JPH02257423A - Magnetic recording medium having excellent electromagnetic conversion characteristics and traveling durability - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and traveling durability by using Co-contg. iron oxide containing Si and having specific value of coercive force as the magnetic material for a second magnetic layer, using both of modified polyurethane and modified vinyl chloride-vinyl acetate copolymer having negative functional groups as a binder and using chromium oxide as an abrasive. CONSTITUTION:Co-contg. iron oxide containing Si and having the coercive force (Hc) of 750 - 1,200 Oe. is used as the magnetic material in the second magnetic layer. Modified polyurethane and modified vinyl chloride-vinyl acetate copolymer having negative functional groups are both used as the binder and chromium oxide is used as the abrasive. By incorporating Si, dispersibility of the magnetic material is improved. By using the magnetic material of high coercive force in the second layer, output in high frequency region can be improved, as well as the output in low frequency region can be enhanced by the presence of the first (lower) layer. Thereby, the electromagnetic conversion characteristics and traveling durability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, magnetic floppy disks, etc., and particularly to magnetic recording media suitably used as video tapes.

[Background of the Invention] As is well known, magnetic recording media are generally produced by mixing and dispersing magnetic substances, lubricants, carbon black, abrasives, dispersants, and other components in a binder (binder resin). It is produced by adding a curing agent to the magnetic paint obtained by this method to improve the durability of the magnetic layer, and then coating the mixture on a support and drying it.

The electromagnetic conversion characteristics and other characteristics of the magnetic recording medium thus manufactured can be varied in various ways by appropriately changing the types and amounts of each of the above-mentioned components constituting the magnetic layer.

By the way, in recent years, as the quality of magnetic recording media such as magnetic tapes has improved, there has been a demand for higher density magnetic materials. A variety of magnetic layers have been proposed, which are sometimes collectively referred to as multilayer structures.

However, in many conventional magnetic recording media with a multilayer structure, for example, the dispersibility of the magnetic material is poor, the electromagnetic conversion characteristics are insufficient, or the balance between high and low frequency characteristics is not good. At present, there has not yet been a product that has well-balanced and satisfactory characteristics.

[Purpose of the Invention] In view of the above, the present inventors have conducted various studies with the aim of developing a magnetic recording medium with improved performance, particularly electromagnetic conversion characteristics and running durability, and have conducted the following research. The present invention as described has been achieved.

[Structure of the Invention] That is, the present invention provides a magnetic recording medium comprising a first magnetic layer (lower layer) and a second magnetic layer (upper layer) on a non-magnetic support, in which the second magnetic layer contains: , coercive force (H
c) is 75 (1 to 1200.Oe (Oersted) and uses a cobalt-containing iron oxide containing St;
The present invention relates to a magnetic recording medium characterized in that a vinyl acetate copolymer and a modified polyurethane with a negative functional group are used in combination, and [3] chromium oxide is used as an abrasive.

As described above, the present invention provides a magnetic recording medium having a multilayer structure in which the second magnetic layer (upper layer) has a coercive force (Hc) of 750 to 1200. Oe (Oersted), using cobalt-containing iron oxide containing Si; ■Using a modified vinyl chloride-vinyl acetate copolymer with a negative functional group and a modified polyurethane with a negative functional group together as a binder. , and [3] is characterized by the use of chromium oxide as an abrasive, but in conventional multilayer tapes, for example, the use of a combination of such components in the upper layer has not been proposed. This is a fact discovered for the first time by the present inventors.

The present invention will be explained below.The magnetic recording medium of the present invention has a coercive force (Hc) of 750 to 1200. oe (Oersted), S
Cobalt-containing iron oxide (Co-7-FeOx
), it is usually preferable to use one with X of 1.4 to 1.5, and the Si content in the magnetic material is usually 0.1 to 2% by weight. , preferably 0.1
-1% by weight.

If the Si content is less than 0.1% by weight, the dispersion of the magnetic material in the magnetic paint will be poor and the electromagnetic conversion characteristics of the magnetic recording medium will deteriorate; if the Si content is more than 2% by weight, the magnetic material will This is undesirable because the magnetic properties such as coercive force of the magnet deteriorate.

In this way, by incorporating Si into the magnetic material, the surface of the magnetic material is modified, making it easier to adsorb the functional group-containing resin that serves as the binder, and thereby improving the dispersibility of the magnetic material in the magnetic paint. can be improved.

In addition, the second layer (upper layer) has a coercive force (Hc) of 750 to 12
By using a magnetic material with high coercive force such as 00°Oe (Oersted), it is possible to improve the output in the high frequency band of the magnetic recording medium, and at the same time, the output in the low frequency band can be improved due to the presence of the first layer (lower layer). can also be made higher.

Coercive force is 750. If less than Oe (Oersted) is used, the RF specific output of the magnetic recording medium and Lumi S
/N decreases, while 1200. If a magnet with a larger Oe (Oersted) is used, the chroma S/N will decrease, so it is not preferable in either case, and the coercive force is usually 800 to 1000. Oe (Oersted) magnetic material is preferably used.

On the other hand, for the first magnetic layer (lower layer), in addition to the magnetic material used for the second magnetic layer described above, any conventionally used magnetic material can be used.

Co-γ-FezOs such as γ-Fe, O,, Co-containing γ-Fe, O, or CO coated-Fe, 01
Jes06. Co-containing FezO4 or Co-coated Fe
Co-γ-FesO such as 3O4, oxide magnetic materials such as Cr01, and others such as Fe%Ni, Fe-Ni
alloy, Fe-Co alloy, Fe-N1-P alloy, Fe-N
i-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Z
n alloy, Fe-Co-Ni-Cr alloy, Fe-Co-N
YeS such as 1-P alloy, Co-P alloy, Co-Cr alloy, etc.
Examples include various ferromagnetic materials (powders) such as metal magnetic powder containing Nis Co as a main component. Additives to these metal magnetic materials include 5i1Cu, Zn, i, and P.

Elements such as Mn and Cr or compounds thereof may be included. Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

The second layer (upper layer) of the magnetic layer of the magnetic recording medium of the present invention includes:
A modified vinyl chloride-vinyl acetate copolymer with a negative functional group and a modified polyurethane with a negative functional group are used together as a binder (binder resin).

By using such a resin in combination, it is possible to improve the dispersibility of the magnetic material, and as a result, it is possible to improve the electromagnetic conversion characteristics of the magnetic recording medium.

The modified vinyl chloride-vinyl acetate copolymer with a negative functional group used in the present invention is a resin obtained by introducing a negative functional group into a so-called vinyl chloride-vinyl acetate copolymer. For example, C(1-C
H*CHtSOsM1CQ-CH1CHaO5OsM1
゜C12-CH*C00M.

OM.

CQ-CH! -P-0 (However, MlM and M represent alkali metals such as lithium, sodium, and potassium, respectively,
) can be easily obtained by condensing a compound containing a negative functional group and chlorine in the molecule by a dehydrochloric acid reaction.

Typical negative groups in the above copolymer include sulfonic acid groups, carboxyl groups, etc.
Of course, it is not limited to these.

The modified polyurethane with a negative functional group used in the present invention is a resin obtained by introducing a negative functional group into a so-called polyurethane.
H2CH! S Os M% CCl2-C)IICH
tO5Qs, .

Cl2-CI (, C00M.

OM.

violence CC11-CII-P= 0O.

(However, 1. MSN and i are respectively lithium,
Hail alkali metals like sodium and potassium. ) can be easily obtained by condensing a compound containing a negative functional group and chlorine in the molecule by a dehydrochloric acid reaction.

Typical negative groups in the above polymers include, for example, sulfonic acid groups and carboxyl groups, but are not limited to these.

On the other hand, for the first magnetic layer (lower layer), in addition to the above-mentioned resin mixture used for the first magnetic layer, any known binder can be used, and a preferable example is a wear-resistant polyurethane resin. .

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,
To this end, the magnetic coating material can contain various curing agents, such as incyanate. Examples of aromatic incyanates include tolylene diisocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and the average molecular weight is 100.
A range of 3.000 to 3.000 is preferred.

Examples of aliphatic isocyanates include hexamethylene diisocyanate (IMDI) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Adducts of these compounds and active hydrogen compounds are preferred.

The magnetic paint used to form the magnetic layer usually contains additives such as a dispersant, a lubricant, an abrasive, a matting agent, and an antistatic agent.

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. , and also negative organic groups (e.g. -〇〇〇〇)
It is also possible to use salts of polymeric dispersants having . 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,
Fatty acid esters (so-called waxes) consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 21 to 23 carbon atoms in total 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.

In the present invention, as the abrasive, the second magnetic layer (upper layer)
using chromium oxide.

By using chromium oxide as an abrasive in the second magnetic layer in this way, it is possible to prevent a decrease in RF output due to clogging of the magnetic head when the magnetic recording medium is run under conditions of high temperature and humidity. .

Therefore, containing chromium oxide in the second magnetic layer can be useful for improving the polishing power of the magnetic head.

The particle size of chromium oxide used for the second magnetic layer is usually 0.1
~1.0 μm, preferably 0.1-0.5 μm. If a particle size smaller than 0.1 μm is used, the polishing effect will be poor; If a larger one than the 0 μ range is used, the electromagnetic conversion characteristics tend to deteriorate.

On the other hand, the abrasive used for the first magnetic layer (lower layer) is of course chromium oxide, but also commonly used materials, such as various aluminas such as fused alumina and σ alumina, silicon carbide, corundum, artificial corundum,
Synthetic diamonds, garnet, emery (main ingredients: corundum and magnetite), etc. are used.

These abrasives have an average particle diameter of 0.05 to 5 .mu.m, particularly preferably 0.1 to 2 .mu.m. 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, an organic powder or an inorganic powder may be used alone or in a mixture.

Preferred organic powders that can be used include acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment. 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, σ-Fe, O, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride,
Examples include molybdenum dioxide.

Antistatic agents include carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponin, alkylene oxides, and glycerin. Cationic surfactants such as higher alkyl amines, quaternary ammonium salts, lysine, other heterocycles, 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, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; methyl vinegar; , esters such as ethyl acetate, butyl acetate, 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, Halogenated hydrocarbons such as 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, 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 in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card shape, the length is about 30 μm to 10 m+i, and in the case of a drum shape, a cylindrical shape is used, 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, gravure 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 (so-called wet-on-wet method), but any 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 first magnetic layer and the second magnetic layer without impairing the effects of the present invention.

By such a method, the magnetic layer coated on the support is optionally subjected to a treatment for orienting the magnetic 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 1200C.
The drying time is approximately 0.1 to 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] Examples and Comparative Examples After thoroughly kneading the components listed in Table 1, a suitable amount of a 7/3 mixture of methyl ethyl ketone/cyclohexanone was added as a solvent to produce a magnetic paint.

Next, this magnetic coating material was coated in multiple layers on a polyethylene terephthalate support according to a conventional method, oriented in a magnetic field, and then dried to produce a magnetic recording tape.

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

As is clear from Table 1 showing the composition of the magnetic paint used and Table 2 showing the composition of the magnetic recording material used, the composition according to the present invention (Example 1) and the composition not according to the present invention (Comparative Examples 1 to 2) 4) The surface roughness of the magnetic recording medium before calendering is Ra
The value is small.

Therefore, it can be seen that the magnetic recording medium of the present invention has good dispersibility of the magnetic material.

In addition, since the magnetic recording medium of the present invention has both a lumi S/N value and a chroma S/N value higher than those not according to the present invention, the video characteristics in the high frequency band (4.2 MHz) and the low It can be seen that the characteristics in the frequency band (0.5 MHz) are well balanced and excellent.

Furthermore, in the present invention, the RF output decrease after 50 passes under the conditions of 40° C. and RH 8G% is smaller than in each comparative example, but this RF output decrease is an indicator of head cleaning. The smaller the decrease in RF output, the better the cleaning state of the magnetic head.

[Effects of the Invention] As is clear from the above description, the magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics and running durability.

Claims (1)

[Claims] (1) A first magnetic layer (lower layer) and a second magnetic layer on a non-magnetic support.
In a magnetic recording medium provided with a magnetic layer (upper layer), the second magnetic layer contains [1] a magnetic substance with a coercive force (Hc) of 7.
50-1200. Oe (Oersted) and Si
using cobalt-containing iron oxide containing [2]
Magnetic recording characterized in that a modified vinyl chloride-vinyl acetate copolymer with a negative functional group and a modified polyurethane with a negative functional group are used together as a binder, and [3] chromium oxide is used as an abrasive. Medium.