JPH0581641A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium hardly undergoing a change in the properties of the back coat layer with the lapse of time, having excellent aging stability and capable of exhibiting stable recording and reproducing performance over a long period of time. CONSTITUTION:When a magnetic layer is formed on one side of a nonmagnetic substrate and a back coat layer on the other side to obtain a magnetic recording medium, polyurethane resin having cyclohexyl groups in the molecule is used as a binder in the back coat layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape having a non-magnetic support having a magnetic layer on one side and a back coat layer on the other side.
Magnetic recording medium such as a magnetic disk.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic tape has a guide roller or a guide roller on the back surface side of the non-magnetic support opposite to the magnetic layer formation side at the time of recording / reproducing and rewinding of feeding / returning. It makes sliding contact with a guide member such as a guide pin at a large relative speed.

For this reason, conventionally, as a means for imparting running stability for proper recording and reproduction, a back coat layer in which a non-magnetic inorganic powder is bound with a binder on the back side of the non-magnetic support. Is used to roughen the back surface to reduce the contact area with the guide member and reduce the frictional resistance. Here, as the binder, a polyurethane resin having good elasticity and flexibility is widely used from the viewpoint of shock absorption and vibration prevention at the sliding contact portion.

By the way, in recent years, as the recording density of magnetic recording media has been increased, it has been strongly demanded that the recording / reproducing performance be stably exhibited over a long period of time. To meet this demand, various means for improving the stability of the magnetic layer over time have been proposed (for example,
U.S. Pat. Nos. 4,568,611 and 4,284,7
50, Japanese Patent No. 1,179,386, etc.).

[0005]

However, in the magnetic recording medium having the back coat layer, the state of the back coat layer tends to affect the electromagnetic conversion characteristics with the increase in the recording density. As in the above-mentioned proposed means, merely improving the temporal stability of the magnetic layer cannot achieve long-term stabilization of the recording / reproducing performance, and it is necessary that the temporal stability of the back coat layer side is good.

However, in a back coat layer using a conventional general polyurethane resin or the like as a binder, blocking tends to occur over time, and the abrasion resistance is lowered, so that the powder drop is remarkably increased. Then, there has been a problem that the recording / reproducing performance of the magnetic recording medium is gradually deteriorated.

In view of the above-mentioned circumstances, an object of the present invention is to provide a magnetic recording medium having a back coat layer on the back side thereof, in which the back coat layer has good stability over time and has stable recording / reproducing characteristics for a long period of time. It is to provide what can demonstrate.

[0008]

The inventors of the present invention have conducted extensive studies in order to achieve the above-mentioned object, and as a result, as a binder of the back coat layer, a special polyurethane having a specific group in the molecule is used. When using resin,
It has been found that the magnetic recording medium is excellent in moist heat resistance and mechanical strength, hardly changes in properties over time, and is highly durable, and that a magnetic recording medium capable of exhibiting stable recording / reproducing performance for a long time can be obtained. Invented the invention.

That is, according to the present invention, in a magnetic recording medium having a magnetic layer on one side of a non-magnetic support and a back coat layer on the other side, a cyclohexyl group is contained in the molecule as a binder of the back coat layer. The present invention relates to a magnetic recording medium containing a polyurethane resin.

[0010]

The back coat layer in the magnetic recording medium of the present invention is excellent due to the action of the polyurethane resin having a cyclohexyl group in the molecule used as the binder (hereinafter referred to as cyclohexyl group-containing polyurethane). Moisture and heat resistance and mechanical strength are imparted, it is tough and exhibits outstanding stability over time, it is hard to cause blocking even when exposed to high temperature and high humidity for a long time, and it maintains good wear resistance over a long period of time. There is almost no increase in powder falling, and it fully has the original running stabilization function of the back coat layer.

Therefore, in the magnetic recording medium of the present invention, the deterioration of the electromagnetic conversion characteristics due to the change in the properties of the back coat layer with time is extremely small, and the recording and reproducing performance is stable and stable over a long period of time. Indicates.

The above-mentioned cyclohexyl group-containing polyurethane is not particularly limited, and any of those having a cyclohexyl group in the main chain and those having a cyclohexyl group at the side chain or at the molecular end can be used.
Among them, those having an average molecular weight of about 30,000 to 150,000 and about 50 to 1,000 cyclohexyl groups per molecule are preferable.

Such a cyclohexyl group-containing polyurethane usually has a cyclohexyl group in the molecule as at least a part of the polyol component when the polyurethane is synthesized by the reaction of the polyol component and the polyisocyanate component. By using a polyol having, especially a polyester polyol, or by using an alcohol having a cyclohexyl group in at least a part of the chain extender,
Easy to manufacture.

Suitable commercial products of the cyclohexyl group-containing polyurethane include CA118 (average molecular weight 70,000, 200 cyclohexyl groups per molecule) manufactured by Morton, USA, and CA139 (average molecular weight 8).
In addition, there are 300 cyclohexyl groups per molecule).

In the present invention, other binder components may be used together with the cyclohexyl group-containing polyurethane as a binder for the back coat layer.
As such a preferable binder component, a cellulose resin, a phenoxy resin, an acetal resin,
Examples thereof include butyral-based resins and polyisocyanate compounds as cross-linking agents, and two or more of these may be used. However, even when these other binder components are used in combination, it is desirable that the content of the cyclohexyl group-containing polyurethane is 10% by weight or more based on the total amount of the binder.

It is recommended that the back coat layer contain the same non-magnetic inorganic compound powder as conventionally used. That is, this composition further improves the anti-blocking effect, and
This has the advantage that the stability and fluidity of the coating material for the back coat are improved and the formation of a high quality back coat layer is facilitated.

Examples of such non-magnetic inorganic compound powder include BaSO ₄ , α-Fe ₂ O ₃ , CaCO ₃ , and TiO 2.
Powders of ₂ , ZnO, Al ₂ O ₃ , SiO ₂ , barite, kaolin, ZrO _{2 and the} like are suitable, and two or more of these may be used in combination.

The amount of these non-magnetic inorganic compounds to be blended is preferably about 5 to 30 parts by weight with respect to 100 parts by weight of the binder. Will be increased.

Furthermore, various additives such as a carbon black, a lubricant, and a dispersant, which have a function as an antistatic agent or a colorant for detecting an end, are conventionally added to the backcoat layer. Agents can be included.

To form the back coat layer, a binder containing the above-mentioned cyclohexyl group-containing polyurethane and, if necessary, various additives containing the above-mentioned non-magnetic inorganic compound,
A coating material for a back coat composed of an organic solvent may be prepared, and the coating material may be applied to one side of a non-magnetic support such as a polyester film having no magnetic layer and dried.

If the surface roughness of the back coat layer thus formed is too large, the irregularities on the back coat layer surface are transferred to the surface of the magnetic layer in a wound state, which causes dropout. .. Therefore, the surface roughness of the back coat layer can be adjusted by adjusting the particle size and amount of the solid powder particles to be blended, or by adjusting the degree of dispersion when preparing the coating material for the back coat. Centerline average roughness (Ra
The value) is preferably 10 μm or less.

On the other hand, for the magnetic layer, a magnetic paint comprising a magnetic powder, a binder, an additive which is added if necessary, and an organic solvent is prepared, and this paint is applied to the back coat layer forming side of the non-magnetic support. Is formed on the opposite surface by applying magnetic field orientation and drying. Either the magnetic layer or the back coat layer may be formed first, and after both layers are formed, the surface may be subjected to a surface smoothing treatment such as calendaring if necessary, and then cut into a desired size. As a result, the magnetic recording medium of the present invention can be obtained.

Examples of the magnetic powder to be mixed in the magnetic layer include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ and Fe.
Any of oxide-based magnetic powders such as ferrite such as ₃ O ₄ , Ba, Sr, and Pb, and metal-based magnetic powders such as Fe, Co, Ni, and alloys thereof can be used.

As the binder for the magnetic layer, vinyl chloride resin, cellulose resin, polyurethane resin, acetal resin, butyral resin, polyester resin,
Those conventionally known for magnetic layers such as radiation curable resins can be used alone or in combination of two or more, and a crosslinking agent such as a low molecular weight polyisocyanate compound may be added if necessary. Further, additives which are added to the magnetic layer as needed include abrasives, dispersants, lubricants, antistatic agents, fillers, colorants and the like.

[0025]

The magnetic recording medium according to the present invention uses the cyclohexyl group-containing polyurethane as the binder of the back coat layer formed on the surface of the non-magnetic support opposite to the magnetic layer. The coating layer has excellent resistance to moist heat and mechanical strength, does not change its properties over time, and is highly durable.There is very little deterioration in electromagnetic conversion characteristics due to changes in the state of the back coat layer over a long period of time. Excellent recording and playback performance that is stable over time.

[0026]

EXAMPLES Next, examples of the present invention will be specifically described in comparison with comparative examples. In the following, "parts" means "parts by weight".

Example 1 Metallic Fe magnetic powder (BET specific surface area 55 m ² / g) 80 parts Vinyl chloride resin (product name MR110 manufactured by Nippon Zeon Co., Ltd.) 10 parts Polyurethane resin (product name UR8300 manufactured by Toyobo Co., Ltd.) 6 parts Al ₂ O ₃ powder (average particle size 0.3 μm) 8 parts Carbon black (BET specific surface area 120 m ² / g) 2 parts myristic acid 1 part n-butyl stearate 1 part cyclohexanone 120 parts toluene 120 parts

The above composition was mixed and dispersed in a sand mill for a residence time of 30 minutes, and then a trifunctional isocyanate compound (trade name: Colone L, manufactured by Nippon Polyurethane Co.) 4
After adding parts, and thoroughly stirring, a magnetic paint was prepared by passing through a filter.

This magnetic paint was applied onto a polyester film having a thickness of 10 μm so that the thickness after drying would be 3.0 μm, and dried to form a magnetic layer, which was then subjected to surface smoothing treatment by a calendar. , The magnetic original fabric was produced. Meanwhile, the following composition:

Cyclohexyl group-containing polyurethane A 15 parts (trade name CA118 above) Cyclohexyl group-containing polyurethane B 10 parts (trade name CA139 above) Nitrocellulose (trade name BTH-1 manufactured by Asahi Kasei Corporation) 20 parts -Bombrak 45 parts (trade name: Blackpal 800, manufactured by KYABOT) BaSO ₄ powder (average particle size 0.3 μm) 5 parts Oleic acid 5 parts Cyclohexanone 180 parts Toluene 180 parts are mixed and dispersed with a sand mill at a residence time of 15 minutes Then, 5 parts of a trifunctional isocyanate compound (same as the magnetic layer) was added, and the mixture was thoroughly stirred and passed through a filter to give a back coat coating material.

This coating material is applied to the surface of the magnetic film opposite to the magnetic layer so that the thickness after drying becomes 0.8 μm.
After being dried to form a back coat layer, it was cut into ½ inch width to prepare a magnetic tape.

Example 2 Instead of nitrocellulose in the coating for back coat, a phenoxy resin (trade name PK manufactured by U.C. Co., USA) was used.
A magnetic tape was produced in the same manner as in Example 1 except that 20 parts of (HH) was used.

Example 3 In the same manner as in Example 1 except that 20 parts of butyral resin (trade name: Eslek K manufactured by Sekisui Co., Ltd.) was used in place of the nitrocellulose in the coating for back coat.
A magnetic tape was produced.

Example 4 In the same manner as in Example 1 except that the amount of the cyclohexyl group-containing polyurethane A in the back coat coating was changed to 17 parts and the amount of the same B was changed to 8 parts, respectively.
A magnetic tape was produced.

Example 5 Instead of the BaSO ₄ powder in the back coat coating,
A magnetic tape was produced in the same manner as in Example 1 except that 4 parts of CaCO ₃ powder (average particle size 0.7 μm) was used.

Example 6 The amount of cyclohexyl group-containing polyurethane A in the coating for back coat was changed to 25 parts, and
Is not used, and α-Fe ₂ O is used instead of BaSO ₄ powder.
_A magnetic tape was produced in the same manner as in Example 1 except that 4 parts of ₃ powders (average particle size 0.7 μm) were used.

Comparative Example 1 In place of the cyclohexyl group-containing polyurethanes A and B in the back coat coating composition, 25 parts of polyurethane C having no cyclohexyl group in the molecule (trade name N2301 manufactured by Nippon Polyurethane Co., Ltd.) was used. BaS
A magnetic tape was produced in the same manner as in Example 1 except that O ₄ powder was not used.

Comparative Example 2 A magnetic tape was prepared in the same manner as in Example 1 except that 25 parts of the same polyurethane C as in Comparative Example 1 was used instead of the cyclohexyl group-containing polyurethanes A and B in the back coat coating composition. It was made.

Comparative Example 3 25 parts of polyurethane D having no cyclohexyl group in the molecule in place of the cyclohexyl group-containing polyurethanes A and B in the back coat coating (trade name: Estan 5701 manufactured by BF Guddleitch USA) A magnetic tape was produced in the same manner as in Example 2 except that was used.

The magnetic tapes of the above Examples and Comparative Examples were stored under high temperature and high humidity of 60 ° C. and 90% RH for 7 days, and then the degree of blocking and the increase rate of dropout before storage were examined. The results shown in Table 1 below were obtained.

The degree of blocking was as follows: ∘: no blocking was observed, ∘: only slight blocking was observed, Δ: slight blocking was observed, ×: severe blocking was generated. It was evaluated on a four-point scale. The dropout was measured using a Sony VTR and EDV-8000 with a recording wavelength of 0.8.
The measurement was performed under the conditions of μm, slice level 40%, and 5 μsec.

[0042]

[Table 1]

From the results shown in Table 1 above, the magnetic tape of the present invention was used.
In all of the samples (Examples 1 to 6), the property change of the back coat layer is extremely small even when stored under high temperature and high humidity for a long time, and the deterioration of stability over time due to the back coat layer is unlikely to occur. It can be seen that stable recording / reproducing performance can be exhibited over a long period of time.

On the other hand, all the magnetic tapes (Comparative Examples 1 to 3) using a normal polyurethane resin having no cyclohexyl group as the binder of the back coat layer are not changed with time. It can be seen that the property changes greatly and the recording / reproducing performance is inferior in stability.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on one side of a non-magnetic support and a back coat layer on the other side, wherein a polyurethane resin having a cyclohexyl group in the molecule is contained as a binder of the back coat layer. A magnetic recording medium characterized by being provided.