JPS6180524A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the output, S/N, traveling property etc. of the titled medium by providing a back layer contg. specified carbon black, a resin of a specified modulus, an anionic surfactant, and a specified amt. of nonmagnetic powder on the surface of a nonmagnetic supporting body opposite to the surface on which a magnetic layer is provided. CONSTITUTION:A back layer, contg. 50-90wt% based on a binder, material classified as M.T and FT or M.T and FT equivalents in the carbon black industry, sufficiently miscible with the binder, and having 0.1-1mu mean single particle diameter and a resin having <=150kg/cm<2> 100 modulus, contg. an anionic surfactant such as alkyl(benzene) sulfate, and contg. nonmagnetic powder of TiO2, SiO2, MoS2, etc. having low surface electric resistance or the magnetic powder obtained b reducing the high electric resistance of the single material by surface treatment in 300/100-40/100 weight ratio to the binder, is provided on the rear surface of a supporting body of a magnetic recording medium wherein a magnetic layer contg. ferromagnetic fine powder is provided on the surface of the nonmagnetic supporting body. A recording medium provided with a back layer having excellent resistance to abrasion and traveling property and without having an unfavorable influence on the magnetic layer is thus obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more particularly, to a method for increasing the sensitivity of a magnetic recording layer (hereinafter referred to as a magnetic layer) and providing support for achieving these characteristics. The present invention relates to a magnetic recording medium in which a bank layer is provided on the opposite side of the body from 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. 50-3927 and Japanese Patent Application Laid-open No. 57-11182.
No. 8, JP-A-52-102004, JP-A-52-96
No. 505.

[Problem that the invention seeks to solve]

However, these technologies also require driving durability.

It is extremely difficult to obtain a magnetic recording medium with high sensitivity. The main reason for this is to improve the surface quality of the magnetic recording medium (smoothing) and to create a smooth surface between the magnetic recording and reproducing head.
-Loss is reduced, but running durability deteriorates and the coefficient of friction increases, causing the magnetic layer to fall off. Furthermore, when the surface of the MEC 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 RF output or signal/noise ratio (S/N) of the magnetic layer. Furthermore, even during initial running when the magnetic layer and back layer do not fall off, the T90 tube out increases and the signal-to-noise ratio decreases. Calender (for example, Japanese Patent Publication No. 49-10244) molding method is a method for smoothing the magnetic layer in order to achieve high sensitivity, but this method achieves the smoothness required for the magnetic layer in order to achieve high sensitivity. Under such conditions, the /2 layer may peel off, making manufacturing difficult.

In view of the above points, the inventors of the present invention conducted various analyzes and as a result of intensive study, the inventors found that the drop during initial and <b return running,
It was concluded that the cause of the out-of-print was due to dust adhesion and scratching of the magnetic recording medium. In many cases, this dust adhesion is thought to be caused by 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. The chargeability is not just the surface electrical resistance characteristics of the magnetic recording medium, which was conventionally thought, but also the charge potential of the medium itself. 1. The selection of the powder and binder resin that govern these characteristics is important. Furthermore, environmental factors during driving are also important, and the electrification of dust and the influence 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 signal-to-noise ratio of the magnetic layer even if it is 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. The 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]

That is, the present invention provides a magnetic recording medium comprising a magnetic layer 1 and a thick layer on the other side of a non-magnetic support, in which the back layer is made of carbon black having an average single particle diameter of 0.1 to 1 μm. , 50 to 95% by weight of the total binder amount is a resin having a 0100% modulus of 150 degrees or less, and an anionic surfactant, and the ratio of the nonmagnetic powder contained in the back layer to the total binder is 300%. /Zoo~50/100
It is a magnetic recording medium that is characterized by the ability to record images.

The present invention will be explained in detail below.

The ferromagnetic fine powder of the magnetic layer used in the present invention is 7"-Fe203-C with a nitrogen adsorption method specific surface area (B, E, T, method) of 25 m" above the blade, preferably 30 m"79 or more.

Containing r -Fe, O,, Fe, O-, Go gold-containing Fe
,O,,Cry,.

Known ferromagnetic fine powders such as Go-Ni-P alloy and Go-Ni-Fe alloy can be used.
4090 Publication, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28466, Japanese Patent Publication No. 46-3
8755 Publication, Japanese Patent Publication No. 47-4286, Japanese Patent Publication No. 12422-1982, Japanese Patent Publication No. 17284-1984, Japanese Patent Publication No. 18509-1989, Japanese Patent Publication No. 47-18
It is described in Publication No. 573, 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.
It is described in the issue.

The carbon black used in the back layer of the present invention is classified into M, T (Medium
m Thermal), FT (Fine Thermal)
al) and Furnace Carbon's MT mei are equivalent to FT. Commercially available carbon plaques include Asahi Thermal (Asahi Carbon) and HTC Su20 (
8 Iron Chemicals) y Sepacarb MT (Sebalco) Tuber 1J990 (7-ba), Leben MTP (Columbia) Thermax P-33, etc. These carbon blacks are characterized by having a nitrogen adsorption specific surface area of 251n"79 or less, and a relatively undeveloped carbon black structure called stracture. This requires excessive dispersion power, which usually destroys the structure of the carbon blank. However, if the carbon blank is not sufficiently mixed, there will be a problem of missing powder after forming the coating. MT, FT, and FT-equivalent carbon have no or little carbon content, and are well mixed with the binder, and there is no increase in the surface electrical resistance of the coating film as the dispersion progresses.Also, these carbon blacks have a moderate roughness. Good durability can be achieved by combining the following resin, powder/binder ratio, and polyisocyanate.The average particle size of carbon black is 0.1 to 1μ depending on the combination with polyisocyanate. is preferable, and 0.15 to 0.5μ is particularly preferable.

The amount of 100 thymodylus used for the back layer in the present invention (according to J.E.S. 6301) is 150 kg/cvt.
The following resins are used as a type of binder, and among those conventionally used as binders for magnetic recording film bodies as listed below, those having the above-mentioned properties are used. In particular, it is preferable that the 100% modulus is 120kllA- or less. If it is larger than 150kl□, the back layer will be defective in terms of cracking and dropout.

These binders include conventionally known thermoplastic resins,
There are thermosetting resins, reactive resins, and mixtures thereof.

The thermoplastic resin has a softening temperature of 150° C. or less, an average molecular weight of io,ooo to 200,000, and a polymerization degree of about 200 to 500, such as vinyl chloride vinyl acetate copolymer, polyurethane resin, Phenoxy resin, epoxy resin, polyester resin, acrylic acid ester styrene polymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicon resin, butadiene acrylonitrile copolymer, polyamide Resin, polyvinyl butyral, cellulose derivatives (cellulose acetate diacetate, cellulose diacetate, cellulose triacetate, cellulose propionate, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, Various synthetic rubber-based thermoplastic resins and mixtures thereof are used.

The 100 thymodylus used for the back layer of the present invention is 150
9/c7I? The resin is about 5% of the total binder amount.
It is used in a range of 0 to 95% by weight. A typical commercially available resin with a 100% modulus of 150 kl/an2 or less is DN-4805 (100 kl/an2 or less).
% modulus = 50 'Q/cvt' (same below)
, DN-4806 (100ψ-), DN-4830 (
120-1”), Nz3oz (25-40kli
'/cm''), N2304 (15 to 30 ψcm) (all manufactured by Nippon Polyurethane), etc.

゛ A polyisocyanate-based curing agent is used in the back layer of the present invention, such as Desmodur (Sumitomo Bini-N),
Coronate L, (Japan Polyurethane).

Tasenate D-102 (Shikinichi Yakuhin Kogyo), Desmodur TT (Sumitomo Bayer), Takenate D-200 (
Shikinichi Yakuhin Kogyo), etc.

The reason why a resin with a 100% modulus of 150'Q/crrr" or less is required by 50 to 95% by weight is to reduce scratches caused by dust between the resin and the GA system, and is mainly used to absorb the impact of dust. It can be considered that at the same time.

The backing layer also needs to be strong, and we created this using J+ fincyanate, which cures quickly and is hard, to create a well-balanced coating. It is desirable to use the diphenylmethane polyisocyanate in an amount of 40 to 5% by weight based on the total weight of the binder.

Examples of anionic surfactants used in the present invention include alkyl sulfates, alkylbenzene sulfates, alkyl sulfonates, 1-alkylbenzene sulfonates, alkyl fatty acid salts, and alkylphosphonic fi salts d! The following are some of the representative compounds.

Compound Structure Formula% Formula% 2) C□7H35COONa Chimiques do la Mer Rouge
4) C8H□7-C6H, -3o3Na7) C,2
H, 0-0H20H20H2-3o, Na These compounds are mixed in the binder and have the effect of increasing the electrostatic properties of the coated film after coating, and are effective in preventing the adhesion of dust.

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

These resins have a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 200 to 2.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic ester acrylonitrile copolymer, acrylic powder ester vinylidene chloride copolymer, acrylic ester styrene copolymer,
Methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane distomer,
Nylon-silicon wm, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose mi conductor (cellulose acetate phthalate, cellulose diacetate) , cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin,
Various synthetic rubber-based thermoplastic resins and mixtures thereof are used.

Examples of these resins are given in Japanese Patent Publication No. 37-6877.

No. 39-12528, No. 39-19282, 40-53
No. 49.

40-20907, 41-9463, 41-140
No. 59, No. 41-16985, No. 42-6428, 42
-11621, 43-4623, 43-15206
No., 44-2889, 44-17947, 44-1
No. 8232, No. 45-14020, No. 45-14500, No. 47-18573, No. 47-22063, No. 47-2
It is described in publications such as No. 2064, No. 47-22068, No. 47-22069, No. 47-22070, and No. 47-27886.

The fine powder other than carbon black used in the back layer of the present invention is T10. T40□, talc, 5as
o4. 'CaC03+Graphite, (OF)n, (B
N-in, St, □, MoS2゜ZnO, α-Fe20
3. k12(Sl,,)2. AJ203. Ca5
103. Zeo-y a), MgCO3, BaC0a
, 0r203. StC, silicon nitride.

Zirconium silicate, Mg5tOn, benzoguanamine resin, CsO, Bed, (CB)n, M
g(OH)2. etc.

Among these, it is preferable that the surface electrical resistance can be lowered by surface treatment for those 1 that individually have a low surface electrical resistance, and those that individually have a high surface electrical resistance. All of these fine powders have an average particle size of 0.01μ to 3μ.
It is preferable that the degree of

The non-magnetic powder of the present invention contains 50% of the above-mentioned carbon black.
It is preferable that the non-magnetic powder contains at least % by weight and the ratio of the non-magnetic powder to the total binder is 300/100 to 40/Zoo. Particularly preferred is 200/100 to 75/Zoo.

The weight ratio of non-magnetic powder to total binder is 30Q/10
If it exceeds 0, the adhesion with the non-magnetic support will deteriorate, dropout after reversing will tend to increase, and 50/10
When the value is less than 0, it is extremely difficult to satisfy the surface electrical resistance of the tape, and noise due to discharge between the tape and the deck head is observed as 30 glob-out.

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

Examples of the dispersant used in the bank layer of the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylinic acid, stearolic acid and the like having 12 carbon atoms. ~18
fatty acid (R1COOH1R□ is an alkyl group having 11 to 17 carbon atoms).

Alkali metals (Li, Na, K, etc.) of the above fatty acids
or alkaline earth metals (Mg, Oa, Ba, P
b, Cu, etc.): lecithin, etc. are used.

The lubricant used in the bank layer of the present invention includes graphite, molybdenum disulfide, tungsten disulfide, carbon number 1,
Fatty acid esters consisting of 2 to 16 monobasic fatty acids and monohydric alcohols with 3 to 12 carbon atoms, monobasic fatty acids with 17 or more carbon atoms, and the total number of carbon atoms in the fatty acid. Fatty acid esters made of monohydric alcohols having 21 to 23 atoms, 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 to be used when cross-coating the composition for the back layer of the present invention includes ketones such as a7tone, methyl ethyl ketone, methyl imbutyl ketone, cyclohexanone, methanol, ethanol, prono ζ-nol, etc. in any ratio.
Alcohols such as methanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid/! Ester systems such as J-cole and monoethyl ether; Glycol ether systems such as ether, glycol dimethyl ether, /licol monoethyl ether, and dioxane; Tar-systems (aromatic hydrocarbons) such as benzene, toluene, and xylene: methylene chlorite 9, ethylene chloride, tetracarbon X, /
For loloform, ethylene chlorohydrin, and dichloro-N, chlorinated hydrocarbons such as benzene, water, and the like can be used.

To form the magnetic recording layer and the back shoulder, 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 support should have a thickness of 2.5 to Z.
The material for the support is about ooμ, preferably about 3 to 40μ. Materials for the support include polyesters such as polyethylene terephthalate and polyethylene acetate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and polyvinyl chloride. In addition to vinyl resins such as, plastics such as polycarbonate, metals such as aluminum and copper, and ceramics such as glass are also used.

The dispersion and preparation of the bank layer composition of the present invention can be carried out using the above-mentioned materials to be dispersed (carbon black, binder, solvent, powder, etc.) using a T-ball mill, a pebble mill, a sand guginder, an attritor, a three-way mill, etc. This can be carried out using a roll mill, a high-speed in-line disperser, a high-speed stone mill, etc.

Methods for applying the above-mentioned back layer onto the support include air dryer coat, flade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, F-sphere roll coat, gravure coat,
Kiss coat, 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" 25 published by Asakura Shoten.
It is described in detail on pages 3 to 277 (published on March 20, 1972).

The thickness of the back layer after coating is particularly preferably 1.5 to 2.5 microns (dry thickness).

〔Example〕

The present invention will be explained in more detail below using examples. It will be readily understood by those skilled in the art that the proportions of ingredients, order of operations, etc. shown herein may be changed without departing from the spirit of the invention.

Therefore, the invention should not be limited to the examples below.

In the examples, "parts" indicate "parts by weight."

Example 【.

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) was added and the mixture was uniformly mixed to prepare a magnetic paint.

GO-containing r-Fe 20s powder 3
00 parts (powder Hc = 6000s) Vinyl chloride-vinyl acetate compound 30 parts (
VMCH, manufactured by Union Carbide 0) (average particle size 17 mμ) Lecithin 3 parts oleic acid 5 parts octyl ucrate 3 parts lauric acid
Tripartite butyl acetate
330 parts methyl ethyl ketone 6
60 parts of this magnetic paint was applied to the surface of the poly-1-ethylene-tere-7-talate substrate, dried, and mixed with a bank liquid of the following composition using a ball mill. In addition, after uniformly dispersing the mixture, it was applied 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 250ma) Cr203 (
Average particle size 0.7 μ) 1 part [Compound A) (listed in Table 1) x parts (Table J Nitsupotsun-
2304 (manufactured by Nippon Polyurethane) 70 parts Saran resin (manufactured by Dow Chemical) 30 parts nitrocellulose 20 parts copper oleate 1 part stearic acid
0.5 part methyl ethyl ketone
450 parts cyclohexanone
50 copies I used a calendar to give this tape a mirror finish, and then slit it into 1-inch pieces to make samples.

The number of dropouts of these tapes was measured after running 500 passes of chargeability RF specific output, and the results are summarized in Table 1.

The charging property was determined by using a roller charging type 7 Alladay gauge electrometer to determine whether the charge on PET was positive or negative.

RF ratio output, output when recording and reproducing at 4MHz relative a
Indicated by B. The number of r dropouts after repeated running of 500 passes is also shown. For dropouts, a dropout counter was used to display the number of times the playback output level decreased by 16+LB or more in a period of 15 μsac or more/1 minute average.

Table 1 * Comparative Example As is clear from the above results, when the ratio of carbon black, binder, and non-magnetic powder to total binder in the back layer satisfies the provisions of the present invention, the anionic type according to the present invention It can be seen that various properties are superior when a surfactant is included.

In particular, when known silicone was used, it was inferior in dropout, charging performance, and RF output.

Example 2 The following composition was thoroughly kneaded in a ball mill, and then 20 parts of Desmosier L-75 (trade name of a polyisocyanate compound manufactured by Bayer AG) was added and uniformly mixed and dispersed to obtain a magnetic paint.

Nitrocellulose 15 parts Epoxy resin (epoxy group content 0.56) 10 parts Lecithin 3 parts Oleic acid 1 part Octyl lauric powder 3 parts Lauric acid
4.5 parts methyl acetate
330 parts methyl isobutyl ketone
660 parts of this magnetic paint was applied to the surface of the polyester base film and dried to form a bank liquid having the composition shown below.

Adjusted with a ball mill, 2μ on the non-magnetic support surface opposite to the magnetic layer.
It was applied thickly.

Merck (bentonite) 50 parts Graphite 500 parts Niraporan-230 (Japan Polyurethane) 50 parts Saran resin (Dow Chemical) 25 parts Compound Example 4
Part 1 Coronate 2014
25 parts methyl ethyl ketone
450 parts cyclohexanone
50 copies of this tape were polished to a mirror finish using a calendar, and then slit to a width of 374 inches to obtain sample number 9.
I created a sample.

Example 3 After a magnetic layer was coated in the same manner as in Example 2, a back solution having the following composition was prepared using a ball mill and coated to a thickness of 2 μm on the opposite side of the nonmagnetic support from the magnetic layer.

Talc (bandonite) 50 parts Goophyte 50 parts Eninlan-2304 (Nippon Polyurethane) 50 parts Saran Resin (Dow Chemical) 25 parts Compound Example 5
Part 1 Coronet) 2014
25 parts methyl ethyl ketone
450 parts cyclohexanone
50 copies A V4 inch diameter slit was made in the same manner as in Example 2 to prepare sample No. 10.

Example 4 After applying a magnetic layer in the same manner as in Example 2, a back solution having the following composition was prepared using a ball mill and applied to a thickness of 2 μm on the opposite side of the non-magnetic support from the magnetic layer.

Niraporan N-2304 (made by Nippon Polyurethane) 5 parts Compound Example 6 1 part Coronet)
2014 30 parts methyl ethyl ketone 450 parts cyclohexanone
50 copies In the same procedure as in Example 2, V
A 4-inch diameter slit was made to prepare sample No. 11.

Comparative Example 1゜After applying the magnetic layer in the same manner as in Example 2, the back liquid carbon black was changed from 7MTP to 100 parts of Asahi Carbona 70 (average particle size 27771μ) to adjust the bank liquid. A sample Jv was prepared in the same manner as in Example 2, and was designated as sample number 12.

The Rag of the bank layer of these tapes, the scratches of the back layer, and the number of dropouts after 50 passes were measured and summarized in Table 2.

The Ra value was measured in accordance with Jl5-Ba2O3-1982, with a cutoff value of 0.8 inch.

The level of pickpocketing in the back layer is determined by the level of pickpocketing in the bank layer when repeatedly running on a deck with a 5 minute length 50 nomo play rewind.
More than a book'6x. In addition, the Doronciaud number after 50 repeated runs is shown. The dropout is
The dropout counter displayed the number of 71 minutes in which the reproduction output level decreased by 16 aB or more during a period of 15 μJ'εC or more.

(*) As can be seen from Comparative Example Table 2, the selection of the carbon black size is important, and those that give a surface roughness of less than O,OS μm in terms of Ra value will improve the dropout increase after reversing. Not done.

〔Effect of the invention〕

As described above, the magnetic recording medium of the present invention has good RF specific output, few scratches on the bank layer, and has a small number of dropouts after repeated running for 50 passes. As described above, the present invention provides magnetic recording with good signal-to-noise ratio with few dropouts, good running properties of the bank layer, and high sensitivity in which the surface roughness of the back layer does not affect the signal-to-noise ratio of the magnetic layer. All media can be provided.

Bt-i, 34)'8

Claims (1)

[Claims] In a magnetic recording medium comprising a magnetic layer on one side of a non-magnetic support and a back layer on the other side, the back layer is made of carbon black with an average single particle diameter of 0.1 to 1 μm and a 100% modulus of 150 kg/ cm^2 or less of resin, 50 to 95% by weight of the total binder amount, and an anionic surfactant, and the weight ratio of the nonmagnetic powder contained in the back layer to the total binder is 300/100 to 300/100. A magnetic recording medium characterized in that it is 40/100.