JPH03263625A - Medium for recording information - Google Patents

Abstract

PURPOSE:To improve initial accuracy and to stabilize the accuracy in spite of an external environmental change by providing a coating layer of a UV curing resin on the front surface side (the side opposite from a recording layer) of a plastic sub strate as well to obtain the stress balance with the UV curing resin on the upper side of the recording layer. CONSTITUTION:The UV curing resin 4 provided on the upper side of the recording layer 3 is required to have excellent flawing resistance, moistureproofness and adhesive property to the recording layer. And this resin must not have corrosion property as this resin is brought into directly contact with the recording layer 3. Meanwhile, the UV curing resin 1 provided on the front surface of the substrate 2 is excellent in the flawing resistance and antistatic effect and the film thickness thereof is prefer ably 1 to 30 mum. These two UV curing resins 1, 4 are made to sufficiently play the role of protecting the recording layer 3 or the front surface of the substrate 2 in such a manner and further, the balance of the tensile stresses by the volumetric shrink age of the two UV curing resins 1, 4 is obtd. The degradation in the accuracy generat ed in the structure of the medium is overcome in this way and the high initial accuracy is obtd. The disk accuracy is stably maintained in spite of the external environmental change.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a disc-shaped information recording carrier used in optical recording or reproducing methods, and improves mechanical precision such as warping and surface runout. The aim is to eliminate changes over time.

[Conventional technology]

Optical recording and reproducing methods using laser light record and reproduce information by providing irregularities, optical shading, or magnetic domain orientation on the recording layer of a rotationally driven disc-shaped information recording carrier (hereinafter referred to as a disk). This is what we do. It is widely used for still image files, document files, computer data files, etc.

Generally, when writing or reproducing information on a disc, light emitted from a laser is irradiated onto the disc surface as condensed light 3 by a pickup 2, as shown in FIG.

When recording and reproducing information, the mechanical precision of the disc is required to be high. The laser beam is focused onto the recording layer by an automatic focusing mechanism with an accuracy of a focus acquisition error of several μm or less. Therefore, in the disk, it is necessary to maintain high precision, especially in terms of substrate warpage, surface runout during rotation, tilt angle, acceleration, etc.

This point needs to be particularly strict when recording.

If the surface runout during rotation is large and the accuracy is poor, off-focus will occur and the laser beam will not be focused enough on the recording surface, resulting in failure to record, or errors during playback due to the inability to reproduce accurate signals. It is. In addition, if warping, surface wobbling, etc. overlap, in severe cases, the disc may hit the pickup and cause a hend crush, which must be avoided.

On the other hand, when the tilt angle is large, astigmatism occurs due to the lens, and the circular beam cannot be focused on the recording surface and becomes an elliptical beam, resulting in a decrease in the laser light intensity and the inability to record, or errors during playback. may occur.

Therefore, certain limits are required for disk warpage, surface runout, 1 angle of latitude, acceleration, etc. In the case of optical disks for recording and playback, the warpage is 2250 μm, although it varies depending on the servo ability of the pickup and the numerical aperture of the lens. Distance≦2
50uffl, tilt angle <0.3° Focus acceleration <
The standard is 20 m/s2.

By the way, acrylic resin, polycarbonate resin, epoxy resin, polystyrene, etc. are used as substrates for optical discs, taking into account damage and cost if they are dropped, but among them, transparency and moldability during injection molding are used. Acrylic resin and polycarbonate resin are widely used.

However, these plastics have the problem of large dimensional deformation due to moisture absorption, and it is difficult to maintain high mechanical accuracy against changes in the external environment.

Regarding the disk structure, first of all, as a single-plate specification, a recording layer is provided on the plastic substrate on which prerecorded recording grooves and address information are engraved, and the recording layer is further protected from external scratches and changes in the external environment. A structure in which an ultraviolet curing resin is provided above the recording layer is widely used. In addition, for double-sided specifications, the entire surface is bonded together with an adhesive with the recording layer inside, or a disk-shaped reinforcing material is inserted between two substrates in some cases, or the inner circumference of the disk is bonded together. There is a structure in which the outer periphery is pasted together like a hollow air sand with a spacer in between, and this double-sided specification was the mainstream in the past.

In the case of single-plate specifications, not only does the plastic substrate itself undergo significant dimensional deformation due to moisture absorption, but also because a recording layer is provided on one side of the substrate, moisture absorption tends to create a transient imbalance in moisture absorption rate between both sides of the substrate, causing warping. is likely to occur. Also,
The ultraviolet curing resin provided above the recording layer is subjected to tensile stress due to volume shrinkage, resulting in large warpage as shown in FIG. The tensile stress of ultraviolet curable resins tends to further increase due to accelerated tests under high temperature and high humidity conditions, and there is a problem that warpage and the like become even greater due to changes in the external environment, resulting in extremely poor accuracy.

Although the degree of deterioration in accuracy is alleviated in a laminated structure with double-sided specifications, the above problems still have the same problems, and the accuracy at the initial stage of lamination is poor, and the accuracy deteriorates due to changes in the external environment. There was a problem.

[Problem to be solved by the invention]

The present invention provides an information recording medium using a plastic substrate that overcomes the deterioration in accuracy that occurs with conventional media structures, has high initial accuracy, and maintains stable disk accuracy even against changes in the external environment. This is what we are trying to provide.

[Means to solve the problem]

The inventors of the present invention have intensively investigated ways to improve the initial accuracy while also preventing the accuracy from deteriorating due to changes in the external environment, especially changes in temperature and humidity. ) by providing a coating layer of ultraviolet curing resin on the recording layer and balancing the stress with the ultraviolet curing resin on the upper side of the recording layer, it is possible to improve the initial accuracy, and it has been shown that there is almost no deterioration in accuracy even with changes in the external environment. Based on this finding, the present invention has been made.

In other words, by providing ultraviolet curable resin on both sides of the substrate, the tensile stress caused by the volumetric shrinkage of the ultraviolet curable resin is offset, providing a medium with high initial accuracy as a whole and stable accuracy even under environmental changes. It is something.

The ultraviolet curing resin provided above the recording layer for the purpose of protecting the recording layer must have excellent scratch resistance, moisture resistance, and adhesion to the recording layer.

Furthermore, since it is in direct contact with the recording layer, it must not be corrosive. The thickness of the ultraviolet curable resin layer is 1 μm to 30 μm.
The thickness is about μm, more preferably 5 μm to 20 μm. 1
If the thickness is less than .mu.m, the moisture-proofing effect will not be sufficient, and especially in a single-plate type medium, pitting corrosion, pinholes, etc. will easily occur in high-temperature tests, and the durability of the recording layer will become a problem.

Furthermore, if the diameter exceeds 30 μm, a considerable amount of energy is required to cure the ultraviolet curable resin, and the heat generated at that time may cause deformation of the plastic substrate, or the substrate may shrink due to curing of the ultraviolet curable resin. Warpage occurs, causing deterioration of accuracy.

On the other hand, the ultraviolet curing resin provided on the substrate surface needs to have excellent scratch resistance and antistatic effect. The thickness of the ultraviolet curable resin layer is preferably 1 um to 30 gts. If the film thickness is less than 1 μm, the hardness is low and there is a problem in scratch resistance. Moreover, if it exceeds 30 DI11, as mentioned above, not only will it cause deterioration of the substrate precision like the ultraviolet curable resin provided on the recording layer side, but also the absorption of laser light by the ultraviolet curable resin will occur, and sufficient energy will not be provided to the recording film. There is a possibility that it will not reach you.

In the present invention, in addition to fully demonstrating the role of protecting the recording layer or substrate surface of both ultraviolet curing resins,
It is characterized by balancing the tensile stress caused by volumetric shrinkage in both UV-curable resins. The magnitude of tensile stress due to volumetric shrinkage can be considered as a quantity related to the product of curing shrinkage rate and film thickness, and can be expressed as (stress) (X: (curing shrinkage rate) x (film thickness). For example, when 20 μm of ultraviolet curable resin with a curing shrinkage rate of 10% is applied, it can be considered that a stress proportional to 2 μm is applied.According to the present invention, the ultraviolet rays provided on both sides of the plastic substrate are applied. As for the stress balance of the cured resin, it is best to keep the difference in stress equivalent amount between the two to 2 μm equivalent or less, preferably 1 μm equivalent or less.If it is 2 μm equivalent or less, it is possible to suppress the warping of the substrate. , the initial accuracy can be improved.Also, there is almost no deterioration in accuracy due to changes in the external environment.

Furthermore, in order to maintain reliability, the recording layer is usually provided with a protective layer above or below the recording layer, or both. As this protective layer, amorphous dielectric materials such as oxides, nitrides, oxynitrides of magnesium, silicon, aluminum, etc., and composites thereof are often used. The method of using a bottom membrane is widely used.

In this case, the recording layer has compressive stress. Therefore, in order to balance the stress on both sides of the plastic substrate using the ultraviolet curable resin, it is desirable that the tensile stress on the upper side of the recording layer be larger than that on the substrate surface (on the opposite side of the recording layer). According to the present invention, it is preferable to increase the stress of the ultraviolet curing resin provided on the recording layer side by 0.5 μm as the difference in stress equivalent amount.

The effect of the present invention is particularly effective in a single-plate disk structure, but it is also effective in a double-sided disk structure in which two disks are bonded together, and high accuracy can be achieved.

As the ultraviolet curing type upper layer that can be used in the present invention, a compound having a molecular weight of less than 12,000 is used, and as an oligomer, one having a molecular weight of 2,000 to 10,000 is used.

These include styrene, ethyl acrylate, ethylene glycol diacrylate, neopentyl glycol diacrylate, ethylene glycol methacrylate, and the like. Particularly preferred are pentaerythritol tetraacrylate or methacrylate, pentaerythritol acrylate or methacrylate, trimethylolpropane triacrylate or methacrylate, trimethylolpropane diacrylate or methacrylate, or derivatives thereof; These ultraviolet curing resins may be used alone or in combination.

As a method for curing the coating film made of the ultraviolet curable resin with ultraviolet rays, various known methods may be used. Also,
The coating film is spin code, gravure coating, spray coating,
Coating may be performed by combining a number of known methods such as deimping, and the coating conditions at this time may be appropriately determined depending on the viscosity of the resin M used or the mixture, the condition of the substrate surface, the thickness of the coating film, etc.

The substrate material used in the present invention includes transparent materials such as polypropylene, acrylic resin, polycarbonate resin, styrene resin, and vinyl chloride resin. Among these, polycarbonate resin and acrylic resin have the best optical properties and moldability. It is suitable in terms of It is also true that by coating both sides of the substrate of the present invention with an ultraviolet curing resin to balance the stress, differences in the inherent properties of the substrate material, such as hygroscopicity or moisture permeability, have less influence on changes in media accuracy over time. This is one of the effects of the invention.

The recording layer in the present invention is not particularly limited; for example, in the case of a write-once type, it may be of an aperture type or phase change type, and in the case of a rewritable type, it may be of a magneto-optical type. , a phase change method may also be used. It may also be of a playback-only type, such as a CD.

〔Example〕

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

In order to clarify the effects of the present invention in Examples, first, a comparative example will be shown for comparison.

Comparative Example: A clean 3.0mm thick 1.2mm bottom molded by injection molding method.
5# On the polycarbonate substrate, 1100 SiN thin films, 220 TbFeCo alloy thin films, SiN Fi[film 3
A magneto-optical disk with 50 layers and 650 Affil layers layered sequentially was formed using the spunter method, and an ultraviolet curing resin (acrylic whose main components are trimethylolpropane triacrylate and neopentyl glycol diacrylate) was coated on top of the recording layer. Acid ester complex) was coated using a spin cord and cured by irradiating it with 280 ml/alT ultraviolet rays for 8 seconds. The curing shrinkage rate of the ultraviolet curing resin used at this time was 8%.

Here, the film thickness of the ultraviolet curing resin is taken as a parameter, and is 8 μm.
When samples of 115 μm and 30 μm were prepared and the accuracy was measured, the following values were obtained.

The above sample was placed in an environment of 80″C180%R)I for 20 minutes.
After conducting the 0-hour accelerated test, the accuracy was measured and the following values were obtained.

Moreover, a significant deterioration in accuracy was observed in accelerated tests under high temperature and high humidity conditions (failing to meet the accuracy specifications of the Optical Disk Standardization Committee).

Example 1 A sample in which a magneto-optical recording film similar to that of the comparative example was formed on a 3.5″ polycarbonate substrate and an ultraviolet curable resin was coated on top of the same as that of the comparative example. 3
I created a seed. The film thickness at this time was 8um, 15μm, 3
It was 0um.

Furthermore, the substrate surface side of the above sample (the side opposite to the recording film)
was coated with ultraviolet curing resin (pentaerythritol acrylate) using a spin cord, and the power output was 220mW/c++1.
It was cured by irradiating it with ultraviolet rays for 5 seconds. The volumetric shrinkage rate of the ultraviolet curable resin used on this surface side is 10%, and the film thickness is 8 μm.In other words, when the ultraviolet curable resin is provided only on the recording film example as in this comparative example, the initial accuracy is also low. When the accuracy of three samples prepared in this manner was measured, the following values were obtained.

(Left below) It can be seen that the precision can be significantly improved by providing a UV-curable resin on the surface of the substrate and balancing the stress. Even when a 30 μm ultraviolet curable resin is provided on the recording film side, the specification of 5 mrad is sufficiently cleared.

The above sample was heated at 80°C and 185%RH for 200 minutes.
After conducting a time acceleration test, the accuracy was measured and the following values were obtained.

(Left below) It can be seen that the disc accuracy was maintained stably with almost no deterioration in accuracy even after the test under high temperature and high humidity.

Example 2 A 3.5" magneto-optical disk was prepared by the same method as shown in Example 1. As the ultraviolet curable resin, pentaerythritol acrylate was used on the substrate surface side, and trimethylolpropane acrylate was used on the recording film side. An acrylic acid ester composite containing acrylate and neopentyl glycol diacrylate as main components was used.The volume shrinkage on the recording film side is 8%, and the volume shrinkage on the substrate surface side is 10%.

In order to balance the stress on both sides of the substrate, we varied the thickness of each film and measured the accuracy. The results are shown in FIG. Here, the product of the volumetric shrinkage rate and the film thickness is taken as the stress equivalent amount which is proportional to the stress, and the difference is expressed in order to see the balance between the two.

According to the results, it can be seen that as the stress balance on both sides of the substrate shifts, the accuracy of the disk warps toward the side with greater tensile stress. Considering the deterioration in accuracy due to changes in the external environment, it is desirable that the difference in stress balance between the two is equal to or less than 2 μm.

Further, it is preferable that the tensile stress of the ultraviolet curable resin provided on the recording film be slightly larger than that provided on the substrate surface. The reason for this is thought to be the balance of compressive stress acting on the recording film.

C. Effects of the Invention] According to the present invention, it is possible to achieve good initial accuracy, and it is also possible to stably maintain good accuracy even against changes in the external environment.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the disk structure according to the present invention, and FIG.
The figure is a schematic diagram of an optical recording and reproducing method using laser light.
FIG. 3 is a schematic diagram showing the deterioration of accuracy in the conventional disk structure, and FIG. 4 is a diagram showing the relationship between stress balance and accuracy. 1, 4, 10---1 ultraviolet curing resin layer, 2
, 8-----1 transparent resin substrate, 3, 9----
-Information recording layer, 5-1---disc, 6------
--Pickup, 7---Laser light, 11---
-----Direction of warping due to one stress.

Claims (1)

[Claims] In an information recording carrier in which an information recording layer is formed on a translucent resin substrate, and the upper side of the information recording layer is coated with an ultraviolet curable resin having a protective effect, the surface of the translucent resin substrate is also coated with an ultraviolet curable resin. An information recording medium characterized by being coated with.