JP2811078B2 - Magnetic recording medium with excellent electromagnetic conversion characteristics and other characteristics - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic disk, and a magnetic floppy disk, and particularly has excellent electromagnetic conversion characteristics and other characteristics, and is suitable as a video tape. The present invention relates to a magnetic recording medium used.

[Background of the Invention]

In recent years, there has been an increasing demand for high-density magnetic recording media. In particular, for example, video tapes have been required to perform very high-density recording in response to a demand for higher recording frequencies. There have been proposed various types in which a magnetic layer having a two-layer structure consisting of an upper layer and a lower layer or a structure having three or more layers (hereinafter, these are sometimes collectively referred to as a multi-layer structure) is provided on a body.

As is well known, a magnetic recording medium is usually made of a powder of a ferromagnetic material in various synthetic or natural polymer materials (so-called resin materials) called a binder.
An abrasive, carbon black, a lubricant, a dispersant, a curing agent and other components are uniformly dispersed, and if necessary, a solvent is appropriately added thereto, and the obtained magnetic paint is applied on a support to obtain a magnetic material. It is manufactured by forming a layer, orienting the magnetic layer in a magnetic field, and then drying.

There are various factors that affect the electromagnetic conversion characteristics and other characteristics of the magnetic recording medium, and typical ones include the type and amount of each component used, and these factors are correlated with each other. In addition, it affects the characteristics of the magnetic recording medium.

By the way, conventionally, in order to improve the characteristics of a magnetic recording medium, there have been many proposals in which the composition of each component used and the ratio thereof are variously changed. There is no present.

[Object of the invention]

In view of such circumstances, the present inventors have developed a magnetic recording medium that has excellent electromagnetic conversion characteristics, does not cause turbidity in a magnetic head, and has little dropout, and is particularly preferably used as a video tape. As a result of various studies, the present inventors have found that the following magnetic recording medium is suitable for the purpose, and have reached the present invention.

[Configuration of the invention]

The present invention relates to a magnetic recording medium having a plurality of magnetic layers on a nonmagnetic support, wherein the magnetic material in the uppermost layer is surface-treated with Si and / or Al, and the uppermost layer has a magnetic chromium oxide Further, the present invention relates to a magnetic recording medium comprising a resin having a negative functional group as a binder.

Hereinafter, the present invention will be described.In the past, various magnetic materials used for magnetic recording media have been proposed, for example, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ or Co-coated γ- _{Fe 2 Co-γ-Fe 2} O 3 , such as _{O 3, Fe 3 O 4,} Co -containing Fe ₃ O ₄
Or _{Co-γ-Fe 3 O 4} , CrO 2 oxide magnetic material such as Co-coated Fe ₃ O _4, and other, for example Fe, Ni, Fe-Ni alloy, Fe
-Co alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co
-Fe, Ni, Co such as Ni-P alloy, Co-P alloy, Co-Cr alloy
Various ferromagnetic substances (powder) such as metal magnetic powders containing as a main component
Further, it is known that an element such as Si, Cu, Zn, Al, P, Mn, and Cr or a compound thereof is contained as an additive to these metal magnetic materials.

For each magnetic layer of the magnetic recording medium having a plurality of magnetic layers of the present invention, any of these known magnetic materials is used as a magnetic material. In the present invention, particularly, the magnetic material in the uppermost magnetic layer is used. Must be surface-treated with Si or Al.

The Si or Al content of the magnetic material in the uppermost layer is usually
Preferably, the amount is 0.1 to 1.0 part by weight based on 100 parts by weight of the magnetic material.

In the present invention, it is an essential requirement that the uppermost magnetic layer contains magnetic chromium oxide.

The amount of this magnetic chromium oxide used depends on the Si or
It can be varied variously depending on the type of the magnetic material containing Al, the content of Si or Al in the magnetic material, and the like.
It is in the range of 1.0 to 200 parts by weight for 100 parts by weight.

Furthermore, in the present invention, it is an essential requirement that a resin containing a negative functional group be contained in the uppermost magnetic layer as a binder from the viewpoint of the effect.

As the resin containing a functional group to be used, there are various ones, and preferable examples thereof include a sulfone potassium-containing vinyl chloride resin and a sodium sulfonate-containing polyurethane.

The amount of the resin containing the above functional group in the uppermost layer is usually in the range of 1.0 to 30 parts by weight based on 100 parts by weight of the magnetic substance.

Conventionally, various types of binders have been proposed for use in this type of magnetic recording medium. However, as long as the effects of the present invention are not impaired, the uppermost magnetic layer, together with the resin containing the above functional group, is known. Can be contained.

Suitable examples of such a binder include, for example, abrasion-resistant polyurethane.

This polyurethane has a strong adhesive strength to other substances, is mechanically tough against repeated application force or bending, and has good abrasion resistance and weather resistance.

In addition, if a cellulose resin and a vinyl chloride copolymer are generally used in combination with the polyurethane, the dispersibility of the magnetic powder in the magnetic layer is improved, and the mechanical strength is increased.

However, the layer becomes too hard with only the cellulose resin and the vinyl chloride copolymer, but this can be prevented by the presence of the above-mentioned polyurethane.

Cellulose ethers, cellulose inorganic acid esters, cellulose organic acid esters, and the like can be used as usable cellulose resins. The above-mentioned polyurethane and vinyl chloride copolymer may be partially hydrolyzed.

As the vinyl chloride copolymer, preferably, a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol is used.

Phenoxy resins can also be used. Phenoxy resin has high mechanical strength, excellent dimensional stability,
It has advantages such as good heat resistance, water resistance, chemical resistance and good adhesiveness.

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

Further, in addition to the binder described above, a mixture with a thermoplastic resin, a thermosetting resin, a reactive resin, and an electron beam irradiation curable resin may be used.

For the magnetic layers other than the uppermost layer, any of the above-mentioned known binders may be used, and a resin containing a functional group used for the uppermost magnetic layer may also be used.

In order to improve the durability of the magnetic layer of the magnetic recording medium of the present invention, various hardeners can be contained in the magnetic paint, for example, isocyanate can be contained.

Examples of the aromatic isocyanate include tolylene diisocyanate (TDI) and the adduct thereof with an isocyanate active hydrogen compound.
Those in the range of 100 to 3,000 are preferred.

Examples of the aliphatic isocyanate include hexamethylene diisocyanate (HMDI) and the like, and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight of preferably
It is in the range of 100-3,000. Of the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used for forming the magnetic layer may contain additives such as a dispersant, a lubricant, an abrasive, a matting agent, and an antistatic agent, if necessary.

Examples of the dispersant used in the present invention include phosphate esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinate esters, known surfactants, and salts thereof. Yes, and negative organic groups (eg-
It is also possible to use salts of polymer dispersants with (COOH).

These dispersants may be used alone or in combination of two or more.

As a lubricant. Silicone oil, graphite,
Carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid,
Fatty acid esters (so-called hunts) composed of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 21 to 23 carbon atoms in total with the number of carbon atoms of the fatty acid can also be used.

These lubricants are usually added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As the abrasive, commonly used materials include fused alumina, various aluminas such as α-alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond,
Garnet, emery (main components: corundum and magnetite) and the like are used.

These abrasives usually have a mean particle size of 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm.
It is.

These abrasives are usually based on 100 parts by weight of binder.
It is added in the range of 1 to 20 parts by weight.

As the matting agent, an organic powder or an inorganic powder is used individually or as a mixture.

As the organic powder used in the present invention, acrylic styrene-based resin, benzoguanamine-based resin powder, melamine-based resin powder, and phthalocyanine-based pigment are preferable, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, and polyimide-based resin are preferable. Powders, polyfluorinated ethylene resin powders and the like can also be used. As inorganic powders, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α-Fe ₂ O
₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide.

Examples of antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponins, alkylene oxides, and glycerin. Surfactants, such as nonionic surfactants, glycidols, etc .; higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, kaiotin surfactants, such as phosphonium or sulfoniums; carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acids Examples include anionic surfactants containing an acidic group such as an ester group and a phosphate group, and amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric esters of amino alcohol.

Examples of the solvent to be blended in the paint or a diluting solvent at the time of application of the paint include acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone,
Alcohols such as methanol, ethanol, propanol, butanol, etc., esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, benzene And aromatic hydrocarbons such as toluene, xylene, and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene.

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

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or a sheet, about 30 μm to 10 mm in the case of a disk or a card, and is cylindrical in the case of a drum. The type 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 doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, and spray coating. A coat, an extrusion coat and the like can be used, but not limited to these.

When a magnetic layer is formed on a support by these coating methods, a system in which coating and drying steps are stacked one by one (so-called wet-on-dry coating system) and a method in which the next layer is placed on a layer that is not dried and is in a wet state Are applied simultaneously or successively (so-called wet-on-wet application method), but any method can be adopted in manufacturing the magnetic recording medium of the present invention.

The present invention does not particularly define the thickness of the uppermost magnetic layer of the magnetic recording medium of the present invention.
Since it is not advantageous in terms of effect to make the thickness too large, it is usually preferable that the thickness is 1.0 μm or less.

Note that a non-magnetic layer may be provided above, below, or in the middle of the magnetic layer, without impairing the effects of the present invention.

According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting the ferromagnetic metal oxide powder in the layer if necessary, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is about 10 to 5000 Gauss in AC or DC, the drying temperature is about 30 to 120 ° C., and the drying time is about 0.1 to 10 minutes.

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

Next, the present invention will be described with reference to examples, but needless to say, the present invention is not limited to these examples.

〔Example〕

Examples and Comparative Examples After the magnetic paints for the top layer and the layers other than the top layer having the compositions shown in Tables 1 and 2 were kneaded well, a polyisocyanate [manufactured by Nippon Polyurethane Industry Co., Ltd. Trade name Coronate L] was added in an amount of 5 parts by weight to prepare a magnetic coating material for application.

Next, the magnetic coating material for the uppermost layer and the magnetic coating material for layers other than the uppermost layer were applied on the support in a conventional manner, and then subjected to magnetic field orientation treatment and drying treatment to produce a magnetic recording medium.

The electromagnetic conversion characteristics and other characteristics of the magnetic recording medium thus obtained were measured.

Table 3 shows the surface treatment amount of the magnetic material used for the uppermost layer with Si or Al, the amount of the magnetic material and the magnetic chromium oxide used, the thickness of the magnetic layer, etc., and the measurement of the characteristics of the obtained magnetic recording medium The results are shown in Table 4.

As is evident from Table 4, the magnetic recording medium of the present invention (Example) maintains a high level of electromagnetic conversion characteristics,
The magnetic recording medium which does not obscure the magnetic head, has little dropout, and is well-balanced among the three, but does not follow the present invention (comparative example) has electromagnetic conversion characteristics,
It cannot be said that there is a balance between cloudiness and dropout for the magnetic head.

 Method of measuring characteristics in Examples and Comparative Examples ・ Chroma output 500KHz, output during reproduction of RF signal was determined.

• Y-CN (1) Fast-forward until the winding thickness of the magnetic recording tape is about 3 mm, and record a 6 MHz signal from here for 10 minutes.

This is played three times. The recording level is + 20% of the optimum recording level of the comparison tape.

(2) A 6.8 MHz signal is recorded for about 3 minutes in the portion where 6 MHz is recorded / reproduced in (1).

Recording] level is + of the optimal recording level of each comparative tape.
20% value.

The RF reproduction output (referred to as C) and C / N are compared with the value of the comparison tape.

・ Measurement of cloudiness of magnetic head and reduction of reproduction output due to this (1) Clean the head before measurement to make the head free of cloudiness.

(2) In the environment of normal temperature and normal humidity (temperature 20 ± 2 ° C, relative humidity 65 ± 5%), a single frequency of 6 MHz at the center of the sample tape is recorded for 10 minutes at a recording level of + 20% with respect to the comparative tape. Then, this portion is reproduced three times, and a running of the head / tape is performed.

(3) 6MHz is also recorded in the portion where 6MHz was re-recorded in (2) above.
A single frequency of 8 MHz is recorded on the sample tape for 2 minutes at a recording level of + 20% with respect to the comparison tape, which is reproduced and the output is measured. (These values are set to 0 db.) (4) The sample tape is run in the SP mode while recording a video signal from the beginning to the end of winding in an environment of normal temperature and low humidity of 20%.

(5) After running at low humidity, record a single frequency of 6 MHz and 8 MHz on the sample tape at the same level as that of (3) for 2 minutes each in a low humidity environment, measure the output, and measure the output.

(6) The drop in output at 6 MHz and 8 MHz due to head turbidity is determined from the difference between the above (3) to (5) of the sample tape.

・ Dropout A 100% white signal is input and reproduced in a fixed section (10m to 30m) of the magnetic tape. At that time, a 10μs dropout is measured at a -12dB level with a Shibasoku counter (VHO1BZ) in one-minute units. The average value of the entire length of the measurement portion was taken as the measurement value.

〔The invention's effect〕

The magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics, less turbidity of the magnetic head, and less dropout.

Claims (1)

(57) [Claims] In a magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, the magnetic material in the uppermost layer is surface-treated with Si and / or Al, and the uppermost layer has a magnetic oxide layer. A magnetic recording medium comprising chromium and a resin containing a negative functional group as a binder.