JP2016026321A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device that exhibits small warpage of a liquid crystal panel and small display irregularity even after being placed in a wet heat environment.SOLUTION: The liquid crystal display device includes: a liquid crystal cell having two cell substrates and a liquid crystal layer sandwiched therebetween; a front-side polarizing plate laminated on a viewing side of the liquid crystal cell through an adhesive layer; a rear-side polarizing plate laminated on a side opposite to the viewing side of the liquid crystal cell through an adhesive layer; and a backlight unit disposed outside the rear-side polarizing plate. The front-side polarizing plate and the rear-side polarizing plate each include a polarizing film and transparent protective films disposed on either side of the polarizing film. Both of the front-side polarizing plate including the adhesive layer and the rear-side polarizing plate including the adhesive layer have a water evaporation rate of less than 5 g/mhr.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid crystal display device in which light leakage generated from a peripheral portion of a screen is small even after being placed in a humid heat environment, and the brightness difference on the panel surface is small and display unevenness is small.

  In recent years, liquid crystal display devices have been rapidly used as information display devices such as mobile phones, personal digital assistants, computer monitors, and televisions by taking advantage of low power consumption, low voltage operation, light weight and thinness. It has become widespread. With the development of liquid crystal technology, liquid crystal display devices of various modes have been proposed, and problems with liquid crystal display devices such as response speed, contrast, and narrow viewing angle are being solved. However, since a polarizing plate is used in a liquid crystal display device, when the polarizing plate absorbs moisture when it is placed in a humid heat environment during transportation, the water generated in the polarizing plate evaporates due to the heat generated when the backlight is turned on. The panel warps. There is a problem that display unevenness occurs due to such warpage of the liquid crystal panel.

  Japanese Unexamined Patent Publication No. 2007-292966 (Patent Document 1) proposes to improve the warpage of the liquid crystal panel under high temperature and high humidity by adjusting the dimensional change rate of the polarizing plate bonded to both sides of the liquid crystal cell. Has been. Japanese Patent Laid-Open No. 2003-50313 (Patent Document 2) uses a polarizing plate on which a pressure-sensitive adhesive layer exhibiting specific creep characteristics is used to improve the warpage of a liquid crystal panel in a humid heat environment. Has been proposed. However, in these improvements, it is necessary to subject the polarizing plate to a pretreatment such as a heat treatment, or the display unevenness due to the warp of the liquid crystal panel after being placed in a humid heat environment is insufficient.

JP 2007-292966 A JP 2003-050313 A

  An object of the present invention is to provide a liquid crystal display device in which the warp of the liquid crystal panel is small and display unevenness is small even after being placed in a humid heat environment. As a result of intensive studies to achieve such an object, the present inventors have conducted a humidification process on the front side polarizing plate located on the viewing side of the liquid crystal cell and the rear side polarizing plate located on the opposite side, respectively. It was found that by adjusting the moisture absorption amount, the warp of the liquid crystal panel can be controlled when the backlight is turned on after being placed in a humid heat environment, which is effective in improving display unevenness. In addition, the front-side polarizing plate located on the viewing side of the liquid crystal cell and the rear-side polarizing plate located on the opposite side thereof are adjusted in their respective moisture evaporation rates to place the backlight after being placed in a humid heat environment. It has also been found that the warping of the liquid crystal panel can be controlled when it is lit, and is effective in improving display unevenness. The present invention has been completed based on these findings.

  A liquid crystal display device according to the present invention includes a liquid crystal cell having two cell substrates and a liquid crystal layer sandwiched therebetween, a front-side polarizing plate laminated via an adhesive layer on the viewing side of the liquid crystal cell, The liquid crystal cell comprises a back side polarizing plate laminated via an adhesive layer on the side opposite to the viewing side, and a backlight unit disposed outside the back side polarizing plate, Each of the plate and the back side polarizing plate has a polarizing film and transparent protective films disposed on both sides thereof.

And the liquid crystal display device of the present invention specified from the first viewpoint includes a moisture absorption amount when the front side polarizing plate provided with the pressure-sensitive adhesive layer is humidified, and a back side polarizing plate provided with the pressure-sensitive adhesive layer. The moisture absorption amount when the humidification treatment is performed is both less than 7 g / m ² .

Further, the liquid crystal display device of the present invention specified from the second standpoint has a water evaporation rate of the front side polarizing plate including the pressure-sensitive adhesive layer and a water evaporation rate of the back side polarizing plate including the pressure-sensitive adhesive layer. Both are less than 5 g / m ² · hr.

  In these liquid crystal display devices, the transparent protective film located on the side far from the liquid crystal cell of each of the front-side polarizing plate and the rear-side polarizing plate is composed of a polypropylene resin, a polyethylene terephthalate resin, or an acrylic resin. In this case, the moisture absorption amount is low as described above, and the water evaporation rate is advantageous as described above.

In these liquid crystal display devices, in the first preferred embodiment, the transparent protective film located on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate has a thickness direction retardation in the range of −10 to +10 nm. . In the second preferred embodiment, one of the transparent protective films located on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate has a thickness direction retardation in the range of −10 to +10 nm, and the other is the range in the retardation of 100~300nm surfaces, the refractive indices n _x in the slow axis direction in the film plane, the fast-axis refractive index n _y in the film plane and the refractive index of the film thickness direction, the when the n _z, wherein _{(n x -n z) / (} n x -n y)
The Nz coefficient defined by is in the range of 0.1 to 0.7.

  In the third preferred embodiment, one of the transparent protective films located on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate has a thickness direction retardation in the range of −10 to +10 nm, and the other A first retardation film made of a polyolefin-based resin, which is located on the polarizing film side constituting the polarizing plate, and a core made of a styrene-based resin, which is located on the pressure-sensitive adhesive layer side of the first retardation film It is a laminate of a second retardation film having a three-layer structure comprising a layer and a skin layer comprising a (meth) acrylic resin composition containing rubber particles laminated on both surfaces of the core layer. In the third preferred embodiment, the first retardation film has an in-plane retardation in the range of 30 to 150 nm, an Nz coefficient defined by the above formula is in the range of more than 1 and less than 2, In the retardation film, it is more preferable that the in-plane retardation is in the range of 20 to 120 nm, and the Nz coefficient defined by the above formula is in the range of more than −2 and less than −0.5.

  Further, in these liquid crystal display devices, in one preferred form from the viewpoint of adhesion between the polarizing film constituting the polarizing plate and the transparent protective film disposed on both surfaces thereof, the front side polarizing plate and the back side polarizing plate are each polarized light The film and the transparent protective film arrange | positioned on both surfaces are bonded through the water-system adhesive containing a polyvinyl alcohol-type resin and a water-soluble epoxy resin. Moreover, in another preferable form from a viewpoint of adhesion | attachment with the polarizing film which similarly comprises a polarizing plate, and the transparent protective film arrange | positioned on both surfaces, a front side polarizing plate and a back side polarizing plate are respectively by irradiation of active energy rays. It is bonded through a curable adhesive composition containing an epoxy compound that cures. In the latter form, the epoxy compound that is cured by irradiation with active energy rays preferably includes an epoxy compound having at least one epoxy group bonded to the alicyclic ring in the molecule.

  In the liquid crystal display device of the present invention, the warp of the liquid crystal panel is small even after being placed in a humid heat environment, light leakage at the four corners and in-plane luminance unevenness are small, that is, display unevenness is small.

It is a cross-sectional schematic diagram which shows the layer structure of the liquid crystal display device which concerns on this invention. It is a cross-sectional schematic diagram which shows the layer structural example of one preferable form of the liquid crystal display device which concerns on this invention. It is a figure which shows typically the state which measures the curvature amount of a liquid crystal panel in an Example, (A) is a top view, (B) is a side view.

  Referring to FIG. 1, a liquid crystal display device of the present invention includes a liquid crystal cell 10, a front side polarizing plate 20 laminated on the viewing side of the liquid crystal cell via an adhesive layer 51, and the viewing side of the liquid crystal cell. The back side polarizing plate 30 laminated | stacked through the adhesive layer 52 on the opposite side, and the backlight unit 70 arrange | positioned on the outer side (namely, the opposite side to the liquid crystal cell 10) of the back side polarizing plate are provided. is there. A liquid crystal cell 10, a front side polarizing plate 20 laminated on the viewing side of the liquid crystal cell via an adhesive layer 51, and a back side polarizing plate 30 laminated on the opposite side of the liquid crystal cell via an adhesive layer 52; Thus, the liquid crystal panel 60 is formed.

  The front-side polarizing plate 20 disposed on the viewing side of the liquid crystal cell 10 includes a polarizing film 21 and transparent protective films 23 and 24 laminated on both surfaces via an adhesive (not shown). Similarly, the back side polarizing plate 30 disposed on the side opposite to the viewing side of the liquid crystal cell 10 (that is, the backlight unit 70 side) is also provided with a polarizing film 31 and an adhesive (not shown) on both sides thereof. It has the transparent protective films 33 and 34 laminated | stacked.

  A liquid crystal display device is configured by combining the liquid crystal panel 60 and the backlight unit 70. When the liquid crystal display device is placed in a humid heat environment and then the backlight is turned on, moisture absorbed in the polarizing plate is absorbed. The liquid crystal panel 60 warps due to evaporation and contraction of the polarizing plate. At this time, a part of the liquid crystal panel 60 may be abnormally close to the backlight unit 70 or may come into contact in an extreme case, resulting in display unevenness. The liquid crystal panel 60 is fixed with a housing and a metal frame so that the liquid crystal panel 60 does not fall to the viewing side. However, when the backlight is turned on after the liquid crystal display device is placed in a humid heat environment, the liquid crystal panel 60 is warped. In some cases, a part of the liquid crystal panel 60 comes into contact with a casing or a metal frame that fixes the liquid crystal panel 60, thereby causing display unevenness.

Therefore, in the present invention, from the first point of view, the moisture absorption amount when the front side polarizing plate 20 including the pressure-sensitive adhesive layer 51 is humidified is A _f and the back-side polarizing plate 30 including the pressure-sensitive adhesive layer 52 is humidified. Assuming that the amount of water absorption when treated is A _r , both A _f and A _r are set to be less than 7 g / m ² . In other words, A _f and A _{r satisfy} the following expressions (1) and (2), respectively.
A _f <7 g / m ² (1)
A _r <7 g / m ² (2)

Here, the moisture absorption when the polarizing plate provided with the pressure-sensitive adhesive layer is humidified is measured as follows. That is, the polarizing plate on which the pressure-sensitive adhesive layer is formed is preliminarily cut into a predetermined size (the area is Sm ² ), and the polarizing plate is glass on the pressure-sensitive adhesive layer side on a glass plate having a slightly larger area. It stuck so as not to protrude from the plate, the mass in this state W ₁ (unit: g) of measuring the. Next, moisture is absorbed under predetermined conditions in this state (humidification treatment). The conditions for absorbing moisture are arbitrary, but, for example, as shown in the examples described later, a process of leaving for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95% is adopted. The mass W ₂ (unit: g) after moisture absorption is measured again. From these values, the water absorption amount A (g / m ² ) after the humidification treatment of the polarizing plate with the pressure-sensitive adhesive is calculated by the following formula (3).
A = (W ₂ −W ₁ ) / S (3)

Thus, in the present invention, the moisture absorption amount A _f when the front side polarizing plate 20 including the pressure-sensitive adhesive layer 51 is humidified and the water content when the back-side polarizing plate 30 including the pressure-sensitive adhesive layer 52 is humidified. the absorption amount a _r, are both important to less than 7 g / m ^2. Accordingly, it has been found that even after the liquid crystal display device is placed in a humid heat environment, the liquid crystal panel 60 can be prevented from warping, display unevenness is not observed, and a liquid crystal display device having excellent display quality can be obtained.

Also from the second aspect, the moisture evaporation rate of the front-side polarizing plate 20 provided with a pressure-sensitive adhesive layer 51 and V _f, the moisture evaporation rate of the back side polarizing plate 30 provided with a pressure-sensitive adhesive layer 52 as V _r, V _f and Both V _r are set to be less than 5 g / m ² · hr. In other words, V _f and V _r are set to satisfy the following expressions (4) and (5), respectively.
V _f <5g / m ² · hr (4)
V _r <5 g / m ² · hr (5)

Here, the water evaporation rate of the polarizing plate provided with the pressure-sensitive adhesive layer is measured as follows. That is, the polarizing plate on which the pressure-sensitive adhesive layer is formed is preliminarily cut into a predetermined size (the area is Sm ² ), and the polarizing plate is glass on the pressure-sensitive adhesive layer side on a glass plate having a slightly larger area. Paste so that it does not protrude from the plate. In this state, moisture is absorbed under predetermined conditions, and its mass W ₃ (unit: g) is measured. The conditions for absorbing moisture are arbitrary, but, for example, as shown in the examples described later, a process of leaving for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95% is adopted. Next, after being left in an environment of a temperature of 50 ° C. and a relative humidity of 0% for 1 hour, it is taken out to a room temperature environment, and the mass W ₄ (unit: g) immediately after taking out is measured again. From these values, the water evaporation rate V (g / m ² · hr) is calculated by the following equation (6).
V = (W ₃ −W ₄ ) / S (6)

Thus, in the present invention, a water evaporation rate V _f of the front-side polarizing plate 20 provided with a pressure-sensitive adhesive layer 51, the water evaporation rate V _f of the back side polarizing plate 30 provided with a pressure-sensitive adhesive layer 52, both 5 g / m it is also important to be less than ² · hr. It has also been found that, after the liquid crystal display device is placed in a wet and heat environment, warpage of the liquid crystal panel 60 can be suppressed, display unevenness is not observed, and a liquid crystal display device excellent in display quality can be obtained.

  Hereinafter, each member constituting the liquid crystal display device of the present invention will be described in detail with reference to the reference numerals attached to FIG.

[Liquid Crystal Cell]
The liquid crystal cell 10 includes two cell substrates 11 and 12 and a liquid crystal layer 15 sandwiched between the substrates. The cell substrates 11 and 12 are generally often made of glass, but may be plastic substrates. In addition, the liquid crystal cell 10 itself in the liquid crystal display device of the present invention can be composed of various types employed in this field.

[Polarized film]
The polarizing films 21 and 31 constituting the front-side polarizing plate 20 and the rear-side polarizing plate 30 are usually formed by uniaxially stretching a polyvinyl alcohol-based resin film, by dyeing the polyvinyl alcohol-based resin film with a dichroic dye. It is manufactured through a step of adsorbing a chromatic dye, a step of treating a polyvinyl alcohol-based resin film adsorbed with a dichroic dye with an aqueous boric acid solution, and a step of washing with water after the treatment with an aqueous boric acid solution.

  The polyvinyl alcohol-based resin can be produced by saponifying a polyvinyl acetate-based resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified, for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of a polarizing film. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. The film thickness of the polyvinyl alcohol resin raw film is, for example, about 10 to 150 μm, preferably about 10 to 100 μm.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing with the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, the uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Of course, uniaxial stretching can also be performed in a plurality of stages shown here. For uniaxial stretching, a method of stretching uniaxially between rolls having different peripheral speeds, a method of stretching uniaxially using a hot roll, or the like can be adopted. Uniaxial stretching may be performed by dry stretching in which stretching is performed in the air, or may be performed by wet stretching in which a polyvinyl alcohol-based resin film is stretched using a solvent such as water. The draw ratio is usually about 3 to 8 times.

  The polyvinyl alcohol resin film can be dyed with a dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye. In addition, it is preferable to perform the process which a polyvinyl alcohol-type resin film swells by immersing in water before a dyeing process.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. It is. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic organic dye is usually employed. The content of the dichroic organic dye in this aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight, preferably 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous dye solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dichroic organic dye solution used for dyeing is usually about 20 to 80 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with the dichroic dye can be performed by a method of immersing the dyed polyvinyl alcohol resin film in a boric acid-containing aqueous solution. The boric acid content in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The content of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably 150 to 600 seconds, and more preferably 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by a method of immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C. The immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain a polarizing film. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of a drying process is about 30-100 degreeC normally, Preferably it is 50-80 degreeC. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds. By the drying treatment, the moisture content in the polarizing film is reduced to a practical level. The moisture content is usually about 5 to 20% by weight, preferably 8 to 15% by weight. When the moisture content is less than 5% by weight, the polarizing film loses its flexibility, and may be damaged or broken after drying. On the other hand, if the moisture content exceeds 20% by weight, the thermal stability tends to be insufficient.

  As described above, a polarizing film having a dichroic dye adsorbed and oriented on a polyvinyl alcohol-based resin film can be produced. The resulting polarizing film can have a thickness of, for example, about 5 to 40 μm.

[Transparent protective film located on the far side from the liquid crystal cell of the front and rear polarizing plates]
The transparent protective films 23 and 33 located on the side far from the liquid crystal cell 10 of the front side polarizing plate 20 and the back side polarizing plate 30 can be preferably made of polypropylene resin, polyethylene terephthalate resin or acrylic resin. . Thus, if the transparent protective films 23 and 33 located in the side far from a liquid crystal cell are comprised with a resin film with a low hygroscopic property, the moisture absorption amount when the polarizing plate with which the adhesive layer was bonded will be humidified. The water evaporation rate of the polarizing plate to which the pressure-sensitive adhesive layer is bonded can be suppressed to a low level. These resin films are a film formed by melt extrusion of a raw material resin, a uniaxially stretched film obtained by transverse stretching after film formation, a biaxially stretched film obtained by longitudinally stretching after film formation and then transversely stretching And so on.

<Polypropylene resin film>
Polypropylene resin is a chain olefin resin obtained by polymerizing a chain olefin monomer whose main component is propylene using a polymerization catalyst, wherein 80% by weight or more of repeating units are composed of propylene. is there. The polypropylene resin may be a homopolymer of propylene, or a comonomer mainly composed of propylene and copolymerizable with it in a proportion of 1 to 20% by weight, preferably 3 to 10% by weight. It may be a copolymer.

  When a copolymer mainly composed of propylene is used, the comonomer copolymerizable with propylene is preferably ethylene, or an α-olefin such as 1-butene and 1-hexene. Especially, since the resin which is comparatively excellent in transparency is obtained, what copolymerized ethylene in the ratio of 1-20 weight%, preferably 3-10 weight% is preferable. By setting the copolymerization ratio of ethylene to 1% by weight or more, an effect of increasing transparency appears. On the other hand, when the ratio exceeds 20% by weight, the melting point of the resin is lowered, and the heat resistance required for the transparent protective film may be impaired.

  The polypropylene resin preferably has a content of a component soluble in xylene at 20 ° C., that is, a CXS (cold xylene soluble) component, of 1% by weight or less, particularly 0.5% by weight or less. Since a propylene homopolymer tends to reduce the CXS component, a propylene homopolymer having a CXS component of 1% by weight or less, particularly 0.5% by weight or less is also a suitable polypropylene resin.

  As the polypropylene resin, a commercially available product can be easily obtained. Examples of commercial products are “Prime Polypro” sold by Prime Polymer Co., Ltd., “Novatech” and “Wintech” sold by Nippon Polypro Co., Ltd., Sumitomo Chemical Co., Ltd. "Sumitomo Noblen" sold by the company, "San Aroma" sold by Sun Allomer.

<Polyethylene terephthalate resin film>
The polyethylene terephthalate resin means a resin in which 80 mol% or more of repeating units are composed of ethylene terephthalate, and other dicarboxylic acid components and diol components may be copolymerized. Examples of other dicarboxylic acid components include isophthalic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 1,4 -Dicarboxycyclohexane etc. are mentioned. Examples of other diol components include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like.

  These other dicarboxylic acid components and diol components can be used in combination of two or more if necessary. Further, hydroxycarboxylic acids such as p-hydroxybenzoic acid and p-β-hydroxyethoxybenzoic acid can be used in combination. Furthermore, a dicarboxylic acid component or a diol component containing a small amount of an amide bond, a urethane bond, an ether bond, a carbonate bond or the like may be used as another copolymerization component.

  The polyethylene terephthalate resin can contain an additive as necessary. Examples of the additive include a lubricant, an anti-blocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light resistance agent, and an impact resistance improving agent. The addition amount is preferably kept in a range that does not adversely affect the optical properties.

  Polyethylene terephthalate-based resins are usually used in the form of pellets granulated by an extruder for blending such additives and for film formation described below. The size and shape of the pellet can be, for example, a cylindrical shape, a spherical shape, or a flat spherical shape having a height and a diameter of 5 mm or less. Such a polyethylene terephthalate resin pellet is melted, formed into a film shape, and stretched to obtain a transparent and homogeneous film having high mechanical strength. As the manufacturing method, for example, the following method can be employed.

  First, dried pellets made of polyethylene terephthalate resin are supplied to a melt extrusion apparatus and heated to a melting point or higher to melt. Next, the melted resin is extruded from a die and rapidly cooled and solidified on the rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unstretched film. This melting temperature is determined according to the melting point of the polyethylene terephthalate resin to be used and the extruder, and is usually about 250 to 350 ° C.

  In order to improve the flatness of the film, it is preferable to improve the adhesion between the film and the rotary cooling drum, and an electrostatic application adhesion method or a liquid application adhesion method is preferably employed. Here, the electrostatic application adhesion method is a method in which a linear electrode is stretched in a direction perpendicular to the film flow on the upper surface side of the film, and a DC voltage of, for example, about 5 to 10 kV is applied to the electrode. In this method, an electrostatic charge is applied to improve the adhesion between the rotary cooling drum and the film. In addition, the liquid application adhesion method is a method in which the liquid is uniformly applied to the entire surface or a part of the surface of the rotating cooling drum (for example, only the portion in contact with both ends of the film), thereby improving the adhesion between the rotating cooling drum and the film. It is a way to improve. If desired, both may be used in combination.

  The polyethylene terephthalate resin to be used may be mixed with two or more kinds of resins having different resin structures and compositions as necessary. For example, pellets containing a particulate filler, an ultraviolet absorber, an antistatic agent and the like as an antiblocking agent can be mixed and used without mixing.

  In addition, the extruded film may be a single layer or may be a multilayer film of two or more layers as necessary. For example, a pellet containing a granular filler as an antiblocking agent and a pellet not containing a filler are prepared, and each is supplied from different extruders to the same die, and a filler compounded resin / non-compounded resin / filler is prepared. A film composed of two types and three layers of compounded resin can also be extruded.

  The polyethylene terephthalate resin film thus melt-extruded is usually longitudinally stretched in the extrusion direction at a temperature equal to or higher than the glass transition temperature. The longitudinal stretching temperature is usually 70 to 150 ° C, preferably 80 to 130 ° C, more preferably 90 to 120 ° C. The longitudinal draw ratio is usually 1.1 to 6 times, preferably 2 to 5.5 times. When this draw ratio is less than 1.1 times, the mechanical strength of the stretched polyethylene terephthalate film tends to be insufficient. On the other hand, when this draw ratio exceeds 6 times, the strength in the transverse direction may be insufficient in practice. This stretching can be completed once or divided into a plurality of times as necessary. Even when stretching is performed a plurality of times, the total stretching ratio is preferably in the above range.

  The longitudinally stretched film thus obtained can then be subjected to heat treatment. Next, if necessary, relaxation treatment can be performed. The heat treatment temperature in this case is usually 150 to 250 ° C, preferably 180 to 245 ° C, more preferably 200 to 230 ° C. The heat treatment time is usually 1 to 600 seconds, preferably 1 to 300 seconds, more preferably 1 to 60 seconds. Next, when the relaxation treatment is performed, the temperature is usually 90 to 200 ° C, preferably 120 to 180 ° C. The amount of relaxation is usually 0.1 to 20%, preferably 2 to 5%. More preferably, the temperature and amount of relaxation treatment are set so that the heat shrinkage rate of the polyethylene terephthalate resin film after relaxation treatment at 150 ° C. is 2% or less.

  The polyethylene terephthalate-based resin film is preferably subjected to transverse stretching by a tenter after the longitudinal stretching treatment, after further heat treatment as necessary, or after further relaxation treatment. On the other hand, in the case of uniaxial stretching, the melt-extruded film is usually stretched as it is. The temperature at which the transverse stretching is performed is usually 70 to 150 ° C, preferably 80 to 130 ° C, more preferably 90 to 120 ° C. The transverse draw ratio is usually 1.1 to 6 times, preferably 2 to 5.5 times. When the draw ratio in the transverse drawing is less than 1.1 times, a sufficient improvement in the film strength due to orientation may not be expected. On the other hand, a draw ratio exceeding 6 times is not practical in production technology.

  After the transverse stretching, a heat treatment and, if necessary, a relaxation treatment can be performed. The heat processing temperature at this time is 150-250 degreeC normally, Preferably it is 180-245 degreeC, More preferably, it is 200-230 degreeC. The heat treatment time is usually 1 to 600 seconds, preferably 1 to 300 seconds, more preferably 1 to 60 seconds. Moreover, when performing a relaxation process, the temperature is 100-230 degreeC normally, Preferably it is 110-210 degreeC, More preferably, it is 120-180 degreeC. The amount of relaxation is usually 0.1 to 20%, preferably 1 to 10%, more preferably 2 to 5%. More preferably, the temperature and amount of relaxation treatment are set so that the heat shrinkage rate of the polyethylene terephthalate resin film after relaxation treatment at 150 ° C. is 2% or less.

  In the uniaxial stretching and biaxial stretching treatments, if the stretching treatment temperature exceeds 150 ° C., the polyethylene terephthalate resin may be thermally deteriorated or the crystallization may proceed excessively, so that the optical performance may be lowered. On the other hand, if the stretching temperature is lower than 70 ° C., excessive stress may be applied to stretching, or stretching itself may be impossible.

  In the uniaxial stretching and biaxial stretching treatments, it is preferable that after transverse stretching, heat treatment is again performed or relaxation treatment is performed in order to relieve distortion of the orientation main axis typified by bowing. The maximum value of strain with respect to the stretching direction of the orientation main axis due to bowing is usually within 45 °, but is preferably relaxed within 30 °, more preferably within 15 °. If the maximum value of the distortion of the orientation main axis exceeds 45 °, when the polarizing plate is formed into a sheet in a later step, optical characteristics may be nonuniform between the sheets.

  Here, the stretching direction refers to a direction having a larger stretching ratio among longitudinal stretching and lateral stretching. In biaxial stretching of a polyethylene terephthalate-based resin film, the transverse stretching ratio is usually slightly larger than the longitudinal stretching ratio, so the stretching direction in this case is the direction orthogonal to the longitudinal direction of the film, that is, The width direction. On the other hand, in uniaxial stretching, since the film is usually stretched in the transverse direction, the stretching direction in this case is the same as the width direction.

  The orientation main axis refers to the orientation direction of molecules at an arbitrary point on the stretched polyethylene terephthalate resin film. The distortion with respect to the stretching direction of the orientation main axis refers to an angle formed between the orientation main axis and the stretching direction. Further, the maximum value of the distortion of the orientation main axis refers to the maximum value in the direction orthogonal to the longitudinal direction. The orientation main axis is, for example, a retardation film / optical material inspection apparatus “RETS” (trade name) sold by Otsuka Electronics Co., Ltd. or a molecular orientation meter “MOA” sold by Oji Scientific Instruments Co., Ltd. (Trade name) can be used for measurement.

  A stretched polyethylene terephthalate resin film can be easily obtained as a commercial product. Examples of commercial products are “Diafoil”, “Hostafan” and “Fusion” sold by Mitsubishi Plastics, Inc., and “Teijin” sold by Teijin DuPont Films, Inc. Tetoron Film, Melinex, Mylar, and Teflex, Toyobo Ester Film, Toyobo Espet Film, Cosmo Shine and Crisper, sold by Toyobo Co., Ltd. "Lumirror" sold by Film Processing Co., Ltd., "Embron" and "Embret" sold by Unitika Ltd., "Skyroll" sold by SCC, Inc. ) "Kofil" sold by Takai, "Zuitsu Polyester Film" sold by Zuitsu Co., Ltd. Chemical sold from (Ltd.) "Taiko polyester film", and the like. Among the polyethylene terephthalate resin films, biaxially stretched products are preferably used.

<Acrylic resin film>
The acrylic resin is generally a polymer mainly composed of methyl methacrylate and is also called methyl methacrylate resin. In this resin, the methyl methacrylate unit is usually 50% by weight or more, preferably 70% by weight or more, and may be 100% by weight. A polymer having a methyl methacrylate unit of 100% by weight is a methyl methacrylate homopolymer.

  This acrylic resin can be usually obtained by polymerizing a monofunctional monomer mainly composed of methyl methacrylate in the presence of a radical polymerization initiator and a chain transfer agent. Further, if necessary, a small amount of a polyfunctional monomer may be copolymerized.

  Examples of monofunctional monomers that can be copolymerized with methyl methacrylate include, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate. Methacrylic acid esters other than methyl methacrylate, such as: methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate Acrylic acid esters such as: 2- (hydroxymethyl) methyl acrylate, 3- (hydroxyethyl) methyl acrylate, 2- (hydroxymethyl) ethyl acrylate and 2- (hydroxymethyl) acrylate Hydroxyalkyl acrylates such as butyl acrylate; unsaturated acids such as methacrylic acid and acrylic acid; halogenated styrenes such as chlorostyrene and bromostyrene; styrene, vinyltoluene and α-methylstyrene Styrenes; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated anhydrides such as maleic anhydride and citraconic anhydride; unsaturated imides such as phenylmaleimide and cyclohexylmaleimide Can do. These monomers may be used alone or in combination of two or more.

  Examples of copolymerizing polyfunctional monomers include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, nona Ethylene glycol di (meth) acrylate and tetradecaethylene glycol di (meth) acrylate, such as those obtained by esterifying both terminal hydroxyl groups of ethylene glycol or its oligomer with acrylic acid or methacrylic acid; both ends of propylene glycol or its oligomer Hydroxyl ester of hydroxyl group with acrylic acid or methacrylic acid; like neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate and butanediol di (meth) acrylate Esterified with hydroxyl group of dihydric alcohol with acrylic acid or methacrylic acid; Bisphenol A, alkylene oxide adduct of bisphenol A, or both terminal hydroxyl groups of these halogen-substituted products with esterified with acrylic acid or methacrylic acid A product obtained by esterifying a polyhydric alcohol such as trimethylolpropane and pentaerythritol with acrylic acid or methacrylic acid; a product obtained by ring-opening addition of an epoxy group of glycidyl acrylate or glycidyl methacrylate to the terminal hydroxyl group of the polyhydric alcohol; Ring-opening addition of epoxy groups of glycidyl acrylate or glycidyl methacrylate to dibasic acids such as succinic acid, adipic acid, terephthalic acid, phthalic acid, their halogen substitution products, and their alkylene oxide adducts Those were; allyl (meth) acrylate; and aromatic divinyl compounds such as divinylbenzene. When copolymerizing a polyfunctional monomer, among these, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and neopentyl glycol dimethacrylate are preferably used.

  The acrylic resin mainly composed of methyl methacrylate may be further modified by a reaction between different functional groups in the copolymer. As the reaction, for example, demethanol condensation reaction in a polymer chain between a methyl ester group of methyl acrylate and a hydroxyl group of methyl 2- (hydroxymethyl) acrylate, a carboxyl group of acrylic acid and 2- (hydroxymethyl) acrylic Examples thereof include a dehydration condensation reaction in a polymer chain with a hydroxyl group of methyl acid.

  A commercially available product can be easily obtained for the acrylic resin mainly composed of methyl methacrylate. Examples of commercial products are “Sumipex” sold by Sumitomo Chemical Co., Ltd., “Acrypet” sold by Mitsubishi Rayon Co., Ltd., and Asahi Kasei Co., Ltd. "Delpet", "Parapet" sold by Kuraray Co., Ltd., and "Acryviewer" sold by Nippon Shokubai Co., Ltd.

<Other explanation about the transparent protective film located on the side far from the liquid crystal cell>
An anti-glare property, that is, haze can be imparted to the transparent protective film 23 which is located on the side far from the liquid crystal cell 10 of the front side polarizing plate 20 and becomes the outermost surface on the viewing side. In order to impart antiglare properties, for example, a method of mixing inorganic fine particles or organic fine particles into the raw material resin to be the protective film to form a film, and when forming a film, one of the fine particles is mixed by multilayer extrusion. A two-layer film in which a resin is used and the other is a resin in which fine particles are not mixed, or a three-layer film in which the resin in which the particles are mixed is arranged outside, and inorganic fine particles or organic fine particles are curable binder resins. For example, a method may be employed in which the coating solution mixed in is coated on one side of the film and the binder resin is cured to provide an antiglare layer.

  Examples of the inorganic fine particles for imparting antiglare properties include silica, colloidal silica, alumina, alumina sol, aluminosilicate, alumina-silica composite oxide, kaolin, talc, mica, calcium carbonate, calcium phosphate, and the like. Examples of the organic fine particles include crosslinked polyacrylic acid particles, methyl methacrylate / styrene copolymer resin particles, crosslinked polystyrene particles, crosslinked polymethyl methacrylate particles, silicone resin particles, and polyimide particles.

  The resin film to which the antiglare property is imparted preferably has a haze value in the range of 6 to 45%. If the haze value of this film is less than 6%, a sufficient antiglare effect may not be exhibited. On the other hand, if the haze value exceeds 45%, the polarizing plate to which this film is bonded is applied to a liquid crystal display device. When applied, it may cause the screen to turn white or the image quality to deteriorate. The haze value can be measured using a commercially available haze meter based on JIS K 7136. An example of a haze meter is the haze / transmittance meter “HM-150” (trade name) sold by Murakami Color Research Laboratory. In measuring the haze value, in order to prevent warping of the film, for example, a measurement sample in which the film is bonded to a glass substrate via an optically transparent adhesive so that the antiglare imparting surface is the surface. Is preferably used.

  The transparent protective films 23 and 33 located on the side far from the liquid crystal cell can be provided with functional layers such as a conductive layer, a hard coat layer, and a low reflection layer. When the above-mentioned antiglare layer is formed by curing a coating solution, a resin composition having these functions can be selected as the coating solution. Further, a smoothing layer, an easy-sliding layer, an anti-blocking layer, an easy-adhesion layer, and the like can be provided. Since this protective film is laminated | stacked on a polarizing film through an adhesive bond layer, when an adhesive force with a polarizing film is insufficient, it is preferable to provide an easily bonding layer on the bonding surface to a polarizing film.

  The component constituting the easy-adhesion layer can be, for example, a polyester resin, a urethane resin, an acrylic resin, or the like that has a polar group in the skeleton and has a relatively low molecular weight and a low glass transition temperature. Moreover, a crosslinking agent, an organic or inorganic filler, surfactant, a lubricant, etc. can be contained as needed.

  The thickness of the transparent protective films 23 and 33 located on the side far from the liquid crystal cell is usually about 1 to 500 μm, preferably in the range of 20 to 300 μm, more preferably in the range of 20 to 100 μm, from the viewpoints of strength and handleability. It is a range. If it is the thickness in this range, a polarizing film will be protected mechanically, and even if it exposes to high temperature and high humidity, a polarizing film will not shrink | contract and it can maintain the stable optical characteristic.

[Transparent protective film located on the liquid crystal cell side]
In the front side polarizing plate 20 and the back side polarizing plate 30, the transparent protective film 23 located on the side far from the liquid crystal cell 10 is used as the resin material constituting the transparent protective films 24 and 34 located on the liquid crystal cell 10 side. The thing similar to having described about 33 can be used, and another resin film can also be used. In particular, since the retardation value is easily controlled and easily available, a cellulose resin or a polyolefin resin including a cyclic olefin resin or a chain olefin resin is preferably used.

  Cellulose-based resins are generally cellulose acetate-based resins in which at least some of the hydroxyl groups in cellulose are acetated, and in addition to acetates, a mixture in which some of the hydroxyl groups are esterified with an acid other than acetic acid It may be an ester. Specific examples of the cellulose resin include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.

  Cyclic olefin-based resins are obtained by polymerizing cyclic olefin monomers such as norbornene and other cyclopentadiene derivatives in the presence of a catalyst, but may be resins obtained by ring-opening metathesis polymerization of cyclic olefin monomers. For example, those in which unsaturated bonds are virtually eliminated by the subsequent hydrogenation reaction are preferred. When such a cyclic olefin resin is used, a transparent protective film having a predetermined retardation value to be described later can be easily obtained.

  Examples of the cyclic olefin resin include ring-opening metathesis polymerization using cyclopentadiene and olefins or (meth) acrylic acid or esters thereof by norbornene or a derivative thereof obtained by Diels-Alder reaction, followed by water Resin obtained by addition; ring-opening metathesis polymerization from dicyclopentadiene and olefins or (meth) acrylic acid or esters thereof by tetracyclododecene or its derivative obtained by Diels-Alder reaction, followed by Resin obtained by hydrogenation; ring-opening metathesis copolymerization of at least two monomers selected from norbornene, tetracyclododecene, derivatives thereof, and other cyclic olefin monomers, followed by water Resins obtained by; norbornene, tetracyclododecene, or cyclic olefins such as derivatives thereof, such as linear olefins and / or resins obtained by addition copolymerization of an aromatic compound having a vinyl group.

  Commercially available products can be easily obtained for the cyclic olefin-based resin. Examples of commercial products are “TOPAS” produced by TOPAS ADVANCED POLYMERS GmbH under the trade name, and sold and sold by Polyplastics Co., Ltd. in Japan. “Arton”, “Zeonor” and “Zeonex” manufactured and sold by Nippon Zeon Co., Ltd., “Apel” manufactured and sold by Mitsui Chemicals, Inc.

  Typical examples of the chain olefin resin are a polyethylene resin and a polypropylene resin. Among them, a homopolymer of propylene, or a copolymer obtained by copolymerizing propylene as a main component and a comonomer copolymerizable therewith, for example, ethylene in a proportion of 1 to 20% by weight, preferably 3 to 10% by weight. Preferably used. As for the polypropylene-based resin, the same description as the description regarding the polypropylene-based resin that can be the transparent protective films 23 and 33 located on the side far from the liquid crystal cell 10 applies.

  As a method for forming a film from a cellulose resin, a polyolefin resin, or the like, a method corresponding to each resin may be selected as appropriate. For example, a solvent cast method in which a resin dissolved in a solvent is cast on a metal band or drum, and the solvent is removed by drying to obtain a film. The resin is heated above its melting temperature, kneaded and extruded from a die. A melt extrusion method for obtaining a film by cooling with a cooling drum can be used. Among these, for the polyolefin-based resin, the melt extrusion method is preferably employed from the viewpoint of productivity. On the other hand, a cellulose resin is generally formed into a film by a solvent casting method. The thickness of the transparent protective films 24 and 34 located on the liquid crystal cell side is also usually about 20 to 300 μm, preferably about 20 to 100 μm.

  When the liquid crystal cell 10 is in an in-plane switching (IPS) mode, the transparent protective films 24 and 34 located on the liquid crystal cell 10 side are not damaged so as not to impair the wide viewing angle characteristics inherent in the IPS mode liquid crystal cell. A preferable example is the first embodiment in which the thickness direction retardation Rth is in the range of -10 to +10 nm. Here, the retardation Rth in the thickness direction is a value obtained by multiplying the value obtained by subtracting the refractive index in the thickness direction from the in-plane average refractive index, and is defined by the following formula (7). . The in-plane retardation Re is a value obtained by multiplying the in-plane refractive index difference by the film thickness, and is defined by the following formula (8).

Rth = _{[(n x + n y) /} 2-n z ] × d (7)
_{Re = (n x -n y)} × d (8)

Wherein, n _x is a refractive index in a slow axis direction (x-axis direction) in the film plane, n _y is the fast axis direction in the film plane of the (y-axis direction orthogonal to the x-axis in a plane) Refractive index, _nz is the refractive index in the film thickness direction (z-axis direction perpendicular to the film surface), and d is the film thickness.

  Here, the retardation value may be a value at an arbitrary wavelength in the range of about 500 to 650 nm near the center of visible light, but in this specification, the retardation value at a wavelength of 590 nm is used as a standard. The retardation Rth in the thickness direction and the in-plane retardation Re can be measured using various commercially available phase difference meters.

  As a method for controlling the retardation Rth in the thickness direction of the resin film within a range of −10 to +10 nm, there is a method of minimizing the distortion remaining in the thickness direction when the film is produced. For example, in the solvent casting method, a method of relaxing residual shrinkage strain in the thickness direction generated when the cast resin solution is dried by heat treatment can be employed. On the other hand, in the above melt extrusion method, the distance from the die to the cooling drum is reduced as much as possible in order to prevent the resin film from being drawn from the die and cooled, and the extrusion amount and the rotation speed of the cooling drum are also reduced. A method of controlling the film so that the film is not stretched can be employed. Moreover, the method of relieving the distortion which remains in the obtained film by heat processing similarly to the solvent casting method is also employable.

When the liquid crystal cell 10 is also in the IPS mode, one of the transparent protective films 24 and 34 positioned on the liquid crystal cell 10 side has a thickness direction retardation Rth in the range of −10 to +10 nm, and the other is a surface. The second embodiment in which the retardation Re is in the range of 100 to 300 nm and the Nz coefficient is in the range of 0.1 to 0.7 is also preferable for realizing even higher viewing angle characteristics. Here, Nz coefficient is defined by the following equation _{(9), n x, n} y and n _z in the formula have the meanings as defined above.
Nz factor _{= (n x -n z) /} (n x -n y) (9)

  As described above, one of the transparent protective films 24 and 34 positioned on the liquid crystal cell 10 side is constituted by a film having a small retardation in the thickness direction, and the other is constituted by a retardation film having a specific refractive index anisotropy. By doing so, the obtained liquid crystal display device can suitably compensate the display characteristics over a wide angle. In this case, the same explanation as in the first embodiment applies to a film having a thickness direction retardation Rth in the range of -10 to +10 nm. The retardation film having an in-plane retardation Re in the range of 100 to 300 nm and an Nz coefficient in the range of 0.1 to 0.7 has a thickness direction retardation Rth in the range of -40 to +40 nm. More preferably.

The retardation film having an in-plane retardation in the range of 100 to 300 nm and an Nz coefficient in the range of 0.1 to 0.7 should be made of, for example, a polyolefin resin, preferably a cyclic polyolefin resin. Can do. A retardation film having such a refractive index characteristic is, for example, a direction in which a polyolefin resin film is stretched, a shrinkable film having a predetermined shrinkage ratio is bonded to it, and heated, and orthogonal to the previous stretching direction in a plane. A stretched polyolefin resin film to which the shrinkable film is bonded, and a method of further stretching while heating and shrinking in a direction perpendicular to the stretching direction in a plane, and a predetermined amount of polyolefin resin film. attaching a shrinkable film having a shrinkage was stretched while heating in this state, by a method of contracting in the direction perpendicular with stretching simultaneously stretching direction and a plane, a relationship n _x> n _z> n _y Can be realized.

  Furthermore, when the liquid crystal cell 10 is also in the IPS mode, one of the transparent protective films 24 and 34 positioned on the liquid crystal cell 10 side has a thickness direction retardation Rth in the range of −10 to +10 nm, and the other A first retardation film made of a polyolefin-based resin, which is located on the polarizing film side constituting the polarizing plate, and a core made of a styrene-based resin, which is located on the pressure-sensitive adhesive layer side of the first retardation film A third layered product of a second retardation film having a three-layer structure comprising a layer and a skin layer made of a (meth) acrylic resin composition containing rubber particles laminated on both surfaces of the core layer This form is also preferable for realizing even higher viewing angle characteristics.

  A layer configuration example of the third embodiment is shown in a schematic cross-sectional view in FIG. In this example, the transparent protective film 24 located on the liquid crystal cell 10 side of the front side polarizing plate 20 is configured with a retardation Rth in the thickness direction in the range of −10 to +10 nm, and the liquid crystal of the back side polarizing plate 30 is formed. The transparent protective film 34 located on the cell 10 side is composed of a laminate of the first retardation film 36 and the second retardation film 37 described above. Parts other than these in FIG. 2 are the same as those in FIG. 1, and the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Of course, the structure in which the positions of the protective film 24 and the protective film 34 in FIG. 2 are reversed with the liquid crystal cell 10 interposed therebetween, that is, the transparent protective film 24 positioned on the liquid crystal cell 10 side of the front-side polarizing plate 20 is the polyolefin-based film. The thickness of the transparent protective film 34, which is composed of a laminate of a first retardation film made of a resin and a second retardation film having a three-layer structure and located on the liquid crystal cell 10 side of the back-side polarizing plate 30, is as described above. A structure composed of those having a direction retardation Rth in the range of −10 to +10 nm is also included in the third embodiment.

  In a third embodiment represented by the example shown in FIG. 2, a film having a thickness direction retardation Rth in the range of −10 to +10 nm (in FIG. 2, located on the liquid crystal cell 10 side of the front polarizing plate 20). For the protective film 24), the same explanation as in the first embodiment applies.

  Next, in this third embodiment, a film composed of a laminate of a first retardation film 36 made of polyolefin resin and a second retardation film 37 having a three-layer structure (in FIG. 2, the back side) The protective film 34) located on the liquid crystal cell 10 side of the polarizing plate 30 will be described. The polyolefin resin constituting the first retardation film 36 includes a cyclic olefin resin and a chain olefin resin as described above. In particular, a cyclic olefin resin is preferably used.

  The first retardation film 36 has an in-plane retardation Re in the range of 30 to 150 nm, and a refractive index in which the Nz coefficient defined by the above formula (9) is in the range of more than 1 and less than 2. It is preferable to have anisotropy. On the other hand, in the second retardation film 37, the in-plane retardation Re is in the range of 20 to 120 nm, and the Nz coefficient defined by the above formula (9) is more than −2 and less than −0.5. It is preferable to have a refractive index anisotropy.

  The first retardation film 36 made of polyolefin resin having refractive index anisotropy as described above is manufactured by known longitudinal uniaxial stretching, tenter transverse uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, or the like. In order to obtain the desired retardation value, the stretching ratio and the stretching speed are appropriately adjusted, and various temperatures such as preheating temperature, stretching temperature, heat setting temperature, cooling temperature during stretching, and the like What is necessary is just to select a pattern suitably.

  The thickness of the first retardation film 36 is preferably in the range of 20 to 80 μm, more preferably in the range of 40 to 80 μm. When the thickness of the film is less than 20 μm, it is difficult to handle the film, and the predetermined retardation value tends to be difficult to develop. On the other hand, when the thickness exceeds 80 μm, the processability is inferior, Moreover, transparency may fall and the weight of the polarizing plate on which it is laminated may increase.

  On the opposite side of the first retardation film 36 to the polarizing film 31 (liquid crystal cell 10 side), a core layer 38 made of a styrene resin and a (meth) acrylic polymer containing rubber particles laminated on both surfaces thereof. A second retardation film 39 having a three-layer structure composed of skin layers 39 and 39 made of a resin composition is disposed.

  The styrenic resin constituting the core layer 38 can be a homopolymer of styrene or a derivative thereof, or can be a binary or higher copolymer of styrene or a derivative thereof and another copolymerizable monomer. There can also be. Here, the styrene derivative is a compound in which another group is bonded to styrene, such as o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, o-ethylstyrene, Alkyl styrene such as p-ethyl styrene, hydroxy styrene, tert-butoxy styrene, vinyl benzoic acid, o-chloro styrene, and p-chloro styrene, benzene nucleus of styrene, hydroxyl group, alkoxy group, carboxyl And substituted styrene introduced with a group such as a group or halogen. A terpolymer as disclosed in JP-A-2003-50316 or JP-A-2003-207640 can also be used. The styrenic resin is preferably a copolymer of styrene or a styrene derivative and at least one monomer selected from the group consisting of acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. The styrenic resin constituting the core layer 38 is preferably heat-resistant, and generally has a glass transition temperature (referred to as “Tg”) of 100 ° C. or higher. A more preferable Tg of the styrene resin is 120 ° C. or more.

  The core layer 38 made of styrene resin is desirably set so that its thickness is 10 to 100 μm. When the thickness is less than 10 μm, a sufficient retardation value may not easily be exhibited by stretching. On the other hand, if the thickness exceeds 100 μm, the impact strength of the film tends to be weak and the retardation change due to external stress tends to increase, and white spots are likely to occur when applied to a liquid crystal display device. , Display performance is likely to deteriorate.

  The skin layers 39, 39 disposed on both surfaces of the core layer 38 made of the styrene resin are made of a (meth) acrylic resin composition in which rubber particles are blended with a (meth) acrylic resin. Examples of the (meth) acrylic resin include a methacrylic acid alkyl ester or a homopolymer of an acrylic acid alkyl ester, and a copolymer of a methacrylic acid alkyl ester and an acrylic acid alkyl ester. Specific examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, and propyl methacrylate. Specific examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, and propyl acrylate. . As such a (meth) acrylic resin, a commercially available (meth) acrylic resin can be used. Some (meth) acrylic resins are called impact-resistant (meth) acrylic resins, and high heat-resistant (meth) acrylic resins having a glutaric anhydride structure or lactone ring structure in the main chain Also called.

  The rubber particles blended in the (meth) acrylic resin are preferably acrylic. Acrylic rubber particles are particles having rubber elasticity obtained by polymerizing in the presence of a polyfunctional monomer mainly composed of an alkyl acrylate ester such as butyl acrylate or 2-ethylhexyl acrylate. Such rubber elastic particles may be formed as a single layer, or may be a multilayer structure having at least one rubber elastic layer. As the acrylic rubber particles having a multilayer structure, particles having rubber elasticity as described above are used as cores, and the periphery thereof is covered with a hard alkyl methacrylate ester polymer, or a hard alkyl methacrylate ester polymer. The core is covered with an acrylic polymer having rubber elasticity as described above, and the hard core is covered with an acrylic polymer having rubber elasticity, and the periphery is further covered with a hard methacrylic polymer. Examples thereof include those covered with an acid alkyl ester polymer. These rubber particles generally have an average diameter of particles formed of an elastic layer in the range of about 50 to 400 nm.

  The content of the rubber particles in the (meth) acrylic resin composition constituting the skin layer 39 is usually about 5 to 50 parts by weight per 100 parts by weight of the (meth) acrylic resin. Since the (meth) acrylic resin and acrylic rubber particles are commercially available in a state where they are mixed, commercially available products thereof can be used. Examples of commercially available (meth) acrylic resins containing acrylic rubber particles include “HT55X” and “Technoloy S001” sold by Sumitomo Chemical Co., Ltd. Such a (meth) acrylic resin composition generally has a Tg of 160 ° C. or lower, but a preferable Tg is 120 ° C. or lower, and further 110 ° C. or lower.

  The skin layers 39 and 39 made of a (meth) acrylic resin composition containing rubber particles, preferably acrylic rubber particles, are desirably 10 to 100 μm in thickness. If the thickness is less than 10 μm, film formation tends to be difficult. On the other hand, if the thickness exceeds 100 μm, the retardation of the (meth) acrylic resin layer tends to be negligible.

  As described above, in the second retardation film 37, the core layer 38 made of a styrene resin preferably has a Tg of 120 ° C. or higher, while a (meth) acrylic resin composition in which rubber particles are blended. The skin layer 39 made of a material preferably has a Tg of 120 ° C. or lower, more preferably 110 ° C. or lower. It is preferable that the core layers 38 made of styrene resin have a higher Tg than the skin layer 39 made of (meth) acrylic resin composition containing rubber particles. .

  In order to produce the second retardation film 37 having a three-layer structure, for example, a styrene resin and a (meth) acrylic resin composition containing rubber particles are coextruded to form a film having a three-layer structure. A film may be formed and then stretched. In addition, a method in which a single-layer film is produced and then thermally fused by heat lamination and then stretched is also possible.

  The second retardation film 37 has a three-layer structure in which skin layers 39 and 39 made of a (meth) acrylic resin composition containing rubber particles are formed on both surfaces of a core layer 38 made of a styrene resin. It is said. In this three-layer structure, the skin layers 39, 39 disposed on both sides are usually substantially the same thickness. By having a three-layer structure in this way, the skin layers 39, 39 made of a (meth) acrylic resin composition containing rubber particles function as a protective layer, and have excellent mechanical strength and chemical resistance. .

  The second retardation film 37 configured as described above is given in-plane retardation by stretching. Stretching can be performed by known longitudinal uniaxial stretching, tenter transverse uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, and the like, and may be performed so as to obtain a desired retardation value.

  The second retardation film 37 is laminated on the first retardation film 36 via the interlayer adhesive 40. The method of laminating the second retardation film 37 on the first retardation film 36 is not particularly limited. Usually, however, first, the surface of the first retardation film 36 or the surface of the second retardation film 37 is first. Interlayer adhesive 40 is formed. Such an interlayer pressure-sensitive adhesive 40 can be formed by a method of applying a pressure-sensitive adhesive solution and drying it, and having a pressure-sensitive adhesive layer formed on a release-treated surface of a support film (separator) subjected to a release treatment. (Adhesive with a separator) is prepared, and can also be formed by a method of adhering it to the adhesive surface of the first retardation film 26 or the second retardation film 37 on the adhesive layer side. As another method, a pressure-sensitive adhesive with a separator in which a pressure-sensitive adhesive layer is formed on the separator described above is prepared, and the adhesive surface of the first retardation film 36 bonded to the polarizing film 31, or the second position. A method of transferring to the adhesive surface of the phase difference film 37 can also be employed. The separator is peeled and removed from the pressure-sensitive adhesive layer immediately before being bonded to the other film.

  Further, when the interlayer adhesive 40 is formed on the surface of the first retardation film 36 or the surface of the second retardation film 37, the adhesive layer forming surface of the first retardation film 36 or The adhesive layer forming surface of the second retardation film 37 may be subjected to a treatment for improving adhesion, such as a corona treatment, and the same treatment is bonded to the first retardation film 36. You may give to the surface of the interlayer adhesive 40, or the surface of the interlayer adhesive 40 bonded to the 2nd phase difference film 37. FIG.

  The pasting of the first retardation film 36 and the second retardation film 37 and the pasting of the polarizing film 31 and the first retardation film 36 can be performed by a conventionally known technique. it can. For example, the slow axis of the retardation film in a state where the first retardation film 36 and the second retardation film 37 are laminated with respect to the polarization transmission axis of the polarizing film 31 using a bonding roll or the like. It is performed by a method of pasting so as to be orthogonal or parallel, or by a method of pasting so that the slow axis of the retardation film in a laminated state has a predetermined angle with respect to the polarization transmission axis of the polarizing film 31. .

[Description common to protective films located on the side far from the liquid crystal cell and on the liquid crystal cell side]
The transparent protective films 23 and 33 located on the side far from the liquid crystal cell and the transparent protective films 24 and 34 located on the liquid crystal cell side are subjected to saponification treatment, corona treatment, plasma treatment prior to bonding with the polarizing film. It is possible to perform easy adhesion treatment such as.

  The thicknesses of these transparent protective films 23, 24, 33, and 34 are usually about 20 to 300 μm, preferably 20 to 100 μm, from the viewpoint of strength and handleability. When the thickness is within this range, the polarizing film is mechanically protected, and even when exposed to high temperature and high humidity, the polarizing film does not shrink and stable optical characteristics can be maintained.

[Adhesion between polarizing film and protective film]
An adhesive is usually used for bonding the polarizing film 21 and the transparent protective films 23 and 24 in the front polarizing plate 20 and bonding the polarizing film 31 and the transparent protective films 33 and 34 in the rear polarizing plate 30. . The adhesive layer for joining the polarizing film and the transparent protective film can have a thickness of about 0.01 to 30 μm, preferably 0.01 to 10 μm, and more preferably 0.05 to 5 μm. If the thickness of the adhesive layer is within this range, the adhesive layer having no practical problem can be obtained without floating or peeling between the transparent protective film and the polarizing film to be laminated. It is also effective to increase the wettability by subjecting the transparent protective film to easy adhesion treatment such as saponification treatment, corona discharge treatment, or plasma treatment prior to adhesion.

  In forming the adhesive layer, an appropriate adhesive can be used as appropriate according to the type and purpose of the adherend, and an anchor coating agent can be used as necessary. Examples of the adhesive include a solvent-type adhesive, an emulsion-type adhesive, a pressure-sensitive adhesive, a rewet-adhesive, a polycondensation-type adhesive, a solventless-type adhesive, a film-type adhesive, and a hot-melt-type adhesive. Can be mentioned.

  One preferred adhesive is an aqueous adhesive, that is, an adhesive component in which the adhesive component is dissolved or dispersed in water. Examples of adhesive components that can be dissolved in water include polyvinyl alcohol resins. An example of an adhesive component that can be dispersed in water is a urethane resin having a hydrophilic group. The water-based adhesive can be prepared by mixing such an adhesive component with water together with an additional additive added as necessary. Examples of commercially available polyvinyl alcohol resins that can be used as water-based adhesives include “KL-318” (trade name), which is a carboxyl group-modified polyvinyl alcohol sold by Kuraray Co., Ltd.

  The water-based adhesive can contain a crosslinking agent as necessary. Examples of the crosslinking agent include amine compounds, aldehyde compounds, methylol compounds, water-soluble epoxy resins, isocyanate compounds, and polyvalent metal salts. When a polyvinyl alcohol resin is used as an adhesive component, an aldehyde compound such as glyoxal, a methylol compound such as methylol melamine, a water-soluble epoxy resin, or the like is preferably used as a crosslinking agent. Here, the water-soluble epoxy resin is, for example, a polyamide obtained by reacting epichlorohydrin with a polyamide polyamine which is a reaction product of a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine and a dicarboxylic acid such as adipic acid. It can be an epoxy resin. Examples of commercially available water-soluble epoxy resins include “Smiles Resin 650 (30)” (trade name) sold by Sumika Chemtex Co., Ltd.

  A polarizing plate can be obtained by applying a water-based adhesive on the adhesive surface of the polarizing film and / or the transparent protective film, bonding them together, and then subjecting them to a drying treatment. A drying temperature can be about 60-100 degreeC, for example. After the drying treatment, curing at a temperature slightly higher than room temperature, for example, at a temperature of about 30 to 50 ° C. for about 1 to 10 days is preferable for further enhancing the adhesive force.

  Another preferred adhesive is a curable adhesive composition containing an epoxy compound that is cured by irradiation with active energy rays or heating. Here, the curable epoxy compound has at least two epoxy groups in the molecule. In this case, the adhesion between the polarizing film and the transparent protective film is performed by irradiating an active energy ray to the coating layer of the adhesive composition or heating it to apply a curable epoxy compound contained in the adhesive. It can be carried out by a curing method. Curing of the epoxy compound is generally performed by cationic polymerization of the epoxy compound. Further, from the viewpoint of productivity, this curing is preferably performed by irradiation with active energy rays.

  From the viewpoint of weather resistance, refractive index, cationic polymerizability, etc., the epoxy compound contained in the curable adhesive composition is preferably one that does not contain an aromatic ring in the molecule. Examples of epoxy compounds that do not contain an aromatic ring in the molecule include hydrogenated epoxy compounds, alicyclic epoxy compounds, and aliphatic epoxy compounds. The epoxy compound suitably used in such a curable adhesive composition is described in detail in, for example, Japanese Patent Application Laid-Open No. 2004-245925, but the outline is also described here.

  The hydrogenated epoxy compound is a glycidyl compound obtained by subjecting an aromatic polyhydroxy compound, which is a raw material of an aromatic epoxy compound, to a nuclear hydrogenated polyhydroxy compound obtained by selectively performing a nuclear hydrogenation reaction in the presence of a catalyst and under pressure. It can be etherified. Examples of the aromatic polyhydroxy compound that is a raw material of the aromatic epoxy compound include bisphenols such as bisphenol A, bispheel F and bisphenol S; Type resins; polyfunctional compounds such as tetrahydroxydiphenylmethane, tetrahydroxybenzophenone and polyvinylphenol. A glycidyl ether can be obtained by performing a nuclear hydrogenation reaction on such an aromatic polyhydroxy compound and reacting the resulting hydrogenated polyhydroxy compound with epichlorohydrin. Suitable hydrogenated epoxy compounds include hydrogenated glycidyl ether of bisphenol A.

  An alicyclic epoxy compound is a compound having at least one epoxy group bonded to an alicyclic ring in the molecule. Here, the “epoxy group bonded to the alicyclic ring” means a bridging oxygen atom —O— in the structure represented by the following formula, wherein m is an integer of 2 to 5.

A compound in which one or more hydrogen atoms in (CH ₂ ) _m in this formula are removed and bonded to another chemical structure can be an alicyclic epoxy compound. Further, one or more hydrogen atoms in (CH ₂ ) _m forming the alicyclic ring may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among alicyclic epoxy compounds, an epoxy compound having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (m = 4 in the above formula) has excellent adhesion. It is preferably used from the indication. Specific examples of the alicyclic epoxy compound are listed below. Here, the compound names are given first, and then the chemical formulas corresponding to each are shown, and the same reference numerals are given to the compound names and the chemical formulas corresponding thereto.

A: 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate,
B: 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate,
C: ethylene bis (3,4-epoxycyclohexanecarboxylate),
D: Bis (3,4-epoxycyclohexylmethyl) adipate,
E: bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate,
F: Diethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
G: ethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispiro [5.2.2.2.5.2] henicosane,
I: 3- (3,4-epoxycyclohexyl) -8,9-epoxy-1,5-dioxaspiro [5.5] undecane,
J: 4-vinylcyclohexene dioxide,
K: Limonene dioxide
L: bis (2,3-epoxycyclopentyl) ether,
M: Dicyclopentadiene dioxide and the like.

  The aliphatic epoxy compound can be a polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof. More specifically, diglycidyl ether of propylene glycol; diglycidyl ether of 1,4-butanediol; diglycidyl ether of 1,6-hexanediol; triglycidyl ether of glycerin; triglycidyl ether of trimethylolpropane; ethylene Polyglycidyl ether of polyether polyol (for example, diglycidyl ether of polyethylene glycol) obtained by adding alkylene oxide (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohol such as glycol, propylene glycol and glycerin It is done.

  In the curable adhesive composition, the epoxy compound may be used alone or in combination of two or more. Among these, the epoxy compound preferably includes an alicyclic epoxy compound having at least one epoxy group bonded to the alicyclic ring in the molecule.

  The epoxy compound used in the curable adhesive composition usually has an epoxy equivalent in the range of 30 to 3,000 g / equivalent, and this epoxy equivalent is preferably in the range of 50 to 1,500 g / equivalent. When an epoxy compound having an epoxy equivalent of less than 30 g / equivalent is used, there is a possibility that the flexibility of the polarizing plate after curing is lowered or the adhesive strength is lowered. On the other hand, in a compound having an epoxy equivalent exceeding 3,000 g / equivalent, compatibility with other components contained in the adhesive composition may be lowered.

  From the viewpoint of reactivity, cationic polymerization is preferably used as the curing reaction of the epoxy compound. For that purpose, it is preferable to mix | blend a cationic polymerization initiator with the curable adhesive composition containing an epoxy compound. The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays or electron beams, or heating, and initiates a polymerization reaction of epoxy groups. From the viewpoint of workability, it is preferable that the cationic polymerization initiator is provided with latency. Hereinafter, a cationic polymerization initiator that generates a cationic species or Lewis acid by irradiation of active energy rays and initiates a polymerization reaction of an epoxy group is referred to as a “photo cationic polymerization initiator”, and generates a cationic species or a Lewis acid by heat. The cationic polymerization initiator that initiates the polymerization reaction of the epoxy group is referred to as “thermal cationic polymerization initiator”.

  The method of curing the adhesive composition by irradiation with active energy rays using a cationic photopolymerization initiator enables curing at room temperature, reducing the need to consider the heat resistance of the polarizing film or distortion due to expansion, This is advantageous in that the transparent protective film and the polarizing film can be favorably bonded. In addition, since the cationic photopolymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an epoxy compound.

  Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts, and iron-allene complexes. The compounding quantity of a photocationic polymerization initiator is 0.5-20 weight part normally with respect to 100 weight part of epoxy compounds, Preferably it is 1 weight part or more, Preferably it is 15 weight part or less. When the amount of the cationic photopolymerization initiator is small, curing is insufficient, and the mechanical strength and adhesive strength of the cured product tend to decrease. On the other hand, when there are too many compounding quantities of a photocationic polymerization initiator, the ionic substance in hardened | cured material will increase, the hygroscopic property of hardened | cured material will become high, and durability performance may fall.

  When using a photocationic polymerization initiator, the curable adhesive composition may further contain a photosensitizer as necessary. By using a photosensitizer, the reactivity of cationic polymerization can be improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo compounds, diazo compounds, halogen compounds, and photoreducible dyes. When mix | blending a photosensitizer, it is preferable to make the quantity into the range of 0.1-20 weight part with respect to 100 weight part of curable adhesive compositions.

  On the other hand, examples of the thermal cationic polymerization initiator include benzylsulfonium salt, thiophenium salt, thioranium salt, benzylammonium, pyridinium salt, hydrazinium salt, carboxylic acid ester, sulfonic acid ester, and amine imide.

  The curable adhesive composition containing the epoxy compound is preferably cured by photocationic polymerization as described above, but can be cured by thermal cationic polymerization in the presence of the above-mentioned thermal cationic polymerization initiator. Cationic polymerization and thermal cationic polymerization can be used in combination. When photocationic polymerization and thermal cationic polymerization are used in combination, the curable adhesive composition preferably contains both a photocationic polymerization initiator and a thermal cationic polymerization initiator.

  The curable adhesive composition may further contain a compound that promotes cationic polymerization, such as an oxetane compound or a polyol compound. An oxetane compound is a compound having a 4-membered ring ether in the molecule. When mix | blending an oxetane compound, the quantity is 5 to 95 weight% normally in a curable adhesive composition, Preferably it is 5 to 50 weight%. The polyol compound may be an alkylene glycol or an oligomer thereof including ethylene glycol, hexamethylene glycol, polyethylene glycol and the like, a polyester polyol, a polycaprolactone polyol, a polycarbonate polyol, and the like. When a polyol compound is blended, the amount is usually 50% by weight or less, preferably 30% by weight or less in the curable adhesive composition.

  In addition, the curable adhesive composition may have other additives such as ion trapping agents, antioxidants, chain transfer agents, sensitizers, tackifiers, thermoplastic resins, fillers, as long as the adhesiveness is not impaired. Agents, flow modifiers, plasticizers, antifoaming agents, and the like. Examples of the ion trapping agent include inorganic compounds including powdered bismuth-based, antimony-based, magnesium-based, aluminum-based, calcium-based, titanium-based, and mixed systems thereof. Examples of the antioxidant include And hindered phenolic antioxidants.

  After applying the curable adhesive composition containing the epoxy compound to the adhesive surface of the polarizing film or the transparent protective film, or to the adhesive surface of both of them, it is bonded to the adhesive-coated surface and activated energy. The polarizing film and the transparent protective film can be bonded by curing the uncured adhesive layer by irradiating the wire or heating. Various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be adopted for the application of the adhesive.

  This curable adhesive composition can basically be used as a solvent-free adhesive that does not substantially contain a solvent, but each coating system has an optimum viscosity range, so that the viscosity is adjusted. For this purpose, a solvent may be contained. The solvent is preferably an organic solvent that dissolves each component including an epoxy compound well without degrading the optical performance of the polarizing film. For example, hydrocarbons typified by toluene, typified by ethyl acetate, etc. Esters can be used.

  When the adhesive composition is cured by irradiation with active energy rays, the above-mentioned various types of active energy rays can be used, but since the handling is easy and the amount of irradiation light is easy to control, ultraviolet rays are not emitted. Preferably used. Active energy rays such as ultraviolet irradiation intensity and dose do not affect various optical performance including polarization degree of polarizing film, and various optical performance including transparency and retardation characteristics of transparent protective film. Within a range, it is determined as appropriate so that moderate productivity is maintained.

  When the adhesive composition is cured by heat, it can be heated by a generally known method. Usually, heating is performed at a temperature higher than the temperature at which the thermal cationic polymerization initiator compounded in the curable adhesive composition generates cationic species and Lewis acid, and the specific heating temperature is, for example, about 50 to 200 ° C. .

[Adhesive layer]
In this invention, with reference to FIG.1 and FIG.2, in the front side polarizing plate 20, on the opposite side to the polarizing film 21 of the transparent protective film 24 bonded by the liquid crystal cell 10, and in the back side polarizing plate 30, Adhesive layers 51 and 52 are provided on the opposite side of the transparent protective film 34 bonded to the liquid crystal cell 10 from the polarizing film 31, respectively. These pressure-sensitive adhesive layers 51 and 52 may be any layer as long as they are excellent in optical transparency and exhibit pressure-sensitive adhesive properties including appropriate wettability, cohesiveness, adhesiveness, and the like, but are particularly excellent in durability and the like. Preferably used. As a pressure-sensitive adhesive suitable for forming the pressure-sensitive adhesive layers 51 and 52, for example, a pressure-sensitive adhesive made of an acrylic resin (also referred to as an acrylic pressure-sensitive adhesive) is exemplified. In the case of adopting the form shown in FIG. 2, an acrylic pressure-sensitive adhesive is also suitably used for the interlayer pressure-sensitive adhesive 40.

  The acrylic adhesive is mainly composed of (meth) acrylate esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. And a copolymer resin using two or more of these (meth) acrylic acid esters are preferably used. These resins are copolymerized with a polar monomer. Examples of polar monomers include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylamide, and 2-N, N-dimethylaminoethyl (meth). A polymerizable compound having a polar functional group such as a carboxyl group, a hydroxyl group, an amide group, an amino group, and an epoxy group, such as acrylate and glycidyl (meth) acrylate, is used. Furthermore, the pressure-sensitive adhesive usually contains a crosslinking agent together with an acrylic resin.

  Various other additives may be blended in the adhesive. Suitable additives include silane coupling agents and antistatic agents. A silane coupling agent is effective in increasing the adhesive strength with glass. Antistatic agents are effective in reducing or preventing the generation of static electricity. That is, when a polarizing plate is attached to a liquid crystal cell via an adhesive layer, the surface protective film (also called a separator) that has been covered and temporarily protected by covering the adhesive layer is peeled off and then attached to the liquid crystal cell. The static electricity generated when the surface protective film is peeled off causes alignment failure in the liquid crystal in the cell, which may cause display failure of the IPS mode liquid crystal display device. In order to reduce or prevent the generation of such static electricity, the addition of an antistatic agent is effective.

[Water absorption and water evaporation rate of polarizing plate]
In the present invention, from the first viewpoint, referring to FIG. 1 and FIG. 2, the moisture absorption amount A _f when the front side polarizing plate 20 including the adhesive layer 51 is humidified and the adhesive layer 52 are provided. a water absorption a _r when the back side polarizing plate 30 and humidification, together with less than 7 g / m ^2. By setting both the moisture absorption amounts after the humidification treatment within this range, when the backlight unit 70 is turned on, the temperature of the liquid crystal panel 60 rapidly increases due to the light supplied from the backlight unit 70, and the polarizing plate 20 , 30 is prevented from contracting when water is evaporated and contracted, and warping of the liquid crystal panel 60 is suppressed.

From a second standpoint, the water evaporation rate V _f of the front side polarizing plate 20 including the pressure-sensitive adhesive layer 51 and the water evaporation rate V _r of the back-side polarizing plate 30 including the pressure-sensitive adhesive layer 52 are both 5 g / m. and less than ² · hr. Even when the moisture evaporation rate of both is within this range, when the backlight unit 70 is turned on, the temperature of the liquid crystal panel 60 rapidly increases due to the light supplied from the backlight unit 70, and moisture from the polarizing plates 20 and 30. The contraction of the liquid crystal panel 60 is suppressed, and the contraction of the liquid crystal panel 60 is suppressed.

  Adjustment of the moisture absorption amount and moisture evaporation rate after the humidification treatment of the polarizing plate can be performed by selecting the protective films 23 and 33 located on the far side from the liquid crystal cell 10 of the polarizing plates 20 and 30. . That is, as described above, as the protective films 23 and 33, by using a polypropylene resin film, a polyethylene terephthalate resin film, or an acrylic resin film having low hygroscopicity, the moisture absorption amount after the above-mentioned humidification treatment or A polarizing plate satisfying the moisture evaporation rate is obtained.

[Backlight unit]
The backlight unit 70 includes at least a light source member for supplying light for display to the liquid crystal cell 10. This light source member is arranged in a form called a side light type composed of a light guide plate and a light source arranged on one side surface or two opposite side surfaces, or on a plurality of light sources and on the side (toward the liquid crystal cell 10). It is possible to use a type called a direct type composed of a light diffusing plate. In any form, the light reflecting layer is usually provided in the form of a sheet or a coating layer on the back surface (the side far from the liquid crystal cell 10) of the light source member. Further, one or more optical members such as a light collecting sheet and a diffusion film may be further arranged on the light emitting side of the light source member (the side facing the liquid crystal cell 10). The backlight unit 70 itself has the members described here, and can have any configuration employed in this field.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the examples, the parts and% representing the content or amount used are based on weight unless otherwise specified. Moreover, each physical property in the following examples was measured by the following method.

(1) Measurement of thickness The thickness was measured using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(2) Measurement of in-plane retardation and thickness direction retardation A phase difference meter “KOBRA-21ADH” based on the parallel Nicol rotation method manufactured by Oji Scientific Instruments Co., Ltd. was used at a wavelength of 590 nm at a temperature of 23 ° C. In-plane retardation and thickness direction retardation were measured.

(3) Measurement of water absorption of polarizing plate with pressure-sensitive adhesive A polarizing plate with pressure-sensitive adhesive cut to 95 mm x 95 mm was bonded to 100 mm x 100 mm soda glass on the pressure-sensitive adhesive side, and the initial weight in that state W ₁ (Unit: g) was measured. Next, the polarizing plate bonded to the soda glass was left in an environment of a temperature of 40 ° C. and a relative humidity of 95% for 96 hours, then taken out to a room temperature environment, and the weight W ₂ (unit: g) immediately after taking it out. Was measured. From these values, the water absorption amount A (g / m ² ) was converted into a size of 1,000 mm × 1,000 mm and obtained by the following formula.
A = (W ₂ −W ₁ ) / (0.095) ²

(4) Measurement of moisture evaporation rate of polarizing plate with pressure-sensitive adhesive A polarizing plate with pressure-sensitive adhesive cut to 95 mm × 95 mm was bonded to a 100 mm × 100 mm soda glass on the pressure-sensitive adhesive side, and in that state, the temperature was 40 ° C., After being left in an environment with a relative humidity of 95% for 96 hours, the sample was taken out into a room temperature environment, and the weight W ₃ (unit: g) immediately after taking out was measured. Next, this was left in an environment of a temperature of 50 ° C. and a relative humidity of 0% for 1 hour, then taken out to a room temperature environment, and the weight W ₄ (unit: g) immediately after taking out was measured. From these values, the water evaporation rate V (g / m ² · hr) was converted into a size of 1,000 mm × 1,000 mm and determined by the following formula.
V = (W ₃ −W ₄ ) / (0.095) ²

(5) Measurement of warping amount of liquid crystal panel A liquid crystal display device constituted by combining the liquid crystal panel 60 and the backlight unit 70 is left in an environment of a temperature of 40 ° C. and a relative humidity of 95% for 96 hours, and then taken out to a room temperature environment and back. The light was turned on and left for 1 hour. After that, as shown in FIG. 2, a thread 65 that connects from one corner of the casing constituting the liquid crystal panel 60 to a diagonal corner is stretched, and another thread 66 is stretched in the other diagonal direction. The vertical distance L from the reference line to the surface of the liquid crystal panel 60 was measured with a ruler at the center portion of the liquid crystal panel 60 using the yarns 65 and 66 as the reference line, and the amount of warpage was obtained.

[Reference Example 1] (Preparation of curable epoxy adhesive)
100 parts of bis (3,4-epoxycyclohexylmethyl) adipate, 25 parts of diglycidyl ether of hydrogenated bisphenol A, and 4,4′-bis (diphenylsulfonio) diphenyl sulfide bis (hexa) as a photocationic polymerization initiator After mixing 2.2 parts of (fluorophosphate), it was defoamed to prepare a curable epoxy adhesive. The cationic photopolymerization initiator was blended as a 50% propylene carbonate solution. The amount of 2.2 parts shown here is the amount of solids (photocation polymerization initiator itself) excluding propylene carbonate.

[Reference Example 2] (Preparation of aqueous adhesive)
3 parts of “KL-318” (trade name) which is a carboxyl group-modified polyvinyl alcohol obtained from Kuraray Co., Ltd. is dissolved in 100 parts of water, and the aqueous solution obtained from Sumika Chemtex Co., Ltd. is dissolved in the aqueous solution. A water-based adhesive was prepared by adding 1.5 parts of “Smilease Resin 650 (30)” (trade name, aqueous solution having a solid content concentration of 30%), which is a conductive polyamide epoxy resin.

[Production Example 1]
A 75 μm-thick polypropylene film prepared by corona treatment at a dose of 16.8 kJ / m ² on one side of a 28 μm-thick polarizing film with iodine adsorbed and oriented on polyvinyl alcohol was prepared in Reference Example 1. Pasted through the cured curable epoxy adhesive, and the other surface of the polarizing film was subjected to corona treatment at an irradiation dose of 16.8 kJ / m ² and a 40 μm thick cyclic olefin resin film [Nippon Zeon ( In-plane retardation 2.1 nm, thickness direction retardation 2.8 nm] was bonded via the same curable epoxy adhesive. Next, using an ultraviolet irradiation device (the lamp is “Fusion D lamp”), the ultraviolet rays are irradiated from the cyclic olefin resin film side with an integrated light quantity of 1,000 mJ / cm ² , and then left at room temperature for 1 hour to be a polarizing plate. Was made. Further, the surface of the cyclic olefin-based resin film was subjected to corona treatment at an irradiation amount of 16.8 kJ / m ² , and then an acrylic pressure-sensitive adhesive sheet was bonded to the corona-treated surface to obtain a polypropylene film / polarizing film / circular. The polarizing plate 1 with an adhesive which consists of a layer structure of an olefin resin film / adhesive was produced. The obtained polarizing plate with the pressure-sensitive adhesive had a good appearance with no film floating or peeling, no bubbles and the like. It was 2.6 g / m < ² > when the water absorption A of this polarizing plate 1 with an adhesive was measured by the method shown previously. Further, the water evaporation rate V of the polarizing plate 1 with the pressure-sensitive adhesive was measured by the method described above, and it was 0.4 g / m ² · hr.

[Production Example 2]
The 75 μm-thick polypropylene film subjected to corona treatment in Production Example 1 was changed to a 38 μm-thick uniaxially stretched polyethylene terephthalate film subjected to corona treatment at an irradiation dose of 16.8 kJ / m ² , and subjected to corona treatment. The 40 μm-thick cyclic olefin-based resin film was subjected to corona treatment at an irradiation dose of 16.8 kJ / m ² and a 40 μm-thick triacetylcellulose film [“KC4UEW” obtained from Konica Minolta Opto Corporation, In the same manner as in Production Example 1, except that the in-plane retardation is 0.7 nm and the thickness direction retardation is 0.1 nm, the layer structure is polyethylene terephthalate film / polarizing film / triacetyl cellulose film / adhesive. A polarizing plate 2 with an adhesive was prepared. The obtained polarizing plate with the pressure-sensitive adhesive had a good appearance with no film floating or peeling, no bubbles and the like. It was 6.6 g / m < ² > when the water absorption amount A of this polarizing plate 2 with an adhesive was measured by the method shown previously. Further, the water evaporation rate V of the polarizing plate 2 with the pressure-sensitive adhesive was measured by the method described above, and it was 1.5 g / m ² · hr.

[Production Example 3]
On one side of the same polarizing film used in Production Example 1, a saponified 80 μm thick triacetyl cellulose film [“KC8UX” obtained from Konica Minolta Opto Co., Ltd.] was used as a reference example. Bonded via the water-based adhesive prepared in Step 2, the other surface of the polarizing film was saponified 40 μm thick triacetyl cellulose film [KC4UEW obtained from Konica Minolta Opto Co., Ltd. "In-plane retardation 0.7 nm, thickness direction retardation -0.1 nm" was bonded through the same aqueous adhesive, and then dried at 80 ° C for 5 minutes to prepare a polarizing plate. Further, the surface of the 40 μm thick triacetyl cellulose film was subjected to corona treatment at an irradiation amount of 16.8 kJ / m ² , and then an acrylic pressure-sensitive adhesive sheet was bonded to the corona treated surface to obtain an 80 μm thick triacetyl cellulose film. / Polarized film / 40 μm thick triacetyl cellulose film / Adhesive polarizing plate 3 having a layer structure of adhesive was produced. The obtained polarizing plate with pressure-sensitive adhesive also had a good appearance with no film lifting or peeling, no bubbles, etc. It was 8.5 g / m < ² > when the water absorption A of this polarizing plate 3 with an adhesive was measured by the method shown previously. Further, the water evaporation rate V of the pressure-sensitive adhesive-attached polarizing plate 2 was measured by the method described above, and found to be 9.0 g / m ² · hr.

[Example 1]
(Cutting polarizing plates with adhesive)
The pressure-sensitive adhesive polarizing plate 1 having a layer structure of polypropylene film / polarizing film / cyclic olefin-based resin film / adhesive produced in Production Example 1 is a 32 type size so that its absorption axis is parallel to the long side [ The front side (viewing side) polarizing plate 20 of the liquid crystal cell 10 was cut into a diagonal of 32 inches (about 81 cm) and a width of about 71 cm × length of about 40 cm]. Similarly, the polarizing plate 1 with pressure-sensitive adhesive comprising the layer structure of polypropylene film / polarizing film / cyclic olefin resin film / pressure-sensitive adhesive produced in Production Example 1 is above so that its absorption axis is parallel to the short side. The back-side (backlight side) polarizing plate 30 of the liquid crystal cell 10 was cut into the same 32 type size. These polarizing plates showed good handling properties during handling.

(Production of liquid crystal display device)
Disassemble the Panasonic IPS mode wide 32 "LCD TV" VIERA "(model number: VIERA TH-L32X1) [diagonal 32 inches (approx. 81cm) width 71cm x height 40cm] The polarizing plate 1 with the adhesive having the absorption axis cut above instead of the original polarizing plate is parallel to the long side as the front side polarizing plate 20, and the absorption axis cut above is short. The polarizing plate 1 with an adhesive parallel to the side was bonded to the liquid crystal cell as the back side polarizing plate 30 of the liquid crystal cell 10 to prepare a liquid crystal panel 60. The front-side polarizing plate 20 and the back-side polarizing plate 30 have their absorption axes orthogonal to each other, and the absorption axis of the front-side polarizing plate 20 is the orientation of the liquid crystal molecules in the liquid crystal cell 10 when no voltage is applied (black display). It is parallel to the direction. This liquid crystal panel 60 was combined with the original backlight unit 70 to assemble a liquid crystal display device. The liquid crystal display device was allowed to stand for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95%, then taken out to a room temperature environment, and the amount of warpage of the liquid crystal panel 60 was measured one hour after the backlight 70 was turned on. It was 0.3 mm, and visual display unevenness was not observed.

[Example 2]
As the front-side polarizing plate 20 and the back-side polarizing plate 30, the pressure-sensitive adhesive polarizing plate 2 having a layer configuration of polyethylene terephthalate film / polarizing film / triacetyl cellulose film / adhesive prepared in Production Example 2 was used. A liquid crystal panel 60 was produced in the same manner as in Example 1 except for the above. This liquid crystal panel 60 was combined with the original backlight unit 70 to assemble a liquid crystal display device. This liquid crystal display device was allowed to stand for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95%, then taken out to a room temperature environment, and the amount of warpage of the liquid crystal panel 60 was measured 1 hour after turning on the backlight. It was 0.2 mm, and there was no visual display unevenness.

[Comparative Example 1]
As the front-side polarizing plate 20 and the back-side polarizing plate 30, the polarizing plate with pressure-sensitive adhesive comprising a layer structure of 80 μm-thick triacetyl cellulose film / polarizing film / 40 μm-thick triacetyl cellulose film / pressure-sensitive adhesive prepared in Production Example 3 A liquid crystal panel 60 was produced in the same manner as in Example 1 except that 3 was used. This liquid crystal panel 60 was combined with the original backlight unit 70 to assemble a liquid crystal display device. This liquid crystal display device was allowed to stand for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95%, then taken out to a room temperature environment, and the amount of warpage of the liquid crystal panel 60 was measured 1 hour after turning on the backlight. It was 0.7 mm, and display unevenness was visually observed.

  Table 1 summarizes the configurations of the front-side and back-side polarizing plates and the test results in the above Examples and Comparative Examples.

10 ... Liquid crystal cell,
11, 12 ... cell substrate,
15 …… Liquid crystal layer
20 …… Front-side polarizing plate,
21 …… Polarizing film,
23, 24 ... Transparent protective film,
30 …… Back polarizing plate,
31: Polarizing film,
33, 34 ... Transparent protective film,
36 …… First retardation film,
37 …… Second retardation film,
38 …… Core layer,
39 …… Skin layer,
40 …… Interlayer adhesive,
51, 52 …… Adhesive layer,
60 …… LCD panel,
70 …… Backlight unit,
65, 66 ... Yarns stretched diagonally to measure the amount of warpage of the liquid crystal panel,
L: The amount of warpage of the liquid crystal panel.

Claims (9)

A liquid crystal cell having two cell substrates and a liquid crystal layer sandwiched therebetween,
A front-side polarizing plate laminated via a pressure-sensitive adhesive layer on the viewing side of the liquid crystal cell,
A back side polarizing plate laminated via an adhesive layer on the side opposite to the viewing side of the liquid crystal cell, and a backlight unit disposed outside the back side polarizing plate,
The front side polarizing plate and the back side polarizing plate each have a polarizing film and transparent protective films disposed on both sides thereof, and
Moisture evaporation rate of the front-side polarizing plate provided with the pressure-sensitive adhesive layer when it is allowed to stand for 96 hours in an environment at a temperature of 40 ° C. and a relative humidity of 95% and then left in an environment at a temperature of 50 ° C. and a relative humidity of 0% And the moisture content of the back-side polarizing plate provided with the pressure-sensitive adhesive layer when left in an environment at a temperature of 40 ° C. and a relative humidity of 95% for 96 hours and then in an environment at a temperature of 50 ° C. and a relative humidity of 0% for 1 hour. A liquid crystal display device characterized in that both evaporation rates are less than 5 g / m ² · hr.   The liquid crystal display device according to claim 1, wherein the transparent protective film located on a side far from the liquid crystal cell of the front side polarizing plate and the back side polarizing plate is made of a polypropylene resin, a polyethylene terephthalate resin, or an acrylic resin.   3. The liquid crystal display device according to claim 1, wherein the transparent protective film positioned on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate has a thickness direction retardation in a range of −10 to +10 nm.   Of the transparent protective films located on the liquid crystal cell side of each of the front side polarizing plate and the rear side polarizing plate, one has a thickness direction retardation in the range of −10 to +10 nm, and the other has in-plane retardation. When the refractive index in the slow axis direction in the film plane is nx, the refractive index in the fast axis direction in the film plane is ny, and the refractive index in the film thickness direction is nz, 3. The liquid crystal display device according to claim 1, wherein the Nz coefficient defined by the formula (nx-nz) / (nx-ny) is in the range of 0.1 to 0.7. Of the transparent protective films located on the liquid crystal cell side of each of the front side polarizing plate and the back side polarizing plate,
One has a thickness direction retardation in the range of −10 to +10 nm,
The other is located on the polarizing film side constituting the polarizing plate, the first retardation film made of polyolefin resin, and the styrenic resin located on the adhesive layer side of the first retardation film. A laminated body of a second retardation film having a three-layer structure comprising a core layer made of the above and a skin layer made of a (meth) acrylic resin composition containing rubber particles laminated on both surfaces of the core layer. The liquid crystal display device according to claim 1 or 2. The first retardation film has an in-plane retardation in the range of 30 to 150 nm,
When the refractive index in the slow axis direction in the film plane is nx, the refractive index in the fast axis direction in the film plane is ny, and the refractive index in the film thickness direction is nz, the formula (nx−nz) / ( Nx coefficient defined by nx−ny) is in the range of more than 1 and less than 2.
The second retardation film has an in-plane retardation in the range of 20 to 120 nm,
6. The liquid crystal display device according to claim 5, wherein the Nz coefficient defined by the above formula is in the range of more than −2 and less than −0.5.   Each of the front-side polarizing plate and the rear-side polarizing plate is bonded via a water-based adhesive containing a polyvinyl alcohol resin and a water-soluble epoxy resin to a polarizing film and a transparent protective film disposed on both surfaces thereof. The liquid crystal display device according to claim 1.   Each of the front side polarizing plate and the rear side polarizing plate has a polarizing film and a transparent protective film disposed on both sides of the polarizing plate and a curable adhesive composition containing an epoxy compound that is cured by irradiation with active energy rays. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is bonded together.   The liquid crystal display device according to claim 8, wherein the epoxy compound includes an epoxy compound having at least one epoxy group bonded to an alicyclic ring in a molecule.

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