JPS62117140A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled magnetic recording medium having excellent surface property, electromagnetic transducing characteristic, and traveling durability by using specified carbon black and a fatty acid or its derivative and specifying the ratio of the mixture to specified acicular Cr2O3 and magnetic powder. CONSTITUTION:The magnetic layer contains, based on the magnetic powder, 2-15wt% acicular Cr2O3 having <=1.0mum major axis, <=0.1mum minor axis, and 5-20 acicular ratio, 0.5-5.0wt% carbon black having preferably <=30mum mean particle diameter, and 0.1-5.0wt% fatty acid or its derivative. Cr2O3 having 0.1-0.95mum major axis, 0.02-0.09mum minor axis, an 8-15 acicular ratio is most preferably used. The deterioration in the traveling durability and the decrease in the electromagnetic transducing characteristic due to the deterioration of the surface property are thus prevented.

Description

[Detailed description of the invention] [Industrial application field].

The present invention relates to a magnetic recording medium having a magnetic layer coated on a non-magnetic support, and particularly to a magnetic recording medium with improved running durability.

[Conventional technology]

Conventionally, γ-F has been used as a tape-shaped or disk-shaped magnetic recording medium for audio, video, computer, etc.
1203, Co-containing iron oxide, chromium dioxide, ferromagnetic alloy powder, etc., are dispersed in a binder and a magnetic layer is coated on a non-magnetic support. Recently, the density of such magnetic recording media has increased, and high S/
In conjunction with N conversion, magnetic materials are being made into fine particles, but as a result of this fine graining, the polishability of the magnetic materials decreases.
For this reason, the running durability of a magnetic recording medium using such a magnetic material deteriorates. Moreover, this slope is remarkable when a ferromagnetic alloy powder with low hardness is used.

[Problem that the invention seeks to solve]

As a measure to prevent such deterioration of running durability, granular At203. It has been proposed to add abrasives such as SiC and Cr2O3 to the magnetic layer, but adding a large amount of such abrasives may deteriorate the magnetic field orientation of the magnetic recording medium, the degree of filling of the magnetic powder, and the dispersibility. The problem is a decrease in electromagnetic conversion characteristics due to deterioration of surface properties accompanied by deterioration.

In addition, reducing the amount of abrasive added to improve the surface properties improves the electromagnetic characteristics, but the friction coefficient of the magnetic layer increases.
Problems such as sticking during running and poor running properties of the magnetic recording medium occur.

Therefore, an object of the present invention is to simultaneously improve the running durability and electromagnetic conversion characteristics of a magnetic layer, and to provide a magnetic recording medium with improved running properties.

[Means for solving problems]

The present applicant has previously proposed, as a means to achieve the above object, an acicular shape having a major axis diameter of 1.0 μm or less, a minor axis diameter of 0.1 μm or less, an acicular ratio of 5 to 20, and a Mohs hardness of 5 or more. proposed the use of inorganic substances as abrasives (patent application Sho 6O-62).
938).

The present invention has been made as a result of repeated research to achieve the above-mentioned objects and to obtain a magnetic recording medium with improved running properties. Among the abrasive materials proposed for the light, in particular, acicular Cr2O having the above-mentioned characteristics,
When dispersed with magnetic powder, the running durability and electromagnetic conversion characteristics of the magnetic layer are significantly improved by mixing specific carbon black and fatty acids or their derivatives with the magnetic powder at a certain ratio to form the magnetic layer. The present invention has been made based on this discovery.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder dispersed in a binder on a non-magnetic support.
The magnetic layer has a major axis diameter of 1.0 μm or less, a minor axis diameter of 0.1 μm or less, contains 1 to 20% by weight of acicular CrO with an acicular ratio of 5 to 20 based on the magnetic powder, and has an average particle size. The present invention is a magnetic recording medium characterized in that it contains 0.5 to 5.0% by weight of carbon black of 50 mμ or less based on the magnetic powder, and 11 to 5.0% by weight of fatty acid or a derivative thereof based on the magnetic powder.

The present invention will be explained in detail below.

The present invention can also be applied to magnetic recording media using conventionally commonly used iron oxide-based ferromagnetic powders, Co-containing iron oxide-based ferromagnetic powders, and chromium dioxide (CrO□)-based ferromagnetic powders. , “Especially when the specific surface area is 25 n171
It is particularly effective when using the above ferromagnetic alloy powder. In other words, ferromagnetic alloy powder has lower hardness than other ferromagnetic powders (magnetic recording media using it tend to have low abrasiveness and poor running durability, but by applying the present invention, these can effectively solve problems.

The nonmagnetic support used in the present invention is not particularly limited, and any commonly used nonmagnetic support can be used. Examples of materials forming the non-magnetic support include polyethylene terephthalate (PET), polypropylene, polycarbonate, polyethylene naphthalate, various synthetic resin films such as polyamide P1, polyamide imide P1, polyimide, and metals such as aluminum foil and stainless steel foil. One example is foil. The thickness of the non-magnetic support is also not particularly limited, but is generally 3 to 50 μm, preferably 5 to 3 μm.
It is 0 μm.

The nonmagnetic support may be provided with a packing layer (packing layer) on the side on which the magnetic layer described below is not provided.

The magnetic recording medium of the present invention is one in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a nonmagnetic support as described above.

The ferromagnetic powder used in the magnetic layer of the present invention includes fine ferromagnetic alloy powder containing iron as a main component, γ-Fe 205, Fe
! , 04, Co-modified ferromagnetic iron oxide CrO2, modified
There are ferromagnetic alloy powders such as strontium ferrite and modified strontium ferrite, but the present invention is a ferromagnetic alloy powder containing iron, cobalt, strontium or nickel, and whose specific surface area is 2.
5n! This is particularly effective when using a ferromagnetic alloy powder of /W or more as the ferromagnetic powder.

As an example of this ferromagnetic alloy powder, the metal content in the ferromagnetic alloy powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one type of ferromagnetic metal or alloy, and the metal content is Mention may be made of alloys that may contain other components within a range of 20% by weight or less. Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide. Methods for producing these ferromagnetic metal powders are already known, and ferromagnetic alloy powder, which is a typical example of the ferromagnetic powder used in the present invention, can also be produced according to these known methods.

When using ferromagnetic alloy powder, its shape is not limited, but it is usually needle-shaped, granular, dice-shaped, rice-grain-shaped, and plate-shaped.

The specific surface area (S BET) of this ferromagnetic alloy powder is 42
n? /1 or more, preferably 45-71
It is preferable to use the above.

As the binder used to form the magnetic layer of the present invention, commonly used thermoplastic resins, thermosetting resins, reactive resins, and the like can be used.

These resins can be used alone or in combination.

Thermoplastic resins generally have an average molecular weight of 10,000 to 2.
00,000 and a polymerization degree of about 200 to 2,000. Examples of such thermoplastic resins include vinyl chloride/vinyl acetate copolymer resins, vinyl chloride/vinylidene chloride copolymers, acrylic resins, cellulose derivatives, various synthetic rubber thermoplastic resins, urethane elastomers,
Examples include polyvinyl fluoride, polyamide P resin, polyvinyl butyrate, styrene/butadiene copolymer, and polystyrene resin, and these can be used alone or in combination.

Thermosetting resins or reactive resins are generally resins with an average molecular weight of 200,000 or less in the coating liquid state, and resins whose molecular weight becomes almost infinite due to condensation reaction or addition reaction after coating. . However, when these resins are thermosetting resins, it is preferable that the resins do not soften or dissolve due to heating during the process leading to curing. Examples of such resins include phenol/
Formalin/novolac resin, phenol/formalin/resol resin, phenol/furfural [t, xylene/formaldehylt fat, urea resin, melamine resin, drying oil-modified Alkyra P resin, phenol resin-modified Alkyato resin, maleic acid resin-modified Alkyra F resin , unsaturated polyester resin, combination of epoxy resin and curing agent,
Examples include a terminal incyanate polyether moisture-curable resin, a polyincyanate prepolymer, a combination of a polyisocyanate prepolymer and a resin having active hydrogen, and these can be used alone or in combination.

The amount of binder used is, based on 100 parts by weight of ferromagnetic powder,
Generally in the range of 10 to 100 parts by weight, preferably 15 to 100 parts by weight.
The range is 50 parts by weight.

The present invention is characterized in that the magnetic layer contains specific acicular Cr2O3.

C r 205 used in the present invention is acicular chromium sesquioxide with a major axis diameter of 1.0 μm or less, a minor axis diameter of 0.1 μm or less, and an acicular ratio of 5 to 200. Long axis diameter is 0.1~0.95μ
The m1 minor axis diameter is 0.02 to 0.09 μm, and the acicular ratio is 8 to 8.
15 Cr2O3 is particularly preferred.

When the long axis diameter of Cr2O3 used as an abrasive is larger than 1.0 μm and the short axis diameter is larger than 0.1 μm, and when the acicular ratio of Cr2O is smaller than 5 or larger than 20, dispersion of Cr2O3 Furthermore, the electromagnetic conversion characteristics are not sufficiently improved.

Furthermore, it may have an adverse effect on the magnetic field orientation treatment of the ferromagnetic powder, and the electromagnetic conversion characteristics of the resulting magnetic recording medium may not be improved.

Note that the upper limit values of the major axis diameter and minor axis diameter defined in the present invention mean the upper limit values of the respective average values of the major axis diameter and minor axis diameter of Cr2O3 contained in the magnetic layer. The numerical values in each preferable range also have the same meaning.

The above-mentioned Cr2O3 used in the present invention has a Mohs hardness of about 9.

The acicular Cr2O3 used in the invention can be produced, for example, by the following known method.

That is, a mixture of Crys and Cr20s is dispersed in water to form a water-dispersed slurry, and this is subjected to a hydrothermal reaction in an autoclave at a temperature of 350 to 370°C and a pressure of 300 to 500 atm. 700～
Acicular Cr2O5 is obtained by heating in air at 900°C, preferably 800-850°C. Also Cr
Cr2(CrO4)3 obtained by partially reducing Os may be used as a starting material.

In the present invention, the above-mentioned acicular Cr 205 is contained in an amount of 1 to 20% by weight, preferably 2 to 20% by weight of the ferromagnetic powder contained in the magnetic layer.
It is contained in the magnetic layer in an amount of 15% by weight.

The magnetic recording medium of the present invention has the above-mentioned acicular Cr2O3 in the magnetic layer.
Although it is not necessary to add other abrasives because the abrasives contain , it is also possible to add other abrasives that are commonly used as long as they do not interfere with achieving the object of the present invention.

The average particle size of the carbon black used in the present invention is 50
The thickness is desirably less than mμ, preferably less than 30 mμ. Also,
The amount added is preferably in the range of 0.5 to 5% by weight of the magnetic powder.

The fatty acids or derivatives thereof used in the present invention include:
Preferred are aliphatic carboxylic acids having 12 to 24 carbon atoms or derivatives thereof, and more preferably saturated aliphatic monocarboxylic acids or derivatives thereof. Preferred examples of the aliphatic carboxylic acid or its derivative include stearic acid, nosorumitic acid, myristic acid, oleic acid, etc., or derivatives thereof. As the fatty acid derivative, preferably fatty acid ester, fatty acid amine F1
Examples include alkali metal salts or alkaline earth metal salts of fatty acids. The alcohol for forming the ester is preferably an aliphatic alcohol having 3 to 12 carbon atoms. Preferred examples of the fatty acid ester include butyl stearate, amyl stearate, butoxyethyl lumitate, and the like. Preferred examples of the fatty acid ester include amyl oleate P, amyl stearate, and the like.

The amount of the fatty acid or its derivative added is preferably in the range of 0.1 to 5% by weight based on the magnetic powder.

When manufacturing the magnetic layer of the magnetic recording medium of the present invention, firstly, the above-mentioned acicular Cr2O3 and ferromagnetic powder such as ferromagnetic alloy powder, a binder, the above-mentioned carbon black and fatty acid or its derivative, or if necessary, are used. Then, other additives are kneaded with a solvent to form a magnetic paint, which is applied onto a support, subjected to magnetic field orientation, etc., and then dried.

As the solvent used in the crosstalk, a solvent commonly used for preparing magnetic paints can be used.

For the method of cross-talk, a method commonly used as a cross-wire method for magnetic paint can be used. Further, the order of addition of each component can be set as appropriate.

Various techniques are known as magnetic obstetric adjustment techniques, and any of these known techniques can be used in manufacturing the magnetic recording medium of the present invention.

When preparing magnetic paint, dispersants other than the above-mentioned carbon black, fatty acids or derivatives thereof, antistatic agents,
Known additives such as lubricants can also be used in conjunction with them in amounts that do not adversely affect the present invention.

Examples of dispersants include aliphatic amines, higher alcohols,
? Known dispersants such as realkylene oxyP alkyl phosphate ester, alkyl phosphate ester, alkyl borate ester, sarcosinates, trialkyl polyolefin oxy quaternary ammonium salt, and lecithin can be mentioned.

Examples of antistatic agents include natural surfactants; nonionic surfactants; cationic surfactants; anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfate ester groups, and ester phosphate groups; amino acids. class, aminosulfone II
and amphoteric activators such as sulfuric acid or phosphoric acid esters of amino alcohols.

Examples of lubricants include higher alcohols, olefin low polymers, lubricants for plastics, etc. In addition, carbon black, fatty acids and their derivatives used in the present invention, and dispersants other than those mentioned above. ,
Additives such as antistatic agents and lubricants are not described with the limitation that they have only the effects strictly described above; for example, when a dispersant acts as a lubricant or an antistatic agent. It is possible. Therefore, it goes without saying that the effects of the compounds exemplified by the above classifications are not limited to those described in the above classifications, and in the present invention, when such substances that have the same effects are used in combination, It is preferable that the amount added be determined in consideration of the action and effect of the substance.

The magnetic paint thus prepared is coated on the above-mentioned non-magnetic support according to a known method. Coating is done directly onto the non-magnetic support through a submerged chamber. However, it can also be applied onto a non-magnetic support via an adhesive layer or the like.

There is no particular limit to the thickness of the magnetic layer coated in this way, but the thickness after drying is generally in the range of about 0.5 to 10 μm, usually in the range of 1.5 to 7.0 μm. is applied to.

A magnetic layer coated on a non-magnetic support is usually subjected to a treatment for orienting the ferromagnetic powder in the magnetic layer, that is, a magnetic field orientation treatment, and then dried. Also, if necessary, surface smoothing treatment is performed. The magnetic recording medium that has been subjected to surface smoothing treatment is then cut into a desired shape.

Next, Examples and Comparative Examples of the present invention will be shown. Note that "parts" in Examples and Comparative Examples indicate "parts by weight."

[Example 1] A slurry obtained by dispersing a weight mixture of CrO5 and Cr2O3 in water was heated to 350°C in an autoclave.
A hydrothermal reaction (reaction time: 5 hours) was carried out under the conditions of ℃ and 300 atm pressure to obtain acicular CrO2. This temperature is 8
The mixture was heated at 00°C for 2 hours in air to obtain needle-like C'203.

The obtained acicular Cr203 was classified and used.

Next, a magnetic paint having the composition shown below was prepared and coated on a polyethylene terephthalate nonmagnetic support having a thickness of 10 μm so that the thickness of the magnetic layer after drying was 3.0 μm.

Magnetic paint composition Ferromagnetic alloy powder ioo part (Fe
-Nr gold alloy Ni approx. 5% by weight) (specific surface area (s-Ba
T): 45m'/1 vinyl chloride/vinyl acetate/maleic anhydride copolymer 12
parts (Nippon Zeon Co., Ltd.: 400X11QA) Polyurethane 8 parts (Nippon Polyurethane Co., Ltd.: N-2301) Polyisocyanate 8 parts (Nippon Polyurethane Co., Ltd.: Nyronate L) Carbon black
2 parts (average particle size: 25 mμ) Stearic acid 1.5 parts Butyl stearate 1 part Methyl ethyl ketone 150 parts Acicular Cr2O3 Major axis diameter 0.3 μm 5 parts Minor axis diameter 0.03
μm Needle ratio 10 A non-magnetic support coated with magnetic paint is subjected to magnetic field orientation treatment while the magnetic paint is not dry, and after drying, calender treatment is performed, and slits are made into 8 mm width. produced a videotape.

As the magnetic properties of this videotape, the B-H curve (B:
The magnetic flux density (H: external magnetic field) was measured and determined, and the squareness ratio (Br78m, [Br'' maximum residual magnetic flux density, Bm: maximum magnetic flux density]) was determined from this value.

The resulting videotape video recorder (F'UJIX)
-8) was used to record and reproduce the 5-part signal.

Relative S/N of the above videotape when the playback output of 5 Mlb recorded on the reference tape (8 mm video tape obtained in Comparative Example 1 below) is set as OdB.

The reproduction output and the decrease in reproduction output after 100 passes were measured.

Using the above video recorder, the vehicle was run repeatedly, and the number of runs until the magnetic tube P became clogged was determined.

The surface gloss was determined by measuring the total reflectance at an incident angle of 45 degrees and a reflection angle of 45 degrees using a standard gloss meter. CrO2 mark cheap 150
%. The measuring device used was a digital standard color difference photometer AUD-CH-GV3 manufactured by Suga Testimonials 01 Co., Ltd.

As for the coefficient of friction, the μ value for a stainless steel rod was determined at 23° C. and 75% RH.

The surface resistance Rs was measured in accordance with JIS standards.

The hardness of the video recorder running system was rated as × if it had a large amount of hardness, ○ if it was good, and △ if it was in the middle.

Comparative Example 1 In Example 1, Cr206 was spherical (size: 0.3μ
A videotape was produced in the same manner, except that m) was used.

Example 2 A videotape was produced in the same manner as in Example 1 except that Cr2O3 was used with a major axis diameter of 0.9 μm and a minor axis diameter of 0.07 μm.

Comparative Example 2 A videotape was produced in the same manner as in Example 1 except that Cr2O was replaced with one having a major axis diameter of 0.08 μm and a minor axis diameter of 0.02 μm.

Comparative Example 3 A videotape was produced in the same manner as in Example 1 except that Cr2O3 was replaced with one having a major axis diameter of 1.2 μm and a minor axis diameter of 0.06 μm.

Example 3 In Example 1, the average particle size of carbon black was changed to 10
A videotape was produced in the same manner except that mμ was used.

Example 1L In the example process, the average particle size of carbon black was 45 mμ.
A videotape was produced in the same manner, except that

Comparative Example 5 In Example 1, carbon black had an average particle size of 80 mμ.
A videotape was made in a similar manner except that stearic acid and butyl stearate were not added.

Comparative Example 6 In Comparative Example 5, carbon black had an average particle size of 10 mμ.
A videotape was produced in the same manner, except that

Example 5 A videotape was produced in the same manner as in Example 1 except that 5 parts of stearic acid was added and butyl stearate was not added.

Example 6 A videotape was produced in the same manner as in Example 1 except that the amount of stearic acid added was 2.5 parts.

Comparative Example 7 A videotape was produced in the same manner as in Example 1 except that the amount of stearic acid added was 3.5 parts to 3.0 parts of butyl stearate.

Comparative Example 8 In Example 1, Cr 205 was spherical (size 0.3μ
A videotape was produced in the same manner as m) except that carbon black, stearic acid, and butyl stearate were not added.

Comparative Example 9 In Example I, Cr2O3 was spherical (size 0.3μ
A videotape was produced in the same manner except that the average particle size of carbon black was 10 mμ, and the amount of stearic acid added was 2.5 parts.

Comparative Example 10 In Example 1, acicular α-
A1203 (long axis diameter: o, 3 μm), needle ratio: 1/
A videotape was produced in the same manner except that the same amount of 15) was used.

The results are shown in the table below. In the table, "actual" indicates "example" and "ratio" indicates "comparative example."

〔Effect of the invention〕

As is clear from the above results, in the present invention, by using specific acicular Cr2O5 and magnetic powder in a certain proportion and specific carbon black and fatty acid or its derivative, the surface properties and electromagnetic conversion characteristics can be improved. A magnetic recording medium with excellent performance and improved running durability can be obtained.

Claims (1)

[Claims] In a magnetic recording medium having a magnetic layer containing magnetic powder dispersed in a binder on a non-magnetic support, the magnetic layer has a major axis diameter of 1.0 μm or less, a minor axis diameter of 0.1 μm or less, and an acicular ratio. 5
~20 acicular Cr_2O_3 to the magnetic powder 1 to 2
0% by weight of carbon black with an average particle size of 50 mμ or less based on the magnetic powder, and 0.1% to 5.0% by weight of fatty acid or its derivative based on the magnetic powder.
A magnetic recording medium containing 5.0% by weight.