JP2732463B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium used for, for example, a video tape, an audio tape, and the like. More specifically, the present invention relates to a magnetic recording medium having a good dispersion state of a ferromagnetic powder, The present invention relates to a magnetic recording medium having excellent conversion characteristics and running durability.

[Prior art and its problems] A magnetic recording medium basically includes a nonmagnetic support and a magnetic layer containing ferromagnetic powder, and is provided by providing a magnetic layer on a nonmagnetic material. .

Generally, the magnetic layer is formed by dispersing ferromagnetic powder in a binder.

In recent years, for example, a magnetic recording medium having such a configuration, particularly a magnetic recording medium for a VTR, has emerged, for example, a width of 8 mm, which is narrower than the conventional 1/2 inch width standard, and is becoming widespread. Under these circumstances, there is a strong demand for high-density recording, and a magnetic recording medium with higher performance, that is, a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability, is desired.

Therefore, for the purpose of improving the electromagnetic conversion characteristics of the magnetic recording medium, a needle-shaped cobalt-containing iron oxide powder in which a cobalt-containing iron oxide layer is formed on the surface of γ-Fe ₂ O ₃ as a ferromagnetic powder is used. It has been used.

However, the needle-shaped cobalt-containing iron oxide powder has a high surface activity, so that when a magnetic layer coating film is formed, for example, a binder or a dispersant having a functional group is adsorbed, and as a result, There is a disadvantage that the lubricant cannot be adsorbed on the surface of the cobalt-containing iron oxide powder.

Therefore, in a magnetic recording medium using a cobalt-containing iron oxide powder that is not subjected to a surface treatment, an unadsorbed lubricant is present on the surface of the magnetic layer, and the dispersion state of the cobalt-containing iron oxide powder is poor. At the same time, during the curing step of the magnetic recording medium, the lubricant that has not been adsorbed is transferred to the support, which causes an increase in the friction coefficient of the magnetic layer, thereby deteriorating the electromagnetic conversion characteristics and running durability. There is.

Therefore, for the purpose of solving this problem, a surface treatment is applied to the cobalt-containing iron oxide powder to suppress the dispersant and the binder having a functional group from blocking the adsorption site at an early stage, and the cobalt-containing iron oxide powder is used. A method has been considered in which the adsorption of the lubricant on the surface is promoted to improve the state of dispersion of the cobalt-containing iron oxide powder in the magnetic layer and to prevent an increase in the coefficient of friction in the curing step.

For example, a method of depositing a silicon compound on the surface of a cobalt-containing iron oxide powder (see Japanese Patent Application Laid-Open No. 55-83208).
Is a needle-like γ-Fe ₂ O ₃ powder and an iron oxide magnetic powder in an intermediate oxidation state between γ-Fe ₂ O ₃ and Fe ₃ O ₄ obtained by partially reducing the powder in a reducing gas. And a metal salt containing a cobalt salt are dispersed in an aqueous alkaline solution to form a cobalt-containing iron oxide layer on the surface of the iron oxide magnetic powder, and then a silicon compound is attached to the surface of the cobalt-containing iron oxide powder. This is a method for producing ferromagnetic powder.

However, in this ferromagnetic powder, although the coercive force is improved to some extent, as shown in FIG. 1, for example, when the content of the silicon compound exceeds 0.3% by weight, the balance of magnetic properties is lost, and A new problem arises in that the characteristics are deteriorated.

On the other hand, a method of depositing a zinc compound on the surface of a cobalt-containing iron oxide powder (see Japanese Patent Application Laid-Open No. 59-159502) is to coat a cobalt compound or a cobalt compound and a ferrous compound on the surface of a magnetic iron oxide powder. This is a method for producing a ferromagnetic powder having an improved coercive force and a stabilized magnetic property by further applying a zinc compound after the application.

However, even in the ferromagnetic powder produced by this method, when the content of zinc exceeds 0.5% by weight, there is a problem that the balance of magnetic properties is lost and the magnetic properties are deteriorated.

That is, it cannot be said that a conventional magnetic recording medium containing cobalt-containing iron oxide powder has sufficient magnetic property stability and running durability.

 The present invention has been made based on the above circumstances.

An object of the present invention is to provide a good dispersion state of ferromagnetic iron oxide powder in a magnetic layer, an excellent balance of magnetic properties such as S / N ratio and squareness ratio, and no increase in friction coefficient in a curing step. Accordingly, it is an object of the present invention to provide a magnetic recording medium which does not cause deterioration of magnetic characteristics, has excellent electromagnetic conversion characteristics, and has improved running durability.

[Means for Solving the Problems] In order to solve the problems, the inventors of the present invention have conducted intensive studies, and as a result, have found that they contain iron oxide powder, silicon and zinc, and have a surface roughness within a specific range. The magnetic recording medium formed with a magnetic layer having a good magnetic property has a good dispersion state of the ferromagnetic iron oxide powder, is excellent in the balance of the magnetic properties, and has no increase in the coefficient of friction in the curing step, and has a high electromagnetic conversion property. The inventors have found that the present invention has excellent running durability and have arrived at the present invention.

That is, the configuration of the present invention provides a magnetic recording medium in which a magnetic layer containing a ferromagnetic iron oxide powder and a binder is provided on a nonmagnetic support, wherein the ferromagnetic iron oxide powder contains silicon and zinc. and, wherein a content of the silicon in the ferromagnetic iron oxide powder is 0.05 to 0.30 wt%, the content of said zinc is from 0.001 to 0.50 wt%, it said binder is -SO ₃ M, -COOM, and —PO (OM ¹ ) (OM ² ) [where M represents a hydrogen atom or an alkali metal, and M ¹ and M ² represent any of a hydrogen atom, an alkali metal and a hydrocarbon residue. Further, M ¹ and M ² may be different even in the same. And at least one hydrophilic polar group selected from the group consisting of
A magnetic recording medium characterized by being in the range of 8 to 0.015 μm.

The nonmagnetic support and the magnetic layer constituting the magnetic recording medium of the present invention will be described below.

(Non-magnetic support) Materials for forming the non-magnetic support include, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate. A plastic such as polycarbonate. Further, metals such as Cu, Al, and Zn, and various ceramics such as glass, so-called new ceramics (for example, boron nitride, silicon carbide, and the like) can also be used.

The form of the non-magnetic support is not particularly limited, and may be any of a tape, a sheet, a card, a disk, a drum, and the like.Depending on the form, and by selecting various materials as necessary, Can be used.

The thickness of the nonmagnetic support is usually in the range of 3 to 100 μm, preferably in the range of 5 to 50 μm in the case of a tape or sheet. In the case of a disk or a card, it is usually in the range of 30 to 100 μm. Further, in the case of a drum shape, a shape corresponding to a recorder to be used, such as a cylindrical shape, can be adopted.

A back coat layer may be provided on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the runnability of the magnetic recording medium, preventing charging and preventing transfer, and the like.

Further, on the surface of the non-magnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the non-magnetic support, and the like,
An intermediate layer (for example, an adhesive layer) may be provided.

(Magnetic Layer) The magnetic layer is provided on the non-magnetic support.

The magnetic layer is a layer formed by dispersing the ferromagnetic iron oxide powder in a binder.

The ferromagnetic iron oxide powder contains cobalt-containing iron oxide.

Examples of the cobalt-containing iron oxide include Co-containing γ
-Fe ₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, Co-containing FeO _x (4/3 <x
<3/2) Powder and the like.

The specific surface area of the ferromagnetic iron oxide powder by the BET method is 20 m ² /
g or more, preferably 20 to 80 m ² / g. This specific surface area is 2
If it is less than 0 m ² / g, the S / N ratio of the magnetic recording medium may decrease.

One of the important points in the present invention is that the ferromagnetic iron oxide powder contains silicon and zinc.

The silicon and zinc are attached to the surface of the ferromagnetic iron oxide powder having a needle-like shape and high surface activity to increase the amount of lubricant adsorbed on the ferromagnetic iron oxide powder, and the ferromagnetic oxidation in the magnetic layer is performed. It has the effect of improving the dispersion state of the iron powder and preventing the friction coefficient of the magnetic layer from increasing during the curing step of the magnetic recording medium.

The content of silicon in the ferromagnetic iron oxide powder is usually in the range of 0.05 to 0.30% by weight, and preferably in the range of 0.05 to 0.20% by weight. This content is 0.05
When the content is less than 10% by weight, the surface activity of the ferromagnetic iron oxide powder cannot be reduced, and the binder or dispersant having a functional group on the ferromagnetic iron oxide powder is prevented from being excessively adsorbed. May not be possible. On the other hand, if it exceeds 0.30% by weight, the effect corresponding to the increase in the content may not be obtained, and the magnetic properties may be deteriorated.

The silicon can be attached to the ferromagnetic iron oxide powder by, for example, adding a soluble silicon compound to a dispersion obtained by dispersing the ferromagnetic iron oxide powder in an aqueous alkaline solution.

As the silicon compound, for example, orthosilicate (H ₄ SiO _4), metasilicate (H ₂ SiO _3), meta disilicate (H ₂
Si ₂ O ₅ ), metatrisilicic acid (H ₄ Si ₃ O ₈ ), metatetrasilicic acid (H ₆
Silicic acids such as Si ₄ O ₁₁ ); silicon monoxide, silicon dioxide; sodium orthosilicate (Na ₄ SiO ₄ ), sodium metasilicate (Na ₂ SiO ₃ ), potassium metasilicate (K ₂ SiO ₃ ), calcium orthosilicate (Ca ₄ SiO ₄ ), calcium metasilicate (Ca ₂ SiO ₃ ), barium metasilicate (Ba ₂ SiO ₃ ), and cobalt silicate metal salts such as cobalt metasilicate (Co ₂ SiO ₃ ).

One of these silicon compounds may be used alone, or two or more thereof may be used in combination.

The content of the zinc in the ferromagnetic iron oxide powder,
Usually in the range of 0.001 to 0.50% by weight, preferably
It is in the range of 0.01-0.50% by weight. This content rate is 0.001
When the content is less than 10% by weight, the surface activity of the ferromagnetic iron oxide powder cannot be reduced, and the binder or dispersant having a functional group on the ferromagnetic iron oxide powder is prevented from being excessively adsorbed. May not be possible. On the other hand, if the content exceeds 0.50% by weight, the effect corresponding to the increase in the content may not be obtained, and the magnetic properties may be deteriorated.

To adhere the zinc to the ferromagnetic iron oxide powder,
For example, it can be carried out by a method of adding a zinc compound to a dispersion in the same manner as in the method of attaching silicon to the ferromagnetic iron oxide powder described above.

Examples of the zinc compound include zinc powder, zinc chloride (ZnCl ₂ ), zinc bromide (ZnBr ₂ ), zinc iodide (ZnI ₂ ),
Examples include zinc nitrate and zinc chlorate.

In the present invention, when silicon and zinc are used in combination, the content of silicon and zinc in the ferromagnetic iron oxide powder is usually in the range of 0.10 to 0.80% by weight, preferably 0.12 to 0.60% by weight. %. If the content is less than 0.10% by weight, the surface activity of the ferromagnetic iron oxide powder cannot be reduced, and the binder or dispersant having a functional group is excessively adsorbed on the ferromagnetic iron oxide powder. May not be suppressed. On the other hand, 0.
If the content exceeds 80% by weight, the effect corresponding to the increase in the content may not be obtained, and the magnetic properties may be deteriorated.

When the silicon (Si) and zinc (Zn) are used in combination,
The ratio of silicon (Si) and zinc (Zn) is (Si) :( Z
In the ratio of n), it is usually in the range of 30: 1 to 1:30, preferably in the range of 20: 1 to 1:10.

The binder (binder) has an average molecular weight of about
Resins in the range of 10,000 to 200,000 can be used.

Specifically, for example, urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, and cellulose derivative (Examples: cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyester resin, various synthetic rubber binders, phenolic resin, epoxy resin,
Urea resin, melamine resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol and high molecular weight diol compound and include a mixture thereof, these resins, -SO ₃ M, -COOM, and ^{-PO (OM 1) (OM 2} ) [ However, M represents a hydrogen atom or an alkali metal, M ¹ and M ² represents any of a hydrogen atom, an alkali metal and a hydrocarbon residue. Further, M ¹ and M ² may be differ be the same. Is not particularly limited as long as it contains at least one hydrophilic polar group selected from the group consisting of:

In this invention, the durability of the magnetic layer can be improved by adding a polyisocyanate-based curing agent together with the resin to the binder.

Examples of the polyisocyanate-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate; Coronate L (trade name; manufactured by Nippon Polyurethane Industry Co., Ltd.); ), Or those which have been conventionally used as a curing agent, such as trifunctional isocyanates such as urethane prepolymers containing isocyanate groups at both ends, and those which are irisocyanates which can be used as curing agents. can do.

The amount of the curing agent used is usually 5 to 80 parts by weight of the total binder amount.

The mixing ratio of the ferromagnetic iron oxide powder and the binder (including the curing agent when using the curing agent) in the magnetic layer is usually based on 100 parts by weight of the ferromagnetic iron oxide powder. The binder is used in an amount of 1 to 200 parts by weight, preferably 1 to 50 parts by weight. If the compounding amount of the binder is too large, the resulting compounding amount of the ferromagnetic iron oxide powder may decrease and the recording density of the magnetic recording medium may decrease.If the amount is too small, the strength of the magnetic layer decreases. The running durability of the magnetic recording medium may decrease.

In the magnetic recording medium of the present invention, the magnetic layer contains, in addition to the ferromagnetic iron oxide powder, silicon and zinc, a binder and the curing agent, a lubricant, an abrasive, and an antistatic agent. Is also good.

Fatty acids and fatty acid esters can be suitably used as the lubricant.

By using the fatty acid and the fatty acid ester in combination, while exhibiting the characteristics of both, cancel the defects that occur when used alone, and improve the lubricating effect, and improve the static image durability, running stability, S / N ratio and the like can be increased. In this case, the amount of the fatty acid to be added is generally 0.2 to 10 parts by weight, preferably 0.3 to 8.0 parts by weight, based on 100 parts by weight of the ferromagnetic iron oxide powder. If the amount of the fatty acid added is less than 0.2 parts by weight, the dispersibility of the ferromagnetic iron oxide powder may be reduced, and the running property of the medium may be reduced. On the other hand, if it exceeds 10 parts by weight, the fatty acid may exude or the output may be reduced. The amount of the fatty acid ester is usually 0.1 to 10 parts by weight, preferably 0.2 to 8.5 parts by weight, based on 100 parts by weight of the ferromagnetic iron oxide powder. If the amount of the fatty acid ester is less than 0.1 part by weight, the running property may not be sufficiently improved. On the other hand, if it exceeds 10 parts by weight, the fatty acid ester may exude or the output may be reduced.

In order to achieve the above-mentioned effects more favorably, the weight ratio between the fatty acid and the fatty acid ester is preferably in the range of (fatty acid) / (fatty acid ester) = 10/90 to 90/10. Since the fatty acid can exert a dispersing effect, it is possible to reduce the amount of another low-molecular-weight dispersant used by using the fatty acid, and to improve the Young's modulus of the magnetic recording medium by that amount. It is presumed.

The fatty acid may be monobasic or dibasic.

The fatty acids are preferably those having 6 to 30 carbon atoms, particularly those having 12 to 22 carbon atoms. Specifically, for example, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid , Maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like.

Examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl maleate, butyl stearate, butyl palmitate, butyl myristate, octyl palmitate, amyl palmitate, isobutyl oleate, stearyl stearate, lauryl oleate Octyl oleate, isobutyl oleate, 2-ethylhexyl stearate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2-ethyl hexalate, dioleyl adipate, diethyl adipate, Examples include diisobutyl adipate and diisodecyl adipate.

In the present invention, in addition to the fatty acids and fatty acid esters, other lubricants such as silicone oil (may be modified with carboxylic acid or ester) may be used.
Graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, and the like can be used.

These may be used alone or in combination of two or more.

The amount of the lubricant to be used is generally 0.05 to 10 parts by weight based on 100 parts by weight of the ferromagnetic iron oxide powder.

Examples of the abrasive include aluminum oxide, titanium oxide (TiO, TiO ₂ ), α-iron oxide, and silicon oxide (Si
O, SiO ₂ ), inorganic powders such as silicon carbide, zinc oxide, cerium oxide, magnesium oxide, silicon nitride, zirconium oxide, chromium oxide and boron carbide, and organic powders such as benzoguanamine resin powder, melamine resin powder and phthalocyanine compound powder. No.

The average particle size of the abrasive is usually in the range of 0.01 to 1.0 μm.

The amount of these abrasives is usually in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic iron oxide powder.

Examples of the antistatic agent include conductive powders such as graphite, carbon black, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers; natural surfactants such as saponin; Nonionic surfactants such as alkylene oxides, glycerins and glycidols; cationic surfactants such as higher alkylamines, quaternary pyridines, other heterocycles, phosphoniums and sulfoniums: carboxylic acids, sulfonic acids, phosphoric acids Anionic surfactants containing an acidic group such as a sulfuric acid ester group or a phosphoric acid ester group: amphoteric surfactants such as amino acids, aluminum sulfonic acids, and sulfuric acid and phosphoric acid esters of amino alcohol;

These may be used alone or in combination of two or more.

The compounding amount of the antistatic agent is the ferromagnetic iron oxide powder 10
It is usually 0.5 to 20 parts by weight with respect to 0 parts by weight.

The lubricant, the antistatic agent, the dispersant described below, and the like do not have only a single function. For example, one compound may function as a lubricant and an antistatic agent.

Therefore, the above-mentioned classification in the present invention shows the main effects, and the effects of the classified compounds are not limited by the effects shown in the classification.

One of the important points in the present invention is that the surface roughness of the magnetic layer is in the range of 0.008 to 0.015 μm.

If the surface roughness of the magnetic layer is less than 0.008 μm, the coefficient of friction of the magnetic recording medium of the present invention becomes too large, and the magnetic recording medium may stick to the magnetic head. On the other hand, if it exceeds 0.015 μm, the electromagnetic conversion characteristics may be deteriorated.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.

(Manufacturing method) In the magnetic recording medium of the present invention, after attaching silicon and zinc to the ferromagnetic iron oxide powder by, for example, the above-described method, the magnetic layer forming components such as the binder are kneaded and dispersed in a solvent. It can be produced by preparing a magnetic paint, applying the obtained magnetic paint on the nonmagnetic support, and drying.

Examples of the solvent used for kneading and dispersing the components for forming the magnetic layer include acetone, methyl ethyl ketone (MEK),
Ketones such as methyl isobutyl ketone (MIBK) and cyclohexanone: alcohols such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate;
Ethers such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride, ethylene chloride,
Halogenated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene can be used.

In kneading the composition of the magnetic paint components, the ferromagnetic iron oxide powder to which the silicon and zinc are adhered and the other magnetic paint components are simultaneously or individually put into a kneader. For example, first, the magnetic powder is added to a solution containing a dispersant, kneaded for a predetermined time, then the remaining components are added, and further kneading is continued to obtain a magnetic paint.

In kneading and dispersing, various kneaders can be used. Examples of the kneading machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper kneader, a high-speed mixer, a homogenizer, and an ultrasonic wave. Dispersing machines and the like are mentioned.

In addition, a dispersant can be used for kneading and dispersing the ferromagnetic iron oxide powder obtained by adhering the silicon and zinc.

Examples of the dispersant include lecithin, phosphate ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinate ester, known surfactants and the like, salts thereof, and negative organic groups ( For example, -COOH, -P
O ₃ H) salts of polymer dispersants.

These may be used alone or in combination of two or more.

The amount of the dispersant to be added is generally 0.1 to 10 parts by weight based on 100 parts by weight of the ferromagnetic iron oxide powder.

The coating solution of the magnetic layer forming component thus prepared is
It is coated on a non-magnetic support by a known method.

Coating methods that can be used in the present invention include, for example, gravure roll coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calender coating, skies coating, kiss coating and fantin coating. And the like.

The thickness of the magnetic layer applied in this way is usually 0.5 to 20 μm in dry thickness.

After the components for forming the magnetic layer are applied in this way, if necessary, a magnetic field orientation treatment (for example, 500 to 3000 Gauss) is performed in an undried state, and a surface smoothing treatment is usually performed using a super calender roll or the like.

Next, by cutting into a desired shape, a magnetic recording medium can be obtained.

The magnetic recording medium of the present invention can be used as a magnetic tape such as a video tape or an audio tape by cutting into a long shape, or as a floppy disk or the like by cutting into a disk shape. In addition, like a normal magnetic recording medium,
A form such as a cylindrical shape can also be used.

[Examples] Next, examples of the present invention and comparative examples will be shown, and the present invention will be described more specifically. In Examples and Comparative Examples described below, “parts” means “parts by weight”.
Shall be expressed.

(Example 1) A magnetic layer composition having the following composition was mixed and dispersed using a sand mill for 3 hours to form a dispersion, and then 5 parts of a polyisocyanate compound was added to the dispersion and mixed. A paint was prepared.

Co-containing γ-Fe ₂ O ₃ powder 100 parts α-Al ₂ O ₃ 7 parts Carbon black 10 parts Potassium sulfonate-containing vinyl chloride copolymer 20 parts Thermoplastic polyurethane resin 10 parts Fatty acid 3 parts Fatty acid ester 1 part Polyisocyanate 10 Parts: methyl ethyl ketone: 150 parts: toluene: 150 parts Table 1 shows the content of silicon and zinc in the Co-containing γ-Fe ₂ O ₃ powder.

The obtained magnetic paint was applied on a 15 μm-thick polyethylene terephthalate film so as to have a dry thickness of 4 μm.

Next, after removing the solvent under heating, a supercalender was used to perform a surface smoothing treatment under the conditions of a temperature of 60 to 80 ° C. and a pressure of 100 to 300 kg / cm, and cut to a predetermined width to produce a video tape. .

 Various characteristics of this video tape were measured.

 The results are shown in Table 1.

 In addition, each characteristic was measured as follows.

Surface roughness of magnetic layer; roughness analyzer [Kosaka Laboratory; “SE”
−3FK ”]. (Cutoff value 0.2
5mm) Coefficient of friction before and after the curing process; curing process (temperature 70 ° C, 12
Before and after (time), the measurement was performed using a MSC tape running tester (manufactured by Yokohama System Co., Ltd.) under the conditions of a tape speed of 3.3 cm / sec and a tape tension of 20 g.

Squareness ratio: The ratio (Bm / Br) of the residual magnetic flux density (Br) to the saturation magnetic flux density (Bm) was measured using a VSM (measuring magnetic field 10KOe).

RF output: The output during reproduction of a 100% white signal was determined by comparing the tape of Example 2 with the tape of Example 2.

Lumi S / N; Use a noise meter (manufactured by Shibasoku)
In comparison with the reference tape [manufactured by Konica Corporation], the difference in S / N of the sample at 100% white signal was determined.

Chromer S / N; Using a noise meter (manufactured by Shibasoku Co., Ltd.)
The S / N difference of the sample in the chroma signal was determined.

(Example 2, Comparative Examples 1 to 7) In Example 1, instead of the ferromagnetic iron oxide powder used in Example 1, a ferromagnetic iron oxide powder shown in Table 1 was used to prepare a magnetic paint. A video tape was produced in the same manner as in Example 1 except that a vinyl chloride copolymer containing no potassium sulfonate group was used (Comparative Example 7). Various characteristics of the obtained video tape were measured.

 The results are shown in Table 1.

(Evaluation) As is clear from Table 1, in the magnetic layer of the magnetic recording medium of the present invention, there is no deterioration in magnetic properties and no increase in friction coefficient before and after the curing step. For this reason, in the present invention, since a specific amount of silicon and zinc are adhered to the ferromagnetic iron oxide powder, the surface activity of the ferromagnetic iron oxide powder can be controlled, and the dispersant and the functional group Binders and lubricants are adsorbed at appropriate ratios, resulting in good dispersion of the ferromagnetic iron oxide powder in the magnetic layer and prevention of lubricant outflow during the curing process. It is thought to be. Further, it can be seen that in the magnetic recording medium of the present invention, the surface roughness of the magnetic layer is small, and the running durability, the magnetic characteristics and the electromagnetic conversion characteristics are all improved.

[Effects of the Invention] According to the present invention, (1) since the ferromagnetic iron oxide powder contains silicon and zinc at a specific ratio, the surface activity of the ferromagnetic iron oxide powder which originally has a high surface activity is reduced. (2) As a result, it is possible to prevent the binder or dispersant having a functional group from adsorbing to the ferromagnetic iron oxide powder before the lubricant in the magnetic layer. There is no large amount of unadsorbed adsorbent present on the surface of the magnetic layer as seen in the magnetic recording medium using the treated ferromagnetic iron oxide powder. Since the unadsorbed adsorbent or the like does not transfer to the support, the friction coefficient does not increase before and after the curing step. (4) In addition, the silicon and zinc contained in the ferromagnetic iron oxide powder Special ratio , The surface roughness of the magnetic layer can be reduced, and there is no deterioration of the magnetic properties. (5) The high performance which has various advantages such as excellent electromagnetic conversion properties and running durability. A magnetic recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the silicon content and the squareness ratio in a ferromagnetic iron oxide powder in a conventional magnetic recording medium.

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a nonmagnetic support and a magnetic layer containing a ferromagnetic iron oxide powder and a binder, wherein the ferromagnetic iron oxide powder contains silicon and zinc, The content of silicon in the ferromagnetic iron oxide powder is 0.05 to 0.30% by weight, and the content of zinc is 0.001 to 0.001%.
0.50 percent by weight, said binder is -SO ₃ M, -COOM, and ^{-PO (OM 1) (OM 2} ) [ However, M represents a hydrogen atom or an alkali metal, M ¹ and M ² hydrogen Represents any of atoms, alkali metals and hydrocarbon residues. Also, M ¹ and M ²
May be the same or different. Comprising at least one hydrophilic polar group selected from the group consisting of
A magnetic recording medium, wherein the surface roughness of the magnetic layer is in the range of 0.008 to 0.015 μm.