JP5233746B2 - Method for producing obliquely stretched film, obliquely stretched film, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to a method for producing an obliquely stretched film, an obliquely stretched film, a polarizing plate, and a liquid crystal display device, and in particular, a method for producing an obliquely stretched film that can further suppress variations in thickness and optical properties, and this production method. The present invention relates to an obtained obliquely stretched film, a polarizing plate provided with the obliquely stretched film, and a liquid crystal display device provided with the polarizing plate.

  Conventionally, in a liquid crystal display device (LCD), a retardation film is used between a polarizer and a liquid crystal cell for the purpose of optical compensation such as prevention of coloring and expansion of a viewing angle. Such a retardation film has a different angle depending on the liquid crystal mode used in the liquid crystal cell, but needs to be laminated so that the orientation direction of molecules is a predetermined angle with respect to the polarization transmission axis of the polarizer. Since a polarizer is usually produced by uniaxially stretching a long PVA (polyvinyl alcohol) film on which a dichroic dye such as iodine is adsorbed, its polarization transmission axis is the flow direction of the long film ( Longitudinal direction) or width direction (short direction).

  On the other hand, as the retardation film, a stretched film in which molecules are oriented in a predetermined direction is usually used by stretching a long transparent resin film (film before stretching). In such a stretched film, when a conventional stretching method such as longitudinal stretching or lateral stretching is used, the molecular orientation direction is either the film flow direction or the width direction. Therefore, when the polarizing transmission axis of the polarizer and the orientation direction of the retardation film are bonded at a predetermined angle, the rectangular film must be cut out so that the molecular orientation direction is at a predetermined angle with respect to the side. However, there is a problem that the amount of the film to be discarded increases and the utilization efficiency of the stretched film is low.

  Therefore, if a stretched film (obliquely stretched film) oriented obliquely at a predetermined angle with respect to the film flow direction can be produced, a long polarizer and a long retardation film are laminated by a roll-to-roll method. In this case, since the laminated film can be cut out in parallel to the sides of the rectangular film, the utilization efficiency of the stretched film can be increased.

  Such a diagonally stretched film can be produced by stretching a long pre-stretched film in an oblique direction, but simply by performing oblique stretching, compared to a stretched film produced by longitudinal stretching or lateral stretching. However, there is a problem that the thickness and optical characteristics (orientation angle, Re) of the stretched film to be obtained vary and are likely to be non-uniform.

  In order to solve such a problem, for example, Patent Document 1 proposes a stretching method in which the stretching direction in each zone constituting the temperature-controlled room satisfies a specific relationship. Patent Document 2 proposes a stretching method in which the film feeding direction during oblique stretching and the winding direction of the film after stretching satisfy a specific relationship. Furthermore, Patent Document 3 attempts to make the molecular orientation direction of the stretched film coincide with the angle formed by the boundary between the heating stretching zone and the cooling zone as much as possible.

JP 2007-90532 A JP 2007-153926 A Japanese Patent Laid-Open No. 2003-311823

  However, in recent years, since even higher uniformity of thickness and optical properties is required, even if an obliquely stretched film is produced by the methods shown in Patent Documents 1 to 3, the thickness of the obtained obliquely stretched film and There may be insufficient variation in optical characteristics.

  An object of the present invention is to provide a method for producing an obliquely stretched film that can further suppress variations in thickness and optical properties, an obliquely stretched film obtained by this production method, a polarizing plate provided with this obliquely stretched film, and this polarizing plate. A liquid crystal display device is provided.

According to the present invention, the following is provided.
<1> A method for producing a long obliquely stretched film in which the orientation direction of molecules intersects the width direction of the film, and is a long stretched film made of a transparent thermoplastic resin A longitudinal uniaxial stretching step in which F0 is longitudinally uniaxially stretched in the longitudinal direction to obtain an elongated longitudinal uniaxially stretched film F1, and stretching having a pair of grippers for gripping both ends in the width direction of the longitudinal uniaxially stretched film F1. And an oblique stretching step of obtaining an obliquely stretched film F2 by stretching in an oblique direction that is neither the longitudinal direction nor the width direction of the film using a machine, and the unstretched film F0 is one of the width directions of the film F0. Diagonal stretching satisfying the following relations (1) and (2), where T1 is the thickness at the end, T2 is the thickness at the other end, and TC is the thickness at the intermediate position between the one end and the other end. F Manufacturing method of Lum.
(1) 1.00 × T1 <TC <1.03 × T1
(2) 1.00 × T2 <TC <1.03 × T2
<2> The method for producing a stretched film, further comprising a pre-stretch film production step of producing the pre-stretch film F0 made of the transparent thermoplastic resin by a melt extrusion method.
<3> An obliquely stretched film produced by the method for producing an obliquely stretched film.
<4> A polarizing plate obtained by laminating the obliquely stretched film and a long polarizer in the same longitudinal direction.
<5> A liquid crystal display device comprising the polarizing plate and a liquid crystal cell.

  According to the present invention, by using a pre-stretched film having a predetermined thickness in the width direction, in an obliquely stretched film in which the orientation direction of molecules is inclined with respect to the longitudinal direction of the film, variations in thickness and optical properties are achieved. There is an effect that it can be made even smaller.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically showing a film manufacturing apparatus used in the present invention. FIG. 2 is a view showing an extrusion molding machine constituting the film manufacturing apparatus. As shown in FIG. 1, the obliquely stretched film of the present invention is manufactured using a film manufacturing apparatus 100. The film manufacturing apparatus 100 includes an extrusion molding machine 30 that molds the unstretched film F0, and a longitudinal uniaxial stretching machine 20 that longitudinally uniaxially stretches the unstretched film F0 obtained by the extrusion molding machine 30 to produce a longitudinal uniaxially stretched film F1. And an oblique stretching machine 60 for producing an obliquely stretched film F2 by obliquely stretching the longitudinal uniaxially stretched film F1.

  As shown in FIGS. 1 and 2, an extrusion molding machine 30 includes an extruder body 6 that melts a transparent thermoplastic resin introduced from a hopper 1, a die 8 that extrudes the molten thermoplastic resin into a film shape, For example, a metal cooling roll 9 that cools the film-like thermoplastic resin extruded from 8 and both ends in the width direction of the film-like thermoplastic resin are charged, and the film-like thermoplastic resin Edge pinning 10 for urging both ends in the width direction toward the cooling roll 9 is provided.

  For the extruder body 6, for example, a single screw extruder, a twin screw extruder, or a melt kneader can be used. When using these apparatuses, it is preferable to vacuum or nitrogen purge the melting zone in the cylinder constituting the hopper 1 and the extruder body 6. According to such a configuration, since the oxygen concentration can be lowered, it is possible to obtain a film having more colorless transparency and less deterioration. In this case, the oxygen partial pressure is preferably 5 kPa or less, more preferably 2 kPa or less, and particularly preferably 1 kPa or less.

  The die 8 can have a shape normally used for forming a film. As the die 8, for example, when forming a film, in addition to a coat hanger type and a straight manifold type, a fishtail type die can be suitably used for a film or sheet having a small width of about 50 to 500 mm. In the case of molding, a manifold die with a choke bar (T die) is common and preferred. When a T die is used, the thickness in the width direction of the obtained film can be adjusted by adjusting the choke bar and the die lip.

  The cooling roll 9 is formed in a cylindrical shape, and a flow path through which a heat (cooling) medium for cooling or heating the surface of the cooling roll is provided, and the film supplied from the die 8 The film-like thermoplastic resin is cooled to produce a pre-stretch film F0. The normal position of the cooling roll 9 is fixed, and the diameter of the cooling roll 9 is usually about 100 to 600 mm. Further, the width (length) of the cooling roll 9 is appropriately selected to be wider than the width of the target sheet. Such a cooling roll 9 may be composed of only one-stage roll, or may be composed of a combination of a plurality of stages of rolls.

  As shown in FIG. 2, the edge pinning 10 is disposed at both ends in the width direction of the film-like thermoplastic resin extruded from the die 8, and is near the vicinity of the point where the film-like thermoplastic resin contacts the cooling roll 9. (Die side). The edge pinning 10 is an edge pinning electrode connected to a high-voltage DC power supply (not shown), and is near the end in the width direction of the film-like thermoplastic resin at a point where the film-like thermoplastic resin is in contact with the cooling roll 9. An electric charge is applied to the two and both ends thereof are urged toward the cooling roll 9 side. Edge pinning 10 can change an installation position with respect to the width direction of a film-like thermoplastic resin. For this reason, the thickness of the width direction of the film F0 before extending | stretching can be adjusted by adjusting the installation position of the edge pinning 10 with respect to a film-like thermoplastic resin suitably.

  As shown in FIG. 1, the first stretching machine 20 is supplied from the first roll unit 40 via the first roll unit 40 that preheats the pre-stretched film F0 obtained by the extruder 30 and the free roll 2. The float-type heating device 3 for heating the pre-stretched film F0 and the pre-stretching film F0 supplied from the heating device 3 via the free roll 4 are removed from heat, and the peripheral speed difference from the first roll portion 40 , The second roll part 50 for producing the longitudinally uniaxially stretched film F1 by longitudinally uniaxially stretching the pre-stretched film F0 in the flow direction is provided in this order from the upstream side.

  The first roll unit 40 is configured by three rolls of a first roll 41 to a third roll 43. Although not shown, each of the rolls 41 to 43 includes a temperature control mechanism for adjusting the surface temperature and a drive mechanism for adjusting the peripheral speed of the roll. By these mechanisms, the peripheral speed and the surface of each roll are adjusted. The temperature can be appropriately controlled. The first roll unit 40 preheats the unstretched film F0 supplied from the cooling roll 9 with the three rolls 41 to 43, and guides the film F0 to the float heating device 3 via the free roll 2. .

  The roll surface temperature of the first roll 41 is usually 40 to 100 ° C., and the glass transition temperature of the transparent thermoplastic resin is Tg (° C.), Tg-100 (° C.) or more and Tg-40 (° C.) or less. preferable. The roll surface temperature of the 2nd roll 42 is 50-110 degreeC normally, and Tg-90 (degreeC) or more and Tg-30 (degreeC) or less are preferable. The roll surface temperature of the 3rd roll 43 is 60-120 degreeC normally, and Tg-80 (degreeC) or more and Tg-20 (degreeC) or less are preferable. By making the surface temperature of each of the rolls 41 to 43 satisfy the above conditions, a sufficient residual heat effect can be achieved and an excessive influence on film physical properties due to heat can be suppressed.

  In the present embodiment, the first roll portion is configured by three rolls, but is not limited thereto, and may be configured by one roll, or two or four or more rolls. You may comprise by. When the 1st roll part is comprised with a some roll like this embodiment, it is made for the temperature difference of a front and back roll to become 0-50 degreeC normally, Preferably it is less than 5-30 degreeC. By ensuring that the temperature difference between the first to third rolls satisfies the above conditions, the film can be preheated uniformly, so that it is possible to produce an effect that variations in thickness and retardation are less likely to occur during stretching described later.

  In the present invention, the pre-stretched film F <b> 0 sent to the rolls 41 to 43 and preheated is guided to the float heating device 3 via the free roll 2. The float type heating device 3 is a device that heats the film in a non-contact state by blowing hot air from both sides of the unstretched film F0. The heating device 3 is partitioned into a plurality of sections in the flow direction of the unstretched film F0, and independent temperature control is possible. The preferred range of the number of compartments is 3-5. By setting the number of compartments within the above range, the physical properties can be controlled more finely, and the scale of the facility can be appropriately set, so that space and cost can be suppressed.

  The second roll unit 50 is configured by three rolls of a first roll 51 to a third roll 53. The surface temperature of the 1st roll 51 is 80-130 degreeC normally, and when the glass transition temperature of a transparent thermoplastic resin is set to Tg (degreeC), Tg-60 (degreeC) or more and Tg-10 (degreeC) or less are preferable. . The surface temperature of the 2nd roll 52 is 70-120 degreeC normally, and Tg-60 (degreeC) or more and Tg-20 (degreeC) or less are preferable. The surface temperature of the 3rd roll 53 is 60-120 degreeC normally, and Tg-70 (degreeC) or more and Tg-20 (degreeC) or less are preferable. By making the surface temperature of each of the rolls 51 to 53 satisfy the above conditions, an excessive influence on film physical properties can be suppressed.

  In the present embodiment, the second roll portion is configured by three rolls, but is not limited thereto, and may be configured by one roll, or may be configured by two or four or more rolls. May be. When the second roll part is constituted by a plurality of rolls as in the present embodiment, the temperature difference between the front and rear rolls is 0 to 50 ° C., preferably 0 to 30 ° C. By making the temperature of the 1st-3rd roll satisfy | fill the said conditions, since a film can be heat-removed uniformly, there exists an effect that it is hard to produce variation in thickness and phase difference at the time of extending | stretching mentioned later.

  A circumferential speed difference is provided between the first roll part 40 and the second roll part 50. Here, the circumferential speed difference refers to the circumferential speed difference between the third roll 43 that is the final roll of the first roll unit 40 and the first roll 51 that is the first roll of the second roll unit 50. Show. By providing such a peripheral speed difference, the unstretched film F0 can be uniaxially stretched in the flow direction (longitudinal direction).

FIG. 3 is a diagram schematically showing an oblique stretching machine.
As shown in FIG. 3, the oblique stretching machine 60 is a so-called tenter stretching machine, and includes a pair of gripping means including two gripping devices 101L and 101R that grip the end portions of the supplied longitudinally uniaxially stretched film F1. 110 and a temperature-controlled room 70 that adjusts the temperature of the longitudinally uniaxially stretched film F1 gripped by the pair of gripping means 110.

  The temperature-controlled room 70 is an area for maintaining the longitudinally uniaxially stretched film F1 gripped by the gripping means 110 at a temperature suitable for stretching. This area may be constituted by a single zone, for example, a preheating zone, stretching It can be divided into three zones, a zone and a heat setting zone, so that the temperature of each zone can be adjusted independently.

  Each gripping device 101L, 101R includes clips 110L, 110R as a plurality of grips for gripping the end of the longitudinal uniaxially stretched film F1, and endless chains 120L, 120R in which the clips 110L, 110R are installed at predetermined intervals (partly (Not shown), a pair of sprockets 12L, 13L, 12R, and 13R over which endless chains 120L and 120R are spanned, a drive mechanism (not shown) that rotates the sprockets 12L and 12R, and a sprocket 12L that is rotated by the drive mechanism. , 12R is provided with a rail (not shown) that guides the direction of the clips 110L and 110R that move with rotation. In the present embodiment, the rotation speed of the sprocket 12L and the rotation speed of the sprocket 12R are adjusted to be the same. For this reason, the moving speeds of the clips 110L and 110R are the same. The gripping device 101L and the gripping device 101R have substantially the same constituent elements, but differ in the arrangement direction and length of the rail.

  In the rail, the direction in which the longitudinally uniaxially stretched film F1 is supplied and the direction in which the obliquely stretched film F2 after oblique stretching is wound are different, that is, the rails proceed in the directions of arrows D1, D2, and D3. Specifically, as shown in FIG. 3, when the film is observed from upstream to downstream in the flow direction of the film, the film is arranged so that the traveling direction of the film bends to the left in the middle. . The rail on the gripping device 101L side and the rail on the gripping device 101R side are arranged in parallel at a constant interval (first parallel portion) on the inlet side to which the film is supplied, and in the middle bent portion The gaps are arranged so as to gradually widen (curved portions), and on the film exit side, the gaps are arranged in parallel at intervals larger than the intervals between the parallel portions (second parallel portions). In this embodiment, the film is arranged so that the traveling direction of the film bends to the left, but may be arranged to bend to the right.

  Since the rails are arranged as described above, the rail length on the gripping device 101R side that is the outside of the bent portion is longer than the rail length on the gripping device 101L side that is on the inside of the bent portion. For this reason, in the first parallel portion, the pair of clips that simultaneously grips both ends in the width direction of the longitudinally uniaxially stretched film F1 shifts in relative position according to the rail length when passing through the bent portion, In the second parallel portion, the clip on the gripping device 101L side moves ahead of the clip on the gripping device 101R side. For this reason, after the pair of clips pass through the bent portion of the rail, the longitudinally uniaxially stretched film F1 is stretched in an oblique direction that is neither the width direction nor the longitudinal direction, and the molecular orientation direction is an oblique direction. A stretched film F2 can be produced.

  When a film is supplied to such an oblique stretching machine 60, the longitudinal uniaxially stretched film F1 is continuously supplied from the upstream (upper left side in FIG. 3) to the oblique stretching machine 60 along the direction of the arrow D1. The supplied longitudinally uniaxially stretched film F1 is gripped by a pair of clips 110L and 110R at both ends in the width direction before entering the temperature-controlled room 70. Next, the longitudinally uniaxially stretched film F1 gripped by the clips 110L and 110R enters the temperature-controlled room 70, and in the temperature-controlled room 70, in a slanting direction by a circular movement along the rail on each side of each clip 110L and 110R. Stretched. The obliquely stretched film F2 stretched in the oblique direction is released from the temperature-controlled room 70 and then released by the clips 110L and 110R, and is carried out in the direction of the arrow D3.

  More specifically, when the both ends of the film F1 in the width direction at the time of the dotted line CS1 are simultaneously gripped, and the clips 110L and 110R at the opposite positions in the width direction move and reach the position indicated by the dotted line CS2, Is stretched in the direction of the dotted line CS2. When the clips 110L and 110R further move and reach the position indicated by the dotted line CS3, the stretch ratio is further increased, and an obliquely stretched film F2 having optical anisotropy in which molecules are oriented in the direction of the dotted line CS3 is obtained.

Next, the manufacturing method of the diagonally stretched film which concerns on this invention is demonstrated.
<Film before stretching F0>
First, the thermoplastic resin charged into the hopper 1 is melted by the extruder main body 6, and then the molten thermoplastic resin is extruded from the die 8 into a film shape and cast onto the cooling roll 9. And cooled to produce a pre-stretching film F0 (pre-stretching film manufacturing process). The obtained unstretched film F0 is adjusted so that the thickness in the width direction has a predetermined relationship.

Specifically, the thickness of the unstretched film F0 supplied to the stretching machine 20 is adjusted by controlling the extrusion flow rate of the molten resin, the lip opening of the die 8, the speed of the cooling roll 9, and the like. In particular, the thickness of the end portion of the film F0 before stretching is adjusted by changing the grounding position of the edge pinning 10 in the width direction of the film F0 before stretching, or the lip opening of the die 8 is appropriately changed. Adjust them by combining them. By using the above means, the thickness in the width direction of the unstretched film F0 supplied to the stretching machine 20 is adjusted so as to satisfy the following relational expressions (1) and (2). The unstretched film F0 has a thickness T1 (μm) at one end in the width direction, a thickness T2 (μm) at the other end, and a thickness TC (μm) at the center between these ends. The relational expressions (1) and (2) are satisfied.
(1) 1.00 × T1 <TC <1.03 × T1
(2) 1.00 × T2 <TC <1.03 × T2

  When the thickness of the pre-stretched film F0 satisfies the above relational expressions (1) and (2), the obliquely stretched film finally obtained has an advantage that variations in thickness and optical properties can be further reduced.

  When the thickness of the pre-stretch film F0 is adjusted by the lip opening, for example, when it is desired to increase the thickness, it can be performed by increasing the opening of the lip at the corresponding location, and it is desired to reduce the thickness. In some cases, this can be done by reducing the opening of the lip at the relevant location. That is, for example, in order to make the end in the width direction of the unstretched film F0 thinner than the center, it can be realized by making the opening on the end of the lip smaller than the center of the lip. In addition, when adjusting the thickness by edge pinning, if the edge pinning is installed, the thickness of the installation location is reduced. For this reason, for example, in order to make the edge part of the film F0 before extending | stretching the width direction thin, it can implement | achieve by installing pinning in the edge part side of the film F0 before extending | stretching.

  Here, the thickness of the end portion of the film F0 before stretching is the average thickness 20 mm inside from the end in the width direction of the film, and the thickness of the center portion is the average of the central portion 20 mm with respect to the entire width of the film F0 before stretching. Value. The average thickness of the unstretched film F0 is 50 μm to 180 μm. Moreover, the width dimension of the film F0 before extending | stretching is although it does not specifically limit, It is 450-2000 mm.

  In the present invention, the average thickness of the film can be measured at a predetermined interval along the width direction of the film using a commercially available film thickness meter, and can be an average value of these values. The film thickness unevenness can be obtained as a difference between the maximum value and the minimum value.

The unstretched film F0 is a long film made of a transparent thermoplastic resin.
Here, the long shape refers to one having a length of at least about 5 times the width of the film, preferably 10 times or more, and specifically in a roll shape. It can be set as a thing (film roll) which has the length of the grade wound and stored or conveyed.

  Further, the transparent thermoplastic resin is a resin having a thickness of 1 mm and a total light transmittance of 80% or more. Examples of such transparent thermoplastic resins include polycarbonate, polyester, polyethersulfone, polyarylate, polyimide, alicyclic polyolefin, and the like. Of these transparent thermoplastic resins, alicyclic polyolefins are preferred. The alicyclic polyolefin is an amorphous resin having an alicyclic structure in the main chain and / or side chain. Examples of the alicyclic structure in the alicyclic polyolefin include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene) structure. From the viewpoint of mechanical strength, heat resistance, etc. A cycloalkane structure is preferred. 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, when the mechanical strength, heat resistance, In addition, the moldability characteristics of the film are highly balanced and suitable. The ratio of the repeating unit having an alicyclic structure constituting the alicyclic polyolefin is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. It is preferable from a viewpoint of transparency and heat resistance that the ratio of the repeating unit which has an alicyclic structure in alicyclic polyolefin exists in this range.

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

The transparent thermoplastic resin preferably has an absolute value of photoelastic coefficient of 10 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 7 × 10 ⁻¹² Pa ⁻¹ or less, and 4 × 10 ⁻ More preferably, it is ¹² Pa ⁻¹ or less. The photoelastic coefficient C is obtained by dividing the birefringence Δn by the stress σ. That is, it is a value represented by C = Δn / σ. When the photoelastic coefficient of the thermoplastic resin exceeds 10 × 10 ⁻¹² Pa ⁻¹ , when a stretched film obtained by stretching the pre-stretched film is produced, the variation in retardation in the in-plane direction may increase.

  The transparent thermoplastic resin includes colorants such as pigments and dyes, fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, ultraviolet absorbers, antistatic agents, antioxidants, lubricants, and solvents. The compounding agent may be appropriately blended. Although the compounding quantity of the said compounding agent is not restrict | limited in particular, For example, it is 0 to 5 weight% in a thermoplastic resin.

  In addition, in the said embodiment, although the film before extending | stretching was produced by the melt extrusion method, you may produce not only this but by the solution casting method. However, the melt extrusion method is preferred from the viewpoint of reducing volatile components in the sheet.

<Vertical uniaxially stretched film F1>
Next, the pre-stretching film F whose thickness is adjusted to satisfy the above relational expressions (1) and (2) is supplied to the stretching machine 20 and subjected to longitudinal uniaxial stretching treatment (longitudinal uniaxial stretching step). In the stretching machine 20, the pre-stretching film F is preheated by the first roll unit 40 and then heated to a predetermined temperature by the heating device 3, and the peripheral speed between the first roll unit 40 and the second roll unit 50. Due to the difference, the film is uniaxially stretched in the longitudinal direction to produce a longitudinally uniaxially stretched film. Here, in the stretching machine 20, the stretch ratio of the film before stretching is preferably 1.1 to 2.5 times. The draw ratio can be adjusted by the difference in peripheral speed between the first roll part 40 and the second roll part 50.

The longitudinally uniaxially stretched film F1 has a thickness TX1 (μm) at one end in the width direction, a thickness at the other end TX2 (μm), and a thickness at the center between these ends as TXC (μm). The following relational expressions (3) and (4) are satisfied. When the thickness of the longitudinally uniaxially stretched film F1 satisfies the following relational expressions (3) and (4), there is an advantage that variation in thickness and optical characteristics can be further reduced in the finally obtained obliquely stretched film.
(3) 1.00 × TX1 <TXC <1.03 × TX1
(4) 1.00 × TX2 <TXC <1.03 × TX2

  The thickness of the end of the longitudinally uniaxially stretched film F1 is the average thickness 20 mm inside from the end in the width direction of the film, and the thickness of the center is the average value of the central portion 20 mm with respect to the entire width of the film F0 before stretching. To do. The average thickness of the longitudinally uniaxially stretched film F1 is 40 to 150 μm.

<Diagonally stretched film F2>
The longitudinally uniaxially stretched film F1 is subjected to heat removal by the second roll unit 50, and then supplied to the oblique stretching machine 60 and stretched in an oblique direction that is neither the longitudinal direction nor the width direction of the film (oblique stretching step). As described above, the longitudinally uniaxially stretched film F1 is continuously supplied from the upstream (upper left side in FIG. 3) to the oblique stretching machine 60 along the direction of the arrow D1, and within the temperature-controlled room 70, each clip 110L, 110R. The obliquely stretched film F2 is manufactured by being stretched in an oblique direction by circular movement along the rails on each side of the film. The obliquely stretched film F2 is released from the temperature-controlled room 70 and released by the clip, and is carried out in the direction of the arrow D3. The obliquely stretched film carried out is wound into a roll after cutting the end in the width direction as necessary.

  The obliquely stretched film has a residual volatile component content of preferably 0.1% by weight or less, more preferably 0.05% by weight or less, and still more preferably 0.02% by weight or less. If the content of residual volatile components is large, the optical characteristics may change over 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.

  By setting the content of the volatile component within the above range, the dimensional stability is improved, and in-plane direction retardation Re (= (nx−ny) × d) and thickness direction retardation Rth (= ((nx + ny) / 2-nz) × d can be reduced with time, and in the polarizing plate and display device using the obliquely stretched film, the display image can be maintained in a good state for a long time. In the direction retardation Re and the Rth, nx is the refractive index in the in-plane slow axis direction, ny is the refractive index in the direction perpendicular to the slow axis in the plane, and nz is the refractive index in the thickness direction. Yes, d is the average thickness of the film.

  The obliquely stretched film F2 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 within the above range, the change with time of Re and Rth can be reduced. The saturated water absorption is a value expressed as a percentage of the increased mass of the film specimen immersed in water at 23 ° C. for 24 hours with respect to the mass of the film specimen before immersion.

  The obliquely stretched film is a direction in which the molecular orientation direction (orientation angle) intersects the width direction of the film, that is, in the range of more than 0 ° and less than 90 °, but can be arbitrarily set to a desired angle, Preferably it is 40-50 degrees, and is 45 degrees as a specific example. Further, the variation in the orientation angle is within ± 0.4 °, preferably within ± 0.3 °. For the orientation angle, for example, using a commercially available polarizing microscope, the angle of the slow axis with respect to the width direction of the film is measured at an interval of 50 to 100 mm along the width direction of the film. The angle can be determined. Further, the variation in the orientation angle can be obtained as a difference between each of the maximum value and the minimum value of the measured values and the average value.

  The in-plane retardation (Re) of the obliquely stretched film is about 50 to 300 nm, and the variation is preferably within 3.5 nm, and more preferably within 3.0 nm. When the variation in Re is in the above preferred range, there is an advantage that the display quality can be kept good when the obliquely stretched film is used in a display device or the like.

  The average thickness of the obliquely stretched film is preferably 20 to 80 μm from the viewpoint of mechanical strength and the like. As described above, the average thickness of the obliquely stretched film can be measured at a predetermined interval along the width direction of the film using a commercially available film thickness meter, and can be an average value of these values. Further, the variation in the thickness in the width direction of the obliquely stretched film can be expressed as the difference between the maximum value and the minimum value, and can affect the availability of winding, and is preferably 2 μm or less, preferably 1 μm or less. More preferably.

  The obliquely stretched film can be easily obtained by the above-described manufacturing method, and it can be used alone or in combination with other members as an optical film such as a retardation film or a viewing angle compensation film. The present invention can be widely applied to display devices, plasma display devices, FED (field emission) display devices, SED (surface electric field) display devices, and the like.

  The polarizing plate of the present invention is formed by laminating the obliquely stretched film according to the present invention and a long polarizer with their longitudinal directions aligned, that is, by a roll-to-roll method. For polarizers, films made of appropriate vinyl alcohol polymers such as polypinyl alcohol and partially formalized polyvinyl alcohol, dyeing treatment with dichroic substances such as iodine and dichroic dyes, stretching Appropriate treatments such as treatment and cross-linking treatment can be performed in an appropriate order and manner, and appropriate materials that transmit linearly polarized light when natural light is incident can be used. In particular, those excellent in light transmittance and degree of polarization are preferable. The thickness of the polarizer is generally 5 to 80 μm, but is not limited thereto.

  As a lamination | stacking form, the diagonally stretched film of this invention may be laminated | stacked on both surfaces of a polarizer, and may be laminated | stacked on one side. In addition, the number of laminated layers of obliquely stretched films is not particularly limited, and may be one or plural. Moreover, although these laminated bodies are not essential structures, they can be laminated | stacked through an adhesive agent or an adhesive, for example. Conventionally, a protective film is laminated on one side or both sides of a polarizer. For example, instead of a conventional protective film, the diagonally stretched film protects the polarizer by laminating the diagonally stretched film of the present invention. Can also be used as a film. When an obliquely stretched film is used instead of the protective film, one conventional protective film can be omitted, which can contribute to the thinning of the liquid crystal display device. Here, when laminating the polarizer and the obliquely stretched film, they are laminated so that the polarization transmission axis of the polarizer and the slow axis of the obliquely stretched film are at a predetermined angle.

  In the polarizing plate of the present invention, another member may be interposed between the stretched film and the polarizer as long as the characteristics of the present invention are not impaired. As another member to interpose, a protective film for protecting a polarizer is mentioned, for example. An appropriate transparent film can be used as the protective film. Among these, a film made of a resin excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, and the like is preferable. Examples of resins forming the protective film include acetate resins such as triacetyl cellulose; alicyclic polyolefins; polyesters such as chain polyolefins, polycarbonates, and polyethylene terephthalates; polyvinyl chloride, polystyrene, polyacrylonitrile, polysulfone, polyethersulfone, Polyamide, polyimide, acrylic resin and the like can be mentioned.

The liquid crystal display device of the present invention comprises the polarizing plate.
The display mode of the liquid crystal cell included in the liquid crystal display device is not particularly limited. For example, in-plane switching (IPS) mode, vertical alignment (VA) mode, multi-domain vertical alignment (MVA) mode, continuous spin wheel alignment ( CPA) mode, hybrid alignment nematic (HAN) mode, twisted nematic (TN) mode, super twisted nematic (STN) mode, and optically compensated bend (OCB) mode.

  The liquid crystal display device of the present invention may include other members. For example, appropriate components such as a prism array sheet, a lens array sheet, a light diffusing plate, a backlight, and a brightness enhancement film can be arranged in one or more layers at appropriate positions. Examples of the backlight include a cold cathode tube, a mercury flat lamp, a light emitting diode (LED), an organic EL, and an inorganic EL.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited only to the following Examples.

<Example 1>
The diagonally stretched film was manufactured using the film manufacturing apparatus 100 as shown in FIGS. A norbornene resin pellet (manufactured by Nippon Zeon Co., Ltd., ZEONOR 1420, Tg = 136 ° C.) as a transparent thermoplastic resin is dried at 100 ° C. for 5 hours, supplied to the hopper 1 of the extrusion molding machine 30, and a polymer pipe (not shown) And through a polymer filter, the sheet 8 is extruded on a cooling roll 9 from a die 8 whose lip opening is appropriately adjusted, cooled by the cooling roll 9, and a long unstretched film F0 having an average thickness of 100 μm is obtained. Obtained (film production process before stretching). The unstretched film F0 had a thickness T1 at one end of 99.5 μm, a thickness T2 at the other end of 99.5 μm, and a thickness TC at the intermediate position of 100.3 μm. Therefore, TC = 1.008 × T1 = 1.008 × T2, and both the following mathematical formulas (1) and (2) were satisfied.
(1) 1.00 × T1 <TC <1.03 × T1
(2) 1.00 × T2 <TC <1.03 × T2

Next, the unstretched film F0 was continuously supplied to the longitudinal uniaxial stretching machine 20. The surface temperature of each roll constituting the longitudinal uniaxial stretching machine 20 is 60 ° C. for the first roll 41 constituting the first roll section 40, 70 ° C. for the second roll 42, 80 ° C. for the third roll 43, and The 1st roll 51 which comprises the 2 roll part 50 was 100 degreeC, the 2nd roll 52 was 100 degreeC, and the 3rd roll 53 was 100 degreeC. The unstretched film F0 continuously supplied to the longitudinal uniaxial stretching machine 20 was subjected to longitudinal uniaxial stretching at a stretching temperature of 150 ° C. and a stretching ratio of 1.3 times to obtain a longitudinal uniaxially stretched film F1 having an average thickness of 87 μm (longitudinal). Uniaxial stretching process). The obtained longitudinally uniaxially stretched film F1 had a thickness TX1 of one end portion of 86.8 μm, a thickness TX2 of the other end portion of 86.7 μm, and a thickness TXC at an intermediate position of 87.7 μm. . For this reason, TXC = 1.010 × TX1 = 1.010 × TX2, and both the following mathematical formulas (3) and (4) were satisfied.
(3) 1.00 × TX1 <TXC <1.03 × TX1
(4) 1.00 × TX2 <TXC <1.03 × TX2

  Next, the longitudinally uniaxially stretched film F1 was continuously supplied to the oblique stretching machine 60, and oblique stretching was performed to obtain a film roll-shaped obliquely stretched film F2 (oblique stretching step). The obtained obliquely stretched film F2 was measured for thickness (average thickness and variation), orientation angle (average value and variation), Re (average value and variation), and the appearance of the film roll-like obliquely stretched film F2 was measured. evaluated. The results are shown in Table 1.

This example and comparative examples were evaluated as follows.
<Average thickness and variation in thickness>
Using an infrared thickness gauge (RX-100 manufactured by Kurabo Industries Co., Ltd.), traverse measurement was performed at a pitch of 5 mm in the width direction, and data at 100 points were obtained at intervals of 5 m in the flow direction for each position. The average value was calculated | required about the obtained data, and it was set as average thickness. In addition, the maximum value and the minimum value of the measured values were obtained, and the difference between the maximum value and the minimum value was determined as variation.
<Thickness of film edge and center>
Using an infrared thickness gauge (Kurabo Co., Ltd. RX-100), the average thickness at a position 20 mm inside from the end in the width direction of the film was taken as the thickness of the film end. Similarly, the average value of the central portion 20 mm with respect to the entire width of the film was taken as the thickness of the central portion of the film.
<Average orientation angle and its variation>
Using a polarizing microscope (Olympus BX51), the angle of the slow axis with respect to the width direction of the film is measured at intervals of 100 mm along the width direction of the film, and the orientation angle at each position is obtained based on this measurement value. It was. In addition, the maximum value-minimum value of the average value in the width direction was regarded as variation.
<Average value of in-plane direction retardation Re and its variation>
Re was measured at a wavelength of 590 nm at intervals of 5 cm along the width direction of the film using a phase difference meter (manufactured by Oji Scientific Co., Ltd., KOBRA21-ADH), and the average value of these values was taken as the average value of Re. Moreover, the maximum value and the minimum value of the measured values were obtained, and the difference between the maximum value and the minimum value was determined as variation.
<Appearance of film roll>
The appearance of the wound rolled film was judged according to the following criteria. Good: No abnormality was observed in the wound form of the wound roll. Bad: The roll wound due to the occurrence of tarmi and wrinkles. Things with a bad roll

As shown in Table 1, the obliquely stretched film F2 (1) obtained in Example 1 has an average thickness of 35.2 μm, a thickness variation of 0.6 μm, an orientation angle average value of 45 °, and an orientation angle variation. The average value of Re was 139.6 nm and the variation in Re was 2.1 nm . In addition, the obtained obliquely stretched film F2 (1) had a good appearance of the film roll.

  Next, the long polarizing plate (Sanlitz Co., Ltd., HLC2-5618S, thickness 180 μm) having the transmission axis in the width direction and the film of Example 1 are bonded together by a roll-to-roll method to obtain a wound body of the polarizing plate. Obtained. The polarizing plate cut out from the wound body is replaced with the upper and lower polarizing plates of a commercially available VA (vertical alignment) mode transflective liquid crystal display device, and the side on which the stretched film is bonded is arranged on the liquid crystal cell side. And the slow axis of the stretched film arrange | positioned up and down was integrated so that it might mutually orthogonally cross. When the display characteristics of the obtained liquid crystal display device were visually confirmed from the front, color unevenness was not observed over the entire width, and the display was good.

<Example 2>
An obliquely stretched film F2 (2) and a liquid crystal display device were produced in the same manner as in Example 1 except that the lip opening was adjusted and the thickness of the film end and center of the unstretched film F0 was changed as follows. . The unstretched film F0 had a thickness T1 at one end of 99.8 μm, a thickness T2 at the other end of 99.8 μm, and a thickness TC at an intermediate position of 100.1 μm. For this reason, TC = 1.003 × T1 = 1.003 × T2, and both of the formulas (1) and (2) were satisfied. The obliquely stretched film F2 obtained in Example 2 has an average thickness of 35.8 μm, a thickness variation of 0.9 μm, an average orientation angle of 45 °, an orientation angle variation of 0.3 °, and an average value of Re. Was 139.8 nm , and the variation in Re was 2.3 nm . In addition, the obtained obliquely stretched film F2 (2) had an excellent appearance of the film roll. Moreover, when the display characteristics of the obtained liquid crystal display device were confirmed from the front by visual observation, the display was good and uniform.

<Comparative Example 1>
A diagonally stretched film F2 (3) was produced in the same manner as in Example 1 except that the lip opening was adjusted and the thickness of the film end and center of the unstretched film F0 was changed as follows. In the film F0 before stretching, the thickness T1 at one end was 100.1 μm, the thickness T2 at the other end was 99.9 μm, and the thickness TC at the intermediate position was 100.0 μm. For this reason, TC = 1.000 × T1 = 0.999 × T2, and neither of the mathematical formulas (1) and (2) was satisfied. The obliquely stretched film F2 (3) obtained in Comparative Example 1 has an average thickness of 36.2 μm, a thickness variation of 1.4 μm, an orientation angle average value of 45 °, and an orientation angle variation of 0.5 °. The average value of Re was 140.4 nm and the variation of Re was 3.6 nm . Moreover, as for the obtained diagonally stretched film F2 (3), the external appearance of the film roll was unsatisfactory.

  As shown in Table 1, in Examples 1 and 2, when the thickness of the end portion and the thickness of the central portion satisfy the relations (1) and (2), each variation in average thickness, orientation angle, and Re is a predetermined value. It was found that the following can be suppressed. Moreover, it turned out that it is excellent in the display performance in a liquid crystal display device provided with the polarizing plate which has the said diagonally stretched film by using such a diagonally stretched film. On the other hand, in Comparative Example 1, since the thickness of the end portion and the thickness of the central portion do not satisfy the relations (1) and (2), at least one of variations in average thickness, orientation angle, and Re is a predetermined value. Therefore, it was found that variations in thickness or optical characteristics are not always sufficient.

It is a figure which shows typically the film manufacturing apparatus used for this invention. It is a figure which shows typically the extrusion molding machine which comprises the said film manufacturing apparatus. It is a figure which shows typically the diagonal stretcher which comprises the said film manufacturing apparatus.

DESCRIPTION OF SYMBOLS 1 Hopper 2, 4 Free roll 3 Heating apparatus 6 Extruder main body 8 Die 9 Cooling roll 10 Edge pinning 12L, 12R, 13L, 13R Sprocket 20 Vertical uniaxial stretching machine 30 Extruder 40 First roll part 41, 51 First roll 42, 52 Second roll 43, 53 Third roll 50 Second roll section 60 Diagonal stretcher 70 Temperature-controlled room 100 Film manufacturing apparatus 101L, 101R Gripping apparatus 110 A pair of gripping means 110L, 110R Clips 120L, 120R Endless chains CS1, CS2 , CS3 dotted line
D1, D2, D3 Arrow F0 Pre-stretch film F1 Longitudinal uniaxial stretch film F2 Diagonal stretch film

Claims (5)

A method for producing a long diagonally stretched film in which the orientation direction of molecules intersects the width direction of the film,
A longitudinal uniaxial stretching step of obtaining a long longitudinal uniaxially stretched film F1 by longitudinally uniaxially stretching a long stretched film F0 made of a transparent thermoplastic resin in the longitudinal direction;
Using a stretching machine having a pair of grips for gripping both ends in the width direction of the longitudinally uniaxially stretched film F1, the film is stretched in an oblique direction that is neither the longitudinal direction nor the width direction of the film to obtain an obliquely stretched film F2. An oblique stretching step,
The film F0 before stretching has a thickness T1 at one end in the width direction of the film F0, a thickness T2 at the other end, and a thickness TC at an intermediate position between the one end and the other end. As for the manufacturing method of the diagonally stretched film which satisfy | fills following relationship (1), (2).
(1) 1.00 × T1 <TC <1.03 × T1
(2) 1.00 × T2 <TC <1.03 × T2 In the manufacturing method of the diagonally stretched film of Claim 1,
A method for producing a stretched film, further comprising a pre-stretch film production step of producing the pre-stretch film F0 made of the transparent thermoplastic resin by a melt extrusion method.   The diagonally stretched film manufactured by the manufacturing method of the diagonally stretched film of Claim 1 or 2.   The polarizing plate formed by laminating | stacking the diagonally stretched film described in Claim 3, and a elongate polarizer, aligning the longitudinal direction.   A liquid crystal display device comprising the polarizing plate according to claim 4 and a liquid crystal cell.

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