JPS6192423A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease drop-out and to improve a signal to noise ratio and the running property of a back layer by using the back layer which contains 50-95wt% carbon black having 0.1-1mum average single grain size and a resin of which the electrification series is plus with respect to polyethylene terephthalate in the total binder. CONSTITUTION:The magnetic layer of a magnetic recording medium provided with a magnetic layer on one side of a non-magnetic substrate and a back layer on the other side contains pulverous ferromagnetic powder having >=27m<2>/g specific surface. The back layer contains 50-95wt% the carbon black having 0.1-1mu average single grain size and the resin of which the electrification series is plus with respect to the polyethylene terephthalate in the total binder. The non-magnetic powder contains >=50wt% carbon black and the ratio of the non- magnetic powder and the total binder is preferably 300/100-50-100, more particularly preferably 200/100-50/100. A thermoplastic resin, thermosetting resin or reaction type resin or the mixture composed thereof is selectably usable for the binder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more particularly, to enhancement of the sensitivity of a magnetic recording layer (hereinafter referred to as a magnetic layer) and support for achieving these characteristics. The present invention relates to a magnetic recording medium in which a magnetic layer is sandwiched between the magnetic layers and a magnetic layer is provided on the other side of the magnetic layer.

[Conventional technology]

In recent years, magnetic recording has been required to have higher sensitivity. Higher sensitivity enables higher image quality, better sound quality, and higher density recording, and these can be achieved by improving the magnetic recording/reproducing deck, the recording method for magnetic recording media, and improving and improving magnetic recording media.

High sensitivity in magnetic recording media can be achieved by increasing the signal part of the signal-to-noise ratio and reducing the noise part, and the former is specifically achieved by making the ferromagnetic powder even finer and shape anisotropy. This can be achieved by increasing the residual magnetic flux density and coercive force of the magnetic recording medium by manipulating the magnetic flux density and the arrangement of single magnetic domains in the fine powder bed.

On the other hand, the latter reduction in the noise portion involves various factors, including smoothing the magnetic layer and controlling the charging characteristics of the magnetic recording medium. Providing a back layer to control charging characteristics and maintain running durability was proposed, and detailed techniques for these are disclosed in Japanese Patent Publication No. 5o-3927 and Japanese Patent Application Laid-open No. 57-11182.
No. 8, JP-A-52-102004, JP-A-52-96
Known in No. 5'05.

[Problem that the invention seeks to solve]

However, even with these technologies, it is extremely difficult to obtain a highly sensitive magnetic recording medium with running durability, and the main reasons for this are 1) improving the surface properties (smoothing) of the magnetic recording medium; Although the spacing loss between the magnetic recording and reproducing head is reduced, the running durability is deteriorated and the coefficient of friction is increased, causing the magnetic layer to fall off. 2) When the surface of the back layer is roughened to improve running durability, the rough surface of the back layer is transferred to the magnetic layer, resulting in a decrease in the signal-to-noise ratio of the magnetic layer. 3) Furthermore, even during initial running when the magnetic layer and back layer do not fall off, dropouts increase and the signal-to-noise ratio decreases.

4) As a means of smoothing the magnetic layer to achieve high sensitivity, a calendar (for example, Japanese Patent Publication No. 49-10244
No.] There is a molding method, but under conditions that achieve the smoothness required for the magnetic layer for high sensitivity, the back layer peels off, making it difficult to manufacture.

In view of the above points, the inventors of the present invention have carried out various analyzes and have conducted intensive studies, and as a result have come to the conclusion that dropouts during initial and repeated running are caused by dust adhesion and scratching of the magnetic recording medium. In most cases, this dust adhesion is thought to be due to problems with the arrangement, insulation, non-insulation, and running speed of the magnetic tape running guide system of the magnetic recording/reproducing deck. It is thought that resistance etc. are the problem. Charging properties are not just the surface electrical resistance properties of a magnetic recording medium, as previously thought, but also the charged potential of the medium itself, and it is important to select the powder and binder resin that control these properties. . Moreover, when selecting these materials, it is necessary to satisfy the calender release characteristics and the like. Environmental factors during driving are also important, and the charging properties of dust and the effects of temperature and humidity on it are extremely subtle and complex. Furthermore, we investigated the frictional properties and came up with a back layer that does not cause a decrease in the magnetic signal-to-noise ratio even when transferred to the magnetic layer.

A first object of the present invention is to provide a novel back layer, thereby controlling the charging potential, thereby providing a magnetic recording medium with less dropout and an excellent signal-to-noise ratio. The second object is to provide a magnetic recording medium whose back layer has good running properties. A third object is to provide a magnetic recording medium with good sensitivity in which the surface roughness of the back layer does not affect the signal-to-noise ratio of the magnetic layer.

[Means to solve the problem]

As a result of various studies, the present inventors have found that the above object can be achieved by the present invention described below.

That is, the present invention provides a magnetic layer on one surface of a non-magnetic support.
In a magnetic recording medium having a back layer on the other side, the magnetic layer has a specific surface area of 27 rr? 50 to 95% by weight of a resin containing a ferromagnetic fine powder of / or more, and whose charge series is positive with respect to cardan black and polyethylene terephthalate with an average single particle size of 0.1 to 1 μm. The weight ratio of the non-magnetic powder contained in the total binder and the total binder is 300/10-0.
~40/] A magnetic recording medium characterized by being OO.

The present invention will be explained in detail below.

The ferromagnetic fine powder of the magnetic layer used in the present invention has a nitrogen adsorption method specific surface area (B, lT, method) of 27rr? /? above, preferably 30 rr//f or above r-Fe2o5,C
0-containing r-Fe20. , Fe3O4, Co-containing F
e 30a, CFe2, Co-Ni-P alloy, Co
Known ferromagnetic fine powder such as -Ni-Fe alloy can be used. Specifically, Japanese Patent Publication No. 44-14090,
5-18372, Japanese Patent Publication No. 47-22062, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-284
Publication No. 66, Special Publication No. 46-38755, Special Publication No. 4
Publication No. 7-4286, Japanese Patent Publication No. 47-12422,
Special Publication No. 47-17284, Special Publication No. 47-1850
9, Japanese Patent Publication No. 47-18573, etc.

The manufacturing method of these ferromagnetic fine powders or powders, additives, supports, and magnetic recording media is disclosed in Japanese Patent Publication No. 56-26890.
listed in the number.

The carbon black used in the back layer of the present invention is classified into M, T (Medfu
n Thermal), FT (Fine Thermal)
mal ) and furnace car setting MT or F
It is equivalent to T. Commercial products of these Carzen Blacks include Asahi Thermal (Asahi Carbon) and HTC-D.
O (8 Iron Chemicals), Sepacarb MT (Se・Truco) Funogu-N990 (Funo-Natsu-), Lepen MTP (
Columbian), Thermax P-33, etc. These carzen blacks have a nitrogen adsorption method specific surface area of 25R.
/1 or less, and the case called stracture is
One of its characteristics is that the black structure is relatively undeveloped. Excessive dispersion power is required to mix Carzen Black with a binder, but the structure of Carzen Black is usually destroyed and the process progresses. However, if the mixing is not sufficient, particles will be lost after forming a coating. It becomes a problem. However, MT, FT, FT with no or little structure
The equivalent Nocasene has good miscibility with the binder, and there is no increase in the surface electrical resistance of the 5fh film, which is related to the progression of dispersion.

Further, these carbon blacks can provide a moderately rough surface, and good durability can be achieved by combining the above-mentioned ferromagnetic powder with the following resin and powder/binder ratio. The average particle size of Chikarazenblack is preferably 0.1 to 1μ, particularly preferably 0.15 to 0.5μ.

The binder used in the ζ-tack layer of the present invention, which has a positive band arrangement relative to PET, is selected from conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. can be used.

Regarding the charge series, for example, Haruo Takenaka, Koya Ogino; Yukagaku, Vol. 6 (No. 6), p. 299 (1957)
; D, J, Le) unicha ; Am, Dyeg
tuff, R-eptr, 28,853 (1'149
), S.P., Hearsh, D.J., montogo
-meryyText, Res, J, ;25
+279 (1955), J, W, Bal 1 o
u;Text,Res,J,;24,14
G (1954), M Hayek, Arn, Dyes.
t.

Reptr, ; 40, 225 (1951), etc.

Specific examples of resins whose charge series is positive with respect to PET include polyethyleneimine, polyvinyl acetate, polybutyl methacrylate, polyethyl methacrylate,
polycation, polyacrylamide, polyacrylic acid,
Cellulose acetate butyrate, natural rubber, butadiene acrylonitrile copolymer, polychlorobutadiene,
Ephoxy resin, polyvinyl butyral, polyurethane,
Polyisobutylene, polystyrene, styrene, butadiene copolymer, styrene-acrylonitrile copolymer, I
Realyl phthalate, polyethylene glycol, azide coating, cellulose acetate, polyethylene glycol succinate, polyamide 6-6, ethyl cellulose,
Examples include polyformaldehyde P% hollyvinyl alcohol, polyethylene, polyvinyl chloride, polycarbonate, and the like.

A polyisocyanate curing agent is used in the back layer of the present invention, such as Desmodur (Sumitomo Taninil), Coronate L (Japan Polyurethane), Takene) D-10.
2 (Shikinichi Yakuhin Kogyo), Desmodur TT (Sumitomo/Guinil), Takenate D-200 (Shikinichi Yakuhin Kogyo) etc.
The reason why the weight is required is to reduce scratches caused by dust between the thread and the guide thread, and it is thought that it mainly absorbs the impact of dust. At the same time, the coating layer needs to be tough, and this is achieved by using a fast-curing and hard polyisocyanate to provide the lance of the coating film. Diphenylmethane polyisocyanate is 4% of the total weight of Nononinder.
It is desirable to use it in 0-5 weight range.

As the resin other than the above-mentioned resin (used within 50% by weight) used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. .

These resins have a softening temperature of 150°C or less and an average molecular weight of io, ooo to 200. (l OO1 polymerization degree is about 200 to 2000, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer,
Vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic Acid ester styrene copolymer, urethane distomer, nylon-silicon resin, nitrocellulose-holamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, Cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.),
Styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

Examples of these resins are given in Japanese Patent Publication No. 37-6877, 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-20907, No. 41-9463, No. 41-14
No. 059, No. 41-16985, No. 42-6428, 4
No. 2-11621, No. 43-4623, No. 43-1520
No. 6, No. 44-2889, No. 44-17” No. 147, 44
-18232, 45-14020, 45-1450
No. 0, No. 47-18573, No. 47-22063, 47
-22064, 47-22068, 47-2206
No. 9, No. 47-22070, No. 47-27886, and the like.

Fine powders other than Kazen Black used in the back layer of the present invention include Ti01TiO□, Talkyu BaSO4,
CaCO3, graphite, (CF')n, (BN)n
.

S102, MoS2, ZnO, α-Fe20
s, Ac2(SiO2)2, M2O6, Ca Si
O3, zeolite, MgcOs, BaCO5, Cr
205.5iC1 silicon nitride, zirconium silicate, Sign, benzoguanamine resin Cs01B eO-(
CB)n, Mg(OH)2, etc. Among these, those having low surface electrical resistance alone and those having high surface electrical resistance alone are more preferably those whose surface electric resistance is reduced by surface treatment. All of these fine powders preferably have an average particle size of about 0.01 μm to 3 μm.

The non-magnetic powder of the present invention contains 50% of the above-mentioned carbon black.
It is preferable that the powder contains heavy weight and upwind, and the ratio of the non-magnetic powder to the total binder is 300/100 to 50/100. Particularly preferably 200/100 to 50/100. The ratio of non-magnetic powder to total ζ inder is 300/10
If it exceeds 0, the adhesion with the non-magnetic support will deteriorate (dropouts after repeated running will tend to increase, and
When the value is less than 00, it is extremely difficult to satisfy the surface electrical resistance of the tape, and noise due to discharge between the tape and the deck spatula F is observed as dropout.

In the present invention, various compounds can be further used as dispersants and lubricants in the back layer.

Dispersants used in the 79-layer of the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, stearolic acid and the like having 12 carbon atoms. ~18
fat o (RlC(X)HlRl has 11 to 1 carbon atoms
7 alkyl groups).

Alkali metals (LiNaK etc.) or alkaline earth metals (Mg, Ca, Ba, Pb, C
metal soaps consisting of u, etc.); lecithin, etc. are used.

The lubricant used in the layer of the present invention includes graphite, molybdenum disulfide, tungsten disulfide, a fatty acid consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 3 to 12 carbon atoms. Esters, carbon number 17
Silicones such as dimethylpolysiloxane, methylphenylsiloxane, etc., can be used. .

These classifications of dispersants and lubricants are not accurate, and many compounds have the characteristics of both.

The solvent used when applying the i'B-h water composition of the present invention is acetone,
Ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; Alcohols such as methanol, ethanol, flonosonol, and phthanol; and esters such as methyl acetate, 0-ethyl acetate, Q-butyl acetate, ethyl lactate, glycol acetate, and monoethyl ether. :ether,
Glycol ethers such as glycol, ) methyl ether, glycol monoethyl ether, and dioxane; Tars (aromatic hydrocarbons) such as benzene, toluene, and xylene; methylene chloride, ethylene chloride F.

Carbon tetrachloride, chloroform, ethylene chloride IJ
7. Chlorinated hydrocarbon accumulations such as dichlorobenzene can be used.

To form the magnetic recording layer and the ζ-tack layer, the above-mentioned components are arbitrarily combined, dispersed in an organic solvent, and applied as a coating solution onto the support. When used as a tape, the thickness of the support is about 2.5 to 100 microns, preferably about 3 to 40 microns. As the material for the support, polyester such as polyethylene terephthalate and polyethylene naphthalate is used.
In addition to polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride, and plastics such as polycarbonate, ceramics such as metal glasses such as aluminum and copper are also used. be done.

To disperse and prepare the thick layer composition of the present invention, the above-mentioned materials to be dispersed (carbon black, liquid, solvent, powder, etc.) are mixed in a ball mill or a pebble mill.

This can be done using a sand grinder, attritor, three roll mill, high speed impeller disperser, high speed stone mill, etc.

Methods for applying the above-mentioned ζ-tsuku layer onto the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, lino roller coating, transfer roll coating, gravure coating,
Giscoat, cast coat, spray coat, barcode, etc. can be used, and other methods are also possible, and detailed explanations of these can be found in "Coating Engineering" 2 published by Asakura Shoten.
It is described in detail on pages 534 to 277 (published on March 20, 1972). Also, the thickness of the two layers is 1.
Particularly preferred is 5μ to 2.5μ (dry thickness).

[Example] The present invention will be explained in more detail below with reference to Examples. It will be readily understood by those skilled in the art that the components, proportions, order of operations, etc. shown herein may be varied without departing from the scope of the present invention.

Therefore, the present invention should not be limited to the implementation series described below.

In the examples, "1 part" indicates "part by weight."

Example 1 After the following composition was thoroughly kneaded in a ball mill, 40 parts of Desmodur L-75 (trade name of a polyisocyanate compound manufactured by Bayer AG) was added and the mixture was uniformly dispersed to prepare a magnetic paint.

Co-containing -Fe 20s powder 300 parts<
ue, M method surface area 30 rrt2/f ) (powder H
e = 6000e) Vinyl chloride-vinyl acetate compound 30 parts (VMCH
, manufactured by Union Carbide) Nisobora 7 N 2304
15 parts (Japan Polyurethane) Carbon black 20 parts (average particle size 17 mμ) Lecithin 3 parts Oleic acid
5 parts octyl laurate
Tripartite lauric acid
3 parts Butyl acetate 330 parts Methyl ethyl ketone 660 parts This magnetic paint was applied to the surface of a polyethylene terephthalate substrate and dried, and after kneading and adjusting a backing liquid of the following composition in a ball mill, 30 parts of Coronate 2061 (polyisocyanate manufactured by Nipponbori Urethane Co., Ltd.) was added, the mixture was uniformly dispersed, and then coated to a thickness of 2 μm on the opposite side of the polyester substrate from the magnetic layer.

Carbon black 200 parts (Leben MTP, average particle size 250 ml) Niraporan - 230480 parts (made by Nippon Polyurethane) ■ Saran resin (made by Dow Chemical) ■ 30 parts Copper oleate 1 part Stearic acid
0.5 part methyl ethyl ketone
450 parts cyclohexanone 5
0 Copies This tape was polished to a mirror finish using a calendar, and then slit into 1-inch pieces to prepare sample No. 1.

(■ and e indicate the electrification series for PET) Example 2 A sample was prepared in the same manner as in Example 1 and coated with a layer thickness of 1.5 μm, and this was designated as sample number 2.

Example 3 A sample was prepared in the same manner as in Example 1, and a back layer having a thickness of 2.5 μm was applied, and this was designated as sample number 3.

Comparative Example 1 Niraporan-2304 with the back liquid composition of Example 1 was mixed with nitrocellulose (nitrification degree 11.196, molecular weight 50,000, 10
(0% modulus 200 Kp/cm2 or more) Q was replaced with a backing liquid, and the sample was coated to a thickness of 2 μm, and this sample was designated as sample number 4.

Example 4 A sample was prepared in the same manner as in Example 1, and a back layer thickness of 3.0 μm was applied, and this was designated as sample number 5.

Example 5 Among the puncture-resistant compositions of Example 1, Niraporan-2304
A puncture solution was prepared by replacing 55 parts and 155 parts of Saran resin with 55 parts and 155 parts of Saran resin, respectively, and applied to a thickness of 2 μm, and this sample was designated as sample number 6.

Comparative Example 2 Among the compositions of the puncture fluid in Example 10, Niraporan-230
4 and Saran resin were replaced with 30 parts/80 parts, respectively, the backing solution was adjusted and applied to a thickness of 2 μm, and this sample was designated as sample number 7.

The scratches on the back layer of these tapes and the number of dropouts (DO) after running 500/ξ cycles were measured and summarized in Table 1.

The scratches on the back layer are comparable to the level of scratches on the back layer when I repeatedly drove the 5 Chairman 500 Pass Play Rewind on a deck. , those that have were marked △. It also shows the number of dropouts after repeated runs of 500 knots. As for dropouts, the dropout counter displayed the number of 15 minutes in which the reproduction output level decreased by 16 dB or more in a period of 5 μsec or more. .

Table 1 (■ e is the electrification series for PET.) [Effects of the Invention] As is clear from the above results, the magnetic recording medium of the present invention has extremely poor performance in in-slip and dropout.

In this way, does the present invention have a charged potential? It is possible to provide a magnetic recording medium with controlled dropouts, an excellent signal-to-noise ratio, and good runnability of the back layer.

(3 others)

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer is provided on one side of a non-magnetic support and a back layer is provided on the other side, the magnetic layer has a specific surface area of 27
The back layer contains 50 to 95% by weight of a resin having a positive charge series relative to carbon black and polyethylene terephthalate with an average single particle size of 0.1 to 1 μm, including ferromagnetic fine powder of m^2/g or more. A magnetic recording medium, characterized in that the weight ratio of nonmagnetic powder contained in a binder and contained in the back layer to the total binder is from 300/100 to 40/100.