JP2016179650A - Obliquely stretched film and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an obliquely stretched film having a highly accurate orientation angle in the longitudinal direction.SOLUTION: There is provided a lengthy obliquely stretched film having a slow axis in not parallel, not vertical but oblique direction in the longitudinal direction. In the obliquely stretched film, the orientation angle of the obliquely stretched film has a cycle below 2,000 mm in the longitudinal direction, and the amplitude of the orientation angle in the cycle is below 0.1°.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an obliquely stretched film and a method for producing an obliquely stretched film.

  The image display apparatus may be provided with a retardation film for improving performance. Such retardation film is, for example. It is used for antireflection applications of organic electroluminescence display devices and optical compensation applications of liquid crystal display devices. When used in such applications, the slow axis of the retardation film is generally required to be neither parallel nor perpendicular to the transmission axis of the polarizer. On the other hand, the transmission axis of the polarizer is usually parallel to the long side direction or the short side direction of the rectangular display surface of the image display device. Therefore, a rectangular retardation film for application to an image display device is required to have a slow axis that is neither parallel nor perpendicular to the sides of the rectangular retardation film.

  Moreover, generally the phase difference film was manufactured by carrying out the longitudinal stretch or the lateral stretch of the elongate resin film. Here, longitudinal stretching represents stretching in the film longitudinal direction, and lateral stretching represents stretching in the film width direction. Therefore, a long retardation film produced by a conventional method usually has a slow axis parallel or perpendicular to the longitudinal direction. Therefore, in order to obtain a rectangular retardation film as described above from such a conventional long retardation film, the long retardation film is cut in a direction that is neither parallel nor perpendicular to the longitudinal direction. Was demanded.

  However, the conventional manufacturing method of cutting a long retardation film in a direction that is neither parallel nor perpendicular to the longitudinal direction increases the amount of discarded film or makes it difficult to manufacture on a roll-to-roll basis. Therefore, the production efficiency is lowered. Therefore, in order to improve the production efficiency, it has been proposed to produce a retardation film as an obliquely stretched film by stretching a long resin film in an oblique direction (see Patent Documents 1 to 3).

International Publication No. 2007/111313 Japanese Patent No. 5333698 Japanese Patent No. 4577033

  In recent years, the required quality of obliquely stretched films has increased in the market, and it has been demanded to improve the accuracy of the orientation angle as compared with the prior art. Here, the orientation angle refers to an angle formed by a slow axis with respect to a certain reference direction. However, since the direction of the slow axis of the conventional obliquely stretched film was not uniform in the longitudinal direction of the obliquely stretched film, the accuracy of the orientation angle was insufficient.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an obliquely stretched film having high orientation angle accuracy in the longitudinal direction and a method for producing the same.

The present inventor has intensively studied to solve the above problems. As a result, the present inventor can reduce the amplitude of the orientation angle in the longitudinal direction by adjusting the tension ratio of the clip chain when the resin film is obliquely stretched by a stretching apparatus using a pair of clip chains. I found out. Further, the present inventor has found that the orientation angle accuracy of the obliquely stretched film can be improved by reducing the amplitude of the orientation angle in the longitudinal direction. The present invention has been completed based on these findings.
That is, the present invention is as follows.

[1] A long obliquely stretched film having a slow axis in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction,
The orientation angle of the obliquely stretched film has a period of less than 2000 mm in the longitudinal direction,
An obliquely stretched film having an amplitude of an orientation angle in the period of less than 0.1 °.
[2] The obliquely stretched film according to [1], wherein an average of the orientation angles with respect to the longitudinal direction of the obliquely stretched film is 40 ° to 50 °.
[3] The obliquely stretched film according to [1] or [2], which has a width of 1000 mm to 1500 mm.
[4] The obliquely stretched film according to any one of [1] to [3], having a thickness of 10 μm to 100 μm.
[5] The obliquely stretched film according to any one of [1] to [4], which is made of a thermoplastic resin.
[6] The obliquely stretched film according to any one of [1] to [5], which is a retardation film.
[7] An inner clip chain having a plurality of inner clips capable of gripping one end of a long resin film, and an outer side having a plurality of outer clips capable of gripping the other end of the resin film It is a production method for producing a long obliquely stretched film by stretching while conveying the resin film by a stretching apparatus equipped with a clip chain,
A first step of gripping both ends of the resin film with the inner clip and the outer clip;
A second step of stretching the resin film with the inner clip and the outer clip while running the inner clip and the outer clip so that the traveling direction of the resin film bends with the inner clip facing inward;
A third step of releasing the resin film from the inner clip and the outer clip to obtain the obliquely stretched film having a slow axis in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the obliquely stretched film. ,
A tension T _in the inner clip chain at a position for gripping one end of the resin film in the first step, the tension of the outer clip chain at a position for gripping the other end of the resin film in the first step the ratio _T in _{/ T out} × 100 with T _out is 80% to 120%, the production method of the oblique stretching the film.
[8] The method for producing an obliquely stretched film according to [7], wherein the stretch ratio is 1.1 to 4.0 times.
[9] The method for producing an obliquely stretched film according to [7] or [8], wherein in the second step, the traveling speed of the inner clip and the traveling speed of the outer clip are the same.

According to the obliquely stretched film of the present invention, the accuracy of the orientation angle can be increased in the longitudinal direction.
According to the method for producing an obliquely stretched film of the present invention, an obliquely stretched film having a high orientation angle accuracy in the longitudinal direction can be produced.

FIG. 1 is a perspective view schematically showing an obliquely stretched film according to the first embodiment of the present invention. FIG. 2 is a graph schematically showing an example of the distribution of the orientation angle θ in the longitudinal direction of the obliquely stretched film according to the first embodiment of the present invention. FIG. 3 is a plan view schematically showing a production apparatus used in the method for producing an obliquely stretched film according to the second embodiment of the present invention. FIG. 4 is a plan view schematically showing a tenter stretching apparatus as a stretching apparatus used in the method for producing an obliquely stretched film according to the second embodiment of the present invention.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and exemplifications, and can be implemented with any modifications without departing from the scope of the claims and their equivalents.

  In the following description, a “long” film refers to a film having a length of at least 5 times the width, preferably a film having a length of 10 times or more, specifically Refers to a film having a length enough to be wound or stored in a roll.

  In the following description, the in-plane retardation Re of the film is a value represented by Re = (nx−ny) × d unless otherwise specified. Further, the retardation Rth in the thickness direction of the film is a value represented by Rth = {(nx + ny) / 2−nz} × d unless otherwise specified. Here, nx represents a refractive index in a direction (in-plane direction) perpendicular to the thickness direction of the film and giving the maximum refractive index. ny represents a refractive index in the in-plane direction of the film and in a direction perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. The measurement wavelength is 590 nm unless otherwise specified.

  Further, in the following description, the directions of the elements “parallel” and “vertical” include errors within a range that does not impair the effects of the present invention, for example, ± 5 °, unless otherwise specified. Also good.

  In the following description, the oblique direction of the long film means an in-plane direction of the film, unless indicated otherwise, and a direction that is neither parallel nor perpendicular to the longitudinal direction of the film.

  In the following description, “polarizing plate” and “wave plate” include not only a rigid member but also a flexible member such as a resin film, unless otherwise specified.

[1. Period of orientation angle of obliquely stretched film]
FIG. 1 is a perspective view schematically showing an obliquely stretched film 10 according to the first embodiment of the present invention.
As shown in FIG. 1, the diagonally stretched film 10 which concerns on 1st embodiment of this invention is a elongate film. Since the obliquely stretched film 10 is manufactured through a process that undergoes an oblique stretching process of stretching in an oblique direction, the obliquely stretched film 10 has a slow axis 10A in the oblique direction. Therefore, the slow axis 10A is neither parallel nor perpendicular to the longitudinal direction MD of the obliquely stretched film 10, and is neither parallel nor perpendicular to the width direction TD of the obliquely stretched film 10.

  The orientation angle θ of the obliquely stretched film 10 will be described. As described above, the orientation angle θ of the obliquely stretched film 10 represents an angle formed by the slow axis 10A of the obliquely stretched film 10 with respect to a certain reference direction. In the present embodiment, an example in which the longitudinal direction MD of the obliquely stretched film 10 is employed as the reference direction will be described. Unless otherwise specified, the orientation angle θ of the obliquely stretched film 10 is measured at the center in the width direction of the obliquely stretched film 10.

FIG. 2 is a graph schematically showing an example of the distribution of the orientation angle θ in the longitudinal direction of the obliquely stretched film 10 according to the first embodiment of the present invention. In the graph of FIG. 2, the horizontal axis represents the position in the longitudinal direction of the obliquely stretched film 10, and the vertical axis represents the orientation angle θ of the obliquely stretched film 10.
As shown in FIG. 2, the orientation angle θ of the obliquely stretched film 10 is nonuniform with periodicity in the longitudinal direction of the obliquely stretched film 10. Specifically, the orientation angle θ of the obliquely stretched film 10 usually repeats increasing and decreasing continuously and periodically in the longitudinal direction of the obliquely stretched film 10. Therefore, in the longitudinal direction of the obliquely stretched film 10, the orientation angle θ has a predetermined range of period λ (θ). Here, the period λ (θ) of the orientation angle θ represents the distance from the maximum point of the orientation angle θ to the next maximum point in the longitudinal direction. At this time, the amplitude A (θ) of the orientation angle θ in the period λ (θ) is expressed by the absolute value of the difference between the maximum value and the minimum value of the orientation angle θ in one period.

  The period λ (θ) of the orientation angle θ of the obliquely stretched film 10 according to this embodiment is usually less than 2000 mm, preferably 1000 mm or less, and more preferably 500 mm or less. The lower limit of the period λ (θ) is not particularly limited, but is preferably 10 mm or more, more preferably 50 mm or more, and particularly preferably 100 mm or more. The period λ (θ) may or may not be constant in the longitudinal direction of the obliquely stretched film 10. In the present embodiment, it is preferable that each period λ (θ) falls within the above range.

  Further, the amplitude A (θ) of the orientation angle θ in the period λ (θ) is usually less than 0.100 °, preferably 0.08 ° or less, more preferably 0.05 ° or less. is there. The lower limit of the amplitude A (θ) is not particularly limited, but is preferably 0.01 ° or more. The amplitude A (θ) may or may not be constant in the longitudinal direction of the obliquely stretched film 10. In the present embodiment, it is preferable that all the amplitudes A (θ) in each period λ (θ) fall within the above range. Conventionally, it has been difficult to reduce the amplitude A (θ) of the orientation angle θ in this way, but by manufacturing the obliquely stretched film 10 by a manufacturing method described later, the amplitude A (θ) as described above. Can be reduced.

  The obliquely stretched film 10 according to the present embodiment has an orientation angle θ in the longitudinal direction of the obliquely stretched film 10 because the period λ (θ) and the amplitude A (θ) of the orientation angle θ are within the above ranges. The accuracy of can be increased. Specifically, the variation Δθ in the orientation angle θ in the longitudinal direction of the obliquely stretched film 10 can be reduced. Here, the “variation Δθ of the orientation angle θ” refers to the absolute value of the difference between the maximum value and the minimum value of the orientation angle θ in the longitudinal direction of the obliquely stretched film 10.

  The variation Δθ of the orientation angle θ in the longitudinal direction of the obliquely stretched film 10 according to this embodiment is preferably 0.3 ° or less, more preferably 0.2 ° or less. The obliquely stretched film 10 having a small variation in the orientation angle θ in the longitudinal direction Δθ can be applied to an image display device such as a liquid crystal display device, thereby suppressing color unevenness of the image of the image display device and improving the contrast. .

  The specific value of the orientation angle θ can be arbitrarily set according to the use of the obliquely stretched film 10. For example, the orientation angle θ with respect to the longitudinal direction MD of the obliquely stretched film 10 can be arbitrarily set in the range of 5 ° <θ <85 °. Among them, the average orientation angle θ with respect to the longitudinal direction MD of the obliquely stretched film 10 is preferably 40 ° or more, more preferably 42 ° or more, particularly preferably 44 ° or more, preferably 50 ° or less, more preferably 48. It is not more than °, particularly preferably not more than 46 °. By keeping the average orientation angle θ within the above range, a rectangular retardation film applicable to an image display device can be easily produced from the obliquely stretched film 10.

  For example, a circularly polarizing plate that can be provided as an antireflection film in an image display device generally includes a retardation film and a polarizer. Such a circularly polarizing plate is manufactured, for example, by laminating a long polarizer and a long retardation film in parallel with each other in the longitudinal direction. Further, the polarization transmission axis of the polarizer is usually parallel or perpendicular to the longitudinal direction of the polarizer. Therefore, by keeping the average orientation angle θ with respect to the longitudinal direction of the long obliquely stretched film 10 within the above range, the polarization transmission axis of the polarizer and the slow axis 10A of the obliquely stretched film 10 are 45 ° ± 5 °. It can be easily pasted to make an angle of. Therefore, it is possible to easily manufacture a circularly polarizing plate using the obliquely stretched film 10 according to the present embodiment as a retardation film.

[2. Material of obliquely stretched film]
The obliquely stretched film is usually a resin film made of a resin. As the resin, a thermoplastic resin is preferable. Examples of thermoplastic resins include: polyolefin resins such as polyethylene resins and polypropylene resins; alicyclic structure-containing polymer resins such as norbornene resins; cellulose resins such as diacetyl cellulose resins and triacetyl cellulose resins; polyimide resins, polyamides Imide resin, polyamide resin, polyether imide resin, polyether ether ketone resin, polyether ketone resin, polyketone sulfide resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin, polyphenylene oxide resin, polyethylene terephthalate resin, polybutylene terephthalate resin , Polyethylene naphthalate resin, polyacetal resin, polycarbonate resin, polyarylate resin, (meth) acrylic resin, polyvinyl Lucol resin, polypropylene resin, cellulose resin, epoxy resin, phenol resin, (meth) acrylic acid ester-vinyl aromatic compound copolymer resin, isobutene / N-methylmaleimide copolymer resin, styrene / acrylonitrile copolymer Resin etc. are mentioned. One of these may be used alone, or two or more of these may be combined in any ratio.

  Among the thermoplastic resins, alicyclic structure-containing polymer resins are preferable. The alicyclic structure-containing polymer resin is a resin containing an alicyclic structure-containing polymer, and is excellent in properties such as transparency, low moisture absorption, dimensional stability, and lightness.

  The alicyclic structure-containing polymer is a polymer having an alicyclic structure in the structural unit of the polymer, a polymer having an alicyclic structure in the main chain, and an alicyclic structure in the side chain. Any of the polymers may be used. Moreover, an alicyclic structure containing polymer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, a polymer containing an alicyclic structure in the main chain is preferable from the viewpoint of mechanical strength, heat resistance, and the like.

  Examples of the alicyclic structure include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structure. Among these, from the viewpoints of mechanical strength, heat resistance and the like, a cycloalkane structure and a cycloalkene structure are preferable, and a cycloalkane structure is particularly preferable.

  The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, particularly preferably per alicyclic structure. Is a range of 15 or less. Thereby, the mechanical strength, heat resistance, and moldability of the obliquely stretched film are highly balanced and suitable.

  The proportion of the structural unit having an alicyclic structure in the alicyclic structure-containing polymer may be appropriately selected according to the purpose of use, preferably 55% by weight or more, more preferably 70% by weight or more, particularly preferably. 90% by weight or more. When the proportion of the structural unit having an alicyclic structure in the alicyclic structure-containing polymer is in this range, it is preferable from the viewpoint of the transparency and heat resistance of the obliquely stretched film.

  Examples of the alicyclic structure-containing polymer include a norbornene polymer, a monocyclic olefin polymer, a cyclic conjugated diene polymer, a vinyl alicyclic hydrocarbon polymer, and hydrogenated products thereof. Can do. Of these, norbornene polymers are preferred because of their good transparency and moldability.

  Examples of the norbornene polymer include a ring-opening polymer of a monomer having a norbornene structure and a hydrogenated product thereof; an addition polymer of a monomer having a norbornene structure and a hydrogenated product thereof. Examples of a ring-opening polymer of a monomer having a norbornene structure include a ring-opening homopolymer of one kind of monomer having a norbornene structure and a ring-opening of two or more kinds of monomers having a norbornene structure. Examples thereof include a copolymer and a ring-opening copolymer of a monomer having a norbornene structure and an arbitrary monomer copolymerizable therewith. Furthermore, examples of the addition polymer of a monomer having a norbornene structure include an addition homopolymer of one kind of monomer having a norbornene structure and an addition copolymer of two or more kinds of monomers having a norbornene structure. And addition copolymers of a monomer having a norbornene structure and an arbitrary monomer copolymerizable therewith. Among these, a hydrogenated product of a ring-opening polymer 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. is there.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7. -Diene (common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4. 0.1 ^2,5 . ^{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 thereof may be bonded to the ring. Moreover, the monomer which has a norbornene structure may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  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 sulfonic acid group.

  Examples of an optional monomer capable of ring-opening copolymerization with a monomer having a norbornene structure include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; cyclic such as cyclohexadiene and cycloheptadiene. Conjugated dienes and derivatives thereof; and the like. As the optional monomer capable of ring-opening copolymerization with a monomer having a norbornene structure, one kind may be used alone, or two or more kinds may be used in combination at any ratio.

  A ring-opening polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing a monomer in the presence of a known ring-opening polymerization catalyst.

  Examples of the optional monomer capable of addition copolymerization with a monomer having a norbornene structure include, for example, α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, and derivatives thereof; cyclobutene, And cycloolefins such as cyclopentene and cyclohexene and derivatives thereof; non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene and 5-methyl-1,4-hexadiene; Among these, α-olefin is preferable and ethylene is more preferable. Moreover, the arbitrary monomer which can carry out addition copolymerization with the monomer which has a norbornene structure may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  An addition polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing a monomer in the presence of a known addition polymerization catalyst.

  The hydrogenated product of the above-described ring-opening polymer and addition polymer is, for example, carbon in the presence of a hydrogenation catalyst containing a transition metal such as nickel or palladium in a solution of these ring-opening polymer or addition polymer. -Carbon unsaturated bonds can be produced by hydrogenation, preferably 90% or more.

Among norbornene polymers, as structural units, 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 amount of these structural units is 90% by weight or more based on the whole structural unit of the norbornene polymer, and the ratio of the ratio of X to the ratio of Y is X: Y weight ratio is preferably 100: 0 to 40:60. By using such a polymer, an obliquely stretched film can be made long-term without dimensional change and excellent in property stability.

  The weight average molecular weight (Mw) of the polymer contained in the resin constituting the obliquely stretched film is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100, 000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. Here, the weight average molecular weight is calculated by polyisoprene or polystyrene measured by gel permeation chromatography using cyclohexane as a solvent (however, toluene may be used when the sample does not dissolve in cyclohexane). The weight average molecular weight of When the weight average molecular weight is in such a range, the mechanical strength and molding processability of the obliquely stretched film are highly balanced and suitable.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer contained in the resin constituting the obliquely stretched film is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably. It is 1.8 or more, preferably 3.5 or less, more preferably 3.0 or less, and particularly preferably 2.7 or less. By making molecular weight distribution more than the lower limit of the said range, productivity of a polymer can be improved and cost can be suppressed. Moreover, since a low molecular weight component can be reduced by making it below an upper limit, relaxation time can be lengthened. Therefore, relaxation at high temperature exposure can be suppressed, and the stability of the obliquely stretched film can be increased.

  The ratio of the polymer in the resin constituting the obliquely stretched film is preferably 50% by weight to 100% by weight, and more preferably 70% by weight to 100% by weight. In particular, when an alicyclic structure-containing polymer resin is used as the resin constituting the obliquely stretched film, the proportion of the alicyclic structure-containing polymer contained in the alicyclic structure-containing polymer resin is preferably 80% by weight to 100 wt%, more preferably 90 wt% to 100 wt%.

  The resin constituting the obliquely stretched film may contain any component other than the polymer as long as the effects of the present invention are not significantly impaired. Examples of the optional components include colorants such as pigments and dyes; plasticizers; fluorescent brighteners; dispersants; thermal stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; An additive such as a surfactant. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The glass transition temperature Tg of the resin constituting the obliquely stretched film is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher, preferably 200 ° C. or lower, more preferably 190 ° C. or lower, particularly Preferably it is 180 degrees C or less. By setting the glass transition temperature of the resin to be equal to or higher than the lower limit of the above range, the durability of the obliquely stretched film in a high temperature environment can be enhanced. In addition, the stretching process can be easily performed by setting the upper limit value or less.

The absolute value of the photoelastic coefficient C of the resin constituting the obliquely stretched film is preferably ¹⁰ × 10 -12 ^{Pa -1} or less, more preferably 7 × ¹⁰ -12 ^{Pa -1} or less, 4 × It is particularly preferably 10 ⁻¹² Pa ⁻¹ or less. The photoelastic coefficient C is a value represented by “C = Δn / σ” where birefringence is Δn and stress is σ. By keeping the photoelastic coefficient of the resin within the above range, the variation in retardation in the obliquely stretched film can be reduced.

  The saturated water absorption of the resin constituting the obliquely stretched film is 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, it is possible to reduce a change with time in characteristics such as retardation of the obliquely stretched film.

  The saturated water absorption is a value expressed as a percentage with respect to the mass of the test piece before immersion, which is obtained by immersing the test piece in water at a constant temperature for a certain period of time. Usually, it is measured by immersing in 23 ° C. water for 24 hours. The saturated water absorption rate of the resin can be adjusted to the above range, for example, by reducing the amount of polar groups in the polymer contained in the resin. Therefore, from the viewpoint of lowering the saturated water absorption, it is preferable that the polymer contained in the resin constituting the obliquely stretched film does not have a polar group.

[3. Properties and dimensions of obliquely stretched film]
The total light transmittance of the obliquely stretched film is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The light transmittance can be measured using a spectrophotometer (manufactured by JASCO Corporation, UV-visible near-infrared spectrophotometer “V-570”) in accordance with JIS K0115.

  The haze of the obliquely stretched film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. Here, according to JIS K7361-1997, haze can measure five places using the Nippon Denshoku Industries Co., Ltd. "turbidimeter NDH-300A", and can employ | adopt the average value calculated | required from it.

  The average of in-plane retardation Re of the obliquely stretched film in the longitudinal direction of the obliquely stretched film is preferably 100 nm or more, more preferably 120 nm or more, particularly preferably 140 nm or more, preferably 300 nm or less, more preferably 200 nm or less. Particularly preferably, it is 150 nm or less. By having such in-plane retardation Re, a film cut out from an obliquely stretched film can be suitably used as an optical compensation film of an image display device. However, the in-plane retardation Re of the obliquely stretched film can be arbitrarily set to an appropriate value depending on the configuration of the display device to be applied. Here, as the in-plane retardation Re of the obliquely stretched film, a value measured at the center in the width direction of the obliquely stretched film can be adopted.

  The variation in the in-plane retardation of the obliquely stretched film in the longitudinal direction of the obliquely stretched film is preferably 5 nm or less, more preferably 3 nm or less, particularly preferably 2 nm or less, and ideally 0 nm. Here, the variation in in-plane retardation refers to the difference between the maximum value and the minimum value in the in-plane retardation at the center in the width direction of the obliquely stretched film. By reducing the variation in the in-plane retardation of the obliquely stretched film as described above, when the film cut out from the obliquely stretched film is applied to a display device, the image quality of the display device can be improved. It becomes possible.

  Variation in retardation Rth in the thickness direction of the obliquely stretched film in the longitudinal direction of the obliquely stretched film is preferably 10 nm or less, more preferably 8 nm or less, particularly preferably 5 nm or less, and ideally 0 nm. Here, the variation in the retardation Rth in the thickness direction refers to the difference between the maximum value and the minimum value of the retardation Rth in the thickness direction at the center in the width direction of the obliquely stretched film.

The amount of the volatile component contained in the obliquely stretched film is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, still more preferably 0.02% by weight or less, and ideally zero. . By reducing the amount of the volatile component, the dimensional stability of the obliquely stretched film can be improved, and the change with time in optical characteristics such as in-plane retardation can be reduced.
Here, 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 amount of the volatile component can be quantified by dissolving the film in chloroform and analyzing it by gas chromatography as the total of substances having a molecular weight of 200 or less contained in the film.

  The thickness of the obliquely stretched film is preferably 10 μm or more, more preferably 15 μm or more, further preferably 20 μm or more, preferably 100 μm or less, more preferably 60 μm or less. Thereby, the mechanical strength of the obliquely stretched film can be increased.

  The width of the obliquely stretched film is preferably 1000 mm or more, more preferably 1300 mm or more, particularly preferably 1330 mm or more, preferably 1500 mm or less, more preferably 1490 mm or less. By increasing the width of the obliquely stretched film in this manner, the obliquely stretched film can be applied to a large display device (organic EL display device or the like).

[4. Method for producing obliquely stretched film]
The long oblique stretched film described above is produced by a production method including a step of stretching in the oblique direction while conveying the long resin film. In addition, the stretching as described above can normally grip an inner clip chain having a plurality of inner clips capable of gripping one end of a long resin film, and the other end of the resin film. This is done using a stretching device with an outer clip chain with a plurality of outer clips. At this time, in order to obtain an obliquely stretched film having an orientation angle θ having the desired period λ (θ) and amplitude A (θ), the tension ratio of the inner clip chain and the outer clip chain is adjusted. It is desirable to do. Hereinafter, an embodiment of a method for producing such an obliquely stretched film will be described. In the following description of the embodiments, “upstream” and “downstream” represent upstream and downstream in the film transport direction unless otherwise specified.

  FIG. 3 is a plan view schematically showing a manufacturing apparatus 100 used in the method for manufacturing the obliquely stretched film 10 according to the second embodiment of the present invention. In FIG. 3, the illustration of the inner clip chain 210L and the outer clip chain 210R is omitted. FIG. 4 is a plan view schematically showing a tenter stretching apparatus 200 as a stretching apparatus used in the method for manufacturing the obliquely stretched film 10 according to the second embodiment of the present invention.

  As shown in FIG. 3, the manufacturing apparatus 100 used in the second embodiment of the present invention includes a tenter stretching apparatus 200 and an oven 300 as stretching apparatuses. The production apparatus 100 is provided so that the resin film 30 as an unstretched film is fed from the feeding roll 20 and the drawn resin film 30 is stretched by the tenter stretching apparatus 200 to produce the obliquely stretched film 10. .

  As shown in FIG. 4, the tenter stretching apparatus 200 includes an inner clip chain 210L, an outer clip chain 210R, an inner guide rail 220L corresponding to the inner clip chain 210L, an outer guide rail 220R corresponding to the outer clip chain 210R, and an inner side. A sprocket (not shown) for driving the clip chain 210L and the outer clip chain 210R to go around is provided.

The inner clip chain 210L is an endless chain provided so as to be able to go around, and includes a plurality of inner clips 230L. These inner clips 230L are provided so that one end 30L of the resin film 30 can be gripped.
On the other hand, the outer clip chain 210R is an endless chain provided so as to be able to go around, and includes a plurality of outer clips 230R. These outer clips 230R are provided so that the other end 30R of the resin film 30 can be gripped.
In the present embodiment, an example is shown in which the inner clip 230L and the outer clip 230R are provided so as to be able to grip the left end 30L and the right end 30R of the resin film 30 with an equal gripping amount, respectively. Here, “right” and “left” indicate directions in the case of observing from the upstream to the downstream in the film conveyance direction unless otherwise specified. The gripping amount represents the amount of the resin film 30 that is gripped by the inner clip 230L and the outer clip 230R.

  The inner clip 230L is provided so as to travel along the inner guide rail 220L. Further, the inner clip 230L grips the end portion 30L of the resin film 30 at the inner grip start position 240L set in the inlet portion 240 of the tenter stretching device 200, and the inner opening is set in the outlet portion 250 of the tenter stretching device 200. It is provided so that the end 30L of the resin film 30 can be opened at the position 250L. Accordingly, the inner clip 230L grips the end 30L of the resin film 30 at the inner grip start position 240L, travels along the inner guide rail 220L while maintaining this gripped state, and the resin film 30 at the inner open position 250L. The end 30L can be opened. Further, the inner clip 230L is provided so as to be able to travel at a constant speed with a constant distance from the front and rear inner clips 230L.

  The outer clip 230R is provided so as to travel along the outer guide rail 220R. The outer clip 230 </ b> R grips the end 30 </ b> R of the resin film 30 at the outer grip start position 240 </ b> R set at the inlet portion 240 of the tenter stretching device 200 and opens outside at the outlet portion 250 of the tenter stretching device 200. It is provided so that the end 30R of the resin film 30 can be opened at the position 250R. Accordingly, the outer clip 230R grips the end 30R of the resin film 30 at the outer grip start position 240R, travels along the outer guide rail 220R while maintaining this gripped state, and the resin film 30 at the outer open position 250R. The end 30R can be opened. Further, the outer clip 230R is provided so as to be able to travel at a constant speed with a constant distance from the front and rear outer clips 230R.

  The inner guide rail 220L is provided on one side of the film conveyance path so as to guide the inner clip 230L. Further, the inner guide rail 220L has an endless continuous track so that the inner clip 230L can go around a predetermined track. For this reason, the inner clip 230L can be sequentially returned to the inner gripping start position 240L after opening the end 30L of the resin film 30 at the inner opening position 250L.

  The outer guide rail 220R is provided on the other side of the film conveyance path so that the outer clip 230R can be guided. Further, the outer guide rail 220R has an endless continuous track so that the outer clip 230R can go around a predetermined track. For this reason, the outer clip 230R can be sequentially returned to the outer grip start position 240R after opening the end 30R of the resin film 30 at the outer opening position 250R.

  Furthermore, the inner guide rail 220L and the outer guide rail 220R have asymmetric shapes according to conditions such as the direction of the slow axis of the obliquely stretched film 10 to be manufactured and the stretch ratio. Specifically, the shapes of the inner guide rail 220L and the outer guide rail 220R are set to be bent so that the traveling direction of the stretched resin film 30 is the inner clip 230L inward. In the present embodiment, an example in which the shapes of the inner guide rail 220L and the outer guide rail 220R are set to a shape in which the traveling direction of the stretched resin film 30 is bent to the left will be described. Here, the traveling direction of the resin film 30 refers to the moving direction of the midpoint of the width direction of the resin film 30.

Since the shapes of the inner guide rail 220L and the outer guide rail 220R are set as described above, the inner clip that is opposed to the direction perpendicular to the traveling direction of the resin film 30 at the inlet 240 of the tenter stretching device 200. The inner clip 230L may precede the outer clip 230R at the outlet 250 of the tenter stretching apparatus 200. Thereby, the tenter stretching apparatus 200 can stretch the resin film 30 in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction (see broken lines L _{D1 to} L _{D3 in} FIG. 4).

  In addition, the tenter stretching device 200 includes a sprocket (not shown) for driving the inner clip chain 210L and the outer clip chain 210R to go around. Usually, these sprockets are provided at the upstream end and the downstream end of the inner clip chain 210L and the outer clip chain 210R, respectively. In the tenter stretching device 200, these sprockets drive the inner clip chain 210L and the outer clip chain 210R so that the inner clip 230L and the outer clip 230R can travel along the inner guide rail 220L and the outer guide rail 220R.

  As shown in FIG. 3, the manufacturing apparatus 100 is provided with an oven 300 so as to cover the tenter stretching apparatus 200. The oven 300 is provided so that the resin film 30 passing through the oven 300 can be heated to a desired temperature while the both ends 30L and 30R are held by the inner clip 230L and the outer clip 230R.

  The oven 300 has a preheating zone 310, a stretching zone 320, and a heat setting zone 330 in this order from the upstream. The oven 300 has a partition wall 340 that can isolate the preheating zone 310, the stretching zone 320, and the heat setting zone 330 so that the temperatures in the preheating zone 310, the stretching zone 320, and the heat setting zone 330 can be adjusted independently. Is provided.

  The preheating zone 310 is a section provided upstream from the stretching zone 320. Usually, the preheating zone 310 is provided so that the inner clip 230L and the outer clip 230R that hold the both ends 30L and 30R of the resin film 30 can travel while maintaining a constant distance D (see FIG. 4). . The temperature of the preheating zone 310 is set so that the resin film 30 can be heated to a desired preheating temperature.

  Here, when the temperature of the resin film 30 being conveyed is measured, if the temperature sensor comes into contact with the resin film 30, the resin film 30 may be damaged. Therefore, in this embodiment, the temperature of a space within a distance of 5 mm from the measurement target region of the resin film 30 can be measured, and this can be adopted as the temperature of the measurement target region of the resin film 30.

  As shown in FIG. 3, the stretching zone 320 is a section until the interval between the inner clip 230 </ b> L and the outer clip 230 </ b> R gripping both end portions 30 </ b> L and 30 </ b> R of the resin film 30 starts to become constant again. In the stretching zone 320, the shapes of the inner guide rail 220L and the outer guide rail 220R are set such that the distance between the inner clip 230L and the outer clip 230R increases toward the downstream. In addition, as described above, in the present embodiment, the inner guide rail 220L and the outer guide rail 220R are configured to be bent with the traveling direction of the resin film 30 in the direction of the inner clip 230L. Therefore, in the stretching zone 320, the moving distance of the outer clip 230R is set longer than the moving distance of the inner clip 230L. The temperature of the stretching zone 320 is usually set so that the resin film 30 can be heated to a desired stretching temperature.

  The heat fixing zone 330 is a section in which the vehicle can travel while the distance between the outer gripper 110R and the inner gripper 110L is kept constant again downstream of the stretching zone 320. The temperature of the heat setting zone 330 is usually set so that the resin film 30 can be adjusted to a temperature lower than the stretching temperature.

Furthermore, in the present embodiment, as shown in FIG. 4, the ratio T _in between the tension T _in of the inner clip chain 210L at the inner grip start position 240L and the tension T _out of the outer clip chain 210R at the outer grip start position 240R. / T _out × 100 is within a predetermined range. Specifically, the tension ratio T _in / T _out × 100 is usually 80% or more, preferably 90% or more, more preferably 95% or more, and usually 120% or less, preferably 110% or less. More preferably, it is 105% or less. Such a tension ratio T _in / T _out × 100 can be within the above range by adjusting the position of the sprocket. By keeping the tension ratio T _in / T _out × 100 in the above range, the period λ (θ) and the amplitude A (θ) of the orientation angle θ of the obliquely stretched film 10 to be manufactured are within the desired ranges described above. Can fit. Furthermore, by keeping the tension ratio T _in / T _out × 100 in the above range, the transportability of the resin film 30 is usually improved, and thus the generation of scratches and wrinkles in the obliquely stretched film 10 can be suppressed.

  Using the manufacturing apparatus 100 described above, the first step of gripping both ends 30L and 30R of the resin film 30 with the inner clip 230L and the outer clip 230R, and the gripped resin film with the inner clip 230L and the outer clip 230R. By performing a manufacturing method including the second step of pulling and stretching, and the third step of releasing the stretched resin film 30 from the inner clip 230L and the outer clip 230R to obtain the obliquely stretched film 10 in this order, An obliquely stretched film 10 having an orientation angle θ having a desired period λ (θ) and amplitude A (θ) is manufactured. Specifically, it is as follows.

  In this manufacturing method, a long resin film 30 is fed from the feeding roll 20 and the fed resin film 30 is continuously supplied to the tenter stretching apparatus 200. As the resin film 30, a film made of the same resin as the obliquely stretched film 10 can be used. Such a resin film 30 can be manufactured by, for example, a cast molding method, an extrusion molding method, or an inflation molding method. Among these, the extrusion molding method is preferable because it has a small amount of residual volatile components and is excellent in dimensional stability.

  When the resin film 30 is supplied to the tenter stretching apparatus 200, the tenter stretching apparatus 200 connects both ends 30L and 30R of the resin film 30 to the inner clip 230L and the outer clip 230R at the entrance 240 of the tenter stretching apparatus 200. The process of sequentially grasping is performed (first process). Then, the tenter stretching apparatus 200 conveys the resin film 30 so as to pass through the oven 300 with both end portions 30L and 30R of the resin film 30 held by the inner clip 230L and the outer clip 230R.

  Specifically, the inner clip 230L grips one end 30L of the resin film 30 at the inner grip start position 240L. Further, the outer clip 230R grips the other end 30R of the resin film 30 at the outer grip start position 240R. Then, the resin film 30 gripped by the end portions 30L and 30R is transported as the inner clip 230L and the outer clip 230R travel and enters the oven 300. Here, the traveling speed of the inner clip 230L and the traveling speed of the outer clip 230R may be different, but are the same in terms of reducing the amplitude A (θ) of the orientation angle θ of the obliquely stretched film 10. Is preferred.

  When the resin film 30 enters the oven 300, the resin film 30 passes through the preheating zone 310 of the oven 300 as the inner clip 230L and the outer clip 230R travel as shown in FIG. In the preheating zone 310, a step of heating the resin film 30 to a predetermined preheating temperature is performed. The preheating temperature of the resin film 30 is usually higher than normal temperature, specifically, preferably 40 ° C. or higher, more preferably Tg + 5 ° C. or higher, particularly preferably Tg + 15 ° C. or higher, preferably Tg + 50 ° C. or lower. More preferably, it is Tg + 30 degrees C or less, Most preferably, it is Tg + 20 degrees C or less. By preheating at such a temperature, the molecules contained in the resin film 30 can be stably oriented by stretching.

  After passing through the preheating zone 310, the resin film 30 passes through the stretching zone 320 of the oven 300. In the stretching zone 320, the interval between the inner clip 230L and the outer clip 230R becomes wider toward the downstream. Therefore, in this extending | stretching zone 320, the process of extending | stretching the resin film 30 with the inner side clip 230L and the outer side clip 230R is performed (2nd process).

In the stretching zone 320, the inner clip 230L and the outer clip 230R travel so that the traveling direction of the resin film 30 is bent with the inner clip 230L facing inward. Therefore, the inner clip 230L and the outer clip 230R, which are opposed to the direction perpendicular to the traveling direction of the resin film 30 at the inlet portion 240 of the tenter stretching device 200, are arranged on the inner clip 230L in the section downstream from the stretching zone 320. Precedes the outer clip 230R (see dashed lines L _D1 , L _D2 and L _{D3 in} FIG. 4). Therefore, in the stretching zone 320, stretching in the oblique direction is performed with respect to the longitudinal direction of the obtained obliquely stretched film 10.

  At this time, the draw ratio is preferably 1.1 times or more, more preferably 1.2 times or more, particularly preferably 1.3 times or more, preferably 4.0 times or less, more preferably 3.0 times. Hereinafter, it is particularly preferably 2.0 times or less. By setting the draw ratio to be equal to or greater than the lower limit of the above range, the amplitude A (θ) of the orientation angle θ in the obliquely stretched film 10 can be controlled more accurately. Moreover, by making a draw ratio below the upper limit of the said range, a film fracture | rupture can be suppressed and a diagonally stretched film can be manufactured stably.

  The stretching temperature is preferably Tg + 3 ° C. or higher, more preferably Tg + 5 ° C. or higher, particularly preferably Tg + 8 ° C. or higher, preferably Tg + 15 ° C. or lower, more preferably Tg + 12 ° C. or lower, more preferably Tg + 10 ° C. or lower. By stretching at such a temperature, the molecules contained in the resin film 30 can be stably oriented by stretching, so that the obliquely stretched film 10 having a desired retardation can be obtained.

  After passing through the stretching zone 320, the resin film 30 passes through the heat setting zone 330 of the oven 300. In the heat setting zone 330, the process of setting the resin film 30 to a temperature range lower than the temperature of the resin film 30 in the stretching zone 320 is performed. By this step, the molecular state in the resin film 30 becomes stable, and the molecular orientation in the resin film 30 is fixed.

  The specific temperature of the resin film 30 in the heat setting zone 330 is preferably Tg-5 ° C or higher, more preferably Tg-2 ° C or higher, particularly preferably Tg ° C or higher, preferably Tg + 10 ° C or lower, more preferably. Tg + 5 ° C. or less, particularly preferably Tg + 2 ° C. or less. By maintaining the resin film 30 at such a temperature, the amplitude A (θ) of the orientation angle θ in the obliquely stretched film 10 can be effectively reduced.

  After passing through the heat setting zone 330, the resin film 30 goes out of the oven 300. And if the resin film 30 is conveyed to the exit part 250 of the tenter stretching apparatus 200, the process of releasing the resin film 30 from the inner clip 230L and the outer clip 230R and obtaining the obliquely stretched film 10 is performed (third process). . The obliquely stretched film 10 obtained in this way is subjected to an arbitrary process such as a trimming process as necessary, and then sent out downstream of the tenter stretching apparatus 200. The sent obliquely stretched film 10 is usually wound up and collected as a film roll 40.

According to the manufacturing method mentioned above, the diagonally stretched film 10 which has a slow axis in the diagonal direction which is neither parallel nor perpendicular | vertical to the longitudinal direction is obtained. The obliquely stretched film 10 is a film formed of the same resin as the resin film 30, and is a film stretched in one direction oblique to the longitudinal direction. In general, the orientation angle θ of the obliquely stretched film 10 is nonuniform with periodicity in the longitudinal direction. Here, in the manufacturing method described above, the tension T _in the inner clip chain 210L in the inner gripping start position 240L for gripping one end 30L of the resin film 30 in the first step, the other resin film 30 in the first step The ratio T _in / T _out × 100 with the tension T _out of the outer clip chain 210R at the outer grip start position 240R that grips the end 30R of the outer end 30R is adjusted to the predetermined range described above. Therefore, in the longitudinal direction of the obliquely stretched film 10 to be manufactured, the period λ (θ) and the amplitude A (θ) of the orientation angle θ can be within the desired ranges described above. The obliquely stretched film 10 having such an orientation angle θ having the period λ (θ) and the amplitude A (θ) has good accuracy of the orientation angle θ in the longitudinal direction of the obliquely stretched film 10 as described above. Therefore, it is possible to suppress variations in the orientation angle θ. Therefore, when such an obliquely stretched film 10 is applied to an image display device as a retardation film, color unevenness of an image of the image display device can be suppressed or contrast can be improved.
Furthermore, in the manufacturing method mentioned above, since generation | occurrence | production of an abrasion and a wrinkle can be suppressed normally, the planarity of the diagonally stretched film 10 manufactured can be made favorable.

  The manufacturing method according to the above-described embodiment may be further modified. For example, as the resin film 30, a film that has been subjected to a stretching process may be used instead of an unstretched film that has not been subjected to a stretching process. Thus, as a method of extending | stretching the resin film 30 before using for the manufacturing method which concerns on embodiment mentioned above, the roll method, the longitudinal stretch method of a float system, the lateral stretch method using a tenter stretch apparatus, etc. are used, for example. sell. Among these, in order to maintain the uniformity of thickness and optical characteristics, a float type longitudinal stretching method is preferable.

[5. Application of obliquely stretched film]
There is no restriction | limiting in the use of the diagonally stretched film mentioned above. The obliquely stretched film can be used as an optical film, for example, alone or in combination with other members. Among these, the obliquely stretched film is preferably used as a retardation film. Examples of the use of such a retardation film include a polarizing plate protective film, a viewing angle compensation film for a liquid crystal display device, a quarter wavelength plate provided on a circularly polarizing plate, and the like. Among them, since the advantage of the obliquely stretched film that it is easy to adjust the optical axis at the time of bonding with the polarizer can be effectively utilized, the obliquely stretched film is used in combination with the polarizer to produce a polarizing plate. It is preferable to use for.

  The polarizing plate includes a polarizer and an obliquely stretched film, and may further include an arbitrary member as necessary. As a polarizer, for example, a film of an appropriate vinyl alcohol polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol, a dyeing treatment with a dichroic substance such as iodine and a dichroic dye, a stretching treatment, a crosslinking treatment, etc. Are applied in an appropriate order and manner. Such a polarizer is capable of transmitting linearly polarized light when natural light is incident thereon, and in particular, a polarizer excellent in light transmittance and degree of polarization is preferable. The thickness of the polarizer is generally 5 μm to 80 μm, but is not limited thereto.

  The obliquely stretched film may be provided on both sides of the polarizer or may be provided on one side. Conventionally, a protective film has been provided on the surface of the polarizer. However, by combining an obliquely stretched film with a polarizer, the obliquely stretched film can serve as a protective film for the polarizer. Therefore, a polarizing plate provided with a combination of a polarizing film and a polarizer can omit a protective film that has been conventionally used, and can contribute to a reduction in thickness.

  The polarizing plate can be produced by laminating a long polarizer and a long obliquely stretched film by roll-to-roll with the longitudinal direction thereof being parallel. In bonding, an adhesive may be used as necessary. By producing using a long film, it is possible to efficiently produce a long polarizing plate.

  In addition to the polarizer and the obliquely stretched film, an arbitrary member may be provided on the polarizing plate. As an arbitrary member, the protective film for protecting a polarizer is mentioned, for example. Any transparent film can be used as the protective film. Among these, a resin film excellent in transparency, mechanical strength, thermal stability, moisture shielding properties and the like is preferable. Examples of such resins include acetate resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, alicyclic structure-containing polymer resins, (meth) acrylic resins, etc. Is mentioned.

  The long diagonally stretched film or the film cut out to a predetermined size from the long polarizing plate can be used as a component of an image display device such as a liquid crystal display device or an organic electroluminescence display device. In particular, as described above, since the amplitude A (θ) of the orientation angle θ is small, the film can be applied to a liquid crystal display device because an excellent effect of improving the viewing angle characteristics by optical compensation of the liquid crystal cell can be exhibited. Is preferred.

  Examples of the liquid crystal display device include those having liquid crystal cells of various driving methods. Liquid crystal cell driving methods include, for example, in-plane switching (IPS) mode, vertical alignment (VA) mode, multi-domain vertical alignment (MVA) mode, continuous spin wheel alignment (CPA) mode, and hybrid alignment nematic (HAN) Mode, twisted nematic (TN) mode, super twisted nematic (STN) mode, optically compensated bend (OCB) mode, and the like.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments shown below, and can be implemented with any modifications without departing from the scope of the claims and their equivalents.
In the following examples and comparative examples, “%” and “parts” representing amounts are based on weight unless otherwise specified. Further, the operations described below were performed in a normal temperature and pressure atmosphere unless otherwise specified.

[Evaluation method]
(Measurement method of orientation angle θ)
In the central portion of the manufactured long diagonally stretched film in the width direction, the orientation angle θ with respect to the longitudinal direction of the diagonally stretched film is determined by a parallel Nicol rotation method phase meter (“KOBRA-WIST-IE” manufactured by Oji Scientific Instruments). ) And measured online. This measurement was performed at a length of 500 m or more in the longitudinal direction for frequency analysis. From the fixed point measurement data of the orientation angle θ thus measured, frequency analysis was performed using spreadsheet software, and the period λ (θ) and amplitude A (θ) of the orientation angle θ in the longitudinal direction of the obliquely stretched film were calculated. . Further, the average orientation angle θ and the variation Δθ in the longitudinal direction were calculated from the fixed point measurement data of the orientation angle θ.

(Measurement method of retardation)
The in-plane retardation Re and thickness direction retardation Rth of the obliquely stretched film in the center in the width direction of the produced long obliquely stretched film were measured using a parallel Nicol rotation method phase difference meter (manufactured by Oji Scientific Instruments). KOBRA-WIST-IE "). The average value of the in-plane retardation Re and the average value of the thickness direction retardation Rth were calculated from the fixed point measurement data of the in-plane retardation Re and the thickness direction retardation Rth thus measured.

(Measurement method of thickness)
Using a snap gauge (“ID-C112BS” manufactured by Mitutoyo Corporation), the thickness was measured at intervals of 5 cm in the width direction of the film, and the average value was taken as the thickness of the film.

(Evaluation method of color unevenness of liquid crystal display device)
A long polarizing plate (“HLC2-5618S” manufactured by Sanlitz, thickness 180 μm, width 1340 mm) having a transmission axis in the width direction was prepared. This long polarizing plate and the manufactured long slanting stretched film were bonded together with a roll-to-roll with their longitudinal directions parallel to each other to obtain a wound body of a circular polarizing plate having a width of 1340 mm. .

  A circularly polarizing plate was pulled out from this wound body and cut into a rectangular shape to obtain a circularly polarizing plate sample. This circularly polarizing plate sample was replaced with a polarizing plate on the side opposite to the viewing side of the reflective liquid crystal display device in IPS (in-plane switching) mode. At this time, the circularly polarizing plate sample was provided so that the surface on the obliquely stretched film side faced the liquid crystal cell.

Images were displayed on the liquid crystal display device thus produced, and the displayed images were observed visually from the front and tilt directions of the screen. Here, the front direction of the screen represents the normal direction of the screen, and the tilt direction of the screen represents a direction in which the polar angle φ with respect to the screen is 0 ° <φ <90 °. From the observed results, the color unevenness of the liquid crystal display device was evaluated according to the following criteria.
“Good”: No color unevenness is observed over the entire width, and the display is good. Moreover, the hue visually recognized by observing the screen from the tilt direction and the color visually recognized by observing the screen from the front direction are the same, and no discoloration of the screen is observed depending on the observation direction.
“Bad”: Color unevenness was observed on the screen. Further, when the screen is observed from the tilt direction, some color unevenness is observed in the screen.

[Example 1]
(1.1. Production of resin film)
A pellet of thermoplastic resin containing a norbornene polymer which is a kind of alicyclic structure-containing polymer (“ZEONOR 1420” manufactured by Nippon Zeon Co., Ltd., glass transition point 137 ° C.) was dried at 100 ° C. for 5 hours. The pellets were supplied to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, and extruded from a T-die onto a casting drum. The extruded resin was cooled by a casting drum to obtain a long unstretched film having a thickness of 55 μm and a width of 1500 mm. The unstretched film thus obtained was stretched in the longitudinal direction at a stretching temperature of 145 ° C. and a stretching ratio of 1.5 times to obtain a long longitudinally stretched film having a thickness of 45 μm and a width of 1000 mm.

(1.2. Production of obliquely stretched film)
As shown in FIGS. 3 and 4, a manufacturing apparatus 100 including a tenter stretching apparatus 200 including an inner clip chain 210 </ b> L and an outer clip chain 210 </ b> R and an oven 300 covering the tenter stretching apparatus 200 was prepared. The longitudinally stretched film was continuously supplied as the resin film 30 to the tenter stretching apparatus 200, and oblique stretching was performed as described in the second embodiment. The stretching conditions were a stretching ratio of 2.0 times, a stretching temperature of 142 ° C., and a tension ratio T _in / T _out × 100 of the inner clip chain 210L and the outer clip chain 210R was 105%. Thereby, the long diagonally stretched film 10 with a width of 1330 mm was obtained.
The obtained obliquely stretched film 10 was evaluated by the method described above.

[Example 2]
(2.1. Production of resin film)
A pellet of thermoplastic resin containing a norbornene polymer which is a kind of alicyclic structure-containing polymer (“ZEONOR 1420” manufactured by Nippon Zeon Co., Ltd., glass transition point 137 ° C.) was dried at 100 ° C. for 5 hours. The pellets were supplied to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, and extruded from a T-die onto a casting drum. The extruded resin was cooled by a casting drum to obtain an unstretched film having a thickness of 70 μm and a width of 1350 mm.

(2.2. Production of obliquely stretched film)
As shown in FIGS. 3 and 4, a manufacturing apparatus 100 including a tenter stretching apparatus 200 including an inner clip chain 210 </ b> L and an outer clip chain 210 </ b> R and an oven 300 covering the tenter stretching apparatus 200 was prepared. The unstretched film was continuously supplied as the resin film 30 to the tenter stretching apparatus 200, and oblique stretching was performed as described in the second embodiment. The stretching conditions were a stretching ratio of 1.5 times, a stretching temperature of 153 ° C., and a tension ratio T _in / T _out × 100 of the inner clip chain 210L and the outer clip chain 210R was 99%. As a result, a long diagonally stretched film 10 having a width of 1490 mm was obtained.
The obtained obliquely stretched film 10 was evaluated by the method described above.

[Comparative Example 1]
A long oblique stretched film was produced and evaluated in the same manner as in Example 1 except that the tension ratio T _in / T _out × 100 of the inner clip chain and the outer clip chain was changed to 125%.

[Comparative Example 2]
A long oblique stretched film was produced and evaluated in the same manner as in Example 2 except that the tension ratio T _in / T _out × 100 of the inner clip chain and the outer clip chain was changed to 75%.

[result]
The results of the examples and comparative examples are shown in Table 1 below. In Table 1, the meanings of the abbreviations are as follows.
Longitudinal stretch: Longitudinal stretched film Unstretched: Unstretched film Re: Average value of in-plane retardation of obliquely stretched film Rth: Average value of retardation in thickness direction of obliquely stretched film

[Consideration]
As can be seen by comparing the Examples and Comparative Examples, the tension ratio T _in / T _out × 100 of the inner clip chain and the outer clip chain of the tenter stretching device is within a predetermined range, so that The amplitude A (θ) of the orientation angle θ can be less than 0.100. Thereby, since the orientation angle accuracy of the orientation angle θ of the obliquely stretched film is enhanced, the variation Δθ of the orientation angle θ of the obliquely stretched film can be reduced. Accordingly, it is possible to improve color unevenness of a liquid crystal display device manufactured using the obliquely stretched film.

DESCRIPTION OF SYMBOLS 10 Obliquely stretched film 10A Slow axis 100 Obliquely stretched film manufacturing apparatus 200 Tenter stretching apparatus 210L Inner clip chain 210R Outer clip chain 220L Inner guide rail 220R Outer guide rail 230L Inner clip 230R Outer clip 240 Inlet part 240L of inner part of tenter stretching apparatus Gripping start position 240R Outer gripping start position 250 Outlet portion of tenter stretching apparatus 250L Inner opening position 250R Outer opening position 300 Oven 310 Preheating zone 320 Stretching zone 330 Thermal fixation zone 340 Septum

Claims (9)

It is a long oblique stretched film having a slow axis in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction,
The orientation angle of the obliquely stretched film has a period of less than 2000 mm in the longitudinal direction,
An obliquely stretched film having an amplitude of an orientation angle in the period of less than 0.1 °.   The obliquely stretched film according to claim 1, wherein an average of the orientation angles with respect to the longitudinal direction of the obliquely stretched film is 40 ° or more and 50 ° or less.   The diagonally stretched film of Claim 1 or 2 which has a width | variety of 1000 mm-1500 mm.   The diagonally stretched film according to any one of claims 1 to 3, having a thickness of 10 µm to 100 µm.   The diagonally stretched film according to any one of claims 1 to 4, comprising a thermoplastic resin.   The diagonally stretched film according to any one of claims 1 to 5, which is a retardation film. An inner clip chain having a plurality of inner clips capable of gripping one end of a long resin film, and an outer clip chain having a plurality of outer clips capable of gripping the other end of the resin film Stretching while transporting the resin film by a stretching device provided, a manufacturing method for producing a long oblique stretched film,
A first step of gripping both ends of the resin film with the inner clip and the outer clip;
A second step of stretching the resin film with the inner clip and the outer clip while running the inner clip and the outer clip so that the traveling direction of the resin film bends with the inner clip facing inward;
A third step of releasing the resin film from the inner clip and the outer clip to obtain the obliquely stretched film having a slow axis in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the obliquely stretched film. ,
A tension T _in the inner clip chain at a position for gripping one end of the resin film in the first step, the tension of the outer clip chain at a position for gripping the other end of the resin film in the first step the ratio _T in _{/ T out} × 100 with T _out is 80% to 120%, the production method of the oblique stretching the film.   The manufacturing method of the diagonally stretched film of Claim 7 whose draw ratio is 1.1 time-4.0 time.   The method for producing an obliquely stretched film according to claim 7 or 8, wherein in the second step, the traveling speed of the inner clip and the traveling speed of the outer clip are the same.

Images