JPS62250519A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To considerably decrease the coefft. of friction of a magnetic recording medium without deteriorating the durability and electromagnetic conversion characteristic thereof by incorporating a graphitized carbon formed by graphitizing part of carbon black and specific carbon black having a specific average particle size into a magnetic layer. CONSTITUTION:This recording medium has the magnetic layer contg. the graphitized carbon formed by graphitizing part of the carbon black and the carbon black having <=30mmu average particle size. Ferromagnetic powder is exemplified by various kinds of ferromagnetic powders including oxide magnetic powders such as nu-Fe2O3, Co-contg. nu-Fe2O3, Co-deposited nu-Fe2O3, Fe3O4, Co- contg. Fe3O4 and CrO2 and metallic magnetic powders essentially consisting of Fe, Ni, and Co such as Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy and Co-Ni alloy. An antistatic agent, and lubricating agent may be added thereto at need in addition to the graphitized carbon and the carbon black of <=30mmu.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium that can be used for audio tapes, video tapes, magnetic disks, and the like.

2. Description of the Related Art In recent years, efforts have been made to smooth the magnetic layer in order to improve the electromagnetic characteristics, especially in video tapes.
Along with this, the coefficient of friction has increased and the running properties of the magnetic tape have become a problem.

Therefore, in the magnetic layer of a magnetic recording medium, solid lubricants such as graphite, molybdenum disulfide, and tungsten disulfide are generally used as lubricants, higher fatty acids, fatty acid esters made of these higher fatty acids and monohydric alcohols, and silicone. Oil etc. are used. Furthermore, carbon black, which is used primarily for the purpose of preventing static electricity, has been recognized to have the effect of reducing the coefficient of friction.

Also, for wear resistance and curl removal, 10 to 30 mμ
Japanese Patent Publication No. 54-9041 discloses that carbon black of 60 to 120 mμ is mixed with carbon black of 60 to 120 mμ.
Although it was proposed in Japanese Patent No. 53-20203, it did not satisfy the above object.

Problems to be Solved by the Invention However, now that camera-integrated VTRs have become widespread, video tapes in particular are often used in harsher environments than ever before, and smoother tapes such as 8mm video tapes A smooth surface is required, and conventional lubricants have had the problem of not being able to maintain smooth running performance.

On the other hand, if a large amount of solid lubricant is added to improve running properties, good running properties can be imparted to the magnetic recording medium, but on the other hand, the degree of filling of the magnetic material in the magnetic layer decreases, resulting in electromagnetic conversion characteristics. This is not preferable because it deteriorates the magnetic properties. On the other hand, using lubricants other than solid lubricants not only fails to provide sufficient lubricity, but also tends to cause pluming at high temperatures and high humidity, causing problems such as tape blocking and stick-slip. It had

The present invention provides a magnetic recording medium that can significantly reduce the coefficient of friction without deteriorating the durability or electromagnetic characteristics of the magnetic recording medium, and that can ensure extremely stable running performance even under poor conditions. The purpose is to provide

Means for Solving the Problems The present invention achieves the above object, and has a structure in which the magnetic layer contains graphitized carbon obtained by graphitizing a part of carbon black, and carbon black having an average diameter of 30 mμ or less. ing.

The total amount of graphitized carbon and carbon black with an average particle diameter of 30 mμ or less is 1 magnetic powder.
The amount is preferably 0.5 to 10 parts by weight per 0.00 parts by weight. If the amount added is too small, the desired running characteristics cannot be obtained, and if it is too large, the electromagnetic conversion characteristics will deteriorate.

The addition ratio of graphitized carbon and carbon black with an average diameter of 30 mμ or less is a weight ratio of 96/S to 6/9.
It is contained in the range of 5.

Operation The present invention not only improves runnability but also exhibits excellent wear resistance compared to the case where carbon black and graphite are simply mixed together.

That is, if abrasives are added in large quantities to satisfy the still life, the damage caused by increased head wear will occur, but it is also a very useful means to solve this problem.

Example Examples of the present invention will be described below.

As the ferromagnetic powder that can be used in the present invention, SeaFe2 (1
5SCo-containing sea Fe2O3, Co-adhered sea ye2o3
, Fe 304, Go-containing Fs504, Qr02 fi
f) Oxide magnetic powder, Fe SNi, Go, Fa
-Ni-Go gold alloy Fe -Mn-Zn alloy, Fe-N
i-Zn alloy, Fa-Co-Ni -Or gold alloy Fa-
Go-Ni-P alloy, Co-Ni alloy, etc. Fe/Mi,
Co 1j! : Examples include various ferromagnetic powders such as metal magnetic powders as the main component.

As the binder resin, thermoplastic resins, thermosetting resins, electron beam curable resins, and mixtures thereof with others are used.

The thermoplastic resin used as the binder resin has a softening temperature of 160°C or less, an average molecular weight of 10.000 to 20,
000. The degree of polymerization is about 2oo~2, OOO,
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinylidene chloride copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer,
Methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, styrene- Butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid ester copolymer, amino resin, cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose globionate, nitrocellulose tocal as a cellulose derivative.

As a thermosetting resin, it is 200, OO in the state of coating liquid.
Those having a molecular weight of 0 or less and becoming insolubilized by reactions such as condensation and addition after coating and drying are used. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, vinyl chloride-vinyl acetate resin, methacrylate copolymer and diincyanate. mixtures of prepolymers, mixtures of polymeric polyester resins and diisocyanate prepolymers, urea formaldehyde resins, mixtures of polyester polyols and (poly)incyanates,
These include polyamide resins, low molecular weight glycols, high molecular weight diols, mixtures of triphenylmethane triisocyanate, and mixtures thereof.

Examples of electron beam curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type,
Polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., and polyfunctional monomers include ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type, etc.

Further, in order to improve the durability of the magnetic recording medium according to the present invention, various hardening agents can be contained in the magnetic layer, for example, incyanate can be contained.

Aromatic incyanates that can be used are, for example, tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (
MIDI), and adducts of these incyanates and active hydrogen compounds, and have an average molecular weight of 1oO to 3
,000 is preferred.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate, and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these incyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3 tOOOO are desirable. Among the aliphatic incyanates, non-alicyclic incyanates and adducts of these isocyanates and active hydrogen compounds are preferred.

Examples of dispersants include lecithin and fatty acids having 8 to 18 carbon atoms such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, and ryleic acid, and the above-mentioned fatty acids. Alkali metals (Li, Na, K, etc.) or alkaline earth metals (
In addition to these, higher alcohols having 12 or more carbon atoms and even sulfuric esters can be used.

As an abrasive, fused alumina, silicon carbide (Sin)
, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. can be used.

Graphitized carbon used in the present invention and 30 mμ
In addition to the carbon black below, the following antistatic agents and lubricants can be added as necessary.0 Antistatic agents include graphite, tin oxide-antimony oxide compounds, titanium oxide, etc. as conductive powders. - Tin oxide - antimony oxide compounds, natural surfactants such as saponin, nonionic surfactants such as alkylene oxides, glycerin, and glycidol, cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, and other complexes. Rings, phosphoniums, sulfoniums, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, phosphoric ester groups, amino acids, aminomashonic acids, amino acids, etc. Examples include amphoteric activators such as sulfuric acid or phosphoric acid esters of alcohols.

As a lubricant, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, carbon number 12
-16 monobasic fatty acids, fatty acid esters with 21 to 23 carbon atoms consisting of -valent alcohols.

Various kneaders are used to mix and disperse magnetic paint. For example, three roll mill, agitator mill, ball mill, pebble mill, sand grinder, high speed stone mill, high speed impact mill, disper, attritor,
A kneader 1 high-speed mixer, a homogenizer, a Copol Minope ultrasonic disperser, etc. are used alone or in combination.

Examples of the present invention will be described in more detail below.

Example 1 Fe-Co-Ni metal magnetic powder 100 parts by weight BIT
Specific surface area 62 emu/g Ha 15000e am 126 emu/g Long axis 0.23 μm Short axis 0.04 μm Graphitized carbon 2 parts by weight (so% graphitized, average particle size 60 mμ) Carbon black 2 parts by weight (average particle size 25111μ) Polyurethane 10 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Al2O, 3 parts by weight Myristic acid 1 part by weight Pentyl stearate 1 part by weight MKK-) Luene-M
IBK 200 parts by weight (weight ratio 2:2:'1
) The above composition was dispersed in a ball mill for 24 hours, and then dispersed in a coball mill for 2 hours.

Next, t-4 parts of polyisocyanate (Coronate L1 manufactured by Nippon Polyurethane Co., Ltd.) is added, and the mixture is filtered through a filter with an average pore size of 1 μm. It is coated on a 10μ thick polyethylene terephthalate film, oriented, dried, calendared and then cured. Furthermore, a back coat layer containing carbon black as a main component was provided on the polyethylene terephthalate film on the side opposite to the magnetic layer to obtain a magnetic tape.

Comparative Example 1 A magnetic tape of 7 tons was obtained in the same manner as in Example 1 except that 2 parts of graphitized carbon was replaced with 2 parts of carbon black having the same particle size (60 mμ).

Comparative Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the average particle size of 2 parts of carbon black was changed to sonμ.

Comparative Example 3 A magnetic tape was obtained in the same manner as in Example 1, except that 2 parts of graphitized carbon and 2 parts of carbon black were replaced with 4 parts of carbon black having an average particle diameter of 301 nμ.

Example 2 Co-deposited v-Fe2O2 100 parts by weight BET specific surface area 4 s mt/g Mayao 0s (Is 65 emu/g Long sleeve 0.25 μm Short axis 0.05 μm Graphitized carbon 2 parts by weight (30 graphitized, average particle Diameter: 60 mμ) Carbon black: 2 parts by weight (average particle size: 3011μ) Polyurethane: 10 parts by weight Nitrocellulose: 10 parts by weight 1203
3 parts by weight palmitic acid
1 part by weight Butyl stearate 1 part by weight MEK-toluene-MIBK 200 weight ratio 2:2:1) The above composition was dispersed in an attritor for 6 hours, and then dispersed in a coball mill for 2 hours.

Next, 4 parts of polyisocyanate (Coronate L1 manufactured by Nippon Polyurethane Co., Ltd.) is added, and the mixture is filtered through a filter with an average pore size of 1 μm. It is coated on a 10 μm thick polyethylene terephthalate film, oriented, dried, calendered and then cured. Further, on the polyethylene terephthalate film on the side opposite to the magnetic layer, a magnetic tape was obtained by disposing a balaf coat containing carbon black as a main component.

Comparative Example 4 A magnetic tape was obtained in the same manner as in Example 2, except that 2 parts of graphitized carbon was replaced with carbon black 2 of the same particle size (eo mμ). Comparative Example 5 Carbon black 2 was used in Example 2. A magnetic tape was obtained in the same manner except that the average particle diameter of the sample was changed to 50 Inμ.

Comparative Example 6 A magnetic tape was obtained in the same manner as in Example 2, except that 2 parts of graphitized carbon and 2 parts of carbon black were replaced with 4 parts of carbon black having an average particle diameter of 30 mμ.

Table 1 shows the characteristics of each magnetic tape obtained.

(L'person-F4, 'white) Surface roughness is "Ta17Stelp"
The surface roughness Ra (arithmetic mean of the deviations from the center line of the surface roughness) was measured using RanK Ta1or (manufactured by Hobgon). The coefficient of friction is ``tape behavior te, t, p.
-J (TAPE BKHAVIORTESTI
Measurement was performed using ER (manufactured by Yokohama System Co., Ltd.). The electromagnetic conversion characteristics were measured using a video tape recorder (NY-8800 manufactured by Matsushita Electric Industrial Co., Ltd.) in which a magnetic tape was wound into a VHS cassette and the recording/reproducing head was changed to a Sendust head. National Videotape 5HG120 (NY-TI 20HG) was used as the standard tape.
The 0 still life with that ayy as QdB is 0°C5
%RH environment is 0. Also, head wear is 1
It shows the amount of wear when running for 100 hours at 0°C and 10% RH.

As mentioned above, as can be seen by comparing Example 1 and Comparative Example 2, and Example 2 and Comparative Example 4, carbon black of 10 to 30 mμ has better characteristics than that obtained only when mixing carbon black of 60 to 120 mμ. It can be seen that the overall properties are also outstanding.

Effects of the Invention As described above, in the present invention, when graphitized carbon and carbon black with an average particle diameter of 30 mμ or less are used together,
The coefficient of friction can be lowered while maintaining the surface properties of the magnetic layer, and stable running properties can be imparted. As a result, improvements in electromagnetic conversion characteristics and wear resistance were observed, and superior properties were obtained in terms of still life and head wear compared to comparative examples.

Claims (1)

[Claims] Graphitized carbon in which a part of carbon black is graphitized and an average particle size of 3 are placed on a non-magnetic support.
A magnetic recording medium characterized by having a magnetic layer containing carbon black of 0 mμ or less.