JPH1040536A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has superior durability, traveling reliability, physical properties, magnetostatic properties and electromagnetic conversion characteristics. SOLUTION: The magnetic recording medium has a magnetic layer obtained by applying a magnetic coating of magnetic particles, a binder and a lubricant on a non-magnetic supporting body. The binder contains 50wt.% or more of polyester polyurethane resin having a number average molecular weight (Mn) of 15000 or smaller, and a weight average molecular weight (Mn)/number average molecular weight (Mn) ratio of 2.5 or larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called coating type magnetic recording medium having a magnetic layer formed by applying a magnetic paint composed of a magnetic powder, a binder and a lubricant on a non-magnetic support.

[0002]

2. Description of the Related Art Heretofore, a so-called coating type magnetic recording medium having a magnetic layer formed by applying a magnetic paint comprising a magnetic powder, a binder and a lubricant on a non-magnetic support has been widely used.

In this coating type magnetic recording medium, a binder is generally composed of a vinyl resin (vinyl chloride, vinyl acetate, etc.) and a copolymer thereof, a cellulose resin, a polyurethane resin, or the like as a main component. ing. Usually, these resins are put to practical use as a binder by optionally combining them according to the purpose.

For example, when a vinyl chloride-vinyl acetate resin copolymer, which is a typical example of a vinyl resin, is used as the binder, the binder has high elasticity, can improve the cross-linking property, and is durable. It contributes to the properties and running properties, but is not satisfactory from the viewpoint of dispersion of the magnetic powder.

For example, when nitrocellulose, which is a cellulose resin, is used as a binder, the binder cannot be adsorbed (kneaded) at a high concentration required for high dispersion due to its molecular structure. However, its use is limited despite its good durability, and when acetylcellulose is used as a binder, the amount of the binder used is limited in terms of magnetic powder dispersion.

Further, for example, when a polyester polyurethane resin is used as the polyurethane resin as the binder, the binder has many good points such as dispersion of magnetic powder and adhesion to a base film which is a nonmagnetic support. On the other hand, limitations on manufacturing conditions due to an increase in viscosity during coating and the like, and deterioration in running properties and durability due to an increase in friction coefficient during tape were inevitable.

[0007] In addition, magnetic powders have been further improved (miniaturized, high coercive force) for high density and high performance of magnetic recording media, and correspondingly high dispersion and durable running stability have been achieved. There has been a demand for a polymer resin as a binder having good properties.

In order to improve this point, for example, a method for introducing a functional group for dispersing a magnetic substance as disclosed in Japanese Patent Publication No. 58-41565, or a method for modifying the surface of a silane coupling agent, citric acid or the like. A method of adding a filler has been reported.

[0009] However, these methods are greatly influenced by the surface treatment state of each magnetic powder, the combinations to be used are limited, and it is difficult to obtain optimum conditions.

[0010]

As described above, the conventional polymer resin system could not have sufficiently satisfactory characteristics as a binder for a magnetic recording medium.

Therefore, the conventional magnetic recording medium has been improved by using various kinds of resins as a binder. However, in such an improvement method, it is necessary to consider physical properties such as compatibility between the organic solvent or the resin, and there is a problem that a process such as a method of charging raw materials is complicated, and improvement is desired. Was.

[0012] Accordingly, the present invention provides durability, running reliability,
It is an object of the present invention to provide a magnetic recording medium which is excellent in physical characteristics and also excellent in magnetostatic characteristics and electromagnetic conversion characteristics.

[0013]

In order to achieve these objects, the present inventors use a polyester polyurethane resin having a small molecular weight and a large molecular weight distribution as a binder, and further study a lubricant. As a result, it has been found that properties higher than the conventional polyurethane resin dispersing ability can be secured, static magnetic properties and electromagnetic conversion properties can be improved, and good durability and physical properties can be imparted to a magnetic recording medium.

The present invention has been completed based on such findings, and has a magnetic layer formed by applying a magnetic paint comprising magnetic powder, a binder and a lubricant on a nonmagnetic support. A magnetic recording medium, wherein the binder comprises a polyester polyurethane resin having a number average molecular weight (Mn) of 15000 or less and a weight average molecular weight (Mw) / number average molecular weight (Mn) ratio of 2.5 or more, and 50% by weight. % Or more.

Here, the number average molecular weight (Mn) is 1500
Must be 0 or less.

The polyester polyurethane resin may have a functional group known per se. In particular, -SO
_{4 M, -SO 3 M, -SO} 2 M, -COOM, -NH 2, -
NR ₂ , -NR ₃ , -OH, -OPO ₃ M ₂ , -OPO ₃ R ₂
(M represents a hydrogen atom or an alkali metal, R represents an alkyl group, an alkenyl group, an alkoxyl group, etc.), and those having at least one kind of functional group are preferable. By having the functional group as described above, the binder can enhance the dispersing effect of the magnetic powder.

These functional groups are preferably contained in an amount of 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻² equivalents per 1 g of the polyester polyurethane resin.

Further, by adding a polyisocyanate-based curing agent as a part of the binder, crosslinking and curing are promoted, and an effect on durability and the like can be expected. As the polyisocyanate-based curing agent, there can be used tolylene diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, a reaction product of these with a polyhydric alcohol, a condensate of isocyanate, and the like.

A specific trade name is Coronate-
L, Coronate-HL, Coronate-2030 (or more,
Nippon Polyurethane Co., Ltd.), Takenate D-200, Takenate D-202 (above, manufactured by Takeda Pharmaceutical Co., Ltd.) and the like, and these can be used alone or in combination.

The content of the total binder in the magnetic layer of the magnetic recording medium of the present invention can be arbitrarily adjusted so as to correspond to each format.
It is preferably 5 to 40 parts by weight. The magnetic recording medium of the present invention, the binder, a magnetic powder, an abrasive, an antistatic agent,
Further, if necessary, a known coating material such as a curing agent and a dispersing agent is mixed with an organic solvent to perform a dispersion treatment to form a magnetic paint, which is applied on a base film as a non-magnetic support, and an alignment treatment, After the processing, it is manufactured through a process such as assembling.

It is preferable that the magnetic recording medium according to the present invention contains an ester lubricant having a melting point of 40 ° C. or higher and silicone oil as a lubricant. The magnetic recording medium using this lubricant has improved running reliability and durability, and has improved tape characteristics related to running performance.

In this lubricant, it is necessary that the melting point of the ester lubricant is 40 ° C. or higher, and when the melting point of the ester lubricant is 40 ° C. or lower, the running reliability, durability and running performance are reduced. Does not improve the tape properties related to

In the present invention, the binder preferably has a glass transition point (Tg) of 20 ° C. (about room temperature) to 80 ° C.

The magnetic recording medium has a glass transition point of 20 ° C.
When the temperature is lower than (about room temperature), the sliding property and the like are deteriorated with the increase in the coefficient of friction under running at room temperature. On the other hand, if the temperature of the magnetic recording medium is much higher than room temperature such that the glass transition point is 80 ° C. or higher, the running properties and durability deteriorate.

[0025] The type of ferromagnetic material used in the present invention, ferromagnetic iron oxide powder _{(γ-Fe 2 O 3,} Fe 3 0 4 , etc.),
Co-containing ferromagnetic iron oxide powder, ferromagnetic chromium dioxide powder, ferromagnetic metal powder, barium ferrite, iron carbide powder and the like.

As the abrasive, inorganic fillers such as metal oxides, sulfides, sulfates, carbonates, nitrides and carbides can be used.

As the antistatic agent, conductive fine powder, surfactant and the like can be used.

Examples of the dispersant include higher fatty acids and their metal salts, esters, amides, silane coupling agents,
Titanium coupling agent systems and the like can be used.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments to which the present invention is applied will be described in detail based on specific experimental results.

The magnetic recording medium according to the present embodiment has a nonmagnetic support, and a magnetic layer formed by applying a magnetic paint composed of a magnetic powder, a binder and a lubricant on the nonmagnetic support. Things. In the magnetic recording medium, various information signals are recorded on the magnetic layer as magnetic signals, and the magnetic signals are recorded or reproduced by a so-called magnetic recording / reproducing apparatus.

This magnetic recording medium has a number average molecular weight (Mn) of 15000 or less as a binder, and
It contains 50% by weight or more of a polyester polyurethane resin having a weight average molecular weight (Mw) / number average molecular weight (Mn) ratio of 2.5 or more.

Further, the magnetic recording medium may contain, as a lubricant, an ester lubricant having a melting point of 40 ° C. or higher and silicone oil.

Preferred embodiments of the magnetic recording medium according to the present invention will be described below, and further comparative examples will be compared with the embodiments.

In this embodiment, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are determined by gel permeation chromatography (GPC).
raphy), but here, high performance liquid chromatography (model name; Model 500, Waters)
Manufactured by the company). The detector is ShodexRI.
SE-61, and the column was Shodex KF-
804 + KF-803 + KF-802 + KF-801 was used.

Examples 1 to 11 Here, the binders used in the magnetic recording medium according to the present invention were made to have various compositions, and the compositions of Examples 1 to 1 were used.
1 is given.

Example 1 Ferromagnetic iron oxide powder (γ-Fe ₂ O ₃ ) 100 parts by weight Binder 20 parts by weight Carbon black 1 part by weight Alumina 2 parts by weight Lubricant A 0.5 part by weight Lubricant B 0 0.5 parts by weight Dispersant (γ-aminopropyltriethoxysilane) 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 100 parts by weight The above raw materials are stirred and homogenized (premixing step).
A sand mill step is optionally performed (about 1 hour) to obtain a magnetic paint. The obtained magnetic paint was applied on a polyester film as a non-magnetic support so as to have a coating thickness of 5 μm, subjected to a magnetic field orientation treatment, and dried to obtain a magnetic recording medium according to Example 1.

In the magnetic recording medium according to the first embodiment, the binder has a number average molecular weight (Mn) of about 24,000.
Weight average molecular weight (Mw) / number average molecular weight (M
n) The ratio is about 2.0, and the glass transition temperature (hereinafter, Tg)
And ) At about 40 ° C., and -SO
₃ Polyester polyurethane resin containing about 0.040 mmol / g Na group (hereinafter referred to as polyester polyurethane resin A) 50% by weight (in the binder), number average molecular weight (Mn) is about 14,000, and weight average molecular weight (M
w) / number average molecular weight (Mn) ratio is about 3.0 and Tg
Is about 45 ° C. (hereinafter referred to as polyester polyurethane resin B) in an amount of 50% by weight (in a binder).

On the other hand, the lubricant A is a polyhydric alcohol ester as a fatty acid ester, and has a melting point of 0 ° C. The lubricant B is a fluorine-containing silicone oil having a number average molecular weight (Mn) of about 7000.
It is said.

The magnetic powder used has a specific surface area of about 25 m ² / g.

Example 2 In Example 2, the binder was 50% by weight of polyester polyurethane resin A (in the binder), the number average molecular weight (Mn) was about 15,000, and the weight average molecular weight (Mw) / number The composition contained 50% by weight (in a binder) of a polyester polyurethane resin having an average molecular weight (Mn) of about 2.5 and a Tg of about 60 ° C. (hereinafter, referred to as polyester polyurethane resin C). Example 2 was made in the same manner as Example 1 except that the binder was as described above.

Example 3 In Example 3, the binder was 50% by weight of polyester polyurethane resin A (in the binder), the number average molecular weight (Mn) was about 14,000, and the weight average molecular weight (Mw) / number It has an average molecular weight (Mn) of about 4.0, a Tg of about 30 ° C., and contains 50% by weight (in a binder) of a hydroxyl group-containing polyester polyurethane resin (hereinafter, referred to as polyester polyurethane resin D). To do. In addition, this embodiment 3
It was prepared in the same manner as in Example 1 except that the binder was as described above.

Example 4 In Example 4, the binder was 30% by weight of the polyester polyurethane resin A (in the binder) and 70% by weight of the polyester polyurethane resin D.
(In the binder). Example 4 was made in the same manner as Example 1 except that the binder was as described above.

Example 5 In Example 5, the binder contained 100% by weight (in the binder) of the polyester polyurethane resin B. In addition, the fifth embodiment
Was prepared in the same manner as in Example 1 except that the binder was as described above.

Example 6 In Example 6, the binder was 70% by weight of polyester polyurethane resin D (in the binder), the number average molecular weight (Mn) was about 35,000, and the weight average molecular weight (Mw) / number It contained 30% by weight (in a binder) of a vinyl chloride-vinyl acetate copolymer having an average molecular weight (Mn) of about 1.8 and a Tg of about 70 ° C. Example 6 was made in the same manner as Example 1 except that the binder was as described above.

Example 7 In Example 7, the binder was a polyester polyurethane resin D 70% by weight (in the binder), the number average molecular weight (Mn) was about 28,000, and the weight average molecular weight (Mw) / number It contained about 30% by weight (in a binder) of nitrocellulose having an average molecular weight (Mn) of about 2.3 and a Tg of about 100 ° C.
Example 7 was made in the same manner as Example 1 except that the binder was as described above.

Example 8 In Example 8, the binder was a polyester polyurethane resin D 70% by weight (in the binder), the number average molecular weight (Mn) was about 28,000, and the weight average molecular weight (Mw) / number An acetal resin having an average molecular weight (Mn) of about 1.6 and a Tg of about 105 ° C. was contained in an amount of 30% by weight (in a binder). Example 8 was made in the same manner as Example 1 except that the binder was as described above.

Example 9 In Example 9, the binder was a polyester polyurethane resin D 70% by weight (in the binder), the number average molecular weight (Mn) was about 24,000, and the weight average molecular weight (Mw) / number It contained about 30% by weight (in a binder) of a phenoxy resin having an average molecular weight (Mn) of about 2.3 and a Tg of about 95 ° C. Example 9 was made in the same manner as Example 1 except that the binder was as described above.

Example 10 In Example 10, the binder had a number average molecular weight (Mn) of about 14000 and a weight average molecular weight (Mw) / number average molecular weight (Mn) of about 3.
2, the Tg is about 30 ° C. and about 0.08 mmol
/ G —OH groups and about 0.02 mmol / g —SO ₃ N
A resin containing 70% by weight (in a binder) of a polyester polyurethane resin containing a group (hereinafter, referred to as polyester polyurethane resin E) and 30% by weight (in a binder) of a phenoxy resin used in Example 11. And Example 10 was made in the same manner as Example 1 except that the binder was as described above.

Example 11 In Example 11, a magnetic paint was prepared in the same manner as in Example 10, and then 2 parts by weight of a hardener was added to the magnetic paint. Example 11 was produced in the same manner as in Example 1 except that the magnetic paint was as described above.

Examples 12 and 13 Examples 12 and 13 will be given below assuming that the lubricant used in the magnetic recording medium according to the present invention has various compositions. The lubricant in the magnetic paint used in Examples 12 and 13 had a melting point of 40.
It contains an ester-based lubricant at a temperature of at least ° C and a silicone oil.

Example 12 In Example 12, the lubricant was composed of 50% by weight of a lubricant B in the lubricant and 50% by weight of a fatty acid ester having a melting point of 40 ° C. or higher (hereinafter, lubricating). Agent C)). Example 12 was produced in the same manner as in Example 6, except that the lubricant was changed as described above.

Example 13 In Example 13, the lubricant was composed of 50% by weight of lubricant B in the lubricant and 50% by weight of sorbitan tristearate (hereinafter referred to as lubricant D) in the lubricant. ). Example 13 was produced in the same manner as in Example 6, except that the above-mentioned lubricant was used.

Examples 14 to 19 Here, Examples 14 to 19 are given assuming that the binder used for the magnetic recording medium contains a polyester polyurethane resin and a cellulose derivative. As shown in Examples 14 to 19, when a cellulose derivative is contained in the binder, the number average molecular weight of the polyester polyurethane resin needs to be 20,000 or less. The content of the polyester polyurethane resin and the cellulose derivative in the binder is 70 to 95% by weight for the polyester polyurethane resin and 5 to 30% by weight for the cellulose derivative.

Example 14 In Example 14, the binder had a number average molecular weight (Mn) of about 16,000 and a weight average molecular weight (Mw) / number average molecular weight (Mn) of about 3.
95% by weight (in the binder) of a polyester polyurethane resin having a Tg of about 45 ° C. (hereinafter referred to as polyester polyurethane resin I) and a number average molecular weight (M
n) of about 35000 and a Tg of about 150 ° C. containing 5% by weight (in binder) of nitrocellulose. Example 14 was made in the same manner as Example 1 except that the binder was as described above.

Example 15 In Example 15, the binder was 90% by weight of the polyester polyurethane resin I (during binding) and the nitrocellulose 10 used in Example 14 was used.
% By weight (during binding). Example 15 was made in the same manner as Example 1 except that the binder was as described above.

(Example 16) In Example 15, the binder was 90% by weight of polyester polyurethane resin I (during binding), acetyl having a number average molecular weight (Mn) of about 55000 and a Tg of about 150 ° C. 10% by weight of cellulose (during binding). Example 15 was made in the same manner as Example 1 except that the binder was as described above.

Example 17 In Example 17, the binder had a number average molecular weight (Mn) of about 15,000 and a weight average molecular weight (Mw) / number average molecular weight (Mn) of about 3.
2, the Tg is about 30 ° C., and the introduced polar group is −
Example 1 80% by weight (in a binder) of a polyester polyurethane resin having a COOH group of 0.090 mmol / g (hereinafter referred to as polyester polyurethane resin J).
And 20% by weight (in the binder) of the nitrocellulose used in Example 4. Example 17 was made in the same manner as Example 1 except that the binder was as described above.

Example 18 In Example 18, the binder was a polyester polyurethane resin J 70% by weight (during binding) and the nitrocellulose 30 used in Example 14 was used.
% By weight (in the binder). Example 18 was made in the same manner as Example 1 except that the binder was as described above.

Example 19 In Example 19, a magnetic paint was prepared in the same manner as in Example 17, and then 2 parts by weight of a hardener was added to the magnetic paint. Example 18 was made in the same manner as Example 1 except that the binder was as described above.

Comparative Examples 1 to 15 Here, for comparison with the above-described Examples 1 to 11, Comparative Examples 1 to 7 are given, and
And Comparative Example 8 to Comparative Example 1 for comparison with Example 13.
5 and Comparative Examples 16 to 20 for comparison with Examples 14 to 19 described above.

Comparative Example 1 In Comparative Example 1, the binder was the polyester polyurethane resin A used in Example 1.
Was used as 100% by weight (in binder). Further, in Comparative Example 1, the production was performed in the same manner as in Example 1 except that the binder was changed as described above.

Comparative Example 2 In Comparative Example 2, the binder was 50% by weight of the polyester polyurethane resin A (in the binder), the number average molecular weight (Mn) was about 17000, and the weight average molecular weight (Mw) Containing 50% by weight (in a binder) of a polyester polyurethane resin having a number average molecular weight (Mn) of about 2.8 and a Tg of about 40 ° C. (hereinafter referred to as polyester polyurethane resin F). And Further, in Comparative Example 2, a battery was manufactured in the same manner as in Example 1 except that the binder was changed as described above.

Comparative Example 3 In Comparative Example 3, the binder was 50% by weight of polyester polyurethane resin A (in the binder), the number average molecular weight (Mn) was about 14,500, and the weight average molecular weight (Mw) / Containing 50% by weight (in a binder) of a polyester polyurethane resin having a number average molecular weight (Mn) of about 2.2 and a Tg of about 40 ° C. (hereinafter referred to as polyester polyurethane resin G). And Further, in Comparative Example 3, a battery was manufactured in the same manner as in Example 1 except that the binder was changed as described above.

Comparative Example 4 In Comparative Example 4, as the binder, 30% by weight of the polyester polyurethane resin C (in the binder) and 70% of the phenoxy resin used in Example 11 were used.
% By weight (in the binder). Further, in Comparative Example 4, the same procedure as in Example 1 was carried out except that the binder was changed as described above.

Comparative Example 5 In Comparative Example 5, the binder was the polyester polyurethane resin A used in Example 1.
Contained 90% by weight (in the binder) and 10% by weight (in the binder) of the polyester polyurethane resin B. Further, in Comparative Example 5, the production was performed in the same manner as in Example 1 except that the binder was as described above.

Comparative Example 6 In Comparative Example 6, the binder was the polyester polyurethane resin A used in Example 1.
Contained 70% by weight (in the binder) and 30% by weight (in the binder) of the polyester polyurethane resin B. Further, in Comparative Example 6, the same procedure was performed as in Example 1 except that the binder was changed as described above.

Comparative Example 7 In Comparative Example 7, the lubricant contained about 0.5 parts by weight of the lubricant A and about 0.5 parts by weight of the lubricant C. In addition, this comparative example 7
Was prepared in the same manner as in Example 6 except that the lubricant was as described above.

Comparative Example 8 In Comparative Example 8, the lubricant was about 0.5 parts by weight of a lubricant A and about 0.5 parts by weight of a fatty acid (myristic acid) (hereinafter referred to as lubricant E). )). Comparative Example 8 was made in the same manner as in Example 6, except that the above-mentioned lubricant was used.

Comparative Example 9 In Comparative Example 9, the lubricant was composed of about 0.5 parts by weight of a lubricant A and about 0.5 parts by weight of a fatty acid salt (Ca stearate) (hereinafter referred to as lubricant F). ). Comparative Example 9
Was prepared in the same manner as in Example 6 except that the lubricant was as described above.

Comparative Example 10 In Comparative Example 10, the lubricant contained about 0.5 parts by weight of the lubricant C and about 0.5 parts by weight of the lubricant F. Comparative Example 1
No. 0 was prepared in the same manner as in Example 6 except that the lubricant was as described above.

Comparative Example 11 In Comparative Example 11, the lubricant contained about 0.5 parts by weight of the lubricant C and about 0.5 parts by weight of the lubricant E. Comparative Example 1
No. 1 was produced in the same manner as in Example 6 except that the lubricant was as described above.

Comparative Example 12 In Comparative Example 12, the lubricant contained about 0.5 parts by weight of the lubricant E and about 0.5 parts by weight of the lubricant B. Comparative Example 1
No. 2 was produced in the same manner as in Example 6, except that the above-mentioned lubricant was used.

Comparative Example 13 In Comparative Example 13, the lubricant contained about 0.5 parts by weight of the lubricant E and about 0.5 parts by weight of the lubricant F. Comparative Example 1
Sample No. 3 was produced in the same manner as in Example 6, except that the above-mentioned lubricant was used.

Comparative Example 14 In Comparative Example 14, the lubricant contained about 0.5 parts by weight of the lubricant F and about 0.5 parts by weight of the lubricant B. Comparative Example 1
No. 4 was produced in the same manner as in Example 6 except that the lubricant was as described above.

Comparative Example 15 In Comparative Example 15, the binder was 60% by weight of the polyester polyurethane resin A (during binding) and the nitrocellulose 40 used in Example 14 was used.
% By weight (during binding). Comparative Example 15 was made in the same manner as in Example 1 except that the binder was as described above.

Comparative Example 16 In Comparative Example 16, the binder was 100% by weight of the polyester polyurethane resin I.
(During binding). Comparative Example 1
No. 6 was prepared in the same manner as in Example 1 except that the binder was as described above.

Performance Evaluation Test The magnetic recording media of Examples 1 to 11 and Comparative Examples 1 to 6 produced as described above were cut out so as to be suitable for a performance evaluation test described later, and each sample was formed. Then, a performance evaluation test (magnetic properties, durability, running properties, physical properties, and paint properties) is performed on each of the samples.
Various characteristics of the magnetic recording media of Examples 1 to 11 and Comparative Examples 1 to 6 were measured and evaluated.

First, the magnetic characteristics were measured using a magnetic characteristic measuring device (V
SM). Here, the magnetic properties were measured particularly with respect to the squareness ratio and the residual magnetic flux density.

The durability was measured by measuring 10 to the fixed head.
After running 0 times, the amount of powder falling off of each sample was detected and the relative evaluation was performed based on Comparative Example 1. Specifically, the amount of powder falling when the comparative example 1 is run 100 times with respect to the fixed head is set as a reference (100%). This amount of powder was detected by transferring the magnetic powder attached to the surface of the fixed head to an adhesive tape. For relative comparison with each sample, the amount of powder falling off at this time was taken as 100% and 5%.
A pressure-sensitive adhesive tape having a powder falling amount of 0%, a powder falling amount of 80%, and a powder falling amount of 120% was prepared and used as a comparison object.

Then, each sample prepared from the magnetic recording media of Examples 1 to 11 and Comparative Examples 1 to 7 was run 100 times on the fixed head, and the magnetic powder attached to the surface of the fixed head was coated on the adhesive tape. The adhesive tape was transcribed, and the pressure-sensitive adhesive tape and a comparative adhesive tape produced as described above were relatively visually compared and evaluated. The evaluation was as follows: Comparative example 1 was evaluated as “○” when the amount of powder falling was 50% or less, “、” when the amount of powder falling was 50 to 120%, and evaluated as “△” when the amount of powder falling was 120% or more. Indicates “×”.

The runnability was determined by measuring wow and flutter during running of each sample and performing a relative evaluation based on the measured value of Comparative Example 1. Then, as the evaluation, those with a measured value of 50% or less based on Comparative Example 1 were evaluated as “○”, those with a measured value of 50 to 120% as “Δ”, and those with a measured value of 120% or more were evaluated. “×” was assigned.

The physical properties were measured by measuring the breaking strength of the tape.
This was performed by comparative evaluation with Comparative Example 1. Then, as an evaluation, the breaking strength was 12 compared to the breaking strength of Comparative Example 1.
Those with 0% or more are marked with "O" and have a breaking strength of 85 to 120.
% And “△” when the breaking strength is 85% or less.

The paint properties were determined by measuring the viscosity of the magnetic paint and performing relative evaluation with Comparative Example 1. Then, as the evaluation, when the viscosity of the magnetic paint is 60% or less as compared with the viscosity of the magnetic paint of Comparative Example 1, “○” is given, and when the viscosity of the magnetic paint is 60 to 100%, “△” is given. When the viscosity of the magnetic paint was 100% or more, it was evaluated as "x".

Table 1 shows the results of the performance evaluation tests described above.

[0085]

[Table 1]

Further, the magnetic recording media of Examples 12, 13 and Comparative Examples 7 to 14 were cut out so as to be suitable for a performance evaluation test described later, and each sample was formed. Then, a performance evaluation test (friction coefficient, running durability) was performed on each sample, and various characteristics were measured and evaluated.

The coefficient of friction is low (5 ° C.) and high (40 ° C.).
C.), the maximum static friction coefficient (μ) with the head material was measured and compared with the maximum static friction coefficient (μ) of Comparative Example 5. The evaluation was 8 in comparison with the maximum static friction coefficient (μ) of Comparative Example 5.
If it is 0% or less, mark it as "○", and the maximum static friction coefficient (μ)
Is 80 to 120%, and "△" is obtained when the maximum static friction coefficient (μ) is 120% or more.

The running durability is as follows: low temperature (5 ° C.) and high temperature (4
At two different temperatures (0 ° C.), each sample was run 100 times with respect to the fixed head, and then the output reduction of each sample was measured and evaluated relative to a reference. here,
The reference is Comparative Example 5 similar to the current commercially available tape.
It shows a decrease in the output in Hz. And, as the evaluation, those with 130% or more with respect to the reference (10 kHz) are marked with “○”, those with 70 to 130% with respect to the reference are marked with “△”, and those with 70% or more with respect to the reference “×” was assigned.

Table 2 shows the results of the above tests on the coefficient of friction and running durability.

[0090]

[Table 2]

Further, with respect to Examples 14 to 19 and Comparative Examples 15 and 16, Examples 1 to
Performance evaluation tests (magnetic properties, durability, running properties, physical properties, and paint properties) performed on Example 12 and Comparative Examples 1 to 6 were performed, and Examples 14 to 19 and Comparative Example 1 were performed.
Various characteristics of the magnetic recording media of Comparative Example 5 and Comparative Example 16 were measured and evaluated.

Table 3 shows the results of performance evaluation tests on Examples 14 to 19 and Comparative Examples 15 and 16.

[0093]

[Table 3]

The following conclusions are drawn from the results of the performance evaluation tests described above.

First, as is clear from Table 1, the magnetic recording medium having the polyester polyurethane resin used in the present example is different from the magnetic recording medium of the comparative example in terms of durability, running properties, physical properties and paint properties. Also showed excellent results. That is, it can be seen that a binder containing a polyester polyurethane resin having a small molecular weight gives better results than the current composition of a polyester polyurethane (having a large molecular weight and a small molecular weight distribution).

Further, by introducing a polar group into the polyester polyurethane resin in the binder, the dispersing effect can be further enhanced, and the durability can be further improved by crosslinking by adding a curing agent. Further, from the viewpoint of the glass transition point, it can be understood that 20 to 80 ° C. is the optimum condition for the magnetic recording medium.

Further, in the magnetic recording medium according to the present invention, as apparent from the results of the squareness ratio and the residual magnetic flux density, the polyester polyurethane resin contained in the binder deteriorates the magnetic characteristics of the magnetic recording medium. No problem, and good magnetic properties are obtained.

On the other hand, if the average glass transition point of the binder resin is lower than 20 ° C. or higher than 80 ° C.,
The durability of the magnetic recording medium deteriorates due to an increase in the coefficient of friction and the like during traveling at room temperature, and it is difficult to ensure reliability.

As described above, in the magnetic recording medium of the present invention, since the polyester polyurethane resin having a small number average molecular weight and a large molecular weight distribution is used as a binder, it has excellent durability and running reliability, and Magnetostatic properties,
It is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics.

Further, as is apparent from Table 2, in Examples 12 and 13, the friction coefficient is stabilized and the running durability is excellent as compared with Comparative Examples 7 to 14. That is, by using a lubricant containing an ester-based lubricant having a melting point of 40 ° C. or higher and silicone oil, the magnetic recording medium has a good friction coefficient at either a low temperature or a high temperature. Thus, it is possible to maintain a high output even after traveling for a long time.

In particular, when a cyclic alkyl ester was used as the above-mentioned ester-based lubricant, more excellent results were obtained in terms of running durability. The use of a solid lubricant such as graphite as the lubricant can further improve the wear coefficient and running durability of the magnetic recording medium.

Further, as is clear from Table 3, a polyester polyurethane resin having a number average molecular weight (Mn) of 20,000 or less and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 2.5 or more was used. A magnetic recording medium using a binder containing 5 to 30% by weight of a cellulose derivative showed better results than the magnetic recording medium of the comparative example in terms of durability, running properties, physical properties, and coating properties. .

In particular, when the content of the cellulose derivative is 10 to
Particularly good results were shown in the range of 20% by weight. In addition, when a polar group is introduced as a functional group introduced into the polyester polyurethane resin, it is possible to further enhance the dispersing effect. Furthermore, it was found that by adding a curing agent to the magnetic paint, crosslinking was formed and durability was improved. Furthermore, the glass transition point is 20-80 ° C.
In the case of, optimal conditions are obtained for various characteristics.

On the other hand, if the average glass transition point of the binder is lower than 20 ° C. or higher than 80 ° C., the durability of the magnetic recording medium deteriorates due to an increase in the coefficient of friction during running at room temperature. It proved difficult to secure reliability. In addition, when a cellulose derivative is added to the current polyester polyurethane resin, that is, a polyester polyurethane resin having a large molecular weight, paint stability decreases,
Nothing that could withstand practical use was obtained. Further, with respect to a binder containing a cellulose derivative in an amount of 40% by weight or more, the stability of the coating material was reduced, and various properties were significantly deteriorated.

As described above, in the magnetic recording medium according to the present invention, by adding a predetermined amount of a cellulose derivative as a binder, durability and running reliability are excellent, and static magnetic characteristics and electromagnetic conversion characteristics are improved. Will also be excellent.

[0106]

As described above in detail, the magnetic recording medium according to the present invention has a small number average molecular weight of 15,000 or less, and a molecular weight such that the weight average molecular weight / number average molecular weight is 2.5 or more. 10% by weight or more, preferably 50% by weight, of the polyester polyurethane resin having a large distribution in the total binder.
By weight or more, durability, running reliability,
It has excellent physical characteristics, and also has excellent magnetostatic characteristics and electromagnetic conversion characteristics.

Further, the magnetic recording medium according to the present invention has good abrasion resistance by using an ester lubricant having a melting point of 40 ° C. or higher, preferably a cyclic alkyl ester. Has a coefficient,
It also has excellent running durability.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C09D 183/04 PMU C09D 183/04 PMU G11B 5/72 G11B 5/72 (72) Inventor Hiroshi Kudo Sony Corporation, 72-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo (72) Inventor Tsuyoshi Koizumi Inside 7-35, Kita-Shinagawa, Shinagawa-ku, Tokyo

Claims (5)

[Claims] 1. A magnetic recording medium having a magnetic layer formed by applying a magnetic paint comprising a magnetic powder, a binder and a lubricant on a non-magnetic support, wherein the binder has a number average molecular weight (Mn) of 15000. Below,
And weight average molecular weight (Mw) / number average molecular weight (Mn)
50 polyester polyurethane resin with a ratio of 2.5 or more
A magnetic recording medium, characterized in that the magnetic recording medium contains at least 10% by weight. 2. The magnetic recording medium according to claim 1, wherein the lubricant contains an ester lubricant having a melting point of 40 ° C. or higher and silicone oil. 3. The magnetic recording medium according to claim 2, wherein the ester lubricant is a cyclic alkyl ester having a melting point of 40 ° C. or higher. 4. The method according to claim 3, wherein the cyclic alkyl ester is sorbitan acid tristearate.
The magnetic recording medium according to the above. 5. The polyester polyurethane resin,
2. The magnetic recording medium according to claim 1, wherein the glass transition point is 20 to 80 [deg.] C. depending on the mixing ratio of the polyester monomer.