JP5257505B2 - Method for producing stretched film and method for producing circularly polarizing plate - Google Patents

Description

  The present invention relates to a method for producing a stretched film and a method for producing a circularly polarizing plate.

  Various retardation films are used in liquid crystal display devices in order to improve performance. This retardation film is a liquid crystal display device in which the slow axis is inclined at various specific angles with respect to the polarization transmission axis of the polarizer, the polarization transmission axis of the liquid crystal cell, etc. Installed. The tilt angle of the slow axis is an angle that is neither parallel nor perpendicular to the side of the display device. By the way, as a method for obtaining a retardation film oriented at an angle that is neither parallel nor perpendicular to the side as described above, a transparent resin film is oriented by longitudinal stretching or lateral stretching to form a long stretched film. After obtaining, a method of cutting into a rectangular shape at a predetermined angle with respect to the side of the stretched film is widely known. However, this method has a problem that even if the cutting is performed so as to obtain the maximum area, a cutting loss always occurs, and the utilization efficiency of the stretched film is low. On the other hand, in the case of a long stretched film oriented obliquely at a predetermined angle, it can be cut parallel to the side edges, and the utilization efficiency of the stretched film is increased. Various methods have been proposed for obtaining such an obliquely oriented film by stretching.

  For example, Patent Document 1 discloses that an optical polymer film is stretched by holding both ends of a continuously supplied polymer film by holding means, and stretching the holding means while moving the holding means in the longitudinal direction of the film. A method is disclosed. In this method, the trajectory L1 of the holding means from the substantial holding start point to the substantial holding release point at one end of the polymer film and the substantial holding release point from the substantial holding start point at the other end of the polymer film. The distance L between the holding means trajectory L2 and the two substantial holding release points satisfies the relationship of | L2-L1 |> 0.4W, and the support of the polymer film is maintained, and the volatile fraction is 5 % Of the volatile matter is reduced while being contracted after being stretched in the presence of more than%.

  Further, in Patent Document 2, it is obtained by stretching a long film made of a thermoplastic resin, and the optical axis (orientation axis) is a direction that is neither parallel nor perpendicular to the winding direction of the long film. A method for producing a long optical film is disclosed. In this method, in a region where the film is substantially stretched, a pair of jigs holding both ends in the width direction of the film having the same moving speed at the opposite ends in the width direction and different moving distances. Stretching is performed so that at least one of the tools is moved on a rail having a wave shape with respect to the film surface. Furthermore, Patent Document 2 discloses that this stretching step may be performed after repeating the stretching step several times, or after stretching in the longitudinal direction or the transverse direction in advance.

JP 2002-86554 A JP 2003-232929 A

  However, in these oblique stretching methods, wrinkles and twists occur obliquely, and thickness unevenness tends to occur. Therefore, to obtain a wide film having a uniform thickness in the width direction and uniformly oriented without variation with an orientation angle particularly inclined by 40 ° or more in the winding direction, for example, a minimum width of 1300 mm which is the minimum width of the polarizer to be bonded. Was practically impossible. Therefore, it was impossible to industrially mass-produce a long and wide optical film in which the orientation axis was oblique (a direction greatly deviating from the width direction or longitudinal direction of the film).

  In view of the above circumstances, the object of the present invention is to provide a wide and long film with no uneven thickness in the width direction and no variation in the alignment direction, excellent optical characteristics, and an alignment axis inclined within a predetermined angle range with respect to the winding direction. The purpose is to produce a stretched film.

  As a result of studies to achieve the above object, the present inventors have stretched a long unstretched film made of a thermoplastic resin in the width direction (a direction perpendicular to the traveling direction of the film), and the orientation angle θ1 is A first stretched film having a small angle range with respect to the width direction and a birefringence Δn in a specific range is obtained, and the first stretched film is drawn out at a specific angle with respect to the winding direction, and the film is stretched. By setting the magnification and the track on both edges of the film within the specified range, the thickness unevenness in the width direction and the variation in the orientation angle are very small, excellent in optical characteristics, and oriented at a relatively large angle with respect to the winding direction. The inventors have found that a wide and long stretched film having an inclined axis can be obtained, and based on this finding, the present invention has been completed.

  That is, according to the first aspect of the present invention, a long unstretched film made of a thermoplastic resin is stretched in a direction perpendicular to the traveling direction of the unstretched film, and the orientation angle θ1 is −1 with respect to the width direction. A step of obtaining a first stretched film in which θ ≦ θ1 ≦ 1 ° and birefringence Δn is in the range of 0.001 to 0.003; and an angle θ of 10 with respect to the winding direction of the first stretched film. Redrawing in the tenter so as to satisfy the conditions of the following formulas (1), (2), and (3) while feeding in the direction of ° <θ <60 °, the orientation angle θ2 is relative to the winding direction. A second stretched film in a range of 40 ° <θ2 <50 °, and the tenter used in the step of obtaining the second stretched film has a film traveling direction substantially parallel to the feeding direction. The first half zone and the film traveling direction are opposite to the winding direction. A long zone with a uniform opening of the inner rail and the outer rail in the latter zone, and a middle zone disposed between the former zone and the latter zone. A method of manufacturing a film is provided.

1.0 ≦ R2 / R1 ≦ 2.0 (1)
0 ° ≦ θo ≦ θi ≦ 6 ° (2)
4 ° ≦ θo _(max) + θi _(max) ≦ 7 ° (3)
In said formula (1), (2), (3), R1 is a draw ratio of said 1st stretched film, R2 is a stretch ratio of said 2nd stretched film. Further, θo is an angle formed between the trajectory of the outer edge of the second stretched film and the winding direction in the latter half zone in which the traveling direction of the second stretched film is substantially parallel to the winding direction, and θi is The angle between the trajectory of the inner edge of the second stretched film in the second half zone and the winding direction, θo _(max) is the maximum value of θo, and θi _(max) is the maximum value of θi. Here, θo, θi, θo _(max) and θi _(max) are positive in the direction in which the outer edge track and the inner edge track are separated from each other, and negative in the approaching direction. The “second half zone in which the film traveling direction is substantially parallel to the winding direction” refers to a zone in which the film traveling direction is within about 3.5 ° with respect to the winding direction.

  In the method for producing a long stretched film according to the first aspect of the present invention, a norbornene resin can be used as the thermoplastic resin.

  According to the 2nd viewpoint of this invention, the process of obtaining a elongate stretched film with the manufacturing method of the stretched film which concerns on the 1st viewpoint of this invention mentioned above, this elongate stretched film, a elongate polarizer, The manufacturing method of the elongate circularly-polarizing plate which has a process of laminating | stacking is provided.

  According to the production method of the present invention, a wide stretched film having a uniform thickness in the width direction, excellent optical characteristics, and a uniform orientation axis in a direction of 40 ° to 50 ° with respect to the winding direction. Can be easily obtained. Since the long stretched film manufactured by the manufacturing method of the present invention can be trimmed in parallel with the longitudinal direction or the width direction, the discarded portion of the film is small and the productivity is excellent.

  In addition, a long stretched film produced by the production method of the present invention and having an orientation axis oriented obliquely is suitable as a retardation plate for a liquid crystal display device or the like. Specifically, when the orientation axis is tilted and overlapped with a certain long angle with another long optical element used in a liquid crystal display device such as a polarizing plate, the orientation axis is inclined with respect to the longitudinal direction. If a film is used, it can be overlapped with other long optical elements by roll-to-roll. In addition, when the circularly polarizing plate of the present invention is used in a liquid crystal display device, particularly a reflective liquid crystal display device, the viewing angle of the display screen is widened, and the contrast and coloration of the display screen can be prevented. it can.

It is a figure which shows the rail arrangement | positioning of the tenter for diagonal extending | stretching used at the 2nd extending | stretching process of embodiment of this invention.

  Hereinafter, the manufacturing method of the elongate stretched film which concerns on embodiment of this invention is demonstrated in detail. In this production method, a long unstretched film made of a thermoplastic resin is stretched in the width direction (a direction perpendicular to the advancing direction of the unstretched film), and the orientation angle θ1 is −1 ° with respect to the width direction. ≦ θ1 ≦ 1 ° and a first stretching step for obtaining a first stretched film having a birefringence Δn in the range of 0.001 to 0.003, and an angle of the first stretched film with respect to the winding direction The orientation angle θ2 is 40 ° <θ2 <50 ° with respect to the winding direction by re-stretching in the tenter so that a predetermined condition is satisfied while the θ is fed in the direction of 10 ° <θ <60 °. And a second stretching step for obtaining a second stretched film in the range.

  In addition, in this-application specification, a long thing means what has a length of about 5 times or more with respect to the width direction of a film or a laminated body, Preferably it has a length of 10 times or more. Specifically, it means a length that is wound in a roll and stored or transported.

  In this embodiment, a thermoplastic resin is used as the material for the stretched film. The thermoplastic resin is not particularly limited as long as it is a transparent resin, but polycarbonate resin, polyethersulfone resin, polyethylene terephthalate resin, polyimide resin, polymethyl methacrylate resin, polysulfone resin, polyarylate resin, polyethylene resin, polyvinyl chloride resin , Diacetylcellulose, triacetylcellulose, polystyrene resin, polyacrylic resin, alicyclic olefin polymer, and the like. Among these, a resin having a positive intrinsic birefringence value is preferable, and an alicyclic olefin polymer is more preferable.

  Examples of the alicyclic olefin polymer include a cyclic olefin random multiple copolymer described in JP-A No. 05-310845, a hydrogenated polymer described in JP-A No. 05-97978, and JP-A No. 11-124429. And thermoplastic dicyclopentadiene-based ring-opening polymers and hydrogenated products thereof.

  The alicyclic olefin polymer will be described more specifically. An alicyclic olefin polymer is a polymer having an alicyclic structure such as a saturated alicyclic hydrocarbon (cycloalkane) structure or an unsaturated alicyclic hydrocarbon (cycloalkene) structure. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The properties of heat resistance and film formability are highly balanced and suitable.

  The proportion of the repeating unit containing the alicyclic structure in the alicyclic olefin polymer may be appropriately selected, but is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight. That's it. When the ratio of the repeating unit having an alicyclic structure in the alicyclic polyolefin polymer is within this range, the transparency and heat resistance of the optical material such as the retardation film obtained by the stretched film of the present embodiment are improved. preferable.

  Examples of the alicyclic olefin polymer include norbornene resins, monocyclic olefin resins, cyclic conjugated diene resins, vinyl alicyclic hydrocarbon resins, and hydrides thereof. Among these, norbornene resin can be suitably used because of its good transparency and moldability.

  Examples of the norbornene resin include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening copolymer of a monomer having a norbornene structure and another monomer, a hydride thereof, or a norbornene structure. Examples thereof include addition polymers of monomers, addition copolymers of monomers having a norbornene structure with other monomers, and hydrides thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly preferable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, and lightness. It can be used suitably.

Examples of monomers having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7-diene. (Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4.0. 1 ^2,5 . 1 ^7,10 ] dodec-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent in the ring). Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. In addition, these substituents may be the same or different and a plurality may be bonded to the ring. Monomers having a norbornene structure can be used singly or in combination of two or more.

  Examples of the polar group include a hetero atom or an atomic group having a hetero atom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfone group.

  Other monomers capable of ring-opening copolymerization with monomers having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; and cyclic such as cyclohexadiene and cycloheptadiene. And conjugated dienes and derivatives thereof.

  A ring-opening polymer of a monomer having a norbornene structure and a ring-opening copolymer of a monomer having a norbornene structure and another monomer copolymerizable with the monomer have a known ring-opening polymerization catalyst. It can be obtained by (co) polymerization in the presence.

  Other monomers capable of addition copolymerization with a monomer having a norbornene structure include, for example, ethylene, propylene, α-olefins having 2 to 20 carbon atoms such as 1-butene and derivatives thereof; cyclobutene, cyclopentene And cycloolefins such as cyclohexene and derivatives thereof; and non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene. These monomers can be used alone or in combination of two or more. Among these, α-olefin is preferable and ethylene is more preferable.

  An addition polymer of a monomer having a norbornene structure and an addition copolymer of a monomer having a norbornene structure with another monomer copolymerizable with a monomer having a norbornene structure are prepared in the presence of a known addition polymerization catalyst. It can be obtained by polymerization.

  A hydrogenated product of a ring-opening polymer of a monomer having a norbornene structure, a hydrogenated product of a ring-opening copolymer of a monomer having a norbornene structure and another monomer capable of ring-opening copolymerization thereof, Hydrogenated products of addition polymers of monomers having a norbornene structure, and hydrogenated products of addition copolymers of monomers having a norbornene structure and other monomers copolymerizable therewith It can be obtained by adding a known hydrogenation catalyst containing a transition metal such as nickel or palladium to the polymer solution and hydrogenating carbon-carbon unsaturated bonds, preferably 90% or more.

Among norbornene resins, as a repeating unit, X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.1 ^2,5 ] decane-7 , 9-diyl-ethylene structure, the content of these repeating units is 90% by weight or more based on the entire repeating units of the norbornene-based resin, and the content ratio of X and the content ratio of Y Is preferably 100: 0 to 40:60 by weight ratio of X: Y. By using such a resin, the optical material obtained by the stretched film manufactured by using the manufacturing method of the present embodiment can be made long-term without dimensional change and excellent in optical property stability. it can.

  The molecular weight of the thermoplastic resin used in the present embodiment is appropriately selected depending on the purpose of use, but polyisoprene measured by gel permeation chromatography using cyclohexane (toluene when the thermoplastic resin does not dissolve) as a solvent. The weight average molecular weight (Mw) in terms of conversion (when the solvent is toluene, in terms of polystyrene) is usually 10,000 to 100,000, preferably 15,000 to 80,000, more preferably 20,000 to 50,000. It is. When the weight average molecular weight is in such a range, the mechanical strength and molding processability of the optical material obtained by the stretched film produced using the production method of the present embodiment are highly balanced and suitable.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the thermoplastic resin is not particularly limited, but is usually 1.0 to 10.0, preferably 1.1 to 4.0, more preferably 1. The range is from 2 to 3.5.

  Although the glass transition temperature of a thermoplastic resin should just be suitably selected according to a use purpose, Preferably it is 80 degreeC or more, More preferably, it is the range of 100-250 degreeC. When the glass transition temperature is in such a range, the optical material obtained by the stretched film manufactured using the manufacturing method of the present embodiment is durable without deformation or stress in use at high temperatures. It can be excellent.

The absolute value of the photoelastic coefficient of the thermoplastic resin is preferably 10 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 7 × 10 ⁻¹² Pa ⁻¹ or less, and particularly preferably 4 × 10 ⁻¹² Pa ^−1. It is as follows. The photoelastic coefficient C is a value represented by C = Δn / σ where birefringence is Δn and stress is σ. When a transparent resin having a photoelastic coefficient in such a range is used, variations in the in-plane retardation Re of the stretched film can be reduced. Furthermore, when such a stretched film is applied to a liquid crystal display device, it is possible to suppress a phenomenon in which the hue of the end portion of the display screen of the liquid crystal display device changes.

  Thermoplastic resins may contain appropriate colorants such as pigments and dyes, optical brighteners, dispersants, heat stabilizers, light stabilizers, UV absorbers, antistatic agents, antioxidants, lubricants, solvents, and other compounding agents. It may be blended. The compounding amount of the compounding agent is not particularly limited, and is 0 to 5% by weight in the thermoplastic resin.

  In the first stretching step in the present embodiment, a long unstretched film made of a thermoplastic resin as described above is stretched in the width direction (a direction perpendicular to the traveling direction of the unstretched film) to obtain an orientation angle θ1. Is a step of obtaining a first stretched film having 0 ° ≦ θ1 ≦ 1 ° in the width direction and a birefringence Δn in the range of 0.001 to 0.003.

  The long unstretched film can be obtained by a known method such as a cast molding method, an extrusion molding method, an inflation molding method, or the like. Of these, the extrusion method is preferable because it has a small amount of residual volatile components and is excellent in dimensional stability. This unstretched film may be a single layer or a laminated film of two or more layers. The laminated film can be obtained by a known method such as a coextrusion molding method, a film lamination method, or a coating method. Of these, the coextrusion method is preferred. In order to make the optical properties after stretching uniform, it is necessary to reduce the thickness unevenness of the unstretched film as much as possible, and the maximum value-minimum value is 3 μm or less, preferably 2 μm or less. In this embodiment, a film roll wound in a roll shape is used as the unstretched film.

  The first stretching step is performed using a transverse stretching tenter (film stretching apparatus). The tenter for transverse stretching is a device that widens a film fed from a film roll in a transverse direction perpendicular to its traveling direction (moving direction of the middle point in the film width direction) in a heating environment by an oven. The feeding direction and the winding direction of the film are substantially the same. The tenter includes an oven, a pair of rails on the left and right on which the grip clips for transporting the film travel, and a number of grip clips that travel on the rails at regular intervals. The grip clips are fed out from the film roll and grip both ends of the film sequentially supplied to the entrance portion of the tenter, guide the film into the oven, and open the film at the exit portion of the tenter. The film released from the gripping clip is wound on the core. Each of the pair of rails has an endless continuous track, and the grip clips that have released the grip of the film at the exit portion of the tenter run outside and are sequentially returned to the entrance portion.

  While passing through the oven, the film is stretched by lateral tension from the grip clips. The temperature in the oven is usually kept constant. Although the temperature in an oven can be selected suitably, it is 135-155 degreeC normally. The grip clip travels on a rail whose arrangement can be changed. The rails are arranged so that the film is stretched at the desired stretch ratio. Here, since the tenter is for lateral stretching, the left and right rails are gradually widened at opposite portions.

  The draw ratio R1 in the first drawing step is preferably 1.1 to 2.0, more preferably 1.2 to 1.8. When the draw ratio is in this range, thickness unevenness in the width direction of the first stretched film and variation in the orientation angle can be suppressed. In addition, the draw ratio in a 1st extending process can be calculated | required from the amount of length change of the width direction. Specifically, when the width of the unstretched film is W0 and the width of the first stretched film after the first stretching step is W1, the stretch ratio R1 can be obtained by W1 / W0.

  The stretching temperature in the first stretching step is appropriately selected from the range of Tg (° C.) or more and Tg + 30 (° C.) or less with respect to the glass transition temperature Tg (° C.) of the thermoplastic resin constituting the unstretched film. If the stretching temperature is less than Tg (° C.), moldability may be insufficient and defects such as craze may occur, and conversely, if it exceeds Tg + 30 (° C.), flow stretching occurs and an effective size birefringence Δn cannot be obtained. Sometimes.

  The first stretched film obtained by the first stretching step has an orientation angle θ1 in the range of −1 ° ≦ θ1 ≦ 1 ° and a birefringence Δn in the range of 0.001 to 0.003 with respect to the width direction. The orientation angle θ1 refers to the smaller angle of the angles formed by the film winding direction and the orientation axis. Birefringence Δn can be obtained by Δn = nx−ny, where nx is the refractive index in the slow axis direction and ny is the refractive index in the direction perpendicular to the slow axis in the plane. The nx and ny can be measured with a known phase difference meter.

  In order to set the orientation angle θ1 and birefringence Δn of the first stretched film within the above ranges, the tension at the oven outlet acting in the running direction is adjusted, or the temperature from stretching to the tenter outlet is adjusted to the heat that constitutes the film. This can be achieved by providing a temperature distribution that is equal to or lower than the glass transition temperature of the plastic resin.

  Here, the first stretched film is wound around the core and made into a wound body, and then supplied to the next second stretching step, but the next second stretching step without being wound around the core. May be supplied sequentially.

  The first stretched film obtained through the first stretching step described above is supplied to the next second stretching step. In the second stretching step, the first stretched film is redrawn in the tenter for oblique stretching so as to satisfy a predetermined conditional expression while feeding the first stretched film in a direction where the angle θ is 10 ° <θ <60 ° with respect to the winding direction. This is a step of obtaining a second stretched film having an orientation angle θ2 in the range of 40 ° <θ2 <50 ° with respect to the winding direction by stretching.

  This second stretching step is performed using a tenter (film stretching device) for oblique stretching. The tenter for oblique stretching is a device that widens a film fed from a film roll in an oblique direction with respect to its traveling direction (moving direction of the middle point in the film width direction) in an oven heating environment. This oblique stretching tenter is similar to the transverse stretching tenter used in the first stretching step described above. The oven, a pair of rails on the left and right on which the grip clip for transporting the film travels, And a plurality of grip clips that travel at regular intervals. The grip clips are fed out from the film roll and grip both ends of the film sequentially supplied to the entrance portion of the tenter, guide the film into the oven, and open the film at the exit portion of the tenter. The film released from the gripping clip is wound on the core. Each of the pair of rails has an endless continuous track, and the grip clips that have released the grip of the film at the exit portion of the tenter run outside and are sequentially returned to the entrance portion.

  In the oblique stretching tenter used in the second stretching step, a pair of rails are sequentially bent as shown in FIG. 1, for example, and the film feeding direction D1 and the winding direction D2 are obliquely crossed with an angle θ. This is different from the tenter for transverse stretching used in the first stretching step. This angle θ is appropriately selected from the range of 10 to 60 degrees according to the design of a display device such as a liquid crystal panel in which the stretched film to be produced is used. The shape of the rail can be arbitrarily changed.

  The stretching ratio in the second stretching step, that is, the stretching ratio R2 of the second stretched film obtained through the second stretching process is the stretching ratio in the first stretching process, that is, the first stretching obtained through the first stretching process described above. The stretch ratio of the film is set as R1 so as to satisfy the following formula (1). By setting the draw ratio to the relationship as in the formula (1), a stretched film having good orientation and stable physical properties such as optical properties can be obtained.

1.0 ≦ R2 / R1 ≦ 2.0 (1)
Moreover, the track | orbit of a pair of rail of the tenter for diagonal extending | stretching is set so that the following formula | equation (2) and Formula (3) may be satisfy | filled.

0 ° ≦ θo ≦ θi ≦ 6 ° (2)
4 ° ≦ θo _(max) + θi _(max) ≦ 7 ° (3)
In Equation (2), θo is the track and winding direction of the outer edge (ie, outer rail) of the second stretched film in the latter half zone where the traveling direction of the second stretched film is substantially parallel to the winding direction D2. It is an angle formed with D2, and θi is an angle formed between the track of the inner edge (that is, the inner rail) of the second stretched film in the latter half zone and the winding direction D2. In FIG. 1, Ro indicates a track of an outer rail that is one of a pair of rails, and Ri indicates a track of an inner rail that is the other of the pair of rails. Here, the outer side means a side with a small curvature of the track (a side with a large radius) when the track is considered as a substantially circular arc, and the inside means a side with a large curvature of the track (a side with a small radius). The latter half zone is a zone where the traveling direction of the film is substantially parallel to the winding direction D2, and specifically refers to a zone within 3.5 ° with respect to the winding direction D2. In FIG. 1, the portion indicated by the symbol LZ is the latter half zone. In FIG. 1, FZ is the first half zone, and MZ is the middle zone.

In Equation (3), θo _(max) is the maximum value of θo, and θi _(max) is the maximum value of θi. In the equations (2) and (3), θo, θi, θo _(max) , θi _(max) are directions in which the track of the outer rail Ro and the track of the inner rail Ri are separated from each other as shown in FIG. Is positive, and the approaching direction is negative. Thus, by setting the outer rail Ro and the inner rail Ri to a relationship satisfying the expressions (2) and (3), the uniformity of the film thickness, the orientation angle, the Nz coefficient, and the like can be improved. .

  The stretching ratio R2 in the second stretching step is set so as to satisfy the formula (1) in relation to the stretching ratio R1 in the first stretching step as described above, but preferably 1.3 to 2.0. More preferably, it is 1.5-1.8. When the draw ratio R2 is within this range, thickness unevenness in the width direction can be reduced. In addition, draw ratio R2 in a 2nd extending process can be calculated | required from the amount of length change of the width direction. Specifically, when the width of the first stretched film before the second stretching step is W1, and the width of the second stretched film after the second stretching step is W2, the stretching ratio R2 can be obtained by W2 / W1.

  The oven provided in the tenter for oblique stretching used in the second stretching step has a preheating zone, a stretching zone, and a fixing zone, and while the film sequentially passes through these zones, the tension from the grip clip is used. Diagonally stretched. The preheating zone, the stretching zone, and the fixed zone can be set independently of each other, and the temperature is normally kept constant in each zone. Although the temperature of each zone can be selected as appropriate, the preheating zone is Tg to Tg + 30 (° C.), the stretching zone is Tg to Tg + 20 (° C.), and the glass transition temperature Tg (° C.) of the thermoplastic resin constituting the film is fixed. The zone is Tg to Tg + 15 (° C.).

  In order to control thickness unevenness in the film width direction, a temperature difference may be applied in the width direction in the stretching zone. In particular, it is preferable that the temperature in the vicinity of the grip clip is higher than that in the center of the film. In order to provide a temperature difference in the width direction in the stretching zone, a method of adjusting the opening degree of the nozzle for sending warm air into the oven so as to make a difference in the width direction, or controlling heating by arranging heaters in the width direction is known. Can be used. The length of the preheating zone, the stretching zone, and the fixed zone can be appropriately selected. The length of the preheating zone is usually 100 to 150% and the length of the fixed zone is usually 50 to 100% with respect to the length of the stretching zone. .

  A partition plate having a slit through which the film can pass is installed at the boundary between the preheating zone and the stretching zone and the boundary between the stretching zone and the fixed zone. It is preferable that the boundary between the preheating zone and the stretching zone and the boundary between the stretching zone and the fixing zone, that is, the partition plate is perpendicular to the traveling direction of the film in the fixing zone.

  A preheating zone is a zone which conveys a film, warming a film, without substantially changing the film length of the direction orthogonal to the advancing direction of the film of a preheating zone. The film traveling direction in the preheating zone is a direction parallel to the film feeding direction, and is generally orthogonal to the rotation axis of the feeding roll.

  The stretching zone is a zone for transporting the film while increasing the film length in the direction perpendicular to the film traveling direction of the stretching zone. The fixed zone is a zone in which the film is conveyed while being cooled without substantially changing the film length in the direction perpendicular to the film traveling direction of the fixed zone. The film traveling direction of the fixed zone is a direction parallel to the film winding direction, and is generally orthogonal to the rotation axis of the winding roll.

  The traveling speed of the grip clip can be selected as appropriate, but is usually 10 to 100 m / min. The difference in travel speed between the pair of left and right grip clips is usually 1% or less, preferably 0.5% or less, more preferably 0.1% or less of the travel speed.

  In the stretching zone, the film traveling direction may be linear without changing, or the film traveling direction may be changed stepwise or continuously. The opening angle of the rail is appropriately set according to the draw ratio so as to satisfy the above-described expressions (2) and (3).

  The traveling direction of the fixed zone (film winding direction D2) is inclined from the traveling direction of the preheating zone (film feeding direction D1) at an angle θ as shown in FIG. For this reason, the outer gripping clip in the drawing goes farther than the inner gripping clip. Accordingly, when viewed from the film width direction at the exit portion of the tenter, the inner gripping clip has advanced to a position ahead of the corresponding outer gripping clip, whereby oblique stretching is performed.

  As described above, the stretched film that has passed through the oven is released from the gripping clip before the take-up roll and is taken up by the take-up roll. Moreover, you may trim the both ends of the film currently hold | gripped with the holding clip of a tenter before winding up to a winding roll as needed. In addition, before winding, for the purpose of preventing blocking between the films, the masking film may be overlapped and wound up at the same time, or at least one of the stretched films, preferably wound up with tape or the like attached to both ends. Also good. The masking film is not particularly limited as long as it can protect the film, and examples thereof include a polyethylene terephthalate film, a polyethylene film, and a polypropylene film.

  By passing through the first and second stretching steps described above, the orientation angle θ2 is in the range of 40 ° <θ2 <50 ° with respect to the winding direction D2, and the variation of the orientation angle θ2 is at least 1300 mm in the width direction. It is possible to produce a long stretched film that is 0 ° or less, has an Nz coefficient in the range of 1.0 to 2.0, and has an Nz coefficient variation of 0.10 or less in at least 1300 mm in the width direction.

The retardation Re in the in-plane direction of the stretched film produced using the production method of the present embodiment is about 100 to 300 nm, and the optimum value is selected within this range depending on the design of the display device used. Incidentally, the retardation Re in the in-plane direction, the average thickness of the film to the difference between the direction of the refractive index n _y perpendicular to the slow axis in the refractive indices n _x and the plane of the slow axis direction in a plane d a multiplication value _{(Re = (n x -n y} ) × d).

  Variation in retardation Re in the in-plane direction of the stretched film is preferably within 10 nm, more preferably within 5 nm, and particularly preferably within 2 nm. By setting the variation of the retardation Re in the in-plane direction within the above range, the display quality can be improved when used as a retardation film for a liquid crystal display device. The in-plane retardation Re is measured using a commercially available retardation measuring device at a light incident angle of 0 ° (incident light beam and stretched film surface perpendicular to each other) at an interval of 50 mm in the width direction. The average value is defined as in-plane retardation Re. Further, the variation in retardation Re in the in-plane direction is a value obtained by subtracting the minimum value from the maximum value of each measurement value.

  The stretched film manufactured using the manufacturing method of this embodiment has an orientation angle θ2 in the range of 40 ° to 50 ° when the film winding direction is 0 °, and is in the in-plane direction. Similar to the retardation value, the optimum value within this range is selected depending on the design of the display device used. In this stretched film, the variation in the orientation angle θ2 is 1.0 ° or less, preferably 0.8 ° or less, in at least 1300 mm in the width direction. When a stretched film having a variation in the orientation angle θ2 exceeding 1.0 ° is bonded to a polarizing plate to obtain a circularly polarizing plate, and this is installed in a liquid crystal display device, light leakage occurs and the contrast may be lowered. is there. In addition, orientation angle | corner (theta) 2 measures a stretched film at a 50 mm space | interval in the width direction using a commercially available polarizing microscope, and makes it an average value. The variation in the orientation angle θ2 is a value obtained by subtracting the minimum value from the maximum value of each measurement value.

Stretched film produced by the production method of this embodiment, a slow axis direction of the refractive indices n _x in the plane of the _film, the direction of the refractive index perpendicular to the slow axis in the film plane n _y, film when the refractive index in the thickness direction is _{n z of, (n x -n z) /} (n x -n y) range Nz coefficient of 1.0 to 2.0 represented by, preferably 1.3 It is -2.0, More preferably, it exists in the range of 1.4-2.0. An optimum value within this range is selected depending on the design of the liquid crystal display device used. This stretched film has an Nz coefficient variation of 0.1 or less, preferably 0.08 or less, at least at 1300 mm in the width direction. If the variation of the Nz coefficient exceeds 0.1, when this is incorporated in a liquid crystal display device, it causes a reduction in display quality such as color unevenness. In addition, Nz coefficient measures a stretched film by 50 mm space | interval in the width direction using a commercially available phase difference measuring apparatus, and makes the average value Nz coefficient. Further, the variation of the Nz coefficient is a value obtained by subtracting the minimum value from the maximum value of each measurement value.

  The average thickness of the stretched film produced according to this embodiment is preferably 30 to 80 μm, more preferably 30 to 60 μm, and particularly preferably 30 to 50 μm from the viewpoint of mechanical strength and the like. Moreover, since the thickness unevenness in the width direction of the stretched film affects the availability of winding, it is preferably 3 μm or less, more preferably 2 μm or less. The average thickness is measured at 50 mm intervals in the width direction using a commercially available thickness measuring device, and the average value is defined as the average thickness. The thickness unevenness is a value obtained by subtracting the minimum value from the maximum value of each measurement value.

  The long stretched film of this embodiment has a width of at least 1300 mm, preferably 1500 mm or more. This elongated stretched film is optionally created in the manufacturing process by cutting off both ends in the width direction after stretching.In this case, the width of the film referred to above is the dimension after cutting off both ends. can do.

In the stretched film of this embodiment, the content of residual volatile components is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, and further preferably 0.02% by weight or less. If the content of residual volatile components is large, the optical characteristics may change over time. The content of volatile components in the above range, dimensional stability is improved, the in-plane direction retardation Re and thickness direction retardation _{Rth (= ((n x +} n y) / 2-n z) × d ; n _x is the in-plane slow axis direction of the refractive index; n _y is the refractive index in the direction perpendicular to the slow axis in the plane; n _z is the thickness direction of the refractive index; d is an average thickness) of the film A change with time can be reduced, and further, deterioration of a circularly polarizing plate and a liquid crystal display device provided with the stretched film can be suppressed, and a display image can be kept in a good state for a long time. The volatile component is a substance having a molecular weight of 200 or less contained in a trace amount in the film, and examples thereof include residual monomers and solvents. The content of the volatile component can be quantified by dissolving the film in chloroform and analyzing it by gas chromatography as the total of substances having a molecular weight of 200 or less contained in the film.

  The stretched film of the present embodiment has a saturated water absorption rate of preferably 0.03% by weight or less, more preferably 0.02% by weight or less, and particularly preferably 0.01% by weight or less. When the saturated water absorption is in the above range, the time-dependent changes in the in-plane direction retardation Re and the thickness direction retardation Rth can be reduced, and further, deterioration of the circularly polarizing plate and the liquid crystal display device can be suppressed. Can be kept in good condition for a long time. The saturated water absorption is determined by immersing a film specimen in water at 23 ° C. for 24 hours in accordance with JIS K7209, and measuring the change in mass of the specimen, that is, the difference in mass before and after immersion. , A value expressed as a percentage before immersion.

  Since the stretched film manufactured using the manufacturing method of the present embodiment described above can highly compensate the refractive index, it can be used as a retardation plate or a viewing angle compensation film by itself or in combination with other members. It can be widely applied to devices, organic EL display devices, plasma display devices, FED (field emission) display devices, SED (surface electric field) display devices, and the like.

  Further, by laminating a long stretched film manufactured using the manufacturing method of the above-described embodiment and a separately manufactured long polarizer (polarizing film), a long circular polarizing plate (circularly polarized light) Film). The polarizer transmits one of two linearly polarized lights that intersect at right angles. For example, a hydrophilic polymer film such as a polyvinyl alcohol film or an ethylene vinyl acetate partially saponified film adsorbed a dichroic substance such as iodine or a dichroic dye and uniaxially stretched, the hydrophilic polymer film Examples include uniaxially stretched and dichroic substances adsorbed, and polyene oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Other examples include reflective polarizers such as grid polarizers and anisotropic multilayer films. The thickness of the polarizer is usually 5 to 80 μm.

  In this case, the stretched film may be laminated on both sides of the polarizer or on one side, and the number of laminated layers is not particularly limited, and two or more may be laminated. When the stretched film is laminated only on one side of the polarizer, a protective film may be laminated on the remaining one side with an appropriate adhesive layer for the purpose of protecting the polarizer.

  An appropriate transparent film can be used as the protective film. Among them, a film having a resin excellent in transparency, mechanical strength, thermal stability, moisture shielding property, etc. is preferably used. Examples of the resin include acetate polymers such as triacetyl cellulose, alicyclic olefin polymers, chain polyolefins, polycarbonates, polyesters such as polyethylene terephthalate, polyvinyl chloride, polystyrene, polyacrylonitrile, polysulfones, polyethersulfones, polyamides. , Polyimide, acrylic polymer and the like.

  A circularly polarizing plate composed of such a laminated film can be produced by bringing the stretched film and the polarizer into close contact with each other while simultaneously drawing the film from the wound body of the stretched film and the wound body of the polarizer. it can. An adhesive may be interposed on the adhesion surface between the obliquely stretched film and the polarizer. As a method for bringing the stretched film and the polarizer into close contact with each other, there is a method in which the stretched film and the polarizer are passed and pressed together through the nip between two parallel rolls.

  A long stretched film or a long circularly polarizing plate is cut into a desired size according to the usage pattern and used as a phase difference plate or a polarizing plate. In this case, it is preferable to cut out along a direction perpendicular or parallel to the winding direction of the long film.

  A liquid crystal display device is manufactured using a stretched film obtained by cutting a long stretched film produced using the production method of the present embodiment or a circularly polarizing plate obtained by cutting a long circularly polarizing plate. Can do. An example of the liquid crystal display device includes a liquid crystal panel in which the polarization transmission axis can be changed by adjusting a voltage, and the above-described circularly polarizing plate arranged so as to sandwich the liquid crystal panel. The stretched film described above is used as a retardation plate in a liquid crystal display device for optical compensation, polarization conversion, and the like. In order to send light to the liquid crystal panel, the liquid crystal display device is usually provided with a backlight device in the transmissive liquid crystal display device and a reflector in the reflective liquid crystal display device on the back side of the display surface. Examples of the backlight device include a cold cathode tube, a mercury flat lamp, a light emitting diode, and an EL. In particular, as a liquid crystal display device to which a stretched film manufactured using the manufacturing method of the present embodiment is applied, a reflective liquid crystal display device including a reflective display type liquid crystal panel is preferable.

  The liquid crystal panel is not particularly limited by the display mode. For example, twisted nematic (TN) mode, super twisted nematic (STN) mode, hybrid alignment nematic (HAN) mode, vertical alignment (VA) mode, multi-domain vertical alignment (MVA) mode, in-plane switching (IPS) mode, etc. Can be mentioned. In addition, in the liquid crystal display device, one or more layers of appropriate components such as a prism array sheet, a lens array sheet, a light diffusion plate, a light guide plate, a diffusion sheet, and a brightness enhancement film may be disposed at appropriate positions. it can.

  The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. Parts and% are based on weight unless otherwise specified. Evaluation in this example is performed by the following method.

(1) Variation in orientation angles θ1, θ2, and θ2 Using a polarizing microscope (Olympus, BX51), the film is measured at intervals of 50 mm in the width direction of the film, the in-plane slow axis is measured, and θ1 is the slow axis The average value of the angle (orientation angle) formed by the direction of the width and the width direction is obtained, and this is defined as θ1, and θ2 is the average value of the angle (orientation angle) formed by the direction of the slow axis and the winding direction. Was the orientation angle θ2. The variation in the orientation angle θ2 is the difference between the maximum value and the minimum value of the orientation angle.

(2) Birefringence Δn, average Re, Nz coefficient and variations thereof Using a phase difference meter (manufactured by Oji Scientific Co., Ltd., KOBRA-21ADH), Δn, Re and Nz coefficient are measured at intervals of 50 mm in the width direction of the film. The average value was calculated | required about each. The variation of the Nz coefficient is the difference between the maximum value and the minimum value of the Nz coefficient.

Example 1
A pellet of thermoplastic norbornene resin (Zeon Corporation, ZEONOR 1420, glass transition point 137 ° C.), which is a kind of alicyclic olefin polymer, was dried at 100 ° C. for 5 hours. The pellets were supplied to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, extruded from a T die onto a casting drum, cooled, and an unstretched film having a thickness of 130 μm and a width of 1200 mm was obtained. .

  The unstretched film is continuously supplied as it is to a tenter for transverse stretching, and the first stretching step is performed at a stretching temperature of 140 ° C. and a stretching ratio of 1.42 times, and the orientation angle θ1 is 0.2 ° with respect to the width direction. A first stretched film oriented to was obtained and wound on a core.

  Next, the first stretched film is pulled out from the winding core, and is obliquely stretched at a feeding angle θ = 40 ° with respect to the winding direction so that the orientation angle θ2 of the film is 45 ° with respect to the winding direction. The second stretching step was performed at a stretching temperature of 145 ° C. and a stretching ratio R2 = 1.82, and the film was trimmed at 180 mm on both ends to obtain a long stretched film having a width of 1340 mm. The obtained long stretched film was uniform in the width direction. Table 1 shows the stretching conditions, and the properties of the first stretched film and the second stretched film.

  A long polarizing plate with a transmission axis in the width direction (manufactured by Sanlitz, HLC2-5618S, thickness 180 μm, width 1340 mm) and a second stretched film are bonded together by a roll-to-roll, and a circle having a width of 1340 mm A roll of polarizing plate was obtained. The circularly polarizing plate cut out from the wound body is replaced with a polarizing plate on the backlight side of a commercially available VA (vertical alignment) mode reflective liquid crystal display device, and the side on which the stretched film is bonded is arranged on the liquid crystal cell side. Thus, a reflection type liquid crystal display device was prepared. When the display characteristics of the created liquid crystal display device were confirmed from the front by visual observation, no color unevenness was observed over the entire width, and the display was good.

Examples 2-3
Except having changed into extending | stretching conditions shown in Table 1, it carried out similarly to Example 1, and obtained the 1st stretched film, the 2nd stretched film, the circularly-polarizing plate, and the reflective liquid crystal display device. Table 1 shows the characteristics of the first stretched film and the second stretched film. When the display characteristics of the reflective liquid crystal display device provided with the circularly polarizing plate using the second stretched film were confirmed from the front by visual observation, no color unevenness was observed over the entire width, and good display was possible.

Comparative Examples 1-4
Except having changed into extending | stretching conditions shown in Table 1, it carried out similarly to Example 1, and obtained the 1st stretched film, the 2nd stretched film, the circularly-polarizing plate, and the reflective liquid crystal display device. Table 1 shows the characteristics of the first stretched film and the second stretched film. The films obtained in Comparative Examples 1 to 4 had large variations in orientation angle and Nz coefficient. Further, a circularly polarizing plate and a reflective liquid crystal display device were prepared in the same manner as in Example 1 except that the obtained second stretched film was used. When the display characteristics of the reflective liquid crystal display device including the circularly polarizing plate using the second stretched film were visually confirmed from the front, color unevenness and a decrease in contrast were observed in the screen.

D1 ... Feeding direction D2 ... Winding direction θ ... An angle Ro between the feeding direction and the winding direction Ro ... Outer rail (track)
Ri ... Inner rail (track)
LZ ... Second half zone

Claims (3)

A long unstretched film made of a thermoplastic resin is stretched in a direction perpendicular to the traveling direction of the unstretched film, the orientation angle θ1 is −1 ° ≦ θ1 ≦ 1 ° with respect to the width direction, and Obtaining a first stretched film having a refraction Δn in the range of 0.001 to 0.003;
While feeding the first stretched film in the direction of the angle θ of 10 ° <θ <60 ° with respect to the winding direction, in the tenter so as to satisfy the following expressions (1), (2), (3) Re-stretching to obtain a second stretched film having an orientation angle θ2 in the range of 40 ° <θ2 <50 ° with respect to the winding direction,
The tenter used in the step of obtaining the second stretched film includes a first half zone in which the film traveling direction is substantially parallel to the feeding direction, and a second half zone in which the film traveling direction is substantially parallel to the winding direction. A method for producing a long stretched film, comprising a middle zone disposed between the first half zone and the second half zone, wherein the opening of the inner rail and the outer rail in the second half zone is uniform.
1.0 ≦ R2 / R1 ≦ 2.0 (1)
0 ° ≦ θo ≦ θi ≦ 6 ° (2)
4 ° ≦ θo _(max) + θi _(max) ≦ 7 ° (3)
However,
R1 is the draw ratio of the first stretched film,
R2 is the draw ratio of the second stretched film,
θo is an angle formed by the winding direction of the outer edge of the second stretched film in the latter half zone where the traveling direction of the second stretched film is substantially parallel to the winding direction,
θi is an angle formed between the track of the inner edge of the second stretched film in the second half zone and the winding direction,
θo _(max) is the maximum value of θo,
θi _(max) is the maximum value of θi,
θo, θi, θo _(max) and θi _(max) are positive in the direction in which the outer edge track and the inner edge track are separated from each other, and negative in the approaching direction.   The method for producing a long stretched film according to claim 1, wherein the thermoplastic resin is a norbornene resin.   A method for producing a long circularly polarizing plate, comprising: a step of obtaining a long stretched film by the production method according to claim 1; and a step of laminating the long stretched film and a long polarizer. .