WO2015190190A1 - Liquid crystal display device - Google Patents

Abstract

The purpose of the present invention is to reduce warping of a liquid crystal display panel in a small-sized liquid crystal display device such as one for use in mobile devices and to suppress display unevenness or the like caused by the warping. A liquid crystal display device according to the present invention comprises: a liquid crystal display panel which comprises a first polarizing plate, a liquid crystal cell and a second polarizing plate; and a backlight. The first polarizing plate comprises a first polarizer, a protective film (F1) that is arranged on the viewing side surface and a protective film (F2) that is arranged on the liquid crystal cell-side surface. The second polarizing plate comprises a second polarizer, a protective film (F3) that is arranged on the liquid crystal cell-side surface and a protective film (F4) that is arranged on the backlight-side surface. The absorption axis of the first polarizer is parallel to the short side direction (β) of the liquid crystal display panel and is perpendicular to the absorption axis of the second polarizer. The ratio of the contraction force (W1) of the protective film (F1) in the long side direction (α), said contraction force being represented by formula (1), to the contraction force (W4) of the protective film (F4) in the long side direction (α), said contraction force being represented by formula (1), namely W1/W4 is more than 0.81 but 2.50 or less.

Description

Liquid crystal display

The present invention relates to a liquid crystal display device.

Liquid crystal display devices are widely used in mobile devices such as smart phones and tablet terminals. These mobile devices are required to be thin.

The liquid crystal display device includes a liquid crystal display panel including a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell. The liquid crystal cell includes a pair of glass substrates and a liquid crystal layer disposed between them. As mobile devices become thinner, liquid crystal display panels, which are constituent members, are required to be thinner. In particular, the glass substrate of the liquid crystal cell has been thinned because the ratio of the thickness to the entire liquid crystal display panel is large. However, when the glass substrate is thinned, there is a problem that the liquid crystal display panel is likely to be warped due to the dimensional change of the polarizing plate.

As a method for suppressing the dimensional change of the polarizing plate that causes the warp of the liquid crystal display panel, there is a liquid crystal display device in which the protective films F1 and F4 are laminated with a base material layer and a control layer for controlling moisture permeability. It has been proposed (for example, Patent Document 1).

As a method for suppressing the warpage of the liquid crystal display panel, the dimensional change rate C1 due to the hygroscopic expansion of the viewing side polarizing plate is made larger than the dimensional change rate C2 due to the hygroscopic expansion of the backlight side polarizing plate; There has been proposed a liquid crystal display device in which the water content W1 is smaller than the water content W2 of the backlight-side polarizing plate (for example, Patent Documents 2 and 3). Further, (the sum of the products of the elastic modulus in the long side direction and the cross-sectional area in the short side direction of the viewing side polarizing plate) / (the product of the elastic modulus in the long side direction and the cross-sectional area in the short side direction of the backlight side polarizing plate) There has also been proposed a liquid crystal display device or the like configured such that the total sum is equal to or less than a certain value (for example, Patent Document 4).

JP 2013-160863 A JP 2013-037104 A JP 2007-292966 A JP 2006-267503 A

However, Patent Documents 1 to 4 described above all suppress the warpage of the liquid crystal display panel that protrudes toward the backlight side in a large-sized liquid crystal display device for television use. For this reason, in a small-sized liquid crystal display device such as a mobile device, the warp of the liquid crystal display panel that protrudes toward the viewing side is not suppressed.

In a small liquid crystal display device, when the liquid crystal display panel that protrudes toward the viewing side is warped, the warped liquid crystal display panel comes into contact with other members (such as a cover glass, a touch panel, or a backlight) to cause display unevenness. Cheap. Furthermore, the warped liquid crystal display panel may float from the casing together with the cover glass and the touch panel. As a result, a gap is generated between the housing and the liquid crystal display panel, and moisture from the outside may enter the apparatus or light leakage may occur. In particular, in a small liquid crystal display device for use in mobile devices and the like, the distance between members is very small, so that the liquid crystal display panel is likely to be lifted from the housing even if the liquid crystal display panel has a small amount of warpage.

The present invention has been made in view of the above circumstances, and provides a liquid crystal display device capable of reducing warpage of a liquid crystal display panel and suppressing display unevenness and the like in a small liquid crystal display device for use in mobile devices and the like. For the purpose.

[1] A liquid crystal display device including a first polarizing plate, a liquid crystal cell, and a second polarizing plate in order, and a backlight, wherein the first polarizing plate is a first polarizing plate. The polarizer, the protective film F1 disposed on the surface of the first polarizer on the viewing side, and the protective film F2 disposed on the surface of the first polarizer on the liquid crystal cell side, The second polarizing plate includes a second polarizer, a protective film F3 disposed on the liquid crystal cell side surface of the second polarizer, and the backlight side surface of the second polarizer. An absorption axis of the first polarizer is parallel to the short side direction β of the liquid crystal display panel, and the absorption axis of the first polarizer and the second The absorption axis of the polarizer is orthogonal to each other, and is a length represented by the following formula (1) of the protective film F1. When the contraction force in the direction α is W1, and the contraction force in the long side direction α represented by the following formula (1) of the protective film F4 is W4, the ratio W1 / W4 of the contraction force is more than 0.81 A liquid crystal display device of 50 or less.

(In Formula (1),
W is the contraction force (N / m) in the long side direction α of the protective film,
T is the tensile elastic modulus (Pa) in the long side direction α of the protective film,
S is a dimensional change rate (%) accompanying the humidity change in the long side direction α represented by the following formula (2) of the protective film:
t represents the thickness (m) of the protective film)

(In Formula (2),
S is the dimensional change rate (%) accompanying the humidity change in the long side direction α of the protective film,
L0 is the length of the long side direction α under 23 ° C. and 55% RH of the protective film,
L1 is the length of the long side direction α under 23 ° C. and 20% RH of the protective film,
L2 represents the length of the long side direction α under 23 ° C. and 80% RH of the protective film)
[2] The distance from the viewing side surface of the liquid crystal cell to the viewing side surface of the protective film F1 is D1, and the contraction moment of the long side direction α represented by the following formula (3) of the protective film F1. M1, and the distance from the backlight side surface of the liquid crystal cell to the backlight side surface of the protective film F4 is D4, the long side direction α of the protective film F4 represented by the following formula (3) The liquid crystal display device according to [1], wherein the contraction moment ratio M1 / M4 is 0.9 or more and 2.0 or less when the contraction moment is M4.

(In Formula (3),
M is the contraction moment (N) of the protective film in the long side direction α,
W is the contraction force (N / m) in the long side direction α of the protective film,
D represents the distance (m) from the surface of the liquid crystal cell of the protective film)
[3] The liquid crystal cell includes a liquid crystal layer and a pair of glass substrates sandwiching the liquid crystal layer. The thickness of the glass substrate is t ′ (mm), and the length in the long side direction α of the liquid crystal display panel. The liquid crystal display device according to [1] or [2], wherein t ′ / l is 0.0003 to 0.0050, where is 1 (mm).
[4] The liquid crystal display device according to any one of [1] to [3], wherein a diagonal length of the liquid crystal display panel is 15 inches or less.
[5] The transparent protective substrate disposed on the viewing-side surface of the liquid crystal display panel, and provided integrally with one of the transparent protective substrate and the liquid crystal display panel, or the transparent protective substrate and the liquid crystal display panel The liquid crystal display device according to any one of [1] to [4], further including a touch panel disposed between the two and the touch panel.
[6] The liquid crystal display device according to any one of [1] to [5], wherein the protective film F1 is a cellulose ester film having a thickness of 40 to 80 μm.
[7] The protective films F2 and F3 are either a cellulose ester film having a thickness of 20 to 60 μm, a cycloolefin film having a thickness of 20 to 60 μm, or omitted, any one of [1] to [6] A liquid crystal display device according to 1.

According to the present invention, it is possible to sufficiently reduce the warpage of the liquid crystal display panel in a small liquid crystal display device for use in mobile devices and the like, thereby providing a liquid crystal display device with little display unevenness.

It is a schematic diagram which shows an example of the fundamental structure of a liquid crystal display device. It is a schematic diagram which shows the positional relationship of the absorption axis of the polarizer and MD direction of a protective film in a liquid crystal display device. It is a figure which shows the state of the curvature of a liquid crystal display panel.

<Liquid crystal display device>
The liquid crystal display device of the present invention is a small liquid crystal display device preferably used for mobile devices such as smart phones and tablet terminals. The liquid crystal display device of the present invention includes a liquid crystal display panel and a backlight. The liquid crystal display panel includes a liquid crystal cell, a first polarizing plate disposed on the surface on the viewing side, and a second polarizing plate disposed on the surface on the backlight side.

The liquid crystal display device of the present invention may further include a touch panel and a transparent protective substrate disposed on the viewing side surface (the surface opposite to the backlight) of the liquid crystal display panel as necessary. The touch panel may be integrally provided on one of the transparent protective substrate and the liquid crystal display panel, or may be disposed between the transparent protective substrate and the liquid crystal display panel. Specifically, the touch panel may be provided in the liquid crystal cell of the liquid crystal display panel (in-cell type); may be provided outside the liquid crystal cell (between the first polarizing plate and the liquid crystal cell). (On-cell type); may be provided integrally with the transparent protective substrate, or may be separately disposed between the liquid crystal display panel and the transparent protective substrate (out-cell type).

FIG. 1 is a schematic diagram showing an example of a basic configuration of a liquid crystal display device. As shown in FIG. 1, the liquid crystal display device 10 of the present invention can include a liquid crystal display panel 20, a backlight 30, and a cover glass (transparent protective substrate) 40. These members can be housed in a housing (not shown) that covers at least the back surface and the peripheral edge.

The planar shape of the liquid crystal display panel 20 can usually be a rectangle including a long side and a short side. The diagonal length of the liquid crystal display panel 20 is preferably 15 inches or less, more preferably 10 inches or less, and even more preferably 6 inches or less. The liquid crystal display panel 20 includes a liquid crystal cell 50, a first polarizing plate 60, and a second polarizing plate 70.

The display mode of the liquid crystal cell 50 may be various display modes such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS. From the viewpoint of obtaining a high contrast, the VA (MVA, PVA) mode is preferable, and from the viewpoint of obtaining a wide viewing angle, the IPS mode is preferable.

The liquid crystal cell 50 has a pair of transparent substrates 51 and 53 and a liquid crystal layer 55 sandwiched between them.

The transparent substrates 51 and 53 are transparent resin substrates or glass substrates, preferably glass substrates. The thickness of the transparent substrates 51 and 53 is preferably 1 mm or less, more preferably 0.5 mm or less, and preferably 0.2 to 0.5 mm in order to reduce the thickness of the liquid crystal display device. Further preferred.

When the thickness of the glass substrate is t ′ (mm) and the length in the long side direction α of the liquid crystal display panel 20 is l (mm), t ′ / l is preferably 0.0001 to 0.0050, More preferably, it is 0.0003 to 0.0050. If t ′ / l is in the above range, the length l of the liquid crystal display panel 20 in the long side direction α is large and the thickness t ′ of the glass substrate is small. Therefore, the liquid crystal display panel 20 warps due to the contraction force of the polarizer. Cheap. In such a case, as described later, the warp of the liquid crystal display panel 20 can be reduced by setting the ratio W1 / W4 of the shrinkage force of the protective films 63 (F1) and 75 (F4) to a predetermined range.

The pixel electrode for applying a voltage to the liquid crystal molecules can be disposed on one of the pair of transparent substrates 51 and 53 (for example, the transparent substrate 51). The counter electrode may be further disposed on the transparent substrate 51 on which the pixel electrode is disposed, or may be disposed on the other transparent substrate 53. The color filter can be usually disposed on the other transparent substrate 53.

The liquid crystal layer 55 includes liquid crystal molecules having negative or positive dielectric anisotropy, for example, when the liquid crystal cell 50 is a VA type. The liquid crystal molecules are liquid crystal when no voltage is applied (when no electric field is generated between the pixel electrode and the counter electrode) due to the alignment regulating force of the alignment film provided on the surface of the transparent substrate 51 on the liquid crystal layer side. The long axis of the molecule is oriented so as to be substantially perpendicular to the surface of the transparent substrate. Then, by applying an image signal (voltage) to the pixel electrode, the liquid crystal molecules are aligned so that the major axis thereof is in the horizontal direction with respect to the substrate surface, thereby changing the transmittance and reflectance of each sub-pixel. To display the image.

The first polarizing plate 60 is disposed on the viewing side surface of the liquid crystal cell 50, and the first polarizer 61 and the protective film 63 (protection) disposed on the viewing side surface of the first polarizer 61. Film F1, hereinafter also referred to as “F1”) and a protective film 65 (protective film F2, hereinafter also referred to as “F2”) disposed on the surface of the first polarizer 61 on the liquid crystal cell side.

The second polarizing plate 70 is disposed on the surface of the liquid crystal cell 50 on the backlight 30 side, and the second polarizer 71 and the protective film disposed on the surface of the second polarizer 71 on the liquid crystal cell side. 73 (protective film F3, hereinafter also referred to as “F3”) and a protective film 75 (protective film F4, hereinafter also referred to as “F4”) disposed on the backlight-side surface of the second polarizer 71. One or both of the protective films 65 (F2) and 73 (F3) may be omitted as necessary.

The first polarizing plate 60 and the second polarizing plate 70 can be bonded to the liquid crystal cell 50 via an adhesive layer 81, respectively. The thickness of the pressure-sensitive adhesive layer 81 is not particularly limited, but may be, for example, about 10 to 80 μm. The adhesive layer 81 may not be disposed.

The thickness of the cover glass 40 may be about 0.050 to 1.000 mm. The cover glass 40 may be integrally provided with a touch panel module (not shown).

FIG. 2 is a schematic diagram showing the positional relationship between the absorption axis of the polarizer and the MD direction of the protective film in the liquid crystal display device. As shown in FIG. 2, the absorption axis of the first polarizer 61 is preferably parallel to the short side direction β (direction perpendicular to the long side direction α) of the liquid crystal display panel 20. In addition, the absorption axis of the first polarizer 61 is preferably parallel to the MD direction of the protective film 63 (F1) (a direction orthogonal to the in-plane slow axis direction). The absorption axis of the second polarizer 71 is preferably parallel to the long side direction α of the liquid crystal display panel 20. The absorption axis of the second polarizer 71 is preferably parallel to the MD direction of the protective film 75 (F4) (preferably a direction orthogonal to the in-plane slow axis direction).

As described above, when a liquid crystal display device used in a mobile device such as a smart phone or a tablet terminal is moved from a high humidity environment to a low humidity environment, the liquid crystal display panel is likely to warp so as to protrude toward the viewing side (see FIG. 3). ). The reason why such a liquid crystal display panel warps is not necessarily clear, but is considered as follows.

That is, in the liquid crystal display device used for the mobile device, as described above, the absorption axis of the first polarizer 61 on the viewing side is parallel to the short side direction β of the liquid crystal display panel 20. Therefore, when the first polarizer 61 is exposed from a high-humidity environment to a low-humidity environment, the first polarizer 61 easily contracts in the short-side direction β of the liquid crystal display panel 20. On the other hand, the absorption axis of the second polarizer 71 on the backlight side is parallel to the long side direction α of the liquid crystal display panel 20. Therefore, when the second polarizer 71 is exposed from a high-humidity environment to a low-humidity environment, the second polarizer 71 tends to contract in the long-side direction α of the liquid crystal display panel 20. Since the contraction force of the second polarizer 71 contracting in the long side direction α of the liquid crystal display panel 20 is larger than the contraction force of the first polarizer 61 contracting in the short side direction β of the liquid crystal display panel 20, It is considered that the liquid crystal display panel 20 tends to warp so as to be convex toward the viewing side (see FIG. 3).

If the warpage of the liquid crystal display panel 20 exceeds a certain level, the liquid crystal display panel 20 comes into contact with the cover glass 40 and the backlight 30 to cause display unevenness; It is thought that it is easy to lift from the figure.

On the other hand, the present inventors increase the contraction force in the long side direction α of the liquid crystal display panel of the first polarizing plate 60 on the viewing side, thereby increasing the second polarization on the backlight side. It has been found that the contraction force in the long side direction α of the liquid crystal display panel of the plate 70 can be offset. The contraction force of the first polarizing plate 60 on the viewing side can be adjusted by, for example, the protective film 63 (F1) or 65 (F2). Among them, the protective film 65 (F2) disposed on the liquid crystal cell side is less likely to contract when moved from a high humidity environment to a low humidity environment, and is less likely to generate contraction force. On the other hand, the protective film 63 (F1) disposed on the viewing side is easily contracted when it is moved from a high humidity environment to a low humidity environment, and a contraction force is easily generated. Therefore, it has been found that it is effective to adjust the ratio of the shrinkage force between the protective film 63 (F1) of the first polarizing plate 60 and the protective film 75 (F4) of the second polarizing plate 70.

That is, the contraction force of the protective film 63 (F1) of the first polarizing plate 60 on the viewing side expressed by the following formula (1) in the long side direction α of the liquid crystal display panel is W1, and the second on the backlight side. When the contraction force represented by the following formula (1) of the protective film 75 (F4) of the polarizing plate 70 in the long side direction α of the liquid crystal display panel is W4, the ratio W1 / W4 of the contraction force is 0.81. It is preferably 2.50 or less, more preferably 0.9 or more and 2.0 or less, and further preferably 1.0 or more and 1.5 or less. By setting W1 / W4 to be equal to or greater than a certain value, the contraction force in the long side direction α of the liquid crystal display panel 20 of the second polarizing plate 70 on the backlight side is used to reduce the contraction force of the first polarizing plate 60 on the viewing side. Can be offset moderately by the contraction force in the long side direction α. By setting W1 / W4 to a certain value or less, the contraction force of the first polarizing plate 60 on the viewing side becomes too large, and the liquid crystal display panel can be prevented from warping so as to protrude toward the backlight side. Thus, by setting W1 / W4 in the above range, the contraction force in the long side direction α of the liquid crystal display panel of the first polarizing plate 60 on the viewing side is appropriately increased, and the liquid crystal of the polarizing plate on the backlight side is increased. The contraction force in the long side direction α of the display panel can be canceled appropriately. As a result, the warp of the liquid crystal display panel 20 can be sufficiently reduced.

T in Formula (1) indicates the tensile elastic modulus (Pa) of the protective film in the long side direction α of the liquid crystal display panel. The tensile elastic modulus of the protective film can be measured by the following procedure.
1) A protective film is cut into a shape of No. 1 with a size of 150 mm (long side direction α) × 10 mm (short side direction β) to obtain a test piece.
2) After humidity-conditioning this test piece for 24 hours in an environment of 23 ° C. and 55% RH, the tensile modulus of elasticity in the long side direction α is measured according to the method described in JIS K 7127. The tensile tester uses Tensilon RTC-1225A manufactured by Orientec Co., Ltd., and the tensile speed is 100 mm / min. The tensile modulus is calculated by setting the elastic modulus analysis start point to 2 (MPa) and the elastic modulus analysis end point to 60 (MPa).

S in the formula (1) indicates a dimensional change rate (%) accompanying a humidity change in the long side direction α of the liquid crystal display panel of the protective film, which is represented by the following formula (2).

The dimensional change rate S (%) of the protective film can be measured by the following procedure.
1) Cut out into a size of 25 cm in length (measurement direction) × 5 cm in width so that the long side direction α of the liquid crystal display panel 20 of the protective film becomes the longitudinal direction, and use it as a test piece. Pin holes are formed at intervals of 20 cm in the longitudinal direction of the test piece, and after humidity conditioning at 23 ° C. and a relative humidity of 55% for 24 hours, the distance between the pin holes is measured with a pin gauge to obtain a measured value L0.
2) Next, the test piece is conditioned for 24 hours in a humid heat environment of 23 ° C. and a relative humidity of 20%, and then the distance between the pin holes is measured with a pin gauge to obtain a measured value L1.
3) Further, after adjusting the test piece for 24 hours at 23 ° C. and 80% relative humidity, the distance between the pin holes is measured with a pin gauge to obtain a measured value L2.
4) Apply these measurement values to the following equation to calculate the dimensional change rate (%).
Dimensional change rate (%) = {(L2-L1) / L0} × 100

T of Formula (1) shows the thickness (m) of a protective film.

In order to set W1 / W4 within the above range, the shrinkage force W4 of the protective film 75 (F4) in the long side direction α of the liquid crystal display panel may be reduced, or the liquid crystal display panel of the protective film 63 (F1). The contraction force W1 in the long side direction α may be increased; however, it is preferable to increase the contraction force W1 in the long side direction α of the liquid crystal display panel of the protective film 63 (F1). Specifically, the thickness t1 of the protective film 63 (F1) is made larger than the thickness t4 of the protective film 75 (F4); the dimensional change rate of the protective film 63 (F1) in the stretching direction (preferably the TD direction) In addition, it is preferable to make it larger than the dimensional change rate in the extending direction (preferably TD direction) of the protective film 75 (F4).

The shrinkage force W1 of the protective film 63 (F1) can be adjusted by the thickness of the protective film, stretching conditions, and the like. The extending direction of the protective film 63 (F1) may be parallel to the long side direction α of the liquid crystal display panel. For example, in order to increase the shrinkage force of the liquid crystal display panel of the protective film 63 (F1), 1) the thickness of the protective film 63 (F1) is increased, or 2) the residual solvent amount of the film-like material at the start of stretching. It is preferable to increase the number, 3) lower the stretching temperature, 4) lower the stretching ratio; more preferably satisfy the above 2) to 4); satisfy all of the above 1) to 4) More preferably.

The shrinkage force of the protective film 63 (F1) and the protective film 75 (F4) in the long side direction α of the liquid crystal display panel may be set so that the ratio of shrinkage force (W1 / W4) is in the above range. Not limited. The contraction force in the long side direction α of the liquid crystal display panel of the protective films 63 (F1) and 75 (F4) can be in the range of 48 × 10 ³ to 100 × 10 ³ N / m, for example.

Furthermore, based on the principle of the lever, the second polarizing plate located on the backlight side becomes larger as the distance from the surface of the liquid crystal cell 50 of the protective film 63 (F1) of the first polarizing plate 60 on the viewing side that generates contraction force increases. A force that cancels the contraction force of 70 can act greatly.

Accordingly, the distance from the viewing side surface of the liquid crystal cell 50 to the viewing side surface of the protective film 63 (F1) of the first polarizing plate 60 is represented by D1 and the following formula (3) of the protective film 63 (F1). The contraction moment in the long side direction α is M1, and the distance from the backlight side surface of the liquid crystal cell 50 to the backlight side surface of the protective film 75 (F4) of the second polarizing plate 70 is D4, and the protective film 75 When the contraction moment in the long side direction α represented by the following formula (3) of (F4) is M4; the ratio M1 / M4 of the contraction moment is preferably more than 0.81 and less than or equal to 2.60. It is more preferably 9 or more and 2.0 or less, and further preferably 1.0 or more and 1.5 or less.

W of Formula (3) shows the contraction force (N / m) in the long side direction α of the liquid crystal display panel of the protective film represented by Formula (1). D shows the distance (m) from the surface of the liquid crystal cell of a protective film. For example, in FIG. 1, the distance D1 of the protective film 63 (F1) from the surface of the liquid crystal cell is the thickness of the pressure-sensitive adhesive layer 81, the thickness of the protective film 65 (F2), the thickness of the first polarizer 61, and the protective film. This is the total thickness of 63 (F1).

In order to set M1 / M4 within the above range, the shrinkage force W1 of the protective film 63 (F1) is set to a certain value or more, for example, to increase the shrinkage force ratio W1 / W4; and the protective film 63 (F1) It is preferable to make the distance D1 from the surface of the liquid crystal cell larger than the distance D4 from the surface of the liquid crystal cell of the protective film 75 (F4). When the distance D1 from the surface of the liquid crystal cell of the protective film 63 (F1) is larger than the distance D4 from the surface of the liquid crystal cell of the protective film 75 (F4), D4 / D1 is, for example, 0.5 or more and less than 1. Preferably it may be 0.7 or more and less than 1.

The distance D1 from the surface of the liquid crystal cell of the protective film 63 (F1) can be adjusted by the thickness of the adhesive layer 81, the protective film 65 (F2), the first polarizer 61, the protective film 63 (F1), and the like. The total thickness of the protective film 65 (F2), the first polarizer 61 and the protective film 63 (F1) is TT1; the protective film 73 (F3), the second polarizer 71 and the protective film 75 (F4) When the total thickness is TT4, TT4 / TT1 may be 0.5 or more and less than 1, preferably 0.7 or more and less than 1.

<About protective films 63 (F1) and 75 (F4)>
The protective films 63 (F1) and 75 (F4) are preferably films mainly composed of cellulose ester.

(Cellulose ester)
The cellulose ester is a compound obtained by esterifying cellulose and at least one of an aliphatic carboxylic acid having 2 to 22 carbon atoms and an aromatic carboxylic acid. Examples of the cellulose ester include cellulose triacetate, cellulose diacetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose benzoate, cellulose acetate benzoate, and the like. Among them, those having low retardation are preferable, and cellulose triacetate is preferable.

The total degree of substitution of acyl groups in the cellulose ester is about 2.0 to 3.0, preferably 2.5 to 3.0, more preferably 2.7 to 3.0, and even more preferably 2.8 to 3.0. 2.95. In order to reduce the retardation development property, it is preferable to increase the total substitution degree of the acyl group.

The number of carbon atoms of the acyl group contained in the cellulose ester is preferably 2 to 7, and more preferably 2 to 4. In order to obtain good heat resistance, the acyl group contained in the cellulose ester preferably contains an acetyl group. The substitution degree of the acyl group having 3 or more carbon atoms is preferably 0.9 or less, and more preferably 0.

The degree of substitution of the acyl group of the cellulose ester can be measured by the method prescribed in ASTM-D817-96.

The weight average molecular weight of the cellulose ester is preferably 5.0 × 10 ⁴ to 5.0 × 10 ⁵ in order to obtain a certain level of mechanical strength, and 1.0 × 10 ⁵ to 3.0 ×. 10 ⁵ is more preferable, and 1.5 × 10 ⁵ to 2.9 × 10 ⁵ is even more preferable. The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the cellulose ester is preferably 1.0 to 4.5.

The weight average molecular weight and molecular weight distribution of the cellulose ester can be measured by gel permeation chromatography (GPC). The measurement conditions are as follows.
Solvent: Methylene chloride Column: Three Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used.
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 1.0 × 10 ⁶ to 5.0 × 10 ² 13 calibration curves are used. The 13 samples are preferably selected at approximately equal intervals.

The content of cellulose ester can be 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more based on the film.

The protective films 63 (F1) and 75 (F4) may further contain various additives such as a plasticizer, an ultraviolet absorber, a peeling aid, and a matting agent (fine particles) as necessary.

(UV absorber)
The ultraviolet absorber may be a benzotriazole compound, a 2-hydroxybenzophenone compound, a salicylic acid phenyl ester compound, or the like. Specifically, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- Triazoles such as (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2'-dihydroxy-4 -Benzophenones such as methoxybenzophenone.

The UV absorber may be a commercially available product. Examples thereof include Tinuvin 109, Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, and Tinuvin 928 manufactured by BASF Japan, or 2, 2'-methylenebis [6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol] (molecular weight 659; examples of commercially available products are manufactured by ADEKA Corporation LA31) and the like.

The content of the ultraviolet light inhibitor may be about 1 ppm to 5.0%, preferably about 0.5 to 3.0% by mass with respect to the cellulose ester.

(Matting agent)
The matting agent can be fine particles made of an inorganic compound or an organic compound. Examples of inorganic compounds constituting the matting agent include silicon dioxide (silica), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated calcium silicate. , Aluminum silicate, magnesium silicate and calcium phosphate. Of these, silicon dioxide and zirconium oxide are preferable, and silicon dioxide is more preferable in order to reduce an increase in haze of the obtained film.

Specific examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (above, Nippon Aerosil Co., Ltd.), Sea Hoster KEP-10, Sea Hoster KEP -30, Seahoster KEP-50 (manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), nip seal E220A (manufactured by Nippon Silica Kogyo), Admafine SO (manufactured by Admatechs) and the like.

The particle shape of the matting agent is indefinite, needle-like, flat or spherical, and may preferably be spherical in view of easy transparency of the resulting film. One kind of matting agent may be used, or two or more kinds may be used in combination.

When the size of the matting agent particles is close to the wavelength of visible light, the light is scattered and the transparency is lowered. Therefore, the size of the particles of the matting agent is preferably smaller than the wavelength of visible light. / 2 or less is preferable. However, if the size of the particles is too small, the effect of improving slipperiness may not be manifested. Therefore, the size of the particles is preferably in the range of 80 to 180 nm. The particle size means the size of an aggregate when the particle is an aggregate of primary particles. When the particles are not spherical, the size of the particles means the diameter of a circle corresponding to the projected area.

The content of the matting agent can be about 0.05 to 1.0% by mass, preferably 0.1 to 0.8% by mass with respect to the cellulose ester.

(Thickness)
The thicknesses of the protective films 63 (F1) and 75 (F4) may be set so that the ratio M1 / M4 of the contraction moment is in the above range, and may be in the range of 10 to 100 μm, for example. In particular, the thickness of the protective film 63 (F1) is preferably 30 to 80 μm, and more preferably 40 to 80 μm. For example, the thickness t1 of the protective film 63 (F1) can be made larger than the thickness t4 of the protective film 75 (F4) from the viewpoint of making the contraction force ratio (W1 / W4) easily within the above range. In that case, the thickness ratio t4 / t1 of the protective film 63 (F1) and the protective film 75 (F4) can be 0.5 or more and less than 1, preferably 0.55 or more and less than 1.

(Tensile modulus)
The tensile elastic modulus in the in-plane slow axis direction (preferably TD direction) and the direction orthogonal to it (preferably MD direction) of the protective films 63 (F1) and 75 (F4) is the ratio of the shrinkage force (W1 / W4) and the ratio of contraction moments (M1 / M4) may be set so as to fall within the above ranges, and are not particularly limited, but may be, for example, 3500 to 5500 MPa, preferably 4000 to 5000 MPa. The tensile modulus can be adjusted mainly by the stretching temperature. The tensile modulus can be measured by the method described above.

(Dimensional change rate)
The dimensional change rate of the protective films 63 (F1) and 75 (F4) in the in-plane slow axis direction (preferably the TD direction) and the direction orthogonal thereto (preferably the MD direction) is the ratio of the shrinkage force (W1 / W4) and the ratio of contraction moments (M1 / M4) may be set so as to be in the above range, and are not particularly limited, but may be in the range of 0.15% to 0.5%, for example. Among them, the dimensional change rate in the in-plane slow axis direction (preferably TD direction) of the protective film 63 (F1) is, for example, preferably 0.25% or more, more preferably 0.28% or more; The dimensional change rate in the in-plane slow axis direction (preferably in the TD direction) of F4) can be, for example, 0.25% or less. The dimensional change rate in the in-plane slow axis direction (preferably TD direction) of the protective film 63 (F1) is larger than the dimensional change rate in the in-plane slow axis direction (preferably TD direction) of the protective film 75 (F4). Can be big. The dimensional change rate can be adjusted mainly by the draw ratio, the draw temperature, and the residual solvent amount at the start of the draw. The dimensional change rate can be measured by the method described above.

(Retardation)
In the protective films 63 (F1) and 75 (F4), the in-plane retardation R ₀ measured under the conditions of a measurement wavelength of 590 nm and 23 ° C. and 55% RH is preferably 0 to 20 nm. More preferably, it is 10 nm. The retardation Rth in the thickness direction measured under the conditions of a measurement wavelength of 590 nm and 23 ° C. and 55% RH of the protective film is preferably 0 to 80 nm, and more preferably 0 to 50 nm.

Retardations _R0 and Rth are defined by the following equations, respectively.
Formula (I): R ₀ = (nx−ny) × d (nm)
Formula (II): Rth = {(nx + ny) / 2−nz} × d (nm)
(In formulas (I) and (II),
nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the in-plane direction of the film; ny represents the refractive index in the direction y perpendicular to the slow axis direction x in the in-plane direction of the film. Nz represents the refractive index in the thickness direction z of the film; d (nm) represents the thickness of the film)

The retardations _R0 and Rth can be determined by the following method, for example.
1) Condition the protective film at 23 ° C. and 55% RH. The average refractive index of the protective film after humidity adjustment is measured with an Abbe refractometer or the like.
The protective film after 2) humidity, measuring the _{R 0} when the light is incident in parallel to the measurement wavelength 590nm to normal of the film surface, KOBRA21ADH, in Oji Scientific Corporation.
3) With KOBRA21ADH, the slow axis in the plane of the protective film is set as the tilt axis (rotation axis), and light having a measurement wavelength of 590 nm from the angle (incident angle (θ)) with respect to the normal of the surface of the retardation film Is measured for the retardation value R (θ). The retardation value R (θ) can be measured at 6 points every 10 °, with θ ranging from 0 ° to 50 °. The in-plane slow axis of the protective film is an axis in the direction in which the in-plane refractive index is maximized, and can be confirmed by KOBRA 21ADH.
4) nx, ny, and nz are calculated by KOBRA21ADH from the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, and Rth at a measurement wavelength of 590 nm is calculated. The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

The protective film preferably has a total light transmittance of 80% or more, more preferably 90% or more, and still more preferably 93% or more.

The haze value of the protective film is preferably 1.0% or less, and more preferably 0.5% or less. The haze can be measured with a haze meter (turbidimeter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) in accordance with JIS K-7136.

(Method for producing protective films 63 (F1) and 75 (F4))
The protective films 63 (F1) and 75 (F4) are preferably manufactured by a solution casting method (cast) in order to reduce streak-like failure. That is, the protective films 63 (F1) and 75 (F4) are: 1) a step of obtaining a dope containing a cellulose ester, 2) a step of casting the dope on a support and drying it to obtain a film-like product, 3) A step of peeling the obtained film-like material from the support, and 4) a step of drying and stretching the film-like material.

1) Dissolution process The organic solvent used for the preparation of the dope solution can be used without limitation as long as it sufficiently dissolves each of the above components such as cellulose ester. Examples of the chlorinated organic solvent include methylene chloride. Examples of non-chlorine organic solvents include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone and the like. Of these, methylene chloride is preferred.

In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. By containing alcohol in the dope solution, the film-like material is gelled, and peeling from the metal support becomes easy. 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. Of these, methanol and ethanol are preferable because the stability of the dope, the boiling point is relatively low, and the drying property is good.

Dissolution of cellulose ester and the like includes a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, and a method performed under pressure above the boiling point of the main solvent. Is preferred.

2) Casting step The dope solution is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump). Then, the dope solution is cast from the slit of the pressure die to a casting position on an endless metal support (for example, a stainless belt or a rotating metal drum) that is transferred infinitely.

¡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.

3) Solvent evaporation / peeling step The dope solution cast on the metal support is heated on the metal support to evaporate the solvent in the dope solution to obtain a film-like material.

In order to evaporate the solvent, there are a method of blowing wind from the dope liquid surface side, a method of transferring heat from the back surface of the support by a liquid, a method of transferring heat from the front and back by radiant heat, etc. The drying efficiency is good and preferable. The dope solution on the metal support is preferably dried on the support in an atmosphere within the range of 40 to 100 ° C. In order to maintain the atmosphere in the range of 40 to 100 ° C., it is preferable to apply hot air at this temperature to the dope liquid surface on the metal support or to heat by means such as infrared rays.

The film-like material obtained by evaporating the solvent on the metal support is peeled off at the peeling position. The temperature at the peeling position on the metal support is preferably in the range of 10 to 40 ° C, more preferably in the range of 11 to 30 ° C.

The residual solvent amount of the film-like material on the metal support at the time of peeling can be, for example, in the range of 50 to 120% by mass. The amount of residual solvent in the film-like material is defined by the following formula.
Residual solvent amount (%) = (mass before heat treatment of film-like material−mass after heat treatment of film-like material) / (mass after heat treatment of film-like material) × 100
The heat treatment for measuring the residual solvent amount represents performing a heat treatment at 140 ° C. for 1 hour.

The peeling tension when peeling the metal support from the film is usually in the range of 196 to 245 N / m. However, if wrinkles easily occur during peeling, peeling with a tension of 190 N / m or less is preferable. Further, it is more preferable to peel with a tension of 80 N / m or less.

4) Stretching step The stretching of the film-like material is preferably performed in the width direction (TD direction), transport direction (MD direction) or oblique direction of the film; more preferably in the width direction (TD direction). When stretching in both the width direction (TD direction) and the transport direction (MD direction) of the film, stretching in the width direction (TD direction) of the film and stretching in the transport direction (MD direction) may be performed sequentially. You may do it simultaneously.

The shrinkage force of the protective film can be adjusted by stretching ratio, stretching temperature, stretching speed, residual solvent amount at the start of stretching, and the like. In order to increase the shrinkage force in the stretching direction of the protective film, it is preferable to lower the stretching ratio, lower the stretching temperature, increase the stretching speed, and increase the amount of residual solvent in the film-like material at the start of stretching.

Therefore, the protective film 63 (F1) and the protective film 75 (F4) in which the ratio of shrinkage force (W1 / W4) satisfies the above range may be films manufactured under different stretching conditions. For example, the stretch ratio of the protective film 63 (F1) can be made lower than the stretch ratio of the protective film 75 (F4). The stretching ratio is defined as (stretching direction length of the film after stretching−stretching direction length of the film before stretching) / (length in the stretching direction of the film before stretching) × 100 (%).

In order to obtain the protective film 63 (F1) having a high shrinkage force in the stretching direction, the stretching ratio is lowered, the stretching temperature is lowered, the stretching speed is increased, and the amount of residual solvent in the film-like material at the start of stretching is large. It is preferable to do.

低 く Lowering the draw ratio can increase the dimensional change rate of the protective film in the drawing direction. The draw ratio can be preferably 1 to 22%, more preferably 5 to 15%. If the draw ratio is too low, the tensile elastic modulus may be too low. On the other hand, when the draw ratio is too high, the resulting protective film may be whitened.

低 く Lowering the stretching temperature can increase the tensile modulus and dimensional change rate of the protective film in the stretching direction. The stretching temperature is in the range of (Tg-40) to (Tg + 20) ° C. when the glass transition temperature of the cellulose ester is Tg; specifically, it is preferably 135 to 165 ° C., and preferably 140 to 165 ° C. It is more preferable. If the stretching temperature is too low, the resulting protective film may be whitened.

¡By increasing the amount of residual solvent in the film-like material at the start of stretching, the dimensional change rate in the stretching direction of the protective film can be increased. The residual solvent amount of the film-like material at the start of stretching is preferably 7 to 18%, and more preferably 10 to 15%. If the residual solvent amount is too small, the resulting protective film may be whitened. The residual solvent amount of the film-like material at the start of stretching can be calculated by the same method as the residual solvent amount of the film-like material at the time of peeling.

As described above, in order to sufficiently increase the shrinkage force in the stretching direction of the protective film 63 (F1), the stretching ratio is in the range of 1 to 22%, the stretching temperature is in the range of 135 to 160 ° C., and the stretching is started. The residual solvent amount is preferably in the range of 7 to 18%.

The protective film 75 (F4) can be manufactured under the same stretching conditions as those of a normal protective film. For example, the stretch ratio in producing the protective film 75 (F4) can be in the range of 15-40%; the stretch temperature can be in the range of 150-170 ° C .; and the residual solvent amount can be in the range of 5-15%.

<About protective films 65 (F2) and 73 (F3)>
The protective films 65 (F2) and 73 (F3) preferably contain a cellulose ester as a main component or a cycloolefin resin as a main component.

(Cellulose ester)
The cellulose ester may be the same as the cellulose ester described above. The cellulose ester may preferably be cellulose triacetate. The total substitution degree of the acyl group of the cellulose ester is about 2.0 to 3.0. If there is no need to increase the phase difference, the total substitution degree of the acyl group may be more than 2.5 and not more than 3.0, preferably 2.7 to 3.0. When the phase difference is set to a certain value or more, the total substitution degree of the acyl group can be 2.0 or more and 2.5 or less. The number of carbon atoms of the acyl group contained in the cellulose ester is more preferably 2 to 4, and in order to obtain good heat resistance, the acyl groups contained in the cellulose ester are all preferably acetyl groups.

(Cycloolefin resin)
The cycloolefin resin is a polymer containing a structural unit having an alicyclic structure derived from a cycloolefin. The cycloolefin resin may be a cycloolefin addition (co) polymer or a bicycloolefin ring-opening addition (co) polymer. Examples of cycloolefins include cyclohexene and the like; examples of bicycloolefins include norbornene and tetracyclododecene, preferably norbornene.

Examples of the copolymer component in the cycloolefin copolymer include an α-olefin and an aromatic compound having a vinyl group. Examples of α-olefins include ethylene and propylene. Examples of the aromatic compound having a vinyl group include styrene and α-methylstyrene. The proportion of structural units derived from cycloolefin in the copolymer of cycloolefin may be 50 mol% or less (preferably 15 to 50 mol%). The copolymer component contained in the cycloolefin copolymer may be only one type or two or more types. For example, the copolymer of cycloolefin may be a ternary copolymer of a cycloolefin, a chain olefin, and an aromatic compound having a vinyl group.

Examples of the cycloolefin resin include cycloolefin resins described in JP 2010-78700 A. Examples of commercially available cycloolefin resins include ZEONOR (manufactured by ZEON Corporation), ZEONEX (manufactured by ZEON Corporation), APEL (manufactured by Mitsui Chemicals, Inc.) and the like. It is done. Examples of commercially available cycloolefin resin films include Essina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), ZEONOR film (manufactured by Nippon Zeon Co., Ltd.), and the like. .

(Thickness)
The thickness of the protective films 65 (F2) and 73 (F3) may be about 10 to 80 μm, preferably 20 to 60 μm, depending on the required retardation value. By making the thickness of the protective films 65 (F2) and 73 (F3) below a certain value, the polarizing plate can be thinned, and the dimensional change of the polarizing plate due to heat and humidity can be reduced. On the other hand, by setting the thicknesses of the protective films 65 (F2) and 73 (F3) to a certain value or more, it is easy to obtain a retardation value of a certain value or more.

(Retardation)
The retardation of the protective films 65 (F2) and 73 (F3) can be set according to the type of liquid crystal cell to be combined. For example, the in-plane retardation R ₀ (590) measured at a wavelength of 590 nm under 23 ° C. RH 55% of the protective films 65 (F2) and 73 (F3) can be 20 to 130 nm, preferably 30 to 100 nm. The retardation Rth (590) in the thickness direction can be 100 to 300 nm, preferably 100 to 200 nm. A protective film having a retardation in the above range is suitable as a retardation film such as a VA mode liquid crystal cell.

Further, the in-plane retardation R ₀ (590) of the protective films 65 (F2) and 73 (F3) measured at a wavelength of 590 nm under 23% RH 55% can be −10 to 10 nm, preferably −5 to 5 nm. . The retardation Rth (590) in the thickness direction can be −10 to 10 nm, preferably −5 to 5 nm. A protective film having a retardation in the above range is suitable as a retardation film such as an IPS mode liquid crystal cell.

The retardations _R0 and Rth are defined as described above.

<Regarding First Polarizer 61 and Second Polarizer 71>
The first polarizer 61 and the second polarizer 71 are elements that allow only light having a plane of polarization in a certain direction to pass through. A typical polarizer currently known is a polyvinyl alcohol polarizing film. The polyvinyl alcohol polarizing film includes those obtained by dyeing iodine on a polyvinyl alcohol film and those obtained by dyeing a dichroic dye.

The polyvinyl alcohol polarizing film may be a film (preferably a film further subjected to durability treatment with a boron compound) dyed with iodine or a dichroic dye after uniaxially stretching the polyvinyl alcohol film; A film obtained by dying an alcohol film with iodine or a dichroic dye and then uniaxially stretching (preferably a film further subjected to a durability treatment with a boron compound) may be used.

The thickness of the first polarizer 61 and the second polarizer 71 is preferably 2 to 30 μm and more preferably 3 to 15 μm from the viewpoint of reducing the thickness of the liquid crystal display device.

<About the manufacturing method of the 1st polarizing plate 60 and the 2nd polarizing plate 70>
The first polarizing plate 60 (or the second polarizing plate 70) has a protective film 63 (F1) (or a protective film 75 (F4) on one surface of the first polarizer 61 (or the second polarizer 71). )) Can be obtained through a step of attaching the protective film 65 (F2) (or the protective film 73 (F3)) to the other surface via an adhesive. The adhesive used for the bonding may be a completely saponified polyvinyl alcohol aqueous solution (water glue) or an active energy ray-curable adhesive.

The active energy ray-curable adhesive composition is a photo radical polymerization composition using photo radical polymerization, a photo cation polymerization composition using photo cation polymerization, or a hybrid type using both photo radical polymerization and photo cation polymerization. It can be a composition or the like.

A radical photopolymerizable composition is a composition comprising a radically polymerizable compound containing a polar group such as a hydroxy group or a carboxy group and a radically polymerizable compound not containing a polar group described in JP-A-2008-009329 in a specific ratio. It can be a thing. The radical polymerizable compound is preferably a compound having an ethylenically unsaturated bond capable of radical polymerization. Preferable examples of the compound having an ethylenically unsaturated bond capable of radical polymerization include a compound having a (meth) acryloyl group. Examples of the compound having a (meth) acryloyl group include an N-substituted (meth) acrylamide compound and a (meth) acrylate compound. (Meth) acrylamide means acrylamide or methacrylamide.

The cationic photopolymerization type composition comprises (α) a cationic polymerizable compound, (β) a cationic photopolymerization initiator, and (γ) light having a wavelength longer than 380 nm, as disclosed in Japanese Patent Application Laid-Open No. 2011-028234. It may be a composition containing each component of a photosensitizer exhibiting maximum absorption and (δ) naphthalene photosensitizer.

Such a polarizing plate is, for example, a step of subjecting the surface of the protective film to easy adhesion (corona treatment, plasma treatment, etc.); a step of applying an active energy ray-curable adhesive to at least one of the polarizer and the protective film; It can be manufactured through a step of bonding the polarizer and the protective film through the obtained adhesive layer; a step of curing the adhesive layer in a state where the polarizer and the protective film are bonded.

<About the backlight 30>
The backlight 30 is disposed so as to face the protective film 75 (F4). An arbitrary optical member can be disposed between the backlight 30 and the protective film 75 (F4).

The backlight 30 may be a side light (edge light) type surface light source in which a known light source is disposed on the side surface of the light guide plate, or a direct type surface light source in which a known light source is arranged under the diffusion plate. Examples of known light sources include cold cathode fluorescent lamps (CCFL), hot cathode fluorescent lamps (HCFL), external electrode fluorescent lamps (EEFL), flat fluorescent lamps (FFL), light emitting diode elements (LEDs), organic electroluminescent elements (OLEDs). ) Is included.

A rechargeable battery (not shown) can be further disposed below the backlight 30. The rechargeable battery can be, for example, a lithium ion secondary battery.

Thus, in the present invention, the ratio W1 / W4 of the shrinkage force between the protective film 63 (F1) of the first polarizing plate 60 and the protective film 75 (F4) of the second polarizing plate 70 is adjusted to a predetermined range, Preferably, the ratio M1 / M4 of the contraction moment is further adjusted to a predetermined range. Thereby, the curvature of the liquid crystal display panel which protrudes toward the viewing side in a small liquid crystal display device can be reduced. As a result, the liquid crystal display panel can be prevented from coming into non-uniform contact with other members such as the backlight 30 and the cover glass 40, and display unevenness in a small liquid crystal display device can be reduced. In addition, the liquid crystal display panel can be prevented from floating together with the cover glass and touch panel, so that moisture can be prevented from entering the device through the gap between the housing and the liquid crystal display panel, and light leakage can be prevented. it can.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

1. Production of protective film <Production of film 1>
(Preparation of fine particle additive solution 1)
11 parts by mass of fine particles A (Aerosil R976 manufactured by Nippon Aerosil Co., Ltd.) and 89 parts by mass of ethanol were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to obtain a fine particle dispersion 1.

99 parts by mass of methylene chloride was added to the dissolution tank, and 5 parts by mass of the fine particle dispersion 1 was slowly added with sufficient stirring. Furthermore, the secondary particles were dispersed by an attritor so that the particle size of the secondary particles became a predetermined size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to obtain a fine particle additive solution 1.

(Preparation of dope)
First, methylene chloride and ethanol were charged into a pressure dissolution tank, and then cellulose ester (cellulose triacetate having an acetyl group substitution degree of 2.9) was charged with stirring. This was completely dissolved with heating and stirring. The obtained solution was prepared as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. Filtration using 244 gave a main dope solution. The obtained main dope solution was put into a sealed container and further dissolved with stirring to obtain a dope solution.
(Dope solution composition)
Cellulose ester (A) (cellulose triacetate: acetyl group substitution degree 2.9, weight average molecular weight Mw: 282000): 100 parts by mass Additive A: 10 parts by mass Fine particle additive solution 1: 10 parts by mass Tinuvin 928 (Ciba Japan ( Co., Ltd.): 2.5 parts by mass Methylene chloride: 340 parts by mass Ethanol: 64 parts by mass

The above-prepared dope solution was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1.7 m using an endless belt casting apparatus. The temperature of the stainless steel belt was adjusted to 30 ° C. After the solvent was evaporated on the stainless steel belt support until the amount of residual solvent in the cast dope solution reached 75%, the obtained film-like material was supported on the stainless steel belt with a peeling tension of 130 N / m. It peeled from the body.

The peeled film was stretched 22% in the width direction (TD direction) with a tenter while applying heat at 160 ° C. The residual solvent amount at the start of stretching was 10%. The residual solvent amount was determined from the following equation.
Residual solvent amount of film-like material (%) = (mass before film-heat treatment−mass after heat-treatment of film-like material) / (mass after heat-treatment of film-like material) × 100
(The heat treatment means a heat treatment at 140 ° C. for 1 hour)

The obtained film was dried while being transported by a number of rolls in the drying zone. The drying temperature was 130 ° C. and the transport tension was 100 N / m. The obtained film was cut into a predetermined width with a slitter, and then embossed to give an emboss height of 6 μm at the end in the width direction of the film by an embossing device. Thereby, a film 1 having a film width of 1.89 m and a film thickness of 40 μm was obtained.

<Preparation of films 2 to 4 and 20>
Films 2 to 4 and 20 were produced in the same manner as Film 1 except that the film thickness of the obtained film was changed as shown in Table 1. The film thickness was adjusted according to the casting amount.

<Production of films 5 to 8>
Films 5 to 8 were produced in the same manner as film 1 except that the draw ratio was changed as shown in Table 1.

<Production of films 9 to 12>
Films 9 to 12 were produced in the same manner as film 1 except that the stretching temperature was changed as shown in Table 1.

<Preparation of film 13>
A film 13 was produced in the same manner as the film 1 except that the stretching temperature and the stretching ratio were changed as shown in Table 1.

<Production of films 14 to 16>
Films 14 to 16 were produced in the same manner as Film 1 except that the amount of residual solvent at the start of stretching was changed as shown in Table 1.

<Production of films 17 to 19>
Films 17 to 19 were produced in the same manner as film 1 except that the amount of residual solvent at the start of stretching, the stretching temperature, the stretching ratio, and the film thickness were changed as shown in Table 1.

<Preparation of film 21>
A (meth) acrylic resin having a lactone ring structure represented by the following general formula (1) was prepared. This (meth) acrylic resin has a copolymerization monomer mass ratio = methyl methacrylate / 2- (hydroxymethyl) methyl acrylate = 8/2, a lactone cyclization rate of about 100%, and a lactone ring structure content ratio of 19.4. %, Weight average molecular weight 133000, melt flow rate 6.5 g / 10 min (240 ° C., 10 kgf), Tg 131 ° C. A pellet (Tg 127 ° C.) of a mixture of 90 parts by mass of this (meth) acrylic resin and 10 parts by mass of acrylonitrile-styrene (AS) resin (Toyo AS AS20, manufactured by Toyo Styrene Co., Ltd.) was prepared.

(In the general formula (1), R ¹ is a hydrogen atom, and R ² and R ³ are methyl groups)

The pellets were supplied to a biaxial extruder and melt extruded into a sheet at about 280 ° C. to obtain a film having a lactone ring structure with a thickness of 80 μm. This film was stretched 1.5 times in length and 1.8 times in width under a temperature condition of 160 ° C., and had a thickness of 40 μm, an in-plane retardation Δnd: 0.8 nm, and a thickness direction retardation Rth: 1.5 nm. A (meth) acrylic resin film was obtained.

The tensile modulus and dimensional change rate of the obtained film were measured by the following methods.

<Tensile modulus>
(Tensile modulus in MD direction)
The obtained film was cut into a shape of No. 1 with a size of 150 mm (MD direction) × 10 mm (TD direction), and used as a test piece. The test piece was conditioned at 23 ° C. and 55% RH for 24 hours, and then pulled in the MD direction according to the method described in JIS K 7127, and the tensile modulus in the MD direction was measured. As the tensile tester, Tensilon RTC-1225A manufactured by Orientec Co., Ltd. was used, and the tensile speed was 100 mm / min. The tensile elastic modulus in the MD direction was calculated by setting the elastic modulus analysis start point to 2 (MPa) and the elastic modulus analysis end point to 60 (MPa).

(Tensile modulus in TD direction)
The obtained film was cut into a No. 1 shape with a size of 150 mm (TD direction) × 10 mm (MD direction) to obtain a test piece; the same as described above except that the test piece was pulled in the TD direction. The tensile elastic modulus in the TD direction was measured.

<Dimensional change rate>
(Dimension change rate in MD direction)
1) The obtained film was cut into a size of 25 cm in length (measurement direction) × 5 cm in width so that the MD direction was the longitudinal direction, and used as a test piece. Pin holes were formed at intervals of 20 cm in the MD direction of this test piece, and after adjusting the humidity for 24 hours at 23 ° C. and 55% relative humidity, the distance between the pin holes was measured with a pin gauge to obtain a measured value L0.
2) Subsequently, the test piece was conditioned for 24 hours in a humid heat environment of 23 ° C. and a relative humidity of 20%, and then the interval between the pin holes was measured with a pin gauge to obtain a measured value L1.
3) Further, the specimen was conditioned at 23 ° C. and 80% relative humidity for 24 hours, and the distance between the pin holes was measured with a pin gauge to obtain a measured value L2.
4) These measurement values were applied to the following formula to calculate the dimensional change rate (%) in the MD direction.
Dimensional change rate (%) = {(L2-L1) / L0} × 100

(Dimension change rate in TD direction)
The obtained film was cut into a size of 25 cm in length (measurement direction) × 5 cm in width so that the TD direction was the longitudinal direction, and used as a test piece. The dimensional change rate (%) in the TD direction was measured in the same manner as described above, except that pin holes were formed at intervals of 20 cm in the TD direction of the test piece and the distance between the pin holes was measured.

<Shrink force>
The shrinkage force of the obtained film was calculated based on the above formula (1).

The production conditions and physical properties of the obtained film are shown in Table 1.

As shown in Table 1, the film thickness is large (see films 1 to 4 and 20), the amount of residual solvent in the film-like material at the start of stretching is large (see films 1 and 13 to 15), and the stretching temperature is low. (See Films 1 and 9-12) It can be seen that the lower the draw ratio (see Films 1 and 5-8), the greater the shrinkage force in the drawing direction (TD direction) of the resulting film. However, if the amount of residual solvent at the start of stretching is too small (film 16), the stretching temperature is too low (film 12), or the stretching ratio is too high (film 5), the resulting film will be whitened and a protective film It turns out that it is not suitable as.

2. Production of Liquid Crystal Display Device <Example 1>
(Production of polarizer)
A polyvinyl alcohol film having a thickness of 25 μm was swollen with water at 35 ° C. The obtained film was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and further immersed in an aqueous solution at 45 ° C. consisting of 3 g of potassium iodide, 7.5 g of boric acid and 100 g of water. . The obtained film was uniaxially stretched under conditions of a stretching temperature of 55 ° C. and a stretching ratio of 5 times. The uniaxially stretched film was washed with water and dried to obtain a polarizer having a thickness of 7 μm.

(Preparation of the first polarizing plate)
The surface of the produced film 3 was subjected to alkali saponification treatment as follows. Specifically, the film 3 prepared above was immersed in a 1.5N sodium hydroxide aqueous solution at 55 ° C. for 2 minutes, then washed in a water-washing bath at room temperature, and 0.1N sulfuric acid was used at 30 ° C. It was summed up. The obtained film 3 was again washed in a water-washing bath at room temperature and then dried with hot air at 100 ° C. Similarly to this, Konica Minolta Tac KC4CR (manufactured by Konica Minolta Co., Ltd.) was prepared, and the surface was subjected to alkali saponification treatment.

The film 3, the polarizer, and the KC4CR subjected to the alkali saponification treatment and the alkali saponification-treated KC4CR were bonded to each other via a 3% by weight aqueous solution of polyvinyl alcohol (PVA-117H, manufactured by Kuraray) as an adhesive, and film 3 / polarizer / A laminate of KC4CR was obtained. Bonding is performed such that the saponification surface of the film 3 and the saponification surface of KC4CR are in contact with the polarizer; and the MD direction of the film 3 and the slow axis of KC4CR are the absorption axis of the polarizer. It went so that it might become parallel. The obtained laminate was dried to obtain a first polarizing plate.

(Production of second polarizing plate)
A second polarizing plate was produced in the same manner except that the film 3 was changed to the film 1 in the production of the first polarizing plate.

(Production of liquid crystal display device)
VA liquid crystal display device having a diagonal line length of 9.7 inches and t ′ / l of 0.0014 (liquid crystal display device having a laminated structure of a cover glass integrated with a cover glass / liquid crystal display panel / backlight) : Asura 9) manufactured by nJoy was prepared. The two polarizing plates are peeled off from this device, the first polarizing plate prepared above is arranged on the surface on the viewing side of the liquid crystal cell, and the second polarizing plate prepared above is arranged on the surface on the backlight side of the liquid crystal cell. , KC4CR (protective films F2 and F3) were attached to each other via an adhesive so that the liquid crystal cell side was obtained to obtain a liquid crystal display device. The thickness of the adhesive layer was 0.02 mm in all cases. The absorption axis of the first polarizing plate (viewing side polarizing plate) and the short side direction β of the liquid crystal display panel are parallel; the absorption axis of the second polarizing plate (backlight side polarizing plate) and the long side of the liquid crystal display panel It arranged in crossed Nicols so that direction (alpha) might become parallel. The thickness of the two glass plates used in the liquid crystal cell was 0.5 mm.

The shrinkage force W1 of the film 3 and the shrinkage force W4 of the film 1 were calculated based on the above-described formula (1), and the ratio W1 / W4 of the shrinkage force was calculated. Similarly, the contraction moment M1 of the film 3 and the contraction moment M4 of the film 1 were calculated based on the above-described formula (3), and the ratio M1 / M4 of the contraction moment was calculated.

<Examples 2 to 10 and 18, Comparative Examples 1 to 6>
A liquid crystal display device was produced in the same manner as in Example 1 except that the type of the protective film F1 of the first polarizing plate was changed as shown in Table 2.

<Example 11>
As the first polarizing plate and the second polarizing plate, a liquid crystal display device was obtained in the same manner as in Example 4 except that polarizing plates prepared by the following methods were used.
(Preparation of photocurable adhesive)
After mixing the following components, defoaming was performed to prepare a photocurable adhesive liquid. Triarylsulfonium hexafluorophosphate was blended as a 50% propylene carbonate solution, and the solid content of triarylsulfonium hexafluorophosphate was shown below.
(Composition of photocurable adhesive liquid)
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate: 45 parts by mass Epolide GT-301 (alicyclic epoxy resin manufactured by Daicel Chemical Industries): 40 parts by mass 1,4-butanediol diglycidyl ether: 15 parts by mass Triarylsulfonium hexafluorophosphate: 2.3 parts by mass 9,10-dibutoxyanthracene: 0.1 parts by mass 1,4-diethoxynaphthalene: 2.0 parts by mass

(Preparation of the first polarizing plate)
The surface of the produced film 8 was subjected to corona discharge treatment. The conditions for the corona discharge treatment were a corona output intensity of 2.0 kW and a line speed of 18 m / min. Next, the adhesive solution prepared above was applied to the corona discharge-treated surface of the film 8 with a bar coater so that the film thickness after curing was about 3 μm to form an adhesive layer. The produced polarizer was bonded to the obtained adhesive layer.

Similarly, KC4CR (manufactured by Konica Minolta Co., Ltd.) was prepared, and the surface thereof was subjected to corona discharge treatment. The conditions for the corona discharge treatment were the same as described above. Next, the adhesive solution prepared above was applied to the corona discharge treated surface of the film with a bar coater so that the film thickness after curing was about 3 μm to form an adhesive layer. A polarizer of a polarizer having a polarizing plate protective film bonded on one side was bonded to this adhesive layer to obtain a laminate of film 8 / polarizer / KC4CR. This laminate was irradiated with ultraviolet rays so that the accumulated light amount became 750 mJ / cm ² using an ultraviolet irradiation device with a belt conveyor (the lamp uses a D bulb manufactured by Fusion UV Systems), and an adhesive layer was formed. Cured to obtain a first polarizing plate.

(Production of second polarizing plate)
A second polarizing plate was produced in the same manner except that the film 8 was changed to the film 1 in the production of the first polarizing plate.

<Example 12>
IPS liquid crystal display device having a diagonal line length of 9.7 inches and t ′ / l of 0.0014 (liquid crystal display device having a laminated structure of a cover glass integrated cover glass / liquid crystal display panel / backlight) Ipad 2) manufactured by Apple was prepared. The two polarizing plates of this device were peeled off, and the first polarizing plate prepared in Example 4 was formed on the viewing side surface of the liquid crystal cell; the second polarizing plate prepared in Example 1 was formed on the backlight side surface of the liquid crystal cell. A polarizing plate was attached via an adhesive to obtain a liquid crystal display device. The thickness of the adhesive layer was 0.02 mm in all cases. The absorption axis of the first polarizing plate (viewing side polarizing plate) and the short side direction β of the liquid crystal display panel are made parallel; the absorption axis of the second polarizing plate (backlight side polarizing plate) and the liquid crystal display panel Were arranged in crossed Nicols so that the long side direction α was parallel. The thickness of the two glass plates used in the liquid crystal cell was 0.5 mm.

<Examples 13 to 14>
A liquid crystal display device was obtained in the same manner as in Example 4 except that the thickness of the pressure-sensitive adhesive layer for bonding the first polarizing plate and the liquid crystal cell was changed as shown in Table 2.

<Example 15, Comparative Examples 7 and 8>
A liquid crystal display device was obtained in the same manner as in Example 4 except that the thickness of the protective film F4 for the second polarizing plate and the type of the protective film F1 for the first polarizing plate were changed as shown in Table 2.

<Example 16>
Implementation was performed except that the protective film F2 of the first polarizing plate and the protective film F3 of the second polarizing plate were changed to the cycloolefin resin films (Zeonor film (manufactured by Nippon Zeon Co., Ltd., thickness 50 μm) shown in Table 2. A liquid crystal display device was produced in the same manner as in Example 8.

<Example 17>
Example 1 except that the protective film F2 of the first polarizing plate and the protective film F3 of the second polarizing plate are not arranged, and the type of the protective film F1 of the first polarizing plate is changed as shown in Table 2. In the same manner as in Example 12, a liquid crystal display device was produced.

<Comparative Examples 9-12>
A liquid crystal display device was produced in the same manner as in Example 1 except that the protective film F1 for the first polarizing plate and the protective film F4 for the second polarizing plate were changed as shown in Table 2.

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

<Display unevenness in the front direction>
The obtained liquid crystal display device was held in an environment of 40 ° C. and 95% RH for 24 hours, and then held in an environment of 40 ° C. and 20% RH for 2 hours. After that, it was moved to an environment of 23 ° C. and 55% RH, and the liquid crystal display device was kept on in a black display state. At this time, when observed from the front of the liquid crystal display device, luminance unevenness during black display was observed, and the degree of occurrence of luminance unevenness was evaluated according to the following criteria.
◎: Unevenness is hardly visually recognized ○: Light unevenness is visually recognized △: Clear unevenness is visually recognized at the edge (corner) of the screen ×: Clear unevenness is visually recognized in the middle of the screen according to the above unevenness

The manufacturing conditions of the liquid crystal display devices of Examples 1 to 18 and Comparative Examples 1 to 12 are shown in Table 2, and the evaluation results are shown in Table 3.

It can be seen that in the liquid crystal display devices of Examples 1 to 18 in which the shrinkage force ratio W1 / W4 is in the range of more than 0.81 and less than 2.50, display unevenness due to warpage of the liquid crystal display panel is suppressed. In contrast, the liquid crystal display devices of Comparative Examples 1 to 7 and 9 to 12 in which the ratio W1 / W4 of contraction force is 0.81 or less, and the liquid crystal display device of Comparative Example 8 in which W1 / W4 is greater than 2.50 In each case, display unevenness due to warpage of the liquid crystal display panel was observed.

Specifically, in the liquid crystal display devices of Comparative Examples 1 to 7 and 9 to 12 in which the ratio W1 / W4 of contraction force is 0.81 or less, the contraction force of the polarizing plate on the viewing side is relatively insufficient. It is considered that the warpage of the film could not be reduced sufficiently. On the other hand, in the liquid crystal display device of Comparative Example 8, it is considered that the contraction force of the polarizing plate on the viewing side is too large, causing the warp of the liquid crystal display panel that protrudes toward the backlight side.

Further, from the comparison between Example 1 and Example 15, the liquid crystal display device of Example 1 in which the contraction moment ratio M1 / M4 is 0.9 or more and 2.0 or less has a contraction moment ratio M1 / M4 of 2. It can be seen that display unevenness can be further reduced as compared with the liquid crystal display device of Example 15 which is more than 0.0.

This application claims priority based on Japanese Patent Application No. 2014-120649 filed on June 11, 2014. The contents described in the application specification and the drawings are all incorporated herein.

According to the present invention, it is possible to reduce the warpage of the liquid crystal display panel in a small-sized liquid crystal display device for use in mobile devices and the like, thereby suppressing display unevenness.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 20 Liquid crystal display panel 30 Backlight 40 Cover glass (transparent protective substrate)
50 Liquid crystal cell 51, 53 Transparent substrate 55 Liquid crystal layer 60 First polarizing plate 61 First polarizer 63 Protective film (F1)
65 Protective film (F2)
70 Second polarizing plate 71 Second polarizer 73 Protective film (F3)
75 Protective film (F4)

Claims (7)

1. A liquid crystal display device including a first polarizing plate, a liquid crystal cell, a liquid crystal display panel including a second polarizing plate in order, and a backlight,
   The first polarizing plate is disposed on the surface of the first polarizer, the protective film F1 disposed on the viewing side of the first polarizer, and the surface of the first polarizer on the liquid crystal cell side. Protective film F2 made,
   The second polarizing plate includes a second polarizer, a protective film F3 disposed on the liquid crystal cell side surface of the second polarizer, and the backlight side surface of the second polarizer. And a protective film F4 disposed in
   The absorption axis of the first polarizer is parallel to the short side direction β of the liquid crystal display panel, and the absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal to each other. And
   The shrinkage force in the long side direction α represented by the following formula (1) of the protective film F1 is W1, and the shrinkage force in the long side direction α represented by the following formula (1) of the protective film F4 is W4. When the liquid crystal display device has a contraction force ratio W1 / W4 of more than 0.81 and not more than 2.50.
   

   

   (In Formula (1),
   W is the contraction force (N / m) in the long side direction α of the protective film,
   T is the tensile elastic modulus (Pa) in the long side direction α of the protective film,
   S is a dimensional change rate (%) accompanying the humidity change in the long side direction α represented by the following formula (2) of the protective film:
   t represents the thickness (m) of the protective film)
   

   

   (In Formula (2),
   S is the dimensional change rate (%) accompanying the humidity change in the long side direction α of the protective film,
   L0 is the length of the long side direction α under 23 ° C. and 55% RH of the protective film,
   L1 is the length of the long side direction α under 23 ° C. and 20% RH of the protective film,
   L2 represents the length of the long side direction α under 23 ° C. and 80% RH of the protective film)
2. The distance from the surface on the viewing side of the liquid crystal cell to the surface on the viewing side of the protective film F1 is D1, and the contraction moment of the long side direction α represented by the following formula (3) of the protective film F1 is M1, The distance from the backlight side surface of the liquid crystal cell to the backlight side surface of the protective film F4 is D4, and the contraction moment of the protective film F4 in the long side direction α represented by the following formula (3): When M4
   The liquid crystal display device according to claim 1, wherein a ratio M1 / M4 of the contraction moment is 0.9 or more and 2.0 or less.
   

   

   (In Formula (3),
   M is the contraction moment (N) of the protective film in the long side direction α,
   W is the contraction force (N / m) in the long side direction α of the protective film,
   D represents the distance (m) from the surface of the liquid crystal cell of the protective film)
3. The liquid crystal cell includes a liquid crystal layer and a pair of glass substrates sandwiching the liquid crystal layer,
   The t ′ / l is 0.0003 to 0.0050, where the thickness of the glass substrate is t ′ (mm) and the length in the long side direction α of the liquid crystal display panel is l (mm). 2. A liquid crystal display device according to 1.
4. The liquid crystal display device according to claim 1, wherein a diagonal length of the liquid crystal display panel is 15 inches or less.
5. A transparent protective substrate disposed on the viewing side surface of the liquid crystal display panel;
   The liquid crystal according to claim 1, further comprising: a touch panel provided integrally with one of the transparent protective substrate and the liquid crystal display panel, or disposed between the transparent protective substrate and the liquid crystal display panel. Display device.
6. 2. The liquid crystal display device according to claim 1, wherein the protective film F1 is a cellulose ester film having a thickness of 40 to 80 μm.
7. 2. The liquid crystal display device according to claim 1, wherein the protective films F2 and F3 are cellulose ester films having a thickness of 20 to 60 μm, cycloolefin films having a thickness of 20 to 60 μm, or are omitted.

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