WO2012114762A1

WO2012114762A1 - Vertical alignment liquid-crystal display device and manufacturing method thereof

Info

Publication number: WO2012114762A1
Application number: PCT/JP2012/001250
Authority: WO
Inventors: 梅田　博紀
Original assignee: コニカミノルタオプト株式会社
Priority date: 2011-02-24
Filing date: 2012-02-23
Publication date: 2012-08-30
Also published as: JP2014095729A

Abstract

An objective of the present invention is to provide a vertical alignment liquid-crystal display device whereby improved frontal contrast and transmittance is achieved, as well as reduced color shift and wide viewing angle. This vertical alignment liquid-crystal display device comprises vertically aligned liquid-crystal cells, a pair of polarizing plates which sandwich same, and a backlight. The backlight-side polarizing plate further comprises a protective film (F2) which is positioned on the liquid-crystal cell side. The viewing-side polarizing plate further comprises a protective film (F3) which is positioned on the liquid-crystal cell side. The closer of the protective film (F2) or (F3) to the color filter is a phase difference film (A), and the further thereof from the color filter is a phase difference film (B). At least all of the following formulae are satisfied thereby: (1) Rt (A) < Rt (B); (2) 70nm < Rt (A) < 130nm; (3) 130nm < Rt (B) < 200nm; (4) 20nm < Rt (B) - Rt (A) < 130nm; (5) Rt / Ro (A) < Rt/Ro (B).

Description

Vertical alignment type liquid crystal display device and manufacturing method thereof

The present invention relates to a vertical alignment type liquid crystal display device that achieves an improvement in the use efficiency of a backlight and an improvement in front contrast leading to power saving, a small color shift, and a wide viewing angle, and a manufacturing method thereof.

The liquid crystal display device is advantageous in that it is thinner and lighter than a CRT (Cathode Ray Tube), can be driven at a low voltage, and consumes less power. Therefore, liquid crystal display devices are used in various electronic devices such as televisions, notebook PCs (personal computers), desktop PCs, PDAs (mobile terminals), and mobile phones.

In recent years, a vertical alignment type liquid crystal display device (also referred to as a “VA (vertical alignment) type”) liquid crystal display device using a vertical alignment type liquid crystal (liquid crystal having negative dielectric anisotropy) has been compared with a conventional TN type liquid crystal display device. Wide viewing angle due to its excellent viewing angle characteristics.

In recent years, there has been an increasing demand for power saving in vertical alignment type liquid crystal display devices, and miniaturization of light shielding portions and higher aperture ratios by color filter on array (COA) have been promoted.

In addition, a method of increasing the transmittance of the polarizing plate has been proposed as a means of saving power, but if only the transmittance of the polarizing plate is increased, there is a problem that the degree of polarization decreases and the front contrast decreases. To do.

In order to solve this, a method of suppressing depolarization by a protective film disposed between a polarizer (also referred to as a “polarizing film”) and a liquid crystal cell, such as a retardation film and a viewing angle widening film, is used. However, it is not possible to meet the demand by itself.

Patent Document 1 and Non-Patent Document 1 disclose that the front contrast is increased by the configuration of the retardation film. Although these methods suggest the possibility that the front contrast can be maintained even if the transmittance of the polarizing plate is increased, the front contrast improving means using these methods causes a very large color shift. Originally, the vertical alignment type liquid crystal display device has a small color shift, but with this configuration, the goodness inherent in the vertical alignment type liquid crystal display device is lost.

On the other hand, increasing the use efficiency of the backlight is also effective for realizing power saving. Therefore, for example, by selectively reflecting the polarized light by the multilayer thin film structure, the polarized light is transmitted more efficiently on the backlight side than the polarizing plate, thereby preventing the loss of light and brightening the liquid crystal screen without disturbing the viewing angle. The technology to do is known. However, in this case, the number of members increases, and the direction is opposite to the trend of thinning the liquid crystal TV.

On the other hand, there is also a method of performing antireflection processing (AR processing, LR processing) on the surface of the protective film disposed on the most backlight side among the protective films of the polarizing plate included in the liquid crystal display device. In this method, the transmittance can be improved by reducing the reflectance of the surface of the protective film, but the cost becomes high.

Further, it is possible to increase the transmittance of the polarizing plate by thinning the dyeing of the polarizer, but the contrast is lowered and the performance of the liquid crystal display device is lowered.

Therefore, it is desired to improve the backlight utilization efficiency by a method different from the above method and thereby save power.

In recent years, in the manufacturing process of liquid crystal display devices, a “roll-to-panel manufacturing method” in which a roll-shaped polarizing plate is directly bonded instead of a method of bonding a sheet-shaped polarizing plate to a liquid crystal panel has begun to be adopted. However, even in such a manufacturing method, it is desired that there is no variation in optical performance between lots of polarizing plates.

In the present application, a polarizing plate manufactured in a rolled state is referred to as a “rolled polarizing plate”, and a piece cut from the polarizing plate to a predetermined dimension is referred to as a “single sheet polarizing plate”.

JP 2010-54736 A

The present invention has been made in view of the above circumstances, and its solution is to achieve an improvement in front contrast and transmittance (brightness) that lead to power savings, and to reduce the color shift and reduce the viewing angle. A wide vertical alignment type liquid crystal display device and a manufacturing method thereof are provided.

The above-mentioned problem according to the present invention is solved by the following means.
[1] A vertical alignment type liquid crystal display device having a vertical alignment type liquid crystal cell, a first polarizing plate and a second polarizing plate sandwiching the vertical alignment type liquid crystal cell, and a backlight. The type liquid crystal cell includes two transparent substrates and a liquid crystal layer disposed between the two transparent substrates and including liquid crystal molecules, and a color filter is disposed on one of the two transparent substrates. The first polarizing plate is disposed on the backlight side surface of the vertical alignment type liquid crystal cell, and includes a first polarizer containing polyvinyl alcohol, and the backlight side surface of the first polarizer. A protective film F1 disposed on the surface of the first polarizer and a protective film F2 disposed on the surface of the first polarizer on the vertical alignment liquid crystal cell side, and the second polarizing plate includes the vertical alignment liquid crystal Placed on the visible side of the cell A second polarizer containing nyl alcohol, a protective film F3 disposed on the surface of the second polarizer on the side of the vertically aligned liquid crystal cell, and a surface on the viewing side of the second polarizer. A protective film F4, the absorption axis of the first polarizer and the in-plane slow axis of the protective film F2 are orthogonal, and the absorption axis of the second polarizer and the protective film F3 An in-plane slow axis is orthogonal, and of the protective films F2 or F3, the one disposed on the transparent substrate side where the color filter is provided is the retardation film A, and the color filter is provided. The one arranged on the transparent substrate side that is not formed is a retardation film B, and the retardation value Rt in the thickness direction of the retardation film A measured at a measurement wavelength of 590 nm at 23 ° C. and 55% RH is obtained. Rt (A), in-plane direction The retardation value Ro is set to Ro (A), and the retardation film B measured at a measurement wavelength of 590 nm at 23 ° C. and 55% RH has a thickness direction retardation value Rt of Rt (B). When the phase difference value Ro is Ro (B),
Satisfy all of the following formulas (1) to (5),
Formula (1): Rt (A) <Rt (B)
Formula (2): 70 nm <Rt (A) <130 nm
Formula (3): 130 nm <Rt (B) <200 nm
Formula (4): 20 nm <Rt (B) -Rt (A) <130 nm
Formula (5): Rt / Ro (A) <Rt / Ro (B) [Ro and Rt are defined by the following formulas.
Formula (I): Ro = (nx−ny) × d (nm)
Formula (II): Rt = {(nx + ny) / 2−nz} × d (nm)
In the formulas (I) and (II)
nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the plane of the retardation film; ny is in the fast axis direction y orthogonal to the slow axis in the plane of the retardation film. Represents the refractive index; nz represents the refractive index in the thickness direction z of the retardation film; d represents the thickness of the retardation film]
The refractive index in the direction parallel to the transmission axis of the first polarizer on the surface on the backlight side of the protective film F1 is smaller than the average refractive index of the protective film F2, and the average refractive index of the protective film F3. Vertical alignment type liquid crystal display device smaller than the rate.
[2] The vertical alignment liquid crystal display device according to [1], wherein a thin film transistor and the color filter are arranged on one of the two transparent substrates.
[3] The refractive index in the direction parallel to the transmission axis of the second polarizer on the second polarizer side surface of the protective film F1 is np, and the second polarized light on the backlight side surface is np. The vertical alignment liquid crystal display device according to [1] or [2], wherein np is larger than na, where na is a refractive index in a direction parallel to the transmission axis of the child.
[4] The protective film F2 is the retardation film A, and the retardation value Ro (A) in the in-plane direction of the retardation film A further satisfies the following formula (6): [1] to [ 3]. The vertical alignment type liquid crystal display device according to any one of [3].
Formula (6): 40 nm <Ro (A) <90 nm
[5] The refractive index of the protective film F1 in the direction parallel to the transmission axis of the second polarizer continuously changes in the thickness direction of the film. The vertical alignment type liquid crystal display device described.
[6] The refractive index na in the direction parallel to the transmission axis of the second polarizer on the backlight side surface of the protective film F1 is in the range of 1.350 to 1.480. [5] The vertical alignment type liquid crystal display device according to any one of [5].
[7] The method for producing a vertical alignment type liquid crystal display device according to any one of [1] to [6], wherein the retardation film A is disposed on a polarizer and at least one surface of the polarizer. Or the polarizing plate containing retardation film B prepares the roll-shaped polarizing plate wound up in the perpendicular | vertical direction with respect to the width direction of a film, The polarizing plate unwound from the said roll-shaped polarizing plate, and the said A method of manufacturing a vertical alignment type liquid crystal display device, comprising: bonding a vertical alignment type liquid crystal cell to each other by a roll-to-panel.

A vertical alignment type liquid crystal display device that achieves an improvement in front contrast and transmittance (brightness) that leads to power saving, a small color shift, and a wide viewing angle by the above means of the present invention, and a method for manufacturing the same. Can be provided.

1 is a conceptual diagram showing an example of a configuration of a vertical alignment type liquid crystal display device according to the present invention. The conceptual diagram which shows the other example of a structure of the vertical alignment type liquid crystal display device based on this invention. Conceptual diagram showing the roll-to-panel manufacturing method

Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present application, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

The vertical alignment type liquid crystal display device of the present invention has a vertical alignment type liquid crystal cell, a first polarizing plate and a second polarizing plate sandwiching the vertical alignment type liquid crystal cell, and a backlight. The vertical alignment type liquid crystal display device of the present invention preferably satisfies all the requirements a, b and c described below, and more preferably further satisfies the requirement d.

(Vertical alignment type liquid crystal cell)
A vertical alignment type liquid crystal cell (also simply referred to as “liquid crystal cell”) includes two transparent substrates and a liquid crystal layer that is disposed between them and includes liquid crystal molecules.

A thin film transistor and a pixel electrode connected to the thin film transistor are arranged on one of the two transparent substrates. The counter electrode may be disposed on the one transparent substrate, or may be disposed on the other transparent substrate, and may preferably be disposed on the one transparent substrate. The transparent substrate may be a conventionally known transparent glass substrate or resin substrate.

The color filter is disposed on one of the two transparent substrates, and is disposed on the one transparent substrate in order to increase the aperture ratio of the liquid crystal cell; that is, on one of the two transparent substrates, a thin film transistor ( TFT) and a color filter are preferably arranged.

That is, the vertical alignment type liquid crystal cell of the present invention preferably employs a color filter on array (hereinafter referred to as “COA”) system.

The COA method includes, for example, a color filter integrated drive substrate in which a color filter is directly formed on a drive side substrate of a liquid crystal cell, and a counter electrode (conductive layer) as described in JP-A-10-206888. And a counter substrate with a spacer interposed therebetween, and a liquid crystal material is sealed in the gap, and a color filter is formed on the reflective electrode to provide a bonding margin in high definition. The yield and the aperture ratio can be improved by widening. Further, the configuration of the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 2010-44362 is also helpful.

The liquid crystal molecules contained in the liquid crystal layer are preferably liquid crystal molecules having negative dielectric anisotropy, and more preferably nematic liquid crystals having negative dielectric anisotropy. As the nematic liquid crystal having negative dielectric anisotropy, conventionally known ones described in JP-A-2004-204133, JP-A-2004-250668, JP-A-2005-047980, etc. should be used. Can do.

Specifically, a nematic liquid crystal material having a negative dielectric anisotropy and Δn = 0.0815 and Δε = −4.5 is preferably used.

The thickness d of the liquid crystal layer is not particularly limited, but can be set to about 3.5 μm, for example, when a liquid crystal having the above characteristics is used.

The liquid crystal layer may further include a chiral material generally used in a TN mode liquid crystal display device in order to reduce alignment failure of liquid crystal molecules while minimizing a decrease in dynamic response characteristics of the display device. Good.

When the vertical alignment type liquid crystal cell has a multi-domain structure, it is advantageous for adjusting the alignment of the liquid crystal molecules in the boundary region between the domains.

Note that the “multi-domain structure” refers to a structure in which one pixel of a liquid crystal display device is divided into a plurality of regions. For example, in a vertical alignment type (VA type) liquid crystal display device, the liquid crystal molecules are tilted during white display, so the birefringence of the liquid crystal molecules when viewed from an oblique direction differs between the tilt direction and the opposite direction. Although a difference occurs in luminance and color tone, a multi-domain structure is preferable because viewing angle characteristics of luminance and color tone are improved.

Specifically, each pixel is composed of two or more regions having different initial alignment states of liquid crystal molecules and averaged, whereby luminance and color tone bias depending on the viewing angle can be reduced. Further, the same effect can be obtained even if each pixel is constituted by two or more different regions where the orientation direction of the liquid crystal molecules continuously changes in a voltage application state.

In order to obtain a uniform viewing angle in all directions, the number of divisions may be increased. However, a substantially uniform viewing angle can be obtained by using four or more divisions. In particular, it is preferable that the polarizing plate absorption axis can be set at an arbitrary angle when dividing into eight.

In the vertical alignment type liquid crystal cell, the liquid crystal molecules are aligned so that their long axes are substantially perpendicular to the surface of the transparent substrate when no voltage is applied between the pixel electrode and the counter electrode. . When a voltage is applied between the pixel electrode and the counter electrode, the liquid crystal molecules are aligned so that the major axis thereof is substantially horizontal to the surface of the transparent substrate. Thereby, image display is performed by changing the transmittance and reflectance of each sub-pixel.

Such a vertically aligned liquid crystal cell can be obtained by enclosing a nematic liquid crystal having negative dielectric anisotropy in a space surrounded by two transparent substrates.

The first polarizing plate is disposed on the backlight side surface of the vertical alignment type liquid crystal cell, the first polarizer, and the protective film F1 disposed on the backlight side surface of the first polarizer. And a protective film F2 disposed on the liquid crystal cell side surface of the first polarizer. The second polarizing plate is disposed on the viewing side surface of the vertical alignment type liquid crystal cell, the second polarizer, and the protective film F3 disposed on the liquid crystal cell side surface of the second polarizer, And a protective film F4 disposed on the viewing side surface of the second polarizer. The protective films F2 and F3 are preferably retardation films.

The absorption axis of the first polarizer and the in-plane slow axis of the protective film F2 (retardation film) are orthogonal to each other; the absorption axis of the second polarizer and the in-plane of the protection film F3 (retardation film) It is orthogonal to the slow axis (requirement a).

FIG. 1 is a conceptual diagram showing an example of the configuration of a vertical alignment type liquid crystal display device according to the present invention. As shown in FIG. 1, the vertical alignment type liquid crystal display device 10 includes a vertical alignment type liquid crystal cell 30, a first polarizing plate 50 and a second polarizing plate 70 sandwiching the vertical alignment type liquid crystal cell 30, and a backlight 90. .

The vertical alignment type liquid crystal cell 30 includes a first transparent substrate 31, a second transparent substrate 33, and a liquid crystal layer 35 having liquid crystal molecules 34 disposed therebetween. A thin film transistor 37, a pixel electrode (not shown) connected to the thin film transistor 37, and a color filter 39 are disposed on the first transparent substrate 31. That is, the vertical alignment type liquid crystal cell 30 has a COA (color filter on array) structure.

The first polarizing plate 50 includes a first polarizer 52, a protective film 54 (F1) disposed on the backlight side surface, and a protective film 56 (F2) disposed on the liquid crystal cell side surface. Have The second polarizing plate 70 includes a second polarizer 72, a protective film 74 (F3) disposed on the surface on the liquid crystal cell side, and a protective film 76 (F4) disposed on the surface on the viewing side. Have. The protective films 56 (F2) and 74 (F3) are preferably retardation films.

FIG. 2 is a conceptual diagram showing another example of the configuration of the vertical alignment type liquid crystal display device according to the present invention. As shown in FIG. 2, the vertical alignment type liquid crystal display device 10 ′ can be configured in the same manner as in FIG. 1 except that the vertical alignment type liquid crystal cell 30 is replaced with the vertical alignment type liquid crystal cell 30 ′.

The vertical alignment type liquid crystal cell 30 ′ has a first transparent substrate 31, a second transparent substrate 33, and a liquid crystal layer 35 having liquid crystal molecules 34 disposed therebetween. A thin film transistor 37 and a pixel electrode (not shown) connected to the thin film transistor 37 are disposed on the first transparent substrate 31; a color filter 39 is disposed on the second transparent substrate 33.

When trying to increase the front contrast of a vertical alignment type liquid crystal display device, the color shift tends to increase. That is, there is a demand for a vertical alignment type liquid crystal display device having a high transmittance and a high front contrast and a reduced color shift.

Therefore, in the present invention, of the protective films F2 or F3, the one disposed on the transparent substrate side (color filter side) provided with the color filter is referred to as a retardation film A; the transparent substrate side (not provided with the color filter) ( The one disposed on the side opposite to the color filter is referred to as a retardation film B. For example, in FIG. 1, the protective film F2 becomes the retardation film A; the protective film F3 becomes the retardation film B. In FIG. 2, the protective film F3 becomes the retardation film A; the protective film F2 becomes the retardation film B. And the retardation value of retardation film A and B satisfy | fills a specific relationship, It is characterized by the above-mentioned.

Protective films F2 and F3 (retardation films A and B) Retardation values Rt in the thickness direction of the retardation films A and B measured at 23 ° C. and 55% RH at a measurement wavelength of 590 nm are respectively Rt ( A) and Rt (B); the in-plane retardation value Ro is assumed to be Ro (A) and Ro (B), respectively; the in-plane retardation value Ro of the thickness direction retardation value Rt. When the ratio to is Rt / Ro (A) and Rt / Ro (B), respectively, all the following formulas (1) to (5) are satisfied (requirement b).
Formula (1): Rt (A) <Rt (B)
Formula (2): 70 nm <Rt (A) <130 nm
Formula (3): 130 nm <Rt (B) <200 nm
Formula (4): 20 nm <Rt (B) -Rt (A) <130 nm
Formula (5): Rt / Ro (A) <Rt / Ro (B)

Ro and Rt are defined by the following formula.
Formula (I): Ro = (nx−ny) × d (nm)
Formula (II): Rt = {(nx + ny) / 2−nz} × d (nm)
[In the above formula,
nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the plane of the retardation film;
ny represents the refractive index in the fast axis direction y perpendicular to the slow axis in the plane of the retardation film;
nz represents the refractive index in the thickness direction z of the retardation film;
d represents the thickness of the retardation film. The measurement conditions are the same as above. ]

In the present invention, it is preferable that a thin film transistor and a color filter are disposed on one of the two transparent substrates, and the one transparent substrate is disposed on the backlight side (the embodiment in FIG. 1). That is, when the protective film F2 on the liquid crystal cell side of the polarizing plate on the backlight side (first polarizing plate) is the retardation film A, the retardation value Ro (A) in the in-plane direction of the retardation film A is It is preferable that the relationship represented by the following formula (6) is satisfied.
Formula (6): 40 nm <Ro (A) <90 nm

The arrangement of the retardation film A or B according to the present invention with respect to the color filter of the liquid crystal cell is very important.

In the present invention, it is necessary to dispose retardation films on both sides of the liquid crystal cell. Regarding the retardation Rt in the thickness direction, the retardation Rt (A) in the thickness direction of the retardation film A on the color filter side is equal to the retardation Rt in the thickness direction of the retardation film B on the opposite side to the color filter. It is necessary to make it relatively smaller than (B).

The difference between Rt (A) of the retardation film A and Rt (B) of the retardation film B (Rt (B) −Rt (A)) is more than 20 nm and less than 130 nm, more preferably more than 30 nm and more than 120 nm. It is smaller, more preferably larger than 35 nm and smaller than 110 nm. If this value is small, the front contrast of the liquid crystal display device cannot be improved, and if it is too large, the color shift of the liquid crystal display device becomes large. Especially, the color mixture when viewed from the periphery is remarkable, and the display quality of the liquid crystal display device is high. Is significantly reduced.

Of the retardation films A and B (or retardation layer) used on both sides of the liquid crystal cell, the Rt (A) of the retardation film A on the color filter side needs to be larger than 70 nm and smaller than 130 nm, more preferably. Is from 80 nm to 120 nm, more preferably from 85 nm to 115 nm.

The Rt (B) of the retardation film B on the side opposite to the color filter needs to be larger than 130 nm and smaller than 200 nm, preferably 140 nm or more and 185 nm or less, and more preferably 145 nm or more and 170 nm or less.

The phase differences Ro and Rt of the phase difference films A and B affect the viewing angle of the liquid crystal display device. When each phase difference falls within a desired range, it is possible to obtain viewing angle characteristics that are closer to the target in the vertical and horizontal directions.

Of the retardation films A and B used on both sides of the liquid crystal cell, Rt / Ro (A) of the retardation film A on the color filter side is changed to Rt / Ro (B) of the retardation film B on the opposite side of the color filter. ) Must be smaller. When the Rt / Ro (A) of the phase difference film A on the color filter side of the liquid crystal cell is larger than the Rt / Ro (B) of the phase difference film B on the opposite side of the color filter, the color shift increases. The display quality of the liquid crystal display device is significantly reduced.

Of the retardation films A and B used on both sides of the liquid crystal cell, the Ro (A) of the retardation film A on the color filter side is more than the Ro (B) of the retardation film B on the opposite side to the color filter. Is preferably small.

The Ro (A) of the retardation film A on the color filter side is 40 nm <Ro (A) <90 nm, and the Ro (B) of the retardation film B on the side opposite to the color filter is 45 <Ro (B) <100 nm. Preferably there is. By setting the Ro (B) of the retardation film B on the side opposite to the color filter to 45 nm <Ro (B) <100 nm, the viewing angle can be sufficiently widened, and the Ro of the retardation film A on the color filter side. By making (A) relatively smaller than Ro (B) of the retardation film B on the side opposite to the color filter, color shift can be suppressed.

The angle θ1 (orientation angle) formed by the in-plane slow axis of the retardation films A and B and the width direction of the film is preferably −1 ° or more and + 1 ° or less, more preferably −0.5 or more and +0. It is 5 ° or less, more preferably −0.1 ° or more and + 0.1 ° or less. The orientation angle θ1 of the retardation films A and B can be measured using an automatic birefringence meter KOBRA-WX (Oji Scientific Instruments). The orientation angle can be adjusted depending on the stretching conditions.

The retardation films A and B used on both sides of the liquid crystal cell in the liquid crystal display device of the present invention may be manufactured by various film forming methods, and it is preferable to control the phase difference during film formation.

The retardation films A and B used in the liquid crystal display device of the present invention are a cellulose ester film, a polyester film, a cycloolefin film, a polycarbonate film, a polyolefin film, a polyacryl film, a mixed resin film of an acrylic resin and a cellulose ester resin, and the like. It may be.

Examples of the retardation film A include stretched polymer films mainly composed of polycarbonate, cellulose ester resin, polyethylene, and polypropylene. Particularly preferred is a cellulose ester resin.

For example, when using a cellulose ester resin, the retardation control method for these retardation films may include changing the degree of ester substitution or substituent, changing the solvent, adding a retardation control material, adjusting stretching conditions, and the like. it can. The retardation control of the retardation film A on the color filter side used in the liquid crystal display device of the present invention is performed mainly by the stretching magnification, and the retardation control of the retardation film B on the side opposite to the color filter is performed by adjusting the stretching temperature and It is preferable to carry out by controlling the film thickness. By using the retardation films A and B in which the retardation is controlled by this means, it is often possible to alleviate the warpage of a liquid crystal panel having a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell.

This is probably because the distortion remaining in the film differs depending on the phase difference control means. That is, the phase difference film A on the color filter side, the phase difference of which is controlled mainly by the stretching ratio, and the phase difference film B, the phase difference of which is controlled mainly by the stretching temperature and the film thickness control, on the side opposite to the color filter. The remaining distortion on the film is different. Thus, the retardation films A and B having different strains remaining in the film are arranged on both sides of the liquid crystal cell so as to cancel the warpage of the liquid crystal cell, so that the warpage of the liquid crystal cell is not alleviated. I guess.

The composition of the retardation film used in the liquid crystal display device of the present invention will be described later.

Refractive index of protective film F1 The refractive index in the direction parallel to the transmission axis of the first polarizer on the backlight side surface of the protective film F1 constituting the first polarizing plate is the protective film F2 (first polarizer). It is also characterized by being smaller than the average refractive index of the retardation film on the liquid crystal cell side) and smaller than the average refractive index of the protective film F3 (the retardation film on the liquid crystal cell side of the second polarizer). c).

“Average refractive index” refers to the refractive index of the protective film in the three-axis direction (the x-axis direction in the film plane, the y-axis direction perpendicular to the film plane, and the z-axis direction parallel to the normal to the film plane) at a predetermined wavelength. And the refractive index calculated as the average value thereof.

The refractive index in the direction parallel to the transmission axis of the first polarizer on the backlight side surface of the protective film F1 is made smaller than the average refractive index of the protective film F2 and the protective film F3 (retardation films A and B). Thus, the transmittance (white luminance) of the vertical alignment type liquid crystal display device can be increased.

In the present invention, the first polarizer transmits on the first polarizer side surface of the protective film F1 (the first polarizer backlight side protective film) constituting the first polarizing plate. When the refractive index in the direction parallel to the axis is np and the refractive index in the direction parallel to the transmission axis of the first polarizer on the backlight side surface is na, it is preferable that np is larger than na (requirement d). .

It is preferable that the refractive index in the direction parallel to the transmission axis of the first polarizer of the protective film F1 continuously changes in the thickness direction of the film.

In addition, it can be measured in the following procedures whether the refractive index is changing continuously in the thickness direction of a film.
1) The film is sliced in parallel with the MD direction (slow axis direction) or TD direction (fast axis direction) so that the slice plane (cut plane) is inclined with respect to the film plane. obtain. For example, the length in the direction parallel to the slow axis of the slice plane (cut plane) obtained by cutting parallel to the TD direction (fast axis direction) is set to 5 mm.
2) Then, the obtained sample film is placed on a sample stage of a lens reflectometer (for example, Olympus lens reflectometer USPM-RUIII). Then, the reflectance in the front direction of the slide surface is measured while sliding the sample stage in a direction corresponding to the thickness direction of the film (direction perpendicular to the MD direction or TD direction) one field of view. In this manner, the reflectance distribution in the thickness direction of the slide surface of the sample film can be measured. Thereby, it can confirm that the average refractive index in a film surface is changing continuously in the thickness direction.

In the present invention, the refractive index na of the surface of the protective film F1 on the backlight side (surface opposite to the first polarizer) in the direction parallel to the transmission axis of the first polarizer is 1.350 to It is preferable to be within the range of 1.480.

In the present invention, it is important to lower the refractive index of the surface on the backlight side of the protective film F1 in the direction parallel to the transmission axis of the first polarizer.

As a method for reducing the refractive index of the protective film F1, a method using a resin film substrate having a low refractive index and a method of mixing an additive having a low refractive index are known, but there are various other methods. It can be carried out.

For example, the refractive index can be lowered by providing a gap having a diameter sufficiently smaller than the wavelength of visible light in the film. This void can be provided by mixing bubbles when kneading melts and kneading bubbles, or by adjusting the drying conditions to form bubbles when forming solution films. Alternatively, it can also be obtained by dispersing hollow fine particles in the form of primary particles.

When bubbles are generated by solution casting, if bubbles are generated while the web is soft, bubbles are likely to be generated, but the bubbles are likely to become large, causing scattering and often causing deterioration of the LCD quality. . Therefore, it is preferable to generate bubbles by performing one or both of heating and depressurization of the film after reducing the residual solvent amount to 2% or less, which is a state in which the film has the required hardness.

The film is preferably heated at a temperature 20 ° C. or more higher than the glass transition temperature of the film, and the decompression treatment is preferably performed at a pressure lower than 0.7 atm. Alternatively, as a method for generating bubbles, there is a method using a foaming agent. The generation of bubbles by the foaming agent is difficult to control the diameter of the bubbles, but the control by heating and decompression is preferable as in the case of generating bubbles by the solvent.

Alternatively, it is possible to reduce the refractive index by a film forming method. By adding an additive that relaxes the orientation of the film, it is possible to lower the refractive index of the film below the average refractive index of the material, and to further localize such material by adjusting the film forming method. By making it, it is possible to lower the refractive index more effectively. A typical example is a method using a plasticizer whose refractive index is relatively close to that of the resin.

For example, by adjusting the speed of the drying process by the solution casting method, the refractive index can be lowered by making the plasticizer on one side of the film a high concentration and breaking the film orientation more actively. It is thought that it becomes.

Note that, by reducing the refractive index by about 0.01, the transmittance of the above-described vertical alignment type liquid crystal display device can be increased by, for example, 0.1%, which directly leads to power saving and longer life of the LCD. This effect is very large.

Protective film F1 or F4 When the above-described retardation film A or B is provided on one surface of a polarizer (first polarizer or second polarizer), the other surface of the polarizer is separately provided. A retardation film or a protective film may be used. For example, as a protective film, commercially available cellulose ester films (for example, Konica Minoltak KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4UE, KC4FR, KC4FR-4, KC4HR-1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used. Moreover, the protective film formed into a film by the method mentioned later can also be used.

A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound.

The polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the protective film used in the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate types and oxidized polyether methacrylates, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-pack type instantaneous pressure-sensitive adhesives.

The above-mentioned pressure-sensitive adhesive may be a one-component type or a type in which two or more components are mixed before use.

The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or may be an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solventless type. The concentration of the pressure-sensitive adhesive liquid may be appropriately determined depending on the film thickness after adhesion, the coating method, the coating conditions, and the like, and is usually 0.1 to 50% by mass.

About Composition of Protective Films F1 to F4 The protective films F1 to F4 (including the retardation films A and B) used in the present invention preferably contain a thermoplastic resin. Here, the “thermoplastic resin” refers to a resin that becomes soft when heated to the glass transition temperature or melting point and can be molded into a desired shape.

General thermoplastic resins include cellulose esters, polyethylene (PE), high density polyethylene, medium density polyethylene, low density polyethylene, polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene chloride, polystyrene. (PS), polyvinyl acetate (PVAc), Teflon (registered trademark) (polytetrafluoroethylene, PTFE), ABS resin (acrylonitrile butadiene styrene resin), AS resin, acrylic resin (PMMA), etc., soluble in solvents It is preferable to dissolve the material appropriately and treat it by the method of the present invention.

When strength and resistance to breakage are particularly required, polyamide (PA), nylon, polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE, modified PPE, PPO), polybutylene terephthalate (PBT) ), Polyethylene terephthalate (PET), glass fiber reinforced polyethylene terephthalate (GF-PET), cyclic polyolefin (COP), and the like.

If higher heat distortion temperature and long-term use characteristics are required, polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone, polyethersulfone, amorphous polyarylate, liquid crystal polymer, polyetherether A ketone, thermoplastic polyimide (PI), polyamideimide (PAI), or the like can be used.

In addition, it is possible to combine the kind of resin and molecular weight according to the use of the present invention.

As for the thickness of the protective film, it is preferable to select an appropriate thickness according to the application. The upper limit of the thickness is not particularly limited, but in the case of forming a film by a solution casting method, the upper limit is about 150 μm from the viewpoint of applicability, foaming, solvent drying, and the like.

The protective film preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

Hereinafter, a particularly suitable resin in the present invention will be described in detail.

<Cellulose ester resin>
Cellulose ester resins that can be used in the protective film used in the present invention are cellulose (di, tri) acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and It is preferably at least one selected from cellulose phthalates.

Among these, particularly preferred cellulose esters include cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate.

As the substitution degree of the mixed fatty acid ester, when an acyl group having 2 to 4 carbon atoms is used as a substituent, the substitution degree of the acetyl group is X, and the substitution degree of the propionyl group or butyryl group is Y. It is preferable that it is a cellulose resin containing the cellulose ester which satisfy | fills following formula (i) and (ii) simultaneously.

Formula (i) 1.5 ≦ X + Y ≦ 3.0
Formula (ii) 0 ≦ X ≦ 2.5
Further, the cellulose ester used in the present invention preferably has a weight average molecular weight Mw / number average molecular weight Mn ratio of 1.5 to 5.5, particularly preferably 2.0 to 5.0, The cellulose ester is preferably 2.5 to 5.0, more preferably 3.0 to 5.0.

The raw material cellulose of the cellulose ester used in the present invention may be wood pulp or cotton linter, and the wood pulp may be softwood or hardwood, but softwood is more preferable. A cotton linter is preferably used from the viewpoint of peelability during film formation. The cellulose ester made from these can be mixed suitably or can be used independently.

For example, the ratio of cellulose ester derived from cellulose linter: cellulose ester derived from wood pulp (coniferous): cellulose ester derived from wood pulp (hardwood) is 100: 0: 0, 90: 10: 0, 85: 15: 0, 50:50: 0, 20: 80: 0, 10: 90: 0, 0: 100: 0, 0: 0: 100, 80:10:10, 85: 0: 15, 40:30:30.

In the present invention, 1 g of cellulose ester resin is added to 20 ml of pure water (electric conductivity 0.1 μS / cm or less, pH 6.8), and the pH is 6 when stirred in a nitrogen atmosphere at 25 ° C. for 1 hr. It is preferable that the electric conductivity is 1 to 100 μS / cm.

<Sugar ester compound>
In the present invention, it is also preferable to include an ester compound in which at least one pyranose structure or furanose structure is one or more and twelve or less and all or part of the OH groups of the structure are esterified together with the cellulose ester resin.

The proportion of esterification is preferably 70% or more of the OH groups present in the pyranose structure or furanose structure.

Examples of ester compounds used in the present invention include the following, but the present invention is not limited to these.

Glucose, galactose, mannose, fructose, xylose, or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose Can be mentioned.

Other examples include gentiobiose, gentiotriose, gentiotetraose, xylotriose, and galactosyl sucrose.

Among these compounds, compounds having both a pyranose structure and a furanose structure are particularly preferable.

As examples, sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose and the like are preferable, and sucrose is more preferable.

The monocarboxylic acid used for esterifying all or part of the OH group in the pyranose structure or furanose structure is not particularly limited, and is a known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic A monocarboxylic acid or the like can be used. The carboxylic acid used may be one kind or a mixture of two or more kinds.

Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid , Saturated fatty acids such as tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, Examples include unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid.

Examples of preferable alicyclic monocarboxylic acids include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include aromatic monocarboxylic acids having an alkyl group or alkoxy group introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, biphenylcarboxylic acid, and naphthalene. Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralincarboxylic acid, or derivatives thereof. More specifically, xylyl acid, hemelic acid, mesitylene acid, prenicylic acid, γ-isoduric acid, jurylic acid, mesitic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropic acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid , Creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyroca Succinic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p- Although coumaric acid can be mentioned, benzoic acid is particularly preferable.

Oligosaccharide ester compounds can be applied as compounds having 1 to 12 of at least one of the pyranose structure or furanose structure according to the present invention.

Oligosaccharides are produced by allowing an enzyme such as amylase to act on starch, sucrose, etc. Examples of oligosaccharides that can be applied to the present invention include maltooligosaccharides, isomaltooligosaccharides, fructooligosaccharides, galactooligosaccharides, and xylooligos. Sugar.

Moreover, the said ester compound is a compound which condensed 1 or more and 12 or less of at least 1 type of the pyranose structure or furanose structure represented with the following general formula (A). R ₁₁ to R ₁₅ and R ₂₁ to R _{25 each} represents an acyl group having 2 to 22 carbon atoms or a hydrogen atom, m and n each represents an integer of 0 to 12, and m + n represents an integer of 1 to 12.

R ₁₁ to R ₁₅ and R ₂₁ to R ₂₅ are preferably a benzoyl group or a hydrogen atom. The benzoyl group may further have a substituent, for example, an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group. Further, these alkyl group, alkenyl group, and phenyl group may have a substituent. Good. Oligosaccharides can also be produced in the same manner as the ester compound according to the present invention.

Although the specific example of the ester compound used for this invention below is given, this invention is not limited to this.

The protective film used in the present invention preferably contains the aforementioned sugar ester compound in an amount of 0.5 to 30% by mass of the protective film in order to stabilize the display quality by suppressing the fluctuation of the retardation value. In particular, the content is preferably 5 to 30% by mass.

<Acrylic resin>
The protective film used in the present invention may contain an acrylic resin. Acrylic resin also includes methacrylic resin. The resin is not particularly limited, but a resin comprising 50 to 99% by mass of methyl methacrylate units and 1 to 50% by mass of other monomer units copolymerizable therewith is preferable.

Examples of other copolymerizable monomers include alkyl methacrylates having 2 to 18 alkyl carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, alkyl acrylates such as acrylic acid and methacrylic acid. Saturated acids, maleic acids, fumaric acids, divalent carboxylic acids containing unsaturated groups such as itaconic acid, aromatic vinyl compounds such as styrene, α-methylstyrene, and nucleus-substituted styrene, α, β- such as acrylonitrile, methacrylonitrile, etc. Examples thereof include unsaturated nitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and the like. These can be used alone or in combination of two or more.

Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate and the like are preferable, and methyl acrylate and n-butyl acrylate are particularly preferable.

Commercially available acrylic resins can also be used. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dianal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. .

<Cyclic olefin resin>
The protective film used in the present invention may contain a cyclic olefin resin. Examples of the cyclic olefin resin include norbornene resins, monocyclic olefin resins, cyclic conjugated diene resins, vinyl alicyclic hydrocarbon resins, and hydrides thereof. Among these, norbornene-based resins can be suitably used because of their good transparency and moldability.

Examples of the norbornene-based resin include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening copolymer of a monomer having a norbornene structure and another monomer, a hydride thereof, and a norbornene structure. An addition polymer of a monomer having a monomer, an addition copolymer of a monomer having a norbornene structure and another monomer, or a hydride thereof.

Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly suitable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can be used.

As monomers having a norbornene structure, bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.12,5] deca-3,7-diene ( Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.12,5] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4.0.12, 5.17,10] dodec-3-ene (common name: tetracyclododecene) and derivatives of these compounds (for example, those having a substituent in the ring). Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. In addition, these substituents may be the same or different and a plurality may be bonded to the ring. Monomers having a norbornene structure can be used singly or in combination of two or more.

Examples of the polar group include heteroatoms or atomic groups having heteroatoms. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfone group.

Other monomers capable of ring-opening copolymerization with monomers having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof, cyclic conjugated dienes such as cyclohexadiene, cycloheptadiene, and the like. And derivatives thereof.

A ring-opening polymer of a monomer having a norbornene structure and a ring-opening copolymer of a monomer having a norbornene structure and another monomer copolymerizable with the monomer have a known ring-opening polymerization catalyst. It can be obtained by (co) polymerization in the presence.

Examples of other monomers that can be addition-copolymerized with a monomer having a norbornene structure include, for example, α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, and 1-butene, and derivatives thereof; cyclobutene, cyclopentene, Examples thereof include cycloolefins such as cyclohexene and derivatives thereof; non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene. These monomers can be used alone or in combination of two or more. Among these, α-olefin is preferable, and ethylene is more preferable.

An addition polymer of a monomer having a norbornene structure and an addition copolymer of another monomer copolymerizable with a monomer having a norbornene structure can be used in the presence of a known addition polymerization catalyst. It can be obtained by polymerization.

A hydrogenated product of a ring-opening polymer of a monomer having a norbornene structure, a hydrogenated product of a ring-opening copolymer of a monomer having a norbornene structure and another monomer capable of ring-opening copolymerization thereof, Hydrogenated products of addition polymers of monomers having a norbornene structure, and hydrogenated products of addition copolymers of monomers having a norbornene structure and other monomers capable of addition copolymerization with these A known hydrogenation catalyst containing a transition metal such as nickel or palladium is added to the polymer solution, and the carbon-carbon unsaturated bond is preferably hydrogenated by 90% or more.

Among norbornene-based resins, as a repeating unit, X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.12,5] decane-7, 9-diyl-ethylene structure, the content of these repeating units is 90% by mass or more with respect to the entire repeating units of the norbornene resin, and the content ratio of X and the content ratio of Y The ratio is preferably 100: 0 to 40:60 in terms of mass ratio of X: Y. By using such a resin, it is possible to obtain a protective film (optical film) having no dimensional change in the long term and excellent optical property stability.

The molecular weight of the cyclic olefin resin used in the present invention is appropriately selected according to the purpose of use. Polyisoprene or polystyrene-equivalent weight average molecular weight (Mw) measured by gel permeation chromatography using cyclohexane (toluene if the polymer resin does not dissolve) as a solvent, usually 20,000 to 150,000. . It is preferably 25,000 to 100,000, more preferably 30,000 to 80,000. When the weight average molecular weight is in such a range, the mechanical strength and molding processability of the film are highly balanced and suitable.

The glass transition temperature of the cyclic olefin resin may be appropriately selected according to the purpose of use. From the viewpoint of durability and stretchability, it is preferably in the range of 130 to 160 ° C, more preferably 135 to 150 ° C.

The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the cyclic olefin resin is 1.2 to 3.5, preferably 1.5 to 3.0, from the viewpoint of relaxation time, productivity and the like. More preferably, it is 1.8 to 2.7.

The cyclic olefin resin used in the present invention preferably has an absolute value of photoelastic coefficient of 10 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 7 × 10 ⁻¹² Pa ⁻¹ or less, and more preferably 4 × 10 12 It is particularly preferably ⁻¹² Pa ⁻¹ or less. The photoelastic coefficient C is a value represented by C = Δn / σ where birefringence is Δn and stress is σ.

In the present invention, it is preferable that the cyclic olefin resin does not substantially contain particles. Here, “substantially free of particles” means that even if particles are added to a film made of a cyclic olefin resin, the amount of increase in haze from the non-added state is allowed to be in the range of 0.05% or less. Means you can. In particular, the alicyclic polyolefin resin lacks affinity with many organic particles and inorganic particles. Therefore, when a cyclic olefin resin film to which particles exceeding the above range are added is stretched, voids are easily generated, and as a result, There is a risk that a significant increase in haze may occur.

<Polycarbonate resin>
The protective film used in the present invention may contain various known polycarbonate resins. In the present invention, it is particularly preferable to use an aromatic polycarbonate. There is no restriction | limiting in particular about the said aromatic polycarbonate, and there will be no restriction | limiting in particular if it is an aromatic polycarbonate from which the various characteristics of a desired film are acquired.

In general, a polymer material collectively referred to as polycarbonate is a generic term for a polymer material in which a polycondensation reaction is used in its synthesis method and the main chain is linked by a carbonic acid bond. , Phosgene, diphenyl carbonate and the like obtained by polycondensation. Usually, an aromatic polycarbonate represented by a repeating unit having 2,2-bis (4-hydroxyphenyl) propane called bisphenol-A as a bisphenol component is preferably selected. Various bisphenol derivatives should be selected as appropriate. Thus, an aromatic polycarbonate copolymer can be constituted.

In addition to this bisphenol-A, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 9,9-bis (4-hydroxyphenyl) fluorene, 1,1 -Bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxyphenyl) -2-phenyl Ethane, 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane, bis (4-hydroxyphenyl) diphenylmethane, bis (4-hydroxyphenyl) sulfide, bis ( 4-hydroxyphenyl) sulfone, 1,1-bis (4-hydroxyphenyl) -3,3,5-to It can be exemplified methyl cyclohexane.

It is also possible to use an aromatic polyester carbonate partially containing terephthalic acid and / or isophthalic acid components. By using such a structural unit as a part of the structural component of the aromatic polycarbonate composed of bisphenol-A, the properties of the aromatic polycarbonate, such as heat resistance and solubility, can be improved. The present invention is also effective for coalescence.

The viscosity average molecular weight of the aromatic polycarbonate used here is preferably 10,000 to 200,000. A viscosity average molecular weight of 20,000 to 120,000 is particularly preferred. If a resin having a viscosity average molecular weight lower than 10,000 is used, the mechanical strength of the resulting film may be insufficient, and if it has a high molecular weight of 400000 or more, the viscosity of the dope becomes too large, causing problems in handling. The viscosity average molecular weight can be measured by commercially available high performance liquid chromatography.

The glass transition temperature of the aromatic polycarbonate used in the present invention is preferably 200 ° C. or higher for obtaining a highly heat-resistant film, and more preferably 230 ° C. or higher. These can be obtained by appropriately selecting the copolymerization component. The glass transition temperature can be measured with a DSC apparatus (differential scanning calorimetric analyzer). For example, the baseline is unevenly determined by a temperature rising condition of 10 ° C./min with RDC220 manufactured by Seiko Instruments Inc. It is the temperature that begins to do.

<Polyester resin>
The polyester resin used in the present invention is obtained by polymerizing a dicarboxylic acid and a diol, and 70% or more of the dicarboxylic acid structural unit (the structural unit derived from the dicarboxylic acid) is derived from the aromatic dicarboxylic acid, and the diol structure. More than 70% of the units (constituent units derived from the diol) are derived from the aliphatic diol.

The proportion of the structural unit derived from the aromatic dicarboxylic acid is 70% or more, preferably 80% or more, and more preferably 90% or more.

The proportion of the structural unit derived from the aliphatic diol is 70% or more, preferably 80% or more, and more preferably 90% or more. Two or more polyester resins may be used in combination.

Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and the like, 4,4'-biphenyldicarboxylic acid 3,4'-biphenyldicarboxylic acid and the like, and ester-forming derivatives thereof.

As the polyester resin, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid, and monocarboxylic acids such as benzoic acid, propionic acid, and butyric acid can be used without departing from the object of the present invention.

Examples of the aliphatic diol include ethylene glycol, 1,3-propylene diol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and ester-forming derivatives thereof.

As the polyester resin, monoalcohols such as butyl alcohol, hexyl alcohol, and octyl alcohol, and polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol can be used as long as the object of the present invention is not impaired.

A known esterification method or transesterification method can be applied to the production of the polyester resin. Examples of the polycondensation catalyst used in the production of the polyester resin include known antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds such as germanium oxide, titanium compounds such as titanium acetate, and aluminum compounds such as aluminum chloride. Although it can, it is not limited to these.

Preferred polyester resins include polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer resin, polyethylene-2,6-naphthalene dicarboxylate resin, polyethylene-2, 6-naphthalene dicarboxylate-terephthalate copolymer resin, polyethylene-terephthalate-4,4'-biphenyldicarboxylate resin, poly-1,3-propylene-terephthalate resin, polybutylene terephthalate resin, polybutylene-2,6-naphthalene There are dicarboxylate resins and the like.

More preferable polyester resins include polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer resin, polybutylene terephthalate resin, and polyethylene-2,6-naphthalene dicarboxylate. Resin.

The intrinsic viscosity of the polyester resin (phenol / 1,1,2,2-tetrachloroethane = value measured at 25 ° C. in a 60/40 mass ratio mixed solvent) is preferably 0.7 to 2.0 dl / g, more Preferably, it is 0.8 to 1.5 dl / g. Since the molecular weight of the polyester resin is sufficiently high when the intrinsic viscosity is 0.7 or more, the molded product comprising the polyester resin composition obtained by using the polyester resin has mechanical properties necessary for the molded product and is transparent. Property is improved. When the intrinsic viscosity is 2.0 or less, the moldability is good.

<Other additives>
The protective film used in the present invention can contain various compounds as additives depending on the purpose. For example, it contains retardation increasing agent, plasticizer, antioxidant, acid scavenger, light stabilizer, UV absorber, optical anisotropy control agent, matting agent, antistatic agent, release agent, etc. Can be made.

The retardation increasing agent is preferably an aromatic compound having at least two aromatic rings. The aromatic compound is preferably used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of the resin. And it is preferable to use in 0.05-15 mass parts, and it is still more preferable to use in 0.1-10 mass parts. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring. The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring). The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of aromatic heterocycles include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring , Pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring. Details of these are described in JP-A No. 2004-109410, JP-A No. 2003-344655, JP-A No. 2000-275434, JP-A No. 2000-1111914, JP-A No. 12-275434, and the like.

<Matting agent>
In the protective film used in the present invention, it is also preferable to add fine particles as a matting agent in order to prevent the produced film from being scratched or having poor transportability when handled.

As fine particles, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include magnesium silicate and calcium phosphate. Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

The average primary particle size of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 80 to 400 nm. preferable. The content of these fine particles in the film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a protective film (optical film) having a multilayer structure by the co-casting method, it is preferable to contain the added amount of fine particles on the surface.

Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.). it can.

Zirconium oxide fine particles are commercially available under the trade names of Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

Examples of the resin include silicone resin, fluororesin and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the haze of the protective film (optical film) low. In the protective film (optical film) used in the present invention, it is preferable that the dynamic friction coefficient of at least one surface is 0.2 to 1.0.

Method for Producing Protective Film As a method for producing the protective film used in the present invention, production methods such as a normal inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. However, the solution casting method by the casting method and the melt casting method are preferable from the viewpoints of suppression of coloring, suppression of defects of foreign matters, suppression of optical defects such as die lines, and the like.

Hereinafter, a method for producing the protective film used in the present invention by the solution casting method will be described in detail.

<Solution casting method>
Regarding the organic solvent When the protective film (optical film) according to the present invention is produced by the solution casting method, the organic solvent useful for forming the dope is one that dissolves a thermoplastic resin such as a cellulose ester resin. Can be used without limitation.

For example, as a chlorinated organic solvent, methylene chloride, as a non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, ethyl lactate, lactic acid , Diacetone alcohol, etc., preferably methylene chloride, methyl acetate, ethyl acetate, acetone, ethyl lactate, etc. Get.

In addition to the organic solvent, the dope may contain 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the proportion of alcohol in the dope increases, the web gels, facilitating peeling from the metal support, and when the proportion of alcohol is small, the dissolution of the thermoplastic resin in a non-chlorine organic solvent system is promoted. There is also a role.

In particular, the thermoplastic resin should be a dope composition in which at least 10 to 45% by mass of the thermoplastic resin is dissolved in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. preferable.

Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

The solvent used in the dope composition containing the aromatic polycarbonate is preferably a mixed solvent containing 4 to 14 parts by mass of methylene chloride and a linear or branched aliphatic alcohol having 1 to 6 carbon atoms.

The mixing amount of the linear or branched aliphatic alcohol having 1 to 6 carbon atoms is preferably 4 to 12 parts by mass. By using such a mixed solvent, the web is peeled off at a higher residual solvent concentration than before, thereby suppressing the generation of strong static electricity when the web is peeled off, thereby causing damage to the belt, film streaks, unevenness, and minuteness. Scratches can be prevented from occurring.

The type of alcohol added is limited by the solvent used. It is a necessary condition that the alcohol and the solvent are compatible. These may be added alone or in combination of two or more. The alcohol in the present invention is preferably a linear or branched aliphatic alcohol having 1 to 6, preferably 1 to 4, more preferably 2 to 4 carbon atoms. Specific examples include methanol, ethanol, isopropanol, and tertiary butanol. Of these, ethanol, isopropanol, and tertiary butanol can achieve almost the same effect, but methanol is slightly less effective. Although the reason is not clear, it is presumed that the boiling point of the solvent, that is, the ease of flying during drying is related. Higher alcohols higher than that are not preferred because they have a high boiling point and are likely to remain after film formation.

The amount of alcohol to be added must be carefully selected. These alcohols are completely poor in solubility in aromatic polycarbonate and are completely poor solvents. Therefore, it cannot be added too much, and should be the minimum amount that provides satisfactory peelability. As described above, it is 4 to 14 parts by mass, preferably 4 to 12 parts by mass with respect to methylene chloride. When the addition amount is in the range of 4 to 14 parts by mass with respect to the amount of methylene chloride, the solubility of the solvent in the polymer and the dope stability are improved, and the effect of improving the peelability is increased.

In the present invention, the dope composition is composed of the above methylene chloride and an aliphatic alcohol, but other solvents can also be used. The remaining solvent is not particularly limited as long as it dissolves the aromatic polycarbonate at a high concentration and is compatible with alcohol, and is a low-boiling solvent. For example, as a solvent having a solubility in aromatic polycarbonate, in addition to methylene chloride, halogen solvents such as chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, chlorobenzene, 1,3-dioxolane, 1, Examples include cyclic ether solvents such as 4-dioxane and tetrahydrofuran, and ketone solvents such as cyclohexanone.

When using other solvents, there is no particular limitation, and the effect may be taken into consideration. The effects here include mixing the solvent without sacrificing solubility and stability, for example, improving the surface properties of the film formed by the solution casting method (leveling effect), evaporation rate and system These include viscosity adjustment and crystallization suppression effects. What is necessary is just to determine the kind and addition amount of the solvent to mix by the degree of these effects, and you may use 1 type, or 2 or more types as a solvent to mix.

Other solvents preferably used include halogen solvents such as chloroform and 1,2-dichloroethane, hydrocarbon solvents such as toluene and xylene, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, ethyl acetate and butyl acetate. Examples include ester solvents, ether solvents such as ethylene glycol dimethyl ether and methoxyethyl acetate.

The dope composition may be prepared by any method as long as a transparent solution having a low haze is obtained as a result. A predetermined amount of alcohol may be added to the aromatic polycarbonate solution dissolved in a certain solvent in advance, or the aromatic polycarbonate may be dissolved in a mixed solvent containing alcohol. However, as described above, since alcohol is a poor solvent, the method of adding the latter after the former may cause clouding of the dope due to the precipitation of the polymer. Therefore, the method of dissolving in the latter mixed solvent is preferable.

1-1) Dissolution Step In this step, a thermoplastic resin and other additives are dissolved in an organic solvent mainly composed of a good solvent for the thermoplastic resin while stirring to form a dope.

For the dissolution of the thermoplastic resin, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557 Alternatively, various dissolution methods such as a method using a cooling dissolution method as described in JP-A-9-95538 and a method using a high pressure as described in JP-A-11-21379 can be used. The method of pressurizing at a boiling point or higher is preferred.

Recycled material is a finely pulverized film, which is generated when the film is formed, and has been cut off on both sides of the film, or a film original that has been speculated out due to scratches, etc. Reused.

1-2) Casting Step An endless metal belt such as a stainless steel belt or a rotating metal drum that feeds the dope to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it indefinitely. This is a step of casting a dope from a pressure die slit to a casting position on a metal support.

¡Pressure dies that can adjust the slit shape of the die base and make the film thickness uniform are preferred. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

1-3) Solvent evaporation step This is a step in which a web (a dope is cast on a casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent. .

To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, etc. High efficiency and preferable. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or heat by means such as infrared rays.

From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 120 seconds.

1-4) Peeling Step This is a step of peeling the web where the solvent has evaporated on the metal support at the peeling position. The peeled web is sent to the next process.

The temperature at the peeling position on the metal support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C.

The amount of residual solvent at the time of peeling of the web on the metal support at the time of peeling is preferably 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. If the web is peeled off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be lost, and slippage and vertical stripes are likely to occur due to the peeling tension. The amount of solvent is determined.

The amount of residual solvent in the web is defined by the following formula.

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

The peeling tension at the time of peeling the metal support and the film is usually 196 to 245 N / m. However, if wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. It is preferable to peel at a minimum tension of ˜166.6 N / m, and then peel at a minimum tension of ˜137.2 N / m, and particularly preferable to peel at a minimum tension of ˜100 N / m.

In the present invention, the temperature at the peeling position on the metal support is preferably −50 to 40 ° C., more preferably 10 to 40 ° C., and most preferably 15 to 30 ° C.

1-5) Drying and stretching step After peeling, a drying device that alternately conveys the web through a plurality of rolls arranged in the drying device and / or a tenter stretching device that clips and conveys both ends of the web with a clip is used. And dry the web.

The drying means is generally to blow hot air on both sides of the web, but there is also a means to heat by applying microwaves instead of wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout, drying is generally performed at 40-250 ° C. In particular, drying at 40 to 160 ° C. is preferable.

When using a tenter stretching apparatus, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) left and right by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity.

It is also preferable to provide a neutral zone between different temperature zones so that each zone does not cause interference.

The stretching operation may be performed in multiple stages, and it is also preferable to perform biaxial stretching in the casting direction and the width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.
Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction

Also, simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension. The preferred draw ratio for simultaneous biaxial stretching can be in the range of x1.01 to x1.5 in both the width direction and the longitudinal direction.

When the tenter is used, the amount of residual solvent in the web is preferably 20 to 100% by mass at the start of the tenter, and drying is preferably performed while the tenter is applied until the amount of residual solvent in the web is 10% by mass or less. More preferably, it is 5% by mass or less.

When performing the tenter, the drying temperature is preferably 30 to 160 ° C., more preferably 50 to 150 ° C., and most preferably 70 to 140 ° C.

In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable.

1-6) Winding process In this process, the amount of residual solvent in the web becomes 2% by mass or less and the film is wound by a winder. A film having good properties can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

As a winding method, a generally used one may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc., and these may be used properly.

The protective film obtained after winding is preferably a long film. Specifically, the protective film has a thickness of about 100 m to 5000 m and is usually provided in a roll form. The film width is preferably 1.3 to 4 m, more preferably 1.4 to 2 m.

The thickness of the protective film used in the present invention is not particularly limited, but is preferably 20 to 200 μm.

<Melt casting method>
The method in the case of manufacturing the protective film used for this invention by the melt casting method is demonstrated.

2-1) Melt Pellet Production Process It is preferable that the composition constituting the thermoplastic resin film used for melt extrusion is usually kneaded in advance and pelletized.

Pelletization may be performed by a known method. For example, a dry thermoplastic resin and an additive depending on the purpose are fed to an extruder with a feeder and kneaded using a uniaxial or biaxial extruder, and then formed into a strand from a die. Can be extruded, water-cooled or air-cooled, and then cut.

It is important to dry the raw material before extruding to prevent the raw material from being decomposed. In particular, since cellulose ester easily absorbs moisture, it is preferable to dry it at 70 to 140 ° C. for 3 hours or more with a dehumidifying hot air dryer or a vacuum dryer so that the moisture content is 200 ppm or less, and further 100 ppm or less.

Additives may be fed into the extruder and fed into the extruder, or may be fed through individual feeders. In order to mix a small amount of additives such as an antioxidant uniformly, it is preferable to mix them in advance.

The antioxidant may be mixed with each other, and if necessary, the antioxidant may be dissolved in a solvent, impregnated with a thermoplastic resin and mixed, or mixed by spraying. May be.

A vacuum nauter mixer is preferable because it can dry and mix simultaneously. Moreover, when touching with air, such as an exit from a feeder part or die | dye, it is preferable to set it as atmosphere, such as dehumidified air and dehumidified N2 gas.

The extruder is preferably processed at as low a temperature as possible so as to be able to be pelletized so that the shear force is suppressed and the resin does not deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

Film formation is performed using the pellets obtained as described above. It is also possible to feed the raw material powder directly to the extruder with a feeder and form a film as it is without pelletization.

2-2) Extruding the molten mixture from a die to a cooling roll First, using a uniaxial or biaxial type extruder, the melt temperature Tm when extruding is about 200 to 300 ° C. After removing foreign matter by filtering with a filter or the like, it is coextruded into a film form from a T-die, solidified on a cooling roll, and cast while pressing with an elastic touch roll.

When introducing into the extruder from the supply hopper, it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere. Tm is the temperature of the die exit portion of the extruder.

∙ If foreign matter such as scratches or plasticizer aggregates adheres to the die, streaky defects may occur. Such a defect is also called a die line, but in order to reduce surface defects such as the die line, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

The inner surface that comes into contact with the molten resin, such as an extruder or a die, is preferably subjected to surface processing that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material with low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

In the present invention, there is no particular limitation on the cooling roll, but it is a roll having a structure in which a heat medium or a coolant that can be controlled in temperature flows with a highly rigid metal roll, and the size is not limited. It is sufficient that the film is large enough to cool the film, and the diameter of the cooling roll is usually about 100 mm to 1 m.

The surface material of the cooling roll includes carbon steel, stainless steel, aluminum, titanium and the like. Further, in order to increase the hardness of the surface or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

The surface roughness of the cooling roll surface is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable that the surface processed is further polished to have the above-described surface roughness.

In the present invention, examples of the elastic touch roll include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97 / 028950, JP-A-11-235747, A silicon rubber roll coated with a thin-film metal sleeve can be used as described in JP-A-2002-36332, JP-A-2005-172940, and JP-A-2005-280217.

When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

2-3) Stretching Step In the present invention, the film obtained as described above can be further stretched 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll.

Preferably, the film is stretched 1.1 to 2.0 times in both the longitudinal (film transport direction) and lateral (width direction) directions.

As the stretching method, a known roll stretching machine or tenter can be preferably used. In particular, when the protective film (optical film) also serves as the polarizer protective film, it is preferable to make the stretching direction the width direction because lamination with the polarizing film can be performed in a roll form.

The slow axis of the protective film (optical film) becomes the width direction by stretching in the width direction.

Usually, the stretching ratio is 1.1 to 3.0 times, preferably 1.2 to 2 times, and the stretching temperature is usually a temperature of Tg to Tg + 50 ° C., preferably Tg to Tg + 50 ° C. of the resin constituting the film. Done in a range.

The stretching is preferably performed under a uniform temperature distribution controlled in the longitudinal direction or the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

When the film-like resin film produced by the above method is used as a retardation film, the film is formed in the longitudinal direction or width for the purpose of adjusting the retardation (retardation) of the retardation film (optical film) and reducing the dimensional change rate. It may be contracted in the hand direction.

In order to shrink in the longitudinal direction, for example, there is a method in which the film is shrunk by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

Uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the film width direction, more preferably in the range of −1 to + 1 °, particularly −0. A range of 5 to + 0.5 ° is preferable, and a range of −0.1 to + 0.1 ° is particularly preferable. These variations can be achieved by optimizing the stretching conditions.

The protective film used in the present invention is preferably a long film. Specifically, the protective film has a thickness of about 100 m to 10000 m and is usually provided in a roll shape. The width of the film is preferably 1.3 to 4 m, more preferably 1.4 to 2.5 m.

There is no particular limitation on the film thickness of the protective film used in the present invention, and it is preferably changed according to the purpose. For example, when used for a polarizer protective film, the thickness is preferably 20 to 200 μm.

(Manufacturing method of vertical alignment type liquid crystal display device)
In the vertical alignment type liquid crystal display device, 1) a polarizing plate including a polarizer and a retardation film A or retardation film B disposed on at least one surface thereof is wound in a direction perpendicular to the width direction of the film. It can be manufactured through a step of preparing the taken long roll-shaped polarizing plate and 2) a step of bonding the polarizing plate and the liquid crystal cell unwound from the long roll-shaped polarizing plate with a roll-to-panel.

In the present application, the “roll-to-panel manufacturing method” means that a long polarizing plate (rolled polarizing plate) wound in a roll shape is not cut into both the vertical and horizontal sizes of the liquid crystal cell in advance, This is a production method in which a polarizing plate is unwound directly from a roll-shaped polarizing plate, bonded to a liquid crystal cell, and then cut into the size of the liquid crystal cell with a laser cutter or the like. FIG. 3 is a conceptual diagram showing an example of a roll-to-panel manufacturing method. As shown in FIG. 3, the vertical alignment type liquid crystal display device has a plurality of liquid crystal cells 110 arranged on the conveyor belt 100 and a long polarizing plate 130 </ b> A unwound from the roll-shaped polarizing plate 130. Bonding is performed with a matching roll 150.

Thus, when the polarizing plate 130A is bonded to the liquid crystal cell 110, the bonding roll 150 is pressed. Since the polarizing plate 130A is long, generally, an excessive force is easily applied to the polarizing plate 130A during bonding, and unevenness is likely to occur in the polarizing plate 130A. However, when the retardation film satisfying the above-mentioned formulas (1) to (5) used in the present invention is used, the unevenness of the polarizing plate 130A hardly occurs, and the variation in optical performance among lots can be ignored. It is.

Hereinafter, although an example is given and the present invention is explained, the present invention is not limited to these.

1. Production of protective film F2 or F3 Production of film 101 Preparation of fine particle dispersion The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to obtain a fine particle dispersion.
(Composition of fine particle dispersion)
Fine particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.)): 11 parts by mass (average diameter of primary particles 16 nm, apparent specific gravity 90 g / liter)
Ethanol: 89 parts by mass

Preparation of fine particle additive liquid Cellulose acetate (acetyl group substitution degree 2.10, Mn = 14000) was added to a dissolution tank containing methylene chloride, and heated to completely dissolve, then, this was manufactured by Azumi Filter Paper Co., Ltd. No. Azumi filter paper No. Filtered using 244. While finely stirring the filtered cellulose acetate solution, the fine particle dispersion was slowly added thereto. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.
(Composition of fine particle addition liquid)
Methylene chloride: 99 parts by mass Cellulose acetate (above): 4 parts by mass Fine particle dispersion: 11 parts by mass

Preparation of main dope liquid A main dope liquid having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose acetate (total substitution degree 2.48, acetyl group substitution degree 1.58, propionyl group substitution degree 0.90, Mn = 16000) was added to the pressure dissolution tank containing the solvent with stirring. This was heated and stirred to be completely dissolved, and sucrose benzoate having an average substitution degree of 5.5 as a plasticizer was added and dissolved. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.
(Main dope composition)
Methylene chloride: 390 parts by mass Ethanol: 80 parts by mass Cellulose acetate (total substitution degree 2.48, acetyl group substitution degree 1.58, propionyl group substitution degree 0.90, Mn = 16000): 100 parts by mass Sucrose benzoate (average substitution) Degree 5.5): 10.0 parts by mass

In addition to 100 parts by mass of the main dope solution and 5 parts by mass of the fine particle additive solution, the dope solution was obtained by sufficiently mixing with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ).

Next, the obtained dope solution was uniformly cast on a stainless steel band support having a width of 2 m using a belt casting apparatus. On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110%, and the stainless steel band support was peeled off. Next, both ends of the web were gripped with a tenter and stretched in the width direction. Thereafter, the film was held for 4 seconds while holding the end in the width direction of the film, and after the tension in the width direction was relaxed, the width holding was released. The obtained film is transported in a third drying zone set at 125 ° C. for 30 minutes and further dried to produce a film 101 having a width of 1.49 m, a length of 500 m, and a knurling having a width of 1 cm at the end. did. The above method is referred to as “Prescription A”.

Production of films 102 to 108 Films 102 to 108 were the same as described above except that the conditions of the stretching zone (stretching ratio, heating temperature) and the residual solvent amount when entering the tenter were changed as shown in Tables 1 and 2. Was made.

Production of films 109 to 129 The same method as the production of film 101 except that the cellulose acetate contained in the main dope composition was changed to cellulose acetate (total substitution degree 2.41, acetyl substitution degree 2.41, Mn = 18000). Thus, films 109 to 129, 118 and 128 were produced. The lengths of the films 109 to 129 were 500 m, and the lengths of the films 118 and 128 were 1000 m. The production method of the films 109 to 129 is referred to as “Prescription B”.

Production of Films 130 to 141 The cellulose acetate contained in the main dope composition was changed to cellulose acetate (total substitution degree 1.90, acetyl substitution degree 1.90, Mn = 14000), and sucrose having an average substitution degree of 5.5 Films 500 to 141 each having a length of 500 m were prepared in the same manner as the film 101 manufacturing method except that the benzoate was changed to sucrose benzoate having an average substitution degree of 5.1. The manufacturing method of the films 130 to 141 is “prescription C”.

The average refractive index and retardation of the obtained film were measured by the following method.

(Measurement of average refractive index of film)
The refractive index of the obtained film in the triaxial direction at the measurement wavelength of 590 nm (the x-axis direction in the film plane, the y-axis direction perpendicular to the film plane, and the z-axis direction parallel to the normal to the film plane) The average value thereof was defined as “average refractive index”.

The measurement results of the average refractive index of the obtained film are shown in Tables 1 and 2.

(Measurement of phase difference)
After the prepared film was conditioned at 23 ° C. and 55% RH, the phase difference at a measurement wavelength of 590 nm was measured using KOBRA 31WPR manufactured by Oji Scientific Instruments. For calculating Rt, the average refractive index was measured in three directions with an Abbe refractometer, and the average value was used. Further, Rt was calculated by using the value of Ro and the retardation value when tilted by 40 ° with respect to the normal of the film surface with the slow axis in the film plane as the tilt axis.

Tables 3 and 4 show the measurement results of the retardation of the film.

2. Production of protective film F1 (Preparation of compound X)
Methyl acrylate: 100 parts by mass Wako Pure Chemical Industries, Ltd. V65: 5 parts by mass Methanol: 500 parts by mass were prepared, heated to 55 ° C. with stirring in a nitrogen atmosphere, and stirred for 4 hours. Subsequently, it was poured into cold water, and the deposited one was washed with water and methanol at 5 ° C. and dried.

In molecular weight measurement (GPC), the weight average molecular weight of Compound X in terms of polystyrene was 920.

Production of Film X1 A main dope liquid X having the following composition was prepared.
(Composition of main dope liquid X)
Methylene chloride: 390 parts by mass Ethanol: 80 parts by mass Cellulose acetate (total substitution degree 2.79, acetyl group substitution degree 2.79, Mn = 14000): 100 parts by mass Compound X: 7 parts by mass

In addition to 100 parts by mass of the main dope liquid X and 5 parts by mass of the fine particle addition liquid prepared above, the dope liquid X is mixed thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ). Obtained.

The obtained dope liquid X was cast on a stainless steel band support using a belt casting apparatus in the same manner as described above. A film having a thickness of 41 μm and a length of 1000 m, the temperature of the stainless steel band support is lowered by 2 ° C. as a whole from the temperature at the time of manufacturing the film 101, and the drying temperature after stretching with a tenter is 140 ° C. and the drying time is 10 minutes X1 was produced.

Of the surfaces of the obtained film X1, the surface that was in contact with the stainless steel band support at the time of film formation was defined as b surface, and the opposite surface as a surface, parallel to the transmission axis of the polarizer on each surface of the film X1. When the refractive index in the direction was measured by the following method, the refractive index of the a-plane was 1.474. Moreover, when the reflectance was measured along the thickness direction, it was confirmed that the reflectance continuously changed from the a-plane toward the b-plane.

(Measurement of refractive index in the plane of the film parallel to the transmission axis of the polarizer)
A polarizer was set on the eyepiece of the Abbe refractometer, and the refractive index on the surface affixed to the main prism surface was measured by optically contacting the a-plane or b-plane of the film with the main prism surface. At that time, the film was arranged so that the direction parallel to the transmission axis of the polarizer was parallel to the short side of the main prism. The main prism portion was cooled to 21 ° C. Also, the a-side of the film is the surface opposite to the surface that was in contact with the stainless steel band support during film formation; the b-side of the film was the surface that was in contact with the stainless steel band support. It is.

Manufacture of film X2 The method of manufacturing film X1 was the same as that of film X1, except that the temperature of the stainless steel band support was returned to the temperature at which the film 101 was manufactured, and the drying temperature after stretching with a tenter was 130 ° C. Thus, a film X2 having a film thickness of 41 μm and a length of 500 m was produced.

As a result of measuring the refractive index in the direction parallel to the transmission axis of the polarizer on each surface of the film X2 in the same manner as described above, the refractive index of the a surface is 1.480, and the refractive index of the b surface is 1.482. From the reflectivity in the thickness direction, it was confirmed that the refractive index continuously changed in the film thickness direction.

Production of Film X3 The temperature of the stainless steel band support was raised by 2 ° C. above the temperature at the time of production of the film 101, and the drying temperature after stretching with a tenter was 125 ° C. and the drying time was 14 minutes. In the same manner as in the manufacturing method, a film X3 having a film thickness of 41 μm and a length of 500 m was produced.

As a result of measuring the refractive index in the direction parallel to the transmission axis of the polarizer on each surface of the film X3 in the same manner as described above, the refractive index is 1.482 on both the a surface and the b surface, and from the reflectance in the thickness direction, A continuous change in the refractive index in the film thickness direction was not confirmed.

Production of Film Y1 Hollow fine particles were prepared with reference to the description in paragraph [0266] of JP-A-2007-3766. Then, 0.5% by mass of hollow fine particles with respect to cellulose acetate was added to the main dope liquid X to prepare main dope liquid Y. And the film Y1 of length 500m was produced like the manufacturing method of the film X3 except having changed the main dope liquid X into the main dope liquid Y.

As a result of measuring the refractive index in the direction parallel to the transmission axis of the polarizer on the a-plane of the obtained film Y1 in the same manner as described above, it was 1.452.

The obtained films X1 to X3 and commercially available films A1 to A3 are cut in accordance with the size of the liquid crystal cell to form a backlight side polarizing plate (first polarizing plate). It was set as protective film F1.
X1: (41 μm, refractive index: a-plane 1.474, b-plane 1.480)
X2: (41 μm, refractive index: a-plane 1.480, b-plane 1.482)
X3: (41 μm, refractive index: a-plane 1.481, b-plane 1.481)
A1: NEOFRON ETFE (25 μm, refractive index 1.401) manufactured by Daikin Industries, Ltd.
A2: NEOFRON PFA (25 μm, refractive index 1.342) manufactured by Daikin Industries, Ltd.
A3: TPX manufactured by Mitsui Chemicals, Inc. (50 μm, refractive index 1.464)
A4: Konica Minolta KC-8UX2MW (80μm, refractive index 1.481)

3. Production of Polarizing Plate Production of Polarizer A 75 μm-thick polyvinyl alcohol film was swollen with water at 35 ° C. and immersed in an aqueous solution consisting of 0.075 g iodine, 5 g potassium iodide and 100 g water, and then iodinated. After immersing in a 45 ° C. aqueous solution composed of 3 g of potassium, 7.5 g of boric acid, and 100 g of water, the film was uniaxially stretched (temperature 55 ° C., stretch ratio 5 times). This was washed with water and dried to obtain a polarizer.

1) Polarizing plate on the viewing side (second polarizing plate)
The prepared films 101, 108 to 114, 119 to 120, 126 to 132, 134, 136 to 141, and 104 were prepared as the protective film F3 having a retardation function. On the other hand, KC6UA-SW manufactured by Konica Minolta Opto was prepared as the protective film F4. The produced film and KC6UA-SW were subjected to saponification treatment for 60 seconds using a 2N KOH aqueous solution at 50 ° C., washed with water and dried.

The saponified KC6UA-SW is applied to one surface of the prepared polarizer, and the saponified protective film F3 shown in Table 5 or 6 is applied to the other surface of the polarizer via water glue, respectively. Then, a laminate was obtained in which the polarizer was sandwiched between the protective film F3 shown in Table 5 or 6 and saponified KC6UA-SW. The laminate was bonded at a pressure of 20 to 30 N / cm ² and a conveyance speed of about 10 m / min, and subjected to a drying treatment at 70 ° C. for about 2 minutes and then at 60 ° C. for about 2 minutes. The polarizing plates (second polarizing plates) 201, 208 to 214, 219 to 220, 226 to 232, 234 and 236 to 241 and 259 on the viewing side as shown in FIG.

An adhesive layer was provided on the peeled polyethylene terephthalate film, and the surface of the adhesive layer was attached to the protective film F3 side of the obtained polarizing plate. The obtained polarizing plate was wound up in the direction perpendicular to the width direction of the film to prepare a roll-shaped adhesive polarizing plate.

2) Production of backlight side polarizing plate (first polarizing plate) As protective film F2 having a retardation function, produced films 102 to 105, 107, 115 to 118, 121, 123 to 125, 133, 135 and 109 was prepared.

These films were saponified in the same manner as the production of the polarizing plate on the viewing side. Next, the protective film F2 shown in Table 5 or 6 was bonded to only one side of the produced polarizer, and then dried. Then, on the protective film side, adhesive processing is performed in the same manner as the polarizing plate on the viewing side, and an adhesive polarizing plate having a protective film on only one side of the polarizer is produced and wound into a roll to obtain a roll-shaped adhesive polarizing plate. It was.

The pressure-sensitive adhesive polarizing plate was bonded to the backlight side of the liquid crystal cell so that the pressure-sensitive adhesive layer unwound from the roll-shaped pressure-sensitive polarizing plate was in contact with the liquid crystal cell. Thereafter, a backlight-side protective film F1 (any one of films A1 to A4 and X1 to X3) shown in Table 5 or 6 is bonded onto the polarizer, and the backlight as shown in Table 5 or 6 is attached. Side polarizing plates (first polarizing plates) 202 to 205, 207, 215 to 218, 221, 223 to 225, 233, 235, and 242 to 258 were obtained.

The structures of the obtained polarizing plates 201 to 259 are shown in Tables 5 and 6.

4). Production of liquid crystal display device 1) Production of liquid crystal display device having COA structure The two polarizing plates of BRAVIA KDL-46HX800 manufactured by Sony Corporation were peeled off, and the first and second polarizing plates produced above were shown in Tables 7 and 10 The liquid crystal display devices (1001 to 1051) were manufactured by being attached to both surfaces of the liquid crystal cell so that the combination described in the above was obtained, and the following evaluation was performed. The produced polarizing plates were bonded so that the absorption axis of the produced polarizing plate and the absorption axis of the previously bonded polarizing plate were parallel to each other. Moreover, the absorption axis of the polarizer and the in-plane slow axis of the protective film (retardation film) disposed on the liquid crystal cell side of the polarizer were orthogonal to each other. The liquid crystal cell of this liquid crystal display device is a cell in which a color filter and a thin film transistor are disposed on one of two transparent substrates (see FIG. 1), and is described as “Liquid Crystal Cell X” in Tables 7, 9, 10 and 12. did.

2) Production of a liquid crystal display device having no COA structure The two polarizing plates of BRAVIA KDL40V5 manufactured by SONY were peeled off, and the first and second polarizing plates produced above were combined on both sides of the liquid crystal cell in the combination of Table 10 The liquid crystal display devices (3001 to 3006) were manufactured by bonding, and the following evaluation was performed. The produced polarizing plates were bonded so that the absorption axis of the produced polarizing plate and the absorption axis of the previously bonded polarizing plate were parallel to each other. Moreover, the absorption axis of the polarizer and the in-plane slow axis of the protective film (retardation film) disposed on the liquid crystal cell side of the polarizer were orthogonal to each other. The liquid crystal cell of this liquid crystal display device is a cell in which a thin film transistor is disposed on one transparent substrate and a color filter is disposed on the other transparent substrate (see FIG. 2). It was described.

<Front contrast and white brightness>
The front luminance when the screen was displayed in white with the backlight turned on was measured from a distance of 1 m using CS2000 manufactured by Konica Minolta Sensing. Similarly, the front luminance when the screen was displayed in black with the backlight on was measured. Using these measurement results, the front contrast (= front brightness when displaying white / front brightness when displaying black) was calculated. In addition, the calculated value is rounded down to the nearest 10th place, rounded down from 25 to 50, and rounded up to 50.

The front contrast was evaluated according to the following criteria.
1) In the case of liquid crystal cell X ◎: 5000 or more ○: More than 4000 and less than 5000 ×: 4000 or less 2) In the case of liquid crystal cell V ◎: 4000 or more ○: More than 3000 and less than 4000 ×: 3000 or less

The white luminance was evaluated as follows based on the luminance of the product.
1) In the case of liquid crystal cell X Luminance of X (KDL-46HX800): With respect to 400 cd / m ² ◎: Product ratio over 103% ○: Product ratio 100 to 103%
×: Less than 100% product ratio 2) In case of liquid crystal cell V V (KDL-40V5) brightness: 300 cd / m ² ◎: Product ratio over 103% ○: Product ratio 100-103%
×: Less than 100% of product ratio

(Viewing angle)
Using an EZ-Contrast 160D manufactured by ELDIM, the luminance in a direction oblique to the surface of the display screen when the screen was displayed in white was measured in the same manner as the front contrast measurement. The measurement of the luminance in the oblique direction was performed in the range where the inclination angle with respect to the display screen was 0 to 80 °. Similarly, the luminance in a direction oblique to the surface of the display screen when the screen was displayed in black was measured. Then, the contrast at each tilt angle (= brightness when displaying white / brightness when displaying black) was calculated, and the minimum angle among the tilt angles at which the contrast was 100 was defined as the viewing angle. In addition, when the viewing angle exceeds 80 ° in all directions, it is described as 80 °. The viewing angle was evaluated according to the following criteria.
◎: 60 ° or more ○: 50 ° or more, less than 60 ° ×: less than 50 °

(Color shift)
Using the EZ-Contrast 160D manufactured by ELDIM, the hue of the azimuth 360 ° and the azimuth 360 ° is measured from the normal line of the display screen of the liquid crystal display device when displaying black. (U1 ′, v1 ′). Then, the color shift ΔCS is a value having the largest distance from the color coordinates (u2 ′, v2 ′) in the front direction among the coordinates (u1 ′, v1 ′) measured at an inclination angle of 60 °.
Color shift (ΔCS) = ((u1′−u2 ′) ² + (v1′−v2 ′) ² ) ^1/2
Color shift (ΔCS) was evaluated according to the following criteria.
◎: Less than 0.040 ○: 0.040 or more and 0.060 or less ×: More than 0.060

(Comprehensive evaluation)
Of the evaluation items of front contrast, white luminance, viewing angle, and color shift, the evaluation was evaluated as x when there was an item that was at x, and the other was evaluated as o.

The above evaluation results are summarized in Tables 7-12.

As is apparent from the results shown in Tables 7 to 12, it can be seen that the vertical alignment type liquid crystal display device of the present invention is excellent in evaluation of front contrast, viewing angle, and color shift.

(Relation between slit method of polarizing plate and uneven brightness)
The polarizing plate 218 produced above is slit to 1151 mm width and the polarizing plate 228 to a width of 647 mm using a laser slitter to produce a roll-shaped polarizing plate 218A1 having a width of 1151 mm and a roll-shaped polarizing plate 228B1 having a width of 647 mm, respectively. A set of polarizing plates 218A1-228B1 was obtained.

These roll-shaped polarizing plates were set in a liquid crystal display manufacturing system, which is a panel laminating apparatus. And the polarizing plate unwound from the roll-shaped polarizing plate and 10 liquid crystal cells were bonded together by the roll to panel manufacturing method, and the liquid crystal panel was obtained.

Then, a liquid crystal panel (a laminate of a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell) was peeled off from BRAVIA KDL-46HX8001 manufactured by Sony. Then, the liquid crystal panel obtained above was incorporated into the liquid crystal display device described above, and liquid crystal display devices 2001 to 2010 were manufactured.

Further, 10 pieces of the polarizing plates 218 and 228 produced above were cut into 52-inch sizes to obtain a sheet-like polarizing plate. The obtained sheet-like polarizing plate was bonded to each of 10 liquid crystal cells using the panel bonding apparatus described above to obtain a liquid crystal panel. Then, liquid crystal display devices 2011 to 2020 were manufactured in the same manner as described above.

The luminance unevenness of the obtained liquid crystal display device was evaluated by the following method.

(village)
The obtained liquid crystal display device was subjected to wet heat treatment at 50 ° C. and 90% RH for 24 hours, and then the backlight was turned on for 2 hours. Visual evaluation was made according to the criteria.
◎: Brightness unevenness is not visible ○: Weak brightness unevenness is visible, but it is not bothered by image display △: Brightness unevenness is strong, but it is hardly anxious about image display ×: Brightness unevenness is strong, and image display is bothering

The evaluation results are shown in Table 13.

As apparent from the results shown in Table 13, as a method for manufacturing the vertical alignment type liquid crystal display device for manufacturing the vertical alignment type liquid crystal display device of the present invention, at least one of the retardation film A and the retardation film B is used. It turns out that the manufacturing method of the aspect which prepares the elongate roll-shaped polarizing plate which has this retardation film, and is bonded with the roll to panel manufacturing method with respect to the said liquid crystal cell is preferable.

This application claims priority based on Japanese Patent Application No. 2011-037986 filed on Feb. 24, 2011. The contents described in the application specification and the drawings are all incorporated herein.

10, 10 ′ Vertical alignment type liquid

crystal display device

30, 30 ′ Vertical alignment type liquid crystal cell 31 First transparent substrate 33 Second transparent substrate 34 Liquid crystal molecule 35 Liquid crystal layer 37 Thin film transistor 39 Color filter 50 First polarizing plate 52 First One polarizer 54 protective film (F1)
56 Protective film (F2) (retardation film)
70 Second polarizing plate 72 Second polarizer 74 Protective film (F3) (retardation film)
76 Protective film (F4)
90 Backlight 100 Conveying belt 110 Liquid crystal cell 130 Roll-shaped polarizing plate 130A Polarizing plate 150 Bonding roll

Claims

A vertical alignment type liquid crystal display device comprising a vertical alignment type liquid crystal cell, a first polarizing plate and a second polarizing plate sandwiching the vertical alignment type liquid crystal cell, and a backlight,
The vertical alignment type liquid crystal cell includes two transparent substrates, and a liquid crystal layer disposed between the two transparent substrates and including liquid crystal molecules,
A color filter is disposed on one of the two transparent substrates,
The first polarizing plate is disposed on the backlight side surface of the vertical alignment type liquid crystal cell, and includes a first polarizer containing polyvinyl alcohol, and a surface of the first polarizer on the backlight side. A protective film F1 disposed, and a protective film F2 disposed on the surface of the first polarizer on the vertical alignment liquid crystal cell side;
The second polarizing plate is disposed on a viewing side surface of the vertical alignment type liquid crystal cell, and includes a second polarizer containing polyvinyl alcohol, and a surface of the second polarizer on the vertical alignment type liquid crystal cell side. A protective film F3 disposed on the viewing side of the second polarizer, and a protective film F4 disposed on the viewing side of the second polarizer,
The absorption axis of the first polarizer and the in-plane slow axis of the protective film F2 are orthogonal to each other, and the absorption axis of the second polarizer and the in-plane slow axis of the protective film F3 are orthogonal to each other. And
Of the protective films F2 or F3, the one disposed on the transparent substrate side provided with the color filter is the retardation film A, and the one disposed on the transparent substrate side not provided with the color filter. Is retardation film B,
For the retardation film A measured at 23 ° C. and 55% RH at a measurement wavelength of 590 nm, the retardation value Rt in the thickness direction is Rt (A), the retardation value Ro in the in-plane direction is Ro (A), In the retardation film B measured at 23 ° C. and 55% RH at a measurement wavelength of 590 nm, the retardation value Rt in the thickness direction was Rt (B), and the retardation value Ro in the in-plane direction was Ro (B). When
Satisfy all of the following formulas (1) to (5),
Formula (1): Rt (A) <Rt (B)
Formula (2): 70 nm <Rt (A) <130 nm
Formula (3): 130 nm <Rt (B) <200 nm
Formula (4): 20 nm <Rt (B) -Rt (A) <130 nm
Formula (5): Rt / Ro (A) <Rt / Ro (B) [Ro and Rt are defined by the following formulas.
Formula (I): Ro = (nx−ny) × d (nm)
Formula (II): Rt = {(nx + ny) / 2−nz} × d (nm)
In the formulas (I) and (II)
nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the plane of the retardation film;
ny represents the refractive index in the fast axis direction y perpendicular to the slow axis in the plane of the retardation film;
nz represents the refractive index in the thickness direction z of the retardation film;
d represents the thickness of the retardation film]
The refractive index in the direction parallel to the transmission axis of the first polarizer on the surface on the backlight side of the protective film F1 is smaller than the average refractive index of the protective film F2, and the average refractive index of the protective film F3. Vertical alignment type liquid crystal display device smaller than the rate.
2. The vertical alignment type liquid crystal display device according to claim 1, wherein a thin film transistor and the color filter are disposed on one of the two transparent substrates.
The protective film F1 has a refractive index np parallel to the transmission axis of the second polarizer on the second polarizer side surface, and the second polarizer transmits on the backlight side surface. 2. The vertical alignment liquid crystal display device according to claim 1, wherein np is larger than na, where na is a refractive index in a direction parallel to the axis.
The protective film F2 is the retardation film A,
The vertical alignment liquid crystal display device according to claim 2, wherein the retardation value Ro (A) in the in-plane direction of the retardation film A further satisfies the following formula (6).
Formula (6): 40 nm <Ro (A) <90 nm
The vertical alignment type liquid crystal display device according to claim 1, wherein the refractive index of the protective film F1 in the direction parallel to the transmission axis of the second polarizer continuously changes in the thickness direction of the film.
The vertical axis according to claim 1, wherein a refractive index na in a direction parallel to a transmission axis of the second polarizer on a surface on the backlight side of the protective film F1 is in a range of 1.350 to 1.480. Alignment type liquid crystal display device.
A method of manufacturing a vertical alignment type liquid crystal display device according to claim 1,
A roll-shaped polarized light in which a polarizing plate including a polarizer and the retardation film A or the retardation film B disposed on at least one surface of the polarizer is wound in a direction perpendicular to the width direction of the film Preparing the board,
And a step of bonding the polarizing plate unwound from the roll-shaped polarizing plate and the vertical alignment type liquid crystal cell with a roll to panel.