JP4623257B2 - Optical film and method for producing the same - Google Patents

Description

【００４０】
表１が示すように、本発明の実施例の光学用フィルムは、比較例の場合に比べて、Ｄ_ｒ／Ｄ_ａｖｅ、Ｒｅ及びＲｅ_４０／Ｒｅ_０の平均値が所定の範囲にあるため、ロール巻き性、色ムラ、３０傾斜°透過率比、接着性に優れている。比較例１はＤ_ｒ／Ｄ_ａｖｅ、Ｒｅの最大値は所定の範囲にあるが、Ｒｅ _{４ ０}／Ｒｅ_０の平均値が外れているため、ロール巻き性、色ムラ、３０傾斜°透過率比、接着性のいずれも劣っている。比較例２はＤ_ｒ／Ｄ_ａｖｅ、Ｒｅ _{４ ０}／Ｒｅ_０の平均値は所定の範囲にあるが、Ｒｅの最大値が外れているため、ロール巻き性、色ムラ、３０傾斜°透過率比、接着性のいずれも劣り、特に色ムラと接着性が著しく悪い。比較例３はＤ_ｒ／Ｄ_ａｖｅの値が外れているため、ロール巻き性が著しく悪い。
【００４１】
表２には、各実験例について、延伸後のＲｅムラを測定した結果を示す。
【００４２】
【表２】

【００４３】
表２が示すように、本発明の実施例の光学用フィルムは、比較例の場合に比べて、Ｄｒ／Ｄａｖｅ、Ｒｅ及びＲｅ_４０／Ｒｅ_０の平均値が所定の範囲にあるため、延伸加工後のリターデーションムラが小さくて優れており、本発明の光学用フィルムが位相差フィルムの原料フィルムとして適している。
【００４４】
【発明の効果】
本発明により、厚さが１００μｍ以下で、レターデーションの値が小さくて一定で、残留溶剤がなく、ロール状に巻いて保存したときに巻きジワが少なく、他のフィルムとの接着性に優れた光学用フィルムとその製造方法が提供される。本発明の光学用フィルムは、偏光子の保護フィルムや液晶セル基板用フィルムなどのフラットパネルディスプレイ用の各種の光学用フィルムとして有用である。また、本発明の光学用フィルムは、レターデーションが小さく均一なものであるが、その後に延伸加工することによって、所定のレターデーションをもち、その値が均一である位相差フィルムとすることができるから、本発明の光学用フィルムは位相差フィルムなどの原料フィルムとしても有用である。[0001]
  The present invention is an optical film.Manufacturing methodMore specifically, the retardation value is small and uniform, excellent in adhesion to other substrates, various films used for flat panel displays and the like, and optical films suitable as raw material films thereofManufacturing methodConcerningThe
[0002]
  The object of the present invention is that the thickness is 100 μm or less, the retardation value is small and constant, there is no residual solvent, there are few wrinkles when stored in a roll shape, and excellent adhesion to other films. Optical filmManufacturing methodIs to provide.
[0003]
Conventionally, an optical film made of a thermoplastic resin and having a small and constant retardation has been proposed. Conventionally, a film produced by a solution casting method of triacetyl cellulose (TAC) has been mainly used as a protective film for a polarizer. TAC solution casting film has relatively small retardation and is relatively constant within the film surface, but is inferior in productivity, and cannot completely remove the solvent when drying after solution casting. However, due to the solvent remaining in the film, there is a problem that the volatilizing solvent adversely affects the electronic circuit and other parts of the flat panel display and causes malfunctions and display defects. Therefore, recently, as a protective film, a film by a melt extrusion method of a thermoplastic resin has been studied in place of a film by a solution casting method of TAC. For example, Japanese Patent Laid-Open No. 2000-273204 discloses that a specific thermoplastic resin is melt-extruded under specific conditions to obtain a sheet thickness of 150 to 1000 μm, an in-plane thickness tolerance (Rmax) of 15 μm, and a rough sheet surface. A technique is disclosed in which a sheet having a thickness of 0.06 μm and a sheet surface retardation (maximum value) of 15 nm and a relatively small retardation and a relatively small value can be obtained. However, the technique disclosed in this publication is a technique for a thick sheet having a sheet thickness of 150 μm or more. Generally, as the thickness becomes thinner, the thickness variation tends to become larger than the thickness, and the optical distortion becomes severe. Therefore, it cannot meet the recent demand for thinner flat displays.
[0004]
In addition, a film obtained by melt extrusion of a thermoplastic resin is usually wound and stored in a roll shape, and is provided for the subsequent process. However, when the present inventors examined, a thin film having a thickness of 100 μm or less is used. It was found that when winding in a roll shape, winding wrinkles are likely to occur, and if there are winding wrinkles, scratches and defects are likely to occur on the film surface, which leads to display defects. Further, as a result of investigations by the present inventors, it has been found that a film obtained by melt extrusion of a thermoplastic resin has a problem that it tends to cause poor adhesion to a polarizer after a durability test when the thickness is 100 μm or less. It was.
[0005]
[Problems to be solved by the invention]
The object of the present invention is that the thickness is 100 μm or less, the retardation value is small and constant, there is no residual solvent, there are few wrinkles when stored in a roll shape, and adhesion to other films The object is to provide an excellent optical film.
[0006]
[Means for solving the problems]
As a result of intensive studies to solve the above problems, the present inventors,It has a transfer process with a specific configuration and is performed under specific cooling drum peripheral speed conditions and specific temperature conditionsAverage thickness D obtained from thermoplastic resin film obtained by melt extrusion method_aveIs a film having a thickness of 100 μm or less, and the difference D between the maximum value and the minimum value of the thickness over the entire film surface._rAnd the average thickness D_aveRatio D_r/ D_aveIs 7% or less, retardation Re is 4 nm or less, and the phase difference Re is 40 °.₄₀And phase difference Re at a viewing angle of 0 °₀Ratio Re₄₀/ Re₀If the average is 0.8 or more and 1.3 or less, the retardation value is small and constant, there is no residual solvent, and there are few wrinkles when stored in a roll shape. It has been found that it becomes an optical film excellent in adhesiveness with the film. Further, the present inventors have found that an alicyclic structure-containing polymer is preferable as the thermoplastic resin used as a raw material for the optical film.It was.The present invention has been completed based on these findings.
[0007]
Thus, according to the present invention,
“Having a step of transferring the molten thermoplastic resin extruded from the extruder in a circumscribed manner to the three cooling drums of the first cooling drum, the second cooling drum and the third cooling drum in order,
The peripheral speed R of the third cooling drum₃The peripheral speed R of the second cooling drum₂R to₃/ R₂Less than 0.999 and 0.990 or more,
The resin contact time on the first cooling drum is t₁(Seconds), the temperature of the molten thermoplastic resin when leaving the first cooling drum is T₁(° C.), t when the glass transition temperature of the thermoplastic resin is Tg (° C.)₁× (T₁-Tg) (unit: second.deg)-40 or more +15 or lessThe average thickness Dave is 100 μm or less, the ratio Dr / Dave of the difference Dr / Dave between the maximum value and the minimum value of the thickness and the average thickness Dave is 7% or less over the entire film surface, and the retardation Re is1.4Phase difference Re at nm or less and at a viewing angle of 40 °₄₀And phase difference Re at a viewing angle of 0 °₀Ratio Re₄₀/ Re₀The average value of0.95Above1.20The method of manufacturing the following optical films. "
As a preferred example of the method for producing the optical film,
“The method for producing the optical film as described above, wherein the thermoplastic resin is an alicyclic structure-containing polymer.”
Is provided.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The thermoplastic resin used for manufacturing the optical film of the present invention is not particularly limited as long as it is a film used for manufacturing a normal optical film. Specific examples include polyethylene, polypropylene, ethylene-propylene copolymer, polystyrene, polyacrylonitrile, acrylonitrile-styrene copolymer, polyvinyl chloride, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polycarbonate and alicyclic structure. A polymer etc. are mentioned. Among these thermoplastic resins, polyethylene terephthalate, polybutylene terephthalate and alicyclic structure-containing polymers are preferred because of their high transparency and excellent film strength, and since the retardation can be further reduced, alicyclic structures are contained. Polymers are particularly preferred.
[0009]
The alicyclic structure-containing polymer is a polymer having a cyclic structure composed of a carbon-carbon saturated bond in the repeating unit (in the present invention, referred to as “alicyclic structure”). Ring-opening polymers of monomers having a norbornene ring structure (hereinafter referred to as “norbornenes”) and hydrogenated products thereof, addition polymers of norbornenes and hydrogenated products thereof, addition copolymers of norbornenes and vinyl compounds And hydrogenated products thereof: polymers obtained by hydrogenating aromatic rings of polymers of aromatic vinyl hydrocarbon compounds such as polystyrene, addition polymers of monomers having an alicyclic structure and a vinyl group, rings comprising carbon-carbon Examples thereof include addition polymers of monomers having one or more unsaturated bonds in the structure and hydrogenated products thereof.
[0010]
The thermoplastic resin is usually supplied to an extruder in the form of pellets suitable for extrusion molding by blending various compounding agents as required. The compounding agent is not particularly limited, but is a stabilizer such as an antioxidant, a heat stabilizer, a light stabilizer, a weathering stabilizer, an ultraviolet absorber, a near infrared absorber, and the like; a resin modifier such as a lubricant and a plasticizer. Colorants such as dyes and pigments; antistatic agents and the like. These compounding agents can be used alone or in combination of two or more, and the compounding amount is appropriately selected within a range not impairing the object of the present invention.
[0011]
Examples of the antioxidant include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. Among them, phenolic antioxidants, particularly alkyl-substituted phenolic antioxidants are preferable. By blending these antioxidants, it is possible to prevent coloration and strength reduction of the molded product due to oxidative degradation during molding without lowering transparency, low water absorption and the like. These antioxidants can be used alone or in combination of two or more, and the blending amount thereof is appropriately selected within a range not impairing the object of the present invention, but 100 parts by weight of the thermoplastic resin. The amount is usually 0.001 to 5 parts by weight, preferably 0.01 to 1 part by weight.
[0012]
In the present invention, a film obtained by processing the above thermoplastic resin into a film by a melt extrusion method is used. The melt extrusion method is a method in which a thermoplastic resin is heated and melted in a cylinder, pressurized with a screw, and extruded from a die such as a T die. Usually, a molten thermoplastic resin extruded from a die is sequentially circumscribed and transferred to a plurality of cooling drums, cooled in the meantime, and then subjected to necessary steps to form a thermoplastic resin film. Compared to the width of the molten thermoplastic resin immediately after being extruded from the die (same as the width of the lip of the die), the width of the thermoplastic resin film after passing through the cooling drum is 2 to 2, It becomes narrower by about 10%. And the edge (henceforth only an "edge") of the width direction of a film made from a thermoplastic resin becomes thick compared with the other part of the film, and retardation also becomes large. When used in an optical application as in the present invention, an appropriate portion of the end is usually cut out before winding with a winding drum. In the present invention, this portion that is cut off is referred to as “mimi”. In the present invention, the portion of the unstretched thermoplastic resin film excluding the portion that becomes a stain is referred to as “optical film”. When used in a state where the retardation is close to zero, such as a protective film or a liquid crystal substrate, take a mim from an unstretched thermoplastic resin film, take out the optical film, and wind it with a take-up drum . After the optical film is wound up in a roll shape by a winding drum, it is subjected to a subsequent step, ie, a stretching step or a bonding step with another film.
[0013]
The optical film of the present invention has an average thickness D_aveIs 100 μm or less. The average thickness Dave can be arbitrarily set by changing the feeding speed of the raw material pellets to be fed into the melt extruder, the rotation speed of the cooling drum, and both. The optical film of the present invention is suitable for a thin flat panel display or the like, and is also suitable for use in a thickness of 100 μm or less, 80 μm or less, particularly 60 μm or less.
[0014]
The optical film of the present invention has a difference D between the maximum value and the minimum value of the thickness over the entire film surface._rAnd the average thickness D_aveRatio D_r/ D_aveIs 7% or less. Average thickness D_aveAnd the difference D between the maximum and minimum thicknesses_rIs an appropriate length of the length in the extrusion direction (hereinafter also simply referred to as “length”), for example, by a contact type continuous thickness meter. It is possible to adopt a value that can be obtained as a substitute value by measuring over several points and measuring several points including a portion close to the end of the optical film in the width direction. D_r/ D_aveThe value of is preferably as small as possible, but is usually 7% or less. D_r/ D_aveWhen the value is in this range, there is little wrinkle when stored in a roll shape, and it becomes an optical film excellent in adhesiveness to other films.
[0015]
The optical film of the present invention needs to have a retardation Re of 4 nm or less over the entire film surface. The value of Re can be measured by an optical technique such as an ellipsometer, and the maximum value is measured over an appropriate length, and several points including the portion near the edge of the optical film in the width direction. By measuring the above, a value that can be obtained can be adopted as a substitute value. The smaller the maximum value of Re, the better. However, it is usually 4 nm or less, preferably 3 nm or less, particularly preferably 2.5 nm. When Re is in this range, not only is the color unevenness when flat panel display is small, but there are few wrinkles when rolled and stored, and it has excellent adhesion to other films. Become a film.
[0016]
The optical film of the present invention has a retardation Re at a viewing angle of 40 °.₄₀And phase difference Re at a viewing angle of 0 °₀Ratio Re₄₀/ Re₀Must be 0.8 or more and 1.3 or less on average. Re₄₀And Re₀Is obtained by measuring the retardation at an angle of the film surface of 40 ° and 0 °, respectively. The maximum value and the minimum value are measured over an appropriate length, and further with respect to the width direction. The value which can be obtained by measuring several points including the part near the end of the optical film can be used as a substitute value. Re₄₀/ Re₀Shows viewing angle dependence of retardation, ideally 1.0, but on average, usually 0.8 or more and 1.3 or less, preferably 0.9 or more and 1.25 or less, Preferably it is 0.95 or more and 1.20 or less. Re₄₀/ Re₀When the average value is within this range, the obtained flat panel display has excellent color unevenness and contrast.
[0017]
D as above_r/ D_ave, The maximum value of Re and Re₄₀/ Re₀The method for producing an optical film satisfying the range of the average value is not particularly limited. For example, there is a method in which the ratio of the portion of the mimi occupying the entire film is made larger than in the conventional case so as to satisfy the above-described conditions over the entire film surface. In this case, the ratio of the Mimi portion is usually 3% or more for each of the left and right, preferably 5% or more for each of the left and right, particularly preferably 7% or more of each of the left and right, preferably 40% or less of each of the left and right. Each is 20% or less.
[0018]
Moreover, the film made from the thermoplastic resin used when manufacturing the optical film of this inventionMade ofAs a manufacturing method, it has a step of transferring the thermoplastic resin in a molten state extruded from an extruder by sequentially circumscribing the three cooling drums of the first cooling drum, the second cooling drum, and the third cooling drum, The peripheral speed R of the third cooling drum₃The peripheral speed R of the second cooling drum₂R to₃/ R₂Is less than 0.999 and 0.990 or more, and the resin contact time on the first cooling drum is t₁(Seconds), the temperature of the thermoplastic resin of the molten body when leaving the first cooling drum is T₁(° C), t when the glass transition temperature of the thermoplastic resin is Tg (° C)₁× (T₁−Tg) (unit: second · deg) is set to be −50 or more and +20 or less.TheThis method will be described below.
[0019]
In this manufacturing method, a thermoplastic resin that has been extruded from an extruder and melted into a sheet (hereinafter also referred to as a “sheet thermoplastic resin”) is used as a first cooling drum, a second cooling drum, and a third cooling drum. The three cooling drums are sequentially circumscribed and transferred. The peripheral speed R of the third cooling drum₃The peripheral speed R of the second cooling drum₂R to₃/ R₂Is set to less than 0.999 and 0.990 or more, preferably less than 0.998 and 0.995 or more. R₃/ R₂If the value is excessively large, the sheet-like thermoplastic resin is stretched to increase the retardation value and its variation, which is not preferable. On the other hand, R₃/ R₂Even if the value of the sheet is excessively small, the sheet-like thermoplastic resin sags and sags, its weight becomes tension, and the sheet-like thermoplastic resin is stretched, resulting in an increase in retardation value and its variation, which is also not preferable. . R₃/ R₂In order to determine the set value of the resin, when the sheet-like thermoplastic resin is transferred from the second cooling drum to the third cooling drum, the resin is caused by lowering from the vicinity of the second cooling drum temperature to the vicinity of the third cooling drum temperature. The resin temperature is set so as to meet the shrinkage rate. By adopting the above peripheral speed ratio, the sheet-like thermoplastic resin is not loosened, and a uniform thermoplastic resin sheet having a small retardation value can be produced while being pulled with an appropriate tension.
[0020]
Also, the peripheral speed R of the second cooling drum₂The peripheral speed R of the first cooling drum₁R to₂/ R₁Is preferably set to less than 1.01 and 0.990 or more, and more preferably set to less than 1.000 and 0.995 or more. R₂/ R₁When the value is within this range, the retardation unevenness of the obtained optical film is particularly small, and winding wrinkles are less likely to occur, which is preferable.
[0021]
Further, when the sheet-like thermoplastic resin leaves the third cooling drum, the resin temperature T₃Is preferably 50-100 ° C. lower than the glass transition temperature (Tg) of the thermoplastic resin, more preferably 60-80 ° C. lower than Tg. T₃Is within this range, the retardation unevenness of the resulting optical film is particularly small, and winding wrinkles are less likely to occur, which is preferable. Temperature T₃Is set to the above range, the temperatures of the third cooling drum and the second cooling drum are controlled.
[0022]
Temperature T of the sheet-like thermoplastic resin when the sheet-like thermoplastic resin leaves the second cooling drum₂Is preferably 0 to 60 ° C. lower than its Tg, more preferably 20 to 40 ° C. T₂When the value is within this range, the retardation unevenness of the obtained optical film is particularly small, and winding wrinkles are less likely to occur, which is preferable.
[0023]
It is preferable that the temperature difference between the first cooling drum and the second cooling drum is less than 10 ° C.
[0024]
The contact time of the sheet-like thermoplastic resin on the first cooling drum is t₁(Seconds), the resin temperature when leaving the first cooling drum is T₁(° C.), t when the glass transition temperature of the thermoplastic resin is Tg (° C.)₁× (T₁−Tg) (unit: second · deg) is usually −50 to +20, preferably −40 to +15. When the thickness is within this range, the thickness uniformity of the resulting optical film D_r/ D_aveIs small, and the maximum value of Re is small, which makes it easy to obtain the optical film of the present invention, which is preferable.
[0025]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
“Part” and “%” in these examples are based on mass unless otherwise specified.
Various sample preparations and tests were performed according to the following.
[0026]
(1) Average thickness D of the film_aveAnd variation D_r
Using a contact-type film thickness meter, the length of the film is 10 m every 500 mm (20 places), and the thickness of the film is measured at five places at equal intervals in the width direction._aveAnd the difference D between the maximum and minimum values_rAsked.
[0027]
(2) Retardation value Re and its maximum value
Retardation values are measured using a phase difference measuring device [manufactured by Oji Scientific Instruments: KOBRA-21ADH], the length direction of the film is 10 m every 500 mm (20 locations), and the width direction is equal to 5 locations at equal intervals. Re was measured and the maximum value was determined.
The measurement wavelength was 550 nm and the incident angle was 0 °.
[0028]
(3) Retardation Re at a viewing angle of 40 °₄₀And retardation Re at a viewing angle of 0 °₀Ratio Re₄₀/ Re₀Average value
For the same measurement point as in (2), the same measurement method as in (2)₀And the measurement method with the incident angle of the measurement light changed to 40 °.₄₀Measure Re₄₀/ Re₀Was calculated, and the average value was obtained.
[0029]
(4) Roll rollability
A roll-shaped optical film wound up by a take-up drum is visually observed, ○ for those in which no winding wrinkles are observed, Δ in which slight wrinkles are observed, and those in which winding wrinkles are clearly recognized × It was.
[0030]
(5) Color unevenness
When used as a protective film for a polarizer, color unevenness and color loss, which are problems, were simply tested. In the actual configuration of the liquid crystal display, both sides of the polarizer are sandwiched between two protective films to form a polarizing plate, and both sides of the liquid crystal are sandwiched between two polarizing plates (with other necessary layers) It has become. If the protective film is optically distorted, it may cause color unevenness and color loss on the entire liquid crystal display. The optical distortion of the optical film serving as each protective film was simply tested as follows. Prepare two commercially available polarizers in which liquid crystal polyvinyl alcohol is doped with iodine, align the two polarizers so that their polarization axes are perpendicular, and sandwich the optical film obtained in the experiment between them. As a three-layer structure composed of a polarizer / optical film / polarizer, the degree of transmission of non-polarized light (natural light) is visually observed, ◯ when no light leakage is observed, △ when slightly observed, What was clearly recognized was marked with x. The measurement was performed at 5 points at equal intervals in the width direction over 10 m (20 places) in the length direction of the film every 500 mm.
[0031]
(6) 30 ° slope transmittance ratio
Further, a 30 ° inclined transmittance ratio was measured as one index of color unevenness and color leakage.
Sample pieces were cut out at five positions at equal intervals in the width direction of the optical film obtained in the experiment, and NDH300A type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. was used for these sample pieces in accordance with JIS K7105. Then, the direct transmittance and the 30 ° inclined transmittance were measured, the 30 ° inclined transmittance / the orthogonal transmittance was obtained, and the average value was obtained as the 30 ° inclined transmittance ratio. A larger value is preferable. If the value is 1000 or more, color unevenness and color leakage of the obtained flat panel display do not cause a problem and are favorable.
[0032]
(7) Adhesiveness
Optical films are often used by being bonded to other film-like members, and in particular, adhesion after a durability test is often a problem. The same polarizer used in (5) and a sample piece of the same area cut out from the optical film obtained in the experiment were bonded together with a 10% by mass aqueous solution of polyvinyl alcohol. The obtained laminate was subjected to an endurance test under the conditions of 80 ° C., 90% RH, 100 hours, and then the state of the laminate was visually observed. The case where the peeling of the interface occurred was taken as x.
[0033]
(8) Re unevenness after stretching
The optical film obtained in the present invention can be made into a retardation film by subsequent stretching. The retardation film is required to have a predetermined retardation (retardation value) and a uniform value. In order to investigate the performance of the optical film of the present invention as a raw material film for a retardation film, the following test was conducted. The optical film obtained in the experiment was cut out (width 100 mm, length 150 mm) to obtain a test piece, and the test piece was stretched 1.1 to 2 times in the longitudinal direction at 140 ° C. at a speed of 100 mm / min. did. The draw ratio was adjusted so that the average retardation was 275 ± 10 nm. Retardation was measured by the same measurement method as in (2), and the variation (difference between the maximum value and the minimum value) was divided by the average value to obtain Re unevenness. The measurement point was the central part in the width direction, and 10 points were set around the center in the length direction every 10 mm.
[0034]
Example 1
  A pellet of ZEONOR1420 (hydrogenated ring-opening polymer of norbornenes, manufactured by Nippon Zeon Co., Ltd., Tg 140 ° C.) was used. The pellets were melt extruded at a barrel temperature of 260 ° C. with a single screw extruder (manufactured by Nippon Steel) with a cylinder inner diameter of 50 mm and a screw L / D of 28, and a sheet-like molten resin having a width of 650 mm from a coat hanger die with a die temperature of 260 ° C. The first cooling drum (diameter 200 mm, temperature T₁: 135 ° C, peripheral speed R₁12:50 m / sec) immediately, the first cooling drum was immediately put on by a knife coater, and then the second cooling drum (diameter 350 mm, temperature T₂: 125 ° C, peripheral speed R₂: 14.46 m / sec), then the third cooling drum (diameter 350 mm, temperature T₃: 80 ° C, peripheral speed R₃: 14.40 m / sec) in order to be transferred in close contact with each other, and the front and back surfaces are smoothed by successive cooling and cooling drum surface transfer to obtain a thermoplastic resin film having a width of 550 mm (neck-in is 50 mm each on the left and right). After passing through the adjustment drum, 30 mm each was removed from both ends with a cutter and wound into a roll with a winding drum to obtain a roll-shaped optical film. At this time, the contact time t of the sheet-like thermoplastic resin on the first cooling drum₁3.1 (seconds), the resin temperature when leaving the first cooling drum is T₁Is 132 (° C), t₁× (T₁-Tg) is-24.8(Unit: second · deg).
  Table 1 shows the results of the above test items performed on the obtained optical film.
[0035]
Example 2
In Example 1, R₁7.10 m / s, R₂7.07 m / s, R₃An optical film was produced in the same manner as in Example 1 except that the value was changed to 7.04 m / sec. The test results of the obtained optical film are shown in Table 1.
[0036]
Comparative Example 1
In Example 1, T₁An optical film was produced in the same manner as in Example 1 except that was changed to 120 ° C. The test results of the obtained optical film are shown in Table 1.
[0037]
Comparative Example 2
In Example 1, T₁At 120 ° C, T₂An optical film was produced in the same manner as in Example 1 except that was changed to 110 ° C. The test results of the obtained optical film are shown in Table 1.
[0038]
Comparative Example 3
In Example 1, T₁110 ° C, T₂An optical film was produced in the same manner as in Example 1 except that was changed to 100 ° C. The test results of the obtained optical film are shown in Table 1.
[0039]
[Table 1]

[0040]
  As Table 1 shows, the optical film of the example of the present invention has D as compared with the comparative example._r/ D_ave, Re and Re₄₀/ Re₀Since the average value is within a predetermined range, the roll winding property, color unevenness, 30 tilt angle transmittance ratio, and adhesiveness are excellent. Comparative Example 1 is D_r/ D_aveThe maximum value of Re is within a predetermined range, but Re _{4 0}/ Re₀Since the average value of the above is deviated, all of roll rollability, color unevenness, 30 tilt angle transmittance ratio, and adhesiveness are inferior. Comparative Example 2 is D_r/ D_ave, Re _{4 0}/ Re₀Although the average value is within a predetermined range, since the maximum value of Re is deviated, all of roll rollability, color unevenness, 30 slope transmittance ratio, and adhesiveness are inferior. bad. Comparative Example 3 is D_r/ D_aveRoll rollability is remarkably poor because the value of.
[0041]
Table 2 shows the measurement results of Re unevenness after stretching for each experimental example.
[0042]
[Table 2]

[0043]
As shown in Table 2, the optical films of the examples of the present invention have dr / dave, re and re compared to the comparative examples.₄₀/ Re₀Is within a predetermined range, the retardation unevenness after stretching is small and excellent, and the optical film of the present invention is suitable as a raw material film for a retardation film.
[0044]
【The invention's effect】
According to the present invention, the thickness is 100 μm or less, the retardation value is small and constant, there is no residual solvent, there are few wrinkles when stored in a roll shape, and excellent adhesion to other films. An optical film and a method for producing the same are provided. The optical film of the present invention is useful as various optical films for flat panel displays such as a polarizer protective film and a liquid crystal cell substrate film. Further, the optical film of the present invention has a small retardation and a uniform film, but it can be made into a retardation film having a predetermined retardation and a uniform value by subsequent stretching. Therefore, the optical film of the present invention is also useful as a raw material film such as a retardation film.

Claims (2)

A step of transporting the molten thermoplastic resin extruded from the extruder by sequentially circumscribing the three cooling drums of the first cooling drum, the second cooling drum, and the third cooling drum;
The ratio R ₃ / R ₂ of the peripheral speed R ₃ of the _third cooling drum to the peripheral speed R ₂ of the second cooling drum is less than 0.999 and 0.990 or more,
The resin contact time on the first cooling drum is t ₁ (seconds), the temperature of the molten thermoplastic resin when leaving the first cooling drum is T ₁ (° C.), and the glass transition temperature of the thermoplastic resin. By setting t ₁ × (T ₁ −Tg) (unit: second · deg) where Tg (° C.) is −40 to +15, the average thickness Dave is 100 μm or less. The ratio Dr / Dave of the difference Dr between the maximum value and the minimum value of the thickness and the average thickness Dave is 7% or less, the retardation Re is 1.4 nm or less, and the phase difference Re ₄₀ and the viewing angle 0 ° at a viewing angle 40 °. A method for producing an optical film having an average value of the ratio Re ₄₀ / Re ₀ of the phase difference Re ₀ of 0.95 to 1.20. The method for producing an optical film according to claim 1, wherein the thermoplastic resin is an alicyclic structure-containing polymer .