JP2005107099A - Method for manufacturing sequential biaxially stretched retardation film and uniaxially stretched cast film to be used for the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a retardation film which has little variance of the retardation and the optical axis in the plane direction of the film comprising polycarbonate, which has excellent display quality such as contrast in a wide viewing field range in the front and oblique viewing directions, and which can be directly stuck with a polarizing plate so that a liquid crystal display having uniform display in the plane without having speckles of leaked light in a black display screen can be formed. <P>SOLUTION: The method for manufacturing a retardation film includes: a step of preparing a cast film from polycarbonate by a solution casting method; a longitudinal stretching step to stretch the cast film in the casting direction; and a transverse stretching step to stretch the film in the direction orthogonal to the casting direction. The variance of the film thickness in the plane direction of the longitudinally (or transversely) uniaxially stretched cast film in the longitudinal (or transverse) stretching step is within 5 μm. The uniaxially stretched cast film containing a solvent by 0.1 to 1.0 wt.% in the film is stretched in a direction almost orthogonal to the first stretching direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a sequential biaxially stretched retardation film and a uniaxially stretched cast film used therefor. Specifically, a method for producing a biaxially stretched phase difference film that is excellent in retardation controllability and can be directly bonded to a polarizing plate suitable for improving the viewing angle and contrast of a liquid crystal display device, and the longitudinal direction used for the production thereof. The present invention relates to a uniaxially stretched film.

  While it is required to expand the viewing angle and improve the contrast of liquid crystal display devices, it is required to provide a retardation film capable of compensating for the phase difference due to birefringence of a liquid crystal panel that can realize the viewing angle. As a method for controlling the retardation of a conventional retardation film, Patent Document 1 discloses a stretching method by uniaxial or biaxial, a heat shrink film, and a stretch treatment under the action of the heat shrink force. There has been known a method for obtaining a phase difference film in which the phase difference is controlled.

  In particular, in order to enlarge the viewing angle of the vertical alignment mode liquid crystal display device, the refractive index in the slow axis direction of the retardation film is nx, the refractive index in the fast axis direction is ny, and the refractive index in the thickness direction is nz. In this case, a retardation film having characteristics satisfying the relationship of nx ≧ ny> nz is required, and in order to obtain these characteristics, production by a biaxial stretching method is suitable.

  However, in the conventional biaxial stretching method, in the polycarbonate having a large intrinsic birefringence, a retardation film having greatly different optical characteristics due to a slight control difference is obtained, and also in the in-plane characteristics, There is a problem that the compensation effect such as contrast is poor due to large variations in phase difference and optical axis.

Furthermore, the retardation film manufactured by the transverse stretching method manufactured conventionally has an angle between the film width direction and the slow axis deviated from 0 degree to 2 to 3 degrees, and is continuously bonded in a roll shape. You can't do it first. In such a case, it is necessary to punch out the retardation film and the polarizing plate at a predetermined angle and bond them by a batch method. However, the batch method has a problem that punching loss always occurs and the use efficiency of the film is very poor. In addition, the process is complicated because it is necessary to change the punching angle in accordance with the degree of shift of the slow axis, and there are many problems such that defects are likely to occur due to dust generated during punching.
JP-A-5-157911

  The main object of the present invention is that there is little variation in retardation and optical axis in the plane of a retardation film formed from polycarbonate, and it has excellent display quality such as contrast in a wide field of view in the front and perspective directions. Another object of the present invention is to provide a method for producing a retardation film that can be directly bonded to a polarizing plate capable of forming a liquid crystal display device that can obtain a uniform display in a plane that does not cause spotted light on a black display screen.

  In order to solve the above problems, the present inventors have intensively studied a method for producing a sequential biaxially stretched retardation film made of polycarbonate. Then, the polycarbonate is made into a cast film by a solution cast film forming method, the amount of solvent (residual solvent amount) of the uniaxially stretched cast film obtained by stretching the cast in the longitudinal (or transverse) direction, and the film thickness of the film It is extremely important to suppress variation, and a manufacturing method for obtaining a uniform sequential biaxially stretched retardation film in a plane by stretching the stretched film in a direction orthogonal to the stretching direction has been completed, and the present invention has been completed. It came to do.

That is, the present invention can be achieved by the following [1] to [4].
[1] A step of converting polycarbonate into a cast film by a solution cast film forming method, a longitudinal stretching step of stretching the cast film in the casting direction (hereinafter referred to as the longitudinal direction), and a direction orthogonal to the casting direction (hereinafter referred to as the lateral direction). ) In a longitudinal stretching process, and a longitudinal (or transverse) stretched uniaxially stretched cast film stretched in a longitudinal (or transverse) stretching process has an in-plane film thickness variation. Is 5 μm or less, and the uniaxially stretched cast film containing 0.1 to 1.0% by weight of the solvent in the uniaxially stretched cast film (hereinafter referred to as residual solvent amount) is substantially perpendicular to the stretching direction. A method for producing a sequentially biaxially stretched retardation film, characterized by stretching.

（上記式（Ｉ）において、Ｒ_１〜Ｒ_８はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜６の炭化水素基から選ばれる少なくとも１種の基であり、Ｘは下記式 [2] Polycarbonate is represented by the following formula (I)

(In the above formula (I), R _{1 to} R ₈ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 6 carbon atoms;

であり、Ｒ_９およびＲ_１０はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜３の炭化水素基から選ばれる少なくとも１種の基である）
で示される繰り返し単位aを３０〜７０ｍｏｌ％と、下記式（ＩＩ）

R ₉ and R ₁₀ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 3 carbon atoms)
30 to 70 mol% of the repeating unit a represented by the following formula (II)

（上記式（ＩＩ）において、Ｒ_１１〜Ｒ_１８はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜２２の炭化水素基から選ばれる少なくとも１種の基であり、Ｙは下記式群である。）

(In the above formula (II), R _{11 to} R ₁₈ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, and Y is the following group of formulas: .)

（ここでＲ₁₉〜Ｒ₂₁、Ｒ₂₃及びＲ₂₄はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜２２の炭化水素基から選ばれる少なくとも１種の基であり、Ｒ₂₂及びＲ₂₅は炭素数１〜２０の炭化水素基から選ばれる少なくとも１種の基であり、また、Ａｒ₁〜Ａｒ_３はそれぞれ独立に炭素数６〜１０のアリール基から選ばれる少なくとも１種の基である。）
で示される繰り返し単位ｂが全体の７０〜３０ｍｏｌ％を占めるポリカーボネート共重合体及び／またはブレンド体である［１］の位相差フィルム。

(Wherein R ₁₉ ~R _21, R ₂₃ and R ₂₄ are each independently a hydrogen atom, at least one group selected from a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, R ₂₂ and R ₂₅ It is at least one group selected from hydrocarbon groups having 1 to 20 carbon atoms, and Ar _{1 to} Ar ₃ are each independently at least one group selected from aryl groups having 6 to 10 carbon atoms. )
The retardation film of [1], which is a polycarbonate copolymer and / or a blend in which the repeating unit b represented by the formula occupies 70 to 30 mol% of the whole.

[3] A uniaxially stretched cast film for use in the method for producing a sequential biaxially stretched retardation film of [1] above, wherein the in-plane film thickness variation is 5 μm or less, and the in-plane retardation variation is 3 nm. A uniaxially stretched cast film comprising: 0.1 to 1.0% by weight of a residual solvent.

[4] A sequential biaxially stretched retardation film for laminating a roll-shaped sequential biaxially stretched phase difference film on a roll-shaped polarizing plate from the roll-shaped state. The axial stretch retardation film has an in-plane retardation (R value) R = 0 to 200 nm and a thickness direction retardation (K value) K = 0 to 500 nm, and a slow axis with respect to the film flow direction. A sequential biaxially stretched retardation film characterized by being in a substantially orthogonal direction.
(Here, given by _{R = Δn × d = (n} x -n y) × d, K = ((n x + n y) / 2-n z) × d. _However, n _{x, n} y, n _z, d is, n _x: the main stretching direction of the refractive index in the phase difference film plane, n _y: refractive index of the direction perpendicular to the main stretching direction in the retardation film plane, n _z: normal direction of the film surface Refractive index, d: film thickness)

  That is, according to the present invention, the residual solvent amount of the longitudinal (or lateral) stretched film obtained in the uniaxial stretching step in the middle of the sequential biaxial stretching step is set to a specific range, and the film thickness variation in the film plane is set to a specific value. By making the following, a liquid crystal display device with excellent display quality such as contrast in a wide field of view in the front and perspective directions is formed with little variation in retardation and optical axis in the successive biaxially stretched retardation film surface. Has been successfully developed. Moreover, since the sequential biaxially-stretched phase difference film of the present invention has the above-mentioned properties, even if it is in a roll shape, it can be bonded directly to the roll-shaped polarizing plate, that is, in a roll-shaped state. Therefore, productivity is dramatically improved.

  According to the present invention, it is possible to obtain a retardation film composed of a sequentially biaxially stretched film with little variation in retardation, film thickness and optical axis in the plane of the retardation film composed of polycarbonate. With this retardation film, it becomes possible to provide a liquid crystal display device that is excellent in display quality such as contrast in a wide visual field range in the front and perspective directions, and can contribute to an improvement in image quality in combination with a liquid crystal display device or the like. Has an effect.

[Polycarbonate]
The polycarbonate used in the present invention is a polyester of carbonic acid and glycol or dihydric phenol, and usually includes carbonic acid and 2,2′-bis (4-hydroxyphenyl) -propane (commonly called bisphenol-A) as structural units. However, the present invention is not limited to this. For example, 1,1-bis (4-hydroxyphenyl) -alkylcycloalkane, 1,1-bis (3-substituted- 4-hydroxyphenyl) -alkylcycloalkane, 1,1-bis (3,5-substituted-4-hydroxyphenyl) -alkylcycloalkane, selected from the group consisting of 9,9-bis (4-hydroxyphenyl) fluorenes Copolymer and homopolymer having at least one dihydric phenol as a monomer component -A mixture of these and a polycarbonate having bisphenol-A as a monomer component, and a polycarbonate copolymer having the above dihydric phenol and bisphenol-A as monomer components.

  Specific examples of 1,1-bis (4-hydroxyphenyl) -alkylcycloalkane include 1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,1-bis (4-hydroxyphenyl) ) -3,3-dimethyl-5,5-dimethylcyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3-dimethyl-5-methylcyclopentane and the like.

  1,1-bis (3-substituted-4-hydroxyphenyl) -alkylcycloalkane includes 1,1-bis (4-hydroxyphenyl) -alkyl substituted with an alkyl group having 1 to 12 carbon atoms or a halogen group. Cycloalkanes such as 1,1-bis (3-methyl-4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,1-bis (3-ethyl-4-hydroxyphenyl) -3,3- Dimethyl-5,5-dimethylcyclohexane, 1,1-bis (3-chloro-4-hydroxyphenyl) -3,3-dimethyl-4-methylcyclohexane, 1,1-bis (3-bromo-4-hydroxyphenyl) ) -3,3-dimethyl-5-methylcyclopentane.

  1,1-bis (3,5-substituted-4-hydroxyphenyl) -alkylcycloalkane includes 1,1-bis (4-hydroxyphenyl) substituted with an alkyl group having 1 to 12 carbon atoms or a halogen group. Alkylcycloalkanes such as 1,1-bis (3-methyl-4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,1-bis (3,5-dichloro-4-hydroxyphenyl)- 3,3-dimethyl-5-methylcyclohexane, 1,1-bis (3-ethyl-5-methyl-4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,1-bis (3,5- Dimethyl-4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,1-bis (3,5-dimethyl-4-hydroxyphenyl) -3,3-di Chill -5-methyl cyclopentane, and the like.

  Examples of 9,9-bis (4-hydroxyphenyl) fluorenes include 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (3-methyl-4-hydroxyphenyl) fluorene, Examples include 9-bis (3-ethyl-4-hydroxyphenyl) fluorene.

  Furthermore, as other bisphenol components, 2,2′-bis (4-hydroxyphenyl) propane (bisphenol-A), 4,4 ′-(α-methylbenzylidene) bisphenol, bis (4-hydroxyphenyl) methane, 2 , 2′-bis (4-hydroxyphenyl) butane, 3,3′-bis (4-hydroxyphenyl) pentane, 4,4′-bis (4-hydroxyphenyl) hebutane, 4,4′-bis (4- Hydroxyphenyl) 2,5-dimethylhebutane, bis (4-hydroxyphenyl) methylphenylmethane, bis (4-hydroxyphenyl) diphenylmethane, 2,2′-bis (4-hydroxyphenyl) octane, bis (4-hydroxy) Phenyl) octane, bis (4-hydroxyphenyl) 4-fluorophenylmethane, 2, '-Bis (3-fluoro-4-hydroxyphenyl) propane, bis (3,5-dimethyl-4hydroxyphenyl) methane, 2,2'-bis (3,5-dimethyl-4-hydroxyphenyl) propane, bis ( 3,5-dimethyl-4-hydroxyphenyl) phenylethane, bis (3-methyl-4-hydroxyphenyl) diphenylmethane and the like can be mentioned, and these can be used alone or in combination of two or more.

  In addition to the bisphenol component, the polycarbonate contains a polyester carbonate using a small amount of aliphatic or aromatic dicarboxylic acid as a comonomer of the acid component. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, p-xylene glycol, bis (4-hydroxyphenyl) -methane, 1,1′-bis (4-hydroxyphenyl) -ethane, and 1,1′-. Bis (4-hydroxyphenyl) -butane, 2,2′-bis (4-hydroxyphenyl) -butane and the like can be mentioned. Of these, terephthalic acid and isophthalic acid are preferred.

  The molecular weight of the polycarbonate used is preferably one having a viscosity average molecular weight of 2,000 to 100,000, 0.19 or more expressed in terms of specific viscosity measured at 20 ° C. in a methylene chloride solution having a concentration of 0.7 g / dl, Preferably, it is 0.26-0.45. If it is less than 0.19, the resulting film becomes brittle, so it is not suitable.

で表される繰り返し単位及び
及び下記式（ＩＩ） As the polycarbonate used in the present invention, in particular, the following formula (I)

And a repeating unit represented by the following formula (II)

で表される繰り返し単位からなるポリカーボネートが好ましい。このポリカーボネートは共重合体であっても混合物であってもよい。

Polycarbonate consisting of repeating units represented by This polycarbonate may be a copolymer or a mixture.

In the above formula (I), R _{1 to} R ₈ are each independently at least one group selected from a hydrogen atom, a halogen atom, and a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group include alkyl groups such as a methyl group and an ethyl group, and aryl groups such as a phenyl group. X is the following formula

であり、Ｒ_９およびＲ_１０はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜３の炭化水素基から選ばれる少なくとも１種の基である。かかる炭化水素基としては、メチル基、エチル基等のアルキル基、フェニル基等のアリール基が挙げられる。

R ₉ and R ₁₀ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 3 carbon atoms. Examples of the hydrocarbon group include alkyl groups such as a methyl group and an ethyl group, and aryl groups such as a phenyl group.

In the above formula (II), R _{11 to} R ₁₈ are each independently at least one group selected from a hydrogen atom, a halogen atom, and a hydrocarbon group having 1 to 22 carbon atoms. Examples of the hydrocarbon group include alkyl groups such as a methyl group and an ethyl group, and aryl groups such as a phenyl group. Y is the following formula group

から選ばれる少なくとも１種の基である。ここでＲ₁₉〜Ｒ₂₁、Ｒ₂₃及びＲ₂₄はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜２２の炭化水素基から選ばれる少なくとも１種の基であり、Ｒ₂₂及びＲ₂₅は炭素数１〜２０の炭化水素基から選ばれる少なくとも１種の基である。炭素数１〜２２の炭化水素基及び炭素数１〜２０の炭化水素基としては、例えば、メチル基、エチル基等のアルキル基、フェニル基等のアリール基が挙げられる。

At least one group selected from the group consisting of Here, R _{19 to} R ₂₁ , R ₂₃ and R ₂₄ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, and R ₂₂ and R ₂₅ are carbon atoms. It is at least one group selected from the hydrocarbon groups of number 1-20. Examples of the hydrocarbon group having 1 to 22 carbon atoms and the hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as a methyl group and an ethyl group, and aryl groups such as a phenyl group.

Ar _{1 to} Ar ₃ are each independently at least one group selected from aryl groups having 6 to 10 carbon atoms. Examples of the aryl group include a phenyl group and a naphthyl group.

  In the polycarbonate composed of the repeating units represented by the above formulas (I) and (II), the content of (I) is preferably 30 to 70 mol% of the entire repeating units. In this polycarbonate, when the content of (I) is less than 30 mol% of the whole, it is difficult to obtain an in-plane retardation film because the birefringence of the polymer film is large. On the other hand, when the content of (I) exceeds 70 mol%, the film is easily broken and becomes brittle, and is not suitable as a retardation film. More effectively, the content of (I) is preferably 40 to 60 mol%.

  Among these, bisphenol-A is preferably used in the above formula (II), and a polycarbonate copolymer composed of bisphenol-A and 9,9-bis (4-hydroxyphenyl) fluorene is heat resistant, dimensional stability, Excellent in transparency.

[Production method of polymer film]
The manufacturing method of the retardation film of this invention is demonstrated. The production of the retardation film includes a step of producing a cast film of polycarbonate by a solution cast film forming method, a step of stretching in a casting direction (hereinafter referred to as a longitudinal direction) (longitudinal stretching step), and a direction orthogonal to the casting direction ( Hereinafter, a step of stretching in the lateral direction (transverse stretching step) is included. The solution cast film forming method is excellent in optical characteristics and film thickness accuracy required for a retardation film.

  As a solvent used in the solution cast film forming method, any solvent can be used without limitation as long as it can sufficiently dissolve polycarbonate and form a cast film. For example, methylene chloride, dioxolane and the like are preferably used.

The solution in which the polycarbonate is dissolved is cast on a support to form a film-like cast film. The cast film after this cast film formation is dried by heating or the like, and a cast film containing a solvent (unstretched) is obtained. Although there is no restriction | limiting in the thickness of this film, 20-300 micrometers is preferable from the handling surface of a film and a cost surface, More preferably, it is 30-200 micrometers.
The casting speed of the solution cast is preferably 1 to 30 m / min.

  The present invention is a production in which a uniaxially stretched cast film is drawn by stretching in the longitudinal (or transverse) direction, and then this uniaxially stretched cast film is stretched in a direction perpendicular to the stretched direction to successively produce a biaxially stretched cast film. Is the method. At this time, the variation of the in-plane film thickness of the uniaxially stretched cast film used for two-stage stretching is 5 μm or less, and the amount of residual solvent is controlled to include 0.1 to 1.0% by weight. is important. This residual solvent amount is controlled by appropriately adjusting the drying conditions such as the temperature of the atmosphere and the air volume during film formation.

  The in-plane film thickness variation (difference between the maximum film thickness and the minimum film thickness) is preferably small, and the film thickness variation is 5 μm or less, preferably 4 μm or less, and more preferably 3 μm or less. If the film thickness variation after longitudinal uniaxial stretching exceeds 5 μm, the phase difference is a value calculated by the product of birefringence and film thickness. It becomes difficult to obtain a uniform retardation film.

  The amount of residual solvent in the film is 0.1 to 1.0% by weight, preferably 0.2 to 0.9% by weight, more preferably 0.3 to 0.8% by weight. When the residual solvent amount exceeds 1.0% by weight, the orientation of the polymer chain of the polycarbonate is not sufficiently caused in foaming or stretching, and it becomes difficult to obtain a desired retardation value. On the other hand, if the amount of residual solvent in the film is less than 0.1% by weight, in the stretching process, the film is strongly affected by the heat distribution in the film surface. Therefore, it is difficult to obtain an in-plane retardation film.

  As the stretching method, any known method may be used. For example, methods such as a tenter stretching method and an inter-roll compression stretching method are exemplified. In view of controllability of the refractive index in the thickness direction and uniformity of in-plane retardation of the film, a method of stretching uniaxially by an inter-roll stretching method or a tenter stretching method is preferable.

The stretching temperature varies depending on the polymer structure to be used, but is usually 140 to 280 ° C, preferably 160 to 260 ° C, and particularly preferably 180 to 240 ° C.
The draw ratio is 1.1 to 5.0 times, preferably 1.5 to 4.0 times, and particularly preferably 2.0 to 3.0 times in both the longitudinal direction and the transverse direction.

  In such a film, for the purpose of improving stretchability, phthalate esters such as dimethyl phthalate and dibutyl phthalate which are known plasticizers, phosphate esters such as tributyl phosphate, aliphatic dibasic esters, glycerin derivatives, It may contain a glycol derivative or the like, but is not limited thereto. The organic solvent used at the time of film formation may remain in the film and stretched. The organic solvent is preferably 1 to 25% by weight based on the polymer solid content.

[Phase difference film]
The retardation compensation performance of the retardation film is represented by a so-called retardation value, and is particularly divided into in-plane retardation (R value) and thickness direction retardation (K value). These Re value and K value are defined by the following formulas (a) and (b), respectively.
(A) R = Δn × d = (n x -n y) × d
(B) K = (( _nx + _ny ) / 2- _nz ) * d
However, _nx , _ny , _nz , d is as follows.
_nx : refractive index in the main stretching direction in the film plane _ny : refractive index in the direction perpendicular to the main stretching direction in the film plane _nz : refractive index in the normal direction of the film surface d: film thickness (main The stretching direction means a stretching direction in the case of uniaxial stretching, and a direction in which the degree of orientation increases in the case of biaxial stretching, and indicates the orientation direction of the polymer main chain in terms of chemical structure. )

  In the retardation film obtained by the present invention, the fluctuation in an arbitrary direction along the film surface of the in-plane retardation measured at the wavelength of 550 nm is in any direction with respect to the average value of the R value in each direction. And within a range within ± 5 nm, and any fluctuation along the film surface of the retardation in the thickness direction is within ± 10 nm with respect to the average value of the K values in each direction in any direction. It is more preferable that the fluctuation of the R value is within ± 4 nm with respect to the average value, and the fluctuation of the R value is within ± 8 nm with respect to the average value. Within ± 6 nm with respect to the average value of K values. In order to perform optical compensation uniformly in the display screen of a liquid crystal display device or the like, it is necessary that the change in the optical characteristics of the retardation film is small in any direction along the film surface. For this reason, when the fluctuation of the R value and the fluctuation of the K value in the film plane are ± 5 nm or more with respect to the average value of the R value and 10 nm or more with respect to the average value of the K value, Display uniformity cannot be achieved.

  Further, the variation in the plane of the slow axis in the plane of the retardation film represents the difference between the maximum value and the minimum value in the slow axis direction. In the present invention, the variation in the slow axis is within 1.5 degrees. Preferably, it is within 1.3 degrees, more preferably within 1.0 degree. The variation of the slow axis is preferably in the above range over the entire width in the film width direction. This variation in the slow axis also greatly affects the display uniformity of a liquid crystal display device or the like using the retardation film of the present invention. For this reason, when the variation in the plane of the slow axis is 1.5 degrees or more, a uniform black display cannot be obtained in the plane in a liquid crystal display device or the like. Moreover, it is also extremely difficult to continuously bond such a retardation film in a roll shape. This is because, when the angle difference between the transmission axis of the polarizing plate and the slow axis of the retardation film when bonded is greater than 1.5 degrees, the effect of the phase difference becomes large, and light leakage occurs. This is because a black display contrast cannot be obtained in a liquid crystal display device or the like. In order to enable continuous bonding, it is important to provide a method for producing a roll-shaped retardation film with high uniformity in which the angle between the width direction of the retardation film and the slow axis is controlled. is there. For this reason, the slow axis of the retardation film is in the width direction perpendicular to the longitudinal direction of the retardation film, and the range of the deviation is preferably within 1.5 degrees. It is more preferably within 1.3 degrees, and further preferably within 1.0 degrees.

  The retardation film of the present invention thus obtained is an optical biaxial film, and the R value is preferably 0 to 200 nm, more preferably 0 to 150 nm, and further preferably 0 to 100 nm. And K value is preferably 0 to 500 nm, more preferably 0 to 400 nm, and further preferably 0 to 300 nm. When the R value and K value are outside the above ranges, a sufficient optical compensation effect by a display retardation film such as a liquid crystal display device cannot be obtained, and it is difficult to maintain high contrast and display quality in a perspective direction. .

  In the present specification, polycarbonate has been described as a material polymer for forming a retardation film, but as such a material polymer, a material conventionally used as a retardation film, for example, polyarylate, polyolefin, cellulosic polymer, etc. It can be obtained in a similar way.

  In the retardation film used in the present invention, an optical compensation effect can be obtained by using at least one sheet of a display medium such as a liquid crystal display device, but two or more sheets may be used simultaneously. .

  Further, in the retardation film of the present invention, a polymer modifier such as a heat stabilizer, an antioxidant, an ultraviolet absorber, a light stabilizer, a transparent nucleating agent, a permanent antistatic agent, and a fluorescent brightening agent is simultaneously contained in the film. May be present.

The retardation film obtained by the present invention has good transparency, preferably a haze value of 5% or less and a total light transmittance of 85% or more. The glass transition temperature is preferably 90 ° C. or higher.
The thickness of the retardation film in the present invention is 30 to 120 μm.

[Use of retardation film]
The retardation film obtained by the present invention is excellent in display quality such as contrast by compensating for the phase difference due to the liquid crystal cell in a wide viewing angle range of the front and perspective, and causes spots on the black display screen. A liquid crystal display device capable of obtaining a uniform display within the plane, and particularly in the front orientation of TFT liquid crystal display devices such as twisted nematic mode, vertical alignment mode, optical compensation bend mode, and in-plane switching mode. Highly compensated for phase difference to achieve high contrast and display uniformity, and highly compensated for phase difference in the perspective direction to improve display quality. Suitable for mode optical compensation. In practical use, for example, an adhesive material provided on one or both sides of a retardation film, a polarizing plate, or a protective layer made of an isotropic transparent resin layer or glass layer is bonded via the adhesive material. It can be applied as an optical member of an appropriate form such as a laminated one, and if it is a liquid crystal display device, a transmission type or a reflection type using a backlight, a reflection plate or a semi-transmission type reflection plate in an illumination system, or A transflective type or the like can be formed. Examples of display devices using other retardation films include liquid crystal projectors, ferroelectric liquid crystals, those using antiferroelectric liquid crystals, and optical heads of optical recording devices. Films may be used for them.

Moreover, you may use as a touch panel and may be used for CRT and PDP.
Furthermore, it may be used as a protective layer or a protective plate with improved resistance to wet heat by coating some material on the retardation film, or with improved solvent resistance, or by surface treatment to produce a diffusion plate or anti-glare. It may be used as a layer or an antireflection film.

  The retardation film obtained in the present invention is like another retardation film or a viewing angle widening film (for example, a viewing angle widening film in which a discotic liquid crystal or a polymer liquid crystal layer is oriented in the film thickness direction). The optical compensation film may be used at the same time, or may be used as an optical compensation film by providing an optically anisotropic layer made of liquid crystalline molecules directly on the retardation film surface of the present invention.

  The retardation film can achieve an optical compensation effect by using at least one retardation film for a display medium such as a liquid crystal display device. However, two or more of the retardation films can be used simultaneously. Also good.

The material characteristic values and the like described in the present specification are obtained by the following evaluation methods.
(1) Measurement of slow axis, R value and K value Slow axis, phase difference R value which is the product of birefringence Δn and film thickness d, and phase difference K value perpendicular to the in-plane direction are measured by prince. It is measured by a trade name “KOBRA21-ADH” manufactured by Device Company. R values are measured when the surface of the incident light and the film is _{vertical, R = Δn · d = (} n x -n y) · d, K = ((n x + n y) / 2-n z) D. The unit of R value and K value is nm. _{n x,} n y, n _z is defined herein as follows.
n _x : Refractive index in the main stretching direction in the film plane n _y : Refractive index in the direction orthogonal to the main stretching direction in the film plane n _z : Refractive index in the normal direction of the film surface (the main stretching direction is uniaxial stretching) In the case of (2), it means the stretching direction, and in the case of biaxial stretching, it means the direction of stretching so as to increase the degree of orientation, and in terms of chemical structure, it refers to the orientation direction of the polymer main chain.)
The R value and the K value were obtained by sampling the retardation film at 10 points or more at a 5 cm pitch in the width direction, and calculating an average value. The deviation of the value from the average value was defined as a change in R value and K value.

(2) Measurement of polymer copolymerization ratio Measurement was performed by proton NMR of a trade name “JNM-alpha600” manufactured by JEOL Ltd. In particular, in the case of a copolymer of bisphenol A and biscresol fluorene, heavy benzene was used as a solvent, and calculation was performed from the proton intensity ratio of each methyl group.

(3) Measurement of film thickness variation An arbitrary portion of the retardation film obtained by stretching is cut out with an A4 cut size, and an in-plane thickness of the film is an electronic micro film thickness meter manufactured by Anritsu at a pitch of 5 mm. It measured with "Film Thickness Tester KG601A". The difference between the maximum value and the minimum value of the film thickness at that time was defined as the film thickness variation.

(4) Measurement of amount of residual solvent The retardation film was sampled at 3 points in a size of 4 cm square, and dried at a temperature 10 degrees lower than the glass transition temperature for 5 hours. The weight before and after drying was measured, and all the weight changes were regarded as the residual solvent contained in the retardation film.

(5) Polymerization method of polymer and copolymer polymer The monomer structures of the polycarbonates used in Examples and Comparative Examples are shown below.

  A reactor equipped with a stirrer, a thermometer and a reflux condenser was charged with an aqueous sodium hydroxide solution and ion-exchanged water, and the monomers [A] and [B] having the above structure were added to this with X: Y (mol%, X + Y = 100). ) And dissolved in a small amount of hydrosulfide. Next, methylene chloride was added thereto, and phosgene was blown in at about 20 ° C. over about 60 minutes. Further, p-tert-butylphenol was added for emulsification, triethylamine was added, and the mixture was stirred at 30 ° C. for about 3 hours to complete the reaction. After completion of the reaction, the organic phase is collected, and methylene chloride is evaporated to obtain a polycarbonate copolymer. The composition ratio of the obtained copolymer was almost equal to the monomer charge.

(6) Evaluation Criteria Evaluation criteria for retardation films obtained by sequential biaxial stretching are as follows. Here, the notation by ○ indicates that the in-plane uniformity of the retardation film is good, and x indicates that the characteristics are poor.
Variation of in-plane retardation R: ○ R ≦ 5nm
× R> 5nm
Variation in thickness direction retardation K: ○ K ≦ 10 nm
: × K> 10 nm
Shaft variation: ○ Difference between maximum and minimum values of slow axis ≤ 1.5 degrees
× Difference between maximum and minimum values of slow axis> 1.5 degree display uniformity: Display uniformity when retardation film is mounted on LCD monitor
◎ Extremely high display quality
○ Uniform display and good characteristics
× The display is uneven and the characteristics are poor. Uniformity of the black display: The monitor lights up in black in a dark room environment, and the brightness within the monitor
Observing spots visually
◎ Brightness is not observed in black display, and display quality is extremely high
○ There is almost no luminance unevenness in black display, and the display is uniform on the monitor surface.
× There are multiple brightness spots on the black display, and the black display is not uniform on the monitor surface.

[Example 1]
A polycarbonate copolymer obtained by copolymerizing the monomers [A] and [B] at a ratio of 50:50 (mol%) was used. This polycarbonate copolymer was dissolved in methylene chloride to prepare an 18 wt% dope solution. This dope solution was cast on a steel drum, which was continuously peeled off and dried, and this was uniaxially stretched at 200 degrees and 1.8 times in the longitudinal direction using a roll stretching machine. The obtained uniaxially stretched film had a maximum film thickness of 115 μm and a minimum value of 112 μm, and a variation in film thickness (maximum value of film thickness−minimum value) was 3 μm. The residual solvent amount was 0.8% by weight. This retardation film was subjected to a transverse stretching process 2.4 times in the transverse direction at 224 ° C. with a tenter. The retardation film obtained by this sequential biaxial stretching has a retardation variation of R = 47 ± 2 nm, K = 218 ± 5 nm, the slow axis is perpendicular to the casting direction, and the slow axis The variation was 0.7 degrees. This retardation film was directly bonded with a roll-shaped polarizing plate and rolls to obtain a retardation film of a polarizing plate bonded body. When this retardation film was mounted on a liquid crystal monitor and the uniformity of the display screen was confirmed, it was confirmed that it had good contrast and a wide viewing angle in the surface, and the display quality was extremely high. Also, good in-plane uniformity was shown. Furthermore, when the uniformity of the black display screen was confirmed with this monitor in a dark room environment, no luminance spots were seen, and the display was extremely uniform in the plane.

[Example 2]
A polycarbonate copolymer obtained by copolymerizing the monomers [A] and [B] at a ratio of 50:50 (mol%) was used. This polycarbonate copolymer was dissolved in methylene chloride to prepare an 18 wt% dope solution. This dope solution was cast on a steel drum, which was continuously peeled off and dried, and this was uniaxially stretched at 200 degrees and 1.8 times in the longitudinal direction using a roll stretching machine. The resulting uniaxially stretched film had a maximum film thickness of 108 μm and a minimum value of 103 μm, and a variation in film thickness (maximum value of film thickness−minimum value) was 5 μm. The residual solvent amount was 1.0% by weight. This retardation film was subjected to a transverse stretching process 2.4 times in the transverse direction at 222 ° C. with a tenter. The retardation film obtained by this sequential biaxial stretching has a retardation variation of R = 40 ± 5 nm, K = 215 ± 9 nm, the slow axis is perpendicular to the casting direction, and the slow axis The variation was 0.8 degrees. This retardation film was directly bonded with a roll-shaped polarizing plate and rolls to obtain a retardation film of a polarizing plate bonded body. When this retardation film was mounted on a liquid crystal monitor and the uniformity of the display screen was confirmed, it had good contrast and a wide viewing angle in the plane, and also showed good in-plane uniformity. It was. Furthermore, when the uniformity of the black display screen was confirmed with this monitor in a dark room environment, no luminance spots were seen and the display was in-plane uniform display.

[Comparative Example 1]
A polycarbonate copolymer obtained by copolymerizing the monomers [A] and [B] at a ratio of 50:50 (mol%) was used. This polycarbonate copolymer was dissolved in methylene chloride to prepare an 18 wt% dope solution. This dope solution was cast on a steel drum, which was continuously peeled off and dried, and this was uniaxially stretched at 200 degrees and 1.8 times in the longitudinal direction using a roll stretching machine. The obtained uniaxially stretched film had a maximum film thickness of 116 μm and a minimum value of 110 μm, and a variation in film thickness (maximum value of film thickness−minimum value) was 6 μm. The residual solvent amount was 0.8% by weight. This retardation film was subjected to a transverse stretching process 2.4 times in the transverse direction at 224 ° C. with a tenter. The retardation film obtained by this sequential biaxial stretching has a retardation variation of R = 56 ± 9 nm, K = 215 ± 8 nm, and the slow axis is perpendicular to the casting direction. The variation was 1.7 degrees. This retardation film was directly bonded with a roll-shaped polarizing plate and rolls to obtain a retardation film of a polarizing plate bonded body. When this retardation film was mounted on a liquid crystal monitor and the display screen was confirmed, it was found that portions with different display characteristics were generated in the plane, and uniformity could not be ensured. Furthermore, when the uniformity of the black display screen was confirmed with this monitor in a dark room environment, luminance spots were confirmed and it was found that the black display was not uniform.

[Comparative Example 2]
A polycarbonate copolymer obtained by copolymerizing the monomers [A] and [B] at a ratio of 50:50 (mol%) was used. This polycarbonate copolymer was dissolved in methylene chloride to prepare an 18 wt% dope solution. This dope solution was cast on a steel drum, which was continuously peeled off and dried, and this was uniaxially stretched at 200 degrees and 1.8 times in the longitudinal direction using a roll stretching machine. The obtained uniaxially stretched film had a maximum film thickness of 112 μm and a minimum value of 108 μm, and a variation in film thickness (maximum value of film thickness−minimum value) was 4 μm. The residual solvent amount was 1.5% by weight. This retardation film was subjected to a transverse stretching process 2.4 times in the transverse direction at 215 ° C. with a tenter. The retardation film obtained by this sequential biaxial stretching has a retardation variation of R = 49 ± 7 nm, K = 204 ± 14 nm, the slow axis is perpendicular to the casting direction, and the slow axis The variation was 2.4 degrees. This retardation film was directly bonded with a roll-shaped polarizing plate and rolls to obtain a retardation film of a polarizing plate bonded body. When this retardation film was mounted on a liquid crystal monitor and the display screen was confirmed, it was found that portions with different display characteristics were generated in the plane, and uniformity could not be ensured. Furthermore, when the uniformity of the black display screen was confirmed with this monitor in a dark room environment, luminance spots were confirmed and it was found that the black display was not uniform.

[Comparative Example 3]
A polycarbonate copolymer obtained by copolymerizing the monomers [A] and [B] at a ratio of 50:50 (mol%) was used. This polycarbonate copolymer was dissolved in methylene chloride to prepare an 18 wt% dope solution. This dope solution was cast on a steel drum, which was continuously peeled off and dried, and this was uniaxially stretched at 200 degrees and 1.8 times in the longitudinal direction using a roll stretching machine. The resulting uniaxially stretched film had a maximum film thickness of 121 μm and a minimum value of 114 μm, and a variation in film thickness (maximum value of film thickness−minimum value) was 7 μm. The residual solvent amount was 1.2% by weight. This retardation film was subjected to a transverse stretching process of 2.4 times in the transverse direction at 217 ° C. with a tenter. The retardation film obtained by this sequential biaxial stretching has a retardation variation of R = 47 ± 8 nm, K = 213 ± 12 nm, the slow axis is perpendicular to the casting direction, and the slow axis The variation was 2.6 degrees. This retardation film was directly bonded with a roll-shaped polarizing plate and rolls to obtain a retardation film of a polarizing plate bonded body. When this retardation film was mounted on a liquid crystal monitor and the display screen was confirmed, it was found that portions with different display characteristics were generated in the plane, and uniformity could not be ensured. Furthermore, when the uniformity of the black display screen was confirmed with this monitor in a dark room environment, luminance spots were confirmed and it was found that the black display was not uniform.
The results of Examples 1 and 2 and Comparative Examples 1 to 3 are summarized in the table below.

Claims (4)

  Stretching the polycarbonate into a cast film by a solution casting method, a longitudinal stretching process of stretching the cast film in the casting direction (hereinafter referred to as the longitudinal direction), and stretching in a direction orthogonal to the casting direction (hereinafter referred to as the lateral direction) The method of producing a retardation film having a transverse stretching step, wherein the in-plane film thickness variation in the longitudinal (or transverse) stretched uniaxially stretched cast film stretched in the longitudinal (or transverse) stretching step is 5 μm or less. And stretching the uniaxially stretched cast film containing 0.1 to 1.0% by weight of the solvent amount (hereinafter referred to as residual solvent amount) in the uniaxially stretched cast film in a direction substantially perpendicular to the stretching direction. A method for producing a sequential biaxially stretched phase difference film. Polycarbonate is represented by the following formula (I)

(In the above formula (I), R _{1 to} R ₈ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 6 carbon atoms;

R ₉ and R ₁₀ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 3 carbon atoms)
30 to 70 mol% of the repeating unit a represented by the following formula (II)

(In the above formula (II), R _{11 to} R ₁₈ are each independently at least one group selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, and Y is the following group of formulas: .)

(Wherein R ₁₉ ~R _21, R ₂₃ and R ₂₄ are each independently a hydrogen atom, at least one group selected from a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, R ₂₂ and R ₂₅ It is at least one group selected from hydrocarbon groups having 1 to 20 carbon atoms, and Ar _{1 to} Ar ₃ are each independently at least one group selected from aryl groups having 6 to 10 carbon atoms. )
The retardation film according to claim 1, wherein the repeating unit b represented by the formula (1) is a polycarbonate copolymer and / or a blend that accounts for 70 to 30 mol% of the whole.   A uniaxially stretched cast film for use in the method for producing a sequential biaxially stretched phase difference film according to claim 1, wherein an in-plane film thickness variation is 5 μm or less, and an in-plane retardation variation is 3 nm or less. A uniaxially stretched cast film comprising 0.1 to 1.0% by weight of a residual solvent. A roll-shaped sequential biaxially stretched retardation film for laminating a roll-shaped sequential biaxially stretched phase difference film from the roll-shaped state to each other. The retardation film has in-plane retardation (R value) R = 0 to 200 nm and thickness direction retardation (K value) K = 0 to 500 nm, and the slow axis is substantially perpendicular to the film flow direction. A sequential biaxially stretched retardation film, characterized in that
(Here, given by _{R = Δn × d = (n} x -n y) × d, K = ((n x + n y) / 2-n z) × d. _However, n _{x, n} y, n _z, d is, n _x: the main stretching direction of the refractive index in the phase difference film plane, n _y: refractive index of the direction perpendicular to the main stretching direction in the retardation film plane, n _z: normal direction of the film surface Refractive index, d: film thickness)