Dynamic optical information storage or retrieval – Optical storage medium structure – Disk protection
Reexamination Certificate
2002-12-26
2004-11-23
Miller, Brian E. (Department: 2652)
Dynamic optical information storage or retrieval
Optical storage medium structure
Disk protection
C369S275500, C428S064600
Reexamination Certificate
active
06823528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a protective film for optical disks and an optical disk using the protective film. More particularly, the present invention relates to a protective film for optical disks which is used for protecting an information recording layer of optical disks and exhibits no adverse effects on the functions of recording and regeneration of the optical disk and an optical disk comprising the protective film attached to the information recording layer via an adhesive layer.
2. Description of Related Art
Development of optical disks as the information recording media in recent years is remarkable. Already, disks used only for reading information such as CD and CD-ROM, optomagnetic disks called MOD or MD, phase-transition disks called PD and writable optical disks called CD-R are widely used. The recording capacity of these disks is about 650 MB (megabytes). Disks having greater capacities such as a series of optical disks called DVD (digital video disk) are developed. Specific examples of DVD include DVD-ROM (DVD allowing reading only), DVD-R (DVD allowing additional writing), DVD-RAM and DVD-RW (DVD allowing rewriting). DVDs of these types have two substrates laminated together. DVDs having a capacity of 4.7 GB (gigabytes) on one face and 9.4 GB on two faces have been practically used. For recording and regeneration of the information, a red laser beam having a wavelength of about 630 to 650 nm is used. DVDs are expected to be optical disks of the next generation which replace video cassettes currently used.
However, the DVD of the present stage has a problem in that, for example, the recording is limited to about 30 minutes in the case of high density images. In order that DVD is used more widely, it is desired that high density images of at least two hours can be recorded on one face. An optical disk having a great capacity is required to satisfy the above desire and recording and regeneration using a laser beam having a shorter wavelength is required for this purpose. Therefore, the use of a blue laser beam having a wavelength of about 400 to 432 nm is currently studied.
The track pitch and the pit size can be decreased by using a blue laser beam having a shorter wavelength. However, a problem arises due to the decreased wavelength in that the focal depth decreases and the specifications and methods applied to the currently used DVD which is obtained by laminating substrates each having a thickness of 0.6 mm (the total thickness of the substrates is 1.2 mm) cannot be applied.
Therefore, for example, it is examined that a protective film having a thickness of 0.1 mm and made of the same material as that of the substrate is laminated on the information recording layer disposed on a substrate having a thickness of 1.1 mm. In this case, it can be considered that an adhesive of the ultraviolet light curing type or a pressure-sensitive adhesive is used for lamination of the protective film. It is important that the adhesive or the pressure-sensitive adhesive does not adversely affect the functions of recording and regeneration of the optical disk.
SUMMARY OF THE INVENTION
The present invention has an object of providing a protective film for optical disks which is used for protecting the information recording layer of optical disks and does not adversely affect the functions of recording and regeneration of the optical disks, and an optical disk which has protective film laminated on the information recording layer and exhibits excellent reliability.
As the result of extensive studies by the present inventors to develop the protective film for optical disks having the above advantageous properties and the optical disk having the protective film and exhibiting excellent reliability, it was found that the above object could be achieved by using an adhesive film having an acrylic adhesive layer having specific properties on one face of a light transmitting substrate film and by an optical disk having a light transmitting film laminated on the information recording layer via an acrylic adhesive layer having specific properties. The present invention has been completed based on the above knowledge.
The present invention provides:
(1) A protective film for optical disks which comprises a light transmitting substrate film and a layer of acrylic adhesive disposed on one face of the substrate film, the acrylic adhesive comprising as a main component a polymer which comprises a (meth)acrylic ester-based monomer component, wherein, when T
a
represents an initial transmittance of light having a wavelength of 405 nm through the protective film and T
b
represents a transmittance of light having said wave length through the protective film after the protective film is left standing in an environment of a temperature of 80° C. and a relative humidity of 85% for 1,000 hours, a change in transmittance (X) expressed by equation [1]:
X
(%)=[(
T
a
−T
b
)/
T
a
]×100 [1]
is 10% or smaller and an amount of elution of halogen ions and an amount of elution of alkaline ions from an acrylic adhesive constituting the acrylic adhesive layer are each 10 ppm or smaller.
(2) A protective film according to claim
1
, wherein the polymer has a content of monomer component having nitrogen of 5.0% by mole or smaller based on the amount of the polymer.
(3) A protective film according to any one of (1) and (2), wherein the acrylic adhesive comprises 0.005 to 10% by weight of an antioxidant.
(4) A protective film according to any one of (1) to (3), wherein the acrylic adhesive has a total content of a residual solvent and a residual monomer of 100 ppm or smaller.
(5) A protective film according to any one of (1) to (4), wherein the polymer has a content of monomer component having carboxyl group of 10.0% by mole or smaller based on the amount of the polymer.
(6) An optical disk which comprises a substrate for an optical disk, an information recording layer disposed at least on one face of the substrate and a light transmitting film laminated on the information recording layer via an acrylic adhesive layer, wherein
when T
a
represents an initial transmittance of light having a wavelength of 405 nm through a laminate portion comprising the acrylic adhesive layer and the light transmitting film and T
b
represents a transmittance of light having said wave length through said laminate portion after the laminate portion is left standing in an environment of a temperature of 80° C. and a relative humidity of 85% for 1,000 hours, a change in transmittance (X) expressed by equation [1]:
X
(%)=[(
T
a
−T
b
)/
T
a
]×100 [1]
is 10% or smaller; and
when R
a
represents an initial reflectivity of light having a wavelength of 405 nm by the optical disk and R
b
represents a reflectivity of light having said wavelength by the optical disk after the optical disk is left standing under a same condition as that described above, a change in reflectivity (Y) by the optical disk expressed by equation [2]:
Y
(%)=[(
R
a
−R
b
)/
R
a
]×100 [
2
]
is 20% or smaller.
(7) An optical disk which comprises a substrate for optical disks, an information recording layer disposed at least on one face of the substrate and a light transmitting film laminated on the information recording layer via an acrylic adhesive layer, the optical disk exhibiting a bit error rate of 0.1% or smaller after the optical disk is left standing in an environment of a temperature of 80° C. and a relative humidity of 85% for 1,000 hours; and
(8) An optical disk which comprises a substrate for optical disks, an information recording layer disposed at least on one face of the substrate and a protective film for optical disks described in any one of claims (
1
) to (
5
) attached to the information recording layer via the acrylic adhesive layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The protective film of the present inv
Katoh Kazuya
Yamasaki Takeshi
Yukumoto Tomomi
Frishauf Holtz Goodman & Chick P.C.
Lintec Corporation
Miller Brian E.
LandOfFree
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