JPH06103562A - Magnetic tape - Google Patents

Abstract

PURPOSE:To solve the contradiction that the seizing of a head in an environment at a low humidity is accelerated by reducing the wear loss of the head and the wear loss of the head is increased by imparting polishability so that seizing is prevented while attaining excellent C/N characteristic. CONSTITUTION:When a magnetic layer based on magnetic powder and a resin binder is formed on one side of a nonmagnetic substrate by coating to obtain a magnetic tape, the max. roughness of the surface of the magnetic layer is regulated to <=0.040mum and that of the surface of a residual film after dissolution of the magnetic powder in the magnetic layer to <=0.070mum. The internal state of the magnetic layer is precisely controlled, the wear of a head and the seizing of the head in an environment at a low humidity are balanced and excellent C/N characteristics can also be attained.

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 tape widely used as a storage medium for video, audio, information equipment and the like.

[0002]

2. Description of the Related Art With the recent miniaturization of equipment and higher image quality,
The signal density recorded on the magnetic tape is increasing.
Looking at VTR devices already on the market, the shortest recording wavelength is becoming smaller as the format shifts to higher formats. For example, VHS format 1.3 μm, 8
The shortest recording wavelength, which was 0.7 μm in the mm format, is 0.8 μm in the S-VHS format and 0.49 μm in the Hi-8 format.

It is known that the amount of signals per unit time is further increased in a digital recording device for NTSC signals and a recording device compatible with high-definition broadcasting which are currently under development.

Therefore, it means that the shortest recording wavelength is further reduced by designing the device on the extension line of the related art, and it is expected to be difficult in consideration of stability and reliability of actual recording and reproduction.

Therefore, recently, a technique or a technique for increasing the number of tracks for recording a signal is used, not only the increase in the amount of a signal recorded per unit time is consumed only by high density recording of the signal.
The mainstream is an attempt to deal with the increase in the signal amount per unit time by using a technique of increasing the relative speed between the head and the head to increase the signal amount recorded / reproduced per unit time.

[0006]

However, in order to enable such a technique, stricter contact technique between the tape and the head is required.

For example, in the multi-channel technique, the width of the recording track tends to decrease, and the head is inevitably inevitable.
The area of contact with the pump is very small. Therefore, the contact pressure per unit area of the head tends to increase, and the head tends to be worn away.

Further, in the helical scan system widely used in VTR equipment, increasing the relative speed between the tape and the head means rotating the rotary cylinder at a higher speed, and between the cylinder and the tape. It is a direction that makes it easier for the air layer to be caught. As a result, the contact state between the head and the tape becomes unstable, and there arise problems that the signal strength is lowered in a region where the recording wavelength is short and the C / N characteristic is extremely lowered.

To solve these problems at the same time, there are many contradictions, and the traveling tension of the tape given by the equipment is set to a high value to ensure a contact state in which signals can be surely recorded and reproduced, while the head is less worn. , And various combinations of tapes have been studied.

However, the amount of wear that is abraded by the magnetic tape that allows the head to run at high speed is very large,
It is known that the life of the head becomes extremely short.

On the tape side, an attempt has been made to reduce the polishing power of the magnetic tape so that the head life is gentle.

However, this method cannot maintain the effect of cleaning the head, and the occurrence of a burn-in phenomenon in which foreign matter adheres to the head surface, especially in an environment of low humidity, has emerged as a new problem. This image sticking phenomenon causes a gap between the head and the tape, resulting in a significant decrease in signal strength.

In the direction of the prior art, it has been a priority issue to simply shorten the shortest recording wavelength of the recording system, and to realize excellent high frequency characteristics on the magnetic tape side.
The tape problem that is currently being tried against the increase in the recording signal is to obtain an excellent C / N ratio suitable for recording and reproducing a digital signal.
While maintaining the characteristics, it is more complicated in that it solves various problems related to contact with the head such as head wear and head burn-in under the environment in a well-balanced manner.

The present invention has been made in view of these recent demands, and an object of the present invention is to provide a magnetic tape capable of solving these problems from a new angle in a well-balanced manner.

[0015]

The present invention is a magnetic tape obtained by coating and forming a magnetic layer containing a magnetic powder and a binder resin as a main component on one surface of a non-magnetic support. The maximum roughness (Rt) is 0.040 μm or less, and the maximum roughness on the surface of the residual magnetic layer film after the magnetic powder in the magnetic layer is dissolved is 0.070 μm or less.

[0016]

In the prior art, the surface roughness of the magnetic tape was targeted only at the value when the magnetic layer was viewed from the outside, whereas in the present invention, after the magnetic powder in the magnetic layer is dissolved, By paying attention to the residual film of the magnetic layer, it is possible to know the contents related to the physical and magnetic roughness sensed by the head when the tape actually contacts the head.

Furthermore, by setting the maximum roughness of the residual film of the magnetic layer to 0.070 μm or less, excellent C / N characteristics with a small modulation noise magnetically can be obtained, and physically a head can be obtained. On the other hand, it is possible to obtain an ideal contact state. As a result, it is possible to have a practically minimum head cleaning effect, suppress head seizure in a low humidity environment, and realize a tape with a small amount of head wear in a high temperature and high humidity environment. .

[0018]

EXAMPLES Examples of the present invention will be described below.

Table 1 shows the materials constituting the magnetic layer of the 1 / 2-inch wide metal tape and the composition ratio thereof according to one embodiment of the magnetic tape of the present invention.

[0020]

[Table 1]

As the metal magnetic material, one which is easily available was selected from those being developed and studied for the next-generation VTR.

Four types of standard binder resin binders were used for the VTR tape binder. Here, the best type and ratio of each type and amount are determined based on the results of the tensile mechanical properties of the composite resin coating film and the magnetic coating film mixed with magnetic particles. The resin d was selected for the purpose of predispersing alumina.

Alumina is used as an abrasive and has a particle size of 0.10 to 0.30 μm and a BET specific surface area of 9 to 15.
A typical m ² / g resin was dispersed with 1 part by weight of resin d in advance using a mill disperser at an appropriate viscosity. The remaining 17.5 parts by weight of the binder was added during the kneading and pre-dispersion of the magnetic powder.

Carbon was added for the purpose of improving wear resistance and conductivity, and primary particles having a particle size of 200 to 300 angstrom were used.

As the aliphatic lubricant, three kinds often used in magnetic recording media were selected. As the curing agent, a trifunctional isocyanate compound that is commonly used is used. A magnetic tape was prepared by the following method based on the above-mentioned material structure. First, the method for producing the magnetic paint will be described below.

While the mixed solvent of metal magnetic powder and carbon and methyl ethyl ketone: toluene: cyclohexanone = 3: 3: 1 was added to the mixer, the mixture was stirred for 1 hour to wet the powder with the solvent to degas the powder surface. Well done. After that, a suitable amount of a mixed solvent of resin a, resin b, and resin c was added to the mixer and stirred for 5 hours to make these materials kneaded. The kneading process was performed for a total of 4 hours while adjusting the viscosity of the kneaded product several times. After diluting this magnetic kneaded product, dispersion was promoted by a sand mill which is often used for paint dispersion. After the composition was treated to the saturation point of the sand mill dispersion, the alumina paste separately dispersed by the resin d was added and stirred, and the dispersion treatment was carried out again in the sand mill.

A lubricant and a curing agent were added to the stock solution of the metal magnetic paint thus obtained and stirred immediately before coating to complete the preparation of the magnetic paint.

In the preparation of the magnetic paint described here, Hensyl mixer (powder wetting and binder mixing), dissolver (powder wetting and binder mixing / diluting treatment),
Planetary mixer, pressure kneader, continuous kneader, twin-screw kneading extruder, 3 rolls (powder wetting and binder mixing / kneading / dilution processing), stone mill / attritor (dilution of kneading material), pin mill (kneading) Dilution / dispersion of materials), Sand mill / Spike mill / Ultra disk mill (dispersion)
Equipment is used. For details, see T.P.Putton (TCP
ATTON) 's "Paint flow and pigment dispersion" (paint F
Low and Pigment Dispersion) ”describes a method of making paint.

The method for forming the magnetic layer was to continuously coat the long film with a magnetic paint that had been prepared and dispersed, and apply an orientation treatment immediately after coating. After the orientation treatment, an appropriate amount of warm air is blown by the nozzle to suppress the orientation return of the magnetic particles, and the orientation is fixed so that the surface is not roughened due to the rapid drying of the coating film. Immediately thereafter, a calendar process was performed to give a mirror finish.

As the coater described here, a general gravure coater capable of continuous coating treatment was used, but an air doctor coater as described in "Coating Engineering" (issued by S46.3.20.) Issued by Asakura Shoten. A blade coater, an air knife coater, a kiss coater, a die coater, etc. may be used. The orientation treatment is a treatment for directing the magnetic particles in the longitudinal direction, and a DC magnetic field aligned in the longitudinal direction may be applied from the outside. It is preferable to use a magnet that generates a magnetic field larger than the coercive force of the magnetic particles. The orienting device applying a solenoid coil-shaped electromagnet, which is already known in USP 3,256,112, is widely used.

After the magnetic layer was formed, a curing step was performed at 60 ° C. for 24 hours, and then a back coat layer was formed and slit into a 1/2 inch width to obtain a magnetic tape.

Here, the back coat layer is mainly composed of carbon black having a particle diameter of 100 angstroms, and nitrocellulose and polyurethane are used together with a small amount of large-diameter inorganic particles and a polishing agent. Is dispersed and made into a coating material using a gravure coater, and continuously applied and formed.

For a 1/2 inch wide slit,
A slitter with a rotary blade is used as a general method used when cutting a wide sheet into strips at regular intervals.

With respect to the magnetic tape thus produced, magnetic powder was dissolved by the following method to obtain a magnetic layer residual film.

4N hydrochloric acid is preheated to a range of 40 to 60 degrees Celsius. Next, a sample of the required length was cut out from the magnetic tape thus prepared and immersed in this solution for 5 minutes. Thereafter, the sample was repeatedly washed in pure water several times and dried in a clean environment.

Here, the concentration of the hydrochloric acid solution is set to 4 N and the temperature of the solution is set to the range of 40 to 60 degrees Celsius, because the polymer material used as the binder of the magnetic layer is acid during the dissolution treatment of the magnetic powder. It is set as a condition that does not hurt. As long as the binder does not lose the acid, it may be treated for a long time in an acidic solution state weaker than this condition or for a short time in a strong acidic solution state.

The surface roughness of the residual film of the magnetic layer after dissolving the magnetic layer and the magnetic powder was measured by a non-contact surface roughness meter. Specifically, TOPO-3D made by WYKO
Used with a 20 × objective lens. The minimum lateral resolution at this time was 2.0 μm. In particular, the residual film of the magnetic layer is very easily damaged by dissolving the magnetic powder in the coating film and has many voids. Therefore, measurement with a contact-type surface roughness meter is not preferable, and measurement with a non-contact-type surface roughness meter in a state of high lateral resolution is not preferable because it captures fine pores on the residual magnetic layer coating film. .

In order to obtain information required in the present invention from the aspect of head touch, a non-contact type surface roughness meter having both the magnetic layer and the residual film of the magnetic layer, which have the same ability as the above-mentioned measuring machine, is preferable. As an example, a phase-difference interference-type roughness meter made by WYKO, ZYGO, or Tokyo Seimitsu, or a phototactile roughness meter by Kosaka Laboratory can be used. It is judged that the lateral resolution of 0.5 μm to 2.0 μm is appropriate.

In this measurement, the maximum roughness of the magnetic layer surface is 0.0
Various examinations such as drying conditions and calendering conditions after coating the magnetic layer, the degree of dispersion of the alumina paste, the particle size of the alumina particles, etc., so that the maximum roughness on the surface of the magnetic layer residual film is 40 μm or less and 0.070 μm or less. Then, an example sample was prepared, and a comparative sample out of this range was prepared.

Example 1 was prepared by using a paste in which very fine alumina particles having a particle size of 0.1 μm were sufficiently dispersed, and were processed under standard drying conditions and calendar conditions.

In Example 2, only the calendering conditions were set at a temperature higher than the standard conditions by 20 ° C., and the calendering process was performed at the beginning of the calendering process under the same conditions as in Example 1.

Comparative Example 1 was prepared using a paste in which relatively large alumina particles having a particle size of 0.3 μm were sufficiently dispersed, and the drying was performed under standard drying conditions. It is calendered at a temperature 20 degrees higher than the standard. Similar to Example 2, the portion corresponding to the beginning of the calendar treatment was used as a sample.

In Comparative Example 2, the dispersion time of the alumina paste was extremely shorter than that of Example 1, and the other conditions were the same as those of Example 1.

In Comparative Examples 3 and 4, the middle point of the calendar processing (about 3000
m) and the final point (approximately 6000 m) were applied to this.

In Comparative Example 5, as compared with Example 1, the drying condition was set to be tighter than the standard condition, and instead, the calendar condition was set to a temperature 20 ° C. higher than the standard condition, and the surface roughness due to drying was calendered. It was created in a form supplemented with the conditions.
Also for this sample, the portion corresponding to the beginning of the calendar process was used as the sample.

The maximum roughness (Rt) of the magnetic layer and the residual magnetic layer film of each of these samples is shown in Table 2.

[0047]

[Table 2]

The magnetic tapes of the examples and comparative examples prepared in this way are first of all M2 format 90 for broadcasting stations.
The tape is wound into a cassette as a minute tape, the C / N characteristics, the degree of modulation noise, the amount of head wear during the durability test,
The output change in a low humidity environment was measured.

The C / N characteristics were measured by measuring the deviation between the 7 MHz signal strength and the 6 MHz noise strength when a single signal of 7 MHz was recorded after running for 1.5 hours on each tape and analyzed with a spectrum analyzer. did. This measurement result is shown as a relative value to the Ref tape (M2 metal tape).

At this time, 6 MHz and 6.5 MHz
The noise intensity at was also measured, and the degree of modulation noise was compared by looking at this deviation.

The amount of head wear is 40 for each tape.
A change in the head protrusion amount after traveling for 200 passes (300 hours) under an environment of 80% RH was measured. In the test, a new cylinder unit whose head protrusion amount was previously confirmed was attached to each tape.

Regarding the change in output in a low humidity environment, after confirming the recording / reproducing of the full length of the tape in an environment of normal temperature and normal humidity in advance, the value of the recording / reproducing of 5 minutes in the environment of 23 ° C. 10% RH is set. Measure every 20 minutes (measurement interval: 30 minutes),
The difference between that value and the value in the initial room temperature and normal humidity environment was traced every hour.

The results are shown in (Table 3).

[0054]

[Table 3]

As can be seen from this table, Examples 1 and 2 are C
/ N characteristics are excellent with Ref ratio +3.0 dB or more, and
As for the characteristics of the head, the output change is -1.
A very well-balanced result is obtained such that the wear amount is within 0 dB and the wear amount under high temperature and high humidity is within 5.0 μm.

On the other hand, in Comparative Example 1, as a direct adverse effect of using an abrasive having a large particle diameter, the residual roughness of the magnetic layer is finished in a large maximum roughness, which results in a head under a low humidity environment. It can be seen that the cleaning effect is significantly reduced.

Further, in Comparative Example 2, even though a small abrasive was used as in Example 1, the maximum roughness of the magnetic layer and the residual magnetic layer film was large, so that C / N
Poor results were obtained for each item of characteristics, head wear, and output reduction.

Comparative Examples 3 and 4 are the same tapes as in Example 2, but the maximum roughness of the magnetic layer residual film is particularly large. This is because the components of the magnetic layer adhere to the surface of the metal roll of the calender due to the severe conditions of the calendering process, and can be quantitatively differentiated for the first time by the present invention. Due to such a cause, the maximum roughness of the residual film is larger than that of the second embodiment, and as a result, the C / N and the head wear amount in each characteristic of (Table 3) are deteriorated. .

In Comparative Example 5, the surface roughness due to abrupt drying is not completely covered by the strengthening of the calendar conditions, so that both the C / N characteristics and the head wear amount are inferior to those in the Examples.

Although the magnetic tape using the metal magnetic powder has been described in the above embodiment, the coating type magnetic tape is used.
The effect of the present invention can be obtained with any standard and material system as long as it is a 1/2 inch width is D-
3, M-2, S-VHS, VHS, Beta format tapes, and other 3/4 inch wide commercial VTRs
It can also be applied to a tape for VTR, a tape for VTR having a width of 8 mm, and a tape for audio of 3.8 mm.

As the magnetic powder, in addition to the acicular metal powder, a magnetic material such as acicular gamma iron oxide powder, chromium oxide, iron carbide, iron nitride, barium ferrite is used as a main material. Other elements may be added.

Further, the binder resin is not limited to polyurethane and vinyl chloride copolymer as long as it is a polymeric material exhibiting thermoplasticity, thermosetting property and reactivity, and examples thereof include cellulose derivatives, urethane elastomers and nitrocellulose polyamid resins. It may be. As the abrasive or anti-wear agent, powders such as red iron oxide, chromium oxide, silicon carbide, diamond, corundum, kraphite, molybdenum disulfide, and diversion tank dust can be used in addition to alumina and carbon. Further, as a solvent for forming these materials into a coating material, in addition to toluene, methyl ethyl ketone, cyclohexanone, a ketone type solvent such as acetone and methyl isobutyl ketone, an alcohol type solvent such as methanol, ethanol, propanol, butanol, methyl acetate, ethyl acetate, and ethyl acetate. It may be a simple substance or a mixed system of acetic acid type such as benzene and aromatic hydrocarbon type such as benzene and xylene.

Further, the method of preparing the residual coating film of the magnetic layer and the method of measuring the surface roughness of the magnetic layer and the residual coating film are not necessarily the same in the examples as long as they do not depart from the cautions mentioned in the examples. It is not limited to the adopted method.

[0064]

As is apparent from the above description,
The present invention addresses the problem of a subtle difference in C / N characteristics and wear characteristics of the head under each environment that cannot be explained only by the apparent surface roughness of the magnetic layer, and the roughness of the residual magnetic layer film. Introducing the concept of the thickness, and designing the roughness of the outer surface of the magnetic layer and the roughness of the residual film of the magnetic layer appropriately not only shows excellent C / N characteristics, but also suppresses the amount of wear on the head to a small level. However, it is possible to realize high reliability that does not cause burn-in under the environment.

Claims (1)

[Claims] 1. A magnetic tape comprising a non-magnetic support and a magnetic layer mainly composed of a magnetic powder and a binder resin, which is formed on the surface of the non-magnetic support by a maximum roughness of the surface of the magnetic layer ( A magnetic tape characterized in that Rt) is 0.040 μm or less, and the maximum roughness on the surface of the residual film of the magnetic layer after dissolving the magnetic powder in the magnetic layer is 0.070 μm or less.