JP2003109251A - Optical recording medium, manufacturing method therefor and protective film-forming material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium provided with a protective film which is thin and whose film thickness distribution has no fluctuation and whose surface is smooth. SOLUTION: In the optical recording medium provided with a substrate 1 and an information recording layer 2, the protective film 3 consisting of a light transmissive resin material and having nearly uniform thickness of 50-200 μm and a surface formed by reproducing the smoothness of a surface of a surface treatment medium which is applied on the surface of the protective film when the protective film is film-formed is formed on the information recording layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more specifically to an optical recording medium having a protective film on an information recording layer formed on a substrate. A typical example of the optical recording medium is an optical disc. The present invention also relates to a method for manufacturing an optical recording medium, and a protective film-forming resin material used in such a method.

[0002]

2. Description of the Related Art In recent years, with the progress of multimedia, even video and audio data have been processed by digital signals. In general, video and audio have a large amount of information, and accordingly a large-capacity / high-density recording medium is required. As such a recording medium, a DVD capable of supporting future increase in capacity and density
Optical discs such as (Digital Versatile Disk) and CD (Compact Disk) are receiving attention.

The optical disk comprises a substrate and an information recording layer and a protective film formed on the substrate in order to be easily understood from the optical disk of the present invention described in detail with reference to the drawings. Is common. More specifically, for example, a read-only optical disc has an information recording layer made of aluminum or the like on the surface of a disc-shaped substrate (for example, made of polycarbonate resin) having irregularities serving as pits or guide grooves for carrying information on the surface. Is being worn. Further, the surface of the information recording layer is sealed with a protective film made of a light transmissive resin in order to protect the optical disc from moisture in the atmosphere, mechanical damage and the like. In such an optical disc, information can be reproduced by continuously irradiating the information pits of the guide groove of the substrate with the laser light condensed by the objective lens for the reproduction pickup.

Incidentally, with the recent increase in density and capacity of recording media, it is necessary to improve the protective film. For example, since the protective film reproduces information by irradiating light, it is of course necessary that the protective film has a high transparency to the reproduced light, and the film thickness of the protective film is as thin as possible. It is desirable that the entire surface of the medium is substantially uniform and the surface is smooth.
However, conventional protective films have not been able to sufficiently satisfy such problems.

For example, a protective film for an optical disk is usually manufactured by coating a surface of an information recording layer with an ultraviolet curable resin by a spin coating method or the like to a predetermined film thickness and then curing it by irradiation with ultraviolet rays. . However, as shown in FIG. 1, the protective film 3 formed on the surface of the polycarbonate resin substrate (the information recording layer is not shown for simplification of description) causes the substrate 1 to rotate during spin coating. As a result, the film thickness is thin on the center side of the disk and increases toward the outer side, and a raised portion is formed at the outer peripheral edge. The raised portion is usually 1 to 2 mm wide and 20 to 30 μm high. Such a variation in the film thickness adversely affects the reproduction characteristics and the like, and when a magnetic head is used as the reproducing means, there is a risk of causing a head crash or the like.
When the spin coating method is used, radial defects are likely to occur, which is characteristic of this film forming method.

[0006] The spin coating method is a very useful film forming method.
Japanese Patent Application Laid-Open No. 57297 proposes that the formation of a raised portion is predicted in advance, and the inclined surface is formed by notching the outer peripheral edge portion of the substrate by that amount. However, in this method, not only the work of cutting the substrate is complicated and costly, but also the optimum notched inclined surface and spin coating conditions must be designed each time, which is a generally effective solution. Not a means.

Another method is to attach a protective film sheet.
In this method, a disc-shaped sheet is punched out from a protective film sheet (for example, a polycarbonate sheet) having a thickness of about 70 to 90 μm, and the disc-shaped sheet is attached to the surface of the information recording layer of the optical disc via an adhesive or pressure-sensitive adhesive sheet. But
The original sheet of the protective film sheet is expensive, the usage efficiency of the original sheet is poor because it is used after punching, dust is attached, scratches, bending, etc. are likely to occur, so careful handling of the sheet is necessary, etc. Has the problem of. The adhesive used here is usually an ultraviolet curable adhesive, but a problem peculiar to this adhesive is that the thickness of the adhesive layer varies. Further, when the pressure sensitive adhesive sheet is used, there is a problem that the release liner is discarded in addition to the problem that the sheet is expensive due to the peculiarity of the sheet.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a protective film which is thin, has no variation in film thickness distribution, and has a smooth surface by overcoming the problems of the conventional techniques as described above. Therefore, it is an object to provide a high-quality optical recording medium that can cope with a large capacity and a high density.

Another object of the present invention is to provide a method capable of easily and inexpensively producing a high-quality optical recording medium provided with a protective film which is thin, has a uniform film thickness distribution, and has a smooth surface. To provide.

A further object of the present invention is to provide a method of manufacturing an optical recording medium in which dust, scratches, bending, and radial defects do not occur on the protective film.

These and other objects of the present invention are
It will be readily understood from the detailed description below.

[0012]

According to one aspect of the present invention, in an optical recording medium having a substrate and an information recording layer formed on the substrate, the information recording layer has a light transmitting property. Having a protective film made of an organic resin material on its surface, the protective film having a substantially uniform thickness of 50 to 200 μm, and the surface coated on the surface when the protective film was formed. An optical recording medium having a surface that reproduces the smoothness of the surface of the processing medium.

According to another aspect of the present invention, in the method of manufacturing an optical recording medium provided with a substrate and an information recording layer and a protective film sequentially formed on the substrate, the following steps are carried out. : A light-transmitting protective film-forming resin material is formed on the surface of the information recording layer, and the thickness of the resulting protective film is 5
The surface treatment medium having a smoothness corresponding to a desired smoothness in the protective film is applied to the surface of the layer of the protective film-forming resin material, which is applied in an amount sufficient to achieve 0 to 200 μm. Then, under the condition that the substrate and the surface treatment medium are laminated, the protective film-forming resin material is cured to form the protective film, and thus the smoothness of the surface of the surface treatment medium is applied to the protective film. A method for producing an optical recording medium, which comprises transferring and, if necessary, removing the surface-treated medium.

Further, according to another aspect of the present invention, a light-curable resin material is characterized in that it can be cured by light transmitted through an adjacent medium to form a protective film. A protective film-forming resin material for a recording medium.

In the optical recording medium of the present invention, since the protective film-forming resin material is filled and cured between the medium substrate and the surface-treated medium which are arranged in parallel, the manufacturing process is simplified and the protective film is protected. The film can be easily thinned and the film thickness can be made substantially uniform. In addition, by using a surface treatment medium having excellent flatness and smoothness, the flatness and smoothness of the surface can be accurately transferred to the surface of the protective film. It is also possible to prevent radial defects such as those generated in Step 2. further,
Since the protective film-forming resin material is inexpensive and easily available commercially, the manufacturing cost can be remarkably reduced as compared with the conventional product.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The optical recording medium according to the present invention can have various forms according to the recording and reproducing system of information used. Basically, (1) a substrate,
(2) An information recording layer formed on the substrate, and (3) a protective film covering the surface of the information recording layer. Typical examples of such an optical recording medium are CD, D
It is an optical disk represented by VD and the like. Further, the protective film of the optical recording medium of the present invention may be used in fields other than the optical recording medium, if necessary, by utilizing its excellent quality and the like.

FIG. 2 shows a read-only optical disc (D
It is a perspective view showing one embodiment of (VD). The optical disk 10 is composed of a substrate 1 made of one transparent resin (for example, polycarbonate resin), and the transparent substrate 1
A pit pattern (not shown) corresponding to information is formed on the surface of the. The optical disc 10 has a circular hollow portion (opening) at the center thereof. The optical disc 10 is
When mounting it on an optical disk device, the opening of this optical disk is fitted to the shaft of the device. An information recording layer 2 made of a metal such as aluminum is disposed on the transparent substrate 1 and has a reflectance of about 90%. Further, on the surface of the information recording layer 2, a protective film 3 made of a light transmissive resin material is provided in order to protect it from moisture in the atmosphere, mechanical shock, and the like. Optical disc 1
When laser light L from an optical head (not shown) is focused on and irradiated with 0 by an objective lens, information can be read and reproduced by reflection according to information pits from the information recording layer 2.

In the example shown in the figure, a read-only optical disk is described, but the optical disk of the present invention is not limited to this embodiment. That is, the optical disc of the present invention may be an optical disc capable of recording and reproducing information, or may be an optical disc in which the information recording layer and the protective films thereon are on both sides of the substrate. Further, the optical disk of the present invention may be an optical disk whose recording / reading method is magneto-optical or phase change.

In the optical recording medium of the present invention, the substrate carrying the information recording layer is not particularly limited and may be transparent or translucent depending on the information recording / reproducing system adopted. , Or opaque. The substrate can be formed of a plastic material such as an acrylic resin or a polycarbonate resin by a conventional molding method such as an injection molding method, as is generally performed in this technical field. In some cases, instead of the plastic material, another material such as glass may be used as the substrate. The size of the substrate can be widely changed depending on the desired size of the optical recording medium. For example, in the case of an optical disk such as a commercially available DVD, the diameter of the substrate is 12
cm and the thickness is 0.6 mm. The optical recording medium may take a form other than the disc, if necessary.

Of the surface of the substrate, the surface on which the information recording layer is to be formed is provided with an uneven pattern, uneven pits and the like corresponding to information signals such as video and audio to be recorded on the optical recording medium. A master stamper or photolithography can be used to form the uneven pattern or the like. Further, depending on the information recording / reproducing method, the uneven pattern or the like on the surface of the substrate may not be provided.

As with the substrate, the information recording layer formed on the substrate is not particularly limited. The information recording layer is usually formed as a thin film from a metal material, a ceramic material, or the like suitable for forming a reflective or semitransparent recording layer. As a recording layer forming material suitable for forming the reflective recording layer, a material having a reflectance of about 90% after film formation, for example, aluminum can be mentioned. Further, as a recording layer forming material suitable for forming the translucent recording layer, a material having a reflectance of about 50% after film formation, for example, gold, a silicon-based dielectric (for example, generally represented by the formula SiNx, is used). Silicon nitride, SiC, etc.). These recording layer forming materials can be formed into a film by a conventional thin film forming technique such as a sputtering method or a vacuum evaporation method.
Although the thickness of the information recording layer can be changed in a wide range, it is usually in the range of about 10 to 500 nm.

The protective film provided on the uppermost layer of the optical recording medium is made of a photocurable resin material, that is, a resin material which is curable by irradiation of light. Here, "light" means various kinds of light such as visible light, radiation such as ultraviolet rays, and electron beams. Therefore, a photocurable resin material suitable for forming a protective film is, for example, ultraviolet rays (UV). ) A curable resin material, an electron beam (EB) curable resin material, and the like. Suitable photocurable resin materials are not limited to those listed below, but include isooctyl (meth) acrylate, 2-ethylhexyl carbitol (meth) acrylate, n-butyl (meth) acrylate, and Examples of the resin material include a (meth) acrylic acid ester such as stearyl (meth) acrylate, and an acrylic compound such as urethane acrylate, epoxy acrylate, and polyester acrylate. A photopolymerization initiator is usually used in combination with such a photocurable resin material. Particularly suitable UV curable resin materials are
A mixture of urethane acrylate and dimethyloltricyclodecane acrylate or urethane acrylate and 1,
A photopolymerization initiator was added to a mixture of 6-hexanediol diacrylate. If necessary, various additives generally used in this technical field may be added to the resin material. Examples of suitable additives include thickeners, plasticizers, dispersants, polymerization inhibitors and the like.

The protective film-forming resin material as described above is
Usually, it is applied on the surface of the information recording layer formed on the substrate,
It is hardened. According to another method, the resin material capable of forming a protective film may be applied and cured on the surface of the surface treatment medium in addition to the surface of the information recording layer. By adopting such a double-sided coating method, for example, the thickness of the protective film can be easily controlled. In the case of such a double-sided coating method, the same resin material may be applied to the surface of the information recording layer and the surface of the surface treatment medium, or a resin material having different composition, characteristics, etc. may be applied. You may. For example, when resin materials having different adhesive strengths to the adherend are used, the work of peeling the surface treatment medium from the medium can be improved. Other resin coating methods or thin film forming methods can be used for the protective film-forming resin material, if necessary, but it is advantageous to apply the resin material onto the information recording layer or the like by spin coating. The spin coating method can be carried out using a commercially available spin coater and general coating conditions.

Here, the protective film-forming resin material usually has a viscosity of 1,000 cps or more, preferably 2,000 to 100,000 cps, and more preferably 5,000 to 100, cps. It has a viscosity of 000 cps. This is because in the case of the optical recording medium of the present invention, the selected resin material is applied beforehand on the medium substrate and, if necessary, on the surface-treated medium by a spin coating method or the like so that the thickness becomes uniform, and In order to prevent the thickness of the resin material layer from changing when stacking surface treatment media with,
It is desirable that the viscosity is sufficiently high, but on the other hand, it must be within a range in which the resin material can be applied practically at a desired thickness. Further, if the viscosity of the resin material is too low, the solution may drip at the peripheral edge of the substrate after the application and before the photo-curing. In fact, when the viscosity of the resin material is less than 1,000 cps, the thickness distribution of the protective film becomes uneven, and conversely 100,000 cps.
If it exceeds s, it becomes difficult to apply. The viscosity of the protective film-forming resin material referred to in the present specification is
A Brookfield viscometer (spindle # 2, 12rp) according to the guidelines described in JIS K 7117-1-1999.
m) at 25 ° C.

After coating a predetermined amount of the resin material having a protective film forming property on the information recording layer, the layers of the uncured resin material are sandwiched at equal intervals corresponding to the desired film thickness of the protective film. The surface treatment medium is superposed on the substrate and the resin material is cured. Further, in the case of a double-sided coating method in which a protective film-forming resin material is additionally applied onto the surface treatment medium as necessary, the total amount of the resin material is the predetermined amount necessary for forming the protective film. Become. If the resin material is a UV-curable resin material, a thin glass plate (circle) with excellent UV transparency is used as the surface treatment medium, and the UV light from the high pressure mercury lamp is used. The resin material is irradiated through the glass plate and cured. A plastic sheet or the like may be used as the surface treatment medium. The double-sided coating method can be advantageously carried out in various forms. For example, as the protective film forming resin material, the same resin material may be used on the information recording layer and the surface treatment medium as described above, or different resin materials may be used separately. Further, the resin material after coating may be cured after laminating the substrate and the surface treatment medium, or alternatively, either the resin material on the information recording layer or the resin material of the surface treatment medium is cured first, After that, the substrate and the surface treatment medium may be laminated, and the remaining resin material may be subsequently cured. Further, when applying the resin material, the diameter of the surface treatment medium is set to be larger than the diameter of the substrate supporting the information recording layer, and after the resin material is applied to the entire surface of the surface treatment medium, the area corresponding to the information recording layer is formed. Alternatively, only the resin may be selectively cured to remove the uncured resin material, and then the resin material may be laminated on the substrate. By adopting such a method, it becomes easy to control the film thickness distribution of the protective film, the deviation of the laminated body can be prevented, and the workability is improved.

The thickness of the protective film of the optical recording medium is usually about 50 to 200 μm, preferably about 6
It is 0 to 150 μm. This protective film has a substantially uniform film thickness over the entire surface. That is, when the film thickness of the protective film is 100 μm, the distribution of the film thickness is usually about 100 ± 3 μm.

The protective film preferably has excellent flatness and smoothness. This is because when the protective film-forming resin material is sandwiched between the medium substrate and the surface treatment medium to form the protective film, the excellent smoothness of the surface of the surface treatment medium covered with the layer of the resin material, This is because it was directly transferred to the surface of the protective film. When the smoothness of the protective film is expressed by the average surface roughness Ra, it is usually
It is 0.02-0.08 micrometer.

The surface-treated medium may have a smooth surface exhibiting a wide range of surface energies. When the surface energy of the surface treatment medium that is in close contact with the cured protective film forming resin material is maximum, the surface of the cured resin material is separated by the surface of the surface treatment medium when removing the surface treatment medium in the subsequent step. Therefore, the intended use of the optical recording medium is not denied, and if the surface energy of the surface treatment medium that is in close contact with the uncured protective film-forming resin material is the minimum, the surface treatment is performed. The intended wetting of the medium from the surface is not denied, or the flow of the protective film-forming resin material on or between the surface treatment medium is not hindered.

Although the optical recording medium of the present invention comprises a substrate, an information recording layer and a protective film, it may optionally have other layers. Suitable additional layers can include, for example, printing layers, antireflective coating layers, hard coating layers, antistatic layers, and the like.

The optical recording medium according to the present invention can be advantageously manufactured by forming an information recording layer on a substrate by a conventional method and then forming a protective film by the following procedure. (1) Application of protective film forming resin material A light transmitting protective film forming resin material is applied to the surface of the information recording layer formed on the substrate. Preferably, a thin film of a resin material can be formed on the surface of the information recording layer by dropping a selected resin material from a nozzle while rotating the substrate using a spin coater or the like. Here, it is preferable that the amount of the resin material applied is usually sufficient to bring the desired thickness of the protective film to the desired range of 50 to 200 μm.

According to another method, the protective film-forming resin material is
It may be applied to the surface of the surface treatment medium (the surface on the side of the information recording layer) as well as the surface of the information recording layer. The resin material applied to the surface of the surface treatment medium may be the same as or different from the resin material applied to the surface of the information recording layer. Further, in this case, the total coating amount of the resin material is the amount required to obtain the desired film thickness in the protective film. (2) Pressing of surface treatment medium As a pretreatment step for obtaining a protective film having characteristic properties, the surface treatment medium is pressed against the surface of the layer of the protective film forming resin material. The surface-treated medium used here has a function of transferring smoothness, and thus can be referred to as a “mold”. Although the details are not limited, the surface of this mold is
It is necessary for the protective film to have a smoothness corresponding to the desired smoothness. When the resin material used is photo-curable, in order to achieve curing of the resin material,
It is necessary that the mold itself be transparent to light, for example, transparent to ultraviolet light. Suitable light transmissive surface treatment media are glass disks, plastic sheets and the like. The surface of such a surface-treated medium may be subjected to a release treatment by coating with a silicone resin or the like in order to facilitate peeling from the medium substrate after forming the protective film. As described above, the surface of the surface treatment medium may be preliminarily formed with a layer of the protective film-forming resin material.

After pressing the surface treatment medium against the medium substrate,
Both are superposed so that their surfaces are parallel. A suitable jig may be used if necessary. In this case, the distance between the two, that is, the thickness of the thin film of the sandwiched resin material is almost the same as the desired thickness of the protective film, ignoring shrinkage during curing, and Does not include fine bubbles. Further, in order to remove the excess resin material, the medium substrate and the surface treatment medium may be superposed and then rotated as a whole. (3) Formation of protective film The protective film-forming resin material is cured while being sandwiched between the medium substrate and the surface treatment medium. The curing method and curing conditions can be widely changed according to the type of resin material. For example, if an ultraviolet curable resin material is used, the resin material can be cured by irradiation with ultraviolet rays through a surface treatment medium (glass disk) to form a protective film. In this way, the smoothness of the surface of the surface treatment medium is transferred to the surface of the protective film.
By the way, in the case where the protective film-forming resin material is applied to the surface of the surface treatment medium as well as the surface of the information recording layer, before applying the substrate and the surface treatment medium as described above, 2
Either one of the two resin material layers may be cured in advance. In such a case, the other uncured resin material layer is cured in the curing step described here. The curing method and curing conditions can be arbitrarily changed. (4) Peeling and removal of surface treatment medium After the formation of the protective film is completed, the surface treatment medium used for imparting smoothness is peeled and removed. The surface is smooth,
The desired protective film is obtained. The peeled surface treatment medium can be cleaned and reused, which is economical.

[0033]

The present invention will be described below with reference to its examples. However, it goes without saying that the present invention is not limited to these examples. Also, in the examples below,
"Parts" means "parts by weight" unless otherwise specified. Example 1 (see FIG. 3) An optical disk substrate was formed by depositing an information recording layer with a thickness of 50 nm on a transparent circular substrate made of polycarbonate by sputtering aluminum. Next, as shown in step (A) of FIG. 3, while the optical disk substrate (information recording layer is not shown) 1 was being rotated, the UV curable syrup 3 was dropped from the nozzle 13 to approximately the center of the surface thereof.
The syrup 3 used here was 30 parts of urethane acrylate (trade name "UV6100B", manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 70 parts of dimethylol tricyclodecane diacrylate, and 5 parts of a photopolymerization initiator (trade name "Darocur. (Darocure 1173 ^™ ) ”manufactured by Ciba Geigy). A thin film of UV curable syrup 3 was formed on the surface of the optical disc substrate 1.

Next, as shown in step (B), a disk-shaped glass plate (thickness 1 mm) 5 having the same shape and size as the substrate was placed on the syrup 3 side of the optical disc substrate 1. The surface of the glass plate 5 was previously subjected to a smoothing treatment in order to impart the same level of smoothness as that intended for the protective film.

As shown in step (C), the state where the optical disk substrate 1 and the glass plate 5 were superposed was maintained, and the UV curable syrup 3 was allowed to naturally spread over the entire surface.

Then, as shown in step (D), the UV curable syrup 3 is exposed to ultraviolet rays (wavelength of 20) through the glass plate 5.
(0-400 nm) for 10 seconds to completely cure the syrup. When the glass plate 5 was manually removed from the optical disk substrate, an optical disk having a protective film of about 100 μm on the surface was obtained. [Evaluation test] Thickness of protective film: The thickness of the protective film of the optical disc sample is
Using a thickness measuring device using a multifocal optical sensor manufactured by Keyence Corporation, non-destructive and non-contact measurement was performed under specified measurement conditions. The measurement results shown in Table 1 below were obtained. In Table 1, "average thickness (μm)"
Is the average value of the thicknesses of the protective films of the two samples, and "variation in thickness (difference between maximum and minimum values, μm)"
Are the average values for the entire optical disc and the measured values for each of the six types of tracks (Tr. 1 to Tr. 6) having different circumferential radii when the variation in the thickness of the protective film is measured. . Surface smoothness of protective film: The surface smoothness of the protective film of the optical disk sample was measured with respect to surface roughness. A laser confocal microscope available as Model VF-7500 from KEYENCE CORPORATION in Osaka was used to measure the surface roughness of this protective film. This measuring device was incorporated with software capable of calculating the surface roughness as the average surface roughness Ra according to JIS B 0601-1994. The recorded average surface roughness Ra (μm) is based on JIS B 0601.
It becomes the surface roughness of some measurement sites measured according to -1994. The measurement results shown in Table 1 below were obtained. Absorption in the wavelength region of the recording / reproducing laser (λ = 400 nm):
In order to measure whether or not the protective film of the optical disk sample has absorption in the wavelength region (λ = 400 nm) of the recording / reproducing laser, instead of the actual protective film, the above-mentioned UV curable resin having a thickness of 100 μm was used. The film was used as a mock. Hitachi spectrophotometer 350 for transmittance (%) of light with wavelength of 400 nm
When measured with the 0 type (trade name), the measurement results shown in Table 1 below were obtained. Example 2 (see FIG. 4) An optical disk substrate was formed by depositing an information recording layer with a film thickness of 50 nm on a transparent circular substrate made of polycarbonate by sputtering aluminum. Next, as shown in step (A) of FIG. 4, while the optical disk substrate (information recording layer is not shown) 1 is rotated, the UV curable syrup 3 is dripped from the nozzle 13 in a donut shape in the substantially central portion of the surface thereof. did. The syrup 3 used here was 60 parts of urethane acrylate (trade name "UV6100B", manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 40 parts of 1,6-hexanediol diacrylate and 5 parts of a photopolymerization initiator (trade name " Darocur (Darocure 1173 ^™ ) "manufactured by Ciba Geigy Co., Ltd.). Optical disk substrate 1
A donut-like thin film of UV curable syrup 3 was formed on the surface of the.

Next, as shown in step (B), a disk-shaped glass plate (thickness 1 mm) 5 having the same shape and size as the substrate was placed on the syrup 3 side of the optical disc substrate 1. The surface of the glass plate 5 was previously subjected to a smoothing treatment in order to impart the same level of smoothness as that intended for the protective film.

As shown in step (C), after the optical disk substrate 1 and the glass plate 5 were superposed on each other, they were rotated at a high speed in the direction of the arrow to shake off the excess UV curable syrup 3.
A thin film of UV curable syrup 3 having a predetermined film thickness was formed.

Thereafter, as shown in the step (D), the UV curable syrup 3 is exposed to ultraviolet rays (wavelength of 20) through the glass plate 5.
(0-400 nm) for 10 seconds to completely cure the syrup. When the glass plate 5 was manually removed from the optical disk substrate, an optical disk having a protective film of about 100 μm on the surface was obtained. [Evaluation Test] A series of evaluation tests were conducted according to the same method as that described in Example 1, and the measurement results as shown in Table 1 below were obtained. Comparative Example 1 The procedure described in Example 1 was repeated, but in this example,
For comparison, a UV-curable syrup was spin-coated on the surface of an optical disk substrate to a film thickness of 100 μm, and then irradiated with ultraviolet rays (wavelength 200 to 400 nm) for 10 seconds to completely cure the syrup. In this example, therefore, the glass plate was not used as a smoothness transfer mold.

When a series of evaluation tests were carried out according to the same method as that described in Example 1, the measurement results as shown in Table 1 below were obtained. Comparative Example 2 The procedure described in Example 1 was repeated, but in this example,
For comparison, instead of forming a UV-curable syrup-derived protective film on the surface of an optical disk substrate, a polycarbonate sheet (thickness: about 70 μm) is formed on the surface of the substrate with a pressure-sensitive adhesive layer (thickness: about 30 μm). To form a protective film.

When a series of evaluation tests were carried out in the same manner as in Example 1, the measurement results as shown in Table 1 below were obtained.

[0042]

[Table 1]

As is apparent from the measurement results shown in Table 1 above, according to the present invention, it is possible to obtain an optical disc having a protective film which is excellent in various characteristics as compared with the conventional optical disc.

[0044]

As described above, according to the present invention, the protective film which is thin, has no variation in film thickness distribution, and has a smooth surface is provided, and thus it is possible to cope with a large capacity and a high density. It is possible to provide a high quality optical recording medium. Further, according to the present invention, such a high quality optical recording medium can be easily manufactured at low cost. further,
According to the present invention, it is possible to prevent problems such as dust, scratches, bending, and radial defects on the protective film during manufacturing of the optical recording medium.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a problem at the time of forming a protective film in a conventional optical disc manufacturing method.

FIG. 2 is a sectional view schematically showing an example of an optical disc according to the present invention and its use.

FIG. 3 is a cross-sectional view sequentially showing one preferable method of manufacturing an optical disc according to the present invention.

4A to 4C are cross-sectional views sequentially showing another preferable method of manufacturing an optical disc according to the present invention.

[Explanation of symbols]

1 ... Optical disc substrate 2 ... Information recording layer 3 ... Protective film 5 ... Surface treatment medium 10 ... Optical disc 13 ... Nozzle

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuya Takamori             Sumitomo 3-8-8 Minami-Hashimoto, Sagamihara City, Kanagawa Prefecture             Within 3M Co., Ltd. F-term (reference) 5D029 LB07 LB20 LC11                 5D121 AA04 EE22 EE23 GG02

Claims (12)

[Claims] 1. An optical recording medium comprising a substrate and an information recording layer formed on the substrate, wherein the information recording layer has a protective film made of a light transmissive resin material on its surface. The protective film has a substantially uniform thickness of 50 to 200 μm, and has a surface that reproduces the smoothness of the surface of the surface treatment medium that was coated on the surface when the protective film was formed. An optical recording medium characterized by the following. 2. The protective film is formed by applying a protective film-forming resin material on the surface of the information recording layer, and curing the resin after coating the surface treatment medium. Item 2. The optical recording medium according to item 1. 3. The protective film-forming resin material is a photocurable resin material, and is cured by light transmitted through the surface treatment medium to form the protective film. 2. The optical recording medium according to 2. 4. The viscosity of the protective film-forming resin material is 25.
The optical recording medium according to claim 2 or 3, wherein the optical recording medium has a temperature of 1,000 to 100,000 cps. 5. A protective film-forming resin material is applied to the surface of the information recording layer from the liquid by a spin coating method, according to any one of claims 2 to 4.
An optical recording medium according to item. 6. A method of manufacturing an optical recording medium comprising a substrate, and an information recording layer and a protective film sequentially formed on the substrate, the method comprising the steps of: transmitting light to the surface of the information recording layer. Of the protective film-forming resin material is applied in an amount sufficient to obtain a film thickness of the protective film of 50 to 200 μm, and the protective film-forming resin material is applied to the surface of the layer of the protective film-forming resin material in the desired protective film. The surface treatment medium having a smoothness corresponding to the surface smoothness is covered, and the protective film-forming resin material is cured under the state where the substrate and the surface treatment medium are laminated to form the protective film. Therefore, the method for producing an optical recording medium, which comprises transferring the smoothness of the surface of the surface-treated medium to the protective film and removing the surface-treated medium as necessary. 7. The protective film-forming resin material, which is the same as or different from the protective film-forming resin material, is further applied to a smooth surface of the surface treatment medium to form two layers of the protective film-forming resin material. 7. The method for manufacturing an optical recording medium according to claim 6, wherein the total thickness is the thickness of the protective film. 8. The optical recording medium according to claim 7, wherein either one of the two layers of the protective film-forming resin material is pre-cured before laminating the substrate and the surface treatment medium. Manufacturing method. 9. A protective film is formed by using a photo-curable resin material as the protective film-forming resin material, and curing the resin material by light transmitted through the surface treatment medium. The method for manufacturing the optical recording medium according to claim 6. 10. The information recording layer and, if necessary,
7. The protective film-forming resin material is applied to the surface of the surface treatment medium by a spin coating method.
10. The method for manufacturing an optical recording medium according to any one of items 9 to 10. 11. A protective film-forming resin material for an optical recording medium, which is a photocurable resin material and can be cured by light transmitted through an adjacent medium to form a protective film. 12. A viscosity of 1,000 to 100 at 25 ° C.,
The protective film forming resin material for an optical recording medium according to claim 11, wherein the resin material is 000 cps.