JP2003326543A - Optical film and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a thin optical film suitable as a film for a light transmitting layer of an optical recording medium, having high smoothness and reduced in the residual amount of a solvent and surface damage. <P>SOLUTION: The optical film is obtained by forming an amorphous thermoplastic resin composition, especially an aromatic polycarbonate into a film by a solution casting or coating method and simultaneously satisfies characteristics (a)-(d), that is, (a) the center line average roughness (Ra) of the film is 0.1-1 nm on both surfaces of the film, (b) the retardation of the film is 0-8 nm, (c) the residual amount of the solvent in the film is 0-0.4 wt.% and (d) the number of surface flaws of not smaller than 30 μm within a range of 1 cm<SP>2</SP>at an arbitrary point in the surface of the film is 0-50. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical film, and more particularly to an optical film having a high surface smoothness, a low retardation property and a low residual solvent amount, which is formed into a film by a solution casting method and is used for an optical recording medium. Regarding film.

[0002]

2. Description of the Related Art As a high density recording medium for recording various kinds of information for computers, audio, etc., there is an optical recording medium such as an optical disk for reproducing and recording by light irradiation. recent years,
Large-capacity disks are required to support terrestrial digital broadcasting and high-definition broadcasting. Conventionally, D
In VD, a structure was used in which two substrates with a thickness of 600 μm were bonded together, but the thinner the light transmission layer through which the laser light passes is the more advantageous for increasing the capacity, so an optical film with a thickness of about 100 μm is used as an adhesive layer. A disc with a structure in which the signal is read from the film side by adhering it to the substrate via is under development. The substrate is mainly made by injection molding, but when molding a thin film by injection molding, optical unevenness is likely to occur due to cooling unevenness during molding, so it is not suitable for making a sheet or film of 300 μm or less. . On the other hand, there is a solution method in which a resin is dissolved in a solution and coating / drying is performed as compared with a melting method such as injection molding, but it is excellent in terms of optical uniformity.
In addition, since the viscosity is low, film formation by a solution method, in which foreign matter can be easily removed by filtration, is suitable as a method for producing an optical film.

[0003]

A film used for a large-capacity optical disk has the following required characteristics in addition to a thin film. The first is surface smoothness. A part called a pickup that reads laser light follows up, down, left and right so that a signal can be read even if there is a change in the inclination of the disk or a change in the surface thickness. However, when a short-period thickness variation that exceeds the position adjustment capability of the pickup occurs, it becomes noise and deteriorates the signal characteristics. In particular, the blue laser used for the next-generation DVD has a shorter wavelength than the red laser of the current DVD, and therefore it is still easily affected by the thickness variation. For that reason,
The film requires a high level of surface smoothness.

The second is the problem of birefringence. When the retardation becomes large, an angle dependency that an error occurs depending on the incident direction of light appears, which causes signal deterioration. Therefore, the retardation should be as small as possible. Polycarbonate having 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) as a main constituent, which is a bisphenol A type polycarbonate, is a CD that is inexpensive and excellent in processability.
Although it is used in large quantities in disc materials such as DVDs and DVDs, it has a large birefringence, and thus the conventional manufacturing method involving transport by tension causes a problem that the retardation value, which is an index of birefringence, becomes large. there were. In order to solve this problem, for example, by using a polycarbonate having a component oriented in the thickness direction like a fluorene structure as disclosed in JP 2001-243658 A or International Publication No. WO 01/73780, an optical uniform There is a way to improve sex. However, since the polycarbonate having the fluorene structure is used in a small amount, there is a large difference in cost when compared with the bisphenol A type polycarbonate. Therefore, obtaining an optical film for a light transmissive layer from bisphenol A type polycarbonate has a great advantage in industrial and cost aspects.

Further, as a third problem, there is a problem of warp or deformation of the disk called tilt or skew.
Since the warp and deformation of the disk are caused by the dimensional change of the substrate and the film after bonding, dimensional stability is required.

As described above, when a film is used as a light transmitting layer of an optical disc, it is required to have high smoothness, low retardation and low dimensional change rate. Therefore, the present inventor has arrived at the present invention as a result of earnestly investigating a method for producing an optical film having the above-mentioned characteristics at the same time and having less noise when used as a light transmitting layer.

[0007]

The film for a light transmitting layer of the present invention has the following constitution in order to solve the above problems. That is, the main points of the optical film in the present invention are: An optical film formed by a solution casting method using an amorphous thermoplastic resin composition, which simultaneously satisfies the following (a) to (d). (A) The center line average roughness (Ra) of the film surface is 0.1 nm or more and 1 nm or less on both surfaces. (B) The retardation of the film is 0 nm or more and 8 nm.
(C) The residual solvent amount of the film is 0% by weight or more and 0.4% by weight or less (d) The number of surface defects of 30 μm or more is 0 within a range of 1 cm ² at any point on the film surface. 1. The number is not less than 50 and not more than 2. 2. The optical film as described in 1 above, wherein a polycarbonate containing a repeating unit composed of 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) as a main constituent is used as the amorphous thermoplastic resin composition.

The present invention also provides a method for producing an optical film with a protective film, the gist of which is as follows.

3. In the method for producing an optical film, which comprises using an amorphous thermoplastic resin composition and casting a solution of the resin on a support to produce a film, the following (a) to (d)
A method for producing an optical film with a protective film, which comprises the step of. (A) As the support, a support having a center line average roughness (Ra) of the surface on which the solution is cast is 0.1 nm or more and 5 nm or less, and the solution is cast on the substrate, followed by drying. Step (b) of performing a solvent to evaporate the solvent to obtain a primary dry film. Drying the primary dry film obtained in the above (a) to obtain a secondary dry film having a residual solvent of 1.0% by weight or less (c). ) Using the secondary dry film obtained in (b) above,
The film is subjected to a relaxation treatment while being heated at (Tg−10) ° C. or higher and (Tg + 10) ° C. or lower (Tg is a glass transition temperature), the retardation of the film is 0 nm or more and 8 nm or less, and the residual solvent amount is 0% by weight or more and 0. 4% by weight or less (d) a step of laminating a protective film on one side or both sides of the film obtained in (c) above

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the optical film of the present invention will be described in detail.

The amorphous thermoplastic resin composition that can be used in the optical film of the present invention is not particularly limited as long as it is a transparent resin that can be used optically. Among them, polycarbonate, which is excellent in transparency and processability, can be preferably used. Further, among polycarbonates, it is mass-produced and inexpensive, and CD and D
Aromatic polycarbonates, which are used in large quantities in disks such as VDs, and whose main constituents are repeating units composed of 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) are preferred. The term "main constituent component" as used herein means a repeating component composed of a compound that accounts for 50 mol% or more of the dihydroxy compound that is a raw material of polycarbonate. Therefore, 2,2-
Even if bis (4-hydroxyphenyl) propane (bisphenol A) is used alone, it is also possible to use a compound obtained by copolymerizing or mixing with another dihydroxy compound within a range not exceeding 50 mol%. The dihydroxy compound to be copolymerized or mixed is not particularly limited, but examples thereof include 1,1-bis (4-hydroxy2,2-bis (4-hydroxy-3-methylphenyl) propane, 1,1- Bis (4-hydroxy-3-t
-Butylphenyl) propane, 2,2-bis (4-hydroxy-3-t-butylphenyl) propane, 2,2-
Bis (hydroxy) such as bis (4-hydroxy-3-bromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 1,1-bis (4-hydroxyphenyl) ethylbenzene. Aryl) alkanes, 1,1-bis (4-hydroxyphenyl) cyclohexane, bis (hydroxylaryl) cyclohexanes such as 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane,
Fluorenes such as 9,9-bis (4-hydroxyphenyl) fluorene, dihydroxyaryl ethers such as 4,4′-dihydroxydiphenyl ether and 4,4′-dihydroxy-3,3′-dimethylphenyl ether, 4,4 '-Dihydroxydiphenyl sulfide,
Dihydroxyaryl sulfides such as 4,4′-dihydroxy-3,3′-dimethylphenyl sulfide,
4,4'-dihydroxydiphenyl sulfoxide, 4,
Dihydroxyaryl sulfoxides such as 4′-dihydroxy-3,3′-dimethylphenyl sulfoxide,
And compounds derived from the above compounds.
These dihydroxy compounds may be used alone or in combination of two or more with respect to the main component of the repeating unit composed of bisphenol A as long as the transparency is not impaired. However, since bisphenol A is a cheap and easily available raw material, the more bisphenol A component is used, the easier it is to industrially supply a cheap optical film, which is preferable. The repeating unit of bisphenol A is preferably 80 mol% or more, Preferably 90 mol% or more,
Particularly, 100 mol% (that is, single) is preferable.

The average thickness of the optical film in the present invention is preferably 20 μm or more and 300 μm or less, and more preferably 50 μm or more and 150 μm or less, which is suitable for use as a light-transmitting layer for a large-capacity next-generation optical recording medium. It is preferably 60 μm or more and 110 μm or more. When it is used as a light transmitting layer, it is preferable that it is thinner, because it can correspond to higher capacity, but if it is thinner than 20 μm, handling becomes difficult and wrinkles are likely to occur when it is bonded. Further, when the thickness is more than 300 μm, foaming during drying occurs during film formation by the solution casting method, which easily causes defects and is likely to deteriorate productivity.

The center line average roughness (Ra) of the film surface in the present invention is 1 nm or less on both sides, more preferably 0.5 nm or less. The high-capacity disk used as the next-generation optical recording medium uses a conventional DVD as the laser light.
Since the shift from the red laser that was planned by the company to a blue laser with a short wavelength, it is very sensitive to unevenness of the surface thickness. Since unevenness in thickness leads to signal deterioration, the surface of the optical film of the present invention used as a light transmitting layer must be smooth. In the conventional optical film mainly used for displays, the center line average roughness of the surface was about 5 nm, which was not a problem, but when used for an optical disc or the like, it should be 1 nm or less. The film formed by the conventional casting method is
The surface opposite to the support has a good surface property, but the surface property on the support side is affected by the surface property of the support,
It was not suitable for high capacity recording media. The present inventors investigated various optical film production methods, and as a result of examining the relationship between the surface property of the optical film and the degree of reliability deterioration of the signal, the optical film has a surface property of Ra 1 nm or less,
It was confirmed that the reliability without any problems in actual use is secured. When the optical film of the present invention is used as a light transmitting layer for an optical recording medium, the centerline surface roughness is preferably as small as possible, but a practical value is 0.1 nm or more.

The retardation of the film in the present invention is 8 nm or less, preferably 4 nm or less. The retardation is ideally 0 nm, and the smaller the better, but the practical value is 2 nm or more. The retardation indicates that the smaller the value, the more optically uniform the film. When the retardation is large, the traveling speed of light has a distribution depending on the polarization direction. For this reason, the laser light which has passed through the light transmission layer having a large retardation and reaches the recording surface of the disc has a phase shift, which causes signal deterioration. Therefore, the retardation is preferably 8 nm or less.

The residual solvent content of the film in the present invention is 0.4% by weight or less, preferably 0.2% by weight or less. The film formed by the solution method contains the residual solvent inside, and it is ideal to completely remove this residual solvent to make the residual solvent 0% by weight. It is difficult to apply to industrial production because it takes a lot of time. However, when the residual solvent is volatilized and a dimensional change occurs after being processed into an optical disc or the like, it causes warpage or distortion of the disc. for that reason,
It is preferable to remove the residual solvent as much as possible. If the above-mentioned problems are less likely to occur and a realistic numerical value obtained in industrial production is given, it is 0.05% by weight or more and 0.4% by weight or less.

The number of surface defects of 30 μm or more within the range of 1 cm ² at any point in the plane of the film of the present invention is 50 or less, preferably 30 or less, more preferably 10 or less. Even surface defects, especially minute defects that cannot be visually discerned, cause noise in optical discs and the like, and impair the reliability of signals.
It is necessary to keep the number of surface defects to a minimum, and it is needless to say that 0 is preferable, but if the number of defects is within the above numerical range, the reliability of the signal will not be significantly impaired. The term “surface defect of 30 μm or more” refers to a defect having a maximum length or maximum diameter of the defect of 30 μm or more.

Next, a method of manufacturing the optical film according to the present invention will be described.

As a film forming method, a solution casting method represented by a solution coating method or a solution casting method is used.
On the other hand, as a method that does not use a solution, there is a melt extrusion method or a melt injection method. However, when a thin film is formed, the melt method causes large variations in film quality due to transfer of uneven thickness of the mold and uneven temperature in the mold. Is not preferable. Therefore, it is necessary to form a film by a solution casting method that can form a more uniform film.

As the support (carrier) that can be used in the present invention, the support can be processed and replaced relatively easily, and it is possible to use drying equipment together with other grades having different surface properties. In particular, a roll-shaped support is preferable because it can be applied without causing a visual defect due to the seam of the belt. The roll-shaped support may be a film or sheet-shaped molded product made of plastic or metal, but it is based on plastic in consideration of transportability, flexibility, and ease of recovery / reuse by winding. It is preferably a support. As an example, in addition to using a commercially available plastic film as it is, a film obtained by coating the surface of a commercially available film with another resin, a film on which metal is vapor-deposited, or another sheet or film is bonded with an adhesive or the like. But not limited to. When a layer other than plastic is provided, there is no problem as long as the flexibility and the rigidity and thickness that can be wound up as a roll are maintained.

The plastic layer used as the material of the base of the support has high rigidity and high organic solvent resistance, and can be transported. As examples, polyolefin resin, vinyl chloride resin, polyester resin, polyamide resin, polyimide resin, polyketone resin, polyphenylene oxide resin, polyphenylene sulfide resin, polysulfone resin, etc. can be used. It is not limited to these. Among them, polyethylene terephthalate (PET) is a particularly preferable material because it is easy to use because it is inexpensive, has excellent processability, and has high chemical resistance.

The center line average roughness (Ra) of the surface of the support used in the present invention is 0.1 nm or more and 5 nm or less. When the solution is cast on the support to form a film, the surface property of the support is transferred to the optical film. Therefore, the surface of the support is required to have smoothness.

In the present invention, the resin solution is dried and formed into a film, and then a film or a green sheet (these are referred to as a primary dry film in the present specification) is wound together with the support. The residual solvent amount of the primary dry film is preferably 10% by weight or more and 20% by weight or less. When the primary drying is advanced to less than 10% by weight, the orientation is advanced and the retardation of the finally obtained optical film is increased, or the support is easily peeled off, making it difficult to wind the primary dry film together with the support. Prone. On the other hand, when the residual solvent amount exceeds 20% by weight, it may be difficult to peel the film from the support for secondary drying due to lack of self-supporting property. When using an endless belt, a drum, or the like as the support, the primary dry film may be continuously sent to the next step (for example, the secondary drying step) without being wound.

After that, the primary dry film is subjected to secondary drying to obtain a secondary dry film. The residual solvent content of the optical film must be finally reduced to 0.4% by weight or less by secondary drying and heating during the subsequent relaxation treatment. Therefore, in the secondary drying step, at least the residual solvent amount is dried to 1.0% by weight or less, preferably 0.5% by weight or less, more preferably 0.4% by weight or less, and finally obtain an optical product. The amount of residual solvent may be the same as that of the film. Further, in order to evaporate the solvent from both sides of the film, it is preferable to peel off the support during the secondary drying. When the residual solvent amount of the secondary dry film is 1.0% by weight or more, by increasing the heating temperature during the relaxation treatment or increasing the relaxation time,
It is also possible to make the residual solvent amount of the final optical film 0.4% by weight or less, but in this case, the surface property of the film is remarkably deteriorated due to the influence of the solvent evaporated at the time of the relaxation treatment, and the light for the optical recording medium is deteriorated. It may become unusable as a transparent layer.

In the relaxation treatment of the present invention, the temperature is in the vicinity of the Tg of the film, specifically from (Tg-10) ° C. to (Tg
+10) Performed in a state of being heated to ° C. In the relaxation process, it is necessary to take care so that wrinkles do not occur during transportation. In the vicinity of Tg of the optical film, the film may be softened and stretched to make it impossible to carry the film. Therefore, it is necessary to provide the film with supportability in the carrying. The method is not particularly limited, but in addition to the tenter method, there is a method of transporting the optical film with a film having adhesiveness attached thereto. In particular, it can be preferably carried out when the tacky film is a heat-resistant tacky film having a melting point higher than (Tg + 10) ° C., and the relaxation treatment can be performed without stretching and deformation of the optical film.

Further, as a method for producing an optical film in the present invention, in order to prevent defects such as scratches from being generated in the film, a protective film is attached to the optical film so as to cover at least one surface of the plastic. To meet. Co-wrap the plastic film and the protective film. The protective film to be co-wound is preferably a film having weak adhesiveness on one side, for example, one having a weak adhesive layer provided on one side of a polyethylene film,
Examples of the PET film include a pressure-sensitive adhesive layer provided on one side. However, since the surface of the protective film may be transferred after bonding, it is preferable to use a PET film having good thickness accuracy as the protective film. preferable.

[0026]

EXAMPLES The contents of the present invention will be specifically described below based on examples, but the present invention is not limited thereto.

The items measured in the examples were measured by the following methods.

Film thickness: Using a palpation type thickness gauge KG601A manufactured by Anritsu Corporation, 4 in the width direction of the film.
It measured using the sample cut in the width of cm, and read the average value from the obtained thickness curve.

Centerline average roughness (Ra): temperature 23 ° C. ± 2
Three-dimensional surface structure analysis microscope zygo New view 200 (Zygo at 50 ° C., humidity 50% ± 5%
(Manufactured by K.K.) was used to measure the Ra value on a straight line at a cutoff value of 0.144 mm at three points, and the average value was used.

Retardation: KOBRA-21SD
The wavelength was measured at 590 nm using H (manufactured by Oji Scientific Instruments). A sample cut out in a width direction with a width of 4 cm was prepared, the automatic film feed width was set to 5 cm, and measurement was performed over the entire width.

Amount of residual solvent: Using a gravimetric method, the weight before drying and the weight after drying were measured, and the following formula {(weight before drying)-
(Weight after drying)} / (Weight before drying) × 100 (%)
It was calculated by

Method of confirming surface defects in the film: A rectangular mark having a side of 20 × 5 mm is randomly placed on the film, and the surface defect in the rectangle is reflected in a reflection mode by a polarizing optical microscope while moving the sample. Checked in, and counted the total number. This was repeated 3 times and the average value was calculated. In the present specification, the "surface defect at an arbitrary point in the film plane" refers to the number of surface defects obtained by the above measurement.

Example 1 A 20 wt% solution of polycarbonate (manufactured by Teijin Kasei Co., product number Panlite C-1400) was prepared using dichloromethane as a solvent. As the base film of the support, Lumirror K20 (Toray Industries, Inc.) having an average thickness of 125 μm and a center line average roughness of 6.2 nm is used.
A film prepared by applying a hard coat treatment of applying an acrylic resin to the surface of this PET film and curing it by ultraviolet irradiation was prepared as a support. The width of the support is 1200 mm, the length is 300 m, and the thickness is 130 μ.
m, the center line average roughness Ra of the hard-coated surface was 0.6 nm, and the pencil hardness was 3H. Using this support, the above polycarbonate solution was applied to the hard coat-treated surface and dried, and the obtained primary dry film was wound together with the support. Subsequently, the obtained primary dry film was dried by a roll suspension type dryer until the residual solvent amount became 0.25% by weight, and the average thickness was 80 μm.
A film having a length of 150 m and a glass transition temperature of 149 ° C.) was obtained. A heat-resistant adhesive PET film (manufactured by San-A Kaken Co., Ltd., product name: SAT106T) was attached to the film, and heated at 147 ° C. for carrying out relaxation treatment.
After trimming and removing the edges of the obtained film, the heat-resistant adhesive PET film was peeled off, and a newly adhesive-treated PET film (Tuck Co., product name: Tack Protect TK) was used as a protective film on one side. It stuck and the optical film was obtained. After peeling off the protective film of this optical film, the center line average roughness was measured. As a result, the support surface side was 0.4 nm, and the back surface side was 0.4 nm.
Further, the retardation of the full width in the width direction was 5 to 7 nm, the residual solvent amount was 0.20% by weight, and the number of surface defects within the range of 1 cm ² was 20. Using this film, a disk was processed so as to form a light transmitting layer, and the signal characteristics were evaluated. As a result, good signal characteristics were obtained.

Example 2 Using the polycarbonate resin used in Example 1, a 20 wt% solution was prepared using a mixture of 98.5% methylene chloride and 1.5 wt% ethyl alcohol as a solvent. did. A stainless belt having a center line average roughness of 1.5 nm was used as the support.
The resin solution was cast on the support and dried, and then introduced into a roll-suspended dryer to obtain a film having a residual solvent amount of 0.3% by weight and a thickness of 80 μm. Relaxation treatment is performed in the same manner as in Example 1 to obtain adhesive PET.
The protective film of No. 1 was attached to obtain an optical film. After the protective film of this film was peeled off, the center line average roughness was measured. As a result, it was 0.8 nm on the support surface side and 0.4 nm on the reverse surface side of the support. The retardation in the width direction is 5 to 7 nm, the residual solvent amount is 0.23% by weight, 1
The number of surface defects within the range of cm ² was 6. Using this film, a disk was processed so as to form a light transmitting layer, and the signal characteristics were evaluated. As a result, good signal characteristics were obtained.

Comparative Example 1 Using the same resin solution as in Example 1, a surface-treated PET film having a thickness of 125 μm and a length of 450 m (manufactured by Toray Industries, Inc., product name: Lumirror K20) was used as a support. Used as. The center line average roughness of the support surface was 6.2 nm. An optical film was obtained in the same manner as in Example 1 except that the above film was used as the support. After the protective film of this optical film was peeled off, the center line average roughness was measured. As a result, the support surface side was 2.9 nm, and the back surface side was 0.5 nm. In addition, the residual solvent amount was 0.20% by weight, the retardation in the widthwise entire width of the film was 5 to 7 nm, and the number of surface defects within the range of 1 cm ² was 60. Using this film, a disk was processed so as to form a light-transmitting layer, and the signal characteristics were evaluated, but there were many signal errors and it was unsuitable for use.

Comparative Example 2 Film formation and drying were carried out in the same manner as in Example 1 until a secondary dry film was obtained, and the protective film was laminated and wound up without relaxation treatment. After the protective film was peeled off, the center line average roughness of the film was measured. As a result, the support surface side was 0.4 nm, and the back surface side was 0.5 nm. Further, the average thickness was 79 μm, the residual solvent amount was 0.25% by weight, the retardation in the entire width direction of the film was 16 to 18 nm, and the number of surface defects in the range of 1 cm ² was 20. With this film,
The signal characteristics were evaluated by processing into a disk so as to form a light transmitting layer, but there were many signal errors, and it was unsuitable for use.

(Comparative Example 3) A film was formed, dried, and relaxed in the same manner as in Example 1 except that the amount of residual solvent was dried in a roll-suspended dryer to 1.2% by weight. The thickness of the optical film with the protective film removed is 81μ
A film having m and a residual solvent amount of 0.5% by weight was obtained. The center line average roughness of the film is 0.4 n on the support surface side.
m, the reverse surface side of the support was 0.4 nm, the retardation in the widthwise total width was 5 to 7 nm, and the number of surface defects within the range of 1 cm ² was 20. After processing a disc using this film, a warp was observed after 2 weeks, and a warp was observed after one month, and the signal characteristics could not be measured. Therefore, it cannot be used as a film for an optical recording medium.

(Comparative Example 4) An optical film in which the protective film was finally peeled off by the same method as in Example 1 except that the protective film was not finally laminated. Thickness of 81μm, residual solvent amount is 0.20
A weight percent film was obtained. The center line average roughness of the film was 0.4 nm on the side of the support surface and 0.
4 nm, and the full width retardation is 5
The number of surface defects within the range of 7 nm1 cm ² was 120. After processing into a disc using this film,
When the signal characteristics were evaluated, there was much noise, and it was not usable as a film for optical recording media.

[0039]

According to the method for producing an optical film of the present invention, it is suitable as a film for a light transmitting layer of an optical recording medium, has a small surface roughness, high optical isotropy, and is free from warpage and distortion after processing. A small number of optical films can be obtained. Also,
The optical film of the present invention has few surface defects, has a small surface roughness, has high optical isotropy, and has little warpage or distortion after processing. Therefore, by using the film as a light transmitting layer,
It is possible to reduce the scattering of light and obtain an optical disc with less noise and errors when the signal characteristics are evaluated.

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Claims (3)

[Claims] 1. An optical film formed by a solution casting method using an amorphous thermoplastic resin composition, which simultaneously satisfies the following (a) to (d). (A) The center line average roughness (Ra) of the film surface is 0.1 nm or more and 1 nm or less on both surfaces. (B) The retardation of the film is 0 nm or more and 8 nm.
(C) The residual solvent amount of the film is 0% by weight or more and 0.4% by weight or less (d) The number of surface defects of 30 μm or more is 0 within a range of 1 cm ² at any point on the film surface. More than 50 and less than 50 2. An amorphous thermoplastic resin composition comprising:
The optical film according to claim 1, wherein a polycarbonate containing a repeating unit composed of 2-bis (4-hydroxyphenyl) propane (bisphenol A) as a main constituent is used. 3. A method for producing an optical film, which comprises using an amorphous thermoplastic resin composition and casting a solution of the resin on a support to produce a film, which comprises the following steps (a) to (d): A method for producing an optical film with a protective film, which comprises: (A) As the support, a support having a center line average roughness (Ra) of the surface on which the solution is cast is 0.1 nm or more and 5 nm or less, and the solution is cast on the substrate, followed by drying. Step (b) of performing a solvent to evaporate the solvent to obtain a primary dry film. Drying the primary dry film obtained in the above (a) to obtain a secondary dry film having a residual solvent of 1.0% by weight or less (c). ) Using the secondary dry film obtained in (b) above,
The film is subjected to a relaxation treatment while being heated at (Tg−10) ° C. or higher and (Tg + 10) ° C. or lower (Tg is a glass transition temperature), the retardation of the film is 0 nm or more and 8 nm or less, and the residual solvent amount is 0% by weight or more and 0. 4% by weight or less (d) a step of laminating a protective film on one side or both sides of the film obtained in (c) above