JPH10124847A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having a high degree of durability and electromagnetic conversion characteristics. SOLUTION: At least one binder of the binder in the magnetic layer or the binder in a lower layer coating layer of the magnetic recording medium provided with the magnetic layer or the magnetic recording medium provided further with the lower layer coating layer between the magnetic layer and a nonmagnetic base are polyurethane reins including a cyclic structure and ether groups and the magnetic recording media described above contain arom. org. acid compds. in the same layer as the layer of the polyurethane resins. The magnetic recording medium provided with the magnetic layer contains the ferromagnetic powder consisting essentially of iron or the magnetic recording medium provided further with the lower layer coating layer between the magnetic layer and nonmagnetic base contains the polyurethane resins and phosphorus compds. in at least the magnetic layers. The intensity ratio of P to Fe measured by fluorescent X-rays is 0.2 to 2.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium in which a magnetic layer in which a ferromagnetic fine powder and a binder are dispersed is provided on a non-magnetic support. The magnetic recording medium has particularly excellent electromagnetic conversion characteristics and durability. About.

[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 nonmagnetic support. The magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. That is, audio tapes for recording and reproducing music are required to have higher original sound reproduction capabilities. Also, video tapes are required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability.

At the same time as having such excellent electromagnetic conversion characteristics, the magnetic recording medium is required to have good running durability as described above. In order to obtain good running durability, an abrasive and a lubricant are generally added to the magnetic layer.

[0004] However, in order to obtain excellent running durability by the abrasive, it is necessary to increase the addition amount to some extent, so that the filling degree of the ferromagnetic powder is reduced.
When an abrasive having a large particle diameter is used to obtain excellent running durability, the abrasive tends to excessively protrude from the surface of the magnetic layer. Therefore, the improvement of the running durability by the abrasive may cause the deterioration of the electromagnetic conversion characteristics described above.

When the above-mentioned running durability is improved by a lubricant, it is necessary to increase the amount of the added lubricant. Therefore, the binder tends to be plasticized, and the durability of the magnetic layer tends to decrease. In order to improve the durability and the electromagnetic conversion characteristics, the binder, which is one of the main components of the magnetic layer, naturally plays an important role. Conventionally used vinyl chloride resin, cellulose resin, urethane resin, acrylic resin and the like have a problem in that the wear resistance of the magnetic layer is inferior and the running members of the magnetic tape are contaminated.

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, a magnetic recording medium using a binder composed of a polyester polyurethane resin and a polycarbonate polyurethane resin is described in JP-A-6-96437, and in Examples, urethane having a urethane group of 2 to 4 mmol / g is described. However, the content of the long-chain diol is unknown, and the content of the OH group is not clear, and Japanese Patent Publication No. 6-19821 similarly discloses that the total of urethane and urea is 1.8. Binders containing ~ 3.0 mmol / g urethane urea are described,
According to the resin synthesis example, the proportion of the long-chain diol in the obtained polyurethane resin is 61% by weight, and these have a high urethane bond concentration and are excellent in durability, but have high dispersibility due to an increase in the viscosity of the coating solution. There is a drawback that the electromagnetic conversion characteristics decrease due to the decrease.

Further, there has been proposed a binder using a polyurethane resin using a short-chain diol having a cyclic structure as a binder. Japanese Unexamined Patent Publication (Kokai) No. 61-148626 discloses a polyester polyol containing 20% of bisphenol A. According to Examples, the content of bisphenol A is 13% by weight and the content of polyol is 69% by weight based on urethane. There is a drawback that the dispersibility is inferior because of lowering. Further, JP-A-1-251416 describes a polyurethane using bisphenol A as a chain extender and a polycarbonate polyol raw material as a short-chain diol having a cyclic structure. Although 16% by weight and a polyol content of 63% by weight are used, there is also a problem that the dispersibility decreases because the cyclic structure similarly lowers the solubility in a solvent. The use of a lactone-modified polyol containing bisphenol S is described in Japanese Examined Patent Publication No. 7-21851, but the polyol content is 52% by weight and the bisphenol S content is 13% according to the examples. % Polyurethane, but had the same problem because of having a cyclic structure.

Japanese Patent Application Laid-Open No. 1-267829 discloses that a polyurethane resin uses a polyether polyol having a cyclic structure, and bisphenol A, hydrogenated bisphenol A ethylene oxide and propylene oxide adducts are used as diols ( Molecular weight 250-30
However, in each of the examples, the polyol content is 70% by weight or more and the ether content is 8 mmol / g or more, so that the coating film becomes soft and the head becomes dirty. However, there is a disadvantage that the durability of the resin is reduced.

In Japanese Patent Application Laid-Open No. 61-190717, polytetramethylene glycol and polycaprolactone polyol are used as polyurethane resins.
According to the description of the examples, the polyol content is 70% by weight
As described above, similarly, there has been a problem that the coating film is soft and the head is stained and the durability is reduced.

Japanese Patent Publication No. 6-64726 discloses a polyurethane resin obtained by reacting a branched polyester polyol with an isocyanate-terminated prepolymer. The content of an OH group is 8.2 according to a synthesis example. × 10
^-5 eq / g, the content was large, the viscosity of the solution was increased, the dispersibility was poor, and the branched polyol was accompanied by problems such as a decrease in the strength of the resin and a deterioration in the repetitive running property.

Similarly, JP-A-3-44819 discloses a magnetic recording medium using a binder comprising a compound having at least one OH group at both terminals and a polyisocyanate. However, there is a problem such as a decrease in the strength of the resin and a deterioration in the repetitive running property.

JP-A-62-282510 discloses that the number of terminals of the main chain and the branched chain is 3 or more on average,
A binder containing a polyurethane resin having a primary hydroxyl group at at least two terminals is described.Examples include polyester polyols, but those having sufficient resin strength and repeated running durability are not mentioned. Did not.

As described above, conventionally known polyurethane resins and polyurethane urea resins used as binders for magnetic recording media generally use long-chain diols having a hydrophilic segment such as polyester, polyether and polycarbonate. According to the examples described in the respective prior arts, the long-chain diol contained at least 25 mol% of the long-chain diol in the resin.

However, since the above-mentioned polyurethane resin and polyurethane-urea resin have the above-mentioned hydrophilic segment, they hinder the affinity with an organic solvent, so that a hydrophilic polar group easily aggregates, and the molecular chain spreads in the organic solvent. Has a drawback that it acts to hinder the dispersibility of the ferromagnetic fine powder. In the case of polyesters, long-chain diols having these hydrophilic segments have a problem that ester bond groups are easily hydrolyzed and storage stability is deteriorated. Polyethers include polytetramethylene ether glycol and polypropylene. Low Tg like glycol, polyethylene glycol, etc.
It was soft and small in strength.

By the way, there is known a magnetic recording medium in which a magnetic layer is provided on a non-magnetic layer to reduce the thickness of the magnetic layer. However, in order to achieve higher density recording, the thickness of the magnetic layer is reduced. Also, finer ferromagnetic metal powders are required. The miniaturization of the ferromagnetic metal powder causes a decrease in the dispersibility, and consequently, the surface property of the magnetic layer is deteriorated, the electromagnetic conversion characteristics are reduced, and it is difficult to secure the durability.

That is, a polyurethane resin excellent in dispersibility of a ferromagnetic metal powder or a non-magnetic powder and excellent in durability having both hardness (ie, high Tg and high Young's modulus) and toughness (elongation) is desired. Under these circumstances, the above-mentioned polyurethane resin cannot sufficiently meet the above-mentioned problems. Also, there is a tape (ME) using a ferromagnetic metal thin film as an 8 mm video tape or a video tape suitable for consumer DVC today, but a coating tape (MP) using a ferromagnetic metal powder is not available. Compared with ME, there is an advantage that it is superior in durability, economy, etc., but there is a point that it is inferior in electromagnetic conversion characteristics. Further, it is desired that the coating type magnetic recording medium using the fine particle magnetic material has further improved running durability and electromagnetic conversion characteristics.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having a high durability and an electromagnetic conversion characteristic with excellent reproduction output.

[0018]

The present invention has the following arrangement. 1) A magnetic recording medium having a magnetic layer formed by dispersing a ferromagnetic powder in a binder on a non-magnetic support, or further including an inorganic powder and a binder between the magnetic layer and the non-magnetic support. In a magnetic recording medium provided with a lower coating layer, at least one binder of the binder in the magnetic layer or the binder in the lower coating layer is a polyurethane resin containing a cyclic structure and an ether group, and A magnetic recording medium characterized in that an aromatic organic acid compound is contained in a layer and / or a lower coating layer in the same layer as the polyurethane resin. 2) The magnetic recording medium according to 1) above, wherein the aromatic organic acid compound is an organic acid having a pKa of 3 or less or a salt thereof. 3) A magnetic recording medium having a magnetic layer formed by dispersing a ferromagnetic powder containing iron as a main component in a binder on a nonmagnetic support, or an inorganic powder between the magnetic layer and the nonmagnetic support. In a magnetic recording medium provided with a lower coating layer containing a binder and a binder, at least the polyurethane layer and the phosphorus compound according to claim 1 are contained in the magnetic layer, and the P of P with respect to Fe measured by fluorescent X-rays is contained in the magnetic layer. A magnetic recording medium having an intensity ratio of 0.2 to 2.0. 4) 3-20 O per molecule in polyurethane resin
4. The magnetic recording medium according to any one of 1) to 3) above, which has an H group. 5) Polyurethane resin contains -SO ₃ M, -OS
_{O 3 M, -COOM, -PO 3} MM ', - OPO 3 M
M ′, —NRR ′, —N ⁺ RR′R ″ COO ⁻ (where M and M ′ are each independently a hydrogen atom, an alkali metal, an alkaline earth metal or an ammonium ion, and R, R ′ and R '' each independently represents an alkyl group having 1 to 12 carbon atoms), wherein at least one kind of polar group selected from the group consisting of (1) to (4) is included. Medium. 6) At least one of the binder in the magnetic layer or the binder in the lower coating layer is made of a polyurethane resin which is a reaction product of a diol and an organic diisocyanate as main raw materials, and has a cyclic structure. The polyurethane resin contains 17 to 40% by weight of a chain diol unit, and has an ether group of 1.0 to
The magnetic recording medium according to any one of 1) to 5) above, wherein the binder is a binder containing a long-chain diol unit containing 5.0 mmol / g in a polyurethane resin in an amount of 10 to 50% by weight.

According to the first aspect of the present invention, by using a polyurethane resin having a specific structure in combination with an aromatic organic acid compound, various powders such as a ferromagnetic powder, a non-magnetic powder and a soft magnetic powder can be obtained. This is to improve the dispersibility and the durability of the magnetic recording medium. In the polyurethane resin, when the cyclic structure of the polyurethane resin contributes to rigidity and the ether group contributes to the flexibility, the solubility is improved, the radius of inertia (expansion of the molecule) is increased, and the dispersibility of the powder is improved. The hardness of the polyurethane resin itself (high glass transition point Tg, high Young's modulus)
It is considered that the improvement of the durability can be measured because the properties of toughness and elongation are compatible.

Further, since the aromatic organic acid compound is strongly adsorbed on the powder surface, the polyurethane resin is largely and strongly adsorbed by the aromatic organic acid compound adsorbed on the powder surface, so that the dispersibility of the powder is further increased. Is considered to be improved, and the durability is improved.

According to a third aspect of the present invention, the same polyurethane resin as in the first aspect is used, a phosphorus compound is selected as the aromatic organic compound according to the first aspect of the invention, the amount of the phosphorus compound is defined in an appropriate range, and the ferromagnetic compound is used. Electromagnetic conversion characteristics and durability can be improved by selecting a ferromagnetic powder mainly composed of iron as the powder and allowing it to be contained in at least the magnetic layer. According to the third aspect of the present invention, the effects of the polyurethane resin and the phosphorus compound are the same as those of the polyurethane resin and the aromatic organic compound, respectively. There is an effect that an improved magnetic recording medium can be stably provided.

BEST MODE FOR CARRYING OUT THE INVENTION

The content of the OH group in the polyurethane resin is as follows:
The number is preferably 3 to 20 per molecule, more preferably 4 to 5 per molecule. If the number is less than 3 per molecule, the reactivity with the isocyanate curing agent is reduced, so that the strength of the coating film is reduced and the durability tends to be reduced. On the other hand, when the number is more than 20, the solubility in a solvent is reduced, and the dispersibility tends to be reduced.

As the compound used for adjusting the content of the OH group in the polyurethane resin, a compound having three or more OH groups can be used. Specific examples include trimethylolethane, trimethylolpropane, trimellitic anhydride, glycerin, pentaerythritol, hexanetriol, and the like, which are used as polyester polyol raw materials described in Japanese Patent Publication No. 6-64726 described as a conventional technique. Examples include branched polyesters and polyetheresters having a tribasic or higher OH group obtained by using a dibasic acid and the compound as a glycol component. Preferably, it is a trifunctional one, and if it has four or more functionalities, it tends to gel in the reaction process.

[0024] The polyurethane resin of the present invention contains-
SO_Three M, -OSO_Three M, -COOM, -PO_Three M
M ', -OPO_Three MM ', -NRR', -N⁺RR '
R "COO ^-(Where M and M ′ are each independently water
Elementary atom, alkali metal, alkaline earth metal or ammo
R, R ′ and R ″ are each independently
Represents an alkyl group having 1 to 12 carbon atoms).
It preferably contains at least one kind of polar group, particularly preferably
Or -SO_Three M, -OSO_Three M. These poles
The amount of the functional group is preferably 1 × 10^-Five~ 2 × 10^-Foureq /
g, particularly preferably 5 × 10^-Five~ 1 × 10^-Foureq
/ G. 1 × 10^-FiveIf less than eq / g, ferromagnetic powder
Dispersibility decreases due to insufficient adsorption to powder, and 2 ×
10^-FourIf it exceeds eq / g, the solubility in the solvent will decrease.
Therefore, the dispersibility decreases.

The polyurethane resin used in the present invention comprises a polyurethane resin, which is a reaction product of a diol and an organic diisocyanate as main raw materials. The diol component includes a short-chain diol unit having a cyclic structure and an ether group. And a long-chain diol unit containing

The short-chain diol having a cyclic structure means a diol having a saturated or unsaturated cyclic structure and having a molecular weight of less than 500. For example, bisphenol A, hydrogenated bisphenol A represented by the following formula 1, bisphenol S, bisphenol P, and diols having an aromatic or alicyclic group such as ethylene oxide, propylene oxide adduct thereof, cyclohexanedimethanol, cyclohexanediol, etc. preferable.

[0027]

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More preferably, hydrogenated bisphenol A represented by the formula 1 and its ethylene oxide and propylene oxide adducts are exemplified.

The short-chain diol having a cyclic structure is
The molecular weight is selected from those having a molecular weight of 50 or more and less than 500, more preferably 100 to 400, and most preferably 100 to 30.
0. If it is less than 50, the magnetic layer becomes brittle and the durability decreases. When it is 500 or more (that is, when the short-chain diol referred to in the present invention is not used), the glass transition temperature Tg of the magnetic layer decreases, and the magnetic layer becomes soft, and the durability decreases. In addition, another diol having a molecular weight of less than 500 can be used together with the short-chain diol having a cyclic structure. Specifically, ethylene glycol, 1,3-propylene diol, 1,2-propylene glycol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 2,2-dimethyl propane diol ,
1,8-octanediol, 1,9-nonanediol,
Linear or branched diols such as diethylene glycol and ethylene oxide or propylene oxide adducts of N-diethanolamine can be mentioned.

By using these, a coating film having high strength, high Tg and high durability due to the annular structure can be obtained. Furthermore, the introduction of the branched CH ₃ results in excellent solubility in a solvent, so that high dispersibility can be obtained.

The content of the short-chain diol unit in the polyurethane resin is preferably from 17 to 40% by weight, and more preferably from 20 to 30% by weight. If the content is less than 17% by weight, the resulting coating film is too soft to obtain sufficient strength,
Still durability decreases. If it is more than 40% by weight, the solubility in a solvent is reduced, and the dispersibility of the ferromagnetic powder is easily reduced, so that the electromagnetic conversion characteristics are easily reduced.
The strength of the magnetic layer decreases.

The long-chain diol is a diol having a molecular weight of 500
The above-mentioned diols, specifically, bisphenol A, hydrogenated bisphenol A, bisphenol S or bisphenol P to which ethylene oxide, propylene oxide or both thereof are added, polypropylene glycol, polyethylene glycol, polytetramethylene glycol Are preferable, and a compound represented by the following formula 2 is particularly preferable.

[0033]

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The values of n and m are 3 to 24, preferably 3 to 20, and more preferably 4 to 1.
5 If n and m are smaller than 3, the urethane bond concentration increases, the solubility in a solvent is reduced, the coating film is apt to be brittle, and the dispersibility and durability are further reduced. n, m
Is larger than 24, the coating film becomes soft and the still durability decreases.

In the long-chain diol, R is preferably

[0036]

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Are more preferred. In the long-chain diol of the formula 2, X is preferably a hydrogen atom or a methyl group, more preferably a methyl group. Note that n or m
All the Xs in the parentheses need not be the same, and a hydrogen atom and a methyl group may be mixed. Polyurethane resin used in a particularly preferred embodiment of the present invention,
Since it has a cyclic structure, the coating film strength is high, the durability is excellent, and since it has branched CH ₃ of propylene, it has high solubility in solvents and excellent dispersibility.

Weight average molecular weight (Mw) of long chain diol
Is from 500 to 5,000, and if it is more than 5,000, the coating film strength is reduced and becomes soft, so that the durability is reduced. Therefore, a more preferable weight average molecular weight is selected from the range of 700 to 3000. The content of the long-chain diol unit containing an ether group is preferably 10 to 50% by weight, more preferably 30 to 40% by weight in the polyurethane resin.
It is. When the content is less than 10% by weight, the solubility in a solvent is reduced, so that the dispersibility is reduced. On the other hand, if it is more than 50% by weight, the strength of the coating film is reduced, so that the durability is reduced. The content of the ether group in the long-chain diol unit is preferably from 1.0 to 5.0 mmol / g, more preferably from 2.0 to 4.0 mmol / g, in the polyurethane resin. If it is less than 1 mmol / g, the adsorptivity to the magnetic substance is reduced, and the dispersibility is reduced. On the other hand, 5.0 mmol / g
If it is larger, the solubility in a solvent is reduced, and the dispersibility is reduced.

The number average molecular weight (Mn) of the polyurethane resin of the present invention is preferably 18,000 to 56,000, more preferably 23,000 to 34000, and the weight average molecular weight (Mw) is preferably 30,000 to 1,000.
00, more preferably 40,000 to 60,000.
If it is smaller than these ranges, the strength of the magnetic layer decreases, and the durability decreases. On the other hand, if it is larger than these ranges, the solubility in a solvent is reduced, and the dispersibility is reduced.

The glass transition temperature Tg of the polyurethane resin of the present invention is from 0 to 200 ° C., preferably from 30 to 1
The temperature is set to 50 ° C, more preferably 30 to 130 ° C. If the temperature is lower than 0 ° C., the strength of the magnetic layer at a high temperature decreases, so that the durability and the storability deteriorate. If the temperature is higher than 200 ° C., calender moldability decreases, and electromagnetic conversion characteristics decrease.

When the binder of the present invention is used for a magnetic layer, a vinyl chloride synthetic resin may be used in combination with the polyurethane resin of the present invention. The polymerization degree of the vinyl chloride resin that can be used in combination is preferably 200 to 600, and 250 to 600.
450 is particularly preferred. The vinyl chloride resin may be a copolymer of a vinyl monomer, for example, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylonitrile and the like. Further, a cellulose derivative such as a nitrocellulose resin, an acrylic resin, a polyvinyl acetal resin, a polyvinyl butyral resin, an epoxy resin, a phenoxy resin, or the like may be used in combination, and these may be used alone or in combination.

When another synthetic resin is used in combination, the polyurethane resin contained in the magnetic layer may contain less than 10 to 100% by weight in the binder (the total amount of the resin component and the curing agent). Preferably, more preferably, 20 to 10
Less than 0% by weight. If it is less than 10% by weight, the solubility in a solvent is reduced, and the dispersibility is reduced.

Further, the present invention uses a polyisocyanate compound, preferably an organic diisocyanate, as a component for forming a urethane bond of the polyurethane resin of the present invention, or as a curing agent for further crosslinking the polyurethane resin or another resin used in combination. can do.

Examples of the organic diisocyanate compound include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate,
4'-diphenylmethane diisocyanate, 4,4-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 4,4 '
Aromatic diisocyanates such as -diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, and 3,3'-dimethoxydiphenyl-4,4'-diisocyanate And aliphatic alicyclic diisocyanates such as lysine diisocyanate and the like, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate and the like.

The polyisocyanate compound contained in a coating layer such as a magnetic layer and a lower coating layer (hereinafter, also referred to as “lower layer”) is contained in a binder (meaning a total of a resin component and a curing agent; the same applies hereinafter). Is preferably in the range of 5 to 50% by weight, more preferably 10 to 40% by weight.

In the case of performing the curing treatment by electron beam irradiation, a compound having a reactive double bond such as urethane acrylate can be used. The weight of the binder is usually 15 to 4 parts per 100 parts by weight of the ferromagnetic powder.
It is preferably in the range of 0 parts by weight, more preferably 20 to 30 parts by weight. The binder in the case where the lower coating layer is provided as described later is usually 5 to 35 parts by weight based on the nonmagnetic powder or the soft magnetic powder.

Next, the aromatic organic acid compound used in the present invention will be described. The aromatic organic acid compound used in the present invention strongly adsorbs to various powders, and preferably has high affinity to the polyurethane resin. Therefore, as the aromatic organic acid compound, a strong acid having a large dissociation constant (strong acid) is preferable, and an organic acid having a pKa of 3 or less or a salt thereof is suitable. However, in the case of an oxidized magnetic material coated with Co, Co may be eluted by a strong acid. In this case, a material having a pKa of 3 or more, for example, benzoic acid or the like is used. In the present invention, pKa
The aromatic organic acid compound of 3 or less refers to an aromatic organic acid compound having a pKa3 or a stronger acid than the aromatic organic acid compound. Therefore, the numerical value of the pKa value itself is 3 or less.

The aromatic organic acid compound used in the present invention includes free acids, salts and derivatives thereof,
For example, the concept includes an ester or the like. In addition, the above-mentioned adsorption to powder is a concept that includes chemical adsorption including covalent bonding in addition to physical adsorption. Examples of the organic acid having a pKa of 3 or less include α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphonic acid, phenylphosphinic acid, methanesulfonic acid,
There are benzenesulfonic acid, p-toluenesulfonic acid, naphthalene-α-sulfonic acid, naphthalene-β-sulfonic acid and the like, and salts thereof.

The method of using the aromatic organic acid compound is not particularly limited as long as the above characteristics can be exhibited.
Preferably, the powder and the binder are added at the same time when the powder is kneaded in the preparation of the coating material, or the powder is subjected to a surface treatment with an aromatic organic acid compound before kneading the powder with the binder. The amount of the aromatic organic acid compound to be used for the powder is determined by the amount of the aromatic organic acid compound adsorbed on the powder, but usually, 10 to 2 times the saturated adsorption amount of the aromatic organic acid compound is used. ± 50% of the saturated adsorption amount is preferable.
ol / g. The phosphorus compound used in the third aspect of the present invention is preferably an organic phosphorus compound, more preferably an aromatic phosphorus compound. Examples of the aromatic phosphorus compound include the phosphorus compounds exemplified as the organic acids having a pKa of 3 or less in the aromatic organic acid compound. Specific examples include α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, phenylphosphonic acid, phenylphosphinic acid, and the like, and salts thereof. The amount of the phosphorus compound used for the ferromagnetic powder is 0.05 to 0.5 with respect to 1 kg of the ferromagnetic powder.
mol, preferably in the range of 0.1 to 0.45 mol, and is appropriately selected depending on the amount of phosphorus compound adsorbed on the ferromagnetic powder. According to the third aspect of the present invention, the P / Fe ratio of the magnetic layer is defined in the range of 0.2 to 2.0 in terms of intensity ratio by X-ray fluorescence measurement. 4
To 1.6, more preferably 0.5 to 1.2.
Range. If the P / Fe ratio is less than 0.2, the dispersibility of the ferromagnetic powder is inferior, Ra increases, the reproduction output decreases, and the durability deteriorates. On the other hand, if the P / Fe ratio is larger than 2.0, the friction coefficient μ value becomes large, and the durability becomes extremely poor. In the present invention, the P /
The measurement of the Fe ratio indicates a value obtained according to the following conditions. The magnetic layer is peeled off from the sample tape, and the powder is pressed and hardened. The intensity ratio of P to Fe was calculated for the sample obtained above under the following measurement conditions and methods. Intensity ratio of P to Fe: Measuring device A Rigaku Geigerflex 3064M Rh X-ray tube was used, and the voltage and current were 50 kV and 50 mA. For the measurement of the FeKα-ray intensity, the spectral crystal LiF ｛22
A 0 ° detector scintillation counter was used. PK
An α-ray intensity measurement was performed using a proportional counter for a spectral crystal Ge {111} detector. Both are for 20 seconds
Integration was performed, and this was repeated three times to obtain an average. FeKα
The ratio of the PKα line intensity to the line intensity is defined as the intensity ratio of P to Fe.

The shape of the magnetic recording medium of the present invention is basically arbitrary, and includes tapes, disks, sheets, cards and the like. The layer structure of the magnetic recording medium according to the first aspect of the present invention basically has a magnetic layer or a magnetic layer and a lower coating layer on a support, and the aromatic organic acid compound and the polyurethane resin are contained in the same layer. Any configuration may be employed as long as the configuration includes at least one layer. The layer structure of the magnetic recording medium according to the third aspect of the present invention is not particularly limited as long as at least the magnetic layer contains a polyurethane resin and a phosphorus compound. It is necessary to include As the layer constitution of the invention of claims 1 and 3, for example,
Examples include a single magnetic layer, a multilayer magnetic layer, and a multilayer of a magnetic layer and a non-recording layer. Here, the magnetic layer refers to a layer containing a ferromagnetic powder that can be recorded and reproduced by magnetism, and the non-recording layer refers to a layer that does not substantially contain a ferromagnetic powder and refers to a nonmagnetic layer or a soft magnetic layer. , Non-magnetic powder or soft magnetic powder.

The thickness of each layer in the layer structure is as follows, for example. In the case of a single magnetic layer, the thickness is usually 0.2 to 5 μm, preferably 0.5 to 3 μm. The multilayer structure is as follows. The upper layer becomes a magnetic layer provided on the lower layer. a In the case of upper layer: magnetic layer, lower layer: magnetic layer The upper layer is usually 0.2 to 2 μm, preferably 0.2 to 1 μm.
5 μm, and the lower layer is 0.8 to 3 μm.

B Upper layer: magnetic layer, lower layer: non-magnetic layer The upper layer is usually 0.05 to 1 μm, preferably 0.1 to 1 μm.
0.5 μm, and the lower layer is 0.8 to 3 μm. c Upper layer: magnetic layer, lower layer: soft magnetic layer The upper layer is usually 0.05 to 1 μm, preferably 0.1 to 1 μm.
0.5 μm, more preferably 0.1 to 0.4 μm
m, the lower layer is 0.8 to 3 μm.

When the magnetic recording medium according to the first aspect of the present invention has a multilayer structure, it is necessary that the polyurethane resin of the present invention and the aromatic organic acid compound are contained in at least the same layer, but at least in the uppermost layer. Preferably,
More preferably, it is contained in each layer. The ferromagnetic powder used in the magnetic layer according to the first aspect of the invention is ferromagnetic iron oxide, cobalt-containing ferromagnetic iron oxide, barium ferrite powder, ferromagnetic metal powder, or the like. Ferromagnetic powder is S _BET (BET
Specific surface area) of 40 to 80 m ² / g, preferably 50 to 7
0 m ² / g. The crystallite size is 12 to 25 nm, preferably 13 to 22 nm, particularly preferably 14 to
20 nm. The major axis length is 0.05 to 0.25 μm, preferably 0.07 to 0.2 μm, and particularly preferably 0.08 to 0.15 μm. P of ferromagnetic powder
H is preferably 7 or more. The ferromagnetic powder used in the magnetic layer according to the third aspect of the present invention contains iron as a main component, and may be ferromagnetic iron oxide, cobalt-containing ferromagnetic iron oxide, barium ferrite powder, or ferromagnetic metal powder. Particularly, ferromagnetic metal powder is preferable. The S _{BE T} (BET specific surface area) of the ferromagnetic metal powder is usually 30 to 70, preferably 35 to 60 m ^2.
/ G, more preferably 40 to 55 m ² / g. The crystallite size is usually 100-300 °, preferably 100
Å200 °, particularly preferably 130１３０200 °. The major axis length is usually from 0.03 μm to 0.3 μm, preferably from 0.05 to 0.25 μm, and particularly preferably from 0.05 to 0.15 μm. The pH of the ferromagnetic powder is preferably 7 or more. Further, the coercive force Hc of the ferromagnetic metal powder is usually 1000 to 3000 Oe, preferably 1500 to 3000 Oe, more preferably 1800 to 2Oe.
The saturation magnetization σ _S of the ferromagnetic metal powder is usually 100 to 180 emu / g, preferably 110 to 170 emu / g, more preferably 120 emu / g.
１６０160 emu / g. Examples of the ferromagnetic metal powder include Fe, Ni, Fe-Co, Fe-Ni, and Co-N.
i, a simple substance or an alloy such as Co-Ni-Fe,
Aluminum within a range of not more than 20% by weight of the metal component,
Silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten, rhenium,
Examples include silver, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium, and alloys containing bismuth. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The method for producing these ferromagnetic powders is already known, and the ferromagnetic powder used in the present invention can also be produced according to a known method.

The shape of the ferromagnetic powder is not particularly limited, but usually, needle-like, granular, dice-like, rice-granular, plate-like and the like are used. It is particularly preferable to use acicular ferromagnetic powder.

The above-mentioned resin component, curing agent and ferromagnetic powder are kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone, and ethyl acetate which are usually used in the preparation of a magnetic paint to obtain a magnetic paint. The kneading and dispersion can be performed according to a usual method. The magnetic paint is composed of α-Al ₂ O ₃ and Cr ₂ O in addition to the above components.
_It may contain commonly used additives or fillers such as abrasives such as No. ₃ , antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters and silicone oil, and dispersants.

Next, the lower nonmagnetic layer or the lower magnetic layer in the case where the first or third aspect of the present invention has a multilayer structure will be described. The inorganic powder used for the lower layer of the present invention may be either a magnetic powder or a non-magnetic powder. For example, in the case of non-magnetic powder,
It can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like, and non-magnetic metals. As the inorganic compound, for example, titanium oxide (TiO ₂ , TiO), an α conversion rate of 90 to 100%
Α-alumina, β-alumina, γ-alumina, α-iron oxide, chromium oxide, zinc oxide, tin oxide, tungsten oxide, vanadium oxide, silicon carbide, cerium oxide, corundum, silicon nitride, titanium carbide, silicon dioxide ,
Magnesium oxide, zirconium oxide, boron nitride, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, goethite, aluminum hydroxide and the like are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred is titanium dioxide. Examples of the non-magnetic metal include Cu, Ti, Zn, and Al. The average particle diameter of these non-magnetic powders is preferably 0.005 to 2 μm. However, if necessary, non-magnetic powders having different average particle diameters may be combined, or a single non-magnetic powder may have a wide particle diameter distribution to achieve the same effect. Can also be provided. Particularly preferably, the average particle size of the non-magnetic powder is 0.01 μm to 0.2 μm. The pH of the nonmagnetic powder is particularly preferably between 6 and 9.
The specific surface area of the non-magnetic powder is 1 to 100 m ² / g, preferably 5 to 50 m ² / g, more preferably 7 to 40 m ² / g.
It is. The crystallite size of the non-magnetic powder is 0.01 μm to 2
μm is preferred. Oil absorption using DBP is 5-100m
1/100 g, preferably 10-80 ml / 100 g,
More preferably, it is 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape.

As the soft magnetic powder, granular Fe, Ni, granular magnetite, Fe-Si, Fe-Al, Fe-N
i, Fe-Co, Fe-Co-Ni, Fe-Al-Co
(Sendust) alloy, Mn-Zn ferrite, Ni-Z
n ferrite, Mg-Zn ferrite, Mg-Mn ferrite, etc.
Magnetic Properties and Applications ”(Shokabo, 1984), 368-3
76).

The surface of these non-magnetic and soft magnetic powders
Is Al_TwoO_Three , SiO_Two, TiO_Two, ZrO_Two, SnO_Two, Sb_TwoO_Three , ZnO
Surface treatment is preferred. Especially preferred for dispersibility
Al_TwoO _Three , SiO_Two, TiO_Two, ZrO_TwoBut more preferred is
Al_TwoO_Three , SiO_Two, ZrO_TwoIt is. These are used in combination
Or may be used alone. Also the purpose
A surface treatment layer coprecipitated according to may be used.
After treating with alumina, treating the surface layer with silica
The method may be used, or vice versa. Also, the table
The surface treatment layer may be a porous layer depending on the purpose,
Homogeneous and dense are generally preferred.

By mixing carbon black in the lower layer, it is possible to lower the surface electric resistance Rs, which is a known effect, and to obtain a desired micro Vickers hardness. For this purpose, furnace black for rubber, thermal black for rubber, carbon black for color, acetylene black and the like can be used. The specific surface area of carbon black is 100 to 500 m ² / g, preferably 15 to 500 m ² / g.
0-400m ² / g, DBP oil absorption 20-400ml
/ 100 g, preferably 30-200 ml / 100 g. The average particle size of carbon black is 5 nm to 80 n.
m, preferably 10 to 50 nm, more preferably 10 to
40 nm. PH of carbon black is 2-10,
Moisture content is 0.1-10%, tap density is 0.1-1g /
ml is preferred. Specific examples of carbon black used in the present invention include BLACKPE manufactured by Cabot Corporation.
ARLS 2000, 1300, 1000, 900, 8
00, 880, 700, VULCAN XC-72, manufactured by Mitsubishi Chemical Corporation, # 3050B, 3150B, 3250B,
# 3750B, # 3950B, # 950, # 650B,
# 970B, # 850B, MA-600, manufactured by Columbian Carbon, CONDUCTEX SC, RAVEN
8800,8000,7000,5750,5250,3500,2100,2000,1800,150
0,1255,1250 and Ketjen Black EC manufactured by Akzo.

In the lower layer of the present invention, a magnetic powder can be used as the inorganic powder. As magnetic powder, γ-
An alloy mainly composed of Fe ₂ O ₃ , Co-modified γ-Fe ₂ O ₃ , α-Fe, CrO ₂ or the like is used. The magnetic material of the lower layer can be selected according to the purpose, and the effect of the present invention does not depend on the type of the magnetic material. However, depending on the purpose,
Changing the performance of the upper and lower layers is known. 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 non-magnetic layer can be the same as those of the magnetic layer. In particular, with respect to the amount and type of the binder, the amount of the additive and the type of the dispersant, and the type of the magnetic layer, known techniques for the magnetic layer can be applied. A magnetic coating prepared from the above materials is applied on a non-magnetic support to form a magnetic layer.

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 and aromatic polyamide. These non-magnetic supports may be previously subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, and the like. The nonmagnetic support that can be used in the present invention has a surface having excellent smoothness such that the center line average surface roughness is in the range of 0.1 to 20 nm, preferably 1 to 10 nm at a cutoff value of 0.25 mm. Is preferred. It is preferable that these nonmagnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μ or more.

In the method for producing a magnetic recording medium of the present invention, for example, a coating solution is preferably applied to the surface of a running non-magnetic support, preferably after drying the coating layer, in a range of 0.05 to 5 μm. Preferably, it is applied so that the thickness is 0.07 to 3 μm. Here, a plurality of magnetic paints or non-magnetic paints may be sequentially or simultaneously multi-layer coated. As a coating machine for applying the magnetic paint, 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, spray coat, spin coat and the like can be used.

For these, reference can be made, for example, to “Latest Coating Technology” (May 31, 1983) published by Sogo Gijutsu Center.

When the present invention is applied to a magnetic recording medium having two or more layers, the following can be proposed as an example of a coating apparatus and method. (1) Gravure generally applied in the application of magnetic paint,
First, the lower layer is applied by a coating device such as a roll, a blade, an extrusion or the like.
No. 9, JP-A-2-265672, etc., the upper layer is applied by a support pressure type extrusion coating device. (2) JP-A-63-88080, JP-A-2-17
No. 971 and Japanese Unexamined Patent Publication No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965.

A backcoat layer (backing layer) is formed on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied.
May be provided. The back coat layer is provided by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent on a surface of the non-magnetic support on which the magnetic paint is not applied. Layer. Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or as a mixture of these as a binder. . The back coat layer is suitably provided particularly when the magnetic recording medium of the present invention is a tape medium.

An adhesive layer may be provided on the surface of the non-magnetic support on which the magnetic paint and the back coat layer forming paint are applied.

The applied layer of the applied magnetic paint is dried after subjecting the ferromagnetic powder contained in the applied layer of the magnetic paint 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.

Epoxy as a calendering roll,
Use a heat-resistant plastic roll such as polyimide, polyamide, or polyamide-imide. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention has a center line average roughness of 0.1 to 0.1 at a cutoff value of 0.25 mm.
It is preferable that the surface has an extremely excellent smoothness of 4 nm, preferably 1 to 3 nm. As a method for this, for example, a magnetic layer formed by selecting a specific binder as described above is subjected to the above calender treatment. As for the calendering conditions, the temperature of the calender roll is in the range of 60 to 100 ° C, preferably 70 to 1 ° C.
The temperature is in the range of 00 ° C, particularly preferably in the range of 80 to 100 ° C, the pressure is in the range of 100 to 500 Kg / cm,
It is preferably in the range of 200 to 450 kg / cm, particularly preferably in the range of 300 to 400 kg / cm.

The obtained magnetic recording medium can be cut into a desired size using a cutting machine or the like before use.

The polyurethane resin of the present invention contains a large amount of a short-chain diol having a cyclic structure such as an aromatic or alicyclic group, so that a higher strength and a higher Tg can be obtained as compared with a conventional polyurethane resin. In particular, it is excellent for repeated running in a high temperature environment.
Further, since the content of the short-chain diol is large, the urethane bond concentration in the polyurethane resin substantially increases, so that higher strength and higher Tg can be obtained.

In the conventional polyurethane resin, when the cyclic structure or the urethane bond concentration increases, the solubility in a solvent decreases and the dispersibility decreases, but the polyurethane of the present invention has an advantage that the solubility in a solvent is excellent. There is. This is because the polyurethane resin of the present invention preferably contains 10 to 50% by weight of a long-chain diol unit containing 1.0 to 5.0 mmol / g of a hydrophilic ether group. It is considered that the polyurethane is easily adsorbed on the magnetic material without lowering the solubility, and that the aromatic organic acid compound is present on the surface of the magnetic material or other powder, so that the dispersibility is further improved.

Also, since an appropriate stretchability can be imparted, the magnetic layer does not become brittle, so that there is an advantage that the repetitive running property does not decrease. Furthermore, since the short-chain diol has a cyclic structure, steric hindrance is imparted in the vicinity of the urethane bond, making it difficult for the urethane bond to associate with each other between molecules. With no advantage.

When an OH group branched at the terminal of the molecule is further contained, the OH group has a higher mobility and is more easily adsorbed to a magnetic substance than an OH group other than the terminal, so that it has an effect of further improving dispersibility. Conceivable. In addition, the reactivity with a generally used isocyanate-based curing agent is also improved, so that higher durability is obtained.

Hereinafter, examples of the present invention will be shown, and the present invention will be described in more detail.

[0077]

(Preparation of polyurethane resin)

(Synthesis of Polyurethane Resin A) In a vessel equipped with a reflux condenser and a stirrer and previously purged with nitrogen, HBpA as a diol of the formula 1 and BpA-PPO700 as a diol of the formula 2
And DEIS and other diols (PCL400
And / or PPG 400) in a molar ratio as shown in Table 1 and a ratio of cyclohexanone and dimethylacetamide of 50: 5.
0 by weight in a mixed solvent containing
Dissolved at ° C. As a catalyst, 60 ppm may be added to the total amount of raw materials using di-n-dibutyltin dilaurate.

Next, MDI, which is a diisocyanate compound shown in Table 1, was added and reacted by heating at 90 ° C. for 6 hours.
Mw45 to which 8 × 10 ⁻⁵ mol / g of SO ₃ Na group is introduced
000 to obtain a polyurethane resin A having a Mn of 25,000. (Synthesis of Polyurethane Resins B to I) Polyurethane resins B to I were synthesized according to polyurethane resin A by changing the elements shown in Table 1. (Polyurethane resin J) By changing the elements described in Table 1,
Polyurethane resin J was synthesized. (Polyurethane resin K) In the same manner as described in Example 1 of JP-A-1-267829, a polyol obtained by subjecting bisphenol A to ethylene oxide addition reaction and 4,4-diphenylmethanediisocyanate are used. Polyurethane resin K was synthesized using as a polyisocyanate component.

[0079]

[Table 1]

The polyurethane resins A to I fall within the scope of the present invention, and the polyurethane resins J and K fall outside the scope of the present invention. The abbreviations in the table indicate the following. HBpA: hydrogenated bisphenol A (Rikabinol HB manufactured by Nippon Rika) BpA-PPO700: polypropylene oxide adduct of bisphenol A (molecular weight 700) PCL400: polycaprolactone polyol (molecular weight 40)
0) PPG400: polypropylene glycol (molecular weight 400) DEIS: ethylene oxide adduct of sulfoisophthalic acid (DEIS manufactured by Taoka Chemical) MDI: 4,4-diphenylmethane didiisocyanate TDI: tolylene diisocyanate coating solution formulation [single layer magnetic solution formulation or upper layer magnetism liquid formulations a] ferromagnetic metal powder (Fe-Co alloy) 100 parts Co content: 20 wt%, Al: 8 wt%, Y: 4 _{wt% Hc: 2300Oe, σ S:} 140emu / g, S BET: 52m ² / g, major axis length: 0.1 μm, crystallite size: 160 °, pH: 9 aromatic organic acid compound (described in Tables 2 and 3) Polyurethane resin (described in Tables 1 to 8) 8 parts Vinyl chloride resin (Nippon Zeon) : MR110) 10 parts Carbon black (average particle diameter: 80 nm) 1 part Alumina (average particle diameter: 0.2 μm) ) 0.5 parts Butyl stearate 1.2 parts 5 parts stearate Polyisocyanate 6 parts Nippon Polyurethane Coronate L Methyl ethyl ketone 120 parts Cyclohexanone 120 parts [lower nonmagnetic liquid formulations a] nonmagnetic powder TiO ₂ 100 parts Average particle diameter: 35 nm, S _BET : 40 m ² / g, surface treatment with Al, TiO ₂ content: 90% or more, pH: 7.5 Aromatic organic acid compound (Table 3) Polyurethane resin (Table 1, 3) 8 Parts Vinyl chloride resin (Nippon Zeon: MR110) 10 parts Carbon black (average particle diameter: 20 nm) 15 parts Alumina (average particle diameter: 0.2 μm) 10 parts Stearic acid 0.5 part Butyl stearate 1.2 parts Polyisocyanate 6 parts Nippon Polyurethane Coronate L methyl ethyl ketone 120 parts Cyclohexanone 1 0 parts [lower magnetic liquid formulation b] Co-modified magnetite 100 parts Co content: 3 wt%, Al: 1.5 wt%, Si: 0.8 _{wt% Hc: 850Oe, σ S:} 80emu / g, S BET : 35 m ² / g, major axis length: 0.25 μm, crystallite size: 230 °, pH: 8.4 aromatic organic acid compound (benzoic acid) 4.5 parts Polyurethane resin A (described in Tables 1 and 3) 8 parts Vinyl chloride resin (Nippon Zeon: MR110) 10 parts Carbon black (average particle diameter: 20 nm) 15 parts Alumina (average particle diameter: 0.2 μm) 10 parts Stearic acid 0.5 part Butyl stearate 1.2 parts Polyisocyanate 6 Part Coronate L methyl ethyl ketone made by Nippon Polyurethane 120 parts Cyclohexanone 120 parts [Lower layer soft magnetic liquid formulation c] Granular magnetite 100 parts Average particle diameter: ^{_{0nm, S BET: 20m 2 /}} g, oil absorption (DBPA): 20cc / 100g, pH: 9.0 aromatic organic acid compound (benzenesulfonic acid Na) 4.5 parts Polyurethane resin A (Tables 1, 3, wherein) 8 parts Vinyl chloride resin (ZEON: MR110) 10 parts Carbon black (average particle diameter: 20 nm) 15 parts Alumina (average particle diameter: 0.2 μm) 10 parts Stearic acid 0.5 part Butyl stearate 1.2 parts Poly Isocyanate 6 parts Nippon Polyurethane Coronate L methyl ethyl ketone 120 parts Cyclohexanone 120 parts

Examples 1 to 8 and Comparative Examples 1 to 7 The components of the single-layer magnetic liquid formulation or the upper layer magnetic solution formulation a were kneaded and dispersed, and then filtered using a filter having an average pore diameter of 1 μm to obtain a magnetic paint. Prepared. The obtained magnetic paint is 10 μm thick so that the thickness after drying becomes 2.5 μm.
m of polyethylene naphthalate support was coated using a reverse roll. The magnetic coating is applied to the non-magnetic support coated with the magnetic coating with a magnetic field of 3000 gauss in a state where the magnetic coating is not dried, and after drying, the metal roll-metal roll-metal roll-metal roll-metal roll-metal A calendering process using a roll-metal roll combination is performed at a speed of 100 m / min, a linear pressure of 300 Kg / cm, and a temperature of 90.
C.), and slit to a width of 8 mm.

Examples 9 to 13 and Comparative Examples 8 to 10 After kneading and dispersing the components of the lower layer non-magnetic liquid formulation a, the lower layer magnetic solution formulation b and the lower layer soft magnetic solution formulation c, a filter having an average pore diameter of 1 μm was prepared. The solution was then filtered to prepare each coating solution. Polyethylene naphthalate having a thickness of 10 μm such that the thickness of the obtained coating solution after drying is 2.0 μm for formulation a, 2.5 μm for formulation b, and 2.0 μm for formulation c. The surface of the support is coated using a reverse roll, and immediately thereafter, a magnetic coating liquid formulation a is applied thereon. When the thickness after drying is lower layer formulation a, 0.2 μm, lower layer formulation b (Example 10) Is 0.5 μm, lower layer formulation c
In the case of (Example 11), simultaneous multi-layer coating was performed so that the thickness became 0.2 μm. Thereafter, the same treatment as in Example 1 was performed to obtain each sample.

The characteristics of the magnetic recording media of Examples and Comparative Examples obtained as described above were measured by the following measuring methods, and the results are shown in Tables 2 and 3. [Measurement method] 1. Ra: Digital optical profilometer (WY
Cutoff 0.2 by optical interference method using KO
The center line average roughness was set to Ra under the condition of 5 mm. 2. Reproduction output (λ = 0.5μm): VTR on sample tape
A signal of 7 MHz was recorded and reproduced using (Sony: TR705). 7 recorded on the reference tape of Comparative Example 1
The relative reproduction output of the tape when the reproduction output at MHz was 0 dB was measured. 3. Output change after 1000 passes (repeated running property): 6
Using a VTR of 2 for a 0 minute length tape, 40 ° C and 80% RH
The vehicle was run 1000 times continuously under the environment and the output of the first time was set to 0 dB, and the output reduction was measured.

[0084]

[Table 2]

[0085]

[Table 3]

Table 2 shows an example of a magnetic recording medium having a single-layer structure. As shown in Table 2, the polyurethane resin A of the present invention was used.
Examples containing I to I and the aromatic organic acid compound are Comparative Examples 1 to 6 containing the polyurethane resin of the present invention but not containing the aromatic organic acid compound, and both the polyurethane resin of the present invention and the aromatic organic acid compound. It can be seen that the reproduction output and the running durability are superior to Comparative Example 7 which does not include the same.

Table 3 shows examples of the multilayer structure. From Table 3, it can be seen that Examples 9 to 12 in which the polyurethane resin and the aromatic organic acid compound of the present invention are contained in the lower layer and the upper layer are the polyurethane resin of the present invention. In both layers, but in Comparative Examples 8 to 9 in which both layers do not contain an aromatic organic acid compound and in Comparative Example 10 in which both layers use a polyurethane resin other than the polyurethane resin of the present invention. It turns out that it is excellent. It can be seen that Example 13 in which only the upper layer contained the polyurethane resin of the present invention and the aromatic organic acid compound also had better performance than the Comparative Example. Examples 14 to 20, Comparative Examples 10 to 15 [Single-layer magnetic liquid formulation] Ferromagnetic metal powder (Fe-Co alloy) 100 parts Co content: 20% by weight, Al: 8% by weight, Y: 4% by weight Hc : 2300 Oe, σ _S : 140 emu / g, S _BET : 52 m ² / g, major axis length: 0.1 μm, crystallite size: 160 °, pH: 9 phosphorus compound (Table 4) Polyurethane resin (Tables 1 and 4) 8 parts Vinyl chloride resin (Nippon Zeon: MR110) 10 parts Carbon black (average particle diameter: 80 nm) 1 part Alumina (average particle diameter: 0.2 μm) 5 parts Stearic acid 0.5 part Butyl stearate 1.2 parts Polyisocyanate 6 parts Nippon Polyurethane Coronate L methyl ethyl ketone 120 parts Cyclohexanone 120 parts 8 mm video tape using the above-mentioned magnetic liquid formulation as in Example 1. A sample of the loop was prepared. Examples 21 to 22, Comparative Examples 16 to 17 [Prescription of Upper Layer Magnetic Liquid] Ferromagnetic metal powder (Fe-Co alloy) 100 parts Co content: 20% by weight, Al: 8% by weight, Y: 4% by weight Hc: 2300 Oe, σ _S : 140 emu / g, S _BET : 52 m ² / g, long axis length: 0.1 μm, crystallite size: 160 °, pH: 9 phosphorus compound (Table 5) Polyurethane resin (Table 1 and 5) 8 parts Vinyl chloride resin (ZEON: MR110) 10 parts Carbon black (average particle diameter: 80 nm) 1 part Alumina (average particle diameter: 0.2 μm) 5 parts Stearic acid 0.5 part Butyl stearate 1.2 parts Poly Isocyanate 6 parts Nippon Polyurethane Coronate L methyl ethyl ketone 120 parts Cyclohexanone 120 parts Non-magnetic powder formulation Non-magnetic powder TiO ₂ 100 parts Average particle Diameter: 35 nm, S _BET : 40 m ² / g, surface treatment with Al, TiO ₂ content: 90% or more, pH: 7.5 Phosphorus compound (Table 5) 8 parts of polyurethane resin (Table 1, 5) Vinyl chloride resin (Nippon Zeon: MR110) 10 parts Carbon black (average particle diameter: 20 nm) 15 parts Alumina (average particle diameter: 0.2 μm) 10 parts Stearic acid 0.5 part Butyl stearate 1.2 parts Polyisocyanate 6 Part Nippon Polyurethane Coronate L methyl ethyl ketone 120 parts Cyclohexanone 120 parts After kneading and dispersing each component of the lower layer non-magnetic liquid formulation, 1 μm
Each coating solution was prepared by filtration using a filter having an average pore size of. The thickness of the obtained coating solution after drying is 2.0
μm, applied to the surface of a 10 μm thick polyethylene naphthalate support using a reverse roll,
Immediately thereafter, a magnetic coating liquid formulation was simultaneously coated thereon so that the thickness after drying was 0.2 μm. Thereafter, the same treatment as in Example 1 was performed to obtain each sample.

Examples 15 to 2 obtained as described above
The characteristics of the magnetic recording media of Comparative Example 3 and Comparative Examples 10 to 17 were measured by the same measuring method as described above, and the results are shown in Tables 4 and 5. The coefficient of friction μ was measured by the following method. Load: 20g / 8mm, speed: 14mm / se
c, member: SUS420J, Ra 0.08 μm, wrap angle: 180 °, number of passes: 1 → 100 The maximum value was adopted as the μ value, environment: 40 ° C., 80%

[0089]

[Table 4]

[0090]

[Table 5]

Table 4 shows an example of a magnetic recording medium having a single-layer structure. As shown in Table 4, the magnetic recording medium contains the polyurethane resin and the phosphorus compound of the present invention and has a P / Fe ratio within the range of the present invention. Are Comparative Examples 11 to 12 containing the polyurethane resin of the present invention but not containing a phosphorus compound (Comparative Example 10) or not satisfying the P / Fe ratio (Comparative Example 11 is smaller than the lower limit, Comparative Example 1
2 is larger than the upper limit), Comparative Example 13 not containing both the polyurethane resin of the present invention and the phosphorus compound, the phosphorus compound and P /
It can be seen that the Fe ratio is satisfied, but the reproduction output and running durability are superior to Comparative Examples 14 and 15 using polyurethane resins other than the present invention.

Table 5 shows an example of the multilayer structure. From Table 5, it can be seen that Example 21 in which the polyurethane resin and the phosphorus compound of the present invention are contained in at least the upper layer and the P / Fe ratio falls within the range of the present invention. And 22 (provided that the polyurethane resin in the lower layer of Example 22 is other than the present invention) includes Comparative Example 16 in which the polyurethane resin of the present invention is contained in both layers but does not contain a phosphorus compound in both layers, and polyurethane resin of the present invention in both layers. Although the P / Fe ratio exceeds the upper limit of the present invention and the lower layer does not contain the phosphorus compound, the μ value is lower than that of Comparative Example 17 in which the phosphorus compound is contained in the upper layer and the upper layer contains a large amount of the phosphorus compound. It turns out that it is excellent.

[0093]

The magnetic recording medium containing the polyurethane resin of the present invention and the aromatic organic acid compound, and the magnetic recording containing the polyurethane resin and the phosphorus compound of the present invention in the magnetic layer so that the P / Fe ratio becomes a predetermined value. As the medium, the dispersibility of ferromagnetic powder and other powders is further improved, the surface properties are further improved, the electromagnetic conversion characteristics are improved, and the coating film strength is high, and the running durability especially in high temperature environments Is improved.

Claims (6)

[Claims] 1. A magnetic recording medium having a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, or an inorganic powder and a binder between the magnetic layer and the non-magnetic support. In a magnetic recording medium provided with a lower coating layer including: a binder in the magnetic layer or at least one binder of the binder in the lower coating layer is a polyurethane resin containing a cyclic structure and an ether group, A magnetic recording medium characterized in that an aromatic organic acid compound is contained in the same layer as the polyurethane resin in the magnetic layer and / or the lower coating layer. 2. The magnetic recording medium according to claim 1, wherein the aromatic organic acid compound is an organic acid having a pKa of 3 or less or a salt thereof. 3. A magnetic recording medium having a magnetic layer formed by dispersing a ferromagnetic powder containing iron as a main component in a binder on a nonmagnetic support, or between the magnetic layer and the nonmagnetic support. Further, in a magnetic recording medium provided with a lower coating layer containing an inorganic powder and a binder, at least the polyurethane resin and the phosphorus compound according to claim 1 are contained in the magnetic layer, and the magnetic layer is measured by X-ray fluorescence. Strength ratio of P to 0.2 to
2.0. 4. The polyurethane resin contains 3 to 3 molecules per molecule.
4. It has 20 OH groups.
The magnetic recording medium according to any one of the preceding claims. 5. The polyurethane resin has —SO _{3 in its} molecule.
_{M, -OSO 3 M, -COOM,} -PO 3 MM ', - O
_{PO 3 MM ', - NRR'} , - N + RR'R "COO -
(Where M and M ′ are each independently a hydrogen atom, an alkali metal, an alkaline earth metal or an ammonium ion, and R, R ′ and R ″ each independently have 1 to 1 carbon atoms.
And at least one polar group selected from the group consisting of 2 alkyl groups).
Item 7. The magnetic recording medium according to Item 1. 6. A cyclic structure, wherein at least one of the binder in the magnetic layer or the binder in the lower coating layer is made of a polyurethane resin which is a reaction product mainly composed of a diol and an organic diisocyanate. 17 to 40% by weight of a short-chain diol unit having
A binder containing a long-chain diol unit containing 1.0 to 5.0 mmol / g of an ether group with respect to the entire polyurethane resin and containing 10 to 50% by weight in the polyurethane resin. The magnetic recording medium according to any one of claims 1 to 5.