JPH05143965A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To stabilize color tone by forming plural layers of magnetic layers and specifying the film thickness, variation of film thickness of the uppermost layer, and longitudinal variation of the logarithmic value of transmittance T of all magnetic layers. CONSTITUTION:Plural layers of magnetic layers are deposited directly or with proper intermediate layer interposed on a nonmagnetic supporting body. The uppermost layer contains Co-contg. gamma-Fe2O3 powder, etc. It is preferable that the surface area and 1600-1700Oe coercive force. The uppermost magnetic layer is made <=1mm thickness with <=0.02mum variation. Moreover, the transmittance T of all magnetic layers is specified that variation of log T in the longitudinal direction is <=0.05. As for the binder resin, not only urethan polymers, etc., having 10000-200000 average mol.wt. but a resin having negative functional groups such as vinyl chloride is used by 0.01 to 10.0mg/g so as to improve dispersion of the ferromagnetic powder and to obtain high output and stable traveling. By this constitution, the color tone of reproduced pictures is stabilized without variation of chroma output and chroma SN ratio.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to magnetic recording media, and more particularly to stabilizing video images.

[0002]

BACKGROUND OF THE INVENTION Stability of reproduced sound and images of a magnetic recording medium is deeply related to the thickness of a magnetic layer and its variation.

In JP-A-63-187419, the thickness of the uppermost layer is 2
The thickness is preferably less than or equal to μm, particularly preferably less than or equal to 1 μm, and the reason is that electromagnetic conversion deteriorates when the uppermost layer is greater than or equal to 2 μm.

In Japanese Patent Laid-Open No. 2-154320, the thickness of the uppermost layer is
It is said that the sound output is improved by setting it to 0.1 μm or more and 1.5 μm or less.

When the uppermost layer of the multi-layer magnetic recording medium is set to 1 μm or less, the chroma signal is recorded over two or more layers. However, in a multi-layer magnetic recording medium, the properties such as Hc, σs, powder particle size, and axial ratio of the magnetic powder of each magnetic layer are usually different, and when recording is performed over two or more layers, each layer has different quality. Is played. Therefore, if the film thickness of the uppermost layer is not constant, the chroma signal output and the noise output are not constant, and the chroma output and the chroma S / N become unstable. If you look at this on the playback screen, the color tone of the entire screen will be unstable, so
Even if the chroma output and S / N are high, the chroma output and S / N are low, but they are inferior to the stable ones.

On the other hand, in the prior art, although the uppermost layer film thickness with which a desired electromagnetic conversion performance can be obtained has been studied, the film thickness fluctuation has not been studied at all.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium which compensates for the deficiency of the prior art and provides a reproduction screen with stable color tone without variations in chroma output and chroma S / N.

[0008]

The above object of the present invention is as follows: (1) A plurality of magnetic layers are laminated on a non-magnetic support, and the uppermost layer of these magnetic layers has a thickness of 1 μm or less and a film. A magnetic recording medium characterized by a thickness variation in the longitudinal direction of 0.02 μm or less, and / or (2) a plurality of magnetic layers laminated on a non-magnetic support, This is achieved by a magnetic recording medium characterized in that the uppermost layer among them contains metallic magnetic powder, and the variation width of the logarithm logT of the light transmittance T of all magnetic layers in the longitudinal direction is 0.05 or less.

In the present invention, the regulation of the film thickness and the variation control of the two characteristics can be achieved by suppressing the variation of the liquid feed amount of the magnetic paint and the variation of the base tension applied to the coater head.

The relationship between the thickness of the magnetic layer and the light transmittance is such that in the magnetic layer using the metal magnetic powder, the light transmittance varies by about 0.025 with respect to the fluctuation of the film thickness of 0.01 μm. In the case of a magnetic layer, by suppressing the light transmittance of all magnetic layers to 0.05 or less, the variation in the film thickness of the uppermost layer can be suppressed to 0.02 μm or less.

In the present invention, the magnetic layer is formed by coating a non-magnetic support with a coating material in which a ferromagnetic powder is dispersed in a binder, either directly or through an appropriate intermediate layer.

As the ferromagnetic powder contained in the magnetic layer,
For example, Co-containing γ-Fe ₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, Co-containing F
eO _x (4/3 <x <3/2) powder, etc. iron oxide magnetic powder; Fe powder, Ni
Powder, Co powder, FeN powder, Ba-ferrite powder, Fe-Al alloy powder, Fe-Ni alloy powder, Fe-Al-Ni alloy powder, Fe-Al-P alloy powder, Fe-Ni-Si-Al alloy powder , Fe-Ni-Si Al-Mn alloy powder, Ni-Co alloy powder, Fe-Mn-Zn alloy powder, Fe-Ni-Zn alloy powder, Fe-Co-Ni-Cr alloy powder, Fe-Co-Ni- P alloy powder, Co-
Examples include ferromagnetic alloy powders such as Ni alloy powder and Co-P alloy powder.

Of these, Co-containing γ-F is preferable.
e ₂ O ₃ powder, Fe-Al alloy powder, Fe-Ni alloy powder, Fe powder,
Ba-ferrite powder.

The shape of the ferromagnetic powder is preferably needle-like, but may be spherical, ellipsoidal or plate-like.

[0015] The specific surface area of the ferromagnetic powder (by BET method) is usually, 25 m ² / g or more, preferably 30~80m ² / g.

The ferromagnetic powder has a coercive force of 500 to 2,000 oersteds, preferably 600 to 1,700 oersteds.

The average major axis length of the ferromagnetic powder is usually
0.1 to 0.4 μm, especially 0.15 to 0.30 μm. If this average major axis length is less than 0.1 μm, it may be difficult to obtain good dispersibility. On the other hand, when it exceeds 0.4 μm, the electromagnetic conversion characteristics may be deteriorated.

As the binder according to the present invention, a resin having an average molecular weight of about 10,000 to 200,000 can be generally used.

Specifically, for example, urethane polymer, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide Resin, polyvinyl butyral, cellulose derivative (eg: cellulose acetate butyrate, cellulose diacetate, cellulose propionate,
Nitrocellulose, etc.), styrene-butadiene copolymer,
Polyester resin, various synthetic rubber binders, phenol resins, epoxy resins, urea resins, melamine resins, silicone resins, acrylic reaction resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates , Urea formaldehyde resin, a mixture of a low molecular weight glycol and a high molecular weight diol compound, and a mixture thereof.

In the present invention, a resin having a negative functional group can be preferably used together with these resins or alone.

As the resin having this negative functional group,
^{_{SO 3 M 1, -OSO 2 M}} 1, -OSO 3 M 1, - [(M ² O
-) PO (-OM ^3)] (wherein, M ¹ is a hydrogen atom, an alkali metal, M ² and M ³ are each a hydrogen atom, either an alkali metal and an alkyl group.
Further, M ² and M ³ may be different from each other or may be the same. ) And the like.

The resin having a negative functional group is, for example,
It can be obtained by modifying a resin such as a vinyl chloride resin, a polyester resin or a polyurethane resin to introduce the negative functional group.

The amount of the negative functional group in the resin having the negative functional group is preferably 0.01 to 10.0 mg / g.

When the amount of the negative functional group is within the above range, the dispersibility of the ferromagnetic powder is improved, and as a result, the output of the magnetic recording medium is large and the running stability is improved.

On the contrary, if the amount is out of the above range, these effects may not be sufficiently exhibited.

When the resin having a negative functional group is used, the compounding amount thereof is usually 2 to 50 parts by weight, preferably 5 to 40 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

When the blending ratio is less than 2 parts by weight, the desired effect to be obtained when the resin having a negative functional group is blended may not be sufficiently exhibited. If the amount is more than 50 parts by weight, sliding noise and head turbidity may be deteriorated.

In the present invention, the durability of the magnetic layer can be improved by using a polyisocyanate curing agent together with the resin having the negative functional group.

Examples of the polyisocyanate type curing agent include, for example, tolylene diisocyanate, diphenylmethane diisocyanate, hexane diisocyanate, and the like.
Functional isocyanate, Coronate L (trade name; manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (trade name;
A trifunctional isocyanate such as Bayer), or a urethane prepolymer having an isocyanate group at both ends, which has been conventionally used as a curing agent, or a polyisocyanate usable as a curing agent. Any one can be used.

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

In the present invention, various additives may be used in addition to the various binders described above, if necessary.

Examples of the dispersant include lecithin, phosphoric acid ester, fatty acid, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, known surfactants and salts thereof. , Negative organic groups (eg -C
OOH, —PO ₃ H) Polymer dispersant salts and the like can be used.

These may be used alone or in combination of two or more. A fatty acid ester can be used as a plasticizer. Examples of the fatty acid ester include oleyl oleate, oleyl stearate, isocetyl stearate, dioleyl maleate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, amyl stearate, amyl palmitate. Tate,
Stearyl stearate, lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, butoxyethyl palmitate, butoxyethyl stearate, 2-ethylhexyl stearate, 2-ethylhexyl myristate, ethyl stearate, 2-ethylhexyl. Examples thereof include palmitate, isopropyl palmitate, isopropyl myristate, isooctyl palmitate, isooctyl myristate, butyl laurate, cetyl-2-ethylhexarate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate and the like. Of these, butyl stearate, butyl palmitate, butoxyethyl palmitate, butoxyethyl stearate, isooctyl palmitate, and isooctyl myristate are particularly preferred.

The various fatty acid esters may be used alone or in a mixture of two or more.

The amount of the dispersant such as lecithin and the plasticizer such as fatty acid ester added is within a range that does not impair the running durability of the magnetic recording medium under high temperature and high humidity.

The magnetic layer in the magnetic recording medium of the present invention is
It may contain a lubricant.

Examples of the lubricant include fatty acids, silicone lubricants, fatty acid-modified silicone lubricants, fluorine lubricants, liquid paraffin, squalane, carbon black, graphite, carbon black graft polymers, molybdenum disulfide, and tungsten disulfide. And so on.

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

In the present invention, among the above-mentioned lubricants, fatty acids can be preferably used. Examples of the fatty acid include 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 can be mentioned.

Of these, myristic acid, oleic acid and stearic acid are particularly preferable.

The blending ratio of the lubricant is the ferromagnetic powder.
Generally, 20 parts by weight or less, preferably 1 part by weight per 100 parts by weight
It is 0 parts by weight or less. If this blending ratio exceeds 20 parts by weight, blooming and bleed-out may occur easily.

In the present invention, the magnetic layer has an average grain size of 10 to 10.
It may contain 100 mμ of carbon black.

When the magnetic layer contains carbon black having an average particle size of 10 to 100 mμ, preferably 20 to 30 mμ, the running durability is further improved without deteriorating the electromagnetic conversion characteristics of the magnetic recording medium of the present invention. be able to.
However, when the average particle size of carbon black is less than 10 mμ, running durability may be poor. On the other hand, when the average particle size of carbon black exceeds 100 mμ, the electromagnetic conversion characteristics may be deteriorated when the addition amount is increased.

The blending ratio of the carbon black for sufficiently exhibiting the above-mentioned effects is 100% of the ferromagnetic powder.
The amount is 0 to 5 parts by weight, preferably 0 to 3 parts by weight. However, this does not apply to the lower layer when a plurality of magnetic layers are provided.

The magnetic layer may further contain an abrasive and an antistatic agent in addition to the above various components.

The antistatic agent or the dispersant described above does not have only a single action, but for example, one compound may act as a lubricant and an antistatic agent.

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

Examples of the non-magnetic support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; and polycarbonate. Examples thereof include plastics such as aromatic polyamide and polyimide. Further, metals such as Cu, Al and Zn, glass, various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) and the like can also be used.

The thickness of the support is usually 3 to 150 μm,
It is preferably 4 to 100 μm.

The form of the non-magnetic support may be any of tape, sheet, card, disk, drum and the like.

The thickness of the non-magnetic support is usually 4 to 150 μm, preferably 5 to 5 when it is in the form of a tape or sheet.
It is 100 μm. In the case of a disc or a card, it is usually 30 to 100 μm. Further, in the case of a drum shape, a cylindrical shape can be adopted, and a shape corresponding to the recorder to be used can be adopted.

If desired, a back coat layer may be provided on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed for the purpose of improving the running property of the magnetic recording medium, preventing electrification and preventing transfer. ..

An intermediate layer (for example, an adhesive layer) may be provided on the surface of the nonmagnetic support on which the magnetic layer is formed for the purpose of improving the adhesiveness between the magnetic layer and the nonmagnetic support.

In the magnetic recording medium of the present invention, the ferromagnetic powder, for example, a binder such as a vinyl chloride resin having a negative functional group and other magnetic layer forming components are kneaded and dispersed in a solvent to prepare a magnetic coating material. This magnetic coating material can be applied on the non-magnetic support to be dried.

Examples of the solvent used for kneading and dispersing the magnetic layer forming components include acetone and methyl ethyl ketone (ME
K), ketone systems such as methyl isobutyl ketone (MIBK) and cyclohexanone; alcohol systems such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate. System; ether system such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane; aromatic hydrocarbon such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene And the like can be used.

When kneading the composition of the components for forming the magnetic layer,
The above-mentioned ferromagnetic powder and other magnetic paint ingredients are charged into a kneader simultaneously or individually. For example, first, the ferromagnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and further kneading is performed to obtain a magnetic paint.

For kneading and dispersing, various kneaders can be used. Examples of this kneader include a two-roll mill, a three-roll mill, a pressure kneader, a continuous kneader, an open kneader, 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, and a disper. A kneader, a high speed mixer, a homogenizer, an ultrasonic disperser, etc. may be mentioned.

As a coating method which can be used for coating the magnetic paint, for example, gravure roll coating,
Examples include Mayer bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, skis coating, kiss coating, extrusion coating and fantin coating.

In the case of multi-layer coating, we
It may be t on dry or wet on wet.

The magnetic layer thus coated has a dry thickness of usually 0.1 to 10 μm, preferably 0.5 to 5
μm. Of these, the uppermost layer is 1 μm or less.

Thus, after applying the magnetic layer-forming component,
In the undried state, magnetic field orientation treatment is performed if necessary, and further surface smoothing treatment is performed using, for example, a super calender roll.

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

The magnetic recording medium of the present invention can be used, for example, as a magnetic tape such as a video tape or an audio tape by cutting into a long shape, or as a floppy disk by cutting into a disk shape. .. Further, like a normal magnetic recording medium, it can be used in a card shape, a cylindrical shape, or the like.

[0064]

EXAMPLES Next, examples and comparative examples of the present invention will be shown.
The present invention will be described more specifically. In the examples and comparative examples described below, "part" means "part by weight".

<Magnetic paint for lower and upper layers> Magnetic powder (shown in the table below) 100 parts Sodium sulfonate-containing vinyl chloride resin 10 parts Sodium sulfonate-containing polyurethane 5 parts Alumina (average particle size; 0.6 μm) 5 parts Carbon black (Average particle size; 30 nm) 1 part Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts The above formulation is prepared by kneading and dispersing, and 5 parts of polyisocyanate is used for the lower layer and upper layer, respectively. Was added, and the mixture was sequentially applied on a polyethylene terephthalate film (thickness is shown in Tables 1 and 2 below) by a wet-on-wet method, subjected to magnetic field orientation treatment, and calendered to form a magnetic layer.

Further, a back coat layer coating material having the following formulation was applied to the surface of the polyethylene terephthalate film opposite to the magnetic layer to form a 0.6 μm back coat layer.

<Coat for back coat layer> Carbon black (Raven 1035) 40 parts Barium sulfate (average particle size; 300 nm) 10 parts Nitrocellulose 25 parts Polyurethane 25 parts Polyisocyanate 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The obtained raw fabric was cured at 60 ° C. and then slit to prepare a VHS (registered trademark) video tape or 8 mm video tape (shown in Tables 1 and 2 below).

<Evaluation of characteristics> Chroma output fluctuation: Measure the chroma output for 60 minutes using NV-6200 (manufactured by Matsushita Electric) for VHS video tape and V-900 (manufactured by Sony) for 8 mm video tape, and measure the maximum value. The difference between the minimum values was taken.

Chroma S / N: the above deck and noise meter 925
Chroma S / N was measured for 60 minutes using R (manufactured by Shibasoku), and the difference between the maximum value and the minimum value was taken.

LogT fluctuation: BC of the tape was removed with acetone J
The light transmittance T was measured over 100 m of tape by the light transmittance measuring method (JVC method) conforming to IS standard C6280, and its logarithm logT
The difference between the maximum value and the minimum value of was taken.

The evaluation results are shown in Tables 1 and 2.

The magnetic powders A, B and C in Tables 1, 2 and 3 have the following characteristics.

Magnetic powder A: Co-γ-Fe ₂ O ₃ BET 50m ² / g Hc 900 Oe B: Co-γ-Fe ₂ O ₃ BET 30m ² / g Hc 650 Oe C: Fe-Al BET 50m ² / g Hc 1500 O
e

[0074]

[Table 1]

[0075]

[Table 2]

As is clear from Tables 1 and 2, the sample of the present invention has a very small variation in chroma output and chroma S / N, and the screen color tone is stable.

[0077]

According to the structure of the present invention, it is possible to provide a video tape having a stable color tone without variations in chroma output and chroma S / N.

Claims (3)

[Claims] 1. A plurality of magnetic layers are laminated on a non-magnetic support, and the film thickness of the uppermost layer of these magnetic layers is 1 μm.
A magnetic recording medium having a thickness of m or less and a fluctuation width of the film thickness in the longitudinal direction of 0.02 μm or less. 2. A plurality of magnetic layers are laminated on a non-magnetic support, the uppermost layer of these magnetic layers contains magnetic metal powder, and the logarithm of the light transmittance T of all magnetic layers. A magnetic recording medium characterized in that the fluctuation width of logT in the longitudinal direction is 0.05 or less. 3. A plurality of magnetic layers are laminated on a non-magnetic support, the thickness of the uppermost magnetic layer containing metal magnetic powder is 1 μm or less, and the variation of the thickness in the longitudinal direction. Width is 0.0
2 μm or less, and the logarithm of light transmittance T of all magnetic layers log
A magnetic recording medium in which the fluctuation width of T in the longitudinal direction is 0.05 or less.