JP2008114369A - Manufacturing method of stretched film and use of stretched film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase difference film excellent in optical characteristics in its width direction, especially excellent in retardation and the precision of an angle of orientation using a simultaneous biaxial stretching method. <P>SOLUTION: A thermoplastic resin film is grasped at both side edges in its lateral direction using a large number of grasping elements, moved in its longitudinal direction, and simultaneously stretched in its longitudinal and lateral directions by widening the interval between the lateral direction of the resin film and the interval between the grasping elements in the longitudinal direction of the resin film accompanied by the movement of the resin film in its longitudinal direction to obtain the stretched film. In this manufacturing method of the stretched film, the thermoplastic resin film satisfies that width is 1,000 mm or above (1), the retardation Re in an in-plane direction is 20 nm or below (2), the standard deviation in the in-plane direction is 0.60 μm or below (3), θc+10° is θc+10°<θe (4) and θc is θc<10° (5). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a stretched film suitable for a retardation film used for a liquid crystal display device and the like, particularly a retardation film used for improving a viewing angle and a contrast, and in detail, a retardation and an orientation angle are in the width direction. The present invention relates to a method for producing a uniform wide simultaneous biaxially stretched film.

  In recent years, with the increase in size of liquid crystal display devices, the size of related members has been increasing. A long and wide retardation film, which is a member for improving the display quality of a liquid crystal display device, is also demanded. Until now, various methods for manufacturing the retardation film have been proposed. Among them, a method of manufacturing a resin film by orientation by stretching is one of the simplest methods.

Particularly recently, biaxially stretched films have become the mainstream of retardation films. Examples of a method for obtaining a biaxially stretched film include a sequential biaxial stretching method in which longitudinal stretching is performed and then transverse stretching, and a simultaneous biaxial stretching method in which longitudinal stretching and lateral stretching are simultaneously performed.
Among them, the simultaneous biaxial stretching method has an advantage that it is easy to obtain a large orientation because there is no process in which the relaxation of the orientation can be shortened as compared with the sequential biaxial stretching method. However, the simultaneous biaxial stretching method has a more complicated mechanism than the sequential biaxial stretching method, is difficult to control, and the stretching is not uniform in the plane. In fields where control of physical properties is required, it is difficult to apply, and various studies have been conducted.
For example, Patent Document 1 attempts to equalize physical properties by providing a lateral relaxation step after simultaneous biaxial stretching. However, the relaxation in the transverse direction is difficult to control, such as the deterioration of the flatness of the film, and is not sufficiently satisfactory as a means for achieving stretching uniformity in simultaneous biaxial stretching.

JP 2002-196134 A

  In view of the above circumstances, an object of the present invention is to provide a retardation film excellent in accuracy in optical characteristics in the width direction, particularly retardation and orientation angle, using a simultaneous biaxial stretching method.

According to the study of the present inventors, it has been found that the unstretched film for obtaining the stretched film described in the above-mentioned patent document has a large thickness standard, a small orientation angle distribution, and / or a large retardation. Thereby, it was found that it is difficult to achieve stretching uniformity by simultaneous biaxial stretching.
As a result of further intensive studies, the present inventors have found that a uniform biaxially stretched film can be obtained by simultaneously biaxially stretching a thermoplastic resin film having a specific retardation, thickness standard deviation, and orientation angle distribution. The headline has led to the present invention.

Thus, according to the present invention, the following is provided:
(1) The thermoplastic resin film is gripped on both side edges in the width direction using a plurality of gripping tools and moved in the longitudinal direction, and the spacing between the gripping tools in the width direction of the resin film and the length of the resin film In the method for producing a stretched film by simultaneously stretching the resin film in the longitudinal direction and the width direction by widening the distance between the gripping tools in the direction as the film moves in the longitudinal direction, the thermoplastic resin film comprises: The manufacturing method of the stretched film characterized by satisfy | filling the following [1]-[5].
[1] The width is 1000 mm or more.
[2] In-plane retardation Re is 20 nm or less.
[3] The standard deviation of thickness is 0.60 μm or less.
[4] θc + 10 ° <θe
[5] θc <10 °
In the above formulas [4] and [5], θc represents the absolute value of the orientation angle of the center portion with respect to the width direction of the film, and θe represents the absolute value of the orientation angle of the edge portion with respect to the width direction of the film.
(2) The stretched film according to (1), wherein the area of the portion of the gripping tool that contacts the film is 75 to 1,000 mm ² , and the initial interval between the gripping tools is 50 mm or less. Manufacturing method.
(3) The method for producing a stretched film according to (1) or (2), wherein the shape of the portion of the gripping tool that contacts the film is a circle, an ellipse, or an approximate ellipse, respectively.
(4) A stretched film obtained by the methods (1) to (3).
(5) A polarizing plate obtained by laminating the stretched film according to (4) on at least one surface of a polarizer.
(6) A liquid crystal display device comprising the polarizing plate according to (5).

  According to the production method of the present invention, a wide and long biaxially stretched film having uniform optical properties such as retardation in the width direction and orientation angle can be easily obtained by the simultaneous biaxial stretching method. Moreover, the biaxially stretched film obtained by the manufacturing method of this invention is suitable as retardation films, such as a liquid crystal display device. Specifically, other long optical elements used in a liquid crystal display device such as a polarizing plate can be superposed by a roll, a toe, and a roll.

  In the method for producing a stretched film of the present invention, the thermoplastic resin film is gripped on both side edges in the width direction using a plurality of grippers, and the thermoplastic resin film is moved in the longitudinal direction thereof. The resin film is stretched to obtain a stretched film by widening the gap in the width direction and the gap in the longitudinal direction of the resin film in association with movement in the film longitudinal direction. .

  The thermoplastic resin used in the present invention is not particularly limited as long as it is a transparent resin. Polycarbonate resin, polyether sulfone resin, polyethylene terephthalate resin, polyimide resin, polymethyl methacrylate resin, polysulfone resin, polyarylate resin, polyethylene resin, Examples include polyvinyl chloride resin, diacetyl cellulose, triacetyl cellulose, polystyrene resin, polyacrylic resin, and alicyclic olefin resin. Among these, a resin having a positive intrinsic birefringence value is preferable, and an alicyclic olefin resin is more preferable.

The alicyclic olefin resin suitably used in the present invention is an amorphous resin having an alicyclic structure in the main chain and / or side chain.
Examples of the alicyclic structure in the alicyclic olefin resin include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene) structure. From the viewpoint of mechanical strength, heat resistance, and the like. A saturated alicyclic hydrocarbon (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 olefin resin 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 an alicyclic olefin resin exists in this range.

  Specific examples of the alicyclic olefin resin include norbornene resin, monocyclic olefin resin, cyclic conjugated diene resin, vinyl alicyclic hydrocarbon resin, 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, or a hydride thereof; Examples thereof include addition polymers of monomers having a monomer, addition copolymers of monomers having a norbornene structure and other monomers, and hydrides thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly suitable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can be used.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene) and 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 . ^{17, 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. Moreover, 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. To obtain a film with a small saturated water absorption rate. It is preferable that the amount of polar groups is small, and it is more preferable not to have polar groups.

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; cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene; Derivatives thereof; and the like.
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.

Examples of other monomers that can be addition copolymerized with a monomer having a norbornene structure include α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, and 1-butene, and derivatives thereof; cyclobutene, cyclopentene, And cycloolefins such as cyclohexene and derivatives thereof; non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, and the like. 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.

  Hydrogenated product of ring-opening polymer of monomer having norbornene structure, hydrogenated product of ring-opening copolymer of monomer having norbornene structure and other monomer capable of ring-opening copolymerization, norbornene structure The hydride of an addition polymer of a monomer having a monomer, and the hydride of an addition copolymer of a monomer having a norbornene structure and another monomer capable of addition copolymerization with these ring-opening (copolymerization) ) A known hydrogenation catalyst containing a transition metal such as nickel or palladium is added to a polymer or addition (co) polymer solution, and brought into contact with hydrogen, so that the carbon-carbon unsaturated bond is preferably 90% or more. It can be obtained by hydrogenation.

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 with respect to the entire repeating unit of the norbornene-based resin, and the content ratio of X and the content ratio of Y It is preferable that the ratio is 100: 0 to 40:60 by weight ratio of X: Y. By using such a resin, it is possible to obtain an optical film that has no dimensional change in the long term and is excellent in stability of optical characteristics.

  The thermoplastic resin used in the present invention is not particularly limited by its molecular weight. The molecular weight of the thermoplastic resin is a weight average molecular weight (Mw) of polyisoprene (in terms of polystyrene when the solvent is toluene) measured by gel permeation chromatography using cyclohexane (toluene if the resin is not dissolved) as a solvent. ) Is usually 10,000 to 100,000, preferably 15,000 to 80,000, more preferably 20,000 to 50,000. When the weight average molecular weight is in such a range, the mechanical strength and formability of the film are highly balanced, which is preferable.

  Although the glass transition temperature of the thermoplastic resin used for this invention should just be selected suitably according to a use purpose, Preferably it is 80 degreeC or more, More preferably, it is the range of 100-250 degreeC.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the thermoplastic resin used in the present invention is not particularly limited, but is usually 1.0 to 10.0, preferably 1.1 to 4.0, More preferably, it is the range of 1.2-3.5.

The thermoplastic resin used in the present invention 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. It is particularly preferably ⁻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. If the photoelastic coefficient of the alicyclic olefin resin exceeds 10 × 10 ⁻¹² Pa ⁻¹ , the variation in the in-plane retardation of the stretched film may increase.

  The thermoplastic resin used in the present invention includes colorants such as pigments and dyes, optical brighteners, dispersants, heat stabilizers, light stabilizers, ultraviolet absorbers, antistatic agents, antioxidants, lubricants, solvents, and the like. The compounding agent may be appropriately blended. The compounding amount of the compounding agent is not particularly limited, and is 0 to 5% by weight in the thermoplastic resin.

The thermoplastic resin film used in the present invention must satisfy the following [1] to [5].
[1] The width is 1000 mm or more.
[2] In-plane retardation Re is 20 nm or less.
[3] The standard deviation of thickness is 0.60 μm or less.
[4] θc + 10 ° <θe
[5] θc <10 °
In the above formulas [4] and [5], θc represents the absolute value of the orientation angle of the center portion with respect to the width direction of the film, and θe represents the absolute value of the orientation angle of the edge portion with respect to the width direction of the film.

In the above [1], the width of the thermoplastic resin film is 1000 mm or more, preferably 1200 mm or more.

In the above [2], the retardation Re in the in-plane direction of the thermoplastic resin film is 20 nm or less, preferably 15 nm or less. When the retardation Re exceeds 20 nm, the retardation of the stretched film increases in the width direction.
Incidentally, the retardation Re in the in-plane direction is multiplied by the mean thickness d 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 it is a value _{(Re = (n x -n y} ) × d). Further, the in-plane retardation Re is measured using a commercially available phase difference measuring device at a light incident angle of 0 ° (incident light beam and film surface perpendicular to each other) at an interval of 50 mm in the width direction. The value is defined as in-plane direction retardation Re. The retardation Re in the in-plane direction of the stretched film described later can also be measured by the same measurement method.

  In the above [3], the standard deviation of the thickness of the thermoplastic resin film is 0.60 μm or less, preferably 0.50 μm or less. When the standard deviation of the thickness of the thermoplastic resin film exceeds the above range, variations in the retardation and orientation angle of the stretched film increase. The standard deviation of the thickness can be obtained by measuring the thickness using a commercially available thickness gauge such as an infrared transmission thickness gauge and calculating the standard deviation.

In the above [4], θc + 10 ° <θe, preferably θc + 15 ° <θe.
In [5] above, θc <10 °, preferably θc <8 °. When the above [4] and [5] are out of the above ranges, the variation in retardation (in-plane direction and thickness direction) and orientation angle in the width direction of the stretched film increases.
The θc represents the orientation angle of the central portion with respect to the width direction of the film, and θe represents the orientation angle of the edge portion with respect to the width direction of the film. The edge orientation angle θe is the orientation angle of the film at a location 100 mm from the edge of the film. The orientation angle is measured using a commercially available polarizing microscope.

  The thermoplastic resin film used in the present invention can be obtained by a known method, for example, 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.

  In the present invention, the retardation Re and the orientation angles θc and θe in the in-plane direction of the thermoplastic resin film used are the draft ratio of casting in melt extrusion, the electrode shape and applied voltage of electrostatic pinning, the position, the surface temperature of the casting drum, etc. It is possible by adjusting

  For example, if the drafting ratio of casting is excessively large, the thermoplastic resin film tends to be oriented in the flow direction, making it difficult to satisfy the requirements of the present invention. Although this phenomenon can be mitigated by strengthening pinning or adjusting the cooling temperature, the range of the casting draft ratio is preferably between 6: 1 and 3: 1.

  The electrostatic pinning technique can be performed within a known range. As the shape of the electrode, a wire type, a needle type or the like can be used, and the applied voltage may be appropriately selected within the range of 3 to 20 kV, preferably 5 to 15 kV. Excessive voltage application is not preferable because it causes deterioration of the film thickness.

  The surface temperature of the casting drum is controlled by a known method, and the surface temperature Ts is appropriately set in the range of Tg-100 ° C. <Ts <Tg with respect to the glass transition temperature Tg (° C.) of the thermoplastic resin by water cooling or oil cooling. Select to cool. When the surface temperature exceeds Tg (° C.), the film surface shape is deteriorated due to adhesion, which is not preferable.

  Moreover, the standard deviation of the thickness of a thermoplastic resin film can be achieved by a well-known method, for example, the method as described in Unexamined-Japanese-Patent No. 2004-233604 and Unexamined-Japanese-Patent No. 2003-236915 can be mentioned.

The thermoplastic film used in the present invention 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. By setting the content of the volatile component in the above range, the dimensional stability is improved, and in-plane direction retardation (Re) and thickness direction retardation Rth (= ((n _x + _ny ) / 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 the average thickness of the film )), The deterioration of the polarizing plate and the liquid crystal display device using the stretched film obtained by the present invention can be suppressed, and the 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 a residual monomer and a solvent. The content of volatile components 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 thermoplastic resin film used in the present invention 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 change with time of Re and Rth can be reduced, and further, deterioration of the circularly polarizing plate and the liquid crystal display device of the present invention can be suppressed, and the display image can be kept in a good state for a long time. Can keep.
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 thermoplastic resin film used in the present invention has an average thickness of 80 to 200 μm, preferably 90 to 170 μm, particularly preferably 100 to 150 μm, from the viewpoint of preventing breakage due to the gripping tool during stretching.

  The thermoplastic resin film used in the present invention may be a single layer film or a multilayer film in which two or more layers are laminated. A specific example of the multilayer film is a multilayer film formed by laminating a layer of a thermoplastic resin having negative intrinsic birefringence and a layer of a thermoplastic resin having positive intrinsic birefringence.

  The thermoplastic resin film used in the present invention is preferably long. The long shape means one having a length of at least about 5 times or more with respect to the width direction of the film or laminate, preferably 10 times or more, and specifically in a roll shape. It has a length that is wound and stored or transported.

In the present invention, the thermoplastic resin film is gripped on both side edges in the width direction using a plurality of gripping tools and moved in the longitudinal direction thereof, and the distance between the gripping tools in the width direction of the resin film and the resin film The resin film is stretched simultaneously in the longitudinal direction and the width direction to obtain a stretched film by widening the gap between the gripping tools in the longitudinal direction as the film moves in the longitudinal direction.
Here, stretching at the same time in the longitudinal direction and the width direction means a state in which both longitudinal and transverse stretching are carried out in a time of 70% or more, preferably 80% or more of the time during which the long thermoplastic resin film is stretched. Means that. Either stretching in the longitudinal direction (hereinafter sometimes referred to as “longitudinal stretching”) or stretching in the width direction (hereinafter sometimes referred to as “lateral stretching”) may be started first, and which is first. You may end it.

  As the simultaneous biaxial stretching machine used for simultaneously stretching the film in the longitudinal direction and the width direction (simultaneous biaxial stretching), known simultaneous biaxial stretching machines such as a pantograph type tenter stretching machine and a linear motor type tenter stretching machine are available. Although it can be used, a pantograph type tenter stretching machine having a relatively simple structure is preferable.

How to stretch the thermoplastic resin film in the production method of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing an embodiment of a simultaneous biaxial stretching machine that can be used in the production method of the present invention.
The simultaneous biaxial stretching machine in FIG. 1 is called a pantograph type tenter stretching machine. In the simultaneous biaxial stretching machine of FIG. 1, a plurality of gripping tools 2 for gripping the end portion of the thermoplastic resin film 1 are provided on both side ends of the thermoplastic resin film 1, and a plurality of the like formed in a fold shape is provided. By providing an endless link device (part of the link and one endless link in the figure are omitted) 3 constituted by a long link device, and driving the endless link device 3 by an inlet-side sprocket 4 of the thermoplastic resin film 1 Guided by guide rails 5, 6, 7 and 8 arranged in a divergent shape in the advancing direction (from left to right in FIG. 1), the gap between the gripping tools 2 was gradually increased to grip the end. The thermoplastic resin film 1 is stretched simultaneously in two longitudinal and transverse directions to obtain a stretched film 10, and after stretching, the end of the stretched film 10 is removed from the gripping tool 2, and the endless link device 3 is driven by the outlet side sprocket 9. It is configured to return to the inlet side sprocket 4 Te.

The simultaneous biaxial stretching machine suitably used in the manufacturing method of the present invention is configured such that a member that supports each node of the pantograph between the left and right (upper and lower in FIG. 1) guide rails 5 and 6 and 7 and 8 is a guide. It is clamped so as to be movable in the longitudinal direction of the rail. One set of guide rails 5 and 6 and one set of guide rails 8 and 7 can be slid independently, and how to extend the gripping tool interval in the MD direction (film longitudinal direction) by the rail layout that can be made by this sliding, It is possible to adjust the way in which the gap between the gripping tools in the TD direction (film width direction) spreads.
That is, when the distance between the guide rail 6 and the guide rail 8 changes, the opening width of the pantograph changes, and the MD direction interval of the gripping tool attached to the tip of the pantograph can be adjusted. When the distance between the guide rail 6 and the guide rail 8 is increased, the pantograph of the link device 3 is closed, and the gripping tool interval in the MD direction is reduced. Conversely, when the distance between the guide rail 6 and the guide rail 8 is shortened, the pantograph of the link device 3 is opened, and the MD-direction gripping tool interval is increased. Since each guide rail can slide independently, the distance between the upper guide rail 6 and the guide rail 8 in the figure and the distance between the lower guide rail 6 and the guide rail 8 in the figure are independent. By adjusting, the way of spreading the upper MD direction gripping tool interval in FIG. 1 and the way of spreading the lower MD direction gripping tool spacing can be made the same or different.

On the other hand, the distance in the TD direction of the gripping means can be adjusted by the distance between the TD directions of the left and right guide rails 5. Since each guide rail can slide independently, the spread width (t1 in FIG. 1) of the upper guide rail 5 in the TD direction and the TD of the lower guide rail 5 in the figure.
The spreading width downward in the direction (t2 in FIG. 1) can be made the same or different.
The place where the change between the distance between the guide rail 6 and the guide rail 8 and the distance between the upper and lower guide rails 5 in the TD direction and the place where the change ends may be the same place or different places. If the change start place or the change end place is the same, stretching in the MD direction and the TD direction starts at the same time and ends at the same time. When the change start location or the change end location is different, the stretching start and stretching end times in the MD direction and the TD direction can be shifted.

Since the distance between the gripping means 2 is substantially determined by the arrangement of the guide rails, the speed at which the distance between the gripping means is spread and how to spread by changing the speed at which the link device 3 moves on the guide rail, that is, the moving speed in the film longitudinal direction. Etc. change as the film moves in the longitudinal direction.

  In the stretching machine through which the film passes, a preheating section (section A in FIG. 1) for heating to a temperature suitable for stretching the thermoplastic resin film 1 and a stretching section (FIG. 1) in which stretching is performed while the holding means interval is widened. 1) and a fixed section (C section in FIG. 1) for stabilizing the stretched state of the stretched film 10. The temperature in each section is not particularly limited, but is usually Tg ° C. to Tg + 30 ° C. in the A section, usually Tg ° C. to Tg + 30 ° C. in the B section, and usually in the C section with respect to the glass transition temperature Tg of the thermoplastic resin film. It is adjusted to Tg ° C. to Tg + 30 ° C. Each section is preferably maintained at a constant temperature, and specifically, it is preferably in an atmosphere having a temperature distribution in a range of ± 0.5 ° C. If stretching is performed in a region where the temperature is lower than Tg ° C., an excessive load is applied to the stretching apparatus, which is not preferable. Conversely, when stretching is performed in a region exceeding Tg + 30 ° C., the thickness unevenness of the stretched film and the accuracy of retardation Rth in the thickness direction may decrease. Moreover, in the said B section, in order to extend | stretch uniformly, a temperature difference is made in the width direction, and it sets and stretches so that the temperature of an edge part may become higher in the range of 0-10 degreeC than the temperature of a center part. It is also possible to do this.

In the present invention, it is preferable area of a portion in contact with the film of the gripper in each 75～1,000Mm ^2, and the initial spacing of the grippers is 50mm or less, respectively. Here, the initial interval of the gripping tools refers to the interval between the gripping tools at the time of unstretched gripping at the B section entrance. When the shape of the gripping tool is a circle or an ellipse, the distance is the distance between the centers of adjacent gripping tools. For gripping tools whose gripping tool shape is not a circle or an ellipse, Point to the distance. In the present invention, unless these conditions are satisfied, the stretching of the edge portion becomes non-uniform, and as a result, the orientation angle uniformity in the width direction of the stretched film may be adversely affected.
The area of the portion in contact with the film of the grippers, respectively, preferably 200 to 800 mm ^2, more preferably 300~600mm ^2. The initial interval between the gripping tools is preferably 40 mm or less, and more preferably 30 mm or less.

  In the present invention, the shape of the portion of each gripping tool that contacts the film is preferably a circle, an ellipse, or an approximate ellipse, and more preferably a circle. An approximate ellipse refers to a shape with rounded corners of a polygon, such as a shape with rounded corners of a rectangle. When a contact surface is circular, the diameter becomes like this. Preferably it is 10-30 mm, More preferably, it is 14-25 mm.

  In the present invention, the stretching ratio in simultaneous biaxial stretching is selected within the range of 1.1 to 2.0 times, preferably 1.2 to 1.8 times, respectively, in the longitudinal direction of the film and the width direction of the film. The In this invention, it is preferable that the draw ratio of the longitudinal direction of a film is below the draw ratio of the width direction of a film. By setting the draw ratio in the longitudinal direction of the film to be equal to or less than the draw ratio in the width direction of the film, the accuracy of the orientation angle in the width direction of the stretched film can be improved.

  After going through the above steps, both ends of the film held by the holding tool can be trimmed, and then wound on a winding core to obtain a wound body of a stretched film.

The retardation Re in the in-plane direction of the stretched film obtained by the production method of the present invention is appropriately adjusted in the range of 40 to 150 nm according to the liquid crystal mode of the liquid crystal display device to be used.
By the production method of the present invention, the variation in the width direction of retardation Re in the in-plane direction of the stretched film obtained can be reduced, specifically within 5 nm, preferably within 4 nm. By setting the variation in the width direction of the retardation Re in the in-plane direction within the above range, display quality can be improved when used as a retardation film for a liquid crystal display device. Here, the variation in the width direction of the retardation Re in the in-plane direction is determined by measuring the in-plane direction retardation at 50 mm intervals in the width direction using a commercially available phase difference meter, and the difference between the maximum value and the minimum value of the measured values. And

The retardation Rth in the thickness direction of the stretched film obtained by the production method of the present invention is appropriately adjusted in the range of 100 to 300 nm according to the liquid crystal mode of the liquid crystal display device to be used.
By the production method of the present invention, the variation in the width direction of the retardation Rth in the thickness direction of the stretched film obtained can be reduced, specifically within 10 nm, preferably within 8 nm. By setting the variation in the width direction of the retardation Rth in the thickness direction within the above range, the display quality can be improved when used as a retardation film for a liquid crystal display device. Here, the retardation Rth in the thickness direction is an average value when the thickness direction retardation is measured at intervals of 50 mm in the width direction using a commercially available phase difference meter, and the variation in the width direction is the maximum of the thickness direction retardation. The difference between the value and the minimum value.

  The average orientation angle of the stretched film obtained by the production method of the present invention is preferably in the range of −0.3 ° to 0.3 ° when the width direction of the film is 0 °. The variation in the orientation angle in the width direction of the film is preferably within 1.2 °, more preferably within 1.0 °. When the variation in the orientation angle is in the above range, the display quality can be improved when used as a retardation film for a liquid crystal display device. Here, the average orientation angle is an average value when the orientation angle is measured at intervals of 50 mm in the width direction using a commercially available polarizing microscope, and the variation is the maximum value and the minimum value of the orientation angle in the width direction. It is the difference from the value.

  The stretched film of the present invention can be easily obtained by the above production method, and can be highly compensated for refractive index, so that it can be used alone or in combination with other members as a retardation plate or a viewing angle compensation film. The present invention can be widely applied to liquid crystal display devices, organic EL 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 stretched film of the present invention on at least one surface of a polarizer.
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 stretched film of this invention may be laminated | stacked on both surfaces of a polarizer, or may be laminated | stacked on one side, and there is no limitation in particular in the number of lamination | stacking, You may laminate | stack two or more sheets. Moreover, as a lamination | stacking method, although it is not an essential method, it can laminate | stack using an adhesive agent. Conventionally, a protective film is laminated on one side or both sides of a polarizer. However, by laminating the stretched film of the present invention, the stretched film of the present invention also serves as a protective film for the polarizer. When the stretched film is directly laminated on the polarizer in this manner, one conventionally used protective film can be omitted, which contributes to thinning of the liquid crystal display device.

  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 olefin resins; chain polyolefin resins, polycarbonate resins, polyester resins such as polyethylene terephthalate; polyvinyl chloride resins, polystyrene resins, polyacrylonitrile resins, Examples thereof include a polysulfone resin, a polyether sulfone resin, a polyamide resin, a polyimide resin, and an acrylic resin.

The liquid crystal display device of the present invention includes the polarizing plate.
The display mode of the liquid crystal cell provided 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 light source used for the backlight include a cold cathode tube, a mercury flat lamp, a light emitting diode, and an EL.

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) Thickness standard deviation of thermoplastic resin film Using an infrared transmission thickness gauge (Kurabo Co., Ltd .: RX-100) installed on the film production line, the entire surface of the thermoplastic resin film is stretched over a length of 500 m. The standard deviation was calculated by measuring online.
(2) Orientation angle (θc, θe) of thermoplastic resin film, orientation angle θ of stretched film
Measurement was performed using a polarizing microscope (Olympus polarizing microscope, “BX51”), and the absolute value was calculated as the orientation angle. The orientation angle θc at the center is an average value obtained by measuring the center of the thermoplastic resin film at five points in the flow direction at intervals of 50 mm, and the orientation angle θe at the edge is set at a point of 100 mm from the edge of the film at intervals of 50 mm in the flow direction. The average value of the values measured at five points was used.
The orientation angle θ of the stretched film was measured at an interval of 50 mm with respect to the width direction of the film using a polarizing microscope (Olympus, BX51), and the average value was defined as the orientation angle θ. Moreover, the maximum value-minimum value at that time was evaluated as variation, and a variation of 1.0 ° or less was regarded as acceptable.
(3) Retardation Re in the in-plane direction of the thermoplastic resin film or stretched film, retardation Rth in the thickness direction of the stretched film
The retardation in the in-plane direction or the retardation in the thickness direction is measured at 50 mm intervals in the width direction using a phase difference meter (manufactured by Oji Scientific Co., Ltd., KOBRA-21ADH), and the average value thereof is retardation Re in the in-plane direction. Or it was set as retardation Rth of the thickness direction.
Variation in retardation in the in-plane direction or retardation in the thickness direction was a value obtained by subtracting the minimum value from the maximum value of the measured values.
The variation in retardation Re in the in-plane direction of the stretched film was 4 nm or less and / or the variation in retardation in the thickness direction was 10 nm or less.

(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 are supplied to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, and then on a casting drum having a surface temperature of 120 ° C. from a T die, a draft ratio (ratio between die opening and film thickness) of 5: 1. Was extruded and cooled to obtain a thermoplastic resin film 1 having a thickness of 150 μm and a width of 1200 mm. At that time, a T die having Ra = 0.05 μm with chrome plating inside was used. Table 1 shows the orientation angle (θc, θe), the in-plane retardation Re, and the standard deviation of the thickness of the obtained thermoplastic resin film 1.

The thermoplastic resin film is continuously supplied as it is to a pantograph type simultaneous biaxial stretching machine as shown in FIG. 1, and stretched at a stretching temperature of 145 ° C., a longitudinal stretching ratio of 1.3 times, and a transverse stretching ratio of 1.5 times. The film was axially stretched to obtain a stretched film 1 having a width of 1500 mm, an in-plane retardation Re of 60 nm, and a thickness direction retardation Rth of 210 nm, and wound around a core. The starting point and the ending point of the longitudinal stretching and the lateral stretching were made simultaneously. Table 2 shows the shape of each gripping tool, the area of the portion of each gripping tool that contacts the film, and the initial spacing of the gripping tools.
The obtained stretched film 1 was uniform over the entire width. Table 2 shows the in-plane retardation Re of the stretched film 1 and its variation, the retardation Rth in the thickness direction and its variation, and the orientation angle θ and its variation.

  A long polarizing plate having a transmission axis in the width direction (manufactured by Sanlitz, HLC2-5618S, thickness 180 μm) and a stretched film 1 are bonded to each other by a roll-to-roll, and a winding body of a polarizing plate having a width of 1500 mm is obtained. Obtained. The polarizing plate cut out from the wound body is replaced with a polarizing plate on the backlight side of a commercially available 32-inch VA (vertical alignment) mode transmissive liquid crystal display device, and the side on which the stretched film 1 is bonded is the liquid crystal cell side. The liquid crystal display device was obtained by being assembled so as to be arranged. When the display screen of the obtained liquid crystal display device was visually confirmed from the front, no color unevenness was observed over the entire width, and the display was good.

(Example 2)
A stretched film 2, a polarizing plate and a VA-type transmissive liquid crystal display device were obtained in the same manner as in Example 1 except that the film gripper shown in Table 2 was changed. The evaluation results of this stretched film 2 are shown in Table 1. When the display screen of the VA-type transmissive liquid crystal display device incorporating the polarizing plate using the stretched film 2 was visually confirmed from the front, color unevenness was not observed over the entire width, and the display was good.

(Comparative Example 1)
When producing the thermoplastic resin film, a thermoplastic resin film 2 was obtained in the same manner as in Example 1 except that the surface temperature of the casting drum was changed to 100 ° C. Table 1 shows the orientation angle, in-plane retardation Re, and standard deviation of the thickness of the thermoplastic resin film 2.
A stretched film 3 was obtained by performing simultaneous biaxial stretching in the same manner as in Example 1 except that the thermoplastic resin film 2 was used instead of the thermoplastic resin film 1. Since the thickness standard deviation of the thermoplastic resin film 2 exceeds 0.6, the obtained stretched film 3 lacks uniformity in the width direction (alignment angle variation, in-plane retardation variation, and thickness direction deviation). Variation in retardation was large). When the display screen of the VA-type transmissive liquid crystal display device incorporating the polarizing plate using the stretched film 3 was visually confirmed from the front, color unevenness was observed in the screen and the display quality deteriorated.

(Comparative Example 2)
A thermoplastic resin film 3 was obtained in the same manner as in Example 1 except that the draft ratio was changed to 7: 1 when producing the thermoplastic resin film. Table 1 shows the orientation angle, in-plane retardation Re, and standard deviation of the thickness of the thermoplastic resin film 3.
A stretched film 4 was obtained by carrying out simultaneous biaxial stretching in the same manner as in Example 1 except that the thermoplastic resin film 3 was used instead of the thermoplastic resin film 1. Since the in-plane retardation Re of the thermoplastic resin film 3 exceeds 20 nm, the obtained stretched film 3 lacks uniformity in the width direction (the variations in retardation in the in-plane direction and the retardation in the thickness direction are large). ) When the display screen of the VA-type transmissive liquid crystal display device incorporating the polarizing plate using the stretched film 3 was visually confirmed from the front, color unevenness was observed in the screen and the display quality deteriorated.

(Comparative Example 3)
When producing the thermoplastic resin film, a thermoplastic resin film 4 was obtained in the same manner as in Example 1 except that the casting drum surface temperature was 140 ° C. and the draft ratio was 3: 1. Table 1 shows the orientation angle of the thermoplastic resin film 4, the in-plane retardation Re, and the standard deviation of the thickness.
A stretched film 5 was obtained by carrying out simultaneous biaxial stretching in the same manner as in Example 1 except that the thermoplastic resin film 4 was used instead of the thermoplastic resin film 1. Since the difference between the orientation angle at the center portion of the thermoplastic resin film 4 and the orientation angle at the edge portion is smaller than 10 °, the obtained stretched film 5 lacks uniformity in the width direction (the variation in the orientation angle is large). It was a thing. When the display screen of the VA-type transmissive liquid crystal display device incorporating the polarizing plate using the stretched film 5 was visually confirmed from the front, color unevenness was observed in the screen and the display quality deteriorated.

The top view which shows one Embodiment of the simultaneous biaxial stretching machine which can be used for the manufacturing method of this invention

Explanation of symbols

1: thermoplastic resin film 2: gripping means 3: endless link device 4: inlet side sprocket 5, 6, 7, 8: guide rail 9: outlet side sprocket 10: stretched film A: preheating section B: stretching section C: fixed section

Claims (6)

The thermoplastic resin film is gripped at both ends in the width direction by using a plurality of gripping tools and moved in the longitudinal direction thereof, and the spacing between the gripping tools in the width direction of the resin film and the gripping in the longitudinal direction of the resin film. In the method for producing a stretched film by simultaneously stretching the resin film in the longitudinal direction and the width direction by widening the spacing of the tool along with the movement in the film longitudinal direction, the thermoplastic resin film has the following [ 1]-[5] is satisfied, A method for producing a stretched film.
[1] The width is 1000 mm or more.
[2] In-plane retardation Re is 20 nm or less.
[3] The standard deviation of thickness is 0.60 μm or less.
[4] θc + 10 ° <θe
[5] θc <10 °
In the above formulas [4] and [5], θc represents the absolute value of the orientation angle of the center portion with respect to the width direction of the film, and θe represents the absolute value of the orientation angle of the edge portion with respect to the width direction of the film. ^{2. The} method for producing a stretched film according to claim 1, wherein an area of a portion of the gripping tool that contacts the film is 75 to 1,000 mm ² , and an initial interval between the gripping tools is 50 mm or less.   The method for producing a stretched film according to claim 1 or 2, wherein the shape of the portion of the gripping tool that contacts the film is circular, elliptical, or approximate elliptical.   The stretched film obtained by the method of Claims 1-3.   A polarizing plate formed by laminating the stretched film according to claim 4 on at least one surface of a polarizer.   A liquid crystal display device comprising the polarizing plate according to claim 5.

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