JPH05128484A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To attain to make high density recording by constituting a binder in a coating type magnetic recording medium of a polyvinylacetoacetal resin and a resin having a specific glass transition point. CONSTITUTION:The coating type magnetic recording medium is constituted by applying a ferromagnetic powder such as gamma-Fe2O3 and the binder on a non- magnetic supporting body such as a polyester. In this case, the polyvinylacetoacetal resin having high dispersibility is used as a resin constituting the binder so as to uniformly disperse the magnetic powder into the magnetic layer even when the magnetic powder is a fine particle. And to secure adhesive strength, the polyester resin or the like having <=70 deg.C glass transition point is mixed. The mixing ratio is controlled so that the content of the polyvinylacetoacetal resin is 20-80wt.% per total binder. By the constitution, high recording density is attained and the recording medium excellent in environmental protection is obtained as the binder does not contain a harmful material such as Cl.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium,
Particularly, it relates to improvement of a binder constituting a magnetic layer in a coating type magnetic recording medium.

[0002]

2. Description of the Related Art In a so-called coating type magnetic recording medium,
The magnetic layer is formed by applying a magnetic paint prepared by dispersing and kneading a ferromagnetic powder, a binder, a dispersant, a lubricant and the like in an organic solvent onto a non-magnetic support such as a polyester film.

As a binder used in such a coating type magnetic recording medium, a glass for imparting good electromagnetic conversion characteristics to the magnetic recording medium, excellent abrasion resistance and heat resistance and durability. It is required to have a low transition point, and for example, nitrocellulose-urethane resin, polyvinyl chloride-urethane resin and the like have been put into practical use.

[0004]

However, the conventionally used binders are unsuitable from the viewpoint of compatibility with high-density recording in the field of magnetic recording in recent years or from the viewpoint of environmental protection. The development of binders is becoming more desirable.

That is, in the field of magnetic recording, high density recording has been progressing year by year, and even in such a coating type magnetic recording medium, in order to meet the high density recording, the magnetic powder to be used is miniaturized. Is promoted, for example, specific surface area 4
Magnetic powders of 0 cm ² / g or more have been used. However, when the magnetic powder becomes finer, it becomes difficult to disperse it in the binder. For example, when it is attempted to disperse the above-mentioned fine particle magnetic powder with the nitrocellulose-urethane resin as the binder, the nitrocellulose-urethane resin is dispersed. However, the viscosity is too high to disperse uniformly. For this reason, the magnetic powder exists in the magnetic layer with unevenness, which causes a problem that the recording / reproducing characteristics of the magnetic recording medium deteriorate.

On the other hand, the polyvinyl chloride-polyurethane resin has a certain degree of dispersion and is suitable for uniformly dispersing the fine magnetic powder particles. However, since chlorine introduced into the molecule causes acid rain, dioxins, etc., it is not preferable from the viewpoint of global environment protection, and the amount used is being regulated.

In addition, polyester-urethane resin is also used as a binder, but this resin alone is likely to cause problems in durability and running property.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, is not a cause of acid rain, dioxin, etc., and is excellent from the viewpoint of environmental protection. It is an object of the present invention to provide a magnetic recording medium that can be uniformly dispersed in a magnetic recording medium and that enables high density recording.

[0009]

In order to achieve the above-mentioned object, the present inventors have examined many kinds of resins and examined their dispersibility and environmental impact when discarded, It has been found that the polyvinyl acetoacetal resin is excellent in dispersibility and has no problem in terms of environmental protection and is suitable as a binder for a high density recording medium.

Based on such knowledge, the magnetic recording medium of the present invention is a magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly containing magnetic powder and a binder,
The binder is composed of a polyvinyl acetoacetal resin and a resin having a glass transition point Tg of 70 ° C. or lower. Further, the polyvinyl acetoacetal resin is the polyvinyl acetoacetal resin shown in Chemical formula 2.

[0011]

[Chemical 2]

Here, the magnetic recording medium to which the present invention is applied is a so-called coating in which a magnetic coating film is formed by coating a magnetic coating mainly composed of magnetic powder and a binder on the surface of a non-magnetic support. Type magnetic recording medium.

In the above magnetic recording medium, the magnetic powder contained in the non-magnetic support or the magnetic coating film may be any conventionally known magnetic powder and is not limited in any way.

For example, as the non-magnetic support,
A polymer support typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates, metal substrates made of aluminum alloys, titanium alloys, glass substrates, and the like. The shape is not particularly limited, and may be any shape such as a tape shape, a sheet shape, and a drum shape. Further, the non-magnetic support may be subjected to a surface treatment for forming fine irregularities in order to control the surface property.

Examples of the magnetic powder include ferromagnetic iron oxide particles such as γ-Fe ₂ O ₃ and cobalt-coated γ-Fe ₂ O ₃ , ferromagnetic chromium dioxide particles, metals such as Fe, Co and Ni, and the like. Examples thereof include ferromagnetic metal-based particles made of an alloy containing, hexagonal plate-shaped hexagonal ferrite fine particles, and the like.

In the present invention, even when the above magnetic powder is fine particles, it can be dispersed uniformly in the magnetic layer, and in consideration of the environmental impact when the magnetic recording medium is discarded. A polyvinyl acetoacetal resin is used as a constituent resin of the binder. This polyvinyl acetoacetal-based resin has high dispersibility and does not have a cause of generation of harmful substances such as Cl in the molecule, and therefore is excellent in terms of environmental protection,
It is extremely suitable as a binder resin.

The above polyvinyl acetoacetal resin is
Although it has the chemical structure shown in Chemical formula 2, here, in order to achieve the above object, the degree of polymerization of the polyvinyl acetoacetate-based resin shown in Chemical formula 2 is 200 to 600,
The composition ratio (mol%) of each monomer component k, l, m is k +
l + m = 100, 65 ≦ k ≦ 85, 1 ≦ l ≦ 20, 5 ≦
It is preferred to use those with m ≦ 30 as binder.

That is, when k is less than 65, the hardness is insufficient and the durability of the magnetic recording medium cannot be sufficiently secured.
Those with a value of more than 85 are difficult to synthesize and practically not available. Further, l has an influence on the solubility with other resins, durability, and softening property, and the above range is preferable in order to improve these characteristics. Further, m is in the above range from the viewpoint of compatibility with other resins, water resistance, and reactivity with isocyanate.

The polyvinyl acetoacetal can be synthesized by saponifying polyvinyl acetate into polyvinyl alcohol and reacting the polyvinyl alcohol with acetaldehyde.

Although such a polyvinyl acetoacetal resin is extremely excellent as a binder resin in terms of dispersibility, environmental protection and electromagnetic conversion characteristics as described above, it has a relatively high glass transition point, so that it can be used in magnetic recording media. Hard and brittle in the environment. Therefore, when used alone as a binder, the adhesion of the magnetic layer to the non-magnetic support becomes insufficient, and it is difficult to ensure durability. Therefore, in the present invention, flexibility is added to the binder by mixing the polyvinyl acetoacetal resin with a low Tg resin having a glass transition point Tg of 70 ° C. or less to ensure the durability of the magnetic recording medium. To do.

The resin having a glass transition point Tg of 70 ° C. or lower is preferably selected in consideration of the influence on the environment and the desired magnetic properties, for example, polyester resin, polyester polyurethane resin, polyether polyurethane. Examples thereof include resins, polycarbonate resins, acrylonitrile-butadiene copolymers, and the like.

Here, in the binder, the composition ratio of the above polyvinyl acetoacetal resin to the low Tg resin is such that the mixing ratio of the polyvinyl acetoacetal resin is 20% of the total binder resin.
It is necessary to be up to 80% by weight. When the mixing ratio of the polyvinyl acetoacetal resin is 20% by weight or less, the magnetic recording medium becomes too soft and is likely to stick to the head during running. When it exceeds 80%, the magnetic recording medium is May become hard and brittle, and durability may be insufficient.

The magnetic coating film contains the magnetic powder,
In addition to the resin binder, a dispersant, an abrasive, an antistatic agent, a rust preventive, etc. may be added as an additive. Furthermore, those who have not formed the magnetic layer surface or the magnetic layer on the non-magnetic support. A top coat layer or a back coat layer made of a rust preventive agent or the like may be provided on each of the surfaces.

[0024]

In a coating type magnetic recording medium, when a polyvinyl acetoacetal resin is used as a binder for the magnetic layer, the polyvinyl acetoacetal resin is excellent in dispersibility, so that even if the magnetic powder is fine particles, it can be contained in the magnetic layer. Disperse evenly. Moreover, since the polyvinyl acetoacetal resin does not have an element such as Cl that causes a harmful substance in the molecule, it is also excellent in environmental protection. Further, in the present invention, since the polyvinyl acetoacetal resin is mixed with the resin having the glass transition point Tg of 70 ° or less, the low Tg resin adds flexibility to the binder and ensures the durability. The Rukoto.

[0025]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

Example 1 First, a magnetic paint composition having the composition shown below was mixed to prepare a magnetic paint. Co deposition γ-Fe ₂ O ₃ (specific surface area 40 m ₂ / g) 100 parts by weight Polyvinyl acetoacetal resin 10 parts by weight Polyester polyurethane resin 10 parts by weight (Tg = 50 ° C., containing SO ₃ Na) Carbon (average particle size 75 nm) ) 5 parts by weight Alumina (average particle size 0.3 μm) 5 parts by weight Stearic acid 2 parts by weight Butyl stearate 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 41 parts by weight

As the polyvinyl acetoacetal resin, among the polyvinyl acetoacetal resins shown in Chemical formula 3, the degree of polymerization is 300, and the composition ratio (mol%) k, l, m of each monomer is 75, 10, respectively. The one that was 15 was used.

[0028]

[Chemical 3]

The magnetic coating composition is mixed by mixing the magnetic powder, carbon, alumina and polyvinyl acetoacetal resin with a kneader, adding other materials with a stirrer with a disperser, and then using a sand mill. It was done by making it into a paint.

20 parts by weight of the hardener Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic coating material thus prepared, and then the thickness was 5 μm in polyethylene terephthalate.
Then, the magnetic recording medium was produced by applying an alignment treatment, a calendar treatment, and a curing treatment. Then, the produced magnetic recording medium was cut into a 1/2 inch width to produce a magnetic tape (sample tape 1).

Examples 2 to 7 As the polyvinyl acetoacetal resin, other than the polyvinyl acetoacetal resin represented by Chemical formula 3, those having the degree of polymerization and the constitutional ratios k, l, m of each monomer shown in Table 1 were used. In the same manner as in Example 1, magnetic tapes (Sample Tape 2 to Sample Tape 7) were produced.

[0032]

[Table 1]

Example 8 A magnetic tape (sample tape 8) was prepared in the same manner as in Example 1 except that metal magnetic powder (specific surface area 54 m ² / g) was used in place of Co-coated γ-Fe ₂ O _{3 as} the magnetic powder. ) Was produced.

Examples 9 to 12 Magnetic tapes (Sample Tapes 9 to Samples) were prepared in the same manner as in Example 1 except that the polyvinyl acetoacetal resin content and the polyester polyurethane resin content were changed as shown in Table 2. Tape 12) was prepared.

[0035]

[Table 2]

Example 13 An acrylonitrile-butadiene copolymer having a glass transition point Tg of -20 ° C. was used in place of the polyester polyurethane resin, the acrylonitrile-butadiene copolymer content was 7 parts by weight, and the polyvinyl acetoacetal resin was used. Example 1 except that the content of was 13 parts by weight
A magnetic tape (sample tape 13) was produced in the same manner as.

Example 14 Polyester polyurethane resin having glass transition point Tg
Is 70 ° C., the content of the acrylonitrile-butadiene copolymer is 7 parts by weight, and the content of the polyester polyurethane resin is 13 parts by weight. A sample tape 14) was produced.

Comparative Example 1 A magnetic tape (Comparative Tape 1) was produced in the same manner as in Example 1 except that a polyvinyl chloride copolymer (trade name MR-110) was used instead of the polyvinyl acetoacetal resin.

Comparative Example 2 A magnetic tape (Comparative Tape 2) was produced in the same manner as in Example 1 except that nitrocellulose 1 / 8H type was used instead of the polyvinyl acetoacetal resin.

Comparative Example 3 A magnetic tape (Comparative Tape 3) was prepared in the same manner as in Example 1 except that the polyvinyl acetoacetal resin content was changed to 17 parts by weight and the polyester urethane resin content was changed to 3 parts by weight. ..

Comparative Example 4 The polyvinyl acetoacetal resin content was 3 parts by weight,
A magnetic tape (Comparative Tape 4) was produced in the same manner as in Example 1 except that the content of the polyester urethane resin was changed to 17 parts by weight.

The magnetic characteristics and still characteristics of the sample tapes 1 to 14 and the comparative tapes 1 to 4 thus produced were measured.
The results are shown in Tables 3 and 4.

[0043]

[Table 3]

[0044]

[Table 4]

First, in Examples 1 to 14 in which a mixture of a polyvinyl acetoacetal resin and a low Tg resin having a glass transition temperature of 70 ° C. or lower is used as a binder, magnetic powder is preferable in the binder. Disperse with dispersibility. Further, as shown in Table 3, the produced magnetic tapes (Sample Tape 1 to Sample Tape 16) are excellent in both magnetic characteristics and still characteristics.

On the other hand, in Comparative Example 2 in which a mixture of nitrocellulose and polyurethane resin was used as the binder, the magnetic powder was not well dispersed in the binder, and the magnetic paint could not be prepared. Further, in Comparative Example 1 in which a mixture of a polyvinyl chloride copolymer and a polyurethane resin is used as a binder, the magnetic tape prepared (Comparative Tape 1) has a polychlorinated material when burned, although the magnetic paint can be adjusted. It was shown that hydrochloric acid is generated by Cl of the vinyl copolymer, which is inconvenient for environmental protection.

From this, therefore, it was shown that a mixture of a polyvinyl acetoacetal resin and a resin having a glass transition point of 70 ° C. or lower is suitable as a binder from the viewpoint of dispersibility and environmental protection.

Among the magnetic tapes using the polyvinyl acetoacetal resin and the low Tg resin as the binder, the comparative tape 3 in which the mixing ratio of the polyvinyl acetoacetal resin in the binder is out of the range of 20 to 80% and the comparison tape The tape 4 has insufficient still characteristics.
From this, it was shown that the composition ratio of the polyvinyl acetoacetal resin and the low Tg resin is important for ensuring the durability when the resin is used as a binder.

[0049]

As is apparent from the above description, the magnetic recording medium of the present invention has polyvinyl acetoacetal as a binder constituting the magnetic layer and a glass transition point Tg of 70 °.
Since the mixture of the following resins is used, it is possible to uniformly disperse the fine particle magnetic powder in the magnetic layer, and it is also possible to provide excellent environmental protection and durability.

Therefore, according to the present invention, it is possible to obtain a magnetic recording medium which enables high density recording and is extremely highly practical.

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[Procedure amendment]

[Submission date] May 20, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction content]

That is, in the field of magnetic recording, high density recording has been progressing year by year, and even in such a coating type magnetic recording medium, in order to meet the high density recording, the magnetic powder to be used is miniaturized. Is promoted, for example, specific surface area 4
Magnetic powders of 0 m ² / g or more have been used. However, when the magnetic powder becomes finer, it becomes difficult to disperse it in the binder. However, the viscosity is too high to disperse uniformly. For this reason, the magnetic powder exists in the magnetic layer with unevenness, which causes a problem that the recording / reproducing characteristics of the magnetic recording medium deteriorate.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

In addition, polyester polyurethane resin is also used as a binder, but this resin alone is likely to cause problems in durability and running property.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

Here, in the binder, the composition ratio of the above polyvinyl acetoacetal resin to the low Tg resin is 2 when the mixing ratio of the polyvinyl acetoacetal resin is 2 % of the total binder resin.
It is necessary to be 0 to 80% by weight. When the mixing ratio of the polyvinyl acetal resin is 20 wt% or less, it will be a magnetic recording medium is too Yawa, there is a high possibility that stick to the head during the running, exceeds 80 wt% fly
In that case , the magnetic recording medium becomes hard and brittle, and the durability may be insufficient.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

Example 1 First, a magnetic paint composition having the composition shown below was mixed to prepare a magnetic paint. Co-deposited γ-Fe ₂ O ₃ (specific surface area 40 m ² / g) 100 parts by weight Polyvinyl acetoacetal resin 10 parts by weight Polyester polyurethane resin 10 parts by weight (Tg = 50 ° C., containing SO ₃ Na) Carbon (average particle size 75 nm) ) 5 parts by weight Alumina (average particle size 0.3 μm) 5 parts by weight Stearic acid 2 parts by weight Butyl stearate 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 41 parts by weight

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction content]

Comparative Example 4 The polyvinyl acetoacetal resin content was 3 parts by weight,
A magnetic tape (Comparative Tape 4) was produced in the same manner as in Example 1 except that the content of the polyester polyurethane resin was changed to 17 parts by weight.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, wherein the binder is polyvinyl acetoacetal resin and the glass transition point Tg is 70 ° C. A magnetic recording medium comprising the following resin. 2. The magnetic recording medium according to claim 1, wherein the polyvinyl acetoacetal resin is the polyvinyl acetoacetal resin shown in Chemical formula 1. [Chemical 1]