JP2006077121A - Coating agent and magnetic recording medium using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in durability, abrasion resistance, heat resistance, blocking resistance, adhesiveness to nonmagnetic supports, electroconductivity and low friction characteristics of a back coat layer. <P>SOLUTION: The coating agent comprises a polyurethane resin comprising one or more diols (A) selected from a group consisting of a specific structural formula such as general formula (I) or the like, dimer diols and hydrogenated dimer diols, a polyester polyol (B) prepared by copolymerizing an aromatic acid component with an alicyclic acid component, an aromatic polyisocyanate (C) and, if needed, a compound (D) having a side chain containing ≥2 functional groups reacting with isocyanate in one molecule and <1000 molecular weight, and carbon-based powder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coating agent obtained by using a binder having excellent characteristics, and to a magnetic recording medium such as a magnetic tape or a magnetic disk using the same as a back coat layer.

  Magnetic tapes and flexible disks, which are general-purpose magnetic recording materials, are prepared by dispersing needle-like magnetic particles with a long axis of 1 μm or less in a binder solution together with additives such as dispersants, lubricants, antistatic agents, etc. This is applied to a polyethylene terephthalate film as a support, and a back coat layer in which a filler mainly composed of carbon powder is dispersed is applied to the support opposite to the magnetic layer.

  In magnetic recording media, to improve the S / N ratio (signal / noise ratio) and increase the recording density, the surface of the magnetic layer is smoothed or more finely divided magnetic particles are filled into the magnetic layer. For these reasons, binders with good dispersion of magnetic particles are required. The smoother the surface of the magnetic layer, the higher the coefficient of friction and the worse the running performance and running durability of the magnetic tape. Therefore, there is a demand for a binder that has good durability, wear resistance, heat resistance, and adhesion to a nonmagnetic support.

  On the other hand, as the surface of the magnetic layer becomes smooth, a decrease in the smoothness of the magnetic layer due to the transfer of irregularities in the backcoat layer cannot be ignored. Therefore, as a binder for the back coat, it is essential to improve the dispersibility of the carbon-based powder and obtain a smooth back coat layer. However, when the back coat layer becomes smooth, the magnetic layer and the back coat layer may stick to each other when stored in a taped state under high temperature and high humidity. When this sticking phenomenon occurs, deposits remain on the surface of the magnetic layer, causing problems such as hindering recording and reproduction.

  Therefore, the properties required for the binder of the backcoat layer include the dispersibility and filling properties of the carbon-based powder, the durability of the backcoat layer, the wear resistance, the heat resistance, the blocking resistance, and the nonmagnetic support. The bonding agent plays a very important role because of its low adhesiveness, electrical conductivity and low friction. In order to impart such characteristics, various binders such as polyurethane resin and nitrocellulose or vinyl chloride copolymer are mainly used as the binder.

  For example, Patent Document 1 discloses that a vinyl chloride resin containing a tertiary amine is used as a binder for backcoat, but in recent years, the dispersibility of the finely divided carbon-based powder is insufficient. Further, when the tape was stored under high temperature and high humidity, there was a problem that the magnetic layer and the back coat layer were adhered.

  In addition, in order to improve the dispersibility of the carbon-based powder, the use of a polyurethane resin binder (see, for example, Patent Document 2) having better dispersibility of the magnetic particles than before has been studied, but the dispersibility of the magnetic particles is good. Even if a binder was used, the carbon-based powder dispersibility was insufficient.

JP-A-6-195680 Japanese Patent Laid-Open No. 10-320749

  The object of the present invention is to use a binder having good dispersibility, filling property, wear resistance, heat resistance, etc. of the carbon-based powder, and thus the durability, wear resistance, heat resistance, blocking resistance of the backcoat layer. Another object of the present invention is to provide a magnetic recording medium excellent in adhesion with a nonmagnetic support, conductivity, and low friction.

（但し、式中
Ｒ¹、Ｒ²；どちらか一方あるいは合計の炭素数が６以上となる脂肪族基、脂環族基または芳香族基
Ｒ；水素、脂肪族基、脂環族基または芳香族基でありそれぞれ異なっていても良い
ｌ、ｎ；０〜３の整数
ｍ；１〜３の整数
を表す）

（但し、式中
Ｒ³；炭素数が６以上となる脂肪族基、脂環族基または芳香族基
Ｒ⁴；水素、脂肪族基、脂環族基または芳香族基でありそれぞれ異なっていても良い
Ｒ；水素、脂肪族基、脂環族基または芳香族基でありそれぞれ異なっていても良い
ｏ、ｑ；０〜３の整数
ｐ；１〜３の整数
を表す） As a result of intensive studies on polyurethane resins, the present inventors have reached the present invention. That is, the present invention comprises at least one diol (A), aromatic acid component or alicyclic acid component selected from the group consisting of general formula (I), general formula (II), dimer diol and hydrogenated dimer diol. A copolymerized polyester polyol (B), an aromatic polyisocyanate (C), and a compound (D) having a side chain with a molecular weight of less than 1000 having two or more functional groups in one molecule that react with isocyanate as necessary. It is a coating agent containing a polyurethane resin and carbon-based powder as constituent components.

(However, in the formula, R ¹ and R ² ; either one or an aliphatic group, alicyclic group or aromatic group having a total carbon number of 6 or more R; hydrogen, aliphatic group, alicyclic group or aromatic And may be different from each other l, n; an integer of 0 to 3 m; an integer of 1 to 3)

(Wherein R ³ is an aliphatic group, alicyclic group or aromatic group having ⁴ or more carbon atoms, R ^{4 is} hydrogen, aliphatic group, alicyclic group or aromatic group, and is different from each other. R is hydrogen, an aliphatic group, an alicyclic group or an aromatic group, and may be different from each other o, q: an integer of 0 to 3 p; an integer of 1 to 3)

  In addition, the magnetic recording medium has the coating agent applied to the backcoat layer.

  Since the polyurethane resin used in the present invention has long side chains, it has excellent dispersibility of the carbon-based powder, and since it has a higher glass transition temperature, the coating film has excellent toughness and heat resistance. As a result, a coating layer having excellent durability, wear resistance, heat resistance, and blocking resistance can be obtained, which is useful as a backcoat layer for magnetic recording media.

（但し、式中
Ｒ¹、Ｒ²；どちらか一方あるいは合計の炭素数が６以上となる脂肪族基、脂環族基または芳香族基
Ｒ；水素、脂肪族基、脂環族基または芳香族基でありそれぞれ異なっていても良い
ｌ、ｎ；０〜３の整数
ｍ；１〜３の整数
を表す）

（但し、式中
Ｒ³；炭素数が６以上となる脂肪族基、脂環族基または芳香族基
Ｒ⁴；水素、脂肪族基、脂環族基または芳香族基でありそれぞれ異なっていても良い
Ｒ；水素、脂肪族基、脂環族基または芳香族基でありそれぞれ異なっていても良い
ｏ、ｑ；０〜３の整数
ｐ；１〜３の整数
を表す） In the polyurethane resin used in the present invention, it is necessary to use at least one of the group consisting of general formula (I), general formula (II), dimer diol and hydrogenated dimer diol as diol (A).

(However, in the formula, R ¹ and R ² ; either one or an aliphatic group, alicyclic group or aromatic group having a total carbon number of 6 or more R; hydrogen, aliphatic group, alicyclic group or aromatic And may be different from each other l, n; an integer of 0 to 3 m; an integer of 1 to 3)

(Wherein R ³ is an aliphatic group, alicyclic group or aromatic group having ⁴ or more carbon atoms, R ^{4 is} hydrogen, aliphatic group, alicyclic group or aromatic group, and is different from each other. R is hydrogen, an aliphatic group, an alicyclic group or an aromatic group, and may be different from each other o, q: an integer of 0 to 3 p; an integer of 1 to 3)

  Here, the number average molecular weight of the diol represented by the general formula (I) or general formula (II) is preferably less than 1000. If it exceeds 1000, the urethane group concentration is lowered and the glass transition temperature is lowered, whereby the durability of the backcoat layer may be lowered.

  Specific examples of the diol (A) include glycerol monostearate, glycerol monopalmitate, glycerol monooleate, glycerol monolinoleate, glycerol monolaurate, and dimer diol. The amount of copolymerization is preferably 5 to 50 parts by weight with respect to 100 parts by weight of the polyester polyol (B). More preferably, it is 10-30 weight part. When the amount is less than 5 parts by weight, the dispersibility of the carbon-based powder may be insufficient. On the other hand, if it exceeds 50% by weight, the glass transition temperature becomes low and the blocking resistance may be insufficient.

  As an acid component constituting the polyester polyol (B), aromatic dibasic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 2,2′-diphenyldicarboxylic acid, 4 4,4'-diphenyl ether dicarboxylic acid and the like, and examples of the alicyclic dibasic acid component include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid and the like. Preferably, the aromatic dibasic acid includes terephthalic acid, isophthalic acid, and orthophthalic acid, and the alicyclic dibasic acid component includes 1,2-cyclohexanedicarboxylic acid. In addition, sulfonic acid metal salt-containing aromatic dicarboxylic acid such as 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoterephthalic acid may be copolymerized in all acid components.

  As the glycol component constituting the polyester polyol (B), ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-dodecanediol, diethylene glycol, triethylene glycol, dipropylene glycol Neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl- 1,3-pentanediol, 2-methyloctanediol, neopentylhydro Cipivalic acid ester, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol A alkylene oxide adduct, poly Examples include polyethers such as tetramethylene glycol, polypropylene glycol, and polyethylene glycol. Among them, ethylene glycol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, neopentylhydroxypivalate ester, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol and hydrogenated bisphenol A are preferred. In addition, tri- or higher functional compounds such as trimellitic anhydride, glycerin, trimethylolpropane, pentaerythritol, etc. are used as part of the polyester diol raw material within a range that does not impair the organic solvent solubility and coating workability of the polyester resin. May be.

  As the aromatic polyisocyanate (C) used in the present invention, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, m-phenylene diisocyanate, 3, 3'-dimethoxy-4,4'-biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate Examples include diphenyl ether, 1,5-naphthalene diisocyanate, and m-xylene diisocyanate. The polyisocyanate (C) is preferably 5 to 100 parts by weight with respect to 100 parts by weight of the polyester polyol (B). More preferably, it is 10-60 weight part. If it is less than 5 parts by weight, the durability of the backcoat layer may be insufficient. If the amount exceeds 100 parts by weight, the dispersibility of the carbon-based powder may be insufficient.

  The polyurethane resin used in the present invention contains, in addition to the diol (A), a compound (D) having a side chain with a molecular weight of less than 1000 having two or more functional groups that react with isocyanate in one molecule, if necessary. May be used in combination. Specifically, as compound (D), 1,2-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2,2-dimethyl-1,3-propanediol 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate, 2-normalbutyl-2-ethyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol 2,2-diethyl-1,3-propanediol, 3-octyl-1,5-pentanediol, 3-phenyl-1,5-pentanediol, , 5-dimethyl-3-sodiumsulfo-2,5-hexanediol and the like. Among these, 2,2-dimethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl- 2 ′, 2′-dimethyl-3-hydroxypropanoate, 2-normalbutyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol are particularly preferable from the viewpoint of dispersibility. . Moreover, you may use the compound which has a polar group as a compound (D). A compound having a sulfonic acid metal base is particularly preferable, and examples thereof include a polyester diol having a number average molecular weight of 1000 or less obtained from a sulfonic acid metal base-containing aromatic dibasic acid and a side chain-containing glycol. Specifically, an ester condensate comprising 5-sodium sulfoisophthalic acid dimethyl ester and 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanoate, or 5-sodium sulfoisophthalic acid There is an ester condensate consisting of dimethyl ester and neopentyl glycol. Further, N-methyldiethanolamine may be used as a polar group as a compound having a tertiary amino group.

  The compound (D) having these side chains contributes to the improvement of the solubility of the polyurethane resin, and in the present invention, it can be copolymerized at a high ratio in combination with the polyester polyol (B) and the aromatic polyisocyanate (C). Is possible. An increase in the copolymerization ratio of the compound (D) component leads to an increase in the urethane bond group concentration, making the urethane resin tougher. That is, by adjusting these quantitative ratios, a polyurethane resin having both high solubility in general-purpose solvents and strong mechanical properties can be obtained. These properties as a urethane resin contribute to the improvement of the high carbon-based powder dispersion ability and the tape durability as a binder resin for a magnetic tape back coat. Specifically, the compound (D) is preferably 0 to 50 parts by weight with respect to 100 parts by weight of the polyester polyol (B). More preferably, it is 0-30 weight part. If the weight exceeds 50 parts by weight, the durability of the backcoat layer may be insufficient.

Further, when a branched compound having 3 or more functional groups that react with isocyanate is used as the compound (D), it is effective for improving the reactivity with a general-purpose curing agent.
Specific examples of the compound include polyols such as trimethylolpropane, glycerin, triethanolamine, pentaerythritol, and dipentaerythritol, and ε-caprolactone adducts to one of these polyols.

The amount of copolymerization of these compounds (D) is preferably used in such a range that the urethane bond group concentration of the polyurethane resin does not exceed 4000 eq / 10 ⁶ g. When the urethane bond group concentration exceeds 4000 eq / 10 ⁶ g, it is possible to further improve the mechanical properties as a polyurethane resin, but the solubility in general-purpose solvents decreases, and as a binder resin for magnetic tape back coating High carbon-based powder dispersion performance may not be obtained. The urethane bond group concentration can be adjusted by the copolymerization amount of the compound (D) and the molecular weights of the chain extender (A) and the polyester polyol (B). Here, the urethane bond group concentration is a numerical value indicating how many urethane groups are present per 1 t of the resin weight, and is 1 equivalent when there is one urethane group. Therefore, the unit is expressed as eq / 10 ⁶ g.

  The glass transition temperature of the polyurethane resin used in the present invention is preferably 85 ° C. or higher from the viewpoint of durability and blocking resistance. 90 degreeC or more is especially preferable. Although an upper limit is not specifically limited, When application property is considered, less than 160 degreeC is preferable.

 In the present invention, it is desirable to add another resin or mix a crosslinking agent for the purpose of adjusting flexibility of the polyurethane resin, improving cold resistance and heat resistance, and the like. Examples of other resins include vinyl chloride, cellulose resin, polyester resin, epoxy resin, phenoxy resin, polyvinyl butyral, acrylonitrile / butadiene copolymer, and the like. On the other hand, examples of the crosslinking agent include polyisocyanate compounds, epoxy resins, melamine resins, urea resins, acid anhydrides and the like, and among these, polyisocyanate compounds are particularly preferable. Examples of the polyisocyanate compound include those obtained by adding a polyhydric alcohol or an isocyanurate ring to isocyanate. Examples of the isocyanate compound here include TDI (tolylene diisocyanate), MDI (diphenylmethane diisocyanate), IPDI (isophorone diisocyanate), HDI (hexamethylene diisocyanate), XDI (xylene diisocyanate), hydrogenated XDI and the like.

  Examples of the shape of the magnetic recording medium formed according to the present invention include a tape, a disk, a sheet, and a card.

  The layer structure of the magnetic recording medium formed according to the present invention is preferably such that a backcoat layer is provided under a nonmagnetic support, and a magnetic layer or a magnetic layer and a lower coating layer are provided on the support. Examples of the layer structure above the support include a magnetic layer single layer, a magnetic layer multilayer, and a multilayer of a magnetic layer and a nonmagnetic layer.

  Carbon-based powder is used as the filler used in the coating agent of the present invention. The filler described here refers to a material obtained by removing the binder component and the curing agent component from all solid components in the paint. The carbon-based powder is carbon black or graphite, and carbon black is particularly preferable. Here, the average particle size of the carbon-based powder is preferably 70 nm or less. If the average particle diameter exceeds 70 nm, the stability as a backcoat agent may be reduced. The lower limit of the average particle system is 10 nm or more from the viewpoint of dispersibility. Moreover, it is preferable to contain 70 weight% or more of carbon-type powder with respect to the whole quantity of a filler. The carbon-based powder is preferably contained in an amount of 20 to 200 parts by weight with respect to 100 parts by weight of the polyurethane resin.

  The coating agent of the present invention includes other plasticizers such as dibutyl phthalate and triphenyl phosphate, dioctyl sodium sulfosuccinate, t-butylphenol polyethylene ether, ethyl naphthalene sulfonate sodium, dilauryl succinate, zinc stearate as necessary. Further, lubricants such as soybean oil lecithin and silicone oil and various antistatic agents can be added.

  In addition, inorganic pigments such as calcium carbonate and alumina can be added to the coating agent of the present invention as necessary. These additions can be expected to further improve the blocking resistance. The addition amount is preferably 1 to 10 parts by weight with respect to 100 parts by weight of the polyurethane resin.

On the other hand, conventionally known magnetic powders can be used for the magnetic layer. For example, γ-Fe ₂ O ₃ , γ-Fe ₂ O ₃ and Fe ₃ O ₄ mixed crystal, γ-Fe ₂ O ₃ or Fe ₂ O ₄ coated with cobalt, ferromagnetic oxide such as barium ferrite, Examples thereof include ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni. Examples of particles used for the nonmagnetic layer include iron oxide, iron oxide, and carbon black.

  The present invention is specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”.

（ｎ＝１６〜１８）
ＤＡＤ：水添ダイマージオール
ＭＤＩ：４，４’−ジフェニルメタンジイソシアナート
ＨＰＮ：２，２−ジメチル−３−ヒドロキシプロピル−２’，２’−ジメ チル−３−ヒドロキシプロパネート
ＭＥＫ：メチルエチルケトン Abbreviations in the tables and examples are as follows.
TPA: terephthalic acid IPA: isophthalic acid OPA: orthophthalic acid NDC: naphthalenedicarboxylic acid HHPA: 1,2-cyclohexanedicarboxylic acid AA: adipic acid DSN: 5-sodium sulfoisophthalic acid dimethyl ester PG: propylene glycol NPG: 2,2- Dimethyl-1,3-propanediol 2MG: 2-methyl-1,3-propanediol EG: ethylene glycol 1,4-CHDM: 1,4-cyclohexanedimethanol DMH: 2-butyl-2-ethyl-1,3 -Propanediol GS: Glycerin monostearate AOG: AOG-X68 manufactured by Daicel Chemical Industries, Ltd.

(N = 16-18)
DAD: hydrogenated dimer diol MDI: 4,4′-diphenylmethane diisocyanate HPN: 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate MEK: methyl ethyl ketone

The evaluation method for resin characteristics is described below.
(Hydroxyl value of polyester polyol (B))
Polyester polyol: 50 g is dissolved in a mixed solvent of MEK: 120 g, and MDI:
70 g was added and reacted at 70 ° C. for 2 hours. Subsequently, the residual isocyanate group concentration in the reaction solution was quantified by titration to obtain the hydroxyl value.

(Acid value of polyester polyol (B))
0.2 g of polyester polyol was dissolved in 20 cm ³ of chloroform and titrated with a 0.1N potassium hydroxide ethanol solution to obtain an equivalent (eq / 10 ⁶ g) per 10 ⁶ g of resin. Phenolphthalein was used as the indicator.

(Number average molecular weight)
It was measured by water permeation gel permeation chromatography (GPC) using polystyrene as a standard substance and tetrahydrofuran as a solvent. In addition, the low molecular peak of 300 or less was deleted at the time of analysis, and the number average molecular weight was calculated | required by data-processing the peak of 300 or more high molecular.

(Composition analysis)
¹ H-NMR analysis was performed using a nuclear magnetic resonance analyzer (NMR) Gemini-200 manufactured by Varian in a deuterated chloroform solvent, and the integral ratio was determined.

(Glass-transition temperature)
A polyurethane resin film having a thickness of 30 μm is prepared, cut to 4 mm × 15 mm, and then used with a dynamic viscoelasticity measuring device DVA-220 manufactured by IT Measurement Control Co., Ltd., frequency 10 Hz, measurement temperature range 30 to 180 ° C., temperature rise Dynamic viscoelasticity was measured at a rate of 4 ° C./min. At the refraction point of the storage elastic modulus (E ′), the temperature at the intersection of the extended line of the base line below the glass transition temperature and the tangent showing the maximum inclination above the refraction point was defined as the glass transition temperature.

(Polar group concentration)
The sulfonic acid metal base concentration was determined by atomic absorption analysis of metal, and the sulfonic acid metal base concentration was determined by a calculation formula. That is, 0.1 g of a sample was carbonized and dissolved in an acid, and then the Na concentration was determined by atomic absorption analysis, and the polar group concentration was calculated from the following formula.
Na concentration (ppm) / 23 (Na atomic weight) = polar group concentration (eq / 10 ⁶ g)

Synthesis example 1 of polyester polyol (B)
A reaction vessel equipped with a thermometer, stirrer, Vigreux tube and Liebig condenser was charged with 163 parts of terephthalic acid, 5 parts of 5-sodium sulfoisophthalic acid, 152 parts of 1,2-propylene glycol, and 0.2 part of tetrabutoxy titanium. The esterification reaction was performed at 200 to 230 ° C. for 4 hours. Next, the temperature was raised to 240 ° C. over 10 minutes and at the same time the pressure was gradually reduced to react for 30 minutes to complete the polymerization. The polyester diol (a) obtained had a hydroxyl value of 950 eq / 10 ⁶ g and an acid value of 5 eq / 10 ⁶ g. The composition and other characteristics are shown in Table 1.

Synthesis example 2 of polyester polyol (B)
Table 1 shows the composition, hydroxyl value, and acid value of polyester polyol (b) synthesized using the raw materials listed in Table 1 by the same method as in Synthesis Example 1.

Synthesis example 3 of polyester polyol (B)
In a reaction vessel equipped with a thermometer, stirrer and Liebig condenser, 158 parts isophthalic acid, 15 parts 5-sodiumsulfoisophthalic acid, 90 parts 2-methyl-1,3-propanediol, 144 parts 1,4-cyclohexanedimethanol And 0.3 part of tetrabutoxy titanate was added as a catalyst. The reaction was carried out at 220 ° C. for about 8 hours under a N ₂ stream, and the produced water was distilled off. Subsequently, the pressure was reduced at the same temperature for about 5 minutes to complete the reaction. The polyester polyol (c) obtained had a hydroxyl value of 6400 eq / 10 ⁶ g and an acid value of 7 eq / 10 ⁶ g.

Synthesis examples 4 and 5 of polyester polyol (B)
Table 1 shows the composition, hydroxyl value, and acid value of polyester polyols (d) and (e) synthesized by the same method as in Synthesis Example 3.

Synthesis example 6 of polyester polyol (B)
100 parts of terephthalic acid, 61 parts of isophthalic acid, 7 parts of 5-sodium sulfoisophthalic acid, 83 parts of 2,2-dimethyl-1,3-hydroxypropane, and 74 parts of ethylene glycol are charged into the same reaction vessel as in Synthesis Example 1. As a catalyst, 0.3 part of tetrabutoxy titanate was added. The reaction was carried out at 220 ° C. for about 6 hours under a N ₂ stream, and the produced water was distilled off. Then, the pressure was reduced at the same temperature for 20 minutes to complete the polymerization reaction. The polyester polyol (f) obtained had a hydroxyl value of 980 eq / 10 ⁶ g and an acid value of 5 eq / 10 ⁶ g.

Synthesis example 7 of polyester polyol (B)
In a reaction vessel similar to Synthesis Example 3, 140 parts of adipic acid, 9 parts of 5-sodium sulfoisophthalic acid and 208 parts of 2,2-dimethyl 1,3-propanediol were added, and 0.3 part of tetrabutoxy titanate was added as a catalyst. Added. The reaction was carried out at 220 ° C. for about 6 hours under a N ₂ stream, and the produced water was distilled off. Subsequently, the pressure was reduced at the same temperature for about 5 minutes to complete the reaction. The polyester polyol (g) obtained had a hydroxyl value of 6000 eq / 10 ⁶ g and an acid value of 7 eq / 10 ⁶ g.

Synthesis example 8 of polyester diol having polar group
888 parts of 2-sodium sulfoisophthalic acid dimethyl ester, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate in a reaction vessel equipped with a thermometer, stirrer and Liebig condenser Of 1836 parts and 0.2 parts of tetrabutoxy titanium were charged and transesterified at 240 ° C. for 5 hours. The temperature was lowered to 100 ° C. and diluted with 633 parts of toluene to obtain a polyester diol (h) solution (solid content concentration 80%). The number average molecular weight of the obtained polyester diol (h) was 620 (however, since there was an unreacted glycol component, it was excluded). The composition and other characteristics are shown in Table 2.

Synthesis example 1 of polyurethane resin
Polyester polyol (a): 100 parts, glycerin monostearate 20 parts are dissolved in MEK (methyl ethyl ketone): 48 parts and toluene: 48 parts, MDI: 25 parts are added, and dibutyltin dilaurate: 0.05 parts as a catalyst. The mixture was added and reacted at 80 ° C. for 5 hours. Subsequently, the solution was diluted with 121 parts of MEK and 121 parts of toluene to obtain a polyurethane resin (i). Table 3 shows the molecular weight and mechanical properties of the polyurethane resin (i).

Synthesis examples 2 to 4 of polyurethane resin
Polyurethane resins (ii) to (iv) were synthesized in the same manner as in Synthesis Example 1, and the resin composition, molecular weight, and mechanical properties are shown in Table 3.

Synthesis example 5 of polyurethane resin
Polyester polyol (e): 100 parts, AOG: 15 parts, polyester polyol (h): 10 parts are dissolved in MEK: 68 parts and toluene: 66 parts, MDI: 78 parts are added, and 1.5 hours at 80 ° C. are added. Reacted. Subsequently, the solution was diluted with MEK: 169 parts and toluene: 1 part, 0.1 parts of dibutyltin dilaurate was added as a catalyst, and reacted at the same temperature for 5 hours to obtain a polyurethane resin (v). Table 3 shows the molecular weight and mechanical properties of the polyurethane resin (v).

Comparative synthesis example 6 of polyurethane resin
Polyurethane resin (vi) was synthesized by the same method as in Synthesis Example 1, and the resin composition, molecular weight, and mechanical properties are shown in Table 3.

Comparative synthesis example 7 of polyurethane resin
A polyurethane resin (vii) was synthesized in the same manner as in Synthesis Example 1, and the resin composition, molecular weight, and mechanical properties are shown in Table 3.

(Application of magnetic paint on support)
First, 12 parts of magnetic powder (metal powder 2000 Oe), 5 parts of polyester polyurethane resin (Byron UR8200 manufactured by Toyobo Co., Ltd.), 5 parts of vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.) and alumina are kneaded and dispersed as a curing agent. An isocyanate compound, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to obtain a magnetic paint. This magnetic coating was applied and dried on a polyethylene terephthalate film having a thickness of 8 μm while applying a magnetic field of 2,000 gauss to a thickness of 4 μm to form a magnetic layer.

Example 1
A mixture of 4 parts of a polyurethane resin solution, a carbon-based powder, calcium carbonate, and alumina is kneaded and dispersed at a solid content of 70%, and then the remaining 6 parts of polyurethane resin solution, silicone oil, stearic acid, butyl stearate as a lubricant, solvent Add cyclohexanone, MEK, and toluene, and disperse in a sand mill for 3 hours. Add an isocyanate compound coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.): 0.6 parts as a curing agent, and mix uniformly. Back coat A paint was obtained. This was applied to the side opposite to the magnetic layer so that the thickness after drying was 0.5 μm, thereby forming a backcoat layer.
Formulation Solution of polyurethane resin obtained in Polymerization Example 1 (30% solution of methyl ethyl ketone / toluene = 1/1) 10 parts Carbon-based powder (average particle size 20 nm, trade name Raven 1255) 4.5 parts Calcium carbonate 0.5 parts Alumina (Average particle size 0.05μ) 0.5 part Silicon oil 0.1 part
Cyclohexanone 6 parts Toluene 9 parts Methyl ethyl ketone 15 parts Myristic acid 0.4 parts Stearic acid n-butyl 0.4 parts

  The magnetic tape on which the magnetic layer and the backcoat layer were formed was calendered, slit into a 1/2 inch width, and incorporated into a cassette to produce a magnetic tape. Using this magnetic tape, the following evaluation items were evaluated. Table 4 shows the characteristics of the obtained magnetic tape.

Gloss of the back coat layer of the magnetic tape;
The 45 degree gloss was measured. The surface roughness was measured using a light interference three-dimensional surface roughness meter (manufactured by WYKO) under the conditions of a measurement area of 200 × 200 μm ² .

Running durability;
A commercially available S-VHS video deck was used to observe scratches on the backcoat layer after running 100 times at a running temperature of 40 ° C., and the degree was evaluated according to the following 6 levels.
6: Almost scratched 5: Slightly scratched 4: Slightly conspicuous 3: Slightly conspicuous with scratch, not reaching PET film 2: Scratched prominently, PET film surface slightly visible 1: Scratched prominently, Many PET film surfaces are visible

Coefficient of friction;
Under the measurement condition of 40 ° C., a weight was attached to the magnetic tape, and it was measured by holding it on a mirror-finished stainless steel roll with a diameter of 50 mm and traveling at a speed of 1 cm / S at an angle of 180 degrees.

Adhesion test;
Distilled water was heated to 80 ° C. in a water bath, and the magnetic tape prepared in the cassette was immersed in warm water and heated for 3 hours. After 3 hours, the removed cassette was dried under reduced pressure at 60 ° C. for 2 hours to completely remove moisture. Thereafter, when the magnetic tape could be pulled out smoothly from the cassette, it was indicated as “◯”, when there was a slight resistance, “Δ”, when the magnetic layer and the backcoat layer were adhered, and when a force was required when pulling out, it was indicated as “x”.

Squareness ratio;
Using a vibration test type magnetometer, the squareness ratio in the vertical direction was measured.

Surface roughness;
It measured with the contact-type surface roughness meter.

Examples 2-6, Comparative Examples 7-8
Using the polyurethane resin described in Table 4, a magnetic tape was prepared and evaluated in the same manner as in Example 1. However, in Example 3, MR110 manufactured by Nippon Zeon Co., Ltd. was dissolved in a mixed solvent of MEK / toluene = 50/50 (weight ratio) to a solid content concentration of 30%, and polyurethane resin (iii) / MR110 = It mixed and used for 50/50 (solid content ratio). The characteristics of each magnetic tape are shown in Table 4.

  From Table 4, it can be seen that Examples 1 to 6 are superior to Comparative Examples 7 and 8 in terms of running durability, 40 ° C., coefficient of friction after 100 runs, and adhesion test.

  The polyurethane resin used in the present invention is excellent in the dispersibility of the carbon-based powder and the mechanical properties of the resin. Therefore, a magnetic recording medium having both excellent durability and running property can be supplied by using the coating agent comprising the polyurethane resin and the carbon-based powder as a back coating agent for the magnetic recording medium.

Claims (5)

Polyester polyol obtained by copolymerizing at least one diol (A), aromatic acid component or alicyclic acid component from the group consisting of general formula (I), general formula (II), dimer diol and hydrogenated dimer diol A polyurethane comprising (B), an aromatic polyisocyanate (C), and, if necessary, a compound (D) having a side chain with a molecular weight of less than 1000 having two or more functional groups that react with isocyanate in one molecule. Coating agent containing resin and carbon powder.

(However, in the formula, R ¹ and R ² ; either one or an aliphatic group, alicyclic group or aromatic group having a total carbon number of 6 or more R; hydrogen, aliphatic group, alicyclic group or aromatic And may be different from each other l, n; an integer of 0 to 3 m; an integer of 1 to 3)

(Wherein R ³ is an aliphatic group, alicyclic group or aromatic group having ⁴ or more carbon atoms, R ^{4 is} hydrogen, aliphatic group, alicyclic group or aromatic group, and is different from each other. R is hydrogen, an aliphatic group, an alicyclic group or an aromatic group and may be different from each other o, q: an integer of 0 to 3 p; an integer of 1 to 3   The coating agent according to claim 1, wherein the number average molecular weight of the general formula (I) and the general formula (II) is less than 1,000.   The coating agent according to claim 1 or 2, wherein the glass transition temperature of the polyurethane resin is 85 ° C or higher.   The coating agent according to any one of claims 1 to 3, which is used as a coating material for a backcoat layer on the side opposite to the magnetic layer in a magnetic recording medium.   A magnetic recording medium, wherein the coating agent according to claim 4 is applied to a backcoat layer.