JP2008281667A - Method for producing retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a retardation film having the relation of n<SB>x</SB>>n<SB>z</SB>>n<SB>y</SB>using a resin film in which the absolute value of a photoelastic coefficient is low, the retardation film capable of easily adjusting the phase difference value in the plane and the phase difference value in the thickness direction, further capable of dealing with the change of the phase difference values, and also capable of efficiently producing the same. <P>SOLUTION: The retardation film 18 is produced through: a pasting step where one side or both sides of a stretched olefin based resin film 11 is/are pasted with a shrinkable film 12 in which the shrinkage ratio in the longitudinal direction is 0 to 20% and the shrinkage ratio in the width direction is 10 to 45% at 160°C, to obtain a laminated film 15; and a heat shrinking step where the laminated film is heated, and is shrunk in such a manner that the olefin based resin film shows the retardation value in the plane of 150 to 300 nm and an Nz coefficient of 0.2 to 0.6 equivalent to (n<SB>x</SB>-n<SB>z</SB>)/(n<SB>x</SB>-n<SB>y</SB>), and also, the shrinkage magnification in the longitudinal direction reaches 0.8 to 0.98 times and the shrinkage magnification in the width direction reaches 0.6 to 0.9 times. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a retardation film.

  The retardation film is used in liquid crystal display devices such as TN (Twisted Nematic) mode, VA (Vertical Alignment) mode, IPS (In-plane Switching) mode, FFS (Fringe Field Switching) mode, OCB (Optically Compensated Bend) mode, etc. It is often used for viewing angle compensation of liquid crystal cells.

  In a liquid crystal display device, polarizing plates are generally disposed on both sides of a liquid crystal cell. In order to optically compensate for the phase difference due to the birefringence of the liquid crystal cell in the front direction and the oblique direction, a retardation film is often disposed between the liquid crystal cell and the polarizing plate. In order to improve the display characteristics in the oblique direction in the liquid crystal display device, it is very important how the retardation value in the oblique direction of the retardation film varies depending on the angle.

In view of this, a retardation film having a substantially constant retardation value regardless of the angle has been proposed. For example, Japanese Patent Laid-Open No. 2-160204 (Patent Document 1) discloses that the intrinsic birefringence is positive and the molecule is on the film surface. It is disclosed that by stretching a film oriented in the normal direction, the phase difference at normal incidence and the phase difference at incidence from a direction inclined by 40 ° from the normal are substantially the same. ing. The retardation film has an in-plane slow axis direction, a refractive index in the in-plane fast axis direction and the thickness direction respectively n _x, when the n _y and n _z, a relationship n _x> n _z> n _y Show.

  There is also a proposal for improving the oblique viewing angle characteristics by combining such a retardation film with a polarizing plate and applying it to an IPS mode or VA mode liquid crystal display device. For example, Japanese Patent Laid-Open No. 11-305217 (Patent Document 2) discloses disposing an optical compensation film between one polarizing plate and a liquid crystal cell substrate in an IPS mode liquid crystal display device. JP 2000-39610 A (Patent Document 3) has a first polarizing plate, a biaxial optically anisotropic sheet, a VA mode liquid crystal layer, and a second polarizing plate in this order. A liquid crystal display device is disclosed in which a uniaxial optically anisotropic sheet is disposed between a liquid crystal layer and a biaxial optically anisotropic sheet or between a liquid crystal layer and a second polarizing plate.

As a method for producing a retardation film which satisfies a relation of _{n x> n z> n y} , in Japanese Laid-5-157911 (Patent Document 4), by bonding a shrinkable film to one or both surfaces of the resin film laminated A method is disclosed in which a body is formed and the laminate is heated and stretched. This method shrinks the resin film in the direction perpendicular to the stretching axis at the same time as stretching, causing orientation in the thickness direction (Z direction), and the refractive index distribution of the resin film changes greatly before and after stretching. I am letting. For this reason, the resin film to be used is preferably one that easily causes a phase difference at a low stretch ratio, and usually an aromatic resin film such as a polycarbonate resin, a polyarylate resin, or a polysulfone resin has been used. .

  JP-A-7-230007 (Patent Document 5) discloses a film having heat shrinkability on at least one surface of a uniaxially stretched thermoplastic resin film, and the direction of the heat shrinkage axis is the uniaxially stretched thermoplastic resin. A method for producing a retardation film in which the uniaxially stretched thermoplastic resin film is also oriented in the thickness direction by pasting the film so as to be orthogonal to the stretched axis direction of the film and causing heat shrinkage is disclosed. This method is also oriented in the thickness direction by utilizing the shrinkage of the uniaxially stretched thermoplastic resin film accompanying the heat shrinkage of the heat shrinkable film, so that mainly the aromatic resin film that easily develops the phase difference. Has been applied.

  Since such an aromatic resin film has a large absolute value of the photoelastic coefficient, the phase difference is likely to change with respect to stress. For this reason, the phase difference value may deviate from the design value due to the contraction stress of the polarizer when exposed to a high temperature in a state where the liquid crystal cell and the polarizer are bonded, and the heat of the backlight in the liquid crystal display device. Due to the unevenness of the stress caused by the above, there has been a problem that the unevenness of the phase difference value occurs and the display characteristics are deteriorated.

  On the other hand, since an aliphatic resin film such as a norbornene resin film has a small absolute value of a photoelastic coefficient, movement to apply it to a retardation film has been increasing in recent years. However, since an aliphatic resin film generally does not easily develop a retardation, a desired retardation value can be obtained even with a high draw ratio as well as a low draw ratio like an aromatic resin film. was difficult. In particular, it is difficult to align the film so that a predetermined retardation value can be obtained in the thickness direction as well as in the stretching axis direction, and the methods of Patent Document 4 and Patent Document 5 have limitations.

Therefore, in JP 2006-72309 A (Patent Document 6), a shrinkable film having a large shrinkage in the width direction is bonded to one side or both sides of a norbornene-based resin film, and an in-plane retardation value is 100 to 100. A method has been proposed in which the film is heated and stretched so that the coefficient represented by (n _x −n _z ) / (n _x −n _y ) is 0.1 to 0.9. Here, _nx , _ny and _nz have the meanings as defined above. According to this method, the expression was hardly norbornene resin retardation, also oriented in the thickness direction with a direction of stretching axis, it is possible to produce a retardation film which satisfies a relation of _{n x> n z> n y} .

JP-A-2-160204 JP-A-11-305217 JP 2000-39610 A JP-A-5-157911 Japanese Unexamined Patent Publication No. 7-230007 JP 2006-72309 A

In the method described in Patent Document 6, since the film is contracted in the direction orthogonal to the stretching axis simultaneously with stretching, _nx and _nz change simultaneously. Therefore, since _nx and _nz are linked, it has been difficult to design each individually. On the other hand, with the expansion of the application field of liquid crystal display devices, there is a demand for retardation films that exhibit various retardation values, and they are independently adjusted according to the required retardation values in the plane and in the thickness direction. As a method for producing a possible retardation film, the above method is not always satisfactory.

It is an object of the present invention, by using the absolute value is less resin film of the photoelastic coefficient, a method for producing a retardation film having a relation of _{n x> n z> n y} , in-plane retardation value It is an object of the present invention to provide a method that can easily adjust the retardation value in the thickness direction, can easily cope with the change of the retardation value, and can efficiently produce the retardation film. Another object of the present invention is to provide a method for producing a retardation film that can efficiently produce a retardation film having a small angle dependency and can easily cope with a change in the retardation value. It is in.

  That is, according to this invention, the manufacturing method of retardation film which includes each process of the following (A) and (B) is provided.

(A) On one or both sides of the stretched olefin resin film, the longitudinal shrinkage S ¹⁶⁰ (MD) at 160 ° C. is 0 to 20%, and the width shrinkage S ¹⁶⁰ (TD) is 10 to 10%. A pasting step of laminating a 45% shrinkable film to obtain a laminated film; and (B) heating the laminated film so that the olefin-based resin film has an in-plane slow axis direction, an in-plane advance and the refractive index of the axis direction and a thickness direction, respectively n _x, and n _y and n _z, the thickness is taken as d, the following equation (1) and (2):
_{150nm ≦ (n x -n y)} × d ≦ 300nm (1)
_{0.2 ≦ (n x -n z)} / (n x -n y) ≦ 0.6 (2)
And shrinking so that the shrinkage ratio in the longitudinal direction is 0.8 to 0.98 times and the shrinkage ratio in the width direction is 0.6 to 0.9 times.

Here, appearing in equation _{(1) (n x -n y} ) × d corresponds to the in-plane retardation value Ro. Further, appearing in Equation _{(2) (n x -n z} ) / (n x -n y) is an index representing the degree of orientation in the thickness direction, and is also called a Nz coefficient.

  In the above method, the olefin resin used as the retardation film can be a resin mainly composed of units derived from alicyclic olefins. Specific examples thereof include hydrogenated ring-opening polymers of norbornene monomers. This polymer may be a copolymer with another copolymerizable monomer, if necessary.

  Moreover, in said method, it is preferable that the olefin resin film provided to a bonding process (A) has a thickness of about 10-200 micrometers. The stretched olefin resin film also preferably has an in-plane retardation value of 200 to 400 nm. Further, the olefin resin film is preferably uniaxially stretched.

  On the other hand, the shrinkable film can be uniaxially stretched or biaxially stretched, but is particularly preferably biaxially stretched. The shrinkable film can be composed of, for example, a norbornene resin or a propylene resin, and in particular, a biaxially stretched propylene resin film is advantageously employed.

  Furthermore, it is preferable to perform the said heat shrinking process (B) at the temperature 1-50 degreeC higher than the glass transition temperature of an olefin resin film. In addition, the heat shrinking step is performed in such a manner that the laminated film obtained in the bonding step (A) is supplied to the heating zone in a state where the laminated film is undulated and moved in the longitudinal direction so that the waving is eliminated in the heating zone. It is preferable to carry out by shrinking in the width direction and also in the width direction, particularly using a pin tenter.

  The above method is usually performed by a method in which both the olefin-based resin film and the shrinkable film are supplied in a roll form, both are bonded by a roll-to-roll, and the heat shrinkage process is applied as it is. Usually, after the heat-shrinking step (B), a peeling step (C) for peeling the shrinkable film from the laminated film and isolating the retardation film is included.

  According to this method, in the retardation film after heat shrinkage, the in-plane retardation value variation can be within ± 5 nm, and the orientation angle (direction formed by the in-plane slow axis) varies. Can be within ± 0.5 °.

In the present invention, on one or both sides of the pre-stretched olefin resin film, by bonding a shrinkable film having a predetermined shrinkage rate, by heat shrinking, have a relation of n _x> n _z> n _y And the retardation film which satisfies the said Formula (1) and Formula (2) is obtained. According to this method, since the olefin resin film having a small absolute value of the photoelastic coefficient is contracted and oriented in the thickness direction, a wide range of retardation values are expressed by adjusting the contraction magnification and the line speed. A retardation film can be produced. And since the obtained retardation film has a small absolute value of the photoelastic coefficient, even when applied to a liquid crystal cell, it is difficult to cause a shift or unevenness of the retardation value due to stress, and a liquid crystal display device with high display quality can be obtained. it can.

  Hereinafter, the present invention will be described in detail. In the present invention, a shrinkable film having a predetermined shrinkage rate is bonded to one side or both sides of an olefin-based resin film that has been previously stretched, and is heated and shrunk.

[Olefin resin]
The olefin resin used in the present invention is a resin mainly composed of units derived from aliphatic olefins such as ethylene and propylene, or alicyclic olefins including norbornene monomers. This resin may be a copolymer using two or more monomers.

  Among these, a unit derived from an alicyclic olefin, particularly a cyclic olefin resin in which a cyclic structure remains in the main chain after polymerization is preferably used. Typical examples of the cyclic olefin constituting the cyclic olefin-based resin include norbornene and substituted products thereof (hereinafter sometimes collectively referred to as norbornene-based monomers). Norbornene is a compound in which one site of norbornane is a double bond, and according to the IUPAC nomenclature, it is named bicyclo [2,2,1] hept-2-ene. Examples of the substituent include a norbornene double bond at the 1,2-position, 3-substituted, 4-substituted, 4,5-disubstituted, and further dicyclopentadiene and dimethanoocta And hydronaphthalene. Resins mainly composed of units derived from such norbornene monomers are generally called norbornene resins.

  In the norbornene-based resin, a norbornene-based monomer is used as a starting material. However, in a polymerized state, the constituent unit may or may not have a norbornane ring. Examples of the norbornene-based resin having no norbornane ring in the structural unit include, for example, those that become a 5-membered ring by ring opening, typically norbornene, dicyclopentadiene, 1- or 4-methylnorbornene, 4-phenyl. Examples include norbornene. When the norbornene-based resin is a copolymer, the arrangement state of the molecules is not particularly limited, and may be a random copolymer, a block copolymer, or a graft copolymer. May be.

  Examples of the norbornene-based resin include, for example, a ring-opening polymer of a norbornene-based monomer, a ring-opening copolymer of a norbornene-based monomer and another monomer, a modified polymer obtained by adding maleic acid, cyclopentadiene, or the like to these, These include resins obtained by hydrogenation of these; addition polymers of norbornene monomers, addition copolymers of norbornene monomers and other monomers, and the like. In the case of a copolymer, other monomers include α-olefins, cycloalkenes, non-conjugated dienes and the like. Moreover, the copolymer using 2 or more types of alicyclic olefin may be sufficient.

  Among these, a resin obtained by hydrogenating a ring-opening polymer using a norbornene monomer is preferably used. Such a norbornene-based resin is excellent in molding processability, and in particular, in accordance with the present invention, in a state in which a stretch treatment has been performed in advance, a shrinkable film having a predetermined shrinkage rate is bonded and heat-shrinked, thereby achieving uniformity. And a retardation film having a large retardation value can be provided. Resins marketed as hydrogenated ring-opening (co) polymers using such norbornene-based monomers include “Zeonex”, “Zeonor”, and JSR ) "Arton" and so on. These norbornene-based resin films and stretched films are also available, for example, under the trade name “ZEONOR FILM” from Optes Co., Ltd., under the trade name “ARTON FILM” from JSR Corporation, and from Sekisui Chemical Co., Ltd. It is sold under the name “Essina”.

  Moreover, the film which consists of a mixed resin containing 2 or more types of olefin resin, or the film which consists of mixed resin of an olefin resin and another thermoplastic resin can also be used. For example, as an example of a mixed resin containing two or more types of olefinic resins, there can be mentioned a mixture of a cyclic olefinic resin and an aliphatic olefinic resin as described above. When a mixed resin of an olefin resin and another thermoplastic resin is used, an appropriate one is appropriately selected as the other thermoplastic resin according to the purpose. Specific examples include polyvinyl chloride resin, cellulose resin, polystyrene resin, acrylonitrile / butadiene / styrene copolymer resin, acrylonitrile / styrene copolymer resin, (meth) acrylic resin, polyvinyl acetate resin, polyvinyl chloride. General-purpose plastics such as vinylidene resins; general-purpose engineering plastics such as polyamide resins, polyacetal resins, polycarbonate resins, modified polyphenylene ether resins, polybutylene terephthalate resins and polyethylene terephthalate resins; polyphenylene sulfide resins, polysulfone resins , Polyethersulfone resin, polyetheretherketone resin, polyarylate resin, liquid crystalline resin, polyamideimide resin, polyimide resin and polytetra Such as such as super engineering plastics Ruoroechiren resins. These thermoplastic resins can be used alone or in combination of two or more. The thermoplastic resin can be used after any appropriate polymer modification. Examples of polymer modification include copolymerization, crosslinking, molecular terminal modification, and stereoregularity.

  When a mixed resin of an olefin resin and another thermoplastic resin is used, the content of the other thermoplastic resin is generally about 0 to 50% by weight, preferably 0 to 40% by weight based on the entire resin. %. By setting this range, the obtained retardation film has a small absolute value of the photoelastic coefficient, exhibits good wavelength dispersion characteristics, and can be excellent in durability, mechanical strength, and transparency. .

  The olefin resin as described above can be formed into a film by a casting method or a melt extrusion method from a generally used solution. When forming a film from two or more kinds of mixed resins, the mixing method is not particularly limited. For example, when producing a film by a casting method, the mixed components are stirred and mixed together with a solvent at a predetermined ratio, and uniform. It can be used as a solution. Moreover, when producing a film by the melt extrusion method, the mixed components can be melt-mixed at a predetermined ratio and used. In order to improve the smoothness of the obtained retardation film and obtain good optical uniformity, a casting method from a solution is preferably used.

In the present invention, the film made of such an olefin resin is previously subjected to stretching treatment. Stretching may be performed uniaxially or may be carried out with a twin-screw, but the present invention, the production of the retardation film satisfying the relation of n _x> n _z> n _y by final shrinking treatment purposes Therefore, the stretching performed in advance is preferably uniaxial stretching, which is also longitudinal uniaxial stretching. However, stretching in a direction orthogonal to the stretching axis may be added to such an extent that uniaxiality is not impaired. As an example of uniaxial stretching, there can be mentioned a method of longitudinally uniaxial stretching between rolls having different peripheral speeds while maintaining the film at a constant temperature.

  The olefin resin film contains other components such as residual solvent, stabilizer, plasticizer, anti-aging agent, antistatic agent, and ultraviolet absorber as necessary, as long as the object of the present invention is not impaired. Also good. Further, a leveling agent can be contained in order to reduce the surface roughness.

  The thickness of the film obtained by stretching can be selected according to the designed retardation value, shrinkage, and the ease of occurrence of the retardation value, but is preferably in the range of 10 to 500 μm. More preferably, it is in the range of 10 to 300 μm, further 10 to 200 μm, especially 20 to 200 μm. If it is this range, sufficient self-supporting property of a film will be obtained and a wide range retardation value can be obtained.

  The thickness of the stretched olefin-based resin film is appropriately selected within the above range according to the retardation value required for the retardation film obtained by subsequent heat shrinkage. For example, when a retardation film obtained by heat shrinkage is used as a λ / 2 plate, the stretched olefin resin film bonded to the shrinkable film preferably has a thickness of 70 to 150 μm, and more More preferably, it has a thickness of 70 to 130 μm.

  The olefin resin film preferably has a light transmittance of 80% or more at a wavelength of 590 nm, both before and after stretching. This light transmittance is more preferably 85% or more, and even more preferably 90% or more. It is preferable that the retardation film obtained by subsequent heat shrinkage also exhibits the same light transmittance.

  In addition, the glass transition temperature (Tg) of the olefin resin film is not particularly limited, but is generally preferably in the range of 110 to 185 ° C. If the glass transition temperature is 110 ° C. or higher, a highly durable retardation film can be easily obtained. If the glass transition temperature is 185 ° C. or lower, the film is in-plane and in the thickness direction by stretching and subsequent heat shrinkage. Easy to control the phase difference value. A more preferable glass transition temperature is 120 to 170 ° C. The glass transition temperature of the resin can be determined by differential scanning calorimetry (DSC) according to JIS K 7121-1987.

[Shrinkable film]
In the present invention, a shrinkable film is bonded to one or both sides of the stretched film of the olefin-based resin as described above, and the film is heated and shrunk. At this time, the shrinkable film has a shrinkage ratio S ¹⁶⁰ (MD) in the longitudinal direction at 160 ° C. of 0 to 20% and a shrinkage ratio S ¹⁶⁰ (TD) in the width direction of 10 to 45%. Use. The heat shrinkage is a retardation film obtained by the shrinking process, the equation (1) and (2) so as to satisfy, i.e., in-plane retardation value corresponding to the (n _x -n _y) × d range of 150 nm to 300 nm, carried out such that the Nz coefficient of 0.2 to 0.6 corresponding to _{(n x -n z) / (} n x -n y). Furthermore, in this heat shrinkage, the shrinkage ratio in the longitudinal direction is 0.8 to 0.98 times and the shrinkage ratio in the width direction is 0.6 to 0.9 in a state where the shrinkable film is laminated on the olefin resin film. Shrink to double.

  At this time, as can be seen from the above definition, the olefin-based resin film is stretched so that the longitudinal direction (machine direction (MD) of the roll film) is the main stretching axis. Usually, it is bonded by roll-to-roll so that the longitudinal direction (also the machine direction (MD) of the roll film) matches. The shrinkable film preferably has a shrinkage ratio in the width direction larger than that in the longitudinal direction.

  The shrinkable film is used for applying a shrinkage force in a direction (width direction) perpendicular to the longitudinal direction during heat shrinkage. Examples of the material used for the shrinkable film include, but are not limited to, polyester, polystyrene, cyclic olefin resin, polyethylene, polypropylene, polyvinyl chloride, and polyvinylidene chloride. From the viewpoints of excellent shrinkage uniformity and heat resistance, a film of a cyclic olefin resin or a propylene resin, a stretched film whose transverse direction is the main stretch axis, particularly a propylene resin film is preferably used. .

  The shrinkable film is preferably a stretched film such as a biaxially stretched film or a uniaxially stretched film. Such a shrinkable film is obtained, for example, by uniaxially stretching a raw film formed into a sheet by an extrusion method at a predetermined magnification in the vertical or horizontal direction, or simultaneously at a predetermined magnification in the vertical and horizontal directions. Alternatively, it can be obtained by successive biaxial stretching. The molding and stretching conditions can be appropriately selected according to the composition, type, purpose, etc. of the resin used. A biaxially stretched propylene-based resin film is particularly preferably used from the viewpoints of excellent uniformity of shrinkage force and excellent heat resistance.

In the present invention, a film having a shrinkage ratio S ¹⁶⁰ (MD) in the longitudinal direction of the film of 0 to 20% and a shrinkage ratio S ¹⁶⁰ (TD) in the width direction of 10 to 45% at 160 ° C. is shrinkable. Used as a film. Preferably, a film having S ¹⁶⁰ (MD) of 0 to 15% and S ¹⁶⁰ (TD) of 20 to 40% is used. By using a shrinkable film having a shrinkage ratio in the longitudinal direction and width direction at 160 ° C. within this range, the olefin resin film can be efficiently shrunk. S ¹⁶⁰ (MD) and S ¹⁶⁰ (TD) are in the above range, and normally S ¹⁶⁰ (TD) is larger.

This shrinkable film has a shrinkage ratio S ¹⁴⁰ (MD) in the longitudinal direction of the film in the range of 0 to 15% and a shrinkage ratio S ¹⁴⁰ (TD) in the width direction of 0 to 30% at 140 ° C. It is preferable. More preferably, S ¹⁴⁰ (MD) is 0 to 10% and S ¹⁴⁰ (TD) is 0 to 25%. By using a shrinkable film having a shrinkage ratio in the longitudinal direction and width direction at 140 ° C. within this range, the olefin resin film can be efficiently shrunk. S ¹⁴⁰ (TD) may be 0 as described above, but is preferably 3% or more from the viewpoint of efficiently shrinking the olefin-based resin film. The shrinkage rate at 160 ° C. and the shrinkage rate at 140 ° C. can be determined by a method according to the heating dimensional change measurement method of JIS K 7133: 1999, as shown in Examples described later.

The shrinkable film preferably has a shrinkage stress T ¹⁶⁰ (TD) in the width direction at 160 ° C. in the range of 0 to 1.3 N / 2 mm, particularly in the range of 0 to 1.1 N / 2 mm. If T ¹⁶⁰ (TD) is in the above range, the target phase difference value can be obtained and uniform shrinkage can be performed.

The shrinkable film further widthwise shrinkage stress T ¹⁴⁰ at 140 ° C. (TD) is in the range of 0.2~1.2N / 2mm, especially preferably in the range of 0.25~1N / 2mm. If this T ¹⁴⁰ (TD) is in the above range, the olefin resin film can be efficiently contracted.

  The thickness of the shrinkable film can be selected in accordance with the shrinkage rate and shrinkage stress described above, the retardation value of the target retardation film, and the like. For example, the thickness is preferably about 10 to 500 μm, especially 20 More preferably, it is -300 micrometers. When the thickness of the shrinkable film is within this range, a sufficient shrinkage rate can be obtained, and a retardation film having good optical uniformity can be produced.

  As long as the shrinkable film satisfies the object of the present invention, a commercially available shrinkable film used for general packaging, food packaging, pallet packaging, shrink label, cap seal, electrical insulation, etc. A suitable film can also be selected and used as appropriate. These commercially available shrinkable films may be used as they are, or after being subjected to secondary processing such as stretching treatment or shrinkage treatment. Among the commercially available products, specific examples of the biaxially stretched polypropylene resin that can be used for the shrinkable film in the present invention include trade names “Alphan” series and Gunze Co., Ltd. sold by Oji Paper Co., Ltd. Product name "Fancy Top" series sold by Toray Industries, Inc. Product name "Trephan" series sold by Toray Industries, Inc. Product name "Santox-OP" series sold by Sun Tox Corporation And “Tosero OP” series sold by Tosero Co., Ltd.

[Bonding process]
The shrinkable film as described above is bonded to the stretched olefin resin film. Under the present circumstances, it bonds so that the shrink direction of a shrinkable film may contain the component of the direction orthogonal to the main extending | stretching axis direction of an olefin resin film at least. That is, it is performed so that all or part of the shrinkage force of the shrinkable film acts in a direction perpendicular to the main stretching axis direction of the olefin resin film. Therefore, the shrink direction of the shrinkable film may be obliquely intersected with the main stretch axis direction of the olefin resin film, but generally the shrink direction of the shrink film is orthogonal to the main stretch axis direction of the olefin resin film. Is preferred. Here, the main stretching axis direction refers to the direction in which the stretching ratio is maximum in the stretched film.

  The method for attaching the shrinkable film to the olefin resin film is not particularly limited, but the method of providing an adhesive layer between the olefin resin film and the shrinkable film for adhesion is preferably used because of its excellent productivity. It is done. Here, an adhesive layer can be formed in the bonding surface of an olefin resin film, or the bonding surface of a shrinkable film. Usually, since the shrinkable film is peeled off after the retardation film is produced, the pressure-sensitive adhesive layer combines adhesiveness and heat resistance in the heat shrinking process, and shrinks from the surface of the retardation film in the subsequent peeling process. Preferably, the adhesive film can be easily peeled off together with the adhesive film and the pressure-sensitive adhesive does not remain on the surface of the retardation film subjected to the shrinkage treatment. Then, since it shows favorable peelability, it is more preferable to provide an adhesive layer on the bonding surface of a shrinkable film.

  As the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer, a material mainly composed of an acrylic, synthetic rubber, rubber or silicone polymer is used. Among these, an acrylic pressure-sensitive adhesive having an acrylic polymer as a base polymer is preferable because of excellent adhesion, heat resistance, and peelability. In acrylic adhesives, alkyl esters of (meth) acrylic acid having an alkyl group with 20 or less carbon atoms such as methyl, ethyl and butyl groups, and (meth) acrylic acid and hydroxy (meth) acrylate A functional group-containing acrylic monomer composed of ethyl or the like is blended so that the glass transition temperature is preferably 25 ° C. or less, more preferably 0 ° C. or less, and the weight average molecular weight is 100,000 or more, preferably 2.5 million or less. These acrylic copolymers are useful as the base polymer. Here, the weight average molecular weight is a value measured in terms of polystyrene by gel permeation chromatography (GPC). Usually, such a base polymer is blended with a crosslinking agent to form an adhesive composition in the form of an organic solvent solution.

  The method for forming the pressure-sensitive adhesive layer is not particularly limited. For example, the pressure-sensitive adhesive composition is applied to a release film, dried, and then transferred to the surface of the shrinkable film (transfer method). A method of directly applying the pressure-sensitive adhesive composition and drying it (coating method) can be employed.

  The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is appropriately determined according to the pressure-sensitive adhesive force and the surface conditions of the shrinkable film and the olefin resin film. For example, it is preferably about 1 to 100 μm, and more preferably about 5 to 50 μm. Within this range, the shrinkage of the shrinkable film can be sufficiently propagated to the stretched film, and a retardation film having good optical uniformity can be produced. The pressure-sensitive adhesive layer can be used by laminating different compositions or different types. In addition, the pressure-sensitive adhesive layer is blended with natural additives such as tackifying resins or synthetic resins, and further appropriate additives such as antioxidants for the purpose of controlling the adhesive force as necessary. May be.

  As described above, the pressure-sensitive adhesive layer is provided on the surface of the shrinkable film or the olefin-based resin film, but on the exposed surface, release paper or release film ( (Also called a separator) is temporarily attached and covered. Thereby, it can prevent contacting an adhesive layer in a normal handling state. As the separator, for example, an appropriate thin leaf body such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foamed sheet, metal foil, or a laminate thereof, and a silicone-based or long chain as necessary. Appropriate ones according to the prior art, such as those coated with a release agent such as alkyl, fluorine, and molybdenum sulfide, can be used. In general, a plastic film such as a polyethylene terephthalate film that has been subjected to a release treatment is preferably used.

The adhesive force at the interface between the olefin resin film and the pressure-sensitive adhesive layer is not particularly limited, but is preferably 0.1 to 5 N / 25 mm at 23 ° C. More preferably, it is 0.1 to 0.25 N / 25 mm. This adhesive force is obtained by attaching a shrinkable film to an olefin resin film through an adhesive layer and then reciprocating a manual roller in accordance with JIS Z 0237: 2000 three times to make a sample for measuring the adhesive force. After being autoclaved for 15 minutes at a temperature of 50 ° C. and a pressure of 5 kg / cm ² , it can be measured by the 90-degree pull-off method (pulling speed: 300 mm / min) according to the above JIS. In order to achieve such an appropriate adhesive force, for example, the surface of the olefin-based resin film on which the pressure-sensitive adhesive layer is provided is subjected to an easily-adhesive surface treatment such as corona treatment or plasma treatment, or a pressure-sensitive adhesive layer. It is possible to adopt a method in which an easy adhesion treatment such as a heat treatment or an autoclave treatment is performed in a state where the olefin resin film and the shrinkable film are bonded via the substrate.

  The shrinkable film can be bonded to one or two or more appropriate numbers on one or both sides of the olefin resin film depending on the shrinkage force to be designed. When the shrinkable film is bonded to both sides of the olefin-based resin film, or when a plurality of shrinkable films are bonded to one side, the shrinkage rate of the shrinkable film on the front and back and top and bottom may be the same. It may be different.

[Heat shrinkage process]
In this manner, the heat shrinkage treatment is performed in a state where the shrinkable film is bonded to one side or both sides of the stretched olefin resin film. At this time, as the phase difference film after shrinkage to satisfy the formula (1) and (2), i.e., (n _x -n _y) ranges plane retardation value corresponding to × d is 150nm~300nm next, (n _x -n _z) / as Nz coefficient corresponding to (n _x -n _y) is 0.2 to 0.6, to heat shrinking. In the heat shrinking step, the shrinkage film in the longitudinal direction is 0.8 to 0.98 times and the shrinkage ratio in the width direction is 0.6 in the state where the shrinkable film is laminated on the stretched olefin resin film. Shrink to ~ 0.9 times.

  At this time, a large shrinkage force in the width direction acts on the shrinkable film, and a large shrinkage force in the longitudinal direction acts on the stretched olefin-based resin film, so that these shrinkage forces can be received. A conventionally known shrinkage treatment method may be employed. In particular, the laminated film in which the olefin resin film and the shrinkable film are bonded together is allowed to shrink in the longitudinal direction by dragging in the longitudinal direction and running in a corrugated form, and further shrinking in the width direction. It is preferable to adopt an acceptable method. For example, shrinkage treatment using a pin tenter is a preferred form. The shrinking process using the pin tenter will be described in more detail later with reference to the drawings.

  It is easy to make the retardation value of the obtained retardation film uniform, and the film is crystallized when the laminated film is heated and shrunk at a temperature equal to or higher than the glass transition temperature (Tg) of the olefin resin film. This is preferable in that it is difficult to cause white turbidity. This temperature is preferably 1 to 50 ° C. higher than the glass transition temperature of the olefin resin film (that is, Tg + 1 ° C. to Tg + 50 ° C.). More preferably, a temperature 2 to 40 ° C. higher than the glass transition temperature of the olefin resin film is employed. If the temperature at the time of heat shrinkage is in the above range, uniform heat shrinkage can be performed. In addition, it is preferable that the temperature at this time is constant in the film width direction in order to produce a retardation film having small variations in retardation value and good optical uniformity.

  If the temperature at this time has a large variation, the shrinkage unevenness will increase, resulting in a variation in the retardation value of the finally obtained retardation film. Therefore, it is preferable that the temperature variation in the width direction of the film is as small as possible. For example, it is desirable that the temperature variation in the width direction plane is ± 1 ° C. or less.

  The specific method for maintaining the temperature in the heat shrinking step is not particularly limited, but for example, a method of blowing air under temperature control, a method of using a heater using microwaves or far infrared rays, temperature control, etc. A known temperature control method such as a method using a rolled roll, a heat pipe roll, or a metal belt can be employed.

In the heat shrinking process, the shrinkage ratio in the longitudinal direction is 0.8 to 0.98 times (2 to 20% in terms of shrinkage ratio), and the shrinkage ratio in the width direction is 0.6 to 0.9 times (shrinkage ratio). 10 to 40%). Here, the shrinkage ratio is a ratio of the dimension of the reference portion in the film after the heat shrinkage treatment to the dimension of the reference portion in the film before the heat shrinkage treatment. Specifically, the shrinkage factor S (MD) in the longitudinal direction is expressed by the following formula, assuming that the length in the longitudinal direction of the film before the heat shrinking treatment is L ₀ and the length is L ₁ by the heat shrinking treatment. Calculated in (3). Further, the shrinkage factor S (TD) in the width direction is W ₀ as the width direction reference length (for example, film width) of the film before the heat shrink treatment, and the length becomes W ₁ by the heat shrink treatment. It is obtained by the following formula (4).

S (MD) = L ₁ / L ₀ (3)
S (TD) = W ₁ / W ₀ (4)

  The shrinkage ratio is influenced by the type of the olefin resin film or the shrinkable film, but may be appropriately selected from the above range according to the designed retardation value or the like. The shrinkage ratio in the width direction is more preferably 0.65 to 0.85 times. Moreover, the feed speed of the laminated film in the heat shrinking step is not particularly limited, but is preferably 0.5 m / min or more, more preferably 1 m / min or more, from the mechanical accuracy and stability of the shrinking device.

  The heat shrinkage treatment can be performed in two or three or more stages. For example, it is also a useful technique to perform the first stage heat shrinkage treatment at a relatively high temperature within the above range, and then to perform the second stage heat shrinkage treatment at a relatively low temperature within the above range. .

[Peeling process]
As described above, an appropriate phase difference is imparted to the olefin resin film by laminating the shrinkable film to the olefin resin film that has been previously stretched and subjecting it to a heat shrink treatment. The shrinkable film after undergoing the heat shrinking process may be allowed to function as a protective film until it is used in a state of being bonded to the retardation film as it is, but in general, it is peeled off from the retardation film after undergoing the heat shrinking process. Removed. When a pressure-sensitive adhesive is used for adhesion between the olefin resin film and the shrinkable film, the pressure-sensitive adhesive layer is also peeled off together with the shrinkable film in this peeling step.

[Example of equipment layout]
In FIG. 1, the example of arrangement | positioning of an apparatus suitable for enforcing the manufacturing method of the retardation film by this invention is shown with a schematic side view. In the illustrated example, the stretched olefin resin film 11 is fed out from the first delivery roll 1, while the shrinkable film 12 has a pressure-sensitive adhesive layer on the bonding surface to the olefin resin film 11. In this state, the second feeding roll 2 is fed out. Then, the pressure-sensitive adhesive layer side of the shrinkable film 2 is bonded to the olefin resin film 1 by the laminate rolls 5 and 5, thereby forming the laminated film 15. Subsequently, the laminated film 15 is guided to the heating zone 20, where a heat shrinking process is performed. The laminated film 16 after undergoing the heat shrinking process is then guided to the peeling roll 6, where the shrinkable film 13 is peeled off together with the adhesive layer, and the shrinkable film 13 is wound around the shrinkable film collection roll 3. The phase difference film 18 after the shrinkable film is peeled off is wound around the product roll 8. In FIG. 1, white straight arrows represent the film flow direction, and curved arrows in each roll represent the roll rotation direction.

  FIG. 1 shows an example in which the shrinkable film 12 is bonded to one side of the stretched olefin-based resin film 11, but the case where the shrinkable film is bonded to both sides of the olefin-based resin film 11 is not shown. The shrinkable film 12 may be supplied to the other surface. In the figure, the stretched olefin-based resin film 11 is once wound up on the roll 1, and is drawn out therefrom and bonded to the shrinkable film 12. It is also possible to continuously bond the shrinkable film 12 from stretching of the film.

  In the heating zone 20, as described above, the laminate film 15 is supplied in a state where the laminated film 15 is moved in the longitudinal direction and undulated, thereby allowing contraction in the longitudinal direction and simultaneously contracting in the width direction. Is preferred. At the same time, tension in the thickness direction is applied by shrinkage of the shrinkable film 12. For this purpose, a pin tenter is preferably used. The pin tenter is a device that has been conventionally used to adjust the width of a fabric, and is a machine that adjusts the width while sequentially suppressing both ends of the workpiece (film in the present invention) in the width direction with pins.

FIG. 2 schematically shows a state in which heat shrinkage treatment is performed using a pin tenter. 2A is a plan view, and FIG. 2B is a side view. A large number of laminated films 15 bonded with a bonding roll 5 with reference to FIG. 1 are arranged in a chain shape at the end in the width direction while moving in the direction of a white straight arrow on a base 25 (for example, a belt conveyor). The pins 22 are sequentially held. Then, on the inlet side of the heating zone, the laminated film 15 is fed in the longitudinal direction by the pins 22 and supplied in a state where the undulations 17 are generated. Thereafter, the waviness 17 is gradually relaxed by shrinkage due to heating, and is also shrunk in the width direction to become a flat film 16 (after the heat shrinking treatment). The film width before the heat shrinkage treatment is represented by W ₀ , and the film width after the heat shrinkage treatment is represented by W ₁ , and the ratio W ₁ / W ₀ is the shrinkage magnification in the width direction. Also in FIG. 2, the white straight arrow represents the film flow direction.

  In this way, the laminated film 15 is fed to the heating zone 20 in a state in which the laminating film 15 is drawn in the longitudinal direction, and is shrunk in the longitudinal direction so that the waving is eliminated in the heating zone 20, and in the width direction. The shrinkage force due to the shrinkable film 12 can be effectively applied to the stretched olefin resin film 11 to obtain a retardation film having a desired retardation value.

[Phase difference film]
The retardation film obtained by the present invention consists of the such olefinic resin, satisfies the above formula (1) and _{(2), (n x -n} y) × plane retardation value equivalent to d but at 150 to 300 nm, it becomes Nz coefficient of 0.2 to 0.6 corresponding to _{(n x -n z) / (} n x -n y). The phase difference value can be represented by a value for light having a wavelength of 590 nm.

  The thickness of the retardation film may be in the range of about 20 to 500 μm. Preferably it is 20-300 micrometers. If the thickness is within this range, sufficient self-supporting property of the film can be obtained, and a wide range of retardation values can be obtained.

  When the retardation film is used as a λ / 2 plate, the in-plane retardation value may be in the range of about 200 to 300 nm. Preferably it is 240-300 nm. By setting the in-plane retardation value to about ½ of the measurement wavelength, the display characteristics of the liquid crystal display device can be further improved. When used as a λ / 2 plate, the thickness is preferably in the range of 80 to 160 μm. More preferably, it is 85-145 micrometers.

  The retardation film also preferably has a thickness direction retardation value Rth in the range of −20 nm to +20 nm. The retardation value in the thickness direction can also be represented by a value for light having a wavelength of 590 nm. The retardation value Rth in the thickness direction is defined by the following equation (5).

Rth = _{[(n x + n y) /} 2-n z ] × d (5)
(In the formula, _nx , _ny , _nz and d are as defined above.)

The retardation value Rth in the thickness direction can be calculated from the retardation value R ₄₀ measured by tilting 40 degrees with the in-plane slow axis as the tilt axis and the in-plane retardation value R ₀ . That is, the retardation value Rth in the thickness direction according to the above formula (5) is the in-plane retardation value Ro, the retardation value R ₄₀ measured by tilting the slow axis by 40 degrees, the thickness d of the film, and using the average refractive index n ₀ of the film to obtain the n _x, n _y and n _z numerically from the following equation (6) to (8), these are substituted into the equation (5), is calculated be able to.

_{R 0 = (n x -n y} ) × d (6)
_{R 40 = (n x -n y} ') × d / cos (φ) (7)
(n _x + _ny + _nz ) / 3 = n ₀ (8)
here,
φ = sin ^-1 [sin (40 °) / n ₀ ]
n _y ′ = _ny × _nz / [ _ny ² × sin ² (φ) + _nz ² × cos ² (φ)] ^1/2

The retardation film can also be as shown in the equation (2) are those Nz coefficient of 0.2 to 0.6 corresponding to _{(n x -n z) / (} n x -n y). The Nz coefficient is more preferably in the range of 0.3 to 0.6. If the value of the Nz coefficient of the retardation film is around 0.5, it is possible to achieve the characteristic that the retardation value is almost constant regardless of the angle, and the display characteristics of the liquid crystal display device can be further improved. .

  In general, when an external force is applied to an isotropic material, that is, a material having birefringence of 0, an internal anisotropy is temporarily exhibited to exhibit birefringence. This is called a photoelastic effect. The index is a photoelastic coefficient. That is, when σ is a stress acting on a substance (a force acting per unit area, that is, a value obtained by dividing a shearing force by a cross-sectional area) and birefringence is Δn, the stress σ and birefringence Δn are theoretically Can be expressed as Δn = Cσ, where C is a photoelastic coefficient. In other words, when the stress σ acting on the substance is taken on the horizontal axis and the birefringence Δn is taken on the vertical axis, the relationship between them is theoretically a straight line, and the gradient of this straight line is the photoelastic coefficient. A smaller absolute value of the photoelastic coefficient is more preferable because it is excellent in optical uniformity and is less likely to cause phase difference unevenness due to distortion. For example, the absolute value of the photoelastic coefficient can be measured by applying an elliptical polarization measuring device “KOBRA-WPR” manufactured by Oji Scientific Instruments Co., Ltd. while applying stress to a 2 cm × 5 cm test piece at 23 ° C. The phase difference value can be measured and calculated from the slope of the function of the phase difference value and stress.

The absolute value of the photoelastic coefficient of the resin constituting the retardation film is preferably in the range of 1 × 10 ^{−12 to} 12 × 10 ⁻¹² m ² / N as a value measured at a wavelength of 590 nm. More preferably, it is in the range of 1 × 10 ^{−12 to} 9 × 10 ⁻¹² m ² / N. Using the resin absolute value of the photoelastic coefficient is in this range, the shift or unevenness in retardation values easily occur due to heat shrinkage stress and the backlight of the polarizer have a relation of n _x> n _z> n _y A retardation film can be obtained.

  Further, when the retardation value in the film plane for light having a wavelength of 450 nm and wavelength of 590 nm of this retardation film is Ro (450) and Ro (590), respectively, Ro (450) / Ro ( 590) is preferably in the range of 0.8 to 1.2. This value is more preferably in the range of 0.9 to 1.1, more preferably in the range of 0.95 to 1.05. As the chromatic dispersion value Ro (450) / Ro (590) of the phase difference is smaller in this range, the phase difference value becomes constant in a wider visible light region, so that the contrast ratio and the color shift of the liquid crystal panel are improved. be able to.

  According to the method of the present invention, a retardation film having a small in-plane retardation value variation can be obtained. Specifically, the in-plane retardation value variation at five measurement points provided at equal intervals in the film width direction can be within ± 10 nm, and further within ± 5 nm. The dispersion of the in-plane retardation value here means that even the most widely separated values are within the above range centering on the average value at the five measurement points.

  In the retardation film, when the variation in the orientation angle (direction formed by the slow axis) is large, the degree of polarization decreases when laminated on a polarizer or a polarizing plate, so the variation in the orientation angle is preferably as small as possible. The retardation film obtained by the present invention has a variation in orientation angle at 5 measurement points provided at equal intervals in the film width direction within ± 2 °, further within ± 1 °, especially within ± 0.5 °. can do. Here, the variation in orientation angle means that even the most separated values are within the above range, centering on the average value at the five measurement points.

  The retardation film obtained by the present invention is designed so that the in-plane retardation value Ro becomes a predetermined value. This retardation film may be used alone or in a form in which two or more films are laminated at an arbitrary angle. Furthermore, the retardation film obtained by the present invention can be used in combination with other retardation films. Even when combined with other retardation films, one or more retardation films can be used according to the present invention. One or more of the other retardation films can be used. A pressure-sensitive adhesive or an adhesive can be used for laminating the retardation film.

  Examples of the material for the other retardation film include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, cellulose resins such as diacetyl cellulose and triacetyl cellulose, acrylic resins such as polymethyl methacrylate, polystyrene, acrylonitrile / Styrene copolymer, acrylonitrile / butadiene / styrene copolymer, acrylonitrile / ethylene / styrene copolymer, styrene / maleimide copolymer, styrene resin such as styrene / maleic anhydride copolymer, polycarbonate resin, etc. It is done. Also, vinyl chloride resins, amide resins such as nylon and aromatic polyamide, imide resins such as aromatic polyimide and polyimide amide, sulfone resins, polyether sulfone resins, polyether ether ketone resins, polyphenylene sulfide resins A film in which birefringence characteristics are imparted to a polymer film made of resin, vinyl alcohol resin, vinylidene chloride resin, vinyl butyral resin, arylate resin, polyoxymethylene resin, epoxy resin, or a blend of these resins Alternatively, a film in which a solution containing a liquid crystal compound is applied on a substrate and cured to fix the orientation can be used. Furthermore, a retardation film made of an olefin resin such as a cyclic olefin resin, a norbornene resin, polyethylene, polypropylene, or an ethylene / propylene copolymer and obtained by a method different from the present invention can also be used. These birefringence characteristics can be used as they are when they spontaneously occur when a polymer film is formed, or can be imparted by stretching the polymer film uniaxially or biaxially.

  The birefringence characteristics of other retardation films are not particularly limited. For example, in the case of using for an IPS mode, VA mode, and OCB mode liquid crystal display device, the in-plane retardation value is 80 to 140 nm and the Nz coefficient is 0. A uniaxial retardation film having a thickness of 0.9 to 1.3, an in-plane retardation value of 0 to 5 nm, a thickness direction retardation value of 90 to 400 nm, and an optical axis substantially in the film normal direction. Uniaxial retardation film, uniaxial inclined alignment retardation film whose optical axis is inclined from 10 to 80 ° from the substrate normal, in-plane retardation value is 30 to 60 nm, and Nz coefficient is 2 to 6 An axial retardation film, a biaxial retardation film having an in-plane retardation value of 100 to 300 nm and an Nz coefficient of 0.2 to 0.8, a discotic liquid crystal molecule or a rod-like liquid crystal molecule is a substrate normal. In contrast, the tilt is gradually changed and tilted. A brid alignment retardation film or the like is preferably used. Among these, the uniaxial retardation film and the biaxial retardation film can be expected to further improve the viewing angle characteristics of the liquid crystal display device when used in combination with the optical film obtained by the present invention.

[Laminated optical film]
The retardation film obtained by the present invention can be used as a laminated optical film laminated on at least one side of a polarizer or a polarizing plate. The polarizing plate usually has a transparent protective film on one or both sides of the polarizer. When providing a transparent protective film on both surfaces of a polarizer, the transparent protective film of the front and back may be comprised with the same material, and may be comprised with a different material. The polarizing plates are usually arranged on both sides of the liquid crystal cell, and the two polarizing plates are arranged so that the absorption axes are orthogonal to each other. The retardation film obtained by this invention can be laminated | stacked with a polarizer or a polarizing plate using an adhesive agent or an adhesive.

  In this laminated optical film, those laminated so that the slow axis of the retardation film is parallel or orthogonal to the absorption axis of the polarizer are preferably used. When arranging the slow axis of the retardation film in parallel with the absorption axis of the polarizer, the angle formed by the slow axis of the retardation film and the absorption axis of the polarizer is preferably 0 ° ± 2 °, Further, 0 ° ± 0.5 ° is more preferable. In addition, when the slow axis of the retardation film is arranged perpendicular to the absorption axis of the polarizer, the angle formed by the slow axis of the retardation film and the absorption axis of the polarizer is 90 ° ± 2 °. More preferably, it is 90 ° ± 0.5 °. As the degree of deviation from these angle ranges increases, the degree of polarization of the polarizing plate decreases, and the contrast tends to decrease when used in a liquid crystal display device. The laminated optical film is not particularly limited, but the retardation film is preferably a λ / 2 plate. Two λ / 4 plates can be laminated so that their slow axes are parallel to each other and used as a λ / 2 plate.

  Various known materials can be used for the polarizer. For example, from iodine and dichroic dyes to hydrophilic polymer films such as polyvinyl alcohol resin films, partially formalized polyvinyl alcohol resin films, and films made of complete or partially saponified ethylene / vinyl acetate copolymers. And a uniaxially stretched dichroic material, a polyene-based oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product. Among these, a polarizer obtained by adsorbing and orienting a dichroic substance such as iodine on a polyvinyl alcohol-based resin film is preferably used because of its high polarization dichroic ratio. The thickness of the polarizer is not particularly limited, but is generally about 5 to 80 μm.

  The transparent protective film provided on one side or both sides of the polarizer is preferably one that is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, retardation value stability, and the like. Examples of the material for forming the transparent protective film include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, cellulose resins such as diacetyl cellulose and triacetyl cellulose, acrylic resins such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene. Examples thereof include styrene resins such as copolymers, acrylonitrile / butadiene / styrene copolymers, acrylonitrile / ethylene / styrene copolymers, styrene / maleimide copolymers, styrene / maleic anhydride copolymers, and polycarbonate resins. . Also, cyclic olefin resins, norbornene resins, polyethylene, polypropylene, olefin resins such as ethylene / propylene copolymers, vinyl chloride resins, amide resins such as nylon and aromatic polyamide, aromatic polyimides and polyimide amides. Imide resin, sulfone resin, polyether sulfone resin, polyether ether ketone resin, polyphenylene sulfide resin, vinyl alcohol resin, vinylidene chloride resin, vinyl butyral resin, arylate resin, polyoxymethylene resin Polymer films made of resins, epoxy resins, blends of these resins, and the like can also be used as the transparent protective film. Furthermore, the said transparent protective film can also be formed as a hardened layer of thermosetting or ultraviolet curable resins such as acrylic, urethane, acrylurethane, epoxy, and silicone.

  The thickness of the transparent protective film can be appropriately determined, but is generally about 1 to 500 μm from the viewpoints of workability such as strength and handleability, and thin layer properties. More preferably, it is 5-200 micrometers. If it is said range, a polarizer will be protected mechanically, and even if it exposes to high temperature and high humidity, a polarizer will not shrink | contract and it can maintain the stable optical characteristic.

  Since the retardation value in the film plane and the retardation value in the thickness direction may affect the viewing angle characteristics of the liquid crystal display device, it is preferable to use a transparent protective film having an optimized retardation value. . However, the transparent protective film for which optimization of the retardation value is desired is a transparent protective film laminated on the surface of the polarizer on the side close to the liquid crystal cell, and is laminated on the surface of the polarizer on the side far from the liquid crystal cell. This is not the case because the transparent protective film does not change the optical characteristics of the liquid crystal display device. Therefore, it is preferable that the transparent protective film disposed on the side closer to the liquid crystal cell of the polarizer has the smallest possible birefringence and photoelastic coefficient absolute values.

Further, the transparent protective film, the slow axis direction in the plane, the fast axis direction and the refractive index in the thickness direction of the plane respectively and n _x, n _y and n _z, the thickness is taken as d, ( n _x -n _y) retardation value Ro in the plane represented by × d is at 5nm or less, _{[(n x + n y) /} 2-n z ] × retardation value in the thickness direction represented by d Rth is preferably 60 nm or less.

  The in-plane retardation value Ro is more preferably 3 nm, and further preferably 2 nm or less. The thickness direction retardation value Rth is more preferably 10 nm or less, and further preferably 6 nm or less. If the retardation value of the transparent protective film arranged on the liquid crystal cell side of the polarizing plate is in the above range, when applied to a liquid crystal display device, it does not adversely affect the display characteristics such as contrast ratio and color shift, Good display characteristics can be obtained.

  Since the absolute value of the photoelastic coefficient of the retardation film obtained by the present invention is smaller than that of a conventional aromatic polymer film, the liquid crystal display device can be directly laminated on a polarizer via an adhesive or an adhesive. When applied to the LCD, it is difficult to cause deviation or unevenness of the retardation value due to the contraction stress of the polarizer or the heat of the backlight, and good display characteristics can be obtained, but the absolute value of the birefringence and the photoelastic coefficient is small. By laminating this retardation film on the surface of the transparent protective film, the shrinkage stress of the polarizer propagating to this retardation film and the influence of the heat of the backlight can be reduced. Can be reduced.

  The method of laminating the transparent protective film on the polarizer is not particularly limited. For example, an adhesive made of acrylic polymer or vinyl alcohol polymer, boric acid, borax, glutaraldehyde, melamine, oxalic acid, water-soluble epoxy It can be carried out via an adhesive or the like obtained by blending a water-soluble crosslinking agent of a vinyl alcohol polymer such as a resin with the vinyl alcohol polymer. Thereby, it is hard to peel off under the influence of humidity and heat, and it can be excellent in light transmittance and polarization degree. As the adhesive, it is preferable to use a polyvinyl alcohol-based adhesive from the viewpoint of excellent adhesiveness with a polyville alcohol-based resin that is a raw material of the polarizer.

  Even when the retardation film is used as a transparent protective film and laminated on a polarizer, an adhesive or a pressure-sensitive adhesive can be used. For example, an adhesive made of an acrylic polymer or a vinyl alcohol polymer, or a water-soluble cross-linking agent of a vinyl alcohol polymer such as boric acid, borax, glutaraldehyde, melamine, oxalic acid, water-soluble epoxy resin, etc. It can be performed through an adhesive or the like blended with the polymer. In addition, the retardation film and the polarizer are bonded via an adhesive that reacts and cures the monomer or oligomer by heating or irradiation of active energy rays, for example, an epoxy-based adhesive containing a cationic polymerization initiator. You can also.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In addition, the physical property measuring method in each example is as follows.

(1) Measurement of shrinkage rate of shrinkable film:
It calculated | required according to the heating dimensional change measuring method of JISK7133: 1999. However, instead of the kaolin floor defined in JIS, a floor on which powder containing talc was spread was used. Specifically, two marked lines are marked in the width direction and the length direction on a test piece having a width of 120 mm and a length of 120 mm, and the distance between the marked lines before the test is measured. The test piece is placed on the talc floor of an air circulation dryer maintained at a specified temperature and heated for a predetermined time. After cooling, the distance between the marked lines in the width direction and the length direction is measured again to determine the dimensional change between the marked lines.

(2) Measurement of shrinkage stress in the width (TD) direction of the shrinkable film:
Using the following apparatuses, the shrinkage stress T ¹⁴⁰ (TD) in the width (TD) direction at 140 ° C. and the shrinkage stress T ¹⁶⁰ (TD) in the width (TD) direction at 160 ° C. by TMA (Thermo Mechanical Analysis) method. Was measured.
・ Stress load device: “TMA / SS 6100” manufactured by Seiko Instruments Inc.
・ Data processing device: “EXSTAR 6000” manufactured by Seiko Instruments Inc.
・ Measurement mode: Constant temperature increase at 10 ° C./min ・ Measurement atmosphere: In the air at room temperature ・ Load: 20 mN
-Sample size: 15mm x 2mm (film width direction (TD) is 15mm)

(3) Measurement of film thickness:
Measurement was performed using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(4) Measurement of shrinkage ratio in heat shrinking process:
In a state where the shrinkable film is bonded to the retardation film precursor (stretched film), the surface of the shrinkable film is marked with a square marked line of 10 cm in the longitudinal direction and 10 cm in the width direction. The length was measured, and the shrinkage factor was determined from these values. If the square marked line of 10 cm in the longitudinal direction and 10 cm in the width direction before shrinkage becomes 9 cm in the longitudinal direction and 8 cm in the width direction after heat shrinkage, the shrinkage factor in the longitudinal direction is 0.9 times and the shrinkage factor in the width direction is 0. .8 times.

(5) Measurement of retardation value, birefringence, wavelength dispersion characteristic and orientation angle:
A value at a wavelength of 590 nm was measured using a phase difference meter (“KOBRA-21ADH” manufactured by Oji Scientific Instruments) based on the parallel Nicol rotation method. When determining the wavelength dispersion characteristic, the value at a wavelength of 450 nm was also measured.

(6) Measurement of light transmittance A haze meter “HGM-2DP” manufactured by Suga Test Instruments Co., Ltd. was used.

(7) Measurement of contrast ratio of liquid crystal display device:
The backlight of the liquid crystal display device is turned on in a dark room at 23 ° C. to display a white image and a black image. 30 minutes after the backlight is turned on, the liquid crystal viewing angle / chromaticity characteristic measuring device “EZ Contrast” manufactured by ELDIM With 160D ", the Y value of the XYZ color system was measured in the direction of the azimuth angle 45 ° and polar angle 60 ° of the display screen, which is one of the directions in which light leakage is greatest on the display screen. Then, the contrast ratio (YW / YB) in the oblique direction was calculated from the Y value (YW) in the white image and the Y value (YB) in the black image. An azimuth angle of 45 ° means an azimuth rotated 45 ° counterclockwise when the long side direction of the panel is 0 °, and a polar angle of 60 ° is 0 ° in the front direction of the display screen. Means a direction inclined at an angle of 60 °.

In the following examples, the following two types were used as shrinkable films. These physical properties are as shown in Table 1.
Shrinkable film A: Transverse uniaxially stretched film (thickness 60 μm) of norbornene resin.
Shrinkable film B: a biaxially stretched film (thickness 60 μm) having a higher transverse stretch ratio of polypropylene resin.

In addition, the shrinkable film A exhibited a maximum shrinkage stress at a temperature slightly lower than 160 ° C., the shrinkage stress rapidly decreased at a temperature higher than that, and the shrinkage stress became zero at 160 ° C. The state shrunk just before 160 ° C. appears as S ¹⁶⁰ (TD). Further, the method for measuring the shrinkage rate and the method for measuring the shrinkage stress are as described above, and the methods are different, and accordingly, the method of applying heat is also different. In particular, the measurement of the shrinkage rate is based on the ambient temperature, whereas the measurement of the shrinkage stress is based on the temperature of the sample itself. This difference in measurement method is presumed to be the cause of the shrinkable film A having S ¹⁴⁰ (TD) of zero and T ¹⁴⁰ (TD) showing a certain value.

[Example 1]
A film having a thickness of 80 μm obtained by longitudinally uniaxially stretching a resin film (“Zeonor film” manufactured by Optes Co., Ltd.) obtained by hydrogenating a ring-opening polymer of a norbornene monomer was used as a retardation film precursor. The film had a glass transition temperature of 136 ° C., a photoelastic coefficient of 3.1 × 10 ⁻¹² m ² / N, an in-plane retardation value of 300 nm, and a thickness direction retardation value of 145 nm. The shrinkable film A was bonded to both surfaces of this uniaxially stretched film via an acrylic adhesive layer having a thickness of 25 μm. Then, while holding the width direction of the film with a pin tenter, it is passed through an air circulation type thermostatic oven at 175 ° C ± 1 ° C and an air circulation type thermostatic oven at 160 ° C ± 1 ° C in order, and shrinks 0.70 times in the width direction. I let you. The shrinkage ratio in the longitudinal direction at this time was 0.92 times. Then, the shrinkable film stuck on both surfaces was peeled off together with the adhesive to obtain a retardation film made of a norbornene resin. The properties of this retardation film are shown in Table 2.

[Example 2]
A retardation film was produced in the same manner as in Example 1 except that the shrinkable film A was changed to the shrinkable film B in Example 1. Table 2 shows the properties of the obtained retardation film.

[Example 3]
In Example 2, a retardation film was produced in the same manner as in Example 2 except that the shrinkable film B was bonded to only one side of the uniaxially stretched film. Table 2 shows the properties of the obtained retardation film.

[Example 4]
(A) Production of Polarizing Plate The polarizing plate surface of a polarizing plate in which a triacetyl cellulose film having a thickness of 40 μm on one side of a polarizer in which iodine is adsorbed and oriented on a polyvinyl alcohol film was obtained in Example 1. The retardation film was bonded so that the slow axis thereof was parallel to the absorption axis of the polarizer to obtain a polarizing plate. For the adhesion between the polarizer and the retardation film, a polyvinyl alcohol resin (“Kuraray K Polymer” obtained from Kuraray Co., Ltd.) and a water-soluble polyamide epoxy resin (“Sumirez Resin 650” obtained from Sumika Chemtex Co., Ltd.) ] Was used.

(B) Production and evaluation of liquid crystal display device The backlight is removed from the liquid crystal display device including the IPS mode liquid crystal cell ["W32L-H9000" manufactured by Hitachi, Ltd.], and further disposed on the backlight side of the liquid crystal cell. The polarizing plate was removed and the glass surface was washed. Next, on the backlight side of the liquid crystal cell, the polarizing plate obtained in (A) is arranged such that its absorption axis is the same as the absorption axis of the original polarizing plate, and the retardation film is on the liquid crystal cell side. The liquid crystal panel was prepared by adhering via an acrylic pressure-sensitive adhesive. Finally, the backlight that had been removed once was assembled again to produce a liquid crystal display device.

  With respect to this liquid crystal display device, the contrast ratio at an azimuth angle of 45 ° and a polar angle of 60 ° was measured 30 minutes after the backlight was turned on. As a result, a contrast ratio of 241 was shown.

[Example 5]
In Example 4, a liquid crystal display device was produced in the same manner as in Example 4 except that the retardation film obtained in Example 2 was used instead of the retardation film obtained in Example 1. With respect to this liquid crystal display device, the contrast ratio at an azimuth angle of 45 ° and a polar angle of 60 ° was measured 30 minutes after the backlight was turned on. As a result, a contrast ratio of 286 was shown.

[Example 6]
In Example 4, a liquid crystal display device was produced in the same manner as in Example 4 except that the retardation film obtained in Example 3 was used instead of the retardation film obtained in Example 1. With respect to this liquid crystal display device, the contrast ratio at an azimuth angle of 45 ° and a polar angle of 60 ° was measured 30 minutes after the backlight was turned on. As a result, a contrast ratio of 311 was shown.

It is a side view which shows roughly the example of arrangement | positioning of an apparatus suitable for implementing this invention. It is a figure which shows the state which performs a heat shrink process using a pin tenter, Comprising: (A) is a top view, (B) is a side view.

Explanation of symbols

1 …… First feeding roll,
2 ... Second feed roll,
3 ... Shrink film take-up roll,
5 ... Laminate roll,
6 …… Peeling roll,
8 …… Product roll,
11 ... Stretched olefin resin film,
12 ... shrinkable film,
13 …… The peeled shrinkable film,
15 …… Laminated film before heat shrinkage treatment,
16 ... Laminated film after heat shrinkage treatment,
17 …… Rippled laminated film,
18 ... retardation film,
20 ... Heating zone (pin tenter),
22 …… Pin tenter pin,
25 …… Pedestal.

Claims (13)

On one or both sides of the stretched olefin-based resin film, the shrinkage S ¹⁶⁰ (MD) in the longitudinal direction at 160 ° C. is 0 to 20%, and the shrinkage S ¹⁶⁰ (TD) in the width direction is 10 to 45%. A laminating step of bonding a certain shrinkable film to obtain a laminated film, and heating the laminated film so that the olefin-based resin film has an in-plane slow axis direction, an in-plane fast axis direction, and a thickness direction. and the refractive index of the respective n _x, and n _y and n _z, the thickness is taken as d, the following equation (1) and (2):
_{150nm ≦ (n x -n y)} × d ≦ 300nm (1)
_{0.2 ≦ (n x -n z)} / (n x -n y) ≦ 0.6 (2)
And a heat shrinking step of shrinking so that the shrinkage ratio in the longitudinal direction is 0.8 to 0.98 times and the shrinkage ratio in the width direction is 0.6 to 0.9 times. A method for producing a retardation film.   The method according to claim 1, wherein the olefin resin is a resin mainly composed of units derived from an alicyclic olefin.   The method according to claim 1 or 2, wherein the olefin-based resin film subjected to the bonding step has a thickness of 10 to 200 µm.   The method according to any one of claims 1 to 3, wherein the olefin resin film subjected to the bonding step has an in-plane retardation value of 200 to 400 nm.   The method according to any one of claims 1 to 4, wherein the olefin-based resin film provided for the bonding step is uniaxially stretched.   The method according to claim 1, wherein the shrinkable film is biaxially stretched.   The method according to claim 1, wherein the shrinkable film is composed of a norbornene resin or a propylene resin.   The method according to claim 1, wherein the heat shrinking step is performed at a temperature 1 to 50 ° C. higher than the glass transition temperature of the olefin resin film.   In the heat shrinking step, the laminated film is supplied to the heating zone in a state where the laminated film is undulated in the longitudinal direction, and is contracted in the longitudinal direction and also contracted in the width direction so that the waving is eliminated in the heating zone. The method according to any one of claims 1 to 8, which is carried out by   The method according to claim 9, wherein the heat shrinking step is performed using a pin tenter.   The method in any one of Claims 1-10 including the peeling process which peels a shrinkable film from a laminated | multilayer film and obtains a phase-difference film after a heat shrink process.   The method according to claim 1, wherein the obtained retardation film has an in-plane retardation value variation of within ± 5 nm.   The method according to claim 1, wherein the obtained retardation film has an orientation angle variation of within ± 0.5 °.

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