JPH02260233A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain excellent traveling durability by forming the magnetic recording medium so as to have >=2 yield points. CONSTITUTION:The magnetic recording medium formed by providing plural magnetic layers on a nonmagnetic base has >=2 yield points. The ratios of binders which respectively vary in viscoelastic behaviors (for example, glass transition point) are generally variously varied and are used in the respective layers in order to impart >=2 yield points to the magnetic recording medium. The magnetic recording medium having the excellent traveling durability is obtd. in this way and even if the medium is made to travel under severe conditions, the generation of the tape damages is obviated and the dropouts of a deposition type based on the peeling of the magnetic layers are decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a magnetic recording medium, particularly to a magnetic recording medium suitably used as a videotape.

[Background of the Invention 1 Magnetic recording media are usually manufactured by coating a magnetic coating material on a support made of a synthetic polymeric material such as polyethylene tele-7 tally (PETT) and then drying the coating.

The magnetic paint used in this case is made by dispersing or dissolving magnetic powder and small amounts of other additives in a natural or synthetic polymeric material generally called a binder.

Therefore, from a macroscopic perspective, a magnetic recording medium can be said to be made of a polymeric material (plastic) filled with fine magnetic powder.

By the way, in general, as the external force acting on an object increases, when the stress reaches a certain value exceeding the elastic limit, the permanent strain begins to increase rapidly, although the external force hardly increases.

A certain value exceeding this elastic limit is called the yield point.

In a tensile test, the specimen elongates in proportion to the increase in load, and when it reaches the yield point, the elongation increases regardless of overcurrent.
Eventually it will be severed.

As shown in FIG. 1, there are an upper yield point and a lower yield point, and the upper yield point (point A) is the point at which elongation begins to increase, and is usually called the yield point.

The lowest stress during which the unstable state of the yield phenomenon continues is called the lower yield point (point B).

Generally, the yield phenomenon is not clearly recognized in many cases, but the yield point clearly appears in metals and other viscoelastic substances such as plastics and rubber.

Conventionally, magnetic recording media comprising multiple layers, for example, magnetic recording media comprising an undercoat layer, a carbon black layer, a magnetic layer, etc. laminated on a support, have had only one yield point.

This is because the binders used in each layer are often the same type of material or closely related materials in terms of viscoelastic behavior (multilayer coating is done by the so-called wet-on-wet method [multilayer coating in a wet state). When using Method J, when adjoining layers use different binders, agglomeration or poor compatibility may occur at the interface between the layers. However, such magnetic recording media having only one yield point have the following drawbacks.

Originally, binders can be roughly divided into two types: those with a high glass transition point and high rigidity, and those with a low glass transition point and good adhesive properties.

Magnetic recording media using the former have high rigidity and are effective in preventing edge damage in running durability tests of the media, but have low adhesion to the support and are susceptible to peeling of the magnetic layer. cause and increase dropouts.

On the other hand, in the latter case, the adhesion of the magnetic layer to the support is strong and dropouts are small, but the rigidity of the magnetic recording medium is low and the running durability is poor. Furthermore, the tackiness of the surface of the magnetic layer also increases, causing problems such as stickiness of guide rollers and the like when the magnetic recording medium runs.

Thus, no matter which binder is used, a magnetic recording medium with satisfactory characteristics cannot be obtained.

[Objective of the Invention 1] In view of the above circumstances, the present inventors have conducted various studies in an attempt to rectify the above-mentioned drawbacks found in conventional multilayer magnetic recording media, and as a result, have found that the following magnetic recording medium can achieve the objective. I learned this and arrived at the present invention.

[Structure of the Invention] That is, the present invention provides a magnetic recording medium comprising a plurality of magnetic layers on a non-magnetic support, characterized in that the magnetic recording medium has two or more yield points. That is.

The present invention will be explained below.

Examples of the magnetic material used in the present invention include γ-Fe
20. , Co-containing-Fe2J or Co-coated-Fe
Co-γ-Fe2O3 like 2O2, Fe50-Co
Co-containing Fe5Oa or Co-coated Fe30a
-γ-Fe30. ．． Cry, etc. oxide magnetic materials, others such as Fe, Ni, Fe-Ni alloy, Fe-
Co alloy, Fe-N1-P alloy, Fe-N1-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe
-Co-Ni-Cr alloy, Fe-Co-N1-P alloy,
Fe, Ni such as Co-P alloy and Co-Cr alloy.

Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing Co as a main component. Additives to these metal magnetic materials include Sl-Cu-, Zns An, p, Mn,
Elements such as Cr or compounds thereof may be included.

Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

The binder used in the present invention includes abrasion-resistant polyurethane.

It has strong adhesion to other materials, is mechanically strong to withstand repeated applied forces or bending, and has good abrasion and weather resistance.

Furthermore, if a cellulose resin and a vinyl chloride copolymer are used in combination with polyurethane, the dispersibility of the magnetic powder in the magnetic layer will be improved and its mechanical strength will be increased. However, if only the cellulose resin and the vinyl chloride copolymer are used, the layer becomes too hard, but this can be prevented by the presence of the above-mentioned polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. The above polyurethane and vinyl chloride copolymers may be partially hydrolyzed. Preferable examples of the vinyl chloride copolymer include a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to those of the polyurethane described above, and the stability of the physical properties of the magnetic recording medium over time can be significantly improved.

Furthermore, in addition to the binders described above, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

As already mentioned, when manufacturing a magnetic recording medium by coating multiple magnetic paints in layers on a non-magnetic support, even if the binders used in each layer are the same or different materials, If these materials are closely related in terms of viscoelastic behavior, the magnetic recording medium will have only one yield point, and such magnetic recording media will have various drawbacks.

Therefore, in order to correct such drawbacks, the present invention provides a magnetic recording medium having two or more yield points, and there are various methods for providing a magnetic recording medium with two or more yield points. However, this can generally be achieved by using various ratios of binders each having a different viscoelastic behavior (eg, glass transition temperature) in each layer.

For example, it is desirable to use different types of polymeric materials as binders in each layer, but even if the same type of material is used in each layer, it is possible to use different types of materials if they have different rheological properties. Similar effects can be expected in this case.

On the other hand, if materials with similar rheological properties are used as a binder in each layer even if they are different materials, the resulting magnetic recording field will have only one yield point, and the expected effect of the present invention will not be achieved. may not be obtained.

In order to improve the durability of the magnetic layer of the magnetic tape of the present invention, the magnetic paint can contain various curing agents, such as incyanate. Examples of aromatic isocyanates include tolylene diinocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and have an average molecular weight of 100 to 100.
A range of 3,000 is preferred.

Further, examples of aliphatic isocyanates include hexamethylene diisocyanate (IMDI) and the like, and U-forms 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 3,000 are preferred. Among the aliphatic incynates, non-alicyclic incynates and adducts of these compounds with active hydrogen compounds are preferred.

A dispersant is used in the magnetic paint used to form the magnetic layer, and additives such as a lubricant, an abrasive, a matting agent, an antistatic agent, etc. may be included as necessary. Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. It is also possible to use salts of polymeric dispersants having negative organic groups (eg -COOH). These dispersants may be used alone or in combination of two or more. In addition, as a lubricant, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acid with 12 to 16 carbon atoms, etc. Total number of carbon atoms is 21-2
Fatty acid esters (so-called wA) consisting of three monohydric alcohols can also be used. These lubricants are usually added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

Commonly used abrasive materials include various aluminas such as fused alumina and alpha alumina, silicon carbide, chromium oxide, corundum, artificial flundum, artificial diamond, garnet, and emery (main components: corundum and magnetite). used. These abrasives have an average particle size of 0.05 to 5μ
A size of 0.1 to 0.1 is particularly preferred.
It is 2 μm. These abrasives are usually added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.

As the matting agent, organic powder or inorganic powder may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferred. Powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, <1-Fe2
0s, talc, kaolin, calcium sulfate, boron nitride,
Examples include zinc fluoride and molybdenum dioxide.

Antistatic agents include carbon black, graphite, conductive powders such as tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponin, alkylene oxides, and glycerin. nonionic surfactants such as glycidol-based, higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfonium, carboxylic acids, sulfonic acids, phosphoric acids, vit Examples include anionic surfactants containing acidic groups such as acid ester groups and phosphate ester groups, and amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols.

Solvents to be added to the above paint or diluting solvents for coating this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohols such as methanol, ethanol, propatool, and butanol, methyl acetate, ethyl acetate, butyl acetate,
Esters such as ethyl lactate and ethylene glycol monoacetate, ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene, and xylene, methylene chloride, ethylene chloride, carbon tetrachloride, Halogenated hydrocarbons such as chloroform and dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polyamide and polycarbonate, metals such as Cu, kQ, and Zn, and glass. , boron nitride, and ceramics such as Si carbide can also be used.

The thickness of these supports is about 3 to 100 μm thick in the case of a film or sheet, preferably 5 to 50 μm thick.
In the case of a disk or card shape, the diameter is about 30 μm to 10 μm, and in the case of a drum shape, it is used in a cylindrical shape, and the shape is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, clavier coating, kiss coating, cast coating, Spray coats, extrusion coats, etc. can be used, but are not limited to these.

When constructing a magnetic layer on a support using these coating methods, there are two methods: one method involves stacking the coating and drying steps layer by layer (so-called wet-on-dry coating method), and the other method involves stacking the coating and drying steps layer by layer (so-called wet-on-dry coating method). There is a method in which layers are coated simultaneously or sequentially (a so-called wet-on-wet method), and either method can be used in manufacturing the magnetic recording medium of the present invention.

Note that a nonmagnetic layer may be provided above and below or between the magnetic layers without impairing the effects of the present invention.

By such a method, the magnetic layer coated on the support is optionally treated to orient the ferromagnetic metal oxide powder in the layer, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is approximately 500 to 50
00 Gauss, and the drying temperature is approximately 50 to 120°C.
The drying time is about 0.1-10 minutes.

Further, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing treatment or cutting it into a desired shape, if necessary.

Next, the present invention will be explained with reference to examples, but it goes without saying that the present invention is not limited to these examples.

[Example] After kneading magnetic paints having the compositions listed in Table 1 (upper layer) and Table 2 (lower layer) to disperse each component well in the paint, a mixture of methyl ethyl ketone and toluene was added as a solvent. The viscosity was adjusted to 1 to 20 poise.

Next, 5 parts by weight of Coronate [manufactured by Nippon Polyurethane Co., Ltd., trade name] as a hardening agent was added to this paint.

The above magnetic paint was coated in multiple layers on a support made of polyethylene terephthalate according to a conventional method.

Next, a magnetic recording medium was manufactured by performing a magnetic field orientation treatment and a drying treatment.

Table 3 shows the relationship between the type and amount of the binder used and the yield point of the magnetic recording media thus obtained, and Table 4 shows the results of measuring the electromagnetic characteristics.

Table 1〈Magnetic paint for upper layer〉 See Table 3.

Table 4 Characteristics of magnetic recording media> ■Measurement method in Examples and Comparative Examples <Tape edge damage> Damage to the tape edge after running the sample magnetic tape 50 times at a temperature of 40°C and a relative humidity of 80%. The degree of this was visually evaluated.

<RF output decrease> Pack the sample tape into a VHS cassette and use NY-6200 (manufactured by Matsushita Electric) at a temperature of 40°C and a relative humidity of 80%.
Using a deck, the RF output fluctuation was measured after running the deck 50 times.

<Dropout> VTR dropout counter (VH0 manufactured by Shibatsuku Co., Ltd.)
1BZ) was used, and an output that decreased by 114 dB or more of the RF envelope output over a long period of time of 1025 or more was defined as one dropout, and was measured over the entire length of the tape, and the average value per minute of light was determined.

[Effect of the Invention 1 The magnetic recording medium of the present invention has excellent running durability. In particular, the magnetic layer does not wear off even after running the first 5 minutes of the tape (SP mode) 400 times at room temperature and humidity, and even under harsh conditions such as 40°C and 80% relative humidity. Even when running 50 passes under the same conditions, no tape edge damage occurs.

Furthermore, the magnetic recording medium of the present invention has less dropout. In particular, if the slitting conditions of the original fabric are poor, there will be less deposit-type dropouts due to peeling of the magnetic layer.

[Brief explanation of drawings]

Figure 1 shows the relationship between stress acting on an object and elongation, and Figure 2 shows the stress (kg/am'') acting on the magnetic recording medium of the present invention (magnetic recording medium of Example 1). and elongation (%
) is a diagram showing the relationship between The horizontal axis in FIGS. 1 and 2 represents the elongation of the object, and the vertical axis represents the stress.

Claims (1)

[Claims] A magnetic recording medium comprising a plurality of magnetic layers on a non-magnetic support, characterized in that the magnetic recording medium has two or more yield points.