Protecting film for optical recording medium and optical recording medium

• US 20030043730A1
• Filed: 11/27/2001
• Published: 03/06/2003
• Est. Priority Date: 03/29/2000
• Status: Abandoned Application

• Current Assignee: Teijin Limited
• Original Assignee: Teijin Limited
• Inventors: Uchiyama, Akihiko, Kushida, Takashi, Tsujikura, Masakazu
• Application Number:
  US09/979,746
• Publication Number:
  US 20030043730A1
• Time in Patent Office: Days
• US Class Current: 369/275.5
• CPC Class Codes: G11B 7/24056 Light transmission layers lying on the light entrance side and being thinner than the substrate, e.g. specially adapted for Blu-ray® discs
• CPC Class Codes: G11B 7/244 comprising organic materials only
• CPC Class Codes: G11B 7/253 of substrates
• CPC Class Codes: G11B 7/254 of protective topcoat layers
• CPC Class Codes: G11B 7/2542 consisting essentially of organic resins

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=[n_z−(n_x+n_y)/2]×d {where n_x, n_y and n_z 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.

Claims

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=[n_z−

(n_x+n_y)/2]×

d (where n_x, n_y and n_z 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;

2. An optical recording medium protecting film according to claim 1, wherein the retardations at wavelengths of 450 nm and 550 nm satisfy (A) both the following inequalities (3) and (4), (B) the following inequality (3), or (C) the following inequality (4).

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=[n_z−

(n_x+n_y)/2]×

d (where n_x, n_y and n_z 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.

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.

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.

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.

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.

7. An optical recording medium protecting film according to claim 1, wherein said transparent film comprises a polycarbonate with a fluorene skeleton.

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)

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)

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.

11. An optical recording medium protecting film according to claim 1, characterized in that the transparent film is fabricated by solution cast film formation.

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.

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=[n_z−

(n_x+n_y)/2]×

d (where n_x, n_y and n_z 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.

14. An optical recording medium according to claim 13, wherein the retardations of said protecting film at wavelengths of 450 nm and 550 nm satisfy (A) both the following inequalities (3) and (4), (B) the following inequality (3), or (C) the following inequality (4).

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=[n_z−

(n_x+n_y)/2]×

d (where n_x, n_y and n_z 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.