WO2005091285A1

WO2005091285A1 - Method of manufacturing transparent layer of optical disk

Info

Publication number: WO2005091285A1
Application number: PCT/KR2005/000804
Authority: WO
Inventors: Myong-Do Ro; Hee-Sung Park
Original assignee: Samsung Electronic Co., Ltd.
Priority date: 2004-03-19
Filing date: 2005-03-19
Publication date: 2005-09-29
Also published as: KR20050093423A

Abstract

Provided is a method of manufacturing a transparent layer of an optical disk, which can control the radius of a bump according to transparent layer manufacturing conditions. The method includes: setting the size of the optical disk, the position of a bump formed in the rim area, the material of the transparent layer, and dispensing conditions; calculating the spinning speed of a stage on which the transparent layer is to be formed using the set values and the quation 1.

Description

Description METHOD OF MANUFACTURING TRANSPARENT LAYER OF OPTICAL DISK Technical Field

[1] The present invention relates to a method of manufacturing a transparent layer of an optical disk, and more particularly, to a method of manufacturing a transparent layer of an optical disk, which can control the radius of a bump according to transparent layer manufacturing conditions. Background Art

[2] In general, optical disks are widely used as information recording media for optical pickups that record and reproduce information in a non-contact manner. The optical disks are classified into compact disks (CDs), digital versatile disks (DVDs), and Blu- ray disks (BDs) according to information recording capacity. The optical disks generally have a diameter of 120 mm or 80 mm under standards.

[3] The BDs include a transparent layer with a thickness of 0.1 mm through which an incident beam is transmitted to reproduce or record information. The transparent layer is made of a curable acrylate resin. The resin is a visco-elastic material having both viscosity and elasticity. Here, elasticity is a mechanical property of a resin to return to its original shape after it has been deformed due to stress according to Hook's law. Due to the property, when a transparent layer is formed by a spin coating method, the resin is puffed up around an outer circumference of the transparent layer after spinning, thereby forming a bump. Thereafter, when the resin is hardened by exposure of ultraviolet, the bump is hardened.

[4] The standards for BD-RW(Rewritabe) disks specify that when an optical disk has a radius of 60 mm, the radius of an information recording area should ranges from 21.0 to 58.5 mm. Accordingly, if the information recording area has a radius of 58.5 mm, a rim area formed around an outer circumference of the information recording area has a small radius of 1.5 mm, and a bump should be formed within the rim area. Disclosure of Invention Technical Problem

[5] However, if a transparent layer with a required thickness of 100 m m is manufactured using a conventional spin coating method, a bump formed around the transparent layer has a width greater than 1.5 mm. Accordingly, a desired information recording area cannot be secured.

[6] Further, next generation information storage media require that the width of the rim area should be reduced to 1.0 mm or less from the present width of 1.5 mm to enhance recording capacity. To satisfy such requirements, the uniformity of the thickness of the transparent layer need to increase and the bump needs to be formed as near as possible to an outermost circumference. Technical Solution

[7] The present invention provides a method of manufacturing a transparent layer of an optical disk, which can control the radius of a bump by grasping and using a relationship between the thickness of the transparent layer and the position of the bump and factors that determine the thickness of the transparent layer.

[8] In accordance with an aspect of the present invention, there is a method of manufacturing a transparent layer of an optical disk that includes an information recording area and a rim area with a predetermined width formed along an edge of the information recording area, the method comprising: setting the size of the optical disk, the position of a bump formed in the rim area, the material of the transparent layer, and dispensing conditions; calculating the spinning speed of a stage on which the transparent layer is to be formed using the set values and the following equation

[9]

[10] where r' denotes the radius of the bump, R denotes the radius of the optical disk, ? denotes the viscosity coefficient of the material of the transparent layer, r denotes the density of the material of the transparent layer, s denotes the surface tension of the material of the transparent layer, Q denotes the quantity of flow, w denotes the angular speed of rotation of the stage, and A, a, b, and g are constants satisfying A = 0.8782, a = 0.0017, β = -0.0104, and ? = 0.003; and rotating the stage at the calculated spinning speed. Description of Drawings

[11] FIGS. 1A through 1C are graphs illustrating positions of bumps when transparent layers respectively with viscosities of 1300 centipoises (cps), 3000 cps, and 5000 cps are formed on optical disks with a diameter of 32 mm.

[12] FIGS. 2A through 2C are graphs illustrating positions of bumps when transparent layers respectively with viscosities of 1300 cps, 3000 cps, and 5000 cps are formed on optical disks with a diameter of 50 mm.

[13] FIGS. 3A through 3C are graphs illustrating positions of bumps when transparent layers respectively with viscosities of 1300 cps, 3000 cps, and 5000 cps are formed on optical disks with a diameter of 120 mm.

[14] FIGS. 4 through 6 are graphs when optical disks respectively have diameters of 32 mm, 50.8 mm, and 120 mm, particularly, FIGS. 4A, 5A, and 6A illustrating a relationship between a spinning speed and an average coating thickness, FIGS. 4B, 5B, and 6B illustrating a relationship between a spinning speed and a standard deviation.

[15] FIGS. 7A through 7C are graphs illustrating a relationship between a spinning speed and a value r'/R when optical disks respectively have diameters of 32 mm, 50.8 mm, and 120 mm.

[16] FIGS. 8 A through 8C are graphs illustrating relations between the viscosity of a resin, a spinning speed, and the position of a bump when optical disks respectively have diameters of 32 mm, 50.8 mm, and 120 mm. Best Mode

[17] The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown.

[18] A method of manufacturing a transparent layer of an optical disk according to an embodiment of the present invention grasps through experiments a relationship between the thickness of the transparent layer and the position of a bump and factors that determine the thickness of the transparent layer, analyzes the grasped data through regression analysis, and numerically expresses the analyzed results.

[19] First, when it comes to a relationship between a bump and a transparent layer, the width of the bump depends on the viscosity of a resin used for manufacturing the transparent layer, a spinning speed during spin coating of the resin, a spinning time, and the thickness of the transparent layer made of the resin. That is, the thickness of the transparent layer is determined by the spinning speed and the spinning time of a stage on which the transparent layer is to be formed and the viscosity of the resin, and the width of the bump is determined by the determined thickness and the viscosity of the resin. Here, the stage on which the transparent layer is to be formed by a spin coating method may be a substrate of an optical disk subjected to stamping.

[20] For example, the thickness of the transparent layer increases as the spinning speed and the spinning time of the stage increase, and the thickness of the transparent layer decreases as the viscosity of the resin decreases. The width of the bump increases as the thickness of the transparent layer increases. This relationship will be explained in detail through experiments.

[21] Experiments were made with the following three variables, that is, the spinning speed of a transparent layer, the size of an optical disk, and the viscosity of a resin, and experiment results are shown in FIGS. 1 through 3.

[22] 1. (1) Spinning speed : 1000, 2000, 3000 [rpm] [23] 1. (2) Size (diameter) of optical disk : 32, 50.8, 120 [mm]

[24] 1. (3) Viscosity : 1300, 3000, 5000 [cps]

[25] FIGS. 1A through 1C are graphs illustrating positions of bumps when transparent layers respectively with viscosities of 1300 centipoises (cps), 3000 cps, and 5000 cps are formed on optical disks with a diameter of 32 mm. In those graphs, the horizontal axis represents a ratio r/R of the radius r of a bump to the radius R of an optical disk, and the vertical axis represents a ratio h/h ave of the thickness h at each position to the average thickness h ave of a transparent layer.

[26] FIGS. 2A through 2C are graphs illustrating positions of bumps when transparent layers respectively with viscosities of 1300 cps, 3000 cps, and 5000 cps are formed on optical disks with a diameter of 50 mm. FIGS. 3A through 3C are graphs illustrating positions of bumps when transparent layers respectively with viscosities of 1300 cps, 3000 cps, and 5000 cps are formed on optical disks with a diameter of 120 mm.

[27] Referring to FIGS. 1 through 3, as the viscosity of a resin increases, a coating thickness variation decreases. Also, as the spinning speed of a stage increases, a thickness variation increases. As the size of an optical disk increases, a coating thickness variation decreases.

[28] To know the causes of the results, an average coating thickness and a standard deviation in respective conditions will be explained with reference to FIGS. 4 through 6.

[29] FIGS. 4 through 6 are graphs when optical disks respectively have diameters of 32 mm, 50.8 mm, and 120 mm. Particularly, FIGS. 4A, 5A, and 6A illustrate a relationship between a spinning speed and an average coating thickness, and FIGS. 4B, 5B, and 6B illustrate a relationship between a spinning speed and a standard deviation. Referring to the graphs, a relationship between a spinning speed and an average coating thickness and a relationship between a spinning speed and a standard deviation are constant in all the optical disks, irrespective of the size of the optical disks.

[30] To obtain an equation for the bump based on the experimental results, a function of variables that affect the position r' of the bump was assumed as follows

[31] r ^' = f i i . , . H. ω , > ^{■ ■ ■} 0 )

[32] where ? denotes the viscosity coefficient of a fluid, ? denotes the density of the material of the transparent layer, s denotes the surface tension of the material of the transparent layer, R denotes the radius of the optical disk, ? denotes the angular speed of rotation of the stage on which the transparent layer is to be formed, and Q denotes the quantity of flow. [33] The variables in equation 1 are defined as non-dimensional variables according to Buckingham's PI theorem of dimensional analysis as shown in equation 2. Referring to equation 2, a ratio of the position r' of the bump to the radius R of the optical disk can be expressed in terms of three non-dimensional values. In equation 2, if the left side of the equation is 1, it means that no bump has been generated. If the left side of the equation is lower than 1, the bump is formed closer to an inner side of the radius of the transparent layer.

[34] . r ^f <J /. ωr i o r \ r v (2)

[35] where A, a , β , and ? are constants obtained using regression analysis based on the experimental results of FIGS. 1 through 3, and A = 0.8782, a = 0.0017, β = -0.0104, and ? = 0.003.

[36] FIGS. 7A through 7C are graphs illustrating a relationship between a spinning speed and a value r'/R calculated based on equation 2 and obtained by experiments, when optical disks respectively have diameters of 32 mm, 50.8 mm, and 120 mm.

[37] Referring to FIGS. 7A through 7C, calculated position values and experimental position values of the bump are very similar to each other within an error range of 2%.

[38] FIGS. 8A through 8C are graphs illustrating relations between the viscosity of a resin, a spinning speed, and the position of a bump when optical disks respectively have diameters of 32 mm, 50.8 mm, and 120 mm.

[39] The physical property of the bump based on the experimental results and the theoretical results is as follows.

[40] First, as the size of the optical disk increases, inertia increases and the bump is formed at an outer circumference. Second, as the spinning speed of the stage increases during the manufacturing of the transparent layer, inertia increases and thus the position of the bump can be moved closer to an outermost circumference. In the meantime, since the coating thickness variation of the transparent layer increases in proportion to the spinning speed of the stage, a proper spinning speed should be selected. Third, the viscosity of the resin does not directly affect the position of the bump. However, since the thickness variation increases as the viscosity decreases, the viscosity of the resin indirectly affects the position of the bump.

[41] Accordingly, when the size of the optical disk, the position of the bump formed in the rim area, the material of the transparent layer, and dispensing conditions are set, the spinning speed of the stage can be calculated based on equation 2 to generate the bump at a desired position. In addition, since the bump can be generated at a desired position by rotating the stage at the calculated spinning speed, the width of the rim area can be freely adjusted. [42] <Experiment>

[43] An angular speed of rotation w determined to generate the bump within 1 mm from the outer circumference of the optical disk will be explained based on the theoretical results an the experimental results. [44] First, in the experiment, an optical disk with a radius R of 120 mm, and a resin of a transparent layer with a density ? of 1200 Kg/m , a viscosity ? of 0.00239 m /s, and a surface tension s of 0.0398 N/m were used, a quantity of flow Q that determines the dispensing position of the resin was 1.04 x 10 7 m 3 /s. Here, since the bump should be formed within 1 mm from the outermost circumference, r' was 0.059 [m].

[45] If the conditions and values are input to equation 2, an angular speed of rotation ? of 130.2 rad/s is obtained. If the angular speed of rotation ? is calculated in terms of a stage spinning speed, the spinning speed is 1243 rpm.

[46] Accordingly, if the transparent layer of the optical disk with the diameter of 120 mm is formed by rotating the stage at the spinning speed of 1243 rpm and dispensing the resin, the bump can be generated within 1 mm from the outer circumference of the optical disk.

[47] While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. Industrial Applicability

[48] As described above, the method of manufacturing a transparent layer of an optical disk according to the present invention can generate a bump at a desired position by grasping factors that determine the position of the bump, inputting the factors in equation 2, and controlling the spinning speed of a stage. That is, the method can freely adjust the width of the rim area.

[49] Consequently, since the method can freely set the position of the bump in optical disks with various diameters, a desired information recording area can be freely secured and thus recording density can be increased.

Claims

[1] 1. A method of manufacturing a transparent layer of an optical disk that includes an information recording area and a rim area with a predetermined width formed along an edge of the information recording area, the method comprising: setting the size of the optical disk, the position of a bump formed in the rim area, the material of the transparent layer, and dispensing conditions; calculating the spinning speed of a stage on which the transparent layer is to be formed using the set values and the following equation

where r' denotes the radius of the bump, R denotes the radius of the optical disk, ? denotes the viscosity coefficient of the material of the transparent layer, r denotes the density of the material of the transparent layer, s denotes the surface tension of the material of the transparent layer, Q denotes the quantity of flow, w denotes the angular speed of rotation of the stage, and A, a , b , and g are constants satisfying A = 0.8782, a = 0.0017, β = -0.0104, and ? = 0.003; and rotating the stage at the calculated spinning speed.

[2] 2. The method of claim 1, wherein when the radius R of the optical disk is 120 mm, the density r of the material of the transparent layer is 1200 Kg/m , the viscosity coefficient v is 0.00239 m /s, the surface tension s is 0.0398 N/m, and 7 3 the quantity of flow Q is 1.04 x 10 m /s, the angular speed of rotation w of the optical disk is 130.2 rad/s so that the bump can be formed within 1 mm from an outer circumference of the optical disk.