JPH0770090B2 - Optical disk - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical disc as an optically recordable or recordable / reproducible information recording carrier, and particularly excellent in long-term storability of information. Optical disc.

[Conventional technology]

2. Description of the Related Art Conventionally, an optical information recording medium, for example, a read-only optical disc or a write-once optical disc (hereinafter simply referred to as an optical disc) is mainly formed of polymethyl methacrylate (PMMA) by injection molding to form information pits and recording guide grooves. After that, for the purpose of forming an Al reflective film (reproduction-only type) by vapor deposition / sputtering method and a memory film (write-once type) made of chalcogenide compounds such as Sb, Se, Bi, Te, etc., to protect the surface. Covered with a polymer protective film (hereinafter referred to as single-sided disc), magazine "Electronics" P1289 1980 1980
As shown in the monthly issue, one disk is made by double-sided bonding.

From the viewpoint of productivity, the adhesive used for bonding is disclosed in JP-A-58-58.
Adhesive hot melt adhesives are often used, as seen in 108044.

On the other hand, the above-mentioned optical disc is used as a large capacity memory.
Its applications have been diversified, and long-term storability has been desired more than ever before.

[Problems to be solved by the invention]

As shown in FIG. 1, the structure of the optical disc is a PMMA substrate 1-thin film 2-on which information pits and guide grooves (not shown) are formed.
This is a laminated structure composed of the protective film 3 and the adhesive 4, and the so-called disc adhesion durability largely depends on the adhesive force of the adhesive. On the other hand, as the adhesive strength of the adhesive increases, the information pits and recording guide grooves formed on the PMMA surface may deform when the optical disc is stored in a high temperature and high humidity state for a long time, and eventually noise may occur during signal reproduction. However, in the conventional technology, no consideration is given to such noise generation, and there is a problem of long-term storability of the optical disc.

An object of the present invention is to improve long-term storage stability of information recorded on an optical disc. [Means for Solving Problems] The inventors have found that the above-described noise generation occurs in response to the warp (deformation due to temperature / moisture absorption) of the one-sided disk, and
In the bonded optical disks, the adhesive strength of the adhesive is PM
It was found that it acts as a force for pulling up the signal forming surface of MA, and finally it is the deformation (creep deformation) of the signal forming surface.

Also, as a result of various studies on the adhesive strength of the adhesive, noise reduction and excellent adhesiveness were obtained by using styrene / ethylene / butylene / styrene copolymer (SEBS) as the rubber component contained in the hot melt adhesive. It was found that

[Action]

The force applied to the signal forming surface of the optical disc is the warp deformation force of the single-sided disc and the adhesive force of the adhesive. Here, the adhesive force of the adhesive is substantially determined by its viscosity and the cohesive force of the rubber component in the case of an adhesive hot melt adhesive containing rubber as a main component.

Now, the warp deformation (ω) of the single-sided disk shown in Fig. 2 under the condition of 60 ° C and 95% PH is almost the same as that of the PMMA replica at the time of molding and from the one-sided moisture absorption effect until t _A → t _B. Elongation is observed, and after that, moisture absorption (t _B → t _C → t _D ) causes relaxation (contraction) of PMMA orientation and reverse warpage deformation.

Here, such deformation also occurs in the bonded optical disc, but the flatness is maintained by the adhesive force, that is, the force that constantly pulls up the signal forming surface.

On the other hand, the viscosity of the adhesive is an important factor in ensuring the productivity of the optical disc. That is, when the surface to be bonded to which the adhesive is applied is a low melting point paraffin material, the upper limit of the application temperature of the adhesive is naturally determined, and the thickness of the adhesive applied to the optical disk bonding surface is 40 μm or less. In order to achieve this, it is necessary to have a low viscosity.

The inventors of the present invention have conducted various studies as a result of preventing the occurrence of noise that occurs under the severe conditions of the optical disc as described above, and as a result, (1) the rubber component of the rubber-based adhesive hot melt material has been conventionally frequently used. Styrene, butadiene, styrene (SB
S) or styrene-isoprene-styrene (SIS) copolymer, which has a smaller cohesive force than styrene-ethylene-butylene-styrene copolymer (SEBS), which reduces the pulling force of the signal forming surface. (2) The melt viscosity of the adhesive is 200 to 6000 at 120 ° C.
The productivity is secured by setting the poise at 20 to 200 poise at 160 ° C. (3) The adhesive strength of the adhesive is ^{2 to 4} kg / cm ² , at 50 ° C.
By setting the range to 0.5 to 2.0 kg / cm ² at 60 ° C., it was possible to prevent noise generation, secure disk productivity, and satisfy adhesive durability.

〔Example〕

 Hereinafter, the present invention will be described in more detail based on examples.

The single-sided optical disk used for confirming the effect of the present invention was made of PMMA (methyl methacrylate / ethyl acrylate copolymer) having a high fluidity of MFI = 22 g / 10 min at a resin temperature of 280 ° C. and an injection filling speed of 0.2 sec. After that, an Al vapor deposition film (0.1 μm) was formed, and then a paraffin wax moisture-proof protective film (thickness: about 10 μm) was formed.

In order to confirm the performance of the optical disc, the adhesive was applied using a roll coater at an adhesive temperature of 120 ° C and an application speed of 4 m / min.
Adhesive coating thickness was 30 μm.

To measure the viscosity of the adhesive, use a Shimadzu Koka Flotester,
To measure the adhesive strength, a 2 cm x 2.5 cm sample was taken from the optical disc, and the tensile shear (σ _S ) was applied at 50 ° C and 60 ° C in the load speed.
It was calculated at 50 mm / min.

Disc playback noise is evaluated by leaving the optical disc at 60 ° C and 75% PH, and using a noise measuring device (not shown) consisting of a random noise generator and a waveform monitor, the playback signal S / N of 3 dB.
It was calculated as the time until the drop.

In addition, the amount of disc peeling was the amount of peeling that occurred at the outer peripheral portion of the disc after 60 hours at 75 ° C and 75% PH.

The characteristics obtained with the adhesive hot-melt adhesive containing SIS + SBS as the rubber component are shown in Table 1 as Nos. 1 to 3 and SE according to the present invention.
Optical discs using an adhesive hot melt adhesive containing BS as a rubber component are shown as numbers 1 to 3 as examples, and various characteristics are compared.

From the results in Table 1, it is recognized that in any of the examples using SEBS, the change in S / N under severe conditions is significantly smaller than that of the examples of Nos.

Here, when SEBS is 15 parts or less, the melt viscosity is 500 poi.
Since the adhesive strength is less than se, the disc peels off 3m.
When the amount is 30 parts or more, the melt viscosity is 6000 poise or more, and the softening temperature is more than 100 ° C, resulting in poor disk productivity.

Further, since SEBS is a saturated polymer elastomer having no double bond like SIS and SBS, it has an advantage that it has good heat stability and does not generate a thermal decomposition product in the roll coater.

Needless to say, in addition to the rubber component, the hot-melt adhesives shown in Examples 1 to 5 are natural resins such as rosin and rosin ester for the purpose of imparting tackiness in addition to the rubber component without departing from the gist of the present invention. The modified resin, terpene, terpene phenol; modified aromatic terpene, and petroleum resin consisting of C _{5 to} C ₉ fraction obtained by decomposition of naphtha and its hydrogenated resin are mixed in an amount of 10 to 60 wt% and the viscosity is adjusted. As the agent, process oil, polyisoprene, and if necessary, a coloring agent such as carbon black or phthalocyanine blue, an antiaging agent, and the like can be mixed in a range of several wt% to 20 wt%.

In addition, the above-mentioned viscosity measuring method is suitable for obtaining the viscosity of the adhesive, the flow starting temperature, and the approximate softening temperature,
For example, the viscosity (η _B ) obtained with a so-called B-type viscometer and the viscosity (η _F ) of a Koka type flow tester are η _B = 1.3
・ There is a relationship of η _F +50 (poise).

As described above, in the embodiments of the present invention, the coated surface is shown as a paraffin-based protective film, but the same applies to other protective film materials, for example, a protective film material made of an ultraviolet curable resin, and PMMA resin. Similar effects are found with alternative substrate materials, such as polycarbonate substrates.

〔The invention's effect〕

According to the present invention, it is possible to obtain an optical disk excellent in long-term storage of information, and there is an economic effect such as not changing the conventionally used optical disk manufacturing equipment.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical disk which is the object of the present invention, and FIG. 2 is a graph showing the warp deformation behavior of a single-sided disk during heating and moisture absorption. 1 ... PMMA substrate, 2 ... metal thin film 3 ... protective film, 4 ... adhesive

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Narumi Nakamura Inventor Nakamura Yokohama, Kanagawa Prefecture 292 Yoshida-cho, Totsuka-ku, Ltd. Inside the Yokohama Plant of Hitachi Ltd. (72) Inventor Masazawa Ozawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Address Company Hitachi Co., Ltd. Yokohama factory (56) Reference JP-A-58-108044 (JP, A)

Claims (2)

[Claims] 1. An optical disc having a double-sided adhesive bonding structure, such as a read-only optical disk, wherein the adhesive hot-melt adhesive used for the bonding is (a) a styrene / ethylene / butylene / styrene copolymer. The blending ratio of the thermoplastic rubber is in the range of 15 or more and 35 wt% or less, (b) the melt viscosity at 120 ° C is in the range of 200 or more and 6000 poise or less, and (c) the tensile shear strength at 60 ° C is 0.5 kg / in cm ² or more 2.0 kg / cm ² or less in the range, an optical disk, characterized in that it consists of a pressure-sensitive adhesive hot-melt adhesive. 2. The optical disc according to claim 1, wherein the adhesive comprises an adhesive having a coloring pigment attached thereto.