JPH02206020A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durability of a medium having two magnetic layers by specifying the values of stearic acid adsorption of iron oxide ferromagnetic powder respectively for the upper and the lower magnetic layers, incorporating a polymer having a specific polar group into the binder and incorporating fatty acid into the upper magnetic layer. CONSTITUTION:The two-layered magnetic layer comprising a binder and ferromagnetic powder dispersed therein are formed on a nonmagnetic supporting substance. The values of stearic acid adsorption for the upper and lower layers are specified to 3X10<-6> - 6X10<-6> and 6X10<-6> - 10X10<-6>mol/m<2>, respectively. Such a polymer having one or more kinds of polar groups expressed by formula I is incorporated into the binder, and fatty acid is incorporated in the upper layer. By this method, the ferromagnetic powder is highly dispersed to enhance the electromagnetic conversion characteristics. Moreover, durability of the medium is enhanced because a proper amt. of fatty acid is supplied to the surface of the medium. In formula, M is Na, Li, K, H, NR4 or NHR3, M is Na, Li, K, H, NR4, NHR3 or alkyl group, and R is lower alkyl group.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an improvement in a magnetic recording medium comprising a non-magnetic support and a two-layer overlapping magnetic layer.

[Background of the invention and description of prior art]

Magnetic recording media (hereinafter also referred to as magnetic tape) for audio, video, or computers are generally used for magnetic recording media such as γ-Fe2O3, Co-containing magnetic iron oxide, C
A magnetic recording medium is used in which a magnetic layer in which ferromagnetic powder made of acicular crystals such as rO□ is dispersed in a binder is provided on a nonmagnetic support.

Recently, there has been an increasing demand for higher density recording in magnetic recording media, and ferromagnetic powders with finer particles than conventionally used ferromagnetic powders are being used. In particular, in the case of video tapes, as methods such as shortening the recording wavelength and narrowing the track width are used, it becomes necessary to perform extremely high-density recording. Videotapes using digitalized video tapes have come into use.

If such finely divided ferromagnetic powder (for example, ferromagnetic powder with a BET specific surface area of 30 nf/g or more) can be used and the surface of the magnetic layer can be made smooth, even higher density recording can be achieved. can be expected to improve the electromagnetic conversion characteristics of magnetic recording media. However, the finely divided ferromagnetic powder has a problem in that its dispersibility decreases, making it difficult to fully demonstrate its performance. Recently, the dispersibility of this finely divided ferromagnetic powder has been considerably improved through the use of binders with polar groups and improvements in dispersion methods, resulting in excellent electromagnetic conversion characteristics of magnetic recording media. Now you can.

On the other hand, if the surface of the magnetic layer is made smooth, the friction coefficient of the contact between the magnetic layer and the device system increases while the videotape is running, resulting in damage to the magnetic layer of the magnetic recording medium after short-term use. The magnetic layer tends to peel off. In particular, in the case of a video tape, since the video head and the recording medium run in contact with each other at high speed, ferromagnetic powder tends to fall off from the magnetic layer, which can cause clogging of the magnetic head. Therefore, it is desired to improve the running properties of the magnetic layer of video tapes.

Conventionally, a method of adding abrasives (hard particles) such as corundum, silicon carbide, or chromium oxide to the magnetic layer has been proposed as a measure to improve the running properties of the magnetic layer. When an abrasive is added to the magnetic layer for the purpose of improving the magnetic layer, the effect of the addition is difficult to be seen unless the abrasive is added in a fairly large amount. However, a magnetic layer with a large amount of abrasive added causes significant wear on magnetic heads, etc., and also goes against the purpose of smoothing the magnetic layer and improving electromagnetic characteristics, so it is not a preferable method. do not have.

Furthermore, fatty acids or esters of fatty acids and aliphatic alcohols are added to the magnetic layer as lubricants to reduce the friction coefficient. However, in the case of magnetic recording media using finely divided ferromagnetic powder, the effect of the lubricant is often not sufficiently exhibited.

Therefore, although it is possible to obtain relatively excellent electromagnetic conversion characteristics, it is difficult to obtain good running properties at the same time.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a magnetic recording medium with improved electromagnetic conversion characteristics and running properties.

[Means for solving problems]

The above object of the present invention is to provide a magnetic recording medium having two layers, a non-magnetic support and a magnetic layer formed by dispersing ferromagnetic powder provided on the support in a binder, in which the upper layer has an adsorbed amount of stearic acid. iron oxide ferromagnetic powder with a stearic acid adsorption amount in the range of 3X10-' to 6x10-6 mol/rrf is used as the lower layer powder, and the binder as a polar group; -503M, -OSO3M, -COOM
, -PO(OM')2 and POP(OM')2 (
However, M is Na, Li, K, hydrogen atom, NR,
Or represents NHR3, where N゛ is Na, , Lj, K
, represents a hydrogen atom, NR4, NHI'lff or an alkyl group.

(wherein R is a lower alkyl group) A magnetic recording medium comprising a polymer having at least one selected from the group consisting of Ru.

The magnetic layer of the magnetic recording medium of the present invention includes the above-mentioned (magnetic iron oxide-based ferromagnetic powder having adsorption amounts of stearic acid in different ranges in the upper layer and the lower layer, the above-mentioned polymer having a specific polar group, and Contains at least fatty acids.

By using the magnetic iron oxide ferromagnetic powder in which the amount of stearic acid adsorbed is within the above specified range, it is possible to prevent excessive adsorption of the fatty acid, which is a lubricant, to the magnetic iron oxide ferromagnetic powder. This allows the fatty acid to fully function as a lubricant. However, magnetic iron oxide-based ferromagnetic powders with stearic acid adsorption within the above specified range have poor dispersibility, and ordinary polymers cannot achieve sufficient dispersion, resulting in a highly smooth magnetic layer surface. I can't get sex. Therefore, excellent dispersibility can be obtained by using a polymer having the above-mentioned specific polar group.

That is, by using the magnetic iron oxide-based ferromagnetic powder, the polymer, and the fatty acid, it is possible to simultaneously obtain excellent dispersibility and improved lubricating effect, that is, running performance.

In the magnetic recording medium of the present invention, the amount of stearic acid adsorbed by the ferromagnetic powder dispersed in the multilayer magnetic layer is different between the upper layer and the lower layer, and the value is smaller in the upper layer than in the lower layer.
Moreover, the feature is that the range of the value is specified.

By making the amount of stearic acid adsorbed by the ferromagnetic powder in the upper layer relatively small, the amount of fatty acid that acts as a lubricant becomes relatively large, and the coefficient of friction of the magnetic layer decreases. As a result, the running durability of the magnetic recording medium of the present invention is improved.

On the other hand, in the lower layer, a ferromagnetic powder with a relatively large adsorption amount of stearic acid is used, which also promotes the adsorption of the polar group-containing polymer used as a binder in the present invention. It is believed that the dispersion of the powder was improved, resulting in a lower layer with low surface roughness, which improved the surface properties of the magnetic layer of the magnetic recording medium of the present invention and improved the electromagnetic conversion characteristics.

In addition, by setting the stearic acid adsorption amount of the ferromagnetic powder in the upper layer and the lower layer within a specific range based on the above relationship, the magnetic recording medium of the present invention can have good running durability and electromagnetic conversion characteristics. It has become a thing.

The ferromagnetic powder of the present invention has an adsorption amount of stearic acid per unit surface area in the range of 3X10-' to 6X10-6 mol/rI'f in the upper layer and 6X10-6 to 9X1 in the lower layer.
It is an iron oxide-based ferromagnetic powder in the range of 0-'mol/rrr.

The amount of stearic acid adsorbed by the magnetic material used in the upper layer is 3X10
If it is smaller than -' to 6X10-', the surface gloss will deteriorate, and if it is larger than this, the friction coefficient will increase and the running performance will deteriorate.

The amount of stearic acid adsorbed by the magnetic material used in the lower layer is 6X10
If it is smaller than -'~9X10-6 mol/bo, the mold retention is not sufficient, and if it is larger than this, the friction coefficient after 100 passes becomes large, causing a problem in runnability.

The magnetic recording medium of the present invention has a basic structure in which a nonmagnetic support and an overlapping magnetic layer containing ferromagnetic powder are provided on the nonmagnetic support.

Examples of the nonmagnetic support used in the present invention include various synthetic resin films such as polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, and polyimide;
and metal foils such as amyl foil and stainless steel foil.

In addition, the thickness of the non-magnetic support is generally 2.5 to 100 mm.
μm, preferably 3 to 70 μm.

The nonmagnetic support may be provided with a backing layer on the side on which the magnetic layer described below is not provided.

The magnetic recording medium of the present invention is one in which a multilayer magnetic layer containing ferromagnetic powder is provided on a nonmagnetic support as described above.

Magnetic iron oxide-based ferromagnetic powder, St, A1, Ca, Sn
, by surface treatment with a compound of Zr and Ti (for example, by surface treatment of magnetic iron oxide-based ferromagnetic powder with water glass or a combination of aluminum chloride, calcium chloride, etc. and water glass 9), A ferromagnetic powder is obtained in which the amount of stearic acid adsorbed is controlled within an appropriate range. This treatment prevents excessive adsorption of the fatty acid, which is a lubricant, to the magnetic iron oxide-based ferromagnetic powder, and allows the fatty acid to fully function as a lubricant. and,
By using this ferromagnetic powder in the upper layer of the magnetic layer, running durability can be improved. In this case, although it is possible to increase the effect with lubricants other than fatty acids such as fatty acid esters and higher alcohols, a particularly large lubrication effect can be achieved when fatty acids are used as the lubricant.

However, if the amount of surface treatment of the magnetic iron oxide-based ferromagnetic powder is too large and is less than the adsorption amount of stearic acid, not only will the fatty acid not be adsorbed, but the adsorption amount of the binder will also decrease, and the amount of adsorption of the above-mentioned ferromagnetic powder will decrease. Dispersion becomes insufficient.

Furthermore, by keeping the amount of surface treatment of the ferromagnetic iron oxide powder low and making the adsorption amount of stearic acid relatively large, the adsorption of the binder used in the present invention is promoted and the ferromagnetic powder is better dispersed. By using such ferromagnetic powder in the lower layer of the magnetic layer, the smoothness of the magnetic layer can be increased and the electromagnetic conversion characteristics can be improved.

The binder of the present invention has as polar groups; SO3M, -OSO3M, -(:OOM, -PO(
OM')2 and POP(OM')2 (M is Na, 1.i, K, hydrogen atom, NR4 or N
HR3 is represented, and i' represents Na, Li, K, a hydrogen atom, NR4, NHR+ or an alkyl group.

(However, R is a lower alkyl group, and preferably has 1 to 8 carbon atoms, and the two N'' may be the same or different from each other.) A polymer having at least one member selected from the group consisting of: Contains.

The above-mentioned surface-treated ferromagnetic powder has poor dispersibility, and ordinary polymers cannot achieve sufficient dispersion, making it impossible to obtain a high degree of smoothness on the surface of the magnetic layer. Therefore, excellent dispersibility can be obtained by using a polymer having the above-mentioned specific polar group. That is, by using the magnetic iron oxide-based ferromagnetic powder, the polymer, and the fatty acid, excellent dispersibility and improved lubricating effect can be obtained at the same time.

The ferromagnetic powder used in the present invention is a specific magnetic iron oxide-based ferromagnetic powder. Examples of magnetic iron oxide-based ferromagnetic powder suitable for the above surface treatment include 7-Ve20:+,
Heldride iron oxide which is Fe0x (1,33<x<1.5), Fe, O= and CO modified iron oxide, Co-Ti
Mention may be made of modified hexagonal ferrite powders such as modified barium ferrite and Co-Ti modified strontium ferrite. The BET specific surface area of these ferromagnetic powders is generally 25 po/g or more, preferably 40 rd/g or more.

The above magnetic iron oxide ferromagnetic powder is made of Si, Aj2, Ca
By surface treatment with a compound of , Sn, Zr and Ti, it is possible to obtain a magnetic iron oxide-based ferromagnetic powder having an adsorption amount of stearic acid per unit area in the range of 3X10-' to 9X10-6 mol/bo. can. The above surface treatment can be performed, for example, by mixing magnetic iron oxide-based ferromagnetic powder and water glass in an alkaline solution and heating the mixture. The pH of the alkaline solution is 8-13, preferably 8-11. Processing temperature is 40-250°C1
Preferably the temperature is 50-200°C, and the processing time is 0.5
~5 hours is preferred.

A fine ferromagnetic metal powder may be used in combination with the magnetic iron oxide-based ferromagnetic powder. As an example of a ferromagnetic metal powder, the metal content in the ferromagnetic metal fine powder is 75% or more, and 80% or more of the metal content is at least one ferromagnetic metal or alloy (e.g., Fe, , Co, , Ni
, Fe-Co, Fe-Ni, C.

Ni, Co-N1-Fe), and other components (e.g., An, Si, S) within a range of 20% by weight or less of the metal content.
, Sc, Ti, V, Cr, Mn, Cu, Zn
, Y, MoXRh, Pd, Ag.

Sn, Sb, Te, Ba,, Ta', W, R
e, ＾u, Hg, Pb, Bi.

Mention may be made of alloys that may contain (La=Ce, Pr, Nd, B, P). Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide. Methods for producing these ferromagnetic metal powders are already known, and the ferromagnetic alloy powder used in conjunction with the present invention can also be produced according to these known methods.

When using ferromagnetic powder, there are no particular restrictions on its shape, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used.

The polar group-containing polymer used as the binder for forming the magnetic layer of the present invention is a vinyl chloride copolymer resin (e.g., vinyl chloride copolymer, vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate copolymer, etc.). Vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinyl acetate/maleic acid copolymer, vinyl chloride/vinylidene chloride copolymer), acrylic resin (e.g. vinyl chloride/acrylonitrile copolymer, vinylidene chloride/acrylonitrile copolymer) polymer, (meth)acrylic ester/acrylonitrile copolymer, (meth)acrylic ester/vinylidene chloride copolymer, (meth)acrylic ester/styrene copolymer, butadiene/acrylic nitrile copolymer), polyurethane resin,
The above polar groups (-5O3M, -oso3M, -c
ooh, PO(OM')2 and one0PO(OM')
) Selected from polymers into which at least one of 2) is introduced. Preferably, it is a polymer in which a polar group is introduced into a vinyl chloride copolymer resin, and the molecular weight is 10,000 to 100,000, preferably 20,000 to 50,000, and the preferable polar group is SO.
3Na, -3O3H, -0PO3Hz, -COOI
It is I.

The polar group is preferably contained in the polymer in an amount of 10-6 to 10-3 equivalents/g, preferably 10-6 to 10-4 equivalents/g.

In addition to the polar group-containing polymer described above, resins such as thermoplastic resins, thermosetting resins, and reactive resins can be used in combination, and these resins can be used alone or in combination.

Thermoplastic resins generally have an average molecular weight of 10,000 to 2.
00,000 and a polymerization degree of about 200 to 2,000. Examples of such thermoplastic resins include vinyl chloride/vinyl acetate copolymer resins (e.g., vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinyl acetate) /maleic acid copolymer), vinyl chloride/vinylidene chloride copolymer, acrylic resin (e.g., vinyl chloride/acrylonitrile copolymer, vinylidene chloride/acrylonitrile copolymer,
meth)acrylic ester/acrylonitrile copolymer, (meth)acrylic ester/vinylidene chloride copolymer, (meth)acrylic ester/styrene copolymer,
butadiene/acrylonitrile copolymer), cellulose derivatives (e.g., cellulose acetate butyrate, cellulose diacetate, cellulose triatate, cellulose propionate, cellulose acetate propionate, nitrocellulose, cellulose acetate), various synthetic rubber-based Thermoplastic resin (polybutadiene, chloroprene, polyisoprene, styrene-butadiene copolymer),
Examples include polyurethane resins, vinyl fluoride, polyamide resins, polyvinyl butyrate, styrene/butadiene copolymers, and polystyrene resins.
These can be used alone or in combination.

The thermosetting resin or reactive resin is generally a resin with an average molecular weight of 200,000 or less, preferably 20,000 or more and 200,000 or less in the state of a coating solution, and after coating, the molecular weight is reduced by a condensation reaction or an addition reaction. A resin that grows to infinity is used. However, when these resins are thermosetting resins, it is preferable that the resins do not harden or dissolve due to heating during the process leading to hardening. Examples of such resins include phenol/formalin/novolac resins, phenol/formalin/resole resins, phenol/furfural resins, xylene/formalin resins, urea resins, melamine resins, drying oil-modified alkyd resins, and phenolic resin-modified alkyd resins. , maleic acid resin-modified alkyd resins, unsaturated polyester resins, combinations of epoxy resins and curing agents (e.g. polyamines, acid anhydrides, polyamide resins), terminal isocyanate polyether moisture-curable resins, polyisocyanate prepolymers (e.g. Compounds having three or more isocyanate groups in one molecule, which are the reaction products of diisocyanates and low molecular weight triols, diisocyanate trimers and tetramers), polyisocyanate prepolymers and resins containing active hydrogen (e.g. polyester polyols, polyester polyols, diisocyanate trimers and tetramers), Ether polyol, acrylic acid copolymer, maleic acid copolymer, 2-hydroxyethyl methacrylate copolymer, p
-hydroxystyrene copolymer), and these can be used alone or in combination.

As the binder, it is preferable to use a mixture of the vinyl chloride copolymer (A) having a polar group of the present invention and the polyurethane resin CB). The weight ratio used is A:B from 1:3.
i: preferably in the range of o, i.

The amount of binder used is, based on 100 parts by weight of ferromagnetic powder,
Generally 10-100 parts by weight are used, preferably 15-50 parts by weight.

The fatty acids used in the present invention are not particularly limited, but include:
Fatty acids having 8 to 22 carbon atoms, preferably 14 to 20 carbon atoms (e.g.
caprylic acid, capric acid, lauric acid, myristic acid,
Valmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolic acid, stearolic acid, behenic acid) are preferred.

It is preferable to add these fatty acids to the magnetic coating liquid in order to simplify the process. When added to a magnetic coating solution, the amount added is 0.01% to 10% by weight based on the ferromagnetic powder.
Preferably 0% by weight, more preferably from 0.05% by weight
It is 6% by weight.

The magnetic layer of the magnetic recording medium of the present invention preferably further contains inorganic particles having a Mohr hardness of 5 or more. The particle size of these inorganic particles is 0.05 to 1.0 μm, preferably 0.05 to 1.0 μm. It is 1 to 0.5 μm.

The inorganic particles used are not particularly limited as long as they have a Mohs hardness of 5 or more. An example of an inorganic particle having a Mohs hardness of 5 or more is α-AI! , zO: + (Mohs hardness 9)
, Ti0z (6.5), 5iOz (7)
, 5nOz (6.5), CrzO, (9),
and cr-FezO3 (5.5).

The content of the inorganic particles is usually in the range of 0.1 to 20 parts by weight, preferably in the range of 1 to 10 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

In addition to the above-mentioned inorganic particles, the magnetic layer preferably contains carbon black (particularly one having an average particle size of 10 to 300 μm).

Next, a method for manufacturing the magnetic recording medium of the present invention will be explained.

In producing the magnetic layer of the magnetic recording medium of the present invention, ferromagnetic powder, a binder, a fatty acid, and, if necessary, an abrasive or other filler are usually kneaded together with a solvent to form a magnetic paint.

As the solvent used during kneading, a solvent such as methyl ethyl ketone, which is normally used in preparing magnetic paints, can be used.

The kneading method is not particularly limited as long as it is a method normally used for preparing magnetic paints, and the order of addition of each component can be set as appropriate.

For the preparation of magnetic paints, conventional kneading machines are used, such as two-roll mills, three-roll mills, ball mills, pebble mills, thoron mills, sand grinders, attritors, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, A Disper Kneader-1 high-speed mixer, a homogenizer, an ultrasonic disperser, etc. are used. Using such a kneader, a magnetic paint can be prepared by carrying out cross-dispersion according to a known method.

When preparing a magnetic paint, known additives such as a dispersant and an antistatic agent may also be used.

The magnetic paint thus prepared is applied onto the aforementioned non-magnetic support. Coating can be performed directly onto the non-magnetic support, but it can also be applied onto the non-magnetic support via a direct agent layer or the like.

Coating methods for forming multilayer magnetic layers are disclosed in JP-A-61-139929 and JP-A-61-54992.
The simultaneous or sequential lubrication application method (hereinafter referred to as wet-on-wet application method) disclosed in the above publication is effective.

That is, the wet-on, wet coating method is a so-called sequential coating method in which one layer is first coated and then the next layer is coated on top of it as soon as possible in a wet state, and the extrusion coating method is in which multiple layers are simultaneously coated. Refers to methods, etc.

As the wet-on-wet coating method, for example, an extrusion type simultaneous multilayer coating method shown in FIG. 1 is used.

That is, the first coating liquid 2 and the second coating liquid 3 are simultaneously applied onto a continuously running non-magnetic support such as a flexible support 1 made of polyethylene terephthalate using a simultaneous multilayer coating injector 5. A method can be used.

Furthermore, the wet-on-wet coating method of the present invention is not limited to this method; for example, a sequential coating method may be used. That is, a first coating liquid is pre-coated onto a flexible support using a coating machine, the coated surface is immediately smoothed using a smoothing roll, and another extrusion coating is performed while the first coating liquid is in a wet state. This is carried out by applying the next second coating liquid using a machine.

In the case of a single layer, the thickness of the magnetic layer coated in this way is the thickness after drying, and -i is in the range of about 0.5 to 10 μm, preferably in the range of 1.5 to 7.0 μm. It is applied so that

In the case of a multilayer magnetic layer, the upper magnetic layer has a temperature of 0.1
It is desirable that the thickness be in the range of ~3 μm.

The total thickness of the upper and lower magnetic layers is the same as in the case of the single layer described above.

When the magnetic recording medium is used in the form of a tape, the magnetic layer coated on the non-magnetic support is usually subjected to a treatment to orient the ferromagnetic powder in the magnetic layer, that is, a magnetic field orientation treatment.
dried. In addition, surface smoothing treatment is performed if necessary.

The magnetic recording medium that has been subjected to surface smoothing treatment is then cut into a desired shape.

〔Effect of the invention〕

In the present invention, the magnetic layer provided on the non-magnetic support has a multilayer structure consisting of two layers, and the value of the stearic acid adsorption amount of the ferromagnetic powder dispersed in the magnetic layer is determined from the upper layer to the lower layer. The ferromagnetic powder can be made highly It is possible to provide a magnetic recording medium which has excellent dispersed electromagnetic conversion characteristics and which has good running durability by always supplying an appropriate amount of the fatty acid to the surface of the magnetic layer.

Next, Examples and Comparative Examples of the present invention will be shown. Note that "parts" in the examples indicate "parts by weight."

[Example] 1) Co-modified acicular magnetic iron oxide (specific surface area 45.7rd/g,
Long axis length 0.13 μm) 300g, aqueous sodium hydroxide solution 2I with pH 10! , and was dispersed in a homomixer to obtain an aqueous slurry of Co-modified magnetic iron oxide. The temperature of this slurry was raised to 60°C, and water-soluble water glass was dissolved in distilled water of 100% relative to Fo in the Co-modified magnetic iron oxide so that the amount was 0.3 wt% in terms of Si. It was added dropwise into the slurry while stirring at a rate of 5 mβ/min. After dropping, carbon dioxide gas was passed through at a rate of 0.21/min to adjust the pH of the slurry to 7.5. After stirring for 30 minutes, the slurry was filtered and dried at 70°C in a nitrogen gas atmosphere to form a surface-treated Co-modified magnetic oxidizer. Iron [Sample No. C] was prepared.

Magnetic iron oxides of Samples A to D were prepared by the above method by changing the iyt% of water-soluble water glass (Si equivalent) with respect to Fe in the Co-modified magnetic iron oxide. Similarly, Co-modified acicular iron oxide (specific surface area 30nf/g, major axis length 0.32
Samples E-H were prepared by surface treatment using μ).

The stearic acid adsorption amount of each sample is shown in the first amount.

Table 1 The amount of stearic acid adsorbed in Table 1 above was measured by the following method.

5 g of the obtained surface-treated Co-modified magnetic iron oxide ferromagnetic powder
was added to a 100-mL Erlenmeyer flask containing 50% of methyl ethyl ketone solution containing 2 wt% stearic acid,
Seal the flask and stir using a magnetic stirrer for 25 minutes.
Stirred at °C for 25 hours.

Next, solid-liquid separation was performed using a centrifuge, and the stearic acid concentration C (wt%) in the supernatant was measured using gas chromatography.

The amount of stearic acid adsorbed per unit area of the ferromagnetic powder was determined from the following formula.

5XSSAXMA However, SSA: Ferromagnetic powder specific surface area MW nystearic acid molecular weight (284) Impressive paint Toyosato Seiji The following magnetic paint composition was mixed with a sand grinder.
Spread out time. Then, 8 parts of an isocyanate curing agent (Coronate, manufactured by Nippon Polyurethane), 5 parts of stearic acid, and 5 parts of butyl stearate were added, dispersed for 15 minutes, and then filtered using a filter with an average pore size of 1 μm. Then, a magnetic coating liquid was prepared.

Table 2 With the above composition, the upper and lower layers were formed using the combinations of ferromagnetic powder (samples A-H) and binders (samples I-K) shown in Table 3, and the video tape No. 1~
I got No. 12.

Then, for each videotape sample, the surface gloss of the magnetic layer, running durability, and electromagnetic exchange characteristics were evaluated by the methods described below.

The results are shown in Table 3.

■ Using an extrusion type coating head with two slits in the head, the first coating liquid was applied onto a polyethylene terephthalate support with a thickness of 15 μm at a coating speed of 100 m/min and a liquid supply amount of 20 cc/rrf. 2 coating liquids were applied simultaneously in multiple layers at a supply amount of 4 cc/rd,
It was oriented, dried, and calendered. After heat curing, each portion was slit to a width of 2 inches to produce a 2-inch videotape.

Here, the combinations of the ferromagnetic powder and the functional group-containing vinyl chloride/vinyl acetate copolymer were changed as shown in Table 2 to obtain video tapes Nos. 1 to 12.

The surface gloss, friction coefficient (1 bus, 100 passes), and still durability of the obtained video tapes Nos. 1 to 12 were measured using a commercially available video recorder (NV8200, manufactured by Matsushita Electric). The measurement method was as follows.

"Sai" L Eizawa.

The gloss of the surface of the magnetic layer was measured at a light incident angle of 60°C.

Note that the values shown are relative values when the specular gloss of the glass surface with a refractive index of 1.567 is taken as 100%. Also,
The measuring device used was a digital photometer (manufactured by Suga Test Instruments).

The obtained videotape and stainless steel pole are brought into contact (wrapping angle 180 degrees) with a tension of 50g (T1), and the videotape is run at a speed of 3.3cm/s under these conditions. The tension (T2) required for this was measured. Based on the measured values, the friction coefficient μ of the first pass of the videotape was determined using the following calculation formula.

g-1/ π・ln (T2/T+) Furthermore, 10
The friction coefficient at the 0th pass was measured as described above using a vinyl tape that had been run for 99 passes.

A constant video signal was recorded on each videotape using a videotape recorder, and the time at which the output of the reproduced still image began to rapidly decrease was measured.

(The experiment was conducted at 5°C and 180% RH.)
■ A gray signal with a 50% setup was recorded using a Matsushita Electric ■ NV8200 video tape recorder, and the noise was measured using a Shibaku 925C S/N meter. Video sensitivity and video S/N are relative comparison values when sample No. 7 is set to OdB.

As is clear from the results in Table 3, Examples (Tape No. 3,
1 to No. 6) exhibit high surface gloss, low coefficient of friction, excellent still durability, and video S/N.

On the other hand, when the polymer having a specific polar group of the present invention is used, the amount of stearic acid adsorbed in the upper layer ferromagnetic powder is 3X10-
When the stearic acid adsorption amount of the ferromagnetic powder in the lower layer is within the range of 6X10-b to 9X10-' of the present invention other than 6X10-b to 6X10-b (Tape No., 7, No.

8, No. 11) are not compatible with surface gloss, friction coefficient, still durability, and video S/N. In addition, the stearic acid adsorption amount of the upper layer ferromagnetic powder is 3 x 10-6 ~
In 6X10-6, if the stearic acid adsorption amount of the ferromagnetic powder in the lower layer is other than 6X10-6 to 9XlO-6 (tape No. 9, No. 10, No. 12),
Surface gloss, friction coefficient, still durability, and video S/N are not compatible.

Patent applicant: Fuji Photo Film Co., Ltd. Mezuki 1995 〆

Claims (1)

[Claims] A magnetic recording medium having two layers: a non-magnetic support and a magnetic layer formed by dispersing ferromagnetic powder provided on the support in a binder, wherein the upper layer has an adsorbed amount of stearic acid. 3×10^
- Using iron oxide ferromagnetic powder in the range of 6 to 6 x 10^-6 mol/m^2, the lower layer has an adsorption amount of stearic acid of 6
-SO_3M, -OSO_3M, -COOM, -PO(
OM')_2 and -OPO(OM')_2 (however,
M is Na, Li, K, hydrogen atom, NR_4 or NHR
_3, M' is Na, Li, K, hydrogen atom, NR
_4, NHR_3 or an alkyl group. (wherein R is a lower alkyl group)) A magnetic recording medium characterized in that the upper magnetic layer further contains a fatty acid.