Coating processes – Optical element produced
Reexamination Certificate
1998-11-30
2001-01-23
Evans, Elizabeth (Department: 1774)
Coating processes
Optical element produced
C427S294000, C427S296000, C428S064400, C428S457000, C428S913000, C430S270140, C430S495100, C430S945000
Reexamination Certificate
active
06177132
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical recording medium, and more particularly to an optical recording medium (or optical recording disk) on which data (or information) can be recorded and from which the recorded data can be read out (or reproduced) by using a semiconductor laser, the optical recording medium having on a substrate, a recording film formed of a compound known as a pigment material that exhibits a particularly large absorption at a specific wavelength region, for example 400 to 800 nm (for example, that absorbs light having a wavelength in this region at a relatively large amount), and a production method of the optical recording medium.
BACKGROUND ART
As an optical recording medium as described above, an optical disk (the so-called CD-R disk) of “write-once” type is practically available into which a user can write (or record) data only once. This optical recording medium Attachment A includes a recording film made of a pigment material, for example, an organic pigment material such as a cyanine based compound, a phthalocyanine based compound and so on.
In order to form the recording film on a substrate in the production of the optical disk as described above, a spin coating method is generally employed in which a pigment material is dissolved in a solvent to obtain a solution, which is applied onto the substrate by means of a spin coater and dried.
The recording film formed as described above generally has a thickness of 0.1 to 0.3 &mgr;m, and uniformity of thickness over the entire surface of the substrate is required. In order to meet this requirement, various measures are proposed such as developments of techniques for applying the pigment material including selection of solvents and precise control of a rotating table of the spin coater as well as thorough management of a surrounding atmosphere for performing the coating process and surface conditions of the substrate.
However, with the spin coating method as mentioned above, it is not easy to control thickness variation of the recording film among individual disks and/or thickness variation of the recording film within a single disk within a given degree by means of the conventional technique for forming the recording film or the management of the surrounding atmosphere for forming the recording film as described above when the thickness of the recording film to be formed is smaller, for example, near 0.1 &mgr;m.
Also, the spin coating method has an inherent problem that the thickness of the recording film changes along a radial direction of the disk, namely that the thickness of the recording film to be formed tends to be larger on an outer peripheral side than on an inner peripheral side of the disk. This renders it extremely difficult to stably form a recording film having a thickness which is uniform among individual disks or within a single disk.
Further, instead of the above-mentioned spin coating method, there is known a method of producing the optical recording medium characterized by forming the recording film on the substrate by means of a vacuum deposition method which is one of the so-called dry processes. It is expected that this method would improve the uniformity of the thickness of the recording film to be formed. However, this method involves other problems such as low productivity and dust adhesion. Therefore, in order to efficiently perform the vacuum deposition method, it is desired that these problems are at least suppressed or preferably substantially solved.
DISCLOSURE OF THE INVENTION
The purpose of the present invention is to alleviate the above-mentioned problems or preferably to substantially solve them. The present invention aims at suppressing variation in performance of the recording medium due to the variation in the thickness of the recording film among individual optical recording media and/or over a single optical recording medium, and thereby suppressing or eliminating the variation (or fluctuation) of the thickness of the recording film, hence the variation in performance, preferably to such a degree that substantially no problem occurs upon using the optical recording medium. In other words, the purpose of the invention is to provide an optical recording medium with improved quality and stability, thus being suitable for mass production, as well as a method of producing the optical recording medium.
The means provided by the present invention for solving the problems in order to achieve the above-mentioned object resides in a process of forming a recording film made of a pigment (or dye) material on a substrate by vapor deposition, wherein the pigment material is evaporated at a temperature of an evaporation vessel containing the pigment material, and then deposited on the substrate, the temperature being not less than an evaporation starting temperature of the pigment material and not more than 2.5 times as high as the evaporation starting temperature. It is noted that the temperature as used in this specification refers to a temperature expressed in Celsius scale (° C).
Thus, according to the first aspect of the present invention, there is provided a method of producing an optical recording medium including a recording film on a substrate by means of vapor deposition of a pigment material on the substrate under a high vacuum, the method comprising the step of heating an evaporation vessel containing the pigment material to a temperature which is not less than an evaporation starting temperature of the pigment material (i.e. a temperature at which the pigment material starts to evaporate) and not more than 2.5 times as high as the evaporation starting temperature of the pigment material, and preferably to a temperature which is 1.2 to 2.3 times as high as the evaporation starting temperature, whereby the pigment material is evaporated and then deposited on the substrate.
In other words, the present invention provides a method of producing an optical recording medium, for example, a recording medium of the “write-once” type, comprising the steps of:
(1) forming the recording film on the substrate as described above,
(2) forming a reflective film on the recording film, and
(3) forming a protective film on the reflective film.
Therefore, the state of the substrate on which the recording film is formed (i.e. the substrate having the recording film thereon) can be regarded as a precursor of the optical recording medium (a preliminary optical recording medium).
The steps (2) and (3) can be performed by means of a known method using a known material.
According to the second aspect of the present invention, there is provided an optical recording medium (for example, CD-R or DVD-R) comprising a recording film with improved uniformity of its thickness formed by means of vapor deposition of a pigment material onto a substrate under a high vacuum, wherein the pigment material is evaporated and then deposited on the substrate by heating an evaporation vessel which contains the pigment material to a temperature which is not less than an evaporation starting temperature of the pigment material (a temperature at which the pigment material starts to evaporate) and not more than 2.5 times as high as the evaporation starting temperature of the pigment material.
In other words, the present invention provides an optical recording medium comprising the recording film formed on the substrate by the above-mentioned method of the present invention, a reflective film formed on the recording film and a protective film formed on the reflective film.
It is noted that the uniformity of thickness of the recording film as used in the present invention refers to a state in which the variation of the thicknesses of the recording film among individual optical recording media or the variation of the thickness within a single optical recording medium, and preferably both of these variations are approximately the same as, preferably smaller than the variation of the thickness of the optical recording medium (or media) produced by the conventional spin coating method. Concretel
Kamiyama Toshibumi
Kunieda Toshiaki
Okazaki Sadayuki
Evans Elizabeth
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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