METHOD OF PRODUCING STAMPER FOR OPTICAL RECORDING MEDIUM, METHOD OF PRODUCING SUBSTRATE, AND METHOD OF PRODUCING OPTICAL RECORDING MEDIUM

Abstract

A method of producing a stamper for roughening a substrate of an optical recording medium contains the steps of placing a conductive ring having a hole at the center thereof on a major surface of an original metal plate, electroforming a metal layer over a portion of the metal plate exposed in the hole of the conductive ring, an inner end-face of the conductive ring, and a portion of a major surface of the conductive ring, and entirely or partly roughening a major surface of the metal layer by a blasting treatment to obtain an original stamper.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a stamper for an optical recording medium, a method of producing a substrate, and a method of producing an optical recording medium, particularly a method of producing a stamper for an optical recording medium containing a substrate having an entirely or partly roughened major surface, a method of producing such a substrate, and a method of producing such an optical recording medium.

2. Description of the Related Art

In several known optical recording media such as CD-Rs and DVD-Rs, electronic information is recorded on a recording surface, and a label is attached to the reverse surface. Visible information of the contents of the electronic information, such as a song title of music data or a title of recorded data, is printed on the label, and the reverse surface is called a label surface.

Such optical recording media are produced by printing a title or the like on a circular label sheet using a printer, and by attaching the label sheet to the label surface.

Thus, the printer is needed in addition to a disc drive for producing the optical recording media. Data is recorded by the disc drive on the recording surface of the optical recording medium, the medium is removed from the disc drive, and then the label sheet printed by the printer is attached thereto. Therefore, complicated operations are required for producing the optical recording media.

Optical recording media with label surfaces, on which information can be displayed by changing the contrast using laser markers, have been proposed in Japanese Laid-Open Patent Publication No. 11-66617, etc. In the optical recording media, by using only an optical recording medium drive, information can be recorded on the recording surface and a visible image can be recorded on the label surface. Thus, additional printers are not needed, and also the complicated operations of attaching the label sheet are not required.

In optical recording media such as DVD-Rs, a substrate for a recording layer may have regular grooves, and also another substrate for a visible image recording layer may have such regular grooves. In this case, the grooves on the other substrate act as a diffraction grating for external lights to cause strong interference, thereby resulting in poor visibility of a recorded visible image.

Accordingly, there has been a demand for further improving the visibility of an image recorded on the label surface.

SUMMARY OF THE INVENTION

In view of the above problem, an object of the present invention is to provide a method for producing a stamper useful for producing an optical recording medium excellent in visibility of an image on a label surface, and a method for producing a substrate.

Another object of the present invention is to provide a method for producing an optical recording medium excellent in visibility of an image on a label surface.

According to a first aspect of the present invention, there is provided a method of producing a stamper for roughening a substrate of an optical recording medium, the method comprising the steps of: placing a conductive ring having a hole at a center thereof on a major surface of an original metal plate; electroforming a metal layer over a portion of the metal plate exposed in the hole of the conductive ring, an inner end-face of the conductive ring, and a portion of a major surface of the conductive ring; and entirely or partly roughening a major surface of the metal layer by a blasting treatment to obtain an original stamper.

In the first aspect, the obtained original stamper can be used for producing a stamper for an optical recording medium. Further, by using the stamper, an optical recording medium excellent in the visibility of an image on a label surface can be produced.

In the first aspect, the inner end-face of the conductive ring may contain a stepped surface or a tapered surface. The inner end-face may contain a tapered, stepped surface, and may have no steps, or no taper.

Further, in the first aspect, it is preferred that a pressing jig having a hole at the center thereof is used for pressing the conductive ring against the metal plate in the electroforming step, an inner diameter of the conductive ring being smaller than that of the pressing jig.

The major surface of the metal layer exposed in the hole of the conductive ring may be entirely or partly roughened by the blasting treatment after removing the metal plate.

In the first aspect, the method may further comprise the step of electroforming another metal layer on the roughened metal layer of the original stamper to obtain a second-generation stamper comprising the other metal layer.

The obtained second-generation stamper can be used for producing the product stamper. Further, a third-generation, fourth-generation, or fifth-generation . . . stamper may be produced by using the second-generation stamper, and may be used for producing the product stamper.

In the first aspect, a pit forming site for forming a pre-pit on the optical recording medium may be formed on the major surface of the metal plate. It is preferred that a transfer pattern of the pit forming site is formed on the major surface of the metal layer and the transferred pattern is protected before the blasting treatment for roughening the major surface of the metal layer.

According to a second aspect of the present invention, there is provided a method of producing a substrate for an optical recording medium having an image recording layer on which a visible image is recorded, the method comprising the steps of producing a stamper having an entirely or partly roughened major surface, and producing the substrate having an entirely or partly roughened major surface by using the stamper. The stamper producing step comprises the steps of: placing a conductive ring having a hole at a center thereof on a major surface of an original metal plate; electroforming a metal layer over a portion of the metal plate exposed in the hole of the conductive ring, an inner end-face of the conductive ring, and a portion of a major surface of the conductive ring; and entirely or partly roughening a major surface of the metal layer by a blasting treatment to obtain an original stamper.

By using the substrate produced by the method of the second aspect, an optical recording medium excellent in the visibility of an image on a label surface can be produced.

According to a third aspect of the present invention, there is provided a method of producing an optical recording medium having a substrate and an image recording layer on the substrate, a visible image being recorded on the image recording layer, the method comprising the steps of producing a stamper having an entirely or partly roughened major surface, and producing the substrate having an entirely or partly roughened major surface by using the stamper, and forming the image recording layer on the substrate. The stamper producing step comprises the steps of: placing a conductive ring having a hole at a center thereof on a major surface of an original metal plate; electroforming a metal layer over a portion of the metal plate exposed in the hole of the conductive ring, an inner end-face of the conductive ring, and a portion of a major surface of the conductive ring; and entirely or partly roughening a major surface of the metal layer by a blasting treatment to obtain an original stamper.

An optical recording medium excellent in the visibility of an image on a label surface can be produced by the method of the third aspect.

As described above, by using the stamper producing method, or the substrate producing method of the present invention, the optical recording medium excellent in the visibility of an image on a label surface can be obtained.

Further, by using the optical recording medium producing method of the present invention, the visibility of an image on a label surface can be improved.

The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view partly showing an optical recording medium according to an embodiment of the present invention;

FIG. 2 is a plan showing an optical recording medium of a modification example according to the embodiment;

FIG. 3 is an enlarged cross-sectional view showing a pre-pit region of the optical recording medium of FIG. 1;

FIG. 4 is a cross-sectional view partly showing a master stamper according to the embodiment;

FIG. 5 is a production process chart of a method according to the embodiment;

FIG. 6A is a cross-sectional view showing a metal plate used in the method according to the embodiment;

FIG. 6B is an enlarged cross-sectional view showing a portion of the metal plate;

FIG. 7A is a cross-sectional view showing a conductive ring placed on a metal plate;

FIG. 7B is an enlarged cross-sectional view showing a portion of the conductive ring;

FIG. 8 is a perspective view showing the conductive ring;

FIG. 9 is a cross-sectional view showing a conductive ring of a first modification example placed on the metal plate;

FIG. 10 is a cross-sectional view showing a conductive ring of a second modification example placed on the metal plate;

FIG. 11 is a cross-sectional view showing a conductive ring of a third modification example placed on the metal plate;

FIG. 12 is a cross-sectional view showing a conductive ring of a fourth modification example placed on the metal plate;

FIG. 13 is a cross-sectional view showing the conductive ring pressed against the metal plate by a pressing jig;

FIG. 14 is a cross-sectional view showing a first metal layer formed by Ni electroforming on a portion of the major surface of the conductive ring, the inner surface of the conductive ring, and a portion of the major surface of the metal plate;

FIG. 15 is a cross-sectional view showing an original stamper subjected to a blasting treatment after removing the metal plate;

FIG. 16 is an enlarged cross-sectional view showing a portion of the original stamper of FIG. 15;

FIG. 17A is a cross-sectional view showing a conductive ring pressed against a metal plate by a pressing jig in a first process;

FIG. 17B is a cross-sectional view showing a metal layer formed by Ni electroforming on a portion of the inner end-face of the conductive ring and a portion of a major surface of the metal plate;

FIG. 18A is a cross-sectional view showing an original stamper subjected to a blasting treatment after removing the metal plate;

FIG. 18B is a cross-sectional view showing the metal layer (a metal sheet) of the original stamper, isolated from the conductive ring after a blasting treatment;

FIG. 18C is a cross-sectional view showing the metal sheet greatly deformed after a blasting treatment;

FIG. 19A is a cross-sectional view showing a metal layer formed by Ni electroforming on a portion of a metal plate while using a pressing jig for pressing the metal plate in a second process;

FIG. 19B is a cross-sectional view showing the metal layer (a metal sheet) of an original stamper, isolated from the metal plate and subjected to a blasting treatment;

FIG. 19C is a cross-sectional view showing the metal sheet greatly deformed by the blasting treatment;

FIG. 20 is a cross-sectional view showing a second metal layer formed by Ni electroforming on a portion of a major surface of the first metal layer and a portion of the other major surface of the conductive ring in the method according to the embodiment;

FIG. 21A is a cross-sectional view showing a second-generation stamper of the second metal layer isolated from the major surface of the original stamper;

FIG. 21B is an enlarged cross-sectional view showing a portion of the second-generation stamper of FIG. 21A;

FIG. 22 is a cross-sectional view showing a third-generation stamper produced from the second-generation stamper by Ni electroforming;

FIG. 23 is a cross-sectional view showing a fourth-generation stamper produced from the third-generation stamper by Ni electroforming; and

FIG. 24 is a table showing the results of evaluating shape and warping state after blasting, probability of producing a second-generation stamper, and probability of producing a master stamper, in Example 1 and Comparative Examples 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the stamper producing method, the substrate producing method, and the optical recording medium producing method according to the present invention will be described below with reference to FIGS. 1 to 24.

An optical recording medium 10 according to this embodiment is such that information can be recorded thereon by irradiating one surface with a laser light, and a desired visible image can be recorded thereon by irradiating the other surface with the laser light. Thus, in this optical recording medium, at least an information recording layer and an image recording layer are formed in this order on a first substrate, and a second substrate is placed on the image recording layer. A third substrate may be disposed between the information recording layer and the image recording layer.

In the optical recording medium, a surface of the second substrate facing the image recording layer is partly roughened. The roughened portion of the surface of the second substrate may be referred to as “the roughened substrate surface” in the following description. The roughened substrate surface is formed by transferring a roughened pattern on a stamper for an optical recording medium onto the second substrate as hereinafter described.

The optical recording medium may have a structure of a DVD such as a DVD-R, an HD-DVD, etc. The structure is such a bonded structure that the first substrate having the information recording layer is attached to the second substrate having the image recording layer by an adhesion layer.

Further, the optical recording medium of the embodiment may have a structure of Blu-ray Disc (BD).

A specific structure example of the optical recording medium 10 according to this embodiment will be described below with reference to FIGS. 1 to 3.

The optical recording medium 10 shown in FIG. 1 has a first stack 12 and a second stack 14. The first stack 12 contains a transparent first substrate 16, an information recording layer 18 formed on the first substrate 16, and a first reflective layer 20 formed on the information recording layer 18. The second stack 14 contains a transparent second substrate 22, an image recording layer 24 formed on the second substrate 22, and a second reflective layer 26 formed on the image recording layer 24. The first stack 12 is attached to the second stack 14 by an adhesion layer 28, and the first reflective layer 20 faces the second reflective layer 26.

For example, data (pit information) can be recorded on and/or reproduced from the information recording layer 18 by irradiating the layer with a laser light through the first substrate 16.

For example, a visible image can be recorded on the image recording layer 24 by irradiating the layer with a laser light through the second substrate 22.

In the optical recording medium 10, a roughened substrate surface 30 is formed on a portion of the surface of the second substrate 22 facing the image recording layer 24. The surface roughness of the roughened substrate surface 30 of the second substrate 22 is preferably such that the arithmetic average roughness Ra is 0.05 to 0.3 μm and the ten-point average roughness Rz is 0.1 to 5 μm. The image visibility of the optical recording medium 10 is largely improved when the roughened substrate surface 30 has such a surface roughness. The values of Ra and Rz of the roughened substrate surface 30 on the second substrate 22 can be measured by an atomic force microscope (AFM), an optical interference-type roughness meter, a stylus-type roughness meter, or the like. The stylus-type roughness meter is particularly preferred because it has a long scanning length and a large dynamic range in the depth direction. Thus, the values of Ra and Rz are obtained by the stylus-type roughness meter in the present invention.

The roughened substrate surface 30 may be formed over the entire surface of the second substrate 22. The roughened substrate surface 30 is formed preferably in a region of 20 to 60 mm, more preferably in a region of 24 to 58 mm, from the center of the medium. When the roughened substrate surface 30 is formed in a region of less than 20 mm from the center, the visibility is seldom improved by the roughened substrate surface 30 because an optical pickup is hardly placed in the region. On the other hand, when the roughened substrate surface 30 is formed in a region of more than 58 mm from the center, it becomes difficult to wash the edge of the image recording layer 24.

In the optical recording medium 10, there is a pre-pit region 32 on a portion of the surface of the second substrate 22 (the surface on which the image recording layer 24 is formed). One or more pre-pits 34, preferably a plurality of pre-pits 34, are formed in the pre-pit region 32.

The combination of the pre-pits 34 may provide various information of the optical recording medium 10 such as information for distinguishing the presence of the image recording layer 24, information of output or a spot diameter of a laser light for forming a visible image on the image recording layer 24, or information of tone of a visible image.

Thus, by detecting the pre-pits 34, the presence of the image recording layer 24 in the optical recording medium 10 can be easily detected, and a visible image can be recorded on the image recording layer 24 under an optimum laser output with excellent imaging properties. Further, the combination of the pre-pits 34 may provide manufacturer information, etc.

The position of the pre-pit region 32 on the second substrate 22 is not particularly limited. For example, as shown in FIG. 2, the pre-pit region 32 may be formed inside a region having the image recording layer 24 (an imaging region 36) in an optical recording medium 10a of a modification example. In this case, the pre-pits 34 are not filled with a dye compound, so that a light returned from the pre-pits 34 is easily detected advantageously. It should be noted that, to prevent the image recording layer 24 from being formed in the pre-pit region 32, it is necessary to form a certain margin between the outer circumference of the pre-pit region 32 and the inner circumference of the imaging region 36.

As shown in FIG. 1, the pre-pit region 32 may be partly overlapped with the imaging region 36 to make the imaging region 36 as large as possible. Thus, a portion of the image recording layer 24 may be formed on a part of the pre-pit 34.

In the case of forming the pre-pit region 32 on an inner portion of the second substrate 22 as shown in FIGS. 1 and 2, the pre-pit region 32 is preferably in a region of 21 to 24 mm in the radius direction from the center of the second substrate 22.

The average of the depths hp of the pre-pits 34, shown in FIG. 3, is 150 to 400 nm, preferably 200 to 300 nm. When the average depth is 150 to 400 nm, a light returned from the pre-pits 34 can be converted to an electronic signal (a returned light signal) having a large signal amplitude, whereby the accuracy of reading the returned light signal can be improved. Further, when the average depth is 200 to 300 nm, the returned light signal can be detected more accurately.

The average of the widths W (the half widths, which are widths at half the depths hp) of the pre-pits 34 in the radius direction is preferably 200 to 500 nm, more preferably 250 to 450 nm. When the average width is 200 to 500 nm, the inter-track crosstalk superposed with the returned light signal is reduced, whereby a signal amplitude sufficient for detection can be obtained. The lengths (the half widths) of the pre-pits 34 in the circumferential direction are appropriately controlled depending on information to be recorded.

The ratio h1/h2, in which h1 represents an average thickness of the image recording layer 24 on the convex portions 34A of the pre-pits 34, and h2 represents an average thickness of the image recording layer 24 on the concave portions 34B, is preferably 0.1 to 0.9. The depth hp+h1−h2 of depression of the image recording layer 24 on the concave portions 34B is preferably 70 to 250 nm.

When the ratio h1/h2 and the depth hp+h1−h2 are within the above ranges, a surface of the image recording layer 24, on which the second reflective layer 26 is formed, has appropriate convexes and concaves suitable for reading a laser light, so that an excellent reproduced signal can be obtained. The ratio h1/h2 is more preferably 0.2 to 0.8, and the depth hp+h1−h2 is more preferably 100 to 200 nm, further preferably 120 to 180 nm.

The second reflective layer 26 is preferably formed along the image recording layer 24 as shown in FIG. 3. The ratio t1/t2, in which t1 represents an average thickness of the second reflective layer 26 on the convex portions 34A, and t2 represents an average thickness of the second reflective layer 26 on the concave portions 34B, is preferably 0.8 to 1.2, more preferably 0.9 to 1.1.

The above values of hp, h1, h2, etc. can be obtained by an AFM, a transmission spectrum, or an ellipsometer. Further, the values can be obtained by observing a cross-section of the produced optical recording medium 10 using an SEM, etc.

Stamper and Method of Producing the Same:

The above second substrate 22, which has the pre-pits 34 and the roughened substrate surface 30 on a portion of the surface, can be produced by using a master stamper 40 according to the present embodiment.

As shown in FIG. 4, in the master stamper 40, a pit forming site 42 for forming the pre-pits 34 on the inner surface of the second substrate 22 is formed in a portion of a major surface, and a roughened stamper surface 44 for forming the roughened substrate surface 30 on the second substrate 22 is formed in a portion of the major surface other than the pit forming site 42. The pit forming site 42 contains concave portions and convex portions, and the average height of the convex portions is preferably 150 to 400 nm. The optical recording medium 10 can be efficiently produced by using the master stamper 40.

The method of the present invention for producing the master stamper 40 will be described below with reference to FIGS. 5 to 23.

First, an original metal plate 46 is prepared as shown in step S1 of FIG. 5, and FIGS. 6A and 6B. First pit forming sites 48 for forming the pit forming site 42 on the master stamper 40 are formed on a flat major surface 46a of the metal plate 46. The metal plate 46 is a Ni disc produced by Ni (nickel) electroforming. The enlarged view of FIG. 6B illustrates only an area near the center line m, as with the other enlarged views to be hereinafter described.

The thickness ta of the metal plate 46 may be approximately 300 μm, which is a usual thickness for producing the master stamper 40. The thickness ta may be 140 to 160 μm, and in this case, the time required for the Ni electroforming for producing the metal plate 46 can be reduced, resulting in a high productivity. In addition to the above Ni, Cu (copper), Al (aluminum), Ni alloys, Cu alloys, Al alloys, etc. may be used for the metal plate 46.

Then, as shown in step S2 of FIG. 5, and FIGS. 7A, 7B, and 8, a conductive ring 52 having a hole 50 at the center is placed on the major surface 46a of the metal plate 46. The conductive ring 52 is, for example, composed of a stainless steel, and one or more steps 54 are formed on the inner end-face 56 of the hole 50. In other words, as shown in FIG. 7B, the inner end-face 56 of the conductive ring 52 contains two or more stepped surfaces 58a, 58b with different diameters. Step 54 is a surface parallel to a major surface 52a of the conductive ring 52, and the stepped surfaces 58a, 58b are surfaces perpendicular to the major surface 52a, facing the central axis (shown by a dashed-dotted line m) of the conductive ring 52. In the example of FIGS. 7A, 7B, and 8, one step 54 is formed in the inner end-face 56 of the conductive ring 52, and two stepped surfaces (a first stepped surface 58a and a second stepped surface 58b) are formed in the inner end-face 56. The inner diameter D1 of the first stepped surface 58a is larger than the inner diameter D2 of the second stepped surface 58b. The inner end-face 56 may contain three or more stepped surfaces.

A plurality of modification examples of the conductive ring 52 with various shapes will be described below.

As shown in FIG. 9, in a conductive ring 52A of a first modification example, the inner end-face 56 is a tapered surface 60. More specifically, the tapered surface 60 of the conductive ring 52 is such that the inner diameter D1 of the major surface 52a is larger than the inner diameter D2 of the other major surface 52b (the surface in contact with the metal plate 46), and the inner diameter is continuously reduced from the major surface 52a to the other major surface 52b.

As shown in FIG. 10, in a conductive ring 52B of a second modification example, the inner end-face 56 has a shape of a combination of the conductive ring 52 shown in FIG. 7A and the conductive ring 52A shown in FIG. 9. Thus, the first stepped surface 58a of the inner end-face 56 corresponds to the tapered surface 60.

As shown in FIG. 11, in a conductive ring 52C of a third modification example, the inner end-face 56 has a shape of a combination of the conductive ring 52 shown in FIG. 7A and the conductive ring 52A shown in FIG. 9. Thus, the second stepped surface 58b of the inner end-face 56 corresponds to the tapered surface 60.

As shown in FIG. 12, in a conductive ring 52D of a fourth modification example, the inner end-face 56 has a shape of a combination of the conductive ring 52 shown in FIG. 7A and the conductive ring 52A shown in FIG. 9. Thus, the first and second stepped surfaces 58a and 58b of the inner end-face 56 correspond to the tapered surface 60.

The above modification examples of the conductive ring 52 are considered in all respects to be illustrative and not restrictive, and various changes may be made in the number of the steps, the number of the tapered surfaces, etc.

Then, the electroforming step S3 of FIG. 5 is carried out. As shown in FIG. 13, a pressing jig 64 for pressing the conductive ring 52 against the metal plate 46, which has a hole 62 at the center, is used in the electroforming. The inner diameter D3 of the pressing jig 64 is larger than the inner diameter D1 of the largest stepped surface of the conductive ring 52 (the first stepped surface 58a in this case), and smaller than the outer diameter D4 of the metal plate 46. Thus, the conductive ring 52 can be brought into tight contact with and pressed against the metal plate 46 by the pressing jig 64 while preventing the center portion of the conductive ring 52 from rising. Further, because the inner diameter D3 of the pressing jig 64 is larger than the inner diameter D1 of the first stepped surface 58a of the conductive ring 52, a portion of the major surface 52a around the hole 50 is exposed in the hole 62 of the pressing jig 64.

A Ni electroforming process is carried out while using the pressing jig 64 for pressing the conductive ring 52 against the metal plate 46. A portion of the major surface 46a exposed in the hole 50, the inner end-face 56 of the conductive ring 52, and a portion of the major surface 52a of the conductive ring 52 are covered with a first metal layer 66 (an Ni layer) by the Ni electroforming. The first metal layer 66 formed by the Ni electroforming has a thickness of approximately 300 μm, moreover the thickness can be increased more than 300 μm.

Then, step S4 of the blasting treatment in FIG. 5 is carried out. As shown in FIG. 15, the metal plate 46 is removed, and the major surface 66a of the first metal layer 66, exposed in the hole 50 of the conductive ring 52, is partly roughened by the blasting treatment. Thus, first roughened surfaces 68 are formed on a portion of the major surface 66a of the first metal layer 66 by the blasting treatment. In the blasting treatment, metal particles or non-metal particles such as silica sand, emery, glass beads, resin beads, or SiC particles are sprayed onto a blasting subject surface at a high speed, to roughen the surface.

When the metal plate 46 is removed, the first pit forming site 48 of the metal plate 46 (shown in FIGS. 6A and 6B) is transferred onto the first metal layer 66 to form a second pit forming site 70. Thus, the second pit forming site 70 is protected before the blasting treatment to prevent the second pit forming site 70 from being broken by the blasting treatment. The second pit forming site 70 may be protected by placing a metal sheet mask 72, or by forming a mask 74 of an adhesive tape, an oxide film or the like.

Thus, after the second pit forming site 70 is protected, a portion of the major surface 66a of the first metal layer 66 is roughened by the blasting treatment to form the first roughened surfaces 68. In this step, an original stamper 76 composed of the first metal layer 66 and the conductive ring 52 is produced. In a case where the pre-pits 34 are not formed in the optical recording medium 10, the first pit forming site 48 on the metal plate 46 and the second pit forming site 70 on the first metal layer 66 are not needed, and the major surface 66a of the first metal layer 66 may be entirely roughened by the blasting treatment.

The following two processes (a first process and a second process) for producing the master stamper 40 have been examined in view of accomplishing the present invention.

In the first process, as shown in FIG. 17A, a conductive ring 80, which has a hole 78 at the center and has no stepped surfaces, is placed on a major surface 46a of a metal plate 46. Then, a Ni electroforming step is carried out while pressing the conductive ring 80 against the metal plate 46 by using a pressing jig 82. The inner diameter D3 of the pressing jig 82 is equal to the inner diameter D5 of the conductive ring 80 in the first process, whereby a metal layer 84 is formed by the Ni electroforming on a portion of the major surface 46a of the metal plate 46 exposed in the hole 78 of the conductive ring 80 and a portion of the inner end-face of the conductive ring 80 as shown in FIG. 17B. Thus, when the metal plate 46 is removed, the metal layer 84 is held only by the inner end-face 86 of the conductive ring 80 as shown in FIG. 18A.

When the metal layer 84 is then subjected to a blasting treatment, the metal layer 84 is isolated from the conductive ring 80 by the pressure of non-metal particles or metal particles colliding with the metal layer 84 as shown in FIG. 18B. The metal layer 84 isolated from the conductive ring 80 is represented as a metal sheet 88. During the blasting treatment, the non-metal particles or metal particles are colliding with the metal sheet 88, which is disadvantageously warped and greatly deformed such that a major surface 88a becomes a convex surface as shown in FIG. 18C. As a result of the examination, the height ha between the edge and the top of the warped metal sheet 88 was several tens of mm.

In the second process, as shown in FIG. 19A, a pressing jig 82 is placed directly on a metal plate 46 without a conductive ring 80, and then a Ni electroforming step is carried out. A metal layer 84 is formed only on the metal plate 46 by the Ni electroforming in the second process. When the metal plate 46 is removed, the metal layer 84 is in the state of a metal sheet 88 as shown in FIG. 19B, as with the first process. Thus, when the non-metal particles or metal particles are colliding with the metal sheet 88 during a blasting treatment, the metal sheet 88 is disadvantageously warped and greatly deformed such that a major surface 88a becomes a convex surface as shown in FIG. 19C. As a result of the examination, the height ha between the edge and the top of the warped metal sheet 88 was several tens of mm.

In the above first and second processes, the metal sheet 88 is greatly deformed, so that a master stamper 40 with a partly roughened surface cannot be produced.

In contrast, in this embodiment of the present invention, the first metal layer 66 is formed over the inner end-face 56 and a portion of the major surface 52a in the conductive ring 52 as shown in FIG. 15, and further the two or more stepped surfaces with different diameters (the first stepped surface 58a and the second stepped surface 58b) are formed on the inner end-face 56, whereby the contact area between the first metal layer 66 and the conductive ring 52 is remarkably large and the first metal layer 66 is not isolated from the conductive ring 52 in the following blasting treatment. Thus, the master stamper 40 having a partly roughened surface can be produced with high accuracy by the method of the present embodiment.

In this embodiment, in step S5 of FIG. 5, a further Ni electroforming is carried out using the original stamper 76 having the first metal layer 66 with a major surface 66a partly roughened. As shown in FIG. 20, a second metal layer 90 is formed by the Ni electroforming on a major surface 76a of the original stamper 76. Specifically, the second metal layer 90 (an Ni layer) is formed over a portion of the major surface 66a of the first metal layer 66 exposed in the hole 50 and a portion of the other major surface 52b of the conductive ring 52. The second metal layer 90 formed by the Ni electroforming has a thickness of approximately 300 μm.

In step S6 of FIG. 5, as shown in FIGS. 21A and 21B, the second metal layer 90 is isolated from the major surface of the original stamper to obtain a second-generation stamper 92 made of the metal. A third pit forming site 94 is formed on a major surface 92a of the second-generation stamper 92, and it has a transfer pattern of the second pit forming site 70 on the major surface 66a of the first metal layer 66 in the original stamper 76 shown in FIG. 16. In addition, a second roughened surface 96 is formed in the major surface 92a, and it has a transfer pattern of the first roughened surface 68 formed in the major surface 66a of the first metal layer 66.

A plurality of the second-generation stampers 92 can be produced using the original stamper 76 by repeating steps S5 and S6 of FIG. 5.

The second-generation stamper 92 may be used as the master stamper 40 for producing the above second substrate 22, or a third-generation stamper 98 shown in FIG. 22 may be produced from the second-generation stamper 92 by Ni electroforming and may be used as the master stamper 40 for producing the second substrate 22. In this case, a fourth pit forming site 100 is formed on a major surface 98a of the third-generation stamper 98, and it has a transfer pattern of the third pit forming site 94 on the major surface 92a of the second-generation stamper 92 shown in FIG. 21B. In addition, a third roughened surface 102 is formed in the major surface 98a, and it has a transfer pattern of the second roughened surface 96 formed in the major surface 92a of the second-generation stamper 92. An example of the third-generation stamper 98 used as the master stamper 40 is shown in FIG. 4. Thus, the fourth pit forming site 100 of FIG. 22 corresponds to the pit forming site 42 of FIG. 4, and the third roughened surface 102 of FIG. 22 corresponds to the roughened stamper surface 44 of FIG. 4.

Further, a fourth-generation stamper 104 shown in FIG. 23 may be produced using the third-generation stamper 98 by Ni electroforming and may be used as the master stamper 40. In this case, a fifth pit forming site 106 is formed on a major surface 104a of the fourth-generation stamper 104, and it has a transfer pattern of the fourth pit forming site 100 on the major surface 98a of the third-generation stamper 98 shown in FIG. 22. In addition, a fourth roughened surface 108 is formed in the major surface 104a, and it has a transfer pattern of the third roughened surface 102 formed in the major surface 98a of the third-generation stamper 98.

The third-generation stamper 98 and the fourth-generation stamper 104 can be repeatedly produced by the Ni electroforming using the second-generation stamper 92 and the third-generation stamper 98 respectively. Thus, a large number of the master stampers 40 can be more easily produced with lower production costs and higher productivity in the case of using the third-generation or fourth-generation stampers, as compared with the case of using the second-generation stamper 92 as the master stamper 40.

As described above, in this embodiment, a portion of the major surface 66a of the first metal layer 66 in the original stamper 76 is roughened by the blasting treatment to form the first roughened surface 68, and any one of the second-generation stamper 92, the third-generation stamper 98, and the fourth-generation stamper 104, having the transfer pattern of the first roughened surface 68, can be used as the master stamper 40. Therefore, an incident light is easily scattered on the roughened substrate surface 30 of the second substrate 22 produced by using the master stamper 40, whereby an image formed thereon is visible from any direction. Thus, the resultant optical recording medium 10 has an excellent visibility of the image on the label surface.

The surface roughness of the roughened stamper surface 44 of the master stamper 40 is preferably such that the arithmetic average roughness Ra is 0.05 to 0.3 μm and the ten-point average roughness Rz is 0.1 to 5 μm. The values of Ra and Rz of the roughened stamper surface 44 of the master stamper 40 are measured by a stylus-type roughness meter.

The structure of the optical recording medium 10 is not particularly limited as long as it contains the pre-pit region 32 with one or more pre-pits 34 and the image recording layer 24 on which a visible image can be formed by irradiation of a laser light. Thus, the optical recording medium 10 may be a read-only-, WORM (Write Once, Read Many)-, or rewritable-type medium, and is preferably a WORM-type medium. The recording manner of the optical recording medium 10 may be selected from phase change-, magnetic optical-, and dye-type recording manners without particular restrictions, and is preferably dye-type.

The optical recording medium 10 shown in FIG. 1 is such that the information recording layer 18 on the first substrate 16 is attached to the image recording layer 24 on the second substrate 22. Thus, the optical recording medium 10 is preferably used for DVDs such as DVD-Rs, DVD-RWs, and HD DVDs.

Examples of the layer structure of the optical recording medium 10 include the following first to sixth unillustrated layer structures in addition to the above structure shown in FIG. 1.

(1) The first layer structure is such that the information recording layer 18, the first reflective layer 20, and the adhesion layer 28 are formed in this order on the first substrate 16, and the second substrate 22 having the image recording layer 24 is attached to the adhesion layer 28.

(2) The second layer structure is such that the information recording layer 18, the first reflective layer 20, a protective layer, and the adhesion layer 28 are formed in this order on the first substrate 16, and the second substrate 22 having the image recording layer 24 is attached to the adhesion layer 28.

(3) The third layer structure is such that the information recording layer 18, the first reflective layer 20, a first protective layer, the adhesion layer 28, and a second protective layer are formed in this order on the first substrate 16, and the second substrate 22 having the image recording layer 24 is attached to the second protective layer.

(4) The fourth layer structure is such that the information recording layer 18, the first reflective layer 20, a first protective layer, the adhesion layer 28, a second protective layer, and a third protective layer are formed in this order on the first substrate 16, and the second substrate 22 having the image recording layer 24 is attached to the third protective layer.

(5) The fifth layer structure is substantially equal to the structure of FIG. 1, and is such that the information recording layer 18, the first reflective layer 20, the adhesion layer 28, and the second reflective layer 26 are formed in this order on the first substrate 16, and the second substrate 22 having the image recording layer 24 is attached to the second reflective layer 26.

(6) The sixth layer structure is such that the information recording layer 18, the first reflective layer 20, and a first protective layer are formed in this order on the first substrate 16, the image recording layer 24, the second reflective layer 26, and a second protective layer are formed in this order on the second substrate 22, and the first protective layer is attached to the second protective layer by the adhesion layer 28.

The layer structure of FIG. 1 and the first to sixth layer structures are considered in all respects to be illustrative and not restrictive, and the above layers may be formed in another order and the layers other than the image recording layer 24 may be removed. Further, each of the layers may have a single- or multi-layer structure.

When an optical information is recorded or reproduced on the optical recording medium 10, the first substrate 16 side of the optical recording medium 10 is irradiated with a laser light having a predetermined wavelength, which may be 650 to 670 nm for DVD-Rs and 400 to 410 nm or less for HD-DVDs.

When a visible image is recorded on the image recording layer 24, the second substrate 22 side of the optical recording medium 10 is irradiated with a laser light (such as a laser light having a linear speed of 3.5 m/s, a wavelength of 660 nm, an NA value of 0.6, and a medium surface power of 10 mW), and the irradiated portions are degenerated to change the contrast, which results in the visibility of the image.

In the present invention, the desired image can be efficiently recorded on the label surface (the image recording surface) of the optical recording medium 10 by the laser light using an optical recording medium drive without a printer or the like. Further, the surface of the second substrate 22, facing the image recording layer 24, is roughened, whereby the visibility of the image can be improved.

In this embodiment, the first substrate 16 is disposed on one side of the information recording layer 18, etc., and the second substrate 22 is disposed on the other side. The second substrate 22 may have a cover layer, a transparent sheet, or the like. Thus, the optical recording medium 10 of this embodiment may have a structure of CDs such as CD-Rs, in which an information recording layer, an image recording layer, and a cover layer are formed in this order on a substrate.

In the CD-type structure, the information recording layer 18, the first reflective layer 20, a protective layer, the second reflective layer 26, and the image recording layer 24 are formed in this order on the first substrate 16, and a roughened cover layer is formed on the image recording layer 24. In this structure, the surface of the cover layer, facing the image recording layer 24, is roughened, whereby the image visibility can be improved.

In this case, when optical information is recorded or reproduced on the CD-type optical recording medium 10, the first substrate 16 side of the optical recording medium 10 is irradiated with a laser light having a predetermined wavelength of 660 nm, etc.

When a visible image is recorded on the image recording layer 24, the cover layer side (the second substrate 22 side) of the CD-type optical recording medium 10 is irradiated with a laser light, and the irradiated portions are degenerated to change the contrast as a visible image.

Thus, even when the optical recording medium has the CD-type structure, an image can be formed thereon by a laser light. The desired image can be efficiently recorded on the label surface (the image recording surface) of the optical recording medium 10 by using an optical recording medium drive without a printer or the like. Further, the surface of the second substrate 22, facing the image recording layer 24, is roughened, whereby the visibility of the image can be improved.

The optical recording medium 10 having the DVD-type structure shown in FIG. 1 may be produced in the following manner. Thus, for example, the master stamper 40 having the roughened stamper surface 44 on one major surface is prepared, the second substrate 22 having the roughened substrate surface 30 on one major surface is prepared using the master stamper 40, the image recording layer 24 is formed on the second substrate 22, the information recording layer 18 is formed on the first substrate 16, and the first substrate 16 and the second substrate 22 are bonded such that the information recording layer 18 and the image recording layer 24 face each other, whereby the optical recording medium 10 can be produced.

A reflective layer or a protective layer may be formed in the step of forming the information recording layer and the step of image recording layer if necessary.

The optical recording medium having the CD-type structure can be produced by forming at least the information recording layer 18, the image recording layer 24, and a cover layer (the second substrate 22) having a roughened surface on the first substrate 16.

The layer structure of FIG. 1 and the first to sixth layer structures are considered in all respects to be illustrative and not restrictive, and the above layers may be formed in another order and the layers other than the image recording layer 24 may be removed. Further, each of the layers may have a single- or multi-layer structure.

The layers and forming methods thereof will be described below with reference to the layer structure of the optical recording medium 10 shown in FIG. 1.

(Information Recording Layer 18)

The information recording layer 18 is a layer on which information, particularly code information such as digital information, is recorded and reproduced by a laser light.

The information recording layer 18 may be a dye recording layer or a phase change recording layer, and is preferably a dye recording layer.

Examples of dyes used in the information recording layer 18 include cyanine dyes, oxonol dyes, azo dyes, phthalocyanine dyes, triazole compounds such as benzotriazole compounds, triazine compounds, merocyanine compounds, aminobutadiene compounds, cinnamic acid compounds, benzoxazole compounds, pyrromethene compounds, and squarylium compounds. The dyes may have a metal atom as a coordination center.

Dyes described in Japanese Laid-Open Patent Publication Nos. 4-74690, 8-127174, 11-53758, 11-334204, 11-334205, 11-334206, 11-334207, 2000-43423, 2000-108513, and 2000-158818 may be used in the present invention.

When the optical recording medium is a CD-R, preferred ones among the above are the cyanine dyes, azo dyes, and phthalocyanine dyes. When the optical recording medium is a DVD-R, preferred ones are the cyanine dyes, oxonol dyes, azo dyes (including Ni complexes and Co complexes), and pyrromethene compounds. When the optical recording medium is a Blu-ray disc or an HD-DVD, preferred ones are the cyanine dyes, oxonol dyes, azo dyes, phthalocyanine dyes, benzotriazole compounds, and triazine compounds.

Further, the cyanine dyes, azo dyes, and phthalocyanine dyes are more preferred in the case of the CD-R, the cyanine dyes, oxonol dyes, and azo dyes (including Ni complexes and Co complexes) are more preferred in the case of the DVD-R, and the cyanine dyes, oxonol dyes, azo dyes, and phthalocyanine dyes are more preferred in the case of the Blu-ray disc or HD-DVD.

The information recording layer 18 may be formed by the steps of dissolving a binder, etc. and a recording substance such as the dye in an appropriate solvent to prepare a coating liquid, applying the coating liquid to the first substrate 16, and drying the applied liquid. The concentration of the recording substance in the coating liquid is generally 0.01% to 15% by mass, preferably 0.1% to 10% by mass, more preferably 0.5% to 5% by mass, most preferably 0.5% to 3% by mass.

The information recording layer 18 may be formed by vapor deposition, sputtering, CVD, or liquid coating, and is preferably formed by liquid coating. In the case of the liquid coating, a quencher, a binder, or the like is dissolved in the solvent together with the dye, etc. if necessary, and the obtained coating liquid is applied to the substrate and dried.

Examples of the solvents for the coating liquid include esters such as butyl acetate, ethyl lactate, and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; chlorinated hydrocarbons such as dichloromethane, 1,2-dichloroethane, and chloroform; amides such as dimethylformamide; hydrocarbons such as methylcyclohexane; ethers such as dibutyl ether, diethyl ether, tetrahydrofuran, and dioxane; alcohols such as ethanol, n-propanol, isopropanol, n-butanol, and diacetone alcohol; fluorine-containing solvents such as 2,2,3,3-tetrafluoropropanol; and glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether.

These solvents may be used singly or in combination depending on the solubility of the dye. Various additives such as antioxidants, UV absorbers, plasticizers, and lubricants may be added to the coating liquid if necessary.

Examples of the binders include natural organic high-molecular substances such as gelatins, cellulose derivatives, dextrans, rosins, and rubbers, and synthetic organic high-molecular substances. The synthetic organic high-molecular substances include hydrocarbon resins such as polyethylenes, polypropylenes, polystyrenes, and polyisobutylene; vinyl resins such as polyvinyl chlorides, polyvinylidene chlorides, and vinyl chloride-vinyl acetate copolymers; acrylic resins such as polymethyl acrylates and polymethyl methacrylates; and initial condensation products of thermosetting resins such as polyvinyl alcohols, chlorinated polyethylenes, epoxy resins, butyral resins, rubber derivatives, and phenol-formaldehyde resins.

In the case of using the binder in the information recording layer 18, the mass of the binder is generally 0.01 to 50 times the dye, preferably 0.1 to 5 times the dye.

The coating liquid may be applied by a spraying method, a spin coating method, a dipping method, a roll coating method, a blade coating method, a doctor roll method, a screen printing method, etc. The information recording layer may have a single- or multi-layer structure. The thickness of the information recording layer is generally 10 to 500 nm, preferably 15 to 300 nm, more preferably 20 to 150 nm.

An anti-fading agent may be added to the information recording layer 18 to increase the light fastness. In general, the anti-fading agent is a singlet oxygen quencher.

The singlet oxygen quencher may be selected from those described in known publications such as patent publications.

Specific examples of the singlet oxygen quenchers include those described in Japanese Laid-Open Patent Publication Nos. 58-175693, 59-31194, 60-18387, 60-19586, 60-19587, 60-35054, 60-36190, 60-36191, 60-44554, 60-44555, 60-44389, 60-44390, 60-54892, 60-47069, 63-209995, and 4-25492, Japanese Patent Publication Nos. 1-38680 and 6-26028, Germany Patent No. 350399, Nippon Kagakukaishi, 1992, October issue, Page 1141, etc.

The ratio of the anti-fading agent such as the singlet oxygen quencher to the dye is generally 0.1% to 50% by mass, preferably 0.5% to 45% by mass, further preferably 3% to 40% by mass, particularly preferably 5% to 25% by mass.

In a case where the information recording layer 18 is a phase change-type recording layer, it is preferred that the layer comprises a phase change-type optical recording material containing Ag, Al, In, Te, or Sb, which can be converted to at least two stages of the crystalline state and the amorphous state. Specific examples of such optical recording materials include Sb—Te alloys, Ge—Sb—Te alloys, Pd—Ge—Sb—Te alloys, Nb—Ge—Sb—Te alloys, Pd—Nb—Ge—Sb—Te alloys, Pt—Ge—Sb—Te alloys, Co—Ge—Sb—Te alloys, In—Sb—Te alloys, Ag—In—Sb—Te alloys, Ag—V—In—Sb—Te alloys, and Ag—Ge—In—Sb—Te alloys. Among them, Ge—Sb—Te alloys and Ag—In—Sb—Te alloys are capable of rewriting many times, and thus are preferably used. The thickness of the phase change-type information recording layer 18 is preferably 10 to 50 nm, more preferably 15 to 30 nm.

The phase change-type information recording layer 18 may be formed by a gas-phase film deposition method such as a sputtering method or a vacuum vapor deposition method. A known dielectric layer may be formed on the information recording layer 18 if necessary.

(Image Recording Layer 24)

As described above, the optical recording medium 10 contains the image recording layer 24, which is closer to the second substrate 22 (or the cover layer) than the information recording layer 18. A desired visible image (visible information) such as character, figure, or picture is recorded on the image recording layer 24. The visible image is an image that can be visually detected, and may contain any visible information such as a character (text), picture, or figure.

The visible image recorded on the image recording layer 24 may contain a desired image such as a character, figure, or picture. Specifically, the visible image may contain a disc title, content information, a thumbnail of contents, a related picture, a design picture, a copyright notice, a recording date, a recording method, a recording format, a bar code, etc.

Further, the visible image may contain character information such as accessible personal information, accessible period information, accessible number information, rental information, resolution information, layer information, user designation information, copyright holder information, copyright number information, manufacturer information, manufacturing date information, sale date information, vendor or seller information, set number information, regional designation information, language designation information, use designation information, user information, or use number information.

The image recording layer 24 is not particularly limited as long as a visible image such as a character, image, or picture can be recorded thereon by irradiation of a laser light. It is preferred that the image recording layer 24 contains a dye compound from the viewpoint of forming a clear visible image by the irradiation of a laser light. The dye compound for the image recording layer 24 is preferably selected from the above described examples of the dyes for the information recording layer 18. It is preferred from the viewpoint of costs that the image recording layer 24 is formed by applying a coating liquid containing the dye compound by spin coating.

In the optical recording medium 10, the component (the dye or the phase change recording material) of the information recording layer 18 may be the same as or different from the component of the image recording layer 24. Because the desired functions are different between the information recording layer 18 and the image recording layer 24, the components thereof are preferably different. Specifically, it is preferred that the information recording layer 18 comprises a component excellent in recording/reproducing properties, and the image recording layer 24 comprises a component capable of forming a high-contrast image. In the case of using the dye, it is particularly preferred that the image recording layer 24 comprises a cyanine dye, a phthalocyanine dye, an azo dye, an azo metal complex, or an oxonol dye from the viewpoint of increasing the contrast of the recorded image.

The image recording layer 24 may comprise a leuco dye. Specifically, preferred examples of the leuco dyes include crystal violet lactones; phthalide compounds such as 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide and 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; and fluoran compounds such as 3-cyclohexylmethylamino-6-methyl-7-anilinofluoran, 2-(2-chloroanilino)-6-dibutylaminofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-xylidinofluoran, 2-(2-chloroanilino)-6-diethylaminofluoran, 2-anilino-3-methyl-6(N-ethylisopentylamino)fluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-benzylethylamino-6-methyl-7-anilinofluoran, and 3-methylpropylamino-6-methyl-7-anilinofluoran.

The image recording layer 24 may be formed by dissolving the dye in a solvent to prepare a coating liquid, and by applying the coating liquid. The solvent may be the same as that of the coating liquid for the information recording layer 18. Additives and application methods for the image recording layer 24 are the same as those for the information recording layer.

The thickness of the image recording layer 24 is preferably 0.01 to 50 μm, more preferably 0.02 to 20 μm, further preferably 0.03 to 5 μm.

It is preferred that the visible information is recorded on the image recording layer 24 by repeatedly moving a laser light having a predetermined power in approximately the same trajectory. Further, it is preferred that the laser light having a predetermined power is oscillated in the radius direction of the optical recording medium and moved in approximately the same trajectory.

(First Substrate 16)

The first substrate 16 may comprise a material selected from materials used in conventional optical recording medium substrates.

Examples of the materials for the first substrate 16 include glasses, polycarbonates, acrylic resins such as polymethyl methacrylates, vinyl chloride resins such as polyvinyl chlorides and vinyl chloride copolymers, epoxy resins, amorphous polyolefins, and polyesters. These materials may be used in combination. The materials may be used in the state of a film or a rigid substrate as the first substrate 16. Among the materials, polycarbonates are preferred from the viewpoints of humidity resistance, dimensional stability, and cost.

The thickness of the first substrate 16 is preferably 0.05 to 1.2 mm, more preferably 0.1 to 1.1 mm.

Guide grooves for tracking or concavities (pregrooves) with information of address signal, etc. are formed in the first substrate 16.

In a case where the optical recording medium is a DVD-R or DVD-RW, the track pitch of the pregrooves is preferably 300 to 900 nm, more preferably 350 to 850 nm, further preferably 400 to 800 nm.

The depth (the groove depth) of each pregroove is preferably 100 to 160 nm, more preferably 120 to 150 nm, further preferably 130 to 140 nm. The groove width (the half width) of each pregroove is preferably 200 to 400 nm, more preferably 230 to 380 nm, further preferably 250 to 350 nm.

The first substrate 16 may have grooves with a track pitch smaller than those of conventional DVD-Rs, to achieve a higher recording density. In this case, the track pitch of the grooves is preferably 280 to 450 nm, more preferably 300 to 420 nm, further preferably 320 to 400 nm. The depth (the groove depth) of each groove is preferably 15 to 150 nm, more preferably 25 to 100 nm. The groove width of each groove is preferably 50 to 250 nm, more preferably 100 to 200 nm.

In a case where the optical recording medium is a CD-R, the track pitch of the grooves is preferably 1.2 to 2.0 μm, more preferably 1.4 to 1.8 μm, further preferably 1.55 to 1.65 μm. The depth (the groove depth) of each groove is preferably 100 to 250 nm, more preferably 150 to 230 nm, further preferably 170 to 210 nm. The groove width of each pregroove is preferably 400 to 650 nm, more preferably 480 to 600 nm, further preferably 500 to 580 nm.

An undercoat layer may be formed on the grooved surface of the first substrate 16, on which the information recording layer 18 is formed, to improve flatness and adhesion and to prevent deterioration of the recording layer.

Examples of materials of the undercoat layer include polymers such as polymethyl methacrylates, acrylic acid-methacrylic acid copolymers, styrene-maleic anhydride copolymers, polyvinyl alcohols, N-methylolacrylamide, styrene-vinyltoluene copolymers, chlorosulfonated polyethylenes, nitrocelluloses, polyvinyl chlorides, chlorinated polyolefins, polyesters, polyimides, vinyl acetate-vinyl chloride copolymers, ethylene-vinyl acetate copolymers, polyethylenes, polypropylenes, and polycarbonates, and surface modifying agents such as silane coupling agents. The undercoat layer may be formed by dissolving or dispersing the material in an appropriate solvent, and by applying thus-obtained coating liquid to the substrate by a coating method such as spin coating, dip coating, or extrusion coating. The thickness of the undercoat layer is generally 0.005 to 20 μm, preferably 0.01 to 10 μM.

(First Reflective Layer 20 and Second Reflective Layer 26)

The first reflective layer 20 and the second reflective layer 26 are preferably formed on the information recording layer 18 and the image recording layer 24 to increase the reflectance to the laser light for information reproduction.

The first reflective layer 20 and the second reflective layer 26 preferably comprise a light reflective substance having a high reflectance to the laser light. Examples of the light reflective substances include metals of Mg, Se, Y. Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi, etc., metalloids, stainless steels, and semiconductor materials. These substances may be used singly or in combination, or as an alloy.

Among them, the light reflective substance is preferably Cr, Ni, Pt, Cu, Ag, Au, Al, or a stainless steel, particularly preferably Au, Ag, Al, or an alloy thereof, most preferably an Ag alloy such as an Ag—Nd—Cu alloy or an Ag—Pd—Cu alloy.

For example, the first reflective layer 20 and the second reflective layer 26 can be formed on the information recording layer 18 and the second substrate 22 by vapor-depositing, sputtering, or ion-plating the light reflective substance. The thickness of each of the first reflective layer 20 and the second reflective layer 26 is generally 10 to 300 nm, preferably 50 to 200 nm.

(Adhesion Layer 28)

The adhesion layer 28 is formed to bond the first stack 12 containing the first substrate 16 to the second stack 14 containing the second substrate 22 in production of a bond type optical recording medium such as a DVD. The adhesion layer 28 is preferably composed of a light curing resin. It is preferred that the light curing resin has a small cure shrinkage ratio from the viewpoint of preventing warping of the resultant disc. Examples of such light curing resins include SD-640 and SD-661 available from Dainippon Ink and Chemicals, Inc., and SK6100, SK6300, and SK6400 available from Sony Chemical Corporation. The thickness of the adhesion layer 28 is preferably 1 to 100 μm, more preferably 5 to 60 μm, particularly preferably 20 to 55 μm, in view of flexibility.

(Protective Layer, not Shown)

The protective layer is optionally formed to prevent penetration of water and scratching. The protective layer preferably comprises a UV curing resin, a visible light curing resin, a thermosetting resin, or silicon dioxide, particularly preferably comprises a UV curing resin. For example, SD-640 available from Dainippon Ink and Chemicals, Inc. can be used as the UV curing resin. Further, SD-347 and SD-694 available from Dainippon Ink and Chemicals, Inc., and SKCD1051 available from SKC can be used in the protective layer. The thickness of protective layer is preferably 1 to 200 μm, more preferably 50 to 150 μm.

(Second Substrate 22)

The step of roughening the second substrate 22 is described in detail above, and thus duplicate explanations therefor are omitted.

The second substrate 22 having the roughened substrate surface 30 faces the first substrate 16 in the bond type optical recording medium 10. The second substrate 22 may comprise the same material as the first substrate 16. It is not necessary to form a groove on the surface of the second substrate 22, on which the image recording layer 24 is formed, as with the first substrate 16. The thickness of the second substrate 22 is preferably 0.05 to 1.2 mm, more preferably 0.1 to 1.1 mm, further preferably 0.5 to 0.7 mm.

In a case where the second substrate 22 is the cover layer, generally the cover layer is formed to physically and chemically protect the information recording layer 18, the image recording layer 24, etc. In this embodiment, the cover layer on the image recording layer 24 is roughened to increase the image visibility. The cover layer preferably has a thickness of 10 nm to 5 μm.

A transparent sheet of a polycarbonate or cellulose triacetate may be used as the cover layer. In this case, the transparent sheet preferably has a thickness of 0.01 to 0.2 mm. It is preferred that a surface of the transparent sheet, facing the image recording layer, is roughened by the stamper.

As described above, at least the image recording layer 24 and the information recording layer 18 are formed in this order on one surface of the roughened second substrate 22 in the optical recording medium 10.

The second substrate 22 can be used in an optical member having an image recording layer 24 on which an image is formed by a light, other than the optical recording medium 10. Thus, in the optical member, at least the image recording layer is formed on the roughened surface of the substrate. Examples of such optical members include stickers.

In the optical recording medium 10 of this embodiment, an intermediate layer adjacent to the second substrate 22 may have a roughened surface facing the image recording layer 24. When the intermediate layer has the roughened surface facing the image recording layer 24, it is not necessary to form the roughened substrate surface 30 on the second substrate 22. The intermediate layer may be the protective layer, which may comprise a UV curing resin.

Recording Method:

Specifically, an image is recorded on the image recording layer 24 in the optical recording medium 10 of the embodiment by using at least a recording apparatus capable of recording image information.

In this embodiment, by using only one optical recording medium drive (a recording apparatus), image information can be recorded on the image recording layer 24 and optical information can be recorded on the information recording layer 18. In the case of using only one optical recording medium drive, for example, information is recorded on one of the image recording layer 24 and the information recording layer 18, the optical recording medium 10 is reversed, and then another information is recorded on the other layer. Examples of such optical recording medium drives having a function of recording a visible image on an image recording layer are described in Japanese Laid-Open Patent Publication Nos. 2002-203321, 2003-203348, and 2003-242750, etc.

In this embodiment, by detecting the pre-pits 34, the presence of the image recording layer 24 in the optical recording medium 10 can be easily detected. Further, based on the information of the pre-pits 34, a visible image can be recorded on the image recording layer 24 under an optimum laser output with excellent imaging properties. The combination of the pre-pits 34 may provide manufacturer information.

EXAMPLES

An original stamper 76 and metal sheets 88 of Example 1 and Comparative Examples 1 and 2 were produced in the following manner. Each of them was evaluated with respect to shape and warping state after blasting, probability of producing a second-generation stamper, and probability of producing a master stamper. The results are shown in FIG. 24.

Example 1

The original stamper 76 was produced by steps S1 to S6 shown in FIG. 5 of the method of the above embodiment. The conductive ring 52A of the first modification example shown in FIG. 9 was used in this example, and the inner diameter D1 of the major surface was 193 mm and the inner diameter D2 of the other major surface was 180 mm.

As shown in FIG. 24, the original stamper 76 was flat without warping after the blasting treatment. Thus, a second-generation stamper 92 could be produced by using the original stamper 76, and further a master stamper 40 could be produced by using the second-generation stamper 92.

Comparative Example 1

The metal sheet 88 (the original stamper) was produced by the first process of FIGS. 17A to 18C using the conductive ring 80. The conductive ring 80 had an inner diameter of 193 mm.

As shown in FIGS. 18C and 24, the metal sheet 88 was curved by the blasting treatment. The warping of the metal sheet 88 was such that the height ha between the edge and the top of the metal sheet 88 was within a range of several mm to several tens mm. Thus, a second-generation stamper 92 could not be produced by using the metal sheet 88, and a master stamper 40 could not be produced naturally.

Comparative Example 2

The metal sheet 88 (the original stamper) was produced by the second process of FIGS. 19A to 19C using no conductive rings.

As shown in FIGS. 19C and 24, the metal sheet 88 was curved by the blasting treatment. The warping of the metal sheet 88 was such that the height ha between the edge and the top of the metal sheet 88 was within a range of several mm to several tens mm. Thus, a second-generation stamper 92 could not be produced by using the metal sheet 88, and a master stamper 40 could not be produced naturally.

It should be noted that the stamper producing method, the substrate producing method, and the optical recording medium producing method according to the present invention are not limited to the above embodiment, and various changes and modifications may be made therein without departing from the scope of the present invention.

Claims

1. A method of producing a stamper for roughening a substrate of an optical recording medium, the method comprising the steps of:

placing a conductive ring having a hole at a center thereof on a major surface of an original metal plate;

electroforming a metal layer over a portion of said metal plate exposed in said hole of said conductive ring, an inner end-face of said conductive ring, and a portion of a major surface of said conductive ring; and

entirely or partly roughening a major surface of said metal layer by a blasting treatment to obtain an original stamper.

2. A method of producing a stamper according to claim 1, wherein said inner end-face of said conductive ring contains a stepped surface.

3. A method of producing a stamper according to claim 1, wherein said inner end-face of said conductive ring contains a tapered surface.

4. A method of producing a stamper according to claim 1, wherein a pressing jig having a hole at a center thereof is used for pressing said conductive ring against said metal plate in said electroforming step, and an inner diameter of said conductive ring is smaller than that of said pressing jig.

5. A method of producing a stamper according to claim 1, wherein in said blasting treatment step, said major surface of said metal layer exposed in said hole of said conductive ring is entirely or partly roughened by said blasting treatment after removing said metal plate.

6. A method of producing a stamper according to claim 1, further comprising the step of electroforming another metal layer on said roughened metal layer of said original stamper to obtain a second-generation stamper comprising said other metal layer.

7. A method of producing a stamper according to claim 1, wherein a pit forming site for forming a pre-pit on said optical recording medium is formed on a portion of said major surface of said metal plate.

8. A method of producing a stamper according to claim 7, wherein a transfer pattern of said pit forming site is formed on said major surface of said metal layer and the transferred pattern is protected before said blasting treatment for roughening said major surface of said metal layer.

9. A method of producing a substrate for an optical recording medium having an image recording layer on which a visible image is recorded, the method comprising the steps of producing a stamper having an entirely or partly roughened major surface, and producing said substrate having an entirely or partly roughened major surface by using said stamper, wherein said stamper producing step comprises the steps of:

placing a conductive ring having a hole at a center thereof on a major surface of an original metal plate;

electroforming a metal layer over a portion of said metal plate exposed in said hole of said conductive ring, an inner end-face of said conductive ring, and a portion of a major surface of said conductive ring; and

entirely or partly roughening a major surface of said metal layer by a blasting treatment to obtain an original stamper.

10. A method of producing an optical recording medium having a substrate and an image recording layer on said substrate, a visible image being recorded on said image recording layer, the method comprising the steps of producing a stamper having an entirely or partly roughened major surface, and producing said substrate having an entirely or partly roughened major surface by using said stamper, and forming said image recording layer on said substrate, wherein said stamper producing step comprises the steps of:

placing a conductive ring having a hole at a center thereof on a major surface of an original metal plate;

electroforming a metal layer over a portion of said metal plate exposed in said hole of said conductive ring an inner end-face of said conductive ring, and a portion of a major surface of said conductive ring; and

entirely or partly roughening a major surface of said metal layer by a blasting treatment to obtain an original stamper.