JPH10320747A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium with a slight variation of the amt. of a binder in the surface. SOLUTION: A magnetic layer contg. at least ferromagnetic powder and a binder is formed on a non-magnetic substrate to obtain the objective magnetic recording medium. The binder is polyurethane resin consisting of a polyisocyanate, a diol having a polar group and a polyether polyol having <=0.02 meq/g unsaturation value prepd. by adding an alkylene oxide to a diol or further contg. another diol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In a magnetic recording medium having a magnetic layer on which a ferromagnetic fine powder and a binder are dispersed on a nonmagnetic support, extremely excellent electromagnetic conversion characteristics, running durability and high temperature and humidity TECHNICAL FIELD The present invention relates to a magnetic recording medium having a storage property under a magnetic field, and more particularly to a magnetic recording medium which does not cause head contamination.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, floppy disks and the like. In a magnetic recording medium, a magnetic layer in which ferromagnetic powder is dispersed in a binder is laminated on a non-magnetic support. The magnetic recording medium is required to have excellent characteristics such as electromagnetic conversion characteristics, running durability and running performance. In other words, in audio tapes for music recording and playback,
A higher level of original sound reproduction capability is required. Also, video tapes are required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability. The magnetic recording medium is required to have good running durability while having such excellent electromagnetic conversion characteristics. In order to obtain good running durability, an abrasive and a lubricant are generally added to the magnetic layer.

In a device using a magnetic recording medium, since the medium and the magnetic head are in sliding contact with each other, low-molecular components in the binder of the magnetic recording medium float near the surface of the magnetic layer and adhere to the magnetic head. There was a problem that occurs. The dirt on the magnetic head causes deterioration of the electromagnetic conversion characteristics. In particular, in a device for high-density recording, the rotation speed of a magnetic head is increasing. In a digital video tape recorder, the rotation speed of a magnetic head is 9600 rotations / minute, which is 1800 rotations / minute for a consumer analog video tape recorder.
The rotation speed is much higher than that of 5000 rpm for business use, and the sliding speed between the magnetic recording medium and the magnetic head is high. Also, a small magnetic head such as a thin film head is used. It is used, and there is a demand for improvement of contamination of a magnetic head by a component generated from a magnetic recording medium.

As a method of solving such a problem, a method of increasing the hardness of the magnetic layer using a hard binder has been used. For example, JP-A-62-229523 discloses that
As a method of removing low molecular weight components having a molecular weight of 2,000 or less, a magnetic coating having a magnetic layer formed thereon is applied, dried, and then exposed to a supercritical fluid at a critical temperature or more and a critical pressure or more at a temperature of 200 ° C. or less and 200 ° C. or less. It removes low molecular weight components in the magnetic layer, but the magnetic layer contains low molecular components such as lubricants that are highly soluble in supercritical fluids. The substance was also extracted and removed at the same time, and the performance as a magnetic recording medium could not be achieved. JP-A-63-263629 discloses that a polyurethane having a weight average molecular weight of 20,000 to 80,000 and a weight average molecular weight of 0.3000 or less is less than 3% by weight to reduce low molecular weight components in a binder. By this, it is possible to obtain a magnetic recording medium having excellent magnetic properties and high running durability and large running friction, but this polyurethane uses polyurethane polyol, and even if the content of polyester polyol is small, 60% by weight and a high polyester polyol content, so that the hydrophilic ester bond concentration becomes high, so that the solubility of the polyurethane in the solvent is reduced, the dispersibility is reduced, and the ester bond during long-term storage is reduced. There is also an unsatisfactory aspect that hydrolysis may occur and storage stability is reduced.

Japanese Patent Application Laid-Open No. Hei 6-52539 discloses that
40 to 60% by weight of the polyester polyurethane resin is
By using a polyester polyurethane resin having a glass transition temperature of 60 to 80 ° C. and from which low molecular weight components due to urethane are removed as a binder, interlayer adhesion between the magnetic layer and the non-magnetic support is prevented, Although this layer eliminates distortion generated in the layer and improves running stability, the polyester polyol is used, so that it is easily hydrolyzed, and at such a glass transition temperature, the coating film strength is not sufficient. In addition, when used in a device using a high-speed rotating cylinder such as a digital video tape recorder, the coating film tends to flow due to the heat of sliding between the tape and the head, so that there is a problem that the durability of the head is easily reduced due to contamination of the head. there were.

Further, a method using fractional precipitation with a poor solvent after the synthesis of the resin to be used requires a large amount of solvent,
Since high-molecular components that do not need to be removed are removed, there is a problem that the yield is lowered, and this is industrially disadvantageous. Distillation under reduced pressure is disadvantageous because the vapor pressure of a component having a molecular weight of about 5,000 is high and the efficiency is low industrially. The separation method using an ultrafiltration membrane needs to lower the viscosity of a processing solution below a certain value in order to increase the separation efficiency, and in some cases, there are many problems such as dilution with a large amount of a solvent, treatment, and concentration again. GPC fractionation requires further dilution with a large amount of solvent, which increases the throughput and is not industrially feasible.

In addition, even when the average molecular weight is increased by adjusting the type and conditions of the polymerization catalyst in the resin synthesis stage, or by using a long-chain diol or the like, an alkylene oxide-based polyether is used as a raw material for the binder. When using a urethane resin, it is difficult to adjust the low-molecular component to a predetermined amount or less because impurities at the carbon double bond terminal generated when adding the alkylene oxide do not react with the isocyanate-based curing agent. It is.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium in which the coating layer has a high dispersibility and the magnetic layer has excellent surface smoothness and electromagnetic conversion characteristics. It is an object of the present invention to provide a magnetic recording medium which has excellent running durability in which dirt and clogging are prevented, has excellent storage stability under high temperature and high humidity, and has a small amount of surface binder before and after running. .

[0009]

According to the present invention, there is provided a magnetic recording medium provided with a magnetic layer containing at least a ferromagnetic powder and a binder on a non-magnetic support, wherein the binder comprises a polyisocyanate and a polar group. Having an unsaturated value of 0.02 m
A magnetic recording medium comprising a polyurethane resin comprising a polyether polyol of eq / g or less, or a polyurethane resin comprising these and other diols. The polyether polyol constituting the polyurethane resin has a weight average molecular weight of at least 500 to 5,000 in which an alkylene oxide is added to a diol having a cyclic structure, a long chain diol having a weight average molecular weight of 200 to 500 in which an alkylene oxide is added to a diol having a cyclic structure. The magnetic recording medium as described above, wherein at least one of the short-chain diols is less than. As a polyether polyol constituting the polyurethane resin, a long-chain diol obtained by adding an alkylene oxide to a diol having a cyclic structure and having a molecular weight of 500 to 5,000 is contained in the polyurethane resin in an amount of 0 to 50% by weight. Oxide-added short-chain diols having a molecular weight of 200 to less than 500
-50% by weight, and ether groups derived from polyether polyol are contained in an amount of 1-5
mmol / g of the magnetic recording medium. The above magnetic recording medium, wherein the polyether polyol constituting the polyurethane resin has an unsaturated value of 0.01 meq / g or less. The above magnetic recording medium, wherein the polyether polyol constituting the polyurethane resin has an unsaturated value of 0.005 meq / g or less. Polar group -SO ₃ M contained in the polyurethane resin, -OSO ₃ M (where M is hydrogen, alkali metal, alkaline earth metal, shows the ammonium salt) the magnetic recording is at least one selected from Medium. The average polar group content contained in the polyurethane resin is 1 × 10 ⁻⁵ to 30 × 10 ⁻⁵ eq.
/ G in the above magnetic recording medium. On a non-magnetic support, a lower non-magnetic layer containing at least a non-magnetic powder and a binder, and an upper magnetic layer containing at least a ferromagnetic powder and a binder on which a plurality of at least two or more layers are provided. A magnetic recording medium comprising the polyurethane resin as a binder for at least one of the lower nonmagnetic layer and the upper magnetic layer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, low molecular weight components in a polyurethane resin cause head dirt and the like which are observed when a polyurethane resin having excellent properties such as durability is used as a binder. In particular, in the case of a polyurethane resin using an alkylene oxide-based polyether polyol, it has been found that impurities at the terminal of the carbon double bond contained in the alkylene oxide have a great effect on the formation of low molecular weight components.

[0011] Therefore, by using a polyether polyol which does not contain impurities at the terminal of the carbon double bond, that is, is composed of an alkylene oxide having a low unsaturated value, as a raw material for producing a polyurethane resin, it is possible to reduce the amount of polyether polyol in the synthesis step. This makes it possible to prevent the generation of molecular components. For this purpose, the present invention provides a reaction using a polyether polyol obtained by removing a polyether having no OH group and having an unsaturated group at a non-reactive terminal from a raw material polyether polyol. It is a thing.

That is, conventionally, as a binder for a magnetic recording medium, a polyurethane resin and a vinyl chloride resin having good mechanical strength and high solubility in a selected solvent are used together with a polyisocyanate. As a polyurethane resin to be used, polyester polyurethane has conventionally been much studied, but higher heat resistance,
For example, polyether polyurethane has been studied because moisture resistance and hydrolysis resistance are required. However, polyether polyurethane is generally soft and has a problem in durability at high temperatures, and has poor solubility in a solvent due to its hydrophilic ether group, and thus has poor dispersibility of a magnetic substance and a non-magnetic powder. Many were seen.

[0013] In order to solve such problems, polyisocyanates, diols having a polar group, polyether polyols obtained by adding an alkylene oxide to a diol having a cyclic structure, and / or ethers derived from the polyether polyols, comprising cyclic diols. It has been proposed to use polyether polyurethanes whose groups are from 1 to 5 mmol / g based on the total polyurethane resin.

However, even with these means, all of the binder molecules used in the magnetic layer and the non-magnetic layer are strongly adsorbed on the magnetic powder and the non-magnetic powder, or react with the polyisocyanate used in combination to crosslink and fix. Do not
Some remain uncrosslinked in the magnetic coating film and, over time, ooze into the surface layer of the magnetic layer, especially during storage at high temperature and high humidity, and contact with the magnetic layer such as the head by sliding during running. It turned out to be the cause of dirt. The bleeding to the surface of the magnetic layer depends on the thickness of the magnetic layer, but not only in the case of a single-layer magnetic layer, but also in the case of a magnetic recording medium in which two or more coating layers using nonmagnetic powder are formed in the lower layer. This is observed even when the magnetic layer is extremely thin.

[0015] The bleeding occurs when a polyether polyol to which an alkylene oxide, which is a raw material of the polyether polyurethane, is added, generates impurities having an unsaturated bond at the terminal, and low molecular components which are easily leached out during the urethane-forming reaction. It has been found that, since the terminal is not an OH group in the coating film and does not react with the polyisocyanate curing agent and is not fixed in the coating film, it easily leaches into the magnetic layer.

Therefore, at least two or more layers in which a lower non-magnetic layer containing at least a non-magnetic powder and a binder and an upper magnetic layer containing at least a ferromagnetic powder and a binder are provided on a non-magnetic support. In a magnetic recording medium having a plurality of layers, a) a polyisocyanate, b) a diol having a polar group, c) a diol and an alkylene oxide are used as a binder for at least one of a magnetic layer, a lower nonmagnetic layer, and an upper magnetic layer. Is 0.0
A polyurethane resin comprising a polyether polyol having a content of 2 meq / g or less, preferably 0.01 meq / g or less, more preferably 0.005 meq / g or less, and further comprising d) a diol having a cyclic structure. A polyurethane resin may be used. Also,
As a polyether polyol constituting the polyurethane resin, a long-chain diol obtained by adding an alkylene oxide to a diol having a cyclic structure and having a weight average molecular weight of 500 to 5,000 is contained in the polyurethane resin in an amount of 0 to 50% by weight. An oxide-added short-chain diol having a weight average molecular weight of 200 to less than 500 is contained in an amount of 15 to 50% by weight, and an ether group derived from a polyether polyol is contained in an amount of 1 to the entire polyurethane resin.
It has been found that a magnetic recording medium excellent in not only the electromagnetic conversion characteristics but also the running durability and the storage stability can be obtained when the content is within 5 mmol / g.

The polyester polyol having a small unsaturated value to which an alkylene oxide is added, which is preferable in the binder of the present invention, may be one having a long-chain diol or one having a short-chain diol. And those having a short-chain diol may be used in combination. A polyester polyol to which an alkylene oxide having a small unsaturated value is added can be produced by reacting a diol with an alkylene oxide in the presence of a catalyst. This method is described, for example, in U.S. Pat. No. 5,185,420 and U.S. Pat. No. 4,764,567.

When the diol constituting the polyester polyol having a small unsaturated value to which an alkylene oxide has been added is a long-chain diol, a long-chain diol having a molecular weight of 500 to 5,000 in which an alkylene oxide is added to a diol having a cyclic structure is used. Preferably, there is.

Specifically, bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P
Of polyethylene oxide and polypropylene oxide. The content of these in the polyurethane is preferably up to 50% by weight,
More preferably, it is 5 to 40% by weight, and if it is more than 50% by weight, the obtained coating film becomes too soft, cannot obtain sufficient strength, and is not preferable because durability is reduced. On the other hand, if the molecular weight is less than 500, the magnetic layer becomes brittle and the durability is lowered. If it is more than 5000, the glass transition temperature of the magnetic layer is lowered, and the magnetic layer becomes soft and the durability is lowered.

When the diol constituting the polyester polyol having a small unsaturation value to which an alkylene oxide is added is a short-chain diol, a diol having a cyclic structure to which an alkylene oxide is added has a molecular weight of 20.
Preferably, it is a short-chain diol of 0 to less than 500.
Specific examples include polyethylene oxide and polypropylene oxide adducts of bisphenol A, hydrogenated bisphenol A, bisphenol S, and bisphenol P. The content of these in the polyurethane is preferably up to 50% by weight, more preferably 15 to 50% by weight, and even more preferably 20 to 4% by weight.
When it is 0% by weight and more than 50% by weight, the obtained coating film is too soft, and it is not preferable because sufficient strength cannot be obtained. On the other hand, if the molecular weight is less than 200, the magnetic layer becomes brittle and the durability decreases. If the molecular weight is more than 500, the resulting coating film becomes too soft to obtain sufficient strength and the durability deteriorates.

In the present invention, other diols which can be used for the polyurethane resin include the following short-chain diols or long-chain diols which do not have a polar group and have no alkylene oxide added thereto. . Specifically, the content of the short-chain diol having a cyclic structure in the polyurethane is preferably 20 to 35% by weight. If it is less than 20% by weight, the mechanical strength is reduced and the durability is reduced. If the content is more than 35% by weight, the solubility of the solvent decreases,
Dispersibility decreases. Further, the coating film tends to be brittle, and the durability is also reduced.

Specifically, bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, cyclohexanedimethanol, cyclohexanediol, hydroquinone, bis (2-hydroxyethyl)
Tetrabromobisphenol A, bis (2-hydroxyethyl) tetrabromobisphenol S, bis (2-hydroxyethyl) tetramethylbisphenol S, bis (2-hydroxyethyl) diphenylbisphenol S, bis (2-hydroxyethyl) diphenylbiphenol, Bis (2-hydroxyethyl) thiodiphenol, bis (2-hydroxyethyl) bisphenol F,
Biphenol, bisphenol fluorene, and bisphenol fluor orange hydroxyethyl ether are preferred. Among them, preferred are aromatic and alicyclic diols such as bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, cyclohexane dimethanol, and cyclohexanediol.
More preferably, hydrogenated bisphenol A is used. The molecular weight is preferably 50 to 500 in weight average molecular weight. If it is less than 50, the coating film becomes brittle and the durability is reduced. If it is 500 or more, the glass transition temperature Tg of the coating film decreases, and the coating film becomes soft, so that the durability decreases.

The content of the long-chain diol that can be used in the polyurethane resin is preferably 25% by weight to 45% by weight, more preferably 30% by weight to 40% by weight. If the content is less than 25% by weight, the solubility in a solvent is reduced, and the dispersibility is reduced. If it exceeds 45% by weight, the strength of the coating film is reduced, so that the durability is reduced. Specifically, bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, polypropylene glycol,
Polyethylene glycol. Examples thereof include polytetramethylene glycol, and more preferred are bisphenol A and hydrogenated bisphenol A.

The molecular weight is from 500 to 500.
0 is preferred. If it exceeds 5,000, the glass transition temperature Tg of the coating film decreases, and the coating film becomes soft, so that the durability decreases.

The content of ether groups in the polyurethane resin is preferably 2 mmol / g to 4 mmol / g. 2m
If the amount is less than mol / g, the adsorptivity to the magnetic substance decreases, and the dispersibility decreases. If it is 5 mmol / g or more, the solubility in a solvent decreases, and the dispersibility decreases.

It is preferable that the polyurethane resin contains an OH group, and that a branched OH group has curability,
It is preferable from the viewpoint of durability. The number of OH groups is preferably 2 to 40 per molecule, and more preferably 3 to 20 per molecule. If the number is less than 2 per molecule, the reactivity with the isocyanate curing agent decreases, so that the coating film strength decreases and the durability decreases. If the number is 40 or more per molecule, the solubility in a solvent is reduced, so that the dispersibility is reduced.

The molecular weight of the polyurethane is from 5,000 to 10
0000 is preferred. More preferably, 10,000-5
0000. If it is less than 5000, the obtained magnetic coating film becomes brittle, the strength of the magnetic layer decreases, and the durability of the magnetic tape or the like is affected. If it exceeds 100,000, the solubility in a solvent decreases, and the dispersibility decreases. Further, the viscosity of the paint at a predetermined concentration becomes high, so that workability is remarkably deteriorated and handling becomes difficult.

The Tg of the polyurethane is 50 ° C. to 200 ° C.
Is preferred. More preferably from 80C to 150C,
More preferably, the temperature is 100 ° C to 130 ° C. If the temperature is lower than 50 ° C., the strength of the coating film at a high temperature is reduced, so that the durability and the storage stability are reduced. If the temperature exceeds 200 ° C., calender moldability decreases, and electromagnetic conversion characteristics decrease.

In the magnetic recording medium of the present invention,
It is preferable to use a polyvinyl chloride resin having good mechanical strength and high solubility in a selected solvent together with a polyurethane resin and a polyisocyanate. Furthermore, in a magnetic recording medium having a ferromagnetic powder used for a magnetic layer and a non-magnetic lower layer for higher recording density, a polar group-containing chloride is used to further improve the dispersibility of the lower non-magnetic powder together with the upper magnetic layer. It is preferable to use a vinyl resin and a polar group-containing polyurethane resin in combination. Further, other binder resins may be used together in an amount equal to or less than the equivalent amount of these resins. Can be used together. As other binder resins, thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof used as binder resins for magnetic recording media can be used.

The polar groups contained in the binder resin of the present invention include -SO ₃ M,-introduced into the binder resin for the purpose of improving the dispersibility of the ferromagnetic fine powder and the non-magnetic powder.
PO (OM) ₂ (M represents a hydrogen atom, an alkali metal or an ammonium salt) is preferred. Particularly -SO ₃ M are preferable excellent dispersibility. The preferred polar group content is 1 × 1
0 ^-5 to 30 × 10 ^-5 eq / g-binder resin, more preferably 2 × 10 ^{-5 to} 20 × 10 ^-5 eq / g-binder resin. If the amount is less than 1 × 10 ⁻⁵ eq / g-binder resin, no effect can be obtained. If the amount exceeds 30 × 10 ⁻⁵ eq / g-binder resin, the viscosity of the coating material becomes high, the workability becomes extremely poor, and the handling becomes difficult. Becomes

In addition, other polar group-containing vinyl chloride resins and polar group-containing polyurethane resins may be used together with these polar groups in an amount equal to or less than the total amount of these polar groups. The other polar group that can be used in combination is not particularly limited, and a polar group conventionally used as a binder resin for a magnetic recording medium and a mixture thereof can be used.

The polar group-containing vinyl chloride resin which can be used in the present invention can be prepared by a method of reacting a polar group-containing compound with a vinyl chloride resin or a method of converting a copolymerizable polar group-containing compound into a vinyl chloride monomer or other copolymer. It is obtained by copolymerization with possible compounds. These production methods are known, for example, as described in "Experimental Method for Polymer Synthesis" (Takayuki Otsu, published by Kagaku Dojinsha 1972), and can be used in the present invention. In the method of reacting a polar group-containing compound with a vinyl chloride resin, the polar group can be added to a vinyl chloride resin containing no polar group by a reaction to be synthesized. For example, the case of introducing -SO ₃ M vinyl chloride resin was initially copolymerizing copolymerizable with these other compounds optionally copolymerisable compound and having a vinyl chloride monomer and a glycidyl group, co It is obtained by reacting a compound having a -SO ₃ M after obtaining the polymer simultaneously or copolymers.

Examples of the copolymerizable compound for introducing a glycidyl group include glycidyl acrylate, glycidyl methacrylate, and glycidyl vinyl ether. These may be used alone or in combination of two or more.

A polar group-containing compound is copolymerized with a vinyl chloride monomer and other copolymerizable compounds to introduce a polar group. As the copolymerizable polar group-containing compound, a copolymerizable compound containing the polar group can be used, and specifically, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate,
Vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral vinyl acetal, vinyl ether, acrylamide, hydroxyethyl acrylate,
A glycidyl acrylate or the like having a polar group introduced. As the copolymerizable compound for introducing a -SO ₃ M 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, acrylic acid, methacrylic acid, p- styrenesulfonic acid, etc. unsaturated Examples thereof include hydrocarbon sulfo acids and salts thereof, and sulfoalkyl esters of acrylic acid or methacrylic acid such as sulfoethyl methacrylate and sulfopropyl methacrylate, and salts thereof. These may be used alone or in combination of two or more. The vinyl chloride unit is preferably from 57 to 98% by weight. If the amount is less than 57% by weight, the strength of the obtained resin coating film is reduced, and if it exceeds 98% by weight, the solubility of the resin in organic solvents such as ketones and esters is hindered.

The content of the vinyl alcohol unit is preferably 2 to 16% by weight. If the content is less than 2% by weight, the solubility in organic solvents such as ketones and esters when preparing the coating, non-magnetic powder,
The effect on the dispersibility of the magnetic powder, the reactivity with the isocyanate compound used in combination with the present resin, and the compatibility with other resins cannot be obtained. When the content exceeds 16% by weight, the viscosity of the paint becomes too high, The pot life when adding is shortened, which is disadvantageous in practical use.

[0036] The other vinyl unit is preferably from 0 to 26% by weight. If it exceeds this range, the mechanical properties and dispersibility of the entire resin will be reduced. Other copolymerizable monomers include vinyl acetate, vinyl propionate, (meth) acrylate, (meth) acrylic acid, (anhydride) maleic acid, acrylonitrile, vinylidene chloride, and hydroxyethyl (meth).
Acrylate, glycidyl (meth) acrylate and the like can be mentioned.

Further, the obtained vinyl chloride copolymer can be saponified to convert vinyl acetate, vinyl propionate and the like into a vinyl alcohol component. Further, the average degree of polymerization is preferably from 200 to 800. Furthermore, 250-700
Is preferred. If it is less than 200, the resulting magnetic coating film becomes brittle, and the obtained magnetic coating film becomes brittle, resulting in a decrease in physical strength, which also affects the durability of a magnetic tape or the like.

If it exceeds 800, the viscosity of the paint at a predetermined concentration becomes high, the workability becomes extremely poor, and the handling becomes difficult. As the polymerization initiator, suspension stabilizer, emulsifier, and molecular weight regulator, for example, compounds described in JP-A-60-238306 can be used.

Examples of the ferromagnetic powder include ferromagnetic iron oxide, cobalt-containing ferromagnetic iron oxide and ferromagnetic alloy powder conventionally used in magnetic recording media. Fe, Ni, Fe-C
o, Fe-Ni, Co-Ni, Co-Ni-Fe and the like, and aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, Ferromagnetic powder containing zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten, rhenium, silver, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, samarium, tellurium, bismuth Can be mentioned. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The shape of the ferromagnetic powder is not particularly limited, but usually a needle shape, a granular shape, a dice shape, a rice grain shape, a plate shape or the like is used. It is particularly preferable to use acicular ferromagnetic powder.

Next, the lower non-magnetic layer or lower magnetic layer when the magnetic recording medium of the present invention has a multilayer structure will be described. The powder used for the lower layer of the present invention may be an inorganic substance or an organic substance. Further, carbon black or the like can be used. Examples of the nonmagnetic powder include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Specifically, TiO ₂ , TiO _X , cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO
₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina, β-alumina, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, magnesium oxide, boron nitride having an α conversion of 90% or more; Molybdenum disulfide, copper oxide, Mg
CO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO
₄ , silicon carbide, titanium carbide, etc. are used alone or in combination of two or more.

Preferred are α-iron oxide and titanium oxide, and particularly preferred is α-iron oxide.

On the surface of these nonmagnetic powders, Al ₂ O ₃ ,
SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , Z
It is preferable to perform a surface treatment with nO and a hydrated oxide thereof. Particularly preferred for dispersibility are Al ₂ O ₃ , Si
O ₂ , TiO ₂ , and ZrO ₂ are more preferred.
Al ₂ O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Alternatively, a co-precipitated surface treatment layer may be used, or a method of treating the surface layer with silica after treating with alumina first,
Alternatively, the reverse method can be adopted. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

By mixing carbon black in the lower layer, Rs, which is a known effect, can be reduced, and a desired stiffness can be obtained. For this purpose, furnace black for rubber, thermal black for rubber, carbon black for color, conductive carbon black, acetylene black and the like can be used.

In the lower layer of the present invention, a magnetic powder can also be used. As the magnetic powder, γ-Fe ₂ O ₃ , Co
Modified γ-Fe ₂ O ₃ , alloy mainly composed of α-Fe, Cr
O ₂ or the like is used. Particularly, Co-modified γ-Fe ₂ O ₃ is preferable. The ferromagnetic powder used in the lower layer of the present invention preferably has the same composition and performance as the ferromagnetic powder used in the upper magnetic layer. However, it is known that the performance is changed between the upper and lower layers according to the purpose. For example, in order to improve long-wavelength recording characteristics, it is desirable that Hc of the lower magnetic layer is set lower than that of the upper magnetic layer, and that Br of the lower magnetic layer is higher than that of the upper magnetic layer. It is valid. In addition to the above, an advantage obtained by adopting a known multilayer structure can be provided. The binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the lower magnetic layer or the lower nonmagnetic layer can be the same as those of the magnetic layer.

The kneaded product, binder, and ferromagnetic powder of the present invention are kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone, and ethyl acetate used in preparing a coating solution for the magnetic layer. Make it a coating solution.
Preparation of a coating solution using the kneaded material of the present invention, ferromagnetic powder,
After kneading the binder and the organic solvent, kneading by adding the kneaded material of the present invention and other coating liquid forming substances, sand grinder, ball mill, sand mill, bebble mill,
It may be dispersed by a commonly used dispersing device such as a tron mill, a high-speed stone mill, a high-speed impact mill, or a homogenizer, or the kneaded product of the present invention may be a ferromagnetic powder, carbon black, a binder, an organic solvent. At the same time, they may be kneaded and dispersed.

Examples of the nonmagnetic support that can be used in the present invention include biaxially stretched polyethylene naphthalate,
Known materials such as polyethylene terephthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, and polybenzoxdazole can be used. Preferred are polyethylene naphthalate, polyethylene terephthalate and aromatic polyamide. These non-magnetic supports are treated in advance by corona discharge, plasma treatment, easy adhesion treatment,
Heat treatment or the like may be performed. The nonmagnetic support that can be used in the present invention has a center line average surface roughness of 0.1 to 20 nm, preferably 1 to 20 at a cutoff value of 0.25 mm.
It is preferable that the surface has excellent smoothness in the range of 10 to 10 nm. It is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μ or more.

For the magnetic recording medium, for example, a magnetic layer coating solution is applied to the surface of a running nonmagnetic support. Here, a plurality of coating liquids may be sequentially or simultaneously applied in a multilayer manner. Examples of a coating machine for applying the above coating liquid include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, and spray coat. Coat, spin coat, etc. can be used. Also, an abrasive, a non-magnetic support on the surface of the non-magnetic layer is not formed,
The back coat layer may be provided by applying a back coat layer coating solution in which a particulate component such as an antistatic agent and a binder are dispersed in an organic solvent. In the preparation of the coating liquid for forming the back coat layer, by using the kneaded product of the present invention, a resin such as a back coat urethane having excellent properties can be used alone or in combination.

The magnetic coating layer produced by using the kneaded product of the present invention is dried after subjecting the ferromagnetic powder contained in the coating layer of the magnetic layer coating liquid to a magnetic field orientation treatment. After being dried in this manner, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, voids generated by the removal of the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyamideimide, or a metal roll can be used.

[0049]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is described below by showing embodiments of the present invention. In addition, in an Example, a part shows a weight part. (Preparation of alkylene oxide adduct) Production Example 1 The preparation method followed the method disclosed in US Pat. No. 5,185,420. In a 7.5 liter pressure vessel, zinc hexacyanocobaltate containing 2,280 parts of bisphenol A and 1,2-dimethoxyethane as a catalyst was used.
After charging 2 parts, it was sealed and flushed with nitrogen three times. Thereafter, the mixture was heated to 100 ° C., 200 g of propylene oxide was added, and it was confirmed that the reaction was started by lowering the pressure. Further, 3800 parts of propylene oxide was added over 4 hours so that the partial pressure of propylene oxide was maintained at 2 atm.
After completion of the reaction, the reaction solution was filtered to remove the catalyst. The unsaturated value of the obtained polypropylene oxide adduct of bisphenol A was 0.018 meq / g. Unsaturation value is J
According to ISK1557-1970 (Testing method for polyether for polyurethane), acetic acid liberated by allowing mercuric acetate to act on unsaturated bonds in the sample was titrated with a potassium hydroxide solution to obtain an unsaturated value.

Preparation Examples 2 to 3 Preparation was carried out in the same manner as in Preparation Example 1, except that the reaction temperature was changed to 80 ° C. and 50 ° C. Bisphenol A obtained
Table 1 shows the unsaturated values of the polypropylene oxide adducts.

Comparative Preparation Example 4 A catalyst was prepared in the same manner as in Preparation Example 1, except that the catalyst was changed to KOH.

Production Example A of Polyurethane Resin 300 parts of hydrogenated bisphenol A (Rikabinol HB manufactured by Nippon Rika Co., Ltd.) was placed in a reaction vessel equipped with a reflux condenser and a stirrer and purged with nitrogen in advance. It melt | dissolved at 60 degreeC under nitrogen stream with 150 parts of polypropylene oxide adducts (weight average molecular weight 1000), 20 parts of ethylene oxide sulfoisophthalate adducts, and 3000 parts of cyclohexanone. Then, as a catalyst,
60 ppm was added to the total amount of the raw materials using n-dibutyltin dilaurate, and the mixture was further dissolved for 15 minutes.

Next, 510 parts of phenylmethane diisocyanate and 20 parts of trimethylolpropane were added, and the mixture was added at 90 ° C.
For 4 hours to obtain a polyurethane resin A. The obtained polyurethane resin A had a weight average molecular weight of 2500.
0, molecular weight of 5000 or less of the low molecular weight component weight 3.0%, polar group (-SO ₃ M) content 6.1 × 10 ^-5 eq / g,
The average OH group content was 3 per molecule.

The amount of the low molecular component was determined by gel permeation chromatography HLC-8020 manufactured by Tosoh (column structure: G2000HXL × 30 cm × 1 + G4000).
HXL × 30cm × 1 + G5000HXL × 30cm × 1,
Eluent: tetrahydrofuran, flow rate: 1 ml / min,
(Temperature: 40 ° C., detector: RI) was obtained from the area ratio of a molecular weight of 5000 or less in a standard polystyrene-converted molecular weight distribution curve obtained. The OH content of the polyurethane resin is determined according to JIS
The number of OH groups per molecule was shown from the OH value obtained by the test method of K0070 and the number average molecular weight in terms of polystyrene obtained by using GPC.

Production Examples B and C of Polyurethane Resins Preparation examples A and B were prepared in the same manner as in Production Example A except that the polypropyleneoxy adduct of bisphenol A (average molecular weight: 1000) was changed to Production Examples 2 and 3.

Preparation Example D of Polyurethane Resin Preparation was carried out in the same manner as in Preparation Example A, except that the polypropylene oxide adduct of bisphenol A (average molecular weight 1000) was changed to Comparative Preparation Example 4.

The following is an example of a magnetic recording medium manufactured using the binder resin manufactured in the above manufacturing example.

Example 1 (Preparation of Magnetic Coating Liquid) Ferromagnetic alloy powder 100 parts Composition: Fe / Zn / Ni = 92/4/4 (atomic ratio), Hc: 2000 Oe, crystallite size: 15 nm, BET specific surface area : 59 m ² / g, major axis diameter: 0.12 μm, needle ratio: 7, s: 140 emu / g Polyurethane resin (Production Example A) 10 parts Vinyl chloride resin (MR110: manufactured by Zeon Corporation) 8 parts α-Al ₂ O ₃ (particle size 0.3 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part Each component of the above magnetic coating composition is opened. After kneading in a kneader for 60 minutes, the mixture was dispersed in a sand mill for 120 minutes. The resulting dispersion is mixed with a trifunctional low molecular weight polyisocyanate compound (Coronate 304 manufactured by Nippon Polyurethane).
After adding 6 parts of 1) and stirring and mixing for another 20 minutes, 1
The solution was filtered using a filter having an average pore diameter of μm to prepare a magnetic coating liquid.

The nonmagnetic paint obtained on a 10 μm thick polyethylene naphthalate support was dried to a thickness of 3.0.
μm, and 30% with the magnetic layer not dried.
After performing a magnetic field orientation with a 00 Gaussian magnet and drying further,
After performing a surface smoothing treatment at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a temperature of 90 ° C. using a seven-stage calender composed of only metal rolls, a heat curing treatment is performed at 70 ° C. for 24 hours to obtain 6.35 mm. The sheet was cut into a width to produce a magnetic tape.

Examples 2 and 3 Examples 2 and 3 were produced in the same manner as in Example 1 except that the polyurethane resin A used in the preparation of the magnetic coating composition was changed to polyurethane resin B or C.

Example 4 (Preparation of Upper Layer Magnetic Coating Liquid) Ferromagnetic Alloy Powder 100 parts Composition: Fe / Zn / Ni = 92/4/4 (atomic ratio), Hc: 2000 Oe, Crystallite Size: 15 nm, BET Ratio Surface area: 59 m ² / g, major axis diameter: 0.12 μm, needle ratio: 7, s: 140 emu / g Polyurethane resin (Production Example A) 10 parts Vinyl chloride resin (MR110: manufactured by Zeon Corporation) 8 parts α -Al ₂ O ₃ (particle size 0.3 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part (Preparation of lower layer nonmagnetic paint liquid ) nonmagnetic inorganic powder 85 parts α- iron oxide, major axis length: 0.12 .mu.m, acicular ratio: 7, BET specific surface area 55m ² /g,pH6.5 Urethane resin (Production example A) 10 parts Vinyl chloride resin (MR110: manufactured by Zeon Corporation) 8 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part Magnetic coating composition for upper layer and non-magnetic coating for lower layer For each of the compositions, each component is 6 open kneaders.
After kneading for 0 minutes, the mixture was dispersed in a sand mill for 120 minutes.
To the resulting dispersion, 6 trifunctional low molecular weight polyisocyanate compounds (Coronate 3041 manufactured by Nippon Polyurethane) were added.
After stirring and mixing for another 20 minutes, the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a magnetic paint and a non-magnetic paint.

The nonmagnetic paint obtained on a polyethylene naphthalate support having a thickness of 10 μm was dried to a thickness of 2.5 μm.
μm, and immediately thereafter, the magnetic paint was simultaneously and multi-layer coated so that the thickness after drying was 0.5 μm. Both layers are oriented in a magnetic field with a 3,000 gauss magnet in an undried state. After drying, the layers are dried at a speed of 100 m / min and a linear pressure of 30 using a seven-stage calender consisting of metal rolls only.
After performing a surface smoothing treatment at 0 kg / cm and a temperature of 90 ° C., a heat hardening treatment is performed at 70 ° C. for 24 hours to obtain 6.35 m.
The resulting tape was cut into a width of m to prepare a magnetic tape.

Examples 5 and 6 The magnetic tapes of Examples 5 and 6 were produced in the same manner as in Example 4 except that the polyurethane resin A was changed to the polyurethane resin B or C.

Comparative Example 1 A magnetic tape of Comparative Example 1 was produced in the same manner as in Example 1, except that the polyurethane resin A was changed to Comparative Production Example D.

Comparative Example 2 A magnetic tape of Comparative Example 2 was produced in the same manner as in Example 4 except that polyurethane resin A was changed to polyurethane resin D.

Table 1 shows the binder resins produced in the production examples. Table 2 shows the properties of the obtained tape. However, Table 1
, The unsaturated value is shown by meq / g.

[0067]

[Table 1]

[0068]

[Table 2]

[Measurement Method] Surface roughness Ra: The center line average roughness was defined as Ra by an optical interference method using a digital optical profile meter (manufactured by WYKO). Electromagnetic conversion characteristics: Recording and reproduction were performed on a sample tape using a drum tester at a recording wavelength of 0.5 μm and a head speed of 10 m / sec. The relative reproduction output with respect to the tape of Example 1 was evaluated. Repeatability (output drop, head dirt, change in surface binder amount): A tape of 60 minutes length was heated at 40 ° C. using a digital video tape recorder (NV-BJ1) manufactured by Matsushita Electric.
The vehicle was run continuously and repeatedly 100 times in an environment of 80% RH, and the dirt on the video head was observed. Also, the video output was continuously reproduced, and the output was reduced at the first output of 0 dB. The video head dirt was evaluated by the following evaluation scores. 5: No stain was observed. 4: The head has a little dirt on the shoulder portion on the tape exit side. 3: A stain is recognized on the shoulder portion of the head on the tape exit side. 2: In addition to the above, stains are also observed in the head gap portion. 1: Recording / reproduction is practically impossible on the entire sliding portion of the head. In order to remove the lubricant existing in the surface layer of the magnetic layer, the tape before and after running was extracted with n-hexane at room temperature for 30 minutes to change the amount of surface binder before and after running.
400W (15 kV), M
g Measured at the anode for 10 minutes and for N, 2P3 of Fe
The peak intensity ratio of 1S of N to the peak of / 2 is expressed as Cl
For the peak of 2P3 / 2 of Fe
The 1S peak intensity ratio of 1 was determined. Storage property: The magnetic tape was stored at 60 ° C. and 90% RH for one week, and changes in friction coefficient (μ value) before and after the storage were evaluated by the following evaluation scores. 5: No change in μ value was observed. 4: Those whose μ value increase is less than 0.05. 3: The increase in μ value is 0.05 to 0.1. 2: Those whose μ value increase is larger than 0.1. 1: Sticking occurs.

[0070]

The magnetic recording medium according to the present invention is excellent not only in the dispersibility of the magnetic powder but also in the lower non-magnetic layer because of the excellent dispersibility of the non-magnetic powder. A magnetic recording medium having excellent electromagnetic conversion characteristics can be provided, and a polyether polyol having a low unsaturated value is used as a raw material of a polyurethane resin. Prevents seepage on the surface and prevents head dirt,
Provided is a magnetic recording medium which does not cause clogging and has excellent running durability. In particular, it is possible to provide a magnetic recording medium which is excellent in storage stability under high temperature and high humidity and has little change in the amount of surface binder before and after running.

Claims (8)

[Claims] 1. A magnetic recording medium having a magnetic layer containing at least a ferromagnetic powder and a binder on a nonmagnetic support, wherein the binder is a polyisocyanate, a diol having a polar group, and the diol is an alkylene oxide. A magnetic recording medium comprising a polyurethane resin comprising a polyether polyol having an unsaturated value of 0.02 meq / g or less and a polyurethane resin comprising these and another diol. 2. The polyether polyol constituting the polyurethane resin is a long-chain diol having a weight average molecular weight of 500 or more and 5000 or more in which an alkylene oxide is added to a diol having a cyclic structure, and a weight in which an alkylene oxide is added to a diol having a cyclic structure. Average molecular weight 200-5
2. The magnetic recording medium according to claim 1, wherein the medium is at least one of short-chain diols of less than 00. 3. A polyether polyol constituting the polyurethane resin, which has a molecular weight of 500 to 5 obtained by adding an alkylene oxide to a diol having a cyclic structure.
000 long chain diol in the polyurethane resin
15 to 50% by weight of a short-chain diol having a molecular weight of 200 to less than 500, in which an alkylene oxide is added to a diol having a cyclic structure. 2. The magnetic recording medium according to claim 1, wherein the amount is from 5 to 5 mmol / g. 4. The magnetic recording medium according to claim 1, wherein the unsaturated value of the polyether polyol constituting the polyurethane resin is 0.01 meq / g or less. 5. The magnetic recording medium according to claim 1, wherein the unsaturated value of the polyether polyol constituting the polyurethane resin is 0.005 meq / g or less. 6. The polar group contained in the polyurethane resin is at least one selected from —SO ₃ M and —OSO ₃ M (where M represents hydrogen, an alkali metal, an alkaline earth metal, or an ammonium salt). 2. The magnetic recording medium according to claim 1, wherein: 7. The magnetic recording medium according to claim 6, wherein the average polar group content in the polyurethane resin is in a range of 1 × 10 ⁻⁵ to 30 × 10 ⁻⁵ eq / g. 8. At least two or more layers in which a lower nonmagnetic layer containing at least a nonmagnetic powder and a binder is provided on a nonmagnetic support, and an upper magnetic layer containing at least a ferromagnetic powder and a binder is provided thereon. In a magnetic recording medium having a plurality of layers,
The magnetic recording medium according to claim 1, wherein the polyurethane resin according to claim 1 is included as a binder of at least one of the lower nonmagnetic layer and the upper magnetic layer.