JP2010139661A - Method for manufacturing polarizing plate, the polarizing plate, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing plate having a high level of viewing angle compensation capability, in which light leakage as seen obliquely, has been improved, and which can be manufactured at low cost, and to provide a polarizing plate obtained by the manufacturing method. <P>SOLUTION: The method for manufacturing a polarizing plate includes a process for manufacturing a polarizing plate protection film A and a sticking process for sticking the polarizing plate protection film A to one surface of a polarizer. The process for manufacturing a polarizing plate protection film A includes a process for causing molten materials of a composition, containing negative birefringence resin, to pass between a first sandwiching and pressing surface and a second sandwiching and pressing surface that constitute a sandwiching and pressing device and forming them into a belt-like film shape; and a process for making the moving speed of the first sandwiching and pressing surface faster than the moving speed of the second sandwiching and pressing surface. The sticking process comprises a process for sticking the polarizing plate protective film A and the belt-like polarizer by overlapping them, such that the longitudinal direction of belt-like film is mutually aligned. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polarizing plate. The present invention also relates to a polarizing plate and a liquid crystal display device.

  In recent years, various films have been developed with the rise of the liquid crystal display market. For example, Patent Documents 1 to 3 disclose tilted retardation films. In a method for producing a polarizing plate using such a retardation film for a liquid crystal display device as a polarizing plate protective film, the obtained film and the polarizer are overlapped with each other in the longitudinal direction of each belt-like film. Bonding together (hereinafter, also referred to as “roll-to-roll”, “roll-to-roll”) is required to reduce manufacturing costs. In addition, a polarizing plate for a liquid crystal display device is also required to have a wide viewing angle without light leakage of the polarizing plate when viewed obliquely.

  For such a problem, for example, Patent Document 1 discloses that a positive birefringent resin film obtained by solution casting is passed between two rolls having different peripheral speeds, whereby a shear force is applied to the film. And a method for producing a film having an inclined optical axis is described. In this document, the obtained film is further stretched in the film width direction (hereinafter also referred to as TD direction or transverse direction), so that the slow axis is the TD direction and the tilt direction is the film longitudinal direction (hereinafter referred to as MD). Is also referred to as a direction or a longitudinal direction). However, in the method of applying shear stress to the positive birefringent resin film described in the document, it is difficult to manage the peripheral speed difference between the two rolls and maintain the peripheral speed difference accuracy, There was a limit to the magnitude of the shearing force that could be applied, and there was a limit to the range of temperature applied in the stretching process. Therefore, the obtained film has problems such as insufficient stability over time of the inclined structure. Furthermore, since the film manufactured by the method described in Patent Document 1 has large variations in retardation and tilt direction, it was used as a polarizing plate protective film, and a polarizing plate was manufactured by directly bonding to a polarizer with a roll-to-roll. In this case, the liquid crystal display device incorporating the obtained polarizing plate has a problem of deteriorating display quality. Further, this document did not suggest that a film forming method for applying a shear stress to the melt was applied.

On the other hand, an example in which a film forming method for applying a shear stress is applied to a melt is known. For example, in Patent Documents 2 to 4, an elastic roll having a low hardness (for example, a rubber roll whose surface is coated with a metal described in Patent Document 2) and a metal roll having different peripheral speeds are used. A film forming method for sandwiching a melt and applying a shearing force to the melt is disclosed.
However, when a film produced by the method described in these documents is used as a polarizing plate protective film and a polarizing plate is produced by laminating with a polarizer directly with a roll-to-roll, the obtained polarizing plate is viewed from an oblique direction. There is a problem that light leaks sometimes, and a liquid crystal display device incorporating the polarizing plate also has a problem that a viewing angle is narrow.
Furthermore, the film manufactured by the method described in Patent Documents 2 and 3 has not solved the problem that the inclined structure is still small. For example, Patent Document 3 discloses a very small film having an optical axis inclination of ± 0.3 degrees. Patent Document 4 discloses an optical film having an optical axis inclined by 11.5 to 18.2 ° in the embodiment, but does not describe any relationship between the optical axis inclination angle and the optical compensation of the liquid crystal display. . Patent Document 4 discloses that a positive birefringent resin film is formed by applying shear stress to a melt and then stretched in the longitudinal direction. Since the slow axis and the tilt direction cannot be orthogonal, it is difficult to realize a wide viewing angle. Furthermore, when a shearing stress is applied by applying pressure using a metal roll and an elastic roll having low hardness, a film having a large inclined structure could not be obtained no matter how the production conditions were changed. Therefore, in order to actually perform optical compensation for transmissive TN, ECB, and OCB liquid crystal displays, the tilt structure is large, and the slow axis and tilt orientation that can compensate both the polarizing plate compensation function and the viewing angle of the liquid crystal cell. There has been a demand for a polarizing plate having a retardation film in which the two are orthogonal to each other.

In this way, using a retardation film having a large inclined structure as a polarizing plate protective film, the polarizing plate protective film and the polarizer are overlapped with each other in the longitudinal direction of each band-shaped film, and bonded together to form a polarizing plate. In the case of manufacturing a polarizing plate, a method for manufacturing a polarizing plate having a large viewing angle compensation ability and an improved light leakage when viewed from an oblique direction at a low cost has not been known.
JP-A-6-222213 JP 2003-25414 A JP 2007-237495 A JP 2007-38646 A

  The present invention has been made in view of the above circumstances, and the first object of the present invention is a low manufacturing cost, a large viewing angle compensation capability of a liquid crystal display device, and improved light leakage when viewed from an oblique direction. Another object of the present invention is to provide a method for producing a polarizing plate and a polarizing plate obtained by the production method. A second object of the present invention is to provide a liquid crystal display device using the polarizing plate.

Therefore, in order to solve the above-mentioned problems, the present inventor has made a series of studies on a method for producing a polarizing plate. In the process, attention was paid to the optical characteristics of the polarizing plate protective film used for the polarizing plate. In the liquid crystal display device, it was considered that the slow axis and the tilt direction of the polarizing plate protective film to be used need to be orthogonal in order to improve the light leakage at the time of black display from a wide viewing angle and an oblique direction. In the present invention, the use of a negative birefringent resin was studied. Surprisingly, the tilt structure is large, the slow axis faces the film width direction, and the tilt direction faces the film transport direction. It turns out that can be obtained. In addition, when the film and the polarizer are overlapped with each other in the longitudinal direction of each band-shaped film and the bonded polarizing plate is incorporated into a liquid crystal display device, the viewing angle can be greatly widened and viewed from an oblique direction. It was found that light leakage at the time was improved. Conventionally, a film having such characteristics has not been known, and the film having such characteristics and a polarizer are overlapped with each other so that the longitudinal directions of the respective band-shaped films coincide with each other (to be bonded) There has been no suggestion or disclosure of a method for producing a polarizing plate including a step of laminating by roll-to-roll. For example, in order to improve a film obtained by a conventionally known method for producing a film and to make the slow axis and the tilt direction orthogonal to each other, a process of transverse stretching using an expensive transverse stretching apparatus (for example, a tenter) It is expected that it could not be manufactured without passing through. Therefore, according to the polarizing plate manufacturing method of the present invention in which transverse stretching is not an essential configuration, it was found that the manufacturing cost can be greatly reduced even when the method described in Patent Document 1 is improved. .
In general, when forming a film by applying a shear stress to a melt of a negative birefringent resin, it has been considered that the orientation direction of the main chain can be predicted. On the other hand, in negative birefringent resins, the mobility of the side chain, which is a structure exhibiting negative intrinsic birefringence, is high. It was thought that there was a high possibility of facing in any direction. Since the tilt direction and orientation direction of the resulting film change depending on the direction of the side chain, it is not expected that the side chain will be directed uniformly in the same direction. It was unexpected that the phase axis and the tilt direction were orthogonal.
Furthermore, when the inventor incorporated the polarizing plate protective film into the polarizing plate, the viewing angle compensation ability of the polarizing plate and the viewing angle compensation ability of the polarizing plate when viewed from an oblique direction are also practically used. It was found that the light leakage of was affected. Therefore, as a result of examining the improvement of the stability over time of the tilted structure, the polarizing plate protective film manufactured in the method for manufacturing a polarizing plate of the present invention is greatly improved in the stability over time of the tilted structure that could not be achieved conventionally. It turns out that it can be improved.

  That is, as a result of earnestly studying a film forming method for applying a shear stress to the melt in order to solve the above-mentioned problems, the present inventor has a negative pressure between the first clamping surface and the second clamping surface constituting the clamping device. The tilt structure is large by continuously pressing the melt of the composition containing the birefringent resin while forming a bank (the surplus of the melt stays on the roll and the formed stay). It has been found that a film in which the slow axis and the tilt direction are orthogonal to each other and the aging stability of the tilt structure is improved can be obtained. As a result, a method for producing a polarizing plate in which the film and the polarizer are directly bonded to each other by roll-to-roll, so that the production cost is low, the viewing angle compensation ability is large, and light leakage is improved when viewed obliquely. I came to find.

  Specifically, the inventors have found that the following production method and a polarizing plate prepared by the method can solve the above problems, and have completed the present invention described below.

[1] A method for producing a polarizing plate, comprising: a step of producing a polarizing plate protective film A; and a laminating step of laminating the polarizing plate protective film A on one surface of a polarizer. The step of manufacturing the film A is a band-like film shape in which a melt of a composition containing a negative birefringent resin is passed between a first clamping surface and a second clamping surface constituting the clamping device clamping device. And the step of making the moving speed of the first pinching surface faster than the moving speed of the second pinching surface, and the bonding step includes the polarizing plate protective film A and the band-shaped polarizing light. A method for producing a polarizing plate, comprising: a step of superposing and bonding together a child in a manner that the longitudinal directions of the respective band-shaped films are matched.
[2] The step of producing the polarizing plate protective film A includes a step of melt-extruding a composition containing a negative birefringent resin from a die, a first clamping surface and a second clamping surface constituting a clamping device. A step of forming a film by continuously passing the melt-extruded melt while forming a bank and forming a film, and a first clamping surface of the clamping device defined by the following formula (I): The method of manufacturing a polarizing plate according to claim 1, further comprising: controlling a moving speed ratio of the second clamping surface to 0.60 to 0.99.
Movement speed ratio = speed of the second clamping surface / speed of the first clamping surface Formula (I)
[3] The step of manufacturing the polarizing plate protective film A includes a temperature difference of 0.1 ° C. to 50 ° C. between the surface temperature of the first pressing surface and the surface temperature of the second pressing surface of the pressing device. The manufacturing method of the polarizing plate as described in [1] or [2] characterized by including the process to give.
[4] The step of producing the polarizing plate protective film A includes a step of conveying the melt formed into the film shape using a cast roll of Tg-10 ° C to Tg-100 ° C. The manufacturing method of the polarizing plate of any one of [1]-[3] (however, said Tg represents the glass transition temperature of the said negative birefringent resin).
[5] The method for producing a polarizing plate according to any one of [1] to [4], wherein the pressing device is two rolls having different peripheral speeds.
[6] The method according to any one of [1] to [5], wherein the step of manufacturing the polarizing plate protective film A includes a step of sandwiching the melt with a pressure of 20 to 500 MPa. Manufacturing method of polarizing plate.
[7] The method for producing a polarizing plate according to any one of [1] to [6], comprising a step of stretching the polarizing plate protective film A in at least one direction.
[8] The polarizing plate protective film A is a negative birefringent resin, and is selected from an acrylic resin, a styrene resin, a maleimide resin, a polyvinyl acetal resin, a cyclic olefin resin, and a polycarbonate resin. The method for producing a polarizing plate according to any one of [1] to [7], comprising one kind.
[9] In the bonding step, the polarizing plate protective film A, the strip-shaped polarizer, and the strip-shaped polarizing plate protective film B are overlapped in this order by matching the longitudinal directions of the strip-shaped films. The method for producing a polarizing plate according to any one of [1] to [8], further comprising a step of bonding.
[10] The method for producing a polarizing plate according to any one of [1] to [9], wherein the polarizing plate protective film B is a cellulose acylate film or an acrylic film.
[11] A polarizing plate produced by the method for producing a polarizing plate according to any one of [1] to [10].
[12] The polarizing plate according to [11], wherein the slow axis of the polarizing plate protective film A and the tilt direction of the polarizing plate protective film A are orthogonal to each other.
[13] The polarizing plate according to [11] or [12], wherein the polarizing plate is for TN mode, OCB mode, or ECB mode.
[14] A liquid crystal display device using at least one polarizing plate according to any one of [11] to [13].

  According to the present invention, a manufacturing method of a polarizing plate with low manufacturing cost, large viewing angle compensation capability of a liquid crystal display device, and improved light leakage when viewed from an oblique direction, and a polarizing plate obtained by the manufacturing method are provided. can do. In addition, the polarizing plate production method of the present invention has a slow axis and a tilt direction orthogonal to each other, can be processed with a polarizer and a roll-to-roll, and can realize sufficient optical compensation when used in a liquid crystal display device. The manufacturing method of a board protective film is included. Specifically, since the film having the above optical characteristics has a slow axis and an inclination direction orthogonal to each other, it is sufficient when a polarizing plate using the film is used for a liquid crystal display of a TN mode, an ECB mode, or an OCB mode. Optical compensation can be realized. For example, in a TN mode liquid crystal display, since the viewing angle is narrow, an optical compensation film (for example, WV film (Fuji Film)) provided with an optical compensation layer made of a liquid crystal composition that realizes optical compensation is usually polarized. When a film having the above optical characteristics is used, it has an optical compensation layer made of a conventional liquid crystal composition without using an optical compensation layer made of a liquid crystal composition. Viewing angle compensation can be performed more easily than those using an optical compensation film. Further, the method for producing a polarizing plate of the present invention can omit the transverse stretching step, and can provide a polarizing plate at a low production cost. Furthermore, the said polarizing plate protective film obtained by a part of process in the manufacturing method of the polarizing plate of this invention is excellent also in the temporal stability of an inclination structure.

  Hereinafter, the present invention will be described in more detail. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. In the present specification, the “film longitudinal direction” means the MD (machine direction) direction.

[Polarizer]
The polarizing plate of the present invention is manufactured by the manufacturing method of the polarizing plate of the present invention. Specifically, the polarizing plate of the present invention has the polarizing plate protective film A on one surface of a polarizer. When the slow axis of the polarizing plate protective film A and the inclination direction of the polarizing plate protective film A are orthogonal, the viewing angle compensation ability when processed with a polarizer and a roll-to-roll, and when viewed from an oblique direction It is preferable from the viewpoint of improving light leakage.
The polarizing plate of the present invention preferably has a polarizing plate protective film B on the other surface of the polarizer.

  The polarizing plate of this invention may have an adhesive layer for sticking with another member in the at least one surface. Moreover, in the polarizing plate of this invention, if the surface of the said polarizing plate protective film A has an uneven structure, it will have an anti-glare (anti-glare) function. Furthermore, in the polarizing plate of the present invention, an antireflection film in which an antireflection layer (low refractive index layer) is further laminated on the surface of the polarizing plate protective film A, or an optically anisotropic material on the surface of the polarizing plate protective film A is provided. It is also preferable to use an optical compensation film in which a conductive layer is laminated.

  In general, since a liquid crystal display device is provided with a liquid crystal cell between two polarizing plates, when the polarizing plate has a polarizing plate protective film on both sides, the liquid crystal display device has four polarizing plate protective films. The polarizing plate protective film A may be used for any of two polarizing plates, but the polarizing plate protective film A is a polarizing plate protective film disposed between a liquid crystal cell and a polarizer in a liquid crystal display device. And can be used particularly advantageously.

  As for the polarizing plate of this invention, it is more preferable that the said polarizing plate protective film B, the polarizer, and the said polarizing plate protective film A are the structures laminated | stacked in this order. Moreover, the structure which the said polarizing plate protective film B, the polarizer, the said polarizing plate protective film A, and the adhesive layer are laminated | stacked in this order is also more preferable.

<Polarizing plate protective film A>
The polarizing plate protective film A is used for the polarizing plate of the present invention.
Further, the polarizing plate protective film A may be subjected to a surface treatment. Examples of the surface treatment method include corona discharge, glow discharge, UV irradiation, flame treatment, and saponification treatment of an alkaline aqueous solution.
Hereinafter, the polarizing plate protective film A will be described in detail.

  The polarizing plate protective film A is a film containing a negative birefringent resin and has a slow axis and a tilt direction, and the slow axis and the tilt direction are orthogonal to each other. The tilt azimuth represents an azimuth in which | Re [+ 40 °] −Re [−40 °] | Further, “the slow axis and the tilt direction are orthogonal” means that the angle formed by the slow axis and the tilt direction is approximately 90 °. Hereinafter, the polarizing plate protective film A will be described in detail.

(In-plane retardation Re, thickness direction retardation Rth, γ, Δγ)
The polarizing plate protective film A has an in-plane retardation Re [measured from a direction inclined 40 ° toward the tilt azimuth side with respect to the normal in a plane including the film tilt azimuth and the film normal. + 40 °] and retardation Re [−40 °] in the in-plane direction at a wavelength of 550 nm measured from a direction inclined by 40 ° to the opposite side of the tilt direction with respect to the normal line, both satisfy the following formula (II): It is preferable.
10 nm <γ ≦ 300 nm Formula (II)
γ = | Re [+ 40 °] −Re [−40 °] | Formula (II ′)

  In this specification, the “direction inclined by θ ° from the film normal” is defined as a direction inclined in the film surface direction by θ ° from the normal direction to the inclination direction. That is, the normal direction of the film surface is a direction with an inclination angle of 0 °, and an arbitrary direction within the film surface is a direction with an inclination angle of 90 °.

  In the polarizing plate protective film A, the γ is preferably 40 to 300 nm, more preferably 50 to 280 nm, and particularly preferably 60 to 250 nm.

In the plane including the film tilt direction and the film normal, the polarizing plate protective film A satisfies the following formula (III) in the in-plane retardation Re [0 °] at a wavelength of 550 nm measured from the normal direction. It is preferable to do.
20 nm ≦ Re [0 °] ≦ 300 nm Formula (III)

  The polarizing plate protective film A has an in-plane retardation Re [0 °] of preferably 30 to 300 nm, more preferably 40 to 250 nm, and particularly preferably 50 to 200 nm.

Furthermore, the polarizing plate protective film A preferably satisfies the following formulas (IV) to (V) at the same time.
50 nm ≦ Re [0 °] ≦ 200 nm (IV)
40 nm ≦ γ ≦ 250 nm (V)

In the polarizing plate protective film A, the change rate Δγ of γ before and after 500 hours in an environment of 60 ° C. and 90% relative humidity is preferably 15% or less, more preferably 10% or less, It is particularly preferable that it is 5% or less. Δγ represents the rate of change with time of the wet heat durability of the inclined structure, and if Δγ is small, it is preferable because the optical compensation ability can be sufficiently exhibited in a long period even in a wet heat environment. The Δγ is calculated by the following formula.
Δγ = {(γ after lapse of 500 hours in an environment of 60 ° C. and relative humidity 90%) − (γ before lapse of 500 hours in an environment of 60 ° C. and relative humidity 90%)} / (60 ° C., relative humidity Γ before elapse of 500 hours in 90% environment)

  The polarizing plate protective film A in which γ, Δγ, and Re [0 °] are in the preferable ranges can be produced by a method for manufacturing the polarizing plate protective film A described later. In addition, when the polarizing plate using the polarizing plate protective film A having the above preferable optical characteristics is used for optical compensation of a liquid crystal display such as a TN mode, an ECB mode, and an OCB mode, it contributes to an improvement in viewing angle characteristics. Wide viewing angle can be achieved.

  Variations in Re [0 °], Re [+ 40 °], and Re [−40 °] appear as display unevenness when used in a liquid crystal display. Therefore, the variation is preferably as small as possible. It is preferably within ± 3 nm, and more preferably within ± 1 nm.

  Similarly, the variation in the angle of the slow axis also causes display unevenness. Therefore, the variation is preferably as small as possible, specifically within ± 1 °, preferably within ± 0.5 °. It is more preferable that the angle is within ± 0.25 °.

The optical characteristic value can be measured by the following method.
In the present invention, Re [0 °], Re [+ 40 °] and Re [−40 °] of the polarizing plate protective film A are KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments Co., Ltd.). In the plane including the azimuth and the film normal, the phase difference at an inclination angle of 0 °, the phase difference at an inclination angle of 40 °, and the phase difference at an inclination angle of −40 ° were measured.
Here, the inclination direction was determined by the following method.
(1) The slow axis direction in the film plane is 0 °, the fast axis direction in the film plane is 90 °, and the temporary tilt direction is set in increments of 0.1 ° between 0 ° and 90 °.
(2) Re [+ 40 °] and Re [−40 °] are measured in the plane including each provisional tilt direction and film normal, and | Re [+ 40 °] −Re [−40 °] | Ask.
(3) The direction in which | Re [+ 40 °] −Re [−40 °] | is maximized is determined as the tilt direction.
The measurement wavelength is 550 nm. Note that a film made of a general thermoplastic resin by a melt film-forming method has γ≈0 nm regardless of the orientation. That is, the characteristic of the polarizing plate protective film A is that when | Re [+ 40 °] −Re [−40 °] | is measured in the tilt direction, a retardation of 0 nm or more is expressed.
In addition, variations in Re [0 °], Re [+ 40 °], and Re [−40 °] can be measured by the following method. Sampling is performed at any 10 or more positions on the film surface 2 mm or more away from each other, and Re [0 °], Re [+ 40 °] and Re [−40 °] are measured by the above method. The difference in value is defined as the variation of Re [0 °], Re [+ 40 °], and Re [−40 °]. When the values of Re [0 °], Re [+ 40 °], and Re [−40 °] are positive, the slow axis is in the TD direction. When the values of Re [0 °], Re [+ 40 °], and Re [−40 °] are negative, the slow axis is in the MD direction.
Further, the slow axis and the variation of Rth described later are measured in the same manner.

式中、Ｒｅ（θ）は法線方向から角度θ傾斜した方向におけるレターデーション値をあらわす。また、数式（Ｂ）中のβは、屈折率楕円体が一様傾斜したことを仮定した場合の傾斜角度を表し、傾斜型位相差フィルムの構造を単純に把握するときに使用される。
上記の測定において、平均屈折率の仮定値は、ポリマーハンドブック（ＪＯＨＮ ＷＩＬＥＹ＆ＳＯＮＳ，ＩＮＣ）、各種光学補償フィルムのカタログの値を使用することができる。また、平均屈折率の値が既知でないものについては、アッベ屈折計で測定することができる。主な光学補償フィルムの平均屈折率の値を以下に例示する：セルロースアシレート（１．４８）、シクロオレフィンポリマー（１．５２）、ポリカーボネート（１．５９）、ポリメチルメタクリレート（１．４９）、ポリスチレン（１．５９）である。 Rth is calculated by calculating the refractive indices nx, ny, and nz in each direction of the refractive index ellipsoid and substituting them into the following formula (A), assuming that the refractive index ellipsoid is uniformly inclined by β °. be able to.
Rth = ((nx + ny) / 2−nz) × d Formula (A)
Said x is an inclination azimuth | direction of the polarizing plate protective film A, y is a direction orthogonal to an inclination azimuth within a film plane, and z is a film thickness direction.
In the polarizing plate protective film A, ny is a refractive index in the y direction. nx is the refractive index in the direction in which the projection component to the x-axis of the film is larger than the projection component to the z-axis, and nz is the refractive index in the direction in which the projection component to the z-axis is larger than the projection component of the x-axis.
The method for obtaining nx, ny, and nz is described in the technical data of Oji Scientific Instruments Co., Ltd. (http://www.oji-keisoku.co.jp/products/kobra/kobra.html). For example, it is possible to calculate from the values of Re [0 °], Re [+ 40 °] and Re [−40 °], the value of average refractive index n _ave , and the film thickness value d using the following formula (B). I can do it.

In the formula, Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction. In addition, β in the mathematical formula (B) represents an inclination angle when it is assumed that the refractive index ellipsoid is uniformly inclined, and is used when the structure of the inclined retardation film is simply grasped.
In the above measurement, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical compensation films can be used. Moreover, about the thing whose average refractive index value is not known, it can measure with an Abbe refractometer. The average refractive index values of the main optical compensation films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49) Polystyrene (1.59).

(Elongation at break)
The polarizing plate protective film A preferably has a breaking elongation at 25 ° C. of 5 to 200% from the viewpoint of improving the brittleness of the film and the handleability.
The breaking elongation is more preferably 10 to 180%, and particularly preferably 15 to 180%.
The breaking elongation at 25 ° C. of the polarizing plate protective film A is measured according to the following method. Sample 10 mm × 150 mm, humidity adjusted at 25 ° C., relative humidity 65% for 2 hours, using Toyo Baldwin Universal Tensile Tester STM T50BP, at 23 ° C. in 60% RH atmosphere, initial sample length 100 mm, 10% / The stress-strain curve is measured by stretching in minutes to determine the elongation at break. The measurement is repeated 10 times, and the average value is obtained as the elongation at break.

  The film thickness of the polarizing plate protective film A is preferably 100 μm or less. When used for a liquid crystal display or the like, it is preferably 80 μm or less, more preferably 60 μm or less, and particularly preferably 40 μm or less from the viewpoint of thinning. Such a thin film can be produced by the manufacturing method of the polarizing plate protective film A described later.

(Negative birefringent resin)
The polarizing plate protective film A contains a negative birefringent resin.
The negative birefringent resin refers to light having a refractive index of light in the orientation direction perpendicular to the orientation direction when light is incident on a layer formed by molecules having a uniaxial stretch orientation. A resin that is smaller than the refractive index.
The negative birefringent resin used in the present invention is not particularly limited as long as it has the above optical characteristics, and a known negative birefringent resin can be used. When the polarizing plate protective film A is produced using a melt extrusion method, it is preferable to use a material having good melt extrusion moldability. From this viewpoint, a cyclic olefin resin (however, positive birefringence) A resin, that is, a resin in which the refractive index of light in the orientation direction is larger than the refractive index of light in a direction perpendicular to the orientation direction when light is incident on a layer formed by molecules having a uniaxial stretch orientation; ), Cellulose acylate resins (except those that are positive birefringent resins), maleimide resins, acrylic resins, styrene resins such as polystyrenes, polyacrylonitrile polymers, polyvinyl acetal resins It is preferable to select a polycarbonate-based resin (excluding those which are positive birefringence resins).
The polarizing plate protective film A may contain one kind of the negative birefringent resin, or may contain two or more kinds of resins different from each other. In addition, one type of resin having negative birefringence may be used alone, or two or more types may be used in combination when two or more types are blended to exhibit negative birefringence. Good. When the negative birefringent resin is a polymer blend consisting of a resin that is a single negative birefringent resin and a resin that is a single positive birefringent resin, it is a single negative birefringent resin. The blending ratio of the resin to the resin that is a single positive birefringent resin varies depending on the magnitude of the absolute value of both intrinsic birefringence values, the manifestation of birefringence at the molding temperature, and the like. The polymer blend may contain other components in addition to the resin that is a negative birefringent resin alone and the resin that is a positive birefringent resin alone. The component is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected depending on the purpose. The compatibilizing agent can be suitably used in the case where phase separation does not occur during blending, and by using the compatibilizing agent, a resin that is a single negative birefringent resin and a single Thus, the mixed state with a resin which is a positive birefringent resin can be improved.
The polarizing plate protective film A preferably contains 30% by mass to 100% by mass, more preferably 40% by mass to 100% by mass, of the resin that is a single negative birefringent resin with respect to the entire film. The amount is preferably 100% by mass. Moreover, it is preferable that the ratio of resin which is a single negative birefringent resin to the whole resin contained in the said polarizing plate protective film A is 30 mass%-100 mass%, and 40 mass%-100 mass. % Is more preferable, and 100% by mass is particularly preferable.
In the polarizing plate protective film A, the negative birefringent resin is selected from an acrylic resin, a styrene resin, a maleimide resin, a polyvinyl acetal resin, a cyclic olefin resin (preferably an addition polymer), and a polycarbonate resin. It is preferable that at least one kind is included, and it is more preferable that at least one kind selected from an acrylic resin, a styrene resin, and a maleimide resin is included. Also, styrene / maleic anhydride copolymer, styrene / (meth) acrylonitrile copolymer, styrene / (meth) acrylate copolymer, styrene / maleimide copolymer, vinyl ester / maleimide copolymer, or olefin / maleimide It preferably contains a resin such as a copolymer.

In the manufacturing method of the polarizing plate protective film A described later, acrylic resin, styrene resin, maleimide resin, polyvinyl acetal resin, cyclic olefin resin showing negative intrinsic birefringence, polycarbonate showing negative intrinsic birefringence The polarizing plate protective film A in which the slow axis and the tilt direction are orthogonal can be obtained using a negative birefringent resin such as a resin. For example, when a styrenic resin is produced by a film forming method in which shear deformation is imparted by two rolls, the fast axis is oriented in the tilt direction, and in the case of a general method in which two rolls are arranged in parallel with the die exit, The orientation is the same as the film longitudinal direction.
In contrast, a cellulose acylate resin showing positive intrinsic birefringence, a cyclic olefin resin showing positive intrinsic birefringence, a polycarbonate resin showing positive intrinsic birefringence, etc. When the film is produced by a film forming method that imparts shear deformation, the slow axis faces the tilt direction. For example, when two rolls are arranged in parallel to the die exit, the tilt direction is the same as the film longitudinal direction.

  When the polarizing plate protective film A is applied to a liquid crystal display device as a viewing angle compensation film, the negative intrinsic birefringence resin is appropriately selected in consideration of the characteristics of the liquid crystal display device and the convenience of polarizing plate processing. You can select and use.

The styrenic resin that can be used in the present invention refers to a resin obtained by polymerizing styrene and derivatives thereof as a main component, and copolymers of other resins, and is not particularly limited as long as the effects of the present invention are not impaired. A known styrene-based thermoplastic resin can be used, and a copolymer resin that can improve birefringence, film strength, and heat resistance is particularly preferable.
Examples of the copolymer resin include styrene-acrylonitrile resins, styrene-acrylic resins, styrene-maleic anhydride resins, and multi-component (binary, ternary, etc.) copolymer polymers thereof. Among these, styrene-acrylic resins and styrene-maleic anhydride resins are preferable from the viewpoints of heat resistance and film strength.
In the styrene-maleic anhydride resin, the mass composition ratio of styrene and maleic anhydride is preferably styrene: maleic anhydride = 95: 5 to 50:50, and styrene: maleic anhydride = 90: 10. More preferably, it is ˜70: 30. In order to adjust the intrinsic birefringence, hydrogenation of a styrene resin can be preferably used.
Examples of the styrene-maleic anhydride resin include “Daylark D332” manufactured by Nova Chemical Co., Ltd.
As the styrene-acrylic resin, “Delpet 980N”, “XSR9251” manufactured by Asahi Kasei Chemical Co., Ltd., which will be described later, and the like can be used.

The acrylic resin that can be used in the present invention refers to a resin obtained by polymerizing acrylic acid, methacrylic acid and derivatives thereof as main components, and further derivatives thereof, as long as the effects of the present invention are not impaired. It does not specifically limit, A well-known methacrylic acid type thermoplastic resin etc. can be used.
Examples of the resin obtained by polymerizing acrylic acid, methacrylic acid and derivatives thereof include a resin obtained by polymerizing one having a structure represented by the following general formula (1).

前記一般式（１）中、Ｒ¹およびＲ²は、それぞれ独立に、水素原子または炭素数１〜２０の有機残基を示す。有機残基とは、具体的には、炭素数１〜２０の直鎖状、分枝鎖状、もしくは環状のアルキル基を示す。

In the general formula (1), R ¹ and R ² each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue specifically represents a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms.

Specific examples of resins obtained by polymerizing the acrylic acid, methacrylic acid and derivatives thereof include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and (meth) acrylic. N-butyl acid, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxy (meth) acrylate Propyl, 2,3,4,5,6-pentahydroxyexyl (meth) acrylate and 2,3,4,5-tetrahydroxypentyl (meth) acrylate are preferred, and in terms of excellent thermal stability (meta ) Methyl acrylate (hereinafter also referred to as MMA) is more preferable. Among these, only 1 type may be used and 2 or more types may be used together. Further, among these, it may be a single polymer, a copolymer of two or more, or a copolymer of other resins, but from the viewpoint of increasing the glass transition temperature, Particularly preferred is a copolymer with a resin.
Among the acrylic copolymer resins, those containing 30 mol% or more of MMA units (monomer) in all monomers constituting the resin are preferable. In addition to MMA, lactone ring units, maleic anhydride units, glutaric anhydrides More preferably, at least one unit of units is included, and for example, the following can be used.

(1) Acrylic resin containing a lactone ring unit JP 2007-297615 A, JP 2007-63541 A, JP 2007-70607 A, JP 2007-100044 A, JP 2007-254726 A, JP 2007-254727 A , JP 2007-261265, JP 2007-293272, JP 2007-297619, JP 2007-316366, JP 2008-9378, and JP 2008-76764. Can be used. Among these, the resin described in JP-A-2008-9378 is more preferable.
(2) Acrylic resin containing maleic anhydride unit JP 2007-113109 A, JP 2003-292714 A, JP 6-279546 A, JP 2007-51233 A (described here), JP JP-A-2001-270905, JP-A-2002-167694, JP-A-2000-302988, JP-A-2007-111110, JP-A-2007-11565 can be used. Among these, the one described in JP 2007-113109 A is more preferable. A commercially available maleic acid-modified MAS resin (for example, Delpet 980N manufactured by Asahi Kasei Chemicals Corporation) can also be preferably used.
(3) Acrylic resin containing glutaric anhydride unit JP-A-2006-241263, JP-A-2004-70290, JP-A-2004-70296, JP-A-2004-126546, JP-A-2004-163924, JP-A-2004 -291302, JP-A-2004-292812, JP-A-2005-314534, JP-A-2005-326613, JP-A-2005-331728, JP-A-2006-131898, JP-A-2006-134882, JP-A-2006- 206881, JP 2006-241197, JP 2006-283013, JP 2007-118266, JP 2007-176982, JP 2007-178504, JP 2007-197703, JP 2008-74918. No., International Publication WO2005 / 105 Those described in each publication such as 918 can be used. Among these, those described in JP-A-2008-74918 are more preferable.
The glass transition temperature (Tg) of these resins is preferably 106 ° C to 170 ° C, more preferably 110 ° C to 160 ° C, still more preferably 115 ° C to 150 ° C.

The maleimide-based resin that can be used in the present invention refers to a resin obtained by polymerizing maleimide and a derivative thereof as a main component, and a derivative thereof, and is not particularly limited unless the effects of the present invention are impaired. A well-known maleimide type thermoplastic resin etc. can be used.
Examples of the resin obtained by polymerizing maleimide and derivatives thereof include resins containing a unit structure represented by the following general formula (2).

In the general formula (2), R ¹¹ represents a hydrogen atom, a heterocyclic group formed of an aromatic ring or a non-aromatic ring, or a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms.

R ^{12 to} R ¹⁹ each independently represent a hydrogen atom, a halogen atom, an oxygen atom, a nitrogen atom, a sulfur atom or a silicon atom, or a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, Alternatively, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms is preferable, and a hydrogen atom is more preferable.
m and n each independently represents an integer of 0 to 5, preferably 0 to 2, and more preferably 0.

Although the specific example of the unit structure of the maleimide-type resin represented by the said General formula (2) is given, this invention is not limited to these.

Specific examples of the maleimide resin include R as phenyl group, naphthyl group, halogen element, carboxylic acid, carboxylic ester, hydroxyl group, cyano group, nitro group, linear alkyl group having 1 to 8 carbon atoms, carbon It preferably has a phenyl group or a naphthyl group substituted with a branched alkyl group of 1 to 8, and N-phenylmaleimide, N- (2-methylphenyl) maleimide and the like are more preferable in terms of excellent thermal stability. Among these, only 1 type may be used and 2 or more types may be used together. Further, among these, it may be a single polymer, a copolymer of two or more, or a copolymer of other resins, but from the viewpoint of increasing the glass transition temperature, It may be a copolymer with a resin.
Among the maleimide resins, those containing 30 mol% or more of maleimide and its derivative units are preferable in all monomers constituting the resin, and more preferably a homopolymer of maleimide and its derivative units.

一般式（３）中、Ｒ²¹はメチル基である。Ｒ²²はフェニル基；炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基、炭素数６〜２０のアリール基、炭素数１〜２０のアシル基、炭素数１〜２０のアルコキシ基、カルボキシル基、ハロゲン基、水酸基又は炭素数１〜５のアシル基で置換されたフェニル基；ベンジル基；炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基、炭素数６〜２０のアリール基、炭素数１〜２０のアシル基、炭素数１〜２０のアルコキシ基、カルボキシル基、ハロゲン基、水酸基又は炭素数１〜５のアシル基で置換されたベンジル基；ナフチル基；炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基、炭素数６〜２０のアリール基、炭素数１〜２０のアシル基、炭素数１〜２０のアルコキシ基、カルボキシル基、ハロゲン基、水酸基又は炭素数１〜５のアシル基で置換されたナフチル基；炭素数６〜２０の環状アルキル基を表す。 As the polyvinyl acetal resin that can be used in the present invention, for example, a thermoplastic resin represented by the general formula (3) can be used. Moreover, it will not specifically limit unless the effect of this invention is impaired, The polyvinyl acetal type thermoplastic resin etc. which have a well-known negative refractive property can be used.

In the general formula (3), R ²¹ is a methyl group. R ²² is a phenyl group; an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an acyl group having 1 to 20 carbon atoms, and an alkoxy group having 1 to 20 carbon atoms. , A phenyl group substituted by a carboxyl group, a halogen group, a hydroxyl group or an acyl group having 1 to 5 carbon atoms; a benzyl group; an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 1 to 20 carbon atoms, or 6 to 20 carbon atoms An aryl group, an acyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a carboxyl group, a halogen group, a hydroxyl group, or a benzyl group substituted with an acyl group having 1 to 5 carbon atoms; a naphthyl group; An alkyl group having 1 to 20 carbon atoms, an alkenyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an acyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a carboxyl group, a halogen group, water Naphthyl groups substituted with one or acyl group of 1 to 5 carbon atoms; represents a cyclic alkyl group having 6 to 20 carbon atoms.

Specific examples of R ²² in the general formula (3) include a phenyl group, o-methylphenyl group, m-methylphenyl group, p-methylphenyl group, 2,3-dimethylphenyl group, 2, 4-dimethylphenyl group, 2,5-dimethylphenyl group, 2,6-dimethylphenyl group, 3,4-dimethylphenyl group, 3,5-dimethylphenyl group, 2,3,4-trimethylphenyl group, 2, 3,5-trimethylphenyl group, 2,4,5-trimethylphenyl group, 2,4,6-trimethylphenyl group, 2,3,4,5-tetramethylphenyl group, 2,3,4,6-tetra Methylphenyl group, 2,3,5,6-tetramethylphenyl group, 2,4,5,6-tetramethylphenyl group, 3,4,5,6-tetramethylphenyl group, pentamethylphenyl group, o- Echi Phenyl group, m-ethylphenyl group, p-ethylphenyl group, 2,3-diethylphenyl group, 2,4-diethylphenyl group, 2,5-diethylphenyl group, 2,6-diethylphenyl group, 3,4 -Diethylphenyl group, 3,5-diethylphenyl group, 2,4,6-triethylphenyl group, pnpropylphenyl group, p-isopropylphenyl group, ptbutylphenyl group, p-carboxylphenyl group, p -Methoxyphenyl group, p-acetophenone group, p-chlorophenyl group, 2,6 dimethyl-4-tbutylphenyl group, α-naphthyl group, β-naphthyl group, benzyl group, p-methylbenzyl group, p-ethylbenzyl Group, p-isopropylbenzyl group, cyclohexyl group, 2-norbornane group and the like.

  In the general formula (3), the ratio of p, q, and r can be appropriately selected according to the type and purpose of the substituent. Preferably, when the sum of p, q and r is 100 (mol%), p is 20 to 80 (mol%), q is 10 to 70 (mol%), and r is 1 to 50 (mol%). Particularly preferably, p is 25 to 75 (mol%), q is 15 to 60 (mol%), r is 2 to 40 (mol%), and most preferably, p is 30 to 70 (mol%). Mol%), q is 20 to 50 (mol%), and r is 2 to 30 (mol%). By setting it as the above range, a retardation film exhibiting a negative birefringence and having excellent molding processability, stretchability, retardation value stability, and tilt orientation can be obtained.

The cyclic olefin-based resin that is a thermoplastic resin exhibiting negative birefringence that can be used in the present invention includes, for example, a cyclic olefin resin having at least one aromatic ring structure in the side chain, and at least one ring structure in the side chain. The spiro-type cyclic olefin resin which has is included.
The cyclic olefin-based resin may be a resin obtained by any polymerization method of ring-opening polymerization and addition polymerization, but is preferably a resin obtained by ring-opening polymerization.
The cyclic olefin resin is preferably a norbornene polymer, and is preferably a ring-opening norbornene polymer.
When the cyclic olefin resin is a cyclic olefin resin having at least one aromatic ring structure in the side chain, the aromatic ring structure may have one or a plurality of substituents, and when it has a plurality of substituents The substituents may be bonded to each other to form a ring structure. Further, the three-dimensional structure of the side chain is not particularly limited, and the aromatic ring structure may be bonded in an exo form or in an end form.
When the cyclic olefin-based resin is a spiro-type cyclic olefin resin having at least one ring structure in the side chain, the ring structure may or may not be aromatic. The ring structure may have one or a plurality of substituents, and when there are a plurality of substituents, the substituents may be bonded to each other to form a ring structure, particularly between the substituents. May be bonded to each other to form an aromatic ring structure. The functional group preferably has a functional group containing an oxygen atom (for example, a carbonyl group, an ester group, an oxy group, etc.). Moreover, there is no restriction | limiting in particular also about the three-dimensional structure of a side chain.
Examples of the cyclic olefin-based resin having negative birefringence obtained by ring-opening polymerization include those described in JP-A Nos. 2003-292639, 2006-189474, and 2008-52119. Can be mentioned.

  Examples of the polycarbonate resin that is a thermoplastic resin exhibiting negative birefringence that can be used in the present invention include the following general formula (4).

で示されるメチル基を有するフルオレン骨格を持つ繰り返し単位を重合させたものや、前記一般式（４）示される繰り返し単位と下記一般式（５）

A polymer obtained by polymerizing a repeating unit having a fluorene skeleton having a methyl group represented by formula (5) or a repeating unit represented by the general formula (4) and the following general formula (5)

(In the general formula (5), R ^{39 to} R ⁴⁶ are each independently selected from a hydrogen atom, a halogen atom, and a hydrocarbon group having 1 to 3 carbon atoms;

(In the above formula group, R ^{47 to} R ⁴⁹ , R ⁵¹ and R ⁵² are each independently selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, and R ⁵⁰ and R ⁵³ are each independently carbon. A hydrocarbon group having 1 to 20 carbon atoms, and Ar ^{1 to} Ar ³ are each independently selected from an aryl group having 6 to 10 carbon atoms. it can.

Examples of the halogen atom of R ^{47 to} R ⁴⁹ , R ⁵¹ and R ⁵² in the general formula (5) include fluorine, chlorine, bromine and iodine. Examples of the hydrocarbon group having 1 to 3 carbon atoms include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group.

In the formula group of Y, the halogen atom may be the same as the halogen atom in the general formula (5). Examples of the hydrocarbon group having 1 to 22 carbon atoms include (cyclo) alkyl group having 1 to 22 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, butyl group, pentyl group, and cyclohexyl group, and phenyl group. And aryl groups having 6 to 18 carbon atoms such as biphenyl group, terphenyl group and naphthyl. Examples of the hydrocarbon group for R ⁵⁰ and R ⁵³ include 6 to 18 carbon atoms such as a divalent (cyclo) alkylene group having 2 to 20 carbon atoms such as an ethylene group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. And a divalent arylene group. Ar ^{1 to} Ar ³ may include aryl groups having 6 to 10 carbon atoms such as a phenyl group and a naphthyl group.

  Examples of the polycarbonate resin exhibiting negative birefringence include polycarbonates having the following repeating units having a fluorene skeleton having no methyl group having a structure similar to that of the general formula (4).

The polycarbonate-based resin exhibiting negative birefringence is a polycarbonate mainly composed of a repeating unit represented by the above formula (4), and a co-polymer comprising such repeating units represented by the above formula (4) and the above formula (5). A polymer, a composition of a polycarbonate comprising a repeating unit represented by the above formula (4) and a polycarbonate comprising a repeating unit represented by the above formula (5), a composition containing two or more kinds of the copolymer, The composition of a polymer and the polycarbonate which consists of a repeating unit represented by the said Formula (5) is included.
The repeating unit represented by the general formula (4) is a resin that occupies 71 to 98 mol% of the whole polycarbonate, and the repeating unit represented by the general formula (5) occupies 29 to 2 mol%. May be.

  As a method for producing the polycarbonate, interfacial polycondensation between dihydroxy compounds and phosgene, melt polycondensation, or the like is preferably used.

  When blending two or more types of polycarbonate, a compatible blend is preferable, but even if they are not completely compatible, the light scattering between the components can be suppressed and transparency can be improved by adjusting the refractive index between the components. It is.

  Although there is no restriction | limiting in particular as the molecular weight of the said polycarbonate, Although it prescribes | regulates by the intrinsic viscosity measurement which used the methylene chloride as a solvent, it is preferable that the intrinsic viscosity in 20 degreeC is 0.30-2.0 dl / g.

  Examples of the polycarbonate resin exhibiting negative birefringence include those described in JP-A Nos. 2001-194530 and 2001-194668, and can be preferably used.

  In addition, when the negative birefringent resin is a copolymer, it may be a random copolymer or a block copolymer.

  The glass transition temperature (Tg) of the thermoplastic resin having negative birefringence is preferably 100 ° C to 185 ° C, more preferably 110 ° C to 170 ° C, and particularly preferably 120 ° C to 150 ° C. is there. If Tg is 90 ° C. or higher, a film having good thermal stability is easily obtained, and if it is 185 ° C. or lower, molding processability is excellent. The glass transition temperature (Tg) can be determined by a DSC method according to JIS K7121.

(Additive)
The polarizing plate protective film A may contain a material other than the negative birefringent resin, but contains one or more of the negative birefringent resins as a main component (all the components in the composition). In the material, it means a material with the highest content ratio, and in an embodiment containing two or more of the resins, it means that the total content ratio is higher than the content ratio of each of the other materials) It is preferable. Examples of materials other than the negative birefringent resin include various additives, examples of which include stabilizers, ultraviolet absorbers, light stabilizers, plasticizers, fine particles, and optical adjusting agents. It is.

Stabilizer:
The polarizing plate protective film A may contain at least one stabilizer. The stabilizer is preferably added before or when the negative birefringent resin is heated and melted. The stabilizer has effects such as preventing oxidation of the film constituting material, capturing an acid generated by decomposition, and suppressing or inhibiting a decomposition reaction caused by radical species caused by light or heat. Stabilizers are useful for suppressing the occurrence of alterations such as coloring and molecular weight reduction and the generation of volatile components due to various decomposition reactions including unresolved decomposition reactions. Even at the melting temperature for forming a resin film, the stabilizer itself is required to function without being decomposed. Typical examples of stabilizers include phenol-based stabilizers, phosphorous acid-based stabilizers (phosphite-based), thioether-based stabilizers, amine-based stabilizers, epoxy-based stabilizers, and lactone-based stabilizers. Stabilizers, amine stabilizers, metal deactivators (tin stabilizers) and the like are included. These are described in JP-A-3-199201, JP-A-5-1907073, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, and the like. Then, it is preferable to use at least one or more of a phenol-based or phosphorous acid-based stabilizer. Among phenolic stabilizers, it is particularly preferable to add a phenolic stabilizer having a molecular weight of 500 or more. Preferable phenolic stabilizers include hindered phenolic stabilizers.

  These materials are readily available as commercial products and are sold by the following manufacturers. From Ciba Specialty Chemicals, Irganox 1076, Irganox 1010, Irganox 3113, Irganox 245, Irganox 1135, Irganox 1330, Irganox 259, Irganox 565, Irganx 565, Irganx 565, Ir35x10 Moreover, it can obtain from Asahi Denka Kogyo Co., Ltd. as ADK STAB AO-50, ADK STAB AO-60, ADK STAB AO-20, ADK STAB AO-70, and ADK STAB AO-80. Furthermore, from Sumitomo Chemical Co., Ltd., it can obtain as Sumilizer BP-76, Sumilizer BP-101, Sumilizer GA-80. In addition, it is also possible to obtain as Sinox 326M and Sinox 336B from Sipro Kasei Corporation.

  Moreover, as said phosphorous acid type stabilizer, the compound as described in [0023]-[0039] of Unexamined-Japanese-Patent No. 2004-182979 can be used more preferably. Specific examples of the phosphite ester stabilizer include JP-A-51-70316, JP-A-10-306175, JP-A-57-78431, JP-A-54-157159, Examples thereof include compounds described in Japanese Utility Model Laid-Open No. 55-13765. Furthermore, as other stabilizers, the materials described in detail on pages 17 to 22 of the Japan Institute of Invention Disclosure Bulletin (Public Technical No. 2001-1745, issued March 15, 2001, Japan Society of Invention) are preferably used. be able to.

  The phosphite stabilizer is useful to have a high molecular weight in order to maintain stability at high temperature, has a molecular weight of 500 or more, more preferably a molecular weight of 550 or more, and particularly a molecular weight of 600 or more. Is preferred. Furthermore, at least one substituent is preferably an aromatic ester group. The phosphite ester stabilizer is preferably a triester, and is desirably free of impurities such as phosphoric acid, monoester and diester. When these impurities are present, the content is preferably 5% by mass or less, more preferably 3% by mass or less, and particularly 2% by mass or less. These include compounds described in [0023] to [0039] of JP-A No. 2004-182979, JP-A-51-70316, JP-A-10-306175, JP-A-57. The compounds described in JP-A-78431, JP-A-54-157159, and JP-A-55-13765 can also be mentioned. Preferred specific examples of the phosphite stabilizer include the following compounds, but the phosphite stabilizer that can be used in the present invention is not limited thereto.

  These are commercially available from Asahi Denka Kogyo Co., Ltd. as ADK STAB 1178, 2112, PEP-8, PEP-24G, PEP-36G, and HP-10, and Sandostab P-EPQ from Clariant. Is possible. Furthermore, a stabilizer having phenol and phosphite in the same molecule is also preferably used. These compounds are further described in detail in JP-A-10-273494. Examples of the compounds are included in the examples of the stabilizer, but are not limited thereto. As a typical commercial product, Sumitizer GP is available from Sumitomo Chemical Co., Ltd. These are commercially available from Sumitomo Chemical Co., Ltd. as Sumilizer TPL, TPM, TPS, TDP. Also available from Asahi Denka Kogyo Co., Ltd. as ADK STAB AO-412S.

  The stabilizers 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. Preferably, the addition amount of the stabilizer is preferably 0.001 to 5% by mass, more preferably 0.005 to 3% by mass, and still more preferably 0.005% by mass with respect to the mass of the negative birefringent resin. 01 to 0.8 mass%.

UV absorber:
The polarizing plate protective film A may contain one type or two or more types of ultraviolet absorbers. From the viewpoint of preventing deterioration, the ultraviolet absorbent is preferably excellent in the ability to absorb ultraviolet light having a wavelength of 380 nm or less and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of transparency. Examples include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Particularly preferred ultraviolet absorbers are benzotriazole compounds and benzophenone compounds. Among these, a benzotriazole-based compound is preferable because unnecessary coloring with respect to the cellulose mixed ester is small. These are disclosed in JP-A-60-235852, JP-A-3-199201, 5-1907073, 5-194789, 5-271471, 6-107854, 6-118233, 6 -148430, 7-11056, 7-11055, 7-11056, 8-29619, 8-239509, and JP-A-2000-204173.
The addition amount of the ultraviolet absorber is preferably 0.01 to 2% by mass of the negative birefringent resin, and more preferably 0.01 to 1.5% by mass.

Light stabilizer:
The polarizing plate protective film A may contain one or more light stabilizers. Light stabilizers include hindered amine light stabilizer (HALS) compounds, more specifically, US Pat. No. 4,619,956, columns 5-11 and US Pat. No. 4,839. 2,405, 2,2,6,6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds. These are commercially available from Asahi Denka as ADK STAB LA-57, LA-52, LA-67, LA-62, LA-77, and TINUVIN 765, 144 from Ciba Specialty Chemicals. .

  These hindered amine light stabilizers can be used alone or in combination of two or more. These hindered amine light stabilizers may of course be used in combination with additives such as plasticizers, stabilizers, UV absorbers, etc., or may be introduced into a part of the molecular structure of these additives. Good. The blending amount is determined within a range that does not impair the effects of the present invention, and is generally about 0.01 to 20 parts by mass, preferably about 0.1 to 20 parts by mass with respect to 100 parts by mass of the negative birefringent resin. It is about 02-15 mass parts, Most preferably, it is about 0.05-10 mass parts. The light stabilizer or agent may be added at any stage of preparing the melt of the negative birefringent resin composition, for example, at the end of the melt preparation process.

Plasticizer:
The polarizing plate protective film A may contain a plasticizer. The addition of a plasticizer is preferable from the viewpoint of film modification such as improvement of mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability. Moreover, when manufacturing the said polarizing plate protective film A with a melt film-forming method, it aims at lowering the melting temperature of a film constituent material by addition of a plasticizer rather than the glass transition temperature of the negative birefringent resin to be used. Or for the purpose of lowering the viscosity at the same heating temperature than an additive negative birefringent resin. For the polarizing plate protective film A, for example, a plasticizer selected from a phosphoric acid ester derivative and a carboxylic acid ester derivative is preferably used. Further, a polymer obtained by polymerizing an ethylenically unsaturated monomer having a weight average molecular weight of 500 to 10,000 described in JP-A No. 2003-12859, an acrylic polymer, an acrylic polymer having an aromatic ring in the side chain, or cyclohexyl An acrylic polymer having a group in the side chain is also preferably used.

Fine particles:
The polarizing plate protective film A may contain fine particles. Examples of the fine particles include fine particles of inorganic compounds and fine particles of organic compounds, and any of them may be used. The average primary particle size of the fine particles contained in the negative birefringent resin in the present invention is preferably 5 nm to 3 μm, more preferably 5 nm to 2.5 μm, from the viewpoint of keeping haze low. More preferably, it is 2.0 μm. Here, the average primary particle size of the fine particles is determined by observing a negative birefringent resin with a transmission electron microscope (magnification of 500,000 to 1,000,000 times) and obtaining an average value of the primary particle sizes of 100 particles. To do. The addition amount of the fine particles is preferably 0.005 to 1.0 mass% with respect to the negative birefringent resin, more preferably 0.01 to 0.8 mass%, still more preferably 0.00. It is 02-0.4 mass%.

Optical adjusting agent:
The polarizing plate protective film A may contain an optical adjusting agent. Examples of the optical adjusting agent include a retardation adjusting agent, and an optical adjusting agent that improves negative birefringence is particularly preferable. Examples of such additives include JP-A-2006-52329, JP-A-2007-65184, 2008-15118, JP-A-2001-166144, JP-A-2003-344655, and JP-A-2003-248117. And those described in JP-A-2003-66230. By adding an optical adjusting agent, in-plane retardation (Re) and thickness direction retardation (Rth) can be controlled. A preferable addition amount is 0 to 10% by mass, more preferably 0 to 8% by mass, and further preferably 0 to 6% by mass.

<Polarizing plate protective film B>
As the polarizing plate protective film B of the polarizing plate of the present invention, a known polarizing plate protective film for a polarizing plate is used. The polarizing plate protective film B is preferably a cellulose acylate film or an acrylic film. For example, a known triacetyl cellulose (TAC) film (for example, Fujitac T-60 manufactured by Fuji Film Co., Ltd.) can be preferably used. The lurose acylate film may be surface treated. Examples of the surface treatment method include saponification treatment.

<Polarizer>
As the polarizer, for example, a film obtained by immersing and stretching a polyvinyl alcohol film in an iodine solution can be used.

  As the polarizer used in the present invention, any appropriate one can be selected as long as the object of the present invention can be achieved. Examples of the polarizer include a uniaxially stretched film obtained by adsorbing a dichroic substance such as iodine or a dichroic dye on a hydrophilic polymer film, a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product. And polyene-based oriented films. Examples of the hydrophilic polymer film include a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, and an ethylene / vinyl acetate copolymer partially saponified film. In the present invention, a polarizer in which iodine is adsorbed on a polyvinyl alcohol film is preferable.

  The polarizer preferably further contains at least one of potassium and boron. When the polarizer contains potassium and boron, a polarizer (polarizing plate) having a composite elastic modulus (Er) in a preferable range and having a high degree of polarization can be obtained. For production of a polarizer containing at least one of potassium and boron, for example, a film which is a material for forming a polarizer may be immersed in a solution of at least one of potassium and boron. The solution may also serve as a solution containing iodine.

  The polarizer may be subjected to any surface modification treatment in order to improve the adhesion with the adhesive. Examples of the surface modification treatment include corona treatment, plasma treatment, glow discharge treatment, flame treatment, ozone treatment, UV ozone treatment, and ultraviolet treatment. These treatments may be used alone or in combination of two or more.

<Adhesive layer>
The polarizing plate of the present invention may have an adhesive layer as at least one of the outermost layers (such a polarizing plate may be referred to as an adhesive polarizing plate). As a particularly preferred embodiment, a pressure-sensitive adhesive layer for adhering to another member such as another optical film or a liquid crystal cell can be provided on the side of the polarizing plate protective film A where the polarizer is not adhered.

  The polarizing plate of the present invention is preferably used in a liquid crystal display device, and may be provided on either the viewing side or the backlight side of the liquid crystal cell or on both sides, and is not limited. Specific examples of the image display device to which the polarizing plate of the present invention can be applied include a self-luminous display device such as an electroluminescence (EL) display, a plasma display (PD), and a field emission display (FED: Field Emission Display). Can be mentioned. The liquid crystal display device is applied to a transmissive liquid crystal display device, a reflective liquid crystal display device, and the like.

[Production method of polarizing plate]
The manufacturing method of the polarizing plate of this invention is demonstrated.
The manufacturing method of the polarizing plate of this invention is a manufacturing method of a polarizing plate including the process of manufacturing the polarizing plate protective film A, and the bonding process of bonding the said polarizing plate protective film A to one surface of a polarizer. And the step of producing the polarizing plate protective film A includes a melt of a composition containing a negative birefringent resin between the first clamping surface and the second clamping surface constituting the clamping device clamping device. A step of forming the film into a band-shaped film, and a step of making the moving speed of the first pinching surface faster than the moving speed of the second pinching surface, wherein the bonding step protects the polarizing plate. The film A and the strip-shaped polarizer are overlapped with each other so that the longitudinal directions of the strip-shaped films coincide with each other.
In the present specification, “matching in the longitudinal direction of each strip-shaped film and overlapping and bonding” is also referred to as “bonding by roll-to-roll”. Here, typically, the term “bonding by roll-to-roll” means that a film wound from a roll is bonded to another film without being cut in the width direction and wound around the roll again. May be expressed. However, the term “bonding by roll-to-roll” in the present specification is not limited to the above-described typical embodiment, and the film is bonded to another film without being cut once in the width direction. This means broadly, and the step of winding the film from the roll and the step of finally winding it on the roll are not essential. Therefore, both the mode in which each manufactured strip-shaped film is continuously pasted on-line and the mode in which each strip-shaped film is once wound on a roll and then pasted together are finally cut without being wound on a roll. Thus, a mode of producing a polarizing plate is also included.
In general, the polarizing plate protective films A and B and the polarizer are each continuously manufactured as a belt-like film. From the viewpoint of productivity, the length in the longitudinal direction of each film (the length to form a film) is It becomes considerably long with respect to the length in the width direction.
Thus, when it can bond together by a roll to roll, compared with the case where it cuts out from a strip | belt-shaped film to a polarizing plate size and bonds together, continuous production becomes easy and the manufacturing cost of a polarizing plate becomes remarkably low. Conventionally, a method for producing a polarizing plate by bonding a film having a slow axis and a tilt direction orthogonal to each other with a polarizer and a roll-to-roll has not been known and has not been studied.
The present invention is characterized by having a step of laminating a film having a slow axis and an inclination direction orthogonal to each other and a polarizer by roll-to-roll. Specifically, the step of passing the melt of the composition containing such a negative birefringent resin between the first clamping surface and the second clamping surface constituting the clamping device clamping device and molding it into a film shape And having a step of laminating the polarizing plate protective film A obtained by the step of making the moving speed of the first pinching surface faster than the moving speed of the second pinching surface with the polarizer and roll to roll, This is a feature of the present invention that is different from the conventional method. As described above, in the present invention, the use of a negative birefringent resin as the material of the polarizing plate protective film A was studied. Surprisingly, the tilt structure is large, the slow axis faces the film width direction, and the tilt orientation. It has been found that a film having the characteristic that the film faces the film transport direction can be obtained. In addition, when the polarizing plate of the present invention in which the film and the polarizer are directly bonded to each other by roll-to-roll is incorporated into a liquid crystal display device, the viewing angle can be greatly widened, and light leakage when viewed obliquely is improved. I found out that In the present invention, the use of a negative birefringent resin as a material for the polarizing plate protective film A was examined. Surprisingly, contrary to the conventional expectation, the side chain of the negative birefringent resin is uniformly formed. It was found that the films were arranged in an orderly manner in the same direction, and the slow axis and the tilt direction of the obtained film were orthogonal.
Furthermore, in order to increase the expression of optical properties (retardation), the method for producing a polarizing plate of the present invention preferably includes a step of stretching the polarizing plate protective film A in at least one direction.

<< Process for Producing Polarizing Plate Protective Film A >>
First, the process for producing the polarizing plate protective film A will be described.
In the method for producing a polarizing plate of the present invention, a melt of a composition containing a negative birefringent resin (hereinafter, also referred to as a melt) is formed between a first clamping surface and a second clamping surface constituting a clamping device clamping device. It has the process of making it pass in between and shape | molding in a strip | belt-shaped film form, and making the moving speed of said 1st pressing surface faster than the moving speed of said 2nd pressing surface.
Examples of the clamping device having different speeds on the first clamping surface and the second clamping surface include, for example, a combination of two rolls having different peripheral speeds, and rolls having different speeds described in Japanese Patent Application Laid-Open No. 2000-219752. Examples include a combination of touch belts (single-sided belt method), a combination of belts and belts (double-sided belt method), and the like. Among these, it is preferable that the two rolls have different peripheral speeds because the melt can be uniformly applied to the melt.
Hereinafter, the manufacturing method of the said polarizing plate protective film A is demonstrated in detail.

In the manufacturing method of the polarizing plate protective film A, a composition containing a negative birefringent resin is melt-extruded from a die, and a bank is formed in a gap between the first and second pressing surfaces constituting the pressing device. It is preferable. When the bank is formed, the melt resin is crushed between the pinching devices to cause a large elongation deformation, and the melt resin can be sufficiently deformed. Therefore, a film having a preferable range of γ, Re, Rth can be obtained. can get. The presence / absence of bank formation and the amount of bank can be measured and photographed using a camera, an ultrasonic transmitter / receiver or a sensor. For example, the bank measurement methods described in JP-A-7-195395, JP-A-9-174663, and JP-A-10-26438 can be used.
In the conventional known technique, for example, in Patent Document 3 (Japanese Patent Laid-Open No. 2007-237495), when a bank is generated, there is a problem that a viewing angle becomes narrow due to the bank being crushed in the thickness direction, which is not preferable. That is described. In the present invention, when a negative birefringent resin is formed, a bank is formed as described above, and a shear rate is applied by applying a difference in moving speed between the first and second clamping surfaces. Surprisingly, it was also found that the polarizing plate protective film A having a large tilt structure, a slow axis in the film width direction, and a tilt direction in the film transport direction can be obtained by performing the film formation. It was.

<Supply of melt of negative birefringent resin composition>
In the manufacturing method of the polarizing plate protective film A, a composition containing a negative birefringent resin (sometimes referred to as “negative birefringent resin composition”) is a first clamping surface constituting a clamping device; Including a step of passing between the second clamping surfaces and continuously clamping to form a belt-like film, and supplying the molten resin containing a negative birefringent resin to the clamping step from the supply means . At that time, there is no particular limitation on the means for supplying the melt (melt) of the composition. For example, as a specific means for supplying the melt, an embodiment using an extruder that melts and extrudes the composition into a film may be used, or an embodiment using an extruder and a die may be used. Alternatively, it may be melted by a heating means to form a melt and then supplied to the film forming process.
The method for producing a film of the present invention preferably includes a step of melt-extruding the composition from a die from the viewpoint of suppressing unevenness in optical properties of the resulting film. Moreover, it is preferable from a viewpoint of suppressing the nonuniformity of the optical characteristic of the film obtained more to include the process of allowing the melt-extruded melt to pass between said 1st pressing surface and said 2nd pressing surface.
When the thermoplastic resin composition is melt-extruded, it is preferable to pelletize the negative birefringent resin composition before melt-extruding. Commercially available negative birefringent resins (for example, Delpet 980N, DayLark D332, Polyimilex PSX0371, Polyimilex PAS1460, Polyimilex PML203) may be pelletized, but if not pelletized The following method can be used. As said negative birefringent resin, what was demonstrated as a negative birefringent resin contained in the said polarizing plate protective film A can be used, and its preferable range is also the same. The same applies to additives.
The negative birefringent resin composition is dried, melted at 150 ° C. to 300 ° C. using a twin-screw kneading extruder, and then extruded into noodles, and solidified in air or water and cut. . Further, after melting by an extruder, it can be pelletized by an underwater cutting method in which it is cut while being directly extruded from a die into water. Extruders used for pelletization include single screw extruders, non-meshing different direction rotating twin screw extruders, meshing different direction rotating twin screw extruders, and meshing same direction rotating twin screw extruders. Etc. can be used. The number of revolutions of the extruder is preferably 10 rpm to 1000 rpm, more preferably 20 rpm to 700 rpm. The extrusion residence time is 10 seconds to 10 minutes, more preferably 20 seconds to 5 minutes.
No particular limitation is imposed on the size of the pellets is generally about 10mm ³ ~1000mm ^3, more preferably about 30 mm ³ 500 mm ^3.

  It is preferred to reduce the moisture in the pellets prior to melt extrusion. A preferable drying temperature is 40 to 200 ° C, more preferably 60 to 150 ° C. Thereby, the moisture content is preferably 1.0% by mass or less, and more preferably 0.1% by mass or less. Drying may be performed in air, nitrogen, or vacuum.

  When melt extrusion is performed using an extruder, it is preferable that the dried pellets are then fed into a cylinder via a feed port of the extruder, kneaded and melted. The inside of the cylinder is composed of, for example, a supply unit, a compression unit, and a measurement unit in order from the supply port side. The screw compression ratio of the extruder is preferably 1.5 to 4.5, the ratio of the cylinder length to the cylinder inner diameter (L / D) is preferably 20 to 70, and the cylinder inner diameter is preferably 30 mm to 150 mm. The extrusion temperature of the supply means (for example, a die) for supplying the thermoplastic resin composition (hereinafter, also referred to as discharge temperature) is determined according to the melting temperature of the negative birefringent resin. About 190-300 degreeC is preferable. Furthermore, in order to prevent the molten resin from being oxidized by residual oxygen, it is also preferable to carry out the inside of the extruder in an inert (nitrogen or the like) air flow or while evacuating using an extruder with a vent.

  It is preferable to provide a filtration device incorporating a breaker plate type filtration or a leaf type disk filter for foreign matter filtration in the negative birefringent resin composition. Filtration may be performed in one stage or may be performed in multistage filtration. The filtration accuracy is preferably 15 μm to 3 μm, more preferably 10 μm to 3 μm. It is desirable to use stainless steel as the filter medium. As the configuration of the filter medium, a knitted wire, a sintered metal fiber or metal powder (sintered filter medium) can be used, and among them, a sintered filter medium is preferable.

  In order to reduce the variation in the discharge amount and improve the thickness accuracy, it is preferable to provide a gear pump between the extruder and the supply means (for example, die) for supplying the thermoplastic resin composition. Thereby, the resin pressure fluctuation width in the supply means (for example, die | dye) which supplies the said thermoplastic resin composition can be made into less than +/- 1%. In order to improve the quantitative supply performance by the gear pump, a method of controlling the pressure before the gear pump to be constant by changing the number of rotations of the screw can also be used.

  The molten resin is melted by the extruder configured as described above, and the molten resin is continuously sent to a supply means (for example, a die) for supplying the thermoplastic resin composition via a filter and a gear pump as necessary. The die may be any of a T die, a fish tail die, and a hanger coat die. It is also preferable to insert a static mixer immediately before the supply means (for example, die) for supplying the thermoplastic resin composition in order to increase the uniformity of the resin temperature.

When the supply means is a die, the clearance at the die exit portion (hereinafter also referred to as lip gap) is generally 1.0 to 30 times the film thickness, preferably 5.0 to 20 times. Specifically, it is preferably 0.1 to 30 mm, more preferably 0.2 to 20 mm, and particularly preferably 0.3 to 15 mm.
In the manufacturing method of the polarizing plate protective film A, the radius of curvature of the tip of the die lip is not particularly limited, and a known die can be used.

It is preferable that the die can be adjusted in thickness at intervals of 5 to 50 mm. An automatic thickness adjustment die that calculates downstream film thickness and thickness deviation and feeds back the results to die thickness adjustment is also effective.
In addition to the single layer film forming apparatus, it is also possible to manufacture using a multilayer film forming apparatus.
In this way, the residence time from when the resin enters the extruder through the supply port until it exits from the supply means (for example, die) for supplying the thermoplastic resin composition is preferably 3 to 40 minutes, more preferably 4 Minutes to 30 minutes.

<Cast>
Next, a negative birefringent resin composition melt supplied from any supply means is continuously passed between the first clamping surface and the second clamping surface constituting the clamping device while forming a bank. The film is pressed to form a film, preferably cooled and solidified to obtain a film. At this time, from the viewpoint of stabilization of productivity, one of the first clamping surface and the second clamping surface is peeled off first from the melt, and then the other surface is peeled off from the other surface. preferable. In the manufacturing method of the polarizing plate protective film A, the moving speed of the first pressing surface is faster than the moving speed of the second pressing surface, but the surface to be peeled first is the second pressing surface. Although it may be a pressing surface, from the viewpoint of suppressing the peeling dan, it is preferable that the first surface to be peeled first is the first pressing surface (the pressing surface having a high moving speed).

(Surface temperature difference of the clamping surface)
The method for producing the polarizing plate protective film A is a conventional method in which a melt-extruded melt is continuously sandwiched between a first sandwiching surface and a second sandwiching surface constituting a sandwiching device to form a film. In addition, a temperature difference of 0.1 ° C. to 50 ° C. is provided between the surface temperature of the first clamping surface and the surface temperature of the second clamping surface of the clamping device. It is preferable from the viewpoint that the inclined structure can be enlarged when the shear stress is applied to the melt.
The temperature difference is preferably 1 to 40 ° C., more preferably 5 to 30 ° C., from the viewpoint of increasing the inclined structure and maintaining a good surface shape. If the temperature difference is less than 0.1 ° C., the gradient structure of the negative birefringent film does not increase. On the other hand, if the temperature difference exceeds 50 ° C., the surface condition of the film may be deteriorated.

  Here, the surface temperature of the first pinching surface is the first temperature in the portion 1 cm above the first pinching surface from the pinching start portion of the section where the negative birefringent resin-containing composition is pinched. Represents the temperature of the clamping surface. The surface temperature of the second pressure-clamping surface is the second pressure-clamping surface in a portion 1 cm above the second pressure-clamping surface from the pressure-clamping start portion of the section where the negative birefringent resin-containing composition is pinched. Represents temperature.

At that time, the surface temperature of both of the nipping surfaces is Tg-50 ° C to Tg + 40 ° C, more preferably Tg-40 ° C to Tg + 30 ° C, more preferably using the glass transition temperature Tg of the negative birefringent resin. Set to Tg-30 ° C to Tg + 20 ° C. Although there is no restriction | limiting in particular as such a temperature control method, For example, it can achieve by letting the liquid and gas which temperature-controlled inside each clamping surface.
The glass transition temperature of the negative birefringent resin is determined by placing the resin in a measurement pan using a scanning differential calorimeter (DSC), and placing the resin in a nitrogen stream at 30 ° C. to 300 ° C. at 10 ° C./min. The temperature was raised to 30 ° C. at −10 ° C./min, and the temperature was raised again from 30 ° C. to 300 ° C. at 10 ° C./min (2nd-run). The temperature at which the baseline starts to deviate from the low temperature side in 2nd-run can be obtained as the glass transition temperature (Tg).

(Movement speed ratio)
In the manufacturing method of the polarizing plate protective film A, the moving speed ratio between the first clamping surface and the second clamping surface of the clamping device defined by the formula (I) is controlled to 0.60 to 0.99, Shear stress is applied when the molten resin passes through the clamping device. The moving speed ratio between the clamping surfaces of the clamping device is preferably 0.75 to 0.98, and more preferably 0.85 to 0.95.

(pressure)
In the method for producing the polarizing plate protective film A, there is no particular limitation on the pressure applied when the melt is clamped, but it is preferable that the melt is clamped at a pressure of 20 to 500 MPa in the present invention. It is preferable from the viewpoint of expressing to the range. The pressure is more preferably 25 to 300 MPa from the viewpoint of expressing Re [0 °] to the preferred range in the present invention in addition to γ, and particularly preferably 30 to 200 MPa. For example, when two rolls are used, the pressure applied to the melt by the sandwiched surface can be measured by passing a pressure measurement film (such as a prescale for medium pressure manufactured by Fuji Film) through the two rolls. In the case of other pinching devices, it can be measured by the same or similar method.

(Discharge temperature)
In the production method of the polarizing plate protective film A, the discharge temperature (resin temperature at the outlet of the supply means) is preferably Tg + 50 to Tg + 200 ° C., and Tg + 70 to Tg + 180 ° C. from the viewpoint of improving the moldability of the resin and suppressing deterioration. It is more preferable that it is Tg + 90-Tg + 150 degreeC. That is, if Tg + 50 ° C. or higher, the viscosity of the resin is sufficiently low and the moldability is good, and if Tg + 200 ° C. or lower, the resin is less likely to deteriorate.

(Air gap)
In the manufacturing method of the polarizing plate protective film A, for example, when the thermoplastic resin composition is supplied from a supply means such as a die to the pinching device, an air gap (from the die outlet of the supply means to the melt landing point of the pinching device). Is preferably as close as possible from the viewpoint of heat retention of the melt between the air gaps, specifically, preferably 10 to 300 mm, more preferably 20 to 250 mm, particularly preferably, 30-200 mm.

(Transport temperature)
In the manufacturing method of the said polarizing plate protective film A, after passing through the location which narrows the melt of the said clamping apparatus, the said film-form melt is conveyed using the cast roll of Tg-100 degreeC-Tg-10 degreeC. It is preferable from the viewpoint of reducing the rate of change Δγ of γ around 500 hours in an environment of 60 ° C. and 90% relative humidity. That is, it is preferable to arrange 1 to 6 metal rigid cast rolls continuously, except for the cast rolls (chill rolls) constituting the clamping device, and more preferably 2 to 4 rolls in the transport direction. It is preferable to cool slowly according to the downstream side. It is preferable that the temperature of all the cast rolls is the said range except the cast roll (chill roll) which comprises a pinching apparatus. The temperature of the cast roll is more preferably Tg-100 ° C to Tg-15 ° C, and particularly preferably Tg-40 ° C to Tg-15 ° C. Thereby, by removing the residual strain of the film formed by applying a shear stress, it is difficult for a change in optical properties to occur in a dimensional change or a high-temperature and high-humidity environment, and a stable inclined structure can be maintained. Moreover, you may convey the melt shape | molded by the said film form using the cast roll which can control surface temperature distribution at Tg-10 degreeC-Tg-100 degreeC. As such a special apparatus, for example, a film manufacturing apparatus in which a heating means (apparatus) and a cooling means (apparatus) are further installed at suitable positions in a conventionally known clamping apparatus, or Japanese Patent Application Laid-Open No. 2006-256159. Mention may be made of the described rolls.
When the pinching device is a roll, the diameter of the transport cast roll excluding the cast roll (chill roll) constituting the pinching device is preferably 50 to 5000 mm, more preferably 100 to 2000 mm, More preferably, it is 150-1000 mm. The interval between the rolls is preferably 0.3 to 300 mm between the surfaces, more preferably 1 to 100 mm, and further preferably 3 to 30 mm.

(Line speed)
In the manufacturing method of the polarizing plate protective film A, the line speed (film forming speed) is preferably 2 m / min or more, and more preferably 5 m / min or more, from the viewpoint of heat retention of the melt in the air gap. It is particularly preferably 10 m / min or more. When the line speed is increased, cooling of the melt in the air gap can be suppressed, and more uniform shear deformation can be imparted by the pinching device while the melt temperature is high. The line speed represents the speed at which the melt passes between the clamping apparatuses and the film conveyance speed in the conveyance apparatus.

  In the manufacturing method of the said polarizing plate protective film A, the width | variety of a film-form melt does not have a restriction | limiting in particular, For example, it can be 200-2000 mm.

(Cast using two rolls)
Among the methods of forming a film by continuously pressing the supplied melt between a first clamping surface and a second clamping surface constituting a clamping device, two rolls (for example, touch roll (first 1 roll) and chill roll (second roll)). In addition, in this specification, when it has two or more casting rolls which convey the said melt, the casting roll nearest to the said thermoplastic resin composition supply means (for example, die | dye) of the most upstream is also called a chill roll. . Hereinafter, the preferable aspect of the manufacturing method of the said polarizing plate protective film A using two rolls is demonstrated.

  In the manufacturing method of the polarizing plate protective film A, the landing point of the melt extruded from the supplying unit is not particularly limited, and the landing point of the melt extruded from the supplying unit is closest to the touch roll and the chill roll. The distance from the vertical line passing through the midpoint of the gap in the part to be performed may be zero or may be shifted. The landing point of the melt refers to a point where the melt extruded from the supply means contacts (lands) the touch roll or chill roll for the first time. The midpoint of the gap between the touch roll and the chill roll refers to the midpoint of the touch roll surface and the chill roll surface where the gap between the touch roll and the chill roll is the narrowest.

  The surface of the two rolls (for example, touch roll and chill roll) preferably has an arithmetic average height Ra of 100 nm or less, more preferably 50 nm or less, and further preferably 25 nm or less.

  In the manufacturing method of the polarizing plate protective film A, the width of each of the two rolls is not particularly limited, and can be freely changed and employed in accordance with the width of the film-like melt.

  The roll pressure between two rolls rotating at different peripheral speeds is preferably 20 to 500 MPa, more preferably 25 to 300 MPa, and particularly preferably 30 to 200 MPa.

  In the manufacturing method of the said polarizing plate protective film A, in order to pressurize the roll pressure of the said range, a cylinder setting value will be changed suitably. The cylinder set value varies depending on the resin material used and the material of the two rolls. For example, when the effective width of the film-like melt is 200 mm, it is preferably 3 to 100 KN, and preferably 3 to 50 KN. Is more preferable, and 3 to 25 KN is particularly preferable.

In the manufacturing method of the said polarizing plate protective film A, in order to pressurize the roll pressure of the said range, it is preferable to use the roll whose Shore hardness of a roll is 45 HS or more. The Shore hardness of the two preferable rolls is preferably 50 HS or more, and more preferably 60 to 90 HS.
The Shore hardness can be determined from the average value of values measured at 5 points in the roll width direction and 5 points in the circumferential direction using the method of JIS Z 2246.

The material of the two rolls is preferably a metal from the viewpoint of achieving the Shore hardness, more preferably stainless steel, and a roll whose surface is plated is also preferred. Moreover, if the material of two rolls is a metal, since the surface unevenness | corrugation is small and the surface of a film is hard to be damaged, it is preferable. On the other hand, a rubber roll or a metal roll lined with rubber can be used as long as it does not contradict the spirit of the present invention.
As for the touch roll, for example, JP-A-11-314263, JP-A-2002-36332, JP-A-11-235747, WO97 / 28950, JP-A-2004-216717, JP The thing of 2003-145609 gazette can be utilized.

Furthermore, in the manufacturing method of the said polarizing plate protective film A, a shear stress is provided when molten resin passes two rolls by controlling the peripheral speed ratio of two rolls which let a film-form melt pass. The polarizing plate protective film A is manufactured. The peripheral speed ratio of the two rolls is 0.60 to 0.99, more preferably 0.75 to 0.98, and particularly preferably 0.85 to 0.95. Here, the peripheral speed ratio of the two rolls means the peripheral speed of the slow roll / the peripheral speed of the fast roll.
When the peripheral speed ratio of the two rolls is 0.60 to 0.99, a film having an inclined structure and having an inclined orientation orthogonal to the slow axis can be obtained. In addition, it is possible to stably produce a film that is hardly scratched on the film surface and has good smoothness.
In order to obtain the polarizing plate protective film A, whichever of the two rolls may be fast, when the touch roll is slow, a bank (excess of the melt stays on the roll) on the touch roll side. , Formed stays) are formed. Since the touch roll has a short contact time with the melt, the bank formed on the touch roll side cannot be sufficiently cooled, and a peeling dan is generated, which easily causes a surface failure. Therefore, it is preferable that the slow roll is a chill roll and the fast roll is a touch roll.

  Furthermore, in the manufacturing method of the said polarizing plate protective film A, it is preferable to use a roll with a large diameter as said two rolls, respectively, Specifically, two diameters are 350-600 nm, More preferably, 350-500 nm. It is preferable to use a roll. When a roll with a large diameter is used, the contact area between the film-like melt and the roll becomes wide, and the time for shearing becomes longer. Therefore, a film with a large γ, and Re [0 °] and Re [+ 40 °] And Re [−40 °] can be produced while suppressing variations. In the method for producing the polarizing plate protective film A, the diameters of the two rolls may be the same or different.

  In the manufacturing method of the polarizing plate protective film A, the two rolls are driven at different peripheral speeds. The two rolls may be driven or driven independently. However, in order to suppress variations in Re [0 °], Re [+ 40 °] and Re [−40 °], the two rolls are preferably driven independently. .

Furthermore, the manufacturing method of the polarizing plate protective film A is characterized in that a temperature difference of 0.1 ° C. to 50 ° C. is applied to the surface temperatures of the two rolls in order to increase the γ. The temperature difference is preferably 1 to 40 ° C., more preferably 5 to 30 ° C., from the viewpoint of increasing the inclined structure and maintaining a good surface shape.
At that time, the temperature of the two rolls is Tg-50 ° C to Tg + 60 ° C, more preferably Tg-40 ° C to Tg + 30 ° C, more preferably Tg, using the glass transition temperature Tg of the negative birefringent resin. Set to −30 ° C. to Tg + 20 ° C. Such temperature control can be achieved by passing a temperature-controlled liquid or gas through the touch roll.

Further, in the method for producing the polarizing plate protective film A, the melt of the negative birefringent resin composition supplied from the supply unit is melted until it reaches the pressing surface of the pressing device from the supply unit. It is preferable to keep the object warm and to reduce the temperature distribution in the width direction. Specifically, the temperature distribution in the width direction is preferably within 5 ° C. In order to reduce the temperature distribution, it is preferable to dispose a member having a heat insulating function or a heat reflecting function in at least a part of the air gap to shield the melt from the outside air. Thus, by arranging the heat insulating member in the passage and shielding it from the outside air, it is possible to suppress the influence of the external environment, for example, wind, and to suppress the temperature distribution in the width direction of the film. The temperature distribution in the width direction of the film-like melt is more preferably within ± 3 ° C., and even more preferably within ± 1 ° C.
Furthermore, when the shielding member is used, since the film-like melt can be passed between rolls in a high temperature state, that is, in a state where the melt viscosity is low, the effect of easily producing the polarizing plate protective film A is also obtained. is there.
The temperature distribution of the film-like melt can be measured with a contact thermometer or a non-contact thermometer.

The said shielding member is provided inside the both ends of two rolls and the width direction side surface and clearance gap of the supply means (for example, die | dye) of a thermoplastic resin composition, for example. The shielding plate may be directly fixed to the side surface of the supply means, or may be supported and fixed by a support member. For example, the width of the shielding member is preferably equal to or greater than the width of the side surface of the supply means so that the rising airflow due to the heat radiation of the supply means can be efficiently blocked.
The gap between the shielding member and the end in the width direction of the film-like melt is preferably narrow so as to efficiently shield the rising airflow flowing along the surface of the roll. More preferably, it is about 50 mm from the part. Note that the gap between the side surface of the supply unit and the shielding member is not necessarily provided, but is preferably formed to a degree that allows airflow in the space surrounded by the shielding member to be discharged, for example, 10 mm or less.
In addition, as the material having a heat insulating function and / or a heat reflecting function, a material excellent in wind insulation and heat retention is preferable. For example, a metal plate such as stainless steel can be preferably used.

  As a method for eliminating variations in Re [0 °], Re [+ 40 °], and Re [−40 °], there is a method of increasing adhesion when a film-like melt comes into contact with a roll. Specifically, the adhesion can be improved by combining electrostatic application method, air knife method, air chamber method, vacuum nozzle method and the like. Such an adhesion improving method may be performed on the entire surface of the film-like melt or may be partially performed.

After film formation in this way, it is preferable to cool the film by using one or more casting rolls in addition to two rolls (for example, a casting roll and a touch roll) that allow the film-like melt to pass through. The touch roll is usually arranged so as to touch the first casting roll (chill roll) on the most upstream side (the thermoplastic resin composition supply means, for example, the one closer to the die). In general, it is relatively common to use three cooling rolls, but this is not a limitation. The interval between the plurality of casting rolls is preferably 0.3 mm to 300 mm, more preferably 1 mm to 100 mm, and even more preferably 3 mm to 30 mm between the surfaces.
In the manufacturing method of the said polarizing plate protective film A, it is preferable that especially the temperature of the casting rolls other than two rolls which let a film-form melt pass is Tg-100 degreeC-Tg-10 degreeC, Tg-100 More preferably, it is C-Tg-15 degreeC, and it is especially preferable that it is Tg-40 degreeC-Tg-15 degreeC.

  Further, it is preferable to trim both ends of the processed film. The portion cut off by trimming may be crushed and used again as a raw material. Further, it is also preferable to perform a thickness increasing process (knurling process) on one or both ends. The height of the unevenness due to the thickness increasing process is preferably 1 μm to 50 μm, more preferably 3 μm to 20 μm. Thickening processing may be convex on both sides or convex on one side. The width of the thickness increasing process is preferably 1 mm to 50 mm, more preferably 3 mm to 30 mm. Extrusion can be performed at room temperature to 300 ° C.

  It is also preferable to attach a lami film on one side or both sides before winding. The thickness of the laminated film is preferably 5 μm to 100 μm, more preferably 10 μm to 50 μm. The material is not particularly limited, such as polyethylene, polyester, and polypropylene.

  The winding tension is preferably 2 kg / m width to 50 kg / width, more preferably 5 kg / m width to 30 kg / width.

  The film thickness of the film obtained by the method for producing the polarizing plate protective film A when unstretched is preferably 100 μm or less. When used for a liquid crystal display or the like, from the viewpoint of thinning, it is more preferably 80 μm or less, particularly preferably 60 μm or less, and particularly preferably 40 μm or less.

<Stretching and relaxation treatment>
Furthermore, after forming into a film by the said method, you may extend | stretch and / or relax the said polarizing plate protective film A. FIG. For example, each process can be implemented by the following combinations (a) to (g).
(A) Longitudinal stretching (b) Longitudinal stretching → Relaxation treatment (c) Longitudinal stretching → Lateral stretching (d) Longitudinal stretching → Lateral stretching → Relaxation treatment (e) Lateral stretching (f) Lateral stretching → Relaxation treatment (g) Lateral stretching → relaxation treatment → longitudinal stretching → relaxation treatment The production method of the polarizing plate protective film A preferably includes a step of stretching in at least one direction from the viewpoint of expanding the expression range of optical properties, and is preferable among these combinations. Are the steps (a) to (d). In addition, the method for producing a polarizing plate of the present invention preferably includes a longitudinal stretching step from the viewpoint of making the slow axis and the tilt direction of the polarizing plate protective film A orthogonal to each other and reducing the production cost. It is preferable to include a longitudinal stretching step without including a step, and it is particularly preferable to include only a longitudinal stretching step. Moreover, when it is necessary to reduce manufacturing cost further, the manufacturing method of the polarizing plate of this invention does not need to include the process of extending | stretching the polarizing plate protective film A. FIG.

The transverse stretching can be performed using a tenter. That is, the film is stretched by holding both ends in the width direction with clips and widening the film in the lateral direction. At this time, the stretching temperature can be controlled by sending wind at a desired temperature into the tenter. The stretching temperature is preferably Tg-20 ° C to Tg + 30 ° C, more preferably Tg-15 ° C to Tg + 20 ° C, and further preferably Tg-10 ° C to Tg + 10 ° C or less. Moreover, a preferable lateral stretch ratio is 1.2 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.2 to 2.0 times.
By performing preheating before stretching and heat setting after stretching, the Re and Rth distribution after stretching can be reduced, and the variation in orientation angle associated with bowing can be reduced. Either preheating or heat setting may be performed, but both are more preferable. These preheating and heat setting are preferably performed by holding with a clip, that is, preferably performed continuously with stretching.
Preheating can be performed at a temperature about 1 ° C to 50 ° C higher than the stretching temperature, preferably 2 ° C to 40 ° C or less, more preferably 3 ° C to 30 ° C. The preheating time is preferably 1 second to 10 minutes, more preferably 5 seconds to 4 minutes, and even more preferably 10 seconds to 2 minutes. During preheating, it is preferable to keep the width of the tenter substantially constant. Here, “substantially” refers to ± 10% of the width of the unstretched film.
The heat setting can be performed at a temperature lower by 1 ° C. to 50 ° C. than the stretching temperature, more preferably 2 ° C. to 40 ° C., further preferably 3 ° C. to 30 ° C. More preferably, it is less than the stretching temperature and less than Tg. The preheating time is preferably 1 second to 10 minutes, more preferably 5 seconds to 4 minutes, and even more preferably 10 seconds to 2 minutes. During the heat setting, it is preferable to keep the width of the tenter substantially constant. Here, “substantially” refers to 0% (the same width as the tenter width after stretching) to −10% (shrinking by 10% from the tenter width after stretching = reduced width) of the tenter width after stretching. If the width is wider than the stretched width, residual strain tends to occur in the film, which is not preferable.

Longitudinal stretching can be achieved by making the peripheral speed on the outlet side faster than the peripheral speed on the inlet side while heating between two pairs of rolls. Under the present circumstances, the expression property of the retardation of the thickness direction can be changed by changing the space | interval (L) between and the film width (W) before extending | stretching. When L / W (referred to as aspect ratio) is 2 to 50 or less (long span stretching), it is easy to produce a film having a small Rth, and when L / W is 0.01 to 0.3 (short span), a film having a large Rth is used. Can be created. In this embodiment, any of long span stretching, short span stretching, and a region between them (intermediate stretching = L / W exceeds 0.3 and 2 or less) may be used. Span stretching and short span stretching are preferred. Further, when aiming at high Rth, it is more preferable to use short span stretching, and when aiming at low Rth, it is distinguished from long span stretching.
The stretching temperature is preferably Tg-20 ° C to Tg + 30 ° C, more preferably Tg-15 ° C to Tg + 20 ° C, and further preferably Tg-10 ° C to Tg + 10 ° C or less. Moreover, a preferable longitudinal draw ratio is 1.2 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.2 to 2.0 times.

Furthermore, dimensional stability can be improved by performing relaxation treatment after these stretching. Thermal relaxation is preferably performed either after film formation, after longitudinal stretching, or after lateral stretching, or both. The relaxation treatment may be performed online continuously after stretching, or may be performed offline after winding after stretching.
Thermal relaxation is (Tg-30) ° C to (Tg + 10) ° C, more preferably (Tg-20) ° C to (Tg + 5) ° C, more preferably (Tg-10) ° C to (Tg + 3) ° C for 1 second to 10 minutes. More preferably 5 seconds to 4 minutes, further preferably 10 seconds to 2 minutes, 0.1 kg / m to 20 kg / m, more preferably 1 kg / m to 16 kg / m, still more preferably 2 kg / m to 12 kg / m. It is preferable to carry out while carrying with tension.

<< Process for Producing Polarizer >>
As the method for producing the polarizer, a conventionally known method can be applied. For example, as a method for obtaining the polyvinyl alcohol-based film, any appropriate forming method can be adopted. A conventionally known method can be applied as the molding method. Moreover, a commercially available film can be used as it is for the polyvinyl alcohol film. Examples of commercially available polyvinyl alcohol films include the product name “Kuraray Vinylon Film” manufactured by Kuraray Co., Ltd., the product name “Tosero Vinylon Film” manufactured by Tosero Co., Ltd., and the products manufactured by Nippon Synthetic Chemical Industry Co., Ltd. Names include “Nippon Vinylon Film”.

  Regarding an example of a method for producing a polarizer, for example, a polymer film (raw film) mainly composed of a polyvinyl alcohol resin is immersed in a swelling bath containing pure water and a dyeing bath containing an aqueous iodine solution. Swelling treatment and dyeing treatment are performed while applying tension in the film longitudinal direction with different rolls. Next, the film subjected to the swelling treatment and the dyeing treatment is immersed in a crosslinking bath containing potassium iodide, and is subjected to crosslinking treatment and final stretching treatment while tension is applied in the longitudinal direction of the film with rolls having different speed ratios. Is given. The film subjected to crosslinking treatment is immersed in a washing bath containing pure water by a roll and subjected to a washing treatment. The film subjected to the water washing treatment is dried and wound up after adjusting the moisture content. Thus, the polarizer can be obtained by stretching the original film, for example, 5 to 7 times the original length.

<< Bonding process >>
In the manufacturing method of the present invention, the laminating step includes a step of laminating the polarizing plate protective film A and the strip-shaped polarizer so that the longitudinal directions of the strip-shaped films coincide with each other.
The polarizing plate of the present invention can be produced by bonding one side of the polarizing plate protective film A (a surface-treated surface in the case of surface treatment) to at least one side of the polarizer using an adhesive. When the polarizing plate protective film B, the polarizer, and the polarizing plate protective film A are bonded together in this order, the polarizing plate of the present invention is bonded to the polarizer and other films using an adhesive on both sides of the polarizer. Can be manufactured.
In the manufacturing method of the polarizing plate of this invention, the said polarizing plate protective film A is directly bonded with a polarizer.
Moreover, in the manufacturing method of the polarizing plate of this invention, from the viewpoint of reducing manufacturing cost, the said polarizing plate protective film A and the said strip | belt-shaped polarizer are overlap | superposed so that the longitudinal direction of each strip | belt-shaped film may correspond (roll). To produce by bonding (to roll). In a transmissive liquid crystal panel such as TN, OCB, and ECB, it is preferable that the slow axis of the retardation film used and the tilt direction are orthogonal to each other in order to realize a wide viewing angle. Even when the polarizing plate protective film A is manufactured without including a stretching step, the slow axis and the tilt direction are orthogonal to each other. Thus, the polarizing plate of the present invention can be produced at a lower cost and more easily than bonding a film and a polarizer.
The method of laminating the polarizing plate protective film A and the strip-shaped polarizer with a roll-to-roll is, for example, using an adhesive in the longitudinal direction of the polarizing plate protective film A in the step of producing the polarizing plate protective film A ( MD) roll-shaped film can be unwound and bonded directly on one side of the dyed and stretched polarizer film on a roll-to-roll basis.
Moreover, the method of bonding the polarizing plate protective film B and the polarizer with a roll-to-roll method is to unwind the roll-shaped polarizing plate protective film B using an adhesive, and then dye and stretch the polarizing plate. The protective film A can be bonded directly on the surface opposite to the side to which the protective film A is bonded, in a roll-to-roll manner. At this time, the polarizing plate protective film A, the polarizer, and the polarizing plate protective film B may all be bonded simultaneously or sequentially. Preferably, the adhesive is applied to both sides of the dyed and stretched polarizer film, and the roll-shaped polarizing plate protective film B is unwound on one surface of the polarizer and the roll-shaped polarizing plate protective film A unwound. This is a method in which an object is simultaneously bonded to the other surface of the polarizer. That is, in the method for producing a polarizing plate of the present invention, in the bonding step, the polarizing plate protective film A, the strip-shaped polarizer, and the strip-shaped polarizing plate protective film B are arranged in this order. It is more preferable from the viewpoint of reducing the manufacturing cost to have a process of making the longitudinal directions coincide with each other so as to overlap and bond.

  As the adhesive, a known polarizing plate-producing adhesive can be used unless it is contrary to the gist of the present invention. Moreover, the aspect which has an adhesive bond layer between the said polarizer and each film is also preferable. Specific examples of the adhesive include an aqueous solution of polyvinyl alcohol or polyvinyl acetal (eg, polyvinyl butyral) and a latex of a vinyl-based polymer (eg, polybutyl acrylate). A particularly preferred adhesive is an aqueous solution of fully saponified polyvinyl alcohol. The polyvinyl alcohol-based adhesive preferably contains a polyvinyl alcohol-based resin and a crosslinking agent.

  The manufacturing method of the polarizing plate of the present invention is not limited to the above method as long as it does not contradict the gist of the present invention, and other methods can also be used. For example, JP 2000-171635, JP 2003-215563, JP 2004-70296, JP 2005-189437, JP 2006-199788, JP 2006-215463, JP 2006-227090. JP, 2006-243216, JP 2006-243681, JP 2006-259313, JP 2006-276574, JP 2006-316181, JP 2007-10756, JP 2007-128025, Use methods described in JP 2007-140092, JP 2007-171943, JP 2007-197703, JP 2007-316366, JP 2007-334307, JP 2008-20891, etc. it can. Among these, the methods described in JP2007-316366A and JP2008-20891A are more preferable.

[Liquid Crystal Display]
The polarizing plate of the present invention can be used in various modes of liquid crystal display devices. Preferably, it can be used for TN (Twisted Nematic), OCB (Optically Compensatory Bend), ECB (Electrically Controlled Birefringence) mode liquid crystal display devices, and more preferably for TN and ECB mode liquid crystal displays.

  When a polarizing plate other than the polarizing plate of the present invention is provided on one side of the liquid crystal display device, the polarizing plate preferably has a polarizing plate protective film attached to one or both surfaces of the polarizer. The polarizing plate protective film may be the polarizing plate protective film A. Moreover, the various films conventionally used as a polarizing plate protective film, such as a cellulose acylate film and a cyclic polyolefin polymer film, can be used.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[Production Example 1] Production of pellets of styrene-maleic anhydride resin A-1 As a styrene-maleic anhydride resin, pellets of "Dylark D332" manufactured by Nova Chemical Co. were used. “Dylark D332” indicates negative intrinsic birefringence. The glass transition point of the resin was 130 ° C.

[Production Example 2] Production of pellets of N-phenylmaleimide-acrylonitrile-styrene copolymer resin A-2 As an acrylonitrile-styrene copolymer, pellets of "Polyimilex PAS1460" manufactured by Nippon Shokubai Co., Ltd. were used. “Polyimilex PAS1460” exhibits negative intrinsic birefringence. Further, the glass transition point of the copolymer resin was 167 ° C.

[Production Example 3] Production of pellets of styrene-acrylic resin A-3 As acrylic resins, pellets of "Delpet 980N" manufactured by Asahi Kasei Chemicals Co., Ltd., which is a styrene-acrylic copolymer, were used. “Delpet 980N” indicates negative intrinsic birefringence. The glass transition point of the resin was 123 ° C.

[Production Example 4] Production of methyl methacrylate-styrene copolymer resin A-4 As methyl methacrylate-styrene copolymer resin, Estyrene MS600 manufactured by Nippon Steel Chemical Co., Ltd. (trade name, methyl methacrylate / styrene = 6/4 copolymer resin) and 60 parts by mass of pellets of a copolymer resin “polyimilex PML203” of methyl methacrylate-styrene-N-phenylmaleimide manufactured by Nippon Shokubai Co., Ltd. Kneading extrusion was performed under nitrogen with a twin-screw extruder to obtain pellets of the resin composition. The Tg of the resin composition was 118 ° C. The mixed resin exhibits negative intrinsic birefringence.

[Production Example 5] Production of pellets of polyvinyl acetal resin A-5 After dissolving 100 parts by mass of a polyvinyl alcohol resin having a polymerization degree of 700 and a saponification degree of 98 mol% in 700 parts by mass of distilled water, the temperature was kept at 20 ° C. To this was added 29 parts by mass of 35% by weight hydrochloric acid, and 50 parts by mass of benzaldehyde was further added. Next, the resin was precipitated by cooling to 12 ° C.
Next, after hold | maintaining for 30 minutes, 108 mass parts of hydrochloric acid was added, and it heated up at 45 degreeC, and kept for 6 hours. After completion of the reaction, the mixture was washed with distilled water for 10 hours, and sodium hydroxide was added to the polyvinyl acetal resin after washing with water to adjust the pH of the dispersion to 9. The dispersion was held at 55 ° C. for 6 hours and then cooled. The pH of the dispersion at this time was 8.5. Next, after washing the dispersion with 100 times the amount of distilled water with respect to the solid content, the dispersion is kept at 50 ° C. for 5 hours, washed with 10 times the amount of distilled water, dehydrated and then dried. A polyvinyl acetal resin having a glass transition temperature of 132 ° C. was obtained. The mixture was kneaded and extruded under nitrogen with a twin-screw extruder to obtain resin composition pellets.
About the obtained polyvinyl acetal resin, when the ratio of a structural component was measured by the method based on JISK6729 "polyvinyl formal test method", the structural unit p represented by the said General formula (3) is 40 mol%, q Was 58.3 mol% and r was 1.7 mol%. Moreover, the obtained polyvinyl acetal resin exhibits negative intrinsic birefringence.

[Production Example 6] Production of Comparative Polycarbonate Resin C-1 Pellets As comparative polycarbonate resin, pellets of "Taflon MD1500" manufactured by Idemitsu Kosan Co., Ltd. were used. “Taflon MD1500” exhibits positive intrinsic birefringence. Moreover, the glass transition point of the said resin was 150 degreeC.

[Example 1]
(Preparation of polarizing plate protective film A)
Using pellets of resin A-1 shown in Table 1 below as a negative birefringent resin, drying is performed at 100 ° C. for 2 hours or more, and stabilizer IRGANOX-1010 (manufactured by Ciba Specialty Chemicals Co., Ltd.) is used as resin 100 weight. 0.6 part by weight was added to the part, melted at 265 ° C., kneaded and extruded using a single-screw kneading extruder. At this time, a screen filter, a gear pump, and a leaf disk filter with a filtration accuracy of 5 μm were arranged in this order between the extruder and the die, and these were connected by a melt pipe. Extrusion was performed from a die having a T-die extrusion discharge temperature of 265 ° C., a width of 1500 mm, and a lip gap of 1 mm.
Thereafter, a melt (molten resin) was extruded between the cast roll and the touch roll. At this time, the cylinder is set so that the material has a width of 1800 mm on the uppermost stream side and a diameter of 400 mm is made of carbon steel subjected to hard chrome plating surface treatment so that the touch pressure shown in Table 1 below is obtained. A touch roll made of carbon steel, which is made of a material having a width of 1400 mm, a diameter of 350 mm, and a metal surface thickness of 30 mm and subjected to a hard chrome plating surface treatment, was brought into contact. The touch roll was a drum-shaped rigid roll with a clan amount of 3 mm. Touch pressure is measured by sandwiching a pre-scale for medium pressure (made by Fuji Film Co., Ltd.) between two rolls controlled at 25 ° C. at a constant circumferential speed (5 m / min) without melt. It was set as the pressure at the time of film forming. Touch rolls and chill rolls having a Shore hardness of 65 HS were used. In addition, the melt was dropped on the central part sandwiched between the cast roll and the touch roll. The distance between the die and the melt landing point was set to 110 mm. Using these rolls, the touch roll peripheral speed is high, the chill roll peripheral speed is low, the peripheral speed ratio is set to the conditions shown in Table 1 below, and the film is formed at the transport speed (chill roll speed) shown in Table 1 below. did. The temperature of the chill roll was Tg−5 ° C., and the temperature of the touch roll was set based on the temperature difference between the chill roll and the touch roll described in Table 1 below. The temperature of the chill roll and the temperature of the touch roll are the surface temperature of each roll in the portion 1 cm above each roll from the pinching start portion of the section where the negative birefringent resin-containing composition is pinched. Was measured. The bank formation control can be adjusted by the film forming conditions (gap between the pressing devices, film forming temperature, speed, touch pressure, roll temperature). The presence or absence of bank formation was observed using a cable type endoscope equipped with a CCD camera, and is shown in Table 1. Further, the determination of the presence or absence of bank formation can be measured by the following simple method instead when the presence or absence of bank formation cannot be determined by the method using the CCD camera. When touching in the state where the bank is formed, the touch roll is pulled away from the chill roll at about 10 cm / second to suddenly return to the state without touch. Banks accumulated in the gaps of the clamping device are released all at once, and the bank marks remain in stripes on the film after solidification after cooling. If a change in thickness has occurred in the flow direction of the portion where no film is touched, it can be confirmed that a bank has been formed. The film forming atmosphere was 25 ° C. and 50%.
Thereafter, the obtained film was conveyed by a chill roll (which is also the first cast roll), then the second cast roll set to the temperature described in Table 1 below, and further 10 ° C. from the surface temperature of the second cast roll. It was conveyed by a lower third cast roll. Then, after trimming both ends (5 cm each) of the touched portion immediately before winding, the both ends were subjected to thicknessing (knurling) with a width of 10 mm and a height of 20 μm. The film forming width was 1300 mm and the film was wound up by 450 m. The thickness of the film after film formation was set to the thickness of the following Table 1, and the polarizing plate protective film A of Example 1 was produced.

(Optical characteristics of polarizing plate protective film A)
The optical properties of the obtained film of Example 1 are also shown in Table 1. In addition, the inclination direction which measured Re [+40 degree] and Re [-40 degree] of the polarizing plate protective film A including another Example is all the longitudinal directions of a film.
Moreover, (gamma) at the time of making the polarizing plate protective film A of obtained Example 1 pass for 60 hours in a 60 degreeC and the relative humidity of 90% was measured. The rate of change Δγ with γ before exposure to a humid heat environment was calculated, and the results obtained are shown in Table 1 below.

[Examples 2 to 18, Comparative Examples 1 and 2]
Polarizing plate protective films A of Examples and Comparative Examples were obtained in the same manner as in Example 1 except that the resin used and the film forming conditions were changed as described in Table 1 below. The optical properties of the polarizing plate protective film A of each example and comparative example are shown in Table 1 below. In Example 12, instead of the touch roll, a touch belt made of carbon steel having a material of 800 mm in width, 20 mm in thickness of the metal surface, and 30 mm in length of the pinched portion is subjected to hard chrome plating surface treatment instead of the touch roll. The film was manufactured. In addition, the film forming temperature of each resin is as follows. A-2 resin film forming temperature is 280 ° C., A-3 resin film forming temperature is 260 ° C., A-4 resin film forming temperature is 265 ° C., A-5 resin film forming temperature is 255 ° C., C− The film forming temperature of one resin is 265 ° C.

From Table 1, it was found that Examples 1 to 18 all had a slow axis and a tilt direction, and the slow axis and the tilt direction were orthogonal. On the other hand, Comparative Example 1 was sandwiched between the touch roll and the chill roll without providing a difference in peripheral speed, and the obtained film did not express γ and there was no tilt orientation. Moreover, since the comparative example 2 uses resin made from positive birefringence as resin, the obtained resin has the slow axis in the MD direction, and the tilt direction is also in the MD direction. The tilt directions were not orthogonal. In Examples 1 to 18, γ is large, a gradient structure having a good phase difference is formed, the amount of Re [0 °] expressed is sufficiently large, the heat and heat durability of γ is excellent, and the elongation at break is also preferable. It turned out to be.
As described above, according to the manufacturing method of the present invention, while the bank is formed, the temperature difference between the two pressing surfaces between the pressing devices is defined as the scope of the present invention, and the moving speed within the range of the present invention is between the two pressing surfaces. By giving the difference, it was found that a film having a slow axis and a tilt direction and having a slow axis and a tilt direction orthogonal to each other can be produced.
Moreover, from Examples 1-18, it turned out that the polarizing plate protective film A of Examples 1-18 of this invention is a film suitable for an optical use, and can be used for a polarizing plate suitably as an optical compensation film especially. .

<Mounting and evaluation on TN liquid crystal panel>
(Preparation of polarizing plate for TN mode)
A polyvinyl alcohol (PVA) film having a thickness of 80 μm is dyed by immersion for 60 seconds in an iodine aqueous solution (30 ° C.) having an iodine concentration of 0.05 mass% and a KI concentration of 3 mass%, and then boric acid concentration is 4 mass%. The film was longitudinally stretched 5.5 times the original length while immersed in an aqueous solution (55 ° C.) with a KI concentration of 3.5% by mass for 55 seconds, and then dried at 50 ° C. for 4 minutes to obtain a thickness. A 20 μm polarizer was obtained.
Separately, a roll-like cellulose acylate film (Fujifilm KK, Fujitac TD80UL) was used as the protective film B for the polarizer. After saponification treatment in a sodium hydroxide aqueous solution at a concentration of 2.0 mol / L and 55 ° C., the sodium hydroxide was sufficiently washed away with water. Then, after being immersed for 1 minute in 35 degreeC dilute sulfuric acid aqueous solution at 0.005 mol / L, it was immersed in water, the dilute sulfuric acid aqueous solution was washed away sufficiently, and it dried at 105 degreeC.
The surface of the roll-shaped unstretched polarizing plate protective film A of Examples 1 to 18 and Comparative Examples 1 and 2 was subjected to corona discharge treatment so that the contact angle was 30 ° or less, and used as a protective film A for a polarizer. .
The roll-shaped unstretched films of Examples 1 to 18 and Comparative Examples 1 and 2 subjected to corona discharge treatment on the surface and the saponified roll-shaped Fujitac TD80UL were disposed on both sides of the dye-stretched polarizer film, respectively. Using a polyvinyl alcohol-based adhesive, a polarizer is directly affixed on a roll-to-roll basis, and after drying, a polarizing plate protective film A, a polarizing plate, a polarizing plate protective film B is obtained in this order. It was.

(Production of TN liquid crystal display device)
A pair of polarizing plates provided in a liquid crystal display device (AQUAS LC-20C1-S, manufactured by Sharp Corporation) using a TN type liquid crystal cell is peeled off, and the film of each example and comparative example is used instead. Each polarizing plate was attached to the viewer side and the backlight side one by one through an adhesive so that the film of each example and comparative example was on the liquid crystal cell side. The configuration of the liquid crystal display panel employed in each of the examples and comparative examples is shown in Table 1 and FIGS. In addition, the VAZ film (a slow axis has in a TD direction) made from a Fuji film was used for the biaxial retardation film used when making the panel configuration of FIG. The liquid crystal display device thus obtained was measured for a viewing angle with a contrast ratio of 10 or more during white display and black display by EZ-contrast manufactured by ELDIM. The display visibility was evaluated from the measured viewing angle by the following method, and the obtained results are shown in Table 1 above.
◯: The range of the tilt angle from the normal direction to the panel surface showing a contrast ratio of 10 or more in white display and black display of the liquid crystal cell is 60 ° or more in the vertical and horizontal directions with respect to the normal direction.
Δ: The range of the tilt angle from the normal direction to the panel surface where the contrast ratio at the time of white display and black display of the liquid crystal cell is 10 or more is 40 ° C. or more and less than 60 ° both vertically and horizontally with respect to the normal direction.
X: The range of the inclination angle from the normal direction with respect to the panel surface showing the contrast ratio of 10 or more in white display and black display of the liquid crystal cell is less than 40 ° C. in the vertical direction and the horizontal direction.
From Table 1, it was found that the polarizing plate of the present invention using the polarizing plate protective film A has good display visibility when incorporated in a TN liquid crystal display device. Furthermore, the polarizing plate of the present invention has little light leakage when viewed from an oblique direction during black display. In addition, it was found that such characteristics could be obtained when the polarizer was bonded by roll-to-roll, and from the viewpoint of not including a transverse stretching step that requires the use of an expensive apparatus, It turned out that the manufacturing cost of the polarizing plate with a characteristic can be reduced significantly.

(Extension of polarizing plate protective film A)
The unstretched film after film formation of Example 1 was stretched 1.2 times longitudinally while being heated at a temperature of Tg + 2 ° C. between two pairs of rolls. The thickness of the obtained stretched film is 74 μm, the slow axis is in the TD direction, the tilt direction is in the MD direction, Re [0 °] = 140 nm, Re [40 °] = 198 nm, Re [−40 °]. = 49 nm, γ = 149 nm, and Δγ = 0.4%. Like the unstretched Example 1 film, a polarizing plate was produced by roll-to-roll, and this was evaluated as a TN type liquid crystal panel in the same manner as described above. The contrast ratio between the white display and the black display of the liquid crystal cell was It was confirmed that the range of the inclination angle from the normal direction with respect to the panel surface showing 10 or more was 60 ° or more in both the upper, lower, left and right directions with respect to the facing direction. It was found that the retardation value was improved as compared with the unstretched film.

(Production and evaluation of ECB mode liquid crystal display device)
A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and the alignment film was rubbed. The obtained two glass substrates were opposed to each other so that the rubbing directions were antiparallel, and the cell gap was set to 2.8 μm. Injection was performed using a nematic liquid crystal material having a positive dielectric constant anisotropic layer, and an ECB cell having a liquid crystal cell Δnd LC of 300 nm (Δn is the refractive index anisotropy of the liquid crystal material) was produced. The manufactured liquid crystal display device was placed on a backlight, and a voltage was applied to the ECB cell with a 55 Hz rectangular wave.
Two polarizing plates prepared in each example and comparative example are bonded to the panel configuration shown in FIGS. 1 and 3 (the panel cell is the manufactured ECB cell) so as to sandwich the manufactured ECB cell, and the same tendency was gotten.
Thus, the polarizing plate of the present invention using the polarizing plate protective film A can perform large viewing angle compensation when incorporated in an ECB mode liquid crystal display device. Furthermore, the polarizing plate of the present invention has little light leakage when viewed from an oblique direction during black display. In addition, it was found that such characteristics could be obtained when the polarizer was bonded by roll-to-roll, and from the viewpoint of not including a transverse stretching step that requires the use of an expensive apparatus, It turned out that the manufacturing cost of the polarizing plate with a characteristic can be reduced significantly.

It is the schematic showing the absorption axis of the polarizing plate in the TN mode liquid crystal display device of this invention, the orientation direction of a liquid crystal cell, the slow axis of a film, and the inclination direction of a film. It is the schematic showing the absorption axis of the polarizing plate in the TN mode liquid crystal display device of this invention, the orientation direction of a liquid crystal cell, the slow axis of a film, and the inclination direction of a film. It is the schematic showing the absorption axis of the polarizing plate in the TN mode liquid crystal display device of the comparative example 2, the orientation direction of a liquid crystal cell, the slow axis of a film, and the inclination direction of a film.

Explanation of symbols

1a, 1b Polarizer 2a Polarizer absorption axis 2b Polarizer absorption axis (MD direction)
3a, 3b Polarizing plate protective film A in each example and film 4 in comparative example 1 In-plane slow axis direction (TD direction) of the film in each example and comparative example 1
5 Inclination direction (MD direction) of film of each example
6 Liquid crystal cell 7 Biaxial retardation film 8a, 8b Film 9 of Comparative Example 2 In-plane slow axis direction (MD direction) of film of Comparative Example 2
10 Inclination orientation (MD direction) of the film of Comparative Example 2

Claims (14)

A step of producing a polarizing plate protective film A;
A bonding step of bonding the polarizing plate protective film A to one surface of a polarizer, and a method for producing a polarizing plate,
The step of producing the polarizing plate protective film A is performed by passing a melt of a composition containing a negative birefringent resin between the first clamping surface and the second clamping surface constituting the clamping device clamping device. A step of forming a belt-like film, and a step of making the moving speed of the first pinching surface faster than the moving speed of the second pinching surface,
Production of a polarizing plate characterized in that the laminating step includes a step of laminating and laminating the polarizing plate protective film A and the strip-shaped polarizer by matching the longitudinal directions of the strip-shaped films. Method. The step of producing the polarizing plate protective film A comprises
Melt extruding a composition containing a negative birefringent resin from a die;
A step of forming a film by continuously pressing the melted and extruded melt between the first clamping surface and the second clamping surface constituting the clamping device while forming a bank; and
Controlling the moving speed ratio of the first clamping surface and the second clamping surface of the clamping device defined by the following formula (I) to 0.60 to 0.99;
The manufacturing method of the polarizing plate of Claim 1 characterized by the above-mentioned.
Movement speed ratio = speed of the second clamping surface / speed of the first clamping surface Formula (I)   The step of producing the polarizing plate protective film A includes the step of giving a temperature difference of 0.1 ° C. to 50 ° C. between the surface temperature of the first clamping surface and the surface temperature of the second clamping surface of the clamping device. The manufacturing method of the polarizing plate of Claim 1 or 2 characterized by the above-mentioned.   The step of producing the polarizing plate protective film A includes a step of conveying the melt formed into a film shape using a cast roll of Tg-10 ° C to Tg-100 ° C. The manufacturing method of the polarizing plate of any one of 1-3, (However, the said Tg represents the glass transition temperature of the said negative birefringent resin.).   The method for producing a polarizing plate according to any one of claims 1 to 4, wherein the pinching device is two rolls having different peripheral speeds.   The method for producing a polarizing plate according to any one of claims 1 to 5, wherein the step of producing the polarizing plate protective film A includes a step of sandwiching the melt with a pressure of 20 to 500 MPa. .   The method for producing a polarizing plate according to claim 1, comprising a step of stretching the polarizing plate protective film A in at least one direction.   The polarizing plate protective film A is a negative birefringent resin, and includes at least one selected from an acrylic resin, a styrene resin, a maleimide resin, a polyvinyl acetal resin, a cyclic olefin resin, and a polycarbonate resin. The manufacturing method of the polarizing plate of any one of Claims 1-7 characterized by the above-mentioned.   In the bonding step, the polarizing plate protective film A, the strip-shaped polarizer, and the strip-shaped polarizing plate protective film B are overlapped in this order so that the longitudinal directions of the strip-shaped films coincide with each other. The method for producing a polarizing plate according to claim 1, further comprising a step of combining.   The said polarizing plate protective film B is a cellulose acylate film or an acrylic film, The manufacturing method of the polarizing plate of any one of Claims 1-9 characterized by the above-mentioned.   A polarizing plate produced by the method for producing a polarizing plate according to claim 1.   The polarizing plate according to claim 11, wherein the slow axis of the polarizing plate protective film A and the tilt direction of the polarizing plate protective film A are orthogonal to each other.   The polarizing plate according to claim 11 or 12, wherein the polarizing plate is for TN mode, OCB mode, or ECB mode.   A liquid crystal display device using at least one polarizing plate according to claim 11.

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