JPH076348A - Magnetic recording medium - Google Patents

Abstract

(57) [Summary] The back coat layer is composed of a binder containing a vinyl chloride copolymer having an epoxy group and carbon black having a total ion extraction amount of alkali metal and alkaline earth metal of 500 ppm or less. [Effect] To obtain a magnetic recording medium which has an excellent friction reducing effect, an antistatic effect, wear resistance, and a back coat layer which does not generate inorganic crystals on the surface and which is excellent in running property and durability. Is possible.

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, and more particularly to improvement of a backcoat layer formed on the surface of a non-magnetic support opposite to the surface on which the magnetic layer is formed.

[0002]

2. Description of the Related Art Magnetic tapes such as audio tapes and video tapes are obtained by kneading a ferromagnetic powder, a binder, a dispersant, a lubricant and the like in an organic solvent on a non-magnetic support such as a polyester film. A so-called coating type magnetic tape in which a magnetic layer is formed by applying a magnetic paint, or a so-called metal thin film type in which a magnetic layer is formed by directly applying a ferromagnetic metal by means such as vacuum deposition Magnetic tape is known.

In these magnetic tapes, slidability with a guide roller or the like is made good, stability of running property is improved, frictional resistance between tapes which are in contact with each other when wound is reduced, and charging characteristics are improved. For the purpose of improvement and prevention of dust adhesion due to charging, a non-magnetic powder having an antistatic effect and a friction reducing effect is formed on the surface of the non-magnetic support opposite to the side on which the magnetic layer is formed by a resin binder. It is common to provide a back coat layer dispersed therein.

As the non-magnetic powder used for such a back coat layer, carbon black is used because of its excellent antistatic effect, and the binder is polyurethane resin,
Polyester resins, polyether resins, polycarbonate resins, phenoquino resins, styrene resins, acrylic resins, butadiene resins, acrylonitrile resins are widely used.

However, the back coat layer using these resins as a binder has low wear resistance, and when it is slid many times on a running system such as a guide roller, it gradually wears and its function deteriorates. Further, there is a drawback that the adhesiveness is high, and it cannot be said that the tapes stick to each other when wound and the slidability with respect to the guide roller is good.

Therefore, in order to improve abrasion resistance and tackiness, it has been attempted to use a vinyl chloride copolymer as a binder. A back coat layer using a vinyl chloride copolymer as a binder and carbon black as a non-magnetic powder is excellent in antistatic effect and friction reducing effect,
It has high abrasion resistance and low tackiness, and exhibits excellent functions as a back coat layer.

[0007]

However, in this back coat layer, it has been confirmed that chloride crystals are formed upon aging and precipitate as white powder on the surface, which poses a problem in terms of practicality. is there.

Therefore, the present invention has been proposed in view of such a conventional situation, and is excellent in a friction reducing effect and an antistatic effect, and has high abrasion resistance, low adhesiveness, and a surface. An object of the present invention is to provide a magnetic recording medium which has a back coat layer in which white powder is not deposited and which is excellent in running property and durability.

[0009]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies, and as a result, introduced an epoxy group into a vinyl chloride-based copolymer as a binder in the back coat layer. In addition, it has been found that the formation of chloride crystals can be suppressed by controlling the total amount of alkali metal and alkaline earth metal ions extracted from carbon black.

The magnetic recording medium of the present invention has been completed based on such findings, and a magnetic layer is formed on one surface of a non-magnetic support and a back coat layer is formed on the other surface. In the magnetic recording medium thus obtained, the back coat layer is one in which carbon black is dispersed in a binder containing a vinyl chloride copolymer having an epoxy group, and the alkali metal of the carbon black and The total extraction amount of alkaline earth metal ions is 500
It is characterized by being below ppm.

Further, the content of the monomer having an epoxy group constituting the vinyl chloride copolymer is 2 to 10 mol%.

The magnetic recording medium of the present invention has a magnetic layer formed on one side surface of a non-magnetic support and a back coat layer formed on the other side surface.

The back coat layer is formed by dispersing a non-magnetic powder having an antistatic effect and a friction reducing effect in a binder, and improves the running stability of the magnetic tape, reduces the friction resistance, and the charging property. It is provided for the purpose of improving.

In the present invention, a vinyl chloride copolymer having an epoxy group is used as the binder constituting the back coat layer, and the total amount of alkali metal and alkaline earth metal ions extracted as the non-magnetic powder dispersed in the binder. Is 500 ppm or less. In this way, it is necessary to use the vinyl chloride-based copolymer having an epoxy group in particular and to regulate the total ion extraction amount of the alkali metal and the alkaline earth metal of the carbon black, because the white powder is deposited on the back coat layer surface. This is to prevent

That is, in the backcoat layer composed of a vinyl chloride-based copolymer having no epoxy group and the above-mentioned carbon black having a total ion extraction amount of more than 500 ppm, inorganic crystals are formed to form white powder on the surface of the backcoat layer. Precipitates and adversely affects its properties. It is considered that the inorganic crystals precipitated as the white powder are formed by hydrochloric acid liberated from the vinyl chloride-based copolymer and the alkali metal and alkaline earth metal retained by the carbon black.

On the other hand, in a back coat layer composed of a vinyl chloride copolymer having an epoxy group and carbon black having a total ion extraction amount of alkali metal or alkaline earth metal of 500 ppm or less, a vinyl chloride copolymer is used. Hydrochloric acid is less likely to be released from the polymer, and the amount of alkali metal and alkaline earth metal retained in carbon black is small, so that the formation of inorganic crystals as described above can be suppressed. Therefore, excellent friction reduction effect and antistatic effect.
Since abrasion resistance is obtained and white powder is not deposited on the surface during standing, it contributes effectively to improvement of running property and durability of the magnetic recording medium.

The total amount of alkali metal and alkaline earth metal ion extraction of carbon black regulated in the present invention is 2 g of carbon black put in 100 ml of pure water and boiled at 100 ° C. for 5 hours to extract water. The extracted water was measured by supplementing pure water for evaporation with an ion chromatograph (manufactured by Dionex) for component analysis.

The vinyl chloride copolymer used as the binder of the back coat layer is a copolymer of at least vinyl chloride and a monomer having an epoxy group. The vinyl chloride content of this vinyl chloride-based copolymer is preferably 70 mol% or more, and the content of the epoxy group-containing monomer is preferably 2 to 10 mol%. For example,
If the content of the epoxy group-containing monomer is less than 2 mol%, hydrochloric acid may be liberated from the copolymer to form chloride crystals.

In addition to the vinyl chloride and epoxy group-containing monomer, a third component monomer may be copolymerized with the copolymer for the purpose of improving dispersibility. As the third component monomer, a monomer having a polar group such as a hydroxyl group, a carboxylic acid group, a carboxylate group, a sulfonic acid group, a sulfonate group, a sulfuric acid group, a sulfate group, a primary to tertiary amine group, and a quaternary ammonium salt group. Can be mentioned. If the content of the third component monomer in the copolymer is too large, the tackiness of the back coat layer may be increased. Therefore, when copolymerizing the third component monomer, the amount should be optimized. is necessary.

The vinyl chloride-based copolymer is composed of such a monomer, but the degree of polymerization thereof is preferably 200 or more. If the degree of polymerization of the vinyl chloride-based copolymer is less than 200, the back coat layer will have high tackiness, which will increase the friction coefficient with respect to the running system.

As the binder for the back coat layer, such a vinyl chloride copolymer having an epoxy group may be used alone. For example, a vinyl chloride copolymer having an epoxy group and a conventional vinyl chloride copolymer may be used. You may make it mix and use the resin used more. In this case, the proportion of the vinyl chloride-based copolymer in the total binder is preferably 40% by weight or more. If the proportion of the vinyl chloride-based copolymer in the binder is less than 40% by weight, the back coat layer also has high tackiness and the friction coefficient with the running system increases.

On the other hand, the total amount of ion extraction of alkali metal and alkaline earth metal dispersed in such a binder is 5
Carbon black having a primary particle size of 15 to 30 mμm is suitable as carbon black of 00 ppm or less, but by adding a large particle size of primary particle size of 30 to 400 mμm to such a small particle size, The coefficient of friction of the coat layer may be controlled.

The composition ratio of the above carbon black in the binder (carbon black amount / total binder amount) is 0.5.
It is preferable to set it to / 1 to 3/1. When the composition ratio of carbon black in the binder is less than 1/1, the ratio of the binder on the surface of the back coat layer increases and the tackiness increases, while when it is more than 3/1, it depends on the binder. The carbon black cannot be retained, and the carbon black comes off during tape running.

In the magnetic recording medium, the back coat layer as described above is formed on the surface of the non-magnetic support opposite to the side on which the magnetic layer is formed. The magnetic layer is a magnetic coating film formed by applying a magnetic coating material such as magnetic powder or a resin binder onto the surface of a non-magnetic support, or a ferromagnetic metal thin film deposited on the non-magnetic support. Is.

In the case where the recording magnetic layer is a magnetic coating film, any known magnetic powder, resin binder, etc. can be used without any limitation. As magnetic powder,
γ-Fe ₂ O ₃ , ferromagnetic iron oxide particles such as γ-Fe ₂ O ₃ coated with cobalt, ferromagnetic chromium dioxide particles, Fe, C
Examples thereof include ferromagnetic metal-based particles made of metals such as o and Ni and alloys containing these, and hexagonal plate-shaped hexagonal ferrite fine particles.

As the resin binder, a polymer such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, acrylonitrile, or a copolymer of two or more of them is used. Examples include coalesce, polyurethane resin, polyester resin, and epoxy resin. A hydrophilic group such as a sulfonic acid group, a carboxyl group, or a phosphoric acid group may be introduced into these binders in order to improve the dispersibility of the magnetic powder.

In addition to the above magnetic powder and resin binder, a dispersant, an abrasive, an antistatic agent, a rust preventive, etc. may be added to the magnetic coating film as additives.

On the other hand, when the recording magnetic layer is a ferromagnetic metal thin film, the ferromagnetic metal thin film is formed as a continuous film by a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method and a sputtering method.

The vacuum vapor deposition method is 10 ^-4 to 10 ^-8 Tor.
resistance heating, high frequency heating of ferromagnetic metal materials under vacuum of r
The evaporation metal (ferromagnetic metal material) is deposited on the disk substrate by evaporating it by electron beam heating or the like. Generally, in order to obtain a high coercive force, the ferromagnetic metal material is obliquely deposited on the substrate. The vapor deposition method is adopted.
Alternatively, the above vapor deposition is also included in order to obtain a higher coercive force.

The above-mentioned ion plating method is also a kind of vacuum deposition method, and DC glow discharge and RF glow discharge are generated in an inert gas atmosphere of 10 ^-4 to 10 ^-3 Torr,
That is, the ferromagnetic metal material is vaporized during discharge.

The above-mentioned sputtering method is 10 ^-3 to 10 ^-1
A glow discharge is caused in an atmosphere containing Torr's argon gas as a main component, and the atoms on the target surface are knocked out by the generated argon gas ions. The glow discharge method is a direct current 2-pole or 3-pole sputtering method or a high frequency wave. There are a sputtering method, a magnetron sputtering method using magnetron discharge, and the like. When this sputtering method is used, a base film of Cr, W, V or the like may be formed.

In any of the above methods,
Bi, Sb, Pb, Sn, Ga, on the non-magnetic support in advance
A base film of a nonmagnetic metal such as In, Cd, Ge, Si, Tl is formed in advance, and the above ferromagnetic metal material is vapor-deposited or sputtered from the vertical direction to diffuse these nonmagnetic metals in the ferromagnetic metal thin film. The orientation may be eliminated and the coercive force may be secured.

When forming a metal magnetic thin film by such a vacuum thin film forming technique, as a ferromagnetic metal material used, in addition to metals such as Fe, Co and Ni, Co-Ni alloy and Co-Pt are used. Alloy, Co-Ni-Pt alloy, Fe-C
o alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe
-Co-B alloy, Co-Ni-Fe-B alloy, Co-C
Examples include r alloys and alloys containing metals such as Cr and Al. In particular, when a Co—Cr alloy is used, a perpendicular magnetization film is formed.

A top coat layer made of a rust preventive agent or a lubricant may be provided on the recording magnetic layer.

The non-magnetic support on which the above back coat layer and magnetic layer are formed is typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polyesters and the like. Such a polymer support may be mentioned.

[0036]

[Function] The total amount of ion extraction of the vinyl chloride copolymer having an epoxy group and the alkali metal or alkaline earth metal is 5
In the backcoat layer composed of carbon black of less than 00 ppm, hydrochloric acid is less likely to be released from the vinyl chloride-based copolymer, and the amount of alkali metal and alkaline earth metal retained in the carbon black is small, so that inorganic crystal Are difficult to form. Therefore, excellent friction reduction effect,
An antistatic effect and abrasion resistance are obtained, and white powder is not deposited on the surface during standing, which effectively contributes to the improvement of running property and durability of the magnetic recording medium.

[0037]

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

Table 1 shows the types and contents of the epoxy group-containing monomer and the third component monomer constituting the vinyl chloride copolymer used in this example, and the degree of polymerization of the copolymer.

[0039]

[Table 1]

The following Examples 1 to 9 and Comparative Examples 1 to
In Comparative Example 3, these vinyl chloride copolymers were used as a binder for the back coat layer, and Raven 2500U and Raven 1 were used.
255 (above, product name of Columbian Chemicals, Inc.)
Various magnetic tapes were prepared by using Black Pearls 700 (trade name, manufactured by Cabot Corporation) as carbon black in which the back coat layer is dispersed.

Example 1 First, various magnetic coating compositions were weighed and mixed based on the following magnetic coating compositions. Magnetic paint composition Magnetic powder Metal magnetic powder (specific surface area 50 m ² / g) 100 parts by weight Abrasive 7 parts by weight alumina (Sumitomo Chemical Co., Ltd., trade name AKP-50) Dispersant 1 part by weight oleic acid Lubricant butyl stearate 2 Parts by weight Binder Vinyl chloride copolymer 12 parts by weight (Sekisui Chemical Co., Ltd., trade name S-Rex A) Polyester polyurethane 8 parts by weight (Nippon Polyurethane Industry Co., Ltd., trade name N-2304) Solvent Methyl ethyl ketone 180 parts by weight Toluene 80 parts by weight

This mixture was put into a sand glider mill, mixed for 6 hours to give a magnetic coating, filtered, and then 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added. Then, the magnetic paint containing this Coronate L was applied onto a polyethylene terephthalate film having a thickness of 8 μm and dried to obtain a film thickness of 2.5 μm.
The magnetic layer of was formed and calendered.

On the other hand, various backcoat coating compositions were weighed and mixed based on the following backcoat coating compositions. Backcoat paint composition Non-magnetic powder Carbon black 100 parts by weight (Colombian Chemicals, trade name Raven 2500U) Binder 60% by weight epoxy group-containing vinyl chloride copolymer (300A5 in Table 1) Polyester polyurethane 7 parts by weight (Nippon Polyurethane Industry Co., Ltd., trade name N-3109) Dispersant Phosphate ester 0.5 parts by weight Solvent Methyl ethyl ketone 400 parts by weight Toluene 100 parts by weight In addition, the total amount of alkali metal and alkali metal ions extracted from the carbon black is 270 ppm. there were.

This mixture was put into a sand glider mill and mixed for 8 hours to give a back coat paint. After filter treatment, 12 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added. Then, the backcoat paint containing this Coronate L is applied to the surface of the PET film opposite to the side on which the magnetic layer is formed and dried to form a backcoat layer having a thickness of 0.5 μm. Then, it was calendered.

The PET film on which the magnetic layer and the back coat layer were formed in this manner was slit into a width of 8 mm to form a magnetic tape, and then mounted in an 8 mm cassette.

Examples 2 to 9 In preparing backcoat paints, the type and amount of epoxy group-containing vinyl chloride copolymer, the amount of polyester polyurethane added, and the type of carbon black are shown in Table 2. A magnetic tape was produced in the same manner as in Example 1 except that it was changed, and the magnetic tape was incorporated into the cassette.

Comparative Example 1 As shown in Table 2, as in Example 1 except that a vinyl chloride-based copolymer containing no epoxy was used in place of the epoxy group-containing vinyl chloride-based copolymer in preparing the back coat coating composition. A magnetic tape was prepared in the same manner and incorporated in a cassette.

Comparative Example 2 As shown in Table 2, in the same manner as in Example 1 except that carbon black having an ion extraction total amount of alkali metal and alkaline earth metal of 500 ppm or more was used as the carbon black when preparing the back coat paint. A magnetic tape was prepared and incorporated into a cassette.

Comparative Example 3 As shown in Table 2, a vinyl chloride-based copolymer containing no epoxy was used in place of the epoxy group-containing vinyl chloride-based copolymer in the preparation of the back coat paint, and an alkali metal and carbon black were used as carbon black. A magnetic tape was prepared in the same manner as in Example 1 except that an alkaline earth metal having a total ion extraction amount of 500 ppm or more was used, and then incorporated into a cassette.

[0050]

[Table 2]

With respect to the magnetic tapes manufactured as described above, the friction coefficient of the back coat layer, the adhesiveness, the state of white powder generation, and the state of carbon black loss were evaluated. The results are shown in Table 3.

The coefficient of friction was 90 ° under an environment of a temperature of 25 ° C. and a relative humidity of 60% with respect to the cylindrical surface of a stainless steel (product name SUS304) cylinder having an outer diameter of 4 mm.
The back coat layer of the magnetic tape was slid under a sliding condition of a load of 20 g and a sliding speed of 5 m / sec, and the friction coefficient at that time was measured by a friction tester (manufactured by Sony Corporation).

Regarding the adhesiveness, the cassette with the magnetic tape incorporated was tested under the conditions of a temperature of 60 ° C. and a relative humidity of 90%.
After leaving for a week, recording was performed by a recording / reproducing apparatus, and the magnitude of the tension generated on the magnetic tape at that time was measured and evaluated. In Table 1, the case where the increase in tension is small is described as good, and the case where the increase in tension is severe is described as bad.

The state of generation of white powder was determined by aging a cassette incorporating a magnetic tape, and observing the presence or absence of chloride crystals on the back surface of the magnetic tape with a differential interference microscope (objective lens × 50) after aging. evaluated.

[0055]

[Table 3]

As can be seen from Table 3, a vinyl chloride copolymer having epoxy as a binder component of the back coat layer is used, and ions of alkali metal and alkaline earth metal are used as the non-magnetic powder dispersed in the back coat layer. In the magnetic tapes of Examples 1 to 9 in which the total extraction amount of carbon black was 500 ppm or less, white powder was not generated on the back coat layer surface, the back coat layer had low tackiness, and the friction coefficient was also low. It is a value.

On the other hand, a magnetic tape of Comparative Example 1 using a vinyl chloride copolymer having no epoxy as a binder component of the back coat layer, an alkali metal as a non-magnetic powder dispersed in the back coat layer, and A magnetic tape of Comparative Example 2 using a carbon black having an alkaline earth metal ion extraction total amount of 500 ppm or more, a vinyl chloride-based copolymer having no epoxy as a binder component of the back coat layer, and a back coat layer. In the magnetic tape of Comparative Example 3 in which carbon black having a total ion extraction amount of alkali metal and alkaline earth metal of 500 ppm or more was used as the non-magnetic powder to be dispersed in the white powder, generation of white powder was recognized on the surface of the back coat layer. It is remarkable in the magnetic tape of 3.

From this, the vinyl chloride type copolymer having an epoxy group is used as the binder component of the back coat layer, and the total amount of ion extraction of alkali metal and alkaline earth metal of carbon black dispersed in the back coat layer is 500 ppm or less. It was found that suppressing the occurrence of white powder on the surface of the back coat layer is effective in obtaining a magnetic tape having excellent practicability.

Next, in order to examine the conditions when using a carbon chloride having a vinyl chloride copolymer having an epoxy group and an alkali metal or alkaline earth metal ion extraction total amount of 500 ppm or less, the magnetic property of Example 1 was examined. Magnetic tapes (Sample Tape 1 to Sample Tape 5) were produced by changing the monomer composition of the vinyl chloride-based copolymer, the addition amount, and the addition amount of carbon black based on the tape as shown in Table 4.

[0060]

[Table 4]

Then, regarding the produced magnetic tape,
In the same way as above, friction coefficient, adhesiveness, white powder generation,
The state of carbon black loss was evaluated. The results are shown in Table 5 together with the results of the magnetic tape of Example 1.

[0062]

[Table 5]

As can be seen from Table 5, sample tape 1 in which the amount of vinyl chloride copolymer in the back coat layer is smaller than that of polyester polyurethane 1, a sample using a vinyl chloride copolymer having a low degree of polymerization Tape 2, the sample tape 3 using a vinyl chloride-based copolymer having a large amount of epoxy group-containing monomer has suppressed the generation of white powder on the surface of the back coat layer, but has a high tackiness in the back coat layer. The friction coefficient is also high. Further, the sample tape 4 having a small amount of carbon black in the back coat layer also has a high adhesiveness and a high friction coefficient, and conversely, the sample tape 5 having a large amount of carbon black is formed from the back coat layer. Problems such as black falling out occur.

From this fact, a vinyl chloride-based copolymer having an epoxy group was used as the binding component of the back coat layer, and the total amount of alkali metal and alkaline earth metal ions extracted as the non-magnetic powder dispersed in the back coat layer was 50.
It is understood that when using carbon black of 0 ppm or less, it is necessary to optimize the monomer composition of the vinyl chloride-based copolymer, the addition amount, and the addition amount of carbon black.

That is, in the vinyl chloride copolymer, the vinyl chloride content is preferably 70 mol% or more, the epoxy group-containing monomer content is 2 to 10 mol%, and the polymerization degree is preferably 200 or more. . Further, the proportion of the vinyl chloride copolymer in the total binder is preferably 40% by weight or more. On the other hand, carbon black is preferably dispersed in the binder so that the amount of carbon black / total amount of binder is 0.5 / 1 to 3/1.

[0066]

As is clear from the above description, in the magnetic recording medium of the present invention, the back coat layer has carbon black dispersed in a binder containing a vinyl chloride copolymer having an epoxy group. In addition, since the total amount of ion extraction of the alkali metal and alkaline earth metal of the carbon black is 500 ppm or less, it is excellent in the friction reducing effect and the antistatic effect, and has high abrasion resistance and low tackiness. It is possible to obtain a magnetic recording medium which is excellent in running property and durability because a back coat layer in which no inorganic crystal is generated is formed on the surface.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic layer is formed on one surface of a non-magnetic support and a back coat layer is formed on the other surface of the non-magnetic support, wherein the back coat layer is a vinyl chloride having an epoxy group. A magnetic recording in which carbon black is dispersed in a binder containing a system copolymer, and the total amount of ion extraction of alkali metal and alkaline earth metal of the carbon black is 500 ppm or less. Medium. 2. The magnetic recording medium according to claim 1, wherein the content of the epoxy group-containing monomer constituting the vinyl chloride-based copolymer is 2 to 10 mol%.