JPH0358334A - Optical disk - Google Patents

Abstract

PURPOSE:To reduce warpage of substrates by providing an adhesive layer comprising thermosetting resin between two substrates with recording layers facing to each other. CONSTITUTION:The optical disk consists of, for example, a transparent disk substrate 1 of synthetic resin such as polycarbonate having the glass transition point at 130 deg.C, dielectric layer 2 comprising silicon nitride formed on the substrate 1, recording layer 3 comprising an amorphous magnetic film such as Te-Fe-Co having perpendicular anisotropy, and protective layer 4. Two disks of this structure are disposed with the recording layers 3 facing to each other and an adhesive layer 5 is provided between the protective layers 4. The adhesive layer 5 consists of such a thermosetting resin that has higher glass transition point than the environment temp. for use and is hardened at room temp. By this constitution, deformation due to hardening of the adhesive layer can be suppressed since the adhesive layer is hardened at room temp. Moreover, with higher glass transition point of the adhesive layer than the temp. of use environment, peeling of the recording layers and generation of pinholes can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc used in an optical disc device or the like which is an external device of a computer.

[Conventional technology]

This type of optical disc records information using laser light irradiation. Optical discs that perform playback are widely used, and optical discs that have a recording layer on at least one base and are bonded together with adhesive with the side with the recording layer inside are widely used. ing.

Figure 4 shows the configuration of a -1'l2 optical disc. The recording layer constitutes a base body together with the substrate f1+. (5)
is a thermosetting adhesive layer interposed between the opposing surfaces of two substrates on which the recording layer (3) is disposed facing each other.

In an optical disc constructed in this way, an adhesive layer (
5) Because we used a heat-curing adhesive,
Due to the force-heating process during curing of the adhesive, distortion remained in the adhesive layer (5), which caused defects in the optical disc, such as warping of the base layer (11).

In order to solve this problem, a adhesive layer (5) that does not use a heat curing type is available, for example,
This method is proposed in Japanese Patent No. 67258. In the method disclosed in this publication, a photomelt adhesive coated with a thermoplastic resin is applied as an adhesive layer (5) onto a recording layer (3) formed on one substrate (11).Next, The other substrate (1) is placed on the true-melt adhesive with the recording layer (3) on the inside, and when it is cooled to room temperature, the true-melt adhesive hardens and the two substrates are bonded together. , the optical disc is complete.

In the optical disc manufactured in this way, since the adhesive layer (5) made of a true melt adhesive does not require heating during curing, the distortion of the adhesive layer (5) is small, and the substrate (1)
The amount of warpage can be suppressed to a small level, and the number of defects as an optical disc can be reduced.

[The issue that the problem is trying to solve]

However, since optical discs configured in this way are used interchangeably with optical disc devices, they may be exposed to harsh environments, and the operating environment temperature may vary.
Td) must be guaranteed, for example, from -20°C to 60°C.

When we conducted a humidity resistance test and a temperature/humidity cycle test on an optical disc in which two substrates were bonded together using the above-mentioned true melt adhesive within such a range of usage environment temperature (Td), we found that the recording film ( 3) Peeling and pinholes occurred, the bint error rate increased rapidly, and sufficient reliability could not be obtained.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to obtain an optical disc that is durable, does not warp, has excellent heat resistance and moisture resistance, and has high reliability over time.

[Means for solving yA problem]

The optical disc according to the present invention has two substrates facing each other, a recording layer formed on at least one opposing surface of the substrates, and a space between the two substrates that is higher than the upper limit of the operating environment temperature. It has an adhesive layer that has a glass transition point and hardens at room temperature.

[Effect]

At the same time, it is also possible to suppress the occurrence of warping of the substrate and the occurrence of peeling of the recording layer when used within the operating environment temperature range.

〔Example〕

Embodiments of the present invention will be explained below based on FIG. ) is a dielectric layer made of silicon thioside (SiNx) formed on this substrate (11), and (3) is a dielectric layer formed on this dielectric layer (2). A recording substrate (Tbl!eCo) made of an amorphous magnetic film with perpendicular anisotropy such as
l). The dielectric layer (2) and the recording layer (3) constitute a base. (5) is an adhesive layer interposed between two substrates on which the recording layer (3) is disposed facing each other, and is used at a working environment temperature of -20°C to 60°C.
It is made of a thermosetting resin that has a glass transition point higher than the upper limit temperature shown below and hardens at room temperature.

Next, to explain the production of an optical disc configured in this way, first, two substrates are formed on which a dielectric layer (2), a recording layer (3), and a protective layer (4) are sequentially formed on the substrate +1+. prepare. Then, apply adhesive on the protective layer (4) of one substrate, place the other substrate on f2 so that its protective layer (4) is in contact with the adhesive, and cure the adhesive at room temperature to form two sheets. The optical disc is made by bonding the substrate together.

In the optical disc configured in this way, the adhesive layer (5
) is cured at room temperature, the adhesive layer (5
) has almost no distortion due to curing, and furthermore, the glass transition point of the adhesive layer (5) is higher than the upper limit temperature of the usage environment temperature and the bond between the adhesive layer (5) and the substrate +11 is lower than the glass transition point. Since the coefficients of linear thermal expansion are almost the same, even if a writeability test and a temperature/humidity cycle test within the usage environment temperature range are performed, the recording layer (3) remains unchanged. No separation or bottle holes were observed, and the reliability was sufficiently high.

Specific examples of the present invention will be described below along with comparative examples.

(Bisame Example 1) The adhesive layer (5) of this optical disc uses a photomelt adhesive that has a glass transition point of 5°C and hardens at room temperature.

In Comparative Example 1, the amount of warpage after the two substrates were pasted together was 2. It was small and good, 0 mrad. Next, a humidity resistance test was performed in which the substrate (1) was stored for 100 hours in a constant temperature and humidity chamber at a temperature of 60'C and a relative humidity of 90% RI{. It became used as.

In addition, a temperature/humidity cycle trial based on JIS-C5024 method H was conducted. (Temperature: -10°C to 65°C. 30 cycles) As shown by dotted line b in Figure 2, 20
When the number of cycles exceeded, the bit error rate increased rapidly and sufficient reliability could not be obtained.

(Comparative Example 2) For the adhesive layer (5) of this optical disc, a mixture of a main agent (Ebicoat 808) of bisphenol A type epoxy resin and a curing agent consisting of polythiol was used in a ratio of 1:1. This adhesive has a glass transition temperature of 50° C. and is cured at room temperature.

In Comparative Example 2, the amount of warpage after the two substrates were pasted was 2. Although it was small and good at 4 mrad, when the same moisture resistance test as in Comparative Example 1 was conducted, the amount of warpage of base material (1) increased to 17.2 mrad, and furthermore, in the temperature cycle test, there were no bit errors.・Rapid Jv rate
However, the durability and reliability were poor.

(Comparative Example 3) The adhesive layer (5) of this optical disc was made of bisphenol
A mixture of a type of epoxy resin (Ebicor 828) and an imidazur compound at a ratio of 100:2 was used. This adhesive is heated at 80°C,
The glass transition point is 130°C.

In Comparative Example 3, the amount of warpage after the two substrates were bonded was extremely large, 10.3 mrad, and could not be used practically as an optical disc.

(Example 1) The adhesive layer (5) of this optical disc is made of a wood agent made of bisphenol A type epoxy resin (Thread TB2022 manufactured by ThreeBond) and a hardening agent made of modified aliphatic polyamine (TB2131D manufactured by ThreeBond) in a ratio of 3:1. 11;
It uses a two-component epoxy adhesive that is mixed and foamed during brining. This adhesive layer (5) is cured at room temperature and has a glass transition point of 70°C, and as shown in FIG.
In the following, the linear thermal expansion coefficient is approximately the same as that of the polycarbonate substrate (1).

In Example 1, since the adhesive layer (4) is cured at room temperature, the distortion during curing of the adhesive is small, and the results of measuring the amount of warpage of the substrate (11) after the two substrates are bonded together are as follows: , 1.5 mrad, which was smaller and better than those of Comparative Examples 1 to 3 above.

Moreover, when the same moisture resistance test as in Comparative Example 1 was conducted, the amount of warpage of the board fl) after the moisture resistance test was 1.6 mrad.
There is almost no change when compared with before storage, and Comparative Example 1-3
The amount of warpage was smaller and better than that immediately after bonding. Furthermore, when we performed the same warm cycle experiment as in Comparative Example 1 and then measured the recording characteristics of the optical disc, we found that the bit error rate was lower than the initial state, as shown by the solid line [8] in Figure 2. Good results were obtained without any increase, and high reliability was obtained even under harsh surrounding environments.

(Example 2) The adhesive layer (5) of this optical disc is a wood agent made of bisphenol A type epoxy resin (TB202 manufactured by ThreeBond).
A mixture of 2) and a curing agent made of a modified alicyclic polyamine (manufactured by Three Pond, TB2106) in a ratio of 2 to 1 was used. This adhesive has a glass transition point of 90°C and hardens at room temperature.

In this Example 2, the amount of warpage after the two substrates were bonded was 1. 4 mrad] It is smaller than those of drawing examples 1 to 3, and the amount of warpage after the moisture resistance test is also 1. 3
The amount of warpage was smaller than that of mrad and those of Comparative Examples 1 to 3 immediately after bonding, and the recording properties after the temperature/humidity cycle test were also good.

(Example 3) The adhesive layer (5) of this optical disc has a glass transition point of 80
Acrylic ultraviolet rays that cure at room temperature
ThreeBond, TB3033) was used.

In this Example 3, the warpage after bonding the two substrates was 1. 7 mrad, which is smaller than those of Comparative Examples 1 to 3, and has good resistance. The amount of warpage after the older brother test was also 1.9 mrad.
The warpage was smaller than that of Comparative Examples 1 to 3 immediately after bonding, and the recording properties after the /M'/W cycle test were also good.

(Example 4) The adhesive layer (5) of this optical disc is made of methyl methacrylate (hereinafter abbreviated as MMA), 2-hydroxyethyl methacrylate (hereinafter abbreviated as 2HEMA), and acryloni-1-lilbucdiene rubber (hereinafter abbreviated as NBR). A?, which contains cumene hydroveroxide, paraffin wax, and gintrotoluene. An acrylic non-anaerobic two-component adhesive was used, which was a mixture of liquid B containing & and MMA, NBi tetramethylthiourea, paraffin wanox, and ditrotoluene. This adhesive has a glass transition point of 80°C,
It hardens at room temperature.

In Example 4, the amount of warpage after the two substrates were bonded was 1,5 mrad, which was smaller than that of Comparative Examples 1 to 3, and the amount of warp after the moisture resistance test was 1,7 mrad. The amount of warpage is smaller than that of Examples 1 to 3 immediately after bonding,
Furthermore, the recording characteristics after the temperature-humidity cycle test were also good.

(Example 5) The adhesive layer (5) of this optical disc was made of A?, which is a combination of MMA, ethyl styrene acrylate-butadiene rubber, tert-butyl hydroperoxide, and P-hendquinone. Night and MMA. Ethyl acrinoleate.
Polymethyl methallylate, 2-mercaptohentazole. It uses an acrylic non-anaerobic two-component adhesive mixed with B't& containing methacrylic acid. This adhesive has a glass transition point of 90°C and hardens at room temperature.

In this Example 5, the warpage after bonding the two substrates was 2. It is as small as Comparative Example 1, which has the smallest amount of warping among the comparative examples at 0 mrad, and the amount of warping after the humidity test is 2.
It's small at 4mrad, and even '/L? 8C after W cycle test! The recording characteristics were also good.

(Example 6) The adhesive layer (5) of this optical disc was made of a wood agent (ThreeBond fi. TB2022C) and a hardening agent (T manufactured by ThreeBond).
A two-component epoxy adhesive containing B2131D) mixed at a ratio of 3:1 is used. This adhesive has a glass transition point of 60° C. and hardens at room temperature.

In this Example 6, the amount of warpage after the two substrates were bonded was 2. The amount of warpage after the moisture resistance test is as small as Comparative Example 1, which has the smallest amount of warpage among the comparative examples at 0 mrad.
Although it increased slightly, it did not pose a problem in practical use. In addition, in the temperature/humidity cycle test, one point of 1 liter is shown in Figure 2.
As shown in i-line C, the Binot error rate almost maintains its initial state up to 20 cycles, indicating sufficient durability and reliability as an optical disc, and although it begins to increase slightly at 30 cycles, There were no problems in use.

Table 1 shows the evaluation results for Examples 1 to 6 and Comparative Examples 1 to 3 described above.

As is clear from Table 1, the adhesive layer (5) interposed between the two substrates of the optical disk has a glass transition point (Tg
z) is the upper limit temperature (60'c) of the operating environment temperature (Td)
In addition, if the substrate (1) is cured at room temperature, the amount of warpage of the substrate (1) is small and sufficient durability and reliability can be obtained when used within the operating environment temperature (Td). It is something that exists.

The reason why such good results were obtained is considered to be due to the following points. In other words, as shown in Fig. 3, the relationship between the density and the coefficient of linear expansion, the adhesive layer (4
) has a high glass transition point (Tgz) of more than the upper limit temperature (60°C) of use environment/packing. Because they are almost the same, there is no possibility that a significant temperature change will occur, causing distortion in the adhesive N (5), causing the optical disc to warp, or causing the recording layer (3) to peel off. The adhesive layer (5) has a glass transition point (Tg: +) lower than the upper limit temperature (60'c) of the usage environment temperature (Td).
Td), the coefficient of linear expansion differs greatly, and temperature changes may cause warping or peeling of recording N(3).

Furthermore, since adhesives made of resin have extremely high water absorption at temperatures above the glass transition point, Comparative Examples 1 and 2 have low glass transition points, so the adhesive layer ( 4) contains moisture, which causes the optical disc to warp and corrode, leading to a rapid increase in the error rate. l. 1L indicates that the adhesive layer (4) having a glass transition point higher than the upper limit of the operating environment temperature (60° C.) gave good results.

In addition, the glass transition point is 130 as in the ratio 1 bite case 3.
Even if the material is as high as
The adhesive layer (5) is distorted during curing, resulting in large warping of the optical disc, making it unsuitable for use as an optical disc.

[Effects of the Invention] As described above, in the present invention, the glass transition point between the opposing surfaces of two substrates is above the operating environment temperature. Since the adhesive layer is made of a thermosetting resin that is higher than the temperature and hardens at room temperature, it is possible to suppress the warpage of the substrate to a very small level, and it also has excellent heat resistance and heat resistance when used within the operating environment temperature. It has excellent moisture resistance and curing properties over time.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional view showing an embodiment of the present invention, and Fig. 2 shows changes in bit error rate when a product temperature cycle test is conducted based on JTS-C5024 method. 3 are diagrams showing changes in the expansion coefficients of the adhesive layer (5) and the substrate (1) due to temperature, and FIG. 4 is a partial sectional view showing a conventional optical disc. In the figure, fl) is a substrate, (3) is a recording layer, and (5) is an adhesive layer. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] two substrates disposed facing each other and having a recording layer formed on at least one opposing surface, interposed between the opposing surfaces of the two substrates, and having a glass transition point higher than the upper limit temperature of the usage environment temperature; An optical disc equipped with an adhesive layer made of thermosetting resin that hardens at room temperature.