JP2012133301A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device less in warp of a liquid crystal panel and display unevenness even after placed in humid hot environment.SOLUTION: The liquid crystal display device comprises: two cell substrates 11 and 12; a liquid crystal cell 10 with a liquid crystal layer 15 sandwiched between them; a front side polarizer 20 laid on the visible side of the liquid crystal cell 10 via an adhesive layer 51; a back side polarizer 30 laid opposite to the visible side of the liquid crystal cell 10 via an adhesive layer 52; and a back light unit 70 arranged outside the back side polarizer 30. The front side polarizer 20 and the back side polarizer 30 respectively have polarization films 21 and 31 and transparent protective films 23 and 24, and 33 and 34 arranged on both sides of each of the corresponding films. The ratio V/Vof the moisture evaporation speed Vof the front side polarizer 20 having the adhesive layer 51 to the moisture evaporation speed Vof the back side polarizer 30 having the adhesive layer 52 is in the range of 0.01 or more to less than 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, taking advantage of its low power consumption, low voltage operation, light weight and thinness, liquid crystal displays have rapidly spread as information display devices such as mobile phones, personal digital assistants, computer monitors, and televisions. Have been doing. With the development of liquid crystal technology, liquid crystal displays in various modes have been proposed, and problems with liquid crystal displays 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. Due to such warpage of the liquid crystal panel, display unevenness occurs in 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 this object, the present inventors have found that the front-side polarizing plate located on the viewing side of the liquid crystal cell when the backlight is turned on after being placed in a humid heat environment and its By adjusting the water evaporation rate of each polarizing plate by the heat of the backlight between the opposite side polarizing plate located on the opposite side, it is possible to control the warpage of the liquid crystal panel and to be effective in improving display unevenness I found it. The present invention has been made based on such knowledge.

That is, according to the present invention, a liquid crystal cell having two cell substrates and a liquid crystal layer sandwiched therebetween, a front side polarizing plate laminated on the viewing side of the liquid crystal cell via an adhesive layer, the liquid crystal The back side polarizing plate laminated | stacked through the adhesive layer on the opposite side to the visual recognition side of a cell, and the backlight unit arrange | positioned on the outer side of the back side polarizing plate, Said front side polarizing plate and back side Each polarizing plate has a polarizing film and transparent protective films disposed on both sides thereof, and a water evaporation rate V _f of the front side polarizing plate provided with the pressure-sensitive adhesive layer and a back-side polarizing plate provided with the pressure-sensitive adhesive layer A liquid crystal display device in which the ratio V _f / V _r to the water evaporation rate V _r is in the range of 0.01 or more and less than 1 is provided.

  In this liquid crystal display device, the transparent protective film located on the far side from the liquid crystal cell of the front side polarizing plate is preferably composed of a polypropylene resin, a polyethylene terephthalate resin, or an acrylic resin. Moreover, it is preferable to comprise the transparent protective film located in the side far from the liquid crystal cell of a back side polarizing plate with a cellulose resin.

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.

  Furthermore, 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 sides thereof, at least one of the front side polarizing plate and the back side polarizing plate is The polarizing film and the transparent protective film disposed on both surfaces thereof are bonded via an aqueous adhesive containing a polyvinyl alcohol resin and a water-soluble epoxy resin. Further, in another preferred form from the viewpoint of adhesion between the polarizing film constituting the polarizing plate and the transparent protective film disposed on both sides thereof, at least one of the front side polarizing plate and the back side polarizing plate is a polarizing film and its The transparent protective film arrange | positioned on both surfaces is bonded through the curable adhesive composition containing the epoxy compound hardened | cured by irradiation of an active energy ray. 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.

  According to the present invention, it is possible to provide a liquid crystal display device in which the warp of the liquid crystal panel is small even after being placed in a humid heat environment, and 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, when the moisture evaporation rate of the front side polarizing plate 20 including the adhesive layer 51 is V _f and the moisture evaporation rate of the back side polarizing plate 30 including the adhesive layer 52 is V _r , The ratio V _f / V _{r of} both is in the range of 0.01 or more and less than 1. In this specification, the temperature at which the water evaporation rate is measured is basically 50 ° C. The relationship between the water evaporation rate V _f of the front side polarizing plate 20 and the water evaporation rate V _r of the back side polarizing plate 30 corresponds to both satisfying the following expression (1).
0.01 ≦ V _f / V _r <1 (1)

Here, the moisture evaporation rate 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 Am 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 the weight W ₁ (unit: g) is measured. This is left for 1 hour in an environment of a temperature of 50 ° C. and a relative humidity of 0%, then taken out to a room temperature environment, and the weight W ₂ (unit: g) immediately after taking out is measured. From these values, the water evaporation rate C (g / m ² · hr) is obtained by the following equation (2).
C = (W ₁ −W ₂ ) / A (2)

  The conditions for absorbing moisture to determine the moisture evaporation rate are arbitrary, but, for example, as shown in the examples described later, a treatment that is allowed to stand for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95% should be adopted. Can do.

Thus, the moisture evaporation rate V _f of the front side polarizing plate 20 is set to a value smaller than the moisture evaporation rate V _r of the back side polarizing plate 30, and the back side polarizing plate 30 is made to have a moisture content compared to the front side polarizing plate 20. It is important to configure it with a high evaporation rate. 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.

  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.

[Visible side transparent protective film on front polarizing plate]
The transparent protective film 23 located on the side far from the liquid crystal cell 10 of the front polarizing plate 20, that is, on the viewing side, can be preferably composed of a polypropylene resin, a polyethylene terephthalate resin, or an acrylic resin. 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. In addition, 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.

  Polyethylene terephthalate resin can be produced by directly polycondensing terephthalic acid and ethylene glycol (and other dicarboxylic acids or other diols as required), dialkyl esters of terephthalic acid and ethylene glycol (and as required) A method of transesterification with a dialkyl ester of another dicarboxylic acid or other diol), followed by polycondensation, ethylene glycol ester of terephthalic acid (and other dicarboxylic acid if necessary) (and if necessary) For example, a method of polycondensation of other diol esters may be employed.

  For each polymerization reaction, a polymerization catalyst made of an antimony, titanium, germanium, or aluminum compound, or a polymerization catalyst made of a composite compound thereof can be used.

  The conditions for this polymerization reaction may be appropriately selected according to the monomer, catalyst, reaction apparatus, and desired resin physical properties to be used. For example, the reaction temperature is usually in the range of about 150 to 300 ° C., preferably in the range of about 200 to 300 ° C., and more preferably in the range of about 260 to 300 ° C. The pressure is usually in the range from atmospheric pressure to about 2.7 Pa, but it is preferable that the pressure be reduced in the latter half of the reaction. The polymerization reaction proceeds by devolatilization of elimination reaction products such as alcohol and water by stirring under such high temperature and high reduced pressure conditions.

  In addition, the polymerization apparatus may be completed with a single reaction tank, or may be a combination of a plurality of reaction tanks. In the latter case, the reactant is usually polymerized while being transferred between the reaction vessels according to the degree of polymerization. Further, a method in which a horizontal reaction apparatus is provided in the latter half of the polymerization and devolatilized while heating and kneading can be employed.

  After the polymerization is completed, the resin is extracted from the reaction vessel or the horizontal reactor in a molten state, and then cooled by a cooling drum, a cooling belt, or the like, and is crushed in the form of flakes or introduced into an extruder to form a string. After being extruded, it is obtained in the form of a cut pellet.

  Furthermore, the molecular weight can be improved or the low molecular weight component can be reduced by performing solid phase polymerization as necessary. The low molecular weight component that can be contained in the polyethylene terephthalate resin includes a cyclic trimer component, and the content of the cyclic trimer component in the resin is particularly preferably 5,000 ppm or less, More preferably, it is 3,000 ppm or less. If the cyclic trimer component exceeds 5000 ppm in the resin, the optical properties of the film may be adversely affected.

  The molecular weight of the polyethylene terephthalate resin is usually 0.45 to 1 dL / wt when dissolved in a 50/50 mixed solvent of phenol and tetrachloroethane and expressed in terms of intrinsic viscosity measured at 30 ° C. g, preferably 0.5 to 1 dL / g, more preferably 0.52 to 0.8 dL / g. When this intrinsic viscosity is less than 0.45 dL / g, productivity at the time of film production may be lowered, or the mechanical strength of the film may be lowered. Moreover, when this intrinsic viscosity exceeds 1 dL / g, the melt extrusion stability of the polymer in film manufacture may be reduced.

  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 later. 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.

  The polyethylene terephthalate-based resin thus obtained can be formed into a film and stretched to obtain a transparent and homogeneous film with 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 molten 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. You may use both together as needed.

  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.

  Further, 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 particulate filler as an anti-blocking agent and a non-compounded pellet are prepared, and each is supplied to the same die from a different extruder, and a filler-containing resin / non-compounded resin / filler-containing resin is prepared. A film composed of two types and three layers 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. This is because, when the draw ratio is less than 1.1 times, the mechanical strength of the stretched polyethylene terephthalate film tends to be insufficient. Moreover, when this draw ratio exceeds 6 times, the strength in the transverse direction may be practically insufficient. 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 a 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. Moreover, heat processing time is 1 to 600 second normally, Preferably it is 1 to 300 second, More preferably, it is 1 to 60 second. 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. 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 performed again or relaxation treatment is performed in order to relieve distortion of the orientation main axis as represented 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 °. When the maximum value of the distortion of the orientation main axis exceeds 45 °, the optical characteristics may be non-uniform between the sheets when a polarizing plate is formed in a subsequent process to form a sheet.

  In addition, a extending | stretching direction here means the direction with a large draw ratio among longitudinal stretching and horizontal stretching. In the biaxial stretching of the polyethylene terephthalate-based resin film, the transverse stretching ratio is usually slightly larger than the longitudinal stretching ratio. In this case, the stretching direction is a direction orthogonal to the longitudinal direction of the film, That is, it refers to the width direction. Since uniaxial stretching is usually stretched in the transverse direction, the stretching direction in this case also refers to the direction perpendicular to the longitudinal direction of the film, that is, 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 above 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 sold by Oji Scientific Instruments “ It can be measured using “MOA” (trade name).

  The stretched polyethylene terephthalate resin film can be easily obtained as a commercial product. For example, “Diafoil”, “Hostafan” and “Fusion” sold by Mitsubishi Plastics, Inc. under the trade name, respectively. "Teijin Tetron Film", "Melinex", "Mylar" and "Teflex" sold by Teijin DuPont Films, Ltd., "Toyobo Ester Film", "Toyobo" sold by Toyobo Co., Ltd. "Espet Film", "Cosmo Shine" and "Chrisper", "Lumirror" sold by Toray Film Processing Co., Ltd., "Embron" and "Emblet" sold by Unitika Ltd., SK・ "Skyroll" sold by Sea Co., Ltd. I le, etc. ", Ltd. sold by Rui through" Rui communication polyester film ", sold by Futamura Chemical Co." Taiko polyester film ". 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. The polymer having a methyl methacrylate unit of 100% by weight is a methyl methacrylate homopolymer obtained by polymerizing methyl methacrylate alone.

  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.

  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. Among them, ethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate and neopentyl glycol di (meth) acrylate are preferably used when copolymerizing a polyfunctional monomer.

  The acrylic resin containing methyl methacrylate as a main component may be further modified by a reaction between functional groups derived from monomers. 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.

  Acrylic resins based on methyl methacrylate can be easily obtained as commercial products. For example, “Sumipex”, Mitsubishi Rayon (trade name) sold by Sumitomo Chemical Co., Ltd. "Alippet" sold by Asahi Kasei Co., Ltd., "Delpet" sold by Asahi Kasei Corporation, "Parapet" sold by Kuraray Co., Ltd., and sold by Nippon Shokubai Co., Ltd. Such as “Acuribua”.

<Other explanation about the visible side transparent protective film of the front side polarizing plate>
The polypropylene resin film, polyethylene terephthalate resin film, or acrylic resin film used as the transparent protective film 23 located on the far side from the liquid crystal cell 10 of the front polarizing plate 20, that is, on the viewing side, has an antiglare property (haze). Can be granted. In order to impart antiglare properties, for example, a method in which inorganic fine particles or organic fine particles are mixed into the raw material resin to form a film, and at the time of forming a film, by multi-layer extrusion, one is from a resin layer in which fine particles are mixed. The other is a method of forming a two-layer film consisting of a resin layer in which fine particles are not mixed, or forming a three-layer film with the resin layer mixed with fine particles on the outside, inorganic fine particles or organic fine particles on one side of the film For example, a method of coating a coating solution obtained by mixing a curable binder resin with a curable binder resin and curing the binder resin to provide an antiglare layer may be employed.

  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.

  It is preferable that the protective film to which anti-glare property is imparted 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 using an optically transparent adhesive so that the antiglare property-imparting surface is the surface. Is preferably used.

  These protective films can be provided with functional layers such as a conductive layer, a hard coat layer, and a low reflection layer. Moreover, as a binder resin which comprises a transparent protective film, the resin composition which has these functions can be selected, and the film itself can also have any one or several of these functions. 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, it is preferable to provide an easily bonding layer in the bonding surface to a polarizing film especially.

  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.

  If said functional layer is a polypropylene resin film or an acrylic resin film, it can be directly formed on the formed film, for example. On the other hand, if it is a stretched polyethylene terephthalate-based resin film, for example, a method of forming in a film after all stretching steps, a method of forming between the longitudinal stretching and the lateral stretching step, for example, during stretching of the resin film, A method of forming the film immediately before or after being bonded to the polarizing film can be employed. Among these, in the case of a polyethylene terephthalate resin, a method in which a functional layer is formed after longitudinal stretching and then lateral stretching is preferably employed from the viewpoint of productivity.

[Transparent protective film located on the far side from the liquid crystal cell of the rear polarizing plate]
The transparent protective film 33 located on the side farther from the liquid crystal cell 10 of the back side polarizing plate 30 is preferably composed of a cellulose resin film. The cellulose resin film is a film made of a cellulose part or a completely esterified product. Examples thereof include films made of cellulose acetate, propionate, butyrate, mixed esters thereof, and the like. Of these, a triacetyl cellulose film, a diacetyl cellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film, and the like are preferably used.

  Cellulosic resin films can be easily obtained from commercial products. For example, “Fujitac TD” sold by Fuji Film Co., Ltd. and Konica Minolta Opto Co., Ltd. “Konica Minolta TAC Film KC” and the like.

[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 chain polyolefin resin or a cyclic polyolefin resin is preferably used.

  The cyclic polyolefin resin referred to here is obtained by polymerizing a cyclic olefin monomer such as norbornene and other cyclopentadiene derivatives in the presence of a catalyst. The cyclic olefin monomer is subjected to ring-opening metathesis polymerization. If it is a resin, a resin in which unsaturated bonds are substantially eliminated by the subsequent hydrogenation reaction is preferable. When such a cyclic polyolefin-based resin is used, a transparent protective film having a predetermined retardation value described later can be easily obtained.

  Examples of the cyclic polyolefin resin include ring-opening metathesis polymerization using cyclopentadiene and olefins or (meth) acrylic acid or esters thereof as a monomer with norbornene or a derivative thereof obtained by Diels-Alder reaction. 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; at least two monomers selected from norbornene, tetracyclododecene, their derivatives, and other cyclic olefin monomers are similarly copolymerized by ring-opening metathesis, followed by Resins obtained by hydrogenation; resins obtained by addition copolymerization of aromatic compounds having chain olefins and / or vinyl groups with cyclic olefins such as norbornene, tetracyclododecene, or derivatives thereof It is done.

  As the cyclic polyolefin-based resin, a commercially available product can be easily obtained. Examples of commercial products are “TOPAS” produced by TOPAS ADVANCED POLYMERS GmbH under the trade name, and sold in Japan by Polyplastics Co., Ltd. “Arton” from JSR Co., Ltd. "Zeonor" and "Zeonex" sold by Nippon Zeon Co., Ltd., and "Appel" sold by Mitsui Chemicals.

  Typical examples of the chain polyolefin 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 a method for forming a film from a cellulose resin, a polyolefin resin, or the like, a method corresponding to each resin may be appropriately selected. For example, a resin dissolved in a solvent is cast on a metal band or drum, and the solvent is dried to remove the solvent 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.

  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 represented by the following formula (3). . The in-plane retardation Re is a value obtained by multiplying the in-plane refractive index difference by the film thickness, and is represented by the following formula (4).

Rth = _{[(n x + n y) /} 2-n z ] × d (3)
_{Re = (n x -n y)} × d (4)

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 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 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 _{(5), 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) (5)

  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.

  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.

  Among the water-based adhesives, those containing a polyvinyl alcohol resin and a water-soluble epoxy resin are preferable.

  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. Prior to adhesion, it is also effective to give the transparent protective film an easy adhesion treatment such as a saponification treatment, a corona discharge treatment, or a plasma treatment to enhance wettability. 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, bisphenol F, and bisphenol S; phenol novolac resins, cresol novolac resins, and hydroxybenzaldehyde phenol novolac resins. And novolak type resins; polyhydroxy 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. The “epoxy group bonded to the alicyclic ring” means a bridged oxygen atom —O— in the structure represented by the following formula, and 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 [5.2.2.5.2.2] 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 Can be mentioned.

  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 or heating with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and initiates an epoxy group polymerization reaction. 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 blending amount of the cationic photopolymerization initiator is less than 0.5 parts by weight with respect to 100 parts by weight of the epoxy compound, curing becomes insufficient, and the mechanical strength and adhesive strength of the cured product tend to decrease. On the other hand, when the blending amount of the cationic photopolymerization initiator exceeds 20 parts by weight with respect to 100 parts by weight of the epoxy compound, the ionic substance in the cured product increases, resulting in an increase in the hygroscopic property of the cured product and durability performance. May be reduced.

  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 alkylene glycol including ethylene glycol, hexamethylene glycol, polyethylene glycol or the like, or an oligomer thereof, polyester polyol, polycaprolactone polyol, 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. As an adhesive coating method, for example, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be adopted.

  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. .

  The bonding of the polarizing film 21 and the transparent protective films 23 and 24 in the front polarizing plate 20 and the bonding of the polarizing film 31 and the transparent protective films 33 and 34 in the rear polarizing plate 30 have been described so far. A curable adhesive composition containing an aqueous adhesive or an epoxy compound that is cured by irradiation with active energy rays can be used. The adhesive used for the front side polarizing plate 20 and the adhesive used for the back side polarizing plate 30 may be the same or different. For example, one polarizing plate uses a water-based adhesive to join a polarizing film and transparent protective films on both sides thereof, and the other polarizing plate contains a curable composition containing an epoxy compound that is cured by irradiation with active energy rays. A form in which the polarizing film and the transparent protective films on both sides thereof are bonded using the adhesive composition is also possible. The adhesive for joining the polarizing film on one polarizing plate and the transparent protective film on both sides thereof may be the same or different, but the same adhesive is used in one polarizing plate to simplify the manufacturing process. It is preferable when making it.

[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) can be cited. 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.

[Moisture evaporation rate of polarizing plate]
In the present invention, referring to FIGS. 1 and 2, the moisture 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 described. The ratio V _f / V _r to the range of 0.01 or more and less than 1. By setting the relationship between the moisture evaporation rates of the two in 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 plates 20 and 30. Therefore, the balance when the moisture evaporates and contracts is improved, and the warpage of the liquid crystal panel 60 is suppressed.

  The adjustment of the water evaporation rate 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. By using a polypropylene resin film, a polyethylene terephthalate resin film, or an acrylic resin film having a low moisture permeability for the front polarizing plate 20, and using a cellulose resin film having a high moisture permeability for the back polarizing plate 30, A liquid crystal display device satisfying the moisture evaporation rate relationship can be 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. In addition, 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:
In-plane retardation and thickness direction retardation at a wavelength of 590 nm were measured at a temperature of 23 ° C. using a phase difference meter “KOBRA-21ADH” based on the parallel Nicol rotation method manufactured by Oji Scientific Instruments.

(3) Measurement of moisture evaporation rate:
The adhesive-attached polarizing plate cut to 95 mm × 95 mm was bonded to a 100 mm × 100 mm soda glass plate on the adhesive side. Next, the polarizing plate bonded to this glass plate was allowed to stand for 96 hours in an environment of a temperature of 40 ° C. and a relative humidity of 95% for moisture absorption, then taken out to a room temperature environment, and the weight W ₁ (unit) immediately after removal. : G) was measured. Furthermore, the polarizing plate after being bonded to the glass plate and absorbing moisture by placing it in a moist heat environment is left in an environment at a temperature of 50 ° C. and a relative humidity of 0% for 1 hour, and then taken out to a room temperature environment. The weight W ₂ (unit: g) was measured. From these values, the water evaporation rate C (g / m ² · hr) was determined by the following equation.
C = (W ₁ −W ₂ ) / (0.095) ²

(4) Measurement of the amount of warpage of the 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, 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.

(5) Measurement of in-plane brightness difference of liquid crystal panel:
A liquid crystal display device constituted by combining the liquid crystal panel 60 and the backlight unit 70 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, turned on the backlight, and left for 1 hour. . Thereafter, the in-plane of the liquid crystal panel 60 is divided into a lattice shape so that 17 points can be measured in the short side direction and 31 points in the long side direction, and a total of 527 points are analyzed for luminance / color unevenness manufactured by I-System Co., Ltd. The luminance was measured using the device “EyeScale-3W”, and the difference between the maximum value and the minimum value was defined as the in-plane luminance difference.

[Reference Example 1] (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.

[Reference Example 2] (Preparation of adhesive comprising curable epoxy resin composition)
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 (hexafluorophosphate as a photocationic polymerization initiator ) 2.2 parts were mixed and defoamed to prepare an adhesive composed of a curable epoxy resin composition. 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 3] (Preparation of polarizing plate 1 with adhesive)
A dose of 16.8 kJ / m ^{2 is} applied to one side of a polarizing film having a thickness of 28 μm in which iodine is adsorbed and oriented on polyvinyl alcohol via an adhesive made of the curable epoxy resin composition prepared in Reference Example ^2. A uniaxially stretched polyethylene terephthalate film having a thickness of 38 μm that has been subjected to corona treatment is bonded to the other surface, and an irradiation amount of 16.8 kJ / m is applied to the other surface via an adhesive made of the same curable epoxy resin composition. triacetyl cellulose film having a thickness of 40μm ^{to 2} by corona treatment has been performed [Konica Minolta Opto Co., Ltd. "KC4UEW", plane retardation 0.7 nm, a thickness direction retardation -0.1nm] was pasted with . Next, from the triacetyl cellulose film side, using a UV irradiation device (the lamp is a “Fusion D lamp”), UV irradiation is performed with an integrated light quantity of 1,000 mJ / cm ² , and the polarizing plate is left at room temperature for 1 hour. Produced. Further, the surface of the triacetylcellulose 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 produce a polarizing plate 1 with pressure-sensitive adhesive. . This polarizing plate with an adhesive 1 had a good appearance with no film floating or peeling, no bubbles and the like. The moisture evaporation rate C of the pressure-sensitive adhesive polarizing plate 1 was 1.69 g / m ² · hr.

[Reference Example 4] (Preparation of polarizing plate 2 with adhesive)
On one side of the same polarizing film used in Reference Example 3, a saponification-treated triacetylcellulose film [Konica Minolta Opt ( "KC8UX" manufactured by Kogyo Co., Ltd.] and a saponification-treated 40 μm thick triacetylcellulose film [Konica Minolta Opto Co., Ltd.] through the same aqueous adhesive on the other side “KC4UEW”, in-plane retardation 0.7 nm, thickness direction retardation −0.1 nm] were pasted and then dried at 80 ° C. for 5 minutes to prepare a polarizing plate. Next, after corona treatment was applied to the surface on the 40 μm thick triacetylcellulose film side at an irradiation amount of 16.8 kJ / m ² , the same adhesive sheet as used in Reference Example 3 was bonded to the corona treatment surface. A polarizing plate 2 with an adhesive was prepared. This pressure-sensitive adhesive-attached polarizing plate 2 also had a good appearance with no film floating or peeling, no bubbles, etc. The water evaporation rate C of the pressure-sensitive adhesive polarizing plate 2 was 9.72 g / m ² · hr.

[Example 1]
(Cutting polarizing plates with adhesive)
The polarizing plate 1 with adhesive prepared in Reference Example 3 is cut into a 32 type size (diagonal 32 inches (about 81 cm), width about 71 cm × length about 40 cm) so that the absorption axis is parallel to the long side. Thus, the front side (viewing side) polarizing plate 20 of the liquid crystal cell 10 was obtained. In addition, the polarizing plate 2 with the adhesive produced in Reference Example 4 was cut into the same 32 type size as above so that the absorption axis was parallel to the short side, and the back side (backlight side) polarization of the liquid crystal cell 10 A plate 30 was obtained. These polarizing plates showed good handling properties during handling.

(Production of liquid crystal display device)
Disassemble the IPS mode wide 32 type (diagonal 32 inches (approx. 81 cm) wide 71 cm × vertical 40 cm) LCD TV “VIERA” (model number: VIERA TH-L32X1) The polarizing plate 1 with the pressure-sensitive adhesive layer cut above is used as the front side (viewing side) polarizing plate 20 in place of the original polarizing plate, and no voltage is applied to the liquid crystal molecules in the liquid crystal cell 10 (black display). ) Arranged so as to be parallel to the orientation direction. Moreover, the polarizing plate 2 with the adhesive layer cut | judged above is bonded as the back side (backlight side) polarizing plate 30 of the liquid crystal cell 10 so that the absorption axis may be orthogonal to the absorption axis of the front side polarizing plate 20. Thus, the liquid crystal panel 60 was produced. At this time, the ratio V _f / V _r between the water evaporation rate V _f of the front side polarizing plate 20 and the water evaporation rate V _r of the back side polarizing plate 30 is 1.69 / 9.72 = 0.17. The liquid crystal display device was assembled by combining the liquid crystal panel 60 with the original backlight unit 70. 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, the backlight 70 was turned on, and an in-plane luminance difference of the liquid crystal panel 60 was measured one hour later. However, the in-plane brightness difference was 2.20 cd / cm ² , and visual display unevenness was not observed.

[Comparative Example 1]
A liquid crystal panel 60 was prepared in the same manner as in Example 1 except that the polarizing plate 2 with the adhesive prepared in Reference Example 4 was used as the front polarizing plate 20 and the back polarizing plate 30. At this time, the ratio V _f / V _r between the water evaporation rate V _f of the front side polarizing plate 20 and the water evaporation rate V _r of the back side polarizing plate 30 is 1. The liquid crystal display device was assembled by combining the liquid crystal panel 60 with the original backlight unit 70. 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, the backlight 70 was turned on, and an in-plane luminance difference of the liquid crystal panel 60 was measured one hour later. However, the in-plane luminance difference was 6.55 cd / cm ² , and display unevenness was visually observed.

[Comparative Example 2]
Except that the front side polarizing plate 20 is composed of the polarizing plate 2 with the adhesive prepared in Reference Example 4 and the rear side polarizing plate 30 is composed of the polarizing plate 1 with the adhesive layer prepared in Reference Example 3, A liquid crystal panel 60 was produced in the same manner as in Example 1. At this time, the ratio V _f / V _r between the water evaporation rate V _f of the front side polarizing plate 20 and the water evaporation rate V _r of the back side polarizing plate 30 is 5.75. The liquid crystal display device was assembled by combining the liquid crystal panel 60 with the original backlight unit 70. 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, the backlight was turned on, and the in-plane luminance difference of the liquid crystal panel 60 was measured one hour later. The in-plane luminance difference was 5.90 cd / cm ² , and display unevenness was visually observed.

  Table 1 summarizes the water evaporation rate, the ratio and evaluation results of the pressure-sensitive adhesive polarizing plates 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 (10)

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
The ratio V _f / V _r of the water evaporation rate V _f of the front side polarizing plate provided with the pressure-sensitive adhesive layer and the water evaporation rate V _r of the back side polarizing plate provided with the pressure-sensitive adhesive layer is in the range of 0.01 or more and less than 1. And a liquid crystal display device.   2. 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 is made of polypropylene resin, polyethylene terephthalate resin or acrylic resin.   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 back side polarizing plate is made of a cellulose resin.   The liquid crystal according to any one of claims 1 to 3, 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 the range of -10 to +10 nm. Display device. 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. in the range of 100 to 300 nm, the refractive indices n _x in the slow axis direction in the film plane, the refractive index n _y in the fast axis direction in the film plane, and the refractive index of the film thickness direction is n _z when the liquid crystal display according to claim 1, Nz coefficient defined by the equation _{(n x -n z) / (} n x -n y) is in the range of 0.1 to 0.7 apparatus. 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
A first retardation film made of a polyolefin-based resin, located on the polarizing film side constituting the polarizing plate, and a core made of a styrene-based resin, located closer to the pressure-sensitive adhesive layer than the first retardation film 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. The liquid crystal display device in any one of 1-3. The first retardation film is in the range retardation is 30~150nm surfaces, the refractive indices n _x in the slow axis direction in the film plane, the fast-axis refractive index in the film plane n _y, and a refractive index of the film thickness direction is taken as n _z, Nz coefficient defined by the equation _{(n x -n z) / (} n x -n y) is in less than 2 ranges than 1,
The in-plane retardation of the second retardation film is in a range of 20 to 120 nm, and an Nz coefficient defined by the above formula is in a range of more than −2 and less than −0.5. Liquid crystal display device.   At least one of the front-side polarizing plate and the rear-side polarizing plate is a polarizing film and a transparent protective film disposed on both sides of the polarizing film and a water-based adhesive containing a polyvinyl alcohol resin and a water-soluble epoxy resin. The liquid crystal display device according to any one of claims 1 to 7.   At least one of the front-side polarizing plate and the rear-side polarizing plate is a curable adhesive composition containing an epoxy compound in which a polarizing film and a transparent protective film disposed on both surfaces thereof are cured by irradiation with active energy rays. The liquid crystal display device in any one of Claims 1-7 currently bonded through.   The liquid crystal display device according to claim 9, 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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