JP2011203642A - Polarizing plate, and liquid crystal panel, liquid crystal display device and polarizing plate set using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate, which does not cause degradation in optical characteristics, in particular, in transmittance even when exposed in a high temperature environment and which is durable when used in a high temperature environment, and to provide a liquid crystal display device having improved front contrast using the polarizing plate.SOLUTION: The polarizing plate comprises a polarizing film made of a polyvinyl alcohol resin and a transparent protective film laminated on each surface of the polarizing film via an adhesive, wherein one of the transparent protective films is a retardation film made of a norbornene resin showing a retardation within the plane of 40 to 300 nm and a retardation in the thickness direction of 80 to 300 nm, and the other transparent protective film is made of a polypropylene resin having a xylene soluble content of 1 wt.% or less at 20°C. A liquid crystal panel, a liquid crystal display device and a polarizing plate set using the above polarizing plate are also provided.

Description

  The present invention is a polarizing plate in which a norbornene-based resin film is laminated on one surface of a polarizing film made of a polyvinyl alcohol-based resin and a polypropylene-based resin film is laminated on the other surface, and a liquid crystal panel using the same, The present invention relates to a liquid crystal display device and a polarizing plate set.

  A polarizing plate is usually a transparent protective film, for example, a transparent cellulose resin represented by triacetyl cellulose, with an adhesive layer on one or both sides of a polarizing film made of a polyvinyl alcohol resin to which a dichroic dye is adsorbed and oriented. It is the structure which laminated | stacked the protective film. If necessary, this is bonded to the liquid crystal cell via another optical film with an adhesive to form a component of the liquid crystal display device.

  Applications of liquid crystal display devices are rapidly expanding as thin display devices such as liquid crystal televisions, liquid crystal monitors, and personal computers. In particular, the market for liquid crystal televisions is remarkably expanding, and the demand for cost reduction is very high. A polarizing plate for a liquid crystal television is usually formed by laminating a triacetyl cellulose film (TAC film) with a water-based adhesive on both sides of a polarizing film made of a polyvinyl alcohol-based resin film, and an adhesive on one side of the polarizing plate. A retardation film is laminated.

  As the retardation film laminated on the polarizing plate, a stretched product of a polycarbonate-based resin film or a stretched product of a cycloolefin-based resin film is used. Retardation films composed of very few cycloolefin resin films are frequently used. The laminated product of such a polarizing plate and a retardation film made of a cycloolefin resin film reduces the number of components or simplifies the manufacturing process in order to improve productivity and reduce product cost. For example, JP-A-8-43812 (Patent Document 1) discloses a laminated structure of a cycloolefin-based (norbornene-based) resin film / polarizing film / TAC film having a retardation function. Yes.

  Japanese Patent Application Laid-Open No. 2007-334295 (Patent Document 2) has resistance to organic solvents such as acetone, toluene, and ethyl acetate, and has dimensional stability particularly under wet heat conditions, and a polarizing film and a protective film. A polarizing plate excellent in adhesiveness is disclosed. The configuration is such that protective films are laminated on both sides of the polarizing film, and a polypropylene resin is used for at least one of the protective films.

  In a polarizing plate using a polypropylene-based resin, the transmittance of the polarizing plate may be lowered under a severe high temperature environment. Such a decrease in transmittance reduces the luminance of the liquid crystal display device. In JP 2009-258588 A (Patent Document 3), even when exposed to a high temperature environment, optical characteristics, particularly transmittance, do not deteriorate, and it is sufficient for use in a high temperature environment. An endurable polarizing plate is disclosed. The constitution is such that a protective film is laminated on both surfaces of a polarizing film, and at least one of the protective films is made of a polypropylene resin having a xylene-soluble content at 20 ° C. of 1% by weight or less. However, in the liquid crystal display device using this polarizing plate, the front contrast is not sufficient, and there are cases where it cannot meet the market demand.

JP-A-8-43812 JP 2007-334295 A JP 2009-258588 A

  The present invention has been made in order to solve the above-mentioned problems, and the purpose thereof is that even when exposed to a high temperature environment, the optical characteristics, in particular, the transmittance is not deteriorated. It is to provide a polarizing plate that can sufficiently withstand the use of.

  Another object of the present invention is to provide a liquid crystal display device using the polarizing plate as described above and having an improved front contrast.

  The present invention is a polarizing plate in which a transparent resin film is bonded to both surfaces of a polarizing film made of a polyvinyl alcohol resin via an adhesive, and one of the transparent resin films has an in-plane retardation. 40 nm to 300 nm, a retardation film made of a norbornene resin having a thickness direction retardation of 80 nm to 300 nm, and the other transparent resin film is polypropylene having a xylene-soluble content at 20 ° C. of 1% by weight or less. A polarizing plate made of a resin is provided.

In the polarizing plate of the present invention, the transparent resin film made of the polypropylene resin has the following formula:
Change amount of xylene-soluble content by melt extrusion = xylene-soluble content at 20 ° C of a film produced by melt extrusion [wt%]
-Xylene soluble content at 20 ° C of resin raw material subjected to melt extrusion [wt%]
It is preferable that the xylene-soluble matter change amount by melt extrusion defined by is produced by a melt extrusion method in which it is 0.5 or less.

  The transparent resin film made of the polypropylene-based resin in the polarizing plate of the present invention is cooled by air blown from an air chamber when melt-kneaded and then extruded from a T-die and brought into contact with a cooling roll in the form of a molten sheet. It is preferable that it is manufactured by being in close contact with each other.

  The polypropylene resin in the polarizing plate of the present invention is preferably a polymer containing 99% by weight or more of a structural unit derived from propylene.

  In the present invention, the front side polarizing plate is bonded to the viewing side of the liquid crystal cell via the pressure-sensitive adhesive layer, and the back side polarizing plate is bonded to the opposite side of the liquid crystal cell via the pressure-sensitive adhesive layer. The back side polarizing plate is the polarizing plate of the present invention described above, and also provides a liquid crystal panel that is bonded so that the retardation film side faces the liquid crystal cell.

  In the liquid crystal panel of the present invention, the front side polarizing plate has a cellulose resin film bonded to one surface of a polarizing film made of polyvinyl alcohol resin, and a haze of 0.1% to 40% on the other surface. It is preferable that the polyester resin film is bonded and bonded so that the cellulose resin film side faces the liquid crystal cell.

  The present invention also includes a backlight, a light diffusing plate, and the above-described liquid crystal panel of the present invention in this order, and the liquid crystal panel is a liquid crystal disposed so that the polypropylene resin film faces the light diffusing plate. A display device is also provided.

  The present invention further includes a set of polarizing plates bonded to both surfaces of the liquid crystal cell, wherein the polarizing plate disposed on the back side of the liquid crystal cell is the above-described polarizing plate of the present invention, and the retardation film thereof A pressure-sensitive adhesive layer is provided on the side, and a polarizing plate disposed on the front side of the liquid crystal cell is a cellulose resin film bonded to one surface of a polarizing film made of a polyvinyl alcohol resin, The present invention also provides a set of polarizing plates in which an adhesive layer is provided on the cellulose resin film side.

  According to the present invention, as a protective film, by using a polypropylene-based resin film having a xylene-soluble content at 20 ° C. of 1% by weight or less, a decrease in transmittance under a severe high temperature environment is greatly suppressed, A polarizing plate that can sufficiently withstand use in a severe high-temperature environment is provided. Furthermore, in the liquid crystal display device using the polarizing plate of the present invention, the front contrast is improved while using such a polarizing plate.

[Polarizing plate of the present invention (back (rear) side polarizing plate)]
(Polarizing film)
Specifically, the polarizing film used in the polarizing plate of the present invention is obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film. The polyvinyl alcohol resin can be obtained by saponifying a polyvinyl acetate resin. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymers. Etc. 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 85 mol% to 100 mol%, preferably 98 mol% or more. These polyvinyl alcohol resins may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Moreover, the polymerization degree of polyvinyl alcohol-type resin is in the range of 1000-10000 normally, Preferably it exists in the range of 1500-5000.

  A film obtained by forming such a polyvinyl alcohol resin is used as a raw film of a polarizing film. The method for forming the polyvinyl alcohol-based resin is not particularly limited, and can be formed by a conventionally known appropriate method. Although the film thickness of the raw film which consists of polyvinyl alcohol-type resin is not specifically limited, For example, it is about 10 micrometers-150 micrometers.

  A polarizing film usually includes a process of dyeing a polyvinyl alcohol resin film with a dichroic dye and adsorbing the dichroic dye (dyeing process), and a polyvinyl alcohol resin film on which the dichroic dye is adsorbed. It is manufactured through a step of treating with an acid aqueous solution (boric acid treatment step) and a step of washing with water after the treatment with the boric acid aqueous solution (water washing treatment step).

  Further, in the production of the polarizing film, the polyvinyl alcohol-based resin film is usually uniaxially stretched, but this uniaxial stretching may be performed before the dyeing treatment step or during the dyeing treatment step, It may be performed after the dyeing process. When uniaxial stretching is performed after the dyeing treatment step, this uniaxial stretching may be performed before the boric acid treatment step or during the boric acid treatment step. Of course, it is also possible to perform uniaxial stretching in these plural stages. Uniaxial stretching may be performed uniaxially between rolls having different peripheral speeds, or may be performed uniaxially using a hot roll. Moreover, the dry-type extending | stretching which extends | stretches in air | atmosphere may be sufficient, and the wet extending | stretching which extends | stretches in the state swollen with the solvent may be sufficient. The draw ratio is usually about 3 to 8 times.

  The dyeing of the polyvinyl alcohol-based resin film with the dichroic dye in the dyeing treatment step is performed, for example, by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing the dichroic dye. As the dichroic dye, for example, iodine, a dichroic dye or the like is used. Examples of dichroic dyes include C.I. I. Dichroic direct dyes composed of disazo compounds such as DIRECT RED 39 and dichroic direct dyes composed of compounds such as trisazo and tetrakisazo are included. In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to 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 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. It is. When iodine is used as the dichroic dye, the temperature of the aqueous solution used for dyeing is usually 20 ° C. to 40 ° C., and the immersion time (dyeing time) in this aqueous solution is usually 20 seconds to 1800 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing an aqueous dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually 1 × 10 ⁻⁴ parts by weight to 10 parts by weight, preferably 1 × 10 ⁻³ parts by weight to 1 part by weight, particularly preferably 100 parts by weight of water. 1 × 10 ⁻³ parts by weight to 1 × 10 ⁻² parts by weight. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. When a dichroic dye is used as the dichroic dye, the temperature of the dye aqueous solution used for dyeing is usually 20 ° C to 80 ° C, and the immersion time (dyeing time) in this aqueous solution is usually 10 seconds to 1800. Seconds.

  The boric acid treatment step is performed by immersing a polyvinyl alcohol-based resin film dyed with a dichroic dye in a boric acid-containing aqueous solution. The amount of boric acid in the boric acid-containing aqueous solution is usually 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 in the dyeing process described above, the boric acid-containing aqueous solution used in this boric acid treatment process preferably contains potassium iodide. In this case, the amount of potassium iodide in the boric acid-containing aqueous solution is usually 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 60 seconds to 1200 seconds, preferably 150 seconds to 600 seconds, and more preferably 200 seconds to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 ° C. to 85 ° C., more preferably 60 ° C. to 80 ° C.

  In the subsequent washing process, the polyvinyl alcohol-based resin film after the boric acid treatment described above is washed with water, for example, by immersing it in water. The water temperature in the water washing treatment is usually 5 ° C. to 40 ° C., and the immersion time is usually 1 second to 120 seconds. After the water washing treatment, a drying treatment is usually performed to obtain a polarizing film. The drying process is preferably performed using, for example, a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually 30 ° C to 100 ° C, preferably 50 ° C to 80 ° C. The time for the drying treatment is usually 60 seconds to 600 seconds, preferably 120 seconds to 600 seconds.

  In this way, the polyvinyl alcohol resin film is uniaxially stretched, dyed with a dichroic dye, treated with boric acid and washed with water to obtain a polarizing film. The thickness of this polarizing film is usually in the range of 5 μm to 40 μm. In the polarizing plate of the present invention, a norbornene resin film is laminated on one surface of such a polarizing film via an adhesive layer, and a specific polypropylene resin film is laminated on the other surface via an adhesive layer. With a structure.

(Norbornene resin film)
The polarizing plate of the present invention comprises a norbornene-based resin having an in-plane retardation and a thickness-direction retardation within a specific range as a transparent protective film via an adhesive on one surface of the polarizing film described above. A retardation film is bonded. The norbornene-based resin film used for the polarizing plate of the present invention is, for example, a film made of a thermoplastic resin having a monomer unit made of a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene-based monomer. The norbornene-based resin film can be a hydrogenated product of the ring-opening polymer of the cycloolefin or a ring-opening copolymer using two or more kinds of cycloolefin, and has a cycloolefin and a cyclic olefin or a vinyl group. An addition copolymer with an aromatic compound or the like may be used. Those having a polar group introduced are also effective.

  When using a copolymer of a cycloolefin and a chain olefin or an aromatic compound having a vinyl group, examples of the chain olefin include ethylene and propylene, and examples of the aromatic compound having a vinyl group include styrene, Examples include α-methylstyrene and nuclear alkyl-substituted styrene. In such a copolymer, the unit of the monomer composed of cycloolefin may be 50 mol% or less (preferably 15 mol% to 50 mol%). In particular, when a terpolymer of a cycloolefin, a chain olefin, and an aromatic compound having a vinyl group is used, the amount of the monomer unit composed of the cycloolefin can be made relatively small as described above. In such a terpolymer, the monomer unit composed of a chain olefin is usually 5 mol% to 80 mol%, and the monomer unit composed of an aromatic compound having a vinyl group is usually 5 mol% to 80 mol%. is there.

  Cycloolefin-based resins are commercially available as appropriate, such as Topas (manufactured by Topas Advanced Polymers GmbH), Arton (manufactured by JSR Corporation), ZEONOR (manufactured by Nippon Zeon Co., Ltd.), ZEONEX (manufactured by Nippon Zeon). (Made by Mitsui Chemical Co., Ltd.) etc. can be used conveniently. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. Further, for example, escina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), zeonoa film (manufactured by Nippon Zeon Co., Ltd.), arton film (manufactured by JSR Co., Ltd.) and the like are formed in advance. You may use the commercial item of the film made from the made cycloolefin resin as a transparent protective film.

Since the norbornene-based resin film is stretched in at least one direction, the optical compensation of the liquid crystal can be performed and the viewing angle of the liquid crystal display device can be increased. Norbornene resin film used in the present invention, the refractive index n _y in the refractive index in the in-plane slow axis direction n _x of the stretched film, a direction perpendicular thereto in the plane (fast axis direction), and the thickness direction Where n _{z is} the refractive index of the film and d is the thickness of the film, the in-plane retardation value R ₀ and the thickness direction retardation value R _th of the film represented by the following equations are respectively the in-plane retardation value R _0. There 40Nm～300nm (preferably 40Nm～120nm) in the range of, and the thickness direction retardation R _th is 80Nm～300nm (preferably 100Nm～250nm) in the range of.

_{R 0 = (n x -n y} ) × d
R _th = [(n _x + _ny ) / 2−n _z ] × d
When the in-plane retardation value R ₀ is less than 40 nm or exceeds 300 nm, the viewing angle compensation ability of the panel is lowered. In addition, when the thickness direction retardation value _Rth is less than 80 nm or exceeds 300 nm, the viewing angle compensation ability of the panel is also lowered. The in-plane retardation value R ₀ and the thickness direction retardation value R _th described above can be measured using, for example, KOBRA 21ADH (manufactured by Oji Scientific Instruments).

  In order to obtain the norbornene-based resin film having the refractive index characteristics as described above, the stretching ratio and stretching speed are adjusted appropriately, and various temperatures such as preheating temperature, stretching temperature, heat set temperature, and cooling temperature during stretching are used. And the pattern may be selected as appropriate. Such a refractive index characteristic can be obtained by stretching under relatively loose conditions. For example, the stretching ratio is preferably in the range of 1.05 to 1.6 times, and more preferably 1.1 to More preferably, it is 1.5 times. In the case of biaxial stretching, the stretching ratio in the maximum stretching direction may be in the above range.

  The norbornene-based resin film subjected to stretching used in the present invention is not particularly limited with respect to the thickness, but is preferably in the range of 20 μm to 80 μm, and more preferably in the range of 40 μm to 80 μm. This is because when the thickness of the norbornene-based resin film is less than 20 μm, it is difficult to handle the film and it is difficult to express a predetermined retardation value. On the other hand, the thickness of the norbornene-based resin film is 80 μm. When exceeding, it will become inferior to workability, there exists a possibility that transparency may fall or the weight of the obtained polarizing plate may become large.

(Polypropylene resin film)
The transparent resin film (polypropylene resin film) made of a polypropylene resin used as a protective film in the polarizing plate of the present invention has a xylene-soluble content at 20 ° C. of 1% by weight or less, preferably 0.8% by weight. Hereinafter, it is more preferably 0.5% by weight or less. When the xylene-soluble content of the polypropylene resin film exceeds 1% by weight, when the polarizing plate is exposed to a high temperature environment, the surface of the polypropylene resin film is whitened, and the transmittance of the polarizing plate is significantly reduced. . The whitening of the surface of the polypropylene resin film in such a high temperature environment is presumed to be caused by a bleed out due to a low molecular weight component or a component inferior in stereoregularity present in the resin film. A typical example of such a low molecular weight component is an atactic low molecular weight oligomer.

  In the present invention, the xylene soluble content [wt%] of the polypropylene resin film is measured as follows. That is, first, a predetermined amount, usually 5 g, of a polypropylene resin film is weighed, added to 500 ml of boiling xylene, dissolved completely, cooled to 20 ° C., and held at 20 ° C. for 4 hours. Next, the xylene liquid is filtered to separate into a precipitate and a filtrate, and the solvent is removed from the filtrate, followed by drying at 70 ° C. under reduced pressure to obtain a dried xylene-soluble component. And the xylene soluble part in 20 degreeC is calculated | required by the following Formula (1).

Xylene solubles [wt%]
= (Weight of xylene-dissolved component dried) /
(Weight of resin first dissolved in boiling xylene (5 g)) × 100 (1)

  The polypropylene-based resin film used in the present invention is preferably produced by a melt extrusion method, in which case the amount of change in xylene solubles by melt extrusion defined by the following formula (2) is 0.5 or less. It is preferable.

Amount of change in xylene-soluble content by melt extrusion = xylene-soluble content in film produced by melt extrusion at 20 ° C [wt%]-
Xylene soluble content at 20 ° C. [wt%] of the resin raw material subjected to the melt extrusion
... Formula (2).

  In the melt extrusion method, powder-form or pellet-form polypropylene-based resin raw materials are supplied to an extruder heated to 180 ° C. to 300 ° C., melted and kneaded by an extruder screw, and melt extruded into a sheet form from a slit of a T die. Then, the film is produced by bringing the film into contact with a cooling roll by various means and cooling. Here, since the polypropylene-based resin is melt-kneaded at a high temperature, it may deteriorate due to shearing by the screw and the temperature to generate, for example, a low molecular weight oligomer that becomes a xylene-soluble component. In that case, the amount of change in the xylene solubles by melt extrusion defined by the formula (2) may be large. In the present invention, it is preferable that the amount of change is small, and the amount of change is preferably 0.5 or less. When this amount of change is large, since the degree of deterioration of the polypropylene resin is relatively large by melt extrusion, there is a possibility that the quality of the polarizing plate such as foreign matters in the film is impaired.

  The temperature of the molten sheet-like polypropylene resin to be extruded is about 180 ° C to 300 ° C. If the temperature of the molten sheet at this time is lower than 180 ° C., the spreadability is not sufficient, the thickness of the resulting film becomes non-uniform, and there is a possibility that the film has phase difference unevenness. Further, when the temperature exceeds 300 ° C., the resin is easily deteriorated or decomposed, and bubbles may be generated in the sheet or carbides may be contained.

The extruder may be a single screw extruder or a twin screw extruder. For example, when a single screw extruder is used, L / D, which is the ratio of the screw length L to the diameter D, is about 24 to 36, the screw groove space volume V ₁ in the resin supply section, and the screw groove in the resin metering section. The compression ratio, which is the ratio (V ₁ / V ₂ ) to the space volume V ₂ , is about 1.5 to 4 and is a full flight type, a barrier type, or a screw having a Maddock type kneading part. Can be used. From the viewpoint of suppressing deterioration and decomposition of the polypropylene resin and uniformly melting and kneading, it is preferable to use a screw having an L / D of 28 to 36 and a compression ratio V ₁ / V _{2 of 2} to 3. Moreover, in order to suppress deterioration and decomposition | disassembly of a polypropylene resin, it is preferable to purge oxygen in an extruder by carrying out nitrogen purge. Furthermore, it is also preferable to provide an orifice having a diameter of 1 mmφ to 5 mmφ at the tip of the extruder to increase the resin pressure at the tip of the extruder. Increasing the resin pressure at the leading end of the extruder by installing an orifice means increasing the back pressure at the leading end, thereby improving the stability of extrusion. The diameter of the orifice to be used is more preferably 2 mmφ to 4 mmφ.

The T die used for extrusion has a channel hanger shape and is designed so that the flow rate and pressure of the molten polypropylene resin are uniform in the width direction of the T die slit portion. preferable. Also, it is preferable that the surface of the resin flow path does not have minute steps or scratches, and the lip portion is plated or coated with a material having a low friction coefficient with the molten polypropylene resin, and the lip tip is 0.3 mmφ or less. A sharp edge shape that has been polished is preferred. Examples of the material having a small friction coefficient include tungsten carbide ceramics and fluorine special plating. By using such a T-die, it is possible to suppress the generation of eyes and simultaneously suppress the die line, so that a resin film excellent in appearance uniformity can be easily obtained. It is also effective for the T die to satisfy the following condition (A) or (B), and further to satisfy the condition (C) or (D).
(A) When the lip width of the T die is less than 1500 mm: the thickness direction length of the T die> 180 mm,
(B) When the lip width of the T die is 1500 mm or more: length in the thickness direction of the T die> 220 mm,
(C) When the lip width of the T die is less than 1500 mm: the length of the T die in the height direction> 250 mm,
(D) When the lip width of the T die is 1500 mm or more: Length in the height direction of the T die> 280 mm.

  By using a T die that satisfies these conditions, the flow of the molten polypropylene resin inside the T die can be adjusted, and the lip portion can be extruded while suppressing thickness unevenness, so that the thickness is increased. A protective film made of a polypropylene resin film having excellent accuracy and more uniform retardation can be obtained.

  In addition, it is preferable to attach a gear pump via an adapter between an extruder and a T die from a viewpoint of suppressing the extrusion fluctuation | variation of polypropylene resin. In addition, it is preferable to attach a leaf disk filter to remove foreign substances in the polypropylene resin.

  In order to suppress the amount of change in the xylene solubles by melt extrusion defined by the above formula (2) to 0.5 or less, it is effective to reduce the polymerization catalyst residue in the polypropylene resin raw material as much as possible. It is also effective to add an antioxidant such as phenol or phosphorus in a range that does not impair the effects of the present invention. Furthermore, the screw shape in the extruder is preferably within a range where stable melt extrusion can be performed, so that the mixing portion giving high shear is reduced and the compression ratio is made as small as possible. It is often effective to lower the temperature in the extruder. Furthermore, the polypropylene resin material is purged with nitrogen using a hopper dryer of a nitrogen gas reflux type, for example, at a temperature of 30 ° C. or higher for 0.5 hours or more and a purity of 99% or more. It is also effective as a measure to reduce the amount of change in xylene solubles by the melt extrusion method described above, by allowing impurities (especially oxygen) in the raw material to flow out.

The molten sheet-like polypropylene resin extruded from the T-die is subsequently brought into contact with a metal cooling roll (also referred to as a chill roll or a casting roll) and is cooled by being in close contact with the cooling roll. At this time, the adhesion method to the cooling roll may affect the transparency. The adhesion to the cooling roll is, for example,
a) A method in which static electricity is imparted to a molten sheet-like polypropylene resin, and the surface state is closely adhered to a mirror-like cooling roll to cool it,
b) The molten sheet-like polypropylene resin is sandwiched between a cooling roll having a mirror surface and a metal roll (also referred to as a touch roll) or a metal belt having a mirror surface having a mirror surface and is in close contact with the cooling roll. Cooling method,
c) When the molten sheet-like polypropylene resin is brought into contact with the cooling roll, it can be carried out by a known method such as a method in which the molten sheet is brought into close contact with the cooling roll by air blown from the air chamber.

  Among these molding methods, the polypropylene-based resin film produced by the method c) (hereinafter sometimes referred to as “air chamber method”) has an appropriate surface roughness. When the combined polarizing plate of the present invention is applied to a liquid crystal display device, the front contrast is particularly high, which is preferable. In addition, the polypropylene-based resin film manufactured by the air chamber method has a moderate degree of crystallinity because the crystal growth on the surface opposite to the surface that is in close contact with the cooling roll easily proceeds. There is also a tendency that the decrease in transmittance in the use environment is small, which is preferable.

  In the air chamber method, specifically, when the polypropylene resin material is melt-kneaded and then extruded from a T die and brought into contact with the cooling roll in the form of a molten sheet, the air from the opposite side to the cooling roll. Air is blown onto the molten sheet-like polypropylene resin by an air chamber, thereby bringing the molten sheet-like polypropylene resin into close contact with the cooling roll. As the air chamber, a commercially available appropriate one can be used without particular limitation. For example, the air to be blown is sucked in through a high-performance air filter (HEPA filter) with a blower or the like in the manufacturing environment space. It is preferable that the air chamber is in a pressurized state of 100 to 300 Pa. If the pressure in the air chamber is within this range, the air pressure applied to the film will be moderate. Therefore, in the distance from the T-die discharge port to the molten sheet resin (referred to as the air gap). Thus, stable film formation is possible without causing flapping, and naturally, stability such as film thickness accuracy is also improved. For this reason, it is more preferable that the pressure in the air chamber is 120 to 220 Pa.

  The cooling roll preferably has a low surface temperature to rapidly cool the molten sheet-like polypropylene resin. It is preferable that the surface temperature of the cooling roll is adjusted to a range of 0 ° C to 30 ° C, for example. When the surface temperature of the cooling roll exceeds 30 ° C., it takes time to cool and solidify the molten sheet-like polypropylene resin, so that the crystal component in the polypropylene resin grows, and the resulting film is inferior in transparency. It may become. On the other hand, if the surface temperature of the chill roll is less than 0 ° C., the surface of the chill roll is dewed and water droplets are attached, which tends to deteriorate the appearance of the resulting film.

  Since the surface state of the chill roll is transferred to the polypropylene resin film, the thickness accuracy of the obtained polypropylene resin film may be lowered if the surface has irregularities. Therefore, it is preferable that the surface of the cooling roll is in a mirror surface state as much as possible. Specifically, the surface roughness of the cooling roll is preferably 0.3 S or less, more preferably 0.1 S to 0.2 S, expressed as a standard sequence of maximum heights.

  The processing speed when producing a polypropylene resin film is determined by the time required to cool and solidify the molten sheet-like polypropylene resin. When the diameter of the cooling roll to be used is increased, the distance at which the molten sheet is in contact with the cooling roll becomes longer, so that production at a higher speed is possible. Specifically, when a 600 mmφ metal cooling roll is used, the processing speed is about 50 m / min at the maximum.

  The polypropylene resin constituting the polypropylene resin film also preferably has a xylene-soluble content at 20 ° C. defined above with reference to formula (1) of 1% by weight or less, More preferably, it is 0.8 weight% or less, More preferably, it is 0.5 weight% or less. The method for measuring the xylene-soluble content of the polypropylene resin is the same as that for the polypropylene resin film. The polypropylene resin may be a homopolymer of propylene or a copolymer of propylene and another monomer copolymerizable therewith. These may be used in combination.

  Examples of other monomers copolymerizable with propylene include ethylene and α-olefin. The α-olefin has 4 or more carbon atoms, preferably an α-olefin having 4 to 10 carbon atoms. Specific examples of the α-olefin having 4 to 10 carbon atoms include linear monoolefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and 1-decene; Branched monoolefins such as methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene; vinylcyclohexane and the like. The copolymer of propylene and other monomers copolymerizable therewith may be a random copolymer or a block copolymer.

  When the copolymer is used as a polypropylene resin, a polypropylene resin having a xylene-soluble content at 20 ° C. of 1% by weight or less is relatively easily obtained. It is preferable to copolymerize so that it may contain. In addition, the content rate of the structural unit derived from the said other monomer in a copolymer is infrared (IR) according to the method described on page 616 of "Polymer Analysis Handbook" (1995, published by Kinokuniya) ) It can be obtained by performing a spectrum measurement.

  Among the above, as a polypropylene resin constituting a polypropylene resin film, a propylene homopolymer, a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, and a propylene-ethylene-1-butene random copolymer are used. A polymer is preferably used. These homopolymers and copolymers are relatively easy to obtain a polymer having a reduced xylene-soluble content by selecting an appropriate polymerization catalyst. In particular, by using a propylene homopolymer, a polymer having a reduced xylene-soluble content tends to be obtained more easily.

In the present invention, the polypropylene resin may be a polymer or copolymer polymerized using a known polymerization catalyst, and examples of the polymerization catalyst include the following.
(A) a Ti—Mg-based catalyst comprising a solid catalyst component containing magnesium, titanium and halogen as essential components;
(B) a catalyst system in which a solid catalyst component containing magnesium, titanium and halogen as essential components is combined with an organoaluminum compound and, if necessary, a third component such as an electron donating compound,
(C) Metallocene catalyst.

  Examples of the solid catalyst component (A) include catalyst systems described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. Preferred examples of the organoaluminum compound in the catalyst system of (B) include triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, tetraethyldialumoxane, and the like. Preferable examples include cyclohexylethyldimethoxysilane, tert-butylpropyldimethoxysilane, tert-butylethyldimethoxysilane, dicyclopentyldimethoxysilane and the like. Examples of the metallocene catalyst (C) include catalyst systems described in Japanese Patent No. 2587251, Japanese Patent No. 2627669, Japanese Patent No. 2668732, and the like.

  Among the above, a metallocene catalyst is preferably used because a polymer or copolymer having a reduced xylene-soluble content is easily obtained.

  Polypropylene resins are, for example, solution polymerization methods using an inert solvent typified by hydrocarbon compounds such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, and liquid monomers as solvents. It can be produced by a bulk polymerization method to be used or a gas phase polymerization method in which a gaseous monomer is polymerized as it is. Polymerization by these methods may be carried out batchwise or continuously.

  The method for reducing the xylene soluble content at 20 ° C. of the polypropylene resin to 1% by weight or less is not particularly limited. For example, in the polymerization stage, the degree of polymerization of the polypropylene resin is increased and a relatively low molecular weight component is reduced. Methods known to those skilled in the art, such as a method of reducing the ratio, a method of washing a polypropylene resin obtained by polymerization with a solvent, extracting and removing solvent-soluble components such as low molecular weight components, and a combination of these methods, Can be mentioned. Note that, for example, a polypropylene catalyst obtained by appropriately selecting a polymerization catalyst and controlling the stereoregularity of the polypropylene resin to isotactic or syndiotactic and / or polymerizing with propylene alone. When the xylene-soluble content of the resin is 1% by weight or less, the treatment for reducing the xylene-soluble content of the polypropylene resin obtained by polymerization is not necessarily required.

  The polypropylene resin used in the present invention has a melt flow rate (MFR) measured in a temperature of 230 ° C. and a load of 21.18 N in a range of 1 g / 10 min to 20 g / 10 min in accordance with JIS K 7210. It is preferably within a range of 2 g / 10 min to 18 g / 10 min, more preferably within a range of 4 g / 10 min to 15 g / 10 min. By using a polypropylene resin having an MFR within this range, it is easy to obtain a uniform polypropylene resin film without imposing a large load on the extruder.

  A known additive may be blended in the polypropylene resin as long as the effects of the present invention are not impaired. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent. Examples of antioxidants include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, hindered amine light stabilizers, and the like, and for example, phenolic antioxidant mechanisms in one molecule. It is also possible to use a composite antioxidant having a unit having both a phosphorus-based antioxidant mechanism and a phosphorus-based antioxidant mechanism. Examples of the UV absorber include UV absorbers such as 2-hydroxybenzophenone and hydroxyphenylbenzotriazole, and benzoate UV blockers. The antistatic agent may be polymer type, oligomer type or monomer type. Examples of the lubricant include higher fatty acid amides such as erucic acid amide and oleic acid amide, higher fatty acids such as stearic acid, and salts thereof. As the anti-blocking agent, fine particles having a spherical shape or a shape close thereto can be used regardless of inorganic type or organic type.

  The nucleating agent may be either an inorganic nucleating agent or an organic nucleating agent. Examples of the inorganic nucleating agent include talc, clay, calcium carbonate and the like. Examples of the organic nucleating agent include metal salts such as aromatic carboxylic acid metal salts and aromatic phosphoric acid metal salts, high-density polyethylene, poly-3-methylbutene-1, polycyclopentene, and polyvinylcyclohexane. It is done. Among these, organic nucleating agents are preferable, and the above-described metal salts and high-density polyethylene are more preferable. The amount of the nucleating agent added to the polypropylene resin is preferably 0.01% by weight to 3% by weight, and more preferably 0.05% by weight to 1.5% by weight. A plurality of these additives may be used in combination.

  The polypropylene resin film used as a protective film in the polarizing plate of the present invention can be obtained by forming the polypropylene resin. Such a polypropylene resin film is preferably excellent in transparency. Specifically, the total haze value measured according to JIS K 7136 is preferably 10% or less, more preferably 7% or less. preferable.

  The thickness of the polypropylene resin film in the polarizing plate of the present invention is preferably about 5 μm to 200 μm. More preferably, it is 10 μm or more, and more preferably 150 μm or less.

(adhesive)
In the polarizing plate of the present invention, a norbornene resin film is bonded to one surface of the polarizing film described above via an adhesive, and a polypropylene resin film is bonded to the other surface of the polarizing film via an adhesive. To configure. In the polarizing plate of the present invention, the same type of adhesive may be used on both sides of the polarizing film, or different types of adhesive may be used. Examples of the adhesive include water-based adhesives, that is, an adhesive component dissolved in water or dispersed in water from the viewpoint of thinning the adhesive layer. For example, a composition using a polyvinyl alcohol resin or a urethane resin as a main component can be mentioned as a preferred adhesive.

  When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin may be partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, or methylol group. Modified polyvinyl alcohol resins such as modified polyvinyl alcohol and amino group-modified polyvinyl alcohol may also be used. In this case, an aqueous solution of a polyvinyl alcohol resin is used as the adhesive. The density | concentration of the polyvinyl alcohol-type resin in an adhesive agent is 1 weight part-10 weight part normally with respect to 100 weight part of water, Preferably it is 1 weight part-5 weight part.

  It is preferable to add a curable component such as glyoxal or a water-soluble epoxy resin or a cross-linking agent to the adhesive composed of an aqueous solution of a polyvinyl alcohol resin in order to increase the adhesiveness. As the water-soluble epoxy resin, for example, a polyamide polyamine epoxy resin obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a polycarboxylic acid such as adipic acid and epichlorohydrin. Can be suitably used. Commercially available products of such polyamide polyamine epoxy resins include Sumire's Resin 650 (manufactured by Sumika Chemtex Co., Ltd.), Sumire's Resin 675 (manufactured by Sumika Chemtex Co., Ltd.), WS-525 (manufactured by Nippon PMC Corporation). Etc. The addition amount of these curable components or crosslinking agents (the total amount when added together) is usually 1 to 100 parts by weight, preferably 1 to 50 parts by weight, per 100 parts by weight of the polyvinyl alcohol resin. Parts by weight. When the addition amount of the curable component or the crosslinking agent is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving adhesiveness tends to be small, and the curable component or This is because the adhesive layer tends to be brittle when the addition amount of the crosslinking agent exceeds 100 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin.

  When a urethane resin is used as the main component of the adhesive, examples of a suitable adhesive composition include a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group. The polyester-based ionomer-type urethane resin here is a urethane-based resin having a polyester skeleton, into which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer type urethane resin is suitable as a water-based adhesive because it is emulsified directly into water without using an emulsifier and becomes an emulsion. Polyester ionomer-type urethane resins are known per se. For example, JP-A-7-97504 describes an example of a polymer dispersant for dispersing a phenolic resin in an aqueous medium. In JP-A-2005-70140 and JP-A-2005-208456, a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group is used as an adhesive to form a cycloolefin on a polarizing film made of a polyvinyl alcohol resin. The form which joins a system resin film is shown.

  As a method for laminating the above-described norbornene-based resin film and polypropylene-based resin film to the polarizing film, generally known methods may be used, for example, casting method, Mayer bar coating method, gravure coating method, comma coater method. And a method in which an adhesive is applied to the adhesive surface of the polarizing film and / or the film bonded thereto by a doctor blade method, a die coating method, a dip coating method, a spraying method, etc., and the both are overlapped. The casting method is a method of spreading and spreading an adhesive on the surface of a film to be coated while moving it in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two. After applying the adhesive, the polarizing film and the film bonded thereto are sandwiched by nip rolls and bonded together. In addition, when a method in which an adhesive is dropped between films and then pressed with a roll or the like and spreads uniformly is adopted, the material of the roll to be used can be a metal or rubber, and the gap between the two rolls. The rolls used for passing may be made of the same material or different materials.

  In order to improve adhesiveness, the surface of each of the norbornene resin film and the polypropylene resin film may be appropriately subjected to a surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, or flame (flame) treatment.

  A norbornene-based resin film and a polypropylene-based resin film are laminated on the polarizing film via an adhesive layer, respectively, and then dried to cure the adhesive layer. This drying treatment is performed, for example, by blowing hot air, and the temperature is usually in the range of 40 ° C to 100 ° C, preferably in the range of 60 ° C to 100 ° C. The drying time is usually 20 seconds to 1200 seconds.

  The thickness of the adhesive layer after drying is usually about 0.01 μm to 5 μm, preferably 2 μm or less, more preferably 1 μm or less. If the thickness of the adhesive layer is less than 0.01 μm, the adhesion may be insufficient, and if the thickness of the adhesive layer is too large, the appearance of the polarizing plate may be poor.

  After pasting, curing may be performed at room temperature or slightly higher than that for at least half a day, usually several days, so that sufficient adhesive strength can be obtained. The preferable curing temperature is in the range of 30 ° C to 50 ° C, more preferably 35 ° C to 45 ° C. When the curing temperature exceeds 50 ° C., so-called “roll tightening” is likely to occur in the roll winding state. In addition, the humidity at the time of curing may be moderate, and the relative humidity may be in the range of 0% to 70%. The curing time is usually 1 day to 10 days, preferably 2 days to 7 days.

  Moreover, a photocurable adhesive agent can also be used for the adhesive agent in the polarizing plate of this invention. As a photocurable adhesive agent, mixtures, such as a photocurable epoxy resin and a photocationic polymerization initiator, are mentioned, for example. In this case, the photocurable adhesive is cured by irradiating with active energy rays. The light source of the active energy ray is not particularly limited, but an active energy ray having a light emission distribution at a wavelength of 400 nm or less is preferable. Specifically, the low-pressure mercury lamp, the medium-pressure mercury lamp, the high-pressure mercury lamp, the ultrahigh-pressure mercury lamp, the chemical lamp, and the black light lamp A microwave excitation mercury lamp, a metal halide lamp and the like are preferable. The light irradiation intensity and light irradiation time for the photocurable adhesive are appropriately determined depending on the composition of the photocurable adhesive. When using a photocurable adhesive, the thickness of the adhesive layer after curing is usually about 0.01 μm to 10 μm, preferably 0.1 μm or more, and preferably 5 μm or less.

  When curing a photo-curable adhesive by irradiation with active energy rays, curing should be performed under conditions that do not deteriorate the functions of the polarizing plate such as the degree of polarization of the polarizing film, the transmittance and hue, and the transparency of the transparent resin film. preferable.

(Other layers optionally provided on the back side polarizing plate)
In the polarizing plate of the present invention, the norbornene-based resin film preferably has a pressure-sensitive adhesive layer on its outer surface (the surface opposite to the side bonded to the polarizing film). This pressure-sensitive adhesive layer is used for bonding to a liquid crystal cell or for bonding to another optical film. As the pressure-sensitive adhesive used for such a pressure-sensitive adhesive layer, a conventionally known appropriate pressure-sensitive adhesive can be used without particular limitation, and examples thereof include an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, and a silicone pressure-sensitive adhesive. Among these, an acrylic pressure-sensitive adhesive is preferably used from the viewpoints of transparency, adhesive strength, reliability, reworkability, and the like. The pressure-sensitive adhesive layer can be provided by a method in which such a pressure-sensitive adhesive is used, for example, in the form of an organic solvent solution, applied to a norbornene-based resin film with a die coater or a gravure coater, and dried. It can also be provided by a method of transferring a sheet-like adhesive formed on a treated plastic film (referred to as a separate film) to a norbornene resin film. Although there is no restriction | limiting in particular also about the thickness of an adhesive layer, Generally it is preferable to exist in the range of 2 micrometers-40 micrometers.

  Moreover, when the adhesive layer mentioned above is formed in the outer surface of a norbornene-type resin film, another optical functional film can also be stuck through the said adhesive layer. Examples of the optical functional film used in such a form include an optical compensation film in which a liquid crystal compound is applied to the substrate surface and oriented, a retardation film made of a polycarbonate resin or other transparent resin, and the like. It is done. When such an optical compensation film is stuck on a norbornene-based resin film, an adhesive layer for pasting to the above-described liquid crystal cell may be further provided on the optical compensation film. Commercially available products corresponding to an optical compensation film coated with a liquid crystal compound on the substrate surface and oriented are WV film (Fuji Film Co., Ltd.), NH film (Shin Nippon Oil Co., Ltd.), LC Examples include films (manufactured by Nippon Oil Corporation).

  Another optical functional film can be attached to the outer surface of the polypropylene resin film (the side opposite to the surface bonded to the polarizing film) via the pressure-sensitive adhesive layer. As an optical functional film used in such a form, for example, a reflective polarizing film that transmits a certain kind of polarized light and reflects polarized light that shows the opposite property, a reflective film having a reflective function on the surface, Examples thereof include a transflective film having both a reflection function and a transmission function. For example, DBEF (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) is a commercially available product corresponding to a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties. Etc.

[LCD panel]
In the present invention, a front (front) polarizing plate is bonded to the viewing side of the liquid crystal cell via an adhesive layer, and a back (rear) polarizing plate is bonded to the opposite side of the liquid crystal cell via an adhesive layer. Also provided is a liquid crystal panel in which the back side polarizing plate is the polarizing plate of the present invention described above, and is bonded so that the retardation film side faces the liquid crystal cell.

(Liquid crystal cell)
The liquid crystal cells constituting the liquid crystal panel may be those conventionally used in liquid crystal televisions and the like. For example, various types of liquid crystal such as twisted nematic (TN) mode, vertical alignment (VA) mode, horizontal electrolysis (IPS) mode, etc. A cell can be used.

[Front (front) side polarizing plate]
The front side polarizing plate constituting the liquid crystal panel of the present invention has a cellulose resin film bonded to one surface of a polarizing film made of polyvinyl alcohol resin, and a haze of 0.1% to 40% on the other surface. It is preferable that the polyester-type resin film is bonded. In the liquid crystal panel of this invention, such a front side polarizing plate is bonded so that the cellulose resin film side may face a liquid crystal cell. Hereinafter, the front side polarizing plate used in the present invention will be described.

(Polarizing film)
As a polarizing film in a front side polarizing plate, the polarizing film similar to what was mentioned above about the polarizing plate (back side polarizing plate) of this invention can be used.

(Polyester resin film)
The polyester resin film in the front side polarizing plate is a film made of a polyester resin derived from a polycondensation reaction using dicarboxylic acid and diol as constituent monomers, such as a polyethylene terephthalate film and a polyethylene naphthalate film. A film can be particularly preferably used. Polyethylene terephthalate is a resin in which 80 mol% or more of repeating units are composed of ethylene terephthalate. Other copolymer components include isophthalic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthale Acid, dicarboxylic acid components such as 1,4-dicarboxycyclohexane, and also propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene Examples include diol components such as glycol. These dicarboxylic acid components and glycol components can be used in combination of two or more if necessary. It is also possible to use hydroxycarboxylic acids such as p-hydroxybenzoic acid and p-β-hydroxyethoxybenzoic acid as a copolymerization component. Such other copolymerization component may contain a compound containing a small amount of amide bond, urethane bond, ether bond, carbonate bond and the like.

  As a method for producing polyethylene terephthalate, any production method such as a so-called direct polymerization method in which terephthalic acid and ethylene glycol are directly reacted and a so-called transesterification method in which dimethyl ester of terephthalic acid and ethylene glycol are transesterified is applied. can do. Moreover, a well-known additive can be contained as needed. For example, a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light resistance agent, an impact resistance improver, and the like may be contained. However, since transparency is required in optical applications, it is preferable to keep the additive amount to a minimum.

  A stretched polyethylene terephthalate film can be produced by forming the raw material resin into a film and subjecting it to a stretching treatment. Stretching is uniaxial stretching in the MD direction (flow direction) or TD direction (direction orthogonal to the flow direction), biaxial stretching in both the MD direction and the TD direction, and stretching in a direction that is neither the MD direction nor the TD direction. Any method such as oblique stretching may be used. By performing such stretching operation, a polyethylene terephthalate film having high mechanical strength can be obtained. A polyethylene terephthalate film stretched in this way, particularly a biaxially stretched polyethylene terephthalate film, is preferable because interference unevenness tends to be difficult to see in the liquid crystal display device using the polarizing plate of the present invention.

  A method for producing a uniaxially stretched polyethylene terephthalate film is arbitrary and is not particularly limited, but the non-oriented film obtained by melting the raw material resin and extruding into a sheet is formed at a temperature equal to or higher than the glass transition temperature. A method of performing heat setting treatment after transverse stretching (stretching in the TD direction) with a tenter can be mentioned. The stretching temperature is preferably 80 ° C to 130 ° C, more preferably 90 ° C to 120 ° C, and the stretching ratio is preferably 2.5 times to 6 times, more preferably 3 times to 5.5 times. When the draw ratio is low, the polyethylene terephthalate film tends not to exhibit sufficient transparency. In the case of biaxial stretching, for example, a method of longitudinally stretching (stretching in the MD direction) a non-oriented film extruded into a sheet shape at a temperature equal to or higher than the glass transition temperature, and then laterally stretching (stretching in the TD direction) And a method of stretching in the vertical and horizontal directions.

  In addition, it is preferable to perform a relaxation process after extending | stretching from a viewpoint of reducing the distortion of the orientation main axis | shaft in a polyethylene terephthalate film. For example, in the case of producing a uniaxially stretched film by the above-described transverse stretching, there can be mentioned a method of relaxing the film in the longitudinal direction after the transverse stretching and before the heat setting treatment. The temperature during the relaxation treatment is 90 ° C to 200 ° C, preferably 120 ° C to 180 ° C. Although the amount of relaxation varies depending on the stretching conditions, it is preferable to set the amount of relaxation and the temperature so that the heat shrinkage rate at 150 ° C. of the film after the relaxation treatment is 2% or less.

  The temperature of the heat setting treatment is usually 180 ° C to 250 ° C, preferably 200 ° C to 245 ° C. In the heat setting treatment, first, treatment is performed at a constant length and at the temperature, and further, the relaxation treatment is performed so that the relaxation ratio in the width direction of the film is 1% to 10% (preferably 2% to 5%). It is preferable to do so. In this way, a stretched polyethylene terephthalate film with reduced orientation main axis distortion and excellent heat resistance can be obtained. In the present invention, a polyethylene terephthalate film having a maximum value of the distortion of the orientation main axis of 10 degrees or less, more preferably 8 degrees or less, and further preferably 5 degrees or less is suitably used. When a polyethylene terephthalate film having a maximum value of the strain of the orientation main axis exceeding 10 degrees is used, when a polarizing plate using such a polyethylene terephthalate film is bonded to a liquid crystal display screen of a liquid crystal display device, coloring is applied. Defects tend to increase. In addition, the maximum value of the distortion | strain of the orientation main axis | shaft of the polyethylene terephthalate film mentioned above can be measured by using retardation film inspection apparatus RETS system (made by Otsuka Electronics Co., Ltd.), for example.

  The polyester resin film used for the front side polarizing plate preferably has a thickness in the range of 20 μm to 50 μm. This is because when a polyester resin film having a thickness of less than 20 μm is used, handling of the film is difficult, and when a polyester resin film having a thickness exceeding 50 μm is used, the merit of thinning is reduced.

  Moreover, this polyester-type resin film is comprised with what has a haze in the range of 0.1%-40%. When a polyester resin film having a haze of less than 0.1% is used, the unevenness of the surface is reduced, so the effect of preventing unevenness is small, and a polyester resin film having a haze of more than 40% is used. In such a case, the light diffusion is too strong and the front luminance and the visibility tend to decrease. Haze is defined as the ratio of diffuse transmittance to total light transmittance as defined in JIS K 7136, and can be measured with a commercially available haze meter.

  As a method for imparting haze to a polyester resin film, a method of mixing inorganic fine particles or organic fine particles in a polyester resin that is a raw material resin, a coating liquid in which inorganic fine particles or organic fine particles are mixed with a resin binder on the surface of the film Although the method of coating etc. is mentioned, it is not limited to these. Typical examples of the inorganic fine particles include silica, colloidal silica, alumina, alumina sol, aluminosilicate, alumina-silica composite oxide, kaolin, talc, mica, calcium carbonate, calcium phosphate, and the like. As the organic fine particles, heat-resistant resin particles such as crosslinked polyacrylic acid particles, crosslinked polystyrene particles, crosslinked polymethyl methacrylate particles, silicone resin particles, and polyimide particles can be used.

In addition, the polyester resin film used in the present invention preferably has an in-plane retardation value R ₀ of 1000 nm or more, and more preferably 3000 nm or more. This is because when a polyester resin film having an in-plane retardation value R ₀ of less than 1000 nm is used, coloring from the front tends to be conspicuous. The upper limit of the in-plane retardation value R ₀ of the polyester resin film used in the present invention is sufficient up to about 10000 nm.

  The polyester-based resin film having the above-described characteristics is generally excellent in mechanical properties, solvent resistance, cost, and the like, and can be particularly suitably used for the front side polarizing plate in the present invention.

  The polyester resin film used in the present invention may be provided with an easy adhesion layer. The method for forming the polyester-based resin film provided with the easy-adhesion layer is not particularly limited. For example, a method for forming an easy-adhesion layer on a film that has been subjected to all stretching steps, a polyester resin film, A method of forming an easy-adhesion layer during the stretching process, that is, between the longitudinal stretching process and the lateral stretching process, and a method of forming an easy-adhesion layer immediately before or after being bonded to the polarizing film are adopted. Is done. In the case of a biaxially stretched film, from the viewpoint of productivity, a method in which an easy-adhesion layer is formed after the polyester-based resin film is stretched in the longitudinal direction and then laterally stretched is preferably employed. The easy adhesion layer can be applied to both surfaces of the polyester resin film or one surface bonded to the polarizing film made of polyvinyl alcohol resin through an adhesive.

  The component constituting the easy-adhesion layer is not particularly limited. For example, a polyester-based resin, a urethane-based resin having a polar group in the skeleton, a relatively low molecular weight, and a relatively low glass transition temperature, Or acrylic resin etc. are mentioned. Moreover, a crosslinking agent, an organic or inorganic filler, a surfactant, a lubricant and the like can be contained as necessary.

  The surface of the polyester resin film opposite to the surface to be attached to the polarizing film may be subjected to a surface treatment such as an antiglare treatment, a hard coat treatment, or an antistatic treatment.

(Cellulosic resin film)
The cellulose-based resin film used in the front side polarizing plate in the present invention is a film made of a partially esterified product or a completely esterified product of cellulose, such as cellulose acetate ester, propionate ester, butyrate ester, mixed ester thereof, and the like. The film which consists of can be mentioned. More specifically, a triacetyl cellulose film, a diacetyl cellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film, and the like can be given. As such a cellulose-based resin film, an appropriate commercially available product, for example, Fujitac TD80 (manufactured by Fuji Film Co., Ltd.), Fujitac TD80UF (manufactured by Fuji Film Co., Ltd.), Fujitac TD80UZ (manufactured by Fuji Film Co., Ltd.), KC8UX2M (manufactured by Konica Minolta Opto Co., Ltd.), KC8UY (manufactured by Konica Minolta Opto Co., Ltd.) and the like can be used.

(adhesive)
In the front side polarizing plate described above, the polarizing plate (back side polarizing plate) of the present invention is used as an adhesive for bonding the polarizing film and the polyester resin film and bonding the polarizing film and the cellulose resin film. From among the various adhesives described above for), those suitable for each film can be appropriately selected and used.

[Liquid Crystal Display]
The present invention also includes a backlight, a light diffusing plate, and the above-described liquid crystal panel of the present invention in this order, and the liquid crystal panel is disposed such that the polypropylene resin film faces the light diffusing plate. A device is also provided. Such a liquid crystal display device of the present invention is provided with a liquid crystal panel in which the polarizing plate of the present invention is bonded to the back surface of the liquid crystal cell, and thus has sufficient mechanical strength while corresponding to thinning. In addition, this liquid crystal display device has a significantly reduced decrease in transmittance under severe high temperature environment, and the front contrast is improved while using the polarizing plate of the present invention that can sufficiently withstand use under severe high temperature environment. It is a thing.

  In the liquid crystal display device of the present invention, regarding the portions other than the above-described features, an appropriate configuration of a conventionally known liquid crystal display device can be adopted, and the liquid crystal display device appropriately includes constituent members that are normally provided in addition to the liquid crystal panel. Can do. The light diffusing plate and the backlight constituting the liquid crystal display device can be the same as those used in general liquid crystal display devices. The “rear side” of the liquid crystal cell and liquid crystal panel described above means the backlight side when the liquid crystal panel is mounted on the liquid crystal display device, and the “front side” of the liquid crystal cell and liquid crystal panel means the liquid crystal panel. Means the viewing side when mounted on a liquid crystal display device.

[Polarizing plate set]
The present invention further includes a set of polarizing plates bonded to both surfaces of the liquid crystal cell, wherein the polarizing plate disposed on the back side of the liquid crystal cell is the above-described polarizing plate of the present invention, and the retardation film thereof A pressure-sensitive adhesive layer is provided on the side, and a polarizing plate disposed on the front side of the liquid crystal cell is a cellulose resin film bonded to one surface of a polarizing film made of a polyvinyl alcohol resin, The present invention also provides a set of polarizing plates in which an adhesive layer is provided on the cellulose resin film side. By using such a set of polarizing plates of the present invention, the above-described liquid crystal cell and liquid crystal display device of the present invention can be suitably manufactured. As described above, the polarizing plate disposed on the front side of the liquid crystal cell has a haze of 0.1% to 40% on the surface of the polarizing film opposite to the surface on which the cellulose resin film is bonded. The polyester-based resin film can be bonded.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. In the examples, “%” and “part” representing the content or amount used are based on weight unless otherwise specified. In the following examples, the in-plane retardation value and the thickness direction retardation value of the stretched film indicate values measured using KOBRA 21ADH (manufactured by Oji Scientific Instruments). Moreover, haze points out the value measured using the haze meter HM-150 type (made by Murakami Color Research Laboratory) based on JISK7136.

<Example 1>
A propylene homopolymer pellet having a melt flow rate of 8 g / min and isotactic stereoregularity was placed in a tank and purged with nitrogen to remove oxygen. This pellet is melt-kneaded with an extruder, extruded from a T-die, and then formed into an air chamber system in which a molten sheet is brought into close contact with a cooling roll by air blown from an air chamber, and a polypropylene resin film having a thickness of 80 μm. A protective film consisting of

  The pellets subjected to melt extrusion have a xylene soluble content at 20 ° C. of 0.28%, and the protective film obtained by melt extrusion has a xylene soluble content at 20 ° C. of 0.28%. The amount of change in the xylene solubles due to the film formation was calculated as 0.28% −0.28% = 0.00.

A polarizing film having iodine adsorbed and oriented on polyvinyl alcohol was prepared. And the corona discharge process was given to the single side | surface of the polypropylene-type protective film produced above, and the said corona treatment surface and the said polarizing film were bonded through the epoxy-type ultraviolet curable adhesive within 30 second after that. . Separately, one side of a stretched norbornene-based resin film (in-plane retardation value R ₀ : 63 nm, thickness direction retardation value R _th : 225 nm) having a thickness of 60 μm was subjected to corona discharge treatment, and the corona-treated surface within 30 seconds thereafter. And the other surface of the polarizing film were bonded via the same epoxy-based ultraviolet curable adhesive. Then, the ultraviolet-ray was irradiated from the polypropylene resin film side using the ultraviolet irradiation system made from Fusion UV Systems, and the adhesive agent was hardened. Thus, a polarizing plate was produced in which a protective film made of a polypropylene resin film was laminated on one side of a polarizing film, and a retardation film made of a norbornene resin was laminated on the other side with an epoxy ultraviolet curable adhesive. The epoxy ultraviolet curable adhesive used here contains the trade name “Celoxide 2021P” manufactured by Daicel Chemical Industries, Ltd. as an adhesive component, and a product manufactured by ADEKA Corporation as a photocationic polymerization initiator. It is a solventless type containing the name “Adeka Opton CP77”.

  When the obtained polarizing plate was subjected to a heat resistance test for 500 hours under drying at 80 ° C., the surface of the protective film made of a polypropylene resin film was as good as before the test. Moreover, when the haze (unit is%) before and after the heat resistance test was measured using a haze meter HM-150 manufactured by Murakami Color Research Laboratory, the amount of change (the haze after the heat test (%)). -Haze (%) before the heat test, the same applies hereinafter) was 0.05, and it was confirmed that almost no change occurred.

<Example 2>
A polypropylene resin film was formed in the same manner as in Example 1 except that no nitrogen purge was performed in the tank. The xylene soluble content at 20 ° C. of the pellets subjected to melt extrusion was 0.28%, and the xylene soluble content at 20 ° C. of the protective film obtained by melt extrusion was 0.31%. Therefore, the amount of change in the xylene solubles due to the film formation from the pellets was calculated as 0.31% −0.28% = 0.03. Using this polypropylene protective film, a polarizing plate was produced in the same manner as in Example 1.

  When the obtained polarizing plate was subjected to a heat resistance test under the same conditions as in Example 1 and the haze before and after the test was measured, the amount of change was 0.10, and it was confirmed that almost no change occurred.

<Example 3>
When forming a film, a polypropylene resin film is produced in the same manner as in Example 1 except that the air chamber method is not used and a nip method in which a molten sheet extruded from a T die is sandwiched between a cooling roll and a touch roll is used. Was formed. The xylene soluble content at 20 ° C. of the pellets subjected to melt extrusion was 0.28%, and the xylene soluble content at 20 ° C. of the protective film obtained by melt extrusion was 0.28%. Therefore, the amount of change in the xylene solubles due to the film formation from the pellets was calculated as 0.28% −0.28% = 0.00. Using this polypropylene protective film, a polarizing plate was produced in the same manner as in Example 1.

  When the obtained polarizing plate was subjected to a heat resistance test under the same conditions as in Example 1 and the haze before and after the test was measured, the amount of change was 0.10, and it was confirmed that almost no change occurred.

<Example 4>
Pellets of propylene-ethylene random copolymer (ethylene content 3.7%, synthesized using a metallocene catalyst) having a melt flow rate of 7 g / min and isotactic stereoregularity in a tank A nitrogen purge was performed to remove oxygen. The pellets were melt-kneaded with an extruder, extruded from a T-die, and then formed into a film by a nip method in which a molten sheet was sandwiched between a cooling roll and a touch roll to produce a film. The xylene soluble content at 20 ° C. of the pellets subjected to melt extrusion was 0.34%, and the xylene soluble content at 20 ° C. of the protective film obtained by melt extrusion was 0.40%. Therefore, the amount of change in xylene solubles due to the film formation from the pellets was calculated to be 0.40% −0.34% = 0.06. Using this polypropylene protective film, a polarizing plate was produced in the same manner as in Example 1.

  About the obtained polarizing plate, the heat resistance test was done on the same conditions as Example 1, and when the haze before and behind a test was measured, the change amount was 0.14 and it confirmed that there was almost no change.

<Comparative Example 1>
Pellets made of propylene-ethylene random copolymer (ethylene content 4.6%) with a melt flow rate of 8 g / min and isotactic stereoregularity are placed in a tank and purged with nitrogen to remove oxygen. did. The pellets were melt-kneaded with an extruder, extruded from a T-die, and then formed into a film by a nip method in which a molten sheet was sandwiched between a cooling roll and a touch roll to produce a film. The xylene soluble content at 20 ° C. of the pellets subjected to melt extrusion was 4.0%, and the xylene soluble content at 20 ° C. of the protective film obtained by melt extrusion was 5.1%. Therefore, the amount of change in the xylene solubles due to the film formation from the pellets was calculated to be 5.1% -4.0% = 1.1. Using this polypropylene protective film, a polarizing plate was produced in the same manner as in Example 1.

  When the obtained polarizing plate was subjected to a heat resistance test under the same conditions as in Example 1, a white bleed was generated on the entire surface of the protective film made of a polypropylene resin film. Moreover, when the haze before and behind a heat resistance test was measured, the amount of change was 14, and the change of the haze was large.

  The results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1. In Table 1, A is the xylene soluble content at 20 ° C. of the polypropylene resin material (pellet) subjected to melt extrusion, B is the xylene soluble content at 20 ° C. of the film produced by melt extrusion, and the difference C Is the amount of change in xylene solubles due to melt extrusion (BA), ΔH is the amount of change in haze after the heat resistance test, that is, haze after test (%)-haze before test (%). Yes.

<Example 5>
A stretched norbornene-based resin film (in-plane retardation value R ₀ : 63 nm, thickness direction retardation value R _th : 225 nm) having a thickness of 60 μm was prepared, and the adhesion surface was subjected to corona treatment. Separately, a biaxially stretched polyethylene terephthalate film (thickness of orientation main axis: 2 degrees, in-plane retardation value R ₀ : 3800 nm) having a thickness of 37 μm and a haze of 3% was prepared, and the adhesive surface was subjected to corona treatment. . A photocurable adhesive is provided with a corona-treated surface of the norbornene resin film on one surface of a polarizing film in which iodine is adsorbed and oriented on polyvinyl alcohol, and a corona-treated surface of the stretched polyethylene terephthalate film on the other surface. And the adhesive was cured with ultraviolet rays to produce a polarizing plate. An acrylic pressure-sensitive adhesive layer having a thickness of 25 μm was provided on the outer surface of the stretched norbornene resin film of this polarizing plate. The polarizing plate was attached to the front surface of the liquid crystal cell on the outer surface side of the stretched norbornene resin film on which the pressure-sensitive adhesive layer was formed. A liquid crystal panel was assembled by sticking via an adhesive, and a liquid crystal display device was fabricated by combining it with a commercially available light diffusion plate and backlight. Front contrast was measured using SR manufactured by Otsuka Electronics. The front contrast was 44251, and good results could be obtained. The front contrast was improved by using a polypropylene resin having a small amount of change in xylene-soluble content due to film formation from a resin raw material. The liquid crystal display device was left to dry at 80 ° C. for 2 hours, and the front contrast was measured. As a result, it was 44051, the difference in contrast with that before the dry heat test was 200, and no significant reduction in contrast was observed. .

<Example 6>
The polarizing plate disposed on the front side of the liquid crystal cell is Example 5 except that norbornene-based resin films having different retardation values (in-plane retardation value R ₀ : 55 nm, thickness direction retardation value R _th : 124 nm) are used. What was produced by the same method as the front side polarizing plate was used. The polarizing plate disposed on the back side of the liquid crystal cell is Example 1 except that norbornene-based resin films having different retardation values (in-plane retardation value R ₀ : 55 nm, thickness direction retardation value R _th : 124 nm) are used. What was produced by the same method was used. Each polarizing plate was attached to the front side and the back side of the liquid crystal cell to assemble a liquid crystal panel, and this was combined with a commercially available light diffusion plate and backlight to produce a liquid crystal display device. The front contrast of this liquid crystal display device was 43500, and good results could be obtained. The liquid crystal display device was left to dry at 80 ° C. for 2 hours, and the front contrast was measured. As a result, it was 43262, the difference in contrast with that before the dry heat test was 238, and no significant reduction in contrast was observed. .

<Example 7>
On the front side of the liquid crystal cell, the same polarizing plate as that used on the front side in Example 5 was attached, and on the back side of the liquid crystal cell, the polarizing plate of Example 2 was acrylic on the retardation film side. A liquid crystal panel was assembled by adhering via an adhesive, and this was combined with a commercially available light diffusion plate and backlight to produce a liquid crystal display device. This liquid crystal display device had a front contrast of 43834, and good results could be obtained. The front contrast was improved by using a polypropylene resin having a small amount of change in xylene-soluble content due to film formation from a resin raw material. When this liquid crystal display device was left to stand at 80 ° C. for 2 hours and the front contrast was measured, it was 43622, the difference in contrast with that before the dry heat test was 212, and no significant reduction in contrast was observed. .

<Comparative example 2>
On the front side of the liquid crystal cell, the same polarizing plate as used on the front side in Example 5 was attached, and on the back side of the liquid crystal cell, the polarizing plate of Comparative Example 1 was acrylic adhesive on the retardation film side. The liquid crystal panel was assembled by sticking via an agent, and this was combined with a commercially available light diffusion plate and backlight to produce a liquid crystal display device. The front contrast of this liquid crystal display device was 42001, which was slightly lower than those of Examples 5-7. When this liquid crystal display device was left to dry at 80 ° C. for 2 hours and the front contrast was measured, it was 41291, and the difference in contrast with that before the dry heat test was 710. It was seen.

Claims (8)

It is a polarizing plate in which a transparent resin film is bonded to both surfaces of a polarizing film made of a polyvinyl alcohol resin via an adhesive,
One of the transparent resin films is a retardation film made of a norbornene-based resin having an in-plane retardation of 40 nm to 300 nm and a thickness direction retardation of 80 nm to 300 nm,
The other of the transparent resin films is a polarizing plate made of a polypropylene resin having a xylene soluble content at 20 ° C. of 1% by weight or less. The transparent resin film made of the polypropylene resin has the following formula:
Amount of change in xylene-soluble content by melt extrusion = xylene-soluble content in film produced by melt extrusion at 20 ° C [wt%]-
Xylene soluble content at 20 ° C. [wt%] of the resin raw material subjected to the melt extrusion
The polarizing plate according to claim 1, which is produced by a melt extrusion method in which the amount of change in xylene solubles by melt extrusion defined by   The transparent resin film made of the polypropylene-based resin is manufactured by being melt-kneaded and then brought into close contact with the cooling roll by the air blown from the air chamber when it is extruded from a T die and brought into contact with the cooling roll in the form of a molten sheet. The polarizing plate according to claim 1, wherein the polarizing plate is a thin film.   The polarizing plate according to claim 1, wherein the polypropylene resin is a polymer containing 99% by weight or more of a structural unit derived from propylene. The front side polarizing plate is bonded to the viewing side of the liquid crystal cell via an adhesive layer, and the back side polarizing plate is bonded to the opposite side of the liquid crystal cell via an adhesive layer,
The said back side polarizing plate is a polarizing plate in any one of Claims 1-4, Comprising: The liquid crystal panel currently bonded so that the phase difference film side may face a liquid crystal cell.   The front-side polarizing plate has a cellulose resin film bonded to one surface of a polarizing film made of polyvinyl alcohol resin, and a polyester resin film having a haze of 0.1% to 40% bonded to the other surface. The liquid crystal panel according to claim 5, wherein the liquid crystal panel is bonded so that the cellulose resin film side faces the liquid crystal cell.   7. A liquid crystal display device comprising a backlight, a light diffusing plate, and the liquid crystal panel according to claim 5 or 6 in this order, wherein the liquid crystal panel is disposed such that the polypropylene resin film faces the light diffusing plate. . A set of polarizing plates to be bonded to both sides of the liquid crystal cell,
The polarizing plate disposed on the back side of the liquid crystal cell is the polarizing plate according to any one of claims 1 to 4, wherein a pressure-sensitive adhesive layer is provided on the retardation film side,
The polarizing plate disposed on the front side of the liquid crystal cell is a cellulose resin film bonded to one surface of a polarizing film made of a polyvinyl alcohol resin, and the pressure-sensitive adhesive layer is on the cellulose resin film side. A set of polarizing plates provided.