JP2002092868A - Production method for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve yield by preventing the form of a magnetic recording medium from being deteriorated without changing the configuration of the magnetic recording medium and production facilities. SOLUTION: This method has a raw sheet production process step S1 for producing the raw sheet of the magnetic recording medium by forming a magnetic layer on the principal surface of a non-magnetic support, a take-up process step S3 for taking up the raw sheet of the magnetic recording medium, a heating processing process step S4 for applying heating processing to the taken-up raw sheet of the magnetic recording medium and a feed-out process step S5 for feeding out the raw sheet of the magnetic recording medium after heating processing and in the tale-up process step S3, the wind tension of the magnetic recording medium raw sheet is made from 3.23 to 5.9 N/mm2 and after the end of the heating processing process, before cooling the magnetic recording medium raw sheet lower than the temperature of the magnetic recording medium raw sheet in the take-up process, the feed-out process is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a magnetic recording medium having a heat treatment step.

[0002]

2. Description of the Related Art In general, a coating type magnetic recording medium having a nonmagnetic support and a magnetic layer is manufactured through the following manufacturing steps. First, a magnetic coating mainly composed of a ferromagnetic powder and a binder is applied on a non-magnetic support, and then dried to form a magnetic layer, thereby producing a raw magnetic recording medium. Next, a process of smoothing the surface of the magnetic layer by a calendering process and winding it into a roll is performed. Next, a step of performing a heat treatment on the raw magnetic recording medium wound in a roll shape is performed. Next, a step of unwinding the heat-treated magnetic recording medium from a roll is performed. Then, by slitting to a desired width and length, for example, a tape-shaped magnetic recording medium is obtained.

In the above-described manufacturing process, the heat treatment process is a process for promoting the crosslinking between the binder and the curing agent in the magnetic layer and curing the same. By subjecting the raw magnetic recording medium to a heat treatment, the crosslinking reaction between the binder and the curing agent is promoted, and the magnetic layer is cured, whereby the magnetic layer is provided with sufficient coating film strength and running durability is improved. . For example, in a magnetic tape which is required to have a strict running durability against contact sliding with a magnetic head, such as a commercial video tape used in a broadcasting station, the above-described heat treatment step is indispensable. .

[0004] In the heat treatment, a magnetic recording medium having a length of about 23000 m after calendering is wound into a roll a number of times (hereinafter referred to as a jumbo roll) at a temperature of 60 ° C to 70 ° C. Carry in a constant temperature bath at ℃ and leave it for several tens of hours.

[0005]

However, when the magnetic recording medium is unwound from the jumbo roll in the next step of the heat treatment step such as cutting, for example, shape deterioration is observed in the magnetic recording medium. . For example, in the raw magnetic recording medium, the portion wound as the outer diameter side of the jumbo roll is stretched, while the portion wound as the inner diameter side of the jumbo roll has intermittent wrinkles of about 5 mm pitch in the longitudinal direction. It is formed.

One possible cause of such shape deterioration is that the thickness of the magnetic layer is partially different (hereinafter, referred to as uneven thickness of the magnetic layer). For example, even if the thickness unevenness of the magnetic layer in the width direction of the magnetic recording medium raw material is set within a range of about 0.1 μm,
In the state of the jumbo roll, the magnetic recording medium raw material is wound in a roll shape by about 17000 layers. Therefore, the thickness unevenness on the surface of the jumbo roll (hereinafter, referred to as lamination thickness unevenness) obtained by accumulating the thickness unevenness of the magnetic layer is 1. It can reach as much as 7 mm. Since such a shape of the uneven thickness of the lamination is transferred to the raw magnetic recording medium, the above-described shape deterioration is caused in the raw magnetic recording medium.

With the recent progress of high-density recording in magnetic recording / reproducing systems, the requirements for dimensional accuracy for magnetic recording media have become more stringent. For this reason, the magnetic recording medium raw material in which the above-described shape deterioration has occurred is regarded as a defective product and is removed from the manufacturing process. Therefore, the yield is reduced and the manufacturing cost is increased.

Therefore, as a means for preventing the shape deterioration occurring in the raw material of the magnetic recording medium, the unevenness in the lamination thickness is 50%.
Improving the thickness unevenness of the magnetic layer so as to be 0 μm or less can be mentioned. In order to reduce the thickness unevenness of the laminated layer to 500 μm or less, it is necessary to reduce the thickness unevenness of the magnetic layer to about 0.03 μm. However, it is almost impossible with current manufacturing facilities to form such a magnetic layer having a small thickness unevenness.

[0009] Even if a manufacturing apparatus capable of forming a magnetic layer with small thickness unevenness has been developed, a large change in manufacturing equipment is required to newly introduce the manufacturing apparatus. For this reason, a large-scale capital investment is required, resulting in an increase in manufacturing costs.

Accordingly, the present invention has been proposed in view of such a conventional situation, and it is possible to prevent the deterioration of the shape of a magnetic recording medium without changing the structure and manufacturing facilities of the magnetic recording medium and to improve the yield. It is an object of the present invention to provide a method for manufacturing a magnetic recording medium to be manufactured.

[0011]

In order to achieve the above-mentioned object, a method of manufacturing a magnetic recording medium according to the present invention comprises forming a magnetic layer on a main surface of a non-magnetic support, and forming a magnetic recording medium into a magnetic recording medium. , A winding step of winding the magnetic recording medium, a heating step of heating the wound magnetic recording medium, and magnetic recording after the heating. An unwinding step of unwinding the medium web, wherein in the winding step, the winding tension of the magnetic recording medium stock is 3.23 N / mm ^{2 to} 5.9 N / mm ² ,
Further, after the heat treatment step is completed, the unwinding step is started before the raw magnetic recording medium is cooled to a temperature equal to or lower than the temperature of the magnetic recording medium raw in the winding step.

In the method of manufacturing a magnetic recording medium configured as described above, the winding tension is defined, and after the heat treatment step is completed, the wound magnetic recording medium is removed in the winding step. It is maintained at a temperature higher than the temperature and is unwound before being cooled below the temperature at which it was wound. For this reason, the magnetic recording medium raw material is prevented from contracting by being cooled more than the winding step.

In the method for manufacturing a magnetic recording medium according to the present invention, it is preferable to start the unwinding step within three hours after the completion of the heating step.

Thus, the magnetic recording medium raw material after the completion of the heat treatment is reliably unwound before being cooled to a temperature equal to or lower than the temperature at the time of winding.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the method for manufacturing a magnetic recording medium according to the present invention will be described in detail.

In the method for manufacturing a magnetic recording medium according to the present invention, for example, a magnetic tape as shown in FIG. 1 is manufactured. This magnetic tape comprises a non-magnetic support 1, a lower base layer 2 obtained by applying a coating for a lower base layer on one main surface of the non-magnetic support 1, and an upper magnetic layer on the lower base layer 2. And an upper magnetic layer 3 coated with a paint for use. In this magnetic recording medium, a back coat layer (not shown) formed on the other main surface of the nonmagnetic support 1 and a top coat layer (not shown) formed on the upper magnetic layer 3. May be provided. The lower underlayer 2 formed between the nonmagnetic support 1 and the upper magnetic layer 3 is not an essential layer in the present invention and may be omitted.

In the following, a series of steps for manufacturing a magnetic tape will be described with reference to the flowchart shown in FIG.

First, in step S1, an upper magnetic layer 3 and a lower underlayer 2 are formed on a non-magnetic support 1 to prepare a magnetic recording medium raw material. Next, in step S2, the surface of the magnetic recording medium is subjected to a surface smoothing process. Next, in step S3, the so-called jumbo roll is manufactured by winding the magnetic recording medium raw material into a roll shape many times. Next, in step S4, a heat treatment is performed on the raw magnetic recording medium in the state of a jumbo roll. Next, in step S5, the magnetic recording medium is unwound from the jumbo roll. Finally, in step S6, the magnetic recording medium is cut to obtain a magnetic tape.

First, in step S1, a paint for an upper magnetic layer and a paint for a lower underlayer are prepared, applied to a wide non-magnetic support 1, dried, and dried.
Then, a raw magnetic recording medium is produced by forming the lower underlayer 2.

The paint for the upper magnetic layer and the paint for the lower underlayer can be prepared according to the conventional methods. That is, in the paint for the upper magnetic layer, it can be obtained by mixing a ferromagnetic powder, a binder, a solvent, and various additives, kneading, and then dispersing. Further, in the coating for the lower underlayer, it can be obtained by mixing a non-magnetic powder, a binder, a solvent, and various additives, kneading and dispersing.

The kneading apparatus used in the kneading step includes, for example, a continuous twin-screw kneader, a continuous twin-screw kneader capable of multi-stage dilution, a kneader, a pressure kneader, a roll kneader and the like.

The dispersion apparatus used in the dispersion step includes, for example, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill,
Examples include a tower mill, DCP, agitator, homogenizer, and ultrasonic disperser.

When the coating for the lower underlayer and the coating for the upper magnetic layer are applied onto the non-magnetic support 1, the lower underlayer coating obtained by applying the coating for the lower underlayer is in a wet state. Apply the upper magnetic layer paint to form an upper magnetic layer coating film,
It is preferable to use a so-called wet-on-wet method. The lower underlayer 2 may be composed of a plurality of layers as necessary. In such a case, at least the lower underlayer 2 and the upper magnetic layer 3 adjacent to the upper magnetic layer 3 are wet-on. -It is preferable that the coating is performed in multiple layers by a wet method. Thereby, the surface properties of the upper magnetic layer 3 are improved, and the adhesion between the lower underlayer 2 and the upper magnetic layer 3 is also improved. Also, by using a wet-on-wet method, a so-called dry
The upper magnetic layer 3 can be made thinner than the on-wet coating method.

Specifically, when the lower underlayer 2 and the upper magnetic layer 3 are formed on the nonmagnetic support 1 by a wet-on-wet method, for example, a coating film forming apparatus as shown in FIG. 10 is used.

The coating film forming apparatus 10 includes a winding roll 12 and a supply roll 13, which are formed by winding the non-magnetic support 1 formed in a long shape and extending the non-magnetic support 1.
A coating device 14 for applying a lower base layer coating material and an upper magnetic layer coating material on the non-magnetic support 1 pulled out from the supply roll 13, an orientation magnet 15 for determining the magnetization direction of the upper magnetic layer 3, And a dryer 16 for drying the paint.

That is, in the coating film forming apparatus 10, the non-magnetic support 1 is conveyed from the supply roll 13 to the take-up roll 12, and the coating apparatus 14 is oriented along the conveying direction. The magnet 15 and the dryer 16 are arranged in this order.

In the coating film forming apparatus 10, the coating material for the lower underlayer and the coating material for the upper magnetic layer are first applied on the non-magnetic support 1 by the coating device 14. As shown in FIG. 4, the coating device 14 includes a first extrusion coater 18 for applying a lower base layer coating material, and a second extrusion coater 19 for applying an upper magnetic layer coating material. Further, in the coating apparatus 14, the second extrusion coater 1
Reference numeral 9 denotes a feed side of the nonmagnetic support 1, and a first extrusion coater 18 is disposed so as to be a feed side of the nonmagnetic support 1.

The first extrusion coater 18 and the second
The extruder coater 19 has slit portions 20 and 21 formed at the tip thereof for extruding the paint, and paint pools 22 and 23 for supplying the paint on the back side of the slit portions 20 and 21, respectively. I have. In such a first extrusion coater 18 and a second extrusion coater 19, the paint for the lower underlayer or the paint for the upper magnetic layer supplied to the paint reservoirs 22 and 23 is supplied to the slit portion 2.
It is extruded to the coater tip through 0 and 21, respectively.

Then, the non-magnetic support 1 to which the paint is applied
Is transported along the distal end surfaces of the first extrusion coater 18 and the second extrusion coater 19 in the direction of arrow A in FIG.

The non-magnetic support 1 thus transported
On the upper side, when passing through the first extrusion coater 18, the lower base layer coating material extruded from the slit portion 20 is applied to form the lower base layer 2. And the second
When passing through the extrusion coater 19, the slit 2
The coating material for the upper magnetic layer extruded from 1 is applied on the lower underlying layer 2 in a wet state to form the upper magnetic layer 3.

The first extrusion coater 18
The supply of the paint to the second extrusion coater 19 may be performed via an inline mixer.

In the above description, wet-on
Lower base layer 2 by wet coating method
Although the method for forming the upper magnetic layer 3 has been described as an example, the lower underlayer 2 and the upper magnetic layer 3 can be formed on the nonmagnetic support 1 by a so-called wet-on-dry method.

Thus, the lower underlayer 2 and the upper magnetic layer 3
The non-magnetic support 1 on which is formed is sequentially conveyed to the magnet 15 for orientation and the dryer 16.

In the magnet 15 for orientation, the upper magnetic layer coating film to be the upper magnetic layer 3 is subjected to magnetic field orientation treatment. In addition, as the magnet 15 for orientation, a magnet for longitudinal orientation, a magnet for vertical orientation, or the like is used. These orientation magnets 15 are provided in the upper magnetic layer 3.
Is appropriately selected according to the type of magnetic powder contained in the powder.
The magnetic field of these orientation magnets 15 is generally 20 gauss to 1 gauss.
Desirably, it is about 000 gauss, but is not limited in the case of random orientation.

In the dryer 16, the upper magnetic layer 3 and the lower underlayer 2 are dried by hot air from nozzles arranged above and below the dryer 16. As drying conditions at this time, the temperature is about 30 ° C. to 120 ° C., and the drying time is about 0.1
It is preferable that the heating time is about 10 minutes to 10 minutes.

The magnetic recording medium having the upper magnetic layer 3 and the lower underlayer 2 formed on the non-magnetic support 1 after passing through the dryer 16 is wound around the winding roll 12 many times.

Next, in step S2, the raw magnetic recording medium is subjected to a surface smoothing process. Specifically, FIG.
As shown in FIG.
From 0, it is carried out in the direction of arrow D, guided to the calendar device 31, and subjected to a surface smoothing process. In the surface smoothing process by the calendar device 31, the temperature, the linear pressure, the transport speed, and the like are important. That is, as the surface smoothing conditions,
Temperature is preferably 50 ° C. to 140 ° C., linear pressure is preferably to ^{50kg / cm 2 ~1000kg / cm 2} , the conveying speed is preferably set to 20 m / min to 1000 m / min. If these conditions are not satisfied, the surface smoothness of the upper magnetic layer 3 may be impaired.

The raw magnetic recording medium that has passed through the calendar device 31 is wound around the winding roll 32 a number of times in step S3 while maintaining the winding tension as described below, and is formed into a so-called jumbo roll. .

Next, in step S4, a jumbo roll obtained by winding the magnetic recording medium raw material a number of times is carried into a constant temperature bath, and the jumbo roll, ie, the magnetic recording medium raw material is subjected to a heating treatment. As the heat treatment, the temperature of the thermostat is preferably set to 60 ° C. to 70 ° C., and the treatment time is preferably set to 15 hours to 70 hours. By subjecting the raw magnetic recording medium to heat treatment, the crosslinking reaction between the binder and the curing agent is promoted, whereby the upper magnetic layer 3 and the lower underlayer 2 are hardened, and the upper magnetic layer 3 and the lower underlayer 2 are sufficiently cured. High coating strength.

After the completion of the heat treatment, the jumbo roll is unloaded from the thermostat, and in step S5, the room temperature (20 ° C. to 2 ° C.)
5 ° C.) Unwind the magnetic recording medium from the jumbo roll in an environment.

Finally, in step S6, the magnetic recording medium unwound from the jumbo roll is cut into a predetermined width and length to complete the magnetic tape.

Here, a description will be given of a temperature change of the jumbo roll carried out of the constant temperature bath after the completion of the heat treatment. An actual magnetic recording medium was actually produced, and the magnetic recording medium after calendering was wound up as a jumbo roll.
The heat treatment was performed on the jumbo roll in a constant temperature bath, and the jumbo roll was transported to a room temperature (20 ° C.) environment and left. FIG. 6 shows the change over time of the surface temperature of the jumbo roll at this time.
The temperature at which the raw magnetic recording medium was wound up as a jumbo roll was 32 ° C.

As shown in FIG. 6, the surface temperature of the jumbo roll starts to drop sharply at time B when the jumbo roll is carried out of the thermostat to the room temperature environment in order to maintain thermal equilibrium with the surroundings.
Then, it can be seen that the surface temperature of the jumbo roll is equal to or lower than the temperature of the raw magnetic recording medium when wound as a jumbo roll at time point C.

After the heat treatment, the surface temperature of the jumbo roll carried out of the constant temperature bath decreases with time, and after time C, when the surface temperature of the jumbo roll falls below the surface temperature of the jumbo roll before the heat treatment, the nonmagnetic support 1 is remarkably formed. Shrink. When the non-magnetic support is significantly shrunk, the jumbo roll itself is tightened in the radial direction, and the uneven thickness on the surface of the jumbo roll (hereinafter, referred to as the uneven thickness of the lamination), which is a result of the accumulated uneven thickness of the magnetic layer, is reflected. As a result, the raw material of the magnetic recording medium is degraded in shape.

Here, the behavior of expansion and contraction of the non-magnetic support 1 when the non-magnetic support 1 is heated and cooled again with a predetermined tension applied to the non-magnetic support 1 is shown. As shown in FIG. From FIG. 7, it can be seen that when the tension exceeds 5.88 N / mm ² , permanent strain that tends to expand remains in the cooled nonmagnetic support 1 after heating. Conversely, if the tension is 3.
If it is less than 92 N / mm ² , a permanent strain having a shrinkage tendency larger than −0.2% remains in the cooled nonmagnetic support 1 after heating. Therefore, in the present invention, the tension applied to the non-magnetic support 1 is 3.92 N / mm ^{2 to} 5.88 N.
/ Mm ² is preferable. This allows
When heating and cooling are repeated for the non-magnetic support 1, reversibility of expansion and contraction is maintained in the non-magnetic support.
As will be described later in detail, the winding tension of the magnetic recording medium raw material is particularly preferably in the range of 3.23 N / mm ^{2 to} 5.9 N / mm ² .

In the conventional method of manufacturing a magnetic recording medium, after the heating process on the jumbo roll is completed, the time from the time when the jumbo roll is unloaded from the constant temperature bath to the time when the raw magnetic recording medium is unwound from the jumbo roll (hereinafter, referred to as the time). , Lead time) depends on the progress of maintenance of the next process. That is, there is substantially no agreement regarding the lead time.

For example, in the conventional method of manufacturing a magnetic recording medium, the jumbo roll after the heat treatment is carried out of a thermostat,
Until the raw magnetic recording medium is unwound, the jumbo roll is left at room temperature for 20 hours or more. During the lead time of 20 hours or more, the raw magnetic recording medium is almost completely cooled to room temperature in the state of a jumbo roll. As a result, the raw material of the magnetic recording medium contracts significantly, and the jumbo roll itself is tightened in the radial direction. Therefore, the original magnetic recording medium causes a shape deterioration such as a wrinkle reflecting the shape of the uneven thickness of the jumbo roll.

[0048] Therefore, in the present invention, a winding tension of the magnetic recording medium raw for the jumbo roll after calendering, and ^{3.23N / mm 2 ~5.9N / mm 2} , and heat treatment process for the jumbo roll (Step S4)
After the completion of the above, before the magnetic recording medium raw material is cooled below the temperature of the magnetic recording medium raw material in the winding step (step S3), the magnetic recording medium raw material is unwound from the jumbo roll (step S5). Get started. Then, the magnetic recording medium raw material unwound from the jumbo roll is deprived of heat by sliding with a guide roller or the like installed in an unwinding device for unwinding the magnetic recording medium raw material from the jumbo roll, Cooled.

The winding tension of the magnetic recording medium raw material is set in the above range, and the temperature of the magnetic recording medium raw material is changed from the completion of the heat treatment step until the magnetic recording medium raw material is unwound. In order to maintain the temperature of the medium at a higher temperature than that of the medium, the magnetic recording medium has expanded more than the point at which the medium is wound. Therefore, the shape of the jumbo roll, such as uneven thickness, is prevented from being transferred to the magnetic recording medium, and the original magnetic recording medium does not deteriorate in shape. Therefore, the yield in manufacturing a magnetic tape using existing manufacturing equipment as it is can be significantly improved.

The original magnetic recording medium is used as a jumbo roll.
The winding tension when winding up is 3.23 N / mm^TwoLess than
Then, the jumbo roll is made as a loose state
As a result, the shape deterioration due to the loosening is affected by the jumbo roll.
Will happen. On the other hand, jumbo low
5.9 N / mm ^Two
If it is larger, the jumbo roll itself is strongly tightened in the radial direction.
Causes deterioration of the shape of the original magnetic recording medium.
You. At the same time, the raw material of the magnetic recording medium was jumbo rolled
The winding tension when winding as 5.9 N / mm^TwoYo
Larger, the residual stress difference in the width direction of the raw magnetic recording medium
Is large, so the shape deterioration of the original magnetic recording medium is improved.
Not done.

After the heat treatment step for the jumbo roll is completed, the magnetic recording medium is cooled to a temperature equal to or lower than the temperature of the magnetic recording medium in the winding step. When the unwinding step is started, the raw magnetic recording medium contracts more in the state of a jumbo roll than in the winding step, and the shape of the jumbo roll is transferred to the raw magnetic recording medium. Is caused.

By the way, as is apparent from FIG. 6, three hours later, from the point B at which the jumbo roll is carried out to the room temperature environment, to a point C at which the surface temperature of the jumbo roll becomes lower than the temperature in the winding step. . Therefore, in the present invention, it is preferable to start the unwinding step within 3 hours after the completion of the heat treatment step on the raw magnetic recording medium formed as a jumbo roll. That is, it is preferable that the lead time be within 3 hours. This prevents the shape of the jumbo roll, such as uneven stack thickness, from being transferred to the magnetic recording medium, and does not cause any deterioration in the shape of the raw magnetic recording medium.

If the lead time is longer than 3 hours, as is apparent from FIG. 6, the surface temperature of the jumbo roll falls below the temperature at the time when the jumbo roll was produced, and the non-magnetic support 1 is in the state of the jumbo roll. Because it shrinks significantly,
The jumbo roll itself is strongly tightened in the radial direction. As a result, shape deterioration reflecting the shape of the jumbo roll in which the thickness is uneven is generated in the raw magnetic recording medium.

When a magnetic recording medium is manufactured by applying the present invention, conventionally known materials can be used.

FIG. 8 shows the relationship between the Young's modulus in the longitudinal direction and the expansion coefficient of the non-magnetic support when the tension on the non-magnetic support is zero. From FIG. 8, the Young's modulus is 7
It can be seen that the nonmagnetic support having a density of 056 N / mm ² or less has a property of expanding when heated. On the other hand, 70
It can be seen that a non-magnetic support having a strength of more than 56 N / mm ² has a property of contracting when heated. However,
When the tension is set to zero, even if the nonmagnetic support contracts when heated, it tends to expand when heated when tension is applied, and the Young's modulus is 980.
Non-magnetic supports below 0 N / mm ² will turn to an expanding tendency by applying tension. Non-magnetic supports used for magnetic recording media generally have a Young's modulus of 3920 N /
mm ^{2 to} 7056 N / mm ² . Therefore, any conventionally known material can be used as long as it is a nonmagnetic support used for a magnetic recording medium.

Examples of the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyamides, and the like. Polymer materials such as polyimides and polycarbonates are exemplified. When forming the upper upper magnetic layer 3 and the lower underlayer 2, an undercoat layer may be provided between the nonmagnetic support 1 and the upper upper magnetic layer 3 or the lower underlayer 2 in order to improve adhesion. . The thickness of the undercoat layer is preferably from 0.01 μm to 1 μm, and more preferably from 0.03 μm to 0.5 μm. In forming the undercoat layer, known ones conventionally used in magnetic recording media can be used.

The thickness of the non-magnetic support 1 is 7 μm to
It is preferably 20 μm. If the thickness of the non-magnetic support 1 is less than 7 μm, there may be a risk of winding deviation and wrinkling when the raw magnetic recording medium is wound. on the other hand,
Even when the thickness of the non-magnetic support 1 is more than 20 μm, a winding deviation when the raw magnetic recording medium is wound is likely to occur.

The surface roughness (Ra) of the non-magnetic support 1 is Zy
Ra measured by a Gomax 3D5700 is 8
nm, preferably 5 nm or less. Further, it is preferable that these non-magnetic supports 1 have no coarse protrusions of 0.4 μm or more. If there are coarse protrusions of 0.4 μm or more on the nonmagnetic support 1, the upper magnetic layer 3 or the lower underlayer 2
Even if it is applied, its shape spreads on the surface, causing deterioration of running durability and dropout. The surface roughness shape is controlled by the size and amount of the filler added to the non-magnetic support 1. These fillers include C
In addition to oxides and carbonates such as a, Si, and Ti, organic fine powders such as an acryl-based organic powder can be given.

Examples of the ferromagnetic powder contained in the upper magnetic layer 3 include metals such as Fe, Co, and Ni, Fe—Co, and Fe—
Ni, Fe-Al, Fe-Ni-Al, Fe-Al-
P, Fe-Ni-Si-Al, Fe-Ni-Si-Al
-Mn, Fe-Mn-Zn, Fe-Ni-Zn, Co-
Ni, Co-P, Fe-Co-Ni, Fe-Co-Ni
-Cr, Fe-Co-Ni-P, Fe-Co-B, Fe
-Co-Cr-B, Mn-Bi, Mn-Al, Fe-C
alloys such as o-V. Of course, Al, Si, added for the purpose of preventing sintering or maintaining the shape during reduction,
Even if metal elements such as P, B, and Y are contained in an appropriate amount, the effects of the present invention are not obstructed. As these ferromagnetic metal powders, those obtained by a known production method can be used, and examples thereof include the following methods. (1) A method of reducing with a reducing gas such as a complex organic acid salt (mainly oxalate) and hydrogen or the like. (2) A method in which iron oxide or the like is obtained by reducing iron oxide with a reducing gas such as hydrogen. (3) A method of thermally decomposing a metal carbonyl compound. (4) sodium borohydride in an aqueous solution of a ferromagnetic metal,
A method of reducing by adding a reducing agent such as hypophosphite or hydrazine. (5) A method of evaporating metal in a low-pressure inert gas to obtain a fine powder.

The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment to form an oxide film on the particle surface in order to make it chemically stable. As the slow oxidation treatment method, there are usually (1) a method of forming an oxide film on the surface by immersing it in an organic solvent and then feeding an oxygen-containing gas and drying it, and (2) a method of inactive with an oxygen gas without using an organic solvent. The method is often performed by adjusting the partial pressure with the gas to form an oxide film on the surface.

Further, the ferromagnetic material contained in the upper magnetic layer 3
As powder, γ-Fe_TwoO_Three, Fe _ThreeO_Four, Γ-Fe_TwoO_Three
And Fe_ThreeO_FourBelt compound with Co, γ-Fe containing Co
_TwoO_Three, Co-containing Fe_ThreeO_Four, Co-containing γ-Fe_TwoO_Three
And Fe_ThreeO_FourBelt compound with CrO_TwoOne or more
Contains the above metal elements (eg, Te, Sb, Fe, B, etc.)
It is also possible to use an oxide or the like which has been made to fall. Furthermore, strong
Hexagonal plate ferrite can also be used as magnetic powder
And M-type, W-type, Y-type, and Z-type barium ferrite
G, strontium ferrite, calcium ferrite
, Lead ferrite, and the purpose of controlling their coercive force
Co-Ti, Co-Ti-Zn, Co-Ti-Nb,
Co-Ti-Zn-Nb, Cu-Zr, Ni-Ti, etc.
Additions can also be used.

The specific surface area of the ferromagnetic powder is 20 m ²
/ G to 90 m ² / g, preferably 25 m ² / g
/ G to 70 m ² / g. When the specific surface area is in the above-mentioned range, the ferromagnetic powder is made finer, and a high recording density becomes possible, so that a magnetic recording medium having excellent noise characteristics can be obtained. Further, the ferromagnetic powder preferably has a major axis length of 0.05 μm to 0.3 μm and an axial ratio of 4 to 15. The major axis length is 0.05μm
If it is less than 3, dispersion in the paint for the upper magnetic layer becomes difficult, and if the major axis length exceeds 0.30 μm, noise characteristics may be deteriorated. If the axial ratio is less than 5, the orientation of the ferromagnetic powder is reduced and the output is reduced. If the axial ratio is more than 15, the short-wavelength signal output may be reduced. In the case of hexagonal plate-like ferrite, the plate diameter is preferably 0.01 μm to 0.5 μm, and the plate thickness is preferably about 0.001 μm to 0.2 μm. In addition, the long axis length, the axial ratio, the plate diameter, and the plate thickness employ an average value of 100 samples or more randomly selected from a transmission electron microscope photograph. Further, the water content of the ferromagnetic powder is preferably 0.1% to 3%.

The thickness of the upper magnetic layer 3 is 0.1 μm to
It is preferably 0.5 μm. When the thickness of the upper magnetic layer 3 is within the above range, recording demagnetization can be reduced, and output at a short wavelength, and electromagnetic conversion characteristics such as overwriting are improved. When the thickness of the upper magnetic layer 3 exceeds 0.5 μm, there is a possibility that the electromagnetic conversion characteristics may be reduced due to the recording demagnetization, and when a lubricant is contained only in the lower underlayer 2, a sufficient amount of lubrication may be obtained. The agent may not be supplied to the surface of the magnetic tape. On the other hand, if the thickness of the upper magnetic layer 3 is less than 0.1 μm, a uniform upper magnetic layer 3 may not be formed.

The upper magnetic layer 3 may contain an abrasive. As the abrasive, a nonmagnetic powder having a Mohs hardness of 7 or more is preferable, for example, aluminum oxide, chromium oxide (Cr ₂ O ₃ ), silicon carbide, diamond, silicon nitride, titanium nitride, titanium carbide, titanium carbide, titanium oxide and the like. No. The content of these abrasives is
It is preferably at most 20 parts by weight, particularly preferably at most 10 parts by weight, per 100 parts by weight of the ferromagnetic powder. The specific gravity of the abrasive is preferably from 2 to 6, and particularly preferably from 3 to 5. The size of the abrasive is preferably 0.05 μm to 0.8 μm.
The shape of the abrasive may be needle-like, spherical, or dice-like. As a specific example of the abrasive, AKP-
30, AKP-50, HIT-50, HIT-55, H
IT-60, HIT-82 and HIT-100 (manufactured by Sumitomo Chemical Co., Ltd.) can be mentioned. Incidentally, these abrasives may be used in a method of mixing and dispersing with the ferromagnetic powder, and after previously dispersing in a binder and forming a coating,
It may be added to the paint for the upper magnetic layer mainly composed of the ferromagnetic powder and the binder.

Examples of the binder contained in the lower underlayer 2 and the upper magnetic layer 3 include known thermoplastic resins, thermosetting resins, and reactive resins conventionally used as binders for magnetic recording media. It can be used and has a number average molecular weight of 5000
~ 100,000 is preferred. Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer,
Vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate -Vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile- Cells such as butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, and nitrocellulose Over scan derivatives, styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber, and the like. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea formaldehyde resin. In addition,
These resins are described in the revised new edition "Plastic Handbook" (Asakura Shoten).

As the polar functional group contained in the above binder,
Is -SO_ThreeM, -OSO_ThreeM, -COOM, P = O (O
M)_Two(Where M is a hydrogen atom or lithium,
It is an alkali metal such as potassium and sodium. ),-
NR₁R_Two, -NR₁R_TwoR_Three ⁺X ^-A side chain having a terminal group of
Type,> NR₁R_Two ⁺X^-Main chain type
(Where R₁, R_Two, R_ThreeIs a hydrogen atom or charcoal
A hydride group, X^-Is fluorine, chlorine, bromine, iodine
Such as halogen element ions or inorganic or organic ions
You. ). Also, -OH, -SH, -CN, epoxy group, etc.
There is also a polar functional group of The amount of these polar functional groups depends on the binder
10 for^-1mol / g-10^-8mol / g, preferred
H10^-2mol / g-10^-6mol / g. Sensuality
If there are too few groups, the effect on the dispersion of the magnetic powder is reduced.
Fruit does not appear, on the other hand, if too much,
This leads to a reduction in dispersion of the ferromagnetic powder. These binders
One type may be used alone, but two or more types may be used.
It is also possible to use them together. These binders in coatings
Is based on 100 parts by weight of the above ferromagnetic powder or nonmagnetic powder.
1 to 200 parts by weight, preferably 10 to 5 parts by weight
0 parts by weight.

Specific examples of trade names of binders include VAG
H, VYHH, VMCH, VAGF, VAGD, VRO
H, VYES, VYNC, VMCC, XYHL, XYS
G, PKHH, PKHJ, PKHC, and PKFE (manufactured by Union Carbide), MR110, MR100, M
R112, MR555, and MR104 (manufactured by Zeon Corporation), Nipporan N2301, N2302, and N2304 (manufactured by Nippon Polyurethane Industry Co., Ltd.), Byron UR8200, UR8300, RV530, and RV
280 (manufactured by Toyobo Co., Ltd.), Diferamine 4020,
9020, 9022, and 7020 (Dainichi Seika Co., Ltd.)
Made), Saran F310 and F210 (Asahi Kasei Corporation)
Manufactured).

It is also possible to use a polyisocyanate for crosslinking and curing the above binder. Specific examples of the polyisocyanate include tolylene diisocyanate, alkylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and adducts thereof. Specific examples of these isocyanates include:
Coronate L, Coronate HL, Coronate 2030,
And Coronate 2031 (Nippon Polyurethane Industry Co., Ltd.)
Manufactured), Takenate D-102, Takenate D-110
N, Takenate D-200 and Takenate D-202 (manufactured by Takeda Pharmaceutical Co., Ltd.). The amount of the polyisocyanate to be added to the binder is 5 parts by weight to 80 parts by weight, preferably 10 parts by weight to 60 parts by weight, based on 100 parts by weight of the binder. These polyisocyanates can be used for both the lower underlayer 2 and the upper magnetic layer 3, or can be used by limiting to only one of them. When used in both the lower base layer 2 and the upper magnetic layer 3, the compounding amount can be added to each layer in the same amount, or can be changed at an arbitrary ratio.

As the lubricant, a conventionally known lubricant can be used. Specifically, graphite, molybdenum disulfide, fine powder such as tungsten disulfide, a fatty acid having 10 to 22 carbon atoms, and a fatty acid ester composed of this and an alcohol having 2 to 26 carbon atoms, fluorocarbons, Silicon oils such as dialkylpolysiloxane and fluoroalkylpolysiloxane are exemplified. These lubricants can be contained only in the upper magnetic layer 3 or in the upper magnetic layer 3 and the lower underlayer 2.
In both layers.

Further, a dispersant can be used to disperse the powder contained in the lower underlayer 2 and the upper magnetic layer 3 well. Specific dispersants include nonionic surfactants such as polyoxyalkylene alkyl ethers and polyoxyalkylene phenol ethers, polyoxyalkylene phosphates, sulfonic acids, anionic surfactants such as various fatty acids, and trialkyl surfactants. Cationic surfactants such as quaternary ammonium salts, and amphoteric surfactants are also included. Various coupling agents such as a silane coupling agent, a titanium coupling agent, and an aluminum coupling agent can also be used as the dispersant. These can be used in different types and amounts for the upper magnetic layer 3 and the lower underlayer 2 depending on the purpose.
It may be used for only one layer. The amount of the dispersant added is 0.5 to 100 parts by weight of the ferromagnetic powder or non-magnetic powder.
The amount is preferably from 20 parts by weight to 20 parts by weight. Further, in order to optimize the amount of the lubricant present on the surface of the magnetic tape, the lubricant may be applied after the calendar processing. In this case, the lubricant is applied after being dissolved in an organic solvent, but a solvent that does not dissolve the binder used is selected as the organic solvent.

As the nonmagnetic powder contained in the lower underlayer 2, any conventionally known material can be used. As a specific non-magnetic powder, for example, α-Fe ₂ O ₃
Such as non-magnetic iron oxide, goethite, rutile type titanium oxide,
Anatase type titanium oxide, tin oxide, tungsten oxide,
Silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, BN, α-alumina, β-alumina, γ
-Alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate and the like. These nonmagnetic powders can be used alone or in combination of two or more.

The non-magnetic powder may be in any shape such as a needle, a sphere or a die. The specific surface area of the nonmagnetic powder is preferably 10m ² / g~80m ² / g, it is particularly preferably 20m ² / g~70m ² / g. The average particle diameter of the nonmagnetic powder is preferably 0.5 μm or less.

When the specific surface area and the average particle size of the nonmagnetic powder contained in the lower underlayer 2 are within the above ranges, the surface smoothness of the lower underlayer 2 is improved, and as a result, the surface smoothness of the magnetic recording medium is improved. The property becomes good. Therefore, it is possible to obtain a magnetic recording medium having excellent modulation noise characteristics and having a small spacing loss. Non-magnetic powder has no magnetic cohesion,
Although the dispersion is easier than the ferromagnetic powder, if the specific surface area is larger than the above range, the dispersion may be difficult. On the other hand, if the specific surface area of the non-magnetic powder is too small, the surface smoothness of the magnetic recording medium deteriorates, and it may not be possible to cope with a high recording density system.

The lower underlayer 2 may contain carbon black to prevent the magnetic recording medium from being charged. As the carbon black contained in the lower underlayer 2, any conventionally known material can be used. Specific examples of carbon black include furnace for rubber, pyrolytic carbon, black for color, and acetylene black. Further, the specific surface area of the carbon black is preferably 10 m ² / g to 1000 m ² / g, and the DBP oil absorption is 20 ml / 100 g to 1000 m ^2.
1/100 g, and the average particle size is 0.1 g.
It is preferably not more than 05 μm. The above DB
The oil absorption of P is determined by adding dibutyl phthalate to carbon black little by little, observing the state of carbon black while kneading the mixture, and finding the point of forming one lump from the dispersed state (ml). ).

More specific carbon blacks include BLACKPEARLS 1000, 900, 80
0, 700, and VULCANXC-72 (manufactured by Cabot Corporation), # 60, # 70, and # 80 (manufactured by Asahi Carbon Co., Ltd.), MA-600, 100, "3950B,"
3750B, $ 3250B, $ 2400B, $ 2300
B, $ 1000, $ 900, $ 40, and $ 30 (manufactured by Mitsubishi Kasei Co., Ltd.), CONDUCTEX SC, RAVE
N 7000, 5750, 5250, 3500, 200
0, 1000, and 850 (manufactured by Konlon Via Carbon), Ketjen Black EC and Ketjen Black ECDJ-600 (manufactured by Lion Aguso Co., Ltd.), Pri
ntex 90, 80, 75, 55, 45 (made by Degussa)
And the like.

When the specific surface area and the average particle size of the carbon black contained in the lower underlayer 2 are within the above ranges, the surface smoothness of the lower underlayer 2 is improved, and as a result, the surface smoothness of the magnetic recording medium is improved. The property becomes good. On the other hand, if the specific surface area of the carbon black is too small, the surface smoothness may deteriorate, and it may not be possible to cope with a high recording density system.

As is apparent from the above description, according to the present invention, the winding tension when winding the raw magnetic recording medium as a jumbo roll is specified, and the magnetic recording medium after the completion of the heat treatment process is defined. The unwinding step is started before the temperature of the raw sheet is cooled below the temperature of the magnetic recording medium raw sheet in the winding step. As a result, the magnetic layer has uneven thickness. As a result, the thickness unevenness of the jumbo roll is 500 μm.
, The shape of the magnetic recording medium can be prevented from deteriorating without being affected by the shape of the jumbo roll. Therefore, it is possible to manufacture the magnetic recording medium in which the shape deterioration is prevented using the current manufacturing equipment, without increasing the manufacturing cost.
It is possible to improve the yield. Further, stagnation between manufacturing steps is eliminated, which can contribute to improvement in productivity.

Further, in the above description, a magnetic recording medium having a structure in which a lower underlayer and an upper magnetic layer are formed on a nonmagnetic support has been described as an example, but the present invention is not limited to this. Instead, the present invention is also applicable to the case of manufacturing a magnetic recording medium in which only a magnetic layer is formed on a non-magnetic support.

[0079]

EXAMPLES Specific examples to which the present invention is applied will be described below based on experimental results.

Experiment 1 First, an appropriate winding tension of an original magnetic recording medium when producing a jumbo roll was examined.

<Sample 1-1> First, a coating material for a magnetic layer was prepared according to the following composition. According to the usual method,
After mixing a pigment, an abrasive, a binder, an additive and an organic solvent, the mixture was kneaded with a continuous kneader and dispersed for 6 hours with a sand mill.

Coating composition for magnetic layer Fe-based metal magnetic powder (BET specific surface area: 55 m ² / g): 100 parts by weight Vinyl chloride resin (Zeon Corporation, trade name: MR-110): 20 parts by weight Alumina (average particle size) Diameter: 0.3 μm): 5 parts by weight Carbon: (average particle size: 0.15 μm): 2 parts by weight Stearic acid: 1 part by weight Butyl stearate: 1 part by weight Methyl ethyl ketone: 100 parts by weight Toluene: 100 parts by weight cyclohexanone: 100 parts by weight After adding 4 parts by weight of a curing agent (trade name: Coronate L, Nippon Polyurethane Co., Ltd.) to the coating material prepared as described above, after drying into a polyethylene terephthalate film having a length of 23000 m, a width of 1240 mm and a thickness of 7 μm. Was applied so that the thickness of the magnetic layer was 2.5 μm to prepare a magnetic recording medium raw material.

Next, while the coating material for the magnetic layer was not dried, a magnetic field orientation treatment was performed, and the raw magnetic recording medium was transported to a dryer. After drying the magnetic layer, the raw magnetic recording medium was calendered by a calender, and the raw magnetic recording medium was wound up as a jumbo roll. The winding tension when winding the magnetic recording medium was 6.86 N / mm ² .

Next, the jumbo roll was carried into a thermostat, and was heated at 70 ° C. for 30 hours to accelerate the curing reaction of the magnetic layer.

Next, the jumbo roll after the completion of the heat treatment was carried out of the constant temperature bath, and after a lead time of 2 hours, the raw magnetic recording medium was unwound from the jumbo roll. At this time, the unwound magnetic recording medium raw material was visually observed, and a portion of the magnetic recording medium raw material in which undulation in the longitudinal direction and deterioration in shape such as wrinkles were observed was removed from the manufacturing process as a defective portion.
Then, the raw material of the magnetic recording medium in which the shape deterioration did not occur was cut into 1/2 inch width and assembled into a cassette half to produce a cassette tape of Sample 1-1.

<Sample 1-2 to Sample 1-5> After the completion of the calendar processing, the winding tension when winding the raw magnetic recording medium as a jumbo roll was changed as shown in Table 1 below. A cassette tape was produced in the same manner as in 1-1.

As described above, the yield at the time of producing the cassette tapes of Sample 1-1 to Sample 1-5 was evaluated. The yield is expressed as follows: X is the number of cassette tapes completed from one jumbo roll, Y is the area of the magnetic tape used per cassette tape, and Z is the length of the raw magnetic recording medium per jumbo roll. age,
When the width of the jumbo roll is W, it was calculated by the following equation. Yield (%) = (X × Y) / (Z × W) × 100 The results are shown in Table 1.

[0088]

[Table 1]

As is clear from Table 1, Samples 1-2 to 1-4 whose winding tension is in the range of 3.23 N / mm ^{2 to} 5.9 N / mm ² are the production targets of 80.
% Showed a good yield. On the other hand, in Sample 1-5 in which the winding tension was less than 3.23 N / mm ² , the winding of the jumbo roll was significantly loosened, and the yield was significantly reduced due to wrinkles caused by the loosening of the jumbo roll. Sample 1-1 having a winding tension of more than 5.9 N / mm ² was strongly affected by the uneven thickness of the jumbo roll when the raw magnetic recording medium contracted. Wrinkles were observed, causing a decrease in yield. From the above Experiment 1, the winding tension of the magnetic recording medium after calendering was 3.23 N / mm ^2-
It turned out that the preferable range is 5.9 N / mm ² .

Experiment 2 Next, the time from the end of the heat treatment step to the start of the unwinding step was examined.

<Samples 1-6 to 1-13> First, in the same manner as in Experiment 1 described above, a coating material for a magnetic layer was applied on a non-magnetic support to prepare a raw material for a magnetic recording medium. The recording medium was calendered and wound up to produce the number of jumbo rolls shown in Table 2 below. The temperature of the magnetic recording medium was 32 ° C. when the magnetic recording medium was wound.

Next, in the same manner as in Experiment 1, the jumbo rolls were carried into a constant temperature bath, and these jumbo rolls were subjected to a heat treatment at 70 ° C. for 30 hours to accelerate the curing reaction of the magnetic layer.

Next, after the completion of the heat treatment, the jumbo roll is unloaded from the thermostat and the unwinding step is started at the time when the surface temperature of the jumbo roll is cooled to the temperature shown in Table 2 below. The magnetic recording medium was unwound from a jumbo roll.

Next, the presence or absence of the shape deterioration of the magnetic recording medium was determined, and samples 1-6 to 1
A -13 cassette tape was produced.

The yield in producing the cassette tapes of Samples 1-6 to 1-13 as described above was evaluated in the same manner as in Experiment 1 described above. Table 2 shows the results. In Table 2, the yield was represented by the average value of all jumbo rolls produced for each sample.

[0096]

[Table 2]

As is clear from Table 2, the surface temperature of the jumbo roll at the time when the unwinding step was started was 32.4.
Samples 1-6 at ° C showed good yields of over 80%. The lead time of Sample 1-6 was within 3 hours. On the other hand, samples 1-7 to 1-13 in which the surface temperature of the jumbo roll at the time of starting the unwinding step is equal to or lower than the temperature in the winding step.
Then, the yield was reduced. Note that the lead times of Samples 1-7 to 1-13 exceeded 3 hours.

From the results of Experiment 2 above, after the heat treatment step was completed, before the surface temperature of the jumbo roll was cooled below the temperature in the winding step, the unwinding step was started, whereby the shape of the jumbo roll was determined. Has no effect on the raw material of the magnetic recording medium, prevents the deterioration of the shape of the raw magnetic recording medium, and improves the yield. Further, by setting the lead time after the calendar process to within 3 hours, the shape of the jumbo roll does not affect the magnetic recording medium raw material, the shape of the magnetic recording medium raw material is prevented from being deteriorated, and the yield is improved. all right.

Experiment 3 Next, various types of magnetic tapes were produced, and the effects of applying the present invention were examined.

<Sample 1> A cassette tape of Sample 1 was prepared in the same manner as in Sample 1-1 except that a polyethylene terephthalate film having a length of 23300 m was used.

<Sample 2> First, a paint for the upper magnetic layer and a paint for the lower underlayer were prepared according to the following composition. According to a conventional method, a pigment, an abrasive, a binder, an additive, and an organic solvent are mixed and kneaded by a continuous kneader. The coating for the upper magnetic layer is 5 hours by a sand mill, and the coating for the lower layer is a sand mill. For 3 hours.

Coating composition for upper magnetic layer Fe-based metal magnetic powder: 100 parts by weight (average major axis length: 0.2 μm, needle ratio: 9, saturation magnetization: 130 Am)^Two/ Kg, coercive force: 135 kA / m) Polyvinyl chloride resin: 14 parts by weight (degree of polymerization: 150, sodium oxysulfonate 5 × 10 as a polar functional group) ^-Five mol / g. ) Polyester polyurethane resin: 6 parts by weight (1 × 10% sodium sulfonate as a polar functional group)^-Fourmol / g) Alumina (Average primary particle size: 0.3 μm): 5 parts by weight Stearic acid: 1 part by weight Heptyl stearate: 1 part by weight Methyl ethyl ketone: 150 parts by weight Cyclohexanone: 150 parts by weight α iron oxide: 100 parts by weight (average major axis length: 0.15 μm, needle ratio: 12, pH: 5, 7) carbon black (iron oxide / carbon black = 90/10): 11 parts by weight polyvinyl chloride resin : 17 parts by weight (Polymerization degree: 150, sodium oxysulfonate as a polar functional group is 5 × 10 ^-Five mol / g. ) Stearic acid: 1 part by weight Heptyl stearate: 1 part by weight Methyl ethyl ketone: 150 parts by weight Cyclohexanone: 150 parts by weight The paint for the upper magnetic layer and the lower layer prepared as described above.
Hardener (Nippon Polyurethane Co., trade name
Lonate L) was added in an amount of 4 parts by weight and 2 parts by weight, respectively.
After that, length 12200m, width 1240mm, thickness 62μm
Polyethylene terephthalate film (surface roughness R
a: 8 nm) and the thickness of the upper magnetic layer after drying is 0.20 μm.
m, 4 l so that the thickness of the lower underlayer is 1.5 μm.
Using a die-type coater,
A stock was made.

Next, the paint for the upper magnetic layer is not dried.
After that, the magnetic field orientation treatment is performed, and the magnetic recording medium
Was transported. After drying the magnetic layer, magnetic recording with a calendar machine
A calendar process is performed on the raw media, and the magnetic recording
Wound as a jamboroll. The magnetic recording medium
The winding tension when winding the anti-roll is 3.44 N / mm. ^Two
And

Next, the jumbo roll is carried into a thermostat,
Heat treatment was performed on the jumbo roll at 70 ° C. for 15 hours to accelerate the curing reaction of the upper magnetic layer and the lower underlayer.

Next, after the completion of the heat treatment, the jumbo roll was carried out of the constant temperature bath, and after a lead time of 2 hours, the raw magnetic recording medium was unwound from the jumbo roll. At this time, the unwound magnetic recording medium raw material was visually observed, and a portion of the magnetic recording medium raw material in which undulation in the longitudinal direction and deterioration in shape such as wrinkles were observed was removed from the manufacturing process as a defective portion.
Then, the raw material of the magnetic recording medium in which the shape deterioration did not occur was cut into 1/2 inch width and assembled into a cassette half to produce a cassette tape of Sample 2.

<Sample 3> First, a coating material for a magnetic layer was prepared according to the following composition. According to a conventional method, the mixture was mixed with a ball mill for 48 hours and filtered.

Coating composition for magnetic layer Fe-based metal magnetic powder: 100 parts by weight (specific surface area: 35 m ² / g, Co-γFe ₂ O ₃ ) Vinyl chloride-vinyl acetate copolymer: 20 parts by weight Lubricant (silicon) Oil): 0.5 parts by weight Dispersant (lecithin): 0.5 parts by weight Abrasive (Cr ₂ O ₃ ): 2 parts by weight Antistatic agent (carbon): 2 parts by weight Lubricant (butyl stearate): 0 0.5 parts by weight Methyl ethyl ketone: 110 parts by weight Methyl isobutyl ketone: 50 parts by weight Toluene: 50 parts by weight After adding 3 parts by weight of a curing agent (Nippon Polyurethane Co., trade name: Coronate L) to the paint prepared as described above. Mix for another 30 minutes, length 16800m, width 1240
The resulting magnetic layer was coated on a polyethylene terephthalate film having a thickness of 6 μm and a thickness of 16 μm so that the thickness of the dried magnetic layer was 6 μm.

Next, while the coating material for the magnetic layer was not dried, a magnetic field orientation treatment was performed, and the magnetic recording medium was transported to a dryer. After drying the magnetic layer, the raw magnetic recording medium was calendered by a calender, and the raw magnetic recording medium was wound up as a jumbo roll. The winding tension when winding the magnetic recording medium was 3.23 N / mm ² .

Next, 70
Heat treatment was performed at 30 ° C. for 30 hours to accelerate the curing reaction of the magnetic layer.

A cassette tape of Sample 3 was prepared in the same manner as in Sample 2 except for the above.

<Sample 4> As the Fe-based metal magnetic powder in the coating material for the magnetic layer, Co having a specific surface area of 45 m ² / g was used.
A coating material for a magnetic layer was prepared in the same manner as in Sample 3, except that -γFe ₂ O ₃ was used.

To the paint prepared as described above, 3 parts by weight of a curing agent (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added, and the mixture was further mixed for 30 minutes.
The resulting magnetic layer was coated on a polyethylene terephthalate film having a thickness of 1 μm, a width of 1240 mm and a thickness of 16 μm so that the thickness of the dried magnetic layer was 6 μm. The winding tension when winding the magnetic recording medium as a jumbo roll was 4.27 N / mm ² .

A cassette tape of Sample 4 was prepared in the same manner as Sample 3 except for the above.

<Sample 5> As the Fe-based metal magnetic powder in the coating material for the magnetic layer, Fe having a specific surface area of 45 m ² / g was used.
A coating for a magnetic layer was prepared in the same manner as in Sample 1, except that metal powder was used.

After adding 4 parts by weight of a curing agent (Coronate L, trade name of Nippon Polyurethane Co., Ltd.) to the paint prepared as described above, it was dried to a polyethylene terephthalate film having a length of 11400 m, a width of 1240 mm and a thickness of 7 μm. Was applied so that the thickness of the magnetic layer was 2.5 μm to prepare a magnetic recording medium raw material.

Next, while the coating material for the magnetic layer was not dried, a magnetic field orientation treatment was performed, and the raw magnetic recording medium was transported to a dryer. After drying the magnetic layer, the raw magnetic recording medium was calendered by a calender, and the raw magnetic recording medium was wound up as a jumbo roll. The winding tension when winding the magnetic recording medium was 4.62 N / mm ² .

A cassette tape of Sample 5 was prepared in the same manner as in Sample 1 except for the above.

<Sample 6> As the Fe-based metal magnetic powder in the coating material for the magnetic layer, Fe having a specific surface area of 40 m ² / g was used.
A coating material for a magnetic layer was prepared in the same manner as in Sample 1, except that the base metal magnetic powder was used.

After adding 4 parts by weight of a curing agent (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) to the paint prepared as described above, it was dried on a polyethylene terephthalate film having a length of 14000 m, a width of 1240 mm and a thickness of 7 μm. Was applied so that the thickness of the magnetic layer was 2.5 μm to prepare a magnetic recording medium raw material.

Next, while the paint for the magnetic layer was not dried, a magnetic field orientation treatment was performed, and the magnetic recording medium was transported to a dryer. After drying the magnetic layer, the raw magnetic recording medium was calendered by a calender, and the raw magnetic recording medium was wound up as a jumbo roll. The winding tension when winding the magnetic recording medium was set to 5.90 N / mm ² .

A cassette tape of Sample 6 was prepared in the same manner as Sample 1 except for the above.

Further, except that the lead time until the jumbo roll after the heat treatment was completed was unloaded from the thermostatic chamber and the magnetic recording medium was unwound was set to 20 hours or more as in the conventional manufacturing method, the above samples 1 to 1 were used. In the same manner as in No. 6, six types of comparative tapes were produced. The yield of these comparative tapes was calculated, and the ratio of improvement in the yield of Tape 1 to Tape 6 with respect to the yield of each comparative tape is shown in Table 3 below.

Table 3 also shows the heat treatment temperature of the jumbo roll, the heat treatment time, the Young's modulus of the nonmagnetic support, and the Young's modulus of the tape.

[0124]

[Table 3]

As is clear from Table 3, all cassette tapes of Samples 1 to 6 differing in the Young's modulus of the non-magnetic support in the longitudinal direction, the composition of the magnetic recording medium raw material, and the composition of the magnetic layer are different. Regarding the above, the yield was improved by starting the unwinding step before the surface temperature of the jumbo roll was cooled to the temperature or lower in the winding step. Therefore, the coating type magnetic recording medium to be subjected to the heat treatment has the winding tension and the lead time set to the above conditions, so that the shape of the jumbo roll does not affect the magnetic recording medium raw material, and It has been found that it is possible to prevent the deterioration of the shape of the sheet and improve the yield.

[0126]

As is apparent from the above description, according to the present invention, after completion of the heat treatment step, the raw magnetic recording medium in the wound state is heated at a temperature higher than the temperature in the winding step. It is maintained and unwound before being cooled below the temperature at which it was wound. For this reason, the shape deterioration due to the contraction of the magnetic recording medium raw material rather than the winding step,
It is prevented that the magnetic recording medium material is generated. Therefore, it is possible to manufacture a magnetic recording medium in which the occurrence of shape deterioration is prevented with a high yield without increasing the manufacturing cost and lowering the characteristics of the magnetic recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part of a magnetic tape manufactured by applying the present invention.

FIG. 2 is a flowchart for explaining a series of flows of a method for manufacturing a magnetic recording medium according to the present invention.

FIG. 3 is a schematic view showing a coating film forming apparatus for forming a lower non-magnetic layer and an upper magnetic layer by a wet-on-wet coating method.

FIG. 4 is a schematic diagram illustrating an example of a coating apparatus of a coating film forming apparatus.

FIG. 5 is a schematic diagram showing a calendar device for performing a surface smoothing process.

FIG. 6 is a characteristic diagram showing a change with time of the surface temperature of a jumbo roll after a heat treatment is completed.

FIG. 7 is a diagram for explaining an appropriate tension for a non-magnetic support.

FIG. 8 is a diagram for explaining the relationship between the Young's modulus in the longitudinal direction and the expansion coefficient of a nonmagnetic support.

[Explanation of symbols]

 1 Non-magnetic support, 2 Underlayer, 3 Upper magnetic layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Keiji Sato 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Seiji Sato 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation F term (reference) 5D112 AA21 GB01 KK02 KK03

Claims (2)

[Claims] 1. An original fabric producing step for producing a magnetic recording medium original by forming a magnetic layer on a main surface of a non-magnetic support, a winding step for winding up the magnetic recording medium original, A heat treatment step of performing a heat treatment on the magnetic recording medium raw material afterward; and an unwinding step of unwinding the magnetic recording medium raw material after the heat treatment. The take-up tension of the web is set to 3.23 N / mm ^{2 to} 5.9 N / mm ² , and after completion of the heat treatment step, the magnetic recording medium raw material is at or below the temperature of the magnetic recording medium raw material in the winding step. Starting the unwinding step before the magnetic recording medium is cooled. 2. The unwinding step is started within 3 hours after the completion of the heating step.
The manufacturing method of the magnetic recording medium according to the above.