JPH06349048A - Magnetic tape - Google Patents

Abstract

PURPOSE:To provide the tape having high coating film strength and good durable traveling property particularly as a digital audio tape of a coating type magnetic recording medium to be formed by applying a magnetic coating material on a base film. CONSTITUTION:A binder resin is incorporated at 20 to 30 pts.wt. into 100 pts.wt. ferromagnetic powder. The binder resin is a polyurethane resin having -20 to 35 deg.C glass transition temp. and 25000 to 65000 weight average mol. wt. Low mol. wt. isocyanate is incorporated into the magnetic coating material at 35 to 50 pts.wt. to 100 pts.wt. binder resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating on a non-magnetic support, and more particularly to a cassette tape for digital audio.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable trend toward high density recording in magnetic tape with the development of equipment. Furthermore, the recording method is changing from the conventional analog recording to digital recording. Particularly in the field of audio, a digital audio tape (hereinafter abbreviated as DAT) is also developed and commercialized and put on the market for consumer use.

However, the head of the DAT is installed on a rotary cylinder similar to that of a conventional video tape recorder (hereinafter abbreviated as VTR), and the tape running mechanism has almost the same structure as that of the VTR, and only the DAT dedicated tape is recorded. Can't play. Therefore, it has been more than 5 years since it was commercialized and put on the market, but it has not yet spread enough. Based on such a background, there has been a demand for the development of a digital recording system compatible with an analog recording compact cassette (hereinafter abbreviated as CC). Although each manufacturer has been keenly developing about this, recently, due to the development of fixed type multi-channel head by applying the semiconductor thin film forming technology, and further the development of signal compression technology,
A digital compact cassette system was developed and proposed. And each tape maker is developing a new high-performance digital compact cassette tape (hereinafter referred to as DCC tape) compatible with the system.

[0004]

In consideration of a system capable of digital recording while maintaining upward compatibility with CC,
The relative speed of the head and tape is very slow (4.8 cm)
/ Sec) to achieve high density recording. For that purpose, it is expected that short wavelength recording with the shortest recording wavelength of 1 μm or less and narrowing of track by multi-channeling of the head.

In order to achieve a good error rate as a system, it is of course important that the magnetic tape is excellent in electromagnetic conversion characteristics, but there is no foreign substance in or on the magnetic layer. It is most important to use a magnetic tape with low dropout. Since it is a fixed type head and its relative speed to the tape is very slow, minute dust and dust adhering to the magnetic layer of the magnetic tape are rotated at a high speed like a rotary head (1800 VHS in the case of VHS).
It is impossible to flip off by self-cleaning by rpm). Considering that short wavelength recording with a minimum recording wavelength of 1 μm or less is essential for the system, the main cause of dropout is micron-order minute dust and dust adhering to the surface of the magnetic layer rather than to the inside of the magnetic layer. Becomes

Dust and dust on the magnetic layer may intrude from the outside, but rather it is often caused by dusting of the tape itself such as scraping of the magnetic layer due to running, powder falling, etc., and how to suppress it. Very important. That is, it has been indispensable to design a magnetic layer with less powder falling and shaving under various environments from extremely low temperature to high temperature and high humidity in order to achieve a good error rate.

[0007]

In order to solve the above-mentioned problems, the structure of the present invention is a magnetic recording medium in which a magnetic layer containing a ferromagnetic powder and a binder resin as a main component is provided on a non-magnetic support. The binder resin is contained in an amount of 20 to 30 parts by weight based on 100 parts by weight of the ferromagnetic powder. The binder resin has a glass transition temperature (Tg) of -20 ° C to 35 ° C,
It is a polyurethane resin having a weight average molecular weight of 25,000 to 65,000.

Further, it is preferable that the low molecular weight isocyanate is contained in an amount of 35 to 50 parts by weight based on 100 parts by weight of the binder resin.

[0009]

According to the constitution of the present invention, it is possible to obtain a magnetic layer which is free from abrasion and dust even when running in an environment of extremely low temperature to high temperature and high humidity, and as a result, a magnetic tape having an excellent error rate can be obtained. You can

According to the study by the present inventor, the amount of the binder resin used should be 20 to 30 parts by weight based on 100 parts by weight of the magnetic powder. If the amount of the binder resin is smaller than this, the binding force with the inorganic powder such as magnetic powder, carbon black or alumina will be insufficient. As a result, the magnetic layer was damaged by the fixed head in running durability, and powder fell off,
Scraping occurs, which is present as foreign matter on the surface of the magnetic layer, causing a sharp deterioration of the error rate. On the other hand, if the amount of the binder resin is larger than this, the absolute amount of the magnetic powder in the magnetic layer decreases, which causes a decrease in magnetic energy and deteriorates the electromagnetic conversion characteristics. As a result, the error rate becomes worse.

The glass transition temperature (Tg) of the entire binder resin used is preferably -20 ° C to 35 ° C. Generally, when the glass transition temperature of the polyurethane resin is high, the proportion of hard segment in the molecule is increased, and as a result, the polyurethane resin tends to be hard. If the glass transition temperature is lower than the above range, the binder resin becomes too soft and the strength of the magnetic layer deteriorates. As a result, tape damage or the like occurs particularly during running durability in a high temperature and high humidity environment, leading to a deterioration in error rate. Conversely, if the glass transition temperature is higher than the above range, the binder resin will be too hard and the strength of the magnetic layer will be improved, but the magnetic coating film will become brittle, and powder will fall off during running durability especially in a low temperature environment, Scraping or the like occurs, leading to a deterioration in error rate.

It is desirable to use only polyurethane resin as the binder resin used. In conventional coating type magnetic recording media, vinyl chloride-vinyl acetate copolymer, phenoxy resin, butyral resin, nitrocellulose and the like may be used in combination in addition to polyurethane resin as a binder resin in order to disperse magnetic powder. Many. However, according to the studies by the present inventors, these resins generally tend to make the magnetic layer hard and brittle. V using a conventional rotary head
In TR and DAT, the relative speed between the head and tape is 4 to 6 m / sec, and the relative speed of DCC is 4.78.
The magnetic layer must be designed to be hard to some extent because it is very large compared to cm / sec, and the head shape used is a bulk type protrusion shape. But D
In the case of CC, since the relative speed is slow and the head shape is a thin film type and flat, the magnetic layer must be designed to be flexible and free from powder drop rather than hardened.

The weight average molecular weight of the polyurethane resin used is preferably in the range of 25,000 to 65,000. If the molecular weight is larger than this, the dispersibility of the magnetic powder is hindered and the packing density of the magnetic layer is lowered. In addition, the reaction with the curing agent becomes insufficient, and as a result, the strength of the coating film deteriorates, and powder falls off from the magnetic layer in the durability running test, resulting in a worse error rate. If the molecular weight is smaller than this, the reaction with the curing agent is facilitated, but the reaction causes the magnetic coating film to become hard and brittle, which causes powder to fall off from the magnetic layer in the durability running test, which also causes deterioration of the error rate.

The amount of low molecular weight isocyanate used as a curing agent is 3 with respect to 100 parts by weight of the binder resin.
It is preferably in the range of 5 to 50 parts by weight. If it is less than the above range, the curing of the polyurethane resin is insufficient and the strength of the magnetic coating film is deteriorated, and especially in a high temperature environment, powder is removed and the error rate is deteriorated. On the contrary, if it is more than this range, unreacted low molecular weight isocyanate remains in the coating film, especially in the calendering step, causing adhesion to the metal roll and leaving it on the magnetic layer as a foreign substance, which deteriorates the error rate. Invite.

[0015]

EXAMPLES Ferromagnetic powders used in the present invention include needle-shaped fine metal oxide-based ferromagnetic materials such as γ-Fe ₂ O ₃ , CrO ₂ and Co-deposited γ-Fe ₂ O _3. Powder can be given. Further, these ferromagnetic powders may be used alone or in combination of two or more kinds.

As the binder resin used in the present invention, a polyurethane resin may be used alone,
Usually, two or more types are mixed and used. It is also possible to impart an appropriate amount of a functional group such as a metal salt of sulfonic acid or sulfobetaic acid to these polyurethane resins for the purpose of improving dispersibility in magnetic powder and adsorbability.

Examples of the curing agent used in the present invention include a low molecular weight polyisocyanate having two or more isocyanate groups and a compound having an isocyanate group at its molecular end by reacting a low molecular weight polyol with a polyisocyanate compound.

As the low molecular weight polyisocyanate having two or more isocyanate groups, in addition to these, 3 mol of diisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate, and trimethylolpropane 1
Examples thereof include reaction products with moles, and polyfunctional isocyanate compounds such as modified diphenylmethane diisocyanate and polyphenylmethane polyisocyanate.

Aluminum oxide, chromium oxide, iron oxide and silicon oxide are added to the magnetic layer as a reinforcing agent and an abrasive, higher fatty acids and fatty acid esters are used as lubricants, and carbon black is used as an antistatic agent. It is also possible to add.

Further, a magnetic coating material is prepared by dispersing the constituent materials of the magnetic layer in an organic solvent, and the magnetic coating material is applied onto a non-magnetic base. In this case, the solvent of the magnetic coating material is a ketone (eg acetone, methyl ethyl ketone). , Methyl isobutyl ketone, cyclohexanone, etc.), alcohols (eg methanol, ethanol, propanol,
Butanol), esters (eg methyl acetate, ethyl acetate, ethyl lactate, glycol acetate, monoethyl ether etc.), glycol ethers (eg ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane etc.), aromatic hydrocarbons ( Examples thereof include benzene, toluene, xylene, etc.), aliphatic hydrocarbons (eg, hexane, heptane, etc.), nitropropane and the like.

The base to which this magnetic paint is applied is non-magnetic and is made of polyester (eg polyethylene terephthalate, polyethylene naphthalate etc.), polyolefin (eg polypropylene, polyethylene etc.), cellulose derivative (eg cellulose triacetate, cellulose diacetate etc.). , Polyvinyl chloride, polyimide, polyamide and the like are preferable.

Examples of the present invention will be described in detail below.

Example 1 100 parts by weight of Co-γ-Fe ₂ O ₃ (coercive force of 45000 A / M specific surface area of 48 m ² / g) 1 part by weight of carbon black (Tokai Carbon Co., Ltd. IST GS) 4 parts by weight of methyl ethyl ketone Toluene 3 Parts by weight Cyclohexanone 2 parts by weight The above materials are put into a 50 liter planetary mixer and stirred and mixed for 1 hour.

Polyurethane resin 1 15 parts by weight (Tg 30 ° C. weight average molecular weight 35000 containing sulfonic acid metal salt) Methyl ethyl ketone 18 parts by weight Toluene 18 parts by weight Cyclohexanone 6 parts by weight Further, the above materials are gradually added from another tank over 2 hours. Then, the mixture is stirred and mixed for 1 hour after the addition.

Methyl ethyl ketone 1 part by weight Toluene 0.5 part by weight Cyclohexanone 0.5 part by weight Next, the above-mentioned amount of the mixed solvent is gradually added over 2 hours to make the kneaded material into a large lump and the power consumption of the kneader is reduced. After confirming the maximum, kneading is continued for 8 hours.

Methyl ethyl ketone 39 parts by weight Toluene 39 parts by weight Cyclohexanone 13 parts by weight Next, the above-mentioned amount of the mixed solvent is gradually added over 3 hours to dilute the kneaded product.

After transferring the diluted product obtained through the above steps to another tank, materials having the compositions shown below are further added and mixed by stirring with a dissolver, followed by further dispersion using a sand grinder. I went and made a magnetic paint.

Diluted product 260 parts by weight Polyurethane resin 2 8 parts by weight (Tg 0 ° C. weight average molecular weight 45000 containing sulfonic acid metal salt) α-Al ₂ O ₃ (0.3 μm granular) 2 parts by weight Methyl ethyl ketone 24 parts by weight Toluene 24 parts by weight Parts cyclohexanone 8 parts by weight Materials having the following compositions were further added to the total amount of the obtained magnetic coating material to perform coating. Stearic acid 3 parts by weight-n-butyl stearate 1 part by weight Coronate L 9 parts by weight Coating is performed so that the dry film thickness is 4 μm on a polyester base film having a thickness of 10 μm and a surface roughness of 15 nm, and then an orientation magnetic field is applied. Was applied for orientation and then dried with hot air. After further carrying out calendering treatment at 80 ° C., it was kept in an oven at 60 ° C. for 24 hours for hardening treatment. After curing, it was cut into a width of 3.8 mm to prepare an audio tape.

Comparative Example 1 A magnetic coating material was obtained in the same manner as in Example 1 except that the weight average molecular weights of the polyurethane resins 1 and 2 used in Example 1 were changed to 20000, and an audio tape was prepared using the magnetic coating material.

Comparative Example 2 A magnetic coating material was obtained in the same manner as in Example 1 except that the weight average molecular weights of the polyurethane resins 1 and 2 used in Example 1 were changed to 80,000, and an audio tape was prepared using the magnetic coating material. .

Comparative Example 3 A magnetic coating material was obtained in the same manner as in Example 1 except that the glass transition temperatures of the polyurethane resins 1 and 2 used in Example 1 were changed to −25 ° C., respectively, and an audio tape was prepared using the magnetic coating material. Created.

Comparative Example 4 A magnetic coating material was obtained in the same manner as in Example 1 except that the glass transition temperatures of the polyurethane resins 1 and 2 used in Example 1 were changed to 45 ° C., respectively, and an audio tape was prepared using the magnetic coating material. did.

Comparative Example 5 A magnetic coating material was obtained in the same manner as in Example 1 except that the total addition amount of the polyurethane resins 1 and 2 used in Example 1 was changed to 33 parts by weight with respect to 100 parts by weight of magnetic iron oxide. An audio tape was created using it.

Comparative Example 6 A magnetic coating material was obtained in the same manner as in Example 1 except that the total addition number of polyurethane resins 1 and 2 used in Example 1 was changed to 18 parts by weight relative to 100 parts by weight of magnetic iron oxide. An audio tape was created using it.

Comparative Example 7 The same procedure as in Example 1 was repeated except that the addition amount of the low molecular weight isocyanate used in Example 1 was changed to 55 parts by weight when the total amount of polyurethane resins 1 and 2 was 100 parts by weight. A magnetic paint was obtained and used to make an audio tape.

Comparative Example 8 The procedure of Example 1 was repeated except that the addition amount of the low molecular weight isocyanate used in Example 1 was changed to 30 parts by weight when the total amount of polyurethane resins 1 and 2 was 100 parts by weight. A magnetic paint was obtained and used to make an audio tape.

Comparative Example 9 A magnetic coating material was obtained in the same manner as in Example 1 except that the polyurethane resin 1 used in Example 1 was changed to a vinyl chloride-vinyl acetate copolymer (containing a metal sulfonate group). An audio tape was created using.

The measurement results of the characteristics of the audio tapes obtained in each of the above Examples and Comparative Examples are shown in Table 1. Here, the measurement conditions of each item are as follows.

[0038]

[Table 1]

Error rate (initial, after endurance) Commercial DCC deck (RS-DC1 manufactured by Matsushita Electric Industrial Co., Ltd.)
0) and error rate measuring device (manufactured by Philips)
Using DEMS, the error rate was measured under normal temperature and normal humidity (23 ° C. 60%) environment (initial). After that, the tape was run for 100 passes in a durable environment (40 ° C. 80%), and the error rate after that was measured (after durability).

Powder falling The state of powder falling onto the mechanical deck portion after the durable running of the tape or inside the cassette (pad, leader tape, guide roller) was visually determined.

○ There is no powder drop and it is in a clean state. △ Slight powder drop affects the error rate. × Severe powder drop causes the error rate to deteriorate significantly. Steel ball scratch characteristics For tape The number of passes until the magnetic layer is completely peeled from the base film when a 3φ steel ball is slid at room temperature and normal humidity (23 ° C., 60%) under a load of 40 g is shown.

Amount of Resin Extracted A 3 m tape was subjected to ultrasonic extraction in THF at 20 ° C. for 30 minutes to measure the amount of resin eluted in THF.

Friction coefficient The values of the entrance side tension Ti and the exit side tension To when running at 4.8 cm / sec while being wound around a stainless steel pin having a diameter of 4φ at an angle of 180 degrees were read and calculated from the following equations. Where μ1 is the friction coefficient of the first pass and μ500 is 5
The friction coefficient at the 00th pass is shown.

As is clear from μk = ln (To / Ti) / π (Table 1), according to the constitution of the present invention, as shown in Example 1, a polyurethane resin having an appropriate molecular weight and a glass transition temperature is sufficient. Since it hardens to form a magnetic layer with a strong coating strength, it has high scratch resistance of steel balls and no powder is dropped inside the mechanical deck or cassette even after running for a long time. As a result, the error rate remains constant with little change from the initial value even after running for a long time.

On the other hand, when the molecular weight of the polyurethane resin is large as in Comparative Example 1, or when the glass transition temperature of the polyurethane resin is high as in Comparative Example 4, or Comparative Example 8
In the case where the addition amount of the curing agent is small, as in Comparative Example 9, when the vinyl chloride-vinyl acetate copolymer is used instead of the polyurethane resin as in Comparative Example 9, the curing of the binder resin is insufficient and the solvent There is a large amount of extractables due to and the coating strength is weak. As a result, there were many powder drops after running for a long time, and the error rate was significantly worse than in the initial stage. On the contrary, when the molecular weight of the polyurethane resin is too small as in Comparative Example 2, when the number of parts added of the polyurethane resin is small as in Comparative Example 6, or when the curing agent is large as in Comparative Example 7, the binder resin Although the curing is sufficient, the coating film becomes hard and brittle, and the scratch characteristics deteriorate.
As a result, in these cases, too much powder will fall off after running for a long time, and the error rate will deteriorate. When the glass transition temperature of the polyurethane resin is low as in Comparative Example 3,
The magnetic layer becomes soft and the strength of the coating film becomes weak, resulting in poor durability. When the number of parts added with the polyurethane resin is too large as in Comparative Example 5, the resin left on the magnetic layer floats especially in the calendering process. As a result, the friction coefficient of the magnetic layer becomes high, and in this case also the durability running property deteriorates.

[0046]

As described above, the present invention provides a digital audio tape having a strong coating film strength and excellent running durability, and its effect is extremely great.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a ferromagnetic layer and a magnetic layer containing a binder resin as a main component on a non-magnetic support, wherein the binder resin is 2 parts with respect to 100 parts by weight of the ferromagnetic powder.
0 to 30 parts by weight, and the binder resin is a polyurethane resin having a glass transition temperature (Tg) of -20 ° C to 35 ° C and a weight average molecular weight of 25,000 to 65,000. 2. The magnetic tape according to claim 1, wherein the low molecular weight isocyanate is contained in the magnetic layer in an amount of 35 to 50 parts by weight based on 100 parts by weight of the binder resin.