JP2005174508A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a magnetic recording medium by which the magnetic recording medium having enhanced durability can be obtained by preventing the sticking of a release agent to the surface of a protective layer. <P>SOLUTION: When the magnetic recording medium formed with a metal thin film magnetic layer, a protective layer and a lubricant layer successively on one surface of a non-magnetic substrate and formed with a back coat layer on the other surface is manufactured, a film having a release agent containing a coating layer on one surface thereof is used as a non-magnetic substrate and after the metal thin film magnetic layer is vapor-deposited on the surface opposite to the release agent containing coating layer, the back coat layer is formed on the release agent containing coating layer of the non-magnetic substrate before the protective layer is formed on the metal thin film magnetic layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a magnetic recording medium (hereinafter, also simply referred to as “medium”), and more particularly to a method for manufacturing a vapor deposition type magnetic recording medium in which durability is improved by improving a manufacturing process.

  As a kind of magnetic recording medium, there is a so-called vapor deposition type magnetic recording medium in which a metal thin film is formed by vapor deposition on a nonmagnetic support (base). The vapor deposition type medium does not contain a binder as compared with the coating type medium, so the filling rate of the magnetic layer is high, the saturation magnetization can be increased, and the film can be thinned, so that the wavelength is short. This has the advantage of being advantageous in high-density recording, such as being able to suppress recording demagnetization.

  The base used for such a vapor deposition type medium is required to have a very smooth surface property. Among these, the recording layer side is desired to be flatter from the viewpoint of spacing loss, and it is necessary to have fine protrusions from the viewpoint of maintaining durability. For this reason, a coating layer in which fine particles are dispersed is usually formed on the surface of the base recording layer.

  Further, the back coat layer side is desired to be smoother in order to improve the adhesion to the cooling can during vapor deposition to improve the surface property of the vapor deposition film and to form a fine recording layer. . However, if both surfaces are smooth, it is difficult to wind up the support, and therefore it is necessary to provide a coating layer on the backcoat layer side surface from the viewpoint of slipperiness.

  However, such a base having a coating layer on both sides has a problem that the coating layers are likely to block each other when wound into a roll. Therefore, when the overlapped part is peeled off again, when a part of one coating layer moves to the other, minute irregularities (surface roughness) occur, and when a magnetic layer is deposited thereon, It will cause problems such as lower output and worsening errors. Therefore, in this case, it is necessary to add a release agent to the coating layer to prevent blocking (for example, described in Patent Document 1).

On the other hand, the production of such a vapor deposition type magnetic recording medium has conventionally been performed by vapor deposition of a recording layer (vacuum process), formation of a protective layer (vacuum process), formation of a backcoat layer (in the atmosphere), topcoat layer (lubricant Layer) (in the atmosphere) and cutting (for example, see Patent Document 2). As a technique for improving the manufacturing process of such a vapor deposition type medium, for example, Patent Document 3 discloses a back coat layer on one surface of a nonmagnetic support, and a magnetic layer, a protective layer, and a top coat on the other surface. In forming each of the layers, a technique is described in which the backcoat layer, magnetic layer, protective layer, and topcoat layer are formed in vacuum throughout the entire process.
JP 2001-167426 A ([0026] etc.) JP 2000-149248 A ([Claims] etc.) JP 7-254148 A ([Claims], [0054], etc.)

  However, in such a conventional manufacturing process, when a base having a release agent-containing coating layer as described above is used, transfer of the release agent to the protective layer occurs during winding after the protective layer is formed. As a result, there is a problem that the adsorption of the lubricant coating liquid to the protective layer is inhibited and the durability is deteriorated. On the other hand, even if the concentration of the lubricant coating solution is increased, the durability cannot be balanced against changes in environmental conditions, and the problem cannot be solved sufficiently.

  Accordingly, an object of the present invention is to provide a method for manufacturing a magnetic recording medium that can obtain a magnetic recording medium having improved durability by solving the above-mentioned problems and preventing transfer of a release agent to the surface of the protective layer. Is to provide.

  As a result of intensive studies, the present inventors have found that the above problem can be solved by adopting the following configuration, and have completed the present invention.

That is, the method for producing a magnetic recording medium of the present invention includes a magnetic thin film magnetic layer, a protective layer, and a lubricant layer sequentially on one surface of a nonmagnetic support, and a backcoat layer on the other surface. When manufacturing recording media,
As the non-magnetic support, using a film having a coating layer containing a release agent on one side,
After depositing the metal thin film magnetic layer on the surface of the nonmagnetic support opposite to the release agent-containing coating layer, prior to forming the protective layer on the metal thin film magnetic layer, The back coat layer is formed on the release agent-containing coating layer of the nonmagnetic support.

In particular, the present invention has a coating layer on both sides as the nonmagnetic support, one of the coating layers is the release agent-containing coating layer, and the surface roughness Ra on both sides is 3 nm or less. This is effective when a polyethylene naphthalate (PEN) film is used. In the present invention, it is preferable that the residual solvent amount of the back coat layer immediately before the protective layer forming step is 7000 μg / m ² or less.

  According to the present invention, the above configuration can surely prevent the release agent from being transferred from the surface of the nonmagnetic support to the protective layer, and durability resulting from poor formation of the lubricant layer. Thus, it is possible to manufacture a magnetic recording medium in which the deterioration is prevented. As described above, Patent Document 2 describes a technique for forming the backcoat layer prior to the magnetic layer, the protective layer, and the topcoat layer. It is a vapor-deposited layer made of metal, and differs from the back coat layer of the present invention made of a coating film containing a binder resin, carbon black, inorganic powder, etc. in that the configuration and sufficient runnability and durability cannot be obtained. Is. In addition, unlike the technique of Patent Document 2 that is formed by a vacuum process, the back coat layer according to the present invention is formed by an application process in the atmosphere. It is considered difficult to apply to the problem of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail.
The method for producing a magnetic recording medium of the present invention is a so-called vapor deposition type in which a metal thin film magnetic layer, a protective layer, and a lubricant layer are sequentially provided on one surface of a nonmagnetic support, and a backcoat layer is provided on the other surface. This relates to a magnetic recording medium.

  In the present invention, after depositing a metal thin film magnetic layer on the surface opposite to the release agent-containing coating layer using a film having a coating layer containing a release agent on one side as a nonmagnetic support. Before forming the protective layer on the metal thin film magnetic layer, a backcoat layer is formed on the release agent-containing coating layer of the nonmagnetic support. That is, unlike the conventional method, the backcoat layer is formed on the release agent-containing coating layer of the nonmagnetic support before forming the protective layer on the metal thin film magnetic layer. For this reason, when the protective layer is formed, the surface of the release agent-containing coating layer is covered with the back coat layer, and the release agent may transfer onto the protective layer even during winding after the protective layer is formed. Absent. Therefore, the lubricant layer can be formed on the protective layer without any problem, and a magnetic recording medium can be produced without causing a decrease in durability. In the present invention, each of the formation of the magnetic layer (in vacuum), the formation of the backcoat layer (in the atmosphere), the formation of the protective layer (in the vacuum), and the formation of the lubricant layer (in the atmosphere) is performed according to the order of the above steps. Since the steps are sequentially performed, the steps in the vacuum and the steps in the air are alternately performed.

  In the present invention, as long as the manufacturing process of the magnetic recording medium is performed according to the above order, other manufacturing conditions and materials used are not particularly limited, and can be appropriately selected according to a conventional method. However, for example, the configuration is as follows.

  As described above, the non-magnetic support used in the present invention is a film having a release agent-containing coating layer on the surface on which the back coat layer is formed. Examples include a layer formed and a release agent contained in one of the layers. The material for the nonmagnetic support is not particularly limited as long as it can withstand the metal thin film deposition process. For example, films such as polyethylene naphthalate, polyethylene terephthalate (PET), polyimide, polyamide, aramid, polyetheretherketone (PEEK), polysulfone and the like can be mentioned, particularly when a PEN film having the above coating layer is used. The present invention is effective. The release agent to be contained in the coating layer is not particularly limited and can be selected from known ones such as dimethylsiloxane. In addition, the thickness is appropriately selected depending on the application in which the magnetic recording medium is used. For example, when the magnetic recording medium is used as a data tape, the thickness is selected according to the recording capacity and the system requirement value. Usually, it is 3-10 micrometers. Further, the surface roughness Ra is preferably 3 nm or less on both surfaces, particularly about 0.5 to 1.5 nm.

As the magnetic material of the magnetic layer, pure metals such as Co and Fe, or Co—Ni, Co—Fe, Co—Ni—Fe, Co—Cr, Co—Cu, Co—Ni—Cr, Co—Pt, Alloys such as Co-Pt-Cr, Co-Cr-Ta, Co-Ni-B, Co-Ni-Fe, Co-Fe-B, and Co-Ni-Fe-B can be used. From the viewpoint of electromagnetic conversion characteristics, it is preferable to use Co or Co alloy. Usually, such a magnetic material is deposited directly on the nonmagnetic support or after vapor deposition of Ni on the nonmagnetic support to form a magnetic layer. The vapor deposition of the magnetic layer is performed when the inside of the vapor deposition chamber is evacuated to about 1.33 × 10 ⁻⁴ Pa (10 ⁻⁶ Torr), and then the magnetic material is melted with an electron gun and the entire magnetic material is melted. The shielding plate that blocks the melted magnetic material and the nonmagnetic support is removed, and vapor deposition is started on the cooling drum with respect to the nonmagnetic support running along the cooling can (drum). At this time, in order to control the magnetic characteristics, an oxidizing gas selected from oxygen, ozone, and nitrous oxide is introduced into the magnetic layer.

  Next, the back coat layer contains a binder resin and inorganic powder and / or carbon black, and a back coat paint in which these are mixed and dispersed in an organic solvent is applied to the surface of the support opposite to the magnetic layer. It is formed by. As the coating composition of the back coat paint, any composition can be used as long as it is used for this kind of magnetic recording medium. For example, the binder resin is a nitrocellulose resin, a polyurethane resin, an acrylic resin, an epoxy resin, a phenoxy resin, a polyester resin, etc., and these may be used alone or in combination as appropriate according to the characteristics and process conditions of the medium. Can do. Examples of the carbon black include furnace carbon black, thermal carbon black, acetylene black, and the like, and examples of the inorganic powder include calcium carbonate, alumina, α-iron oxide, and the like. The particle size of these particles may be appropriately selected from the electrical resistance and friction characteristics required for the medium. As the organic solvent, ketone-based or aromatic hydrocarbon-based, for example, methyl ethyl ketone, toluene, cyclohexanone, or the like can be used, and may be appropriately selected in consideration of the solubility of the binder resin to be used. The thickness of the back coat layer is preferably from 0.1 to 1.0 μm, particularly preferably from 0.3 to 0.6 μm.

In the present invention, the amount of residual solvent in the backcoat layer immediately before the protective layer forming step is preferably 7000 μg / m ² or less, particularly about 1000 to 5000 μg / m ² . If the residual solvent amount is more than 7000 μg / m ² , the backcoat layer forming surface may be lifted from the cooling can in the protective layer forming step, which may cause a problem of heat loss or base breakage, which may cause a decrease in yield. There is. The amount of residual solvent in the backcoat layer can be adjusted by appropriately changing the amount of solvent in the backcoat paint and the drying conditions of the backcoat layer. When the amount of solvent in the paint is large, it is also effective to preliminarily deaerate after application of the backcoat layer to evaporate the solvent in the layer.

The protective layer is provided for the purpose of preventing deterioration of the magnetic layer and is made of a carbon protective film or a hard film containing carbon as a main component, a so-called DLC film. In particular, a protective layer made of a DLC film is used. Here, in the present invention, “mainly containing carbon” means that the carbon content in the film is 60 to 80 atomic%, and hydrogen is usually included in addition to carbon. The atomic ratio (H / C) of hydrogen to carbon is preferably in the range of 0.25 to 0.66. Further, the “hard film” specifically means a film having a Vickers hardness of 6370 N / mm ² (650 kg / mm ² ) or more, and the hardness is 1.9 or more in terms of a refractive index. It has been found that a film having such a refractive index can approximate the hardness from the refractive index. For example, the Vickers hardness when the refractive index is 1.9 is 6370 N / mm ² (650 kg / mm ² ). The upper limit of the refractive index is not particularly limited, but is about 2.25, which corresponds to a Vickers hardness of 29400 N / mm ² (3000 kg / mm ² ). As a method of approximating the hardness from the refractive index, the refractive index of a hard film is measured with an ellipsometer, while the Vickers hardness is measured with a micro hardness meter (manufactured by NEC Corporation) to prepare a calibration curve in advance. The hardness can be known from the refractive index. Further, such a hard film forms an amorphous or a continuous phase close to it, and has broad peaks at 1560 cm ⁻¹ and 1330 cm ⁻¹ in Raman spectroscopic analysis. In the present invention, the term “DLC film” is used to mean such a “hard film mainly composed of carbon”.

  A method for forming the DLC film is not particularly limited, but preferably one of a plasma CVD method, an ionization vapor deposition method, and a sputtering method is used.

  Among these, details of the plasma CVD method are described in, for example, Japanese Patent Laid-Open No. 4-41672. The plasma in the plasma CVD method may be either direct current or alternating current, but it is preferable to use alternating current. When alternating current is used, it can be appropriately used from a few hertz to a microwave band. Further, ECR plasma described in “Diamond Thin Film Technology” (published by General Technology Center) can also be used.

When the DLC thin film is formed by the plasma CVD method, it is preferable to use a compound containing C and H as the source gas, but a compound containing C and a compound containing H can also be used together. Examples of the compound containing C and H include hydrocarbons such as CH ₄ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H ₈ , and C ₆ H ₆ , and examples of the compound containing C include CO, Examples of the compound in which CO _{2 and the} like contain H include H ₂ , H ₂ O, NH _{3 and the} like. Further, a compound containing neither C nor H, for example, a compound represented by NO _x such as NO, NO ₂ , N ₂ O, N ₂ or the like may be used in combination as necessary.

  What is necessary is just to determine suitably the flow volume of source gas at the time of performing plasma CVD according to the kind of source gas. The operating pressure is usually 1.33 to 66.5 Pa (0.01 to 0.5 Torr).

  After the formation of the protective layer, it is preferable to perform a surface activation treatment with plasma in order to increase the affinity between the surface of the protective layer and the lubricant. This surface activation treatment is preferably performed using oxygen or a gas containing oxygen. For example, oxygen, air, carbon dioxide gas, or the like can be used. As a post-treatment method, it is practical and preferable to use the same method as described above when forming the DLC film. The frequency in the surface activation treatment is preferably about 1 kHz to 40 MHz, which is the same as that at the time of forming the DLC film. In particular, if the frequency is in the range of 50 kHz to 13.56 MHz, the effect is easily exhibited.

A lubricant layer is provided on the protective layer in order to reduce the friction coefficient during running. As the lubricant component of the lubricant layer, a lubricant containing a fluororesin, a hydrocarbon ester, or a mixture thereof can be used. Specifically, for example, a basic structure includes a structure represented by R ¹ —A—R ² . here,
R ^{1 is} CF ₃ (CF ₂ ) _n- , CF ₃ (CF ₂ ) _n (CH ₂ ) _m- , CH ₃ (CH ₂ ) _p- , or H;
A: -COO -, - O-, or _{COOCH (C p H 2p + 1} ) CH 2 is COO-,
_{^{R 2: CF 3 (CF 2}} ) n -, CF 3 (CF 2) n (CH 2) m -, CH 3 (CH 2) p -, or H. However, unlike R ¹ and R ² , those satisfying n = 7 to 17, m = 1 to 3, and p = 7 to 30 are preferable. Further, if R ¹ and / or R ² are linear, the lubricating effect is large. If n is less than 7, the water repellent effect is low, and if n is greater than 17, a blocking phenomenon occurs between the lubricant and the nonmagnetic support or the back coat layer, and the friction does not decrease. Among these, a lubricant containing a fluororesin is particularly preferable. Further, two or more of these lubricants may be mixed and used.

  In forming the lubricant layer, the lubricant is dissolved in a solvent such as ketones, hydrocarbons, and alcohols to prepare a lubricant coating solution. Examples of ketones include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, cyclohexanone, and diethyl ketone. Examples of the hydrocarbons include normal systems such as hexane, heptane, octane, nonane, decane, undecane, and dodecane, and iso-series. Examples of alcohols include methanol, ethanol, propanol, isopropanol and the like. A lubricant layer can be formed by applying the prepared lubricant coating solution on the DLC film and drying it. The thickness of the lubricant layer is about several nm. The amount of the lubricant component can be adjusted by the concentration of the coating solution.

  Further, in the present invention, if desired, an S / N characteristic can be improved by providing an underlayer between the magnetic layer and the nonmagnetic support. The underlayer is a nonmagnetic or non-magnetic layer and can be formed by increasing the amount of oxygen introduced relative to the film thickness in the same manner as the magnetic layer. Specific film formation conditions for the underlayer, for example, the conveyance speed of the nonmagnetic support during film formation, the amount of introduced oxygen, and the like can be appropriately determined according to common usage, and are not particularly limited. In particular, as the supply gas at the time of film formation, it is preferable to use not only oxygen but also a gas containing at least one of inert gas such as Ar and nitrogen in oxygen. Can be further improved. This is because the presence of the inert gas causes the underlayer to grow in the form of particles and the micro unevenness increases, so that the magnetic layer grown on the underlayer is more strongly oriented in the film plane and the coercive force is increased. This is thought to be caused by this.

Hereinafter, the present invention will be described specifically by way of examples.
First, the compositions of the supports A to C and the back coat paints A to C used in the examples and comparative examples are shown below.

<Support A>
Polyethylene-2,6-naphthalenedicarboxylate pellets substantially free of inert particles are dried at 170 ° C. for 6 hours and then fed to an extruder and melted at 305 ° C. Then, it was extruded into a sheet form from an extruder and cooled and solidified on a casting drum to produce an unstretched film. The unstretched film thus obtained is preheated at 120 ° C., and further stretched by 3.7 times in the longitudinal direction while being heated by a 900 ° C. infrared heater from above 15 mm between low-speed and high-speed rolls, Then, the aqueous solution of the composition shown below was apply | coated to both surfaces of the film, respectively, and the coating layer was formed.

Composition of coating layer A (deposition layer forming surface):
(1) Acrylic-polyester resin (2) Epoxy compound: Multifunctional epoxy compound (3) Silica particles (average particle size 27 nm)
(4) Surfactant Thickness after drying of layer A: 5 nm

Composition of coating layer B (back coat layer forming surface):
(1) Copolyester (2) Silica particles (average particle size 60 nm)
(3) Hydroxypropylmethylcellulose (4) Surfactant (5) Release agent: Dimethylsiloxane B layer thickness after drying: 15 nm

  Subsequently, the film after forming the coating layer is supplied to a stenter, stretched by 4.9 times in the transverse direction at 150 ° C., and further heat treated while transversely stretching by 1.1 times at 200 ° C., and the thickness is 4.7 μm. A biaxially oriented film was obtained.

<Support B>
A support B was produced in the same manner as the support A, except that the thickness of the coating layer B of the support A after drying was adjusted to 20 nm. The final thickness of the support B was the same as that of the support A.

<Support C>
The thickness was the same as that of Support A except that 0.04% by weight of spherical silica having an average particle size of 55 nm was contained in polyethylene-2,6-naphthalenedicarboxylate during the production of the base film of Support A. A 4.7 μm film was prepared and used as the support C.

<Back coat paint A>
Coating composition carbon black (particle size 80 nm) 50 parts by weight Calcium carbonate (particle size 70 nm) 50 parts by weight Nitrocellulose 40 parts by weight (Asahi Kasei Kogyo Co., Ltd. (BTH1 / 2S))
Polyurethane resin (Toyobo Co., Ltd .: UR-6300) 60 parts by weight Methyl ethyl ketone 880 parts by weight Toluene 640 parts by weight Cyclohexanone 80 parts by weight Polyisocyanate (solid content 50%) 40 parts by weight (manufactured by Nippon Polyurethane Industry Co., Ltd .: Coronate L)

<Back coat paint B>
Coating composition carbon black (particle size 80 nm) 50 parts by weight Calcium carbonate (particle size 70 nm) 50 parts by weight Nitrocellulose 40 parts by weight (Asahi Kasei Kogyo Co., Ltd. (BTH1 / 2S))
Polyurethane resin (Toyobo Co., Ltd .: UR-6300) 60 parts by weight Methyl ethyl ketone 800 parts by weight Toluene 640 parts by weight Cyclohexanone 160 parts by weight Polyisocyanate (solid content 50%) 40 parts by weight (manufactured by Nippon Polyurethane Industry Co., Ltd .: Coronate L)

<Back coat paint C>
Coating composition carbon black (particle size 80 nm) 50 parts by weight Calcium carbonate (particle size 70 nm) 50 parts by weight Nitrocellulose 40 parts by weight (Asahi Kasei Kogyo Co., Ltd. (BTH1 / 2S))
Polyurethane resin (Toyobo Co., Ltd .: UR-6300) 60 parts by weight Methyl ethyl ketone 800 parts by weight Toluene 600 parts by weight Cyclohexanone 200 parts by weight Polyisocyanate (solid content 50%) 40 parts by weight (manufactured by Nippon Polyurethane Industry Co., Ltd .: Coronate L)

Example 1
On one surface of the 4.7 μm-thick PEN support A, a Co 100% magnetic layer having a total thickness of 0.2 μm was formed by vapor deposition. Next, the backcoat paint A was applied onto the opposite surface by a die nozzle method so that the thickness after drying was 0.4 μm, and dried at 110 ° C. to form a backcoat layer. Next, by introducing ethylene and applying a predetermined discharge frequency (50 kHz), a plasma-polymerized hard carbon film (DLC film) was formed to a thickness of 0.01 μm on the magnetic layer. Further, post treatment (plasma treatment) for fixing the lubricant on the DLC film was performed using O ₂ gas. On the post-processed DLC film, a lubricant coating solution was applied by a die nozzle method and dried to form a lubricant layer. In the lubricant coating solution, the succinic acid derivative fluorine-containing compound and the aliphatic ester fluorine-containing compound shown below are equal in weight to MEK / hexane / ethanol = 0.3 wt% so that the total lubricant concentration is 0.3% by weight. The solution was dissolved in a 1/2/7 mixed solvent.
HOOCCH (C ₁₄ H ₂₉ ) CH ₂ COOCH ₂ CH ₂ (CF ₂ ) ₇ CF ₃
CH ₃ (C ₁₆ H ₃₂ ) COOCH ₂ CH ₂ (CF ₂ ) ₇ CF ₃

  The obtained raw material on which each layer was formed was cut into a width of 8 mm to obtain a magnetic tape sample. The magnetic layer had a coercive force (Hc) of 118.5 A / m (1500 Oe) and a saturation magnetic flux density (Bs) of 0.55 T (5500 G).

Examples 2 and 3
A magnetic tape sample was produced in the same manner as in Example 1 except that the support A was changed to the supports B and C, respectively.

Example 4
A magnetic tape sample was produced in the same manner as in Example 1 except that the drying temperature of the backcoat layer was changed to 90 ° C.

Example 5
A magnetic tape sample was prepared in the same manner as in Example 4 except that the backcoat paint B was used in place of the backcoat paint A, and that pre-aeration was performed with a preliminary vacuum machine after the application of the backcoat layer. .

Example 6
A magnetic tape sample was prepared in the same manner as in Example 4 except that the backcoat paint B was used in place of the backcoat paint A.

Example 7
A magnetic tape sample was produced in the same manner as in Example 4 except that the backcoat paint C was used in place of the backcoat paint A.

Comparative Example 1
On one surface of the 4.7 μm-thick PEN support A, a Co 100% magnetic layer having a total thickness of 0.2 μm was formed by vapor deposition. Next, ethylene was introduced and a predetermined discharge frequency (50 kHz) was applied to form a plasma-polymerized hard carbon film (DLC film) with a thickness of 0.01 μm on this magnetic layer. Next, the backcoat paint A was applied on the opposite surface by a die nozzle method so that the thickness after drying was 0.4 μm, and dried at 100 ° C. to form a backcoat layer. Next, a post treatment (plasma treatment) for fixing the lubricant on the DLC film was performed using O ₂ gas. On the post-processed DLC film, a lubricant coating solution was applied by a die nozzle method and dried to form a lubricant layer. The same lubricant coating solution as that used in Example 1 was used.

  The obtained raw material on which each layer was formed was cut into a width of 8 mm to obtain a magnetic tape sample. The magnetic layer had a coercive force (Hc) of 118.5 A / m (1500 Oe) and a saturation magnetic flux density (Bs) of 0.55 T (5500 G).

Comparative Example 2
A magnetic tape sample was produced in the same manner as in Comparative Example 1 except that the support A was changed to the support B.

Comparative Example 3
A magnetic tape sample was produced in the same manner as in Comparative Example 1 except that the support A was changed to the support C.

Comparative Example 4
A magnetic tape sample was produced in the same manner as in Comparative Example 2 except that the concentration of the lubricant coating solution was changed to 0.45%.

Comparative Example 5
A magnetic tape sample was produced in the same manner as in Comparative Example 2 except that the concentration of the lubricant coating solution was changed to 0.15%.

  The following evaluation was performed on the magnetic tape samples of the examples and comparative examples obtained as described above.

Symbol Error Rate (SER) measurement method Examine's Mammath-2 was used as a drive, and the measurement was performed as follows in a room temperature (20 ° C, 60%) environment. First, the drive and the target tape sample were placed in the measurement environment for 6 hours each and allowed to become familiar. Then, using the Agent software provided by Exabite, the SER when the 20 m tape was run in the normal WRITE mode was averaged. In this drive, the required performance is a SER value of 2.50 × 10 ⁻⁴ or less.

Using the Mammath-2 manufactured by Exabite as a short-length durability measurement method drive, the following operation was performed in the following environment using Vista (Visual SCSI Test Application) software provided by Exabyte. First, each of the drive and the target tape sample was placed in the following measurement environment for 6 hours and allowed to become familiar. After that, 288 Mbytes of random data was written / read with the above drive. The running pattern was a repetition of (Write of 288 Mbytes data → Rewind → Read of 288 Mbytes of data → Rewind). The travel was counted by counting the above pattern as one time and traveling 1000 passes.
Measurement environment: room temperature (20 ° C 60%),
40% 20%,
29 ° C 80%,
In each of the three environments, 5 volumes were run. The evaluation criteria are as follows.
○: No travel stop for 5 rolls △: Stop travel for 1 roll ×: Stop travel for 2 or more rolls

The yield defect rate in the productivity DLC process (yield loss due to heat loss and longitudinal loss due to base breakage) was evaluated in stages according to the following criteria.
○: Defect rate 0% to 2%
Δ: Defect rate 2% to 5%
X: Defect rate 5% to 20%
XX: 20% or more

Residual solvent measurement method A test piece having a size of 20 × 20 cm was sampled from each magnetic tape sample, sealed in a 25 cc vial, and heated at 120 ° C. for 60 minutes. Thereafter, the vapor in the vial was sampled, and the amount of solvent was measured with a gas chromatograph. As a measuring apparatus, it measured using the Shimadzu Corporation HSS-2A head space gas chromatograph (column: PEG20M) etc., and calculated | required the residual amount of each solvent from the analytical curve previously calculated | required. The calibration curve was prepared by diluting each solvent to 1/10 with ethyl cellosolve and placing 0.5 μl, 1.0 μl, 2.0 μl, and 4.0 μl in vials at 120 ° C. for 60 minutes. The amount of solvent calibrated when heated was determined by measurement.

  Table 1 below shows the types and surface properties of the substrates and their surface properties, the types and drying temperatures of the back coat paints, the order of the manufacturing process, and the concentration of the lubricant coating solution in each of the above Examples and Comparative Examples. Each is shown in Table 2. In the table, J: vapor deposition layer (magnetic layer), D: DLC film, B: backcoat layer, and T: lubricant layer are shown.

＊）実施例５のみは予備脱気を行った。

*) In Example 5 only, preliminary deaeration was performed.

  In Example 6, since there was a large amount of residual solvent in the backcoat layer, can float occurred in the DLC process, heat loss occurred in the entire roll, and the yield was reduced, but there was no problem with the tape characteristics. . In addition, also in Example 7, since there is a large amount of residual solvent in the backcoat layer, the can float occurred in the DLC process, the base was frequently cut, and the yield was remarkably reduced, but there was no problem with the tape characteristics, In the examples in which the backcoat layer was formed before the DLC process, it was confirmed that good durability was obtained in all cases.

  On the other hand, in Comparative Examples 1 to 3 in accordance with the conventional process order, since the adsorbing force of the lubricant was lowered due to the influence of the transfer of the release agent to the surface of the DLC film, both of them were used in the durability at 40 ° C. and 20%. A seizure occurred and the running stopped. In Comparative Example 4, the absolute amount of fluorine atoms in the lubricant layer was increased by increasing the concentration of the lubricant coating solution, so that the burn-in was slightly improved, but the adsorption power was weak, and the temperature was 29 ° C. The amount of head adhesion in% increased and the running stopped. Further, in Comparative Example 5, since the absolute amount of fluorine atoms in the lubricant layer was reduced by reducing the concentration, seizure occurred even at room temperature, resulting in stoppage of travel.

Claims (3)

When producing a magnetic recording medium comprising a metal thin film magnetic layer, a protective layer and a lubricant layer sequentially on one surface of a nonmagnetic support, and a backcoat layer on the other surface,
As the non-magnetic support, using a film having a coating layer containing a release agent on one side,
After depositing the metal thin film magnetic layer on the surface of the nonmagnetic support opposite to the release agent-containing coating layer, prior to forming the protective layer on the metal thin film magnetic layer, A method for producing a magnetic recording medium, comprising forming the backcoat layer on the release agent-containing coating layer of the nonmagnetic support.   Polyethylene naphthalate film having a coating layer on both sides as the nonmagnetic support, one of the coating layers being the release agent-containing coating layer, and a surface roughness Ra on both sides being 3 nm or less The method for producing a magnetic recording medium according to claim 1, wherein: 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein a residual solvent amount of the back coat layer immediately before forming the protective layer is 7000 μg / m ² or less.