JPS63183621A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability and electromagnetic conversion characteristic of a tape by rewinding a tape-like magnetic recording medium formed with a magnetic layer on a nonmagnetic base during curing by using a curing furnace contg. an automatic tape rewinding machine in a stage for curing said recording medium. CONSTITUTION:The tape is rewound during curing by using the curing furnace contg. the automatic tape rewinding machine in the stage for curing the take- like magnetic recording medium formed with the magnetic layer on the nonmagnetic base. This magnetic layer is formed by solidifying magnetic oxide powder of gamma-Fe2O3 or Co-contg. gamma-Fe2O3 or magnetic metallic powder essentially consisting of Fe, Ni and Co by a binder resin such as thermoplastic resin. This magnetic layer is coated on a PE terephthalate film having 10mum thickness and is subjected to coating, orienting, drying and calender treatment, following which the tape is rolled and is cured for 60hr in the curing furnace at 70 deg.C. A back coat layer essentially consisting of carbon black is provided on the surface of the film on the side opposite from the magnetic layer and the film is taken up to a roll shape. The roll is put into the curing furnace contg. the automatic rewinding machine to cure the layer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic sheets used in audio/video equipment, computers, and the like.

BACKGROUND OF THE INVENTION Magnetic recording media are increasingly becoming more densely packed year by year. As a result, it is necessary to reduce recording and reproducing losses in the short wavelength region, and measures are being taken to further reduce the gap between the magnetic head and the magnetic recording medium. That is, making the surface of the magnetic recording medium highly smooth, making the magnetic powder finer, etc.

However, due to the high smoothness of the surface of the magnetic recording medium, the coefficient of friction of the magnetic recording medium increases, resulting in poor running performance and durability compared to conventional magnetic recording media.

As a method for solving this problem, it is generally known to provide a back coat layer on the surface of the nonmagnetic support of the magnetic recording medium opposite to the magnetic layer. This backcoat layer consists of non-magnetic powder and a binder. Nonmagnetic powder is used as a filler to adjust coating strength, surface electrical resistance, etc. The back coat layer is formed by applying a back coat layer paint onto a non-magnetic support and then subjecting it to a smoothing treatment to impart an appropriate surface roughness.

After the magnetic layer and back coat layer are coated in this manner, the film is wound up into a roll and subjected to a curing treatment. The method was to leave it at a constant temperature of about 60°C to 70°C for a certain period of time.

Problems to be Solved by the Invention Magnetic tape wound into a roll is subjected to a hardening process. At this time, the surface roughness of the magnetic layer is influenced by the surface properties of the back coat layer or base film. This is a phenomenon called set-off, in which the surface roughness of the other surface in contact with the magnetic layer is transferred during curing. in this case,
Because there is a slope in the force applied from the outside to the core, the degree of set-off varies, and the influence is greater on the core.

As a result, the surface properties of the magnetic layer have a gradient in the longitudinal direction, which causes gradients in properties such as electromagnetic time conversion characteristics, powder shedding, and head wear, making it difficult to produce stable products.

Means for Solving the Problems The present invention utilizes a curing furnace equipped with an automatic tape rewinding machine in the curing process during the manufacturing process of a tape-shaped magnetic recording medium in which a magnetic layer is formed on a non-magnetic support. By rewinding the magnetic tape during hardening, it is possible to reduce the slope of surface roughness due to set-off, and it is possible to produce a stable magnetic tape.

Function According to the present invention, by using a curing furnace equipped with an automatic tape rewinding machine in the curing process, it is possible to eliminate gradients in surface roughness due to set-off. As a result, head wear due to variations in surface roughness, especially for power-to-hour conversion,
It is possible to reduce variations in powder falling, etc., or the slope of its characteristics.

In addition, since the amount of residual solvent in the magnetic layer can be reduced, the filling rate of the coating film is increased, and properties such as electromagnetic conversion characteristics and durability are also improved.Wrinkles do not appear during curing, which improves productivity. improves.

Examples The ferromagnetic powder that can be used in the present invention is γ-F e 2
03. C.

Contains r-'Fe2O3, Co-coated r-''2 Q3, etc. oxide magnetic powder, Fe.

Various ferromagnetic powders such as metal-based magnetic powders containing Ni and Co as main components and barium ferrite may be used.

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 curing temperature of 150°C or less and an average molecular weight of 10,000 to 20,00.
0, with a degree of polymerization of about 200 to 2,000, such as vinyl chloride-vinylidene acetate copolymer, vinyl chloride-vinylidene chloride copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer Polymer.

Acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer Polymers, acrylonitrile-butadiene copolymers, polyamide resins, polyvinyl butyral, styrene-butadiene copolymers, polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amine resins, cellulose acetate butyrate as cellulose derivatives.

Examples include cellulose diacetate, cellulose triacetate, cellulose propionate, and nitrocellulose.

As a thermosetting resin, it is 200.000 in the state of coating liquid.
Those having the following molecular weights and which become 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.

Mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polymeric polyester resins and diisocyanate prepolymers, urea formaldehyde resins,
These include mixtures of polyester polyols and (poly)incyanates, polyamide resins, low molecular weight glycols, high molecular weight diols, mixtures of triphenylmethane triincyanate, and mixtures thereof.

Examples of unsaturated prepolymers for electron beam curable resins include maleic anhydride type, urethane acrylic type, and polyester acrylic type.

Polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., or ether acrylic type as a polyfunctional monomer.

Examples include urethane acrylic type, phosphate ester acrylic type, and aryl type.

Furthermore, 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 isocyanates that can be used are, for example, tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate) (
M, XDI), and adducts of these isocyanates and active hydrogen compounds, with an average molecular weight of 100 to 3.
,000 is preferred.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lylene diisocyanate, trimethylhexamethylene diisocyanate, and adducts of these isocyanates and active hydrogen compounds. Among these incyanates and adducts of these incyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferable. Among the aliphatic incyanates, non-alicyclic incyanates and adducts of these incyanates and active hydrogen compounds are desirable.

Dispersants include lecithin, caprylic acid, lauric acid,
Myristic acid, valmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid.

Fatty acids having 8 to 18 carbon atoms, such as lyleic acid.

Examples include metal soaps made of alkali metals (Li, Na, etc.) or alkaline earth metals (Mg, Ca, Ba, etc.) of the above-mentioned fatty acids. In addition, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used.

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

Antistatic agents include graphite, tin oxide-antimony oxide type compounds, titanium oxide-tin oxide-antimony oxide type compounds as conductive powders, saponin as natural surfactants, alkylene oxide type and glycerin type as nonionic surfactants. , glycidol type, higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums, sulfoniums as cationic surfactants, carboxylic acids as anionic surfactants.

Examples include anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups, and amphoteric surfactants such as amino acids, aminomashonic acids, and sulfuric or phosphoric esters of amino alcohols. Another preferable antistatic agent is carbon black.

Lubricants include silicone oil, graphite, molybdenum disulfide, and tungsten disulfide.

There are monobasic fatty acids having 12 to 16 carbon atoms, and fatty acid esters having 21 to 23 carbon atoms consisting of -valent alcohols.

Various types of crosstalk devices are used to disperse magnetic paint crosstalk. For example, three roll mill, agitator mill, ball mill, pebble mill, sand grinder, high speed stone mill, high speed impact mill.

Dispers, attritors, kneaders, planetary mixers, high speed mixers, homogenizers.

A cobal mill, an ultrasonic dispersion machine, etc. are used alone or in combination.

The present invention will be further explained in detail below.

(Example 1) Fe-Co-Ni metal magnetic powder 100 parts by weight BET specific surface area ss tr? /? Hc 1500 0e a8 125 emu/7 Long axis 0.23 μm Short axis 0.04 μm Polyurethane 10 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight α-A1203 6 parts by weight Myristic acid 2 parts by weight Pentyl stearate 1 Weight part ME
K-Tolxun-MIBK 200 parts by weight (weight ratio 2:2:1) The above composition was dispersed using a continuous kneader, a ball mill, and a sand mill.

Next, 4 parts of Incyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added, filtered through a filter with an average pore size of 1 μm, coated on a 10 μm thick polyethylene terephthalate film, oriented, dried, calendered, and then wound into a roll. , in a curing oven at 70 degrees for 60 hours.

Thereafter, 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, and then wound into a roll and cured in a curing oven at 70 degrees for 24 hours. In this way, a 3000 m magnetic tape was obtained. In both of the above two curing treatments,
This is carried out in a curing furnace containing an automatic rewinding machine of the present invention.

Let one end of the tape be A and the other end B. Initially, A is used as the core, and after curing for 1 hour, it is re-wound so that B is the core, and cured for 2 hours. Next, use A as the core for 4 hours, B as the core and continue for 8 hours, and so on.

(Comparative Example 1) In both of the curing steps, the A-end was used as the core for curing, and no rewinding was performed.

(Comparative Example 2) In two curing steps, first, the A end was used as the winding core, and after backcoating, the B end was used as the winding core and hardening was performed, and no rewinding was performed midway.

The characteristics of each magnetic tape obtained are shown in Tables 1 to 4.

In order to observe the gradient of the characteristics of the magnetic tape, samples were taken every 500 m in both the example and the comparative example.

Table 1 Surface roughness Table 2 C (dB) Table 3 Head wear (μ) Table 4 Amount of residual solvent (μy/m) (Note) The amount of residual solvent is the total amount of MEK, ) luene, and MIBK.

Surface roughness Ra (arithmetic mean of deviations from the center line of surface roughness) was measured using Talystop, manufactured by Rank Ta1or Hobson.

Each of the obtained magnetic tapes was cut into 8 sieve widths, loaded into a cassette, and sold by Eastman Kodak Company. C has a value of 5 MHz as the carrier and 4.5 as the noise.
MHz values were used. Note that the A end in the example was set to odB.

Head wear is shown when running 100 passes in an environment of 5° C. and so% RH.

Effects of the Invention As is clear from comparing Examples and Comparative Examples, using the curing furnace with a built-in rewinding machine of the present invention not only reduces the slope of the properties but also reduces the amount of residual solvent, which improves the strength of the tape. We were also able to improve durability and electromagnetic conversion characteristics. This is clearly a result of using a curing oven with a built-in rewinder.

Claims (1)

[Claims] In the curing process of a tape-shaped magnetic recording medium in which a magnetic layer is formed on a non-magnetic support, a curing furnace equipped with an automatic tape rewinding machine is used to perform rewinding during curing. Production method.