JPH0817037A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve running durability and running stability by forming a back coating layer capable of exhibiting superior durability. CONSTITUTION:This magnetic recording medium 4 has a magnetic layer 2 on one side of the nonmagnetic substrate 1 and a back coating layer 3 using polycarbonate polyurethane resin as a binder on the other side. The polycarbonate polyurethane resin contains a tert. amine by 50-250 equiv. per 10<6>g of the resin. A polyisocyanate compd. is preferably contained as a crosslinking agent in the back coating layer and the glass transition temp. of the polycarbonate polyurethane resin is preferably >=60 deg.C.

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, and more particularly to improvement of a binder which constitutes a back coat layer.

[0002]

2. Description of the Related Art A so-called coating type in which a magnetic layer is formed by coating a magnetic coating prepared by dispersing and kneading a magnetic powder, a binder, a dispersant, a lubricant, etc. in an organic solvent on a non-magnetic support. Magnetic recording media, particularly audio tapes, video tapes, and magnetic tapes for cartridges, the magnetic layer-forming surface of the non-magnetic support is used for the purpose of running stability, reduction of frictional resistance between tapes, and improvement of charging property. The back coat layer is provided on the back surface of the.

The back coat layer is mainly composed of solid particles such as an inorganic pigment and a binder. Examples of the binder used in this back coat layer include vinyl chloride resins such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinylidene chloride copolymers, nitrocellulose and epoxy. Resin, acrylic resin and polyurethane resin are widely 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, low-rigidity (low glass transition temperature) polycarbonate polyurethane resin having excellent dispersibility, toughness, and abrasion resistance, and high rigidity that imparts coating strength to the formed backcoat layer Used in combination with nitrocellulose (which has a high glass transition temperature) or vinyl chloride resin.

[0005]

However, in recent years, in the above-mentioned coating type magnetic recording medium, further improvement in running stability and running durability has been demanded, and as described above, as a binder for the back coat layer. When nitrocellulose or vinyl chloride resin is used, there arises a problem that satisfactory characteristics cannot be obtained.

To solve this problem, a method of using a polycarbonate polyurethane resin having a high glass transition temperature in place of the polycarbonate polyurethane resin having a low glass transition temperature has been proposed. The polycarbonate polyurethane resin having a high glass transition temperature is excellent in rigidity, flexibility and dispersibility, and can form a back coat layer having good dispersibility and durability.

The polycarbonate polyurethane resin having a high glass transition temperature has a glass transition temperature of 6
It means one having a temperature of 0 ° C. or higher, and has a higher flexibility than a vinyl chloride resin having the same glass transition temperature due to its structure.

Such a polycarbonate polyurethane resin is synthesized by combining a polyol component having a carbonate bond and a glycol with a bifunctional isocyanate to increase the molecular weight. Further, this polycarbonate polyurethane resin may be introduced with an appropriate proportion of functional groups in order to improve the adsorption of the resin to the inorganic pigment powder and the dispersibility of the back coat paint (for example, JP-B-58). -41565).

At this time, as described above, the backcoating composition may be blended with a crosslinking agent such as a polyisocyanate compound to crosslink the backcoating layer to improve the strength of the backcoating layer. When a polycarbonate polyurethane resin having a high glass transition temperature is used, the concentration of hydroxyl groups contained in the polycarbonate polyurethane resin is generally low, and since the glass transition temperature is higher than the curing temperature, the back coat layer also has a curing temperature. Since the degree of freedom of the resin of
The reaction with the polyisocyanate compound, which is a crosslinking agent, is not promoted, and sufficient crosslinking is not performed. As a result, there arises a problem that the running durability of the obtained back coat layer, particularly the durability against repeated running cannot be obtained sufficiently.

When the curing temperature is set to be equal to or higher than the glass transition temperature of the polycarbonate polyurethane resin, the degree of freedom of the polycarbonate polyurethane resin can be secured, but the non-magnetic support such as polyester flows to cause the shape. Change, which causes deterioration of the electromagnetic conversion characteristics of the obtained magnetic recording medium.

Therefore, when a polycarbonate polyurethane resin having a high glass transition temperature is used as the binder, it is difficult to impart sufficient durability to the back coat layer obtained.

Therefore, the present invention has been proposed in view of the above circumstances, and has a back coat layer capable of exhibiting excellent durability, and further improves running durability and running stability. An object of the present invention is to provide a magnetic recording medium that can be used.

[0013]

Means for Solving the Problems The present invention has achieved the above-mentioned object, and as a result of earnest research, as a result of introducing a certain amount of a tertiary amine as a polar group into a polycarbonate polyurethane resin, the binder is incorporated into a binder. The inventors have found that a binder for a back coat paint having good dispersibility of inorganic pigment powder and good cross-linking efficiency can be obtained, and completed the present invention.

That is, according to the present invention, in a magnetic recording medium having a back coat layer using a polycarbonate polyurethane resin as a binder on the back surface of the magnetic layer forming surface of the non-magnetic support, the polycarbonate polyurethane resin is added per 10 ⁶ g of the resin. It is characterized by containing 50 to 250 equivalents of a tertiary amine.

The magnetic recording medium 4 of the present invention is basically shown in FIG.
As shown in FIG. 1, a single or a plurality of magnetic layers 2 are laminated on the non-magnetic support 1, and an inorganic pigment or the like is formed on the non-magnetic support 1 on the side opposite to the surface on which the magnetic layer 2 is formed. The back coat layer 3 mainly composed of the solid particles and the binder is formed.

An intermediate layer as a so-called undercoat layer may be provided between the magnetic layer 2 and the non-magnetic support 1.

The back coat layer is provided for the purpose of improving the running property of the magnetic recording medium, preventing electrification and preventing transfer. For example, solid particles such as an inorganic pigment are dispersed in a binder, and the binding is performed. It is formed by applying a back coat coating material prepared by kneading with an organic solvent selected according to the type of agent to the back surface of the non-magnetic support.

As the solid particles, any conventionally known material can be used as long as it can impart an antistatic effect and a lubricating effect, and examples thereof include graphite, carbon black, carbon black graft polymer, tungsten disulfide, and disulfide. Examples thereof include molybdenum sulfide and titanium oxide.

In the present invention, a polycarbonate polyurethane resin is used as a binder for forming the back coat paint.

The polycarbonate polyurethane resin can be obtained by reacting a polyhydroxy compound with a polyisocyanate.

As the above-mentioned polyhydroxy compound, in addition to polycarbonate polyol, ethylene glycol, glycol such as 1,4-butanediol, etc. may be used, if necessary.

On the other hand, as the above polyisocyanate,
Examples include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and the like.

To this polycarbonate polyurethane resin, 50 to 250 equivalents of a tertiary amine are introduced per 10 ⁶ g of the resin. The amount of the tertiary amine introduced is 10 ⁶
If it is less than 50 equivalents per gram, the dispersibility of the obtained back coat coating becomes insufficient, and the running stability of the resulting back coat layer becomes unsatisfactory. On the other hand, when the amount of the tertiary amine introduced exceeds 250 equivalents per 10 ⁶ g of the resin, the fluidity of the paint is impaired due to the interaction of the excessive tertiary amine, and the dispersibility deteriorates. As a result, it becomes impossible to obtain a back coat layer having good running stability.

As a method of introducing the tertiary amine into the polycarbonate polyurethane resin, for example, a method of adding a predetermined amount of a glycol having a tertiary amine, such as N-methyldiethanolamine, to the above glycol is added. To be Further, in this back coat paint, it is preferable to use a polyisocyanate compound as a crosslinking agent. Thereby, excellent durability can be secured in the obtained magnetic recording medium. This is due to cross-linking due to the reaction between the hydroxyl group in the binder and the isocyanate group in the cross-linking agent.

In the present invention, good results can be expected when the polycarbonate polyurethane resin having a glass transition temperature of 60 ° C. or higher is used. When the polyisocyanate compound is used as the crosslinking agent as described above, the glass transition temperature of the polycarbonate polyurethane resin exceeds the curing temperature, so that the degree of freedom in the backcoat layer is significantly impaired, and the crosslinking reaction Although it may be hindered, by using a polycarbonate polyurethane resin containing a certain amount of a tertiary amine as in the present invention, the tertiary amine in the binder can be used in the crosslinking reaction between the binder and the crosslinking agent. Acts as a catalyst more efficiently, resulting in high-density cross-linking. Therefore, good durability can be ensured in the obtained back coat layer.

Here, when the polycarbonate polyurethane resin having a low glass transition temperature is used, the rigidity thereof is insufficient, so that the durability of the obtained magnetic recording medium cannot be expected to be improved. . Also,
If the curing temperature of the polycarbonate polyurethane resin is raised above the glass transition temperature, the non-magnetic support composed of polyester or the like will begin to flow, causing deterioration of the shape, resulting in an electromagnetic conversion characteristic of the obtained magnetic recording medium. to degrade.

In the magnetic recording medium of the present invention, the magnetic layer is formed by dispersing magnetic powder in a binder and kneading it with an appropriate organic solvent to coat a magnetic coating on the non-magnetic support. Can be formed.

As the magnetic powder, any material conventionally known as a magnetic powder for a magnetic recording medium of this type can be used. Examples of such magnetic powder include F
e, Co, Ni and other metal materials, Fe-Co, Fe-N
i, Fe-Al, Fe-Ni-Al, Fe-Al-S
Examples thereof include alloy materials such as i and Co—Ni, iron nitride, iron carbide and the like.

Even if a light metal element such as Al, Si, P or B is added in an appropriate amount for the purpose of preventing sintering during reduction or maintaining the shape, the effect of the present invention is not hindered.

Further, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-γ
Ferromagnetic iron oxide particles such as _{-Fe 2 O 3, Co-Fe} 3 O 4,
Both ferromagnetic chromium dioxide particles and hexagonal ferrite fine particles can be used.

These magnetic powders may be used alone or in combination of two or more.

Any conventionally known binder can be used as the binder contained in the magnetic layer. As the conventionally known binder, both a thermoplastic resin and a thermosetting resin can be used.

As the magnetic material forming the magnetic layer, a dispersant, an abrasive, an antistatic agent or the like may be added as an additive in addition to the above-mentioned magnetic powder and binder. As the dispersant, the abrasive, and the antistatic agent, any material usually used in this type of magnetic recording medium may be used.
There is no particular limitation.

These magnetic layer-forming materials are made into a coating material, coated on the above non-magnetic support and dried to form a magnetic layer.
As an organic solvent used for forming a paint, a ketone type,
Alcohol-based, ester-based, ether-based, hydrocarbon-based,
A carbon halide or the like may be appropriately selected and used.

A roll mill, a ball mill, a sand mill, a kneader,
An extruder, a homogenizer, an ultrasonic disperser, etc. are used.

Further, in order to apply the coating material thus produced on the magnetic support, a gravure coater, a knife coater, a blade coater, a reverse roll coater, a die coater or the like is used.

As the non-magnetic support, any of conventionally known materials such as polyesters, polyolefins and celluloses can be used. The form is not limited at all, and may be any form such as tape, sheet, and drum. Further, this non-magnetic support may be subjected to a surface treatment so that fine irregularities are formed in order to control its surface property.

[0038]

By using a polycarbonate polyurethane resin containing a certain amount of tertiary amine in the resin as a binder for forming the back coat paint, the dispersibility of the back coat paint becomes good. This improves the running stability of the obtained backcoat layer.

[0039]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 First, a predetermined polycarbonate polyol and a predetermined amount of N
A binder A made of a polycarbonate polyurethane resin obtained by reacting methyldiethanolamine, glycol and diphenylmethane diisocyanate under predetermined conditions.
Was prepared.

The weight average molecular weight of this binder A was 49500 as measured by the GPC method. The glass transition temperature of this binder A was 60 ° C., and the content of the tertiary amine was 50 equivalents per 10 ⁶ g of the resin.

Using such a binder A, a back coat paint was prepared by mixing in the following blending ratio in a ball mill for 48 hours.

<Backcoat Coating Mixing Ratio> 100 parts by weight of carbon black (RAVEN-1255 manufactured by Colombian) Polycarbonate polyurethane resin (binder A) 50 parts by weight Nitrocellulose 50 parts by weight Methyl ethyl ketone 220 parts by weight Toluene 220 parts by weight Cyclohexanone 220 Parts by weight Next, a magnetic paint was prepared by the following procedure.

That is, the following coating materials were mixed in a predetermined mixing ratio in a sand mill to prepare a magnetic coating.

<Magnetic coating compounding ratio> 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 48,000, glass transition temperature 30 ° C., SO ₃ Na 0.05% as a functional group) Containing) Vinyl chloride type co-weight 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 Parts by weight butyl stearate 1 part by weight methyl ethyl ketone 100 parts by weight toluene 100 parts by weight cyclohexanone 100 parts by weight Hardener Coronate L (manufactured by Nippon Polyurethane Company) for the back coat paint and magnetic paint prepared as follows.
After adding 10 parts by weight of each of the above, a coating material for back coat was applied to 14 μm thick polyethylene terephthalate so that the thickness of the back coat layer after drying was 0.7 μm.

Then, a magnetic coating material is applied to the side opposite to the back coated surface so that the thickness after drying is 4 μm, magnetic field orientation, drying and super calendering are carried out successively, and further at 60 ° C. It was cured for a predetermined time under the conditions to form a back coat layer and a magnetic layer.

Then, this magnetic tape was cut into a 1/2 inch width to obtain a sample tape A.

Example 2 Instead of the binder A used in Example 1 above, GP
The weight average molecular weight measured by the C method is 49000, the glass transition temperature is 60 ° C., and the content of the tertiary amine is the resin 10.
^A sample tape B was prepared by using the binder B prepared so as to be 150 equivalents per ⁶ g and forming a tape by the same method as in Example 1 except for the above.

Example 3 Instead of the binder A used in Example 1 above, GP
Weight average molecular weight measured by the C method is 48800, glass transition temperature is 60 ° C., and tertiary amine content is 10 ⁶ g.
Sample B was prepared by using the binder C prepared so as to have 250 equivalents per unit of tape, and tape-forming by the same method as in Example 1 except for the above.

Example 4 Instead of the binder A used in Example 1 above, GP
The weight average molecular weight measured by the C method is 48500, the glass transition temperature is 50 ° C., and the content of the tertiary amine is 10 ⁶ g.
Sample B was prepared by using the binder D prepared so that the amount thereof was 150 equivalents, and tape-forming by the same method as in Example 1 except for the above.

Comparative Example 1 In place of the binder A used in Example 1 above, GP
Weight average molecular weight measured by the C method is 48900, glass transition temperature is 60 ° C., and tertiary amine content is 10 ⁶ g.
Using the binder a prepared to be 40 equivalents per
Others were formed into a tape by the same method as in Example 1 to prepare a sample tape a.

Comparative Example 2 Instead of the binder A used in Example 1 above, GP
The weight average molecular weight measured by the C method is 49500, the glass transition temperature is 60 ° C., and the content of the tertiary amine is 10 ⁶ g.
A sample tape b was prepared by using the binder b prepared so that the amount thereof was 260 equivalents per unit of tape, and using the same method as in Example 1 except for the above.

Comparative Example 3 First, a predetermined polycarbonate polyol having a sulfonic acid metal salt, glycol and diphenylmethane diisocyanate were reacted under predetermined conditions to prepare a binder c made of a polycarbonate polyurethane resin.

The weight average molecular weight of this binder c was 48500 as measured by GPC method, and the glass transition temperature was 60 ° C. The binder c contained no tertiary amine at all, and the content of the sulfonic acid metal salt was 160 equivalents per 10 ⁶ g of the resin.

Subsequently, this binder c was used in place of the binder A used in Example 1 above, and the others were used in Example 1
A tape was formed by the same method as above to prepare a sample tape c.

Comparative Example 4 In place of the binder c used in Comparative Example 3 above, GP
The weight average molecular weight measured by the C method is 48500, the glass transition temperature is 50 ° C., and the content of the sulfonic acid metal salt is 10
^A sample tape d was prepared by using the binder d prepared so as to be 160 equivalents per ⁶ g and forming a tape by the same method as in Example 1 except for the above.

Therefore, with respect to the sample tapes A to D and the sample tapes a to d produced as described above,
The running stability and running durability were evaluated. The running stability and running durability are evaluated by the surface roughness (R
a), the coefficient of friction, the occurrence of scratches on the back coat layer, and the RF output of the magnetic layer were measured. In addition, the measuring method of these various characteristics is as follows.

Surface Roughness of Backcoat Layer (Ra) As an evaluation of running stability, surface roughness of backcoat layer (R)
The measurement of a) was performed. For this measurement, a surface roughness meter (trade name SE-30H) manufactured by Kosaka Laboratory Ltd. was used.
Magnification 50,000 times, measurement length 2mm, cutoff 0.08
mm. Here, in order to obtain sufficient running stability, the surface roughness (Ra) is preferably 20 μm or less.

Friction coefficient The friction coefficient was evaluated as an evaluation of running durability. This coefficient of friction is the coefficient of friction of the back coat layer with respect to the stainless guide pins, and was measured when the number of shuttles of the tape was 10 passes and 200 passes. Here, in order to obtain good 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 was visually observed after measuring the friction coefficient (when the number of shuttles of the tape was 200 passes). This evaluation is A,
Performed in three stages of B and C, A is a state where there is almost no scratch, B is a state where some scratch is generated (unusable), C
Indicates a state where large scratches are generated (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 and 6 MH was used.
The RF output at z was measured. The measured value represents the relative output of each sample tape when the output of the sample tape A is 0 dB.

The results are shown in Table 1 below.

[0063]

[Table 1]

As is clear from Table 1, in each of the examples, the surface roughness (Ra) of the back coat layer was low and the coefficient of friction was 0.18 as compared with the sample tapes a to d. It was good as below. Further, there was no rise due to the number of tape shuttles, and at the same time, the surface condition of the back coat layer after the friction coefficient measurement was very good. further,
It was found that in these sample tapes A to D, the RF output of the magnetic layer was high, and both running stability and running durability were excellent.

This is because the dispersibility of the inorganic pigment powder in the binder was improved by introducing an appropriate amount of a tertiary amine into the polycarbonate polyurethane resin as the binder.
And, by the fact that the tertiary amine in the polycarbonate polyurethane resin acts as a catalyst for the crosslinking reaction between the polyisocyanate compound used as the crosslinking agent and the polycarbonate polyurethane resin to accelerate the high-density crosslinking reaction, Running stability of the coat layer,
It is considered that the running durability is improved. This is
It is also confirmed that the sample tapes A to D show no occurrence of scratches on 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 a and b, the running stability and running of the obtained back coat layer are improved. Good results cannot be obtained in terms of durability. Therefore, it was found that the amount of the tertiary amine contained in the polycarbonate polyurethane resin as the binder is preferably 50 to 250 equivalents per 10 ⁶ g of the resin.

When a binder containing no tertiary amine in the binder and having a sulfonic acid metal salt introduced as a functional group, as in Comparative Example 3, was used, the dispersion of the back coat paint was dispersed. However, it is not possible to impart sufficient strength to the obtained backcoat layer, and it is not possible to ensure good durability. This is because the sulfonic acid metal salt does not have the function of acting as a catalyst during the crosslinking between the polycarbonate polyurethane resin and the polyisocyanate compound,
It is considered that the high-density crosslinking reaction is not promoted. This is also confirmed by the fact that in the sample tape c, the back coat layer after the shuttle running has scratches.

Further, in Example 4, as compared with the sample tape d of Comparative Example 4, the surface roughness (R
The a) was low, the coefficient of friction was 0.18 or less, the rise due to the number of tape shuttles was small, and the surface condition of the back coat layer after the measurement of the coefficient of friction was good. Further, in this sample tape D, it was found that the RF output of the magnetic layer was also high and the running stability and running durability were both good. This is because a proper amount of tertiary amine was introduced into the polycarbonate polyurethane resin as the binder. By doing so, the dispersibility of the inorganic pigment powder in the binder is improved, and the tertiary amine contained in the polycarbonate polyurethane resin against the crosslinking reaction between the polyisocyanate compound used as the crosslinking agent and the polycarbonate polyurethane resin. It is considered that this is because the high density cross-linking reaction was promoted by acting as a catalyst, and the running stability and running durability of the obtained back coat layer were improved. This is sample tape D
It is also confirmed from the fact that no scratch is found on the back coat layer after the shuttle travel.

On the other hand, when a binder having no tertiary amine in the binder and having a sulfonic acid metal salt introduced as a functional group, such as the sample tape d, is used for the back coat, Although the dispersibility of the coating material is good, it is not possible to impart sufficient strength to the obtained backcoat layer, and it is not possible to secure good durability. this is,
It is considered that the sulfonic acid metal salt does not function as a catalyst when the polycarbonate polyurethane resin and the polyisocyanate compound are crosslinked, and the high-density crosslinking reaction is not promoted. This is also confirmed by the occurrence of scratches on the back coat layer after the shuttle running in the sample tape d.

[0070]

As is apparent from the above description, in the present invention, in a magnetic recording medium having a back coat layer using a polycarbonate polyurethane resin as a binder, an appropriate amount of a tertiary amine is contained in the polycarbonate polyurethane resin. Since it is introduced, the dispersibility of the obtained back coat layer becomes good, and the durability is improved. Therefore, according to the present invention, it is possible to provide a magnetic recording medium having excellent running stability and running durability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a magnetic recording medium according to the present invention.

[Explanation of symbols]

 1 ... Non-magnetic support 2 ... Magnetic layer 3 ... Back coat layer 4 ... Magnetic recording medium

Claims (3)

[Claims] 1. A magnetic recording medium having a back coat layer using a polycarbonate polyurethane resin as a binder on the back surface of a magnetic layer forming surface of a non-magnetic support, wherein the polycarbonate polyurethane resin is a tertiary amine per 10 ⁶ g of the resin. Is contained in an amount of 50 to 250 equivalents. 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 polycarbonate polyurethane resin has a glass transition temperature of 60 ° C. or higher.