Protecting film for optical recording medium and optical recording medium
First Claim
1. An optical recording medium protecting film characterized by being a single transparent film made of a thermoplastic resin, having a glass transition temperature of 120°
- C. or higher and a water absorption of no greater than 1 wt %, and having a retardation at a wavelength of 550 nm that satisfies both of the following inequalities (1) and (2).|R(550)|≦
15 nm
(1)|K(550)|≦
40 nm
(2)where R(550) is the in-plane retardation of the transparent film at a wavelength of 550 nm and K(550) is the value calculated by k=[nz−
(nx+ny)/2]×
d (where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis, y-axis and z-axis directions, respectively, and d is the thickness of the transparent film) for the transparent film at a wavelength of 550 nm;
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Abstract
An optical recording medium protecting film which is a protecting film comprising a single transparent film made of a thermoplastic resin, having a retardation of no greater than 15 nm at a wavelength of 550 nm and a K value of no greater than 40 nm at 550 nm, having a glass transition temperature of 120° C. or higher and a water absorption of no greater than 1 wt %.
|R(550)|≦15 nm (1)
|K(550)|≦40 nm (2)
(the K value being calculated by K=[nz−(nx+ny)/2]×d {where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis, y-axis and z-axis directions, respectively, and d is the thickness of the transparent film}).
Also, an optical recording medium having a data recording layer and the above-mentioned protecting film on a substrate, wherein light is incident from the protecting film side.
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Citations
14 Claims
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1. An optical recording medium protecting film characterized by being a single transparent film made of a thermoplastic resin, having a glass transition temperature of 120°
- C. or higher and a water absorption of no greater than 1 wt %, and having a retardation at a wavelength of 550 nm that satisfies both of the following inequalities (1) and (2).
|R(550)|≦
15 nm
(1)|K(550)|≦
40 nm
(2)where R(550) is the in-plane retardation of the transparent film at a wavelength of 550 nm and K(550) is the value calculated by k=[nz−
(nx+ny)/2]×
d (where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis, y-axis and z-axis directions, respectively, and d is the thickness of the transparent film) for the transparent film at a wavelength of 550 nm;- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
R(450)/R(550)< - 1
(3)K(450)/K(550)<
1
(4)
where R(450) and R(550) are the in-plane retardation of the transparent film at wavelengths of 450 nm and 550 nm, respectively, and K(450) and K(550) are the values calculated by K=[nz−
(nx+ny)/2]×
d (where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis, y-axis and z-axis directions, respectively, and d is the thickness of the transparent film) for the transparent film at a wavelength of 450 nm and 550 nm respectively.
- C. or higher and a water absorption of no greater than 1 wt %, and having a retardation at a wavelength of 550 nm that satisfies both of the following inequalities (1) and (2).
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3. An optical recording medium protecting film according to claim 2, wherein the in-plane retardation of the transparent film in a wavelength range of 380-550 nm is lower as the wavelength is smaller.
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4. An optical recording medium protecting film according to claim 1, which comprises a transparent film
(1) which is a film made of a polymer comprising a monomer unit of a polymer with positive refractive index anisotropy (hereunder referred to as “ - first monomer unit”
) and a monomer unit of a polymer with negative refractive index anisotropy (hereunder referred to as “
second monomer unit”
);
(2) wherein the R(450)/R(550) of the polymer based on the first monomer unit is smaller than the R(450)/R(550) of the polymer based on the second monomer unit; and
(3) which has a positive refractive index anisotropy.
- first monomer unit”
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5. An optical recording medium protecting film according to claim 1, which comprises a transparent film
(1) which is a film made of a polymer comprising a monomer unit that forms a polymer with positive refractive index anisotropy (hereunder referred to as “ - first monomer unit”
) and a monomer unit that forms a polymer with negative refractive index anisotropy (hereunder referred to as “
second monomer unit”
);
(2) wherein the R(450)/R(550) of the polymer based on the first monomer unit is larger than the R(450)/R(550) of the polymer based on the second monomer unit; and
(3) which has a negative refractive index anisotropy.
- first monomer unit”
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6. An optical recording medium protecting film according to claim 1, wherein the thickness irregularity of the transparent film is no greater than 1.5 μ
- m.
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7. An optical recording medium protecting film according to claim 1, wherein said transparent film comprises a polycarbonate with a fluorene skeleton.
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8. An optical recording medium protecting film according to claim 6, characterized in that the transparent film is a transparent film made of a polycarbonate copolymer and/or blend comprising 10-90 mole percent of a repeating unit represented by the following formula (I)
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9. An optical recording medium protecting film according to claim 7, characterized in that the transparent film is a transparent film made of a polycarbonate copolymer and/or blend comprising 30-85 mole percent of a repeating unit represented by the following formula (III)
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10. An optical recording medium protecting film according to claim 5, wherein said polymer with positive refractive index anisotropy is poly(2,6-dimethyl-1,4-phenylene oxide), said polymer with negative refractive index anisotropy is polystyrene, and the polystyrene content is 67-75 wt % based on the total of said polymers with positive and negative refractive index anisotropy.
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11. An optical recording medium protecting film according to claim 1, characterized in that the transparent film is fabricated by solution cast film formation.
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12. An optical recording medium protecting film according to claim 1, characterized in that the film thickness of the transparent film is 5-200 μ
- m.
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13. An optical recording medium characterized by having a data recording layer and a protecting film on a substrate wherein light is incident from the side of said protecting film and said protecting film is a single transparent film made of a thermoplastic resin, having retardation at a wavelength of 550 nm that satisfies both of the following inequalities (1) and (2), a glass transition temperature of 120°
- C. or higher and a water absorption of no greater than 1 wt %.
|R(550)|≦
15 nm
(1)|K(550)|≦
40 nm
(2)where R(550) is the in-plane retardation of the transparent film at a wavelength of 550 nm and K(550) is the value calculated by K=[nz−
(nx+ny)/2]×
d (where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis, y-axis and z-axis directions, respectively, and d is the thickness of the transparent films) for the transparent film at a wavelength of 550 nm.- View Dependent Claims (14)
R(450)/R(550)< - 1
(3)K(450)/K(550)<
1
(4)
where R(450) and R(550) are the in-plane retardation of the transparent film at wavelengths of 450 nm and 550 nm, respectively, and K(450) and K(550) are the values calculated by K=[nz−
(nx+ny)/2]×
d (where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis,,y-axis and z-axis directions, respectively, and d is the thickness of the transparent film) for the transparent film at a wavelength of 450 nm and 550 nm respectively.
- C. or higher and a water absorption of no greater than 1 wt %.
Specification