Plastic article or earthenware shaping or treating: apparatus – Preform assembly means and means for bonding of plural... – With additional shaping means to form or reshape preform...
Reexamination Certificate
2002-02-27
2003-12-09
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Preform assembly means and means for bonding of plural...
With additional shaping means to form or reshape preform...
C425S518000, C425S520000, C425S174400, C425S4360RM, C425S394000, C425S396000, C425S810000
Reexamination Certificate
active
06659759
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk, which is used in a recording and regenerating apparatus beyond NA O. 7, and on which multiple information layers of an optical disk medium is formed, in the optical disk medium used for each of various optical disk apparatuses such as DVD-ROM, DVD-RAM, and DVD-RW.
2. Description of the Related Art
A production method of a conventional optical disk substrate will be described. A plastic substrate on whose surface a concavo-convex pattern is reproduced is completed by injecting plastic substrate material (for example, polycarbonate etc.), which is dissolved at high temperature, in high pressure into a die equipped with a metal stamper, cooling the plastic substrate material, and taking out it. This technique is a present common production technique (injection molding method) of plastic substrates used for CD-Audio, CD-R, CD-ROM, DVD-ROM, DVD-R, DVD-RAM, DVD-RW, MO, etc. Then, a medium is formed by forming a reflective layer or a recording stacked layer on a surface of the concavo-convex pattern by sputtering as a signal-recording surface, and forming a protection layer with a UV cure resin so as to protect the signal-recording surface so that the signal-recording surface may not be damaged.
As means for higher densification, the enlargement of numerical aperture (NA) of a stop down lens and multiple stacking of a recording layer are mentioned. The multi-layer optical recording medium is shown in JP-A-8-297861. This is a multi-layer optical recording medium with large capacity that has two recording layers respectively on a plurality of substrates whose recording media are different from each other, that has the structure where substrates with two-layer recording layers are laminated so that their recording layers may face each other, and that has sufficient record and reproduction characteristics.
Since what is difficult in the case of multi-layer production is to produce uniform intervals (hereafter, thickness of a spacer layer) between layers, it is indispensable to make a substrate, which is in a light-incident side, thinner than 0.6 mm when the NA of a lens is large. In that case, it is difficult to transfer a concavo-convex pattern from a stamper on a substrate in the light-incident side and to form recording stacked layers sequentially on it, like a conventional way. It is because the substrate may be curled due to the stress caused by the formation of the recording stacked layer. Therefore, it is necessary to also transfer the pattern on a surface of the spacer layer and to form the recording stacked layer on it.
As for a production method of a spacer layer, a method of forming the spacer layer with an ultraviolet cure resin by a spin coating method is shown in JP-A-9-73671. A spin coating method is a method of dropping liquid from a nozzle, diffusing the liquid by rotation, and forming a layer. Here, the spacer layer is cured by irradiating the spacer layer with ultraviolet spot light with interlocking with the forming operation of the spacer layer and moving toward a peripheral side from a center of rotation. In addition, another production method of a spacer layer is shown in JP-A-2000-36165 as an example of using a dry photopolymer sheet. A dry photopolymer consists of a polymer, whose functional groups absorb light and react. Here, the production method of a spacer layer is mentioned, the method comprising the steps of placing a resin on a stamper, pressing a sheet with the stamper, transferring a signal, performing UV irradiation to the sheet with the stamper, curing the resin, and stripping the stamper.
As for a production method of a spacer layer, JP-A-9-73671 shows a method of forming the spacer layer with an ultraviolet cure resin by a spin coating method. Nevertheless, for example, when producing a disk with a diameter of 120 mm with this method, the thinner the spacer layer becomes due to shortening of wavelength or achievement of higher NA, the easier the disk is affected by the curvature of a substrate etc., and hence, it is difficult to decrease the dispersion of thickness of the spacer layer. In addition, in an example of using a dry photopolymer sheet in JP-A-2000-36165, it is described that, when a resin layer is heated, the entanglement of a portion where carbon atoms of a polymer lie in a long chain loosens, and hence the resin layer becomes soft to some extent. However, if the extent of this softening is enlarged, thickness becomes uneven when a pattern is transferred with pressing a sheet with a stamper, and when stripping the stamper after transfer as it is, the transferred pattern is collapsed by an adhesion force or the friction in a ramp of the pattern. On the other hand, if the extent of softening is decreased, there is a problem that transfer property is bad since the resin does not go into concavities of the stamper.
Examples of a case where the transfer property is good and a case where the transfer property is poor are shown in
FIGS. 16 and 17
. Since ROM (read only memory) differs in the geometry of a pattern from RAM (random access memory), each is shown. Since a thermoplastic organic material is softened by heating a sheet when the sheet is pressed against a stamper, the thermoplastic organic material is filled into the details of a stamper pattern, and hence, the concavo-convex pattern of the stamper is faithfully transferred by stripping the stamper after curing. When filling in this case is inadequate, it causes the lack of a pattern, and hence, transfer is unsuccessful.
An object of the present invention is to attain further high densification for producing a spacer layer with good pattern transcription.
SUMMARY OF THE INVENTION
The above-described issues are solved by the following methods.
(1) A production method of a spacer layer will be described. This method comprises the steps of forming a first recording stacked layer on a substrate, and heating a sheet with sandwiching the sheet, made by mixing photo-curing organic material with thermoplastic organic material, between the first recording stacked layer and the stamper for pattern transfer to transfer a pattern of the stamper to the sheet. The stamper is stripped after pattern transfer, and after that, light is radiated on the sheet. When photo-curing organic material and thermoplastic organic material softened by heating are mixed, the fundamental geometry, i.e., thickness, of a resin layer is maintained by the photo-curing organic material when the resin layer is heated, and the thermoplastic organic material distributed inside the resin layer in a granular or braided shape is remarkably softened, and hence, it becomes easy to transfer the concavo-convex pattern of the stamper by surface deformation. In photo-curing organic material, there are cationic polymerization type material that gradually performs curing reaction when light is radiated, and another type material that is cured immediately after light is radiated. When a reaction rate is slow, light irradiating is performed before pattern transfer to a spacer layer as a pattern for a second layer, and when a reaction rate is fast, light irradiating is performed after pattern transfer. Photoresistive organic material comprises, for example, a resin and a cationic initiator, and as examples of this type of resins, a cycloaliphatic epoxy resin, a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a phenol novolak type epoxy resin, a vinyl ether compound, an acrylic resin, etc. are mentioned. Photopolymerization initiators are, for example, benzoin, benzoin butyl ether, benzoin isopropyl ether, benzophenone, benzaldehyde, benzyl, benzoin ethyl ether, benzyl dimethyl ketal, xanthone, thio-xanthone, azobisisobutyronitril, benzoyl peroxide, a benzophenone/amine system. Mixing ratio is 0.01 to 10 wt % of cationic initiator to each resin. And photopolymerization initiators (photochemical sensitizers) commonly known are mentioned, whose mixing ratio is 0.1 to 5% to each resin. As thermoplastic resins, for example, a
Anzai Yumiko
Terao Motoyasu
Heckenberg Donald
Mackey James P.
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