JP3588884B2 - Method for measuring magnetic layer thickness of magnetic tape - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention belongs to the technical field of so-called coating type magnetic recording media, and relates to a method for measuring the thickness of a magnetic layer of the coating type magnetic tape.
[0002]
[Prior art]
As a recording medium used in audio devices, video devices, computer devices, etc., a magnetic paint prepared by dispersing and kneading a magnetic powder, a binder and various additives in an organic solvent is coated on a non-magnetic support. A so-called coating type magnetic recording medium, in which a magnetic layer is formed by drying, is dominant because of its excellent productivity and versatility.
[0003]
In recent years, in these various magnetic recording / reproducing apparatuses, miniaturization, weight reduction, high image quality, and long time have been promoted, and accordingly, high-density recording has been strongly demanded for the coating type magnetic recording medium. Has become.
[0004]
In order to improve the characteristics in the high-density recording area of the above-mentioned coating type magnetic recording medium, in recent years, instead of the iron oxide-based magnetic powder conventionally used, it is composed of iron or a metal material mainly containing iron. Metal magnetic powder is used as the magnetic powder to be contained in the magnetic layer.
[0005]
In this type of magnetic recording medium, the magnetic layer is made as thin as possible to reduce self-demagnetization loss during the recording process and thickness loss during the reproduction process. As the thickness of the magnetic layer is reduced, the magnetostatic properties are improved, and the self-time loss during the recording process and the thickness loss during the reproduction process are improved. There is a tendency. Therefore, a method has been proposed in which a nonmagnetic layer is provided as an undercoat layer in order to suppress buffering caused by contact between the magnetic layer and a traveling system such as a head and guide pins.
[0006]
By the way, in this coating type magnetic recording medium, it is desired to simply and accurately measure the coating thickness of the magnetic layer to be formed from the viewpoint of thinning as described above. In particular, in the case of a so-called two-layer magnetic tape in which a lower non-magnetic layer and an upper magnetic layer using ferromagnetic metal powder as magnetic powder are formed on a non-magnetic support, the coating thickness of the upper magnetic layer is further increased. Because of the thin film, accurate measurement is strongly desired.
[0007]
This is because the film thickness greatly affects the electromagnetic conversion characteristics.
[0008]
[Problems to be solved by the invention]
However, in such a coating type magnetic recording medium, X-rays and β-rays have conventionally been used in combination in order to measure the coating film thickness. As this apparatus, there is known an apparatus which uses the principle of measuring the attenuation of X-rays and β-rays in a substance and determining the thickness of the sample using a known absorption coefficient of the substance.
[0009]
However, the measurement using the X-ray and the β-ray together has a problem that the resolution is as low as about 0.1 μm. In the future, the coating film thickness of the magnetic layer of the coating type magnetic recording medium tends to be thinner, but the measurement using the X-ray and the β-ray together cannot sufficiently cope with such a tendency. .
[0010]
Further, measurement using both X-rays and β-rays cannot be displayed on a monitor, and it is difficult to change the measurement range. Furthermore, it can be handled only by a specific skilled person, causing a danger, and has a problem that the device becomes large.
[0011]
The present invention, such has been proposed in view of the conventional circumstances, high resolution, moreover, to provide a measure how that allows measurement of coating thickness of easily and accurately the magnetic tape of the magnetic layer With the goal.
[0012]
[Means for Solving the Problems]
The magnetic layer thickness measuring method of the magnetic tape of the present invention, in order to achieve the above object, for a magnetic tape having a magnetic layer formed of a ferromagnetic metal powder as a magnetic powder on a transparent non-magnetic support, The coating thickness of the magnetic layer is measured by transmitting the laser light having a wavelength λ of 600 nm and measuring the intensity of the transmitted light.
[0013]
Further, the coating thickness of the magnetic layer is less than 1.0 μm.
[0014]
On the other hand, the measuring apparatus used in the method for measuring the thickness of the magnetic layer of the magnetic tape of the present invention emits light to a magnetic tape in which a magnetic layer having a ferromagnetic metal powder as a magnetic powder is formed on a transparent non-magnetic support. The light-emitting device includes a light-emitting unit that transmits light, a light-receiving unit that receives the transmitted light, and a monitor display unit that monitors and displays the light intensity of the light-receiving unit .
[0015]
An aperture lens for reducing the diameter of light from the light emitting unit is provided.
[0016]
A mounting table for mounting a magnetic tape is provided between the light emitting unit and the light receiving unit, and the mounting table is movable .
[0017]
First, according to the method for measuring the thickness of a magnetic layer of a magnetic tape of the present invention, the thickness of a magnetic layer is measured by transmitting light to the magnetic tape and measuring the intensity of the transmitted light. Therefore, by quantitatively measuring the coating thickness of the magnetic layer, the unevenness of the coating thickness of the magnetic layer can be measured.
[0018]
When the wavelength λ of the light is 600 nm or more, the measurement resolution of the coating thickness of the magnetic layer is increased to about 20 nm.
[0019]
However, when the wavelength λ of the light is less than 600 nm, when measuring the intensity of the laser light transmitted through the light receiving unit, the intensity of the light may be too weak to measure. Therefore, laser light having a wavelength of 600 nm or more is preferable for the method for measuring the thickness of the magnetic layer of the sample tape of the present invention.
[0020]
On the other hand, according to the measuring device used in the magnetic layer thickness measuring method of the magnetic tape of the present invention, light is transmitted to the magnetic tape, and when the transmitted light is received by the light receiving portion, the amount of light of the light receiving portion is reduced. Monitor display is possible. Therefore, the measurement of the thickness of the magnetic layer of the magnetic tape can be easily performed, and no special skill is required.
[0021]
Further, the measurement range can be changed by adjusting the spot diameter of the laser beam with the aperture lens.
[0022]
The magnetic tape to be measured in the present invention is a coating type magnetic tape in which a magnetic layer using a ferromagnetic metal powder as a magnetic powder is formed on a transparent non-magnetic support. A so-called vapor deposition tape formed by vapor-depositing a ferromagnetic metal thin film as a magnetic layer is not suitable because of poor light transmittance.
[0023]
The transparent nonmagnetic support needs to be polyethylene terephthalate, polyethylene naphthalate, aramid, or the like.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
[0025]
The measuring apparatus used in the method for measuring the thickness of a magnetic layer of a magnetic tape according to the present invention includes a light emitting unit 1 that emits light, an aperture lens 2, a stage 3 as a mounting table on which a sample tape T is mounted, and a light emitting unit 1. And a monitor display unit 5 for measuring and displaying the amount of light.
[0026]
The light emitting unit 1 is a light source that emits the laser light P1, and in the present embodiment, emits the laser light P1 having a wavelength of 600 nm.
[0027]
The aperture lens 2 adjusts the spot radius of the laser light emitted from the light emitting unit 1, and the laser light P 1 can be stopped down to 10 μm by the aperture lens 2.
[0028]
The stage 3 is for mounting the sample tape T to be measured, and is movable within a certain range in both the vertical direction (y direction) and the horizontal direction (x direction). The stage 3 is connected to the monitor display unit 5 so that the movement amount can be measured.
[0029]
In addition, even if such a movable stage 3 is not used, for example, a long magnetic tape is sequentially conveyed between the light emitting unit 1 and the light receiving unit 3 to measure the coating thickness of the magnetic tape. You may do it.
[0030]
The sample tape T is a so-called coating type magnetic tape in which a magnetic layer using a ferromagnetic metal powder as a magnetic powder is formed on a transparent non-magnetic support.
[0031]
The light receiving section 4 receives the laser light P2 transmitted through the sample tape T on which the magnetic layer is formed, and is connected to a monitor display section 5 for monitoring and displaying the amount of the transmitted laser light.
[0032]
The monitor display unit 5 measures the coating thickness of the magnetic layer by comparing the intensity of the laser light P1 emitted from the light emitting unit 1 with the intensity of the laser light P2 at the light receiving unit 4, for example. It has a built-in arithmetic processing function. Therefore, the monitor display section 5 can measure the applied thickness of the magnetic layer of the sample tape T by measuring the intensity of the laser beam P2 at the light receiving section 4.
[0033]
Since this measuring device has the above-described configuration, the laser light P1 is transmitted through the sample tape T, and when the transmitted laser light P2 is received by the light receiving unit 4, the monitor display unit 5 detects the laser light P2. The intensity of the laser beam P2 can be displayed on a monitor.
[0034]
Therefore, while moving the stage 3 in a certain direction, by performing a quantitative measurement on the coating film thickness of the sample tape, so-called line analysis or surface analysis is performed while looking at the monitor display unit 5.
[0035]
For example, when the object to be measured is a sample tape T having a so-called two-layer structure in which a lower non-magnetic layer and an upper magnetic layer having a ferromagnetic metal powder as a magnetic powder are formed on a non-magnetic support, FIG. As shown in FIG. 2, the laser beam P2 is transmitted. Here, as shown in FIG. 2, if there is unevenness in the coating thickness of the magnetic layer of the magnetic tape, the transmittance of light is different, so that the coating unevenness can be clearly measured. Therefore, the intensity of the laser beam P2 transmitted in a certain range is statistically measured in advance.
[0036]
That is, the coating thickness of the sample tape T to be measured can be measured based on whether the intensity of the laser beam P2 is stronger or weaker than the result of the above-described statistical measurement. As a result, the thickness unevenness of the magnetic layer can be measured by repeating quantitative measurement. Further, by adjusting the spot diameter of the laser beam P1 with the aperture lens 2, the measurement range is narrowed, so that the variation in the thickness of the coating streak which causes the thickness unevenness of the magnetic layer can be evaluated.
[0037]
Then, the thickness of the magnetic layer of the sample tape T on which the magnetic layer using the ferromagnetic metal powder as the magnetic powder was actually formed and the unevenness of the thickness of the magnetic layer were measured using the apparatus having the above configuration. Here, a case is described in which the sample tape T having the two-layer structure is used and the upper magnetic layer is a thin film having a coating thickness of 0.1 to 0.2 μm.
[0038]
Here, the spot diameter of the laser beam P1 emitted from the light emitting section 1 was set to a range of 10 μm to 5 mm by the aperture lens 2. When the light wavelength λ is 600 nm, the measurement resolution of the coating thickness of the magnetic layer can be up to about 20 nm.
[0039]
The unevenness in the coating thickness is evaluated by the intensity of the laser beam P2 transmitted through the sample tape T. Usually, the thickness of the magnetic layer is proportional to the absorbance Abs represented by transmittance = 1 / 10-Abs. Here, the absorbance Abs is expressed as Abs = 1 when the transmittance is 10% = 0.1 = 10-1 and Abs = 2 when the transmittance is 1% = 0.01 = 10-2.
[0040]
Therefore, when measuring the coating thickness of the upper magnetic layer of the sample tape T having the two-layer structure, as shown in FIG. 3, the thickness (μm) of the upper magnetic layer and the absorbance (Abs) of the laser beam P2 are constant. A proportional relationship appears. This can be examined while being displayed on the monitor display unit 5 by using the measuring method by the above-mentioned device. FIG. 3 is an example of a diagram showing the relationship between the thickness of the upper magnetic layer and the transmittance of the magnetic recording medium, and both have a certain proportional relationship. However, even when the coating thickness of the upper magnetic layer is the same, as shown in FIG. 2, it can be seen that the absorbance (Abs) differs between the white line portion and the black line portion or where there is an aggregate. Therefore, unevenness of the coating thickness can be recognized.
[0041]
FIG. 2 shows that the measurement can be performed even when the coating thickness of the magnetic layer is less than 1.0 μm. The measurement can be performed even when a lower nonmagnetic layer and an upper magnetic layer using a ferromagnetic metal powder as a magnetic powder are formed on a nonmagnetic support, and the coating thickness of the upper magnetic layer is 0.5 μm or less.
[0042]
In the following, in the case of the above SL device, it examined the preferred wavelength lambda. FIG. 4 shows the result.
[0043]
As is clear from FIG. 4, when the light wavelength λ was measured in the range of 600 nm to 760 nm, a large difference in the absorbance (Abs) was found when the light wavelength λ was less than 600 nm, and the resolution was high. You can see that. When the light wavelength λ is 600 nm, the evaluation can be performed with a resolution of 10 to 20 nm.
[0044]
On the other hand, when the wavelength λ of the light is less than 600 nm, when measuring the intensity of the laser beam P2 transmitted through the light receiving unit 4, the intensity of the light may be too weak to measure. Therefore, the laser beam P1 having a wavelength of 600 nm or more is preferable for the method and apparatus for measuring the thickness of the magnetic layer of the sample tape T of the present invention.
[0045]
In the case of such an apparatus, an accurate measurement result in actual measurement is obtained when the transmittance of the upper magnetic layer is about three times the transmittance of the lower nonmagnetic layer. In addition, in the case of the above-mentioned apparatus, a single measurement range is within a range of φ10 μm to 10 mm in diameter, and a sampling time can be measured as short as 1 sec / 1 time.
[0046]
FIG. 2 shows the measurement at a light wavelength λ of 760 nm. The lower non-magnetic layer has a transmittance of 40% and a coating thickness of 0.16 μm. The upper magnetic layer has a transmittance of 30% and a coating thickness of 0.1 μm. This is the case of 50 μm.
[0047]
By the way, in the conventional apparatus, since the X-ray and the β-ray are used in combination, the resolution is about 0.1 μm. On the other hand, according to the apparatus having the above configuration, when the light wavelength λ is 600 nm, the evaluation can be performed with a resolution of 10 to 20 nm.
[0048]
Therefore, according to the present invention, the coating film thickness can be measured with a resolution of 1/5 to 1/10 of that of the conventional apparatus. Further, the spot diameter of the laser beam is narrowed down to 10 μm by the aperture lens 2, thereby narrowing the measurement range, thereby making it possible to evaluate the thickness fluctuation of the coating streak which causes the thickness unevenness of the magnetic layer. .
[0049]
As described above, the measurement of the thickness of the upper magnetic layer of the magnetic tape having the two-layer structure has been described in the above description of the embodiment. However, the present invention is limited to a so-called coating type magnetic recording medium having a two-layer structure. Needless to say, it is not. Also, the thickness of the lower non-magnetic layer and the like can be measured by the same principle as the measurement of the thickness of the upper magnetic layer of the magnetic tape having a two-layer structure. In recent years, a magnetic tape having a lower layer has been developed for a magnetic tape having a two-layer structure, but it goes without saying that the present invention is also applied to such a case.
[0050]
【The invention's effect】
According to the present invention, a laser beam having a wavelength λ of 600 nm is transmitted through a magnetic tape in which a magnetic layer having a ferromagnetic metal powder as a magnetic powder is formed on a transparent nonmagnetic support. Because it measures intensity, it is possible to measure the coating film thickness with a resolution of 1/5 to 1/10 compared to the conventional measurement method using both X-rays and β-rays. Therefore, it is possible to accurately measure the thickness of the magnetic layer of the magnetic tape, which tends to be thin.
[0051]
In particular, to accurately measure the coating thickness of the upper magnetic layer of a so-called two-layer magnetic tape in which a lower non-magnetic layer and an upper magnetic layer using a ferromagnetic metal powder as a magnetic powder are formed on a non-magnetic support. can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a measuring device used in a method for measuring a magnetic layer thickness of a magnetic tape of the present invention.
FIG. 2 is a partially enlarged plan view showing a state where laser light is transmitted through a magnetic tape.
FIG. 3 is a diagram showing the relationship between the thickness and the transmittance of the upper magnetic layer of a magnetic recording medium in which a lower nonmagnetic layer and an upper magnetic layer using ferromagnetic metal powder as magnetic powder are formed on a nonmagnetic support. is there.
FIG. 4 is a diagram showing a relationship between light wavelength and transmittance.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light-emitting part 2 Aperture lens 3 Mounting stage (stage)
4 light receiving unit 5 monitor display unit P1 emitted light P2 transmitted light T Magnetic tape (sample tape)

Claims (2)

By transmitting a laser beam having a wavelength λ of 600 nm to a magnetic tape having a magnetic layer formed of ferromagnetic metal powder as a magnetic powder on a transparent non-magnetic support, measuring the intensity of the transmitted light. A method for measuring the thickness of a magnetic layer of a magnetic tape, comprising measuring a coating thickness of the magnetic layer. 2. The method for measuring a magnetic layer thickness of a magnetic tape according to claim 1, wherein the coating thickness of the magnetic layer is less than 1.0 μm .

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