WO2003021591A1

WO2003021591A1 - Method for measuring friction characteristic of surface of optical recording medium

Info

Publication number: WO2003021591A1
Application number: PCT/JP2002/008602
Authority: WO
Inventors: Naoki Hayashida; Hideki Hirata
Original assignee: Tdk Corporation
Priority date: 2001-08-29
Filing date: 2002-08-27
Publication date: 2003-03-13
Also published as: JP2003067980A

Abstract

A method for accurately measuring the friction characteristic of the surface of an optical recording medium, particularly, the surface of a light-transmitting layer or a hard coat layer. A thin-film piece (2) for measurement and a weight (3) are placed on the surface of an optical recording medium, and the optical recording medium is turned is this state. The tensile force produced in the thin-film piece (2) is measured by a transducer (4). Thus, an optical recording medium can be evaluated accurately and simply during its production process when reducing the coefficient of friction of the surface of the optical recording medium to a predetermined value or less thereby to reduce the scratches on the turning optical recording medium caused by the contact of the optical recording medium with the objective or the support supporting the objective.

Description

Description Method for measuring friction characteristics of optical recording medium surface

The present invention relates to a method for measuring friction characteristics of an optical recording medium surface, and more particularly, to a method for measuring a friction force and / or a coefficient of friction on an optical recording medium surface. Conventional technology

In recent years, optical recording media such as CD and DVD have been widely used as recording media for recording large volumes of digital data. Generally, a read-only optical recording medium has a light-transmitting layer (light-transmitting substrate), a reflective layer, and a protective layer laminated in this order from the light incident surface side, and a writable optical recording medium has a light incident surface side. Each layer is laminated in the order of a light-transmitting layer (light-transmitting substrate), a recording layer, a reflective layer, and a protective layer. Regardless of the type of optical recording medium, when reading data, the reproducing power is applied from the light-transmitting layer side. The reflected laser beam is detected by irradiating the laser beam set in the above. In addition, when writing data to a writable optical recording medium, a laser beam set to a recording power is irradiated from the light transmitting layer side, and the thermal state and the optical energy of the laser beam cause the chemical state of the recording layer to change. Or the physical state is changed based on the data to be recorded.

Here, the laser beam applied to the optical recording medium is focused by an optical system such that a beam spot having a predetermined diameter is formed in the reflection layer or the recording layer. For this reason, if there is a scratch on the surface of the light transmitting layer, the beam spot is not formed correctly, and a reading error or a writing error may occur. As a method for preventing the occurrence of such scratches, a method of providing a hard coat layer having high hardness on the surface of the light transmitting layer has been conventionally known.

By the way, in recent years, the objective lens for focusing the recording Z reproduction laser beam The numerical aperture (NA) of the laser beam is increased to 0.7 or more, for example, about 0.85, and the wavelength of the laser beam used for recording and / or reproduction is shortened to about 400 nm. Attempts have been made to reduce the diameter of the light collection spot and thereby record a large amount of digital data. When the NA is increased in this manner, the allowance of the warp and tilt of the optical recording medium, that is, the tilt margin is reduced. Need to be thinner. For example, when NA = 0.85 and A = about 400 nm, the thickness of the light transmission layer must be reduced to about 100 μm to secure a sufficient tilt margin. Required.

When the NA is increased, the working distance (working distance) between the objective lens and the surface of the optical recording medium is reduced. For example, when NA is set to about 0.85, the working distance is 10 mm. It is about 0 m, which is significantly narrower than before.

If the working distance is very narrow, the possibility of contact between the surface of the optical recording medium and the objective lens and the support that supports it during rotation of the optical recording medium becomes extremely high. If such contact occurs during rotation, there is a possibility that a fatal scratch may occur on the surface of the light transmitting layer of the optical recording medium. The occurrence of scratches due to such contact can be suppressed to some extent by providing the above-described hard coat layer. However, when the light transmitting layer is thinned to about 100 im, the surface of the light transmitting layer may be damaged. The focusing diameter of the laser beam used for recording, Z or reproduction is also extremely small, so even if the size of the scratches or dirt does not cause a reading error or writing error with conventional optical recording media, it is easy to read or write. You will get an error. For this reason, simply increasing the hardness of the hard coat layer is not enough to reduce scratches caused by contact during rotation.

In order to effectively reduce scratches on the surface of the optical recording medium caused by contact during rotation, the present inventors not only increase the hardness of the hard coat layer but also reduce the friction coefficient of the hard coat layer surface. Is valid Reached the conclusion. When producing an optical recording medium with a low friction coefficient on the surface of the hard coat layer, the optical characteristics can be measured by accurately measuring the friction characteristics (frictional force and / or coefficient of friction) on the surface of the hard coat layer. It is necessary to evaluate the recording medium. Disclosure of the invention

Accordingly, an object of the present invention is to provide a method for accurately measuring the friction characteristics (frictional force and / or coefficient of friction) of the surface of an optical recording medium, particularly the surface of a light transmitting layer or a hard coat layer.

Another object of the present invention is to provide a method for accurately measuring the frictional characteristics of the surface of an optical recording medium of the type that records and reproduces data without physical contact.

As described above, in order to effectively reduce scratches on the surface of the optical recording medium caused by contact with the objective lens and the support that supports the objective lens during rotation of the optical recording medium, the present invention is intended to reduce the surface damage of the optical recording medium. An object of the present invention is to provide a method capable of accurately measuring such a coefficient of friction based on the idea that it is effective to reduce the coefficient of friction and mitigate damage at the time of contact.

An object of the present invention is to provide a method for measuring frictional characteristics of an optical recording medium surface, which comprises contacting a measuring member in a plane with the surface of an optical recording medium and detecting a tensile force generated on the measuring member. Achieved by According to the present invention, it is possible to very accurately measure the friction characteristics of the optical recording medium surface. Accordingly, the objective lens during rotation of the optical recording medium, or the friction coefficient of the optical recording medium surface that is reduced to a predetermined value or less in order to reduce scratches on the optical recording medium surface caused by contact with the support that supports the objective lens. In this case, it is possible to accurately and easily evaluate the optical recording medium at the time of manufacturing. Therefore, the method for measuring frictional characteristics according to the present invention provides a method for measuring the frictional characteristics of the surface of an optical recording medium in which the light transmitting layer is thinned to about 5 to 300 m, and particularly to about 50 to about 50 μm. Suitable for measurement.

In a preferred embodiment of the present invention, the surface of the optical recording medium Is a light incident surface.

In a further preferred aspect of the present invention, the tensile force is detected while applying a load to the measuring member by surface contact.

Here, the term “surface contact” can be replaced by a number of point contacts in addition to the contact in a plane.

In a further preferred aspect of the present invention, the measuring member is in a thin film shape.

In a further preferred embodiment of the present invention, the measuring member is a non-woven cloth.

In a further preferred embodiment of the present invention, the friction characteristics are a friction force and Z or a coefficient of friction.

In a further preferred aspect of the present invention, the optical recording medium is a type of an optical recording medium that performs data recording and Z reproduction without physical contact. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram for explaining a friction characteristic measuring method according to a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing an example of the optical recording medium 10 to be measured by the friction characteristic measuring method according to a preferred embodiment of the present invention. FIG. 3 is a graph showing the measurement results of the friction coefficients of Sample # 1 to Sample # 6.

FIG. 4 is a graph showing the measurement results of the coefficient of friction of Sample # 2 and Sample # 2 '. Embodiment of the Invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram for explaining a friction characteristic measuring method according to a preferred embodiment of the present invention. As shown in FIG. 1, in the friction characteristic measuring method according to the present embodiment, a rotation mechanism 1 for rotating an optical recording medium to be measured, a thin film piece for measurement 2 as a measuring member, A weight 3 for pressing the thin film piece 2 for measurement against the surface of the optical recording medium to be measured, and a transducer 4 for detecting a tensile force generated on the thin film piece 2 for measurement are used.

The thin film piece for measurement 2 is used to convert a frictional force generated between the rotating optical recording medium and the surface thereof into a tensile force, and is not particularly limited, but a nonwoven fabric is used as the material. Is preferred.

The weight 3 has a columnar shape with a flat bottom surface, and a cushioning material 5 is provided on the bottom surface portion so that the load on the thin film piece 2 for measurement is evenly distributed in a plane. Although not particularly limited, it is preferable to use polyurethane, silicone rubber, or the like as the material of the cushioning material.

FIG. 2 is a cross-sectional view schematically showing an example of the optical recording medium 10 to be measured by the friction characteristic measuring method according to the present embodiment.

As shown in FIG. 2, an optical recording medium 10 which is an example of an object to be measured has a substrate 11 having a thickness of about 1.1 mm and a reflective layer 1 having a thickness of 70 to: L30 nm. 2, a recording layer 13 having a thickness of S 100 to 250 nm, a light transmitting layer 14 having a thickness of 5 to 300 μm, and a thickness of 0.5 to: ίθ. It is composed of a hard coat layer 15 of πι. A hole 16 is provided in the center of the optical recording medium 10. The substrate 11 is made of polycarbonate, and the reflection layer 12 is made of an alloy mainly containing silver. Further, the recording layer 13 has a multilayer structure in which a dielectric film is interposed between the top and bottom of a phase change film in which data is actually recorded. Further, the light transmitting layer 14 and the hard coat layer 15 are made of an ultraviolet curable resin. When reading data from the optical recording medium 10 having such a structure, a laser beam set to a reproduction power is irradiated from the hard coat layer 15 side, and the reflected light amount difference is detected. When writing data to the optical recording medium 10, a laser beam set to a recording power is irradiated from the hard coat layer 15 side, and thereby the state of the recording layer 13 (the crystal of the phase change film) is irradiated. Structure).

As described above, the measurement target of the friction characteristic measurement method according to the present embodiment is The optical recording medium 10 is a type of optical recording medium in which data is recorded and Z-reproduced by irradiation with a laser beam. Incidentally, the measurement object of the friction characteristic measuring method according to the present embodiment may be a magnetic field modulation type optical recording medium such as a magneto-optical recording medium. In this case, the magnetic head is in contact with the magnetic head. Instead, the recording / reproducing light incident surface is the object to be measured.

Next, a method of measuring friction characteristics according to the present embodiment will be described. In measuring the friction characteristics, first, the optical recording medium 10 to be measured is placed on a rotating table (not shown) of the measuring apparatus with the hard coat layer 15 facing upward, and then the hard coat The thin film piece for measurement 2 and the weight 3 are placed on the surface of the layer 15. In this state, the rotation mechanism 1 is operated to rotate the optical recording medium 10. FIG. 1 shows such a state.

At this time, the frictional force generated between the surface of the optical recording medium 10 and the measuring thin film piece 2 loaded by the weight 3 pulls the measuring thin film piece 2 in the rotation direction of the optical recording medium 10. . The tensile force is converted into an electric signal by the transducer 4, whereby it is possible to specify the friction characteristics of the surface of the optical recording medium 10, that is, the friction force and / or the coefficient of friction.

As described above, according to the friction characteristic measuring method according to the present embodiment, the weight 3 having a flat bottom is used to apply a uniform load on the surface of the optical recording medium and the thin film piece 2 for measurement. The frictional characteristics are measured while making contact, so that the frictional characteristics of the light incident surface of the type of optical recording medium that performs data recording / reproduction without physical contact can be measured accurately and with good reproducibility. Can be set. For this reason, especially in an optical recording medium in which the light transmitting layer is thinned, it is necessary to reduce scratches on the surface of the optical recording medium caused by contact with the objective lens and the support supporting the objective lens during rotation. When the friction coefficient of the recording medium surface is suppressed to a predetermined value or less, it is possible to accurately evaluate the optical recording medium at the time of manufacturing.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims. It goes without saying that they are included within the scope of the present invention.

For example, in the above embodiment, the friction characteristics of the light incident surface of the optical recording medium in which the light transmitting layer is thinned are measured, but the optical recording medium that can be measured by the method according to the present invention is not limited to this. As long as it is an optical recording medium of the type that records and reproduces data without physical contact, measurement can be performed on the light incident surface of another type of optical recording medium.

Further, in the above embodiment, the weight 3 having a flat bottom is used so that the surface of the optical recording medium and the thin film piece 2 for measurement are brought into contact with each other by applying a uniform load in a plane. The load may be applied to the thin film piece for measurement 2 by any method as long as it can be brought into contact with a uniform load in a plane. In addition, instead of using the measuring thin film piece, a measuring member having a sufficient weight to perform effective measurement is used. You can get friction.

As described above, according to the present invention, it is possible to accurately measure the friction characteristic of the light incident surface of an optical recording medium of the type that records and reproduces data without physical contact. It is possible to provide a simple friction characteristic measuring method. Example

The friction coefficients of the surfaces of the six optical recording media (Sample # 1 to Sample # 6) on which different hard coat layers were formed were measured using the friction characteristic measuring method according to the present embodiment.

In this measurement, a nonwoven fabric (100 mm in length and 25 mm in width, made by Asahi Kasei Corporation, Bencott Lint Free CT-18) was used as the thin film piece 2 for measurement. . Here, the length of the thin film piece for measurement 2 is a direction in which a tensile force acts, and in FIG. The weight 3 was 2 Omm in diameter and weighed 31 g. The center of the weight 3 is 40 mm from the center of the optical recording medium. Was placed so as to be located at Under these conditions, the rotational speed of the optical recording medium by the rotation mechanism 1 was set to 670 rpm, and the friction coefficient of each optical recording medium was measured.

Here, as the six optical recording media (sample # 1 to sample # 6) to be measured, the hard coat layer 15 was a UV curable resin (Nippon Kayaku Co., Ltd.). Optical recording media composed of HOD-3200) and having different types and amounts of lubricant added to the ultraviolet-curable resin were prepared. Table 1 shows the type and amount of lubricant contained in the hard coat layer 15 of each sample. In each of the samples, the thickness of the hard coat layer was set to 3.

FIG. 3 is a graph showing the measurement results of the friction coefficient of Sample # 1 to Sample # 6. In FIG. 3, the vertical axis represents the friction coefficient, and the horizontal axis represents the cumulative number of rotations of the optical recording medium.

Referring to FIG. 3, it can be seen that the difference in friction coefficient between Sample # 1 to Sample # 6 clearly appears. In addition, referring to FIG. 3, the amount of change in the friction coefficient based on the cumulative number of rotations of the optical recording medium, that is, the number of times the thin film piece 2 for measurement slides clearly appears. Here, the increase in the coefficient of friction based on the cumulative number of rotations of the optical recording medium is due to the fact that the lubricant contained in the hard coat layer 15 was wiped off by the thin film piece 2 for measurement. Therefore, the change in the coefficient of friction in FIG. 3 is due to the fact that the user frequently wipes off dust and dirt adhering to the surface of the optical recording medium with a nonwoven fabric or tissue paper. It can be used as important data to know how it affects the friction coefficient of the recording medium, that is, its durability.

Next, the friction coefficient of Sample # 2, which has the same hard coat layer as Sample # 2, was measured under the same measurement conditions as described above. Figure 4 shows the results of such measurements.

Referring to FIG. 4, it can be seen that the friction coefficients obtained from the two samples # 2 and # 2 'having exactly the same hard coat layer are almost the same. This means that the reproducibility of the friction characteristic measuring method according to the present invention is very good.

As a comparative example, the above-described sample was measured using an apparatus for measuring the frictional characteristics of the surface of the magnetic field modulation head, which is not the optical pickup side, of a magnetic field modulation type optical recording medium, MD (mini disc). The surface friction coefficients of # 1 to # 6 were measured, but no significant differences appeared in the measurement results of each sample. Reproducibility was also poor.

Here, the device for measuring the friction characteristics of the surface of the MD (mini-disc) is a device used for measuring the friction force and / or friction coefficient of the surface on the side where the magnetic field modulation head contacts. Yes, the measurement using such an apparatus is described on page 20 of the Annex of the Mini Disc System Standard (Rainbow Book). As described above, a measuring device for an optical recording medium of a type in which data is recorded and reproduced while making physical contact with a magnetic field modulation head or the like is used to record data without making physical contact. It can be seen that it is not suitable for measuring the frictional force and / or coefficient of friction of the light incident surface of the type of optical recording medium on which reproduction is performed.

Claims

The scope of the claims

1. A method for measuring friction characteristics of an optical recording medium surface, comprising: bringing a measuring member into planar contact with the surface of an optical recording medium and detecting a tensile force generated on the measuring member.

2. The method according to claim 1, wherein the surface of the optical recording medium is a light incident surface.

3. The friction characteristic measuring method according to claim 1, wherein the tensile force is detected while applying a load to the measuring member by surface contact.

4. The method for measuring friction characteristics according to claim 1, wherein the member for measurement is a thin film.

5. The method according to claim 4, wherein the measurement member is a nonwoven fabric.

6. The friction characteristic measuring method according to claim 1, wherein the friction characteristic is a friction force and a friction coefficient.

7. The method according to claim 1, wherein the thickness of the light transmitting layer of the optical recording medium is 5 to 300 / zm.

8. The method according to claim 2, wherein the thickness of the light transmitting layer of the optical recording medium is 5 to 300 // m.

9. The method according to claim 1, wherein the optical recording medium is a type of optical recording medium that records and reproduces data without physical contact.