JPH09120522A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability and running performance of a magnetic recording medium as well as to reduce the frictional resistance by using a specified binder having a specified glass transition temp. as a binder contained in the back coating layer. SOLUTION: This magnetic recording medium has a magnetic layer on one side of the nonmagnetic substrate and a back coating layer consisting essentially of a nonmagnetic powder and a binder on the other side. The glass transition temp. Tg of the entire binder is >=60 deg.C and the binder has been cured with a hexamethylenediisocya-nate curing agent. This magnetic recording medium has reduced frictional resistance and does not cause adhesion to an adjacent magnetic layer.

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 such as a magnetic tape, and more specifically, it is included in a so-called back coat layer provided on the surface opposite to the magnetic layer for preventing winding disorder and charging. It relates to the improvement of binders.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is prepared by coating a non-magnetic support such as a polyester film with a magnetic paint prepared by dispersing and kneading a ferromagnetic powder, a binder, a dispersant, a lubricant and the like in an organic solvent. The magnetic layer is formed by a method in which a ferromagnetic metal is directly deposited by means such as vacuum deposition.
Further, in order to prevent winding disorder and electrification of the magnetic recording medium, improve running properties, etc., conductive carbon black or the like was mixed in a binder on the side of the non-magnetic support on which the magnetic layer was not provided. The provision of a so-called back coat layer is also widely performed.

As a binder contained in the back coat layer, a polyurethane resin having excellent abrasion resistance is often used. Further, in order to increase the softening point of the polyurethane resin and improve the heat resistance, the urethane group concentration is increased during the synthesis of the polyurethane resin.

[0004]

By the way, the softening of the polymer material is caused by the looseness of the entangled molecular chains and the formation of fluidity, and the relaxation time of the entanglement changes very rapidly depending on the molecular weight. Therefore, in general, the higher the molecular weight, the higher the softening point of the polymer material. On the other hand, since the Micro Brownian motion does not move the entire molecular chain, its relaxation time does not largely depend on the molecular weight, and therefore Tg does not change so much.
However, in the vicinity of Tg, the physical properties of the polymer material change significantly, and when it exceeds Tg, it becomes liquid, so in order to discuss the thermal stability of the polymer, not only the softening point but also Tg should be considered. It is also necessary to do. Therefore, even if the conventional method for raising only the softening point is used, the Tg
If there is almost no change, the effect of improving thermal stability cannot be said to be sufficient.

When a binder having a low Tg is used in a magnetic recording medium, the friction coefficient increases, the tackiness increases, or the physical properties change drastically from around Tg and the durability deteriorates at high temperatures. Occurs.

To avoid this, conversely, when a polymer material having a high Tg is used as a binder, the coating film becomes brittle and falls off, or the friction coefficient after running many times increases, and the durability deteriorates. There is a problem of doing.

Therefore, in order to improve the durability of the binder having a high Tg as described above, it is considered to add a tolylene diisocyanate type curing agent which has been widely used in the past. However, these curing agents do not sufficiently undergo a crosslinking reaction in a temperature range (around 60 ° C. or lower) that does not affect the characteristics of the magnetic recording medium, and thus the above-mentioned problems have hardly been solved. Is.

Therefore, an object of the present invention is to provide a magnetic recording medium in which a sufficiently crosslinked coating film is formed even when a binder having a high Tg is used and which is excellent in durability and running property.

[0009]

The present invention has been proposed to achieve the above object. That is, the magnetic recording medium according to the present invention is a magnetic recording medium having a magnetic layer on one surface of a non-magnetic support and a back coat layer mainly composed of non-magnetic powder and a binder on the other surface. The glass transition point Tg of the entire binder is 60 ° C. or higher, and the binder is cured (crosslinked) by a hexamethylene diisocyanate-based curing agent.

Here, the binder having a glass transition temperature Tg of 60 ° C. or higher may be a single polymer material or a mixture of a plurality of polymer materials.

In the magnetic recording medium according to the present invention,
The entire binder contained in the back coat layer has a Tg of 60 ° C. or higher and is crosslinked with a hexamethylene diisocyanate-based curing agent. This prevents so-called sticking of the back coat layer to the magnetic layer when the magnetic recording medium is wound up. Moreover, when the binder of the back coat layer is cured, the magnetic properties of the magnetic layer already formed on the other surface of the non-magnetic support are not deteriorated.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention has a magnetic layer on one surface of a non-magnetic support and a back coat layer mainly composed of non-magnetic powder and a binder on the other surface. The glass transition point Tg of the entire binder is 60 ° C. or higher, and the binder is cured with a hexamethylene diisocyanate-based curing agent.

[0013]

EXAMPLE In order to confirm the effect of the present invention, a sample tape was prepared as a magnetic recording medium sample, and its durability was investigated.

First, a magnetic recording medium having carbon black as a non-magnetic powder and a back coat layer mainly composed of a binder having a total Tg of 60 ° C. or higher, which is cured by a hexamethylene diisocyanate type curing agent, is prepared. did.

In order to prepare such a magnetic recording medium,
First, a polyester / polyurethane resin (isophthalic acid-1,6-hexane glycol-diphenylmethane diisocyanate system, containing 0.06 mmol of carboxyl groups) was used as a binder for the magnetic layer, and a magnetic coating composition was prepared according to the following composition. The thing was prepared.

Magnetic coating composition Composition Co-deposited γ-Fe ₂ O ₃ 100 parts by weight Vinyl chloride / vinyl acetate copolymer VAGH 18 parts by weight Polyester / polyurethane resin (binder) 6 parts by weight Carbon black (antistatic agent) 2 parts by weight Cr ₂ O ₃ (abrasive) 2 parts by weight Stearic acid (dispersant) 1 part by weight Butyl stearate (rust inhibitor) 1 part by weight Methyl ethyl ketone 100 parts by weight Methyl isobutyl ketone 60 parts by weight Toluene 60 parts by weight The above composition was mixed in a ball mill for 24 hours to obtain a hexamethylene diisocyanate-based curing agent, Coronate HL (hexamethylene diisocyanate adduct of trimethylolpropane) manufactured by Nippon Polyurethane Industry Co., Ltd. , HL)) and mixed for an additional 20 minutes to obtain a magnetic paint. Was. Then, this was applied onto a polyethylene terephthalate film having a thickness of 14 μm so that the film thickness after drying would be 6 μm. Then
After magnetic field orientation treatment, it was dried and wound. Further, a super calendar treatment was performed to form a magnetic layer.

Then, according to the compositions shown in Table 1, Binder A to Binder E for use in the back coat layer were prepared. For comparison, binder a and binder b having a total Tg lower than 60 ° C. were also prepared together. This Table 1
Among them, MDI is an abbreviation for diphenylmethane diisocyanate, and hereinafter, diphenylmethane diisocyanate is referred to as MDI. The glass transition point (Tg)
Was measured using a torsion blade analyzer (manufactured by Rigaku Denki Co., Ltd.).

[0018]

[Table 1]

Of the resins used for the above binders, the vinyl chloride copolymer is 88% by weight of vinyl chloride and -OH.
0.85 mmol / g, --SO ₃ Na group 0.04
It is contained in millimoles / g and the degree of polymerization is 420. Polyester / polyurethane resin (isophthalic acid-1,6-hexane glycol-MDI type) is -C
It contains 0.06 mmol of OOH group.

Next, a back coat layer composition was prepared according to the following composition 1 or composition 2 using any of the above-mentioned binder A to binder E.

Backcoat Layer Composition Composition 1 Carbon black 100 parts by weight (Cabot Corporation, trade name Black Pearls L) Binder (AE) 80 parts by weight Methyl ethyl ketone 320 parts by weight Toluene 240 parts by weight Cyclohexanone 160 parts by weight Back Coat layer composition Composition 2 Carbon black 100 parts by weight (Cabot Corporation, trade name Black Pearls L) Binder (AE) 50 parts by weight Methyl ethyl ketone 250 parts by weight Toluene 160 parts by weight Cyclohexanone 150 parts by weight Next, the above composition The mixture was mixed in a ball mill for 48 hours, and HL, a hexamethylene diisocyanate-based curing agent, or Coronate EH manufactured by Nippon Polyurethane Industry Co., Ltd.
(Isocyanuric acid ester type hexamethylene diisocyanate trimer, hereinafter referred to as EH)
Add a predetermined amount in the range of 30 parts by weight and add 20 more
Mixing for a minute gave various back coat layer paints. And
These are coated on the surface of the polyethylene terephthalate film opposite to the surface on which the magnetic layer is formed, and 60
After heat treatment at 24 ° C. for 24 hours, various sample tapes were prepared by cutting into 1/2 inch width.

Binder (AE) and curing agent (HL or EH) in the back coat layer of each of the above sample tapes
The combinations and the amounts used are as shown in Table 2, and such sample tapes are referred to as Examples 1 to 9.

[0023]

[Table 2]

The coefficient of friction and the adhesive peelability of each of the sample tapes of Examples 1 to 9 described above were measured.
The friction coefficient is obtained by measuring the friction generated between the magnetic layer surface of each sample tape and the 1S stainless steel drum at a tape speed of 5 mm / sec and a load of 20 g under the conditions of a temperature of 30 ° C. and a relative humidity of 70%. The measurement was performed after the sample tape was run once and after the sample tape was run 100 times. The adhesive peelability was evaluated by visually observing the degree of peeling of the back coat layer after wrapping each sample tape on a reel and leaving it under conditions of a temperature of 40 ° C. and a relative humidity of 80% for 24 hours. The better the score, the lower the score. These results are also shown in Table 2.

The results shown in Table 2 show that when the curing agent was added to the same binder at the same concentration, HL or E
It can be seen that almost the same good results are obtained with either of the H curing agents. In addition, Example 5 to Example 7
When the combination of the binder and the curing agent is determined as described above, even if the concentration of the curing agent is increased in the range of 10 to 30 parts by weight, almost similar characteristics can be obtained. It is considered to be in the concentration range.

Next, for comparison, a magnetic recording medium was manufactured in which neither the binder nor the curing agent in the backcoat layer, or both of them, is a material limited in the present invention. That is, a sample tape having a back coat layer formed by combining a binder having a Tg of 60 ° C. or more with a tolylene diisocyanate-based curing agent, which is not a curing agent limited in the present invention (Comparative Examples 1 to 4). A sample tape in which a back coat layer is formed by combining binders a and b having a total Tg of less than 60 ° C. and a tolylene diisocyanate curing agent, which is not a binder limited in the present invention (Comparative Examples 5 and 6). , And a total binder having a Tg of less than 60 ° C. and a hexamethylene diisocyanate-based curing agent were combined to form sample tapes (Comparative Examples 7 and 8).

Specifically, first, a magnetic paint similar to the magnetic paint used in Examples 1 to 9 was prepared, and a magnetic layer was formed on a polyethylene terephthalate film. Next, using any of the binders E, C, a, and b among the above-mentioned binders, each back coat was prepared in the same manner as the back coat layer coating composition used in the production of Examples 1 to 9. A layer coating composition was prepared.

Next, using each back coat layer coating composition, various sample tapes were prepared in the same manner as in Examples 1-9. At this time, as the curing agent, in addition to the above-mentioned HL and EH, coronate L (tolylene diisocyanate adduct of trimethylolpropane) manufactured by Nippon Polyurethane Industry Co., Ltd., which is a widely used tolylene diisocyanate-based curing agent in the past, is used. Yes, hereinafter, referred to as L).

The binder (E, C, a, b) and the curing agent (HL, E) in the back coat layer of each sample tape described above.
The combinations and usage amounts of H, L) are as shown in Table 3, and such sample tapes will be referred to as Comparative Examples 1 to 8.

[0030]

[Table 3]

Subsequently, with respect to each of the sample tapes of Comparative Examples 1 to 8, the friction coefficient and the adhesive peeling property were measured in the same manner as in Examples 1 to 9. The results are shown in Table 3.

From the results shown in Table 3, in the case where the binder having a total Tg of 60 ° C. or higher and the tolylene diisocyanate type curing agent which has been frequently used in combination are used in combination (Comparative Examples 1 to 4), one run is performed. After the friction coefficient is relatively small, 10
It can be seen that the durability is inferior after increasing 0 to 3 times after running 0 times.

When a binder having a total Tg of less than 60 ° C. and a tolylene diisocyanate curing agent which has been widely used in the past are used together (Comparative Examples 5 and 6), both the friction coefficient and the adhesive peeling property are further improved. to degrade.

Furthermore, when the binder having a total Tg of less than 60 ° C. and the hexamethylene diisocyanate type curing agent are used together (Comparative Examples 7 and 8), only the lowest characteristics among the above Comparative Examples are obtained. Has not been done.

[0035]

As is apparent from the above description, in the present invention, the binder contained in the back coat layer of the magnetic recording medium has a total glass transition point Tg of 60 ° C. or higher and hexamethylene diisocyanate. A binder that has been hardened with a nate hardener is used. As a result, it is possible to reduce the frictional resistance of the obtained magnetic recording medium, and at the same time, it is possible to provide a magnetic recording medium that does not cause adhesion with an adjacent magnetic layer, and the durability and running property of the magnetic recording medium can be provided. Is also improved.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on one surface of a non-magnetic support and a back coat layer mainly composed of non-magnetic powder and a binder on the other surface, wherein the glass transition of the entire binder is achieved. A magnetic recording medium having a point Tg of 60 ° C. or higher and being cured with a hexamethylene diisocyanate-based curing agent.