JP4379720B2 - Magnetic recording medium - Google Patents

Description

  The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk obtained by using a binder having excellent characteristics.

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. It is made by applying this to a polyethylene terephthalate film.
Properties required for the binder of the magnetic layer include dispersibility, filling properties, orientation of the magnetic particles, durability of the magnetic layer, wear resistance, heat resistance, adhesion to a nonmagnetic support, and the like. Binders play a very important role.
As a binder for the magnetic layer, conventionally, a mixed system of an adipate type or polycaprolactone type polyurethane resin and a nitrocellulose or vinyl chloride copolymer has been mainly used.

  In the magnetic layer provided on the non-magnetic support in the coating type magnetic recording medium, a curing agent is used in combination for the purpose of improving wear resistance, improving heat resistance, improving adhesion, and imparting solvent resistance. Two-component type 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.

  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.

  Recently, in order to improve the S / N ratio (signal / noise ratio) and increase the recording density of magnetic recording media, magnetic powders with higher coercive force (Hc) such as finer magnetic powders and metal magnetic powders are used. However, it is difficult to disperse these magnetic powders with conventional binders. Insufficient dispersion not only reduces the electromagnetic conversion characteristics but also increases the porosity of the magnetic layer, and the increase in the porosity deteriorates the running durability of the magnetic layer. Introduction of a sulfonic acid metal base into a polyester resin or polyurethane resin is extremely effective in improving the dispersibility of magnetic powder (see, for example, Patent Documents 1 and 2). Cannot be satisfied and conventional binders are insufficient for these requirements.

JP 2001-118240 A (Claims) JP 2000-353312 A (Claims)

  An object of the present invention is to provide a magnetic recording medium having excellent running durability, electromagnetic conversion characteristics, etc. by using a binder having good dispersibility, filling properties, wear resistance, heat resistance, etc. of magnetic particles. It is in.

As a result of intensive studies on the above problems, the present inventors have reached the present invention. That is, the present invention relates to a magnetic recording medium characterized by using a hyperbranched polymer as a binder in a magnetic recording medium containing magnetic particles and a binder.

Preferably, the hyperbranched polymer relates to the magnetic recording medium described above formed by a polycondensate of AB _X type molecules (where A and B are organic groups having different functional groups a and b, The functional groups a and b can chemically undergo a condensation reaction and an addition reaction, and X represents an integer of 2 or more).

  In the magnetic recording medium of the present invention, a hyperbranched polymer is used as a binder component of a magnetic layer provided on a nonmagnetic support. The hyperbranched polymer has excellent magnetic powder dispersibility and a cured coating film having a high crosslink density. As a result, a magnetic coating film having a high degree of filling of the magnetic layer and good wear resistance when used as a binder for the magnetic layer can be obtained.

The present invention is characterized in that a hyperbranched polymer is used as a binder in a magnetic recording medium containing magnetic particles and a binder.

  Originally, the term hyperbranched polymer is a term named by Kim and Webster for a multi-branched polymer having regularity of repeating units (see Polym. Prepr., 29 (1988) 310). It is defined as a multi-branched polymer synthesized by self-condensation of compounds having a total of 3 or more of two possible substituents. The hyperbranched polymer described in the present invention applies to the terms proposed by Kim and Webster. As such a multi-branched polymer, various types such as polyester, polyamide, polyurethane, polyether, polyethersulfone, and polycarbonate have been synthesized.

  These hyperbranched polymers have a structure in which a large amount of functional groups are densely present at the molecular ends extending in a dendritic form. Using these reactive functional groups, various functional functional groups are used in large amounts. It is possible to introduce it closely.

  When a hyperbranched polymer is used as in the present invention, a polar group is introduced into the side chain or terminal of a linear polymer by introducing a large amount of polar groups having adsorptivity to the surface of inorganic particles at the molecular terminals. Compared with the conventional binder resin having the above structure, excellent dispersibility of the fine particle metal magnetic powder is exhibited. At the same time, the reactivity with the polyvalent isocyanate curing agent can be remarkably improved, and the highly crosslinked structure formed by the hyperbranch structure forms a cured magnetic coating film having excellent durability. In addition, the viscosity of the magnetic paint is low, the handling workability is excellent, and rheological properties suitable for the multilayer coating process are provided. In addition, by coexisting an organic group having a hydrocarbon group having 10 or more carbon atoms at the molecular end together with the polar group, re-aggregation of the fine-particle metal magnetic powder particles is effectively suppressed, and the dispersion state of the dispersed paint is immediately after dispersion. It is possible to further enhance the performance of stabilizing in this state.

  Examples of the polar group having an adsorptivity to the surface of the inorganic particles include various polar groups such as a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid metal base, a phosphonic acid metal base, and a phosphinic acid metal base. Two or more kinds of groups may be simultaneously present at the molecular ends. Among these, a hydroxyl group alone or a combination of the above polar groups other than a hydroxyl group and a small amount of a hydroxyl group is preferable.

The hyperbranched polymer referred to in the present invention is not particularly limited in its structure, but is preferably obtained by polycondensation reaction or polyaddition reaction of AB _X type compound. Here, A and B represent organic groups having different functional groups, and the AB _X type compound means a compound having two different functional groups a and b in one molecule. These compounds do not undergo intramolecular condensation or intramolecular addition, but the functional group a and the functional group b are functional groups capable of causing a condensation reaction and an addition reaction chemically. Examples of combinations of these functional groups a and b include hydroxyl group and carboxyl group or carboxylate group, amino group and carboxyl group, halogenated alkyl group and phenolic hydroxyl group, acetoxy group and carboxyl group, acetyl group and hydroxyl group, isocyanate group and hydroxyl group, etc. A combination of a carboxyl group or a derivative thereof and a hydroxyl group or a derivative thereof is preferable from the viewpoint of simplicity of the reaction process and reaction control.

Specific examples of AB _X- type compounds include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, diphenolic acid, 5- (2-hydroxyethoxy) isophthalic acid, 5-acetoxyisophthalic acid, 3,5-bis (2-hydroxyethoxy) benzoic acid, 3,5-bis (2-hydroxyethoxy) benzoic acid methyl ester, 4,4- (4′-hydroxyphenyl) pentanoic acid, 5-hydroxycyclohexane-1 , 3-dicarboxylic acid, 1,3-dihydroxy-5-carboxycyclohexane, 5- (2-hydroxyethoxy) cyclohexane-1,3-dicarboxylic acid, 1,3- (2-hydroxyethoxy) -5-carboxycyclohexane, 5- (bromomethyl) -1,3-dihydroxybenzene, 3,5-diaminobenzoic acid, phenol -3,5-diglycidyl ether, one-to-one reaction product of isophorone diisocyanate and diisopropanolamine, one-to-one reaction product of isophorone diisocyanate and diethanolamine, 3,5-bis (4-aminophenoxy) benzoic acid, etc. Is mentioned.

Among these, the type in which an ester bond is generated by reaction is particularly preferable from the viewpoint of the heat resistance of the obtained hyperbranched polymer and compatibility with other resin components and additive components, and the general formula representing the structure of these compounds is a chemical formula It is represented by 1.
Chemical formula 1) KR ′ [(R) _m L] _n
R: Divalent organic group having less than 20 carbon atoms R ′: (b + 1) -valent organic group having less than 20 carbon atoms, or R ″ N (R ″: divalent organic group having less than 20 carbon atoms) Group K, L: different ester bond-forming functional groups m: 0 or 1
n: integer greater than or equal to 2

Examples of the compound represented by the chemical formula 1 include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, diphenolic acid, 5- (2 - hydroxyethoxy) isophthalic acid, 5-acetoxyisophthalic acid, 3, 5-bis (2-hydroxyethoxy) benzoic acid, 3,5-bis (2-hydroxyethoxy) benzoic acid methyl ester, 4,4- (4′-hydroxyphenyl) pentanoic acid, 5-hydroxycyclohexane-1,3 -Dicarboxylic acid, 1,3-dihydroxy-5-carboxycyclohexane, 5- (2-hydroxyethoxy) cyclohexane-1,3-dicarboxylic acid, 1,3- bis (2-hydroxyethoxy) -5-carboxycyclohexane, 5 - Bed Romomechi Le - 1,3-dihydroxybenzene, N, N-bis (Mechirupuropione And monoethanolamine, N- (methylpropionate) diethanolamine, N, N-bis (methylpropionate) -2- (4-hydroxyphenyl) ethylamine, and the like. 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid are preferred from the standpoint of solubility and the simplicity of the polymerization reaction step.

  In addition, the hyperbranched polymer of the present invention is preferably a polyester resin containing a compound having two hydroxyl groups and one carboxyl group in one molecule (that is, condensed) as a constituent component. The hyperbranched polymer obtained from the compound having two hydroxyl groups and one carboxyl group in one molecule to be used is used in a proportion of 70% by weight or more in the polyester resin when the constituent component of the polyester resin is 100% by weight. More preferably, it is 80 weight% or more. If it is less than 70% by weight, the dendritic polymer structure is not sufficiently formed, and as a result, sufficient dispersibility may be difficult to obtain, or the solubility in general-purpose solvents may deteriorate. Examples of the compound having two hydroxyl groups and one carboxyl group in one molecule include dimethylolbutanoic acid, dimethylolpropanoic acid, and 3,5-bishydroxyethoxybenzoic acid. Among them, dimethylol is used. Butanoic acid and dimethylolpropanoic acid are preferred.

The method for synthesizing the hyperbranched polymer used as the binder resin of the present invention includes, for example, condensing the above KR ′ [(R) _m L] _n- type compound in the first stage and a large amount of hydroxyl or carboxyl groups at the terminal, or these After the hyperbranched polymer having a derivative functional group is formed, an organic group having a hydrocarbon group having 10 or more carbon atoms or a polar group other than a hydroxyl group is added to the functional group at the molecular end in the second step. . Alternatively, the hyperbranched polymer itself obtained by the first stage reaction may be used.

In the first stage reaction, the KR ′ [(R) _m L] _n- type compound may be reacted alone in the presence of a condensation reaction catalyst, a polyvalent hydroxy compound, a polyvalent carboxylic acid compound, or these A compound having both may be used as a branch point of a hyperbranched polymer molecule. Examples of the polyvalent hydroxy compound include various general-purpose glycol compounds as a polyester resin raw material and trifunctional or higher functional hydroxyl group-containing compounds such as trimethylolpropane, pentaerythritol, and dipentaerythritol. In addition, examples of the polyvalent carboxylic acid compound include trifunctional or higher functional carboxylic acid compounds such as various dibasic acids, trimellitic acid, pyromellitic acid, and benzophenone tetracarboxylic acid which are generally used as polyester resin raw materials. Furthermore, examples of the compound having both a hydroxyl group and a carboxyl group include glycolic acid, hydroxypivalic acid, 3-hydroxy-2-methylpropionic acid, lactic acid, glyceric acid, malic acid, and citric acid.

  In addition to the above, the compound serving as the branching point of the hyperbranched polymer molecule used as the resin of the present invention is a linear polyester oligomer obtained by a condensation reaction of a dibasic acid component and a glycol component, or a trivalent or more polyvalent polyhydric compound. A branched polyester oligomer obtained by copolymerizing a carboxylic acid or a polyvalent hydroxy compound may be used.

  As a constituent material of the linear or branched polyester oligomer that can be a branching point, general-purpose various dibasic acids and glycol compounds, or tri- or higher functional polycarboxylic acids and polyhydric alcohol compounds can be used. Dibasic acid compounds include aliphatic dibasic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanoic acid, terephthalic acid, isophthalic acid, orthophthalic acid, 1,2-naphthalenecarboxylic acid, 1,6 -An aromatic dibasic acid such as naphthalenedicarboxylic acid, or an alicyclic dibasic acid such as 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid Can be mentioned. Examples of dibasic acids other than the above include dibasic acids having a sulfonic acid metal salt such as sodium 5-sulfoisophthalate.

As glycol components, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol 2-methyl-1,3-propylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,4-diethyl-1, 5-pentanediol, 2-ethyl-1,3-hexanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl- 3′ -hydroxypropanoate, 2-n - butyl-2- Ethyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pen Aliphatic diols such as ethylene diol, 2,2-diethyl-1,3-propanediol, 3-octyl-1,5-pentanediol, 1,3-bis (hydroxymethyl) cyclohexane, 1,4-bis ( Hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethyl) cyclohexane, 1,4-bis (hydroxypropyl) cyclohexane, 1,4-bis (hydroxymethoxy) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane, 2 , 2 - bis (4-hydroxymethoxycyclohexyl) propane, 2,2-bis (4 - hydroxyethoxycyclohexyl) propane, bis (4-hydroxycyclohexyl) methane, 2,2-bis (4-hydroxycyclohexyl) propane, 3, (4), 8 (9) -Tricyclo [5.2.1.02,6] Alicyclic glycols such as decanedimethanol, or aromatic glycols such as ethylene oxide and propylene oxide adducts of bisphenol A.

  Further, examples of the trifunctional or higher polyhydric carboxylic acid and polyhydric alcohol compound include trimellitic acid, pyromellitic acid, benzophenone tetracarboxylic acid, glycerin, trimethylolpropane, pentaerythritol and the like.

  In the first stage reaction, the condensed water produced by the condensation reaction is azeotropically dehydrated with toluene or xylene, or an inert gas is blown into the reaction system to produce water or monoalcohol produced by the condensation reaction together with the inert gas. The process can be carried out by blowing out of the reaction system or distilling off under reduced pressure. As a catalyst used for the reaction, it is possible to use various metal compounds such as titanium-based, tin-based, antimony-based, zinc-based, germanium-based, and strong acid compounds such as p-toluenesulfonic acid and sulfuric acid as in the case of a normal polyester resin polymerization catalyst. I can do it.

  Next, as a method for adding an organic group having a hydrocarbon group having 10 or more carbon atoms in the second stage reaction, monoalcohols having a long-chain alkyl group such as decyl alcohol, undecyl alcohol, dodecyl alcohol, etc. , Dodecanoic acid, myristic acid, palmitic acid, stearic acid, long chain alkyl such as oleic acid having an unsaturated group, monocarboxylic acids having an alkenyl group, or methyl ester derivatives thereof obtained by the first step reaction Examples thereof include a method of condensation addition to a carboxyl group or a hydroxyl group present at the end of the branch polymer.

  Alternatively, a carboxylic anhydride compound having a hydrocarbon group having 10 or more carbon atoms is added to the terminal hydroxyl group of the hyperbranched polymer in the presence of a basic catalyst, and further, carbon is added to the terminal carboxyl group of the hyperbranched polymer. A compound having several tens or more hydrocarbon groups and glycidyl groups can be reacted and added in the presence of a suitable catalyst such as triphenylphosphine. Specific examples of these compounds include dodecenyl succinic anhydride and octadecyl succinic anhydride as anhydride compounds, and compounds having a glycidyl group include various aryl glycidyl ethers such as phenyl glycidyl ether, polyethylene glycol mono Examples thereof include glycidyl ether, polypropylene glycol monoglycidyl ether, polytetramethylene glycol monoglycidyl ether, and various other monoglycidyl ethers such as alkyl, alkenyl and alkynyl glycidyl ether.

  Since the organic group introduced into the terminal group of the hyperbranched polymer has a hydrocarbon group having 10 or more carbon atoms, the effect of further improving the stabilization of the dispersion state of the fine particle metal magnetic powder dispersed paint is obtained. It is done. A hydrocarbon group having less than 10 carbon atoms may not exhibit a sufficient effect. This effect is thought to be due to the steric hindrance of the bulky substituents present at the ends of the hyperbranched polymer, thereby suppressing the phenomenon that the dispersed metal magnetic powder particles reagglomerate. The hydrocarbon group having 10 or more carbon atoms may be linear or branched. Of course, those having a partially unsaturated bond, those having a ring shape, and those having an aromatic ring may be used.

  Examples of a method for introducing a polar group other than a hydroxyl group into the terminal end of the hyperbranched polymer according to the present invention include a hyperbranched polymer having a hydroxyl end obtained by, for example, ortho, meta, or sodium para-sulfonylbenzoate in the first stage reaction. It is possible to introduce a sulfonic acid metal base into the molecular terminal by dehydration condensation. Further, when the above-mentioned acid anhydride compound having a hydrocarbon group having 10 or more carbon atoms is added to the terminal hydroxyl group of the hyperbranched polymer, an equimolar amount of carboxyl groups with the reacted acid anhydride compound is formed. Alternatively, dehydration condensation of monoethanolamine, aminobenzoic acid or the like to the same hydroxyl group can introduce an amino group at the molecular end.

  The number average molecular weight of the hyperbranched polymer of the present invention is preferably 500 to 40,000. Preferably it is 1,000-40,000, More preferably, it is 2,000-20,000, Most preferably, it is 2,000-10,000. If the number average molecular weight is less than 500, the durability of the coating film may be insufficient due to the influence of the curing agent and unreacted residual oligomers. On the other hand, if the number average molecular weight exceeds 40,000, the viscosity of the coating will increase significantly or dissolve in a general-purpose solvent. It may be difficult to obtain a smooth coating film surface.

 In the present invention, it is desirable to add another resin to the hyperbranched polymer for the purpose of adjusting flexibility, improving cold resistance and heat resistance, and / or mixing a cross-linking agent. Examples of other resins include cellulose resins, polyurethane resins, polyester resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, 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 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 of the present invention include a tape, a disk, a sheet, and a card.

  The layer structure of the magnetic recording medium of the present invention is preferably a magnetic layer or a magnetic layer and a lower coating layer provided on a support, and a backcoat layer 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. The magnetic recording medium of the present invention is suitable for a magnetic recording medium having a multilayer structure of a magnetic layer and a nonmagnetic layer suitable for increasing the recording density because of excellent dispersibility, surface smoothness, wear resistance and the like of magnetic particles. The polyester resin of the present invention is suitable not only for the binder for the magnetic layer but also for the binder for the nonmagnetic layer and the backcoat layer.

The magnetic particles used in the magnetic layer of the magnetic recording medium of the present _{invention, γ-Fe 2 O 3,} γ-Fe 2 O 3 and Fe ₃ O ₄ mixed crystal was deposited cobalt gamma-Fe ₂ O ₃ or a ferromagnetic oxide such as Fe ₂ O ₄ and barium ferrite, and a ferromagnetic alloy powder such as Fe—Co and Fe—Co—Ni. Examples of particles used for the nonmagnetic layer include iron oxide and iron oxide and carbon black, and examples of particles used for the backcoat layer include carbon black.

  The magnetic particles are preferably metal powder from the viewpoint of increasing the recording density. The major axis length of the metal powder is preferably 200 nm or less. The lower limit is preferably 1 nm or more. If the thickness is less than 1 nm, the metal powder becomes extremely fine, so the polyester resin of the present invention may have insufficient dispersibility. If the thickness exceeds 200 nm, the performance may be insufficient in terms of the recording density of the magnetic recording medium. Because. The major axis length referred to here refers to a long portion of the magnetic particle on the ellipse, which is obtained by observing this with a microscope and averaging 100 samples of arbitrary measurement results.

  The magnetic recording medium of the present invention may contain other plasticizers such as dibutyl phthalate and triphenyl phosphate, dioctyl sodium sulfosuccinate, t-butylphenol polyethylene ether, ethyl naphthalene sulfonic acid soda, dilauryl succinate, stearic acid. Lubricants such as zinc, soybean oil lecithin and silicone oil and various antistatic agents can be added.

  The present invention is specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”. Analysis and evaluation of the resin were carried out by the following methods.

(Molecular weight and molecular weight distribution)
Using a gel permeation chromatography (GPC) 150c manufactured by Waters with tetrahydrofuran as an eluent, a GPC measurement was performed at a column temperature of 35 ° C. and a flow rate of 1 ml / min. It was. However, Showa Denko Co., Ltd. shodex KF-802, 804, 806 was used for the column.

(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)
5 mg of sample was put in an aluminum sample pan and sealed, and measured using a differential scanning calorimeter DSC-220 manufactured by Seiko Instruments Inc. up to 200 ° C. at a temperature rising rate of 20 ° C./min. It calculated | required in the temperature of the intersection of the extended line of the following base lines, and the tangent which shows the maximum inclination in a transition part.

(Acid value)
In the process of synthesizing the following polyester resins G and H, the acid value of the final product was measured during the synthesis in order to confirm that the reaction proceeded theoretically. As a measurement sample, a resin solid content of 0.5 g was collected and dissolved in 20 ml of chloroform. Next, titration was performed using 0.1N-KOH ethanol solution using phenolphthalein as a reaction indicator.

Synthesis of polyester resin (A) 7 parts of pentaerythritol and 207 parts of dimethylolbutanoic acid are added to a reaction vessel equipped with a thermometer, a stirrer and a Liebig condenser, and 0.4 part of p-toluenesulfonic acid is added as a catalyst. did. The reaction was carried out at 140 ° C. for about 4 hours under normal pressure, the generated water was distilled off, the reaction was terminated, and cyclohexanone was added to make a solution with a solid content concentration of 30%. The properties of the obtained polyester resin (A) are shown in Table 1. In addition, the composition ratio of a table | surface is a weight ratio.

Synthesis of Polyester Resins (B) to (D) Polyester resins (B) to (D) were obtained in the same manner as the polyester resin (A) according to the composition shown in Table 1.

Synthesis of polyester resin (E) Into a reaction vessel equipped with a thermometer, a stirrer, and a partial condenser, 200 parts of dimethylolbutanoic acid and 8 parts of toluene were added, and 0.5 part of p-toluenesulfonic acid was added as a catalyst. The reaction was carried out at 140 ° C. for about 4 hours under normal pressure, and water produced was distilled off azeotropically with toluene to terminate the reaction, and cyclohexanone was added to obtain a solution having a solid content concentration of 30%. The characteristics of the obtained polyester resin (E) are shown in Table 1.

Synthesis of polyester resin (F) In a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, 166 parts of terephthalic acid, 166 parts of isophthalic acid, 64 parts of trimellitic acid, 160 parts of neopentyl glycol, 100 parts of ethylene glycol, and 0.2 parts of tetrabutyl titanate (TBT) was added as a catalyst, and water generated at 240 ° C. for 8 hours was distilled off under nitrogen blowing to obtain a branched polyester oligomer. The number average molecular weight of this polyester oligomer was 1700. Next, 100 parts of the above polyester oligomer, 250 parts of dimethylolbutanoic acid, 10 parts of toluene and 0.8 part of p-toluenesulfonic acid as a catalyst were charged into a reaction vessel equipped with a thermometer, a stirrer and a partial condenser, and generated at 140 ° C. Water was distilled off by toluene azeotropy and reacted for 4 hours, and cyclohexanone was added to obtain a polyester resin (F) solution having a solid content concentration of 30%. The characteristics of the polyester resin (F) are shown in Table 1.

Synthesis of polyester resin (G) Into a reaction vessel equipped with a thermometer, a stirrer and a partial condenser, 400 parts of dimethylolbutanoic acid, 40 parts of trimethylolpropane, 15 parts of toluene and 1.2 parts of p-toluenesulfonic acid as a catalyst were added. Then, the water generated at 140 ° C. was reacted for 4 hours while distilling off by toluene azeotropy to obtain a hyperbranched polymer (g). The number average molecular weight of the hyperbranched polymer (g) obtained here was 1250. Next, 200 parts of the hyperbranched polymer (g), 470 parts of dodecenyl succinic anhydride, 500 parts of toluene, and 0.4 part of triethylamine as a catalyst were charged into a flask equipped with a thermometer, a stirrer, a condenser, and a nitrogen blowing tube. The mixture was reacted at 0 ° C. for 6 hours to obtain a terminal-modified hyperbranched polymer (g ′) having a number average molecular weight of 4400 and an acid value of 2700 eq / ton. Subsequently, 265 parts of phenylglycidyl ether and 5 parts of triphenylphosphine were added and reacted at 130 to 140 ° C. for 6 hours to obtain a polyester resin (G). The solution was diluted with toluene to obtain a solution having a solid concentration of 60%. The number average molecular weight of the polyester resin (G) was 6100, and the acid value was 50 eq / ton. The characteristics of the polyester resin (G) are shown in Table 1.

Synthesis of polyester resin (H) 400 parts of dimethylolbutanoic acid, 40 parts of trimethylolpropane, 15 parts of toluene and 1.2 parts of p-toluenesulfonic acid as a catalyst are put into a reaction vessel equipped with a thermometer, a stirrer and a partial condenser. Then, the water generated at 140 ° C. was reacted for 4 hours while distilling off by toluene azeotropy to obtain a hyperbranched polymer (g). The number average molecular weight of the hyperbranched polymer (g) obtained here was 1250. Next, 200 parts of the hyperbranched polymer (g), 54 parts of sodium meta-sulfonylbenzoate, and 10 parts of toluene are put into a flask equipped with a thermometer, a stirrer, and a partial condenser, and reacted at 140 ° C. for 3 hours to generate condensation. Water was distilled off by toluene azeotropy. Next, 400 parts of toluene, 380 parts of dodecenyl succinic anhydride and 0.4 part of triethylamine as a catalyst were added and reacted at 80 ° C. for 6 hours to obtain a hyperbranched polymer (h) having an average molecular weight of 4100 and an acid value of 2300 eq / ton. It was. Subsequently, 217 parts of phenylglycidyl ether and 5 parts of triphenylphosphine were added and reacted at 130 to 140 ° C. for 6 hours to obtain a polyester resin (H). The number average molecular weight of the polyester resin (H) was 6000, and the acid value was 60 eq / ton. The solution was diluted with toluene to obtain a solution having a solid concentration of 60%. The characteristics of the polyester resin (H) are shown in Table 1.

Synthesis of polyester resin (I) In a reaction vessel equipped with a thermometer, a stirrer and a Liebig condenser, 83 parts of terephthalic acid, 83 parts of isophthalic acid, 74 parts of ethylene glycol, 83 parts of neopentyl glycol and 0.06 part of tetrabutyl titanate Was heated at 180-220 ° C. for 180 minutes to carry out the esterification reaction, and then 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 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 90 minutes. The solution was diluted with cyclohexanone to obtain a solution having a solid concentration of 30%. The properties of the obtained polyester resin (I) are shown in Table 1. In addition, the composition ratio of a table | surface is a weight ratio. The polyester resin (I) does not contain a compound having two hydroxyl groups and one carboxyl group in one molecule, and does not have a hyperbranch structure.

Synthesis of Polyester Resin (J) A polyester resin (J) was obtained according to the composition shown in Table 1 by the same method as for the polyester resin (I). Like the polyester resin (I), the polyester resin (J) does not contain a compound having two hydroxyl groups and one carboxyl group in one molecule, and does not have a hyperbranched structure.

  A magnetic paint was prepared using the polyester resin described above. Furthermore, magnetic tapes were prepared according to the following procedure, and the characteristics were evaluated. The running durability was judged from the degree of contamination of the magnetic head by actually running the tape on the VTR deck. The electromagnetic conversion characteristics were judged by examining the squareness ratio. Specific examples will be described below.

Example 1
After the composition of the following blending ratio was placed in a ball mill and dispersed for 24 hours, 1 part of a polyisocyanate compound: Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent, and further mixed for 1 hour to prepare a magnetic paint. Obtained. In addition, a magnetic paint is applied on a polyethylene terephthalate film having a thickness of 15 μm so that the thickness after drying is 4 μm, dried while applying a magnetic field of 5000 gauss, and passed through a calender roll at 80 ° C. and a linear pressure of 200 kg / cm. The surface of the layer was smoothed to produce a magnetic tape. The obtained magnetic tape was left to stand at 60 ° C. for 1 day and then slit to 1/2 inch. The surface gloss of the magnetic layer before calendering and the squareness ratio of the tape obtained were measured. The squareness ratio was measured by using a vibrating sample magnetometer and measuring the squareness ratio in the vertical direction. The surface roughness of the magnetic layer before and after calendering was also measured. The surface roughness was measured in the range of 200 × 200 μm ² using an optical interference three-dimensional surface roughness meter (manufactured by WYKO). In addition, the state of the magnetic head after running 100 times at 40 ° C. with a commercially available VTR deck was observed and evaluated in stages. On the other hand, after leaving the magnetic paint subjected to the above evaluation in a sealed state for 3 hours, it was applied on a polyethylene terephthalate film by the same method as above, and the surface gloss before surface treatment, surface roughness, squareness of the obtained magnetic coating film was applied. The ratio was compared. The results are shown in Table 2.

Formulation-1
Solution of polyester resin (A) obtained in synthesis example (30% solution of cyclohexanone) 10 parts Metal powder (major axis length 0.07 μm, BET 51 m ² / g, coercive force (Hc) 2400 Oe) 15 parts Cyclohexanone 1 part Toluene 5 parts Methyl ethyl ketone 14 parts Alumina (average particle size 0.05μ) 0.5 part Myristic acid 0.4 part N-butyl stearate 0.4 part

Evaluation criteria for running durability Magnetic head state 5: No dirt on magnetic head 4: Slight dirt on magnetic head
3: Contamination of the magnetic head is conspicuous 2: Contamination of the magnetic head is conspicuous 1: The magnetic head is completely dirty

Examples 2-7 Comparative Examples 1-3
As in Example 1, except that the polyester resins (B), (C), (D), (E), (F) listed in Table 1 are used instead of the polyester resin (A) used for the binder of the magnetic layer. ), (I), (J), UR8300 (a sodium sulfonate group-containing polyurethane resin manufactured by Toyobo Co., Ltd.) was used as a binder to produce a magnetic tape. The evaluation results are shown in Table 2.

Examples 8 and 9
After the composition of the following blending ratio was placed in a ball mill and dispersed for 24 hours, 2 parts of polyisocyanate compound: IPDI-T1890 (manufactured by Huls Co., Ltd.) was added as a curing agent, and further mixed for 1 hour for magnetic properties. A paint was prepared and evaluated in the same manner as in Example 1.

Formulation-2
Polyester resin (G), (H) solution (60% solution of toluene) 5 parts Metal powder (major axis length 0.07 μm, BET 51 m ² / g, coercive force (Hc) 2400 Oe) 15 parts Cyclohexanone 8 parts Toluene 3 parts Methyl ethyl ketone 14 parts Alumina (average particle size 0.05μ) 0.5 part Myristic acid 0.4 part Stearic acid n-butyl 0.4 part

  By using the hyperbranched polymer of the present invention as a binder for magnetic particles, the magnetic recording medium of the present invention is excellent in running durability and powder removal durability due to pigment dispersibility and abrasion resistance. .

Claims (8)

A magnetic recording medium comprising a magnetic layer containing magnetic particles and a binder on a nonmagnetic support, wherein a hyperbranched polymer is used as the binder.   2. The magnetic recording medium according to claim 1, wherein the hyperbranched polymer is a polyester resin obtained by condensing a compound having two hydroxyl groups and one carboxyl group in one molecule.   The magnetic recording medium according to claim 2, wherein 70 wt% or more of a compound having two hydroxyl groups and one carboxyl group in one molecule is used when the constituent component of the polyester resin is 100 wt%. The magnetic recording medium according to claim 1, wherein the hyperbranched polymer is formed by a polycondensate of AB _X type molecules (where A and B are organic groups having different functional groups a and b, and the functional group a , B can cause a condensation reaction and an addition reaction chemically with each other, and X represents an integer of 2 or more). The magnetic recording medium according to claim 1, wherein the hyperbranched polymer is formed of a molecular polycondensate represented by the following chemical formula 1).
Chemical formula 1) KR ′ [(R) _m L] _n
R: a divalent organic group having less than 20 carbon atoms R ′: an (n + 1) valent organic group having less than 20 carbon atoms, or R ″ N (R ″: a divalent organic group having less than 20 carbon atoms) Group K, L: different ester bond-forming functional groups m: 0 or 1
n: integer greater than or equal to 2   The magnetic recording medium according to any one of claims 1 to 5, wherein an organic group having a hydrocarbon group having 10 or more carbon atoms is added to a part or all of the end groups of the hyperbranched polymer. Magnetic recording media.   The magnetic recording medium according to claim 1, wherein the magnetic particles are metal powder. The magnetic recording medium according to claim 7, wherein the major axis length of the metal powder is 200 nm or less.