JPH02244423A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability of magnetic layers by forming the uppermost layer of a multilayered tape to the relaxation point larger than the relaxation point of the magnetic layers exclusive of the uppermost layer. CONSTITUTION:The magnetic layer of the uppermost layer is so formed as to have the relaxation point of tan deltad<tan deltau when the relaxation point of the magnetic layer of the uppermost layer is designated as tan deltau and the relaxation point of the magnetic layers exclusive of the uppermost layer is designated as tandeltad. The relaxation point of the magnetic layers can be changed by variously changing the kinds, contents, etc., of the components in the layers. The relaxation point is usually changed by variously changing the kinds and contents of the binders and hardeners (crosslinking agents) to be incorporated into the magnetic layers for the nature thereof. The medium obtd. in such a manner is not only excellent in electromagnetic conversion characteristics but in excellent in durability as well.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic disk, and a magnetic 70 disk, particularly a magnetic tape suitable for use as a magnetic tape such as an audio tape or a video tape. It is related to recording media.

[Background of the invention]

Magnetic recording media usually contain ferromagnetic powder, dispersants, abrasives, lubricants,
A suitable solvent is added as necessary to a uniformly dispersed matting agent, antistatic agent, curing agent, and other various additives, and the resulting magnetic coating is applied onto a support to form a magnetic layer. It is manufactured by drying this.

Various binders have been proposed to be used in this case, and a representative example is poly-9-urethane, which has abrasion resistance. It has strong adhesion to other substances, is mechanically strong to withstand repeated stress or bending, and has good abrasion resistance, weather resistance, etc.

Furthermore, if a cellulose resin or a vinyl chloride-based fat copolymer is 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. 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.

By the way, there are various factors that affect the electromagnetic conversion characteristics and mechanical characteristics of a magnetic recording medium. Regarding the electromagnetic conversion characteristics, for example, the material of the ferromagnetic powder used,
Uniformity of properties, type of anisotropy, shape, shape distribution, dimensions,
Regarding particle size distribution, filling degree, surface properties, magnetic layer thickness and other factors, mechanical properties, for example, the type of binder used, amount added, copolymerization ratio, average molecular weight', molecular weight distribution, and various other additives. These factors are related to each other and affect the characteristics of magnetic recording media, but regarding binders, it is simply the type of polymer and the amount added, etc. Only the effects of additive amount, average molecular weight, glass transition temperature, etc. on the properties of magnetic recording media have been reported, and there is no research on how its rheological properties, especially its viscoelastic behavior, affect the properties of magnetic recording media. At present, there are very few reports on the impact it will have.

[Purpose of the invention]

In view of these circumstances, the present inventors focused on the viscoelastic behavior of the binder used in magnetic recording media, and by extension the viscoelastic behavior of the magnetic layer, and investigated the viscoelastic properties of this magnetic layer, especially its relaxation. As a result of various studies on how tana affects the characteristics of a magnetic recording medium, the present invention described below has been achieved.

[Structure of the invention]

That is, the present invention provides a magnetic recording medium having a plurality of magnetic layers formed by dispersing ferromagnetic powder in a binder on a non-magnetic support.
The gist of the present invention is a magnetic recording medium characterized in that tana d<tana u, where jantd is the relaxation point of a magnetic layer other than the top layer.

As is well known, polymer materials (synthetic or natural resins) have both elasticity and viscosity, but the magnitude and ratio of elasticity and viscosity change depending on deformation, load, deformation rate, temperature, etc. It is the material. For example, it will flow under a large load, but will not flow under a small load, and will flow after passing the yield point. In other words, it shows plasticity. The academic field that studies the fluidity of materials is called rheology.

By the way, the measurement of the dynamic viscoelasticity of polymeric materials in the field of rheology is generally carried out as follows by examining the stress response when a sinusoidal strain stimulus is applied to the material.

When a sinusoidal strain (C lines) is applied to the material as a stimulus, a stress (4 lines) whose phase is advanced by δ with respect to this strain (g lines)
However, by measuring the sinusoidal stress response (4 lines), the complex modulus of elasticity E! Find (i#).

[E book (i-) = d book (1) / 1 book (1), i = imaginary unit, ω・2rf angular frequency, (・time 1 This complex modulus of elasticity E
Book (i-) is denoted by E car (i-)・E'(ω)+iE"(ω),
E"/E' is equal to tana.

E'(a+): Indicates the magnitude of a stress component that is in phase with the strain that occurs when a unit magnitude of sinusoidal strain is applied, and is called the "storage modulus."

E // (ω): A stress component whose phase is r/2 ahead of the strain, and is called the “loss modulus”.

E ッ/E' 5tan δ This tan a is called a relaxation point, and is a characteristic unique to polymer materials, similar to, for example, a glass transition point.

Regarding the measurement of this relaxation point, with the spread of viscoelasticity measuring devices, especially forced vibration type direct reading elastometers, it has become easy to determine the temperature dependence of the elastic modulus at a constant frequency or several levels of frequency. Results are increasingly presented in the form of temperature dependence.

(For an overview of the viscoelastic behavior of polymer solids and its measurement method, see, for example, the Chemical Society of Japan, New Experimental Chemistry Course, Polymer Chemistry Part 1. 1978 edition, Maruzen Co., Ltd., No. 679-
It is described on page 716. ) The relaxation point of a polymer material can be measured using a commercially available measuring instrument, such as the dynamic viscoelasticity automatic measuring instrument Rheopybron D manufactured by Toyo Baldwin Co., Ltd.
It can be easily measured by DV-...-EA (trade name).

As a result of intensive research into the correlation between the relaxation point of the magnetic layer in a magnetic recording material and the properties of the magnetic recording material, the inventors found that the relaxation point (tan δ) of the top layer in a multilayer tape
U) is the relaxation point (tan) of the magnetic layers other than the top magnetic layer.
The inventors have discovered that magnetic tapes with excellent various properties can be obtained by increasing δd), leading to the present invention.

The relaxation point of the magnetic layer can be changed by variously changing the type and content of each component in the layer. It can be changed by variously changing the content of the agent).

Examples of the magnetic material used in the present invention include γ-Fe
, Os, Co-containing - Fe, O, or Co deposited -
CO-γ-Fe such as Fa,,01,O,,Fe1O
(a) Co-containing Fe, O, or CO-coated Fe50. CO-γ-Fe30. , oxide magnetic materials such as Crag,
Others, such as Fes Nis Fe-Ni alloy, F
e-Co alloy, Fe-N1-P alloy, Fe-Ni-Co
alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy,
Fe1Ni1C such as Fe-Go-Ni-Cr alloy, Fe-Co-N1-P alloy, Co-P alloy, Co-Cr alloy, etc.
Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing o as a main component. Additives to these metal magnetic materials include 5i1Cus Zn, kQ, 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.

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 diisocyanate (↑DI) 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.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic isocyanates 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 incyanates, non-alicyclic isocyanates 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 (for example -〇〇〇〇). These dispersants may be used alone or in combination of two or more. In addition, as lubricants, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acids having 12 to 16 carbon atoms, and the number of carbon atoms of the fatty acids are used. Total number of carbon atoms is 21-2
Fatty acid esters (so-called waxes) consisting of three monohydric alcohols can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As abrasives, commonly used materials such as fused alumina, various types of alumina such as a-alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (main components: corundum and magnetite) are used. be done. These abrasives have an average particle size of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm.
It is μ vote. 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, a-Fe10
3. Talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

As charge blocking agents, conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponin, alkylene oxide compounds, Nonionic surfactants such as glycerin and glycidol, higher alkyl amines, quaternary ammonium salts, pyridine and other heterocycles, cationic surfactants such as phosphonium or sulfonium, carboxylic acids, sulfonic acids, phosphoric acids, Anionic surfactants containing acidic groups such as sulfate ester groups and phosphate ester groups, amino acids,
Examples include amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketonon; alcohol 11 such as methanol, ethanol, gropanol, and butanol; 1M methyl vinegar;
Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate; Ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, benzene,
Aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, 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, A12, and Zn, and glass. , boron nitride, and ceramics such as St carbide can also be used.

The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm in diameter, and approximately 30 μm to 10 layers in the case of a disk or card. In the case of a cylindrical shape, 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. Furthermore, other or non-magnetic layers may be provided above and below or between the magnetic layers without impairing the effects of the present invention.

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, trans770-lu coating, gravure coating, kiss coating, and cast coating. , spray coat, extrusion coat, etc. can be used, but are not limited to these.

When constructing multiple magnetic layers on a support using these coating methods, there are two methods: stacking the coating and drying process layer by layer (the so-called 9-et-on-dry coating method), and stacking the coating and drying process layer by layer (the so-called 9-et-on-dry coating method). There is a method (so-called wet-on-wet method) in which the next layer is coated simultaneously or sequentially, but either method can be used in manufacturing the magnetic recording medium of the present invention.

Although the present invention does not particularly specify the thickness of the top layer in the magnetic recording medium of the present invention, which is composed of a plurality of magnetic layers, if the thickness of the top layer is too thick, the expected effects of the present invention may not be achieved. Since there is a possibility that a sufficient amount may not be obtained, it is preferable that the thickness of the uppermost layer is usually in the range of 0.1-1.5 μl.

By such a method, the magnetic layer coated on the support is treated, if necessary, 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, the drying temperature is about 50 to 120° C., and the drying time is about 0.00 Gauss.

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〕

The magnetic paint described in Tables 1 and 2 was manufactured by the conventional method.

Table 1 Magnetic paint for top layer> After being well dispersed in
Table <Magnetic paint for magnetic layers other than the top layer> Tg Ni glass transition point, the same applies hereinafter.

The above magnetic paint components were kneaded, each component was kneaded into a mixture, and each component was added to the mixture as shown in Table 3 to prepare a magnetic paint.

Next, the obtained magnetic paint was coated on a polyethylene terephthalate support so that the top layer and the layers other than the top layer had a dry film thickness of 0.5 μl (top layer) and 3.5 μl (layers other than the top layer), respectively. After coating in multiple layers under the same conditions, various magnetic recording tapes were manufactured by drying.

Each sample tape thus obtained was tested for its electromagnetic characteristics, durability, adhesion to a non-magnetic support, dropout, etc.

Table 3 shows the results of measuring the ratio of binder and curing agent used and the relaxation point (tanJu and taned) of the magnetic layer for each experimental sample, and Table 4 shows the results of measuring the electromagnetic characteristics and tape durability. , and measurement of adhesion and dropout to a non-magnetic support #: The sample to be measured was previously subjected to a curing treatment (curing treatment) at 60° C. and 30% relative humidity for 24 hours (the same applies hereinafter). Note that samples without reference marks were subjected to measurement without being subjected to such treatment.

(hereinafter referred to as Kai, voice) Table 4 Table 5 Judgment criteria for head dirt ◎: No stains occur at all.

O: Almost no staining occurs.

△: Some stains occurred.

×: Dirt occurs.

×x: Severe staining occurred.

Adhesion criteria O: No peeling of the magnetic layer at all.

○: There is almost no peeling of the magnetic layer.

×: Peeling occurs in the magnetic layer.

XX: The magnetic layer was completely peeled off.

As is clear from the results in Tables 4 and 5, the magnetic recording medium of the present invention (each example) has superior electromagnetic conversion characteristics compared to the magnetic recording medium not according to the present invention (each comparative example). In addition, there is far less chance of contaminating the magnetic head, and there are also far fewer dropouts.

<Method for measuring properties in Examples and Comparative Examples> Relaxation point (tan δ) Dynamic viscoelasticity automatic measuring instrument (manufactured by Toyo Baldwin Co., Ltd.)
Using product name Reovipron DDV-J-EA),
The size of the sample is length x width x thickness: 4.5cm x 4.0m5
A sample of X8G to 100 μm was prepared, and tan δ was determined by measuring in the temperature range from θ°C to 100°C under conditions of a frequency of 110K and a temperature increase rate of 3°C/min.

・Comparative example 3 of RF output 100% why and output during playback of signal
It was determined in comparison with the tape of Comparative Example 3 using the tape of Comparative Example 3 as a reference.

・Put the RF output reduction tape in a VHS cassette, use a NY-6200 (manufactured by Hiromi Denki) deck at 40°C and 80% RH,
I was running 0 passes repeatedly. , and then measured the RF power fluctuation.

- Head dirt Observe the magnetic head on the deck after the above RF output reduction test to determine the degree of dirt.

- Adhesive sample Attach a certain area of adhesive tape to the surface of the tape, and observe the peeling state of the magnetic layer when peeling it off in the vertical direction at a certain speed.

・Dropout VTR dropout counter (VH0 manufactured by Shibatsu)
using 1BZ for a long time of more than 10 μs, and R
An output that decreased by 14 dB or more from the output of the F emperogue was defined as one dropout, and was measured over the entire length of the tape, and the average value over one minute was determined.

〔Effect of the invention〕

The magnetic recording medium of the present invention not only has excellent electromagnetic conversion characteristics, but also excellent durability, good adhesion to non-magnetic materials, and little dropout.

Claims (2)

[Claims] (1) In a magnetic recording medium having multiple magnetic layers formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, the relaxation point of the uppermost magnetic layer is tanδu, and the magnetic layers other than the uppermost layer When the relaxation point of is tanδd, tanδd<
A magnetic recording medium characterized in that tan δu. (2) The magnetic recording medium according to claim (1), wherein the top layer has a thickness of 0.1 μm or more and 1.5 μm or less.