JP2009134257A - Retardation film and elliptical polarizing plate using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film which is extremely thin in thickness, has flat wavelength dispersion of retardation, can exhibit excellent light-shielding performance when a broadband 1/4 wavelength plate is made by combining a 1/4 wavelength plate and a 1/2 wavelength plate and can dissolve attachment unevenness and void upon the attachment, and to provide an elliptical polarizing plate using the same. <P>SOLUTION: The retardation film is made of a laterally stretched film of polypropylene-based resin which has a thickness of ≤25 μm, an in-plane retardation (Ro) of 70 to 400 nm and an Nz coefficient of 0.9 to 1.1 as defined by the formula: Nz=(n<SB>x</SB>-n<SB>z</SB>)/(n<SB>x</SB>-n<SB>y</SB>), wherein n<SB>x</SB>is in-plane refractive index in an in-plane slow axis direction, n<SB>y</SB>is in-plane refractive index in an in-plane fast axis direction, and n<SB>z</SB>is refractive index in the thickness direction. The elliptical polarizing plate using the retardation film is also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a retardation film made of polypropylene resin and an elliptically polarizing plate using the same. Specifically, the present invention relates to a retardation film capable of extremely reducing the film thickness, and an extremely thin elliptical polarizing plate using the retardation film. The present invention also relates to a liquid crystal display device using the elliptically polarizing plate.

  In recent years, low-power consumption, low-voltage, light-weight and thin liquid crystal displays are rapidly spreading as information display devices such as mobile phones, portable information terminals, computer monitors, and televisions. With the development of liquid crystal technology, various modes of liquid crystal displays and optical members have been proposed, and response speed, contrast, viewing angle, and broadband properties have been improved.

  In a reflective or transflective liquid crystal display typified by a cellular phone or the like, a retardation film functioning as a quarter-wave plate or a combination of a quarter-wave plate and a half-wave plate is used in a wide band. An elliptically polarizing plate in which a retardation film functioning as a / 4 wavelength plate is bonded to a linear polarizing plate at a predetermined angle is used. Such an elliptically polarizing plate, particularly a circularly polarizing plate, has an anti-reflection function, and in each application, the internal reflection is sufficient for all incident light in the visible light region that can be seen by human eyes. It is desired to obtain a good light shielding performance that can be suppressed.

Combining a retardation film that functions as a quarter-wave plate at a wavelength in the visible region and a retardation film that functions as a half-wave plate at that wavelength, the incident light in a wide wavelength region is 1/4. Conventionally, a so-called broadband quarter wave plate that functions as a wave plate has been used. For example, Japanese Patent Laid-Open No. 5-100114 (Patent Document 1) discloses a quarter wave plate made of a polycarbonate film. And an example in which a half-wave plate is combined. However, a broadband quarter-wave plate using polycarbonate is difficult to function as a perfect quarter-wave plate at all wavelengths, and it is difficult to sufficiently control internal reflection. It is not done. Furthermore, since the polycarbonate film has a large photoelastic coefficient of about 27 × 10 ⁻¹³ cm ² / dyne, uneven bonding occurs when it is bonded to a linear polarizing plate, or due to temperature changes during use, black display is caused. However, there is a problem that a white spot phenomenon occurs in which light from the backlight is partially lost.

Therefore, Japanese Patent Application Laid-Open No. 11-149015 (Patent Document 2) describes the difference (birefringence) Δn ₄₀₀ between the maximum refractive index and the minimum refractive index in a plane at a wavelength of 400 nm and the maximum refractive index in a plane at a wavelength of 500 nm. Disclosed is a combination of a half-wave plate and a quarter-wave plate having a ratio between the refractive index and the minimum refractive index (birefringence) Δn ₅₀₀ (Δn ₄₀₀ / Δn ₅₀₀ ) of less than 1.05 In the specific example (example), a quarter-wave plate and a half-wave plate each made of a cyclic polyolefin resin film are combined. Since the cyclic polyolefin resin film has a small photoelastic coefficient of about 4 × 10 ⁻¹³ cm ² / dyne, it is also effective in suppressing sticking unevenness and white spots.

  However, when a polycarbonate film or a cyclic polyolefin resin film is stretched, if the stretch ratio is increased too much, the in-plane retardation value decreases due to the thin film thickness. Therefore, in order to express a desired retardation value, all the films have to secure a certain film thickness, and cannot meet the demand for thinning that the market demands. Also, with polycarbonate and cyclic polyolefin-based resins, it is difficult to produce a completely uniaxial retardation film by transverse stretching, and it has been necessary to rely on longitudinal stretching. In general, in longitudinal stretching, the width direction becomes a free end, and neck-in occurs in the stretched film, so that it is difficult to produce a thin retardation film.

More recently, it has been studied to develop a phase difference by coating with a liquid crystal compound as one method of thinning. However, when such a coating type retardation film is used, the liquid crystalline compound usually contains a mesogen having an aromatic ring, so that the wavelength dispersion becomes positive dispersion or the alignment of the liquid crystalline compound is retarded. It may be difficult to obtain a uniaxially oriented monodomain suitable for a film. Furthermore, there is a problem that film thickness unevenness is likely to occur in the drying process at the time of manufacture, and in-plane phase difference control is difficult.
JP-A-5-100114 Japanese Patent Laid-Open No. 11-149015

  Therefore, the problems of the present invention are very thin, and the chromatic dispersion of the phase difference is flat, which is good when a 1/4 wavelength plate and a 1/2 wavelength plate are combined to form a broadband 1/4 wavelength plate. Another object of the present invention is to provide a retardation film including a uniaxial quarter-wave plate and a half-wave plate that exhibits excellent light-shielding performance and further eliminates uneven bonding and white spots during bonding.

  Another object of the present invention is to provide a retardation film that achieves thinning and widening at the same time by producing an almost perfect uniaxial film by transverse stretching, and has excellent utilization efficiency. .

That is, according to the present invention, it is composed of a polypropylene resin laterally stretched film, has a thickness of 25 μm or less, an in-plane retardation value (Ro) in the range of 70 to 400 nm, and an in-plane retardation of the film. the refractive index of the axial n _x, the refractive index in the in-plane fast axis direction n _y, the refractive index in the thickness direction is taken as n _z, wherein: Nz coefficient _{= (n x -n z) /} (n a retardation film Nz coefficient defined by _x -n _y) is in the range of 0.9 to 1.1 is provided.

  The polypropylene resin constituting the retardation film is preferably composed of a copolymer of propylene and ethylene containing 10% by weight or less of ethylene units. It is also preferred that the polypropylene resin is substantially composed of a propylene homopolymer. The polypropylene resin preferably contains a nucleating agent.

  The retardation film can adjust the in-plane retardation value so as to function as a quarter-wave plate. Further, the in-plane retardation value can be adjusted so as to function as a half-wave plate.

  According to this invention, the elliptically polarizing plate formed by laminating | stacking the said retardation film on a linearly-polarizing plate is also provided. Specifically, for example, the above-described retardation film functioning as a quarter wavelength plate can be laminated on a linear polarizing plate to form an elliptical polarizing plate. In addition, the retardation film functioning as the ¼ wavelength plate, the retardation film functioning as the ½ wavelength plate, and the linear polarizing plate may be laminated in this order to form an elliptical polarizing plate. it can.

  Furthermore, according to the present invention, there is also provided a liquid crystal display device in which any one of the above elliptical polarizing plates is laminated on at least one side of a liquid crystal cell.

  In the present invention, a stretched film of polypropylene resin is applied to a retardation film, thereby producing an effect that a desired retardation value can be expressed with an extremely thin film having a thickness of 25 μm or less. In addition, by adopting a polypropylene resin film, there is an advantage that an almost complete uniaxial film can be produced by stretching at a high magnification even in lateral stretching. Furthermore, since the retardation film of the present invention can be produced by transverse stretching, there is also an advantage that the effective width can be widened while the film thickness is reduced.

  Since the elliptically polarizing plate of the present invention is formed by laminating a retardation film having a very thin film thickness as described above on a linearly polarizing plate, the elliptically polarizing plate itself can be thinned, and a liquid crystal display device in which it is laminated It will also contribute to thinning of the wall.

Hereinafter, embodiments of the present invention will be described in detail.
[Phase difference film]
In the present invention, the retardation film is constituted by a laterally stretched film of a polypropylene resin. Since the polypropylene resin film is crystalline, the expression rate of the retardation value is extremely high, and a large retardation value can be easily obtained by stretching. For this reason, the retardation film which has a desired retardation value with a thin film thickness can be obtained.

Further, polypropylene resin, the difference (birefringence) △ n ₄₀₀ between the maximum refractive index and the minimum refractive index in the plane at a wavelength of 400 nm, the difference (double the maximum refractive index and the minimum refractive index in the plane at a wavelength of 500nm the ratio between the _{refractive) △ n 500 (△ n 400} / △ n 500) since it is less than 1.05, the broadband each combination of a half-wave plate and a quarter-wave plate formed of a polypropylene resin Excellent light-shielding performance can be obtained. In this specification, the value of Δn ₄₀₀ / Δn ₅₀₀ is defined as chromatic dispersion of phase difference. This is sometimes simply referred to as “wavelength dispersion”.

Further, since the polypropylene-based resin has a small photoelastic coefficient of about 2 × 10 ⁻¹³ cm ² / dyne, it is bonded when a half-wave plate and a quarter-wave plate are bonded, or a linear polarizing plate. Sometimes sticking unevenness and white spots can be suppressed. In addition, since the polypropylene-based resin can be stretched at a high magnification, it has been found that a completely uniaxial film can be produced by transverse stretching. Thereby, thinning and widening can be achieved simultaneously, and the utilization efficiency is excellent.

  The raw film formed from such a polypropylene resin is laterally stretched to develop a retardation. In this case, the thickness of the retardation film can be 25 μm or less. The film thickness is more preferably 20 μm or less. When the film thickness exceeds 25 μm, the merit of thinning becomes difficult to be exhibited effectively. Moreover, when the film thickness is too small, wrinkles and the like are likely to occur in the film, and the handling property at the time of winding and bonding tends to be deteriorated. Therefore, the film thickness is preferably 5 μm or more, and more preferably 8 μm or more.

In the retardation film of the present invention, the in-plane retardation value (Ro) is in the range of 70 to 400 nm, and more preferably in the range of 80 to 330 nm. The retardation value (Rth) in the thickness direction is preferably in the range of 28 to 240 nm. The Nz coefficient is in the range of 0.9 to 1.1, and more preferably in the range of 0.95 to 1.05. From these ranges, an appropriate selection may be made according to the characteristics required for the applied liquid crystal display device. Here, if approximately a 1 Nz coefficient, the following formula (III), n _y and n _z are means that approximately equal, such a phase difference film, becomes almost perfect uniaxial.

Incidentally, the in-plane slow axis direction of the refractive index of the film n _x, the refractive index n _y in-plane fast axis direction (direction orthogonal with the slow axis and the plane), the refractive index in the thickness direction n _z When the thickness is d, the in-plane retardation value (Ro), the thickness direction retardation value (Rth), and the Nz coefficient are respectively expressed by the following formulas (I), (II), and (III): Defined by

_{Ro = (n x -n y)} × d (I)
Rth = _{[(n x + n y) /} 2-n z ] × d (II)
_{Nz = (n x -n z)} / (n x -n y) (III)
Further, from these equations (I), (II), and (III), the relationship between the Nz coefficient, the in-plane retardation value (Ro), and the thickness direction retardation value (Rth) is expressed by the following equation: (IV).

Nz = Rth / Ro + 0.5 (IV)
[Polypropylene resin]
The polypropylene resin constituting the retardation film of the present invention can be composed of a propylene homopolymer or propylene and another copolymerizable comonomer. Since the homopolymer of propylene has higher crystallinity than the copolymer of propylene and other copolymerizable comonomers, the film rigidity and yield strength can be further increased. Therefore, by constituting the retardation film from a homopolymer of propylene, it becomes possible to further improve the handleability in the retardation film preparation step, the polarizing plate formation step, and the bonding step with the TV.

The polypropylene resin constituting the retardation film of the present invention can be produced by a method of homopolymerizing propylene or a method of copolymerizing propylene and another copolymerizable comonomer using a known polymerization catalyst. it can. Examples of known polymerization catalysts include the following.
(1) a Ti—Mg-based catalyst comprising a solid catalyst component containing magnesium, titanium, and halogen as essential components;
(2) 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,
(3) Metallocene catalysts.

  Among these catalyst systems, in the production of the polypropylene resin used in the retardation film of the present invention, an organic aluminum compound and an electron donating compound are combined with a solid catalyst component containing magnesium, titanium, and halogen as essential components. Is most commonly used. More specifically, the organoaluminum compound is preferably triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, tetraethyldialumoxane, etc., and the electron donating compound is preferably cyclohexylethyldimethoxysilane. Tert-butylpropyldimethoxysilane, tert-butylethyldimethoxysilane, dicyclopentyldimethoxysilane, and the like.

  On the other hand, examples of the solid catalyst component containing magnesium, titanium, and halogen as essential components are described in, for example, JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. Examples of the metallocene catalyst include catalyst systems described in, for example, Japanese Patent No. 2587251, Japanese Patent No. 2627669, Japanese Patent No. 2668732, and the like.

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

  The stereoregularity of the polypropylene resin may be any of isotactic, syndiotactic, and atactic. In the present invention, syndiotactic or isotactic polypropylene resins are preferably used from the viewpoint of heat resistance.

  The polypropylene resin used in the present invention can be composed of a propylene homopolymer, and contains a small amount of a comonomer mainly composed of propylene and copolymerizable therewith, for example, 20% by weight or less, preferably 10% by weight or less. Copolymerized with When a copolymer is used, the amount of comonomer is preferably 1% by weight or more.

  The comonomer copolymerized with propylene can be, for example, ethylene or an α-olefin having 4 to 20 carbon atoms. Specific examples of the α-olefin in this case include the following.

1-butene, 2-methyl-1-propene (above C ₄ );
1-pentene, 2-methyl-1-butene, 3-methyl-1-butene (above C ₅ );
1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3- Dimethyl-1-butene (above C ₆ );
1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2-ethyl-1-pentene, 2-methyl-3-ethyl-1-butene (above C ₇ );
1-octene, 5-methyl-1-heptene, 2-ethyl-1-hexene, 3,3-dimethyl-1-hexene, 2-methyl-3-ethyl-1-pentene, 2,3,4-trimethyl- 1-pentene, 2-propyl-1-pentene, 2,3-diethyl-1-butene (above C ₈ );
1-nonene (C ₉ ); 1-decene (C ₁₀ ); 1-undecene (C ₁₁ );
1-dodecene (C ₁₂ ); 1-tridecene (C ₁₃ ); 1-tetradecene (C ₁₄ );
1-pentadecene (C ₁₅ ); 1-hexadecene (C ₁₆ ); 1-heptadecene (C ₁₇ );
1-octadecene (C ₁₈ ); 1-nonadecene (C ₁₉ ) and the like.

  Preferred among the α-olefins are α-olefins having 4 to 12 carbon atoms, specifically 1-butene, 2-methyl-1-propene; 1-pentene, 2-methyl-1- Butene, 3-methyl-1-butene; 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4- Methyl-1-pentene, 3,3-dimethyl-1-butene; 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2-ethyl-1-pentene, 2-methyl- 3-ethyl-1-butene; 1-octene, 5-methyl-1-heptene, 2-ethyl-1-hexene, 3,3-dimethyl-1-hexene, 2-methyl-3-ethyl-1-pentene, 2,3,4-trimethyl-1-pen And ten-, 2-propyl-1-pentene, 2,3-diethyl-1-butene; 1-nonene; 1-decene; 1-undecene; 1-dodecene, and the like. From the viewpoint of copolymerizability, 1-butene, 1-pentene, 1-hexene and 1-octene are preferable, and 1-butene and 1-hexene are more preferable.

  The copolymer may be a random copolymer or a block copolymer. Preferred copolymers include propylene / ethylene copolymers and propylene / 1-butene copolymers. In the propylene / ethylene copolymer and the propylene / 1-butene copolymer, the ethylene unit content and the 1-butene unit content are, for example, 616 of “Polymer Analysis Handbook” (published by Kinokuniya, 1995). Infrared (IR) spectrum measurement can be performed by the method described on the page.

  From the viewpoint of improving the transparency and workability of the retardation film, it is preferable to use propylene as a main component and a random copolymer with any unsaturated hydrocarbon. Of these, a copolymer with ethylene is preferred. When making a copolymer, it is advantageous that unsaturated hydrocarbons other than propylene have a copolymerization ratio of about 1 to 10% by weight, and a more preferable copolymerization ratio is 3 to 7% by weight. By setting the unit of unsaturated hydrocarbons other than propylene to 1% by weight or more, there is a tendency that an effect of improving processability and transparency appears. On the other hand, if the ratio exceeds 10% by weight, the melting point of the resin tends to decrease and the heat resistance tends to deteriorate, such being undesirable. In addition, when setting it as the copolymer of two or more types of comonomers and propylene, it is preferable that the total content of the unit derived from all the comonomers contained in the copolymer is the said range.

  The polypropylene resin used in the retardation film of the present invention has a melt flow rate (MFR) measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K 7210, 0.1 to 200 g / 10 min. In particular, it is preferably in the range of 0.5 to 50 g / 10 minutes. By using a polypropylene resin having an MFR in this range, a uniform film can be obtained without imposing a large load on the extruder.

  The polypropylene resin may contain a known additive 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 used in the present invention 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 metal salts and high density polyethylene are more preferable. Moreover, 0.01-3 weight% is preferable and, as for the addition amount of the nucleating agent with respect to polypropylene resin, 0.05-1.5 (wt%) is more preferable. A plurality of these additives may be used in combination.
[Polypropylene resin film]
Polypropylene resin can be formed into an original film by any method. This raw film is transparent and has substantially no in-plane retardation. For example, a polypropylene system having substantially no in-plane retardation by extrusion molding from molten resin, solvent casting method in which a resin dissolved in an organic solvent is cast on a flat plate, and the solvent is removed to form a film. A resin raw film can be obtained.

  As an example of a method for producing a raw film, a film forming method by extrusion will be described in detail. The polypropylene resin is melt-kneaded by rotation of a screw in an extruder and extruded from a T die into a sheet. The temperature of the molten sheet to be extruded is about 180 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 obtained film becomes non-uniform, and there is a possibility that the film has a 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, in the case of a single screw extruder, 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 in the resin supply unit, and the screw groove space volume in the resin metering unit The compression ratio, which is the ratio (the former / the latter), is about 1.5 to 4, and a screw of a full flight type, a barrier type, or a type having a Maddock type kneading portion can be used. From the viewpoint of suppressing deterioration and decomposition of the polypropylene resin and uniformly melting and kneading, it is necessary to use a barrier type screw having an L / D of 28 to 36 and a compression ratio of 2.5 to 3.5. preferable. Moreover, in order to suppress deterioration and decomposition | disassembly of polypropylene resin as much as possible, it is preferable to make the inside of an extruder into a nitrogen atmosphere or a vacuum. Furthermore, in order to remove the volatile gas generated by the deterioration or decomposition of the polypropylene resin, it is also preferable to provide an orifice 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 tip of the extruder at the orifice means increasing the back pressure at the tip, thereby improving the stability of extrusion. The diameter of the orifice to be used is more preferably 2 mmφ or more and 4 mmφ or less.

  The T-die used for extrusion preferably has no fine steps or scratches on the surface of the resin flow path, and its lip portion is plated or coated with a material having a low coefficient of friction with the molten polypropylene resin. In addition, a sharp edge shape having a lip tip polished to 0.3 mmφ or less is preferable. Examples of the material having a small friction coefficient include tungsten carbide type and fluorine type 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 having excellent appearance uniformity can be obtained. In the T-die, the manifold has a coat hanger shape and preferably satisfies the following condition (1) or (2), and more preferably satisfies the condition (3) or (4).

(1) When the lip width of the T die is less than 1500 mm: length in the thickness direction of the T die> 180 mm
(2) When the lip width of the T die is 1500 mm or more: Length in the thickness direction of the T die> 220 mm
(3) When the lip width of the T die is less than 1500 mm: Length in the height direction of the T die> 250 mm
(4) 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. An original film having excellent accuracy and a more uniform retardation can be obtained.

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

  The molten sheet extruded from the T-die is between a metal cooling roll (also called a chill roll or a casting roll) and a touch roll containing an elastic body that rotates in pressure contact with the circumferential direction of the metal cooling roll. The desired film can be obtained by clamping and cooling to solidify. In this case, the touch roll may be one in which an elastic body such as rubber is directly on the surface, or may be one in which the surface of the elastic body roll is covered with an outer cylinder made of a metal sleeve. When a touch roll whose surface is covered with an outer cylinder made of a metal sleeve is used, cooling is usually performed by directly sandwiching a molten sheet of polypropylene resin between the metal cooling roll and the touch roll. On the other hand, in the case of using a touch roll whose surface is an elastic body, a biaxially stretched film of a thermoplastic resin can be interposed between the molten sheet of polypropylene resin and the touch roll for sandwiching.

  When the molten sheet of polypropylene resin is sandwiched between the cooling roll and the touch roll as described above and cooled and solidified, both the cooling roll and the touch roll have their surface temperatures lowered, and the molten sheet is rapidly cooled. I need to do it. For example, the surface temperature of both rolls is preferably adjusted to a range of 0 ° C. or higher and 30 ° C. or lower. When these surface temperatures exceed 30 ° C., it takes time to cool and solidify the molten sheet, so that the crystal component in the polypropylene resin grows, and the resulting film may be inferior in transparency. . The surface temperature of the roll is preferably less than 30 ° C, more preferably less than 25 ° C. On the other hand, if the surface temperature of the roll is lower than 0 ° C., condensation may form on the surface of the metallic cooling roll, and water droplets may adhere, resulting in a tendency to deteriorate the appearance of the film.

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

  The touch roll that forms the nip portion with the metal cooling roll has a surface hardness of 65 to 80 as a value measured by a spring type hardness test (A type) defined in JIS K 6301. Is more preferable, and 70 to 80 is more preferable. By using a rubber roll having such a surface hardness, it becomes easy to maintain a uniform linear pressure applied to the molten sheet, and a bank of the molten sheet (resin pool) is provided between the metal cooling roll and the touch roll. ) Can be easily formed into a film.

  The pressure (linear pressure) when sandwiching the molten sheet is determined by the pressure for pressing the touch roll against the metal cooling roll. The linear pressure is preferably 50 N / cm or more and 300 N / cm or less, and more preferably 100 N / cm or more and 250 N / cm or less. By setting the linear pressure within the above range, it becomes easy to produce a polypropylene resin film while maintaining a constant linear pressure without forming a bank.

  When a biaxially stretched film of a thermoplastic resin is sandwiched between a metallic cooling roll and a touch roll together with a molten sheet of polypropylene resin, the thermoplastic resin constituting the biaxially stretched film is strong with the polypropylene resin. Any resin may be used as long as it is not heat-sealed, and specific examples include polyester, polyamide, polyvinyl chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and polyacrylonitrile. Among these, polyesters that have little dimensional change due to humidity, heat, and the like are most preferable. In this case, the thickness of the biaxially stretched film is usually about 5 to 50 μm, preferably 10 to 30 μm.

  In this method, the distance (air gap) from the lip of the T die to the pressure between the metal cooling roll and the touch roll is preferably 200 mm or less, and more preferably 160 mm or less. The molten sheet extruded from the T-die is stretched from the lip to the roll, and orientation tends to occur. By shortening the air gap as described above, a film having a smaller orientation can be obtained. The lower limit value of the air gap is determined by the diameter of the metal cooling roll to be used, the diameter of the touch roll, and the tip shape of the lip to be used, and is usually 50 mm or more.

  The processing speed when producing a polypropylene resin film by this method is determined by the time required for cooling and solidifying the molten sheet. When the diameter of the metal 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 5 to 20 m / min at the maximum.

The molten sheet sandwiched between the metal cooling roll and the touch roll is cooled and solidified by contact with the roll. And after slitting an edge part as needed, it is wound up by a winder and becomes a film. Under the present circumstances, in order to protect the surface until it uses a film, you may wind up in the state which bonded the surface protection film which consists of another thermoplastic resin to the single side | surface or both surfaces. When a molten sheet of polypropylene resin is sandwiched between a metal cooling roll and a touch roll together with a biaxially stretched film made of a thermoplastic resin, the biaxially stretched film is used as one surface protective film. You can also.
[Method for producing retardation film]
The retardation film of the present invention can be produced by laterally stretching a raw film made of a polypropylene resin as described above. Here, transverse stretching refers to stretching a long film unwound from a roll in the width direction (lateral direction).

The transverse stretching usually has the following steps.
(A) A preheating step of preheating the raw film at a preheating temperature near the melting point of the polypropylene resin;
(B) A stretching step in which the preheated film is stretched in the transverse direction at a stretching temperature lower than the preheating temperature; and (C) a heat setting step in which the film stretched in the transverse direction is heat-set.

  As a typical transverse stretching method, there is a tenter method. The tenter method is a method in which an original film, which is fixed at both ends in the film width direction with a chuck, is stretched in an oven with an increased chuck interval. A stretching machine (tenter stretching machine) used for the tenter method is usually provided with a mechanism capable of independently adjusting the temperatures in a zone for performing a preheating step, a zone for performing a stretching step, and a zone for performing a heat setting step. By performing transverse stretching using such a tenter stretching machine, a retardation film having excellent axial accuracy and a uniform retardation can be obtained.

  The pre-heating step for transverse stretching is a step that is installed before the step of stretching the film in the width direction, and is a step of heating the film to a temperature sufficient to stretch the film. The preheating temperature in the preheating step means an atmospheric temperature in a zone where the oven preheating step is performed, and a temperature near the melting point of the polypropylene resin film to be stretched is adopted. The residence time in the preheating step of the stretched film is preferably 30 to 120 seconds. When the residence time in this preheating process is less than 30 seconds, stress is dispersed when the film is stretched in the stretching process, which adversely affects the axial accuracy and retardation uniformity as the retardation film. There is a possibility, and when the residence time exceeds 120 seconds, the film receives heat more than necessary, and the film may partially melt and draw down (drip down). The residence time in the preheating step is more preferably 30 to 60 seconds.

  The stretching process of lateral stretching is a process of stretching the film in the width direction. The stretching temperature in this stretching step is usually lower than the preheating temperature. The stretching temperature in the stretching process means the ambient temperature in the zone where the oven stretching process is performed. By stretching the preheated film at a temperature lower than that of the preheating step, the film can be stretched uniformly, and as a result, a retardation film having excellent optical axis and retardation uniformity can be obtained. . The stretching temperature is preferably 5 to 20 ° C lower than the preheating temperature in the preheating step, and more preferably 7 to 15 ° C. The draw ratio at this time may be appropriately selected from the range of about 3 to 10 times in the direction in which the optical axis is expressed (the direction of the slow axis), preferably 3 according to the required retardation value. It is a range of ~ 6 times. By setting the draw ratio at this time to 3 times or more, the Nz coefficient can be in the range of 0.9 to 1.1. On the other hand, if the draw ratio becomes too large, the uniformity of the retardation value may be impaired, so it is preferable to limit it to about 10 times.

  The transverse stretching heat setting step is a step of passing the film through a zone of a predetermined temperature in the oven while maintaining the film width at the end of the stretching step. In order to effectively improve the stability of optical properties such as phase difference and optical axis of the film, the heat setting temperature is from 5 ° C. lower than the stretching temperature in the stretching step to 30 ° C. higher than the stretching temperature. It is preferable to be within the range.

The transverse stretching process may further include a thermal relaxation process. In the tenter method, this thermal relaxation step is usually performed between the stretching step and the heat setting step, and the thermal relaxation zone is provided so that the temperature can be set independently of other zones. It is customary. Specifically, in the thermal relaxation process, after the film is stretched to a predetermined width in the stretching process, the chuck interval is narrowed by a few percent in order to remove unnecessary strain, and is usually smaller than the interval at the end of stretching. Narrowing by about 0.5 to 7% is performed.
[Optical characteristics when used as a wave plate]
When the retardation film of the present invention is used as a quarter-wave plate, the in-plane retardation value (Ro) is preferably in the range of 70 to 160 nm, and more preferably in the range of 80 to 150 nm. preferable. The quarter-wave plate functions to convert light that is incident as linearly polarized light into elliptically polarized light such as circularly polarized light, and light that is incident as elliptically polarized light such as circularly polarized light into linearly polarized light. Have On the other hand, when the retardation film of the present invention is used as a half-wave plate, the in-plane retardation value (Ro) is preferably in the range of 240 to 400 nm, and more preferably in the range of 260 to 330 nm. Is more preferable. The half-wave plate has a function of rotating the direction of linearly polarized light.
[Elliptically polarizing plate]
The quarter-wave plate can be formed into an elliptical polarizing plate by laminating with a linear polarizing plate at a predetermined axial angle or by laminating with a linear polarizing plate at a predetermined axial angle together with a half-wave plate. . FIG. 1 is a schematic cross-sectional view showing a layer structure and a diagram for explaining the relationship of axial angles for an embodiment of an elliptically polarizing plate according to the present invention, and FIG. 2 is another diagram of the elliptically polarizing plate according to the present invention. It is a cross-sectional schematic diagram which shows a layer structure about one form, and a figure for demonstrating the relationship of an axial angle.

  Referring to FIG. 1A, in one embodiment of the present invention, the quarter-wave plate 10 made of the polypropylene resin film described above is laminated on the linearly polarizing plate 20 to form an elliptically polarizing plate 30. it can. In this case, referring to FIG. 1B, the counterclockwise direction is set positive with respect to the absorption axis 22 of the linearly polarizing plate 20, and the in-plane slow axis 12 of the quarter-wave plate 10 is reached. By disposing the angle θ to be 40 to 50 degrees, preferably approximately 45 degrees, the film substantially functions as a circularly polarizing plate. Alternatively, the angle θ reaching the in-plane slow axis 12 of the quarter-wave plate 10 is 130 to 140 degrees, preferably approximately 135, with the counterclockwise direction being positive with respect to the absorption axis 22 of the linearly polarizing plate 20. Even if it arrange | positions so that it may become a degree, it will come to function as a substantially circularly-polarizing plate. Hereinafter, when expressing an angle, the counterclockwise rotation with respect to the reference axis is positive, as in the description here.

  Further, referring to FIG. 2A, in another embodiment of the present invention, the quarter-wave plate 10 and the half-wave plate 15 each made of the polypropylene resin film are laminated, and The elliptically polarizing plate 35 can be formed by laminating the linearly polarizing plate 20 on the half-wave plate 15 side. In this case, referring to FIG. 2B, the angle φ reaching the in-plane slow axis 17 of the half-wave plate 15 is 10 to 20 degrees with reference to the absorption axis 22 of the linearly polarizing plate 20. Preferably, the angle ψ from the in-plane slow axis 17 of the half-wave plate 15 to the in-plane slow axis 12 of the quarter-wave plate 10 is 55 to 65 degrees, preferably about 60 degrees. By being arranged in this manner, it almost functions as a circularly polarizing plate. Alternatively, on the basis of the absorption axis 22 of the linearly polarizing plate 20, the angle φ reaching the in-plane slow axis 17 of the half-wave plate 15 is 100 to 110 degrees, preferably about 105 degrees. Even if the angle ψ from the in-plane slow axis 17 to the in-plane slow axis 12 of the quarter-wave plate 10 is 55 to 65 degrees, preferably about 60 degrees, the circularly polarizing plate is still substantially circular. Will function as. The latter relationship (the angle from the absorption axis of the linear polarizing plate to the in-plane slow axis of the half-wave plate is 100 to 110 degrees) is represented by the reference numeral 22 in FIG. "Is equivalent to the state that is read as". " In the linear polarizing plate, the absorption axis and the transmission axis are in a relationship orthogonal to each other in the plane.

  In particular, as shown in FIG. 2, a laminate of the quarter wavelength plate 10 and the half wavelength plate 15 functions as a quarter wavelength plate in a wide wavelength range in the visible light region, that is, in a wide band. Thus, the elliptically polarizing plate 35 in which the linearly polarizing plate 20 is laminated on the half-wave plate 15 side can convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light over a wide band. Furthermore, by comprising in this way, the angle dependence of the antireflection effect can also be reduced.

  The linearly polarizing plate 20 is an optical element having a function of absorbing linearly polarized light having a vibration surface in a certain direction and transmitting linearly polarized light having a vibration surface in a direction perpendicular thereto, and is generally used in this field. Can be. Specifically, a polyvinyl alcohol linear polarizing plate in which a transparent protective layer is formed on at least one surface of a polarizer made of a polyvinyl alcohol resin film is generally used. A function of absorbing linearly polarized light having a vibrating surface in a certain direction and transmitting linearly polarized light having a vibrating surface in a direction orthogonal to the above by adsorbing and orienting a dichroic dye on a polyvinyl alcohol resin film. Can be granted. As the dichroic dye, iodine or a dichroic organic dye is used. This polarizer can be obtained by subjecting the polyvinyl alcohol resin film to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment after dyeing.

  The transparent protective layer of the linearly polarizing plate 20 is made of, for example, a film of an acetyl cellulose resin typified by triacetyl cellulose (TAC) or diacetyl cellulose, which has been conventionally used as a protective layer for a polarizer. In addition, a film of a cyclic polyolefin resin typified by a norbornene resin, a film of a polypropylene resin, a film of a polyethylene terephthalate resin, a film of poly (meth) acrylate, and the like may be used.

  In the production of an elliptically polarizing plate, for example, a pressure sensitive adhesive (adhesive) is used for laminating a wave plate and a linear polarizing plate, and laminating wave plates (quarter wave plate and half wave plate). Can be used. As the pressure sensitive adhesive, an adhesive mainly composed of an acrylic polymer having excellent transparency and durability is particularly preferably used. The thickness of the pressure sensitive adhesive layer is usually in the range of 5 to 50 μm.

The elliptically polarizing plates 30 and 35 configured as described above can be bonded to a liquid crystal cell by disposing a pressure-sensitive adhesive (adhesive) on the surface side of the quarter-wave plate 10. Can be. This elliptically polarizing plate is laminated on at least one side of the liquid crystal cell to constitute a liquid crystal display device. The elliptically polarizing plate can be disposed on both sides of the liquid crystal cell, the elliptically polarizing plate can be disposed on one side of the liquid crystal cell, and another polarizing plate can be disposed on the other side. In pasting to a liquid crystal cell, it arrange | positions so that the 1/4 wavelength plate 10 side may face a liquid crystal cell.
[Liquid Crystal Display]
3 and 4 are schematic cross-sectional views each showing an example of a liquid crystal display device in which the elliptically polarizing plate of the present invention is disposed on both surfaces of a liquid crystal cell. FIG. 3 shows an example in which the elliptically polarizing plate 30 which is a laminate of the quarter wavelength plate 10 and the linearly polarizing plate 20 shown in FIG. That is, in this example, an elliptically polarizing plate 30 composed of a quarter wavelength plate 10 / a linearly polarizing plate 20 is disposed on the lower side of the liquid crystal cell 50 via the pressure sensitive adhesive layer 40. The liquid crystal cell 50 is stacked so as to face the liquid crystal cell 50, and the elliptical polarizing plate 30 including the quarter wavelength plate 10 / the linearly polarizing plate 20 is disposed on the upper side of the liquid crystal cell 50 via the pressure-sensitive adhesive layer 40. The four-wave plate 10 side is laminated so as to face the liquid crystal cell 50. Each elliptically polarizing plate 30 is disposed so that the absorption axes of the linearly polarizing plates 20 are orthogonal to each other. When this liquid crystal display device is used as a transmissive type or a transflective type, a backlight 60 is disposed on the outer side (lower side in the drawing) of one elliptical polarizing plate.

  In FIG. 4, elliptical polarizing plates 35, which are a laminate of the quarter-wave plate 10, the half-wave plate 15, and the linear polarizing plate 20 shown in FIG. 2A, are arranged on both sides of the liquid crystal cell 50. An example is shown. That is, in this example, an elliptically polarizing plate 35 composed of a quarter wavelength plate 10/1/2 wavelength plate 15 / linearly polarizing plate 20 is disposed below the liquid crystal cell 50 via a pressure sensitive adhesive layer 40. The quarter-wave plate 10 is laminated so as to face the liquid crystal cell 50, and the quarter-wave plate 10/1 / 2-wave plate 15 / straight line is also provided on the upper side of the liquid crystal cell 50 via the pressure-sensitive adhesive layer 40. An elliptically polarizing plate 35 composed of the polarizing plate 20 is laminated so that the quarter-wave plate 10 faces the liquid crystal cell 50. Each elliptically polarizing plate 35 is disposed so that the absorption axis of the linearly polarizing plate 20 is orthogonal. When this liquid crystal display device is used as a transmissive type or a transflective type, a backlight 60 is disposed outside (on the lower side in the drawing) of one elliptical polarizing plate.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by these examples. In the examples,% representing the content is based on weight unless otherwise specified.

[Example 1]
(A) Production of quarter-wave plate A propylene / ethylene random copolymer containing about 5% ethylene units (“Sumitomo Noblen W151” sold by Sumitomo Chemical Co., Ltd.) was formed into a film having a thickness of 40 μm. The original film was obtained. This raw film was stretched uniaxially with a tenter transverse stretching machine. Stretching is performed at a line speed of 10 m / min, first through a preheating zone in which the temperature is adjusted to 131 ° C., and then in the stretching zone in which the temperature is adjusted to 121 ° C., the final draw ratio is 5 times. I went. The in-plane retardation value Ro, the thickness direction retardation value Rth, the Nz coefficient, and the wavelength dispersion of the retardation of the obtained stretched film (retardation film) are measured by the retardation measuring device “KOBRA” manufactured by Oji Scientific Instruments. -21ADH "and the thickness was measured with a digital micrometer" MH-15M "manufactured by Nikon Corporation. The results are shown in Table 1. This retardation film had an in-plane retardation value Ro of 140 nm and functioned as a quarter-wave plate.
(B) Production of elliptical polarizing plate A structure in which a polarizer film in which iodine is adsorbed and oriented on polyvinyl alcohol is sandwiched between two triacetylcellulose films, and an acrylic pressure-sensitive adhesive layer is provided on one side thereof. A linear polarizing plate [“SR-W062” sold by Sumitomo Chemical Co., Ltd.] was prepared. On the other hand, the quarter-wave plate produced in the above (a) is cut in a direction of 45 ° from the slow axis, and one side thereof is subjected to corona discharge treatment under the condition of an integrated irradiation amount of 1,680 J. Within 30 seconds, the corona discharge treated surface was bonded to the acrylic pressure-sensitive adhesive layer side of the linear polarizing plate. At this time, the absorption axis of the linearly polarizing plate and the slow axis of the quarter wavelength plate were arranged so as to intersect at an angle of 45 degrees. Thus, an elliptically polarizing plate was obtained in which a quarter wave plate made of a propylene-based resin was laminated on a linearly polarizing plate.
(C) Ellipticity measurement of elliptically polarizing plate The ellipticity of the elliptically polarizing plate prepared in (b) was measured using a phase difference measuring device “KOBRA-21ADH” manufactured by Oji Scientific Instruments. Here, the ellipticity is the ratio of the length of the minor axis to the length of the major axis of the elliptically polarized light emitted from the quarter wavelength plate side when light is incident from the linearly polarizing plate side of the elliptically polarizing plate. . The ellipticity of the elliptically polarizing plate obtained in this example was 0.925. This was a value equivalent to an ellipticity of 0.925 of an elliptically polarizing plate using a quarter-wave plate made of a norbornene resin shown in Comparative Example 1 described later.

[Example 2]
A raw film having a thickness of 40 μm obtained by forming the same propylene / ethylene random copolymer (“Sumitomo Noblene W151”) as used in Example 1 was obtained in the same manner as in (a) of Example 1. The film was stretched uniaxially with a horizontal stretching machine. However, the line speed was 5 m / min, the preheating temperature was 136 ° C., the stretching temperature was 126 ° C., and the final stretching ratio was changed to 4 times. The in-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, retardation wavelength dispersion, and thickness of the obtained stretched film (retardation film) are the same as in (a) of Example 1. The results are shown in Table 1. This retardation film had an in-plane retardation value Ro of 90 nm and functioned as a quarter-wave plate.

[Example 3]
The same propylene / ethylene random copolymer (“Sumitomo Noblene W151”) as used in Example 1 was formed into a film having a thickness of 60 μm. This raw film was stretched uniaxially with a tenter transverse stretching machine. Stretching is performed at a line speed of 20 m / min, first through a preheating zone in which the temperature is adjusted to 126 ° C., and then in the stretching zone in which the temperature is adjusted to 116 ° C., the final draw ratio is 5 times. I went. In-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, and thickness of the obtained stretched film (retardation film) were measured by the same method as in (a) of Example 1, and the results were obtained. It is shown in Table 1. This retardation film had an in-plane retardation value Ro of 280 nm and functioned as a half-wave plate.

[Example 4]
(A) Preparation of quarter wave plate 1% by weight of high-density polyethylene G1900 manufactured by Keiyo Polyethylene Co., Ltd. is added to a propylene homopolymer having a melt flow rate of 8 g / 10 min and isotactic stereoregularity. The obtained polypropylene resin film was formed into a raw film having a thickness of 40 μm. This raw film was stretched uniaxially with a tenter transverse stretching machine. Stretching is performed at a line speed of 5 m / min, first through a preheating zone in which the temperature is adjusted to 140 ° C., then in a stretching zone in which the temperature is adjusted to 160 ° C., and then in a heat setting zone in which the temperature is adjusted to 120 ° C. The final draw ratio was 4 times. In-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, and wavelength dispersion of retardation of the obtained stretched film (retardation film) were measured by the same method as in (a) of Example 1. The results are shown in Table 1. This retardation film had an in-plane retardation value Ro of 150 nm and functioned as a quarter-wave plate.
(B) Production of elliptical polarizing plate A structure in which a polarizer film in which iodine is adsorbed and oriented on polyvinyl alcohol is sandwiched between two triacetylcellulose films, and an acrylic pressure-sensitive adhesive layer is provided on one side thereof. A linear polarizing plate [“SR-W062” sold by Sumitomo Chemical Co., Ltd.] was prepared. On the other hand, the quarter-wave plate produced in the above (a) is cut in a direction of 45 ° from the slow axis, and one side thereof is subjected to corona discharge treatment under the condition of an integrated irradiation amount of 1,680 J. Within 30 seconds, the corona discharge treated surface was bonded to the acrylic pressure-sensitive adhesive layer side of the linear polarizing plate. At this time, the absorption axis of the linearly polarizing plate and the slow axis of the quarter wavelength plate were arranged so as to intersect at an angle of 45 degrees. Thus, an elliptically polarizing plate was obtained in which a quarter wave plate made of a propylene-based resin was laminated on a linearly polarizing plate.
(C) Ellipticity measurement of elliptically polarizing plate The ellipticity of the elliptically polarizing plate prepared in (b) was measured using a phase difference measuring device “KOBRA-21ADH” manufactured by Oji Scientific Instruments. The ellipticity of the elliptically polarizing plate obtained in this example was 0.925.

[Example 5]
A 40 μm-thick original fabric film obtained by forming the same polypropylene resin as used in Example 4 was stretched uniaxially with a tenter transverse stretcher in the same manner as in Example 4 (a). However, the line speed was 5 m / min, the preheating temperature was 170 ° C., the stretching temperature was 150 ° C., the heat setting temperature was 120 ° C., and the final stretching ratio was changed to 3 times. In-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, and thickness of the obtained stretched film (retardation film) were measured by the same method as in (a) of Example 1, and the results were obtained. It is shown in Table 1. This retardation film had an in-plane retardation value Ro of 97 nm and functioned as a quarter-wave plate.

[Example 6]
The same polypropylene resin as used in Example 4 was formed to obtain a 40 μm-thick original film. This raw film was stretched uniaxially with a tenter transverse stretching machine. At that time, the line speed was 5 m / min, the preheating temperature was 170 ° C., the stretching temperature was 160 ° C., the heat setting temperature was 120 ° C., and the final stretching ratio was 4 times. In-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, and thickness of the obtained stretched film (retardation film) were measured by the same method as in (a) of Example 1, and the results were obtained. It is shown in Table 1. This retardation film had an in-plane retardation value Ro of 273 nm and functioned as a half-wave plate.

[Example 7]
A 40 μm-thick raw film obtained by forming a propylene homopolymer having an isotactic stereoregularity with a melt flow rate of 8 g / 10 min is the same as in Example 4 (a). The film was stretched uniaxially with a tenter transverse stretching machine. However, the line speed was 5 m / min, the preheating temperature was 160 ° C., the stretching temperature was 140 ° C., the heat setting temperature was 120 ° C., and the final stretching ratio was changed to 4 times. The in-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, retardation wavelength dispersion, and thickness of the obtained stretched film (retardation film) are the same as in (a) of Example 1. The results are shown in Table 1. This retardation film had an in-plane retardation value Ro of 147 nm and functioned as a quarter-wave plate.

[Example 8]
A 40 μm-thick raw film obtained by forming the same polypropylene resin as used in Example 7 was stretched uniaxially with a tenter transverse stretcher in the same manner as in Example 4 (a). However, the line speed was 5 m / min, the preheating temperature was 170 ° C., the stretching temperature was 150 ° C., the heat setting temperature was 120 ° C., and the final stretching ratio was changed to 3 times. In-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, and thickness of the obtained stretched film (retardation film) were measured by the same method as in (a) of Example 1, and the results were obtained. It is shown in Table 1. This retardation film had an in-plane retardation value Ro of 91 nm and functioned as a quarter-wave plate.

[Example 9]
A 40 μm-thick original fabric film obtained by forming the same polypropylene resin as used in Example 7 was stretched uniaxially with a tenter transverse stretcher in the same manner as in Example 4 (a). However, the line speed was 5 m / min, the preheating temperature was 170 ° C., the stretching temperature was 160 ° C., the heat setting temperature was 120 ° C., and the final stretching ratio was changed to 4 times. In-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, and thickness of the obtained stretched film (retardation film) were measured by the same method as in (a) of Example 1, and the results were obtained. It is shown in Table 1. This retardation film had an in-plane retardation value Ro of 277 nm and functioned as a half-wave plate.

[Comparative Example 1]
For a retardation film (“SES440140Z” sold by Sumitomo Chemical Co., Ltd.), which is a quarter-wave plate obtained by longitudinally uniaxially stretching a norbornene-based resin film, an in-plane retardation value Ro, a thickness direction retardation value Rth, Nz coefficient, wavelength dispersion of retardation, and thickness were measured by the same method as in (a) of Example 1, and the results are shown in Table 1. Except for using this retardation film, an elliptically polarizing plate was produced by the same method as in (b) of Example 1, and the ellipticity of the elliptically polarizing plate was further increased by the same method as in (c) of Example 1. It was measured. The ellipticity of the elliptically polarizing plate was 0.925.

[Comparative Example 2]
For a retardation film [“SES360140Y” sold by Optes Co., Ltd.], which is a quarter-wave plate obtained by stretching a norbornene-based resin film laterally uniaxially, an in-plane retardation value Ro and a thickness direction retardation value Rth , Nz coefficient, and thickness were measured by the same method as in Example 1 (a), and the results are shown in Table 1.

[Comparative Example 3]
For retardation film [ZM-300] sold by OPTES Co., Ltd., which is a half-wave plate obtained by longitudinally uniaxially stretching a norbornene resin film, in-plane retardation value Ro, thickness direction retardation The value Rth, Nz coefficient, and thickness were measured by the same method as in Example 1 (a), and the results are shown in Table 1.

[Comparative Example 4]
The same propylene / ethylene random copolymer (“Sumitomo Nobrene W151”) as used in Example 1 was formed into a raw film having a thickness of 50 μm. This raw film was stretched uniaxially. Stretching is performed at a line speed of 6 m / min, first through a preheating zone where the temperature is adjusted to 115 ° C., and then the final draw ratio is 1.37 times in the stretching zone where the temperature is adjusted to 118 ° C. It was done like that. The in-plane retardation value Ro, thickness direction retardation value Rth, Nz coefficient, retardation wavelength dispersion, and thickness of the obtained stretched film (retardation film) are the same as in (a) of Example 1. The results are shown in Table 1. This retardation film had an in-plane retardation value Ro of 275 nm and functioned as a half-wave plate.

  In the case of a norbornene-based resin, as shown in Comparative Examples 1 and 3, a quarter-wave plate and a half-wave plate whose Nz coefficient is almost 1 by longitudinal uniaxial stretching are provided on the market. However, the thickness is 45.5 μm for the quarter-wave plate (Comparative Example 1) and 116 μm for the half-wave plate (Comparative Example 3). On the other hand, as shown in Comparative Example 2, a quarter-wave plate is also provided in the market even with a norbornene resin laterally uniaxially stretched product, but its Nz coefficient is 1.6, indicating biaxiality. The thickness is also 62 μm.

  On the other hand, as shown in Examples 1 to 9, a quarter-wave plate or a half-wave plate having an Nz coefficient of approximately 1 can be produced by transversely uniaxially stretching a polypropylene resin film at a high magnification. Its thickness can also be made extremely thin, 25 μm or less. On the other hand, as shown in Comparative Example 4, when a polypropylene resin film is stretched uniaxially, a half-wave plate can be obtained, but the thickness is not so small due to neck-in, and is extremely 25 μm or less as defined in the present invention. It is difficult to realize a thin wall.

  The quarter-wave plate produced in Example 1 (a) or Example 4 (a) and the half-wave plate produced in Example 3 or Example 6 were previously described with reference to FIG. By laminating at the described axial angle, a broadband quarter-wave plate can be obtained. Furthermore, if the linearly polarizing plate shown in (b) of Example 1 or (a) of Example 4 is laminated on the half-wave plate side at the axial angle described above with reference to FIG. A broadband elliptically polarizing plate (circularly polarizing plate) is obtained.

  A retardation film composed of a polypropylene resin according to the present invention can exhibit a sufficient retardation characteristic while having a small film thickness. Therefore, this retardation film is useful as a quarter-wave plate or a half-wave plate, an elliptical polarizing plate in which the quarter-wave plate is laminated on a linear polarizing plate, a quarter-wave plate and a half-wave plate. The elliptically polarizing plate laminated on the linear polarizing plate by combining the wave plates contributes to further thinning of the liquid crystal display device while exhibiting good antireflection properties.

It is the cross-sectional schematic diagram (A) which shows a layer structure, and the figure for demonstrating the relationship of an axial angle about one form of the elliptically polarizing plate by this invention. It is the cross-sectional schematic diagram (A) which shows a layer structure, and the figure for demonstrating the relationship of an axial angle about another form of the elliptically polarizing plate by this invention. It is a cross-sectional schematic diagram which shows the example which applied the elliptically polarizing plate of this invention to the liquid crystal display device. It is a cross-sectional schematic diagram which shows another example which applied the elliptically polarizing plate of this invention to the liquid crystal display device.

Explanation of symbols

  10 1/4 wavelength plate, 12 1/4 wavelength plate slow axis, 15 1/2 wavelength plate, 17 1/2 wavelength plate slow axis, 20 linear polarizing plate, 22 linear polarizing plate absorption axis, 30 , 35 Elliptical polarizer, θ Angle from the absorption axis of the linear polarizer to the slow axis of the quarter wave plate, φ Angle from the absorption axis of the linear polarizer to the slow axis of the half wavelength plate, ψ 1 / An angle from the slow axis of the two-wave plate to the slow axis of the quarter-wave plate, 40 pressure-sensitive adhesive layer, 50 liquid crystal cell, 60 backlight.

Claims (10)

Consists transverse oriented film of the polypropylene resin, a thickness of 25μm or less, in the range retardation value (Ro) is 70~400nm plane, and the in-plane slow axis direction of the refractive index of the film n _x the refractive index n _y in-plane fast axis direction, a refractive index in the thickness direction is taken as n _z, wherein: defined by Nz factor _{= (n x -n z) /} (n x -n y) A retardation film having an Nz coefficient in the range of 0.9 to 1.1.   The retardation film according to claim 1, wherein the polypropylene resin is a copolymer of propylene and ethylene containing 10% by weight or less of ethylene units.   The retardation film according to claim 1, wherein the polypropylene resin is substantially composed of a propylene homopolymer.   The retardation film according to claim 1, wherein the polypropylene resin contains a nucleating agent.   The retardation film according to claim 1, which functions as a ¼ wavelength plate.   The retardation film according to claim 1, which functions as a half-wave plate.   5. An elliptically polarizing plate, wherein the retardation film according to claim 1 is laminated on a linearly polarizing plate.   An elliptically polarizing plate comprising the retardation film according to claim 5 laminated on a linear polarizing plate.   An retardation film according to claim 5, the retardation film according to claim 6, and a linear polarizing plate are laminated in this order.   A liquid crystal display device comprising the elliptically polarizing plate according to claim 7 laminated on at least one side of a liquid crystal cell.

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