JP2006331474A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent running durability, electromagnetic transducing characteristics and the like by using a binder having satisfactory dispersibility and packing properties of non-magnetic particles. <P>SOLUTION: The magnetic recording medium having a multilayered structure formed by at least a magnetic layer composed of a magnetic particles and a binder and a non-magnetic layer composed of the non-magnetic particles and the binder is characterized in that a polyurethane resin having a metal phosphate group and a carboxyl group in its molecule is used as the binder of the non-magnetic layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a magnetic tape or a magnetic disk having excellent dispersibility and filling properties, and excellent durability and wear resistance.

  Magnetic tapes and flexible disks, which are general-purpose magnetic recording media, make magnetic paint by dispersing acicular magnetic particles with a major axis of 1 μm or less in a binder solution together with additives such as dispersants, lubricants and antistatic agents. Is applied to polyethylene terephthalate film. Recently, computer backup data tape, which has been in increasing demand, has a multilayer coating structure to improve recording density. As a method of creating a multilayer coating tape, nonmagnetic particles such as iron oxide and carbon black are dispersed in a binder solution to create a nonmagnetic coating, and after applying to a polyethylene terephthalate film, the magnetic coating is subsequently applied. ing.

Magnetic layers provided on non-magnetic supports in coated magnetic recording media are now often cured for purposes such as improved wear resistance, improved heat resistance, improved adhesion, and solvent resistance. A two-component type using a combination of agents is used. As the curing agent, polyisocyanate, epoxy resin, melamine resin, urea resin and the like are known. In particular, polyisocyanate is generally used in terms of reactivity, workability, and performance. The reaction using polyisocyanate as a curing agent proceeds even under a relatively mild temperature condition of 100 ° C. or less, and has an advantage that the formed magnetic layer and nonmagnetic support are hardly damaged. Curing reaction is normally performed by processing at 50-70 degreeC.
Alternatively, as another curing reaction treatment method, a method of irradiating an active energy ray such as an electron beam or an ultraviolet ray may be used. Specifically, for example, a method of curing the magnetic layer by irradiating an active energy ray typified by an electron beam as in Patent Documents 1 and 2, a so-called EB curing method can be mentioned.

  Generally, in a magnetic recording medium, in order 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 contained in the magnetic layer. Highly packed and highly oriented are required, and 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. In addition, the role of the nonmagnetic layer is also large in smoothing the surface of the magnetic layer, and high dispersibility of nonmagnetic particles such as iron oxide and carbon black is required.

  Recently, in particular, it has been required to make the surface of the nonmagnetic layer smoother in order to increase the recording density. For this reason, fine-particle iron oxide powders have been studied as finer non-magnetic particles, and it has become difficult to disperse these fine-particle iron oxide powders with conventionally known binders. Insufficient dispersion not only deteriorates the smoothness but also increases the porosity of the nonmagnetic layer. The increase in the porosity deteriorates the running durability of the entire magnetic layer.

JP 59-84337 (Claims) JP 59-8126 (Claims)

  The object of the present invention is to provide excellent running durability, electromagnetic conversion characteristics, etc. as a whole magnetic layer by using a binder having good dispersibility, filling property, heat resistance and the like of fine particle iron oxide powder. An object of the present invention is to provide a magnetic recording medium suitable for an application.

  The inventors of the present invention have arrived at the present invention as a result of intensive investigations on the above-mentioned problem, that is, a polyurethane resin that forms a magnetic layer that is highly dispersed and stabilized with fine non-magnetic particles and excellent in durability. That is, the present invention provides at least an intramolecular molecule as a binder of a nonmagnetic layer in a magnetic recording medium having a multilayer structure formed of a magnetic layer composed of magnetic particles and a binder and a nonmagnetic layer composed of nonmagnetic particles and a binder. The magnetic recording medium is characterized by using a polyurethane resin having a metal phosphate group and a carboxyl group.

  According to the present invention, a nonmagnetic layer having excellent dispersibility and excellent surface smoothness of iron oxide powder having a particle size of 300 nm or less can be obtained, and as a result, an excellent magnetic recording medium can be obtained.

  The magnetic recording medium of the present invention uses a polyurethane resin having a metal phosphate group and a carboxyl group in the molecule as a binder for the nonmagnetic layer.

  The means for introducing the metal phosphate base into the binder is not particularly limited, but for example, a method using at least one phosphorus compound represented by the following formulas (i) to (vii) is preferable. Among these, the phosphorus compound (vii) represented by the following structural formula is particularly preferable. Examples of the introduction method include a method of copolymerizing in the polyester polyol (A) described later, or a method of polymerizing directly using a phosphorus compound as a chain extender.

[X and Y are ester-forming functional groups such as hydroxyl groups, R ¹ is a trivalent hydrocarbon group having 3 to 10 carbon atoms, R ² is an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group, An alkoxy group having 1 to 12 carbon atoms, a cycloalkoxy group, or an aryloxy group is shown. The aryl group and the aryloxy group may be bonded to a halogen atom, a hydroxy group, —OM (M represents an alkali metal), or an amino group. R ³ and R ⁴ are each an alkylene group having 1 to 12 carbon atoms, a cycloalkylene group, an arylene group, or a group represented by the following formula: — (CH ₂ —OR ⁵ ) _m — (R ⁵ has 1 to 12 carbon atoms). An alkylene group, a cycloalkylene group, or an arylene group, wherein m can be any number from 1 to 4. M represents an alkali metal atom.]

  The means for introducing the carboxyl group into the binder is not particularly limited, but dimethylolbutanoic acid, dimethylolpropionic acid, 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4- Pentanetetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride 1,2,5,6-naphthalenetetracarboxylic dianhydride, ethylene glycol bistrimellitic dianhydride, 2,2 ', 3,3'-diphenyltetracarboxylic dianhydride, thiophenetetracarboxylic dianhydride The method using a thing etc. is mentioned. 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid Anhydride, cyclopentanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, ethylene glycol bis trimellitate 2 Acid anhydride compounds (B) such as anhydride, 2,2 ′, 3,3′-diphenyltetracarboxylic dianhydride, thiophenetetracarboxylic dianhydride are hydroxyl groups at the molecular ends of the polyester polyol (A) described later. The acid anhydride ring is opened by reacting with a group, and a carboxyl group is introduced by reacting with an aromatic polyisocyanate (C) described later. That way, and the like. Further, an aromatic polyisocyanate compound (C) using a compound (D) having a carboxyl group in the molecule and having two or more functional groups that react with an isocyanate group, such as dimethylolbutanoic acid and dimethylolpropionic acid. The method of introducing by reacting can also be mentioned. In particular, in the method of reacting the polyester polyol (A) and the acid anhydride (B), 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride or ethylene glycol bistrimellitate dianhydride may be used. Preferably, dimethylolbutanoic acid is preferably used in a method of reacting with a compound (D) having a carboxyl group in the molecule and having two or more functional groups that react with an isocyanate group.

  The polyester polyol (A) is obtained by polycondensation reaction of a normal dibasic acid and glycol. Examples of the aliphatic dibasic acid used for this include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, dodecinyl succinic acid, fumaric acid, maleic acid, itaconic acid, and 3-hexenedicarboxylic acid. 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2-bis (4- Carboxycyclohexyl) methane, 2,2bis (4-carboxycyclohexyl) propane. Among these, aliphatic dibasic acids include adipic acid, sebacic acid, dodecinyl succinic acid, itaconic acid, and alicyclic dibasic acids include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1, It is preferable to use 4-cyclohexanedicarboxylic acid or 4-methyl-1,2-cyclohexanedicarboxylic acid from the viewpoint of dispersibility of the nonmagnetic particles. In particular, the acid component is preferably composed of 50 to 100 mol% of an aliphatic and / or alicyclic dibasic acid from the viewpoint of dispersibility of the nonmagnetic particles.

Examples of the glycol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,3- Propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-3-hydroxy Aliphatic glycols such as propyl-2 ′, 2′-dimethyl-3-hydroxypropanate, 2,2-diethyl-1,3-propanediol, 1,3-bis (hydroxymethyl) cyclohexane, 1,4- Bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethyl) cyclohexane, , 4-bis (hydroxypropyl) cyclohexane, 1,4-bis (hydroxymethoxy) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane, 2,2bis (4-hydroxymethoxycyclohexyl) propane, 2,2-bis (4hydroxyethoxycyclohexyl) propane, bis (4-hydroxycyclohexyl) methane, 2,2-bis (4-hydroxycyclohexyl) propane, 3 (4), 8 (9) -tricyclo [5.2.1.0 ^{2 , 6} ] Alicyclic glycols such as decanedimethanol. Among these, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl- 3-hydroxypropanate, 1,6-hexanediol, and 1,4-bis (hydroxymethyl) cyclohexane are preferred. In addition, tri- or higher functional compounds such as trimellitic anhydride, glycerin, trimethylolpropane, pentaerythritol, etc. are used as part of the raw materials for polyester polyols within the range that does not impair the organic solvent solubility and coating workability of the polyester resin. May be.

  The aromatic polyisocyanate (C) of the polyurethane resin used in the present invention is 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 Examples include '-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate, and the like. Of these, 4,4'-diphenylmethane diisocyanate is particularly preferred.

  If necessary, the polyurethane resin used in the present invention may be copolymerized with a compound (E) having a side chain with a molecular weight of less than 500 having two or more functional groups that react with isocyanate groups. For example, 1,2-propylene glycol, 1,3-propylene 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 -Hydroxypropanoate, 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, 2,5-dimethyl-3 Such as sodium sulfo-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 preferred from the viewpoint of dispersibility.

  The compound (E) having these side chains contributes to improving the solubility of the polyurethane resin, and can be copolymerized at a high ratio in the combination of the polyester polyol (A) and the aromatic polyisocyanate (C) in the present invention. is there. An increase in the copolymerization ratio of the compound (E) 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 characteristics as a urethane resin contribute to the improvement of the high dispersibility and tape durability as a binder resin for magnetic tapes.

Further, when a branched compound having three or more functional groups that react with isocyanate is used as the compound (E), it is effective in improving the reactivity in the crosslinking reaction described later.
Specific examples of such compounds include polyols such as trimethylolpropane, glycerin, triethanolamine, pentaerythritol, dipentaerythritol, and ε-caprolactone adducts and propylene oxide adducts of one of these polyols. .

The copolymerization amount of these compounds (E) is preferably used in such a range that the urethane bond group concentration of the polyurethane resin of the present invention 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 a general-purpose solvent is lowered, and it is high as a binder resin for magnetic tape. Dispersion performance may not be obtained. The urethane bond group concentration can be adjusted by the copolymerization amount of the compound (E) having a side chain and the molecular weight of the polyester polyol (A). The unit represents the number of equivalents per 1 ton of resin weight (eq / t).

  If necessary, the polyurethane resin used in the present invention may be copolymerized with a polyester polyol other than the polyester polyol (A). It is preferable to use an aromatic polyester (F) as the polyester polyol. Constituent acid components include aromatic dibasic acid components such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 2,2'-diphenyldicarboxylic acid, 4,4'-diphenylether And dicarboxylic acid. Preferred are terephthalic acid, isophthalic acid, orthophthalic acid and the like.

Examples of the glycol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,3- Propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-3-hydroxy Aliphatic glycols such as propyl-2 ′, 2′-dimethyl-3-hydroxypropanate, 2,2-diethyl-1,3-propanediol, 1,3-bis (hydroxymethyl) cyclohexane, 1,4- Bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethyl) cyclohexane, , 4-bis (hydroxypropyl) cyclohexane, 1,4-bis (hydroxymethoxy) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane, 2,2bis (4-hydroxymethoxycyclohexyl) propane, 2,2-bis (4hydroxyethoxycyclohexyl) propane, bis (4-hydroxycyclohexyl) methane, 2,2-bis (4-hydroxycyclohexyl) propane, 3 (4), 8 (9) -tricyclo [5.2.1.0 ^{2 , 6} ] Alicyclic glycols such as decanedimethanol. Among these, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl- 3-hydroxypropanate, 1,6-hexanediol, and 1,4-bis (hydroxymethyl) cyclohexane are preferred. In addition, tri- or higher functional compounds such as trimellitic anhydride, glycerin, trimethylolpropane, pentaerythritol, etc. are used as part of the raw materials for polyester polyols within the range that does not impair the organic solvent solubility and coating workability of the polyester resin. May be.

  As a means for imparting EB (electron beam) curability, a polyurethane resin obtained by reacting a compound (H) having an unsaturated bond group and a functional group capable of reacting with isocyanate and having a molecular weight of less than 500 is used as a binder. It is also effective. Examples of the compound (H) include glycerol monomethacrylate and glycerol monoacrylate. Alternatively, as a compound having one functional group that reacts with an isocyanate group, 2-hydroxyethyl acrylate, 2-hydroxymethyl methacrylate, 2-hydroxypropyl acrylate, hydroxyethylene glycol methacrylate, butoxyhydroxypropyl acrylate, phenoxyhydroxypropyl acrylate, hydroxypropyl acrylate , Hydroxypropyl dimethacrylate, glycerol dimethacrylate, monohydroxypentaerythritol triacrylate and the like. Among these, it is preferable to use monohydroxypentaerythritol triacrylate because it exhibits excellent electron beam curability.

  The polyurethane resin used in the present invention has a number average molecular weight of 5,000 to 100,000, preferably 10,000 to 80,000. When the number average molecular weight is less than 5,000, the mechanical strength is insufficient and the running durability may be inferior. When the number average molecular weight exceeds 100,000, the solution viscosity increases, and the workability and dispersibility of iron oxide, abrasive, carbon black, etc. may be deteriorated. The reaction method may be either a method in which the raw material is melted or a method in which the raw material is dissolved in a solution.

As the reaction catalyst, stannous octylate, dibutyltin dilaurate, triethylamine or the like may be used.
Moreover, you may add a ultraviolet absorber, a hydrolysis inhibitor, antioxidant, etc. before manufacture of a polyurethane resin, during manufacture, or after manufacture.

  In the present invention, the polyurethane resin is preferably crosslinked with the polyisocyanate compound (G) from the viewpoint of improving the durability as a magnetic recording medium. Examples of the polyisocyanate compound (G) that is a crosslinking agent include those obtained by adding a polyhydric alcohol or an isocyanurate ring to an 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.

  In the present invention, in addition to the polyurethane resin, it is desirable to add other resins for the purpose of adjusting flexibility, improving cold resistance, and improving durability. Examples of other resins include vinyl chloride resins, polyester resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, and the like. In addition, when imparting EB curability, the resin is subjected to an unsaturated bond-introducing modification work.

  As necessary, the magnetic recording medium of the present invention may contain a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctyl sulfosodium succinate, t-butylphenol / polyethylene ether, ethyl naphthalene / sodium sulfonate, dilauryl succinate, stearin Lubricants such as zinc acid, soybean oil lecithin, silicone oil, and various antistatic agents can be added.

  The urethane resin of the present invention is dissolved in a solvent, mixed with nonmagnetic particles, and coated on a support. Solvents used include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, alcohols such as methanol, esters such as ethyl acetate and ethyl acetate, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane, tetrahydrofuran, etc. Glycols, ethers, aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, N, N-dimethylformamide, or a mixture thereof can be used.

As nonmagnetic powder used for the nonmagnetic layer, in addition to acicular nonmagnetic iron oxide powder (α-Fe ₂ O ₃ ), calcium carbonate (CaCO ₃ ), titanium oxide (TiO ₂ ), barium sulfate (BaSO ₄ ), Examples include various nonmagnetic powders such as α-alumina (α-Al ₂ O ₃ ). In addition, it is preferable to use carbon black in combination with the nonmagnetic layer. As carbon black, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used.
When iron oxide powder and carbon black are used in combination, the blending ratio is preferably 95/5 to 50/50 by weight. If the blending ratio of the iron oxide powder exceeds 95, problems are likely to occur due to surface electrical resistance. The non-magnetic support can be appropriately selected from known resin films such as polyester, polyamide or aromatic polyamide, or laminated resin films thereof, and the thickness thereof is also within a known range and is not particularly limited. It shouldn't be.
The particle size of the iron oxide powder is preferably 300 nm or less from the viewpoint of the surface roughness of the nonmagnetic layer and the magnetic layer. The particle diameter is an average value obtained by measuring the major axis of any 100 samples in a scanning electron micrograph.

  Examples of the ferromagnetic metal particles used in the magnetic layer in the present invention include Fe or alloys with Co, Ca, Mg, Zn, Mn, Sr, Ba, Ni, Cu and the like.

  The magnetic recording medium of the present invention has a multilayer structure having at least a nonmagnetic layer comprising nonmagnetic particles and a binder and a magnetic layer comprising magnetic particles and a binder on at least a substrate. In the manufacturing method, a nonmagnetic layer may be applied and then a magnetic layer may be applied separately, or simultaneous application may be performed.

（なお、ＭはＮａである。）
ＭＲ１１０：塩化ビニル系共重合体（日本ゼオン（株）製）
ＭＥＫ：メチルエチルケトン The present invention is specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”. Abbreviations in the examples are as follows.
AA: adipic acid SA: sebacic acid IA: itaconic acid HHPA: 1,2-cyclohexanedicarboxylic anhydride DMT: terephthalic acid dimethyl ester DMI: isophthalic acid dimethyl ester EG: ethylene glycol HD: 1,6-hexanediol DMH: 2 -Butyl-2-ethyl-1,3-propanediol NPG: 2,2-dimethyl-1,3-propanediol HPN: 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3- Hydroxypropanate BTDA: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride TMEG: ethylene glycol bistrimellitic dianhydride MDI: 4,4′-diphenylmethane diisocyanate DMBA: dimethylolbutanoic acid PETA : Monohydroxypentae Sri tall triacrylate phosphorus compounds:

(M is Na.)
MR110: Vinyl chloride copolymer (manufactured by Zeon Corporation)
MEK: Methyl ethyl ketone

  A method for measuring resin physical properties will be described below.

(Hydroxyl value of polyester polyol (A))
Polyester polyol: 50 g was dissolved in MEK: 120 g of mixed solvent, 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.

(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 having a number average molecular weight of less than 300 was deleted during analysis, and the peak of a polymer having a number average molecular weight of 300 or more was subjected to data processing to obtain a number average molecular weight.

(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.

(Acid value of polyurethane resin)
1 g of polyurethane resin was dissolved in 20 cm ³ of chloroform, titrated with a 0.1 N potassium hydroxide ethanol solution, and divided by the solid content concentration to obtain the equivalent (eq / 10 ⁶ g) per 10 ⁶ g of resin. Phenolphthalein was used as the indicator.

(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)
A 0.1 g sample was carbonized and dissolved in an acid, and then determined by atomic absorption analysis. The polar group concentration was determined by the following formula.
Na concentration (ppm) / 23 (Na atomic weight) = polar group concentration (eq / t)

Synthesis Example 1: Synthesis of polyester polyol (a) 142 parts of adipic acid, 8 parts of phosphorus compound, 30 parts of ethylene glycol, 71 parts of 1,6-hexanediol in a reaction vessel equipped with a thermometer, stirrer and Liebig condenser , 104 parts of 2,2-dimethyl-1,3-propanediol and 0.2 parts of tetrabutyl titanate were charged and heated at 180 to 220 ° C. for 180 minutes to carry out the esterification reaction. The pressure was reduced to 5 mmHg in minutes, and the temperature was raised to 240 ° C. during this time. Further, the pressure inside the system was gradually reduced, and after 10 minutes, the pressure was reduced to 0.3 mmHg or less, and a polycondensation reaction was performed at 240 ° C. for 30 minutes. Table 1 shows the resin composition, hydroxyl value, average molecular weight, and polar group concentration of the obtained polyester polyol (a).

Synthesis Example 2: Synthesis of polyester polyol (b) Table 1 shows the resin composition, hydroxyl value, average molecular weight, and polar group concentration of polyester polyol (b) synthesized by the same method as in Synthesis Example 1.

Synthesis Example 3: Synthesis of polyester polyol (c) In a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, 147 parts of 1,2-cyclohexanedicarboxylic anhydride, 16 parts of phosphorus compound, 2,2-dimethyl-3 -370 parts of hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanoate, 12 parts of ethylene glycol, and 0.2 part of tetrabutyl titanate were charged and heated at 180-220 ° C for 180 minutes for esterification After the reaction, the reaction system was depressurized to 5 mmHg in 20 minutes, and the temperature was raised to 240 ° C. during this time. Further, the pressure in the system was gradually reduced, and after 10 minutes, the pressure was reduced to 0.3 mmHg or less, and a polycondensation reaction was performed at 240 ° C. for 3 minutes. Table 1 shows the resin composition, hydroxyl value, average molecular weight, and polar group concentration of the obtained polyester polyol (c).

Synthesis Example 4: Synthesis of polyester polyol (d) In a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, 124 parts of adipic acid, 40 parts of a phosphorus compound, and 2,2-dimethyl-1,3-propanediol 208 parts and 0.2 part of tetrabutyl titanate were charged and heated at 180 to 220 ° C. for 180 minutes to conduct the esterification reaction, and then the reaction system was decompressed to 5 mmHg for 5 minutes. Table 1 shows the resin composition, hydroxyl value, average molecular weight, and polar group concentration of the obtained polyester polyol (d).

Synthesis Example 5: Synthesis of polyester polyol (e) Table 1 shows the resin composition, hydroxyl value, average molecular weight, and polar group concentration of polyester polyol (e) synthesized by the same method as in Synthesis Example 3.

Synthesis Example 6: Synthesis of polyester polyol (f) Table 1 shows the resin composition, hydroxyl value, average molecular weight, and polar group concentration of polyester polyol (f) synthesized in the same manner as in Synthesis Example 1.

Synthesis Example 7: Synthesis of polyurethane resin (I) 100 parts of polyester polyol (a) and 100 parts of toluene were charged in a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, and heated at 120 degrees after dissolution. Water in the system was distilled off together with toluene in the boiling step (36 parts of toluene was distilled off). 4 parts of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride was added, and the ring opening reaction of the acid anhydride was performed at 90 degrees. Dissolved in 25 parts of 2-butyl-2-ethyl-1,3-propanediol, 10 parts of monohydroxypentaerythritol triacrylate, and 64 parts of methyl ethyl ketone. 0.05 part of phenothiazine was added, and after stirring, 54 parts of 4,4′-diphenylmethane diisocyanate was added, 0.05 part of dibutyltin dilaurate was added as a catalyst, and the mixture was reacted at 80 ° C. for 5 hours. Next, the solution was diluted with 161 parts of toluene and 161 parts of methyl ethyl ketone to obtain polyurethane resin (I). Table 2 shows the resin composition, molecular weight, glass transition temperature, polar group concentration, and acid value of the polyurethane resin (I).

Synthesis Example 8: Synthesis of polyurethane resin (II) In a reaction vessel equipped with a thermometer, a stirrer and a Liebig condenser, 50 parts of polyester polyol (b), 50 parts of polyester polyol (e) and 100 parts of toluene were dissolved and dissolved. It heated at 120 degree | times and distilled the water | moisture content in a system with toluene in the azeotropic process (toluene 64 parts distillation). Dissolved in 5 parts of dimethylol butanoic acid and 46 parts of methyl ethyl ketone. After stirring, 34 parts of 4,4′-diphenylmethane diisocyanate was added, 0.05 part of dibutyltin dilaurate was added as a catalyst, and reacted at 80 ° C. for 5 hours. Subsequently, the solution was diluted with 116 parts of toluene and 116 parts of methyl ethyl ketone to obtain polyurethane resin (II). Table 2 shows the resin composition, molecular weight, glass transition temperature, polar group concentration, and acid value of the polyurethane resin (II).

Synthesis Example 9: Synthesis of polyurethane resin (IV) Polyurethane resin (IV) was synthesized in the same manner as in Synthesis Example 7, and the resin composition, molecular weight, glass transition temperature, polar group concentration, and acid value are shown in Table 2.

Synthesis Examples 10 and 11: Synthesis of polyurethane resins (III) and (V) Polyurethane resins (III) and (V) were synthesized in the same manner as in Synthesis Example 8, and the resin composition, molecular weight, glass transition temperature, and polar group concentration were synthesized. The acid values are shown in Table 2.

Comparative Synthesis Example 1: Synthesis of polyurethane resin (VI) Polyurethane resin (VI) was synthesized in the same manner as in Synthesis Example 8, and the resin composition, molecular weight, glass transition temperature, polar group concentration, and acid value are shown in Table 2. . In this example, no carboxyl group is introduced, which is outside the scope of the claims.

Comparative Synthesis Example 2: Synthesis of polyurethane resin (VII) Polyurethane resin (VII) was synthesized in the same manner as in Synthesis Example 8, and the resin composition, molecular weight, glass transition temperature, polar group concentration, and acid value are shown in Table 2. . In this example, no metal phosphate is introduced, which is outside the scope of the claims.

Synthesis of EB curing type vinyl chloride resin (VIII) MR110, 100 parts were dissolved in 245 parts of methyl ethyl ketone in a reaction vessel equipped with a thermometer, a stirrer, and a condenser, and then phenothiazine and hydroquinone were mixed in an amount of 200 ppm with respect to the following acrylic compound. . Thereafter, 5 parts of 2-isocyanatoethyl methacrylate (MOI) and 1,000 ppm of di-n-butyltin dilaurate as a urethanization catalyst were mixed with respect to the above isocyanate compound, and stirred at a reaction temperature of 60 ° C. for 8 hours. The molecular weight and glass transition temperature of the obtained EB curable PVC resin (VIII) were measured and shown below.
Number average molecular weight: 25000, glass transition temperature: 60 ° C.

[Example]
The gloss and surface roughness of the magnetic layer and nonmagnetic layer of the magnetic tape were measured as 45 ° gloss. 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 .

  In addition, a nonmagnetic coating film was further applied by the following procedure, and a magnetic coating film was applied thereon to form a multilayer coating film, and the characteristics were evaluated. The nonmagnetic particle dispersion performance of the EB curable binder resin was evaluated by measuring the surface gloss and surface roughness of the prepared coating film using a stylus contact surface roughness meter. In addition, the non-magnetic particle dispersion performance of the thermosetting binder resin is extracted before applying the magnetic coating film, and the surface gloss and surface roughness of the coating film are measured using a stylus contact surface roughness meter. And evaluated. Furthermore, the electromagnetic conversion characteristics of the multilayer coating film coated with the magnetic coating film were judged by examining the squareness ratio. Specific examples will be described below.

[Example 1]
(Evaluation of α-iron oxide / carbon black mixed pigment)
Preparation of nonmagnetic paint sample Nonmagnetic powder: 60 parts by weight of acicular α-Fe ₂ O ₃ (average minor axis diameter = 18 nm, aspect ratio = 6.1, pH = 8.9)
15 parts by weight of carbon black (average particle size = 16 nm, BET = 200 m ² / g, DBP oil absorption = 70 ml / 100 g)
Polyurethane resin (I) (solid content 30%) 25 parts by weight EB curable PVC resin (VIII) (solid content 30%) 25 parts by weight MEK 105 parts by weight Toluene 73 parts by weight Cyclohexanone 54 parts by weight The above composition was kneaded. Thereafter, dispersion was performed with a paint shaker to produce a nonmagnetic paint.
Next, the obtained nonmagnetic coating material was applied onto a 15 μm thick PET film so as to have a dry film thickness of 5 μm, dried at a drying temperature of 80 ° C., and then subjected to a linear pressure of 2.9 × 105 N / m and a temperature of 90 μm. A calendar treatment was performed at 0 ° C., followed by EB irradiation (5 Mrad) to produce a cured non-magnetic coating film.
Next, 12 parts of magnetic powder (metal powder 2000 Oe), 5 parts of polyester polyurethane resin (UR8200 manufactured by Toyobo Co., Ltd.) and a vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.) MEK dissolved product: solid content concentration 30% ) 5 parts and alumina were kneaded and dispersed, and 0.9 part of an isocyanate compound Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent to obtain a magnetic paint. This magnetic paint is applied and dried on a cured nonmagnetic paint film while applying a magnetic field of 2,000 gauss to a thickness of 4μ to form a magnetic layer, surface gloss, surface roughness, and squareness ratio. Was measured. Surface gloss was measured and evaluated using a gloss meter, and surface roughness was measured using a stylus contact surface roughness meter. The squareness ratio was measured by using a vibrating sample magnetometer and measuring the squareness ratio in the vertical direction.
In addition, the durability of the magnetic layer was evaluated by the following 6 stages by observing the damage of the magnetic layer after running 100 times at a running temperature of 40 ° C. on a commercially available S-VHS video deck.
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

[Example 2]
(Evaluation of α-iron oxide / carbon black mixed pigment)
Preparation of nonmagnetic paint sample Nonmagnetic powder: acicular α-Fe203 60 parts by weight (average minor axis diameter = 18 nm, aspect ratio = 6.1, pH = 8.9)
15 parts by weight of carbon black (average particle size = 16 nm, BET = 200 m 2 / g, DBP oil absorption = 70 ml / 100 g)
Polyurethane resin (II) (solid content 30%) 35 parts by weight MR110 MEK dissolved product (solid content 30%) 15 parts by weight MEK 105 parts by weight Toluene 73 parts by weight Cyclohexanone 54 parts by weight Dispersion was carried out using a shaker, and then 5 parts of an isocyanate compound, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) as a curing agent was added to prepare a non-magnetic paint.
Next, 12 parts of magnetic powder (metal powder 2000 Oe), 5 parts of polyester polyurethane resin (UR8200 manufactured by Toyobo Co., Ltd.) and a vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.) MEK dissolved product: solid content concentration 30% ) 5 parts and alumina were kneaded and dispersed, and 0.9 part of an isocyanate compound Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent to obtain a magnetic paint.
First, the obtained nonmagnetic coating material was applied on a 15 μm thick PET film so as to have a dry film thickness of 5 μm, and then the magnetic coating material was applied on the nonmagnetic coating film to a thickness of 4 μm so as to have a thickness of 4 μm. The coating was dried while applying a Gaussian magnetic field to form a magnetic layer, and the surface gloss, surface roughness, and squareness ratio were measured. Surface gloss was measured and evaluated using a gloss meter, and surface roughness was measured using a stylus contact surface roughness meter. The squareness ratio was measured by using a vibrating sample magnetometer and measuring the squareness ratio in the vertical direction.
In addition, the durability of the magnetic layer was evaluated by the following 6 stages by observing the damage of the magnetic layer after running 100 times at a running temperature of 40 ° C. on a commercially available S-VHS video deck.
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

[Examples 3 and 4]
Each film sample was prepared in the same manner as in Example 1 except that the polyurethane resins (III) and (IV) were used instead of the polyurethane resin (I) and the EB curable PVC resin (VIII) of Example 1. The surface gloss and surface roughness of the magnetic layer, and the surface gloss, surface roughness, squareness ratio, and running durability of the magnetic layer were evaluated.

[Example 5]
Each film sample was prepared in the same manner as in Example 2 except that polyurethane resin (V) was used instead of the polyurethane resin (II) in Example 2 and MR110 MEK-dissolved product. The roughness and the surface gloss, surface roughness, squareness ratio, and running durability of the magnetic layer were evaluated.

[Comparative Examples 1 and 2]
Using the resins listed in Table 3, each film sample was prepared in the same manner as in Example 1 for Comparative Example 1 and in the same manner as in Example 2 for Comparative Example 2, and the surface gloss and surface roughness of the nonmagnetic layer were prepared. And surface gloss, surface roughness, squareness ratio, and running durability of the magnetic layer were evaluated.

  From Table 3, Examples 1 to 5 are superior in surface roughness of the nonmagnetic layer as compared to Comparative Examples 1 and 2, and thus the surface roughness and squareness ratio of the magnetic layer are good.

  Since the polyurethane resin is excellent in dispersibility of the iron oxide powder, a nonmagnetic layer excellent in smoothness can be obtained, and as a result, a magnetic recording medium excellent in running durability and electromagnetic conversion characteristics can be supplied. .

Claims (7)

  In a magnetic recording medium having a multilayer structure formed of at least a magnetic layer composed of magnetic particles and a binder and a nonmagnetic layer composed of nonmagnetic particles and a binder, a metal phosphate in the molecule as a binder for the nonmagnetic layer A magnetic recording medium comprising a polyurethane resin having a base and a carboxyl group.   A polyurethane resin having a metal phosphate group and a carboxyl group in the molecule is obtained by reacting the polyester polyol (A) with the acid anhydride compound (B) and reacting the reactant with the aromatic polyisocyanate compound (C). Or polyester (A), a compound (D) having a carboxyl group in its molecule and having two or more functional groups that react with an isocyanate group, and an aromatic polyisocyanate compound (C). The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording medium.   The magnetic recording medium according to claim 2, wherein the acid component of the polyester polyol (A) is composed of 50 to 100 mol% of an aliphatic and / or alicyclic dibasic acid.   Compound (E) and / or aromatic polyester having a side chain with a molecular weight of less than 500, wherein the polyurethane resin having a metal phosphate group and a carboxyl group in the molecule further has two or more functional groups that react with isocyanate groups in the molecule 4. The magnetic recording medium according to claim 2, wherein the magnetic recording medium is a polyurethane resin obtained by reacting the polyol (F).   The magnetic recording medium according to any one of claims 1 to 4, wherein the polyurethane resin having a metal phosphate group and a carboxyl group in the molecule is crosslinked with a polyisocyanate compound (G).   A polyurethane resin having a metal phosphate group and a carboxyl group in the molecule is obtained by reacting a compound (H) having a molecular weight of less than 500 having an unsaturated bond group in the molecule and a functional group that reacts with an isocyanate group. The magnetic recording medium according to claim 1, wherein the polyurethane resin is crosslinked.   The magnetic recording medium according to claim 1, wherein the magnetic recording medium includes iron oxide powder as nonmagnetic particles, and the particle size of the iron oxide powder is 300 nm or less.