JP2012207077A - Method for producing polymer composition and method for producing magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for producing a polymer composition which is suitable for preparing a coating liquid for forming a magnetic recording medium.SOLUTION: There is provided a method for producing the polymer composition. The polymer composition contains a polymer obtained by the polymerization reaction of raw material monomers comprising four kinds of prescribed monomers (monomers 1 to 4). A method for producing the polymer composition includes preparing the mixed liquid of the raw material monomers by mixing a solution A prepared by adding the monomer 1 into water or the mixed solvent of water and an alcohol, and a solution B prepared by adding the monomers 2, 3 and 4 into a ketone-based solvent, and performing the polymerization reaction in the mixed liquid of the raw material monomers.

Description

The present invention relates to a method for producing a polymer composition, and more particularly to a method for producing a polymer composition suitable for preparing a coating liquid for a coating type magnetic recording medium.
The present invention further relates to a method for producing a magnetic recording medium comprising producing a polymer composition by the above method.

  In the coating type magnetic recording medium, the binder plays an important role in electromagnetic conversion characteristics, running durability, and the like.

  As binders for magnetic recording media, various resins such as vinyl chloride resin, polyurethane resin, polyester resin, and acrylic resin are used. Among them, vinyl polymers such as vinyl chloride resins and acrylic resins are widely used from the viewpoints of the high degree of freedom of the unit and the ease of the synthesis reaction (see Patent Document 1).

JP 2003-242625 A

  As described above, the vinyl polymer is suitable as a binder for magnetic recording media. Therefore, the applicant of the present application has repeatedly studied on vinyl polymers, and that vinyl polymers obtained by polymerizing monomers 2 to 4 described later can exhibit excellent performance as binders for magnetic recording media. I found it. This is because a vinyl polymer into which a hydroxyl group contained in monomer 2, a substituent having a cyclic structure contained in monomer 3, and a long chain or multi-ring hydrocarbon group contained in monomer 4 are introduced is incorporated into these groups. Contributes to the improvement of dispersibility, so that the magnetic substance and nonmagnetic powder can be highly dispersed. Further, the hydroxyl group introduced by the monomer 2 is cross-linked with the polyisocyanate, so that the magnetic layer having a high coating strength and This is because a magnetic layer can be formed. Furthermore, the vinyl polymer introduced with a substituent having a cyclic structure contained in the monomer 3 and a long chain or polycyclic hydrocarbon group contained in the monomer 4 is improved in glass transition temperature, improved toughness, Essential magnetic properties can be imparted to the magnetic recording medium.

By the way, 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 enhancing the dispersibility of the fine particle magnetic material, a method in which a sulfonic acid (salt) group such as an SO ₃ Na group is contained in a binder is known. In the present specification, the term “sulfonic acid (salt) group” is used to include a salt of a sulfonic acid group and a sulfonic acid group.

  Therefore, it is conceivable to introduce a sulfonic acid (salt) group into the vinyl polymer obtained by polymerizing the monomers 2 to 4 in order to obtain a further excellent dispersibility improvement effect. Examination has revealed that the following problems exist when introducing a sulfonic acid (salt) group into the vinyl polymer.

As solvents for the coating liquid for forming a coating type magnetic recording medium, ketone solvents such as methyl ethyl ketone and cyclohexanone are widely used. This is because a ketone solvent has a relatively low boiling point, and if a ketone solvent is used, the solvent can be easily removed in the drying step, and a magnetic recording medium with a small amount of residual solvent can be obtained. Therefore, in the polymerization reaction of the binder for magnetic recording media, it is desirable that the ketone solvent occupies a part of the reaction solvent. This is because the polymer solution after the reaction can be subjected to a process for preparing a coating liquid for forming a coating type magnetic recording medium without going through an advanced separation and purification process.
However, as a result of the study by the present inventors, when monomers 2 to 4 described later are subjected to a polymerization reaction in a ketone solvent together with monomer 1 to be described later widely used for introducing a sulfonic acid (salt) group, it is obtained. It was revealed that the amount of sulfonic acid (salt) group introduced into the vinyl polymer obtained was greatly reduced from the theoretical value. This is because the monomers 2 to 4 have a high solubility in the ketone solvent, while the solubility of the monomer 1 in the ketone solvent is significantly reduced in the presence of these monomers. On the other hand, examples of the solvent that can dissolve all of the monomers 1 to 4 well include amide solvents. However, the amide solvents need to be considered in terms of safety at the time of operation, and also have high boiling points. When the polymer synthesized therein is used as a binder for a magnetic recording medium, the residual solvent amount of the medium may be increased. A method of synthesizing with an amide solvent and then purifying the polymer by reprecipitation treatment and re-dissolving in a ketone solvent may be considered, but this is not preferable because the production process increases and the cost increases.

  Under such circumstances, the present invention provides means for producing a polymer composition containing a vinyl polymer that is a polymer of monomers 1 to 4 described later, which is suitable for preparing a coating solution for forming a magnetic recording medium. It was made for the purpose of doing.

  In order to achieve the above object, the present inventors have carried out the polymerization reaction of the above monomers 1 to 4 in a reaction system in which a ketone solvent occupies a part of the reaction solvent and the coexisting solvent is easy to handle and remove. Considered to do. As a result, a raw material monomer mixed solution is prepared by mixing a solution prepared by adding monomer 1 to water or a mixed solvent of water and alcohol and a solution prepared by adding monomers 2 to 4 to a ketone solvent. And it discovered that the said objective can be achieved by performing a polymerization reaction in this raw material monomer liquid mixture, and came to complete this invention.

［一般式(I)中、Ｚ¹はスルホン酸（塩）基を表し、Ｒ¹は水素原子またはメチル基を表し、Ｘ¹は酸素原子、硫黄原子または−Ｎ（Ｒ¹¹）−基を表し、Ｒ¹¹は水素原子または置換基を表し、Ｌ¹は置換基を有していてもよいアルキレン基を表す。］
で表されるモノマー１と、
一般式(II)：

［一般式(II)中、Ｒ²は水素原子、ハロゲン原子またはメチル基を表し、Ｌ²は単結合または２価の連結基を表す。］
で表されるモノマー２と、
一般式(III)：

［一般式(III)中、Ｒ³は水素原子、ハロゲン原子、またはメチル基を表し、Ｌ³は単結合または２価の連結基を表し、Ｚ³は環状構造を有する置換基を表す。］
で表されるモノマー３と、
一般式(IV)：

［一般式(IV)中、Ｒ⁴は水素原子、ハロゲン原子、またはメチル基を表し、Ｌ⁴は単結合または２価の連結基を表し、Ｙは炭素数８以上５０以下の炭化水素基を表す。］
で表されるモノマー４と、
を含む原料モノマーの重合反応により得られるポリマーを含み、
モノマー１を水または水とアルコールとの混合溶媒に添加して調製した溶液Ａと、モノマー２、３および４をケトン系溶媒に添加して調製した溶液Ｂとを混合して原料モノマー混合液を調製し、該原料モノマー混合液中で前記重合反応を行うことを特徴とする、前記製造方法。
［２］モノマー２は、一般式(II-1)：

［一般式(II-1)中、Ｒ²は水素原子またはメチル基を表し、Ｘ²は−Ｏ−、−Ｓ−、または−Ｎ（Ｒ²²）−で表される２価の連結基を表し、Ｒ²²は水素原子または置換基を有してもよい炭素数１以上８以下のアルキル基を表し、Ｒ²¹は置換基を有してもよい炭素数２以上８以下のアルキレン基または該アルキレン基が連結基を介して複数連結した２価の基を表す。］
で表されるアクリルモノマーである［１］に記載のポリマー組成物の製造方法。
［３］モノマー３は、一般式(III-1)：

［一般式(III-1)中、Ｒ³は、水素原子またはメチル基を表し、Ｘ³は−Ｏ−、−Ｓ−、または−Ｎ（Ｒ³¹）−で表される２価の連結基を表し、Ｒ³¹は水素原子または置換基を有してもよい炭素数１以上８以下のアルキル基を表し、Ｚ³¹は脂環式の縮合環基を表す。]
で表されるアクリルモノマーである［１］または［２］に記載のポリマー組成物の製造方法。
［４］モノマー４は、一般式(IV-1)：

［一般式(IV-1)中、Ｒ⁴は水素原子またはメチル基を表し、Ｘ⁴は−（Ｏ）ｍ¹−、−（Ｓ）ｍ²−または−｛Ｎ（Ｒ⁴¹）｝ｍ³−で表される２価の連結基を表し、Ｒ⁴¹は置換基を有してもよい炭素数１以上８以下のアルキル基を表し、ｎは１２以上３０以下の整数を表す。]
で表されるアクリルモノマーである［１］〜［３］のいずれかに記載のポリマー組成物の製造方法。
［５］前記溶液Ａの調製時、モノマー１は析出せず溶解する［１］〜［４］のいずれかに記載のポリマー組成物の製造方法。
［６］前記原料モノマー混合液の調製時、前記溶液Ａと溶液Ｂは層分離せず混合する［１］〜［５］のいずれかに記載のポリマー組成物の製造方法。
［７］前記原料モノマー混合液の調製時、モノマー１は析出せず溶解する［１］〜［６］のいずれかに記載のポリマー組成物の製造方法。
［８］前記重合反応後に反応液をろ過し不溶物を除去することを更に含む、［１］〜［７］のいずれかに記載のポリマー組成物の製造方法。
［９］モノマー１は、２−アクリルアミド−２−メチルプロパンスルホン酸またはその塩である［１］〜［８］のいずれかに記載のポリマー組成物の製造方法。
［１０］前記溶液Ｂの調製に使用されるケトン系溶媒は、メチルエチルケトン、シクロヘキサノンまたはこれらの混合溶媒である［１］〜［９］のいずれかに記載のポリマー組成物の製造方法。
［１１］前記溶液Ａの調製に使用されるアルコールはメタノールである［１］〜［１０］のいずれかに記載のポリマー組成物の製造方法。
［１２］非磁性支持体上に強磁性粉末および結合剤を含む磁性層を有する磁気記録媒体の製造方法であって、
［１］〜［１１］のいずれかに記載の方法によりポリマー組成物を製造すること、
製造したポリマー組成物を強磁性粉末と混合することにより磁性層形成用塗布液を調製すること、
調製した磁性層形成用塗布液を用いて前記磁性層を形成すること、
を含む磁気記録媒体の製造方法。
［１３］非磁性支持体上に非磁性粉末および結合剤を含む非磁性層と強磁性粉末および結合剤を含む磁性層をこの順に有する磁気記録媒体の製造方法であって、
［１］〜［１１］のいずれかに記載の方法によりポリマー組成物を製造すること、
製造したポリマー組成物を非磁性粉末と混合することにより非磁性層形成用塗布液を調製すること、
調製した非磁性層形成用塗布液を用いて前記非磁性層を形成すること、
を含む磁気記録媒体の製造方法。 That is, the above object was achieved by the following means.
[1] A method for producing a polymer composition,
The polymer composition is
Formula (I):

[In the general formula (I), Z ¹ represents a sulfonic acid (salt) group, R ¹ represents a hydrogen atom or a methyl group, X ¹ represents an oxygen atom, a sulfur atom or a —N (R ¹¹ ) — group. , R ¹¹ represents a hydrogen atom or a substituent, and L ¹ represents an alkylene group which may have a substituent. ]
Monomer 1 represented by
General formula (II):

[In general formula (II), R ² represents a hydrogen atom, a halogen atom or a methyl group, and L ² represents a single bond or a divalent linking group. ]
Monomer 2 represented by
General formula (III):

[In General Formula (III), R ³ represents a hydrogen atom, a halogen atom, or a methyl group, L ³ represents a single bond or a divalent linking group, and Z ³ represents a substituent having a cyclic structure. ]
Monomer 3 represented by
Formula (IV):

[In General Formula (IV), R ⁴ represents a hydrogen atom, a halogen atom, or a methyl group, L ⁴ represents a single bond or a divalent linking group, and Y represents a hydrocarbon group having 8 to 50 carbon atoms. To express. ]
Monomer 4 represented by:
Including a polymer obtained by polymerization reaction of raw material monomers containing
A solution A prepared by adding the monomer 1 to water or a mixed solvent of water and alcohol and a solution B prepared by adding the monomers 2, 3 and 4 to the ketone solvent are mixed to prepare a raw material monomer mixed solution. The said manufacturing method characterized by preparing and performing the said polymerization reaction in this raw material monomer liquid mixture.
[2] Monomer 2 has the general formula (II-1):

[In General Formula (II-1), R ² represents a hydrogen atom or a methyl group, and X ² represents a divalent linking group represented by —O—, —S—, or —N (R ²² ) —. R ²² represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms which may have a substituent, R ²¹ represents an alkylene group having 2 to 8 carbon atoms which may have a substituent, or A divalent group in which a plurality of alkylene groups are linked via a linking group is represented. ]
The manufacturing method of the polymer composition as described in [1] which is an acrylic monomer represented by these.
[3] Monomer 3 is represented by the general formula (III-1):

[In General Formula (III-1), R ³ represents a hydrogen atom or a methyl group, and X ³ represents a divalent linking group represented by —O—, —S—, or —N (R ³¹ ) —. R ³¹ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms which may have a substituent, and Z ³¹ represents an alicyclic fused ring group. ]
The manufacturing method of the polymer composition as described in [1] or [2] which is an acrylic monomer represented by these.
[4] The monomer 4 is represented by the general formula (IV-1):

[In General Formula (IV-1), R ⁴ represents a hydrogen atom or a methyl group, and X ⁴ represents — (O) m ¹ —, — (S) m ² —, or — {N (R ⁴¹ )} m ^3. -Represents a divalent linking group represented by-, R ⁴¹ represents an ^optionally substituted alkyl group having 1 to 8 carbon atoms, and n represents an integer of 12 to 30. ]
The manufacturing method of the polymer composition in any one of [1]-[3] which is an acrylic monomer represented by these.
[5] The method for producing a polymer composition according to any one of [1] to [4], wherein when the solution A is prepared, the monomer 1 is dissolved without being precipitated.
[6] The method for producing a polymer composition according to any one of [1] to [5], wherein the solution A and the solution B are mixed without layer separation when the raw material monomer mixed solution is prepared.
[7] The method for producing a polymer composition according to any one of [1] to [6], wherein the monomer 1 is dissolved without being precipitated when the raw material monomer mixed solution is prepared.
[8] The method for producing a polymer composition according to any one of [1] to [7], further comprising filtering the reaction solution after the polymerization reaction to remove insoluble matters.
[9] The method for producing a polymer composition according to any one of [1] to [8], wherein the monomer 1 is 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof.
[10] The method for producing a polymer composition according to any one of [1] to [9], wherein the ketone solvent used for the preparation of the solution B is methyl ethyl ketone, cyclohexanone, or a mixed solvent thereof.
[11] The method for producing a polymer composition according to any one of [1] to [10], wherein the alcohol used for preparing the solution A is methanol.
[12] A method for producing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
Producing a polymer composition by the method according to any one of [1] to [11],
Preparing a coating solution for forming a magnetic layer by mixing the produced polymer composition with a ferromagnetic powder;
Forming the magnetic layer using the prepared coating liquid for forming a magnetic layer;
A method of manufacturing a magnetic recording medium including:
[13] A method for producing a magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic support in this order,
Producing a polymer composition by the method according to any one of [1] to [11],
Preparing a coating solution for forming a nonmagnetic layer by mixing the produced polymer composition with a nonmagnetic powder;
Forming the nonmagnetic layer using the prepared nonmagnetic layer forming coating solution;
A method of manufacturing a magnetic recording medium including:

  ADVANTAGE OF THE INVENTION According to this invention, the polymer composition which can be used conveniently for preparation of the coating liquid for magnetic recording medium formation can be provided.

The present invention includes a monomer 1 represented by the following general formula (I), a monomer 2 represented by the following general formula (II), a monomer 3 represented by the following general formula (III), and the following general formula (IV) The manufacturing method of the polymer composition containing the polymer obtained by the polymerization reaction of the raw material monomer containing the monomer 4 represented by these. The method for producing a polymer composition of the present invention comprises a solution A prepared by adding monomer 1 to water or a mixed solvent of water and alcohol, and a solution prepared by adding monomers 2, 3 and 4 to a ketone solvent. B is mixed to prepare a raw material monomer mixed solution, and the polymerization reaction is performed in the raw material monomer mixed solution. Thereby, a polymer composition suitable for the preparation of a coating liquid for forming a magnetic recording medium can be obtained.
Hereinafter, the method for producing the polymer composition of the present invention will be described in more detail.

Monomer 1
The monomer 1 represented by the following general formula (I) used as one of the raw material monomers in the present invention is for introducing a sulfonic acid (salt) group that is an adsorptive functional group into the vinyl polymer to be synthesized. It is an ingredient. As described above, monomer 1 has poor solubility in the ketone solvent in the presence of monomers 2 to 4, and therefore, when the polymerization reaction of monomers 1 to 4 is performed in the ketone solvent, the monomer 1 is calculated from the charged amount of monomer 1. A polymer having a significantly smaller amount of sulfonic acid (salt) groups than the amount of sulfonic acid (salt) groups introduced is obtained. On the other hand, the monomer 1 exhibits higher solubility in water or a mixed solvent of water and alcohol than the solubility in the ketone solvent. Therefore, in the present invention, the monomer 1 is previously dissolved in water or a mixed solvent of water and alcohol and then mixed with another monomer dissolved in a ketone solvent. Thereby, a vinyl polymer having a sulfonic acid (salt) group in an amount close to the sulfonic acid (salt) group introduction amount calculated from the charged amount of the monomer 1 can be obtained.
Hereinafter, the general formula (I) will be described in more detail.

In the general formula (I), R ¹ represents a hydrogen atom or a methyl group, and preferably represents a methyl group.

X ¹ represents an oxygen atom, a sulfur atom or a —N (R ¹¹ ) — group. Here, R ¹¹ represents a hydrogen atom or a substituent. 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), A cyano group, an amino group, a nitro group, an acyl group, a carboxyl group, etc. can be mentioned. Hereinafter, unless otherwise specified, for the “substituent” in the present invention, the description of the substituent can be referred to. R ¹¹ is preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom from the viewpoint of improving dispersibility.
In the present invention, the “carbon number” of a group having a substituent means the carbon number of a portion not containing 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.

In general formula (I), L ¹ represents an alkylene group which may have a substituent. The number of carbon atoms of the alkylene group represented by L ¹ is preferably in the range of 1 to 10, more preferably in the range of 1 to 6, even more preferably in the range of 1 to 3, from the viewpoint of improving dispersibility. It is.

In general formula (I), Z ¹ is a sulfonic acid (salt) group, a sulfonic acid group (—SO ₃ H), a SO ₃ Na group, a SO ₃ K group, a sulfonic acid group such as SO ₃ Li, and the like Can be a salt of The vinyl polymer obtained from the monomers 1 to 4 has the following general formula (I) ′ having a sulfonic acid (salt) group by the monomer 1:

［一般式(I)’中、Ｒ¹、Ｘ¹、Ｌ¹およびＺ¹は、一般式(I)と同義である。］
で表される構造単位が導入されることで、磁気記録媒体において高い分散性向上効果を発揮することができる。そして本発明によれば、反応溶媒の一部にケトン系溶媒を含む反応系において、モノマー１の仕込み量から算出されるスルホン酸（塩）基導入量に近い量のスルホン酸（塩）基を有するビニル系ポリマーを得ることができる。

[In General Formula (I) ′, R ¹ , X ¹ , L ¹ and Z ¹ are as defined in General Formula (I). ]
By introducing the structural unit represented by the formula, a high dispersibility improvement effect can be exhibited in the magnetic recording medium. According to the present invention, in a reaction system including a ketone solvent as a part of the reaction solvent, an amount of the sulfonic acid (salt) group close to the introduction amount of the sulfonic acid (salt) group calculated from the charged amount of the monomer 1 is added. A vinyl polymer having the same can be obtained.

  Specific examples of the monomer 1 include 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof, 2-sulfoethyl (meth) acrylate or a salt thereof, and the like. -Acrylamide-2-methylpropanesulfonic acid or a salt thereof is preferred.

  In order to further improve dispersibility, the sulfonic acid (salt) group content of the obtained vinyl polymer is preferably 10 to 1000 μeq / g. For this purpose, it is preferable to use the monomer 1 in an amount of 0.1 to 10 mol%, preferably 0.5 to 6 mol%, based on the total amount of raw material monomers.

Monomer 2
In the present invention, the following general formula (II):

［一般式(II)中、Ｒ²は水素原子、ハロゲン原子またはメチル基を表し、Ｌ²は単結合または２価の連結基を表す。］
で表されるモノマー２によって、合成されるビニル系ポリマーに下記一般式(II)’：

[In general formula (II), R ² represents a hydrogen atom, a halogen atom or a methyl group, and L ² represents a single bond or a divalent linking group. ]
A vinyl polymer synthesized by the monomer 2 represented by the following general formula (II) ′:

[一般式(II)’中、Ｒ²、Ｌ²は、一般式(II)と同義である。]
で表される水酸基を有する構造単位を導入することができる。合成されるビニル系ポリマーは、水酸基を含むことでより一層の分散性向上に寄与することができ、また、ポリイソシアネートを併用する系ではポリイソシアネートと水酸基が架橋することにより塗膜強度向上に寄与することができる。

[In general formula (II) ′, R ² and L ² have the same meanings as in general formula (II). ]
A structural unit having a hydroxyl group represented by can be introduced. The synthesized vinyl-based polymer can contribute to further improvement of dispersibility by containing hydroxyl groups, and in the system using polyisocyanate together, it contributes to improving coating strength by cross-linking of polyisocyanate and hydroxyl groups. can do.

In general formula (II) and general formula (II) ′, R ² represents a hydrogen atom, a halogen atom, or a methyl group. Examples of the halogen atom include a chlorine atom, a bromine atom and an iodine atom.
R ² preferably represents a hydrogen atom or a methyl group, more preferably a methyl group.

In general formula (II) and general formula (II) ′, L ² represents a single bond or a divalent linking group, and is preferably a linking group containing any of an oxygen atom, a nitrogen atom or a sulfur atom. As the divalent linking group represented by L ² , those bonded to the main chain carbon atom through a —C (O) — group are preferred, and —C ( A divalent linking group represented by O) X ² R ²¹ — is more preferred.

  From the viewpoint of improving dispersibility, the monomer 2 is preferably an acrylic monomer represented by the general formula (II-1). With the monomer represented by the general formula (II-1), the structural unit represented by the general formula (II-1) ′ can be introduced into the obtained polymer.

In general formula (II-1) and general formula (II-1) ′, R ² represents a hydrogen atom or a methyl group.

X ² represents a divalent linking group represented by —O—, —S—, or —N (R ²² ) —, and is preferably —O—.

R ²² represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms which may have a substituent. The number of carbon atoms of the alkyl group represented by R ²² is preferably 1 or more and 4 or less. When the carbon number of the alkyl group represented by R ²² is in the above range, the dispersibility can be further improved while maintaining the solubility of the resulting vinyl polymer.

R ²¹ represents an optionally substituted alkylene group having 2 to 8 carbon atoms or a divalent group in which a plurality of alkylene groups are linked via a linking group. When the number of carbon atoms of the alkylene group contained in the group represented by R ²¹ is within the above range, the dispersibility can be further improved while maintaining the solubility of the resulting vinyl polymer. The linking group for linking the alkylene group is preferably an ester bond from the viewpoint of the solubility of the resulting vinyl polymer. The number of alkylene groups having 2 to 8 carbon atoms contained in the group represented by R ²¹ is preferably 1 to 3 inclusive.

Specific examples of the monomer represented by the general formula (II) or the general formula (II-1) include the following monomers. However, the present invention is not limited to the following specific examples.
Hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol polypropylene glycol mono (meth) acrylate, glycerol mono (meth) acrylate, 3-chloro 2-hydroxyalkyl (meth) acrylates such as hydroxypropyl (meth) acrylate, vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyethyl mono (meth) allyl ether, hydroxypropyl mono (meth) Allyl ether, hydroxybutyl mono (meth) allyl ether, diethylene glycol mono (me ) Allyl ether, dipropylene glycol mono (meth) allyl ether, glycerol mono (meth) allyl ether, 3-chloro-2-hydroxypropyl (meth) allyl ether (meth) allyl ethers, (meth) allyl alcohol.

Monomer 3
Furthermore, in the present invention, the following general formula (III):

［一般式(III)中、Ｒ³は水素原子、ハロゲン原子、またはメチル基を表し、Ｌ³は単結合または２価の連結基を表し、Ｚ³は環状構造を有する置換基を表す。］
で表されるモノマー３によって、合成されるビニル系ポリマーに下記一般式(III)’：

[In General Formula (III), R ³ represents a hydrogen atom, a halogen atom, or a methyl group, L ³ represents a single bond or a divalent linking group, and Z ³ represents a substituent having a cyclic structure. ]
A vinyl polymer synthesized by the monomer 3 represented by the following general formula (III) ′:

[一般式(III)’中、Ｒ³、Ｌ³、Ｚ³は、一般式(III)と同義である。]
で表される、環状構造を有する置換基を有する構造単位を導入することができる。合成されるビニル系ポリマーは、環状構造を有する置換基を含むことで、より一層の分散性向上に寄与することができる。更に、環状構造を有する置換基を含むことで、主鎖の分子運動が抑制され、ガラス転移温度向上および力学特性の向上に寄与することもできる。

[In general formula (III) ′, R ³ , L ³ and Z ³ have the same meanings as in general formula (III). ]
The structural unit which has a substituent which has a cyclic structure represented by these can be introduce | transduced. The synthesized vinyl polymer can contribute to further improvement in dispersibility by including a substituent having a cyclic structure. Furthermore, by including a substituent having a cyclic structure, the molecular motion of the main chain is suppressed, which can contribute to the improvement of the glass transition temperature and the mechanical properties.

In general formula (III) and general formula (III) ′, R ³ represents a hydrogen atom, a halogen atom, or a methyl group. The details are as described for R ² in the general formula (II).

L ³ represents a single bond or a divalent linking group. The divalent linking group represented by L ³ preferably contains a hetero atom, and preferably binds to a substituent having a cyclic structure represented by Z ³ on the hetero atom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, and a sulfur atom. L ³ is preferably a single bond or a divalent linking group bonded to a main chain carbon atom via a —C (O) — group, and —C (O) in the general formula (III-1) described later. A divalent linking group represented by X ³ — is more preferred.

In general formula (III) and general formula (III) ′, Z ³ represents a substituent having a cyclic structure. The substituent represented by Z ³ preferably represents an alicyclic cyclic group from the viewpoint of improving dispersibility. The alicyclic ring group may be saturated or unsaturated, and may be any of a monocyclic ring, a polycyclic ring, and a condensed ring. Moreover, you may have a substituent. The substituent is as described above for R ^{11 in the} general formula (I).

The monocyclic alicyclic group represented by Z ³ is preferably a 5- to 6-membered group, and specific examples thereof include a cyclohexyl group and a cyclopentyl group. The cyclic cyclic group is preferably a 7- to 10-membered group, and specific examples include a bicycloalkyl group, an adamantyl group, a norbornyl group, and an isobornyl group. From the viewpoint of improving dispersibility, Z ³ is preferably an alicyclic fused ring group. As the alicyclic condensed ring, an alicyclic condensed ring represented by Y ³¹ in the general formula (III-1) described later is preferable.

  From the viewpoint of improving dispersibility and mechanical properties, the monomer 3 is preferably an acrylic monomer represented by the following general formula (III-1). With the monomer represented by the general formula (III-1), the structural unit represented by the general formula (III-1) ′ can be introduced into the obtained polymer.

In general formula (III-1) and general formula (III-1) ′, R ³ represents a hydrogen atom or a methyl group, and is preferably a methyl group.

X ³ represents a divalent linking group represented by —O—, —S—, or —N (R ³¹ ) —, and is preferably —O—.

R ³¹ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms which may have a substituent. The number of carbon atoms of the alkyl group represented by R ³¹ is preferably 1 or more and 4 or less. When the carbon number of the alkyl group represented by R ³¹ is within the above range, the dispersibility can be further improved while maintaining the solubility of the resulting vinyl polymer.

Z ³¹ represents an alicyclic fused ring group. The alicyclic fused ring group represented by Z ³¹ is preferably 7 to 10 membered. Specific examples of the preferable condensed ring group include an adamantyl group, a norbornyl group, and a dicyclopentanyl group.

  Specific examples of the monomer 3 are shown below. However, the present invention is not limited to the following specific examples.

Monomer 4
Furthermore, in the present invention, the following general formula (IV):

［一般式(IV)中、Ｒ⁴は水素原子、ハロゲン原子、またはメチル基を表し、Ｌ⁴は単結合または２価の連結基を表し、Ｙは炭素数８以上５０以下の炭化水素基を表す。］
で表されるモノマー４によって、合成されるビニル系ポリマーに下記一般式(IV)’：

[In General Formula (IV), R ⁴ represents a hydrogen atom, a halogen atom, or a methyl group, L ⁴ represents a single bond or a divalent linking group, and Y represents a hydrocarbon group having 8 to 50 carbon atoms. To express. ]
A vinyl polymer synthesized by the monomer 4 represented by the following general formula (IV) ′:

[一般式(IV)’中、Ｒ⁴、Ｌ⁴、Ｙは、一般式(IV)と同義である。]
で表される、長鎖ないしは多環員数の炭化水素基を有する構造単位を導入することができる。合成されるビニル系ポリマーは、長鎖ないしは多環員数の炭化水素基を含むことでより一層の分散性および靭性向上に寄与することができる。

[In the general formula (IV) ′, R ⁴ , L ⁴ and Y are as defined in the general formula (IV). ]
It is possible to introduce a structural unit having a long chain or a polycyclic hydrocarbon group. The synthesized vinyl-based polymer can contribute to further improvement in dispersibility and toughness by including a long chain or a hydrocarbon group having a multi-ring member.

In general formula (IV) (IV) ′, R ⁴ represents a hydrogen atom, a halogen atom, or a methyl group. The details are as described for R ² in the general formula (II).

In the general formulas (IV) and (IV) ′, L ⁴ represents a single bond or a divalent linking group, and is preferably a linking group containing any of an oxygen atom, a nitrogen atom or a sulfur atom. L ⁴ is preferably a single bond or a divalent linking group bonded to the main chain carbon atom via a —C (O) — group, and —C (O) in the general formula (IV-1) described later. A divalent linking group represented by X ⁴ — is more preferred.

  In the general formulas (IV) and (IV) ′, Y represents a hydrocarbon group having 8 to 50 carbon atoms. The hydrocarbon group is a substituted or unsubstituted linear, branched, or cyclic saturated or unsaturated hydrocarbon group, and is preferably a linear or branched hydrocarbon group. When the number of carbon atoms is 8 or more, it can contribute to the improvement of dispersibility, and when the number of carbon atoms is 50 or less, the solubility of the vinyl polymer obtained can be ensured. The number of carbon atoms of the hydrocarbon group is preferably 12 or more and 30 or less from the viewpoint of dispersibility and solubility of the vinyl polymer. The hydrocarbon group represented by Y is more preferably an alkyl group having 12 to 30 carbon atoms, and still more preferably an alkyl group having 12 to 18 carbon atoms.

  From the viewpoint of improving the mechanical properties such as dispersibility and toughness, the monomer 4 is preferably an acrylic monomer represented by the following general formula (IV-1). With the monomer represented by the general formula (IV-1), the structural unit represented by the general formula (IV-1) ′ can be introduced into the obtained polymer.

In general formula (IV-1) and general formula (IV-1) ′, R ⁴ represents a hydrogen atom or a methyl group, and is preferably a methyl group.

  n represents an integer of 12 or more and 30 or less, and is more preferably an integer of 12 or more and 18 or less.

X ⁴ represents a divalent linking group represented by — (O) m ¹ —, — (S) m ² — or — {N (R ⁴¹ )} m ³ —, and — (O) m ¹ — It is preferable to represent the represented bivalent coupling group. Here, m ¹ , m ² , and m ³ each independently represent an integer of 1 or more.

R ⁴¹ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent. The number of carbon atoms of the alkyl group represented by R ⁴¹ is preferably 1 or more and 4 or less. When the carbon number of the alkyl group represented by R ⁴¹ is in the above range, the dispersibility can be further improved while maintaining the solubility of the resulting vinyl polymer.
The m ¹ , m ² , and m ³ are preferably integers of 5 or less from the viewpoint of maintaining the solubility of the vinyl polymer.

  Specific examples of monomer 4 are shown below. However, the present invention is not limited to the following specific examples.

From the viewpoint of achieving both excellent dispersibility and high coating strength, the vinyl polymer obtained from the monomers 1 to 4 is represented by the general formula (II) ′ based on the total polymerization units constituting the polymer. 5 mol% to 80 mol%, more preferably 15 mol% to 70 mol%, and even more preferably 30 mol% to 60 mol%.
From the viewpoint of obtaining further superior dispersibility and mechanical properties, the vinyl polymer preferably contains 5 mol% or more and 75 mol% or less of the structural unit represented by the general formula (III) ′, and 15 mol% or more. More preferably 60 mol% or less, more preferably 30 mol% or more and 50 mol% or less, and more preferably 5 mol% or more and 75 mol% or less of the structural unit represented by the general formula (IV) ′. More preferably, it is contained in an amount of 5 mol% to 50 mol%, more preferably 10 mol% to 30 mol%.
Moreover, as demonstrated previously, it is preferable to use the monomer 1 for 0.1-10 mol% with respect to the total amount of a raw material monomer, and it is preferable to use 0.5-6 mol%.
Therefore, the blending ratio of each monomer during the polymerization reaction is preferably set so as to obtain a polymer having the above preferred composition. In addition to the above-mentioned monomers, ethylenically unsaturated carboxylic acid ester monomers, aromatic vinyl monomers, ethylenically unsaturated nitrile monomers, ethylenically unsaturated acid monomers, alkyl vinyl ether monomers, vinyl ester monomers, ethylene Known polymerizable components such as a polymerizable unsaturated polycarboxylic acid anhydride can also be used.

Polymerization Reaction As described above, the polymerization reaction of the vinyl polymer is carried out by adding the solution A prepared with the monomer 1 in water or a mixed solvent of water and alcohol, and adding the monomers 2, 3 and 4 to the ketone solvent. It is carried out in a raw material monomer mixture prepared by mixing the solution B prepared in the above.

  The concentration of the monomer 1 added to water or a mixed solvent of water and alcohol for preparing the solution A is preferably set in a range in which the monomer 1 is dissolved without being precipitated. This is because when the monomer 1 is precipitated, a vinyl polymer having a sulfonic acid (salt) group introduced in an amount less than the sulfonic acid (salt) group amount calculated from the charged amount of the monomer 1 is generated. However, in this case as well, there is no decrease in the amount of sulfonic acid (salt) group introduced enough to synthesize in a ketone solvent, but in order to obtain a polymer having a desired amount of sulfonic acid (salt) group introduced, It is preferable to completely dissolve the monomer 1 in the solution A. In the present invention, “no precipitation” and “complete dissolution” mean that no insoluble matter is visually observed. Specifically, the concentration of the monomer 1 in the solution A is preferably about 5 to 50% by mass. When a mixed solvent of water and alcohol is used for preparing the solution A, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol can be used as the alcohol. . Water and alcohol are preferable from the viewpoint of high safety, and since they can be removed relatively easily, even if they are brought into the coating liquid for magnetic recording media from the polymer composition, there is no concern that the amount of residual solvent will increase. Is also preferable. Moreover, even if it remains, it is preferable also from the point which does not exert a big influence on medium performance. As the alcohol, methanol is particularly preferable from the viewpoint of the solubility of the monomer 1 and the low boiling point. Moreover, when water is set to 1, the ratio of alcohol to water (mass ratio) is preferably about 0.0 to 0.5 from the viewpoint of the solubility of monomer 1. Solution A can be prepared, for example, by adding monomer 1 to the solvent and stirring at room temperature.

  Examples of the ketone solvent used for preparing the solution B include acetone, methyl ethyl ketone, cyclohexanone, and the like, and these can be used singly or in an arbitrary ratio. It is desirable that the boiling point of the ketone solvent is higher than the decomposition temperature of the polymerization initiator, and preferable ketone solvents from this point include methyl ethyl ketone and cyclohexanone. In order to introduce a desired amount of each structural unit, it is preferable that the monomers 2 to 4 are completely dissolved in the solution B. From this point, the concentration of the three monomers in the solution B is about 20 to 80% by mass. It is preferable to do. The solution B can be prepared, for example, by adding the monomers 2 to 4 to the ketone solvent simultaneously or sequentially and stirring at room temperature.

Next, the solution A and the solution B are mixed to prepare a raw material monomer mixed solution. In the raw material monomer mixed solution, the solution A and the solution B may be separated into two layers, the organic layer and the aqueous layer may be separated into two layers, or may be a uniform solution without layer separation. In addition, it is allowed in the present invention that a part of the monomer is precipitated in the raw material monomer mixed solution. However, in order to introduce a desired amount of structural units, it is preferable that no monomer is precipitated in the raw material monomer mixture. In particular, the monomer 1 as the sulfonic acid (salt) group-introducing component should be dissolved without precipitation of the monomer 1 in the raw material monomer mixture in order to obtain a vinyl polymer having a desired amount of the sulfonic acid (salt) group. Is preferred.
On the other hand, when the polymerization reaction is performed in the raw material monomer mixed solution containing the solution A and the solution B at the mixing ratio for layer separation, a polymer containing a large amount of structural units derived from the monomer 1 is usually synthesized. Since the solubility is poor, it becomes a precipitate in the medium, which is not preferable. In the present invention, “layer separation” refers to the observation of an interface divided into upper and lower layers or three or more layers by visual observation within 1 hour after mixing the solution A and the solution B at an ambient temperature of 25 ° C. It shall be said. Moreover, there exists a tendency for the monomer 1 to precipitate easily, so that there are many ratios which the solution A accounts in a raw material monomer liquid mixture. Therefore, in order to reduce or suppress the precipitation of the monomer 1 and perform the reaction in a homogeneous system without layer separation, it is preferable to mix 10 to 40 times the amount of the solution B with respect to the solution A on a mass basis.

  The polymerization reaction in the prepared raw material monomer mixture can be performed in the presence of a known polymerization initiator, chain transfer agent, and the like. The polymerization conditions vary depending on the monomers used, the polymerization initiator, the type of chain transfer agent, and the like, but in general, the liquid temperature is preferably about 50 to 80 ° C., and the reaction time is preferably about 1 to 30 hours. The polymerization reaction may be performed in the air or in an atmosphere of a gas inert to the reaction such as nitrogen or argon. Moreover, you may carry out under reduced pressure and you may carry out under atmospheric pressure. In the polymerization, in addition to the above-described components, other components generally added to the polymerization reaction may be added to the polymerization reaction system. In addition, in the raw material monomer liquid mixture containing the solution A and the solution B in the ratio which carries out a layer separation, it is preferable to perform a polymerization reaction according to the method shown in the Example mentioned later.

  The vinyl polymer that is a copolymer of monomers 1 to 4 contained in the polymer composition preferably has a mass average molecular weight of 1,000 or more from the viewpoint of obtaining a high-strength coating film, and has good workability. In order to maintain it, it is preferable that it is 200,000 or less from a viewpoint of making the viscosity of a paint in a predetermined concentration into an appropriate range. Moreover, it is preferable that molecular weight distribution (Mw / Mn) which is ratio of the mass average molecular weight Mw and the number average molecular weight is 1.00-5.50. 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. The average molecular weight in the present invention refers to a value determined in terms of standard polystyrene. The molecular weight of the polymer can be controlled by the raw material composition, reaction conditions, and the like.

  In one embodiment, the polymer composition obtained by the production method of the present invention can be the reaction liquid obtained after the polymerization reaction. Alternatively, a polymer composition can be obtained through a step of filtering the reaction solution after the polymerization reaction to remove insoluble matters. Furthermore, you may pass through the process of removing at least one part of water, alcohol, or a ketone solvent. However, any of the solvents used in the method for producing the polymer composition of the present invention is highly safe and has a relatively low boiling point, so that there is little residue in the medium, and even if it remains, the medium performance is greatly reduced. is not. That is, the polymer composition obtained by the present invention is suitably used as a binder composition for a magnetic recording medium or for its preparation. For example, a magnetic layer forming coating solution is prepared by mixing a ferromagnetic powder and various additives into the polymer composition obtained by the present invention, and adding an organic solvent (preferably a ketone solvent) as necessary. A non-magnetic powder and various additives can be mixed, and an organic solvent (preferably a ketone solvent) can be added as necessary to prepare a coating solution for forming a non-magnetic layer. In the layer formed using these coating liquids, various powders can be highly dispersed by the vinyl polymer that is a copolymer of monomers 1 to 4, thereby enabling high density recording applications with high surface smoothness. A suitable magnetic recording medium can be obtained.

That is, the present invention
A method of manufacturing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
Producing a polymer composition by the method of the present invention described above,
Preparing a coating solution for forming a magnetic layer by mixing the produced polymer composition with a ferromagnetic powder; and
Forming the magnetic layer using the prepared coating liquid for forming a magnetic layer;
A method for producing a magnetic recording medium comprising:
A method for producing a magnetic recording medium comprising, in this order, a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
Producing a polymer composition by the method of the present invention described above,
Preparing a coating solution for forming a nonmagnetic layer by mixing the produced polymer composition with a nonmagnetic powder; and
Forming the nonmagnetic layer using the prepared nonmagnetic layer forming coating solution;
A method of manufacturing a magnetic recording medium including
It is also related. As a method for forming a magnetic recording medium using the polymer composition obtained according to the present invention, for example, a known technique relating to a magnetic recording medium such as Japanese Patent Application Laid-Open No. 2004-295926 can be applied without any limitation.

  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. The following operations were performed at room temperature (25 ° C.) unless otherwise specified.

1. Preparation example of raw material monomer mixture

[Preparation Example 1]
In a 200 mL Erlenmeyer flask, methyl ethyl ketone 65.6 g (Wako Pure Chemicals Grade 1), monomer 3 as isobornyl methacrylate (Wako Pure Chemicals Grade 1, hereinafter referred to as IsoBorMA) 36.2 g (162.8 mmol), monomer 4 as stearyl methacrylate (Wako Pure Chemicals Grade 1) Then, 13.6 g (40.3 mmol) of SteMA) and 25.4 g (195.2 mmol) of 2-hydroxyethyl methacrylate (first grade of Wako Pure Chemicals, hereinafter abbreviated as HEMA) as monomer 2 were mixed to prepare Solution B. In a 30 mL beaker, 11.2 g of distilled water and 2.8 g (13.51 mmol) of 2-acrylamido-2-methylpropanesulfonic acid (first grade of Wako Pure Chemical Industries, hereinafter referred to as AMPS) as monomer 1 are mixed and stirred until dissolved. Solution A was prepared. Solution A prepared in a 30 mL beaker was mixed with stirring in Solution B in a 200 mL Erlenmeyer flask and allowed to stand for 1 hour. When the state of the monomer mixture was observed, it was separated into two layers, an organic layer and an aqueous layer. .

[Preparation Example 2]
In the preparation of the monomer mixture of Preparation Example 1, monomer mixing was performed in the same manner as in Preparation Example 1, except that HEMA was changed to 26.2 g (201.3 mmol), AMPS was changed to 0.96 g (4.63 mmol), and distilled water was changed to 7.7 g. When the liquid was prepared and observed, the monomer mixture was separated into two layers, an organic layer and an aqueous layer.

[Preparation Example 3]
In the preparation of the monomer mixture in Preparation Example 1, the monomer mixture was prepared and observed in the same manner as in Preparation Example 1, except that the distilled water was changed to 3.6 g. Although it became a solution, the deposit was confirmed. When the precipitate was collected and analyzed for composition, it was confirmed to be AMPS.

[Preparation Example 4]
In the preparation of the monomer mixture of Preparation Example 1, monomer mixing was performed in the same manner as in Preparation Example 1, except that HEMA was changed to 25.6 g (196.7 mmol), AMPS was changed to 1.92 g (9.26 mmol), and distilled water was changed to 3.8 g. When the liquid was prepared and observed, the monomer mixed liquid was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 5]
In the preparation of the monomer mixture of Preparation Example 1, monomer mixing was performed in the same manner as in Preparation Example 1, except that HEMA was changed to 25.6 g (196.7 mmol), AMPS was changed to 1.22 g (5.89 mmol), and distilled water was changed to 6.1 g. When the liquid was prepared and observed, the monomer mixed liquid was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 6]
In the preparation of the monomer mixture of Preparation Example 1, monomer mixing was performed in the same manner as Preparation Example 1, except that HEMA was changed to 26.2 g (201.3 mmol), AMPS was changed to 0.96 g (4.63 mmol), and distilled water was changed to 3.8 g. When the liquid was prepared and observed, the monomer mixed liquid was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 7]
Solution B was prepared by mixing 65.6 g of methyl ethyl ketone, 36.2 g (162.8 mmol) of IsoBorMA, 13.6 g (40.3 mmol) of SteMA, and 24.8 g (190.6 mmol) of HEMA in a 200 mL Erlenmeyer flask. Further, 11.3 g of distilled water, 3.8 g of methanol (hereinafter abbreviated as MeOH) and 3.8 g (18.24 mmol) of AMPS were mixed in a 30 mL beaker, and stirred until dissolved to prepare solution A. Solution A prepared in a 30 mL beaker was mixed with solution B prepared in a 200 mL Erlenmeyer flask while stirring and allowed to stand for 1 hour, and the state of the monomer mixture was observed. The organic layer and the aqueous layer were separated into two layers. did.

[Preparation Example 8]
In the preparation of the monomer mixture of Preparation Example 7, the same as Preparation Example 7 except that HEMA was changed to 25.4 g (195.2 mmol), AMPS was changed to 2.8 g (13.51 mmol), distilled water was changed to 2.8 g, and MeOH was changed to 0.9 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution became a uniform solution without layer separation, but precipitates were confirmed. When the precipitate was collected and analyzed for composition, it was confirmed to be AMPS.

[Preparation Example 9]
In the preparation of the monomer mixture of Preparation Example 7, the same as Preparation Example 7 except that HEMA was changed to 25.6 g (196.7 mmol), AMPS was changed to 1.9 g (9.26 mmol), distilled water was changed to 3.0 g, and MeOH was changed to 1.0 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution became a uniform solution without layer separation, but precipitates were confirmed. When the precipitate was collected and analyzed for composition, it was confirmed to be AMPS.

[Preparation Example 10]
In the preparation of the monomer mixture of Preparation Example 7, HEMA was changed to 25.4 g (195.2 mmol), AMPS was changed to 2.8 g (13.51 mmol), distilled water was changed to 8.4 g, and MeOH was changed to 2.8 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 11]
In the preparation of the monomer mixture of Preparation Example 7, HEMA was changed to 25.6 g (196.7 mmol), AMPS was changed to 1.9 g (9.26 mmol), distilled water was changed to 6.2 g, and MeOH was changed to 2.1 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 12]
In the preparation of the monomer mixture of Preparation Example 7, HEMA was changed to 25.6 g (196.7 mmol), AMPS was changed to 1.9 g (9.26 mmol), distilled water was changed to 4.5 g, and MeOH was changed to 1.5 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 13]
In the preparation of the monomer mixture of Preparation Example 7, HEMA was changed to 25.6 g (196.7 mmol), AMPS was changed to 1.22 g (5.89 mmol), distilled water was changed to 8.4 g, and MeOH was changed to 2.8 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 14]
In the preparation of the monomer mixture liquid of Preparation Example 7, HEMA was changed to 26.2 g (201.3 mmol), AMPS was changed to 0.96 g (4.63 mmol), distilled water was changed to 3.0 g, and MeOH was changed to 1.0 g. When the monomer mixed solution was prepared and observed by this method, the monomer mixed solution was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 15]
In the preparation of the monomer mixture in Preparation Example 14, the monomer mixture was prepared and observed in the same manner as in Preparation Example 14, except that cyclohexanone (first grade of Wako Pure Chemical Industries) was used instead of methyl ethyl ketone. The liquid was uniform without layer separation, and no precipitate was observed.

[Preparation Example 16]
In the preparation of the monomer mixture in Preparation Example 14, the monomer mixture was prepared and observed in the same manner as in Preparation Example 14 except that dodecyl methacrylate (first grade of Wako Pure Chemical Industries) was used instead of stearyl methacrylate. However, the monomer mixture was uniform without layer separation, and no precipitate was observed.

[Preparation Example 17]
In the preparation of the monomer mixture in Preparation Example 14, the monomer mixture was prepared and observed in the same manner as in Preparation Example 14, except that hexyl methacrylate (first grade of Wako Pure Chemical Industries) was used instead of stearyl methacrylate. However, the monomer mixture was uniform without layer separation, and no precipitate was observed.

[Preparation Example 18]
In the preparation of the monomer mixture in Preparation Example 14, the preparation and observation of the monomer mixture were conducted in the same manner as in Preparation Example 14, except that 2-ethylhexyl methacrylate (first grade of Wako Pure Chemical Industries) was used instead of stearyl methacrylate. As a result, the monomer mixture was uniform without layer separation, and no precipitate was observed.

[Preparation Example 19]
Preparation and observation of the monomer mixture in the same manner as in Preparation Example 14, except that dicyclopentanyl methacrylate (first grade of Wako Pure Chemical Industries) was used instead of isobonyl methacrylate in the preparation of the monomer mixture in Preparation Example 14. As a result, the monomer mixture was uniform without layer separation, and no precipitate was confirmed.

[Preparation Example 20]
In the preparation of the monomer mixture in Preparation Example 14, the monomer mixture was prepared and observed in the same manner as in Preparation Example 14, except that cyclohexyl methacrylate (Wako Pure Chemical) was used instead of isobonyl methacrylate. However, the monomer mixture was uniform without layer separation, and no precipitate was observed.

[Comparative Preparation Example 1]
In a 30 mL beaker, 0.96 g (4.63 mmol) AMPS and 4.0 g MeOH were mixed. Filtration was performed to remove undissolved AMPS. In a 200 mL Erlenmeyer flask, 65.6 g of methyl ethyl ketone, 36.2 g (162.8 mmol) of IsoBorMA, 13.6 g (40.3 mmol) of SteMA, and 26.2 g (201.3 mmol) of HEMA were mixed, and a mixed solution of AMPS and MeOH filtered here Was added while stirring to obtain a monomer mixture. AMPS further precipitated from the resulting monomer mixture.

[Comparative Preparation Example 2]
In a 200 mL Erlenmeyer flask, dimethylformamide (hereinafter abbreviated as DMF) 80.7 g, IsoBorMA 36.2 g (162.8 mmol), SteMA 13.6 g (40.3 mmol), HEMA 24.8 g (190.6 mmol), AMPS 3.8 g (18.24) mmol) were mixed and stirred until dissolved. The mixed solution was uniform and no precipitate was observed.

[Comparative Preparation Example 3]
In a 200 mL Erlenmeyer flask, 95.5 g of methyl ethyl ketone, 35.8 g (161.0 mmol) of IsoBorMA, 13.6 g (40.3 mmol) of SteMA, 26.2 g (201.3 mmol) of HEMA, and 0.96 g (4.63 mmol) of AMPS are mixed and dissolved. Until stirred. The monomer mixture became a homogeneous solution without layer separation, but deposits were confirmed. When the precipitate was collected and analyzed for composition, it was confirmed to be AMPS.

  The details of Preparation Examples 1 to 20 and Comparative Preparation Examples 1 to 3 are shown in Table 1 below.

2. Examples of polymer composition production, comparative examples

[Example 1-1]
(1) Polymerization reaction of acrylic polymer A monomer mixed solution was prepared at the same monomer component ratio and solution mixing ratio as in Preparation Example 1. Since this monomer mixed solution had been separated into two layers, an organic layer and an aqueous layer, a polymerization reaction was performed in the following procedure.
To a 500 mL four-necked flask equipped with a Dimroth condenser and a stirrer, 65.6 parts by mass of methyl ethyl ketone, 36.2 parts by mass of IsoBorMA, 13.6 parts by mass of SteMA, 25.4 parts by mass of HEMA are added. Stir for more than an hour to dissolve completely. Thereafter, 0.4 part by mass of dimethyl-2,2′-azobis (2-methylpropionate) was added and stirred until complete dissolution. After raising the internal temperature to 70 ° C, adjusting the external temperature so that the internal temperature is in the range of 65 to 72 ° C, a solution in which 2.8 parts by mass of AMPS and 11.2 parts by mass of distilled water are mixed for 1 hour It was dripped. After completion of the dropwise addition, the reaction was further continued for 5 hours.
After completion of the reaction, the solution was diluted with methyl ethyl ketone so that the solid content concentration was about 30% by mass, insoluble matter was filtered through a # 225 mesh, and the polymer solution was taken out.
The mass average molecular weight (Mw), number average molecular weight (Mn), and sulfonic acid (salt) group concentration of the polymer in the obtained polymer solution were measured by the following methods, and the state of the polymer solution after filtration was determined by the following method. It was evaluated with.

Evaluation method (1) Measurement of average molecular weight Average molecular weight (Mw, Mn) is obtained in terms of standard polystyrene using GPC (gel permeation chromatography) using a dimethylformamide solvent containing 0.3% lithium bromide. It was.
(2) 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, converted to the amount of sulfur element per kg of polymer, and sulfonic acid (salt) in the polymer The base concentration was determined.
(3) State of polymer solution after filtration About the polymer solution which was allowed to stand for 1 hour after insoluble matter filtration, it was visually determined whether it was a homogeneous solution or clouded.

[Example 1-2]
The monomer mixture obtained in Preparation Example 3 was filtered to remove precipitated AMPS. The mixed solution after filtration was put into a 300 mL Erlenmeyer flask, 0.4 parts by mass of dimethyl-2,2′-azobis (2-methylpropionate) was added, and the mixture was completely dissolved by stirring.
Meanwhile, 23.0 parts by mass of methyl ethyl ketone was added to a 500 mL four-necked flask equipped with a Dimroth condenser and a stirrer, and the temperature was raised to an internal temperature of 70 ° C. under a nitrogen stream. While controlling the external temperature so that the internal temperature was 65 to 72 ° C., the monomer mixture in the 300 mL flask was added dropwise over 3 hours, and after completion of the dropwise addition, the reaction was continued for 5 hours. After completion of the reaction, the solution was diluted with methyl ethyl ketone so that the solid content concentration was about 30 wt%, and the polymer solution was taken out after filtration of insoluble matter with # 225 mesh.
Each evaluation mentioned above was performed about the obtained polymer solution.

[Example 1-3]
The monomer mixture obtained in Preparation Example 4 was put into a 300 mL Erlenmeyer flask as it was, and 0.4 parts by mass of dimethyl-2,2′-azobis (2-methylpropionate) was added and stirred until complete dissolution.
Meanwhile, 23.0 parts by mass of methyl ethyl ketone was added to a 500 mL four-necked flask equipped with a Dimroth condenser and a stirrer, and the temperature was raised to an internal temperature of 70 ° C. under a nitrogen stream. While controlling the external temperature so that the internal temperature was 65 to 72 ° C., the monomer mixture in the 300 mL flask was added dropwise over 3 hours, and after completion of the dropwise addition, the reaction was continued for 5 hours. After completion of the reaction, the solution was diluted with methyl ethyl ketone so that the solid content concentration was about 30% by mass, the insoluble matter was filtered through # 225 mesh, and the polymer solution was taken out.
Each evaluation mentioned above was performed about the obtained polymer solution.

[Example 1-4]
In the polymerization reaction of Example 1-3, in the same manner as in Example 1-3, except that the monomer mixed solution obtained in Preparation Example 5 was used instead of the monomer mixed solution obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-5]
In the polymerization reaction of Example 1-3, in the same manner as in Example 1-3, except that the monomer mixture obtained in Preparation Example 6 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-6]
A monomer mixed solution was prepared at the same monomer component ratio and solution mixing ratio as in Preparation Example 7. Since this monomer mixture was separated into two layers, an organic layer and an aqueous layer, the polymerization reaction was performed in the following procedure.
To a 500 mL four-necked flask equipped with a Dimroth condenser and stirrer, add 65.6 parts by mass of methyl ethyl ketone, 36.2 parts by mass of IsoBorMA, 13.6 parts by mass of SteMA, 24.8 parts by mass of HEMA, and at 25 ° C. under a light-shielding condition under a nitrogen stream. Stir for more than an hour to dissolve completely. Thereafter, 0.4 part by mass of dimethyl-2,2′-azobis (2-methylpropionate) was added and stirred until complete dissolution. A solution in which 3.8 parts by mass of AMPS, 11.3 parts by mass of distilled water, and 3.8 parts by mass of MeOH are mixed while adjusting the external temperature so that the internal temperature is in the range of 65 to 72 ° C after raising the internal temperature to 70 ° C. Was added dropwise over 1 hour. Subsequent operations were carried out in the same manner as in Example 1-1, the polymer solution was taken out, and each evaluation was performed.

[Example 1-7]
In the polymerization reaction of Example 1-2, the monomer mixture liquid obtained in Preparation Example 8 was used instead of the monomer mixture liquid obtained in Preparation Example 3, and the same method as in Example 1-2 was used. A polymer solution was obtained and each measurement was performed.

[Example 1-8]
In the polymerization reaction of Example 1-3, in the same manner as in Example 1-3, except that the monomer mixture obtained in Preparation Example 10 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-9]
In the polymerization reaction of Example 1-3, the same procedure as in Example 1-3 was used, except that the monomer mixture obtained in Preparation Example 12 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-10]
In the polymerization reaction of Example 1-3, in the same manner as in Example 1-3, except that the monomer mixture obtained in Preparation Example 13 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-11]
In the polymerization reaction of Example 1-3, the same procedure as in Example 1-3 was used, except that the monomer mixture obtained in Preparation Example 14 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-12]
In the polymerization reaction of Example 1-3, the same method as in Example 1-3, except that dimethyl-2,2′-azobis (2-methylpropionate) was changed to 1.6 parts by mass instead of 0.4 parts by mass A polymer solution was obtained and each evaluation was performed.

[Example 1-13]
In the polymerization reaction of Example 1-12, in the same manner as in Example 1-12, except that the monomer mixture obtained in Preparation Example 15 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-14]
In the polymerization reaction of Example 1-12, in the same manner as in Example 1-12, except that the monomer mixture obtained in Preparation Example 16 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-15]
In the polymerization reaction of Example 1-12, in the same manner as in Example 1-12, except that the monomer mixture obtained in Preparation Example 17 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-16]
In the polymerization reaction of Example 1-12, in the same manner as in Example 1-12, except that the monomer mixture obtained in Preparation Example 18 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-17]
In the polymerization reaction of Example 1-12, in the same manner as in Example 1-12, except that the monomer mixed solution obtained in Preparation Example 19 was used instead of the monomer mixed solution obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Example 1-18]
In the polymerization reaction of Example 1-12, in the same manner as in Example 1-12, except that the monomer mixture obtained in Preparation Example 20 was used instead of the monomer mixture obtained in Preparation Example 4. A polymer solution was obtained and each evaluation was performed.

[Comparative Example 1-1]
In the polymerization reaction of Example 2, the polymer was prepared in the same manner as in Example 1-2, except that the monomer mixture obtained in Comparative Preparation Example 1 was used instead of the monomer mixture obtained in Preparation Example 3. A solution was obtained and each measurement was performed.

[Comparative Example 1-2]
In the polymerization reaction of Example 1-3, the same method as in Example 1-3 except that the monomer mixed solution obtained in Comparative Preparation Example 2 was used instead of the monomer mixed solution obtained in Preparation Example 4. A polymer solution was obtained and each physical property was evaluated.

[Comparative Example 3]
In the polymerization reaction of Example 1-2, the same method as in Example 1-2, except that the monomer mixture obtained in Comparative Preparation Example 3 was used instead of the monomer mixture obtained in Preparation Example 3. The polymer solution was obtained and each measurement was performed.

Since Comparative Example 1-2 used dimethylformamide that satisfactorily dissolves each monomer, the amount of sulfonic acid (salt) almost coincided with the theoretical value of the sulfonic acid (salt) group concentration calculated from the monomer (AMPS) charge ratio. A polymer with introduced groups could be obtained. However, dimethylformamide needs to be handled with safety and is difficult to remove due to its high boiling point.
In contrast, in Examples 1-1 to 1-18, the ketone solvent occupies a part of the reaction solvent, and the coexisting solvent (water, methanol) is subjected to a polymerization reaction in a reaction system that is easy to handle and remove. A vinyl polymer containing a sulfonic acid (salt) group could be synthesized. Among them, in Examples 1-4, 1-5, and 1-10 to 1-18 in which the monomer mixed solution was uniform and the polymer solution was also uniform, the sulfonic acid (salt) calculated from the monomer (AMPS) charge ratio It was possible to obtain a polymer in which an amount of sulfonic acid (salt) groups was introduced, which almost coincided with the theoretical value of the group concentration.
In Examples 1-2 and 1-7 in which AMPS was precipitated at the stage of the monomer mixture, the measured value of the sulfonic acid (salt) group concentration was lower than the theoretical value due to the precipitation of AMPS. As compared with Comparative Example 1-3 in which the polymerization reaction was performed in a solvent, a polymer having a sulfonic acid (salt) group introduced in an amount close to the theoretical value could be obtained. In Examples 1-1 to 1-3, 1-6, 1-8, and 1-9, the polymer liquid became white turbid after filtration. Therefore, a precipitate causing white turbidity was collected and analyzed by FT-IR. It was confirmed that the polymer contains a large amount of structural units derived from it. Since such precipitates cause a decrease in surface smoothness in the magnetic recording medium, if such precipitates are produced, they should be used for magnetic recording medium preparation after they are removed by a known method. Is preferred.
Comparative Example 1-1 is an example using a monomer solution prepared by adding AMPS to methanol alone solvent, but because of the extremely low solubility of AMPS in methanol, Comparative Example in which a polymerization reaction was performed in a ketone solvent Similar to 3, the measured value of the sulfonic acid (salt) group concentration was significantly lower than the theoretical value.
In addition, about the Example, the polymer in a polymer solution was subjected to NMR analysis, and it was confirmed that structural units derived from the four types of monomers used were introduced.

3. Examples, reference examples, and comparative reference examples for manufacturing magnetic recording media

  Specific examples of the copolymer synthesized using monomers 2 to 4 as essential monomers include the following vinyl polymers. Below, Mw represents a mass average molecular weight, and the numerical value attached | subjected to the right side of each structural unit represents the molar ratio of each structural unit with respect to all the polymer units in a copolymer.

  Among the above exemplified polymers, polymer solutions containing AP-16, AP-26, AP-28, AP-30 obtained from monomers 1 to 4 were prepared according to the method of Example 3. As a result of GPC analysis after the preparation, no peaks of residual monomer and residual oligomer were observed, so it was confirmed that a copolymer having each structural unit introduced at a charging ratio was obtained. The obtained polymer solution was adjusted with methyl ethyl ketone so that the solid content concentration was 30% by mass, and then used for the preparation of each layer forming coating solution described later.

  Among the above exemplified polymers, AP-1, AP-3, AP-15, and AP-20 were synthesized using N-methylpyrrolidone (NMP) as a reaction solvent. Specifically, to a reactor equipped with a stirrer and a reflux condenser, a corresponding monomer and a predetermined amount of a polymerization catalyst (dimethyl 2,2′-azobisisobutyrate) are added, and the reaction is performed by heating in a nitrogen atmosphere. Completed. As a result of GPC analysis after the reaction, no peak of residual monomer and residual oligomer was observed, and it was confirmed that a copolymer having each structural unit introduced at a charging ratio was obtained.

As a first comparative polymer, an acrylic copolymer BP-1 (mass average molecular weight 6.0 × 10 ⁵ ) having the following structural units was synthesized according to the above method.

As a second comparative polymer, an acrylic copolymer BP-2 (mass average molecular weight 8.0 × 10 ⁵ ) having the following structural units was synthesized according to the above method.

As a third comparative polymer, an acrylic copolymer BP-3 (mass average molecular weight 6.0 × 10 ⁵ ) having the following structural units was synthesized according to the above method. The numerical value given to the right side of the following structural unit represents the molar ratio of each structural unit to all the polymerized units in the copolymer.

[Example 2-1]
(1) Preparation of magnetic layer coating solution Ferromagnetic metal powder: 100 parts Composition Fe / Co = 100/25
Hc 2450 Oe (≒ 195kA / m)
Specific surface area by BET method 65m ² / g
Surface treatment agent Al ₂ O ₃ , SiO ₂ , Y ₂ O ₃
Particle size (average major axis length) 45nm
Needle ratio 5
σs 110 emu / g (≈110 A · m ² / kg)
Phenylphosphonic acid: 3 parts 30% by mass solution of acrylic copolymer AP-16 prepared by the above method: 50 parts Methyl ethyl ketone: 115 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

The above components were kneaded with an open kneader and then dispersed using a sand mill. The following components were added to the obtained dispersion and stirred, followed by sonication and filtration using a filter having an average pore size of 1 μm to prepare a magnetic layer coating solution.
Butyl stearate: 1.5 parts Stearic acid: 0.5 parts Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts Toluene: 3 parts Polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts

(2) Preparation of coating solution for nonmagnetic layer Nonmagnetic powder (αFe ₂ O ₃ hematite): 80 parts
Average 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%
30% by mass solution of acrylic copolymer AP-16 prepared by the above method: 63 parts Methyl ethyl ketone: 106 parts Cyclohexanone: 150 parts

The above components were kneaded with an open kneader and then dispersed using a sand mill. The following components were added to the obtained dispersion and stirred, followed by filtration using a filter having an average pore size of 1 μm to prepare a coating solution for the lower coating layer (nonmagnetic layer).
Butyl stearate: 1.5 parts Stearic acid: 1 part Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts Toluene: 3 parts Polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts

(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 Polyurethane resin: 58 parts Copper phthalocyanine dispersant: 2. 5 parts Nippon Run 2301 (manufactured by Nippon Polyurethane Industry Co., Ltd.): 0.5 part Methyl isobutyl ketone: 0.3 part Methyl ethyl ketone: 860 parts Toluene: 240 parts

The above components were pre-kneaded with a roll mill and then dispersed with a sand mill, and 4 parts of a polyester resin (Byron 500, manufactured by Toyobo Co., Ltd.), 14 parts of a polyisocyanate compound (Coronate 3041, manufactured by Nippon Polyurethane Industry Co., Ltd.), α-Al ₂ O ₃ ( 5 parts) (manufactured by Sumitomo Chemical Co., Ltd.) was added and stirred and filtered to prepare a backcoat layer coating solution.

(4) Preparation of magnetic tape The non-magnetic layer coating solution is dried so that the thickness after drying becomes 1.0 μm, and immediately after that, the thickness of the magnetic layer becomes 0.1 μm thereon. Both layers are coated simultaneously on a polyethylene naphthalate resin support having a thickness of 5 μm and a magnetic layer coating surface having a center line surface roughness of 0.001 μm and having a base surface made hydrophilic by pre-corona treatment. Was still wet and oriented with a cobalt magnet having a magnetic force of 0.5T (5000G) and a solenoid having a magnetic force of 0.4T (4000G) and dried. Then, after applying a corona treatment in advance to the surface opposite to the base surface, the backcoat layer coating solution is applied so that the thickness after drying is 0.5 μm, and then composed of a metal roll. Processing was performed at a temperature of 100 ° C. at a speed of 80 m / min with a seven-stage calendar, and a magnetic tape was produced by slitting to a width of ½ mm.

(Examples 2-2 to 2-4)
Example 2-2 was carried out in the same manner as Example 2-1 except that the polymer solution used for the magnetic layer and nonmagnetic layer was one containing an acrylic copolymer shown in Table 3 prepared by the above method. Magnetic tapes of ˜2-4 were produced.

(Reference Examples 2-1 to 2-6)
Acrylic copolymers shown in Table 3 instead of 30 parts by mass of acrylic copolymer AP-16 prepared by the above-described method for preparing a coating solution for forming a magnetic layer: 50 parts and methyl ethyl ketone: 115 parts: 15 parts and 150 parts of methyl ethyl ketone: 150 parts by weight of the acrylic copolymer AP-16 prepared by the above method for preparing the coating solution for forming the nonmagnetic layer: 63 parts and 106 parts of methyl ethyl ketone Magnetic tapes of Reference Examples 2-1 to 2-6 were prepared in the same manner as in Example 2-1, except that 19 parts of an acrylic copolymer and 150 parts of methyl ethyl ketone shown in Table 3 were used.

(Comparative Reference Example 2-1)
Comparative Reference Example in the same manner as in Reference Example 2-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-8-67855. A magnetic tape 2-1 was produced.

(Comparative Reference Example 2-2)
Comparative Reference Example as in Reference Example 2-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-2004-295926. A magnetic tape 2-2 was prepared.

(Comparative Reference Example 2-3)
Comparative Reference Example 2 in the same manner as in Reference Example 2-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-6-111277. -3 magnetic tape was produced.

(Comparative Reference Example 2-4)
Comparative Reference Example as in Reference Example 2-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-2005-310332 2-4 magnetic tape was produced.

(Comparative Reference Examples 2-5 to 2-7)
The magnetic properties of Comparative Reference Examples 2-5 to 2-7 were the same as Reference Example 2-1, except that the type of acrylic copolymer used in the magnetic layer and the nonmagnetic layer was changed to that shown in Table 3. A tape was prepared.

(Example 3-1)
(1) Preparation of ferromagnetic hexagonal ferrite magnetic layer coating solution Ferromagnetic tabular hexagonal ferrite powder: 100 parts Composition excluding oxygen (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 1
Hc: 160 kA / m (2000 Oe)
Average plate diameter: 20nm
Average plate ratio: 2.7
BET specific surface area: 60 m ² / g
σs: 46 A · m ² / kg (46 emu / g)
30% by mass solution of acrylic copolymer AP-16 prepared by the above method: 40 parts α-Al ₂ O ₃ (particle size 0.1 μm): 8 parts Carbon black (average particle diameter: 20 nm): 0.5 Parts Cyclohexanone: 82 parts

The above components were kneaded with an open kneader and then dispersed using a sand mill. The following components were added to the obtained dispersion and stirred, followed by sonication and filtration using a filter having an average pore size of 1 μm to prepare a magnetic layer coating solution.
Butyl stearate: 2 parts Stearic acid: 0.5 parts Methyl ethyl ketone: 50 parts Cyclohexanone: 50 parts Toluene: 3 parts Polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts

  The non-magnetic layer coating solution prepared by the same method as in Example 2-1 was further dried so that the thickness after drying was 1.0 μm, and immediately thereafter, the above-described magnetic layer coating solution was added thereon to the thickness of the magnetic layer. On a polyethylene naphthalate resin support having a thickness of 5 μm and a magnetic layer coated surface having a center line surface roughness of 0.001 μm and having a base surface made hydrophilic by pre-corona treatment The two layers were coated simultaneously, and were oriented by a cobalt magnet having a magnetic force of 0.5T (5000G) and a solenoid having a magnetic force of 0.4T (4000G) while both layers were still wet. Then, the thickness after drying the coating liquid for the back coat layer prepared in the same manner as in Example 2-1 on the surface opposite to the base surface, which has been previously subjected to corona treatment, is 0.5 μm. Then, a magnetic tape of Example 3-1 was prepared by performing a treatment with a seven-stage calendar composed of metal rolls at a temperature of 100 ° C. at a speed of 80 m / min and slitting to a width of ½ mm.

(Examples 3-2 to 3-4)
Magnetic tapes of Examples 3-2 to 3-4 were produced in the same manner as in Example 3-1, except that a polymer solution containing an acrylic copolymer shown in Table 4 prepared by the above method was used. did.

(Reference Examples 3-1 to 3-6)
Acrylic copolymers shown in Table 4 in place of 30 parts by mass of acrylic copolymer AP-16 prepared by the above-described method for preparation of a coating solution for forming a magnetic layer: 40 parts and cyclohexanone: 82 parts: Magnetic tapes of Reference Examples 3-1 to 3-6 were produced in the same manner as in Example 3-1, except that 12 parts and 110 parts of cyclohexanone were used.

(Comparative Reference Example 3-1)
Comparative Reference Example in the same manner as in Reference Example 3-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-8-67855. A magnetic tape of 3-1 was produced.

(Comparative Reference Example 3-2)
Comparative Reference Example in the same manner as in Reference Example 3-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-2004-295926. A magnetic tape of 3-2 was produced.

(Comparative Reference Example 3-3)
Comparative Reference Example 3 in the same manner as Reference Example 3-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Example 1 of JP-A-6-111277. -3 magnetic tape was produced.

(Comparative Reference Example 3-4)
Comparative Reference Example in the same manner as Reference Example 3-1, except that the type of acrylic copolymer used in the magnetic layer and nonmagnetic layer was changed to that described in Reference Example 1 of JP-A-2005-310332. A 3-4 magnetic tape was produced.

(Comparative Reference Examples 3-5 to 3-7)
The magnetic properties of Comparative Reference Examples 3-5 to 3-7 were the same as Reference Example 3-1, except that the types of acrylic copolymers used in the magnetic layer and the nonmagnetic layer were changed to those shown in Table 4. A tape was prepared.

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

<Electromagnetic conversion characteristics: SN ratio>
Using an LTO-Gen4 drive, a signal having a recording track of 11.5 μm, a reproduction track width of 5.3 μm, a linear recording density of 172 kfci and 86 kfci is recorded, a frequency analysis of the reproduction signal is performed by a spectrum analyzer, and a carrier signal at the time of recording a 172 kfci signal Of the output and the integrated noise of the entire spectrum band during 86 kfci signal recording was defined as the SN ratio. Fujifilm LTO-Gen4 tape was used as a reference tape. The S / N ratio of the reference tape was 0 dB, and the S / N ratio of each tape was obtained as a relative value. If the S / N ratio is 0 dB or more, it can be determined that the magnetic recording medium has excellent electromagnetic conversion characteristics as a high-density recording magnetic recording medium.

<Amount of dirt on the tape surface>
The tape is passed at an angle of 150 degrees so that the magnetic layer surface is in contact with the edge of a prismatic bar made of Al ₂ O ₃ / TiC and having a cross section of 7 mm × 7 mm. By sliding the path, the edge part of the prismatic bar was observed with a microscope, and the adhesion state of the dirt was evaluated. Evaluation was made into sensory evaluation and evaluated in 10 steps. 10 is less dirty and 1 is most dirty.
The stain evaluated by the above method is mainly caused by the abrasion of the magnetic layer surface, and the smaller the evaluation result value, the more the surface of the magnetic layer is scraped and the running durability is poor. If the evaluation value is 8 or more, it can be determined that the running durability is good with less contamination (scratching of the magnetic layer surface).

From the results shown in Table 3 and Table 4, the following points can be confirmed.
(1) The magnetic tape of the reference example formed using the copolymer obtained by using monomers 2 to 4 as essential monomers as a binder had high surface smoothness. Thereby, it can confirm that fine particle powder was highly dispersible with the copolymer obtained by making the monomers 2-4 into an essential monomer. As a result, the magnetic tape of the reference example showed excellent electromagnetic conversion characteristics.
(2) The magnetic tape of the reference example was able to realize excellent running durability.
(3) On the other hand, Comparative Reference Examples 2-1 to 2-4 and Comparative Reference Examples 3-1 to 3-4 using vinyl copolymers that have been conventionally used as binders for magnetic recording media The magnetic tape showed results inferior to the magnetic tape of the reference example in all evaluation items of surface smoothness, electromagnetic conversion characteristics, and running durability.
(4) The magnetic tapes of Comparative Reference Example 2-5 and Comparative Reference Example 3-5, Comparative Reference Example 2-6, and Comparative Reference Example 3-6 are all evaluated for surface smoothness, electromagnetic conversion characteristics, and running durability. In the items, the results showed inferior results to the magnetic tape of the reference example, and the magnetic tapes of the comparative reference example 2-7 and the comparative reference example 3-7 showed the same running durability as the reference example. Since surface smoothness and electromagnetic conversion characteristics were inferior to those of the reference example, it can be confirmed that combining the monomers 2 to 4 makes it possible to achieve both electromagnetic conversion characteristics and running durability.
From the above results, it is shown that the copolymer obtained using monomers 2 to 4 as essential monomers is a vinyl copolymer for producing a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability. It was done. According to the present invention, as shown in the above-mentioned examples of polymer solution preparation, the ketone solvent occupies a part of the reaction solvent, and the coexisting solvent (water, alcohol) is easy to handle and remove. In the reaction system, the monomer 1 can be used together with the monomers 2 to 4 to carry out the polymerization reaction, whereby a vinyl containing a structural unit derived from the monomers 2 to 4 and a sulfonic acid (salt) group that is an adsorptive functional group. A polymer solution containing a base polymer can be obtained. The obtained polymer solution can be used as it is for the preparation of a coating liquid for forming a coating type magnetic recording medium as shown in the examples of the magnetic recording medium. A magnetic recording medium having both conversion characteristics and running durability can be obtained.

  The present invention is useful in the field of manufacturing magnetic recording media.

Claims (13)

A method for producing a polymer composition comprising:
The polymer composition is
Formula (I):

[In the general formula (I), Z ¹ represents a sulfonic acid (salt) group, R ¹ represents a hydrogen atom or a methyl group, X ¹ represents an oxygen atom, a sulfur atom or a —N (R ¹¹ ) — group. , R ¹¹ represents a hydrogen atom or a substituent, and L ¹ represents an alkylene group which may have a substituent. ]
Monomer 1 represented by
General formula (II):

[In general formula (II), R ² represents a hydrogen atom, a halogen atom or a methyl group, and L ² represents a single bond or a divalent linking group. ]
Monomer 2 represented by
General formula (III):

[In General Formula (III), R ³ represents a hydrogen atom, a halogen atom, or a methyl group, L ³ represents a single bond or a divalent linking group, and Z ³ represents a substituent having a cyclic structure. ]
Monomer 3 represented by
Formula (IV):

[In General Formula (IV), R ⁴ represents a hydrogen atom, a halogen atom, or a methyl group, L ⁴ represents a single bond or a divalent linking group, and Y represents a hydrocarbon group having 8 to 50 carbon atoms. To express. ]
Monomer 4 represented by:
Including a polymer obtained by polymerization reaction of raw material monomers containing
A solution A prepared by adding the monomer 1 to water or a mixed solvent of water and alcohol and a solution B prepared by adding the monomers 2, 3 and 4 to the ketone solvent are mixed to prepare a raw material monomer mixed solution. The said manufacturing method characterized by preparing and performing the said polymerization reaction in this raw material monomer liquid mixture. Monomer 2 has the general formula (II-1):

[In General Formula (II) -1, R ² represents a hydrogen atom or a methyl group, and X ² represents a divalent linking group represented by —O—, —S—, or —N (R ²² ) —. R ²² represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms which may have a substituent, R ²¹ represents an alkylene group having 2 to 8 carbon atoms which may have a substituent, or A divalent group in which a plurality of alkylene groups are linked via a linking group is represented. ]
The method for producing a polymer composition according to claim 1, wherein Monomer 3 has the general formula (III-1):

[In General Formula (III) -1, R ³ represents a hydrogen atom or a methyl group, and X ³ represents a divalent linking group represented by —O—, —S—, or —N (R ³¹ ) —. R ³¹ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms which may have a substituent, and Z ³¹ represents an alicyclic fused ring group. ]
The method for producing a polymer composition according to claim 1 or 2, wherein Monomer 4 has the general formula (IV-1):

[In General Formula (IV) -1, R ⁴ represents a hydrogen atom or a methyl group, and X ⁴ represents — (O) m ¹ —, — (S) m ² —, or — {N (R ⁴¹ )} m ^3. -Represents a divalent linking group represented by-, R ⁴¹ represents an ^optionally substituted alkyl group having 1 to 8 carbon atoms, and n represents an integer of 12 to 30. ]
The method for producing a polymer composition according to claim 1, wherein the polymer composition is an acrylic monomer represented by the formula: The method for producing a polymer composition according to any one of claims 1 to 4, wherein the monomer 1 is dissolved without being precipitated during the preparation of the solution A. The method for producing a polymer composition according to any one of claims 1 to 5, wherein the solution A and the solution B are mixed without layer separation when preparing the raw material monomer mixture. The method for producing a polymer composition according to any one of claims 1 to 6, wherein the monomer 1 is dissolved without being precipitated during the preparation of the raw material monomer mixture. The method for producing a polymer composition according to claim 1, further comprising filtering the reaction solution after the polymerization reaction to remove insoluble matters. The monomer 1 is 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof. The method for producing a polymer composition according to any one of claims 1 to 8. The method for producing a polymer composition according to any one of claims 1 to 9, wherein the ketone solvent used for the preparation of the solution B is methyl ethyl ketone, cyclohexanone, or a mixed solvent thereof. The method for producing a polymer composition according to any one of claims 1 to 10, wherein the alcohol used for the preparation of the solution A is methanol. A method of manufacturing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
Producing a polymer composition by the method according to any one of claims 1 to 11,
Preparing a coating solution for forming a magnetic layer by mixing the produced polymer composition with a ferromagnetic powder;
Forming the magnetic layer using the prepared coating liquid for forming a magnetic layer;
A method of manufacturing a magnetic recording medium including: A method for producing a magnetic recording medium comprising, in this order, a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
Producing a polymer composition by the method according to any one of claims 1 to 11,
Preparing a coating solution for forming a nonmagnetic layer by mixing the produced polymer composition with a nonmagnetic powder;
Forming the nonmagnetic layer using the prepared nonmagnetic layer forming coating solution;
A method of manufacturing a magnetic recording medium including: