JPS63146250A - Lamination method for optical disk - Google Patents

Abstract

PURPOSE:To extremely reduce the warp of a laminated optical disk even with aging by processing a recording medium having a warp caused with its recording layer and substrate set outside and inside respectively at a high temperature and a high humidity and laminating the optical disk carrier substrates together. CONSTITUTION:Two recording media having recording layers 2 on each substrate 1 are laminated together by an adhesive via spacers 3 and 4 with recording layers set opposite to each other. Thus an optical disk of an air sandwich structure is obtained. In said lamination process the recording medium having a warp caused with its recording layer and substrate set outside and inside respectively is processed at a high temperature and a high humidity. Then these optical disk carrier substrates are laminated together. Thus the warp of the optical disk of an air sandwich structure is extremely reduced owing to said high-temperature/high-humidity process. Then both focus and tracking errors are decreased and furthermore the dimensional change is reduced with the optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for straightening optical discs and bonding optical discs together. More specifically, the present invention relates to a method of bonding two optical discs together after correcting the warping of the optical disc by placing the recording layer on the outside and the substrate on the inside.

(Prior Art) In recent years, information recording media using high energy density beams such as laser beams have been developed and put into practical use. This information recording medium is called an optical disk, and can be used as a video disk, an audio disk, a large-capacity still image file, and a large-capacity computer disk memory. The basic structure of an optical disk is a disc-shaped transparent substrate made of plastic, glass, etc., and Bi, Sn, and In placed on top of this.

It has a recording layer made of metal or metalloid such as Te.

Information is written on an optical disc by, for example, irradiating the optical disc with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally rises in temperature, causing physical or scientific changes. information is recorded by changing its optical properties. Reading information from an optical disc is also performed by irradiating the optical disc with a laser beam, and the information is reproduced by detecting reflected or transmitted light according to changes in the optical characteristics of the recording layer. Recently, as a disk structure for protecting the recording layer, a recording layer is provided on at least one of two disk-shaped substrates, and the recording layer is located inside and the space is separated. An air sandwich structure has been proposed in which a ring-shaped inner spacer and a ring-shaped outer spacer are sandwiched and joined to form a ring-shaped inner spacer and a ring-shaped outer spacer. In optical discs with such a structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate, so the recording layer is generally not subject to physical or chemical damage. There is no possibility that the recording or reproducing of information will be hindered by dust being received or adhering to the surface.

(Problems to be Solved by the Invention) However, during use or storage, this air sandwich structured optical disc may be deformed, warped, or curved due to stress strain at the bonding tube between the disc substrate and the spacer. This deformation increases with time. For example, as shown in Figure 1, the optical disc carrier substrate is warped (curved) with the substrate 1 on the inside and the recording layer 2 on the outside.
In the case of an air sandwich type optical disk, in which the recording layers of two optical disk carriers are bonded together using an adhesive through a spacer so that the recording layers face each other, immediately after bonding, the difference is shown in Figure 2. Just like that,
Although an air sandwich type optical disk without warping (curving) can be obtained, warping (curving) occurs as shown in FIG. 4 due to stress strain caused by the shape of the original substrate as time passes. Such deformation of the substrate tends to cause focus servo failure, and even more extreme deformation leads to destruction of the substrate.

(Means for Solving the Problems) The method of the present invention that corrects the warp (curvature) of an optical disc and then bonds the first disc together is a method in which two recording media each having a recording layer on a substrate are bonded together via a spacer. In the method of bonding optical disks with an air sandwich structure in which the recording layers are bonded together using an adhesive so that they face each other, warping occurs with the recording layer on the outside and the substrate on the inside.The recording medium is exposed to high temperatures, This method is characterized by bonding the optical disc carrier substrate together by processing under high humidity conditions. The method of correcting the warp (curvature) of an optical disk and then bonding the optical disk according to the present invention uses a plastic molded product such as polymethyl methacrylate (PMMA) or polycarbonate (PC) as the optical disk substrate.

Plastic substrates are less likely to break than glass substrates,
It is low cost because it can be easily mass-produced using an injection molding machine. However, plastic substrates are water absorbent,
It also has oxygen permeability, so it can withstand stress, strain, and temperature that occur when a thin film of inorganic, metal, or organic material is provided on one side of the substrate.
Due to changes in environmental conditions such as humidity, the optical disc carrier substrate warps (curves), for example, as shown in FIG. 1, the optical disc carrier substrate warps with the optical disc substrate 1 on the inside and the recording layer 2 on the outside. (It is curved.) When two disk substrates are bonded together using adhesive through a spacer so that the recording layer faces inside, the result will be as shown in Figure 3 immediately after bonding. , Sleigh (Bay 1
An air sandwich type optical disc without any fll) can be obtained. However, as it changes over time, it begins to curve (curvature) as shown in Figure 4. This is because the original optical disk carrier substrate is forcibly flattened to temporarily form a bonded air sandwich type optical disk without warping, but the stress and strain on the original disk carrier substrate will likely ease over time. This seems to be a phenomenon that occurred as a result of this. To make it easier to understand, it can be thought of as shown in Figure 7. Therefore, when the optical disk carrier substrate shown in FIG. 1 is left for several hours, preferably less than 1 hour to 5 hours, under conditions of 60 DEG C. and 290% relative humidity, the optical disk carrier substrate is flattened. The time for which the optical disc is left to stand can be arbitrarily selected depending on the degree of warpage (curvature) of the optical disc carrier substrate. The temperature is preferably 50 to 70 DEG C. If the temperature is higher than this, the disk carrier substrate may undergo thermal deformation, such as waviness or surface wobbling, which is undesirable. Also, if the temperature is lower than the above (
For example, at room temperature), it is undesirable because it takes a long time to flatten the disk substrate.

Further, the humidity is preferably 80 to 95% relative humidity. If the humidity is too high, dew condensation will occur, staining the surface of the disk substrate, and if the humidity is too low, it will take a long time to straighten the warp (curvature), which is not preferable.

Thus, the straightened, warp-free, flat front disc carrier substrates are bonded together via spacers by adhesive and/or thermal welding, such as ultrasonic welding. The principle of this correction is that the water absorption rate of the resin on the optical disk carrier substrate differs between the recording layer side and the opposite side, causing warpage due to the bimetallic phenomenon, and by increasing the amount of water absorption on the opposite side, that part expands and flattens. It seems that it will be done. This suggests that when the bonded optical disk carrier substrates are kept indoors at room temperature, the amount of water absorbed on the opposite side decreases again, causing warping due to the bimetal phenomenon as shown in Figure 4, but surprisingly, over time. In terms of changes, those treated with the method of the present invention have extremely less warp (curvature) than those that are not treated. The method of the present invention can be used not only for optical discs with an air sandwich structure but also for optical discs that are entirely laminated.

(Effects of the Invention) In the optical disc bonding method of the present invention, processing is performed at high temperature and high humidity, and as compared to the conventional method, the warping (curving) of the air sandwich structure optical disc is significantly reduced. Errors and tracking errors are reduced, and dimensional changes are small even with environmental changes, so the long-term reliability of the optical disc is significantly improved.

(Example) Next, the present invention will be further explained with reference to Examples, but the present invention is not limited thereto.

Example 1 Two polycarbonate substrates 1 with a diameter of 300 m/m and a thickness of 1.2 m/m were used, each having T on one side as the recording layer 2.
When thin films consisting of E, Se, Ti, and Ag were deposited to a thickness of 500A and left for one week at a room temperature of 20°C and a relative humidity of 860%, both films exhibited warpage (curvature) as shown in Figure 1. became. The angle of the sled at this time was 0.6 degrees.

Next, to correct this warp (curvature),
When left for 2 hours and 30 minutes under conditions of % relative humidity, both optical disk carrier substrates were obtained as shown in FIG. 2, which were flat and free of warpage. These two optical disk carrier substrates are 3m/m
Thick polycarbonate inner spacer 3. FIG. 3 shows a case in which the recording layer is attached to the inside using an epoxy adhesive 5 using an outer circumferential spacer 4. This bonded optical disk was left at 30°C, 270% relative humidity, and 20°C, 550% relative humidity for one week, but the warpage was 0.1 degree in the former and -0.1 degree in the latter. Curvature) did not occur.

Comparative Example 1 An optical disc carrier substrate manufactured in the same manner as Example 1 was rotated at 60°.
The optical discs bonded together without high temperature treatment at 990% relative humidity were flat as shown in Figure 3 immediately after bonding, but at 30°C, 270% relative humidity and 20°C.
When left for one month under conditions of 250% relative humidity, a warp (curvature) of 0.6 degrees as shown in FIG. 4 occurred.

The warpage angle (curvature degree) was determined by the displacement of the reflected light spot of the laser beam.

Comparative Example 2 An optical disc carrier substrate manufactured in the same manner as Comparative Example 1 was rotated at 60°.
C2 When left for 5 hours under the condition of 90% relative humidity, the disk carrier substrate warped (curved and returned, as shown in Figure 5, and the warp angle at this time was -0.6 degrees. Immediately after bonding in the same manner as in Example 1, a flat optical disk was obtained, but when left for one month in the same manner as in Example 1, it became warped (curved) as shown in FIG. 6, and the warp angle was -
It was 0.6 degrees.

Comparative Example 3 A flat optical disk carrier substrate was obtained by manufacturing the same as in Comparative Example 1 and leaving it at 60°C and 990% relative humidity for 48 hours. There were countless cracks.

[Brief explanation of the drawing]

FIG. 1 shows the optical disc carrier substrate of the present invention after manufacturing.
Warping after being left for one week at 260% relative humidity at °C (
1 shows a longitudinal cross-sectional view of an optical disc carrier substrate having a curved surface; FIG. FIG. 2 shows a longitudinal cross-sectional view of an optical disk carrier substrate free from warpage (curving) after being subjected to high-temperature treatment according to the present invention. Figure 3 shows
1 is a longitudinal cross-sectional view of an optical disk having an air sandwich structure that is bonded together after straightening warpage according to the present invention. Figure 4 shows
A longitudinal cross-sectional view of a front disk of an air sandwich structure bonded together without warpage correction is shown. FIG. 5 shows a longitudinal cross-sectional view of the optical disk carrier substrate when the processing time of the present invention is too long. FIG. 6 shows a longitudinal cross-sectional view of a former disk carrier substrate laminated under conditions in which the processing time of the present invention was too long. FIG. 7 is a longitudinal cross-sectional view of the previous disk carrier substrate showing warping caused by aging of the optical disk bonded together using the conventional method. (Explanation of symbols) 1.1'--==-Optical disc substrate 2=--1 Recording member 3.4 =---------Spacer 5 -=--1 Adhesive layer 6- =−−=−Ichiichi Optical Disc Center Agent
Patent attorney Takashi Koshiba Patent applicant Daicel Chemical Industries, Ltd. NO. (b2 broom 7rif 6

Claims (1)

[Claims] In a method for bonding optical disks with an air sandwich structure in which two recording media each having a recording layer on a substrate are bonded together using an adhesive so that the recording layers of the recording media face each other via a spacer, warpage may occur in the recording layer. A method for bonding optical disks, which comprises processing a recording medium formed with a substrate on the outside and a substrate on the inside under conditions of high temperature and high humidity, and then bonding an optical disk carrier substrate.