JP2004126026A - Optical film and phase differential film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film without causing unevenness of phase difference substantially when a melt-extrusion film is processed into a phase differential film, and without causing display unevenness or the like substantially in the surface when the film is incorporated into a liquid crystal display device, and to provide the phase differential film obtained from the film. <P>SOLUTION: In this optical film made by drawing a thermoplastic polymer film obtained by a melt-extrusion method in the width direction, a variation in thickness is 1.45 μm or less, and unevenness of thickness is 0.2 μm/5 mm or less in the width direction, and the film can be obtained from an optical film having a front phase difference value of 20 nm or less, and an optical film for manufacturing a phase differential film, and can also be obtained by drawing these optical films in a uniaxial or biaxial directions, and is characterized in that the thermoplastic polymer is a nornornene resin. <P>COPYRIGHT: (C)2004,JPO

Description

【００３４】
比較例１〜３、特に比較例３（溶融押出原反をそのまま延伸して位相差を発現させた）と比べて、実施例では位相差ムラ、バラツキとも格段に改善していることが明らかである。
【００３５】
【発明の効果】
本発明の光学フィルムは上述の通りの構成となされており、残留位相差を殆ど持たず、厚みが均一であるので、各種用途の光学フィルムとして好適であり、更に、高生産性であって且つ環境負荷の観点からも、工業的価値の高い光学フィルムである。
特に、一軸延伸又は二軸延伸することによって位相差ムラが実質的に発生しない光学フィルムや液晶表示装置に組み込まれた場合に面内で実質的な表示ムラ等が発生しない光学フィルムが得られるので、位相差フィルム製造用光学フィルムとして好適である。
実際に本発明の光学フィルムを一軸延伸又は二軸延伸して得られる位相差フィルム、特に、ノルボルネン系樹脂製の位相差フィルムは、上記効果を確実に奏し得るものである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical film suitable as a film (raw material) for producing a retardation film or the like applicable to a liquid crystal display device and the like, and a retardation film obtained from the optical film.
[0002]
[Prior art]
In recent years, the display quality of liquid crystal displays has been significantly improved.
This is largely because the birefringence of the liquid crystal molecules is canceled by the retardation film.
In recent years, as a liquid crystal display system, a TFT (thin film transistor) system and a reflection type liquid crystal display occupy the mainstream, and various materials have been studied to cancel birefringence of the liquid crystal. Wavelength dispersibility (the phase difference with respect to the incident light wavelength has little dependence on wavelength), low photoelastic coefficient (the change of the phase difference with respect to stress is small), thin film (mainly 30 to 60 μm), high Tg (130 ° C. or more (Mainstream) is becoming more important.
[0003]
Various resins such as polycarbonate have been studied as resins satisfying these characteristics, but in recent years, norbornene-based resins have attracted attention.
[0004]
In addition, high productivity is required as a method of producing a film in order to contribute to a reduction in the price of a display device. The melt extrusion method has been regarded as the mainstream.
[0005]
However, due to the precision of the lip of the die, the film formed by the melt extrusion method usually produces irregularities of about ± 2% with respect to the film thickness when producing a film having a width of about 1000 mm. I do. The unevenness is generally such that the interval between adjacent peaks is about 5 to 50 mm, and is characteristically present continuously along the flow direction at a position in the width direction corresponding to the accuracy of the lip portion.
When such a film is stretched as it is in the next step to form a retardation film, the unevenness is reflected as it is in the retardation unevenness, and the display quality of a liquid crystal display device using the same is remarkably deteriorated.
For this reason, due to the above problems, an optical film that can be used as a raw material of a retardation film has not yet been industrially manufactured by the melt extrusion method.
[0006]
In order to solve this problem, a method has been proposed in which a molded product made of a norbornene-based resin obtained by an extrusion molding method or an injection molding method is surface-polished to make it a preferable optical member (for example, Patent Document 1). reference).
However, even if this method is applied, not only is it difficult to uniformly polish a wide film, but also it is not practical because the adhesion of polishing powder may become a new optical defect.
[0007]
[Patent Document 1]
JP-A-5-59196 (Claim 3 of the claims and paragraph 0015).
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems in the conventional optical film, by using the most preferable melt-extruded film from the viewpoint of high productivity and environmental load, by optimizing the thickness variation, unevenness and the residual phase difference. It was completed with the knowledge that it could solve the problem, and when the melt-extruded film was processed as a retardation film, the retardation unevenness did not substantially occur and was incorporated into the liquid crystal display device. It is an object of the present invention to provide an optical film that does not cause substantial display unevenness or the like in a plane, and a retardation film obtained from the film.
[0009]
[Means for solving the problem]
In order to achieve the above object, the invention according to claim 1 is a film obtained by stretching a thermoplastic polymer film obtained by a melt extrusion method in a width direction, and has a thickness variation of 1.45 μm or less in the width direction. And an optical film having a thickness unevenness of 0.2 μm / 5 mm or less and a front retardation value of 20 nm or less.
The invention according to claim 2 is a film obtained by stretching a thermoplastic polymer film obtained by a melt extrusion method in the width direction, wherein the thickness variation in the width direction is 1.45 μm or less, and the thickness unevenness is 0. Provided is an optical film for producing a retardation film having a thickness of 2 μm / 5 mm or less and a front retardation value of 20 nm or less.
The invention according to claim 3 provides a retardation film obtained by uniaxially or biaxially stretching the optical film according to claim 1 or 2.
Further, the invention according to claim 4 provides the retardation film according to claim 3, wherein the thermoplastic polymer is a norbornene-based resin.
[0010]
Thermoplastic resin as a thermoplastic polymer used in the optical film of the present invention, it is important that high transparency, for example, norbornene-based resin, polycarbonate-based resin, polysulfone-based resin, polymethyl methacrylate-based resin, A polystyrene-based resin or the like can be used, and a norbornene-based resin having particularly excellent matching properties and durability with a liquid crystal, a low wavelength dispersion, and a small photoelastic coefficient, among which a thermoplastic saturated norbornene-based resin is particularly preferably used.
[0011]
The norbornene-based resin is preferably a thermoplastic saturated norbornene-based resin, for example, a hydrogenated product of a ring-opening (co) polymer of a norbornene-based monomer, an addition copolymer of a norbornene-based monomer and another olefin-based monomer, Examples include addition copolymers of norbornene-based monomers and derivatives thereof. These norbornene resins may be used alone or in combination of two or more.
[0012]
The norbornene-based monomer is not particularly limited as long as it has a norbornene ring.However, since a molded article having excellent heat resistance and a low linear expansion coefficient is obtained, a tricyclic or higher polycyclic norbornene-based monomer is used. Is preferred.
[0013]
Specific examples of the norbornene-based monomer include, for example, bicyclics such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene and dihydroxypentadiene; tetracyclics such as tetracyclododecene; and cyclopentadiene trimers. Pentacyclic; heptacyclic such as tetracyclopentadiene; substituted products thereof, such as alkyl such as methyl, ethyl, propyl, and butyl; alkenyl such as vinyl; alkylidene such as ethylidene; aryl such as phenyl, tolyl, and naphthyl; Other than carbon and hydrogen such as ester group, ether group, cyano group, halogen atom, alkoxycarbonyl group, pyridyl group, hydroxyl group, carboxylic acid group, amino group, acid anhydride group, silyl group, epoxy group, acrylic group, methacryl group, etc. Group containing the element of the above, a substituent having a so-called polar group Gerare, among others, are readily available, excellent reactivity, since the heat resistance of the molded article obtained is excellent, tricyclic body, norbornene-based monomer tetracyclic body and pentacyclic body is preferably used. These norbornene monomers may be used alone or in combination of two or more.
[0014]
Examples of the hydrogenated product of the ring-opening (co) polymer of the norbornene-based monomer include those obtained by subjecting the above-described norbornene-based monomer to ring-opening polymerization by a known method and then hydrogenating the remaining double bond. Widely used. This may be a homopolymer of a norbornene-based monomer or a copolymer of different types of norbornene-based monomers.
[0015]
In the ring-opening polymerization, for example, as a polymerization catalyst, a hydrated salt of Ir, Os, or Ru trichloride, MoCl ₅ , WCl ₆ , ReCl ₅ , (C ₂ H ₅ ) ₃ Al, (C ₂ H ₅ ) ₃ Al / TiCl ₄ , (π-C ₄ H ₇ ) ₄ Mo / TiCl ₄ , (π-C ₄ H ₇ ) ₄ W / TiCl ₄ , (π-C ₃ H ₅ ) ₃ Cr / WCl _6, etc. It can be performed by a conventional method.
[0016]
Examples of the addition copolymer of the norbornene-based monomer and another olefin-based monomer include a copolymer of a norbornene-based monomer and an α-olefin. As the α-olefin, an α-olefin having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, for example, ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1 -Pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, etc., among which, because of high copolymerizability, Ethylene is preferred, and when other α-olefins are copolymerized with norbornene-based monomers, the presence of ethylene increases the copolymerizability.
[0017]
The number average molecular weight (GPC measurement; standard polystyrene equivalent, solvent; THF or cyclohexane) of the thermoplastic saturated norbornene-based resin is not particularly limited, and is usually 5,000 to 40,000, preferably 7000 to 35,000, and more preferably 8,000. ３０30000. When the number average molecular weight is less than 5,000, the mechanical strength of the thermoplastic saturated norbornene-based resin film becomes insufficient, and when it exceeds 40,000, the moldability deteriorates, and both are not preferred.
[0018]
These norbornene resins are known and are commercially available. Specific examples of known norbornene-based resins include, for example, those described in JP-A-1-240517. Specific examples of commercially available norbornene-based resins include, for example, those manufactured by JSR Corporation. "ARTON" series, product name "ZEONOR" series manufactured by Zeon Corporation, and product name "APEL" series manufactured by Mitsui Chemicals, Inc.
[0019]
First, the optical film of the present invention needs to be obtained by stretching a thermoplastic polymer film obtained by a melt extrusion method in the width direction. The melt extrusion method is a film forming method in which the resin is melted at a temperature exceeding the melting point in a closed atmosphere and then extruded from a die into a sheet shape with a screw, and includes a method using a T die, an inflation method, and the like.
Forming of a film raw material by a melt extrusion method is generally performed by melting a thermoplastic resin at a high temperature in an extruder and uniformly extruding it from a die slot to form a film. At that time, if necessary, undissolved components and carbonized components are removed using a sintered filter or the like.
The extruder may be a single screw type or a twin screw type.
[0020]
Since the above-mentioned melt extrusion method does not use a solvent, it is possible to greatly increase the line speed because there is no need for a time to dry volatile components as compared with the solution casting method, and it is environmentally friendly, which is solvent-free. This is a preferred manufacturing method in that it also has aspects.
However, the extruded film is greatly affected by the unevenness of the clearance of the discharge port, and thickness unevenness occurs in the flow direction during extrusion. This is often referred to generally as “die line”.
When a film having a die line is stretched, particularly in the case of so-called “longitudinal uniaxial stretching” in which the film is uniaxially stretched in the flow direction, the die line does not disappear and appears as a phase difference unevenness, and the phase difference in the film width direction (TD). , A phase difference unevenness pattern similar to the thickness unevenness pattern appears. That is, the high thickness portion becomes a high phase difference portion, and the low thickness portion becomes a low phase difference portion.
[0021]
In the optical film of the present invention, the following method is employed to eliminate the die line.
Specifically, a method of stretching (stretching) in the direction perpendicular to the extrusion film forming direction in an atmosphere of Tg of the resin (glass transition point) + 10 ° C. to Tg + 60 ° C., preferably Tg + 30 ° C. to Tg + 50 ° C. is adopted. I have.
If the stretching temperature is too low, stress is generated in the film at the time of deformation, molecules are likely to be oriented, and birefringence (phase difference) is likely to be developed. The direction of the slow axis of the generated phase difference does not point in a fixed direction, which is a great obstacle to stretching in the next step to uniformly develop the phase difference. Conversely, if the temperature at the time of stretching is too high, the strength of the film itself is lost, the film is easily affected by hot air and its own weight, and transport of the film becomes extremely difficult, which is not practical.
[0022]
The front phase difference value developed at this time needs to be 20 nm or less.
Here, the front phase difference value Re is a value calculated as Re = | nx−ny | · d, and nx is the refractive index of light entering in the orientation direction (x direction) of molecules in the film plane. Where ny represents the refractive index of light entering in a direction (y direction) perpendicular to the orientation direction of the molecules in the plane of the film, and d represents the thickness of the film.
If the front phase difference value Re exceeds 20 nm, the uniformity is adversely affected in the development of the phase difference in the next step. More specifically, for example, when Re exceeds 20 nm (in this case, the optical axis is oriented in the width direction), the original orientation remains at the time of reorientation in the subsequent stretching step, and the retardation becomes biaxial. This is because there is a possibility of having
[0023]
In this case, the stretching ratio is preferably as high as possible, but the thickness is, on average, assuming that the stretching ratio is n (1 / √n). Therefore, the stretching is preferably about 1.5 to 3 times. However, it basically depends on the thickness accuracy of the raw material (melt extruded film).
If the draw ratio is too low, the flattening effect of the thickness is thin, and if it is too high, the thickness of the raw fabric is not increased unless the thickness is increased, and it is also considerable to transport a wide-width film uniformly. Because of the difficulty, it is not very desirable.
The thickness accuracy of the film after this operation is such that the variation in the entire width direction (the difference between the maximum value and the minimum value in the measurement range over the entire width direction, hereinafter appropriately referred to as “variation”) is 1.45 μm or less, and the minute range in the width direction. In other words, it is important that the maximum value of the difference (hereinafter, referred to as “unevenness” as appropriate) when measured in arbitrary widths of 5 mm within the measurement range at intervals of 1 mm in the width direction is 0.2 μm / 5 mm or less. It is.
[0024]
This means that a so-called quarter-wave plate (having a phase difference value of 137.5 nm) having a function of generating a quarter-wave retardation, for example, can be developed with a thickness of 40 μm even when a retardation is developed with the film as it is. Since the expression phase difference per 1 μm is about 3.44 nm, by suppressing the thickness variation in the width direction to 1.45 μm or less, the phase difference variation becomes about 5 nm. This is because deterioration in display quality of the panel can be avoided.
In addition, the proximity unevenness in a minute range in the width direction is 0.7 nm / 5 mm in terms of a phase difference, and such a phase difference unevenness cannot be visually confirmed.
[0025]
The thus-obtained optical film of the present invention having a uniform thickness and a very small front retardation value can be used as it is, for example, as a protective film for a polarizer or a disc substrate, and various optical members. And may be further subjected to a stretching step.
Industrially, it is suitable to be used as an optical film for producing a retardation film according to claim 2 and to be subjected to a stretching step.
[0026]
The retardation film according to claim 3 is obtained by uniaxially or biaxially stretching the optical film. In this case, as the uniaxial stretching, a method of stretching in the flow direction (MD) and a method of stretching in the width direction (TD) ), And a roll method and a tenter method are generally used, respectively.
The biaxial stretching method includes a simultaneous biaxial stretching method and a sequential biaxial stretching method, and is usually used in combination with a tenter method and a roll method.
Since the retardation film obtained by the biaxial stretching method has different refractive indexes in the width direction, the flow direction, and the thickness direction of the film, it is suitable for optical compensation of liquid crystal molecules having a special orientation such as vertical orientation. Can be used for
[0027]
In any case, the resin is generally deformed at around Tg ± 10 ° C.
In the present invention, any method can be used as long as the stretching involves deformation.
The deformation is for orienting the molecules, and the oriented molecules are rapidly cooled to a temperature equal to or lower than the Tg of the resin, whereby the orientation is fixed, and the function as a retardation film can be exhibited.
[0028]
The retardation film according to claim 3 can be used as, for example, an elliptically polarizing film by laminating at least one of the retardation films and a polarizing film.
The retardation film is laminated with a polarizing film, a transparent electrode, a transparent substrate, and the like, and is used as various liquid crystal display devices.
[0029]
(Action)
The present invention provides a step (stretching in the width direction) of optimizing the thickness variation, thickness unevenness, and front retardation value of a film formed by a melt extrusion method, so that even if a retardation film is formed in the next step. It has been completed with the knowledge that birefringence can be expressed uniformly in the plane.
Therefore, in particular, it is a film obtained by stretching the thermoplastic polymer film obtained by the melt extrusion method in the width direction, and the thickness variation in the width direction is 1.45 μm or less, and the thickness unevenness is 0.2 μm / 5 mm or less. The retardation film obtained by uniaxially or biaxially stretching an optical film made of a norbornene resin having a front retardation value (Re = | nx−ny | · d) of 20 nm or less has uniform birefringence. Sex can be expressed.
[0030]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
(Examples 1 and 2 and Comparative Examples 1 to 3)
1) Preparation of raw material Commercially available Zeonoa # 1600 (manufactured by Nippon Zeon Co., Ltd.) as a thermoplastic saturated norbornene resin is melted at 230 ° C. by a melt extruder in which a T die is arranged in a single screw melt extruder. Extrusion molding was performed at a temperature to obtain a film having a width of 600 mm and an average thickness of 90 μm.
2) Measurement of Physical Properties The Tg of the resin was determined using DSC220C manufactured by Seiko Denshi Kogyo KK and found to be 161.0 ° C. Further, the thickness of the above film was measured at intervals of 1 mm in the width direction using a continuous thickness meter, and thickness variation and thickness unevenness were obtained.
Note that the variation means the difference between the maximum value and the minimum value in the measurement range, and the unevenness means the maximum value of the difference at arbitrary 5 mm intervals in the measurement range.
[0031]
3) Stretching in the width direction Using a tenter stretching machine, stretching was performed in the direction perpendicular to the extrusion direction (that is, in the width direction) (Examples 1 and 2 and Comparative Examples 1 and 2).
The stretching zone was divided into three in the longitudinal direction and divided into three zones of preheating, stretching, and cooling, and a stretching machine capable of independently controlling the temperature was used for each.
As for the set temperature, the stretching temperature was determined as shown in the table below, the preheating temperature was -10 ° C for the stretching temperature, and the cooling temperature was all 120 ° C. The stretching ratios were all 1.5 times and 2.5 times.
The thickness of the sample after stretching was measured at intervals of 1 mm using a continuous thickness gauge in the stretching direction, and thickness variations and unevenness were determined.
The front phase difference value was also measured using a birefringence meter “KOBRA-21ADH” manufactured by Oji Scientific Instruments.
[0032]
4) Production of Retardation Film The sample obtained by the above operation and an untreated raw material (Comparative Example 3) were subjected to longitudinal uniaxial stretching between rolls to express a retardation.
At that time, the stretching temperature was 165 ° C., and the stretching ratio was 1.5 times.
The retardation value (phase difference value) of the sample after stretching was measured at intervals of 1 mm in the width direction using a birefringence meter “KOBRA-21ADH” manufactured by Oji Scientific Instruments. The method for obtaining the variation and unevenness of the phase difference value was the same as that for the thickness.
Table 1 shows the evaluation results.
[0033]
[Table 1]

[0034]
Compared with Comparative Examples 1 to 3, particularly Comparative Example 3 (where the raw melt extruded material is stretched as it is to develop a retardation), it is apparent that the retardation unevenness and variation are significantly improved in the Examples. is there.
[0035]
【The invention's effect】
The optical film of the present invention is configured as described above, has almost no residual retardation, and has a uniform thickness. Therefore, the optical film is suitable as an optical film for various uses, and has high productivity and It is an optical film of high industrial value from the viewpoint of environmental load.
In particular, an optical film that does not substantially cause phase difference unevenness by uniaxial stretching or biaxial stretching or an optical film that does not substantially cause display unevenness in a plane when incorporated in a liquid crystal display device can be obtained. It is suitable as an optical film for producing a retardation film.
A retardation film obtained by actually uniaxially or biaxially stretching the optical film of the present invention, particularly a retardation film made of a norbornene-based resin, can surely exhibit the above-mentioned effects.

Claims (4)

A film obtained by stretching a thermoplastic polymer film obtained by a melt extrusion method in the width direction, wherein the thickness variation in the width direction is 1.45 μm or less, the thickness unevenness is 0.2 μm / 5 mm or less, and the front surface An optical film having a retardation value of 20 nm or less. A film obtained by stretching a thermoplastic polymer film obtained by a melt extrusion method in the width direction, wherein the thickness variation in the width direction is 1.45 μm or less, the thickness unevenness is 0.2 μm / 5 mm or less, and the front surface An optical film for producing a retardation film, wherein the retardation value is 20 nm or less. A retardation film obtained by uniaxially or biaxially stretching the optical film according to claim 1. The retardation film according to claim 3, wherein the thermoplastic polymer is a norbornene-based resin.