JPH0963037A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium having high electromagnetic transducing output and fit for high density recording by imparting prescribed characteristics to a magnetic recording medium with a magnetic layer contg. magnetic powder of a ferromagnetic metal oxide and a resin binder on the nonmagnetic substrate. SOLUTION: In a magnetic recording medium with a magnetic layer contg. magnetic powder of a ferromagnetic metal oxide and a resin binder on the nonmagnetic substrate, the surface gloss of the magnetic layer is regulated to >=180 gloss units at 20 deg. angle of incidence and 20 deg. angle of reflectance, and the haze value of reflected light at 20 deg. angle of incidence and 20±1.8 deg. angle of reflectance is regulated to <=60. The objective magnetic recording medium having high electromagnetic transducing output and fit for high density recording is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium. Particularly, the present invention relates to a magnetic recording medium having high electromagnetic conversion characteristics, which is suitable for high density recording.

[0002]

2. Description of the Prior Art Ferromagnetic powder is dispersed in a binder resin,
Magnetic paint prepared by adding various auxiliaries and additives
A coating type magnetic recording medium produced by coating a polyester film or the like is widely used as a floppy disk or a magnetic tape. These coating type magnetic recording media are also strongly required to have a high capacity because of competition with other recording media. That is, the advent of magnetic tapes and floppy disks capable of high-density recording and having excellent electromagnetic conversion characteristics is strongly desired.

[0003]

One of the methods for satisfying these requirements is to use finer ferromagnetic powder and increase the packing ratio of the magnetic powder in the magnetic layer.
However, when the magnetic powder becomes fine, the specific surface area becomes large, and it becomes difficult to uniformly disperse the magnetic powder in the paint when preparing the magnetic paint. If a magnetic coating material in which magnetic powder is not sufficiently dispersed is used, naturally, an excellent magnetic recording medium cannot be obtained. One of the drawbacks of the magnetic recording medium obtained by applying such a magnetic paint is that the electromagnetic conversion characteristics deteriorate due to the low flatness of the magnetic layer surface. However, what factor governs the flatness of the surface of the magnetic layer related to this electromagnetic conversion characteristic and what index can be used to display it has not yet been clarified.

[0004]

According to the present invention, in a magnetic recording medium having a magnetic layer containing a ferromagnetic metal oxide magnetic powder and a binder resin formed on a non-magnetic support, a magnetic layer Of which the gloss at the incident angle of 20 degrees / reflection angle of 20 degrees is 180 gloss units or more and the haze value of the reflected light at the incidence angle of 20 degrees / reflection angle of 20 ± 1.8 degrees is 60 or less, It has been found to have excellent electromagnetic conversion properties. It has also been found that such a magnetic recording medium can be manufactured by adjusting the preparation conditions of the magnetic coating material and the formation conditions of the magnetic layer.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION To explain the present invention in more detail, the magnetic powder used in the magnetic layer of the magnetic recording medium according to the present invention is a metal oxide magnetic powder. For example, γ-F
e ₂ O ₃ , Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co
Iron oxide magnetic powder such as Fe ₃ O ₄ content, CrO ₂ , barium ferrite, strontium ferrite and the like are used. These may be used alone or in combination of two or more. These magnetic powders are preferably fine, and usually have a specific surface area of 30 m ² / g or more, preferably 40 m ² / g or more. In particular, it is preferable to use one having 50 m ² / g or more. However, the specific surface area is 65
Since extremely fine magnetic powders exceeding m ² / g are extremely difficult to uniformly disperse in the magnetic paint, magnetic recording media according to the present invention using such magnetic powders having a high specific surface area. It is generally difficult to manufacture a magnetic powder unless special measures are taken to disperse the magnetic powder. Further, it is preferable that the coercive force of the magnetic powder is as high as possible, and normally, one having 800 Oe or more is used. These magnetic powders can be used as they are, or can be used by applying various coatings on the surface in order to enhance the affinity with the binder resin. The proportion of these magnetic powders in the magnetic layer is preferably 50 to 90% by weight, particularly 55 to 85% by weight.

As the binder resin, it is preferable to use one having excellent adhesion to the non-magnetic support and abrasion resistance. Usually, polyurethane resins, polyester resins, cellulose derivatives such as nitrocellulose, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylic copolymers and other vinyl chloride copolymers. Polymers, various synthetic rubbers such as styrene-butadiene,
Epoxy resin, phenoxy resin, etc. are used. These may be used alone or in combination of two or more.
For example, the combined use of a polyurethane resin and a vinyl chloride-based copolymer is one of the preferable usage modes of the binder resin.

As the binder resin, those having various functional groups are preferably used in order to enhance the affinity with the magnetic powder. As the functional group, -OPO (OM) ₂ , -SO
Anionic polar group such as ₃ M, -OSO ₃ M, -COOM (wherein M represents hydrogen or lithium, sodium, potassium or ammonium ion) or a cation such as a tertiary amino group or a quaternary ammonium group. A polar group having a sex.

Further, a low molecular weight polyisocyanate compound having a plurality of isocyanate groups, for example, a cross-linking agent such as a trimethylolpropane adduct of tolylene diisocyanate is used together to form a three-dimensional network structure in the magnetic layer, The target strength can also be improved. Such a cross-linking agent is preferably used in the range of 5 to 100% by weight based on the binder resin. The binder resin including the cross-linking agent is usually 10 to 90% by weight, preferably 1% to the magnetic powder.
It is used so as to be 0 to 70% by weight.

In order to form the magnetic layer according to the present invention having a large gloss and a small haze value of reflected light, it is important to make the combination of the magnetic powder and the binder resin suitable for this. . In general, the combination of magnetic powder and a binder having a high affinity for it is advantageous for forming a magnetic layer having a large gloss and a small haze value of reflected light as defined in the present invention. The degree of affinity is determined by adding the magnetic powder to the liquid in which the binder has been dissolved, stirring the mixture, contacting them well, and then centrifuging to remove the magnetic powder, and measuring the amount of binder remaining in the liquid. It can be known by quantifying.

In addition to the binder resin and the magnetic powder, the magnetic layer may further contain various conventional additives and auxiliaries such as a dispersant, an abrasive, an antistatic agent and a lubricant. Examples of the dispersant include fatty acids such as capric acid, lauric acid, myristic acid, oleic acid, and linoleic acid, and their derivative soaps (that is, alkali metal or alkaline earth metal salts of these fatty acids), fatty acid amides, fatty acid esters. Etc. are used. Further, higher alcohols, aliphatic amines, polyalkylene oxides, alkyl phosphates, sugars, lecithin and the like can also be used. These dispersants are usually used in an amount of 0.1 to 10% by weight based on the magnetic powder. Two or more kinds of these dispersants may be used in combination, if desired.

As the abrasive, alumina, fused alumina, silicon carbide, chromium oxide, silicon nitride, etc. are used.
The number average particle diameter is preferably 2 μm or less. The abrasive is usually 0.5 to 30% by weight with respect to the magnetic powder, preferably 0.5.
It is used so as to be 10% by weight. As the antistatic agent, carbon powder, graphite, tin oxide, indium-tin-oxide, metal powder, or other fine powder of a simple substance or compound having conductivity is used. Further, natural surfactants such as saponins, nonionic surfactants such as alkylene oxides and glycerin, higher alkylamines, quaternary ammonium salts, pyridinium salts and other cationic surfactants such as nitrogen-containing heterocyclic salts, Anionic surfactants containing acidic groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, sulfuric acid ester groups, phosphoric acid ester groups, amphoteric surface active agents such as amino acids, aminosulfonic acids, amino alcohol sulfuric acid or phosphoric acid esters, etc. Is also used. If desired, two or more kinds of these antistatic agents can be used in combination.

As the lubricant, various kinds of lubricants such as aliphatic type, fluorine type, silicone type and hydrocarbon type can be used. Examples of the aliphatic lubricant include fatty acids, fatty acid metal salts, fatty acid esters, fatty acid amides, and aliphatic alcohols. Examples of the fatty acid include oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid and behenic acid.
Examples of the fatty acid metal salt include magnesium salts, aluminum salts, sodium salts and calcium salts of these fatty acids.

Examples of the fatty acid ester include butyl ester, octyl ester, stearyl ester, oleyl ester, isostearyl ester of the above fatty acids,
Alternatively, examples of the fatty acid amide such as glyceride include linoleic acid amide and caproic acid amide in addition to the above-mentioned fatty acid amide. As an aliphatic alcohol,
Examples thereof include lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, and oleyl alcohol. As a fluorinated lubricant,
Examples thereof include perfluoroalkyl polyethers, perfluoroalkyl carboxylic acids, perfluoropolyethers, fluorocarbons, and lubricants of the type in which a fluorine group is partially introduced. Examples of the silicone lubricant include silicone oil and modified silicone oil. In addition, solid lubricants such as molybdenum disulfide and tungsten disulfide, and phosphate esters can also be used. Examples of hydrocarbon lubricants include paraffin and squalane. Furthermore, animal and vegetable oils, mineral oils and the like can also be used.

If desired, two or more kinds of these lubricants may be used in combination. Lubricant is usually 0.5 for magnetic powder
It is used in an amount of 50 to 50% by weight, preferably 0.5 to 10% by weight. When two magnetic layers are laminated, the type and content of the lubricant may be changed between the upper layer and the lower layer. As is clear from the above description, some kinds of additives may have several effects at the same time.
Therefore, this must always be taken into consideration when determining the additives and the amounts used.

As a solvent for preparing the magnetic coating material by mixing the above-mentioned magnetic powder, binder resin and various additives, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, methanol,
Alcohols such as ethanol, propanol, butanol, isopropyl alcohol, etc., esters such as methyl acetate, ethyl acetate, butyl acetate, glycol acetate, etc., monoethyl ether, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane, tetrahydrofuran, etc. , Ethers, aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic or alicyclic hydrocarbons such as hexane, heptane and nitropropane, and derivatives thereof.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyimides, polyamides and polyimides. Examples thereof include amide and polycarbonate. Further, metal foil such as aluminum foil, paper, etc. can be used.

The form of the non-magnetic support is mainly tape, film, sheet, card, disk, drum and the like. The thickness is not particularly limited, but usually 3 to 1
The thickness is 00 μm, preferably 5 to 75 μm. This non-magnetic support may have a single structure or a multi-layer structure. Further, in order to improve the adhesion between the non-magnetic support and the magnetic layer, the non-magnetic support may be subjected to, for example, corona discharge treatment, treatment with a surface modifying agent such as alkane, amine aqueous solution, trichloroacetic acid, phenols, etc. You may give surface treatment.

When the magnetic powder is mixed with the solvent, the binder resin and other additives optionally added to prepare the magnetic paint, various known mixing devices can be used. For example, two roll mill, three roll mill, ball mill, sand mill, sand grinder, coball mill,
High-speed impeller disperser, high-speed impact mill, disperser,
A high speed mixer, a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, a pressure kneader and the like are used. It is preferable that two or more kinds of these mixing devices are usually used in combination so that the magnetic powder can be efficiently dispersed in the preparation of the magnetic coating material.

In order to form the magnetic layer according to the present invention having a large gloss and a small haze value of reflected light, it is important that the magnetic powder is sufficiently dispersed and the composition of the magnetic paint is uniform. Needless to say, in addition to this, the fact that the viscosity of the magnetic paint is small tends to make a large contribution. Therefore, in the preparation of the magnetic paint, it is preferable to increase the amount of the solvent used to keep the solid content concentration relatively low. Even if the final solid content concentration is the same, if the solid content concentration in the initial stage of kneading is too high, the magnetic layer formed using this magnetic coating tends to have a low gloss and a large haze value. is there.

Regarding the order of mixing the respective raw materials in the preparation of the magnetic coating material, a method in which all the raw materials are mixed at once, or the magnetic powder and the binder resin are first mixed, and then the other raw materials are mixed therein. There are several known methods, such as the method of doing, but the order of mixing may also affect the gloss of the magnetic layer and the haze value of reflected light. For example, when a vinyl chloride-vinyl acetate copolymer and polyurethane are used together as a binder resin, first the magnetic powder, the dispersant and the vinyl chloride-vinyl acetate copolymer are mixed with a solvent, and then the polyurethane and the abrasive are mixed. A magnetic paint prepared by adding an agent, an antistatic agent and other additives tends to be advantageous for forming a magnetic layer having a large gloss and a small haze value of reflected light.

In forming the magnetic layer, the magnetic coating material may be applied directly onto the non-magnetic support, or may be applied via an intermediate layer such as an adhesive layer or a conductive layer. As a coating method, any known method such as a gravure method, a reverse method and an extrusion method can be adopted.
Of course, during coating, surface defects such as coating streaks should not be generated.

In the case of producing a tape-shaped magnetic recording medium, it is preferable that a magnetic field orientation treatment is performed subsequent to the application to orient the magnetic powder and then dry. In the case of producing a disk-shaped magnetic recording medium, it is preferable to carry out a non-orientation treatment with a magnetic field to remove the direction dependence of the magnetic characteristics and then dry it. The magnetic layer thus formed is subjected to calendering to improve the smoothness of the surface, and the calendering conditions also considerably affect the gloss of the magnetic layer and the haze value of reflected light. The calendering is carried out at a temperature not lower than the glass transition point of the binder resin within the heat resistance limit of the non-magnetic support. In general, the calendering treatment is advantageous in forming a magnetic layer having a high gloss and a small haze value of reflected light if the calendering treatment is carried out at a temperature as high as possible unless it is restricted by other conditions such as exudation of a lubricant. In addition, a higher calendering pressure is generally advantageous for forming a magnetic layer having a large gloss and a small haze value of reflected light.

The magnetic recording medium according to the present invention may have a back layer on the side opposite to the magnetic layer. The back layer usually contains a conductive substance such as carbon black and a resin, and its surface property may be appropriately selected according to the running speed of the magnetic recording medium. For example, in a DDS tape or the like using a helical scan head whose traveling speed is relatively slow, a gloss at an incident angle of 60 degrees / reflection angle of 60 degrees is 80 to 130.
It is preferably a gloss unit. Further, in a belt drive type QIC tape or the like having a relatively high traveling speed, it is preferable that the gloss of an incident angle of 85 degrees / reflection angle of 85 degrees is 50 to 100 gloss units. When the gloss is within these ranges, the unevenness of the back layer does not affect the magnetic layer, and the tape can be wound stably.

[0024]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples and comparative examples, physical properties were measured as follows. Specific surface area of magnetic powder; measured by Micrometrics Model 2200 manufactured by Shimadzu Corporation. Coercive force of magnetic powder: Measured by VSM-P7 manufactured by Toei Industry Co., Ltd. Gloss and haze values; measured with a Haze Gloss Reflectometer version 2.8 from Big-Gardner (Germany). For the measurement, light was made incident from a light source along the coating direction, and its reflection was measured. Standard black plate is DIN675
At 30 and a reflection index of 1.567 was 100 gloss units. Electromagnetic conversion characteristics: A magnetic recording medium slit to a width of 1/4 inch was loaded in a QIC cartridge and measured with Westlake DDC-140.

Example 1 The following raw materials were supplied to a KRC kneader (Kurimoto Iron Works Co., Ltd.) so that the solid content concentration was 67% by weight, and the residence time was 5
The kneading was carried out for about 1 minute. Next, the kneaded product was placed in a dissolver, a solvent was added so that the solid content concentration became 33% by weight, and then the mixture was mixed for 1.5 hours. This was further treated with a sand grind mill for 1.5 hours (residence time) to prepare a magnetic coating material. This magnetic coating material was applied onto a polyethylene terephthalate film having a thickness of 6.4 μm so that the thickness after drying would be 1.6 μm, and then subjected to a magnetic field orientation treatment for orienting the magnetic powder, followed by drying. Temperature 90
After calendering at 400 ° C. and a linear pressure of 400 kg / cm, a carbon black type back coat having a thickness of 1.3 μm was applied and slit to a width of 1/4 inch to obtain a magnetic recording medium. The gloss of incident light 85 degrees / reflected light 85 degrees of the back coat was 95 gloss units. The results are shown in Table 1.

Γ-Iron oxide magnetic powder A (Hc: 800 Oe, specific surface area; 50 m ² / g) 100 parts by weight Polyurethane resin (Product of Goodrich ESTANE 5799) 7 parts by weight Vinyl chloride-vinyl acetate copolymer (Japan Zeon product MR-113) 16 parts by weight Curing agent (product of Nippon Polyurethane Company, Coronate L) 5.3 parts by weight Dispersant (product of Toho Chemical Co., GAFAC RE610) 2.5 parts by weight α-alumina (Sumitomo Chemical product , AKP50) 5.0 parts by weight Curing acceleration catalyst (Tris iron) 0.05 parts by weight Butyl stearate 0.7 parts by weight Myristic acid 1.4 parts by weight Solvent (methyl ethyl ketone)

Examples 2 to 5 and Comparative Examples 1 and 2 Residence time in KRC kneader and solid content concentration of kneaded product,
Further, a magnetic recording medium was manufactured in the same manner as in Example 1 except that the temperature of the calender treatment was changed as shown in Table 1. The results are shown in Table 1.

Example 6 Magnetic recording was carried out in the same manner as in Example 1 except that a trimer of tolylene diisocyanate (made by itself) was used in place of Coronate L as a curing agent, and tetrahydrofuran was used in place of methyl ethyl ketone as a solvent. The media was manufactured. The results are shown in Table 1.

Examples 7 and 8 and Comparative Examples 3 to 4 CA-2239 (manufactured by Morton Co.) was used in place of ESTANE5799 as the polyurethane resin, and KRC was used.
A magnetic recording medium was produced in the same manner as in Example 1 except that the residence time in the kneader, the solid content concentration of the kneaded product, and the calendering conditions were changed as shown in Table 1. The results are shown in Table 1.

Examples 9 and 10 Magnetic powder B was used in place of magnetic powder A as γ-iron oxide magnetic powder.
(Hc: 890 Oe, specific surface area 40 m ² / g),
A magnetic recording medium was manufactured in the same manner as in Example 1 except that the residence time in the KRC kneader and the solid content concentration of the kneaded product were changed as shown in Table 1. The results are shown in Table 1.

Comparative Example 5 Magnetic powder B was used in place of magnetic powder A as γ-iron oxide magnetic powder.
A magnetic recording medium was produced in the same manner as in Example 1 except that CA-2239 was used as the polyurethane resin in place of ESTANE5799, and the residence time in the KRC kneader and the solid content concentration were changed as shown in Table 1. did. The results are shown in Table 1.

[0032]

[Table 1]

[0033]

The magnetic recording medium according to the present invention has a high electromagnetic conversion output and is suitable for high density recording.

Claims (3)

[Claims] 1. A magnetic recording medium having a magnetic layer containing a ferromagnetic metal oxide-based magnetic powder and a binder resin on a non-magnetic support, comprising: a magnetic layer surface at an incident angle of 20 degrees / reflection angle of 20 degrees. A magnetic recording medium having a gloss of 180 gloss units or more and a haze value of 60 or less for reflected light at an incident angle of 20 degrees / reflection angle of 20 ± 1.8 degrees. 2. The magnetic recording medium according to claim 1, wherein a haze value of reflected light at an incident angle of 20 degrees / a reflection angle of 20 ± 1.8 degrees is 50 or less. 3. The magnetic recording medium according to claim 1, wherein the magnetic powder has a coercive force of 800 Oe or more.