JPS61178728A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve simultaneously both surface property and durability of the titled recording medium by incorporating at least 1 kind among a fatty acid, a fatty acid amide, a fatty acid-modified silicone and an alpha-olefin oxide into the magnetic layer contg. non-magnetic powder. CONSTITUTION:More than 3wt%, based on ferromagnetic powder, non-magnetic powder having >=6 Moh's hardness and >=7wt% at least 1 kind selected from a fatty acid, a fatty acid amide, a fatty acid ester, a fatty acid-modified silicone and an alpha-olefin oxide are incorporated into a magnetic layer. Cr2O3, alumina, SiO, MgO, etc. which are usually called an abrasive and capable of improving the durability can be used, the size of the particle is most preferably regulated to 0.2-0.7mu, and the amt. of the abrasive to be used is optimally controlled to 6-15wt%, based on the ferromagnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium for magnetic disks and magnetic sheets, and particularly to a magnetic recording medium with improved durability.

[Prior art]

For magnetic recording media, especially magnetic disks and magnetic sheets that are suitable for high-density recording and require strong durability, it is necessary to simultaneously improve surface smoothness and durability in order to improve electromagnetic conversion characteristics. required. however,
Conventionally used methods are no longer able to adequately meet the demands for higher densities in magnetic disks and the like.

In other words, in order to increase the density of magnetic disks, etc. (the second important factor is that the surface of the magnetic layer is smooth and that ferromagnetic particles exist in a uniformly dispersed state within the magnetic layer), Adoption of magnetic material Adoption of smoothing treatment conditions such as calendaring, enhancement of magnetic liquid dispersion ability, and other techniques alone cannot provide sufficient durability of the magnetic layer.On the other hand, with the increase in density, the magnetic layer The situation has become such that the thickness has been forced to become thinner than before.

Further, carbon black having an average particle size of about several tens of microns is usually used in the magnetic layer mainly for the purpose of preventing static electricity. Normally, the surface electrical resistance of a magnetic layer with a thickness of 3 to ♂μm is about /x106 to /x109Ω (Ni-control is performed, but of course when the layer is thinned, the surface electrical resistance is In that case, the surface electrical resistance will be lowered, so 1:
requires an increase in the amount of carbon black used.

In addition, it has been known to use fatty acids as a lubricant to increase durability (Special Publication Showa 4t?-394102).
It is known that the usable amount of lubricant for the magnetic material (2:7 weight (hereinafter referred to as wt)) is less than 4.

Regarding α-olefin oxide, it is known to use a lubricant of J wt % or less for a magnetic material (Japanese Patent Publication No. 641-4T6010). In the above case, the invention is particularly used for video tapes, audio tapes, and memory tapes.

The reason why the amount of lubricant used was selected to be 7wt% or less is that in video tapes, if lubricant is used in excess of 2 to 3w1%, the magnetic layer becomes plasticized and weakens, causing dropouts. Also, lubricants based on fatty acids or fatty acid esters may cause sticking to the magnetic head. Also, in audio tapes, if a lubricant of more than j-+wt% is used, the magnetic layer becomes plasticized, similar to video tapes.
This is because "deadness" is likely to occur due to the influence of temperature and humidity, the μ value of the magnetic layer decreases, causing a rise phenomenon during running, and problems such as white powder generation and head staining occur. . However, for magnetic recording media that require a high degree of durability, such as magnetic disks, which have no commercial value unless they are durable for 10 million or more continuous rotations, the binder combinations and lubricants used in the past are When less than 7 wt% of the magnetic fine particles is used, there is a problem that sufficient durability cannot be obtained. Therefore, the inventors of the present invention conducted intensive studies on the type and amount of lubricant used, and as a result, discovered a relationship that could not be expected based on conventional common sense, and thus arrived at the present invention.

[Purpose of the invention]

An object of the present invention is to provide a magnetic recording medium for magnetic disks and magnetic sheets that has improved surface properties and durability at the same time.

[Structure of the invention]

The present invention provides a magnetic recording medium comprising a magnetic layer coated on a non-magnetic support, in which the magnetic layer (1) comprises a non-magnetic powder having a Mohs hardness of 4 or more and a ferromagnetic powder (2 to 3 wt 4 or more). and (2) at least one selected from fatty acids, fatty acid amides, fatty acid esters, fatty acid-modified silicones, and α-olefin oxides to 7w for the ferromagnetic powder.
It relates to a magnetic recording medium characterized by containing t% or more.

Fatty acids, fatty acid amides,
Examples include fatty acid esters, fatty acid-modified silicones, and α-olefin oxides. Both saturated and unsaturated fatty acids can be used as fatty acids.

Specific examples (= include lauric acid, palmitic acid, myristic acid, stearic acid, behenic acid, isostearic acid, erucic acid, oleic acid, etc., and of course, these are necessary (they can also be used in combination).

Examples of fatty acid esters include esters such as ethyl stearate, butyl stearate, amyl stearate, butyl palmitate, hexyl laurate, butyl laurate, butyl myristate, and furthermore, butoxyethyl stearate, butoxybutyl stearate, and stearin. Ethoxyethyl acid, ethoxybutyl stearate, 〕ξ
Alkoxy esters such as butoxyethyl rumitate can be used. Further, fatty acid amides include stearylamide, oleylamide, erucylamide, normitylamide, myristylamide, and the like. As the fatty acid-modified silicone, silicones represented by the following general formulas C1) and (n) can be used.

[II] In the above general formula CI]E, R1%R2 has 7 to 2 carbon atoms
/ is a saturated or unsaturated hydrocarbon group, and j is θ~! is an integer of θ. In the above general formula [■], R3, R4, R
5 is a saturated or unsaturated hydrocarbon group having 2 to 2 carbon atoms, m,
n is an integer from 0 to 10. Specific examples of silicones represented by general formula [I] include capric acid-modified silicones (
Rr, R is -C7H15 and l is -), myristic acid-modified silicone (R1, R2 is -C13H27, l
2), behenic acid-modified silicone (R1 and R2 are -CzIH43 and 2), and oleic acid-modified silicone (R1 and R2 are -C17H33 and ! is 2). Specific examples of silicones represented by the general formula [■] include oleic acid-modified silicones (Ra,
R4 is -CH3, R5 is -C17H33, and m is ♂0.
n is male), myristic acid-modified silicone (Ra,
R4 and R5 are C13H27, m is 73, and n is 2r (
7)) As α-olefin oxide, the following general formula (I
II,) can be used.

(III) In the above general formula [■], R6 represents an alkyl group having 70 to 30 carbon atoms.

These lubricants must be contained in an amount of Zwt% or more based on the ferromagnetic powder.

The non-magnetic powder with a Mohs hardness of 6 or more used in the present invention is particularly effective for the durability of the magnetic layer, such as Cr
Commonly called abrasives such as 2O3, alumina, sho, MgO, etc. can be used. When the Mohs hardness is 6 or less, the effect on durability deteriorates. The particle size of the non-magnetic powder with a Mohs hardness of 6 or more is preferably /μ or less,
In particular, 0.2 to 0.2μ is good. The amount used is preferably 3 wt% or more based on the ferromagnetic powder, particularly 6 to 1/! wt%
is optimal.

As a non-magnetic support, polyethylene terephthalate) 1,
triacetylcellulose, polyethylene naphthalate,
All materials that can be used for normal magnetic recording materials such as polyamide and polyimide can be used, and A! Vapor-deposited polyester film can be used.

In order to further improve the surface properties of the magnetic recording medium, carbon black may be preheated together with a magnetic powder, a binder and an organic solvent. may also be magnetic powder,
Similarly to carbon black, the amount of front coating of each binder can be adjusted as necessary. Normally, ferromagnetic fine particles often give better results when subjected to full-view fronting, but it is essential to set the fronting conditions by carefully considering the type and amount of binder. When only the surface smoothness of the magnetic layer is of interest, it is preferable to add the entire amount of carbon black to the front. However, when the electrical resistance of the magnetic layer surface is required to be below a certain value, it is preferable to add a portion of the carbon black. In many cases, it is best to remove only the amount at the front and use the remaining amount in the subsequent process.

As the front kneading method, it is preferable to use a three-roll mill, a pressure kneader, an open kneader, a Warner kneader, etc., but the method is not limited to these and can be applied as long as it can be used.

As the solvent for front printing, acetic esters such as ethyl acetate and butyl acetate, ketones such as MEKSMl BK and cyclohexanone, and other solvents commonly used in magnetic tapes can be used.

Ferromagnetic powders include r-F'e203, Fe3O4,
Cr Q2, cobalt-added r-Fe203, cobalt-added Fe□x (x=/, j j ~/, j)
In addition to oxides such as, metal powders such as pe-Ni and Fe-Ni-Co can also be used.

As a binder, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, carboxyl group-containing salt-vinyl acetate copolymer,
Vinyl alcohol-containing salt vinyl acetate copolymer, polyvinylidene chloride, vinylidene chloride-acrylonitrile copolymer, nitrocellulose and other cellulose derivatives, acrylonitrile-butadiene rubber, styrene-butadiene rubber,
Ordinary magnetic recording materials such as HoIJ ester, epoxy resin, polyinocyanate, polyamide, etc. can be used.

It is also necessary (: DBP (dibutyl phthalate V) in the magnetic layer.
Plasticizers such as TPP (phenyl phosphate), TPP (phenyl phosphate), and dispersants such as lecithin may be mixed.

The magnetic recording medium for magnetic disks and magnetic sheets of the present invention obtained in this manner has excellent surface smoothness of the magnetic layer and has significantly improved durability.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to two examples, examples, and comparative examples. Hereinafter, "parts" indicate parts by weight.

Example/Co addition-FeQx (x=/, 4t)/θ
0 parts (particle size O, 4t μ × θ, θ! μ) PVC vinyl acetate copolymer 73 parts (product name rUMCf (manufactured by J Union Carbide) Polyurethane part (product name “N-, 2304t” manufactured by Nippon Polyurethane ■) ) Polyincyanate 1 part (trade name: "Urecoated Mylar/Clear") (manufactured by Higashi Nihon Toyo ■) CrzOa part J (manufactured by Nihon Kagaku Kogyo, average particle size 0.jμ, Mohs hardness ♂-ta) Carmen black J part (“Asahisu♂θ” manufactured by Asahi Carbon Products) Oleic acid 3 parts 7.2
・Epoxytetradecane 9 parts Erucylamide 3 parts Solvent Methyl ethyl ketone/Toluene/Methyl isobutyl ketone (Mixing ratio: 2:/) With the exception of the polyinocyanate, the above composition was mixed with a stirrer.
After rough dispersion, fine dispersion treatment was performed using a ball mill.

Then add polyisocyanate and stir until the viscosity is J-7.
The viscosity was adjusted to θ poise, and after filtration, the above magnetic liquid was applied by reverse method onto a 7 μ μ polyethylene terephthalate film. Surface smoothing treatment was performed using a super calender. It was processed into a flexible disk to obtain sample A/.

Example 3 The type of lubricant in Example 381 was changed as shown in Table 1, and A2 to j were obtained in the same manner as in Example.

Table 1 Comparative Example 1 Oleic acid of Example/7.2 Epoxytetradecane,
Sample Aj, 7 was obtained in the same manner as in Example/, except that the amount of erucylamide was changed as shown in Table 2.

Table 2, Example 3 Samples A/~// were obtained in the same manner as in Example/, except that the abrasives and amounts shown in Table 3 were changed from Cr2Q3 in Example/.

Table 3 Comparative Example 2 Samples were obtained in the same manner as in Example, except that the type of Cr 2 Q 3 in Example was changed as shown in Table G.

Table Z Comparative Example 3 Samples &/3 and /4t were obtained in the same manner as in Example/, except that the amount of Cr2Q3 in Example/ was changed as shown in Table 1.

Regarding the samples A/~/4t of the Examples and Comparative Examples described above! ,Ko! Durability and magnetic layer surface properties by inch floppy disk drive (Ra: center line average roughness)
The measurement results are shown in Table 3.

From the study results shown in Table 3 and above, sample A/~ which is an example of the present invention! , Sample A? It can be seen that ~// has a durability of at least 70,000 times or more.

As shown in sample variation 7, it is clear that when the amount of lubricant is 7 wt% or less, the durability is significantly inferior to that of the examples.

Also sample jI6. /2, Mohs hardness 4
The following abrasives are inferior in durability to those with a Mohs hardness of 6 or higher.

In addition, as shown in Comparative Examples /3 and /4t, Mohs hardness is 6
Even if the amount is above, sufficient durability cannot be obtained if the amount used is less than jwt%.

The evaluation method for the data shown in Table 6 is as follows.

(1) Ra: Model 5E-j manufactured by Koita Research Institute
Cut off O, 2! Ra was determined using mmH.

(2) Durability: Using a floppy drive, perform a durability test by rotating it continuously at 23°C, O%RH, and 10g of pad pressure until the output of the floppy disk becomes 20% or less of the initial output. The number of rotations is preferably 10,000,000 or more as a product.

〔Effect of the invention〕

The magnetic recording medium according to the second aspect of the present invention is one in which the surface properties of the magnetic layer and the durability against repeated use are simultaneously improved.

Claims (1)

[Claims] A magnetic recording medium comprising a magnetic layer coated on a non-magnetic support, wherein the magnetic layer comprises (1) 3% or more by weight of non-magnetic powder with a Mohs hardness of 6 or more based on ferromagnetic powder; and (2) at least one selected from fatty acids, fatty acid amides, fatty acid esters, fatty acid-modified silicones, and α-olefin oxides in an amount of 7% by weight or more based on ferromagnetic powder.