JPS6383916A - Magnetic recording medium and its producton - Google Patents

Abstract

PURPOSE:To improve an electromagnetic conversion characteristic and running durability by incorporating a nitrogenous heterocyclic compd. having <10pKa active hydrogen into a magnetic layer. CONSTITUTION:The nitrogenous heterocyclic compd. having <10pKa active hydrogen is incorporated into the magnetic layer. Examples of the nitrogenous heterocyclic compd. having <10pKa active hydrogen include benzoimidazole, benzotriazole, guanine, guanomine, benzoxazolone, benzisoxazolone, benzothiazolone, etc. Said compd. is effective when used at 0.05-5wt% of the weight of the ferromagnetic material powder. There are no particular limitations for the ferromagnetic material powder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium in which a magnetic layer containing ferromagnetic powder and a binder is provided on one or both sides of a non-magnetic support, and a method for manufacturing the same. In particular, the present invention relates to a magnetic recording medium in which ferromagnetic powder is well dispersed in a binder, and a method for manufacturing the same.

[Conventional technology]

In magnetic recording media, there is an increasing demand for higher density recording, and it is known that one way to solve this problem is to smooth the surface of the magnetic layer.

However, when the surface of the magnetic layer is smoothed, the friction coefficient of the contact between the magnetic layer and the device system increases while the magnetic recording medium is running. As a result, the magnetic layer of the magnetic recording medium can be damaged after short-term use, resulting in some damage. The magnetic layer tends to peel off.

Sometimes, in video tapes, the magnetic layer is placed under harsh conditions, such as in still mode, and when used under such conditions, ferromagnetic powder tends to fall off from the magnetic layer, which can lead to clogging of the magnetic head. It can also be a cause.

Conventionally, methods of adding abrasives (hard particles) such as flundum, silicon carbide, and chromium oxide to the magnetic layer have been proposed as a measure to improve the running durability of the magnetic layer. When an abrasive is added to the magnetic layer for the purpose of improving running durability, the effect of the addition is unlikely to appear 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 the magnetic head, and also goes against the purpose of smoothing the magnetic layer and improving electromagnetic conversion characteristics, so it is not a desirable method. I can't say that.

It has also been proposed to add a fatty acid or an ester of a fatty acid and an aliphatic alcohol to the magnetic layer as a lubricant to reduce the coefficient of friction.

However, with the recent spread of portable video tape recorders and flexible disk drive devices for personal computers, various usage conditions for magnetic recording media are expected, such as use at low temperatures or use at high temperatures and high humidity. . Therefore, magnetic recording media must be stable so that their running durability does not change under various expected conditions, but as is known in the past, lubricants are not sufficient. won.

In particular, in video tapes and floppy disks, as the recording wavelength becomes shorter and the size of recording media becomes smaller due to the compression of track width, the magnetic material is becoming more compact than the conventional iron oxide-based ferromagnetic powder. Ferromagnetic alloy powders have come into widespread use, and ferromagnetic powders of smaller size have also come to be used.

Although such rapid miniaturization of ferromagnetic particles allows relatively excellent electromagnetic conversion characteristics to be obtained, it has been difficult to simultaneously improve running durability.

When forming a magnetic layer on the surface of a non-magnetic support using ferromagnetic particles, a binder is usually used to bond the ferromagnetic particles to the support because the ferromagnetic particles themselves do not have binding force. However, in this case, a magnetic layer was formed by mixing and dispersing ferromagnetic powder with a binder and coating the mixture on the support surface. The state of mixing and dispersion has a considerable influence on the physical properties and magnetic properties of the formed magnetic layer.

[Problem that the invention seeks to solve]

When the ferromagnetic powder miniaturized as described above is mixed with a binder and dispersed therein, it takes a considerable amount of mixing time for the particles to be dispersed in the binder because the particles are so small.

If the dispersion is insufficient, it is difficult to obtain good surface properties and squareness ratio.

Therefore, a method of promoting dispersion by introducing a polar group into the substance (compound) used as a binder was considered (Japanese Patent Application Laid-Open No. 151417/1983), but this method did not improve dispersion much. However, it has its limitations, and also has the disadvantage that the magnetic layer becomes brittle. As another method, a method has been proposed in which the surface of ferromagnetic particles is treated with a carboxylic acid and a cyan coupling agent and then dispersed in a binder (Japanese Patent Application Laid-Open No. 170029-1982).
However, this method did not significantly improve the dispersibility, but had the disadvantage of plasticizing the binder.

Therefore, it was necessary to develop a means for sufficiently dispersing ferromagnetic particles in a binder without disadvantages.

[Means for solving problems]

Therefore, as a result of research into various means by which ferromagnetic particles can be dispersed in a binder without the drawbacks of the conventional techniques, the present invention was arrived at.

The magnetic recording medium of the present invention is a magnetic recording medium comprising a magnetic layer containing ferromagnetic powder and a binder on one or both surfaces of a non-magnetic support, in which active hydrogen with a pKa (10) is added to the magnetic layer. This is a magnetic recording medium characterized by containing a nitrogen-containing heterocyclic compound.

In addition, the means for producing this a-air recording medium is to coat a ferromagnetic powder with pxa (a nitrogen-containing heterocyclic compound having 1o active hydrogen), and then disperse it in a binder. This is a method for manufacturing a magnetic recording medium, characterized by forming a magnetic layer containing ferromagnetic powder on one or both surfaces of a nonmagnetic support.

As the nonmagnetic support used in the present invention, commonly used nonmagnetic supports can be used.

Examples of materials forming the non-magnetic support include various synthetic resin films such as polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, and polyimide, and metal foils such as aluminum foil and stainless steel foil. be able to. In addition, the thickness of the non-magnetic support is generally 3 to 50 μm.
m1 is preferably 5 to 30 μm.

The nonmagnetic support may be provided with a back WI (backing layer) on the side where the magnetic layer is not provided.

There are no particular limitations on the ferromagnetic powder used in the present invention.

(1) y -FslOs , (2) Fe104
, (3) intermediate oxide (bertolide) of (υ~(2), (41(!o 'l doped (11~(3), (
5) Oot=adhered (13-(3), (6) Or
0H1(7) Metal or alloy (so-called metal), (
8) Examples include hexagonal ferrite, among which (5) to (8) are preferred.

There is no particular restriction on the shape of the ferromagnetic powder, but it is usually acicular,
Granular, dice-shaped, rice grain-shaped and plate-shaped ones are used. The specific surface area of this ferromagnetic powder is 25 m”/
f or more is preferable in terms of electromagnetic conversion characteristics.

The binder forming the magnetic layer can be selected from binders commonly used in magnetic recording media. Examples of binders include:
Vinyl chloride/vinyl acetate copolymer, vinyl chloride, copolymer of vinyl acetate and vinyl alcohol, maleic acid and/or acrylic acid, vinyl chloride/vinylidene chloride copolymer, vinyl chloride/acrylonitrile copolymer, polyurethane resin , polycarbonate polyurethane resin, and the like.

These binders may be used alone or in combination,
The amount used is 10 to 40 wt%, preferably 15 to 30 wt% of the ferromagnetic powder.

The pKa contained in the magnetic layer (The pKa used in the nitrogen-containing heterocyclic compound having 10 active hydrogens is pKa = -1ogt as defined in physical chemistry.

Ka is defined as follows.

Here, HA: Expression of the compound focusing on active hydrogen y: Activity coefficient (y Biao is the activity coefficient for bile) and pKa (Example of nitrogen-containing heterocyclic compound with 10 active hydrogens) Examples include benzimidazole, benzotriazole, guanine, guanomine, benzoxacilone, benzisoxacilone, benzothiazolone and the like.

The amount of the compound used is Q, 05 for the ferromagnetic powder.
An amount of ~5 wt% is effective; if the amount is less than 5 wt%, the dispersion will not be sufficient, and if it is more than 5 wt%, disadvantages such as weakening of the magnetic layer will occur.

There are two ways to add the compound to the magnetic layer, including a method by surface treatment of ferromagnetic powder and a method by adding it to a mixture. In the surface treatment method, the compound is added to a solvent containing the compound. The compound is coated on the surface of the ferromagnetic powder by immersing the ferromagnetic powder, mixing and stirring if necessary, and then removing the solvent by volatilization. is dispersed in a binder and the mixture is used to form a magnetic layer. In this method, the compound is uniformly present on the ferromagnetic powder, so that the ferromagnetic powder can be dispersed very well, and is therefore a preferred method. In the addition method, the compound may be added to either of the two substances before mixing and dispersing the ferromagnetic powder and the binder;
Further, the above compound may be added during mixing and dispersion, or may be added at both stages.

The magnetic layer of the magnetic recording medium of the present invention preferably further contains inorganic particles having a Mohs hardness of 5 or more.

There are no particular restrictions on the inorganic particles used as long as they have a Mohs hardness of 5 or more. An example of inorganic particles having a Mohs hardness of 5 or more is Mu40s (Mohs hardness 9).

Tio (6th), T1o! (same & 5), day 10! (Same 7), 8nO1 (Same & 5), (!r103 (Same 9), and α-FeBo3 (Same s, s) 6), and these can be used alone or in combination.

Particularly preferred are inorganic particles having a Mohs hardness of 8 or more. When relatively soft inorganic particles with a Mohs hardness of less than 5 are used, the inorganic particles tend to fall off from the magnetic layer and have almost no abrasive action on the head.
Head clogging pt- tends to occur and running durability becomes poor.

The content of the inorganic particles is usually in the range of 111 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 30 Onm).

Next, the process of manufacturing the magnetic recording medium of this invention will be explained.

First, a ferromagnetic powder, a binder, a nitrogen-containing heterocyclic compound having an active hydrogen with a pKa of 10 or less, and other fillers and additives as necessary are kneaded with a solvent to form a mixture (hereinafter referred to as (referred to as "magnetic paint"). In this case, the nitrogen-containing heterocyclic compound may be coated on the ferromagnetic powder in advance by the surface treatment method as described above, without being added at the time of crosstalk. As the solvent used during kneading, solvents commonly used for preparing magnetic paints can be used.

There is no particular restriction on the method of cross-talk, and the order of addition of each component can be set as appropriate.

For the preparation of magnetic paints, conventional mixing machines such as two-roll mills, three-roll mills, ball mills, pebble mills, thoron mills, sand grinders, Zegvariator lighters,
Mention may be made of high speed impeller dispersers, high speed stone mills, high speed impact mills, dispersers, kneader-1 high speed mixers, homogenizers and ultrasonic dispersers.

When preparing a magnetic paint, known additives such as dispersants, antistatic agents, lubricants, etc. can also be used.

Examples of dispersants include fatty acids having 12 to 22 carbon atoms (91
, caprylic acid, capric acid, lauric acid, myristic acid, palmyric acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid), the above fatty acids and alkali metals (e.g. lithium, sodium , potassium, barium), esters of the above fatty acids and chemotactic compounds in which some or all of the hydrogen atoms of their compounds are replaced with fluorine atoms, amides of the above fatty acids, aliphatic amines, higher alcohols, polyalkylenes. Known dispersants such as oxide alkyl phosphates, alkyl phosphates, alkyl borates, sarcoxinates, alkyl ether esters, trialkyl polyolefins, oxyquaternary ammonium salts and lecithin can be mentioned.

When using a dispersant, the ferromagnetic powder 1 usually used is
00 parts by weight, [11 to 10 parts by weight is used.

Examples of antistatic agents include conductive fine powders such as carbon black and carzen black graft polymers; natural surfactants such as saponins; nonionic surfactants such as alkylene oxides, glycerin and glycidol: high grade Cationic surfactants such as alkylamines, quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, phosphoniums or sulfoniums:
Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester groups, and phosphoric ester groups; can be mentioned. When using the above-mentioned conductive fine powder as an antistatic agent, for example, it is used in a range of 1 to 10 parts by weight of IIL per 100 parts by weight of ferromagnetic powder, and similarly when using a surfactant, [ L is used in a range of 12 to 10 parts by weight.

Examples of additional lubricants include the above-mentioned fatty acids, higher alcohols, monobasic fatty acids with 12 to 20 carbon atoms such as bunal stearate, and sorbitan oleate, and monobasic fatty acids with 3 to 20 carbon atoms.
Esters consisting of monohydric or polyhydric alcohols, mineral oils, animal and vegetable oils, olefin low polymers, fatty acid amides,
In addition to silicone oil, modified silicone oil, and alkylene oxide adducts of fatty acids, known lubricants such as graphite fine powder, molybdenum disulfide fine powder, and tetrafluoroethylene polymer fine powder, and lubricants for plastics may be mentioned. can.

Note that the above-mentioned additives such as dispersants, antistatic agents, and lubricants are not strictly limited to having only the above-mentioned effects; for example, if the dispersant is a lubricant, It may also act as an antistatic agent. Therefore, it goes without saying that the effects of the compounds exemplified by the above classifications are not limited to those listed in the above classifications, and when using a substance that has multiple effects, the amount added should be It is preferable to decide in consideration of the action and effect.

The magnetic paint thus prepared is applied onto the non-magnetic support described above. Although it is possible to apply the coating directly onto the non-magnetic support, it is also possible to apply the coating onto the non-magnetic support via an adhesive layer or the like.

Coating methods on non-magnetic supports include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, and casting. coat, spray coat, spin code method, etc.
Moreover, methods other than these can also be used.

Further, the details of the method of dispersing the above-mentioned ferromagnetic powder and binder and the method of applying it to the support can be found in JP-A-54-460'
It is described in various publications such as No. 11 and No. 54-21805.

The thickness of the magnetic layer coated in this way is generally in the range of approximately α5 to 10 μm after drying, and usually t5 to 7 μm.
．． It is coated to a thickness of 0 μm. 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 for orienting the ferromagnetic powder in the magnetic layer, that is, a magnetic field orientation treatment. dried. Further, a surface smoothing treatment is performed if necessary.

[Implementation row]

EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

The following basic composition was used to prepare a magnetic paint by adding and kneading ferromagnetic powder and a binder with other additives. The final magnetic paint was prepared by adding nitrogen-containing heterocyclic compounds having active hydrogen with a pKa of 10 or less to this basic composition in different ways.

Basic composition (parts by weight) Ferromagnetic F'5-Ni alloy powder 100 Vinyl chloride/vinyl acetate copolymer 12 Polyurethane 8 α-mut! 035 Stearic acid 1 Pterstearate 1 Methyl ethyl ketone/Toluene (1/1) 250 Isocyanate
8. Note that the ferromagnetic Fe-14
The No. 1 alloy powder contained 10 atoms of Ni'1t, and its particle size had a major axis length of cL3μ and an axial ratio of 10. The composition of the vinyl chloride/vinyl acetate copolymer at the time of polymerization was 87 vt% vinyl chloride and 13 wt% vinyl acetate.

This magnetic paint was applied to a non-magnetic support of polyethylene terephthalate (10 μm thick), subjected to magnetic field orientation treatment, and then dried.

The characteristics of the magnetic tape thus obtained were measured.

The conditions for the measurement are as follows.

(Measurement conditions) Gloss 45°Gross (Suga Test Instruments) 0/M Tape 8■ Width, Depth Fuji
ix-8 center recording wavelength 5 MHz Δf = I O/N at MH2 Clogging Depth Fujix-8, 25℃
, 60. In addition, clogging occurs when the output level is -3 dB below the steady state.
The following refers to the phenomenon of instantaneous falling. The evaluation will be as follows.

None per hour 0 5-10 times Δ 10 times or more × The measurement results are shown in Table 1 below.

〔Effect of the invention〕

In the present invention, by using a nitrogen-containing heterocyclic compound having an active hydrogen of pKa (10), the ferromagnetic powder can be sufficiently dispersed in the binder, and a large effect can be obtained with a small amount of use. Since only a small amount is required, it is possible to reduce the negative effects on the physical properties of the magnetic layer, such as weakening and plasticization of the magnetic layer caused by the dispersant, and based on this, it is possible to increase the electromagnetic conversion characteristics and running durability, so both As shown in Table 1 of Examples, the obtained magnetic recording medium has a saturation magnetic flux density of B
m(G) is larger than that of piperazine, which is a nitrogen-containing heterocyclic compound having an active hydrogen with pKa≧10, and the squareness ratios sQ and a/m are similarly large.

It is also excellent in terms of clogging and has good running durability.

Agent Patent Attorney (8107) Kiyotaka Sasaki 1
・ Oku, (3 others) - So

Claims (1)

[Scope of Claims] 1) A magnetic recording medium comprising a magnetic layer containing ferromagnetic powder and a binder on one or both surfaces of a non-magnetic support, in which active hydrogen with pKa<10 is provided in the magnetic layer. A magnetic recording medium characterized by containing a nitrogen-containing heterocyclic compound. 2) After coating the ferromagnetic powder with a nitrogen-containing heterocyclic compound having active hydrogen with pKa<10, it is dispersed in a binder, and the dispersion coats the ferromagnetic powder on one or both sides of the non-magnetic support. 1. A method of manufacturing a magnetic recording medium, comprising forming a magnetic layer containing.