JP5437782B2 - Film manufacturing method, polarizing plate and liquid crystal display device - Google Patents

Description

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

  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 a method of tilting the optical axis in the thickness direction of a film as a retardation film for TN liquid crystal, and a tilted retardation film having a tilted structure.

  For example, in Patent Document 1, after forming a film, by passing the film between two rolls having different peripheral speeds, a shearing force is applied to the film (that is, a shear is given), and the optical axis is inclined. Describes a method for producing such a film and its application to a TN liquid crystal display. However, the method described in Document 1 has problems such as large variations in optical characteristics of the film and easy contact scratches on the film surface. Nor did it suggest application to melts. On the other hand, in Patent Document 2, the melt extruded from the die during film formation is sandwiched between a metal roll and a metal roll, and a peripheral speed difference is given to these (hereinafter also referred to as peripheral speed difference film formation). The optical axis is inclined. In Patent Document 3, a metal roll whose surface is covered with rubber is used, and the optical axis is tilted by giving a peripheral speed difference thereto.

  However, the effect of optical compensation is not sufficient simply by using an optical film having an inclined optical axis for a liquid crystal display. For example, Patent Document 3 discloses an optical film in which the optical axis is inclined by 11.5 to 18.2 ° in the embodiment, but there is no description about the relationship between the optical axis inclination angle and the optical compensation of the liquid crystal display. Not. In addition, in order to perform optical compensation of a transmissive TN or ECB liquid crystal display or a transflective TN or ECB liquid crystal display, it is necessary to have a large phase difference until the retardation of the liquid crystal cell can be compensated. It was not sufficient that the optical axis was inclined by 11.5 to 18.2 °. Therefore, an optical film having a larger inclined structure has been desired.

  On the other hand, in recent years, the demand for image quality required for a liquid crystal display device has been increasing year by year, and in particular, development of an optical compensation film that does not cause blurring of an image when incorporated in a liquid crystal display device is desired.

JP-A-6-222213 JP 2003-25414 A JP 2007-38646 A

  When the inventors examined the methods described in Patent Documents 2 and 3, first, an unstretched film was formed at the time of film formation according to these methods. It is observed that streaks extending in the orthogonal direction (strip-shaped unevenness in the width direction that occurs periodically to some extent with a pitch of several mm, so-called horizontal dunes) occur, and this causes blurring of the image when used in a liquid crystal display device I found it. Furthermore, when the longitudinal stretching process (stretching process in the film transport direction), which is an essential constituent element in the production methods described in Patent Documents 2 and 3, was performed on the unstretched film according to these documents, the obtained film was obtained. Although the streak extending in the direction orthogonal to the tilt axis of the film was eliminated to some extent, the tilt structure formed of the unstretched film was greatly broken. Moreover, although various conditions described in these documents were examined, when the inclined structure did not collapse, the horizontal dan could not be eliminated. As described above, the methods described in Patent Documents 2 and 3 have a small amount of horizontal dan, and a film having an inclined structure cannot be obtained.

  The present invention has been made in consideration of the above-mentioned problems, and a first object of the present invention is to provide a film having an inclined structure and a small amount of horizontal dans and a method for producing the same. A second object of the present invention is to provide a polarizing plate and a liquid crystal display device using the film.

  As a result of intensive studies to solve the above problems, the present inventors have performed special temperature control on the nip roll used, particularly in the longitudinal stretching step which is an essential constituent requirement in the production methods described in Patent Documents 2 and 3. The present inventors have found that the horizontal dan can be eliminated while maintaining the inclined structure of the unstretched film (the variation in the distribution in the width direction is very small). That is, the inventors have found that the following production method and a film produced by the method can solve the above problems, and have completed the present invention described below.

[1] A film comprising a thermoplastic resin, having an inclined structure, and having 3 or less 3 cm stripes extending in a direction perpendicular to the inclined axis.
[2] The film according to [1], which satisfies the following formulas (I) and (II):
50 nm ≦ Re [0 °] ≦ 300 nm (I) Formula (In the formula (I), Re [0 °] is a plane at a wavelength of 550 nm measured from the normal direction in a plane including the film tilt direction and the film normal) Represents inward retardation.)
40 nm ≦ γ ≦ 300 nm (II) Formula γ = | Re [+ 40 °] −Re [−40 °] | Formula (II) ′
(In the formula (II), Re [+ 40 °] is an in-plane direction at a wavelength of 550 nm measured from a direction tilted 40 ° toward the tilt azimuth side with respect to the normal in the plane including the film tilt azimuth and the film normal. Re [−40 °] represents retardation in the in-plane direction at a wavelength of 550 nm measured from a direction tilted by −40 ° toward the tilt direction with respect to the normal line.
[3] The film according to [1] or [2], wherein a distribution in a direction perpendicular to the γ inclination axis is 0% to 10%, and a retardation Rth in the thickness direction is 40 to 300 nm.
[4] In any one of [1] to [3], the thermoplastic resin is at least one selected from a polycarbonate resin, a norbornene resin, an acrylic resin, and a cellulose acylate resin. The film described.
[5] A pressing step of forming a film by continuously pressing a melt of a composition containing a thermoplastic resin between a first clamping surface and a second clamping surface constituting the clamping device. (In the pressing step, the moving speed of the first pressing surface is made faster than the moving speed of the second pressing surface), a film is obtained by solidifying the film-like melt, and the obtained film Between the first nip roll made of two rolls and the second nip roll made of two rolls in order, and the peripheral speed of the second nip roll is made higher than the peripheral speed of the first nip roll. Longitudinal stretching step of stretching in the film transport direction at high speed (in the longitudinal stretching step, at least one of the first nip roll and the second nip roll is set to a temperature of 0. 0 between each surface temperature of two rolls constituting the nip roll. 1 ° C to 10 ° C And a temperature difference of 0 ° C. is controlled).
[6] A pressing step for forming a film by continuously pressing a melt of a composition containing a thermoplastic resin between a first clamping surface and a second clamping surface constituting the clamping device. (In the pressing step, the moving speed of the first pressing surface is made faster than the moving speed of the second pressing surface), a film is obtained by solidifying the film-like melt, and the obtained film Between the first nip roll made of two rolls and the second nip roll made of two rolls in order, and the peripheral speed of the second nip roll is made higher than the peripheral speed of the first nip roll. Longitudinal stretching step of accelerating and stretching in the film conveying direction (in the longitudinal stretching step, at least one of the first nip roll or the second nip roll is set to 0 between the peripheral speeds of the two rolls constituting the nip roll. .01-10 % Of the peripheral speed difference is controlled).
[7] In the longitudinal stretching step, at least one of the first nip roll and the second nip roll is given a temperature difference of 0.1 ° C. to 10 ° C. between the surface temperatures of the two rolls constituting the nip roll. The method for producing a film according to [6], wherein the film is controlled as follows.
[8] The method includes a step of melt-extruding a composition containing the thermoplastic resin from a die, and a step of passing the melt-extruded melt between the first pressing surface and the second pressing surface. The method for producing a film according to any one of [5] to [7].
[9] The method for producing a film according to any one of [5] to [8], wherein in the pressing step, the melt is pressed at a pressure of 15 to 500 MPa.
[10] The method for producing a film according to any one of [5] to [9], wherein in the pinching step, the melt is pinched at a pressure of 30 to 500 MPa.
[11] In the clamping step, control is performed so that a difference in moving speed between the first clamping surface and the second clamping surface of the clamping device defined by the following formula (III) is 0.5 to 20%. The method for producing a film according to any one of [5] to [10].
Formula (III)
Difference in moving speed (%) = 100 × [(moving speed of first pressing surface) − (moving speed of second pressing surface)]
/ (Moving speed of the first clamping surface)
[12] The method for producing a film according to any one of [5] to [11], wherein, in the pressing step, the pressing device is two rolls having different peripheral speeds.
[13] The method for producing a film according to [12], wherein a metal touch roll having an outer cylinder thickness of 6 to 45 mm is used for one of the two rolls constituting the pressing device.
[14] A film formed by the method for producing a film according to any one of [5] to [13].
[15] A polarizing plate using at least one film according to any one of [1] to [4] and [14].
[16] A liquid crystal display device using at least one film according to any one of [1] to [4] and [14].

  According to the present invention, it is possible to provide a film having an inclined structure and having few streaks extending in a direction orthogonal to the inclination axis, and a manufacturing method thereof. Further, it is possible to provide a film having a sufficiently large tilt structure and capable of realizing sufficient optical compensation when used in a liquid crystal display, and a method for manufacturing the film. When such a film is incorporated in a liquid crystal display device, the viewing angle can be compensated sufficiently wide, and the liquid crystal display device has very little image blur. Therefore, the image quality of the liquid crystal display device is improved. Specifically, the film having the above optical characteristics can realize sufficient optical compensation when used in a TN mode, ECB mode, or OCB mode liquid crystal display. For example, since a viewing angle is narrow in a TN mode liquid crystal display, an optical compensation film (for example, WV film (manufactured by Fujifilm)) provided with an optical compensation layer made of a liquid crystal composition that realizes optical compensation is usually polarized. When the film of the present invention is used, an optical compensation having an optical compensation layer made of a conventional liquid crystal composition can be used without using an optical compensation layer made of a liquid crystal composition. Viewing angle compensation can be performed more easily than those using a film. Moreover, the film of this invention can be provided with the manufacturing method of the film of this invention.

It is a top view showing the absorption axis of the polarizing plate, the orientation direction of a liquid crystal cell, and the slow axis of a film in the transflective ECB mode liquid crystal display device of the present invention.

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. Further, in the present specification, the “film longitudinal direction” means an MD (machine direction) direction (that is, a film transport direction). Further, “longitudinal stretching” means stretching in the MD direction, and “lateral stretching” refers to stretching in a direction orthogonal to the direction of conveyance in the MD direction (that is, direction orthogonal to the film conveyance direction). means.
In the present specification, the tilted structure refers to a structure in which the orientation characteristics as viewed from the thickness direction are tilted, specifically, those having different retardation values measured by tilting left and right with respect to the film surface.
In the present invention, the melt and the film solidified after the pinching step are sandwiched between the pinching devices during the pinching step and the longitudinal stretching, respectively. When the pinching device is two rolls, the pinching step Two rolls that are sometimes sandwiched are referred to as “touch rolls” or “touch rolls and chill (cooling) rolls”, and a pair of (two) rolls that sandwich a film during the longitudinal stretching process are collectively referred to as “nip rolls”. .

[the film]
The film of the present invention includes a thermoplastic resin, has an inclined structure, and has a horizontal dan of 3/3 cm or less.

(Horizontal Dan)
In the film of the present invention, the number of lines extending in the direction orthogonal to the tilt axis is 3/3 cm or less, preferably 2/3 cm or less, and more preferably 1/3 cm or less. In the present specification, the “muscle extending in the direction orthogonal to the tilt axis” refers to a muscle extending in the direction orthogonal to the tilt axis by 5 mm or more among the muscles extending in the direction orthogonal to the tilt axis. The stripes extending in the direction orthogonal to the tilt axis occur periodically to some extent, for example, at a pitch of several mm. Hereinafter, this “muscle extending in the direction orthogonal to the tilt axis” is also referred to as a horizontal dan. The number of horizontal dunes is counted by placing a sample film between orthogonally arranged polarizing plates (crossed Nicols) and visually detecting the number. If it is below this range, the liquid crystal display device used in the crossed Nicol similarly does not cause actual damage such as image blurring.

(In-plane retardation Re, γ, thickness direction retardation Rth)
The film of the present invention preferably satisfies the following formulas (I) and (II) from the viewpoint of sufficiently achieving optical compensation.
50 nm ≦ Re [0 °] ≦ 300 nm (I) Formula (In the formula (I), Re [0 °] is a plane at a wavelength of 550 nm measured from the normal direction in a plane including the film tilt direction and the film normal) Represents inward retardation.)
40 nm ≦ γ ≦ 300 nm (II) Formula γ = | Re [+ 40 °] −Re [−40 °] | Formula (II) ′
(In the formula (II), Re [+ 40 °] is an in-plane direction at a wavelength of 550 nm measured from a direction tilted 40 ° toward the tilt azimuth side with respect to the normal in the plane including the film tilt azimuth and the film normal. Re [−40 °] represents retardation in the in-plane direction at a wavelength of 550 nm measured from a direction tilted by −40 ° toward the tilt direction with respect to the normal line.

  In this specification, the “direction inclined by θ ° from the film normal” is defined as a direction inclined 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 °. When considering the sign of the inclination angle (θ), the direction in which Re [+ 40 °] is measured and the direction in which Re [−40 °] are measured are positions symmetrical with respect to the film normal.

The film of the present invention more preferably satisfies the following formulas (III) and (IV).
70 nm ≦ Re [0 °] ≦ 250 nm (III) Formula 60 nm ≦ γ ≦ 250 nm (IV) Formula (V) More preferably, Formula (V) and Formula (VI) are satisfied.
100 nm ≦ Re [0 °] ≦ 200 nm (V) formula 80 nm ≦ γ ≦ 180 nm (VI) formula

When γ is large, it means that Re measured by light incident obliquely is different between the left side and the right side, for example, and an inclined structure is formed in the film when viewed from the thickness direction. This tilt structure complements the liquid crystal alignment in the liquid crystal display device and has the effect of improving the viewing angle. When γ is in the range of the formula (II), the contrast when incorporated in a liquid crystal display device is remarkably improved. Here, when the contrast is lowered and it becomes difficult to see the image, the horizontal dan is easily visually recognized. For this reason, the visibility of a horizontal dan can be reduced by setting it as the said range.
Similarly, Re [0 °] is also preferably within the range of the above formula (I), since a contrast improving effect is exhibited, and horizontal dunes are hardly recognized.

  The film of the present invention preferably has a thickness direction retardation (Rth) of 40 nm to 300 nm, more preferably 50 nm to 200 nm, and still more preferably 50 nm to 150 nm. When Rth is in the above preferred range, the contrast when incorporated in a liquid crystal display device is remarkably improved, and similarly, horizontal dan is difficult to be visually recognized.

  A film having γ, Re [0 °] and Rth in the above preferred ranges can be produced by the production method of the present invention described later. In addition, when the optical film having the 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 and achieves a wide viewing angle. be able to.

(Gamma tilt axis and orthogonal distribution)
In the film of the present invention, the slow axis direction distribution of γ is preferably 0% to 10%, more preferably 0% to 7%, and still more preferably 0% to 5%. If the distribution in the direction orthogonal to the tilt axis of γ is 10% or less, display unevenness is difficult to be visually recognized when used for a liquid crystal display panel.

Further, the distribution of the γ tilt axis and the orthogonal direction can be measured by the following method. 30 cm of the slow axis direction of an arbitrary part of the stretched film is divided into 10 equal parts, and γ is measured by a measurement method described later. Of the 10 measured values of γ, the difference between the maximum and minimum points divided by the average value of 10 points and expressed as a percentage was defined as the γ tilt axis and orthogonal distribution (%).
Note that the variations in Re [0 °], slow axis, and Rth are also measured.

The variation in Re [0 °] appears as display unevenness when used in a liquid crystal display. Therefore, the variation is preferably as small as possible. Specifically, it is preferably within ± 3 nm, and within ± 1 nm. More preferably it is.
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 °.

なお、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表す。
また、式（Ａ）において、ｎｘは、面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘ及びｎｙに直交する方向の屈折率を表し、ｄは膜厚を表す。
測定されるフィルム状の測定対象物が１軸、又は２軸の屈折率楕円体で表現できないもの、いわゆる光学軸（ｏｐｔｉｃ ａｘｉｓ）がない測定対象物の場合には、以下の方法により、Ｒｔｈが算出される。
Ｒｔｈは、前記Ｒｅを面内の任意に設定した方位（ＫＯＢＲＡ ２１ＡＤＨ又はＷＲに設定できる）を傾斜軸（回転軸）としてフィルム法線方向に対して−５０°から＋５０°まで１０度ステップで各々その傾斜した方向から波長５５０ｎｍの光を入射させて１１点測定し、その測定されたレターデーション値と、平均屈折率の仮定値、及び入力された膜厚値を基にＫＯＢＲＡ ２１ＡＤＨ又はＷＲが算出する。
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。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と、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。これら平均屈折率の仮定値と膜厚を入力することで、ＫＯＢＲＡ ２１ＡＤＨ又はＷＲは、ｎｘ、ｎｙ、ｎｚを算出する。この算出されたｎｘ、ｎｙ、ｎｚよりＮｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）が更に算出される。
なお、Ｒｅ［θ°］、Ｒｔｈ及び屈折率の測定波長は特別な記述がない限り、測定波長５５０ｎｍでの値である。 In this specification, Re and Rth are the in-plane retardation (nm) and retardation in the thickness direction (nm) of a film-like object to be measured, such as an optically anisotropic layer, a film, or a laminate. Represent.
Re [0 °] is measured by making light having a wavelength of 550 nm incident in the normal direction of a film-like measurement object in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments). In selecting the measurement wavelength λnm, the wavelength selection filter can be exchanged manually, or the measurement value can be converted by a program or the like.
When the film-like measurement object to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth is calculated by the following method.
Rth is defined by using Re as an in-plane slow axis (determined by KOBRA 21ADH or WR) as an inclination axis (rotation axis) (in the case where there is no slow axis, the in-plane of the film-like object to be measured) The light having a wavelength of 550 nm from the inclined direction in steps of 10 degrees from the normal direction to −50 ° to + 50 ° with respect to the normal direction of the film-like object to be measured. The KOBRA 21ADH or WR is calculated based on the retardation value, the assumed value of the average refractive index, and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
Retardation value from two inclined directions with the slow axis as the rotation axis (in the absence of the slow axis, the in-plane arbitrary direction of the film-like object to be measured is the rotation axis). Rth can also be calculated from the following formula (A) and formula (B) based on the measured value, the assumed value of the average refractive index, and the input film thickness value.

In the formula, Re [θ] represents a retardation value in a direction inclined by an angle θ from the normal direction.
In the formula (A), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction orthogonal to nx in the plane, and nz represents the direction orthogonal to nx and ny. Refractive index is represented, d represents a film thickness.
In the case where a film-like measurement object to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a measurement object without a so-called optical axis, Rth is determined by the following method. Calculated.
Rth is an azimuth (respectively set to KOBRA 21ADH or WR) in which Re is set in the plane as a tilt axis (rotation axis) in a step of 10 degrees from −50 ° to + 50 ° with respect to the film normal direction Measured 11 points with light having a wavelength of 550 nm incident from the inclined direction, and KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed average refractive index, and the input film thickness value. To do.
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. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index values of main optical compensation films are as follows: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49) Polystyrene (1.59). The KOBRA 21ADH or WR calculates nx, ny, and nz by inputting the assumed average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.
Note that the measurement wavelengths of Re [θ °], Rth, and refractive index are values at a measurement wavelength of 550 nm unless otherwise specified.

In the present invention, Re [0 °], Re [+ 40 °] and Re [−40 °] of the film are measured using KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments Co., Ltd.). In the plane including the retardation value at a wavelength of 550 nm (at an inclination angle of 0 °) measured from the film normal direction, measured from the direction inclined by 40 ° to the tilt azimuth side or the temporary tilt azimuth side with respect to the normal line The retardation value (at an inclination angle of 40 degrees) and the retardation value (at an inclination angle of -40 degrees) measured from a direction inclined by -40 ° toward the inclination azimuth side or temporary inclination azimuth side with respect to the normal line. Represent.
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 from the direction inclined by 40 ° or −40 ° toward each temporary inclination direction with respect to the film normal, and | Re [+40 of each temporary inclination direction °] −Re [−40 °] |, that is, γ.
(3) The direction in which | Re [+ 40 °] −Re [−40 °] | is maximized is determined as the tilt direction.
That is, in this specification, “having a tilted orientation” means that there is an orientation in which | Re [+ 40 °] −Re [−40 °] |
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, it is a feature of the film of the present invention that when γ is measured in the tilt direction, a phase difference of 0 nm or more is expressed.
In this specification, Rth of the film is calculated by KOBRA 21ADH or WR using the tilt direction as the tilt axis (rotation axis).

  The film thickness of the film of the present invention 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 film production method of the present invention.

(Thermoplastic resin)
The thermoplastic resin used in the present invention is not particularly limited as long as it has the above-mentioned optical characteristics. However, when it is produced using a melt extrusion method, it is preferable to use a material having good melt extrusion moldability. , Cyclic olefin resins, cellulose acylate resins, polycarbonate resins, polyesters, polyolefins such as transparent polyethylene and transparent polypropylene, polyarylates, polysulfones, polyethersulfones, maleimide copolymers, transparent It is preferable to select nylons, transparent fluororesins, transparent phenoxys, polyetherimides, polystyrenes, acrylic resins, and styrene resins. One kind of the resin may be contained, or two or more kinds of the resins different from each other may be contained. In the film of the present invention, polycarbonate resin, cyclic olefin resin, acrylic resin, styrene resin, hydrocarbon vinyl compound (for example, poly α-olefin resin such as polypropylene and polymethylpentene) and cellulose acylate resin are used. It is preferably at least one selected, and more preferably at least one selected from polycarbonate resins, cyclic olefin resins, acrylic resins, and cellulose acylate resins. The cyclic olefins are preferably cyclic olefins obtained by addition polymerization.

In particular, cellulose acylate resins, cyclic olefin resins, and polycarbonate resins that exhibit positive intrinsic birefringence create films with slow axes oriented in the tilt direction when shear deformation is applied with two rolls. For example, if two rolls are placed parallel to the die exit, the tilt orientation is the same as the film longitudinal direction.
Moreover, when the acrylic resin and styrene resin exhibiting negative intrinsic birefringence are processed as described above, a film having a fast axis oriented in a tilt direction can be produced.

  When the film of the present invention is applied to a liquid crystal display device as a viewing angle compensation film, the positive or negative intrinsic birefringent resin is appropriately used in consideration of the characteristics of the liquid crystal display device and the convenience of polarizing plate processing. You can select and use.

Examples of the cyclic olefin resin that can be used in the present invention include a norbornene resin obtained by polymerization of a norbornene compound. Further, it may be a resin obtained by any polymerization method of ring-opening polymerization and addition polymerization.
Examples of the addition polymerization and the cyclic olefin-based resin obtained thereby include, for example, Japanese Patent No. 3517471, Japanese Patent No. 3559360, Japanese Patent No. 3867178, Japanese Patent No. 3871721, Japanese Patent No. 3907908, Japanese Patent No. 3945598, Special Table 2005 No. 5,276,696, JP-A-2006-28993, JP-A-2006-11361, International Publication No. WO 2006/004376, International Publication No. WO 2006/030797. Among these, those described in Japanese Patent No. 3517471 are particularly preferable.
Examples of the ring-opening polymerization and the cyclic olefin-based resin obtained thereby include International Publication WO 98/98499 pamphlet, Japanese Patent No. 30605532, Japanese Patent No. 3320478, Japanese Patent No. 3273046, Japanese Patent No. 3404027, Japanese Patent No. 3428176. , Japanese Patent No. 3687231, Japanese Patent No. 3873934, and Japanese Patent No. 3912159. Among these, those described in International Publication WO 98/14499 pamphlet and Japanese Patent No. 30605532 are particularly preferable.
Among these cyclic olefin resins, those obtained by addition polymerization are preferable from the viewpoint of birefringence and melt viscosity. For example, “TOPAS # 6013” (manufactured by Polyplastics Co., Ltd.) is used. it can.

  Examples of the cellulose acylate resin that can be used in the present invention include any cellulose acylate in which three hydroxyl groups in a cellulose unit are at least partially substituted with an acyl group. The acyl group (preferably an acyl group having 3 to 22 carbon atoms) may be either an aliphatic acyl group or an aromatic acyl group. Among them, cellulose acylate having an aliphatic acyl group is preferable, those having an aliphatic acyl group having 3 to 7 carbon atoms are more preferable, those having an aliphatic acyl group having 3 to 6 carbon atoms are more preferable, and carbon number More preferably has 3 to 5 aliphatic acyl groups. A plurality of these acyl groups may be present in one molecule. Examples of preferred acyl groups include acetyl, propionyl, butyryl, pentanoyl, hexanoyl and the like. Among these, a cellulose acylate having one or more selected from an acetyl group, a propionyl group and a butyryl group is more preferable, and an even more preferable one has both an acetyl group and a propionyl group. Cellulose acylate (CAP). The CAP is preferable in terms of easy resin synthesis and high stability of extrusion molding.

  There is no restriction | limiting in particular about the mass average polymerization degree and number average molecular weight of a cellulose acylate-type resin. In general, the mass average degree of polymerization is about 350 to 800, and the number average molecular weight is about 70000 to 230,000. The cellulose acylate resin can be synthesized using an acid anhydride or acid chloride as an acylating agent. In the industrially most general synthesis method, cellulose obtained from cotton linter, wood pulp, etc. is converted into organic acids (acetic acid, propionic acid, butyric acid) corresponding to acetyl groups and other acyl groups, or their acid anhydrides (anhydrous anhydride). A cellulose ester is synthesized by esterification with a mixed organic acid component containing acetic acid, propionic anhydride, and butyric anhydride). As the method for synthesizing the cellulose acylate, the description of the Japanese Society for Invention and Innovation (public technical number 2001-1745, published on March 15, 2001, Japan Society of Invention), pages 7 to 12, JP-A-2006-45500, Reference can be made to the methods described in JP-A-2006-241433, JP-A-2007-138141, JP-A-2001-188128, JP-A-2006-142800, and JP-A-2007-98917. The total acyl substitution degree of the cellulose acylate resin is preferably 2.1 to 3.0, and the substitution degree of the acetyl group is preferably 0.05 to 2.5, more preferably 0.05 to 0.5 or 1. 5 to 2.5. The degree of propionyl substitution is preferably 0.1 to 2.8, more preferably 0.1 to 1.2 or 2.3 to 2.8.

  Examples of polycarbonate resins that can be used in the present invention include polycarbonate resins having a bisphenol A skeleton, which are obtained by reacting a dihydroxy component and a carbonate precursor by an interfacial polymerization method or a melt polymerization method. JP-A-2006-277914, JP-A-2006-106386, and JP-A-2006-284703 can be preferably used. For example, “Taflon MD1500” (manufactured by Idemitsu Kosan Co., Ltd.) can be used as a commercial product.

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” manufactured by Asahi Kasei Chemical Co., Ltd., which will be described later, 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 those 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 2008-74818. 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.

Among these, the thermoplastic resin is preferably a cyclic olefin resin, more preferably a norbornene resin from the viewpoint of high transparency, birefringence and heat resistance, and an addition polymerization type norbornene. It is particularly preferable that the resin is a series resin.
In addition, when the thermoplastic resin is a copolymer, it may be a random copolymer or a block copolymer.

(Additive)
The film of the present invention may contain a material other than the thermoplastic resin, but contains one or more of the thermoplastic resins as a main component (the highest content ratio among all the materials in the composition). In the aspect which means material and contains 2 or more types of the said resin, it is preferable to contain as the content ratio of those sum total being higher than the content rate of each other material. Examples of materials other than the thermoplastic resin include various additives, and examples thereof include a stabilizer, an ultraviolet absorber, a light stabilizer, a plasticizer, fine particles, and an optical adjusting agent.

Stabilizer:
The film of the present invention may contain at least one stabilizer. The stabilizer is preferably added before or when the thermoplastic 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 Co., Ltd.

  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. Preferable specific examples of the phosphite ester stabilizer include the following compounds, but the phosphite ester 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 0.01 to 0% with respect to the mass of the thermoplastic resin. 0.8% by mass.

UV absorber:
The film of this invention may contain the 1 type (s) or 2 or more types of ultraviolet absorber. 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 thermoplastic resin, and more preferably 0.01 to 1.5% by mass.

Light stabilizer:
The film of the present invention 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 not impairing the effects of the present invention, and is generally about 0.01 to 20 parts by mass, preferably 0.02 to 15 parts per 100 parts by mass of the thermoplastic resin. About mass parts, and particularly preferably about 0.05 to 10 mass parts. The light stabilizer may be added at any stage of preparing the melt of the thermoplastic resin composition, for example, at the end of the melt preparation process.

Plasticizer:
The film of the present invention 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. In addition, when the film of the present invention is produced by a melt film-forming method, for the purpose of lowering the melting temperature of the film constituting material by adding a plasticizer rather than the glass transition temperature of the thermoplastic resin used, or without addition Will be added for the purpose of lowering the viscosity at the same heating temperature than the other thermoplastic resins. For the film of the present invention, for example, a plasticizer selected from phosphoric acid ester derivatives and carboxylic acid ester derivatives 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 film of the present invention 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 thermoplastic resin in the present invention is preferably 5 nm to 3 μm, more preferably 5 nm to 2.5 μm, more preferably 10 nm to 2.0 μm from the viewpoint of keeping haze low. More preferably. Here, the average primary particle size of the fine particles is determined by observing the thermoplastic resin with a transmission electron microscope (magnification of 500,000 to 1,000,000 times) and determining the average value of the primary particle sizes of 100 particles. The addition amount of the fine particles is preferably 0.005 to 1.0% by mass with respect to the thermoplastic resin, more preferably 0.01 to 0.8% by mass, and further preferably 0.02 to 0%. 4% by mass.

Optical modifier:
The film of the present invention may contain an optical adjusting agent. Examples of the optical adjusting agent include a retardation adjusting agent, for example, those described in JP-A Nos. 2001-166144, 2003-344655, 2003-248117, and 2003-66230. Can be used. 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.

[Film Production Method]
The first aspect of the film manufacturing method of the present invention (hereinafter also referred to as the manufacturing method of the present invention) is a composition containing a thermoplastic resin between the first and second clamping surfaces constituting the clamping device. A pinching step in which a melt of the product is passed and continuously pinched to form a film (in the pinching step, the moving speed of the first pressing surface is made faster than the moving speed of the second pressing surface) And a step of solidifying the film-like melt to obtain a film, and between the first nip roll comprising two rolls and the second nip roll comprising two rolls. A longitudinal stretching step in which the film is passed in order and the peripheral speed of the second nip roll is made faster than the peripheral speed of the first nip roll and the film is stretched in the film transport direction (in the longitudinal stretching step, the first nip roll or the second nip roll). At least one of the nip rolls And characterized in that it comprises a control so as to impart a temperature difference of 0.1 ° C. to 10 ° C. between the surface temperature of the two rolls constituting the nip rolls).
Further, in the second aspect of the method for producing a film of the present invention, a melt of a composition containing a thermoplastic resin is continuously passed between the first clamping surface and the second clamping surface constituting the clamping device. A pressing step of forming a film by pressing the film (in the pressing step, the moving speed of the first pressing surface is made faster than the moving speed of the second pressing surface), A step of solidifying to obtain a film, and passing the obtained film between a first nip roll made of two rolls and a second nip roll made of two rolls in order, A longitudinal stretching step in which the circumferential speed of the first nip roll is higher than that of the first nip roll and the film is stretched in the film transport direction (in the longitudinal stretching step, at least one of the first nip roll and the second nip roll is replaced with a nip roll). Configure Characterized in that it includes two controlled to impart a peripheral speed difference of 0.01% to 10% between the peripheral speed of the rolls) and.

As described above, the manufacturing method of the present invention is characterized in that special longitudinal stretching is performed in order to eliminate the transverse dan generated by the pinching process in which the inclined structure is formed in the thickness direction due to the peripheral speed difference of the touch roll. Here, such an inclined structure is an effective method for compensating the viewing angle of the liquid crystal display device. In the pinching step, a soft resin (melt) in a molten state is applied to the pinching surface having different moving speeds from the front and back. Because of rubbing, a horizontal dan derived from the interaction with the clamping surface constituting the clamping device is generated on the surface.
With respect to such a horizontal dan, the horizontal dan can be eliminated by longitudinally stretching in the MD direction orthogonal to the horizontal dan. However, in the normal longitudinal stretching, the inclined structure formed by the circumferential speed difference film formation (slipping film formation) is lost. Although not bound by any theory, the following mechanism can be considered as the cause of this phenomenon. First, in general circumferential speed difference film formation, when two rolls are used in the pressure-clamping step, the melt is fixed by a pair of rolls (touch roll and chill roll), and the shear stress is uniform over the entire width direction. Since (slack) is easily applied to the melt, the distribution in the width direction of γ (that is, the distribution in the direction orthogonal to the tilt axis) is small. That is, the inclined structure is uniformly formed. When such a film (original fabric) formed with a difference in peripheral speed is stretched in the longitudinal direction, the balance of the material balance is matched with the longitudinal stretching (stretching in the MD direction), resulting in shrinkage of the film width and film thickness. This is because the film is stretched between two pairs of nip rolls, so that there is nothing to fix the film, and shrinkage in the orthogonal direction, that is, the width direction and the thickness direction occurs simultaneously with the stretching. In particular, when shrinkage of the film thickness occurs, a compressive force acts in the film thickness direction, so that the inclined structure obtained by the circumferential speed difference film formation is crushed and the original fabric γ is reduced. At this time, since the compressive stress is also generated in the film width direction, a distribution is easily generated in the stretching stress in the width direction applied to the film, and a width direction distribution is generated in γ. More specifically, in the longitudinal stretching, the shrinkage stress is generated in the film width direction and the film thickness direction in order to match the mass balance accompanying elongation, but when considering the central part, both end parts and the film in the film width direction, Since both sides of the central portion are in contact with the film end portions, both ends of the film central portion are both fixed ends, and this is a tug of contraction stress. On the other hand, only one end is in contact with the center of the film at both ends, and one end is a fixed end, but the other is a free end, so the shrinkage stress is reduced. Therefore, a difference in shrinkage stress is generated between the both end portions and the central portion, and this becomes uneven in the width direction. This is considered to be the cause of display unevenness on the liquid crystal display panel.
On the other hand, in the present invention, by performing longitudinal stretching under special conditions, it is different from the conventional method in that the horizontal dan is eliminated while maintaining the original inclined structure (the distribution in the width direction is small). It is said.
Hereinafter, the film production method of the present invention (hereinafter also referred to as the production method of the present invention) will be described in detail.

  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, two rolls having different peripheral speeds are preferable because pressure can be applied uniformly during clamping and the inclined structure can be made more uniform. The roll pressure can be measured by passing a pressure measurement film (manufactured by Fujifilm (for medium pressure) prescale, etc.) through two rolls.

<Supply of melt of thermoplastic resin composition>
In the production method of the present invention, first, a composition containing a thermoplastic resin (sometimes referred to as “thermoplastic resin composition”) is passed between the first clamping surface and the second clamping surface constituting the clamping device. And a step of forming a film by continuously pressing (hereinafter, also referred to as a pressing step), and supplying a melt of the composition containing the thermoplastic resin in the pressing step. There is no particular limitation on the means. For example, as a specific means for supplying the melt, an embodiment using an extruder for melting a thermoplastic resin composition and extruding it into a film may be used, or an embodiment using an extruder and a die may be used. The thermoplastic resin is solidified once. Alternatively, the film may be formed into a film and then melted by a heating means to form a melt and supplied to the film forming process.
The method for producing a film of the present invention comprises a step of melt-extruding a composition containing the thermoplastic resin (hereinafter also referred to as a thermoplastic resin composition) from a die, and the melt-extruded melt in the first compaction surface. And a step of passing between the second pinching surfaces is preferable from the viewpoint of suppressing unevenness in the optical properties of the obtained film.
When the thermoplastic resin composition is melt-extruded, it is preferable to pelletize the thermoplastic resin composition before melt-extruding. Commercially available thermoplastic resins (for example, TOPAS # 6013, Toughlon MD1500, Delpet 980N, DayLark D332, etc.) may be pelletized, but if not pelletized, the following method may be used. it can. As said thermoplastic resin, what was demonstrated as a thermoplastic resin contained in the film of this invention can be used, and its preferable range is also the same.
The thermoplastic 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, the dried pellets are then fed into a cylinder via a feed port of the extruder, and are kneaded and melted. The inside of the cylinder is preferably 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 (hereinafter also referred to as discharge temperature) of a supply means (for example, a die) for supplying the thermoplastic resin composition is determined according to the melting temperature of the thermoplastic resin, but is generally 190 to 300. A temperature of about ° C is preferred. 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 apparatus incorporating a breaker plate type filtration or a leaf type disk filter for filtering foreign matter in the thermoplastic 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 a lip gap) is generally 1.0 to 30 times the film thickness, preferably 5.0 to 20 times. Specifically, it is preferably 0.04 to 3 mm, more preferably 0.2 to 2 mm, and particularly preferably 0.4 to 1.5 mm. In the manufacturing method of the present invention, 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.
Thus, the residence time from the time when the resin enters the extruder through the supply port to the time when 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.

<Clamping process>
Next, a melt of the supplied thermoplastic resin composition is passed between the first clamping surface and the second clamping surface constituting the clamping device, continuously pressed into a film, and cooled. Solidify 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 from the melt first, and then the melt is peeled off from the other surface. preferable. In the manufacturing method of the present invention, 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 even if it is the first pressing surface. However, from the viewpoint of suppressing the peeling dan, the surface on the side to be peeled first is preferably the first pressing surface (the pressing surface having a high moving speed).

(Movement speed ratio)
In the manufacturing method of the present invention, in the clamping step, a difference in moving speed between the first clamping surface and the second clamping surface of the clamping device defined by the following formula (III) is 0.5 to 20%. It is preferable to apply a shear stress when the molten resin passes through the clamping device.
Formula (III)
Difference in moving speed (%) = 100 × {(moving speed of first pressing surface) − (moving speed of second pressing surface)}
/ (Moving speed of the first clamping surface)
The movement speed difference between the clamping surfaces of the clamping device is more preferably 1% to 15%, and further preferably 2% to 10%.
If the moving speed difference is within the above preferable range, it is preferable that the above Re [0 °], γ, and Rth can be controlled within the preferable range. In addition, in the circumferential speed difference film forming using a pinching device, the melt is sandwiched by two pinching surfaces uniformly over the entire width, and therefore, the distribution of the optical characteristics of the obtained film in the width direction is small. .
Further, it is preferable that the moving speed difference is 20% or less because slip is unlikely to occur between the pinching surface of the pinching device and the melt, and horizontal dan is unlikely to occur.

  In the production method of the present invention, in addition to the conventional method of continuously pressing the melt-extruded melt between the first clamping surface and the second clamping surface constituting the clamping device to form a film, In the pinching step, the melt is preferably pinched at a pressure of 15 to 500 MPa, and a film having the optical characteristics of the present invention can be produced more easily. The pressure in the clamping step is more preferably 30 to 500 MPa, particularly preferably 35 to 300 MPa, and further preferably 40 to 200 MPa. If it is 15 MPa or more, the force for pressing the melt is sufficiently strong, and shear stress can be applied to the melt to give a sufficient shear effect, thereby achieving the optical characteristics as described above. Further, if the pressure is 15 MPa or more, the pressing surface of the pressing device can be sufficiently pressed. Therefore, when the peripheral speed difference is applied, slip is unlikely to occur between the melt and the pressing surface of the pressing device. Hard to occur. On the other hand, a pressure of 500 MPa or less is preferable because the force applied to the melt is not too great and the melt does not deform and form a horizontal damper.

(Discharge temperature)
In the production method of the present invention, the discharge temperature (resin temperature at the outlet of the supply means) is preferably Tg + 50 to Tg + 200 ° C., and preferably Tg + 70 to Tg + 180 ° C. from the viewpoint of improving the moldability of the resin and suppressing deterioration. More preferably, 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 production method of the present invention, for example, when the thermoplastic resin composition is supplied from a supply means such as a die to the clamping device, the air gap (distance from the outlet of the supply device to the melt landing point of the clamping device) is: From the viewpoint of heat retention of the melt between the air gaps, it is preferable that they are as close as possible, specifically 10 to 300 mm, more preferably 20 to 250 mm, and particularly preferably 30 to 200 mm. .

(Line speed)
In the production method of the present invention, the film forming speed is preferably 10 m / min to 100 m / min, more preferably 15 m / min to 80 m / min, and further preferably 20 m / min to 60 m / min. If it is 10 m / min or more, the influence of driving unevenness of the pinching surface of the pinching device used in the pinching step is unlikely to occur, and the cause of the occurrence of lateral dumping can be suppressed. On the other hand, if it is 100 m / min or less, the deformation speed of the melt or film does not become too high, and the deformation of the melt or film catches up with the film forming speed, so that unevenness due to this does not occur and the cause of the occurrence of lateral dumping is suppressed. be able to.
Moreover, when the line speed (film forming speed) is 10 m / min or more, cooling of the melt in the air gap can be suppressed, and a more uniform shear deformation is imparted by a pinching device in a state where the melt temperature is high. it can. The line speed represents the speed at which the melt passes between the clamping apparatuses and the film conveyance speed in the conveyance apparatus.

(Film forming width)
In the production method of the present invention, the width of the film-like melt is not particularly limited, and can be, for example, 200 to 2000 mm.
On the other hand, the film width after stretching is preferably 1 m to 4 m, more preferably 1.2 m to 3.5 m, and still more preferably 1.4 m to 3 m. If the film width after stretching is 1 m or more, it is possible to employ a sufficiently heavy clamping surface of a clamping device used in the clamping process, which is less affected by the vibration of the extruder and is derived from this. It is preferable because it can suppress the occurrence of lateral dunes. If the film width after stretching is 4 m or less, it is difficult for the pinching surface of the pinching device to bend, and the pinching surface of the pinching device can contact the melt sufficiently homogeneously, thereby suppressing the occurrence of lateral dumping derived therefrom. Can be preferred.

(Cast using two rolls)
Among the methods of forming into a film by continuously passing the thermoplastic resin melt between the first clamping surface and the second clamping surface constituting the clamping device to form a film, for example, two rolls (for example, It is preferable to pass between the touch roll (first roll) and the 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 this invention using two rolls is demonstrated.

  In the film production method of the present invention, there is no particular restriction on the landing point of the melt extruded from the supply means, and the landing point of the melt extruded from the supply means, the portion where the touch roll and the chill roll are closest to each other The distance from the vertical line passing through the midpoint of the gap 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, a touch roll or a casting 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 production method of the present invention, the width of each of the two rolls is not particularly limited, and can be freely changed and employed according to the width of the film-like melt.

  The roll pressure between two rolls rotating at different peripheral speeds is preferably 15 to 500 MPa, more preferably 30 to 500 MPa, particularly preferably 35 to 300 MPa, and still more preferably. 40 to 200 MPa.

  In the manufacturing method of the present invention, in order to pressurize the roll pressure in the above range, the cylinder set value is appropriately changed. 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 2 to 100 KN, and preferably 3 to 50 KN. Is more preferable, and 3 to 25 KN is particularly preferable.

In the production method of the present invention, in order to pressurize the roll pressure in the above range, it is preferable to use a roll having a roll hardness of 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 without particular limitation as long as the roll pressure can be achieved.
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.

  In the manufacturing method of the present invention, it is preferable to use a metal touch roll having an outer cylinder thickness of 6 to 45 mm as one of the two rolls constituting the clamping device. More preferably, it is a metal roll of 10 mm-40 mm, More preferably, 15 mm-35 mm. If the thickness of the metal outer cylinder is 6 mm or more, the roll has sufficient rigidity, the touch roll does not deform along the chill roll, and the contact area between both rolls does not increase. Can be suppressed. In addition, if the contact area of a touch roll and a chill roll becomes large, the contact area of the melt and metal roll pinched | interposed between this will also increase, and friction will increase. As a result, the deformation of the melt surface becomes too large and a horizontal dan is generated. A metal roll whose surface is covered with rubber or the like is also easily deformed, and similarly, a horizontal dan is easily generated. In addition, if the thickness of the metal outer cylinder is 45 mm or less, the rigidity of the touch roll will not be too strong, and it will be appropriately deformed along the chill roll. Re [0 °], γ, and Rth are preferable because they are less likely to exceed the preferable range. In addition, when the contact area of a touch roll and a chill roll becomes small, the surface pressure for making a touch roll and a chill roll contact will concentrate there. As a result, a large force is locally applied to the melt sandwiched between them, and the melt is deformed there, causing a horizontal dam. Furthermore, due to excessive surface pressure, slippage tends to occur, and Re [0 °], γ and Rth tend to exceed the range of the present invention.

Furthermore, in the manufacturing method of the present invention, by controlling the peripheral speed difference between the two rolls that allow the film-like melt to pass therethrough, shear stress is applied when the molten resin passes through the two rolls, It is preferable to produce a film. The peripheral speed difference here is expressed by the following equation with respect to the peripheral speed of the touch roll and the cooling (chill) roll.
Peripheral speed difference (%) = 100 × [(peripheral speed of the faster roll) − (peripheral speed of the slower roll)]
/ (Peripheral speed of faster roll)
The preferable range of the peripheral speed difference between the two rolls is the same as the preferable range of the moving speed difference in the clamping device.
In order to obtain the film of the present invention, whichever speed of the two rolls may be high, when the touch roll is slow, a bank (excess of melt stays on the roll and forms on the roll side). Formed residue) is 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 (second roll) and the fast roll is a touch roll (first roll).

  Furthermore, in the production method of the present invention, it is preferable to use a roll having a large diameter as each of the two rolls. Specifically, the diameter is 200 to 1500 mm, more preferably 300 mm to 1000 mm, and particularly preferably 350 mm to It is preferable to use two rolls of 800 mm, more particularly preferably 350 to 600 mm, and even more preferably 350 to 500 mm. 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 required for shearing becomes longer. Therefore, a film with a large γ can be used, and a variation in Re [0 °] and a delay in γ can be achieved. It is possible to manufacture while suppressing the distribution (variation) in the phase axis direction. In the production method of the present invention, the diameters of the two rolls may be the same or different.

  In the manufacturing method of the present invention, the two rolls are driven at different peripheral speeds. The two rolls may be driven or driven independently. However, in order to suppress Re [0 °] variation and γ slow axis direction distribution (variation), the two rolls are preferably independent drive.

Further, in order to increase the expression level of γ, the surface temperature of the two rolls may be differentiated. A preferable temperature difference is 5 ° C to 80 ° C, more preferably 20 ° C to 80 ° C, and further preferably 20 ° C to 60 ° C. At that time, the temperature of the two rolls is Tg−70 ° C. to Tg + 20 ° C., more preferably Tg−50 ° C. to Tg + 10 ° C., more preferably Tg−40 ° C. to Tg + 5 ° C., using the glass transition temperature Tg of the resin. Set to. Such temperature control can be achieved by passing a temperature-controlled liquid or gas through the touch roll.
The glass transition temperature of the thermoplastic resin is measured by adding a resin to a measurement pan using a scanning differential calorimeter (DSC) and raising the temperature from 30 ° C. to 300 ° C. at 10 ° C./min in a nitrogen stream. (1st-run), and then cooled to 30 ° C. at −10 ° C./min, and again heated 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).

Further, in the production method of the present invention, the melt of the thermoplastic resin composition supplied from the supply means is kept warm until just before contacting with at least one of the two rolls, and the temperature distribution in the width direction is reduced. 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 said shielding member is used, since it can pass between rolls in the state with the high temperature of a film-form melt, ie, a state with low melt viscosity, there also exists an effect which is easy to produce the film of this invention.
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, for example, and the width direction side surface of the supply means (for example, die | dye) of a thermoplastic resin composition, and a clearance gap. 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 effectively 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 means 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 the variation in Re [0 °] and the distribution in the direction perpendicular to the inclination axis of γ (variation), there is a method of increasing the adhesion when the film-like melt comes into contact with the casting 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 on the most upstream side (the one closer to the thermoplastic resin composition supply means, for example, the die). In general, it is relatively common to use three cooling rolls, but this is not a limitation. The distance between the plurality of casting rolls is preferably 0.3 mm to 300 mm, more preferably 1 mm to 100 mm, and still more preferably 3 mm to 30 mm between the surfaces.

  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. Thickening processing 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 / m width, more preferably 5 kg / m width to 30 kg / m width.

  The film thickness of the film obtained by the production method of the present invention 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>
After the film is formed by the pinching step, in the production method of the present invention, the obtained film is placed between the first nip roll composed of two rolls and between the second nip roll composed of two rolls. Are passed in order, and a longitudinal stretching process is performed in which the peripheral speed of the second nip roll is made faster than the peripheral speed of the first nip roll and the film is stretched in the film transport direction.
Further, other stretching and / or relaxation treatments may be performed as long as they do not contradict the spirit of the present invention. For example, each process can be implemented by the following combinations (a) to (f).
(A) Longitudinal stretching (b) Longitudinal stretching → Relaxation treatment (c) Longitudinal (transverse) stretching → Transverse (longitudinal) stretching (d) Longitudinal stretching → Longitudinal stretching (e) Longitudinal (transverse) stretching → Transverse (longitudinal) stretching → Relaxation treatment (f) Transverse stretching → relaxation treatment → longitudinal stretching → relaxation treatment Among these, the step (a) is particularly preferred.

(Longitudinal stretching)
Longitudinal stretching can be achieved by heating the gap between the two pairs of rolls so that the peripheral speed of the second nip roll on the outlet side (downstream side) is faster than the peripheral speed of the first nip roll on the inlet side (upstream side). Under the present circumstances, the expression of the retardation of the thickness direction can be changed by changing the space | interval (L) between both nip rolls, 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 first nip roll and the second nip roll composed of two rolls are not particularly limited in the arrangement of the two rolls constituting the first nip roll, but from the viewpoint of performing longitudinal stretching while stably transporting the film. It is preferable that two rolls are arranged in the vertical direction (up and down direction) and transported while holding the film substantially horizontally between them.

The production method of the present invention is characterized in that the longitudinal stretching step is carried out in the following first aspect or second aspect.
1st aspect: Giving temperature difference to longitudinally stretched nip rolls (for example, paired upper and lower rolls) The first aspect of the production method of the present invention is the first nip roll or the second nip roll in the longitudinal stretching step. At least one of the two is controlled so as to give a temperature difference of 0.1 ° C. to 10 ° C. between the surface temperatures of the two rolls constituting the nip roll (for example, two rolls arranged above and below). It is characterized by. More preferably, a temperature difference of 0.2 ° C to 7 ° C, more preferably 0.3 ° C to 5 ° C is imparted. Thereby, a temperature difference can be given to the front and back of the stretched film, and a difference in elastic modulus can be given to the front and back of the film. Thereby, an orientation difference can be given to the front surface and the back surface of the film, and a slight shift (shear stress) is given. By stretching in the longitudinal direction while giving a slight shift in this way, it is possible to compensate for the decrease in γ associated with the longitudinal stretching, and the uniform distribution in the width direction of the inclined structure of the unstretched film, that is, the uniform in the slow axis direction. The distribution of γ can be maintained. If this temperature difference is 0.1 ° C. or more, the horizontal dan is sufficiently eliminated, and the distribution in the width direction of γ (distribution in the direction orthogonal to the tilt axis) tends to be difficult. On the other hand, if this temperature difference is 10 ° C. or less, slip is not generated on the nip roll that gives a temperature difference between the surface temperatures of the two rolls. This is preferable because an increase in the distribution in the width direction (distribution in the direction orthogonal to the tilt axis) can be suppressed.
When applying such a temperature difference, increasing the temperature of the roll on the film surface side that is in contact with the first pressing surface (high-speed pressing surface) in the pressing step is a direction in which shear stress is applied. Is preferable from the viewpoint of aligning in the pinching step and the longitudinal stretching step.
Moreover, there is no restriction | limiting in particular as the temperature control method of such two rolls, It can control by a well-known method and it is preferable to control independently.

Second aspect: Giving a peripheral speed difference to a longitudinally stretched nip roll (for example, a pair of upper and lower rolls) The second aspect of the production method of the present invention is the longitudinal stretching step, wherein the first nip roll or the second nip roll At least one of the nip rolls is controlled so as to give a peripheral speed difference of 0.01 to 10% between the peripheral speeds of the two rolls constituting the nip roll (for example, two rolls that can be arranged above and below). It is characterized by doing. The peripheral speed difference more preferably gives a peripheral speed of 0.03% to 7%, more preferably 0.05% to 5%. As a result, as in the first embodiment, the effect of shearing (shear stress) is imparted to the front and back of the film, the decrease in γ is compensated, and the uniformity of the highly inclined structure of the unstretched film after the pinching step can be maintained. it can. If this difference in peripheral speed is 0.01% or more, the horizontal dan is sufficiently eliminated, and the distribution in the width direction of γ (distribution in the direction orthogonal to the tilt axis) tends to be difficult. On the other hand, if this peripheral speed difference is 10% or less, slip is not generated on the nip roll that gives a temperature difference between the surface temperatures of the two rolls. This is preferable because an increase in the distribution of γ in the width direction (distribution in the direction orthogonal to the tilt axis) can be suppressed.
When applying such a circumferential speed difference, it is necessary to increase the peripheral speed of the roll on the film surface side that is in contact with the first clamping surface (the high-pressure side clamping surface) in the clamping step. It is preferable from the viewpoint of aligning the directions in the pinching step and the longitudinal stretching step.
Moreover, there is no restriction | limiting in particular as a method of such peripheral speed control of two rolls, It can control by a well-known method and it is preferable to control independently.

These first and second aspects of the present invention may be carried out independently, but a synergistic effect can be obtained by combining and carrying out simultaneously, which is more preferable. In this case, the nip roll that implements the first aspect and the nip roll that implements the second aspect may be the same nip roll or different nip rolls. It is preferable to implement the embodiment and the second embodiment.
When the temperature difference is applied to both the first nip roll on the upstream side and the second nip roll on the downstream side, the magnitude of the temperature difference applied in the first nip roll and the magnitude of the temperature difference applied in the second nip roll are: Whichever is larger, it is preferably the case of the first nip roll.
Further, in the case where a difference in peripheral speed is provided between both the first nip roll on the upstream side and the second nip roll on the downstream side, the magnitude of the peripheral speed difference applied in the first nip roll and the peripheral speed applied in the second nip roll. Either of the magnitudes of the difference may be large, but the case of the first nip roll is preferable.

Further, at least two nip rolls are used in the longitudinal stretching step, but three or more nip rolls may be used as long as the gist of the present invention is not violated. In the production method of the present invention, an embodiment using two nip rolls is preferable.
Further, the longitudinal stretching process may be performed in one stage or in multiple stages. In that case, even if only the first aspect is implemented in multiple stages, or only the second aspect is implemented in multiple stages, the first aspect and the second aspect are combined and implemented in multiple stages. May be. The production method of the present invention is preferably carried out in one stage.

  The longitudinal stretching step is particularly preferably carried out by using both nip rolls in one stage using two nip rolls and combining the first and second aspects of the present invention simultaneously.

  The longitudinal stretching temperature is preferably Tg-20 ° C to Tg + 80 ° C, more preferably Tg-10 ° C to Tg + 50 ° C, still more preferably Tg-5 ° C to Tg + 30 ° C.

  The draw ratio of longitudinal stretching is preferably 1.05 times to 3 times, more preferably 1.1 times to 2.6 times, and still more preferably 1.2 times to 2.3 times. The ratio (L / W) of the stretching span length (length between nip rolls = L) and the film width (W) before stretching is preferably 0.01 to 50, more preferably 0.02 to 2, and still more preferably 0. 03-1. The above Re [0 °], γ, and Rth can be achieved by a combination of these and the pressing step.

  Moreover, 30 mm-1500 mm are preferable, as for the diameter of a preferable nip roll, More preferably, it is 80 mm-1000 mm, More preferably, it is 150 mm-700 mm. Moreover, the two rolls constituting the nip roll are preferable from the viewpoint of uniformizing the film from which the diameters are equal.

  A preferable nip pressure is preferably 10 kg / cm to 100 kg / cm, more preferably 20 kg / cm to 80 kg / cm, and still more preferably 25 kg / cm to 70 kg / cm.

  The preferred longitudinal stretching speed (the nip roll inlet side (before stretching) speed is preferably 5 m / min to 100 m / min, more preferably 10 m / min to 80 m / min, and even more preferably 15 m / min to 60 m / min. is there.

  The thickness of the film after longitudinal stretching in this manner is preferably 10 μm to 90 μm, more preferably 20 μm to 80 μm, still more preferably 25 μm to 70 μm. If it is 90 micrometers or less, the elasticity of a melt will become low, and since it will not require big force when peeling from a touch roll, it can suppress that this becomes a horizontal dump. Moreover, if it is 10 micrometers or more, a bending elasticity does not fall too much and it is hard to adhere a melt and a film to the clamping surface in a clamping process, and the nip roll in an extending process.

(Lateral stretching)
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-10 ° C to Tg + 60 ° C, more preferably Tg-5 ° C to Tg + 45 ° C, and further preferably Tg-10 ° C to Tg + 20 ° C. 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.

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 + 30) ° C, more preferably (Tg-30) ° C to (Tg + 20) ° C, and more preferably (Tg-15) ° C to (Tg + 10) ° C for 1 second to 10 minutes. More preferably 5 seconds to 4 minutes, still more 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 conveying with tension.

[Polarizer]
The polarizing plate of the present invention can be obtained by laminating at least a polarizer (hereinafter also referred to as a polarizing film) on the film of the present invention. Hereinafter, the polarizing plate of the present invention will be described. Examples of the polarizing plate of the present invention include a polarizing plate formed on the surface of a polarizing film for the purpose of two functions of a protective film and viewing angle compensation, and a composite polarizing plate laminated on a protective film such as TAC. Can be mentioned.

  If the polarizing plate of this invention uses the film and polarizer of this invention, there will be no restriction | limiting in particular in a structure. For example, when the polarizing plate of the present invention is composed of a polarizer and two polarizing plate protective films (transparent polymer films) that protect both sides of the polarizer, the film of the present invention may be used as at least one polarizing plate protective film. it can. Moreover, 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 film of this invention is an uneven | corrugated structure, it will have an anti-glare (anti-glare) function. Further, the polarizing plate of the present invention has an antireflection film of the present invention in which an antireflection layer (low refractive index layer) is further laminated on the surface of the film of the present invention, and further optical anisotropy on the surface of the film of the present invention. It is also preferable to use the optical compensation film of the present invention in which layers are laminated.

  In general, a liquid crystal display device includes four polarizing plate protective films because a liquid crystal cell is provided between two polarizing plates. The film of the present invention may be used for any of the four polarizing plate protective films, but the film of the present invention is particularly advantageous as a protective film disposed between a liquid crystal cell and a polarizing plate in a liquid crystal display device. Can be used.

  The polarizing plate of the present invention more preferably has a configuration in which a cellulose acylate film, a polarizer and a film of the present invention are laminated in this order. Moreover, the structure which the cellulose acylate film, the polarizer, the film of this invention, and the adhesive layer are laminated | stacked in this order is also more preferable.

(Optical film)
The film of the present invention is used for the optical film of the polarizing plate of the present invention. The film can be surface treated. Examples of the surface treatment method include methods such as corona discharge, glow discharge, UV irradiation, and flame treatment.

(Cellulose acylate film)
As the cellulose acylate film of the polarizing plate of the present invention, a known cellulose acylate film for a polarizing plate is used. 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.

  Any appropriate molding method can be adopted as a method for obtaining the polyvinyl alcohol film. 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 product 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.

  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 optical film where the polarizer is not adhered.

(Production method of polarizing plate)
The manufacturing method of the polarizing plate of this invention is demonstrated.
The polarizing plate of the present invention can be produced by bonding one side of the film of the present invention (a surface-treated surface in the case of surface treatment) to at least one side of the polarizer using an adhesive. When the cellulose acylate film, the polarizer, and the film of the present invention are bonded together in this order, the polarizing plate of the present invention can be produced by laminating the polarizer and other films using an adhesive on both sides of the polarizer. . In the manufacturing method of the polarizing plate of this invention, it is preferable that the film of this invention is directly bonded with the polarizer.

  As the adhesive, a known polarizing plate production adhesive can be used. 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 this invention is not limited to said method, Another method 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 JP-A-2007-316366 and JP-A-2008-20891 are more preferable.

  It is preferable that a protective film is also attached to the other surface of the polarizing film, and the protective film may be the film of the present invention. Moreover, the various films conventionally used as a protective film of a polarizing plate, such as a cellulose acylate film and a cyclic polyolefin polymer film, can be used.

  The polarizing plate of the present invention thus obtained 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. Not. 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.

[Liquid Crystal Display]
The film and polarizing plate of the present invention can be used for liquid crystal display devices of various modes. 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.

[Optical compensation film]
The film of the present invention can be preferably used as a film for optical applications, and can be particularly preferably used as an optical compensation film.

<Laminated film>
It can also be set as a laminated | multilayer film by further providing a well-known optically anisotropic layer to the film of this invention.

  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.

<Measurement method>
(1) Horizontal Dunn 10 sampled 3 cm square sample films are prepared. When these sample films are placed between polarizing plates arranged orthogonally and looked in from the front, the number of horizontal dans (light and dark stripes with a width of 0.1 to 5 mm running in the width direction) is visually measured, and 10 samples are obtained. The number of horizontal dan of the sample in which the number of horizontal dan in the film was the maximum was taken as the number of horizontal dan.

(2) Re [0 °], γ, Rth
These optical properties were measured according to the method described in the specification.

(3) Gamma tilt axis and orthogonal direction distribution γ is measured by the method described in the specification at an arbitrary position of the stretched film, and simultaneously the tilt axis direction is determined. The film sampled 30 cm in the direction orthogonal to the tilt axis is divided into 10 equal parts, and γ is measured by the method described in the specification at 10 points. Of the measured values of γ at 10 points, the difference between the maximum value and the minimum value was divided by the average value of 10 points, and expressed as a percentage, was defined as the γ tilt axis and orthogonal distribution (%).

[Production Example 1] Production of pellets of addition polymerization type norbornene resin As addition polymerization type norbornene resin (COC), pellets of "TOPAS # 6013" manufactured by Polyplastics Co., Ltd. were used. “TOPAS # 6013” indicates positive intrinsic birefringence. The glass transition point of the resin was 130 ° C.

[Production Example 2] Production of ring-opening polymerization type norbornene resin pellets A ring-opening polymerization type norbornene resin (COP-1) was produced according to the method described in Example 1 of WO 98/14499, and this was prepared by a conventional method. Pelleted according to The glass transition point of the resin was 136 ° C.

[Production Example 3] Production of ring-opening polymerization type norbornene resin pellets As the ring-opening polymerization type norbornene resin (COP-2), the resin (a-1) described in Example 1 of JP 2007-38646 A was used. It was produced according to the method of the example, and this was pelletized according to a conventional method. The glass transition point of the resin was 130 ° C.

[Production Example 4] Production of polycarbonate pellets As polycarbonate, pellets of "Taflon MD1500" manufactured by Idemitsu Kosan Co., Ltd. were used. “Taflon MD1500” exhibits positive intrinsic birefringence. The glass transition point of the resin was 142 ° C.

[Production Example 5] Production of acrylic resin pellets According to Production Example 1 of Japanese Patent Application Laid-Open No. 2008-9378 [0222] to [0224], acrylic resin was treated with methyl methacrylate = 7500 g, 2- (hydroxymethyl) methyl acrylate. Synthesized from 2500 g, an acrylic compound having a lactonization rate of 98% and a glass transition point of 134 ° C. was obtained.

[Production Example 6] Manufacture of pellets of cellulose acylate resin Cellulose acetate propionate (CAP-1) was produced according to the method described in Example 1 of JP-A-2008-87398, and the pellets were produced according to a conventional method. Turned into. The composition of CAP-1 used was an acetylation degree of 1.95, a propionylation degree of 0.7, and a total acyl substitution degree of 2.65. The glass transition point of the resin was 174 ° C.

[Production Example 7] Manufacture of pellets of cellulose acylate resin Cellulose acetate propionate (CAP-2) was produced according to the method described in Example 101 of JP-A-2008-50562, and the pellets were produced according to a conventional method. Turned into. The composition of CAP-2 used was an acetylation degree of 0.15, a propionylation degree of 2.55, and a total acyl substitution degree of 2.70. The glass transition point of the resin was 137 ° C.

[Example 1]
(Film forming / clipping pressure)
Using a pellet of the cyclic olefin copolymer TOPAS # 6013 (COC) listed in Table 1 below as a thermoplastic resin, drying at 100 ° C. for 2 hours or more, melting at 260 ° C., and kneading using a single screw kneading extruder And extruded. At this time, a screen filter, a gear pump, and a leaf disk filter were arranged in this order between the extruder and the die, and these were connected by a melt pipe. This was extruded from a die having a width of 1300 mm and a lip gap of 0.8 mm at the extrusion temperature (discharge temperature) shown in Table 1 below.
Thereafter, a melt (molten resin) was extruded between the most upstream cast roll (chill roll) and the center of the portion sandwiched between the touch rolls. At this time, a cylinder was set on a stainless steel cast roll (chill roll) coated with hard chrome having a width of 1500 mm and a diameter of 300 mm on the most upstream side so that the touch pressure described in Table 1 below was obtained, and having a width of 1500 mm and a diameter of 200 mm. The touch roll of the material of the following Table 1 was made to contact. The outer cylinder thickness of the touch roll is shown in Table 1 below. The touch pressure was measured by sandwiching a pre-scale for medium pressure (manufactured by Fuji Film Co., Ltd.) between two rolls controlled at 25 ° C. at a constant peripheral speed (5 m / min) without melt. The value was taken as the pressure during film formation. Touch rolls and chill rolls having a Shore hardness of 70 HS were used. In addition, the melt was dropped on the central part sandwiched between the cast roll and the touch roll. Using these rolls, the touch roll peripheral speed is made faster than the chill roll peripheral speed, the peripheral speed difference between these rolls is set to the conditions shown in Table 1 below, and the distance between the die and the melt landing point is set to 50 mm. Then, a film was formed at a conveyance speed (chill roll speed) of 15 m / min. Note that the temperature of the touch roll was Tg-5 ° C, and the temperature of the chill roll was Tg-10 ° C. The film forming atmosphere was 25 ° C. and 60%.
Then, after trimming both ends (5 cm each of the full width) immediately before winding, thicknessing (knurling) with a width of 10 mm and a height of 20 μm was applied to both ends. Further, the film forming width after trimming was set to 1000 mm, and the film of Example 1 was produced by winding up 450 m.

(Stretching)
The obtained film was stretched in the longitudinal direction under the conditions described in Table 1. At this time, longitudinal stretching was performed using two pairs of nip rolls, and the temperature difference and the peripheral speed difference were controlled to the conditions described in Table 1 below for both the upstream nip roll and the downstream nip roll. Further, the draw ratio was calculated as (length of film after stretching) / (length of film before stretching), and is shown in Table 1 below. The other conditions were as follows.
Nip roll diameter: 500 mm
Stretching speed (inlet speed): 20 m / min Nip pressure: 50 kg / cm
Longitudinal stretching temperature: Tg + 10 ° C
Note that the nip roll on the film surface side that was in contact with the high-speed roll (touch roll) in the clamping step was set to a high temperature and / or a high speed.
Moreover, it formed into a film so that the thickness after extending | stretching might be set to 80 micrometers.

(Evaluation)
After stretching, the horizontal axis, γ, Re [0 °], Rth, γ tilt axis and perpendicular distribution were measured by the above method. The results are shown in Table 1 below. In addition, the inclination direction which measured Re [+40 degree] and Re [-40 degree] of the film of this invention was all the longitudinal direction of the film.
Furthermore, the sample film is placed between the polarizing plates arranged orthogonally, and a test pattern (1 mm pitch line & space) is placed on a transparent 30 cm square glass plate between the sample film and the polarizing plate. The number of spots per 30 cm square at which bleeding occurred in the test pattern is shown in Table 1 as “image bleeding”. This corresponds to image unevenness when incorporated in a liquid crystal display device. Therefore, “image blur” is preferably as small as possible. For example, if it is 20 pieces / 30 cm square or less, there is no practical problem.

[Examples 2-37, Comparative Examples 1-5]
Optical films of the respective 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 Tables 1 and 2 below. The optical properties of the optical films of the examples and comparative examples are shown in Table 1 and Table 2 below. In Example 32, the acrylic resin was melted at 230 ° C. In Comparative Example 5 and Example 37, stretching was performed at a longitudinal stretching temperature of Tg according to Example 7 of JP-A-2007-38646.

From Table 1 and Table 2, it was found that the films obtained in the examples of the present invention had few streaks (lateral dans) extending in the direction orthogonal to the tilt axis, and formed a tilt structure. Further, since there is little blur of the image examined by the above method, the blur of the image of the liquid crystal display device using the film of the embodiment of the present invention is remarkably improved. Specifically, Examples 1 to 5 and Comparative Examples 1 and 2 showed the effect of the temperature difference of the nip roll in the longitudinal stretching. Examples 6 to 10 and Comparative Examples 3 and 4 showed the effect of the peripheral speed difference of the nip roll in the longitudinal stretching. Examples 11-13 showed the synergistic effect of the peripheral speed difference and temperature difference of the nip roll. Examples 14-17 showed the effect of the peripheral speed difference of the touch roll in the slip film formation. Examples 18 to 21 showed the effect of the thickness of the touch roll in film formation. Examples 22 to 28 showed the effect of touch pressure in film formation. Examples 29 to 34 showed the effect of the resin on the slip film formation. Examples 35 and 36 showed the effect of the material of the touch roll on the slip film formation. In Comparative Example 5, Example 7 of Japanese Patent Application Laid-Open No. 2007-38646 was implemented, and in Example 37, the present invention was compared with this (COP-2 described in the Example of Japanese Patent Application Laid-Open No. 2007-38646). A-1 in the publication, and longitudinally stretched 1.25 times at a stretching temperature Tg, and the thickness after stretching was 90 μm).
Moreover, from Examples 1 to 37, the film of the present invention exhibited γ, Re [0 °] and Rth in a favorable range, and the distribution of the γ tilt axis and the orthogonal direction was also small. Therefore, it was found that the film of the present invention is a film suitable for optical applications, and can be particularly suitably used as an optical compensation film.

(Polarizer)
A polarizing plate was prepared using the prepared films of Examples 1 to 37. Specifically, first, iodine was adsorbed to a stretched polyvinyl alcohol film to prepare each polarizing film. Using these polarizing films, an 80 μm TAC film (manufactured by FUJIFILM Corporation), a uniaxially stretched norbornene polymer film, and a λ / 2 plate with Re = 270 nm, as shown in FIG. 1, Examples 1 to 37 films were laminated. In this manner, two polarizing plates each using the films of Examples 1 to 37 were produced.

(LCD panel)
The films of Examples 1 to 37 were installed as a viewing angle compensation film between a pair of polarizing plates and a liquid crystal cell. Moreover, the polarizing plate using the film of Examples 1-37 was arrange | positioned at the upper and lower sides of the liquid crystal cell. When TN, ECB, OCB, VA, and IPS mode liquid crystal display devices were used, all of them exhibited good viewing angle compensation performance.

Claims (12)

A sandwiching step of passing a melt of a composition containing a thermoplastic resin between the first sandwiching surface and the second sandwiching surface constituting the sandwiching device and continuously sandwiching and molding into a film (the sandwiching step) In the pressing step, the moving speed of the first pressing surface is made faster than the moving speed of the second pressing surface),
Solidifying the film-like melt to obtain a film;
The obtained film is sequentially passed between a first nip roll made of two rolls and a second nip roll made of two rolls, and the peripheral speed of the second nip roll is made to be the same as that of the first nip roll. Longitudinal stretching step of stretching in the film conveyance direction at a speed higher than the peripheral speed (in the longitudinal stretching step, at least one of the first nip roll and the second nip roll is the surface temperature of the two rolls constituting the nip roll) And control to give a temperature difference of 0.1 ° C. to 10 ° C.)
A method for producing a film, comprising: A sandwiching step of passing a melt of a composition containing a thermoplastic resin between the first sandwiching surface and the second sandwiching surface constituting the sandwiching device and continuously sandwiching and molding into a film (the sandwiching step) In the pressing step, the moving speed of the first pressing surface is made faster than the moving speed of the second pressing surface),
Solidifying the film-like melt to obtain a film;
The obtained film is sequentially passed between a first nip roll made of two rolls and a second nip roll made of two rolls, and the peripheral speed of the second nip roll is made to be the same as that of the first nip roll. A longitudinal stretching step of stretching in the film conveying direction at a speed higher than the peripheral speed (in the longitudinal stretching step, at least one of the first nip roll or the second nip roll is used as each circumference of the two rolls constituting the nip roll) And control to give a peripheral speed difference of 0.01 to 10% between the speeds),
A method for producing a film, comprising: In the longitudinal stretching step, at least one of the first nip roll and the second nip roll is controlled so as to give a temperature difference of 0.1 ° C. to 10 ° C. between the surface temperatures of the two rolls constituting the nip roll. The method for producing a film according to claim 2 , wherein: A step of melt-extruding a composition containing the thermoplastic resin from a die, and a step of passing the melt-extruded melt between the first and second pressing surfaces. film production method according to any one of claims 1 to 3. Wherein the clamping step, method of producing a film according to any one of claims 1 to 4, characterized in that nipping the melt at a pressure of 15～500MPa. The method for producing a film according to any one of claims 1 to 5 , wherein in the clamping step, the melt is clamped at a pressure of 30 to 500 MPa. In the clamping step, the moving speed difference between the first clamping surface and the second clamping surface of the clamping device defined by the following formula (III) is controlled to be 0.5 to 20%. film production method according to any one of claims 1 to 6.
Formula (III)
Difference in moving speed (%) = 100 × [(moving speed of first pressing surface) − (moving speed of second pressing surface)]
/ (Moving speed of the first clamping surface) Wherein the clamping step, method of producing a film according to any one of claims 1 to 7, wherein the nip-pressing unit is a peripheral speed from each other are two different roles. The method for producing a film according to claim 8 , wherein a metal touch roll having an outer cylinder thickness of 6 to 45 mm is used for one of the two rolls constituting the pinching device. Film characterized in that a film was formed by a method of producing a film according to any one of claims 1-9. A polarizing plate comprising at least one film according to claim 10 . A liquid crystal display device comprising at least one film according to claim 10 .

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