JPH06325353A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having good traveling stability and traveling durability consisting of a magnetic layer on the one surface of a nonmagnetic supporting body and a back coating layer on the other surface of the supporting body by using polyester polyurethane resin containing a specified equiv. of tertiary amine per specified grams of the resin in the back coating layer so that the back coating layer has good dispersibility and durability. CONSTITUTION:This magnetic recording medium consists of a nonmagnetic substrate 1, a magnetic layer 2 essentially comprising a magnetic powder and a hinder formed on the substrate, and a back coating layer 3 containing a binder essentially comprising solid particles such as inorg. pigment formed on the back surface of the nonmagnetic substrate 1. The polyester polyurethane resin contains tertiary amine by 80-250 equiv. per 10<6>g of the resin so that the back coating layer has good dispersibility and durability. If the amt. of amine is less than 80 equiv., the obtd. coating material for the back coating layer does not have enough dispersibility or traveling stability. If the amt. exceeds 250 equiv., the excess tertiary amine causes interaction to decrease fluidity of the coating material.

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,
In particular, it relates to improvement of the binder constituting the back coat layer.

[0002]

2. Description of the Related Art In so-called coating type magnetic recording media, particularly audio tapes, video tapes, and magnetic tapes for cartridges, a non-magnetic support is used in order to improve running stability, frictional resistance between the tapes, and charging property. A back coat layer mainly composed of solid particles such as an inorganic pigment and a binder is provided on the back surface of the magnetic layer forming surface.

As a binder used in such a back coat layer, vinyl chloride such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, etc. Resin, nitrocellulose, epoxy resin, acrylic resin,
Polyurethane resin and the like are often used. In these resins, two or more kinds are often used in combination so that the required physical properties can be achieved. For example, among these resins, polyester polyurethane resin having low rigidity (low glass transition temperature) that is excellent in dispersibility, toughness, and abrasion resistance, and high rigidity that imparts coating strength to the formed backcoat layer. Nitrocellulose (high glass transition temperature) or vinyl chloride resin is used in combination.

[0004]

On the other hand, in recent years, further running stability and running durability have been demanded for the above magnetic recording media, and as described above, a nitrocellulose or vinyl chloride based binder is used as a binder for the back coat layer. Satisfactory properties were not obtained when a resin was used.

Therefore, a polyester polyurethane resin having a high glass transition temperature has been proposed in place of the polyester polyurethane resin having a low glass transition temperature. The polyester polyurethane resin is excellent in rigidity, flexibility and dispersibility, and can form a back coat layer having good dispersibility and durability. Here, the polyester polyurethane resin having a high glass transition temperature refers to one having a glass transition temperature of 70 ° C. or higher, and has higher flexibility than a vinyl chloride resin having a similar glass transition temperature due to its structure. It is a thing.

This polyester polyurethane resin is synthesized by combining a polyol component having an ester bond and a glycol with a bifunctional isocyanate to make a high molecular weight. Further, such a polyester polyurethane resin may be introduced with an appropriate ratio of functional groups for improving the adsorption to the inorganic powder and improving the dispersibility of the back coat paint. Examples of such a functional group include a metal sulfonate group (Japanese Patent Publication No. 58-41565).

At this time, as described above, the back coat layer coating composition may be mixed with a cross-linking agent such as a polyisocyanate compound to cross-link the back coat layer to improve the strength of the back coat layer. In the polyester polyurethane resin having a glass transition temperature, the glass transition temperature is higher than the curing temperature, the degree of freedom in the backcoat layer is significantly impaired, and the reaction with the polyisocyanate that is the crosslinking agent is not promoted, Not enough crosslinking. That is, when such a polyester polyurethane resin is used as a binder, there is a problem that the running durability of the obtained back coat layer, especially the durability against repeated running is not sufficiently satisfactory. When the curing temperature is not less than the glass transition temperature of the polyester polyurethane resin, the degree of freedom of the polyester polyurethane resin is secured, but the non-magnetic support such as polyester flows to change the shape and the resulting magnetic recording is obtained. The electromagnetic conversion characteristics of the medium deteriorate. Therefore, when a polyester polyurethane resin having a high glass transition temperature is used as the binder, it is impossible to impart further durability to the back coat layer obtained.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides a binder having good dispersibility of the inorganic application powder in the binder and good cross-linking efficiency, and durability. An object of the present invention is to provide a magnetic recording medium having an excellent back coat layer and excellent running stability and running durability.

[0009]

In order to achieve the above-mentioned object, the present invention provides a magnetic recording medium having a back coat layer using a polyester polyurethane resin as a binder, the third of which is 10 ⁶ g of the polyester polyurethane resin. It is a polyester polyurethane resin containing 80 to 250 equivalents of a primary amine.

In one example of the magnetic recording medium of the present invention, the coating material for the back coat layer contains a polyisocyanate compound as a crosslinking agent, and the binder has a glass transition temperature of 60 ° C. or higher. It is characterized by.

As shown in FIG. 1, the magnetic recording medium of the present invention has a magnetic layer 2 mainly composed of a non-magnetic support 1, a magnetic powder and a binder formed thereon, and a back surface of the non-magnetic support 1. And a back coat layer 3 mainly composed of solid particles such as an inorganic pigment.

In the magnetic layer 2, for example, magnetic powder is dispersed in a binder, and ethers, esters, kents, aromatic hydrocarbons, aliphatic hydrocarbons,
It can be formed by coating the non-magnetic support 1 with a magnetic paint prepared by kneading with an organic solvent selected from chlorinated hydrocarbons and the like.

As the magnetic powder forming the magnetic layer of the magnetic recording medium, any magnetic powder that is usually used as the magnetic powder of this type of magnetic recording medium can be used. Examples of such magnetic powder include γ-Fe ₂ O ₃ and cobalt-coated γ-
Ferromagnetic iron oxide particles such as Fe ₂ O _{3 and the} like, ferromagnetic chromium dioxide particles, ferromagnetic alloy powders composed of metals such as Fe, Co and Ni and alloys containing these, hexagonal plate-shaped hexagonal ferrite fine particles, iron nitride Etc. are illustrated. Further, as the binder forming the magnetic paint, any binder can be used as long as it is usually used in the production of this kind of magnetic recording medium. In addition to the magnetic powder and the binder, a dispersant, an abrasive, an antistatic agent and the like may be added to the magnetic paint as additives.

As the non-magnetic support for the magnetic recording medium, any non-magnetic support can be used as long as it is generally used as a non-magnetic support for this type of magnetic recording medium. For example,
Examples thereof include polymer supports typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates, metal plates made of aluminum alloys, titanium alloys, and glass substrates. The form is not limited at all, and may be any form such as tape, sheet, and drum. Further, the non-magnetic support may be subjected to a surface treatment so that fine irregularities are formed in order to control its surface property.

On the other hand, the backcoat layer is a backcoat layer coating material prepared by dispersing solid particles such as an inorganic pigment in a binder and kneading with an organic solvent selected according to the kind of the binder. As the solid particles formed by coating on the back surface of the non-magnetic support, any conventionally known one can be used as long as it gives an antistatic effect and a lubricating effect, for example, graphite, carbon black, carbon. Examples thereof include black graft polymer, tungsten disulfide, molybdenum disulfide, titanium oxide and the like.

The polyester polyurethane resin used as a binder for forming the back coat layer coating material is obtained by reacting a polyhydroxy compound with a polyisocyanate. As the polyhydroxy compound, in addition to the polyester polyol, ethylene glycol, propylene glycol, glycol such as 1,4-butanediol, or the like is used, if necessary. Examples of polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate.

The amount of the tertiary amine contained in the polyester polyurethane resin is 8 per 10 ⁶ g of the resin.
It is desirable that the amount be 0 to 250 equivalents. When the amount of the tertiary amine is less than 80 equivalents per 10 ⁶ g of the resin, the dispersibility of the obtained coating material for the back coat layer is not satisfactory, and thus the running stability of the obtained back coat layer is not satisfactory. . Further, when the amount of the tertiary amine exceeds 250 equivalents per 10 ⁶ g of the resin, the fluidity of the paint is lost due to the interaction of the excessive tertiary amine, and the dispersibility of the paint for the back coat layer should be satisfactory. However, the running stability of the resulting backcoat layer is not satisfactory. To introduce the tertiary amine into the polyester polyurethane resin, a glycol having a tertiary amine, such as N-methyldiethanolamine, may be added to the above-mentioned glycol in a predetermined amount.

Further, in a magnetic recording medium containing a polyurethane resin having the above-mentioned tertiary amine as a binder and a polyisocyanate compound as a crosslinking agent in the back coat layer, a medium excellent in durability can be obtained. This is due to the cross-linking due to the reaction between the hydroxyl groups in the binder and the isocyanate groups in the cross-linking agent.

At this time, the polyester polyurethane resin has a glass transition temperature of 60 ° C. or higher, preferably 70 ° C. or higher. When polyisocyanate is used as the crosslinking agent as described above, the glass transition temperature of the polyester polyurethane resin exceeds the curing temperature, so that the degree of freedom in the magnetic coating film is significantly impaired and the crosslinking reaction is inhibited. However, in the polyester polyurethane resin containing a tertiary amine according to the present invention, the tertiary amine in the binder acts more efficiently as a catalyst in the crosslinking reaction between the binder and the crosslinking agent, Density cross-linking is performed, and a back coat layer having good durability can be formed.

When a polyurethane resin having a low glass transition temperature is used as a binder, the durability of the magnetic recording medium obtained is not sufficiently satisfactory because the rigidity is insufficient. Further, if the curing temperature is raised above the glass transition temperature of the polyurethane resin, the non-magnetic support such as polyester will start to flow and the shape will deteriorate, and the electromagnetic conversion characteristics of the obtained magnetic recording medium will deteriorate.

[0021]

In the present invention, in a magnetic recording medium having a back coat layer using a polyester polyurethane resin as a binder, the polyester polyurethane resin contains 80 to 250 equivalents of a tertiary amine per 10 ⁶ g of the resin. By forming a back coat layer having good dispersibility and durability, a magnetic recording medium having good running stability and running durability can be obtained.

When a polyisocyanate compound is used as a cross-linking agent, a back coat layer having more excellent durability is formed due to the catalytic action of the tertiary amine contained in the binder, and the running stability and running are improved. A magnetic recording medium having good durability can be obtained. Further, the effect is more exerted when a polyurethane resin having a glass transition temperature of 70 ° C. or higher is used as a binder, and a backcoat layer having particularly excellent durability is formed, and running stability and running durability are excellent. It is possible to obtain an excellent magnetic recording medium.

[0023]

EXAMPLES Specific examples to which the present invention is applied will be described below. First, polyester polyol, N-methyldiethanolamine, glycol and diphenylmethane diisocyanate were reacted under predetermined conditions to prepare binders A to F made of polyester polyurethane resin. The weight average molecular weight of this binder measured by the GPC method was 47,500 to 50,000, and the glass transition temperature was 76 to 81 ° C except for the binder E.

This binder was mixed in the following blending ratio in a ball mill for 48 hours to prepare a coating material for a back coat layer. Incorporation ratio of paint for back coat layer Inorganic pigment: 100 parts by weight of carbon black (RAVEN-1255 manufactured by Colombian) Binder: 50 parts by weight of polyester polywetan resin Nitrocellulose 50 parts by weight Solvent: 220 parts by weight of methyl ethyl ketone Toluene 220 parts by weight Cyclohexanone 220 Parts by weight

A coating for a back coat layer was prepared using the binder A in which the content of the tertiary amine in the polyester polyurethane resin was 101 equivalent per 10 ⁶ g of the resin. Resin content is 10 ⁶ g
The coating material for the back coat layer using the binder B in an amount of 200 equivalents was used as the execution sample 2. For comparison,
The coating material for the back coat layer using the binder C in which the content of the tertiary amine in the above polyester polyurethane resin was 50 equivalents per 10 ⁶ g of the resin was Comparative Sample 1, and the content of the tertiary amine was the resin 10 ⁶ Comparative sample 2 with a coating for backcoat layer using 305 equivalents per gram of binder D, a binder having a tertiary amine content of 104 equivalents per 10 ⁶ g of resin and a glass transition temperature of 52 ° C. The coating material for the back coat layer using E was used as Comparative Sample 3. Furthermore, a polyester polyol having a metal sulfonate group, glycol (not including glycol such as N-methyldiethanolamine), and diphenylmethane diisocyanate are reacted under predetermined conditions to prepare a binder F made of a polyester polyurethane resin. The coating material for the back coat layer using was used as Comparative Sample 4. The binder F contained no tertiary amine at all, and the content of the metal sulfonate group in the binder F was 162 equivalents per 10 ⁶ g of the resin.

Next, a magnetic paint was prepared. The magnetic coating material was prepared by mixing the following materials in a sand mill at the following compounding ratios.

Mixing ratio of magnetic paint Fe metal powder (specific surface area 52 m ² / g) 100 parts by weight Polyester polyurethane resin 10 parts by weight (weight average molecular weight 47,000, glass transition temperature 30 ° C., SO ₃ Na 0.05% as a functional group) Poly Vinyl chloride copolymer 10 parts by weight (Nippon Zeon Co., Ltd. trade name: MR-110) Alumina (average particle size 0, 3 μm) 5 parts by weight Carbon (average particle size 0, 15 μm) 2 parts by weight Stearic acid 1 part by weight Stearin Butyl acid 1 part by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 100 parts by weight

After adding 10 parts by weight of the curing material Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) to the back coat layer coating composition and the magnetic coating composition prepared as described above, a thickness of 1 was obtained.
The back coat layer coating material was applied to a 4 μm polyethylene terephthalate film so that the thickness of the back coat layer after drying was 0.7 μm, and the thickness of the magnetic layer after drying was 4 μm on the opposite surface. Apply magnetic paint, magnetic field orientation, drying, super calendar processing in order,
The back coat layer and the magnetic layer were formed by curing at 0 ° C. for a predetermined time. Then, the sample tapes 1 and 2 and the comparative sample tapes 1 to 1 are cut into 1/2 inch width
Got 4.

The running sample tapes 1 and 2 and the comparative sample tapes 1 to 4 thus produced were evaluated for running stability and running durability. The running stability and running durability were evaluated by the surface roughness (Ra) of the back coat layer,
The friction coefficient, the occurrence of scratches on the back coat layer, and the RF output of the magnetic layer were measured. Each measuring method is as follows.

Surface Roughness (Ra) As an evaluation of running stability, the surface roughness (Ra) of the back coat layer was measured. For the measurement, a surface roughness meter (SE-30H) of Kosaka Laboratory Ltd. was used and a magnification of 50,000 was used.
Double, measurement length 2 mm, cutoff 0.08 mm.
In order to obtain sufficient running stability, the surface roughness is preferably 20 μm or less.

Friction coefficient The friction coefficient was evaluated as an evaluation of running durability. The friction coefficient is a coefficient of friction of the back coat layer with respect to the stainless guide pin, and was measured when the number of shuttles of the tape was 10 passes and 200 passes. In order to obtain sufficient running durability, the friction coefficient is preferably 0.18 or less.

Occurrence of Scratches on Backcoat Layer As an evaluation of running durability, the degree of scratches on the backcoat layer after the friction coefficient was measured (tape shuttle number: 200 passes) was visually observed. Evaluation is 3 of A, B, C
It was performed in stages, and A: a state with almost no scratches, B: a state with some scratches (unusable), and C: a state with large scratches (unusable).

RF output of magnetic layer In order to comprehensively evaluate running stability and running durability, a 1/2 inch video deck manufactured by Sony Corporation was used.
The RF output at MHz was measured. Implementation sample tape 1
The relative output of each sample tape when the output of 0 was set to 0 dB was measured.

Table 1 shows the measurement results of the practical sample tapes 1 and 2 and the comparative sample tapes 1 to 4.

[0035]

[Table 1]

As can be seen from the results in Table 1, in the sample tapes of Examples 1 and 2 to which the present invention was applied, the surface roughness (Ra) of the back coat layer was low and the coefficient of friction was 0.
Below 18 and there is no rise due to the number of tape shuttles,
The surface condition of the back coat layer after measuring the friction coefficient is also good,
It was found that the RF output of the magnetic layer was also high and the running stability and running durability were good. This is because the dispersibility of the inorganic pigment powder in the binder was improved by adding an appropriate amount of tertiary amine to the polyester polyurethane resin as the binder, and the polyisocyanate compound and polyester polyurethane used as the cross-linking agent. Since the tertiary amine contained in the resin worked as a catalyst to promote the high-density crosslinking reaction, the running stability of the obtained backcoat layer,
This is probably because the running durability is improved. This is also confirmed by the fact that in the sample tapes of Examples 1 and 2, no scratches were found in the back coat layer after the shuttle running.

On the other hand, when the amount of the tertiary amine contained in the binder is too small or too large as in the sample tapes of Comparative Examples 1 and 2, running stability and running of the obtained backcoat layer are obtained. Good results cannot be obtained in terms of durability. Therefore, it was also confirmed that the amount of the tertiary amine contained in the binder polyester polyurethane resin is 80 to 250 equivalents per 10 ⁶ g of the resin.
Further, when the glass transition temperature of the binder is less than 60 ° C. (52 ° C. in this case) as in the sample tape of Comparative Example 3, sufficient strength cannot be imparted to the back coat layer and running durability Is not good. This is Comparative Example 3
It is also confirmed from the fact that in the sample tape of No. 1, large scratches are observed in the back coat layer after the shuttle running. When a binder containing no tertiary amine in the binder and having a metal sulfonate group introduced as a functional group, as in the sample tape of Comparative Example 4, was used, the resulting coating for back coat layer was obtained. However, the back coat layer cannot be provided with sufficient strength and the durability is not good. It is considered that this is because the metal sulfonate base does not function as a catalyst during the crosslinking between the polyester polyurethane resin and the polyisocyanate compound, and the high-density crosslinking reaction is not promoted. This is also confirmed by the fact that in the sample tape of Comparative Example 4, scratches were observed in the back coat layer after the shuttle running.

[0038]

As is apparent from the above description, in the present invention, in the magnetic recording medium having the back coat layer using the polyester polyurethane resin as the binder, the polyester polyurethane resin is the resin 10 ⁶
Since it contains 80 to 250 equivalents of tertiary amine per g,
By forming a back coat layer having good dispersibility and durability, a magnetic recording medium having good running stability and running durability can be obtained.

When a polyisocyanate compound is used as the cross-linking agent, a back coat layer having more excellent durability is formed due to the catalytic action of the tertiary amine contained in the binder, and the running stability and running are improved. A magnetic recording medium having good durability can be obtained. Further, the effect is more exerted when a polyurethane resin having a glass transition temperature of 70 ° C. or higher is used as a binder, and a backcoat layer having particularly excellent durability is formed, and running stability and running durability are excellent. It is possible to obtain an excellent magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one structural example of a magnetic recording medium to which the present invention is applied.

[Explanation of symbols]

 1: Non-magnetic support 2: Magnetic layer 3: Back coat layer

Claims (3)

[Claims] 1. A magnetic recording medium in which a magnetic layer is provided on one surface of a non-magnetic support and a back coat layer is provided on the other surface of the non-magnetic support, wherein the back coat layer serves as a binder and is a tertiary grade agent per 10 ⁶ g of polyester polyurethane resin. A magnetic recording medium comprising a polyester polyurethane resin containing 80 to 250 equivalents of an amine. 2. The magnetic recording medium according to claim 1, wherein the backcoat layer contains a polyisocyanate compound as a crosslinking agent. 3. The magnetic recording medium according to claim 1, wherein the polyester polyurethane resin as a binder has a glass transition temperature of 60 ° C. or higher.