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Protecting film for optical recording medium and optical recording medium

  • US 20050007944A1
  • Filed: 07/30/2004
  • Published: 01/13/2005
  • Est. Priority Date: 03/29/2000
  • Status: Abandoned Application
First Claim
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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, 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=[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;

    and the thickness irregularity of the transparent film is no greater than 1.5 μ

    m.

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