JPS61180927A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the title magnetic recording medium having a sufficient S/N characteristic and excellent traveling stability and durability by incorporating a resin contg. a metal sulfonate group and a hydroxyl group and a polyisocyanate compd. into a magnetic layer and a back layer as the essential binder components. CONSTITUTION:A resin contg. a metal sulfonate group and a hydroxyl group and a polyisocyanate compd. are incorporated into a magnetic layer and a back layer as the essential binder components to facilitate the dispersion of magnetic powder and a filler. Consequently, since the magnetic layer and the back layer both having excellent smoothness as compared to conventional layers can be obtained and further a coated film having a high elastic modulus can be formed, a recording medium having a low friction coefficient and excellent durability is obtained. A sodium sulfonate group or a potassium sulfonate group is preferable as the metal sulfonate group. Besides, a coated film having excellent resistance to heat and abrasion and having a low friction coefficient can be formed by allowing the resin contg. a hydroxyl group to react with the polyisocyanate compd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in the electromagnetic conversion characteristics and running durability of magnetic recording media such as magnetic tapes and magnetic sheets used in audio and video equipment, computers, and the like.

BACKGROUND OF THE INVENTION In recent years, the above-mentioned magnetic recording media have become suitable for high-density recording, and for this purpose, the trend has been to shorten the recording wavelength, narrow the recording track width, and reduce the thickness of the recording medium. As a result, the playback output, S
Electromagnetic conversion characteristics such as N ratio are generally disadvantageous. As a countermeasure to this problem, the surface of the magnetic layer must be made even smoother in order to reduce as much as possible the distance loss between the magnetic recording medium and the magnetic head, which leads to a reduction in reproduction output during short wavelength recording. Furthermore, in order to improve the signal-to-noise ratio, the magnetic powder used in recent magnetic recording media has become increasingly finer, but in general, as magnetic powder becomes finer, the specific surface area increases or agglomerates are more likely to form. Dispersion is becoming more difficult.To improve the dispersibility of the magnetic powder and to further improve the surface properties of the magnetic layer, the use of a specific dispersant or the addition of specific hydrophilic groups in the resin structure are methods. There are known methods such as introducing (For example, Special Publick No. 62-334
(No. 82, Japanese Patent Publication No. 5B-41565) On the other hand, as the surface properties of the magnetic layer improve, the friction coefficient of the recording medium increases, which is disadvantageous in terms of running performance and durability.
Generally, for high-performance magnetic tapes such as those described above, a method is known in which a back coat layer (hereinafter abbreviated as back layer) is provided on the surface of the support opposite to the magnetic surface. (For example, Japanese Patent Publication No. 57-50327, Japanese Patent Publication No. 57-20863
(No. 5) Problems to be Solved by the Invention The electromagnetic characteristics and running durability cannot be improved with only the above measures for improving the dispersibility of magnetic powder and the conventional method of applying a back layer using a binder. It is difficult to satisfy them at the same time. In other words, in addition to the above conditions, it is necessary to use a binder with high rigidity (high Young's modulus) in the magnetic layer in order to obtain stable running properties and excellent electromagnetic conversion characteristics. Although the runnability is improved when using this method, the coating film becomes hard, making it difficult to obtain the effect of surface smoothing treatment (calendar treatment) of the magnetic layer. On the other hand, when a binder with a low Young's modulus is used, although it is expected that the surface properties of the magnetic layer will be improved, problems such as a high coefficient of friction and a decrease in rigidity tend to result in increased sliding noise. [IEICE Technical Report, MR82-34 (198
3) On the other hand, in order to obtain a magnetic recording medium with excellent electromagnetic conversion characteristics, runnability, and durability, it is difficult to achieve this by improving the magnetic layer alone, as described above, and similar improvements are required for the back layer. was. In other words, in the conventional back layer using a binder, it is difficult to sufficiently disperse the filler mixed in, and as a result, the surface condition of the back layer becomes too rough, making it difficult to fully disperse the filler. In magnetic recording media that are rolled up into rolls or stacked in sheets, the unevenness of the back layer transfers to the surface of the magnetic layer, reducing the surface properties of the magnetic layer and impairing the electromagnetic conversion characteristics of the magnetic recording medium. Such problems were likely to occur.

In addition, in a back layer that emphasizes this problem, uses an excessive amount of dispersant, or uses a binder with a low Young's modulus that has relatively good filler dispersion, the coefficient of friction increases.
When the tape ran, the paint film was easily scratched and the tape was easily bent.

Means for Solving the Problems In order to solve the above problems, the present invention provides a magnetic recording system in which a magnetic layer is provided on one main surface of a non-magnetic support, and a back layer is provided on the other main surface. By containing a resin containing a sulfonic acid metal base and a hydroxyl group and a polyisocyanate compound as the main binder components for the magnetic layer and back layer, the magnetic layer medium can have good S/N characteristics and run smoothly. A magnetic recording medium with excellent stability and durability is obtained.

Function: As a result of extensive research, the present inventors have found that by containing a resin containing a sulfonic acid metal base and a hydroxyl group and a polyisocyanate compound as the main binder components for the magnetic layer and back layer, magnetic properties can be achieved. It has a high signal-to-noise ratio because powders and fillers can be easily dispersed, and not only can magnetic layers and back layers with superior smoothness compared to conventional methods be obtained, but also a coating film with a high modulus of elasticity can be formed. It has been found that a magnetic recording medium with a low coefficient of friction and excellent durability can be obtained.

The basic skeleton of the resin containing a sulfonic acid metal base and a hydroxyl group used in the present invention is a polyurethane resin, a vinyl chloride copolymer resin, or a polyester resin, which has been commonly used as a binder for magnetic layers or packs. It may be any resin, cellulose resin, acrylic resin, etc., but polyester resin or polyurethane resin is particularly preferred. The sulfonic acid metal base is preferably a sodium sulfonate group or a potassium sulfonate group. By having these functional groups present in the resin, the same effect as using a dispersant can be achieved, resulting in a bag with excellent surface properties and without the various drawbacks (for example, pluming) associated with the use of a dispersant. This makes it suitable as a layer resin. Furthermore, in the resin containing a hydroxyl group in the resin, by reacting with a polyisocyanate compound, it becomes possible to form a coating film having excellent heat resistance and abrasion resistance and a low coefficient of friction.

The polyester resin containing a sulfonic acid metal base and a hydroxyl group used in the present invention is basically obtained by polycondensing carboxylic acid and a polyhydric alcohol, and the sulfonate resin in the resin is Introduction of acid metal bases is obtained by partially using dicarboxylic acids or polyhydric alcohols containing sulfonic acid metal bases. Similarly, the polyurethane resin used in the present invention is obtained by combining the above polyester resin with various diincyanate compounds,
For example, toluene diisocyanate (TDI), diphenylmethane 4,4' diisocyanate (MDI),
It can be obtained by urethanization using inphorone diisocyanate (IPDI) or hexamethylene diisocyanate (HMDI). Average molecular weight (Mw) of these polyester resins or polyurethane resins
is preferably 1ooo to 100,000. If it is less than 1000, it is difficult to obtain sufficient coating film strength (abrasion resistance, etc.) (100
If it is larger than 000, it is not preferable because the suitability of the paint decreases (viscosity increases, etc.).

The polyester resin or polyurethane resin used in the present invention can be used alone or in combination of two or more, and can also be used in combination with a resin that does not contain a sulfonic acid metal base or a hydroxyl group.

However, it is desirable that the blending ratio of the resin containing the sulfonic acid metal base and the hydroxyl group in the pre-binder is approximately 30% or more. If it is less than 30%, the magnetic powder and filler will not be sufficiently effective in terms of dispersibility. In addition, the blending ratio of the polyisocyanate compound in the pre-binder is 10~
40% is appropriate. If it is less than 10%, the elastic modulus and durability (heat resistance, abrasion resistance, etc.) of the coating film cannot be sufficiently improved, and if it is more than 40%, the coating film becomes too hard and brittle.
Problems such as extremely short pot life are likely to occur.

Next, a method for manufacturing the magnetic recording medium of the present invention will be explained using a magnetic tape as an example.

The magnetic layer is formed from the above binder component (including hardening agent), magnetic powder, organic solvent, and additive components (abrasive, antistatic agent, dispersant, lubricant, etc.) used as necessary. A magnetic paint is applied onto a non-magnetic support such as a polyester film, dried and simultaneously subjected to a magnetic field alignment treatment, followed by a surface smoothing treatment using a calender roll and then a heat treatment.

The magnetic powder used in forming the magnetic layer includes rF
e2O3, Fe0x (1,33<!<1.5), Cr
O2, Co addition - Fe203, CO addition Fe0x (1
, 33〈x(1,5), tabular Ba ferrite, F
Examples include e-Co-Ni alloy powder, Fe-Zn alloy powder, and the like.

Abrasive Toshite is Cr2o3,a-A 1203,a
- There are high hardness fine powders such as Fe203, SiC, Ti0x (x = 1 or 2).

Examples of antistatic agents include inorganic particles such as carbon black and graphite, as well as organic antistatic agents. Examples of dispersants include higher fatty acids, phosphoric acid esters, and sodium alkylbenzenesulfonates.

Examples of lubricants include silicone oil, furan oil, and higher fatty acid esters.

Examples of organic solvents for magnetic coatings containing the above magnetic layer components include methyl ethyl ketone, methyl imbutyl ketone, toluene, cyclohexanone, ethyl acetate, butyl acetate, and the like.

The back layer can be formed in substantially the same manner as the magnetic layer, except for the magnetic field orientation treatment. However, for the back layer, a relatively large amount of (non-magnetic) filler is generally dispersed in the binder as described above for the purpose of imparting strength, appropriate surface properties, or conductivity to the coating film. .

The filler required for the pack is carbon black, and if necessary, small amounts of various additives such as abrasives, dispersants, and lubricants may be included.

EXAMPLES Hereinafter, examples of the present invention will be specifically described. Note that all parts of components mentioned in the examples indicate parts by weight.

Polyester resins and polyurethane resins containing sulfonic acid metal bases and hydroxyl groups used in Examples of the present invention are shown below.

Margin below (Example 1) The magnetic paint and the back layer paint were prepared as follows.

1-1. Preparation of paint for magnetic layer CO-containing - Fe203 magnetic iron oxide powder [average particle size length = 0.3 μm1, acicular ratio = 1o/1, coercive force = 6
4oOe] ...100 parts Polyester resin [#1] ...10 parts PVC/vinyl acetate copolymer resin [manufactured by UCC, V A G H] ...1
0 parts Al2O3 powder [average particle size = 0.3 μm]...
...4 parts Soybean oil lecithin ...1 part myristic acid ...1 part butyl stearate ...1 part methyl ethyl ketone ...150 parts toluene
...150 parts cyclohexanone
After mixing and dispersing 50 parts of the above composition in a ball mill for 48 hours and taking out the mixed material, a kneaded product obtained by adding and mixing a polyisocyanate compound [manufactured by Nippon Polyurethane Co., Ltd., Coronate Lee part] was mixed and dispersed for 48 hours. Average pore diameter 1μ
A coating material for the magnetic layer was prepared by filtering the mixture through a filter of 500 mm.

1-2. Adjustment of paint for back layer Polyurethane resin [#3] 26 parts Nitrocellulose resin [Manufactured by Asahi Kasei Co., Ltd., Seltsuba BTH-1/
2] ...... 15 parts carbon black [manufactured by Asahi Carbon Co., Ltd., Asahi Thermal, average particle size 90 mμ] ・
・・・・・・ 6 parts methyl ethyl ketone ・・・
...160 parts toluene...
・100 parts cyclohexanone ・・・・・・
After mixing and dispersing 60 parts of the above composition in a ball mill for 48 hours and taking out the kneaded product, 8 parts of a polyinsyanate compound [Coronate L, manufactured by Nippon Polyurethane Co., Ltd.] was added and mixed. Then, apply the above magnetic paint to a thickness of 14 μm.
After coating, magnetic field orientation, and drying treatment on a thick polyester film, mirror polishing treatment using a super calender roll and then heat treatment were performed to obtain a raw roll having a magnetic layer with a thickness of 5 μm. The above-mentioned back layer coating material was applied to the surface opposite to the magnetic layer on this raw roll, dried, and then heat treated to form a back layer having a thickness of 0.8 μm. One copy of this was cut into 2-inch width pieces and a videotape sample (26
0 manager) was created.

(Example 2) 2-1. Preparation of paint for magnetic layer Polyester resin in the magnetic paint composition of Example 1 [#
1] to [#2], and PVC/PVC copolymer resin to nitrocellulose resin [Seltsuba BTH-1/4', manufactured by Asahi Kasei Co., Ltd.]
A coating material for a magnetic layer was prepared in exactly the same manner as in Example 1, except that .

2-2゜ Adjustment of paint for back layer Polyurethane resin [#4] 25 parts PVC/vinyl acetate copolymer resin [VAGH] 215 parts Calcium carbonate [manufactured by Shiraishi Kogyo Co., Ltd.] Homocal D1 average particle size 70 mμ] 20 parts Carbon blank [Asahi Thermal] 30 parts Methyl ethyl ketone 150 parts Toluene 100 parts Cyclohexanone After mixing and dispersing 50 parts of the above composition in a ball mill for 48 hours and taking out the kneaded product, a polyisocyanate compound [manufactured by Takeda Pharmaceutical Co., Ltd., D-1] was added.
The kneaded product obtained by adding and mixing 0.0216 parts with an average pore size of 3
A paint for the back layer was prepared by filtering through a μm filter.

A videotape sample was prepared in exactly the same manner as in Example 1, except that the magnetic layer paint and back layer paint prepared as described above were used, respectively.

(Example 3) 3-1. Preparation of paint for magnetic layer Polyester resin in the magnetic paint composition of Example 1 [#
Except for replacing 1] with polyurethane resin [#3],
A coating material for a magnetic layer was prepared in exactly the same manner as in Example 1.

3-2. Adjustment of paint for back layer Polyester resin [#1] 20 parts PVC/vinyl acetate copolymer CVAGH] 20 parts Carbon black [Asahi Thermal] 66 Part α-A12o3 [average particle size = 0.2 pm]...
...66 parts Tylethyl ketone ...150 parts Toluene ...100 parts Cyclohexanone ...50 parts The above composition was mixed and dispersed in a ball mill for 48 hours to obtain a kneaded product. After the mixture was taken out, 8 parts of a polyincyanate compound (Takenate D-102, manufactured by Takeda Pharmaceutical Co., Ltd.) was added and mixed, and the resulting kneaded product was filtered through a filter with an average pore size of 3 μm to prepare a paint for the back layer.

A videotape sample was prepared in exactly the same manner as in Example 1, except that the magnetic layer paint and back layer paint prepared as described above were used, respectively.

(Example 4) 4-1゜Preparation of paint for magnetic layer Polyester resin in the magnetic paint composition of Example 1 [#
1] 10 parts to 8 parts of polyurethane resin [#4], PVC.
A coating material for a magnetic layer was prepared in exactly the same manner as in Example 1, except that 10 parts of vinyl acetate copolymer resin (CVAGH) was replaced with 6 parts of nitrocellulose resin (Seltsuba BTH-1/2).

4-2. Adjustment of paint for back layer Polyester resin [#2] 20 parts Nitrocellulose resin [Seltsuba BTH-1/4]
...... 16 parts zinc oxide [average particle size 0
．． 1 μm] 65 parts carbon black [Manufactured by Tokai Carbon Co., Ltd., Geast S1 average particle size 68 μm] ・
... 10 parts methyl ethyl ketone ...
...150 parts toluene ...
・100 parts cyclohexanone ・・・・・・
After mixing and dispersing 50 parts of the above composition in a ball mill for 48 hours and taking out the kneaded product, 10 parts of a polyisocyanate compound (Coronate L) was added and mixed, and the resulting kneaded product was filtered through a filter with an average pore size of 3 μm. A paint for the back layer was prepared.

A videotape sample was prepared in exactly the same manner as in Example 1, except that the magnetic layer paint and back layer paint prepared as described above were used, respectively.

(Comparative Example 1) The polyester resin [#1] in the binder in the magnetic layer paint (1-1) of Example 1 was replaced with -S O3Na-free polyester resin [: Mw = 12000, -OH value = 30]
and the polyurethane resin [#3] in the binder in the back layer paint (1-2) was changed to -8o3 with a non-containing polyurethane resin [Mw = 20000, -〇H value = 8]
A videotape sample was prepared in exactly the same manner as in Example 1, except that .

(Comparative Example 2) The procedure was exactly the same as in Example 1, except that no polyisocyanate compound was used in preparing the magnetic layer paint (1-1) and the back layer paint (1-2) in Example 1. A videotape sample was created.

(Comparative Example 3)' The polyurethane resin [#3] in the binder in the magnetic layer paint (S-1) of Example 3 was replaced with -303Na-free polyurethane resin CMw = 20000. -0I (Value=40
], and the polyester resin [#1] in the binder in the back layer paint (3-2) was replaced with a 5ONa-free polyester resin [Mw = 12000° - H value =
30] and further fillers (carbon black, α
A videotape sample was prepared in exactly the same manner as in Example 3, except that one part of lecithin was used as a dispersant for -A12o3).

(Comparative Example 4) A videotape sample was prepared in exactly the same manner as in 1 except that polyurethane resin C#-4] in the binder in the magnetic layer paint (+-1) of Example 4 was replaced with -SQ3.

The following evaluation tests were conducted on the magnetic tape samples obtained in each of the above Examples and Comparative Examples.

(1) Surface roughness The surface roughness of the magnetic layer and back layer was measured using a Talystep stylus type surface roughness meter manufactured by Taylor Hopson. The value was determined by calculating the root mean square of the peak height in the roughness chart.

(2) Young's modulus of the magnetic layer The Young's modulus of the magnetic layer was determined by measuring the Young's modulus of the entire sample tape and the polyester base film provided with the back layer using a universal tensile compression tester manufactured by Shinko Co., Ltd. The Young's modulus of only the magnetic layer was calculated from the constant values on both sides according to the formula below.

dM: Thickness of the magnetic layer (W) dB: Thickness of the entire sample tape - thickness of the magnetic layer (GL)
ET: Young's modulus of the whole tape EB: Young's modulus of the polyester base film provided with the back layer. (3) Tape running tension VH8 system VTR (manufactured by Matsushita Electric Industrial Co., Ltd., NV-82
00), the inlet tension (T1) and outlet tension (T2) during tape running (3.3 Crn/sec) were measured and determined as the value of T2/T1.

(4) Video S/N Using the same VTR as in (2), record the specified brightness signal (SO% white level signal) from the TV signal generator at the optimum recording current of the reference tape, and reproduce it using the video color noise meter. The ratio between the signal and noise contained in the demodulated signal is measured and compared with that of the reference tape in odB.

The evaluation test results for each magnetic tape sample are shown in the table below.

As is clear from the table above, in the magnetic recording medium of the present invention using a resin containing a sulfonic acid metal base and a hydroxyl group and a polyincyanate compound as the main binder for the magnetic layer and back layer, the electromagnetic It has great practical value because it not only has excellent conversion characteristics but also excellent running properties and durability.

In the above embodiments, a coated magnetic iron oxide magnetic tape was explained, but the present invention is applicable not only to coated or vapor-deposited magnetic metal magnetic tapes or magnetic tapes, but also to other magnetic tapes such as magnetic disks and magnetic cards. Needless to say, it can be applied to magnetic recording media.

Claims (3)

[Claims] (1) A magnetic recording medium in which a magnetic layer is provided on one main surface of a non-magnetic support, and a back coat layer containing a filler dispersed in a binder is provided on the other main surface. hand,
A magnetic recording medium characterized in that the main binder for the magnetic layer and the back coat layer is a resin containing a sulfonic acid metal base and a hydroxyl group, and a polyisocyanate compound. (2) The magnetic recording medium according to claim (1), wherein the basic skeleton of the resin containing a sulfonic acid metal base and a hydroxyl group is a polyester resin or a polyurethane resin. (3) The magnetic recording medium according to claim (1), wherein the sulfonate metal base is sodium sulfonate or potassium sulfonate.