-3-methylbutyl group, 2,3-dihydroxypropyl group, 3-hydroxypropyl group, 3-hydroxybutyl group, and 4-hydroxybutyl group, 1- Methyl-2-hydroxyethyl group, 1-ethyl-2-hydroxyethyl group, -Propyl-2-hydroxyethyl group, 1-butyl-2-hydroxyethyl group, 1-hexyl-2-hydroxyethyl group, 1-methoxymethyl-2-hydroxyethyl group, 1-ethoxymethyl-2-hydroxyethyl group 1-butoxymethyl-2-hydroxyethyl group, 1-phenoxymethyl-2-hydroxyethyl group, 1- (1-methoxyethyl) -2-hydroxyethyl group, 1- (1-methoxy-1-methylethyl) Examples include 2-hydroxyethyl group and 1,3-dihydroxy-2-propyl group. Among these, 2-hydroxybutyl group, 2-hydroxy-3-methoxypropyl group, 2-hydroxy-3-butoxypropyl group, 2-hydroxy-3-phenoxypropyl group, 1-methyl-2-hydroxyethyl group 1-methoxymethyl-2-hydroxyethyl group, 1-butoxymethyl-2-hydroxyethyl group, 1-phenoxyethyl-2-hydroxyethyl group can be preferably exemplified.

  Specific examples of the aralkyl group having 8 or more carbon atoms having at least one hydroxyl group include 2-hydroxy-2-phenylethyl group, 2-hydroxy-2-phenylpropyl group, 2-hydroxy-3-phenylpropyl group, 2-hydroxy-2-phenylbutyl group, 2-hydroxy-4-phenylbutyl group, 2-hydroxy-5-phenylpentyl group, 2-hydroxy-2- (4-methoxyphenyl) ethyl group, 2-hydroxy-2 -(4-phenoxyphenyl) ethyl group, 2-hydroxy-2- (3-methoxyphenyl) ethyl group, 2-hydroxy-2- (4-chlorophenyl) ethyl group, 2-hydroxy-2- (4-hydroxyphenyl) ) Ethyl group, 2-hydroxy-3- (4-methoxyphenyl) propyl group, and 2-hydroxy-3 (4-chlorophenyl) propyl group, 1-phenyl-2-hydroxyethyl group, 1-methyl-1-phenyl-2-hydroxyethyl group, 1-benzyl-2-hydroxyethyl group, 1-ethyl-1-phenyl- 2-hydroxyethyl group, 1-phenethyl-2-hydroxyethyl group, 1-phenylpropyl-2-hydroxyethyl group, 1- (4-methoxyphenyl) -2-hydroxyethyl group, 1- (4-phenoxyphenyl) 2-hydroxy-ethyl group, 1- (3-methoxyphenyl) -2-hydroxyethyl group, 1- (4-chlorophenyl) -2-hydroxyethyl group, 1- (4-hydroxyphenyl) 2-hydroxyethyl group, Examples include 1- (4-methoxyphenyl) -3-hydroxy-2-propyl group. Among these, 2-hydroxy-2-phenylethyl group and 1-phenyl-2-hydroxyphenyl group can be preferably exemplified.

M ¹ in the general formula (2) represents a hydrogen atom or a cation.
The cation may be an inorganic cation or an organic cation. The cation electrically neutralizes —SO ₃ ^— in the general formula (2), and is not limited to a monovalent cation, and may be a divalent or higher cation. Monovalent cations are preferred. When an n-valent cation is used, it means (1 / n) mole of cation with respect to the compound represented by the general formula (2).

Although there is no restriction | limiting in particular as an inorganic cation, An alkali metal ion or an alkaline-earth metal ion can be illustrated preferably, an alkali metal ion can be illustrated more preferably, Li ^<+> , Na ^<+> , K ^<+> , Rb ^<+> or Cs ^<+>. Is more preferable.
Examples of organic cations include ammonium ions, quaternary ammonium ions, pyridinium ions, and the like.

M ¹ is preferably a hydrogen atom or an alkali metal ion, more preferably a hydrogen atom, Li ⁺ , Na ⁺ or K ⁺ , and particularly preferably K ⁺ .

The polyol compound represented by the general formula (2) can have one or more aromatic rings in the molecule in order to further improve the solubility in an organic solvent.
R ¹⁰¹ and R ¹⁰² in the general formula (2) may be the same or different, but are preferably the same from the viewpoint of ease of synthesis.
R ¹⁰¹ and R ¹⁰² in general formula (2) are each preferably a group having 5 or more carbon atoms. In addition, R ¹⁰¹ and R ¹⁰² in the general formula (2) are each preferably a group having an aromatic ring and / or an ether bond.

  JP, 2009-96798, A can be referred to for details of the polyol compound denoted by the general formula (2) explained above. In particular, with respect to the method for synthesizing the polyol compound represented by the general formula (2), paragraphs [0028], [0029] and [0045] of JP-A-2009-96798 and examples of the same publication can be referred to. Moreover, as a polyol compound represented by General formula (2), the compound represented by Formula (2) and Formula (3) of Unexamined-Japanese-Patent No. 2009-96798 can be mentioned. Details thereof are described in paragraphs [0030] to [0034] of the same publication. Specific examples of the polyol compound represented by the general formula (2) include the following exemplary compounds (S-1) to (S-74) and the following exemplary compound (S-71) described in JP-A-2009-96798 described below. ) To (S-74). In the following, Ph represents a phenyl group, and Et represents an ethyl group.

  In addition, as a raw material for synthesizing polyurethane resin B, in addition to the polyol compound represented by the general formula (2), polyester polyol, polyether polyol, polyether ester polyol, polycarbonate polyol, polyolefin polyol, dimer diol and the like are generally synthesized with polyurethane. Known polyol compounds that are sometimes used as chain extenders can also be used. JP, 2009-96798, A paragraphs [0056]-[0065] can be referred to for the polyol compound used together. Moreover, the fluorene derivative alcohol represented by a following formula can also be used.

[In the above formula, R ₁ represents H or CH ₃ , R ₂ represents OH or —OCH ₂ CH ₂ OH, and two R ₁ and R ₂ may be the same or different. . ]

  The polyurethane resin B can be obtained by a urethanization reaction between an isocyanate compound and a polyol compound. The urethanization reaction can be advanced by dissolving the raw material compound in a solvent (polymerization solvent) and performing heating, pressurization, nitrogen substitution and the like as necessary. The reaction conditions such as the reaction temperature and reaction time for the urethanization reaction may be normal reaction conditions for the urethanization reaction. Regarding the urethanization reaction, for example, paragraphs [0067] and [0068] of JP-A-2009-96798 and the examples of the same publication can be referred to.

  The isocyanate compound refers to a compound having an isocyanate group, and a bifunctional or higher polyfunctional isocyanate compound (hereinafter referred to as “polyisocyanate”) is preferable. The polyisocyanate that can be used as a raw material for synthesizing the polyurethane resin B is not particularly limited, and known ones can be used. For example, one or more diisocyanates such as TDI (tolylene diisocyanate), MDI (diphenylmethane diisocyanate), p-phenylene diisocyanate, o-phenylene diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate Two or more types can be used in combination.

  Since the polyurethane resin B is a radiation curable resin, it contains a radiation curable functional group. The radiation-curable functional group contained is not particularly limited as long as it can cause a curing reaction (crosslinking reaction) upon irradiation, but from the viewpoint of reactivity, it is a radically polymerizable carbon-carbon dicarboxylic acid. A heavy bond group is preferred, and an acrylic double bond group is more preferred. Among the acrylic double bond groups, a (meth) acryloyloxy group is preferable from the viewpoint of reactivity.

  The radiation curable functional group may be contained in either one of the isocyanate compound or the polyol compound, and may be contained in both. In view of availability of raw materials and cost, it is preferable to use a polyol compound having a radiation curable functional group.

  Examples of the polyol compound having a radiation curable functional group include glycerin monoacrylate (also referred to as glycerol acrylate), glycerin monomethacrylate (also referred to as glycerol methacrylate) (for example, trade name Blenmer GLM manufactured by NOF Corporation), bisphenol A type epoxy acrylate. A diol having at least one acrylic double bond in the molecule, such as trade name epoxy ester 3000A manufactured by Kyoeisha Chemical Co., Ltd., is suitable. Among these diols, the following compound (glycerin mono (meth) acrylate) is preferable from the viewpoint of curability. In the following, R is a hydrogen atom or a methyl group.

  Next, various physical properties of the polyurethane resin B will be described.

(a) Average molecular weight The polyurethane resin B preferably has a mass average molecular weight of 10,000 to 500,000, more preferably 10,000 to 400,000, and even more preferably 10,000 to 300,000. A mass average molecular weight of 10,000 or more is preferable because the storage stability of the coating layer formed using polyurethane resin B as a binder is good. A mass average molecular weight of 500,000 or less is preferable because good dispersibility can be obtained.

  For example, the mass average molecular weight can be adjusted to a desired range by finely adjusting the molar ratio of the glycol-derived OH group and the diisocyanate-derived NCO group or using a reaction catalyst. The mass average molecular weight can also be adjusted by adjusting the solid content concentration during the reaction, the reaction temperature, the reaction solvent, the reaction time, and the like.

  The molecular weight distribution (Mw / Mn) of the polyurethane resin B is preferably 1.00 to 5.50. More preferably, it is 1.01 to 5.40. A molecular weight distribution of 5.50 or less is preferable because the composition distribution is small and good dispersibility can be obtained.

(b) Urethane group concentration The urethane group concentration of the polyurethane resin B is preferably 2.0 mmol / g to 5.0 mmol / g, more preferably 2.1 mmol / g to 4.5 mmol / g.
If the urethane group concentration is 2.0 mmol / g or more, a coating film having a high glass transition temperature (Tg) and good durability can be formed, and the dispersibility is also good. A urethane group concentration of 5.0 mmol / g or less is preferable because good solvent solubility can be obtained, the polyol content can be adjusted, and the molecular weight can be easily controlled.

(c) Glass transition temperature As described above, the glass transition temperature (Tg) of the polyurethane resin B is 30 ° C to 100 ° C, and preferably 55 ° C to 100 ° C.

(d) Polar group content Since the polyurethane resin B is obtained using a sulfonic acid (salt) group-containing polyol compound as a raw material as described above, it contains a sulfonic acid (salt) group. In addition, other polar groups can be included. Examples of other polar groups include a hydroxyalkyl group, a carboxylic acid (salt) group, a sulfuric acid (salt) group, a phosphoric acid (salt) group, and the like. —OSO ₃ M ′, —PO ₃ M ′ ₂ , — COOM ′ and —OH are preferred. Among this, -OSO ₃ M 'is more preferred. M ′ represents a hydrogen atom or a monovalent cation. Examples of monovalent cations include alkali metals and ammonium. The polar group content in the polyurethane resin B is preferably 1.0 mmol / kg to 3500 mmol / kg, more preferably 1.0 mmol / kg to 3000 mmol / kg, and 1.0 mmol / kg to 2500 mmol. / Kg is more preferable.
If the content of the polar group is 1.0 mmol / kg or more, it is preferable because sufficient adsorptive power to the nonmagnetic powder can be obtained, dispersibility is good, and the amount of free polyurethane can be reduced. Moreover, if it is 3500 mmol / kg or less, since the solubility to a favorable solvent is obtained, it is preferable.

(e) Hydroxyl Content The polyurethane resin B may contain a hydroxyl group (OH group). The number of OH groups contained is preferably 1 to 100,000 per molecule and more preferably 1 to 10,000. When the number of OH groups is within the above range, the solubility in the solvent is improved, and the dispersibility is good.

(f) Radiation-curable functional group content The details of the radiation functional group of the polyurethane resin B are as described above. The content is preferably 1.0 mmol / kg to 4000 mmol / kg, more preferably 1.0 mmol / kg to 3000 mmol / kg, and further preferably 1.0 mmol / kg to 2000 mmol / kg. preferable. If the content of the radiation-curable functional group is 1.0 mmol / kg or more, it is preferable because a coating film having high strength can be formed by radiation curing. Further, if the content of the radiation curable functional group is 4000 mmol / kg or less, it is preferable because a calendering property is good even when calendering is performed after radiation curing, and a magnetic recording medium having good electromagnetic conversion characteristics can be obtained. .

  The nonmagnetic layer of the magnetic recording medium of the present invention is obtained by radiation curing a radiation curable composition containing a radiation curable vinyl chloride copolymer and a radiation curable polyurethane resin together with a nonmagnetic powder. Is a layer. The reason why the radiation curable vinyl chloride copolymer and the radiation curable polyurethane resin are used in combination here is that it is difficult to achieve both the running stability required for the magnetic recording medium and appropriate flexibility with a single resin. It is. The mixing ratio of the radiation curable vinyl chloride copolymer and the radiation curable polyurethane resin in the radiation curable composition is 50 to 80 parts by mass of the polyurethane resin with respect to 100 parts by mass of the vinyl chloride copolymer. It is preferable.

  The solid content concentration of the radiation curable composition is not particularly limited, but is preferably about 10 to 80% by mass, more preferably about 20 to 60% by mass from the viewpoint of ease of handling. Since the radiation curable composition is used for forming a nonmagnetic layer, it contains at least a nonmagnetic powder together with the binder component. The nonmagnetic powder may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. JP, 2011-102372, A paragraph [0120] can be referred to for a specific example of nonmagnetic powder. These nonmagnetic powders are available as commercial products, and can also be produced by a known method.

The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes.
The crystallite size of the nonmagnetic powder is preferably 4 nm to 1 μm, and more preferably 40 to 100 nm. A crystallite size in the range of 4 nm to 1 μm is preferred because it does not become difficult to disperse and has a suitable surface roughness.
The average particle size of these nonmagnetic powders is preferably 5 nm to 2 μm. The range of 5 nm to 2 μm is preferable because a nonmagnetic layer having good dispersion and suitable surface roughness can be formed. However, if necessary, nonmagnetic powders having different average particle diameters can be combined, or even a single nonmagnetic powder can have the same effect by widening the particle size distribution. The average particle size of the particularly preferred nonmagnetic powder is 10 to 200 nm. Paragraphs [0123] to [0132] of JP-A-2009-96798 can be referred to for details of the nonmagnetic powder that can be used in the magnetic recording medium of the present invention.

Carbon black can be mixed in the nonmagnetic layer together with nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain the desired μ Vickers hardness. Μ Vickers hardness of the nonmagnetic layer is normally 25 to 60 kg / mm ^2, preferably in order to adjust the head contact, and a 30 to 50 kg / mm ^2, a thin film hardness meter (NEC Corp. HMA-400) Can be measured using a diamond triangular pyramid needle with a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a VHS magnetic tape. For this purpose, rubber furnace, rubber thermal, color black, acetylene black and the like can be used. JP, 2011-102372, A paragraph [0123] can be referred to for the details of carbon black which can be used for a nonmagnetic layer.

  Further, an organic powder can be added to the nonmagnetic layer according to the purpose. JP, 2011-102372, A paragraph [0124] can be referred to for details of such an organic powder.

  Various additives such as lubricants and dispersants for the nonmagnetic layer, solvents, dispersion methods, etc. can be applied to those for the magnetic layer. In particular, with respect to the addition amount and type of the additive, known techniques relating to the magnetic layer can be applied.

  The radiation curable composition can be prepared by mixing the various components described above. As the radiation to be irradiated for the curing reaction, for example, an electron beam or ultraviolet rays can be used. When using an electron beam, it is preferable at the point that a polymerization initiator is unnecessary. Irradiation can be performed by a known method, and details thereof can be referred to, for example, paragraphs [0021] to [0023] of JP-A-2009-134838. For radiation curing equipment and radiation irradiation curing methods, refer to “UV / EB curing technology” (published by General Technology Center Co., Ltd.) and “Applied technology of low energy electron beam irradiation” (2000, CMC Corporation). (Publication) etc. can be used. Among these, from the viewpoint of obtaining sufficient curability without causing decomposition of the components of the radiation-cured layer or the nonmagnetic support, the curing reaction is preferably performed at a radiation dose of 5 kGy to 100 kGy, and at 10 kGy to 50 kGy. More preferably.

By the way, when mass-producing coating-type magnetic recording media, the coating solution is stored for a long period of, for example, more than half a year. However, vinyl chloride binders are generally low in stability, especially radiation-curable vinyl chloride. When a system resin is used, there may be a phenomenon that the stability of the coating solution is significantly reduced. This is presumably because the molecular weight changes due to the reaction of the radiation-curable functional group during storage.
On the other hand, the synthesis reaction of the radiation curable resin is usually performed in the presence of a polymerization inhibitor for protecting the radiation curable functional group. Therefore, in order to suppress the reaction of the radiation curable functional group during long-term storage, it may be possible to increase the amount of the above polymerization inhibitor. However, simply increasing the amount of the polymerization inhibitor reduces the curability during irradiation. It may be difficult to obtain a tough coating film.
On the other hand, it became clear that the radiation curable vinyl chloride copolymer can maintain the storage stability well for a long time without impairing the curability by storing it in the presence of the benzoquinone compound. . Therefore, the radiation-curable vinyl chloride copolymer used for forming the nonmagnetic layer in the present invention is preferably stored in a composition containing a benzoquinone compound when used after long-term storage. JP, 2011-102372, A paragraphs [0085]-[0090] can be referred to for details, such as a benzoquinone compound and its suitable amount of use.

  The radiation curable vinyl chloride copolymer is stored in a composition containing at least one compound selected from the group consisting of a phenol compound, a piperidine-1-oxyl compound, a nitro compound and a phenothiazine compound together with a benzoquinone compound. It is also preferable. By using one or more of these compounds, preferably in combination with the above-mentioned benzoquinone compound, the long-term storage stability of the radiation-curable vinyl chloride copolymer is satisfactorily maintained without impairing its curability. be able to. JP, 2011-102372, A paragraphs [0091]-[0104] can be referred to for details, such as these compounds and the amount of their suitable use.

Nonmagnetic Supports Examples of the nonmagnetic support that can be used in the present invention include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable.
These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like. The surface roughness of the nonmagnetic support that can be used in the present invention is preferably a center average roughness Ra3 to 10 nm at a cutoff value of 0.25 mm.

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

  The magnetic recording medium of the present invention can have a smoothing layer, an adhesive layer, and the like in addition to a magnetic layer, a nonmagnetic layer, and an optionally formed backcoat layer. Known techniques can be applied to them.

Layer Structure In the magnetic recording medium of the present invention, the preferred thickness of the nonmagnetic support is 3 to 80 μm. Moreover, the thickness of the said backcoat layer is 0.1-1.0 micrometer, for example, Preferably it is 0.2-0.8 micrometer.

  The thickness of the magnetic layer is optimized depending on the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used, but is generally 0.01 to 0.10 μm or less, preferably 0. It is 02 μm or more and 0.08 μm or less, and more preferably 0.03 to 0.08 μm. The thickness variation rate of the magnetic layer is preferably within ± 50%, more preferably within ± 40%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

  The thickness of the nonmagnetic layer is preferably 0.2 to 3.0 μm, more preferably 0.3 to 2.5 μm, and further preferably 0.4 to 2.0 μm. The non-magnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially non-magnetic. For example, even if it contains a small amount of magnetic material as an impurity or intentionally, This shows the effect of the invention and can be regarded as substantially the same configuration as the magnetic recording medium of the invention. “Substantially the same” means that the residual magnetic flux density of the nonmagnetic layer is 10 mT (100 G) or less or the coercive force is 7.96 kA / m (100 Oe) or less, preferably the residual magnetic flux density and the coercive force. It means not having.

Manufacturing method The steps of manufacturing a coating solution for forming each layer such as a magnetic layer, a nonmagnetic layer, and a backcoat layer are at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Preferably it consists of. Each process may be divided into two or more stages. Which process is used for all raw materials such as hexagonal ferrite powder, compound A, nonmagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, dispersant, other additives, solvent, etc. used in the present invention It may be added at the beginning or midway. In addition, individual raw materials may be added in two or more steps. In order to prepare the coating liquid for forming each layer, a conventional known manufacturing technique can be used as a partial process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. In the case of using a kneader, the kneading treatment may be performed using 15 to 500 parts by mass of a binder (preferably 30% by mass or more of the total binder) with respect to 100 parts by mass of the ferromagnetic powder or nonmagnetic powder. preferable. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the magnetic layer coating liquid and the nonmagnetic layer coating liquid. In addition to glass beads, zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media, are suitable. The particle diameter and filling rate of these dispersion media are optimized. A well-known thing can be used for a disperser.

In the magnetic recording medium of the present invention, for example, a nonmagnetic layer coating solution is applied to the surface of a nonmagnetic support under running so as to have a predetermined film thickness and is cured by radiation. Then, a magnetic layer coating solution is applied on the film to a predetermined thickness to form a magnetic layer. Here, it is also possible to apply a plurality of magnetic layer coating solutions successively or simultaneously.
In general, when a lower non-magnetic layer coating solution and an upper magnetic layer coating solution are sequentially applied in multiple layers, the non-magnetic layer may partially dissolve in the solvent contained in the magnetic layer coating solution. If the non-magnetic layer is a radiation-cured layer formed from a radiation-curable composition having high curability, the binder component is polymerized and crosslinked in the non-magnetic layer by irradiation, resulting in a high molecular weight. Dissolution in the solvent contained in the magnetic layer coating solution can be suppressed or reduced. In addition, the high curability of the nonmagnetic layer and the prevention of mixing at the interface with the magnetic layer are advantageous in suppressing deterioration of the magnetic layer surface smoothness due to interface fluctuations. From this point, in the present invention, the non-magnetic layer is a radiation-cured layer. Among them, it is effective to use the above-described copolymer A having high curability.

The coating machine for applying the magnetic layer coating liquid or the nonmagnetic layer coating liquid includes air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure A coat, a kiss coat, a cast coat, a spray coat, a spin coat, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to. When forming the radiation-cured layer, the coating layer formed by coating the coating solution is cured by radiation. The details of the irradiation process are as described above. The medium after the coating process can be subjected to various post-treatments such as magnetic layer orientation treatment, surface smoothing treatment (calendar treatment), and heat treatment for reducing thermal shrinkage.
Details of these processes can be referred to, for example, paragraphs [0146] to [0148] of JP-A-2009-96798. As described above, according to the present invention, it is possible to achieve both suppression of abrasion on the surface of the magnetic layer during traveling and excellent calendar formability.
As an index of having excellent calendar moldability, a magnetic layer measured in an area of 250 μm × 250 μm is measured under the condition of a cutoff value of 0.25 mm using an optical interference type surface roughness meter HD-2000 manufactured by WYKO. A change amount (reduction amount) ΔRa of the center surface average surface roughness Ra of the surface can be used, and according to the present invention, after suppressing the abrasion of the magnetic layer surface during running, ΔRa is 1.5 nm or more, For example, calendar formability with ΔRa of 1.5 to 3.0 nm can be realized. Regarding the calendering conditions, as described in JP-A-2009-96798, the temperature of the calender roll, that is, the calendering temperature is in the range of 60 to 100 ° C, preferably in the range of 70 to 100 ° C, particularly preferably in the range of 80 to 100. The pressure is in the range of 100 ° C. and the pressure is in the range of 100 to 500 kg / cm, preferably in the range of 200 to 450 kg / cm, particularly preferably in the range of 300 to 400 kg / cm. Further, it is preferable to set the calender temperature to be higher than the glass transition temperature of the nonmagnetic layer, since the nonmagnetic layer becomes flexible and the cushioning property is further enhanced during the calendering process. From the viewpoint of improving calendar moldability, the calendar temperature is more preferably in the range of the glass transition temperature Tg + 5 ° C. to the Tg + 30 ° C. of the nonmagnetic layer.
Thereafter, the produced magnetic recording medium original can be cut into a desired size using a cutting machine or the like to obtain a magnetic recording medium.

  The magnetic recording medium of the present invention described above can have a high degree of surface smoothness by improving the calendar moldability as described above. The magnetic recording medium of the present invention has a high surface of 4 nm or less, for example, 2 to 4 nm, as the center surface average surface roughness Ra of the magnetic layer measured by an atomic force microscope (AFM) under the measurement conditions described in the examples below. Smoothness can be realized.

  The present invention further relates to a method for producing the magnetic recording medium of the present invention. In the method for producing a magnetic recording medium of the present invention, a magnetic layer is formed on the formed radiation-cured layer after the radiation-curable composition is applied and radiation-cured, and then the calender is equal to or higher than the glass transition temperature of the radiation-cured layer. Calendar processing is performed at temperature. The details are as described above. According to the production method of the present invention, surface smoothness can be remarkably improved by calendaring in a magnetic recording medium having a magnetic layer in which the occurrence of surface scraping is suppressed.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the embodiment shown in the examples. The “parts” and “%” shown below indicate parts by mass and mass% unless otherwise specified. For the measurement of ¹ H NMR described below, 400 MHz NMR (AVANCE II-400 manufactured by BRUKER) was used.

<Measurement method of glass transition temperature of binder resin and storage modulus at 80 ° C.>
The glass transition temperature Tg of the binder resin and the storage elastic modulus E ′ at 80 ° C. in the following are values determined by the dynamic viscoelasticity measurement described below.
A binder resin solution is prepared by diluting with a solution having a ratio of methyl ethyl ketone: cyclohexanone of 50:50 (mass ratio) to a solid content concentration of 22% by mass. Thereafter, it is applied on an aramid base so that the thickness after drying becomes 20 μm and dried to obtain a clear film. The clear film containing the radiation curable resin is cured by irradiation with radiation of 40 kGy in an atmosphere having an oxygen concentration of 200 ppm or less. Then, the obtained clear film was cut into a width of 3.35 mm and a length of 5 cm, and 30 to 140 ° C. with a dynamic viscoelasticity measuring device (TOYO BALDWIN-made Leo Vibron, heating rate 2 ° C./min, measuring frequency 110 Hz). The peak temperature of the loss elastic modulus (E ″) up to is the glass transition temperature of the binder resin (hereinafter referred to as “Tg1”), and the storage elastic modulus E ′ at 80 ° C. is obtained in the same measurement.

<Method for measuring glass transition temperature of nonmagnetic layer>
The glass transition temperature of the following nonmagnetic layer is a value determined by dynamic viscoelasticity measurement described below.
Corresponding examples, comparative examples, reference examples, nonmagnetic layer coating solutions prepared in the same manner as in the comparative reference examples, the same thickness as the corresponding examples, comparative examples, reference examples, comparative reference examples on the aramid base For a sample obtained by cutting a sheet coated and dried and cured under the same conditions (heated or radiation cured) into a width of 12.65 mm and a length of about 10 mm, a dynamic viscoelasticity measuring device (DMS6100 manufactured by SII Nano Technology Co., Ltd.) is used. The loss tangent (tan δ1) in the measurement temperature range of 20 to 200 ° C. is measured using a temperature increase rate of 2 ° C./min and a measurement frequency of 10 Hz. Separately from this, the loss tangent (tan δ2) in the measurement temperature range of 20 to 200 ° C. is measured for the used base alone by the same method as described above. The difference between the sample and the base film tan δ at each temperature (tan δ 1 (T) −tan δ 2 (T), T is the measured temperature) is plotted against the temperature in the range of 20 to 200 ° C. The temperature at the maximum value obtained from the plot is defined as the glass transition temperature of the nonmagnetic layer (hereinafter referred to as “Tg2”).

1. Dispersibility test

[Test Example 1]
The following ferromagnetic hexagonal ferrite powder 2.2 parts by mass, vinyl chloride resin (MR104 manufactured by Kaneka) 0.22 parts by mass, polyester polyurethane (Toyobo UR4800) 0.088 parts by mass, N-phenylglycine 0.11 parts by mass And suspended in a solution consisting of 2.5 parts by mass of cyclohexanone and 3.7 parts by mass of methyl ethyl ketone (2-butanone). 27 parts by weight of 0.1 mmΦ zirconia beads (Nikkato) was added to the suspension and dispersed for 15 hours to obtain a magnetic paint.
The dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the method described later to be 70 nm. Moreover, it was 3.6 nm when the coating-film surface roughness was measured by the below-mentioned method.
Ferromagnetic hexagonal barium ferrite powder Composition excluding oxygen (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 1
Hc: 176 kA / m (2200 Oe), average plate diameter: 25 nm, average plate ratio: 3
BET specific surface area: 65 m ² / g
σs: 49 A · m ² / kg (49 emu / g)
pH: 7

Method for Measuring Dispersion Particle Size The magnetic coating material was diluted with a mixed solution containing cyclohexanone and methyl ethyl ketone in a volume ratio of cyclohexanone 6.0: methyl ethyl ketone 9.0 to a solid content concentration of 0.2% by mass (solid content Represents the total mass of hexagonal ferrite powder, resin component and N-phenylglycine).
The average particle size of the hexagonal ferrite powder in the diluted solution measured using a dynamic light scattering type particle size distribution analyzer LB-500 manufactured by HORRIBA was defined as the dispersed particle size. A smaller dispersed particle size means that the hexagonal ferrite powder does not aggregate and has better dispersibility.

Method for Measuring Coated Surface Roughness A magnetic coating was applied onto a PEN base manufactured by Teijin Ltd. using a doctor blade having a 19 μm gap, and allowed to stand at room temperature for 30 minutes to dry to prepare a coating.
The surface roughness of the coating film was measured by setting Scan Length to 5 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer New View 5022 manufactured by ZYGO. Objective lens: 20 times, intermediate lens: 1.0 times, and measurement field of view was 260 μm × 350 μm. The measured surface was filtered with HPF: 1.65 μm and LPF: 50 μm to determine the centerline average surface roughness Ra value.

[Test Example 2]
A magnetic paint was obtained in the same manner as in Test Example 1, except that 0.11 part by mass of N-phenylglycine was replaced by 0.12 part by mass of N- (4-hydroxyphenyl) glycine.
When the dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the method described above, it was 64 nm. Moreover, it was 3.0 nm when the coating-film surface roughness was measured by the above-mentioned method.

[Test Example 3]
A magnetic coating material was obtained in the same manner as in Test Example 1 except that 0.11 part by mass of N-phenylglycine was replaced by 0.11 part by mass of phenoxyacetic acid.
The dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the above-mentioned method and found to be 72 nm. Moreover, it was 3.5 nm when the coating-film surface roughness was measured by the above-mentioned method.

[Test Example 4]
A magnetic paint was obtained in the same manner as in Test Example 1 except that 0.11 part by mass of N-phenylglycine was replaced by 0.12 part by mass of 2-phenoxypropionic acid.
The dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the above-mentioned method and found to be 72 nm. Moreover, it was 3.0 nm when the coating-film surface roughness was measured by the above-mentioned method.

[Test Example 5]
A magnetic coating material was obtained in the same manner as in Test Example 1, except that 0.11 part by mass of N-phenylglycine was replaced by 0.11 part by mass of 3-phenylpropionic acid.
The dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the above-mentioned method and found to be 73 nm. Moreover, it was 3.8 nm when the coating-film surface roughness was measured by the above-mentioned method.

[Comparative Test Example 1]
A magnetic coating material was obtained in the same manner as in Test Example 1 except that 0.11 part by mass of N-phenylglycine was replaced by 0.10 part by mass of phenoxyethanol.
When the dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the method described above, it was 100 nm. Moreover, it was 14.8 nm when the coating-film surface roughness was measured by the above-mentioned method.

[Comparative Test Example 2]
A magnetic coating material was obtained in the same manner as in Test Example 1, except that 0.11 part by mass of N-phenylglycine was replaced by 0.13 part by mass of N- (tert-butoxycarbonyl) -β-alanine.
When the dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the method described above, it was 85 nm. Moreover, it was 4.2 nm when the coating-film surface roughness was measured by the above-mentioned method.

[Comparative Test Example 3]
A magnetic coating material was obtained in the same manner as in Test Example 1 except that 0.11 part by mass of N-phenylglycine was not used.
When the dispersed particle size of the hexagonal ferrite powder in the obtained magnetic coating material was measured by the method described above, it was 83 nm. Moreover, it was 4.8 nm when the coating-film surface roughness was measured by the above-mentioned method.

  The above results are summarized in Table 1 below.

[Comparative Test Example 4]
A magnetic coating material was obtained in the same manner as in Test Example 1 except that 0.11 part by mass of N-phenylglycine was replaced by 0.11 part by mass of phenylphosphonic acid.
When the coating film surface roughness was measured by the above-mentioned method using the obtained magnetic coating material, it was 12.0 nm.

  From the above results, according to the compound represented by the general formula A, it is possible to improve the dispersibility of the hexagonal ferrite powder in the magnetic paint, thereby forming a coating film having excellent surface smoothness. It was shown that

2. Preparation of various resins

<Preparation Example I. >
To a 2 L flask, 416 g of a 30% cyclohexanone solution of vinyl chloride copolymer (MR104 manufactured by Kaneka) (solid content 124.8 g) was added and stirred at a stirring speed of 210 rpm. Subsequently, 0.28 g (2.60 mol, 20000 ppm) of 1,4-benzoquinone was added and dissolved by stirring.
Next, 0.125 g of dibutyltin dilaurate was added as a reaction catalyst, and the mixture was heated to 40 to 50 ° C. and stirred. Next, 13.75 g (0.09 mol) of 2-methacryloyloxyethyl isocyanate (MOI manufactured by Showa Denko KK) was added dropwise over 30 minutes as a radiation curable functional group-introducing component, and the mixture was stirred at 40 ° C. for 2 hours after completion of the dropwise addition. Then, it cooled to room temperature and obtained the resin solution (radiation-curable composition) containing a radiation-curable functional group (methacryloyloxy group) containing vinyl chloride copolymer.
The ¹ H NMR data of the above-mentioned radiation curable functional group (methacryloyloxy group) -containing vinyl chloride copolymer and its attribution are shown below.
¹ H-NMR (DMSO-d6) δ (ppm) = 6.2-6.0 (C = C double bond peak), 5.8-5.6 (C = C double bond peak), 4.6-4.2 (br., M ), 4.2-4.0 (m), 3.9-3.1 (m), 3.1-3.0 (br., S), 2.7-2.65 (br., S), 2.60-2.0 (m), 2.0-0.7 (br., m).

  The solid content of the resin solution obtained by the above steps was 31.0%. Within 1 day after preparation of the resin solution, the mass average molecular weight (Mw) and number average molecular weight (Mn) of the radiation curable group-containing vinyl chloride copolymer contained in this solution were determined by the method described below. = 51,000 and Mn = 29,000. When the glass transition temperature (Tg1), sulfate group concentration and methacryloyloxy group concentration of the radiation curable functional group-containing vinyl chloride copolymer were measured by the methods described later, Tg1 = 75 ° C. and sulfate group concentration = 70 mmol / kg. The methacryloyloxy group concentration was 340 mmol / kg.

<Preparation Example II. >
(1) Synthesis of polyester resin 159.7 parts of dimethyl sodium 5-sulfoisophthalate (manufactured by Tokyo Chemical Industry), 275.2 parts of ester glycol (manufactured by Mitsubishi Chemical), zinc acetate dihydrate (manufactured by Wako Pure Chemical Industries) Four parts were heated at 245 ° C. The resulting distillate was stirred for 6 hours while distilling off using a Dean-Stark tube. The obtained solid was taken out to obtain a polyester polyol having the following structure (hereinafter referred to as “polyester polyol 1”). The weight average molecular weight and the weight average molecular weight / number average molecular weight ratio (Mw / Mn) of the obtained polyester polyol were determined in terms of standard polystyrene using a THF solvent. The weight average molecular weight was 1000 and Mw / Mn = 1.85.

(2) Preparation of polyether polyurethane resin In a flask, methyl oxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol as a chain extender (BPX-1000 manufactured by ADEKA, mass average molecular weight 1000) 15.0 g, 3.0 g of polyester polyol 1, 12.0 g of 4,4′-bicyclohexanol, and 43.4 g of cyclohexanone as a polymerization solvent were added. Next, a solution of 17.3 g of methylene bis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) and 20.0 g of cyclohexanone was added dropwise over 15 minutes. Next, 0.047 g of di-n-butyltin laurate was added as a polymerization catalyst, and the mixture was heated to 80 ° C. and stirred for 5 hours. After completion of the reaction, 46.9 g of cyclohexanone was added to obtain a polyether polyurethane resin solution.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. When the mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of the polyurethane resin contained in this solution were measured by the methods described later, Mw = 69,000 and Mn = 4. The content was 30,000 and the sulfonic acid (salt) group content was 70 mmol / kg.

<Preparation Example III. >
(1) Synthesis of sulfonate group-containing diol compound To a flask, 100 ml of distilled water, 50 g (0.400 mol) of taurine and 22.46 g (purity of 87%) of KOH manufactured by Wako Pure Chemical Industries, Ltd. were added, and the internal temperature was raised to 50 ° C. Warm to dissolve the contents completely.
Next, the internal temperature was cooled to 40 ° C., 140.4 g (1.080 mol) of butyl glycidyl ether was added dropwise over 30 minutes, and then the temperature was raised to 50 ° C. and stirred for 2 hours. The solution was cooled to room temperature, 100 ml of toluene was added, liquid separation was performed, and the toluene layer was discarded. Next, 400 ml of cyclohexanone was added, the temperature was raised to 110 ° C., and water was removed with a Dean Stark to obtain a 50% cyclohexanone solution of a sulfonate group-containing diol compound. The ¹ H NMR data of the product is shown below. From the NMR analysis results, the product is a mixture containing other compounds such as the exemplified compound (S-64) described in the publication in addition to the exemplified compound (S-31) described in JP-A-2009-96798. Was confirmed.
¹ H NMR (CDCl3): δ (ppm) = 4.5 (br.), 3.95-3.80 (m), 3.50-3.30 (m), 3.25-2.85 (m), 2.65-2.5 (m), 2.45-2.35 ( m), 1.6-1.50 (5-wire), 1.40-1.30 (6-wire), 1.00-0.90 (3-wire).

(2) Preparation of radiation curable polyurethane resin In a flask, methyl oxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol as a chain extender (BPX-1000 manufactured by ADEKA, mass average molecular weight) 1000) 57.5 g, glycerol methacrylate (Blemmer GLM manufactured by NOF Corporation) 5.0 g (concentration 300 mmol / kg), and 10.5 g of dimethyloltricyclodecane (TCDM manufactured by OXEA), an exemplary compound (S-31) 6.8 g of 50% cyclohexanone solution, 101.6 g of cyclohexanone as a polymerization solvent, and 0.24 g of p-methoxyphenol were added. Next, a solution of 35.8 g of methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) and 50.0 g of cyclohexanone was added dropwise over 15 minutes. Next, 0.11 g of di-n-butyltin laurate was added as a polymerization catalyst, heated to 80 ° C. and stirred for 3 hours. After completion of the reaction, 110.0 g of cyclohexanone was added to obtain a radiation curable polyurethane resin solution.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. When the mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of the polyurethane resin contained in this solution were measured by the methods described below, Mw = 36,000 and Mn = 2. The sulfonic acid (salt) group content was 40,000 / kg. Moreover, since the residual monomer was not confirmed by GPC, the radiation-curable functional group content is calculated as 300 mmol / kg from the charging ratio.

<Preparation Example IV. >
(1) Synthesis of polyester resin 11.1 part of dimethyl sodium 5-sulfoisophthalate (manufactured by Tokyo Chemical Industry), 100.0 parts of adipic acid (manufactured by Tokyo Chemical Industry), 2,2-dimethyl-1,3-propanediol 79. 4 parts, 29.6 parts of 1,6-hexanediol, and 0.4 parts of dibutyltin oxide (manufactured by Tokyo Chemical Industry) were heated at 245 ° C. The obtained distillate was stirred and distilled for 6 hours using a Dean-Stark tube to obtain a polyester polyol having the following structure (hereinafter referred to as “polyester polyol 2”). The weight average molecular weight and the weight average molecular weight / number average molecular weight ratio (Mw / Mn) of the obtained polyester polyol 2 were determined in terms of standard polystyrene using a THF solvent. The weight average molecular weight was 2150 and Mw / Mn = 1.85.

(2) Synthesis of polyester resin 100.0 parts of adipic acid (manufactured by Tokyo Chemical Industry), 74.8 parts of 2,2-dimethyl-1,3-propanediol, 27.7 parts of 1,6-hexanediol, dibutyltin oxide ( 0.4 parts (manufactured by Tokyo Chemical Industry) was heated at 245 ° C. The resulting distillate was stirred for 6 hours while distilling off using a Dean-Stark tube to obtain a polyester polyol having the following structure (hereinafter referred to as “polyester polyol 3”). The weight average molecular weight and the weight average molecular weight / number average molecular weight ratio (Mw / Mn) of the obtained polyester polyol 3 were determined in terms of standard polystyrene using a THF solvent. The weight average molecular weight was 2100 and Mw / Mn = 1.85.

(3) Synthesis of polyester polyurethane resin In a flask, 50.0 parts of polyester polyol 2, 50.0 parts of polyester polyol 3, 100.0 parts of 2-ethyl-butyl-1,3-propanediol, 501.4 of cyclohexanone Part, methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT, manufactured by Nippon Polyurethane Co., Ltd.) was added. Next, 0.72 part of di-n-butyltin laurate was added, the temperature was raised to 80 ° C., and the mixture was stirred for 5 hours. After completion of the reaction, 331.5 parts of cyclohexanone was added to obtain a polyester urethane resin solution.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. When the mass average molecular weight (Mw), the number average molecular weight (Mn), and the sulfonic acid (salt) group content of the polyurethane resin contained in this solution were measured by the methods described above, Mw = 70,000 and Mn = 4. The sulfonic acid (salt) group content was 10,000, and the content was 64.1 mmol / kg. The urethane group concentration was 3.8 mmol / g.

3. Evaluation method of resin (1) Measurement of average molecular weight The average molecular weight (Mw) of each resin was determined by using GPC (gel permeation chromatography) using a DMF solvent containing 0.3% of lithium bromide. It calculated | required in polystyrene conversion.
(2) Sulfuric acid (salt) group concentration, sulfonic acid (salt) group concentration The amount of sulfur element is determined from the peak area of sulfur (S) element by fluorescent X-ray analysis, and converted to the amount of sulfur element per kg of resin. The concentration of sulfuric acid (salt) group or sulfonic acid (salt) group was determined.
(3) Radiation curable functional group content in resin The radiation curable functional group content of the radiation curable resin was calculated from the integral ratio of NMR.
(4) Glass transition temperature Tg1 was measured by the method described above.

  Table 2 below shows the glass transition temperature Tg1 of the resin obtained in the above preparation example and the polyester polyurethane resin (UR4800 manufactured by Toyobo Co., Ltd.) used in Examples and Comparative Examples described later. Table 2 below also shows the storage elastic modulus E ′ at 80 ° C. for the polyurethane resins used in the magnetic layer in Examples and Comparative Examples described later.

4). Examples and comparative examples of magnetic recording tape

[Example 1]
(1) Preparation of magnetic layer coating solution Ferromagnetic hexagonal barium ferrite powder used in Test Example 1: 100 parts Dispersant 3-Phenylpropionic acid (manufactured by Tokyo Chemical Industry): 5 parts Polyvinyl chloride copolymer MR104 (Japan) 10 parts Polyester polyurethane resin UR4800 (Toyobo): 10 parts Methyl ethyl ketone: 150 parts Cyclohexanone: 150 parts α-Al ₂ O ₃ Mohs hardness 9 (average particle size 0.1 μm): 15 parts Carbon black (average particle) Diameter 0.08 μm): 0.5 part

About said coating material, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill. In the resulting dispersion
Butyl stearate: 1.5 parts Stearic acid: 0.5 parts Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts Toluene: 3 parts Polyisocyanate compound (Nihon Polyurethane Kogyo Co., Ltd. Coronate 3041): 5 parts were added and stirred for another 20 minutes. Then, it ultrasonically processed and filtered using the filter which has an average hole diameter of 1 micrometer, and prepared the magnetic layer coating liquid.

(2) Preparation of coating solution for nonmagnetic layer Nonmagnetic powder (αFe ₂ O ₃ hematite): 75 parts
Long axis length 0.15μm
Specific surface area by BET method 52m ² / g
pH 6
Tap density 0.8
DBP oil absorption 27-38 g / 100 g,
Surface treatment agent Al ₂ O ₃ , SiO ₂
Carbon black: 25 parts
Average primary particle size 0.020μm
DBP oil absorption 80ml / 100g
pH 8.0
Specific surface area by BET method: 250 m ² / g
Volatile content: 1.5%
Preparation Example I. Radiation-curable vinyl chloride copolymer obtained in 12: 12 parts Preparation Example III. Radiation curable polyurethane resin obtained in step c: 7.5 parts Methyl ethyl ketone: 150 parts Cyclohexanone: 150 parts

About said coating material, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill.
To the obtained dispersion liquid, butyl stearate: 1.5 parts stearic acid: 1 part methyl ethyl ketone: 50 parts cyclohexanone: 50 parts, stirred, filtered using a filter having an average pore size of 1 μm, and non-magnetic coating solution Was prepared.

(3) Preparation of backcoat layer coating solution Carbon black (average particle size 40 nm): 85 parts Carbon black (average particle size 100 nm): 3 parts Nitrocellulose: 28 parts Polyester resin (Toyobo's Byron 500): 58 parts Copper phthalocyanine Dispersant: 2.5 parts Nipponran 2301 (manufactured by Nippon Polyurethane Industry Co., Ltd.): 0.5 parts Methyl isobutyl ketone: 0.3 parts Methyl ethyl ketone: 860 parts
4 parts polyester resin (Toyobo Co., Ltd. Byron 500),
14 parts of a polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.)
5 parts of α-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd.) was added and stirred and filtered to prepare a backcoat layer coating solution.

(4) Preparation of magnetic recording medium The thickness after drying a sulfonic acid-containing polyester resin as an adhesive layer on a polyethylene naphthalate resin support having a center line surface roughness of 0.003 μm and a thickness of 5 μm on the coated surface of the magnetic layer. It applied using a coil bar so that thickness might be set to 0.05 micrometer.
Next, the nonmagnetic layer coating solution is applied so that the thickness after drying is 1.0 μm, and is sufficiently dried by a dryer, and then the nonmagnetic layer coating solution is used in an atmosphere having an oxygen concentration of 200 ppm or less. The coating layer was irradiated with 40 kGy of radiation to form a nonmagnetic layer (radiation-cured layer).
Further, immediately after that, a magnetic layer coating solution is applied on the magnetic layer so that the thickness of the magnetic layer becomes 0.06 μm, and oriented and dried by a solenoid having a magnetic force of 0.4 T (4000 G), and then the support. The back coat layer coating solution was applied to the back surface of the substrate so that the thickness after drying was 0.5 μm. Part of the coated sheet was used for evaluation of surface properties. Next, a seven-stage calendar composed of metal rolls was used to process at a temperature of 100 ° C. at a speed of 80 m / min, and slit to a 1/2 inch width to produce a magnetic recording tape.

[Example 2]
A magnetic recording tape was produced in the same manner as in Example 1 except that 5 parts of 3-phenylpropionic acid was changed to 5 parts of N- (4-hydroxyphenyl) glycine.

[Example 3]
A magnetic recording tape was produced in the same manner as in Example 1 except that 5 parts of 3-phenylpropionic acid was changed to 5 parts of phenoxyacetic acid.

[Comparative Example 1]
(1) Preparation of Magnetic Layer Coating Solution A magnetic layer coating solution was prepared in Example 1 except that 5 parts of 3-phenylpropionic acid was changed to 5 parts of 4-t-butylphenol.

(2) Preparation of coating solution for nonmagnetic layer Nonmagnetic inorganic powder (α-iron oxide): 85 parts Surface treatment agent: Al ₂ O ₃ , SiO ₂
Long axis length: 0.15 μm
Tap density: 0.8
Needle ratio: 7
BET specific surface area: 52 m ² / g
pH: 8
DBP oil absorption: 33g / 100g
Carbon black: 20 parts DBP oil absorption: 120 ml / 100 g
pH: 8
BET specific surface area: 250 m ² / g
Volatile content: 1.5%
Vinyl chloride copolymer (MR-104 manufactured by Nippon Zeon): 15 parts
Preparation Example II. Polyether polyurethane resin obtained in 1 above: 15 parts phenylphosphonic acid: 3 parts α-Al ₂ O ₃ (average particle size 0.2 μm): 10 parts cyclohexanone: 140 parts methyl ethyl ketone: 170 parts butyl stearate: 2 parts stearic acid: 1 copy

About said coating material, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill.
Butyl stearate: 1.5 parts Stearic acid: 1 part Polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts were added to the dispersion and stirred. Filtration was performed using a filter having an average pore size to prepare a nonmagnetic layer coating solution.

(3) Preparation of Backcoat Layer Coating Solution Same as Example 1.

(4) Preparation of magnetic recording medium The thickness after drying a sulfonic acid-containing polyester resin as an adhesive layer on a polyethylene naphthalate resin support having a center line surface roughness of 0.003 μm and a thickness of 5 μm on the coated surface of the magnetic layer. It applied using a coil bar so that thickness might be set to 0.05 micrometer.
Subsequently, the above-mentioned nonmagnetic coating solution is simultaneously coated so that the thickness after drying becomes 1.0 μm, and then the above-mentioned magnetic layer coating solution is coated simultaneously so that the thickness after drying becomes 0.06 μm. After orientation and drying by a solenoid having a magnetic force of .4T (4000 G), the above backcoat layer coating solution was applied to the back surface of the support so that the thickness after drying was 0.5 μm. Part of the coated sheet was used for evaluation of surface properties. Subsequently, the treatment was performed at a temperature of 100 ° C. at a speed of 80 m / min with a seven-stage calendar composed of metal rolls. Thereafter, heat treatment was performed at 70 ° C. for 36 hours, and slitting to a 1/2 inch width produced a magnetic recording tape.

[Comparative Example 2]
Polyester polyurethane resin used in the magnetic layer coating solution was prepared from Toyobo UR4800 in Preparation Example IV. A magnetic recording tape was produced in the same manner as in Example 1 except that the polyester polyurethane resin obtained in 1 was changed.

Glass transition temperature Tg2 of nonmagnetic layer
The glass transition temperature Tg2 of the nonmagnetic layers of Examples and Comparative Examples was measured. Table 3 below shows measured values of Tg2 together with Tg1 and E ′ of the polyurethane resin used in the magnetic layer and the curing means of the nonmagnetic layer in the above Examples and Comparative Examples. In addition, whether or not the magnetic layer contains a compound represented by the general formula A (Compound A) is also shown in Table 3 below.

Evaluation Method (i) Dispersion Stability of Magnetic Layer Coating Solution Regarding Examples and Comparative Examples, in order to confirm the effect of improving the dispersibility of the added dispersant when the magnetic layer coating solution is completed, the state of the coating solution is changed. Observed. Specifically, after allowing the coating solution to stand for 10 minutes, the coating solution was visually observed according to the following evaluation criteria.
Evaluation criteria ○ Maintains liquid state △ Increases viscosity, but retains liquid state × Becomes a pudding-like mass

(Ii) Evaluation of Dispersibility of Ferromagnetic Powder in Magnetic Layer Coating Solution For Examples and Comparative Examples, in order to evaluate the dispersibility of the ferromagnetic powder in the magnetic layer coating solution, a magnetic sheet for evaluation was obtained by the following method. Was made.
The thickness after drying of the sulfonic acid-containing polyester resin as an adhesive layer on a polyethylene naphthalate resin support having a center line surface roughness of 0.003 μm and a thickness of 5 μm on the coated surface of the magnetic layer is 0.05 μm. It was applied using a coil bar.
Next, the magnetic layer coating solution was applied so that the thickness after drying was 1.0 μm, and was oriented and dried by a solenoid having a magnetic force of 0.4 T (4000 G). Next, a magnetic sheet was obtained by performing treatment at a temperature of 100 ° C. at a speed of 80 m / min with a seven-stage calendar composed of metal rolls.
About the obtained magnetic sheet, the magnetic characteristic when an external magnetic field was applied in parallel with the orientation direction of a ferromagnetic powder was measured using the sample vibration magnetometer (VSM-P7 by Toei Kogyo). Specifically, the ratio of the magnetization (saturation magnetization) when 797.7 kA / m (10 kOe) is applied as an external magnetic field to the magnetization (residual magnetization) when the external magnetic field is zero, that is, the squareness ratio (SQ ) Was measured.
SQ can be used as an indicator of the dispersibility of a ferromagnetic material. If the dispersibility is poor, the SQ is low, and if it is good, the SQ is high. Since the value of SQ affects noise, it is preferably as close to 1.0 as possible.

(Iii) Evaluation of calender moldability The surface roughness of the magnetic layer surface was measured before and after the seven-step calendering process for the magnetic recording tapes of Examples and Comparative Examples. The surface roughness was determined by using an optical interference type surface roughness meter HD-2000 type (optical interference method) manufactured by WYKO, with a center plane average surface roughness Ra (250 μm × 250 μm area) under the condition of a cutoff value of 0.25 mm. Measured as Wyko-Ra). Ra difference before and after the calendar, that is, ΔRa calculated by the following formula was used as an index of calendar moldability.
Wyko-ΔRa = (Wyko-Ra before calendar processing)-(Wyko-Ra after calendar processing)
The case where ΔRa is negative indicates that the formability is too bad and the surface roughness is caused by the calendar process. Note that Wyko-Ra represents surface roughness at a frequency lower than that of the following AFM-Ra, and thus can be used as an index of surface roughness of the entire surface.
Separately from this, for the magnetic sheet produced in (ii) above, Wyko-Ra before and after calendering was measured, and calender moldability (Wyko-ΔRa) of a single magnetic layer was obtained.

(Iv) Surface Roughness Evaluation of Magnetic Recording Tape With respect to the magnetic recording tapes of Examples and Comparative Examples, an atomic force microscope AFM (Nanoscope II manufactured by Digital Instrument) was used, and a tunnel current of 10 nA and a bias current of 400 mV were 30 μm × 30 μm. The range was scanned to determine the surface roughness (AFM-Ra). AFM-Ra represents a surface roughness having a relatively higher frequency than the above Wyko-Ra, and this value affects the following electromagnetic conversion characteristics.

(V) Electromagnetic conversion characteristics (S / N ratio)
The S / N ratios of the magnetic recording tapes of Examples and Comparative Examples were measured by a 1/2 inch linear system with a fixed head. The relative speed of the head / tape was 10 m / sec. For recording, a MIG head with a saturation magnetization of 1.4 T (track width 18 μm) was used, and the recording current was set to the optimum current for each tape. An anisotropic MR head (A-MR) having an element thickness of 25 nm and a shield interval of 0.2 μm was used as the reproducing head.
A signal having a recording wavelength of 0.2 μm was recorded, and the reproduced signal was subjected to frequency analysis using a spectrum analyzer manufactured by Shiba-Soku, and the ratio of the output of the carrier signal (wavelength 0.2 μm) to the integrated noise in the entire spectrum was taken as the S / N ratio.

(Vi) Repeated sliding durability The magnetic recording tapes of the examples and comparative examples shown in Table 6 were monitored while monitoring the output of the carrier signal (wavelength 0.2 μm) with a 1/2 inch linear system with a fixed head. The vehicle was repeatedly run for 10,000 passes as one pass of 800 m, and the output reduction degree (output reduction degree A) after running for 10,000 passes was evaluated by setting the output of the first pass to 0 dB according to the following evaluation criteria. Thereafter, the vehicle was further driven for 5000 passes, and the first pass was set to 0 dB according to the following evaluation criteria, and the output reduction degree (output reduction degree B) after 15000 passes was evaluated. As the amount of deposits on the head increases, the output decreases, and the evaluation result can be used as an index of the deposits on the head.
(Output reduction degree A)
◎ Output reduction after 10,000 passes is higher than -0.5 dB. ○ Output reduction after 10000 passes is higher than -0.5 dB to -1.0 dB. Δ Output reduction after 10000 passes is -1. 0 to -2.0 dB
× Output reduction after 10,000 passes is lower than -2.0 dB (output reduction B)
◎ Output reduction after 15000 passes is higher than -0.5 dB. ○ Output reduction after 15000 passes is higher than -0.5 dB to -1.0 dB. Δ Output reduction after 15000 passes is -1. 0--2.0dB
X Output reduction after 15000 passes is lower than -2.0 dB. Further, the magnetic head after running 15000 passes is taken out and the X-ray fluorescence analysis incorporated in the scanning electron microscope (Hitachi FE-SEM-S800) The presence or absence of a peak derived from phosphorus was confirmed.
The above results are shown in Table 4 below.

From the results of Table 4, as described above, the magnetic recording medium of the present invention has the following (1) to (4), thereby improving the coating strength (reducing head deposits by suppressing the occurrence of coating destruction). ) And improvement of surface smoothness, thereby confirming that it can exhibit excellent electromagnetic conversion characteristics over a long period of time.
(1) The magnetic layer contains a compound represented by the general formula A together with the hexagonal ferrite powder.
(2) The binder of the magnetic layer is a mixture of a vinyl chloride copolymer, a polyurethane resin and a polyisocyanate, and the polyurethane resin has a glass transition temperature in the range of 90 to 130 ° C and a storage elastic modulus at 80 ° C. Is in the range of 2.5 to 5.0 GPa.
(3) The nonmagnetic layer is a radiation curable layer obtained by radiation curing a radiation curable composition containing a nonmagnetic powder and a binder component, and the binder component is a radiation curable vinyl chloride copolymer. Includes a polymer and a radiation curable polyurethane resin.
(4) The radiation curable vinyl chloride copolymer and the radiation curable polyurethane resin both have a glass transition temperature in the range of 30 to 100 ° C.
On the other hand, the magnetic recording tape obtained in Comparative Example 2 was inferior in durability slidability.
In Comparative Example 1, the reason why the durability slidability was lowered as compared with Examples was that 4-t-butylphenol added as a magnetic layer component was partially adsorbed because of its poor adsorptivity to the hexagonal ferrite particle surface. As a result of the function of -t-butylphenol as a plasticizer in the magnetic layer, it is considered that the coating strength was lowered. In Comparative Example 1, the electromagnetic conversion characteristics are greatly inferior to those in Examples, but this is because 4-t-butylphenol cannot sufficiently improve the dispersibility of the hexagonal ferrite powder. Since the magnetic layer becomes soft due to the plasticizing effect of 4-t-butylphenol, the calendar formability and surface smoothness are relatively good, but as described above, it is inferior in durability sliding property, so it has high reliability over a long period of time. However, it does not have sufficient performance as a magnetic recording medium for high-density recording that is required to be usable with a high density.

5). Reference and comparative examples for magnetic tape production and evaluation

[Reference Example 1]
(1) Preparation of coating solution for magnetic layer Ferromagnetic metal powder: 100 parts Composition Fe / Co = 100/25
Hc 195 kA / m (≈2450 Oe)
Specific surface area by BET method 65m ² / g
Surface Al ₂ O ₃ , SiO ₂ , Y ₂ O ₃ treatment Particle size (average major axis length) 35 nm
Needle ratio 5
σs 110 A · m ² / kg (≈110 emu / g)
Dispersant Transcinnamic acid (manufactured by Tokyo Chemical Industry): 5 parts Polyvinyl chloride copolymer MR104 (manufactured by Nippon Zeon Co., Ltd.): 10 parts Polyester polyurethane resin a: 10 parts Methyl ethyl ketone: 150 parts Cyclohexanone: 150 parts α-Al ₂ O ₃ Mohs hardness 9 (average particle size 0.1 μm): 15 parts Carbon black (average particle size 0.08 μm): 0.5 parts

About said coating material, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill. In the resulting dispersion
Butyl stearate: 1.5 parts Stearic acid: 0.5 parts Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts Toluene: 3 parts Polyisocyanate compound (Nihon Polyurethane Kogyo Co., Ltd. Coronate 3041): 5 parts were added and stirred for another 20 minutes. Then, it ultrasonically processed and filtered using the filter which has an average hole diameter of 1 micrometer, and prepared the magnetic layer coating liquid.

(2) Preparation of coating solution for nonmagnetic layer Nonmagnetic powder (αFe ₂ O ₃ hematite): 75 parts
Long axis length 0.15μm
Specific surface area by BET method 52m ² / g
pH 6
Tap density 0.8
DBP oil absorption 27-38 g / 100 g,
Surface treatment agent Al ₂ O ₃ , SiO ₂
Carbon black: 25 parts
Average primary particle size 0.020μm
DBP oil absorption 80ml / 100g
pH 8.0
Specific surface area by BET method: 250 m ² / g
Volatile content: 1.5%
Radiation curable vinyl chloride copolymer b: 12 parts Radiation curable polyurethane resin c: 7.5 parts Methyl ethyl ketone: 150 parts Cyclohexanone: 150 parts

About said coating material, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill.
To the obtained dispersion liquid, butyl stearate: 1.5 parts stearic acid: 1 part methyl ethyl ketone: 50 parts cyclohexanone: 50 parts, stirred, filtered using a filter having an average pore size of 1 μm, and non-magnetic coating solution Was prepared.

(3) Preparation of Backcoat Layer Coating Solution Same as Example 1.

(4) Production of magnetic recording medium The same operation as in Example 1 was performed to produce a magnetic recording tape.

[Reference Example 2]
In the preparation of the nonmagnetic layer coating solution of Reference Example 1, the radiation curable vinyl chloride copolymer d was used instead of the radiation curable vinyl chloride copolymer b, and the radiation curable polyurethane resin was used instead of the radiation curable polyurethane resin c. A magnetic tape was produced in the same manner as in Example 1 except that e was used. Details of the resin preparation methods used in the reference examples and comparative reference examples will be described later.

[Reference Example 3]
A magnetic tape was prepared in the same manner as in Reference Example 2 except that the radiation curable polyurethane resin e was changed to the radiation curable polyurethane resin h in the preparation of the nonmagnetic layer coating solution of Reference Example 2.

[Reference Example 4]
A magnetic tape was produced in the same manner as in Reference Example 2 except that the radiation curable polyurethane resin e was changed to the radiation curable polyurethane resin i in the preparation of the nonmagnetic layer coating solution of Reference Example 2.

[Reference Example 5]
A magnetic tape was produced in the same manner as in Reference Example 2 except that the radiation curable polyurethane resin e was changed to the radiation curable polyurethane resin j in the preparation of the nonmagnetic layer coating solution of Reference Example 2.

[Comparative Reference Example 1]
(1) Preparation of magnetic layer coating solution The same procedure as in Reference Example 1 was performed.

(2) Preparation of non-magnetic layer coating solution Preparation of non-magnetic layer coating solution Non-magnetic powder (αFe ₂ O ₃ hematite): 80 parts
Long axis length 0.15μm
Specific surface area by BET method 52m ² / g
pH 6
Tap density 0.8
DBP oil absorption 27-38 g / 100 g,
Surface treatment agent Al ₂ O ₃ , SiO ₂
Carbon black: 20 parts
Average primary particle size 0.020μm
DBP oil absorption 80ml / 100g
pH 8.0
Specific surface area by BET method: 250 m ² / g
Volatile content: 1.5%
Vinyl chloride copolymer k (manufactured by Nippon Zeon MR-104): 15 parts
Polyether polyurethane resin f: 10 parts Methyl ethyl ketone: 150 parts Cyclohexanone: 150 parts

About said coating material, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill.
Butyl stearate: 1.5 parts Stearic acid: 1 part Polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts were added to the dispersion and stirred. Filtration was performed using a filter having an average pore size to prepare a nonmagnetic layer coating solution.

(3) Preparation of magnetic recording medium Thickness after drying a sulfonic acid-containing polyester resin as an adhesive layer on a polyethylene naphthalate resin support having a center line surface roughness of 0.003 μm and a thickness of 5 μm on the magnetic layer coating surface It applied using a coil bar so that thickness might be set to 0.05 micrometer.
Subsequently, the above-mentioned nonmagnetic coating solution is simultaneously coated so that the thickness after drying becomes 1.0 μm, and then the above-mentioned magnetic layer coating solution is coated simultaneously so that the thickness after drying becomes 0.06 μm. After being oriented and dried by a solenoid having a magnetic force of 4T (4000G), a backcoat layer coating solution prepared in the same manner as in Example 1 on the back surface of the support was dried to a thickness of 0.5 μm. It applied so that it might become. Part of the coated sheet was used for evaluation of surface properties. Subsequently, the treatment was performed at a temperature of 100 ° C. at a speed of 80 m / min with a seven-stage calendar composed of metal rolls. Thereafter, heat treatment was performed at 70 ° C. for 36 hours, and slitting to a 1/2 inch width produced a magnetic recording tape.

[Reference Example 6]
The magnetic layer coating solution was prepared in the same manner as in Reference Example 1 except that the polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) was replaced with 2.5 parts (a ratio equivalent to Experiment 6 described later). A recording tape was obtained.

[Reference Example 7]
In preparing the magnetic layer coating solution, 6 parts of polyester polyurethane resin a, 14 parts of polyvinyl chloride copolymer k (MR104 manufactured by ZEON Corporation), and 7 parts of polyisocyanate compound (CORONATE 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) A magnetic recording tape was obtained in the same manner as in Reference Example 1 except that the ratio was changed to the same ratio as in Experiment 3 described later.

[Comparative Reference Example 2]
A magnetic recording tape was obtained in the same manner as in Reference Example 1 except that polyester polyurethane resin g was used instead of polyester polyurethane resin a in the preparation of the magnetic layer coating solution.

[Comparative Reference Example 3]
In preparing the magnetic layer coating solution, 0 part of polyester polyurethane resin a, 20 parts of polyvinyl chloride copolymer k (MR104 manufactured by Nippon Zeon Co., Ltd.), and 0 part of polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) A magnetic recording tape was obtained in the same manner as in Reference Example 1 except that the ratio was changed to the same ratio as in Experiment 10 described later.

[Comparative Reference Example 4]
In the preparation of the magnetic layer coating solution, 20 parts of polyester urethane resin a, 0 parts of polyvinyl chloride copolymer k (MR104 manufactured by Nippon Zeon Co., Ltd.), and 0 of polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) Parts (ratio equivalent to Experiment 9 described later). However, the dispersion of the ferromagnetic powder did not proceed and a magnetic recording tape could not be produced.

[Reference Example 8]
The magnetic layer coating solution was prepared in the same manner as in Reference Example 5 except that the polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) was replaced with 3.5 parts (a ratio equivalent to Experiment 2 described later). A recording tape was obtained.

[Reference Example 9]
The magnetic layer coating solution was prepared in the same manner as in Reference Example 5, except that the polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) was replaced with 10.5 parts (a ratio equivalent to Experiment 4 described later). A recording tape was obtained.

[Comparative Reference Example 5]
The magnetic recording tape was prepared in the same manner as in Reference Example 1, except that the polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) was replaced with 0 part (a ratio equivalent to Experiment 5 described later) in the preparation of the magnetic layer coating solution. Got.

  With respect to the resins used in the above Reference Examples and Comparative Reference Examples, the glass transition temperature Tg1 and the storage elastic modulus E ′ at 80 ° C. were measured by the above methods. The results are shown in Table 5 below. Further, the storage elastic modulus E ′ of the polyester polyurethane resin a at 80 ° C. was 2.57 GPa.

Glass transition temperature Tg2 of nonmagnetic layer
The glass transition temperature Tg2 of the nonmagnetic layer of the reference example and the comparative reference example was measured. In Table 6 below, the measured values of Tg2 are shown together with the prescriptions and the preparation methods of the above Reference Examples and Comparative Reference Examples.

  For Reference Examples 1, 2, 6 to 9, and Comparative Reference Examples 1 to 5, the same evaluation as in the above-described Examples and Comparative Examples was performed. The results are shown in Table 7 below.

The above reference examples and comparative reference examples are examples in which a ferromagnetic metal powder is used as the ferromagnetic powder. From the results of Table 7, the following (2) to (4) are satisfied to improve the coating film strength (coating It can be confirmed that the reduction of the deposits on the head by suppressing the generation of the film breakage and the improvement of the calendar moldability are achieved.
(2) The binder of the magnetic layer is a mixture of a vinyl chloride copolymer, a polyurethane resin and a polyisocyanate, and the polyurethane resin has a glass transition temperature in the range of 90 to 130 ° C and a storage elastic modulus at 80 ° C. Is in the range of 2.5 to 5.0 GPa.
(3) The nonmagnetic layer is a radiation curable layer obtained by radiation curing a radiation curable composition containing a nonmagnetic powder and a binder component, and the binder component is a radiation curable vinyl chloride copolymer. Includes a polymer and a radiation curable polyurethane resin.
(4) The radiation curable vinyl chloride copolymer and the radiation curable polyurethane resin both have a glass transition temperature in the range of 30 to 100 ° C.

  Separately from this, the calender moldability of the magnetic tapes of Reference Examples 3 to 5 was evaluated by the method described above. For comparison, the results are shown in Table 8 below together with Reference Example 2 and Comparative Reference Example 1. As shown in Table 8, also in Reference Examples 3 to 5, the calendar moldability was good as in the examples shown in Table 7.

Examination of magnetic layer binder mixing ratio Effect of mixing ratio of polyester polyurethane resin a, polyvinyl chloride copolymer k (MR104 manufactured by Nippon Zeon Co., Ltd.), polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) on thermal properties. This was confirmed by the following experiment. The results are shown in Table 9.
A mixture in which the above three components were mixed at a ratio shown in Table 9 was dissolved in a 50:50 (mass ratio) mixture of methyl ethyl ketone and cyclohexanone so as to be 22% by mass. Then, it apply | coated on the aramid base so that it might become 20 micrometers after drying. After drying, the film was thermally cured at 70 ° C. for 36 hours to obtain a clear film. The obtained clear film was cut into a width of 3.35 mm and a length of 5 cm, and a dynamic viscoelasticity measuring device (leovibron manufactured by TOYO BALDWIN, heating rate 2 ° C./min, measuring frequency 110 Hz) was used at 30 to 140 ° C. Measurement is performed in the temperature range, storage elastic modulus (E ′) at 80 ° C. is obtained, and in the same measurement, the glass transition temperature is used as the peak top temperature of loss elastic modulus (E ″) in the same manner as the above-described measurement of Tg2. Asked.
Table 9 also shows the results (Experiment 11) of measuring the glass transition temperature and the storage elastic modulus (E ′) at 80 ° C. of polyurethane resin A described in the above-mentioned Examples of JP-A-2004-319001 in the same manner. Show.

In Table 9, in comparison with Experiment 9 in which the polyurethane resin was used alone, Experiments 2 to 4, 6, and 8 in which the vinyl chloride copolymer and the polyisocyanate compound were used in combination improved Tg and E ′. In contrast, in Experiments 1, 5, and 7 conducted without polyisocyanate, Tg and / or E ′ decreased compared to Experiment 9 in which the polyurethane resin was used alone. It can be seen that the thermal characteristics of the magnetic layer can be improved only by using isocyanate. Further, it can be confirmed from the comparison between Experiment 9 and Experiment 11 that some polyurethane resins with high Tg do not show E ′ to be satisfied in the present invention, and therefore E ′ needs to be defined together with Tg.
In addition, as confirmed in Comparative Reference Example 4, it is difficult to disperse the ultrafine magnetic material with polyurethane alone.

  The preparation methods of the resins used in the above Reference Examples and Comparative Reference Examples are shown below.

<Preparation Example 1-1 (Synthesis of radiation curable vinyl chloride copolymer)>
(1) Polymerization of vinyl chloride copolymer: vinyl chloride: 100 parts allyl glycidyl ether: 11.9 parts 2-hydroxypropyl methacrylate: 4.1 parts allyl-2-hydroxyethyl ether: 3.6 parts sodium lauryl sulfate : 0.8 part Water: 117 parts were charged and stirred at 50 ° C.
after that,
Potassium persulfate: 0.6 part was charged to initiate emulsion polymerization. After 10 hours of reaction, the reactor was cooled when the pressure in the polymerization vessel reached 2 kg / cm ^2, and after recovering unreacted vinyl chloride, the solution was removed, washed and dried to obtain a copolymerization ratio (mol%).
Vinyl chloride: 93.0 mol%
Allyl glycidyl ether: 4.0 mol%
2-hydroxypropyl methacrylate: 1.0 mol%
Allyl-2-hydroxyethyl ether: 1.0 mol%
Unit in which epoxy group of allyl glycidyl ether is ring-opened with sulfuric acid: 1.0 mol%
A vinyl chloride copolymer (1) was obtained.

(2) Introduction reaction of radiation curable functional group To a 2 L flask, 416 g of a 30% cyclohexanone solution (124.8 g of solid content) of the vinyl chloride copolymer (1) was added and stirred at a stirring speed of 210 rpm. Subsequently, 0.28 g (2.60 mol, 20000 ppm) of 1,4-benzoquinone was added and dissolved by stirring.
Next, 0.125 g of dibutyltin dilaurate was added as a reaction catalyst, and the mixture was heated to 40 to 50 ° C. and stirred. Next, 13.75 g (0.09 mol) of 2-methacryloyloxyethyl isocyanate (MOI manufactured by Showa Denko KK) was added dropwise over 30 minutes as a radiation curable functional group-introducing component, and the mixture was stirred at 40 ° C. for 2 hours after completion of the dropwise addition. After cooling to room temperature, a resin solution (radiation curable composition) containing a radiation curable functional group (methacryloyloxy group) -containing vinyl chloride copolymer (radiation curable vinyl chloride copolymer d) is obtained. Obtained.
The ¹ H NMR data of the above-mentioned radiation curable functional group (methacryloyloxy group) -containing vinyl chloride copolymer and its attribution are shown below.
¹ H-NMR (DMSO-d6) δ (ppm) = 6.2-6.0 (C = C double bond peak), 5.8-5.6 (C = C double bond peak), 4.6-4.2 (br., M ), 4.2-4.0 (m), 3.9-3.1 (m), 3.1-3.0 (br., S), 2.7-2.65 (br., S), 2.60-2.0 (m), 2.0-0.7 (br., m).

  The solid content of the resin solution obtained by the above steps was 31.0%. Within 1 day after preparation of the resin solution, the mass average molecular weight (Mw) and number average molecular weight (Mn) of the radiation curable group-containing vinyl chloride copolymer contained in this solution were determined by the method described below. = 51,000 and Mn = 29,000. When the glass transition temperature (Tg1), sulfate group concentration and methacryloyloxy group concentration of the radiation curable functional group-containing vinyl chloride copolymer (specific example compound (1)) were measured by the above-mentioned methods, Tg1 = 75 ° C. The sulfate group concentration was 70 mmol / kg and the methacryloyloxy group concentration was 340 mmol / kg.

<Preparation Example 1-2 (Synthesis of radiation curable vinyl chloride copolymer)>
According to the method described in paragraphs [0040] to [0041] of JP 2004-352804 A, a resin (radiation curable vinyl chloride copolymer b) of Preparation Example 1 of JP 2004-352804 A was obtained. . In the same manner as in Preparation Example 1-1, Tg1 and the radiation curable functional group concentration were measured. As a result, Tg1 was 70 ° C. and the radiation curable functional group concentration was 1283 mmol / kg.

Reference Experiment Normally, it is known that a polyfunctional (meth) acrylate monomer is by-produced during the synthesis of the radiation curable resin. In Preparation Example 1-1, during the synthesis of the radiation curable vinyl chloride copolymer d, The following bifunctional methacrylate monomer (hereinafter referred to as “methacrylate monomer A”) was expected to be a by-product.

  Then, the by-product of the methacrylate monomer A was confirmed by the following method.

(1) Synthesis of methacrylate monomer A 10 g of 2-methacryloyloxyethyl isocyanate (MOI manufactured by Showa Denko KK) was dissolved in 100 ml of acetone. In an internal temperature range of 30 to 50 ° C., 100 g of water was added dropwise and stirred for 2 hours. After adding 200 g of ethyl acetate and stirring for 10 minutes, the aqueous phase was discarded. 100 g of water was added, stirred for 10 minutes, and allowed to stand, then the aqueous phase was discarded. The obtained organic phase was concentrated to dryness using an evaporator at an external temperature of 40 ° C. The NMR data of the product and its assignment are shown below.
¹ H-NMR (400MHz, DMSO, 25 ° C): 6.12 (2H, t), 6.05 (2H, s), 5.68 (2H, t), 4.05 (4H, t), 3.82 (4H, q), 1.88 ( 6H, s) ppm

(2) Confirmation of methacrylate monomer A by-product In the NMR data of 2-methacryloyloxyethyl isocyanate, typical proton assignments are as follows. As is apparent from the NMR data of radiation curable vinyl chloride copolymer d, methacrylate monomer A, and 2-methacryloyloxyethyl isocyanate, the peak of 6.12 ppm proton exists only in methacrylate monomer A, so this peak is present. By doing so, it can be confirmed that the methacrylate monomer A is by-produced. Therefore, when the ¹ H NMR measurement of the resin solution obtained in Preparation Example 1-1 was performed, a proton peak was confirmed at 6.12 ppm. From this result, it can be confirmed that methacrylate monomer A was by-produced in Preparation Example 1-1. In addition, when the content of the methacrylate monomer A in the resin solution obtained in Preparation Example 1-1 was determined by comparing the integral value with the methacrylate monomer A synthesized in the above (1), it was 7.18 g. Further, in the NMR data, by comparing the integral values of the radiation curable vinyl chloride copolymer d and the methacrylate monomer A, it was introduced into the radiation curable vinyl chloride copolymer d of 2-methacryloyloxyethyl isocyanate. When the ratio of the amount and the amount introduced into the methacrylate monomer A was determined, the former: the latter = 47.8: 52.2, and unreacted 2-methacryloyloxyethyl isocyanate was not detected.
From the above results and the charged amount, the production amount of the radiation curable vinyl chloride copolymer d in the resin solution obtained in Preparation Example 1-1 is calculated as 131.4 g.

  As described above, by-product of the methacrylate monomer A was confirmed in Preparation Example 1-1, but the presence of the by-produced methacrylate monomer greatly affects the radiation curable composition and the glass transition temperature of the radiation curable composition. is not. Therefore, the glass transition temperature Tg1 measured by the above method using the resin solution obtained in Preparation Example 1-1 is the glass transition temperature of the radiation-curable vinyl chloride copolymer d synthesized in Preparation Example 1-1. Can be considered. In order to show this point, as Preparation Example 1-1-1, a resin solution containing no methacrylate monomer A was prepared by the following method.

(Preparation Example 1-1-1)
A resin solution was obtained in the same manner as in Preparation Example 1-1. 200 g of acetone was added to 200 g of the obtained resin solution at an internal temperature of 50 ° C. Thereafter, when 500 g of methanol was added dropwise at an internal temperature of 45 to 55 ° C., a solid substance was deposited. The precipitated solid was filtered, 300 g of acetone was added and stirred at 50 ° C. to completely dissolve. When 500 g of methanol was added dropwise at an internal temperature of 45 to 55 ° C., a solid was deposited. The precipitated solid was filtered and dried under vacuum at 30 ° C. for 24 hours.
When ¹ H NMR measurement of the product obtained by the above operation was performed, no proton peak was observed at 6.12 ppm. From this result, it can be judged that the methacrylate monomer A as a by-product was removed from the reaction product by the above operation.
Subsequently, when the radiation-curing property and glass transition temperature of the product obtained by the above operation were measured by the above-described methods, the gel fraction was 84%, the glass transition temperature Tg1 was 75 ° C., and in Preparation Example 1-1 It was equivalent to the obtained result.
From the above results, the polyfunctional (meth) acrylate monomer by-produced at the time of synthesis does not significantly affect the radiation curable composition and the glass transition temperature of the radiation curable composition, and thus the glass transition temperature measured in the resin solution. It can be determined that various physical properties such as are physical properties of the radiation curable resin contained in the resin solution.

<Preparation Example 2-1 (Synthesis of polyurethane resin)>
In a reaction vessel equipped with a thermometer, stirrer, Vigreux tube, Liebig condenser, 190 parts of dimethyl terephthalate, 5.9 parts of dimethyl 5-sulfoisophthalate, 152 parts of propylene glycol, and 0.2 part of tetrabutoxy titanium The transesterification was carried out at 200 to 230 ° C. for 4 hours. Next, the temperature was raised to 240 ° C. over 10 minutes, and at the same time, the pressure was gradually reduced and reacted for 30 minutes to complete the polymerization to obtain polyester polyol 4.
The resulting polyester polyol (4: 100 parts) was dissolved in MEK (methyl ethyl ketone): 37 parts and toluene: 37 parts, MDI (4,4′-diphenylmethane diisocyanate): 12 parts, and neopentyl glycol (1 part) were added as a catalyst. Dibutyltin dilaurate: 0.05 part was added and reacted at 80 ° C. for 5 hours. Next, the solution was diluted with 94 parts of MEK and 94 parts of toluene, and a polyurethane resin (hereinafter referred to as “polyester polyurethane resin a”) (Mn = 25000, SO ₃ Na group concentration = 87 mmol / kg, urethane group concentration = About 1.2 mmol / g) was obtained.

<Preparation Example 2-2 (Synthesis of radiation curable polyurethane resin)>
(1) Synthesis of polyester resin 159.7 parts of dimethyl sodium 5-sulfoisophthalate (manufactured by Tokyo Chemical Industry), 275.2 parts of ester glycol (manufactured by Mitsubishi Chemical), zinc acetate dihydrate (manufactured by Wako Pure Chemical Industries) Four parts were heated at 245 ° C. The resulting distillate was stirred for 6 hours while distilling off using a Dean-Stark tube. The obtained solid was taken out to obtain a polyester polyol having the following structure (hereinafter referred to as “polyester polyol 5”). The weight average molecular weight and the weight average molecular weight / number average molecular weight ratio (Mw / Mn) of the obtained polyester polyol were determined in terms of standard polystyrene using a THF solvent. The weight average molecular weight was 1000 and Mw / Mn = 1.85.

(2) Synthesis of radiation curable polyurethane resin As a chain extender in a flask, methyloxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol (BPX-1000 manufactured by ADEKA, mass average molecular weight) 1000) 60.0 parts, glycerol methacrylate (Blenmer GLM manufactured by NOF Corporation) 6.2 parts (concentration 355.4 mmol / kg), and dimethylol tricyclodecane (TCEA manufactured by OXEA) 10.00 parts, polar group introduction As a component, 5.50 parts of polyester polyol, 159.4 parts of cyclohexanone and 0.24 part of p-methoxyphenol were added as polymerization solvents. Next, 35.7 parts of methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) was added. Subsequently, 0.33 part of di-n-butyltin laurate was added as a polymerization catalyst, heated to 80 ° C. and stirred for 5 hours. After completion of the reaction, 120.2 parts of cyclohexanone was added to obtain a polyurethane resin solution. After urethane synthesis, 50 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-OH-TEMPO) was added to the obtained polyurethane resin solution based on the polyurethane solid content.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of the polyurethane resin contained in this solution (hereinafter referred to as “radiation curable polyurethane resin c”) are measured by the methods described above. As a result, Mw = 48,000, Mn = 25,000, and the sulfonic acid (salt) group content was 60.7 mmol / kg. Moreover, since the residual monomer was not confirmed by GPC, radiation-curable functional group content is computed with 336.0 mmol / kg from a preparation ratio.

<Preparation Example 2-3 (Synthesis of radiation curable polyurethane resin)>

(1) Synthesis of sulfonate group-containing diol compound To a flask, 100 ml of distilled water, 50 g (0.400 mol) of taurine and 22.46 g (purity of 87%) of KOH manufactured by Wako Pure Chemical Industries, Ltd. were added, and the internal temperature was raised to 50 ° C. Warm to dissolve the contents completely.
Next, the internal temperature was cooled to 40 ° C., 140.4 g (1.080 mol) of butyl glycidyl ether was added dropwise over 30 minutes, and then the temperature was raised to 50 ° C. and stirred for 2 hours. The solution was cooled to room temperature, 100 ml of toluene was added, liquid separation was performed, and the toluene layer was discarded. Next, 400 ml of cyclohexanone was added, the temperature was raised to 110 ° C., and water was removed with a Dean Stark to obtain a 50% cyclohexanone solution of a sulfonate group-containing diol compound. The ¹ H NMR data of the product is shown below. From the NMR analysis results, the product is a mixture containing other compounds such as the exemplified compound (S-64) described in the publication in addition to the exemplified compound (S-31) described in JP-A-2009-96798. Was confirmed.
¹ H NMR (CDCl3): δ (ppm) = 4.5 (br.), 3.95-3.80 (m), 3.50-3.30 (m), 3.25-2.85 (m), 2.65-2.5 (m), 2.45-2.35 ( m), 1.6-1.50 (5-wire), 1.40-1.30 (6-wire), 1.00-0.90 (3-wire).
(2) Preparation of radiation curable polyurethane resin In a flask, methyl oxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol as a chain extender (BPX-1000 manufactured by ADEKA, mass average molecular weight) 1000) 57.50 g, glycerol methacrylate (Blenmer GLM manufactured by NOF Corporation) 6.50 g (concentration 355.44 mmol / kg), and dimethylol tricyclodecane (TCDM manufactured by OXEA) 10.50 g, exemplary compound (S-31) ), 80.26 g of cyclohexanone solution, 104.26 g of cyclohexanone as a polymerization solvent, and 0.240 g of p-methoxyphenol were added. Subsequently, a solution of 42.21 g of methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) and 51.47 g of cyclohexanone was added dropwise over 15 minutes. Next, 0.361 g of di-n-butyltin laurate was added as a polymerization catalyst, the temperature was raised to 80 ° C., and the mixture was stirred for 3 hours. After completion of the reaction, 121.28 g of cyclohexanone was added to obtain a polyurethane resin solution. After urethane synthesis, 50 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-OH-TEMPO) was added to the obtained polyurethane resin solution based on the polyurethane solid content.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of the polyurethane resin contained in this solution (hereinafter referred to as “radiation curable polyurethane resin e”) are measured by the methods described above. As a result, Mw = 36,000, Mn = 24,000, and the sulfonic acid (salt) group content was 69.66 mmol / kg. Moreover, since the residual monomer was not confirmed by GPC, radiation-curable functional group content is computed with 355.44 mmol / kg from a preparation ratio.

<Preparation Example 2-4 (Synthesis of polyurethane resin)>
Into a flask, 14.0 parts of the above polyester polyol 4, 61.0 parts of hydrogenated bisphenol A, 60.0 parts of Adeka polyether BPX-1000, 296.4 parts of cyclohexanone, methylene bis (4,1-phenylene) = diisocyanate (MDI) ) (Millionate MT, manufactured by Nippon Polyurethane Co., Ltd.) was added in an amount of 79.6 parts. Next, 0.21 part of di-n-butyltin laurate was added, the temperature was raised to 80 ° C., and the mixture was stirred for 5 hours. After completion of the reaction, 197.5 parts of cyclohexanone was added to obtain a polyurethane resin solution.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of a polyurethane resin (hereinafter referred to as “polyether polyurethane resin f”) contained in this solution were measured by the above-described methods. However, Mw = 7 million, Mn = 41,000, and sulfonic acid (salt) group content was 65.2 mmol / kg.

<Preparation Example 2-5 (Synthesis of radiation curable polyurethane resin)>
As a chain extender, 70,50 g of methyl oxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol (ADEKA BPX-1000, mass average molecular weight 1000) as a chain extender, glycerol methacrylate (Japan) 6.50 g (concentration: 355.44 mmol / kg), and dimethylol tricyclodecane (TCDM manufactured by OXEA) 3.90 g, 6.80 g of 50% cyclohexanone solution of the exemplified compound (S-31), As a polymerization solvent, 116.41 g of cyclohexanone and 0.240 g of p-methoxyphenol were added. Next, a solution of 32.32 g of methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) and 44.64 g of cyclohexanone was added dropwise over 15 minutes. Next, 0.361 g of di-n-butyltin laurate was added as a polymerization catalyst, the temperature was raised to 80 ° C., and the mixture was stirred for 3 hours. After completion of the reaction, 121.29 g of cyclohexanone was added to obtain a polyurethane resin solution. After urethane synthesis, 50 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-OH-TEMPO) was added to the obtained polyurethane resin solution based on the polyurethane solid content.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of a polyurethane resin (hereinafter referred to as “radiation curable polyurethane resin h”) contained in this solution are measured by the methods described below. As a result, Mw = 36,000, Mn = 24,000, and the sulfonic acid (salt) group content was 68.8 mmol / kg. Moreover, since the residual monomer was not confirmed by GPC, radiation curable functional group content is computed with 348 mmol / kg from a preparation ratio.

<Preparation Example 2-6 (Synthesis of polyurethane resin)>
(1) Synthesis of polyester resin 11.1 part of dimethyl sodium 5-sulfoisophthalate (manufactured by Tokyo Chemical Industry), 100.0 parts of adipic acid (manufactured by Tokyo Chemical Industry), 2,2-dimethyl-1,3-propanediol 79. 4 parts, 29.6 parts of 1,6-hexanediol, and 0.4 parts of dibutyltin oxide (manufactured by Tokyo Chemical Industry) were heated at 245 ° C. The obtained distillate was stirred and distilled for 6 hours using a Dean-Stark tube to obtain a polyester polyol having the following structure (hereinafter referred to as “polyester polyol 6”). The weight average molecular weight and the weight average molecular weight / number average molecular weight ratio (Mw / Mn) of the obtained polyester polyol 6 were determined in terms of standard polystyrene using a THF solvent. The weight average molecular weight was 2150 and Mw / Mn = 1.85.

(2) Synthesis of polyester resin 100.0 parts of adipic acid (manufactured by Tokyo Chemical Industry), 74.8 parts of 2,2-dimethyl-1,3-propanediol, 27.7 parts of 1,6-hexanediol, dibutyltin oxide ( 0.4 parts (manufactured by Tokyo Chemical Industry) was heated at 245 ° C. The resulting distillate was stirred for 6 hours while distilling off using a Dean-Stark tube to obtain polyester polyol 7 (hereinafter referred to as “polyester polyol 7”) having the following structure. The weight average molecular weight and the weight average molecular weight / number average molecular weight ratio (Mw / Mn) of the obtained polyester polyol 7 were determined in terms of standard polystyrene using a THF solvent. The weight average molecular weight was 2100 and Mw / Mn = 1.85.

(3) Synthesis of polyester polyurethane resin In a flask, 50.0 parts of polyester polyol 6, 50.0 parts of polyester polyol 7, 100.0 parts of 2-ethyl-butyl-1,3-propanediol, 501.4 parts of cyclohexanone, 163.0 parts of methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) was added. Next, 0.72 part of di-n-butyltin laurate was added, the temperature was raised to 80 ° C., and the mixture was stirred for 5 hours. After completion of the reaction, 331.5 parts of cyclohexanone was added to obtain a polyester urethane resin solution.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. When the mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of the polyurethane resin (hereinafter referred to as “polyester polyurethane resin g”) contained in this solution were measured by the methods described above. Mw = 70,000, Mn = 41,000, and sulfonic acid (salt) group content was 64.1 mmol / kg. The urethane group concentration was 3.8 mmol / g.

<Preparation Example 2-7 (Synthesis of radiation curable polyurethane resin)>
In the flask, 41.10 g of methyloxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol (ADEKA BPX-1000, mass average molecular weight 1000) as a chain extender, glycerol methacrylate (Japan) 6.50 g (Blemmer GLM manufactured by Yushi Co., Ltd.) (concentration: 355.44 mmol / kg), 19.80 g of dimethylol tricyclodecane (TCDM manufactured by OXEA), 6.80 g of 50% cyclohexanone solution of polyester polyol 4, cyclohexanone as a polymerization solvent 97.36 g, p-methoxyphenol (0.240 g was added. Next, a solution of 44.30 g of methylenebis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT, manufactured by Nippon Polyurethane Co., Ltd.) and 61.18 g of cyclohexanone was added. 1 Next, 0.361 g of di-n-butyltin laurate was added as a polymerization catalyst, and the mixture was heated to 80 ° C. and stirred for 3 hours, and 120.41 g of cyclohexanone was added after completion of the reaction. After the urethane synthesis, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-OH-TEMPO) was added to the polyurethane solid content after urethane synthesis. 50 ppm was added.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of a polyurethane resin (hereinafter referred to as “radiation curable polyurethane resin i”) contained in this solution are measured by the above-described methods. As a result, Mw = 36,000, Mn = 24,000, and sulfonic acid (salt) group content was 69.6 mmol / kg. Moreover, since the residual monomer was not confirmed by GPC, radiation curable functional group content is computed with 352 mmol / kg from a preparation ratio.

<Preparation Example 2-8 (Synthesis of radiation curable polyurethane resin)>
As a chain extender, 31.00 g of methyl oxirane adduct of 4,4 ′-(propane-2,2-diyl) diphenol (ADEKA BPX-1000, mass average molecular weight 1000) as a chain extender, glycerol methacrylate (Japan) 6.50 g (Blemmer GLM manufactured by Yushi Co., Ltd.) (concentration: 355.44 mmol / kg), 26.00 g of dimethylol tricyclodecane (TCDM manufactured by OXEA), 6.80 g of 50% cyclohexanone solution of polyester 1, cyclohexanone 92 as a polymerization solvent .39 g, p-methoxyphenol 0.240 g was added. Subsequently, a solution of 49.52 g of methylene bis (4,1-phenylene) = diisocyanate (MDI) (Millionate MT manufactured by Nippon Polyurethane Co., Ltd.) and 61.18 g of cyclohexanone was added dropwise over 15 minutes. Next, 0.361 g of di-n-butyltin laurate was added as a polymerization catalyst, the temperature was raised to 80 ° C., and the mixture was stirred for 3 hours. After the reaction, 121.81 g of cyclohexanone was added to obtain a polyurethane resin solution. After urethane synthesis, 50 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-OH-TEMPO) was added to the obtained polyurethane resin solution based on the polyurethane solid content.
The solid content of the polyurethane resin solution obtained by the above steps was 30%. The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group content of a polyurethane resin (hereinafter referred to as “radiation curable polyurethane resin j”) contained in this solution are measured by the above-described methods. As a result, Mw = 36,000, Mn = 24,000, and the sulfonic acid (salt) group content was 68.9 mmol / kg. Moreover, since the residual monomer was not confirmed by GPC, radiation curable functional group content is computed with 349 mmol / kg from a preparation ratio.

  The magnetic recording medium of the present invention is useful for high-density recording applications.

Claims (10)

A magnetic recording medium having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support and a magnetic layer containing a ferromagnetic powder and a binder in this order,
The magnetic layer has the following general formula A:
[In General Formula A, Ar represents an aryl group which may have a substituent, X represents a divalent linking group, and R ¹¹ and R ¹² each independently represent a hydrogen atom or a substituent. ]
A compound represented by the formula:
The ferromagnetic powder is a hexagonal ferrite powder,
The binder of the magnetic layer is a mixture of a vinyl chloride copolymer, a polyurethane resin and a polyisocyanate, and the polyurethane resin has a glass transition temperature in the range of 90 to 130 ° C. and a storage elastic modulus at 80 ° C. of 2. In the range of 5 to 5.0 GPa
The nonmagnetic layer is a radiation curable layer obtained by radiation curing a radiation curable composition containing a nonmagnetic powder and a binder component, and the binder component is a radiation curable vinyl chloride copolymer. And a radiation curable polyurethane resin, and both the radiation curable vinyl chloride copolymer and the radiation curable polyurethane resin have a glass transition temperature in the range of 30 to 100 ° C. . The magnetic recording medium according to claim 1, wherein the hexagonal ferrite powder has an average plate diameter of 40 nm or less. The compound represented by the general formula A is represented by the following general formula A1:
[In General Formula A1, Z is a hydrogen atom or a hydroxyl group, and R ¹¹ , R ¹² , and X have the same meanings as those in General Formula A, respectively. ]
The magnetic recording medium according to claim 1, which is a compound represented by the formula: The compound represented by the general formula A is selected from the group consisting of N-phenylglycine, N- (4-hydroxyphenyl) glycine, phenoxyacetic acid, 2-phenoxypropionic acid and 3-phenylpropionic acid. 4. The magnetic recording medium according to any one of items 3. The magnetic recording medium according to claim 1, wherein the radiation curable vinyl chloride copolymer is a radiation curable vinyl chloride copolymer including a structural unit represented by the following general formula (1).
[In General Formula (1), R ¹ represents a hydrogen atom or a methyl group, and L ¹ represents a divalent linking group represented by the following Formula (2), Formula (3), or the following General Formula (4). . ]
[In General Formula (4), R ⁴¹ represents a hydrogen atom or a methyl group. ] The radiation curable polyurethane resin is a radiation curable polyurethane resin obtained by using a sulfonic acid (salt) group-containing polyol compound represented by the following general formula (2) as a raw material. 2. A magnetic recording medium according to 1.
[In General Formula (2), X represents a divalent linking group, and R ¹⁰¹ and R ¹⁰² each independently represents an alkyl group having 2 or more carbon atoms having at least one hydroxyl group or carbon having at least one hydroxyl group. It represents an aralkyl group having a number of 8 or more, and M ¹ represents a hydrogen atom or a cation. ] The magnetic recording medium according to claim 1, wherein the polyurethane resin contained in the binder of the magnetic layer is a polyester polyurethane resin. The magnetic recording medium according to claim 1, wherein the binder of the magnetic layer contains 10 to 100 parts by mass of polyisocyanate with respect to 100 parts by mass of the vinyl chloride copolymer. The magnetic recording medium according to claim 1, wherein the magnetic layer contains a compound represented by the general formula A in an amount of 1.5 to 10 parts by mass per 100 parts by mass of the hexagonal ferrite powder. A method for manufacturing a magnetic recording medium according to any one of claims 1 to 9,
After the application and radiation curing of the radiation curable composition, a magnetic layer is formed on the formed radiation cured layer, and then a calendar treatment is performed at a calendar temperature equal to or higher than the glass transition temperature of the radiation cured layer. The manufacturing method.