JP2006073166A - Optical disk and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk having enhanced heat resistance and small deformation even after a high temperature load test and capable of being reproduced by a player and to provide its manufacturing method. <P>SOLUTION: In the optical disk wherein an adhesive 16 and a light transmissive second substrate 14 are successively formed on a first substrate 12, a reflection layer and/or a recording layer is formed on the first substrate side of the second substrate and recording and reproduction of information are performed by irradiation with a laser beam from the second substrate side, the first substrate is made of a plastics consisting essentially of a polylactic acid resin having ≥100°C load deflection temperature (DTUL) under low load (0.45 MPa) specified by ISO and the second substrate is made of a plastics consisting essentially of a polylactic acid having ≥80% transmittance of a beam having the wavelength of the laser beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical disc, and more particularly, to an environmentally-friendly optical disc using a polylactic acid resin, which is a plastic made from plant material, and a method for manufacturing the same.

In recent years, with the development of the petrochemical industry and the progress of plastic synthesis and processing technology, various plastic products are produced in large quantities, and along with this, used plastic products are discarded as industrial waste and general waste. The amount of plastic has also increased rapidly. For example, the amount of waste plastic in Japan in 2002 reached nearly 10 million tons per year. Furthermore, the trend of increasing the amount of waste plastic continues, and the disposal problem of waste plastic is becoming more serious.
Currently, around 60% of such plastic waste is disposed of by simple incineration or landfill. However, when waste plastic with high combustion heat calories is incinerated at a normal garbage incinerator, there is a problem that it burns abnormally and damages the furnace body of the incinerator. And by simply incinerating waste plastics, carbon dioxide released into the atmosphere increases, which is problematic from the viewpoint of global warming.

Furthermore, when waste plastics are disposed of by landfill, the waste plastics are light and bulky, so they occupy a large volume of waste, and the land shortage of landfill sites such as landfills has become urgent. It is difficult to continue such a disposal method for a long time.
In this way, from the viewpoint of the global environment, such as plastic waste treatment, and from the viewpoint of the global resource, that is, depletion of fossil resources (crude oil), plastics made from plants and biodegradable plastics that are decomposed by oxygen and microorganisms Research and development has been actively conducted.

  Among them, polylactic acid resin made from starch such as corn is particularly attracting attention because it is biodegradable and is a low environmental load resin derived from plants, which is a renewable resource. For example, Patent Document 1, Patent Document 2, Patent Document 3 and the like disclose application examples for films and packaging materials, and polylactic acid resin is used for green plastic (pages 205-230, 2002). As an example of application, for example, garbage bags, food containers, packaging containers, packaging films, etc., which are mainly intended for functionally simple applications that do not strictly require heat resistance and impact resistance, are shown. . Further, for example, Patent Document 4, Patent Document 5, Patent Document 6 and the like disclose examples of molding materials mainly composed of polylactic acid resin having improved heat resistance, and recently, automotive interior parts and It has begun to be used in fields and applications that require advanced functions such as housings for electronic and OA devices.

  On the other hand, in recent years, there has been a remarkable spread of optical discs such as compact discs (CDs) and digital versatile discs (DVDs) capable of recording large amounts of information. In particular, a large number of read-only optical discs, in which a metal reflective layer such as aluminum and a protective layer are sequentially laminated on a substrate on which information such as music, images, databases, and computer programs are recorded as fine uneven patterns (so-called pits) Since it can be manufactured at a low cost, a huge number of disks are manufactured and widely used. Furthermore, CD-Rs that can be additionally recorded have started to be produced and consumed more than read-only optical disks (CD-ROMs). Also, disks such as DVD-R, rewritable CD-RW, DVD-RW, and DVD-RAM have begun to spread rapidly.

Here, an example of a conventional optical disk such as a CD or a DVD will be described. FIG. 12 shows an optical disk having a single reflection layer (or recording layer), and FIG. 13 shows an optical disk having a two-layer reflection layer (or recording layer).
In the case shown in FIG. 12, a reflective layer or a recording layer, for example, a reflective layer, is formed on a transparent substrate 4 having a thickness of 1.2 mm or 0.6 mm with irregularities (pits) and grooves formed on the surface and irregularities 2 in the illustrated example. 6 is formed, and another substrate 10 is bonded to the reflective layer 6 side via an adhesive layer 8 to form an optical disk. In this case, the recording or reproducing laser beam L is emitted from the transparent substrate 4 side.

In the case shown in FIG. 13, the transparent substrate 4 having the unevenness 2 and the reflective layer 6 as shown in FIG. 12 is formed, and separately from this, the substrate 4A having the unevenness 2A and the reflective layer 6A is formed, These two substrates 4 and 4A are joined together via an adhesive layer 8 to form an optical disk. In this case, a semi-transmissive reflective layer is used as the reflective layer 6, and the laser beam L is also irradiated to the substrate 4A side. The reflective layer 6A is a totally reflective reflective layer. The optical disk is irradiated with laser light used for reproduction or recording / reproduction, and a large amount of signals are reproduced or recorded through the transparent substrate 4.
As described above, optical disks as described above are widely used as a storage medium for storing a large amount of information, and more than 20 billion pieces are produced worldwide, and the production amount is expected to increase in the future. Along with this, the number of optical discs that are no longer needed and discarded is beginning to increase dramatically, and the impact on the global environment is increasing.

  Of the materials used for these optical disks, the plastic substrate is the most used. Conventionally, a thermoplastic transparent resin made from a depleting fossil (petroleum) resource such as a polycarbonate resin, a polymethyl methacrylate resin, and an alicyclic polyolefin resin is used as the plastic used for the substrate. Among them, most of the actual optical disks use polycarbonate resin from the viewpoints of light transmittance, processability, and productivity. For example, a compact disk (CD) is 98% or more in terms of weight, and a DVD is 95% or more in a plastic substrate. Therefore, from the viewpoint of reducing the burden on the global environment and saving depleted fossil (petroleum) resources, the optical disk substrate is made of a plastic derived from a plant-derived plastic synthesized from renewable plants every year. It is preferable to use a lactic acid resin.

JP-A-3-290461 JP-A-4-146852 JP-A-4-325526 JP 2003-253209 A JP 2003-165717 A JP-A-4-325526

  However, the normal polylactic acid resin as described above has a glass transition temperature of around 60 ° C., a molded product obtained by a normal molding method has poor heat resistance, and a low load deflection temperature (DTUL) is about 55 to 58. When this molded product is used in a relatively high temperature environment at a low temperature of 0 ° C., there is a problem that thermal deformation (shape deformation) occurs. For example, a DVD disk produced using a normal polylactic acid resin having a glass transition temperature of 60 ° C. as a substrate material is used at a temperature specified in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). The disc after performing a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) assuming that the disk is so deformed that it cannot be played back by a player. .

In addition, the above-described molding material mainly composed of polylactic acid resin with improved heat resistance is usually opaque or significantly deteriorated in transparency, so that it cannot be used because it has low light transmittance for use as a transparent substrate for optical disks. There was a problem.
The present invention has been devised to pay attention to the above-described problems and effectively solve them. The object of the present invention is to use a plastic material mainly composed of a polylactic acid resin derived from plant raw materials as a substrate, which has heat resistance, has a small deformation of the disk even after a high temperature load test, and can be reproduced by a player. It is an object of the present invention to provide an optical disc with improved performance and a method for manufacturing the same.

  As a result of intensive studies to solve the above problems when polylactic acid resin is used for a substrate of an optical disk, the present inventors have found that a recording / reproducing laser beam is emitted from an optical disk formed by bonding two substrates together. The substrate on the incident side uses a substrate composed mainly of a polylactic acid resin that maintains transparency, and further includes a polylactic acid resin having a deflection temperature under a certain value or more on the substrate on which the recording / reproducing laser beam is not incident. A bonded optical disk produced by bonding two substrates together using a substrate as a main component is an optical disk with improved heat resistance that can be reproduced by a player with little deformation of the disk even after a high temperature load test. The present invention has been achieved by obtaining the knowledge that can be obtained.

Further, the inventors have used a high temperature load by using an alloy resin, which is a mixture of a polylactic acid resin and a thermoplastic resin having a certain deflection temperature under load, on a substrate on which a recording or reproducing laser beam is incident. The present invention has been achieved by obtaining the knowledge that an optical disk with improved heat resistance that can be reproduced by a player even under a severer environment can be obtained even after the test.
Furthermore, the present inventors further provide a curable resin protective layer on the side of the substrate where the concave and convex pits or grooves are formed and the reflective layer and / or the recording layer are formed. The present invention has been accomplished by obtaining the knowledge that an optical disk having further improved heat resistance can be obtained by annealing and heating the disk at a predetermined temperature or lower.

  That is, in the invention according to claim 1, an adhesive and a light-transmitting second substrate are sequentially formed on the first substrate, and the second substrate is reflected on the first substrate side. In an optical disc in which a layer and / or a recording layer are formed and information is recorded / reproduced by irradiating a laser beam from the second substrate side, the first substrate is under a low load defined by ISO ( 0.45 MPa), which is made of a plastic mainly composed of polylactic acid resin having a deflection temperature under load (DTUL) of 100 ° C. or more, and the second substrate has a transmittance of 80% or more with respect to the wavelength of the laser beam. It is an optical disc characterized by comprising a plastic mainly composed of a polylactic acid resin containing

  According to a second aspect of the present invention, an adhesive and a light transmissive second substrate are sequentially formed on the first substrate, and the first and second substrates are respectively opposite to each other. In the optical disc in which the first and second reflective layers and / or the first and second recording layers are formed, and information is recorded and reproduced by irradiating laser light from the second substrate side, The substrate is made of a plastic mainly composed of polylactic acid resin having a load deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO of 100 ° C. or more, and the second substrate is made of An optical disc comprising a plastic mainly composed of a polylactic acid resin having a transmittance of 80% or more with respect to the wavelength of laser light.

In this case, for example, as defined in claim 3, the plastic is made of an alloy resin made of a mixture of a polylactic acid resin and a light-transmitting thermoplastic resin other than the polylactic acid resin, and the thermoplastic The resin has a deflection temperature (DTUL) under a bottom load (0.45 MPa) specified by ISO of 80 ° C. or more and is dispersed in the alloy resin by 40% or more.
Further, for example, as defined in claim 4, of the first substrate and the second substrate, at least the surface of the second substrate is provided with uneven pits or grooves, and the reflective layer and / or A curable resin protective layer that is cured by heat or ultraviolet rays is formed on the surface on which the recording layer is formed.
The invention according to claim 5 is the method for producing an optical disk according to claim 1 or 2, wherein the polylactic acid resin has a deflection temperature under load (DTUL) as defined by ISO (DTUL) of 100 ° C. or higher. The first substrate made of a plastic containing as a main component is a method for producing an optical disc, wherein the first substrate is subjected to heat treatment under a pressure of 90 ° C. or higher after the molding of the first substrate.
In the invention according to claim 6, the adhesive layer is formed on the first substrate, while the reflective layer and / or the recording layer is formed on the light transmissive second substrate, and then the adhesive layer side is formed. In the method of manufacturing an optical disc, which is disposed by facing the reflective layer and / or the recording layer and bonding the first substrate and the second substrate through the adhesive layer, A method of manufacturing an optical disk, comprising: performing heat treatment at a temperature of 50 to 60 ° C. after bonding the second substrate.

According to the optical disk of the present invention, the following excellent operational effects can be exhibited.
By using as a substrate a plastic material mainly composed of plant-derived polylactic acid resin as a substrate, a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96) assuming the use temperature defined in the DVD standard. The optical disk with improved heat resistance that can be reproduced by a player such as a reproducing apparatus or a recording / reproducing apparatus and a method for manufacturing the same can be obtained.

Hereinafter, an embodiment of an optical disk according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a first embodiment of the optical disk of the present invention, FIG. 2 is a block diagram showing a second embodiment of the optical disk of the present invention, and FIG. 3 is a block diagram showing a third embodiment of the optical disk of the present invention. It is.

<First embodiment>
First, the first embodiment will be described. The optical disk of the first embodiment corresponds to, for example, a reproduction-only single layer DVD disk. The optical disk D1 of the first embodiment in FIG. 1 has a first substrate 12 and a light-transmitting second substrate 14, and the surface of at least one of these substrates 12, 14 A minute unevenness or groove having a reflective layer and / or a recording layer is formed on the substrate, and an adhesive is provided between the two substrates 12 and 14 with the surface side on which the minute unevenness and groove are formed facing each other. It is manufactured by interposing the layer 16 therebetween. Laser light L for recording or reproduction is irradiated from the surface side of the second substrate 14.
In the case of the illustrated example, the case where the unevenness 18 serving as a pit for tracking is formed only on the inner surface of the second substrate 14 is shown, and the entire surface on which the unevenness 18 is formed, A reflective layer 20 is formed.

As described above, a spiral or concentric groove (also referred to as “wobble”) may be formed instead of the irregularities 18. In addition, a recording layer may be provided in place of the reflective layer 20, or the reflective layer 20 and the recording layer may be provided in an overlapping manner. These points are the same in the second and third embodiments described later.
The important point here is that the first substrate 12 is a plastic mainly composed of a polylactic acid resin having a deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO 75 of 100 ° C. or more. The second substrate 14 is formed of a plastic mainly composed of a transparent polylactic acid resin having a transmittance of 80% or more with respect to the wavelength of the laser beam L.

  Specifically, the plastic mainly composed of polylactic acid resin used for the second substrate 14 has transparency of 80% or more with respect to the wavelength of the laser beam L to be reproduced at a thickness of 0.6 mm. If it has, there will be no limitation in particular, For example, the polylactic acid resin synthesize | combined from the monomer which has lactic acid as a main component is preferable. For example, “Lacia H100, H100J” commercially available from Mitsui Chemicals and “Nature Works” manufactured by Cargill Dow are preferable materials. If the transmittance of the second substrate 14 is lower than 80%, the amount of reflected light reflected by the reflective layer 20 is so small that tracking becomes difficult and reproduction becomes difficult. Furthermore, it may be a copolymerized polylactic acid resin copolymerized with other monomer components having ester-forming ability, or a mixed resin mainly composed of a polylactic acid resin obtained by mixing a polylactic acid resin and another transparent plastic.

The second substrate 14 using the polylactic acid resin is attached with a stamper in which minute irregularities (pits) are formed in advance on the mold, as in the case of manufacturing a DVD using an ordinary polycarbonate resin, and is injection molded. Thus, a disk-shaped base plate having a thickness of 0.6 mm is produced. Molding conditions such as the resin temperature, mold temperature, and molding cycle at this time are optimized in consideration of the melting temperature of the polylactic acid resin to be used, the glass transition temperature, and the like.
Next, the light transmissive second substrate 14 mainly composed of the polylactic acid resin obtained by the injection molding is formed with the reflective layer 20 by DC (direct current) or RF sputtering in a vacuum chamber. . Although there is no restriction | limiting in particular in the material used for this reflection layer 20, For example, Au, Al, Ag, or its alloy from which a high reflectance is obtained is preferable.

  Next, the plastic mainly composed of polylactic acid resin used for the first substrate 12 has a deflection temperature under a low load (0.45 MPa) (DTUL) defined by ISO 75 as described above of 100 ° C. or more. The plastic that is. Further, a plastic having a temperature of 125 ° C. or higher is preferably used. When this temperature is lower than 100 ° C., thermal deformation occurs when a high-temperature load test is performed in the shape of a bonded optical disk. At this time, the first substrate 12 is not necessarily transparent, and is a composite material in which an inorganic filler is dispersed in a polylactic acid resin, or a mixed resin with a resin having a good affinity with the polylactic acid resin and high heat resistance. It is preferable to use (alloy). For example, a composite material in which a layered silicate is dispersed in a polylactic acid resin in the order of about 0.5 to 3 wt% or a mixed resin in which a polyacetal resin is melt-kneaded in a polylactic acid resin is suitable.

  The first substrate 12 using the composite material or the mixed resin mainly composed of the polylactic acid resin is mounted with a mirror stamper having no irregularities on the mold in the same manner as when producing a DVD using an ordinary polycarbonate resin. The thickness is 0.6 mm by injection molding. The molding conditions such as the resin temperature, mold temperature, and molding cycle at this time are optimized in consideration of the polylactic acid resin composite material used, the melting temperature of the mixed resin, the glass transition temperature, and the like.

  Next, the read-only single layer DVD disk D1 shown in FIG. 1 is manufactured by bonding the first and second substrates 12 and 14 formed as described above. At this time, the surface of the second substrate 14 on which the reflective layer 20 is formed is opposed to the first substrate 12, and the adhesive layer 16 is interposed therebetween. The material used for the adhesive layer 16 at the time of the bonding is preferably an acrylate-based ultraviolet curable resin from the viewpoint of productivity and yield, and the bonding method is an ultraviolet curable resin on one of the substrates. A so-called spin bonding method is preferable, in which the other substrate is overlaid on top of each other, and the two overlapping substrates 12 and 14 are rotated so that the UV curable resin is spread over the entire surface and bonded together. . Here, as the ultraviolet curable resin, for example, an ultraviolet curable resin mainly composed of epoxy acrylate, urethane acrylate, or a mixture thereof is preferable. The adhesive used at this time does not necessarily need to be transparent, and an adhesive containing an inorganic filler such as silica or mica to improve the heat distortion temperature may be used.

  In this way, it has heat resistance, and the deformation of the disk is small even after a high temperature load test, and the use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2) is assumed. Even after a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours), a read-only single layer DVD disc with improved heat resistance that can be played back by a player can be obtained.

<Second embodiment>
Next, a second embodiment will be described. This second embodiment corresponds to, for example, a read-only dual layer DVD disc in which two reflective layers or recording layers are formed. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.
In the optical disc D2 of the second embodiment in FIG. 2, the surface of the second substrate 14 is provided with irregularities 18 that become pits, and the reflective layer 20A is formed on the entire surface of the pit surface. Although the same as in the case of the first embodiment, in the second embodiment, the reflective layer 20A is a semi-transmissive reflective layer, unlike the total reflective layer 20 of the first embodiment. The laser beam is transmitted through this lower layer. Furthermore, minute irregularities (pits) 22 are also provided on the surface of the first substrate 12, and the reflection layer 20B is formed on the entire pit surface. In addition, a spiral or concentric groove may be provided in place of the unevenness, a recording layer may be formed in place of the reflective layer 20B, or a reflective layer and a recording layer may be provided in an overlapping manner. There is also.

Then, the light-transmitting adhesive layer 24 connects the surface of the first substrate 12 on which the reflective layer 20B is formed and the surface of the second substrate 14 on which the semi-transmissive reflective layer 20A is formed. The optical disk D2 is formed by bonding. The optical disk D2 formed in this manner has heat resistance, and the deformation of the disk is small even after a high temperature load test, and the use specified in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). It is possible to obtain a read-only dual layer DVD disc with improved heat resistance that can be played back by a player even after performing a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) assuming temperature. it can.
Further, the adhesive layer 24 used for bonding in the second embodiment needs to be transparent as described above, and has a transmittance at least with respect to the wavelength of the laser beam for reproduction or recording / reproduction. 90% or more is desirable.

<Third embodiment>
Next, a third embodiment will be described. This third embodiment corresponds to a reproduction-only single layer DVD disc. In addition, the same code | symbol is attached | subjected about the same component as the component shown in FIG.1 and FIG.2, and the description is abbreviate | omitted.
The optical disk D3 of the third embodiment shown in FIG. 3 is a DVD disk having further improved heat resistance than the optical disks of the first and second embodiments, and the temperature is close to 80.degree. This optical disk can be used with small thermal deformation even after being placed in an environment that reaches

  That is, in this optical disk D3, as in the second embodiment shown in FIG. 2, the first substrate 12 has irregularities (pits) 22 formed on its surface, and the entire surface of the pit surface is totally reflected. A reflective layer 20B is formed. The light-transmitting second substrate 26 is made of a plastic mainly composed of a transparent polylactic acid resin having a transmittance of 80% or more with respect to the wavelength of the laser beam. The sheet is biaxially stretched. Then, between the sheet-like second substrate 26 and the reflective layer 20B of the first substrate 12, the substrates 26 and 12 are joined together with a transparent adhesive layer 24 as shown in FIG. Thus, the optical disc D3 is formed.

  Specifically, the plastic mainly composed of polylactic acid resin used for the first substrate 12 has a load deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO 75 of 100 ° C. or more. Using a certain plastic, a 0.6 mm thick base plate having minute irregularities (pits) 22 is produced by injection molding. The pits formed at this time are formed using a stamper in which pits are formed in a spiral shape, contrary to the conventional read-only single layer DVD disc. Further, a reflective layer 20B made of Al or the like is formed to produce a disk intermediate.

  Next, a plastic sheet mainly composed of a transparent polylactic acid resin biaxially stretched to a thickness of 550 microns is punched out to an outer diameter of 120 mm and an inner diameter of 15 mm to produce a light-transmissive second substrate 26. The polylactic acid resin used for the biaxially stretched sheet may be a plain polylactic acid resin without a normal mixture (for example, “Lacia H100, H100J” commercially available from Mitsui Chemicals), A mixed resin with another resin whose main component is a polylactic acid resin having a transmittance of 80% or more with respect to the wavelength of the laser beam L to be reproduced or recorded / reproduced may be used. Thus, by producing from the biaxially stretched sheet, a light-transmissive second substrate 26 having high transparency and improved heat resistance is obtained.

  The surface side on which the reflective layer 20 </ b> B of the disk intermediate body having the first substrate 12 manufactured as described above is formed and the second substrate 26 are bonded together via a light-transmitting adhesive layer 24. At this time, the adhesive used for bonding needs to be transparent. It is desirable that the transmittance is at least 90% with respect to the wavelength of the laser beam L to be reproduced or recorded / reproduced. The reproduction-only single-layer DVD disc D3 thus obtained has further heat resistance, and the deformation of the disc is small even after a high temperature load test, and the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2). .2) Not only can it be replayed by the player after the high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) assuming the operating temperature specified in 2), but also in a car etc. It is a disc that can be used with small thermal deformation even after being placed in an environment where the temperature reaches nearly 80 ° C.

  In the case of the third embodiment, the present invention can be applied not only to a DVD disc but also to a next generation optical disc in which the thickness of the first substrate 12 is increased to 1.1 mm, for example. Good. For example, a reflective layer is formed on a substrate having a thickness of about 1.1 mm on which pits or grooves are formed by injection molding (in the case of a recording mold, recording layers are also formed in order), and a thickness of about 0. An optical disk may be configured by laminating a 1 mm transparent cover layer. According to this, it is possible to adapt to a DVD using a high NA objective lens by shortening the recording wavelength of the laser light and a next-generation optical disc system (so-called Blu-ray Disc) capable of recording a large capacity. .

<Fourth embodiment>
Next, a fourth embodiment will be described. In the first embodiment, the first substrate 12 using a composite material or mixed resin mainly composed of a polylactic acid resin is a mold similar to the case of manufacturing a DVD using a normal polycarbonate resin. A mirror stamper with no irregularities is attached to it, and it is made to a thickness of 0.6 mm by injection molding. At this time, the molding conditions such as resin temperature, mold temperature, molding cycle, etc. Although optimized in consideration of the melting temperature, glass transition temperature, etc., in the fourth embodiment, injection molding is performed at a relatively low mold temperature, for example, a mold temperature of 20 ° C. to 60 ° C. The first substrate 12 after molding is sandwiched between glass heat treatment molds that are flat in contact with the substrate, and is further weighted on the heat treatment mold so that pressure is applied to the first substrate 12 in the heat treatment mold. The first substrate 12 is put into a heat treatment furnace at 90 ° C. or more together with a heat treatment mold and a weight. After the heat treatment mold reaches 90 ° C., after the elapse of a certain time, the first substrate 12 is taken out of the heat treatment furnace together with the heat treatment mold and the weight, and is left as it is until it reaches room temperature. After the heat treatment mold reaches room temperature, the first substrate 12 is taken out from the heat treatment mold, and the deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO is 100 ° C. or higher. A first substrate 12 made of a plastic mainly composed of polylactic acid resin is completed.

At this time, when the first substrate 12 is overlaid on the mold, a convex portion may be provided on the first substrate 12 so that the pit irregularities 18 do not contact. In such a case, this heat treatment is performed. The shape of the mold is a shape that escapes the convex portion. The material of the heat treatment mold is not limited to glass but may be any material that can process a flat surface such as a metal such as stainless steel. In addition, as a method of applying pressure to the first substrate 12 in the heat treatment mold, there are not only a method of placing a weight but also a method of using hydraulic pressure or air pressure. Any method may be used as long as pressure is applied to the substrate.
The first substrate 12 may be heat-treated at 90 ° C. or higher as long as heat is applied after the pressurization or simultaneously with the pressurization. The timing of charging and the temperature and time of the heat treatment furnace may be appropriately selected. The timing of taking out the first substrate 12 from the heat treatment furnace and the timing and method of taking out the first substrate 12 from the heat treatment mold may be appropriately selected. Further, a heating mechanism may be provided in the heat treatment mold itself.

  In the first embodiment, the first substrate 12 made of a plastic mainly composed of polylactic acid resin having a deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO of 100 ° C. or more. As a method for obtaining the above, the polylactic acid resin is crystallized only by the injection molding process to increase the heat resistance. In this case, the injection mold temperature is 90 ° C. or higher, which is a relatively high temperature. At this time, when the first substrate 12 is taken out from the injection mold, the first substrate 12 is pushed by the ejection mechanism in the injection mold in a state close to 90 ° C., which is a relatively high temperature. The warp of the first substrate 12 was sufficient to obtain a flat optical disc D1 that can be reproduced by a commercially available DVD player, but was a relatively large warp. In the fourth embodiment, the warpage is further reduced and a flatter optical disc D1 is obtained. As described above, in the fourth embodiment, after injection molding at a relatively low injection mold temperature, for example, a mold temperature of 20 ° C. to 60 ° C. to obtain a flat first substrate 12, the first The substrate 12 is heat-treated at 90 ° C. or higher under pressure in a flat state to crystallize the polylactic acid resin, thereby improving the heat resistance. By adopting such a method as in the fourth embodiment, a flatter first substrate 12 can be obtained.

<Fifth embodiment>
Next, a fifth embodiment will be described. In the first embodiment, no processing is performed after the optical disk D1 is obtained by bonding. In the fifth embodiment, the optical disk D1 after bonding is made of glass with a flat portion in contact with the disk. The mass of the heat treatment mold on the upper side of the optical disk D1 is adjusted so that the pressure is applied to the optical disk D1 in the heat treatment mold, and the optical disk D1 is heat treated at 50 ° C. or more together with the heat treatment mold. It is thrown in. After the heat treatment mold reaches 50 ° C., after a certain period of time, the optical disc D1 is taken out of the heat treatment furnace together with the heat treatment mold and left as it is until it reaches room temperature. After the heat treatment mold reaches room temperature, the optical disk D1 is taken out from the heat treatment mold, and a flat optical disk D1 is completed.

At this time, a convex portion may be provided on the optical disc D1 so that the signal portion of the optical disc does not contact when the optical disc is superimposed on the die. In such a case, the shape of the heat treatment mold is the convex portion. Let the shape escape. The material of the heat treatment mold is not limited to glass but may be any material that can process a flat surface such as a metal such as stainless steel. Further, as a method of applying pressure to the optical disc D1 in the heat treatment mold, there are not only a method of adjusting the mass of the heat treatment mold but also a method of putting a weight, a method of using hydraulic pressure or air pressure, In any case, any method may be used as long as pressure is applied to the heat treatment mold.
The optical disk D1 may be heat-treated at 50 ° C. or higher as long as the heat is applied after the pressurization or simultaneously with the pressurization. The furnace temperature and time may be appropriately selected. The timing for taking out the optical disk D1 from the heat treatment furnace and the timing and method for taking it out from the heat treatment mold may be appropriately selected. Further, a heating mechanism may be provided in the heat treatment mold itself.

In the first embodiment, the warp is relatively large although it was sufficient to obtain a flat optical disc D1 that can be reproduced by a commercially available DVD player. In the fifth embodiment, D1 can be obtained. By adopting the method as in the fifth embodiment, the residual stress of the first substrate 12, the second substrate 14, and the adhesive layer 16 can be removed, and a flatter optical disc D1 can be obtained. .
The fourth and fifth embodiments described above are performed on the optical disk having the configuration of the first embodiment, but can be similarly performed on the optical disks having the configurations of the second and third embodiments. is there.

<Sixth embodiment>
Next, a sixth embodiment will be described. In the sixth embodiment, the plastics constituting the first substrate and the second substrate used in the first to fifth embodiments are mixed with a polylactic acid resin and a thermoplastic resin other than the polylactic acid resin. The thermoplastic resin has a load deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO of 80 ° C. or more and is contained in the alloy resin by 40% or more. It is characterized in that it is configured as described above.
Specifically, the first substrate 12 used in this embodiment is manufactured in the same manner as in the fourth embodiment. That is, a plastic having a polylactic acid resin as a main component is injection-molded at a relatively low injection mold temperature, for example, a mold temperature of 20 ° C. to 60 ° C. to obtain a flat first substrate 12, and then the first The substrate 12 is flat and subjected to heat treatment at 90 ° C. or higher under pressure to crystallize the polylactic acid resin to increase the heat resistance and to bend under a low load (0.45 MPa) as defined by ISO. A first substrate 12 having a temperature (DTUL) of 100 ° C. or higher is manufactured.

  Next, the second substrate 14 is a mixture of a polylactic acid resin and another transparent thermoplastic resin having a weighted deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO of 80 ° C. or more. Injection molding is performed using an alloy resin. At this time, since the second substrate 14 needs to transmit the laser beam L for recording / reproducing signals, the second substrate 14 needs to have a transmittance of 80% or more with respect to the laser beam L. For this reason, the said alloy resin also needs high transparency, and it is desirable for the refractive index of the said transparent thermoplastic resin which comprises some alloy resins to be close to the refractive index 1.46 of a polylactic acid resin. Specifically, the thermoplastic resin is preferably a resin having a refractive index in the range of 1.53 to 1.40, and more preferably a resin having a refractive index in the range of 1.49 to 1.44. . The transparent thermoplastic resin having a refractive index in the range and having a DTUL of 80 ° C. or higher includes polymethyl methacrylate (PMMA, refractive index 1.49), polymethylpentene (TPX, refractive index 1.47). , Polyacetal (POM, refractive index 1.48), cellulose acetate (refractive index 1.50) and the like.

  Further, when the refractive index of the transparent thermoplastic resin constituting a part of the alloy resin exceeds the range of the refractive index, it is melt kneaded by a kneader or the like when producing the alloy resin. To disperse the thermoplastic resin, and it is necessary to disperse the thermoplastic resin to be smaller than the wavelength of the laser beam used in the recording / reproducing apparatus for the optical disk. The particle diameter (domain) of the thermoplastic resin to be dispersed is preferably dispersed to 600 nm or less. When the thermoplastic resin is dispersed to 600 nm or less, even if a transparent thermoplastic resin having a refractive index different from that of the polylactic acid resin is mixed in the polylactic acid resin, the wavelength of the laser beam used in the optical disk recording / reproducing apparatus In contrast, a thermoplastic resin having higher heat resistance than polylactic acid resin is dispersed like a reinforced fiber, and an alloy resin having improved heat resistance can be obtained. Examples of the transparent thermoplastic resin constituting the polylactic acid resin and the alloy resin include a polycarbonate resin and a polyarylate resin alicyclic polyolefin resin.

Further, the content of the transparent thermoplastic resin having a deflection temperature under load (DTUL) of 80 ° C. or more in the alloy resin produced as described above needs to be at least 40% or more. When this content is less than 40%, there is almost no effect of improving heat resistance, and the effect appears by containing 40% or more. The content is preferably 60% or more.
Here, it is desirable to increase the content of the polylactic acid resin from the viewpoint of using as much polylactic acid resin as possible that is derived from the plant. For this reason, it is desirable to use a resin having a higher deflection temperature (DTUL), but considering the heat resistance required for the final optical disc, compatibility with polylactic acid resin, transparency of the resulting alloy resin, etc. Therefore, it is desirable to determine the content ratio.

<Seventh embodiment>
Next, a seventh embodiment will be described. In this seventh embodiment, uneven pits or grooves are formed on the surface of at least the second substrate of the first and second substrates used in the first to sixth embodiments, Further, the present invention is characterized in that a curable resin protective layer that is cured by heat or ultraviolet rays is formed on the surface on which the reflective layer and / or the recording layer is formed. Here, as an example, an optical disc corresponding to a read-only single layer DVD disc will be described as an example, showing the difference from the first embodiment. FIG. 4 is a block diagram showing a seventh embodiment of the optical disk of the present invention.

The optical disk of the seventh embodiment differs from the previous first embodiment shown in FIG. 1 in that fine irregular pits and grooves formed on the second substrate 14 as shown in FIG. This is characterized in that a curable resin protective phase 30 for protecting the shape change is formed, and the other configurations and materials are the same as those in the first embodiment, and the details are omitted.
That is, the optical disc D7 of the seventh embodiment in FIG. 4 has a first substrate 12 and a light-transmissive second substrate 14, and at least one surface of the second substrate 14 has a reflective layer and / or Alternatively, a microscopic unevenness or groove having a recording layer is formed (the unevenness 18 is formed in FIG. 9), and the curability is cured by heat or ultraviolet light on the surface where the microscopic unevenness or groove is formed. A resin protective layer 30 is provided. At this time, the curable resin protective layer 30 has a glass transition point in the vicinity of 60 ° C., and a second substrate 14 made of a light-transmitting transparent polylactic acid resin having a relatively inferior heat resistance, in which a shape change easily occurs. It is formed for the purpose of suppressing pit shape change (deformation) when an environmental load is applied in the vicinity of the transition point or higher.

  Such a curable resin protective layer 30 is preferably a curable resin that is not thermoplastic but has a high crosslinking density and a high glass transition point. As described above, a thermosetting or ultraviolet curable resin is used. Further, the curable resin is preferably a curable resin having a pencil hardness of H or higher. As such a material, an ultraviolet curable resin mainly composed of an epoxy acrylate resin, a urethane acrylate resin, or a mixture thereof is preferable, specifically, Nippon Kayaku HOD-3200, HOD-3500, HOD-3603, Examples include MH-7421 manufactured by Mitsubishi Rayon, SD-715 manufactured by Dainippon Ink, XR39-C1008 manufactured by GE Toshiba Silicone, SK-5110 manufactured by Sony Chemical, and the like. Such a curable resin protective layer 30 is formed with a thickness of about 1 to 50 microns mainly by spin coating. In particular, it is preferable to form a thickness of about 5 to 20 microns.

  In this way, the second substrate 14 having the reflective layer 20 and the curable resin protective layer 30 formed on at least the side of the second substrate 14 where the pits and grooves are formed, and the adhesive layer 16 are interposed. The optical disk D7 is manufactured by bonding the single substrate 12 together. A laser beam L for recording or reproduction is irradiated from the surface side of the second substrate 14 to the optical disk D7.

The optical disk D7 thus obtained is annealed at a temperature of 50 ° C to 60 ° C. This is by performing an annealing heat treatment below the glass transition temperature point of the polylactic acid resin that mainly constitutes the transparent second substrate 14, while the curable resin protective layer 30 protects the shape of the pit irregularities 18, It becomes possible to relieve the stress generated at the time of forming the substrate, and the subsequent deformation due to a high temperature environment test at 55 ° C., for example, can be reduced.
The annealing temperature is not particularly limited as long as it is not higher than the glass transition temperature point of the polylactic acid resin mainly constituting the second substrate 14, but is preferably in the range of 50 ° C to 60 ° C. Further, although there is no particular limitation on the annealing time, it is preferable to anneal for a time enough to relieve the stress generated during substrate formation. For example, when the temperature is 55 ° C., about 30 minutes to 3 hours is preferable. When the annealing temperature is relatively low, the annealing time is preferably several hours to several tens of hours. Furthermore, if the annealing temperature is lower than 50 ° C., a longer time is required as the annealing time, and the throughput is significantly reduced.

In this way, it has heat resistance, and the deformation of the disk is smaller even after the high temperature load test, and the high temperature (heat resistance) test defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). It is possible to obtain a read-only single-layer DVD disc with improved heat resistance that can be played back by a player even after being performed based on (temperature 55 ° C., relative humidity 50%, 96 hours).
Here, the case where the invention of the seventh embodiment is applied to the first embodiment has been described as an example. However, the present invention is not limited to this, and the seventh embodiment is also applied to the second to sixth embodiments. The invention can be applied. In this case, as in the second embodiment, in the case of a two-layered optical disk having two reflective layers and recording layers, a curable resin protective layer is also provided on the first substrate side. Furthermore, when unevenness and grooves are formed only on the first substrate 12 side as in the third embodiment, a curable resin protective layer is formed on the first substrate 12 side.

<Evaluation of each example>
Next, the optical disks of the above examples were actually manufactured and evaluated, and the evaluation results will be described.
(Evaluation of the first embodiment)
FIG. 5 is a diagram showing the manufacturing process of the optical disk of the first embodiment.
First, using a polylactic acid resin pellet made by Mitsui Chemicals (Lacia H100), a stamper in which signal pits conforming to the DVD standard are formed is attached to a mold of an injection molding machine (Nissei Resin M040E), and a cylinder temperature is 230 ° C. A light-transmissive second substrate 14 having a thickness of 0.6 mm on which signal pits conforming to the DVD standard were formed at a mold temperature of 50 ° C. was produced. At this time, the light transmittance at 650 to 660 nm, which is the wavelength of the DVD reproducing laser beam, on the second substrate 14 was 92%.

Further, when the minute irregularities (pits) 18 formed on the surface of the second substrate 14 are observed with an atomic force microscope, the pit shapes such as pit width, length, and depth are as good as those of the conventional polycarbonate. Met.
A reflective layer 20 made of an Al film having a film thickness of 70 nm was formed on the surface of the second substrate 14 on the side where the signal pits were formed by a DC sputtering method to produce a disk intermediate M2.
Next, 3% by weight of a layered silicate is added to a pellet of a poly-L lactic acid resin having a molecular weight of 200,000 in terms of polystyrene, melt-kneaded at 220 ° C. using a twin-screw extruder, and further pelletized to obtain a poly The resin composition which has as a main component the polylactic acid resin for the 1st board | substrates which have lactic acid resin as a main component was obtained. When the polylactic acid resin of this resin composition was crystallized, a deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO75 was measured and found to be 125 ° C. The obtained pellets were injection-molded using an injection molding machine (Nissei Resin M040E) with a stamper with a mirror on the mold, cylinder temperature 250 ° C., mold temperature 105 ° C., and cooling time 1 minute. A first substrate 12 having a thickness of 0.6 mm was produced. The first substrate 12 was cloudy and did not transmit light, but the surface flatness was sufficient as a bonded substrate.

An ultraviolet curable resin (manufactured by Kyoritsu Chemical Industry Co., Ltd .: modified urethane acrylate (trade name) World Lock No811) is used as an adhesive on the surface of the disk intermediate M2 produced as described above on the side where the Al reflective layer 20 is provided. After coating, the first substrate 12 was overlaid thereon, spin-coated at a rotational speed of 2000 rpm, and then bonded by irradiation with ultraviolet rays. At this time, the thickness of the adhesive layer 16 (see FIG. 1) was 40 μm. In this way, a reproduction-only single layer DVD disk D1 was completed.
A storage test of the obtained optical disk D1 was conducted at a high temperature load (heat resistance) test (temperature 55 ° C., relative temperature) assuming a use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). When the humidity was 50% and 96 hours), the disc was hardly deformed, and the optical disc D1 after the test was reproducible with a commercially available DVD player.

(Evaluation of the second embodiment)
FIG. 6 is a diagram showing a manufacturing process of the optical disc of the second embodiment.
First, the second substrate 14 was produced in exactly the same manner as in the first example. Naturally, the light transmittance of this second substrate 14 at 650 to 660 nm, which is the DVD reproduction wavelength, was 92%.
When the minute irregularities (pits) formed on the surface of the second substrate 14 are observed with an atomic force microscope, the pit shape such as the pit width, length, and depth is as good as a conventional polycarbonate. there were. A disc intermediate M22 was produced by forming a semi-transmissive reflective layer 20A made of an Au film having a thickness of 5 nm on the surface of the second substrate 14 on which the signal pits were formed by DC sputtering.

  Next, in the same manner as in Example 1, 1.0% by weight of layered silicate with respect to the resin was added to pellets of poly-L lactic acid resin having a molecular weight of 200,000 in terms of polystyrene, and melted at 210 ° C. using a twin screw extruder. The resin composition which has the polylactic acid resin for the 1st board | substrate which has a polylactic acid resin as a main component as a main component was obtained by knead | mixing and further pelletizing. When the polylactic acid resin of this resin composition was crystallized, a deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO 75 was measured and found to be 100 ° C. The obtained pellets were attached to a mold of an injection molding machine (Nissei Resin M040E) by attaching a stamper on which minute irregularities (pits) were formed in advance, and the cylinder temperature was 230 ° C, the mold temperature was 95 ° C, and the cooling time was 1 minute. The first substrate 12 having a thickness of 0.6 mm was manufactured by injection molding. The first substrate 12 was cloudy and did not transmit light. However, when the minute irregularities (pits) 22 formed on the substrate surface were observed with an atomic force microscope, the pit width, length, depth, etc. The pit shape was as good as a conventional polycarbonate. A reflective layer 20B made of an Al film having a film thickness of 70 nm was formed on the surface of the first substrate 12 on which the signal pits were formed by DC sputtering to produce a disk intermediate M21.

  An ultraviolet curable resin (manufactured by Kyoritsu Chemical Industry Co., Ltd .: modified urethane acrylate (trade name) World Lock No811) is used as an adhesive on the surface of the disk intermediate M21 produced as described above on the side where the Al reflective layer 20B is provided. After coating, the surface of the reflective layer 20A of the disk intermediate M22 was overlaid, spin-coated at a rotational speed of 2000 rpm, and then bonded by irradiation with ultraviolet rays. At this time, the thickness of the adhesive layer 24 (see FIG. 2) was 40 μm. In this way, a reproduction-only dual layer DVD disk D2 was completed.

  The storage test of the obtained optical disk D2 is a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity) assuming a use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). (50%, 96 hours), the disc was hardly deformed, and the disc after the test was able to reproduce both layer 0 having unevenness 18 and layer 1 having unevenness 22 with a commercially available DVD player.

(Evaluation of the third embodiment)
FIG. 7 is a diagram showing the manufacturing process of the optical disk of the third embodiment.
First, 3% by weight of a layered silicate is added to a pellet of poly-L lactic acid resin having a molecular weight of 200,000 in terms of polystyrene, melt-kneaded at 220 ° C. using a twin screw extruder, and pelletized to form polylactic acid. The resin composition which has as a main component the polylactic acid resin for 1st board | substrates which has resin as a main component was obtained. When the polylactic acid resin of this resin composition was crystallized, a deflection temperature under load (DTUL) under a low load (0.45 MPa) specified by ISO 75 was measured and found to be 125 ° C. The obtained pellet is attached to a mold of an injection molding machine (manufactured by Nissei Plastic M040E) with a stamper in which signal pits conforming to the DVD standard are formed, and the cylinder temperature is 250 ° C., the mold temperature is 110 ° C., and the cooling time is 1 minute. The first substrate 12 having a thickness of 0.6 mm was manufactured by injection molding. This substrate was cloudy and did not transmit light. However, when the minute irregularities (pits) 22 formed on the substrate surface were observed with an atomic force microscope, the pit shape such as pit width, length, and depth was polycarbonate. The shape was as good as when molded with resin.

A reflective layer 20B made of an Al film having a thickness of 70 nm was formed by DC sputtering on the surface of the first substrate 12 on which the signal pits were formed, thereby producing a disk intermediate M31.
Next, a transparent polylactic acid resin sheet biaxially stretched to a thickness of 550 microns was obtained by using a biaxial stretching roll from pellets of a poly L lactic acid resin having a molecular weight of 200,000 in terms of polystyrene. This sheet was punched into an outer diameter of 120 mm and an inner diameter of 15 mm to produce a light transmissive second substrate 26. The light transmittance of this second substrate 26 at 650 to 660 nm, which is the DVD reproduction wavelength, was 85%.

An ultraviolet curable resin (manufactured by Kyoritsu Chemical Industry Co., Ltd .: modified urethane acrylate (trade name) World Lock No811) is used as an adhesive on the surface of the disk intermediate M31 produced as described above on the side where the Al reflective layer 20B is provided. After the coating, the sheet-like second substrate 26 was overlaid thereon, spin-coated at a rotational speed of 2000 rpm, and then bonded by irradiation with ultraviolet rays. At this time, the thickness of the adhesive layer 24 (see FIG. 3) was 50 μm. In this way, a reproduction-only single layer DVD disk D3 was completed.
A storage test of the obtained optical disk D3 was conducted at a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity) assuming a use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). 50%, 96 hours), the disc was not deformed, and the disc after the test was reproducible with a commercially available DVD player.
Further, when a high temperature (heat resistance) test was performed under the test conditions (temperature 80 ° C., relative humidity 60%, left for 96 hours), there was almost no deformation of the disc, and the disc after the test was reproducible with a commercially available DVD player. .

(Evaluation of the fourth embodiment)
The fourth embodiment is the same as the first embodiment except that the manufacturing method of the first substrate 12 is different. The first substrate 12 in the fourth embodiment is manufactured by the following manufacturing method and will be described with reference to FIG.
First, 3% by weight of a layered silicate is added to a pellet of poly-L lactic acid resin having a molecular weight of 200,000 in terms of polystyrene, melt-kneaded at 220 ° C. using a twin screw extruder, and pelletized to form polylactic acid. The resin composition which has as a main component the polylactic acid resin for 1st board | substrates which has resin as a main component was obtained. When the polylactic acid resin of this resin composition was crystallized, a deflection temperature under load (DTUL) under a low load (0.45 MPa) specified by ISO 75 was measured and found to be 125 ° C. The obtained pellets were injection-molded using an injection molding machine (Nissei Resin M040E) with a stamper with a mirror on the mold surface, cylinder temperature 250 ° C, mold temperature 30 ° C, and cooling time 15 seconds. A first substrate 12 having a thickness of 0.6 mm was produced. The molded first substrate 12 is sandwiched between glass heat treatment dies 31A and 31B made of flat glass at a portion in contact with the substrate, and pressure is applied to the first substrate 12 in the heat treatment dies 31A and 31B. A 900 g weight 32 is placed on the upper heat treatment mold 31B, and the first substrate 12 is put together with the heat treatment molds 31A and 31B and the weight 32 into a heat treatment furnace (not shown) at 90 ° C. or higher.

  After the heat treatment molds 31A and 31B have reached 90 ° C. and 10 minutes have passed in that state, the first substrate 12 is taken out of the heat treatment furnace together with the heat treatment molds 31A and 31B and the weight 32 and left as it is until it reaches room temperature. To do. After the heat treatment molds 31A and 31B reach room temperature, the first substrate 12 is taken out from the heat treatment molds 31A and 31B, and thereby, the deflection temperature under a low load (0.45 MPa) defined by ISO. A first substrate 12 made of a plastic whose main component is a polylactic acid resin having a (DTUL) of 100 ° C. or higher is completed.

  In the first embodiment, the first substrate 12 made of a plastic mainly composed of polylactic acid resin having a deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO of 100 ° C. or more. As a method for obtaining the above, the polylactic acid resin is crystallized only by the injection molding process to increase the heat resistance. In this case, the injection mold temperature is 90 ° C. or higher, which is a relatively high temperature. At this time, when the first substrate 12 is taken out from the injection mold, the first substrate 12 is pushed by the ejection mechanism in the injection mold in a state close to 90 ° C., which is a relatively high temperature. The warp of the first substrate 12 was sufficient to obtain a flat optical disc D1 that can be reproduced by a commercially available DVD player, but was a relatively large warp. High-temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50) assuming the use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2) of the optical disk D1 of Example 1 %, 96 hours), the warping angle in the radial direction of the disc was + 0.13 ° and −1.2 °. In addition, the measuring method of the curvature angle was measured by the method defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2).

  In the fourth embodiment, the warpage is further reduced and a flatter optical disc D1 is obtained. As described above, in the fourth embodiment, the first substrate 12 is obtained by injection molding at a mold temperature of 30 ° C., which is a relatively low injection mold temperature, to obtain a flat first substrate 12. Is heat-treated at 90 ° C. or higher under pressure in a flat state to crystallize the polylactic acid resin and increase the heat resistance. By adopting the method as in the fourth embodiment, a flatter first substrate 12 can be obtained, and the DVD standard of the optical disc D1 in this fourth embodiment (DVD Specification for Read-Only Disc Part1) When the radial angle of the disc is measured after performing a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) assuming the use temperature defined in 2.2.2) + 0.24 ° and −0.48 °, and it was confirmed that the improvement can be made more than in the case of the first embodiment. In addition, the measuring method of the curvature angle was measured by the method defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2).

  Moreover, although the experiment of 100 degreeC, 110 degreeC, and 120 degreeC which is 90 degreeC or more of heat processing temperature was conducted, the same result as the case of 90 degreeC was obtained. On the other hand, when the heat treatment temperature is set to 80 ° C., only the first substrate 12 with insufficient crystallization can be obtained by measuring the crystallinity by X-ray diffraction. Radius of the disc after performing a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) assuming a use temperature defined in DVD Specification forRead-Only Disc Part 1 2.2.2) The warp angles in the directions were + 1.6 ° and −2.6 ° or more. In addition, the measuring method of the curvature angle was measured by the method defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2).

(Evaluation of the fifth embodiment)
The fifth embodiment is the same as the first embodiment except that the method of performing the heat treatment after obtaining the optical disc D1 is different.
The optical disk D1 of the fifth embodiment is manufactured by the following manufacturing method and will be described with reference to FIG. In the first embodiment, no processing is performed after the optical disk D1 is obtained by bonding, but in the fifth embodiment, the optical disk D1 after bonding is made of glass with a flat portion in contact with the disk. The mass of the heat treatment mold 33B on the upper side of the optical disk D1 is adjusted to 200 g so that pressure is applied to the optical disk D1 in the heat treatment molds 33A and 33B. The molds 33A and 33B are put into a heat treatment furnace (not shown) at 50 ° C. After 12 hours have elapsed in this state after the heat treatment molds 33A and 33B have reached 50 ° C., the optical disk D1 is taken out of the heat treatment furnace together with the heat treatment molds 33A and 33B and left as it is until it reaches room temperature. After the heat treatment molds 33A and 33B reach room temperature, the optical disk D1 is taken out from the heat treatment molds 33A and 33B, and a flat optical disk D1 is completed.

  In the first embodiment, although it was sufficient to obtain a flat optical disc D1 that can be reproduced by a commercially available DVD player, the warp was relatively large. The high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50) assuming the use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2) of the optical disk D1 of the first embodiment. %, 96 hours), the warping angle in the radial direction of the disc was + 0.13 ° and −1.2 °. In addition, the measuring method of the curvature angle was measured by the method defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). In the fifth embodiment, the warpage is further reduced and a flatter optical disk D1 is obtained. By adopting the method as described in the fifth embodiment, it is possible to remove the residual stress of the first substrate 12, the second substrate 14, and the adhesive layer 16, and to obtain a flatter optical disc D1, High temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50) assuming the use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2) of the optical disk D1 of the fifth embodiment. %, 96 hours), the measured warpage angle in the radial direction of the disk was + 0.15 ° and −0.29 °. In addition, the measuring method of the curvature angle was measured by the method defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2).

  Moreover, although the heat processing temperature was 50 degreeC or more and 55 degreeC and 60 degreeC experiment was conducted, the same result as the case of 50 degreeC was obtained. On the other hand, when the heat treatment temperature is 45 ° C., the residual stress of the first substrate 12, the second substrate 14, and the adhesive layer 16 has not been removed, and the DVD standard of the completed optical disc D 1 ( Of the disc after being subjected to a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) assuming the use temperature specified in DVD Specification for Read-Only Disc Part 1 2.2.2) The warping angles in the radial direction were + 0.11 ° and −1.1 ° equivalent to those in Example 1. In addition, the measuring method of the curvature angle was measured by the method defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). Further, when the heat treatment temperature was 65 ° C., the warp was good, but the disc after the high temperature load test was unreproducible with a commercial DVD player due to the presumed signal deformation. This is because, in the fifth embodiment, the load deflection temperature (DTUL) under a low load (0.45 MPa) defined by ISO75 of the resin material of the second substrate 14 provided with the signal pit irregularities 18 is 55 ° C. This is because when the temperature of deflection of the resin material of the second substrate 14 is higher, a heat treatment temperature of 65 ° C. or more is also effective.

(Evaluation of the sixth embodiment)
The first substrate 12 used in Example 6 was produced in the same manner as in the fourth example.
Next, the following two types of alloy resins used for producing the second substrate 14 were produced.
<Adjustment of alloy resin>
Polymethyl L-lactic acid resin pellets (Laisia H100, manufactured by Mitsui Chemicals) have a deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO75 as another transparent thermoplastic resin of about 80 ° C. A methacrylate resin (PMMA, refractive index 1.49) (Sumitex Chemical Sumipex) was added in an amount of 30, 40, 50, and 60% by weight to the polylactic acid resin, respectively (Examples 6-1, 6-2, 6- 3 and 6-4), and melt-kneading using a twin screw extruder to disperse the polymethyl methacrylate resin in the polylactic acid resin, and further pelletize to prepare an alloy resin. A test sample was prepared by injection molding of the obtained alloy resin, and the light transmittance at a wavelength of 780 nm and 660 nm of a laser beam of a CD or DVD reproducing apparatus was 80% or more, and the light transmittance was good. It was.

  Similarly, poly L-lactic acid resin pellets (Laisia H100 manufactured by Mitsui Chemicals) have a load deflection temperature (DTUL) under a low load (0.45 MPa) specified by ISO75 as another transparent thermoplastic resin of about 100 ° C. Polymethylpentene resin (TPI manufactured by Mitsui Chemicals) was added in an amount of 30, 40, 50, and 60% by weight, respectively (corresponding to Examples 6-5, 6-6, 6-7, and 6-8), Using a twin screw extruder, it was melt kneaded and dispersed, and further pelletized to produce an alloy resin. A test sample was prepared by injection molding of the obtained alloy resin, and the light transmittance at a wavelength of 780 nm and 660 nm of a laser beam of a CD or DVD reproducing apparatus was 80% or more, and the light transmittance was good. It was.

Next, using the alloy resin produced as described above, a stamper in which minute irregularities (pits) and grooves (grooves) are formed in advance is attached to the mold, and signal pits conforming to the DVD standard are formed by injection molding. The prepared second substrate 14 was produced, and an Al reflective layer was further formed by DC or RF sputtering.
Next, the first and second substrates 12 and 14 manufactured as described above are bonded together to manufacture a DVD disk. At this time, the surface of the second substrate 14 on which the reflective layer 20 is formed is opposed to the first substrate 12, and the adhesive layer 16 is interposed therebetween. As a material used for the adhesive layer 16 at the time of bonding, an acrylate ultraviolet curable resin was used. In this way, a reproduction-only single layer DVD disc was produced.
The obtained DVD disk was subjected to a high-temperature (heat-resistant) storage test (test conditions: temperature 70 ° C., relative humidity 50%, allowed to stand for 96 hours), and the state of deformation of the disk after the test and the possibility of reproduction on a commercially available DVD player were investigated. . The results are shown in Table 1.

When the content of the polymethyl methacrylate resin or polymethylpentene resin, which is a thermoplastic resin constituting a part of the alloy resin, is 30% (Examples 6-1 and 6-5), the disk deformation is large, Moreover, playback on a player is also impossible.
On the other hand, the content of the thermoplastic resin is 40% or more, specifically, 40%, 50%, 60% (Examples 6-2, -6-6, 6-6, -6-8). In the case of), the deformation of the disc was “somewhat” or “none”, and it was possible to reproduce with a player. In particular, when the content of the thermoplastic resin is 60% or more, it is confirmed that the disc is hardly deformed and can be reproduced by a player.

(Evaluation of the seventh embodiment)
FIG. 10 is a diagram showing a manufacturing process of the optical disc of the seventh embodiment, and FIG. 11 is a diagram showing an annealing process of the optical disc of the seventh embodiment.
First, a light-transmissive second substrate 14 having a thickness of 0.6 mm on which signal pits conforming to the DVD standard were formed using the same material, apparatus, and conditions as in the first example was produced. A reflective layer 20 made of an Al film having a thickness of 70 nm is formed by DC sputtering on the surface of the second substrate 14 where the irregularities 18 that are pits are formed, and further on the side where the Al reflective layer 20 is formed. , UV curing type resin with pencil hardness of 2H (HOD-3200 manufactured by Nippon Kayaku Co., Ltd.) is spin-coated by spin coating method (rotation speed 2500 rpm) and then cured by UV curing to protect the cured resin consisting of 12 microns in thickness. Layer 30 was formed, and disk intermediate M41 was produced.

Next, a first substrate 12 having a thickness of 0.6 mm was manufactured using the same materials, equipment, and conditions as those in the first example.
An ultraviolet curable resin (manufactured by Dainippon Ink Co., Ltd .: acrylate resin (trade name) SD-661) is used as an adhesive on the surface of the disk intermediate M41 produced as described above on the side where the cured resin protective layer 30 is provided. The adhesive layer 16 was formed by coating, the first substrate 12 was overlaid thereon, spin-coated at a rotational speed of 2000 rpm, and then bonded by irradiation with ultraviolet rays. In this way, a reproduction-only single layer DVD disk 7 having a hard cured resin protective layer 30 for protecting pits was completed.
Further, the obtained disk D7 was sandwiched between two glass plates 40 each having a flat thickness of 900 g and a thickness of 1 cm as shown in FIG. 11, and left in an oven 50 at 55 ° C. for 3 hours for annealing treatment. It was. After this annealing treatment, it was taken out and cooled to room temperature.

  The storage test of the optical disk D7 obtained by this annealing treatment is a high temperature (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96) defined in the DVD specification (DVD Specification for Read-Only Disc Part 1 2.2.2). The optical disk D7 after the test can be reproduced satisfactorily with a commercially available DVD player, and the high temperature load due to the pit protection by the hard cured resin protective layer 30 and the annealing treatment is obtained. It was confirmed that there was hardening in the later disk deformation inhibition.

(Evaluation of comparative example)
Next, the comparative example was evaluated. In this comparative example, signal pits conforming to the DVD standard are formed on the mold of an injection molding machine (Nissei Resin M040E) using Mitsui Chemicals polylactic acid resin pellets (Lacia H100) as in Example 1 above. The stamper was attached, and a light-transmissive second substrate having a thickness of 0.6 mm on which signal pits conforming to the DVD standard were formed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. was produced. Further, the first substrate to be bonded was produced by injection molding using polylactic acid resin pellets (Lacia H100) manufactured by Mitsui Chemicals. Here, the deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO 75 of the resin material of the first substrate was 55 ° C. The two substrates were laminated with a reflective layer in exactly the same manner as in Example 1 to complete a reproduction-only single layer DVD disc.

  The preservation test of the obtained optical disk is a high temperature load (heat resistance) test (temperature 55 ° C., relative humidity 50) assuming a use temperature defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2). %, 96 hours), the deformation of the disc was remarkable, and the disc after the test could not be reproduced by a commercially available DVD player. In addition, a similar experiment was carried out using a resin material having a deflection temperature under load (DTUL) of 55 ° C. and 85 ° C. as a comparative example. However, this disc was also deformed and could not be reproduced by a commercially available DVD player. It was.

(Comparative example 2: Comparative example with respect to the seventh embodiment)
Next, an optical disk produced in the same manner as in Example 7 was evaluated as a comparative example where no annealing treatment was performed in an oven. This comparative example is the same as in the case of manufacturing a reproduction-only single layer DVD disc having a hard cured resin protective layer for pit protection in the same manner as in Example 7 above.

Here, the difference from Example 7 was that a storage test was carried out on the completed disk without annealing in a 55 ° C. oven. That is, the test was carried out based on a high temperature (heat resistance) test (temperature 55 ° C., relative humidity 50%, 96 hours) defined in the DVD standard (DVD Specification for Read-Only Disc Part 1 2.2.2).
The disc after the test was protected with a cured resin protective layer, and no significant change was observed in the pit shape even under microscopic observation. However, since the annealing process was not performed in the oven and left at 55 ° C. near the glass transition temperature for a long time, the transparent second substrate side of the optical disk was deformed as the stress relaxation progressed, resulting in an optical disk shape. Slight warpage occurred. The warp of the optical disk that was not subjected to the annealing treatment was deformed particularly from the middle to the outer periphery of the disk, and could be barely reproduced by a commercially available DVD player.

It is a block diagram which shows 1st Example of the optical disk of this invention. It is a block diagram which shows 2nd Example of the optical disk of this invention. It is a block diagram which shows 3rd Example of the optical disk of this invention. It is a block diagram which shows 7th Example of the optical disk of this invention. It is a figure which shows the manufacture process of the optical disk of 1st Example. It is a figure which shows the manufacture process of the optical disk of 2nd Example. It is a figure which shows the manufacture process of the optical disk of 3rd Example. It is a figure which shows the manufacture process of the optical disk of 4th Example. It is a figure which shows the manufacture process of the optical disk of 5th Example. It is a figure which shows the manufacture process of the optical disk of 7th Example. It is a figure which shows the annealing process of the optical disk of 7th Example. It is a figure which shows the optical disk with a single reflective layer (or recording layer). It is a figure which shows the optical disk with a reflecting layer (or recording layer).

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... 1st board | substrate, 14, 26 ... 2nd board | substrate, 16, 24 ... Adhesive layer, 18, 22 ... Unevenness, 20, 20A, 20B ... Reflective layer, 30 ... Hardening resin protective layer, 31A, 31B 33A, 33B ... heat treatment mold, 32 ... weight, D1, D2, D3, D7 ... optical disc, L ... laser beam.

Claims (6)

An adhesive and a light-transmissive second substrate are sequentially formed on the first substrate, and a reflective layer and / or a recording layer is formed on the first substrate side of the second substrate. In an optical disc that records and reproduces information by irradiating laser light from the second substrate side,
The first substrate is made of a plastic mainly composed of a polylactic acid resin having a load deflection temperature (DTUL) under a low load (0.45 MPa) defined by ISO of 100 ° C. or more.
The optical disc, wherein the second substrate is made of a plastic mainly composed of a polylactic acid resin having a transmittance of 80% or more with respect to the wavelength of the laser beam. An adhesive and a light-transmitting second substrate are sequentially formed on the first substrate, and the first and second reflective layers are respectively formed on opposite sides of the first and second substrates. And / or an optical disc in which first and second recording layers are formed, and information is recorded and reproduced by irradiating a laser beam from the second substrate side,
The first substrate is made of a plastic mainly composed of a polylactic acid resin having a load deflection temperature (DTUL) under a low load (0.45 MPa) defined by ISO of 100 ° C. or more.
The optical disc, wherein the second substrate is made of a plastic mainly composed of a polylactic acid resin having a transmittance of 80% or more with respect to the wavelength of the laser beam.   The plastic is made of an alloy resin made of a mixture of a polylactic acid resin and a light-transmitting thermoplastic resin other than the polylactic acid resin, and the thermoplastic resin is under a bottom load defined by ISO (0 3. The optical disk according to claim 1, wherein a deflection temperature under load (DTUL) of .45 MPa is 80 ° C. or higher and 40% or more is dispersed in the alloy resin.   Of the first substrate and the second substrate, heat is formed on the surface on which at least the concave and convex pits or grooves are formed on the surface of the second substrate and the reflective layer and / or the recording layer are formed. 4. The optical disk according to claim 1, further comprising a curable resin protective layer that is cured by ultraviolet rays.   5. The optical disc manufacturing method according to claim 1, wherein the main component is a polylactic acid resin having a deflection temperature under load (DTUL) under a low load (0.45 MPa) defined by ISO of 100 ° C. or more. A method of manufacturing an optical disc, wherein the first substrate made of plastic is subjected to heat treatment under pressure of 90 ° C. or higher after the first substrate is molded. The adhesive layer is formed on the first substrate, while the reflective layer and / or the recording layer is formed on the light transmissive second substrate, and then the adhesive layer side is placed on the reflective layer and / or the recording layer. In the method of manufacturing an optical disc, the first substrate and the second substrate are bonded to each other through the adhesive layer.
A method of manufacturing an optical disc, comprising: performing heat treatment at a temperature of 50 to 60 ° C. after bonding the first substrate and the second substrate.

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