JPH04325913A - Production of tape-shaped magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the tape-shaped magnetic recording medium which can satisfy both of electromagnetic transducing characteristics and traveling durability even if the thickness over the entire part of the tape is reduced by increasing the rigidity of the tape-shaped magnetic recording medium, thereby suppressing the curling property in the transverse direction of the tape. CONSTITUTION:Arom. polyamide is used for a nonmagnetic base 2 and the ratio of the modulus of elasticity of a magnetic layer 3 and back coat layer 1 formed on the front and rear thereof is specified to 0.4 to 0.7. The magnetic layer 3 and the back coat layer 1 are subjected to a heat treatment in the formed state.

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 tape-shaped magnetic recording medium comprising a nonmagnetic support, a magnetic layer, and a back coat layer.

0002

2. Description of the Related Art Magnetic recording media are widely used for recording electromagnetic signals, and are available in various forms such as tapes, disks, and cards depending on the mode of use. Among such magnetic recording media, various tape-shaped ones have been put to practical use as magnetic recording media for audio and video equipment, computers, and the like.

[0003] In recent years, as the demand for high-density recording of magnetic recording media has increased, the wavelength of recording signals has become shorter and the capacity has increased.

As the wavelength of recording signals becomes shorter, the allowable gap between the magnetic head and the magnetic layer of the magnetic tape becomes smaller.
It is becoming inevitable to make the magnetic layer highly smooth. As the smoothness of the magnetic layer increases, the coefficient of friction of the magnetic layer generally increases, so problems tend to occur particularly in the running properties and durability of tape-shaped magnetic recording media. As a measure to improve this problem, it has already been proposed to form a back coat layer made by dispersing inorganic powder in a binder on the non-magnetic support on the side where the magnetic layer is not provided. There is.

On the other hand, various measures can be taken to increase the capacity of magnetic recording media, but in particular, tape-shaped magnetic recording media are becoming thinner in total tape thickness.

However, as the total thickness of the tape becomes thinner, the tape rigidity decreases significantly, which not only impairs the running durability of the tape but also reduces the contact stability between the tape and the head, resulting in a satisfactory electromagnetic performance. It has also become difficult to obtain conversion characteristics. In particular, V has a large tension load when running the tape.
Since this phenomenon occurs conspicuously in video tapes for HS and S-VHS system VTRs, a solution has been strongly desired.

[0007] As a measure to improve tape rigidity, which decreases significantly as the total thickness of the tape decreases, it is common to increase the modulus of elasticity of the non-magnetic support. omitted) and polyethylene-2
, 6-naphthalate (hereinafter abbreviated as PEN), high-strength materials such as aromatic polyamide and aromatic polyimide have been studied. Among them, aromatic polyamides have a high elastic modulus and excellent heat resistance, so they are effective in improving the rigidity of magnetic recording media over a relatively wide temperature range.

However, using aromatic polyamide as the nonmagnetic support of a tape-shaped magnetic recording medium and simply forming a magnetic layer on one side and a back coat layer on the other side does not make it possible to reduce the total thickness of the tape. Especially VHS, S-VHS system V
For TR video tape, the total thickness of the magnetic tape is 1
When the thickness is less than 3 μm, it is difficult to sufficiently improve running durability and electromagnetic conversion characteristics. In other words, by using aromatic polyamide with relatively high elasticity for the base film, the rigidity of the entire tape can be increased, but since the total thickness of the tape is thin, the strength of the magnetic layer and back coat layer formed on the front and back surfaces ( This is because curling in the tape width direction was likely to occur due to the influence of tape width (rigidity). Since this curl in the width direction of the tape tends to affect the running durability and electromagnetic conversion characteristics of the tape, it is required to have a flat shape (no curl).

[0009] Although studies have been made to solve the above-mentioned problems, it is still difficult to say that it is sufficient to simultaneously satisfy electromagnetic conversion characteristics and running durability. For example, in JP-A-63-39132, the tape width is Trying to prevent directional curliness. In this case, since the elastic modulus of the back coat layer must be equal to or higher than that of the magnetic layer, the back coat layer coating must be designed to be relatively hard, resulting in a high range of elasticity. It has been difficult to repeatedly use the tape over a temperature range, especially to ensure running durability of the back coat layer in a low temperature range.

0010

Problems to be Solved by the Invention As described above, in order to increase the density and capacity of magnetic recording, there is a strong demand for highly smooth media magnetic layers and thinner media. It has been extremely difficult to provide a magnetic tape that has sufficient running durability without impairing its performance.

An object of the present invention is to provide a method for manufacturing a tape-shaped magnetic recording medium that solves the above-mentioned problems.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a magnetic layer mainly composed of ferromagnetic powder and a binder on one side of a non-magnetic support, and a magnetic layer mainly composed of ferromagnetic powder and a binder on the other side. A method for manufacturing a tape-shaped magnetic recording medium in which a back coat layer mainly composed of non-magnetic inorganic powder and a binder is formed, the method comprising: using an aromatic polyamide for the non-magnetic support; The ratio of the elastic modulus to the elastic modulus of the magnetic layer is set to 0.4 to 0.7, and heat treatment is performed in a state where the back coat layer and the magnetic layer are respectively formed on the nonmagnetic support. This is a method of manufacturing a magnetic recording medium obtained by applying the method.

[0013]

[Operation] The present invention has the above-mentioned structure, that is, aromatic polyamide having excellent rigidity and heat resistance is used as the non-magnetic support of the tape-shaped magnetic recording medium, and a back coat layer formed on the front and back surfaces of the non-magnetic support is used. By limiting the ratio of the elastic modulus of the magnetic layer and heat-treating the non-magnetic support with the back coat layer and the magnetic layer formed on the non-magnetic support (in a wound state), the non-magnetic support, Stress relaxation progresses without curling in the magnetic layer and back coat layer in the width direction, improving tape rigidity and reducing curling in the tape width direction, even though the overall thickness of the tape is reduced. First, it becomes possible to provide a magnetic tape that can satisfy both electromagnetic conversion characteristics and running durability.

[0014]

[Examples] Examples of the present invention will be described below.

The thickness of the aromatic polyamide used in the present invention as a nonmagnetic support for a tape-shaped magnetic recording medium having a total thickness of less than 13 μm is preferably 6.5 μm or more and less than 10 μm. If the thickness of the aromatic polyamide exceeds 10 μm, the sum of the thicknesses of the magnetic layer and the back coat layer must be less than 3 μm, which makes it difficult to simultaneously ensure the electromagnetic characteristics and running properties of the tape, and the total thickness is 13 μm. In the above magnetic recording medium, it is also possible to use PET, PEN, etc. as the nonmagnetic support material. In addition, when the thickness of the aromatic polyamide is less than 6.5 μm, the durability of the tape, especially VHS
, it becomes difficult to ensure the durability of video tapes for S-VHS VTRs.

Regarding the elastic strength of the aromatic polyamide nonmagnetic support used in the present invention, the strength ratio in the longitudinal direction and the width direction is not particularly limited, but the sum of the strength values in the longitudinal direction and the width direction is 2400 kg. /mm2 or more is preferable. If this sum is small, thin tape (for example, total thickness 13
It becomes difficult to provide sufficient tape rigidity to satisfy the electromagnetic conversion characteristics and running durability of VHS video tapes (less than .mu.m).

The ratio of the elastic modulus of the back coat layer formed on the front and back surfaces of the aromatic polyamide non-magnetic support used in the present invention and the elastic modulus of the magnetic layer is determined by It is preferable to set it to 0.4 to 0.7 only when the heat treatment is performed after the back coat layer and the magnetic layer are respectively formed. This ratio is 0.
If it is less than 4, curling occurs with the magnetic layer on the inside, which not only impairs the running performance of the tape, but also reduces the contact stability between the tape and the magnetic head, making it difficult to obtain satisfactory electromagnetic conversion characteristics. Become. On the other hand, if this ratio exceeds 0.7, curling with the back coat layer inside tends to occur, and the running performance and electromagnetic conversion characteristics of the tape are impaired. When the above heat treatment is not performed at all, or when the heat treatment is performed only after either the back coat layer or the magnetic layer is formed on the polyamide support, the ratio of the elastic modulus is Even within this range, it is difficult to obtain a tape with little curling property in the width direction.

[0018] The above heat treatment conditions to be applied in the present invention are preferably carried out at a temperature of 40°C to 80°C for 8 to 48 hours. When the treatment temperature is less than 40° C., it is difficult to obtain the above-mentioned effects, and even if they are obtained, the treatment time must be extremely long, which causes problems in terms of productivity. In addition, if the processing temperature exceeds 80°C, although the curling property of the tape can be reduced with a relatively short processing time, the stress relaxation of the tape occurs rapidly and unevenly, resulting in the tape being stretched on one side or wavy. deformation is likely to occur, making it difficult to ensure running performance and running durability.

The magnetic materials used for the magnetic layer of the tape-shaped magnetic recording medium obtained by the present invention include γ-Fe2O3,
Co-containing γ-Fe2O3, Co-containing Fe3O4, CrO
2. In addition to oxide-based magnetic materials such as barium ferrite,
Any magnetic metal or magnetic alloy such as Fe, Fe-Ni, Fe-Co, etc. can be used.

The non-magnetic powder contained in the back coat layer of the tape-shaped magnetic recording medium obtained by the present invention not only improves running properties, but also has carbon black, which has advantages in terms of conductivity and light shielding properties, as well as oxidized powder. Examples include zinc, calcium carbonate, and magnesium sulfate, and these can be used alone or in combination. Furthermore, high hardness powders such as alumina, chromium dioxide, titanium oxide, etc. can be used in combination as necessary to improve the abrasion resistance of the coating film.

Binding materials for the magnetic layer and back coat layer of the tape-shaped magnetic recording medium obtained by the present invention include polyvinyl chloride resin, polyurethane resin, cellulose resin,
Thermoplastic resins such as polyester resins, acrylic resins, and rubber resins are combined with isocyanate compounds, and resins with radiation-sensitive unsaturated double bonds (
A wide variety of conventionally known methods can be used, such as those obtained by irradiating a combination of compounds (compounds).

The elastic modulus of the magnetic layer and back coat layer of the tape-shaped magnetic recording medium obtained by the present invention depends on the type and combination of binders, and the blending ratio of powder components such as magnetic powder and non-magnetic powder with the binder. Adjustment is possible by changing.

[0023] In kneading and dispersing the paint for the magnetic layer and backcoat layer obtained in the present invention, various kneading machines such as a roll mill, a kneader, an attritor, a double planetary mixer, a high-speed mixer, a high-speed stone mill, an agitator mill, Sand mills, pin mills, ball mills, pebble mills, high-speed stirrers, ultrasonic dispersers, and the like can be used alone or in combination.

Hereinafter, embodiments of the present invention will be specifically explained using a videotape as an example. It should be noted that all parts of components mentioned in the examples indicate parts by weight.

First, a magnetic layer paint and a back coat layer paint were prepared according to the following procedure. <Preparation of paint for magnetic layer (M1)> Ferromagnetic Co-containing γ-Fe2O3
--- 1
00 parts polyurethane resin

--- 10 parts Hydroxyl group-containing vinyl chloride copolymer resin
--- 10 parts α-Al2O3

--- Part 7
Carbon black

--- 1 part myristic acid

--- 2 parts Butyl stearate
---
1 part mixed organic solvent (MEK/toluene/cyclohexanone = 3:2:1)

--- 25
0 parts The above composition was kneaded and dispersed using a pressure kneader and a sand mill, and then 5 parts of a polyisocyanate compound was added and mixed. ) was adjusted. <Preparation of magnetic layer paints (M2) and (M3)> In the preparation of magnetic layer paint (M1), the parts of polyurethane resin and hydroxyl group-containing vinyl chloride copolymer resin (10 parts and 10 parts)
Magnetic paints (M2) and (M3) were prepared in exactly the same manner as (M1) except that they were changed to 8 parts and 12 parts, and 12 parts and 8 parts, respectively.
) was obtained.

<Preparation of back coat layer paint (B1)>
Carbon black
--- 1
00 parts α-Al2O3

--- 2 parts Polyurethane resin
--- 45 copies
nitrocellulose resin
---
45 parts mixed organic solvent (MEK/toluene/cyclohexanone = 2:2:1)

---
After mixing and dispersing 600 parts of the above composition in a ball mill and taking out the kneaded product, 10 parts of a polyisocyanate compound and a mixed organic solvent (MEK/toluene/cyclohexanone = 2
:2:1) was added to the kneaded material, and the mixture was stirred and mixed using a high-speed stirrer, and the mixture was filtered through a filter with an average pore size of 2 μm to prepare a back coat layer paint (B1).

<Preparation of back coat layer paint (B2)>
In preparing the back coat layer paint (B1), the same procedure as (B1) was used except that the nitrocellulose resin (45 parts) was replaced with a hydroxyl group-containing vinyl chloride copolymer resin (45 parts). B2) was prepared.

<Preparation of back coat layer paint (B3)>
In preparing the backcoat layer paint (B2), the same procedure as (B2) was carried out except that the numbers of polyurethane resin and hydroxyl group-containing vinyl chloride copolymer resin were changed from 45 parts to 5 parts, 40 parts, and 50 parts, respectively. Paint for back coat layer (B3
) was prepared.

<Back coat layer paint (B4) and (
Preparation of B5)> In the preparation of the back coat layer paint (B1), the numbers of polyurethane resin and nitrocellulose resin were changed from 45 parts each to 40 parts and 50 parts, and 30 parts and 60 parts, respectively. Back coat layer paints (B4) and (B5) were prepared in exactly the same manner as described above.

(Example 1) Magnetic layer paint (M1) was mixed with 8.
A 5 μm thick aromatic polyamide film (elastic modulus in the longitudinal and width directions = 1300 kg/mm2) was coated, oriented in a magnetic field, and dried, and then mirror-finished using a calender roll to create a 2.5 μm thick magnetic film. A raw fabric roll having layers was created. Paint for back coat layer (B1) is applied to the opposite side of the magnetic layer on this raw roll, dried, and then
After heat treatment at 0℃ for 16 hours, the total thickness was 11.6μm (
A magnetic tape raw roll having a back coat layer thickness of 0.6 μm was obtained. This was cut into 1/2 inch width to create a videotape sample (250 m long).

(Example 2) (M2) was added to the paint for the magnetic layer.
A videotape sample (250 m long) was prepared in exactly the same manner as in Example 1, except that (B2) was used as the paint for the back coat layer.

(Example 3) (M3) was added to the paint for the magnetic layer.
A videotape sample (250 m long) was prepared in exactly the same manner as in Example 1, except that (B4) was used as the paint for the back coat layer.

(Examples 4 to 5) A 250 m film was manufactured in exactly the same manner as in (Example 1) except that the aromatic polyamide film in (Example 1) was changed to 9.5 μm thick and 7.5 μm thick, respectively. long videotape sample (total thickness = 12.6μ
m and 10.6 μm).

(Examples 6 to 7) Videotape samples were prepared in the same manner as in (Example 1) except that the heat treatment conditions in (Example 1) were changed to 45°C for 40 hours and 75°C for 10 hours. (250m length) was created.

(Comparative Examples 1 and 2) The aromatic polyamide film (9.5 μm thick) of (Example 4) was
ET (elastic modulus in longitudinal and width directions = 600 kg/mm2)
and PEN (elastic modulus in longitudinal and width directions = 800 kg/m
A videotape sample (250 m long) was prepared in exactly the same manner as in Example 1, except that the length of the sample was changed to 250 m2).

(Comparative Example 3) (M2) was added to the paint for the magnetic layer.
A videotape sample (250 m long) was prepared in exactly the same manner as in Example 1, except that (B3) was used as the paint for the back coat layer.

(Comparative Example 4) (M3) was added to the paint for the magnetic layer.
A videotape sample (250 m long) was prepared in exactly the same manner as in Example 1, except that (B5) was used as the paint for the back coat layer.

(Comparative Example 5) A videotape sample (250 m length) was prepared in exactly the same manner as in (Example 1) except that no heat treatment was performed.

(Comparative Example 6) In (Example 1), heat treatment was performed at 60° C. for 16 hours after the formation of the magnetic layer, but no heat treatment was performed after the formation of the back coat layer. A videotape sample (250 m
long) was created.

(Comparative Example 7) In (Example 1), the order of formation of the magnetic layer and back coat layer was reversed, and heat treatment was performed at 60° C. for 16 hours only after the formation of the back coat layer. A videotape sample (
250m long) was created.

(Comparative Example 8) A 250 m long videotape sample (total thickness = 9.1 μm).

(Comparative Example 9) (Example 1) except that the heat treatment conditions were 30°C and 60 hours.
A videotape sample (250 m length) was prepared in exactly the same manner as described above.

(Comparative Example 10) (Example 1) except that the heat treatment conditions were 90°C and 6 hours.
A videotape sample (250 m length) was prepared in exactly the same manner as described above.

The various videotape samples obtained in the above Examples and Comparative Examples were subjected to the following evaluation tests. (1) Elastic modulus (kg/m2) The elastic modulus of the coating film (magnetic layer, back coat layer) and base film was measured using a universal tensile compression tester manufactured by Orientech. The elastic modulus of the magnetic layer and back coat layer can be determined by measuring the Young's modulus of a sample tape in which a magnetic layer or back coat layer has been applied to a base film, and the Young's modulus of the base film alone, and using both measured values (Equation 1). ),
Each value was calculated according to (Equation 2).

[0045]

[Math 1]

[0046]

[Math 2]

(2) Curling property The curling property was measured by measuring the curling property in the width direction of each sample tape. Curls with the magnetic layer on the inside are shown as +, and curls with the back coat layer on the inside are shown as -. It was shown in Regarding the size of the curl, (Fig. 1) shows the height h (
mm). (3) C/N (dB) Each sample tape was wound into a cassette half, and the ratio (C/N) between a 7 MHz signal and 5 MHz noise was measured using an S-VHS VTR. The values in the table are shown as relative comparison values with the measured values of the reference tape. (4) Running durability of tape After running each sample tape 100 times in an environment of 40°C and 80% RH, visually check the winding appearance of each sample tape and changes in tape shape (folding, stretching, etc.) They were observed and evaluated on a three-level scale: ○ (no change to almost no change), △ (slight change; no practical problem), and × (change to noticeable change; practically problematic).

The evaluation results for each sample tape are shown in (Table 1).

[0049]

[Table 1]

As is clear from Table 1, according to the present invention, a tape-shaped magnetic recording medium that can satisfy both electromagnetic characteristics and running durability can be obtained.

[0051]

Effects of the Invention As detailed above, aromatic polyamide with excellent rigidity and heat resistance is used as the non-magnetic support of the tape-shaped magnetic recording medium, and the back coat layer and magnetic In addition to limiting the ratio of the elastic modulus of the layer,
By applying heat treatment with both the magnetic layer and back coat layer formed, the rigidity of the entire tape can be improved and curling in the width direction of the tape can be suppressed. It becomes possible to provide a tape-shaped magnetic recording medium that can satisfy both electromagnetic conversion characteristics and running durability.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing examples of curls in the width direction of videotape samples obtained in Examples and Comparative Examples of the present invention, and locations where a value h indicating the size of the curls was measured.

[Explanation of symbols]

1 Back coat layer 2 Non-magnetic support 3 Magnetic layer

Claims (3)

[Claims] Claim 1: A magnetic layer mainly composed of ferromagnetic powder and a binder on one side of a non-magnetic support, and a back coat layer mainly composed of a non-magnetic inorganic powder and a binder on the other side. , wherein the nonmagnetic support is made of aromatic polyamide, and the ratio of the elastic modulus of the back coat layer to the elastic modulus of the magnetic layer is 0. .4 to 0.7, and a method for manufacturing a tape-shaped magnetic recording medium, characterized in that the back coat layer and the magnetic layer are heat-treated in a state in which they are respectively formed. 2. The method for manufacturing a tape-shaped magnetic recording medium according to claim 1, wherein the total thickness is 10 to 13 μm. [Claim 3] The heat treatment is performed at a temperature of 40°C to 80°C.
2. The method of manufacturing a tape-shaped magnetic recording medium according to claim 1, comprising the step of holding the magnetic recording medium for 48 hours.