JPS61168120A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain an excellent magnetic disc and a magnetic tape having the improved dispersibility of the magnetic powders and the increased wear resistance of the magnetic layer by incorporating a cellulose type resin having carboxyl groups in the inner molecular to a binder of the magnetic powders. CONSTITUTION:The binder comprises the cellulose type resin which contains 0.5-2 carboxylic groups per 10,000mol.wt. of said resin in the inner molecular, and has the average mol.wt. of 5,000-40,000, for example, the nitrocellulose having the carboxylic groups produced by Asahi chemical Co. 'Cellunova Ex-1(R)'), and one or more of another binder resins selected from the groups consisting of vinyl chloride type copolymer, a polyester type resin, a polyurethane resin, a gum type resin, and also a polyol and a polyisocyanate compd. The magnetic layer dispersed the magnetic powders in said obtd. binder is formed on the base, thereby improving the dispersibility of the magnetic powders and the wear resistance and also improving the sensitivity and the output of the titled medim to obtain the magnetic recording medium having the high density recording and the high performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks.

[Prior Art] In a magnetic recording medium in which a magnetic layer containing a binder and magnetic powder is provided on a base such as a polyester film, improving the dispersibility of the magnetic powder in the magnetic layer is an electromagnetic technique for this type of medium. This is extremely important in improving conversion characteristics.

In particular, since the magnetic powder used in recent high-density recording and high-performance video tapes has become finer, the dispersibility of the magnetic powder tends to become a problem.

In order to improve the dispersibility of such magnetic powder, it is common practice to use a binder suitable for this purpose. Various types of binders have been proposed in the past, one of which uses low molecular weight nitrocellulose as a type of binder component, and usually combines this with resins such as polyvinyl chloride resins, polyurethane resins, and polyols. Furthermore, it is known that a polyisocyanate compound is used in combination (document unknown).

[Problems to be Solved by the Invention] However, with the use of conventional low molecular weight nitrocellulose as a component of the binder described in Section 2, almost satisfactory results were obtained in terms of the dispersibility of the magnetic powder. There are, but
There was a problem in that the wear resistance of the magnetic layer was likely to be impaired.

Therefore, the present invention solves the above-mentioned problems with conventional binder components, and uses a binder component that contributes to improving the dispersibility of magnetic powder and also provides good results for the wear resistance of the magnetic layer. The purpose of the present invention is to obtain a magnetic recording medium that is excellent in both characteristics.

[Means for Solving the Problems] As a result of intensive studies to solve the above-mentioned problems, the present inventor developed a nitrocellulose with a carboxyl group introduced into the molecule instead of the conventional low molecular weight nitrocellulose. When using this nitrocellulose, it was discovered that even if the molecular weight of the nitrocellulose was increased, the dispersibility of the magnetic powder could be improved, and remarkable results could be obtained in improving the abrasion resistance of the magnetic layer, which led to the completion of this invention. Ta.

That is, the present invention provides a magnetic recording medium comprising a magnetic layer containing a binder and magnetic powder on a base, characterized in that at least one component of the binder is made of a cellulose resin having a carboxyl group in the molecule. This relates to a magnetic recording medium.

(Structure and operation of the invention) As the cellulose resin having a carboxyl group in the molecule used as an essential component of the binder in this invention, nitrocellulose having the above-mentioned functional group is a typical example.The oil molecule thereof Cellulose resins other than nitrocellulose may be used as long as they have a carboxyl group therein.

The content of carboxyl groups contained in this cellulose resin is generally 05 to 2 per 10,000 molecular weight, particularly preferably 05 to 1 per 10,000 molecular weight. The number of carboxyl groups per molecule is generally 1 to 8, preferably about 1 to 2. In addition, the average molecular weight of this cellulose resin is 5,000
~40,000.

These cellulose resins tend to lack affinity with magnetic powder because conventionally used nitrocellulose contains only hydroxyl and nitro groups in the molecule, but in addition to these groups, these cellulose resins also contain carboxyl groups. By containing, it has good affinity with the surface of the magnetic powder, and its strong interaction allows it to be well adsorbed to the magnetic powder and increases the amount of adsorption, making it easier to form an adsorption layer on the surface of the magnetic powder.
.

Therefore, even if the molecular weight of this type of resin is high as mentioned above, it is possible to improve the dispersibility of the magnetic powder, and more importantly, it is possible to achieve the above-mentioned good adsorption phenomenon and the use of high molecular weight substances. This can greatly contribute to improving the wear resistance of the magnetic layer.

In addition, when the content of carboxyl groups contained in the cellulose resin is too small or when a monomer whose molecular weight is too low is used, it is difficult to obtain the above-mentioned effects.

Furthermore, if a material with too much carboxyl group content or too high molecular weight is used, the solubility in organic solvents may be impaired, and the dispersibility of the magnetic powder may be impaired due to thickening of the magnetic coating material.

Therefore, the carboxyl group content and molecular weight are
It is preferably within the above range.

The cellulose resin used in this invention can be easily produced by introducing a carboxyl group into a general cellulose resin having a hydroxyl group, a nitro group, etc. by an appropriate means, and is not available as a commercially available product. available. As an example, there may be mentioned Seltsuba EX-1 (trade name) manufactured by Asahi Kasei Corporation. In the present invention, although it is possible to use the above-mentioned specific cellulose resin alone as a binder, it is usually preferable to use it in combination with other binder components. This combination of ingredients mainly includes an ingredient that aims to improve flexibility and adhesion to the base as well as prevent curling, and an ingredient that mainly aims to increase the strength of the coating film. It is desirable to use

Typical examples of the former components aimed at improving the flexibility mentioned above include poly-1-cretane resins, polyvinyl chloride resins, polyester resins, and rubber resins (such as acrylonitrile-butadiene copolymers). ) and polyols (low molecular weight ones are preferred), and it is preferable to use at least one of these. A typical example of the latter component intended to increase the strength of the coating film is a polyisocyanate compound, and this compound broadly includes various conventionally known monomers and oligomers.

Where both of these components are used in combination with the cellulose resin.

In the case of the former component intended to improve flexibility, the number of parts of the cellulose resin used per 100 parts by weight of this component is 5 to 120 parts by weight, preferably 20 to 50 parts by weight. It is best to set the ratio so that

In addition, for the latter component whose purpose is to increase the strength of the coating film, the proportion of this component in the total amount of binder is 2 to 2.
The amount may be 50% by weight, preferably in the range of 5 to 30% by weight.

In addition, as the binder component that can be used in combination with the cellulose resin, in addition to those described above, any of various conventionally known resins can be used, and the binder component is not limited to those described above.

The magnetic recording medium of the present invention can be obtained by preparing a magnetic paint in which magnetic powder is dispersed in the binder described above, and applying this onto a base such as a polyester film according to a conventional method to form a magnetic layer of a desired thickness. can be obtained by

The above magnetic powders include T-Fe203 powder, Fe3.0
Any of the conventionally known magnetic powders can be used, such as oxide-based magnetic powders such as 4 powder, Co-containing iron oxide magnetic powder, and CrO2 powder, and metal magnetic powders such as Fe, Co, Ni, or alloys thereof. The average particle diameter (long axis) of these magnetic powders is approximately 0.15 to 0.4 μm.

In addition, various commonly used additives such as dispersants, antistatic agents, abrasives, lubricants, and pigments can be appropriately included in the above magnetic paint.

[Effects of the Invention] As described above, in the magnetic recording medium of the present invention, by using a cellulose resin having a carboxyl group in the molecule as at least one component of the binder, good results are obtained in the dispersibility of the magnetic powder. In addition, it is possible to obtain the effect that the wear resistance of the magnetic layer can be greatly improved.

[Examples] Below, examples of the present invention will be described in more detail. In addition, in the following, parts shall mean parts by weight.

Example I Co-containing T-Fe203 powder (average major axis diameter 0.3μ) 1
00 parts (Product name: Meiko Suretsu A, manufactured by Tsukumi Kagaku Co., Ltd.) Carbon black 2 parts Alumina powder
After mixing and dispersing 2 parts of each of the above components in a ball mill for 72 hours, 2 parts of myristic acid as a lubricant and a polyisocyanate compound (1 part, manufactured by Polyurethane Co., Ltd. under the trade name Corone L).
4 parts of L) and an appropriate amount of a viscosity-adjusting organic solvent (the above mixed solvent) were added and mixed and dispersed for 2 hours to prepare a magnetic paint.

This coating material was applied onto a polyester base film having a thickness of 12 .mu.m and dried to a thickness of 4 .mu.m after drying, and then cut into a predetermined width to obtain a magnetic tape of the present invention.

Comparative Example 1 Comparison was made in the same manner as in Example 1, except that the same amount of ordinary nitrocellulose without carboxyl groups (HVB manufactured by Mukasei Co., Ltd.: average molecular weight 14,000) was used instead of the carboxyl group-containing nitrocellulose. A magnetic tape was made for this purpose.

The surface smoothness, sensitivity, and abrasion resistance of the magnetic layer of each of the magnetic tapes of Example 1 and Comparative Example 1 were examined, and the results were as shown in Table 1 below. In addition, each performance was measured and evaluated using the following method.

<Surface smoothness> Using a stylus type roughness meter, the surface average roughness (C0L,A) of the magnetic layer was measured under the conditions of a stylus speed of 0.06σ/sec and a cutoff of 0.08 mm. The quality of the surface smoothness was determined based on a relative value calculated according to the following formula using No. 1 as a reference.

<Sensitivity> Determine the output of 5MH2 and use Comparative Example 1 as the reference (OdB
) and expressed as its relative value (dB).

<Abrasion resistance> A still test was conducted using a VH5 video tape recorder at room temperature by inputting a 5MH2 signal for one hour of inch-wide magnetic tape. The time required for the output to reach % of the initial output was measured.

Table 1 Examples 2 to 9 The same amount of magnetic iron powder (average particle size 0.2μ) was used instead of Co-containing T-Fe, 03 powder, and the type and amount (number of parts) of the binder component were changed as shown below. 8 of the present invention in the same manner as in Example 1 except that the procedures were as shown in Table 2.
A seed magnetic tape was made.

Comparative Examples 2 to 9 Eight types of magnetic tapes for comparison were prepared in the same manner as in Examples 2 to 9, respectively, except that nitrocellulose not containing carboxyl groups shown in Comparative Example 1 was used instead of nitrocellulose containing carboxyl groups. was created.

The performance evaluations for each of the magnetic tapes of Examples 2 to 9 and Comparative Examples 2 to 9 were performed in the same manner as in Example 1 and Comparative Example 1, and the results are shown in Table 2 below. there were. In addition, the surface smoothness is expressed as a relative value with the one of Example 1 as the standard as described above, but the sensitivity is expressed as the relative value (dB) with the one of Comparative Example 2 as the standard (OdB).
).

As is clear from the results in Tables 1 and 2 below, the magnetic recording media of the present invention both have good dispersibility of magnetic powder, and therefore can achieve good results in terms of surface smoothness and sensitivity. , it can be seen that it has significantly improved wear resistance.

Patent applicant: Hitachi Maxell, Ltd. -19 Lee---

Claims (3)

[Claims] (1) A magnetic recording medium comprising a magnetic layer containing a binder and magnetic powder on a base, wherein at least one component of the binder is made of a cellulose resin having a carboxyl group in the molecule. Medium. (2) The magnetic recording medium according to claim (1), wherein the carboxyl group content in the cellulose resin having carboxyl groups in the molecule is in the range of 0.5 to 2 per 10,000 molecular weight. (3) The binder contains at least one selected from polyurethane resin, polyvinyl chloride resin, polyester resin, rubber resin, and polyol, and a polyisocyanate compound as well as a cellulose resin having a carboxyl group in the molecule. A magnetic recording medium according to claim (1) or (2).