JPH04366421A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with improved direct-magnet conversion characteristics where a surface smoothness of a magnetic layer is proper regardless of storage for a long time in a wound state by forming a magnetic layer whose surface roughness is a center line average roughness of Ra which is 0.025mum or less, winding up a magnetic recording medium master roll where this magnetic layer is formed, winding again at least once at a temperature exceeding 40 deg.C, and performing heat treatment while performing rolling exchange. CONSTITUTION:After forming a magnetic layer 3 whose surface roughness is a center line average roughness Ra of 0.025mum or less, a magnetic recording medium master roll where this magnetic layer is formed is taken up, is wound again for at least once at a temperature exceeding 40 deg.C, and then is heat-treated while performing rolling exchange.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method of manufacturing a magnetic recording medium, and more particularly, the present invention relates to a method of manufacturing a magnetic recording medium, and more particularly, the surface smoothness of the magnetic layer is maintained well even when stored in a wound state for a long period of time, and the recording and reproducing characteristics are improved. The present invention relates to a method for manufacturing a magnetic recording medium with excellent electromagnetic conversion characteristics that does not deteriorate or increase noise.

0002

[Prior Art] Generally, magnetic recording media are produced by applying a magnetic paint prepared by mixing and dispersing magnetic powder, binder resin, organic solvent, etc. onto the surface of a substrate such as a polyester film, and then drying it to form a magnetic layer. Or, it is made by depositing a ferromagnetic material by vacuum evaporation or the like to form a ferromagnetic metal thin film layer, improving recording and reproducing output, reducing noise,
In order to achieve high-density recording, the magnetic layer is surface-finished by super-calendering to smooth the surface of the magnetic layer. In addition, in order to improve running properties, a back coat layer containing non-magnetic powder, binder resin, etc. is formed on the back surface opposite to the magnetic layer, and the back surface is appropriately roughened. ing. However, if a magnetic recording medium with a smooth magnetic layer surface is stored in a wound state for a long period of time, the unevenness on the back side of the magnetic recording medium will be transferred and the surface of the magnetic layer will become rough and recording This tends to reduce reproduction output and increase noise, and this tendency is particularly noticeable in magnetic recording media in which a back coat layer is formed on the back surface. For this reason, in recent years, improvements have been made to the components and structure of the backcoat layer, as well as the components and structure of the magnetic layer. to prevent it from being transferred to the surface of the magnetic layer,
Attempts have been made to prevent a decrease in recording/reproduction output and an increase in noise. (JP 60-32122, JP 2-265016)

0003

[Problem to be solved by the invention] However, the back cover
In the method of preventing the unevenness of the back coat layer from being transferred to the surface of the magnetic layer by improving the components and structure of the back coat layer and the components and structure of the magnetic layer, the components and structure of the back coat layer and the magnetic layer are improved. Although it is possible to prevent the unevenness of the back coat layer from being transferred to the surface of the magnetic layer, there are restrictions when trying to improve other electromagnetic conversion characteristics, etc.
There are cases where electromagnetic conversion characteristics etc. cannot be sufficiently improved.

0004

[Means for Solving the Problems] The present invention has been made as a result of various studies to overcome the above-mentioned problems.The present invention has been made as a result of various studies to overcome the above-mentioned problems.
After forming a magnetic layer with a thickness of 5 μm or less, the magnetic recording medium with this magnetic layer formed thereon may be rolled up as it is, or after a back coat layer is further formed on the back side of the magnetic recording medium, and heated at 40°C or higher. Re-roll at least once at high temperature,
By heat-treating while rewinding, there is no restriction on the electromagnetic conversion characteristics of the magnetic recording medium, and even if the magnetic recording medium is stored for a long period of time in a wound state, the unevenness on the back side of the magnetic recording medium does not change to the surface of the magnetic layer. to prevent it from being transferred to
This prevents the surface of the magnetic layer from becoming rough due to transfer, thereby preventing a decrease in recording and reproducing output and an increase in noise.

According to the present invention, an original magnetic recording medium having a magnetic layer formed on the surface or a back coat layer formed on the rear side is wound up and heated at a temperature of at least 40°C. Since the heat treatment is performed while being re-wound and re-wound one or more times, the state of contact between the magnetic layer of the original magnetic recording medium and the back surface having the convex portion during heat treatment is schematically shown in Figure 1. , a recess 4a formed on the surface of the magnetic layer 3 by the back surface 2 of the magnetic recording medium original having the convex portion 1 when the convex portion 1 of the back surface 2 contacts the surface of the magnetic layer 3 for the first time; Next, the original magnetic recording medium is re-wound and re-wound to remove the concave portion 4b formed when the convex portion 1 of the back surface 2 contacts the surface of the magnetic layer 3, and the re-wound and re-winding of the original magnetic recording medium. Rewinding the original magnetic recording medium so that the concave portion 4c formed when the convex portion 1 of the back surface 2 comes into contact with the surface of the magnetic layer 3,
Each time the magnetic recording medium is re-wound, the contact position between the back surface 2 of the original magnetic recording medium and the surface of the magnetic layer 3 changes little by little, and as shown in FIG. 2, the maximum surface roughness ha of the magnetic layer surface is small and the surface This results in a magnetic layer with good smoothness. Therefore, the original magnetic recording medium is repeatedly re-wound and re-wound during heat treatment.
The smoothness of the surface of the magnetic layer is well maintained. In addition, the magnetic layer formed by applying magnetic paint to the surface of the substrate is heat treated to sufficiently harden the binder resin in the magnetic layer and remove residual solvent, making the surface of the magnetic layer less likely to deform. ,
Furthermore, for the ferromagnetic metal thin film layer formed on the substrate surface by vacuum evaporation etc., the residual stress generated during the film formation process is sufficiently relaxed and stabilized by heat treatment, so that any of these magnetic layers are Even in the case of a magnetic recording medium, the unevenness transferred by the back surface of the magnetic recording medium becomes smaller, and the surface smoothness of the magnetic layer becomes better. A magnetic recording medium with excellent conversion characteristics can be obtained.

On the other hand, when the original magnetic recording medium on which the magnetic layer is formed is heat-treated at a temperature of 40° C. or higher without being re-wound or re-wound, the heat treatment process shown in FIG. As shown in a schematic diagram of the contact state between the magnetic layer of the magnetic recording medium original fabric and the back surface having convex portions, during the heat treatment, the convex portions 1 on the back side 2 of the magnetic recording medium original fabric are on the same surface of the magnetic layer 3. Since the convex portion 1 is in contact with the magnetic layer 3, the convex portion 1 is pushed deeply into the surface of the magnetic layer 3 over time, and a deep concave portion 4d is formed on the surface of the magnetic layer 3. Therefore, if heat treatment is performed without rewinding or rewinding the original magnetic recording medium while it is still wound, as shown in FIG. The magnetic layer is formed on the surface, and the surface of the magnetic layer becomes rough in a short time compared to room temperature.

[0007] In the present invention, the magnetic recording medium material is wound up, re-wound at least once, and the heat treatment performed while rewinding is performed by leaving it in a heating tank at a temperature of 40° C. or more for one hour or more. The binder resin in the magnetic layer will not be sufficiently cured at a temperature lower than 40°C, and the ferromagnetic metal thin film layer formed on the substrate surface by vacuum deposition etc. Since the residual stress etc. are not sufficiently relaxed, the irregularities on the back surface of the magnetic recording medium are transferred to the surface of the magnetic layer, resulting in a roughened surface of the magnetic layer.

[0008] Furthermore, after winding up the original magnetic recording medium on which the magnetic layer is formed, rewinding and rewinding are preferably performed at least once during heat treatment, and the number of rewinding and rewinding is large. Indeed, the surface smoothness of the magnetic layer is improved. In addition, after winding the original magnetic recording medium, rewinding and rewinding performed during heat treatment are preferably performed in a heated state. You may.

[0009] Furthermore, in the case of a magnetic recording medium material that is re-wound and re-wound at least once during such heat treatment, the smoother the surface of the magnetic layer, the easier it is to transfer the unevenness on the back surface of the magnetic recording medium material. effectively prevented. For this reason, it is particularly effective when manufacturing magnetic tape for high-density magnetic recording such as 8 mm video tape, but even magnetic tape with a considerably rough and uneven back surface can be used. The contact pressure caused by the winding pressure of magnetic tape on the reel or hub of a magnetic cartridge can only roughen the magnetic surface to a center line average roughness Ra of 0.025 μm at most, and the roughness of the magnetic layer surface For magnetic tapes whose centerline average roughness Ra exceeds 0.025 μm, the influence of transfer can be ignored. Therefore, the surface roughness of the magnetic layer is the center line average roughness Ra of 0.
It is effective for objects with a diameter of 0.025 μm or less.

[0010] The magnetic layer formed on the substrate is prepared by mixing and dispersing magnetic powder with a binder resin, an organic solvent, and other necessary components, and then applying this magnetic coating onto the substrate and drying it. It is also formed by depositing a ferromagnetic material on a substrate by means such as vacuum evaporation, ion plating, sputtering, or plating.

[0011] When preparing a magnetic paint, magnetic powders used include γ-Fe2 O3 powder, Fe3 O4
powder, intermediate oxide powder of γ-Fe2O3 powder and Fe3O4 powder, Co-containing γ-Fe2O3 powder,
Any magnetic powder that is generally used for magnetic recording media is suitable, such as Co-containing Fe3O4 powder, CrO2 powder, barium ferrite powder, strontium ferrite powder, and metal powders such as Fe powder, Co powder, and Fe-Ni powder. used as.

[0012] Also, as the binder resin, vinyl chloride-
Vinyl acetate copolymer, polyvinyl butyral resin,
All conventionally used materials for magnetic recording media, such as cellulose resins, polyurethane resins, polyester resins, and isocyanate compounds, are used, and as organic solvents, cyclohexanone, methyl ethyl ketone, ethyl acetate, Organic solvents commonly used in magnetic recording media, such as benzene, toluene, xylene, dimethylformamide, dioxane, and tetrahydrofuran, are used alone or in combination.

[0013] The magnetic paint contains dispersants, abrasives,
Lubricants, antistatic agents, and other substances that are generally added to magnetic paints may be added as necessary.

[0014] When forming a ferromagnetic metal thin film layer by vacuum evaporation or the like, the ferromagnetic material used is Co.
, Ni, Fe, Co-Ni, Co-Cr, Co-P, C
Generally, o-Ni-P, Fe-Ni, Fe-Co, etc.
Any of the ferromagnetic materials used when forming the ferromagnetic metal thin film layer are used, and the ferromagnetic metal thin film layer formed of these ferromagnetic materials has a thickness within the range of 0.03 to 1 μm. is preferable.

[0015] On the back surface of the substrate on which the magnetic layer has been formed, a back coat layer is formed as necessary, and this back coat layer is made of non-magnetic powder such as carbon black or calcium carbonate. , a binder resin, an organic solvent, and other necessary ingredients are mixed and dispersed to prepare a back coat layer paint, and this back coat layer paint is applied to the back side of the substrate on which a magnetic layer is formed, and dried. It is formed by

Here, the binder resin and organic solvent used for forming the back coat layer are preferably the same as those used for forming the magnetic layer.
Dispersants, lubricants, etc. may also be added if necessary.

The substrate for forming the magnetic layer and back coat layer may be made of plastics such as polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, and polycarbonates. Films, as well as metal films made of aluminum alloys, titanium alloys, etc., are all suitable.

[0018]

[Example] Next, an example of the present invention will be described. Example 1 Ferromagnetic metallic iron powder (coercive force 1600 Oe, saturation magnetization 100 parts by weight, amount 1)
20 emu/g, major axis diameter 0.18 μm, axial ratio 10)
Hydroxyl group-containing vinyl chloride resin
1
0 〃 Thermoplastic polyurethane resin

7 Alumina (particle size 0
．． 2μm)
8 〃
myristic acid

2 Red red iron (particle size 0.8μ
m)
2 Carbon black (manufactured by Tokai Carbon Co., Ltd., Seat 5H, particle size
2〃 20mμm) Cyclohexanone

70 Toluene

70
After mixing and dispersing the above composition in a ball mill for 96 hours, 5 parts by weight of a trifunctional polyisocyanate compound was further added and stirred to prepare a magnetic paint. This magnetic paint was applied to the surface of a biaxially oriented polyethylene terephthalate film having a thickness of 10 μm so that the thickness after drying would be 2.5 μm, and after drying, calendering was performed to form a magnetic layer.

Next, a back coat layer composition was prepared by mixing and dispersing the following back coat layer composition in a ball mill for 96 hours. biaxially oriented polyethylene terephthalate formed
A back coat layer was formed on the back side of the coat film so that the thickness after drying was 1.0 μm, and the coated layer was dried to form a back coat layer, and the coated film was wound onto a take-up roll to prepare a magnetic recording medium material. Back coat layer composition Carbon black (manufactured by Tokai Carbon Co., Ltd., Sheet 5H, particle size 60 parts by weight 20
mμm) Red red iron (particle size 0.8μm)

2.5 Calcium carbonate (particle size 0.
05μm)
30 〃 Thermoplastic polyurethane resin
45 〃
nitrocellulose

40 〃 Trifunctional isocyanate compound
15 〃 Cyclohexanone
330 〃
toluene

330 〃

Next, the obtained magnetic recording medium original fabric was heat-treated by leaving it in an atmosphere at 60° C. for 24 hours, and during this heat treatment, the magnetic recording medium original fabric was re-wound every hour. I did a rewind. Thereafter, it was cut to a predetermined width to make magnetic tape.

Example 2 In the heat treatment of the original magnetic recording medium in Example 1,
An original magnetic recording medium was prepared in the same manner as in Example 1, except that the rewinding and rewinding during the heat treatment was changed to 11 times every 2 hours instead of 23 times every 1 hour. I created a pool.

Example 3 In the heat treatment of the original magnetic recording medium in Example 1,
A magnetic recording medium material was prepared in the same manner as in Example 1, except that the rewinding and rewinding during the heat treatment was changed to every 4 hours, 5 times instead of every 1 hour, 23 times. I created a pool.

Example 4 In the heat treatment of the original magnetic recording medium in Example 1,
A magnetic recording medium material was prepared in the same manner as in Example 1, except that the rewinding and rewinding during the heat treatment was changed to 3 times every 6 hours instead of 23 times every 1 hour. I created a pool.

Example 5 In the heat treatment of the original magnetic recording medium in Example 1,
A magnetic recording medium material was prepared in the same manner as in Example 1 except that the rewinding and rewinding during the heat treatment was changed to once every 12 hours instead of 23 times every hour. I created a pool.

Example 6 A biaxially oriented polyethylene terephthalate film with a thickness of 10 μm was loaded into a high frequency sputtering device, and a cobalt-chromium alloy (weight ratio 8:2) was high frequency sputtered to form a biaxially oriented polyethylene terephthalate film. A ferromagnetic metal thin film layer made of a cobalt-chromium alloy and having a thickness of 0.2 μm was formed on the surface of the film. Next, in the same manner as in Example 1, a back coat layer was formed on the back side of the biaxially oriented polyethylene terephthalate film with the ferromagnetic metal thin film layer formed on the surface, and further heat treated to give a predetermined width. It was cut into magnetic tape.

Example 7 In the heat treatment of the original magnetic recording medium in Example 6,
An original magnetic recording medium was prepared in the same manner as in Example 6, except that the rewinding and rewinding during the heat treatment was changed to 11 times every 2 hours instead of 23 times every 1 hour. I created a pool.

Example 8 In the heat treatment of the original magnetic recording medium in Example 6,
A magnetic recording medium material was prepared in the same manner as in Example 6, except that the rewinding and rewinding during the heat treatment was changed to every 4 hours, 5 times instead of every 1 hour, 23 times. I created a pool.

Example 9 In the heat treatment of the original magnetic recording medium in Example 6,
A magnetic recording medium material was prepared in the same manner as in Example 6, except that the rewinding and rewinding during the heat treatment was changed to 3 times every 6 hours instead of 23 times every 1 hour. I created a pool.

Example 10 In the heat treatment of the original magnetic recording medium in Example 6,
A magnetic recording medium material was prepared in the same manner as in Example 6, except that the rewinding and rewinding during the heat treatment was changed to once every 12 hours instead of 23 times every hour. I created a pool.

Comparative Example 1 In the heat treatment of the original magnetic recording medium in Example 1,
A magnetic recording medium material was prepared in the same manner as in Example 1, except that the heat treatment was performed without rewinding or rewinding during the heat treatment, and a magnetic tape was made.

Comparative Example 2 In the heat treatment of the original magnetic recording medium in Example 6,
A magnetic recording medium material was prepared in the same manner as in Example 6, except that the heat treatment was performed without rewinding or rewinding during the heat treatment, and a magnetic tape was produced.

Comparative Example 3 A magnetic recording medium material was prepared in the same manner as in Example 1, except that the heat treatment of the magnetic recording medium material was omitted, and a magnetic tape was made.

Comparative Example 4 A magnetic recording medium material was prepared in the same manner as in Example 6, except that the heat treatment of the magnetic recording medium material was omitted, and a magnetic tape was made.

The surface roughness of the magnetic layer before heat treatment was examined for the magnetic recording media obtained in each of the Examples and Comparative Examples, and the noise level was measured. In addition, the magnetic tape obtained in each example and comparative example was wound into an 8 mm video cassette and stored for 60 days, and the surface roughness of the magnetic layer was examined before and after storage, and the noise level was measured. . The surface roughness of the magnetic layer was determined by measuring the centerline average roughness Ra at a cutoff of 0.08 mm using a stylus type surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd. Also, the noise level is 7M for an 8mm VTR.
Hz signal was input and the noise level at 6 MHz was measured when reproduced, and the measured values of the original magnetic recording medium and magnetic tape before heat treatment in Examples 1 and 2 were set as 0 dB, respectively, and their relative values were calculated. It was evaluated by The surface roughness of the back coat layer of the magnetic recording medium material and magnetic tape obtained in each Example and Comparative Example was 0.014 μm in terms of center line average roughness Ra. Table 1 below shows the measurement results.

[0035]

Further, the relationship between the number of rewinding times of each magnetic tape obtained in each Example and Comparative Examples 1 and 2 and the surface roughness of the magnetic layer is shown graphically in FIG. Graph A is from Example 1
Graph B shows the relationship between the number of rewindings of the magnetic tape obtained in Examples 6 to 10 and Comparative Example 1 and the surface roughness of the magnetic layer. This figure shows the relationship between the number of tape rewinds and surface roughness.

Further, the relationship between the number of rewinding times of each magnetic tape obtained in each Example and Comparative Examples 1 and 2 and the noise level is shown in a graph in FIG. Graph A represents the relationship between the number of rewindings of the magnetic tape and the noise level obtained in Examples 1 to 5 and Comparative Example 1, and graph B shows the relationship between the number of rewindings of the magnetic tape and the noise level obtained in Examples 6 to 10 and Comparative Example 2. This figure shows the relationship between the number of rewindings of the obtained magnetic tape and the noise level.

[0038]

Effects of the Invention As is clear from Table 1 and FIGS. 5 and 6 above, in all of the magnetic tapes obtained in Comparative Examples 1 to 4, the surface of the magnetic layer became rough after storage. Although the noise level has increased, the magnetic tape obtained with this invention (
In Examples 1 to 10), the surface of the magnetic layer did not become rough even after storage for 60 days, and no increase in noise level was observed. It can be seen that even after storage for a long period of time, the surface of the magnetic layer does not become rough, the recording and reproducing characteristics do not deteriorate, and a magnetic recording medium with excellent electromagnetic conversion characteristics can be obtained.

[0039]

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the state of contact between the magnetic layer and the back surface having convex portions of a magnetic recording medium material during heat treatment in the present invention.

FIG. 2 is a partially enlarged cross-sectional view of the surface of the magnetic layer of the original magnetic recording medium fabricated by the manufacturing method of the present invention.

FIG. 3 is a schematic diagram showing the state of contact between the magnetic layer of the original magnetic recording medium and the back surface having convex portions during conventional heat treatment.

FIG. 4 is a partially enlarged cross-sectional view of the surface of a magnetic layer of a magnetic recording medium material formed by a conventional manufacturing method.

FIG. 5 is a diagram showing the relationship between the number of times each magnetic tape was wound and the surface roughness of the magnetic layer obtained in each Example and Comparative Examples 1 and 2.

FIG. 6 is a diagram showing the relationship between the number of rewinding times of each magnetic tape obtained in each Example and Comparative Examples 1 and 2 and the noise level.

[Explanation of symbols]

1 Convex part 2　Back side of magnetic recording medium original fabric 3 Magnetic layer 4a, 4b, 4c recess

Claims (2)

[Claims] 1. After forming a magnetic layer on the surface of the substrate, the surface roughness of which is 0.025 μm or less in terms of center line average roughness Ra,
Winding up the original magnetic recording medium on which this magnetic layer is formed,
A method for producing a magnetic recording medium, which comprises rewinding at least one time at a temperature of 40°C or more and heat-treating while performing rewinding. 2. After forming a magnetic layer on the surface of the substrate, the magnetic layer having a center line average roughness Ra of 0.025 μm or less,
A back coat layer is further formed on the back side of the magnetic recording medium material on which this magnetic layer is formed, and the magnetic recording medium material having this back coat layer is wound up at least once at a temperature of 40°C or higher. A method for producing a magnetic recording medium characterized by heat treatment while rewinding and rewinding.