Optical recording medium and process for producing same

Details Optical recording medium and process for producing same Optical recording medium and process for producing same

1999-08-11

2002-02-12

Evans, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S065800, C428S422000

Reexamination Certificate

active

06346309

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium for recording and reproduction using a floating type optical head, and a process for producing the same. More particularly, it relates to an optical recording medium which is enhanced in seeking resistance while the floating type optical head seeks through the optical recording medium, and is inhibited or prevented from a lubricant of the optical recording medium from sticking to the slider surface of the floating type optical head and to the light emitting face of a solid immersion lens, and to a process for producing the optical recording medium.
With coming of the multimedia age, optical recording media are widely utilized as media capable of recording and reproducing a large quantity of information such as music, animation images, and data of computers. Optical recording media are classified into read-only type optical recording media capable of only reading of information, such as CD and laser disks, write-once type optical recording media capable of writing only one time, such as CD-R, and rewritable optical recording media capable of rewriting and erasing any number of times.
As one of the rewritable optical recording media, for example, magneto-optical recording media are known. Magneto-optical recording media usually have a structure comprising a transparent substrate and, laminated thereon in succession, a first dielectric layer, a magneto-optical recording layer, a second dielectric layer, a reflective layer and a protective layer, and recording and reproduction are carried out using an optical head and a coil for generation of magnetic field.
Recently, with increase of quantity of information to be handled, further increase of storage capacity is demanded for optical recording media. For meeting the demand, a method is proposed which performs recording and reproduction using a floating type head on which a solid immersion lens (SIL) is mounted. According to this method, recording and reproduction can be performed with a smaller light spot diameter than according to conventional methods, and, hence, recording density per unit area can be increased by about one figure as compares with conventional magneto-optical recording media.
When recording and reproduction are carried out using SIL, a proximate light which oozes from the SIL can be used as a light for recording and reproduction. Since the proximate light decays at a distance of about ¼ the wavelength of the light, the distance between the SIL and the recording layer must be less than ¼ the wavelength of the recording and reproducing light. For example, when a red laser beam of 680 nm in wavelength is used, the distance between the light emitting face of the solid immersion lens and the recording layer must be 170 nm or less. Since thickness of the transparent substrate in conventional magneto-optical recording media is about 1.2 mm, it is difficult for the proximate light to reach the recording layer through the substrate. Therefore, in case a proximate light is used, light is projected into the recording media from the side opposite to the substrate. For this reason, the sequence of lamination for making magneto-optical recording media using a proximate light differs from that of conventional media and usually the former media have a structure comprising a transparent substrate and, laminated thereon in succession, a reflective layer, a first dielectric layer, a magneto-optical recording layer and a second dielectric layer. Furthermore, recording and reproduction are carried out using a floating type optical head, and, therefore, the floating type optical head contacts with the medium when the optical head conducts seeking operation. Therefore, a protective layer and a lubricating layer are formed in succession on the second dielectric layer of the medium in order to enhance seeking resistance.
The present inventors disclose, in JP-A-11-7657, an optical recording medium comprising a substrate and, provided thereon, a reflective layer, a recording layer and a dielectric layer and irradiated with a recording light or reproducing light from the side of the dielectric layer, in which a protective layer having self-lubricating property is provided on the dielectric layer and a lubricating layer is further provided on the protective layer. As compounds constituting the lubricating layer, there are disclosed perfluoro polyethers having one hydroxyl group, carboxyl group, ester group or piperonyl group at least one end of the molecule because of their large adsorption energy to the protective layer comprising carbon.
However, when a floating type optical head seeks through the magneto-optical recording medium, there is the possibility of a part of the lubricant being vaporized by the heat of laser beams to move and stick to the light emitting face of SIL or the SIL sliding over the lubricant to cause moving and sticking of the lubricant to the light emitting face of the SIL. If the lubricant moves and sticks to the light emitting face of SIL, optical characteristics of SIL are changed and recording and reproduction cannot be satisfactorily performed. As the causes therefor, the following can be considered. That is, lubricant for optical recording media according to optical recording system using SIL has a high transparency, being different from the lubricant for magnetic recording media according to magnetic recording system such as magnetic tape and magnetic disk, but the lubricant which moves and sticks to the light emitting face of SIL is decomposed with heat of laser beams and changes in its properties to deteriorate the transparency. Thus, it is desired to coat the protective layer with a lubricant which is further improved in adsorption property to the protective layer than the lubricant disclosed in JP-A-11-7657.
SUMMARY OF THE INVENTION
The present invention has solved the above problems, and the object is to provide an optical recording medium which is inhibited or prevented from moving and sticking of lubricant to the light emitting face of an optical element such as SIL and can realize recording and reproduction using SIL.
Another object of the present invention is to provide an optical recording medium in which the lubricating layer comprises a lubricant which is not heat decomposed even if heated by irradiation with light beams and maintains a high transparency.
Still another object of the present invention is to provide a process for producing an optical recording medium in which the lubricant hardly moves and sticks to a light emitting face of optical elements such as SIL and which has a lubricating layer high in sliding resistance.
According to the first embodiment of the present invention, there is provided an optical recording medium comprising a substrate and, provided thereon in succession, a reflective layer, a recording layer, a protective layer and a lubricating layer comprising a lubricant, characterized in that a lubricant bonding rate of the lubricant to the protective layer is 60-100%.
One example of the structure of the optical recording medium according to the present invention is shown in FIG.
1
. The optical recording medium
10
comprises a substrate
1
and, provided thereon in succession, a reflective layer
2
, a first dielectric layer
3
, a recording layer
4
, a second dielectric layer
5
, a protective layer
6
and a lubricating layer
7
. As shown in
FIG. 1
, the lubrication layer
7
comprises a bonding lubricating layer
8
present on the protective layer
6
with bonding to the protective layer and a physical adsorptive lubricating layer
9
present on the bonding lubricating layer
8
and not bonded to the protective layer. As for the lubricating layer, it is known that this layer is also formed on the uppermost layer of conventional magnetic disks in order to reduce wear of the magnetic disk caused by magnetic head. The lubricant bonding rate is known as a measure for expressing the degree of bonding of such lubricating layer to a surface on which the lubricating layer

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