JPH08329459A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To improve the reproduction for high-density recording by specifying the thickness of a nonmagnetic supporting body to 9 to 11μm and specifying the thickness of a magnetic layer after surface smoothening process to 2.5 to 3.0μm to increase the recording capacity per unit volume. CONSTITUTION: A base film 12B on which a magnetic coating material is applied is guided by guide rollers 29, 30 to travel through a drying furnace 15 where the magnetic coating material is dried by hot air to form a sheet-type magnetic recording medium 12c. Then the medium is passed through a calendering zone 31 comprising many rollers 32 where the magnetic layer is smoothed, and then the medium is wound on a hub 33. The sheet-type magnetic recording medium 12c wound on the hub 33 is heat treated in the succeeding process, released and cut into a specified width to produce a magnetic tape. The obtd. tape is again wound to form a pancake.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium suitable for manufacturing a coating type magnetic recording medium.

[0002]

2. Description of the Related Art A magnetic recording medium such as a magnetic tape or a floppy disk is a so-called coating type in which a magnetic layer comprising a magnetic powder, a binder resin, a curing agent and various additives is formed on a non-magnetic support. Magnetic recording media occupy the mainstream because of their excellent productivity and versatility.

In order to manufacture the above coated magnetic tape,
First, magnetic powder, binder resin, hardener, and other materials constituting the magnetic layer are mixed and dispersed with an organic solvent to prepare a magnetic coating material. Then, this magnetic coating material is applied to a continuously running sheet-shaped non-magnetic support, subjected to a heat drying treatment, and further subjected to a flattening treatment (calendar treatment) of the magnetic layer surface and then wound up. Next, the magnetic layer is heat-cured. After this processing, the sheet-shaped magnetic recording medium is unrolled and cut into a predetermined width to form a magnetic tape.

The heat curing treatment promotes a crosslinking reaction between the binder resin and the curing agent in the magnetic layer to ensure the curing of the magnetic layer, and a sheet-like magnetic recording medium before the heat curing treatment step. The purpose is to relieve residual stress accumulated therein.

In the heat curing treatment, the heating temperature is 60 to 70 ° C., the heating time is 20 hours or less, the number of treatments is once, and the heat treatment is performed in consideration of the production efficiency at the time of production and the effect of the heat curing treatment. The winding tension at the time of winding is set to 8 kg / m or more in consideration of the shape of the sheet-shaped magnetic recording medium after the curing treatment (for example, the elongation of the side edge portion due to meandering during traveling during winding).

However, when the heating tension is set to 8 Kg / m or more, the crosslinking reaction is sufficiently carried out and the shape of the sheet-like magnetic recording medium is sufficiently kept within the allowable range. The residual stress accumulated in the magnetic sheet cannot be sufficiently relaxed due to the high tension of the magnetic sheet. This residual stress is the largest cause of dimensional change with time in the completed magnetic tape, and causes dimensional change of about 0.1% or more of the initial length in the tape length direction.

Particularly in the magnetic tape for video, the recording track is inclined by a predetermined track angle with respect to the length direction, and when the above-mentioned dimensional change occurs in the magnetic tape, the recording track is recorded. A deviation occurs from the position traced by the magnetic head during reproduction, which causes a problem that good signal reproduction is not performed.

Particularly, in recent years, the practical use of the digital recording system has progressed, and along with this, the recording capacity per unit time has increased. Therefore, a method of making the magnetic tape thinner to increase the recording capacity per unit volume of the magnetic tape is widely adopted. However, in general, as the thickness of the magnetic tape becomes thinner, the resistance of the magnetic sheet to the external force received during the magnetic sheet manufacturing process decreases, which increases the residual stress accumulated in the magnetic sheet, and the amount of dimensional change over time. Also increases.

Taking the recording method of the digital beta cam format as an example, since the track width is 20 μm and the track width is very narrow, good signal reproduction is required unless the dimensional change occurring in the magnetic tape is 0.02% or less in absolute value. Can't do. For this reason, it is difficult to practically use the magnetic tape whose dimensions change with time as described above in the recording method of the digital beta cam format.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Even if the thickness of the magnetic recording medium is reduced to some extent, the residual stress in the magnetic recording medium is reduced. It is an object of the present invention to provide a method of manufacturing a magnetic recording medium which can be suppressed to a small size and whose dimensional change with time is small and which can perform good signal reproduction even when applied to a digital recording system.

[0011]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, the thickness of the non-magnetic support to be used, the Young's modulus in the lengthwise direction, and the thickness of the magnetic layer. Surprisingly, by keeping the tension during the heat treatment and the heating temperature and the heating time in the heat treatment within a specific limited range, it is possible to surprisingly reduce the aging rate of the longitudinal dimension of the magnetic recording medium, It was found that a magnetic recording medium capable of good signal reproduction can be obtained even when applied to a digital recording system. The present invention has been made based on the above findings.

That is, the present invention comprises a step of forming at least a magnetic layer on a non-magnetic support, a step of subjecting the magnetic layer to a surface flattening treatment, and a step of subsequently performing a heat treatment. In the method for producing a medium, the thickness of the non-magnetic support is set to 9 to 11 μm, and the thickness of the magnetic layer after the surface flattening treatment is set to 2.5 to 3.0 μm. Direction Young's modulus is 600 Kg / mm ² or more, the heat treatment temperature is 60 to 70 ° C, and the treatment time is
The present invention relates to a method for producing a magnetic recording medium, which comprises performing the heat treatment for 18 to 25 hours and applying a tension of 5.0 to 6.5 Kg / m.

It should be noted that it is effective to carry out the above heat treatment in two or more times and to treat each of them for 18 to 25 hours in order to ensure the above-mentioned crosslinking reaction. However, if the heat treatment is performed within the range of the above conditions, the residual stress in the magnetic recording medium can be suppressed to a low level even by one heat treatment, and the dimensional change rate with time can be reduced to an absolute value of 0.02% or less. It is possible.

According to the present invention, a magnetic paint comprising at least a magnetic powder, a binder and a curing agent is applied to a non-magnetic support and the applied layer formed by this application is dried to form a magnetic layer. It is suitable for a method of manufacturing a magnetic recording medium.

In the present invention, a magnetic paint comprising at least a magnetic powder, a binder and a hardener is applied to a non-magnetic support, and the applied layer formed by this application is dried and the surface is flattened to form a magnetic layer. Performing the step under running of the non-magnetic support, winding after the surface flattening treatment,
In this winding state, it is desirable to perform heat treatment while applying tension to heat-cure the magnetic layer.

In the above, it is desirable to use a film-shaped non-magnetic support.

[0017]

Embodiments of the present invention will be described below. This embodiment is an example in which the present invention is applied to manufacture of a magnetic tape.

A magnetic tape used for video and audio is formed by applying a magnetic layer material to an uncoated sheet-shaped base film and drying it to form a magnetic layer, and processing it into a wide and long sheet-shaped magnetic recording medium. It is wound up, then heat-treated, then cut into a certain width and wound up to complete.

FIG. 7 is a schematic front view of the entire apparatus including the magnetic material coating apparatus showing the coating and drying steps.

The uncoated base film 12A wound around the hub 20 is guided by the guide rollers 21, 21, 21 while being conveyed with a proper tension applied thereto, and passes through the guide roller 22 and the backup roller 23, The magnetic paint 35 is applied by being sandwiched between the backup roller 23 and the gravure roller 28.
The magnetic paint is applied by rotating it while partly immersing it in the magnetic paint 35 filled in the paint tank 34.
Base film by gravure roller 28 wiped with 27
It is applied to one side of 12A.

Base film 12B coated with magnetic paint
The magnetic paint is dried by the hot air through the drying oven 15 through the guide rollers 29 and 30, and the sheet-shaped magnetic recording medium 12 is obtained.
C, the magnetic layer is flattened through the calendar portion 31 composed of a large number of rollers 32, and is wound around the hub 33. The sheet-shaped magnetic recording medium 12C wound around the hub 33 is heat-treated in the next step, then fed out and cut into a predetermined width to form a magnetic tape, and then rewound to form a pancake. . The process up to the heat treatment in the magnetic tape manufacturing is shown in FIG.
The process flow diagram is shown in. Then, the magnetic tape fed out from the pancake is cut into a predetermined length, the leader tapes are joined to both ends, and the reel is wound.

FIG. 9 is an enlarged sectional view of the magnetic tape.
The magnetic tape 1 is formed by attaching a magnetic layer 3 on a base film 2.

Magnetic powder, binder,
As the curing agent and the organic solvent, any conventionally known one can be used. Moreover, as the material of the base film, any conventionally known material can be used except that the Young's modulus is 600 Kg / mm ² , and it is not particularly limited.

For example, as magnetic powder, γ-Fe ₂ O
₃ , Fe ₂ O ₃ , ferromagnetic iron oxide particles such as γ-Fe ₂ O ₃ coated with cobalt, ferromagnetic chromium dioxide particles, Fe, C
Examples thereof include ferromagnetic metal-based particles made of metals such as o and Ni and alloys containing these, and hexagonal plate-shaped hexagonal ferrite fine particles.

As the binder, a polymer such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic ester, styrene, butadiene, acrylonitrile, or a copolymer in which two or more kinds of these are combined, or a polyester is used. Resin, epoxy resin, etc. are illustrated.

In particular, from the viewpoint of better dispersing the magnetic powder, it is desirable to use a resin containing a sulfonic acid metal salt or a composite resin of a resin containing a sulfonic acid metal salt and another resin.

As the organic solvent, ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons and the like which are usually used for dispersing magnetic paints can be used.

In addition to the above-mentioned magnetic powder and binder, a dispersant, an antistatic agent, a rust preventive, etc. may be added to the magnetic paint as additives. Any of these commonly used additives can be used.

As the base film to which the magnetic paint is applied, polyethylene terephthalate, polyethylene-2,
Examples thereof include polyesters such as 6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. An intermediate layer or an undercoat layer (4 shown by a virtual line in FIG. 9) may be provided on the surface of these non-magnetic supports in order to improve the adhesiveness of the magnetic layer.

A back coat layer (5 shown by phantom lines in FIG. 9) is formed on the surface of the base film opposite to the side on which the magnetic layer is formed to improve the running property of the magnetic tape.
A top coat layer (6 shown by a virtual line in FIG. 9) made of a lubricant, a rust preventive, etc. may be further formed on the magnetic layer.

The non-magnetic powder used for the back coat layer, the binder, the lubricant used for the top coat layer, and the rust preventive are
Conventionally known materials can be used.

Next, an experiment conducted by comparing a specific example of this embodiment with a comparative example will be described.

A magnetic coating composition was prepared at the compounding ratio shown in Table 1 below.

[0034]

<Example> The above composition was mixed in a planetary mixer for 2 hours and then mixed in a premixer for 2 hours.
Further mix with a sand grind mill for 4 hours. Then
This magnetic coating is hardened with a curing agent (made by Nippon Polyurethane Industry
After adding 4 parts by weight of Coronate L), it was applied to a polyester base film (biaxially stretched polyethylene terephthalate film), dried, and calendered. After that, heat treatment was performed, and the tape was cut into 1/2 inch widths to manufacture magnetic tapes (Examples 1 to 26).

The thickness of the polyester film, the Young's modulus in the longitudinal direction, the thickness of the magnetic layer after calendering, the tension at the time of winding and the treatment time of the heat treatment are predetermined as shown in Tables 2 and 3 below. Within the range (polyester base film: thickness 9 to 11 μm, Young's modulus in longitudinal direction: 60)
0Kg / mm ² or more, thickness of magnetic layer after calendaring: 2.5 ~
3.0 μm, heat treatment time: 18 to 20 hours, and the above tension: 18 to 25 Kg / m). Note that the number of heat treatments is once.

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

The Young's modulus in the lengthwise direction of the base film is
It was changed depending on the manufacturing conditions of the base film. Also,
The tension during winding was changed by adjusting the winding portion of the calendar processing machine.

Comparative Example As shown in Tables 4 and 5 below, the thickness of the polyester base film, the Young's modulus in the longitudinal direction, the calendering condition of the magnetic layer, and the heat treating condition are out of the above-specified ranges. Magnetic tape (Comparative Example 1-Comparative Example)
30) was prepared.

With respect to the produced magnetic tape, the rate of dimensional change with time in the longitudinal direction was measured. A Betacam VTR (manufactured by Sony Corporation, trade name BVW-75) was used for measuring the rate of dimensional change with time in the longitudinal direction. The results are shown in Tables 2 to 5 together with the thickness of the polyester base film, the Young's modulus in the longitudinal direction, the thickness of the magnetic layer after calendering, and the heat treatment conditions.

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

Graphs of FIGS. 1 to 6 are prepared from the data of Examples 1 to 14 in Table 2 and the data of Comparative Examples 1 to 13 in Table 4.

From these graphs, when the thickness of the base film is set to 9 to 11 μm and the thickness of the magnetic layer is set to 2.5 to 3.0 μm, respectively, the Young's modulus in the longitudinal direction of the base film is 600 Kg / mm ² or more. The heat treatment temperature is 60 to 70
The processing time is 18 to 25 hours, and the tension applied to the workpiece during this heat treatment is 5.0 to 6.5 Kg / m.
It is supported that you can:

Data of Examples 1 to 14 and Comparative Example 1
When the data of Examples 13 to 13 of Table 3 and the data of Comparative Examples 14 to 30 of Table 5 are considered together with the data of Examples 13 to 13, the following can be understood.

When the thickness of the base film is less than 9 μm,
The residual stress generated in the base film becomes too large, and the residual stress cannot be sufficiently reduced regardless of other conditions, and the dimensional change rate of the magnetic tape with time exceeds 0.02% in absolute value. When the thickness of the base film is 9 μm or more, the residual stress can be reduced, and the dimensional change rate of the magnetic tape with time can be made 0.02% or less in absolute value.

On the other hand, when the thickness of the base film is 13 μm or more, the above-mentioned dimensional change rate with time is 0.02% or less in absolute value irrespective of the Young's modulus, but when the thickness of the base film exceeds 11 μm, The length of the magnetic recording medium per volume becomes short and the recording capacity becomes insufficient.

The thickness of the magnetic layer after the surface flattening treatment is 2.5 μm.
If it is less than m, the residual stress generated in the magnetic layer becomes too large and the residual stress cannot be sufficiently reduced regardless of other conditions, and the dimensional change rate of the magnetic tape with time is 0.02% in absolute value.
Will be exceeded.

On the other hand, when the thickness of the magnetic layer is 2.5 μm or more, the above dimensional change rate with time can be 0.02% or less in absolute value, but when the thickness of the magnetic layer exceeds 3.0 μm, the thickness of the base film is increased. It is inconvenient because of poor balance with

If the Young's modulus of the base film is less than 600 Kg / mm ² , its mechanical strength is insufficient and residual stress increases,
This large residual stress cannot be sufficiently reduced, and the dimensional change rate of the magnetic tape with time exceeds 0.02% in absolute value regardless of other conditions. Young's modulus above 600Kg / m
It becomes possible to reduce the above-mentioned dimensional change rate with time to an absolute value of 0.02% or less at m ² or more.

When the temperature of the heat treatment is lower than 60 ° C., the crosslinking reaction does not proceed sufficiently, the mechanical strength of the magnetic layer is insufficient, and the residual stress in the magnetic layer is not sufficiently reduced. The absolute value of the dimensional change of magnetic tape exceeds 0.02%. When the temperature of the heat treatment exceeds 70 ° C., the shape of the sheet-shaped magnetic recording medium becomes poor, and as a result, it becomes very difficult to put the magnetic tape into practical use. By setting the temperature of the heat treatment to 60 to 70 ° C, the dimensional change rate of the magnetic tape over time can be made 0.02% or less in absolute value.

When the heat treatment time is less than 18 hours, the crosslinking reaction does not proceed sufficiently, the mechanical strength of the magnetic layer is insufficient, and the magnetic tape cannot have sufficient durability for practical use. In addition, the residual stress in the magnetic tape is not relaxed sufficiently, and the dimensional change rate of the magnetic tape over time is 0 in absolute value.
It will exceed 02%. When the heat treatment time exceeds 25 hours, the bond between the binder and the curing agent is partially broken due to the crosslinking reaction, the mechanical strength of the magnetic layer is lowered, and the dimensional change rate of the magnetic tape with time is an absolute value. It will exceed 0.02%. By setting the heat treatment time to 18 to 25 hours, the dimensional change rate with time can be made 0.02% or less in absolute value.

If the tension at the time of heat treatment is less than 5.0 Kg / m, the shape of the sheet-shaped magnetic recording medium deteriorates even if the Young's modulus of the base film is increased, and the dimensional change rate of the magnetic tape with time is 0.02% in absolute value. Will be exceeded. Also, the above tension
If it exceeds 6.5 kg / m, residual stress is newly generated in the sheet-like magnetic recording medium due to this strong tension, and as a result, the dimensional change rate of the magnetic tape with time exceeds 0.02% in absolute value. By setting the above tension to 5.0-6.5Kg / m,
It is possible to keep the dimensional change rate of the magnetic tape with time at an absolute value of 0.02% or less.

The rate of dimensional change with time refers to the rate of dimensional change in the length direction of the magnetic tape, and takes a negative value. On the other hand, the rate of dimensional change with time in the width direction is a positive value, which is an absolute value, which is about half the rate of dimensional change with time in the length direction. If the absolute value of the dimensional change rate with time in the length direction is suppressed to 0.02% or less, the dimensional change rate with time in the width direction will be correspondingly small, and reproduction of recorded signals will not be hindered.

Although the above embodiment is an example of a magnetic tape for video of 1/2 inch width, the present invention manufactures a magnetic tape for 8 mm video and various audios, and further, it has a wide width such as a floppy disk. The same can be applied to the manufacture of a magnetic recording medium manufactured by punching from a long sheet-shaped magnetic recording medium.

[0066]

According to the present invention, the thickness of the non-magnetic support is 9
~ 11μm, the thickness of the magnetic layer after surface flattening 2.5 ~
The recording capacity per unit volume of the magnetic recording medium is increased by setting each to 3.0 μm, and the following effects can be obtained even though the thickness of the magnetic recording medium is reduced as described above. .

The Young's modulus in the longitudinal direction of the non-magnetic support is 600
By increasing the mechanical strength to Kg / mm ² or more, by setting the treatment temperature of the heat treatment to 60 to 70 ° C and the treatment time to 18 to 25 hours, the binder in the magnetic layer and the curing agent are crosslinked. To ensure the reaction and increase the mechanical strength of the magnetic layer, the heat treatment described above and 5.0-
By applying a tension of 6.0 Kg / m and sufficiently relaxing the residual stress accumulated in the object before this heat treatment, the aging rate of the magnetic recording medium can be reduced to an extremely small value. Can be As a result, the deviation of the trace position of the magnetic head from the recording track during reproduction is reduced, and good reproduction during high density recording is guaranteed.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the thickness of a base film and the rate of dimensional change of a magnetic tape over time according to Examples and Comparative Examples of the present invention.

FIG. 2 is a graph showing the relationship between the thickness of the magnetic layer and the dimensional change rate of the magnetic tape over time.

FIG. 3 is a graph showing the relationship between the Young's modulus of the base film and the dimensional change rate of the magnetic tape over time.

FIG. 4 is a graph showing the relationship between the processing temperature of the heat treatment and the dimensional change rate of the magnetic tape over time.

FIG. 5 is a graph showing the relationship between the heat treatment time and the dimensional change rate of the magnetic tape over time.

FIG. 6 is a graph showing the relationship between the tension applied during the heat treatment and the dimensional change rate of the magnetic tape over time.

FIG. 7 is a schematic front view of an apparatus from magnetic coating application to calendar processing in magnetic tape production according to an embodiment of the present invention.

FIG. 8 is a process flow diagram showing steps up to heat treatment in manufacturing the magnetic tape.

FIG. 9 is an enlarged sectional view of the magnetic tape.

[Explanation of symbols]

 1 ... Magnetic tape 2, 12A ... Base film 3 ... Magnetic layer 15 ... Drying oven 20, 33 ... Hub 21, 22, 29, 30 ... Guide roller 23 ... Backup Roll 27 ・ ・ ・ Doctor blade 28 ・ ・ ・ Gravure roll 31 ・ ・ ・ Calendar 32 ・ ・ ・ Roller 34 ・ ・ ・ Paint tank 35 ・ ・ ・ Magnetic paint

Claims (3)

[Claims] 1. A method for manufacturing a magnetic recording medium, which comprises a step of forming at least a magnetic layer on a non-magnetic support, a step of subjecting the magnetic layer to a surface flattening treatment, and a step of subsequently performing a heat treatment. The thickness of the non-magnetic support is set to 9 to 11 μm and the thickness of the magnetic layer after the surface flattening treatment is set to 2.5 to 3.0 μm. Rate of 600 kg / mm ²
As above, the treatment temperature of the heat treatment is 60 to 70 ° C., the treatment time is 18 to 25
A method for producing a magnetic recording medium, characterized in that the heat treatment is carried out for a period of time under a tension of 5.0 to 6.5 Kg / m. 2. A step of applying a magnetic paint comprising at least a magnetic powder, a binder and a hardener to a non-magnetic support, and drying and flattening the surface of the applied layer to form a magnetic layer. Is performed while the non-magnetic support is running, wound after the surface flattening treatment, and in this wound state, heat treatment is performed while applying tension to heat-cure the magnetic layer. And a method for manufacturing a magnetic recording medium. 3. The method for producing a magnetic recording medium according to claim 2, wherein a film-shaped non-magnetic support is used.