JP2006235085A - Oriented polyolefin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oriented polyolefin film in which the change of optical characteristics under high temperature is improved while using alicyclic polyolefin having a glass transition temperature similar to the conventional one, and also to provide a polarizing plate which has the oriented polyolefin film and is excellent in visibility and durability, and a liquid crystal display device having the oriented polyolefin film. <P>SOLUTION: The oriented polyolefin film is made by bi-axially stretching alicyclic polyolefin resin which has a glass transition temperature of 130 to 150 °C, and a molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of 1.2 to 3.5, and also has the change of retardation (Rth) expressed by the following expression upon the exposure for 72 hours under the condition of 80 °C of ≤2%; 100×[Rth(before treatment)-Rth(after treatment)]/Rth(before treatment). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a stretched polyolefin film comprising an alicyclic polyolefin resin and having little change in optical properties even when exposed to a high temperature environment, a method for producing the stretched polyolefin film, and a polarized light having excellent stability of an image having the stretched polyolefin film. The present invention relates to a plate and a liquid crystal display device.

In a liquid crystal display device, a retardation film is widely used to compensate for a retardation due to birefringence of a liquid crystal cell. Various retardation films have been proposed so far, and stretched films obtained by orienting transparent resins by stretching have been widely used. Examples of the stretched film include a film made of a polycarbonate resin having excellent heat resistance and the like, and in particular, a film made of an alicyclic polyolefin resin having excellent heat resistance, low hygroscopicity, and a small photoelastic constant has recently attracted attention. I'm bathing.
By the way, due to the nature of the resin film as described above, when it is exposed to a high temperature range for a long time, the optical characteristics change, and an undesirable phenomenon of affecting the image characteristics occurs. Such a phenomenon is unavoidable to some extent due to the relaxation phenomenon of the polymer in the production method of expressing optical characteristics by stretching the polymer film. An alicyclic polyolefin resin with a small photoelastic constant is a material that has a small change in optical properties due to relaxation compared to polycarbonate and the like, and has an advantage over the above-mentioned phenomenon. However, the demand for image quality of liquid crystal display devices is increasing year by year. The severity was increasing and further improvements were required. Due to the nature of this phenomenon due to the relaxation phenomenon, it is effective to raise the Tg of the polymer with respect to 130 to 150 ° C. of general alicyclic polyolefins and polycarbonates. This is not preferable for the liquid crystal display industry where the cost requirement is strict because the film processing cost is increased.
Although a film such as Patent Document 1 is disclosed as an optically anisotropic body with relatively little deterioration in display characteristics (change in in-plane retardation) even when used at high temperatures, it still lacks stability at high temperatures. It was. In particular, when the display screen is observed from an oblique direction, a problem that the display quality is lowered has become apparent.

JP-A-8-278406

  Accordingly, an object of the present invention is to provide a stretched polyolefin film that has improved changes in optical properties at high temperatures while using an alicyclic polyolefin having a glass transition temperature that is not different from that of the conventional one, and further, visibility and durability having the same. It is providing the polarizing plate and liquid crystal display device which are excellent in property.

  As a result of diligent research to solve the above-mentioned problems, the present inventor has obtained a retardation film that can achieve the above object by appropriately selecting the stretching conditions when stretching a film made of a transparent alicyclic polyolefin resin. The present invention has been found out and can be completed.

Thus, according to the present invention,
(1) Biaxially stretching an alicyclic polyolefin resin film having a glass transition temperature of 130 to 150 ° C. and a molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of 1.2 to 3.5 A stretched polyolefin film characterized in that a value (ΔRth) represented by the following formula when exposed at 80 ° C. for 72 hours is 2 or less,
ΔRth = 100 × [Rth (before processing) −Rth (after processing)] / Rth (before processing)
(2) When the longitudinal stretch ratio is Rm and the lateral stretch ratio is Rt, the film of the alicyclic polyolefin resin is stretched longitudinally with a roll stretching machine at Rm <1.3, and then Rm + 0.3 <Rt. A method for producing a stretched polyolefin film, characterized by performing transverse stretching with a tenter stretching machine
(3) The method for producing a stretched polyolefin film according to (2), wherein the transverse stretching temperature is 5 ° C. or more higher than the longitudinal stretching temperature.
(4) The method for producing a stretched polyolefin film according to (2), wherein the take-up tension at the exit of the tenter stretching machine is 200 N / m,
(5) The method for producing a stretched polyolefin film according to (2), wherein the tenter chain tension of the tenter stretching machine is 1960 N or less,
(6) A polarizing plate comprising the stretched polyolefin film of (1),
(7) A display device comprising the stretched polyolefin film of (1),
Is to provide.

  The stretched polyolefin film of the present invention is widely applicable to a liquid crystal display device and an organic EL display device as a retardation plate that maintains good optical properties over a long period of time at high temperature and high humidity.

  The stretched polyolefin film of the present invention is obtained by biaxially stretching a film made of a transparent alicyclic polyolefin resin.

  The alicyclic polyolefin resin used in the present invention is a polyolefin resin having an alicyclic structure in the main chain and / or side chain, and contains an alicyclic structure in the main chain from the viewpoint of mechanical strength, heat resistance and the like. Polyolefin resins are preferred.

  Examples of alicyclic structures include saturated alicyclic hydrocarbon (cycloalkane) structures and unsaturated alicyclic hydrocarbon (cycloalkene) structures. From the viewpoint of mechanical strength and heat resistance, cycloalkane structures and cycloalkane structures can be used. Alkene structures are preferred, with cycloalkane structures being most 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 in the mechanical strength, The properties of heat resistance and film formability are highly balanced and suitable. The proportion of the repeating unit containing the alicyclic structure in the alicyclic polyolefin resin used in the present invention may be appropriately selected according to the purpose of use, preferably 55% by weight or more, more preferably It is 70% by weight or more, particularly preferably 90% by weight or more. When the ratio of the repeating unit having an alicyclic structure in the alicyclic polyolefin resin is within this range, it is preferable from the viewpoint of the transparency and heat resistance of the stretched polyolefin film.

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

  Examples of the norbornene-based resin include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening copolymer of a monomer having a norbornene structure and another monomer, a hydride thereof, and a norbornene structure. An addition polymer of a monomer having a monomer, an addition copolymer of a monomer having a norbornene structure and another monomer, or a hydride 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 monomers having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7-diene. (Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4.0. 1 ^2,5 . ^{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.

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.

  A hydrogenated product of a ring-opening polymer of a monomer having a norbornene structure, a hydrogenated product of a ring-opening copolymer of a monomer having a norbornene structure and another monomer capable of ring-opening copolymerization thereof, Hydrogenated products of addition polymers of monomers having a norbornene structure, and hydrogenated products of addition copolymers of monomers having a norbornene structure and other monomers capable of addition copolymerization with these A known hydrogenation catalyst containing a transition metal such as nickel or palladium is added to the polymer solution, and the carbon-carbon unsaturated bond is preferably hydrogenated by 90% or more.

Among norbornene-based resins, as repeating 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 content of these repeating units is 90% by weight or more based on the entire repeating units of the norbornene-based resin, and the content ratio of X and the content ratio of Y Is preferably 100: 0 to 40:60 by weight ratio of X: Y. By using such a resin, 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 molecular weight of the alicyclic polyolefin resin used in the present invention is appropriately selected according to the purpose of use, but it is determined by gel permeation chromatography using cyclohexane (toluene when the polymer resin does not dissolve) as a solvent. The weight average molecular weight (Mw) in terms of isoprene or polystyrene 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 moldability of the film are highly balanced and suitable.

  The glass transition temperature of the alicyclic polyolefin resin may be appropriately selected according to the purpose of use, but is preferably in the range of 130 to 150 ° C, more preferably 135 to 145 ° C. When the glass transition temperature is lower than 130 ° C., the durability at high temperatures is deteriorated. When the glass transition temperature is higher than 150 ° C., the durability is improved, but normal stretching is difficult.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the alicyclic polyolefin resin is 1.2 to 3.5, preferably 1.5 to 3.0, more preferably 1.8 to 2. .7. When this value exceeds 3.5, the low molecular component increases, so the component with a short relaxation time increases, and even when the film has the same in-plane retardation at first glance, relaxation at high temperature exposure increases in a short time. Therefore, there is a possibility that the later-described ΔRth value exceeds 2. On the other hand, those having a molecular weight distribution lower than 1.2 lead to a decrease in resin productivity and an increase in cost, which is not practical as a display member.

Alicyclic polyolefin resin used in the present invention preferably has an absolute value of the photoelastic coefficient is ¹⁰ × 10 -12 ^{Pa -1} or less, more preferably 7 × ¹⁰ -12 ^{Pa -1} or less, 4 It is particularly preferable that it is 10 ⁻¹² Pa ⁻¹ or less. The photoelastic coefficient C is expressed as follows: birefringence is Δn and stress is σ.
C = Δn / σ
It is a value represented by If the photoelastic coefficient of the alicyclic polyolefin resin exceeds 10 × 10 ⁻¹² Pa ⁻¹ , the in-plane retardation of the stretched film may vary greatly.

  In the present invention, the alicyclic polyolefin resin preferably contains substantially no particles. Here, “substantially free of particles” means that even if particles are added to a film made of an alicyclic polyolefin resin, the amount of increase in haze from the non-added state is in the range of 0.05% or less. Means acceptable. In particular, since alicyclic polyolefin resin lacks affinity with many organic particles and inorganic particles, when an alicyclic polyolefin resin film to which particles exceeding the above range are added is stretched, voids are easily generated. As a result, the haze may be significantly reduced.

  You may add well-known additives, such as antioxidant, a heat stabilizer, a light stabilizer, and an ultraviolet absorber, to the alicyclic polyolefin resin used for this invention in the range which does not impair the effect of invention.

There is no restriction | limiting in particular as a method of manufacturing the film which consists of alicyclic polyolefin resin used for this invention, For example, conventionally well-known methods, such as a solution casting method, the injection molding method, and a melt extrusion method, are mentioned. Among these, the melt extrusion method that does not use a solvent can reduce the amount of residual volatile components efficiently, and is preferable from the viewpoints of the global environment and work environment, and excellent manufacturing efficiency.
Examples of the melt extrusion method include an inflation method using a die, but a method using a T die is preferable in terms of excellent productivity and thickness accuracy.

  The stretched polyolefin film of the present invention preferably has a total light transmittance of 80% or more in terms of 1 mm thickness. More preferably, the total light transmittance is 90% or more. In addition, the stretched polyolefin film of the present invention preferably has a haze of 0.3% or less at a thickness of 1 mm. More preferably, the haze is 0.2% or less. If the haze exceeds 0.3%, the transparency of the stretched polyolefin film is lowered and may not be applied to the retardation film.

In the stretched polyolefin film of the present invention, the values of in-plane retardation Re and thickness direction retardation Rth are appropriately selected from the range of about 40 to 120 nm for Re and about 100 to 300 nm for Rth, depending on the design of the display. Note that Re in the present invention is the refractive index nx in the slow axis direction of the film, the refractive index ny in the direction perpendicular to the slow axis in the plane, the refractive index nz in the thickness direction, and the average thickness Tw of the film. to a value defined by _{(nx-ny) × T w} , Rth in the present invention is a value defined by ((nx + ny) / 2 -nz) × T w.

The average thickness of the stretched polyolefin film of the present invention is preferably 60 to 100 μm, more preferably 65 to 95 μm, and particularly preferably 70 to 90 μm from the viewpoint of mechanical strength and the like.
The thickness variation is preferably within ± 3% of the average thickness over the longitudinal direction and the width direction. By setting the thickness variation within the above range, variations in optical characteristics such as Re of the stretched polyolefin film of the present invention can be reduced.

The content of the residual volatile component in the stretched polyolefin film of the present invention is not particularly limited, but is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, and further preferably 0.02% by weight or less. . If the content of the residual volatile component exceeds 0.1% by weight, the optical properties of the stretched polyolefin film of the present invention may change over time. By adjusting the content of the volatile component to the above range, the dimensional stability can be improved, the change with time of Re and Rth of the stretched polyolefin film can be reduced, and further the polarizing plate comprising the stretched polyolefin film of the present invention. And deterioration of the liquid crystal display device can be suppressed, and the display on the display can be kept stable and good 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 stretched polyolefin film of the present invention, and examples thereof include a residual monomer and a solvent. The content of volatile components can be quantified by analyzing the stretched polyolefin film of the present invention by gas chromatography as the sum of substances having a molecular weight of 200 or less.

The saturated water absorption of the stretched polyolefin film of the present invention 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 in the above range, the time-dependent change in Re and Rth of the stretched polyolefin film of the present invention can be reduced, and further, the deterioration of the polarizing plate and liquid crystal display device provided with the stretched polyolefin film of the present invention is suppressed. The display on the display can be kept stable and good for a long time.
The saturated water absorption is a value expressed as a percentage of the mass of the test piece before immersion after the test piece is immersed in water at a constant temperature for a fixed time. Usually, it is measured by immersing in 23 ° C. water for 24 hours.
The saturated water absorption in the stretched polyolefin film of the present invention can be adjusted to the above value by, for example, reducing the amount of polar groups in the thermoplastic norbornene-based resin, but is preferably a resin having no polar groups. It is desirable to be.

  The stretched polyolefin film of the present invention has a Re variation within 10 nm, preferably within 5 nm, and more preferably within 2 nm. By setting the Re variation within the above range, it is possible to improve the display quality when used as a retardation film for a liquid crystal display device. Here, the variation in Re is the maximum value of Re when the light incident angle is 0 ° (when the incident light beam and the stretched polyolefin film surface of the present invention are orthogonal to each other) and the Re is measured in the width direction of the film. It is the difference from the minimum value.

The stretched polyolefin film of the present invention preferably has a value (ΔRe) represented by the following formula of 2 or less when exposed to 80 ° C. for 72 hours.
ΔRe = 100 × [Re (before processing) −Re (after processing)] / Re (before processing)
(Re (before treatment) is an average value obtained by measuring the in-plane retardation before exposure for 72 hours under the condition of 80 ° C. at five arbitrary points, and Re (after treatment) is 80 (This is the average value obtained by measuring the in-plane retardation after being exposed for 72 hours under the condition of 5 ° C. at five points in any place.)
When a film having ΔRe exceeding 2 is used for a display device, there is a risk that a change in color depending on the viewing direction may occur on the display screen at high temperatures.

The stretched polyolefin film of the present invention has a value (ΔRth) represented by the following formula of 2 or less when exposed to 80 ° C. for 72 hours.
ΔRth = 100 × [Rth (before processing) −Rth (after processing)] / Rth (before processing)
(In addition, Rth (before treatment) is an average value obtained by measuring the thickness direction retardation before exposure for 72 hours under the condition of 80 ° C. at an arbitrary place, and Rth (after treatment) (This is an average value obtained by measuring five points of retardation in the thickness direction after exposure for 72 hours at 80 ° C.)
When a film having ΔRth exceeding 2 is used for a display device (particularly, a liquid crystal display device in a vertical alignment mode), the viewing angle of the display screen decreases at a high temperature range.

  The stretched polyolefin film of the present invention is preferably long. The long shape means one having a length of at least about 5 times the width direction of the film, preferably 10 times or more, and specifically wound in a roll shape. It has a length that can be stored or transported.

  As a method for producing the stretched polyolefin film of the present invention, using a difference in peripheral speed between rolls using a roll stretching machine, uniaxially stretching in the longitudinal direction by IR heating method, float method, etc., and then tenter stretching A method of uniaxial stretching in the transverse direction using a machine can be applied.

The method for producing a stretched polyolefin film of the present invention is such that when the longitudinal stretch ratio is Rm and the lateral stretch ratio is Rt, the alicyclic polyolefin resin film is rolled with Rm <1.3, preferably Rm <1.2. After performing longitudinal stretching at, transverse stretching is performed with a tenter stretching machine at Rm + 0.3 <Rt, preferably Rm + 0.4 <Rt. Further, the transverse stretching temperature is preferably 5 ° C. or more higher than the longitudinal stretching temperature, more preferably 10 ° C. or more.
In this case, although the detailed mechanism is unknown, in the longitudinal stretching of the former stage, a large orientation is obtained at a low stretching ratio to suppress a decrease in thickness, and in the lateral stretching of the latter stage, high temperature and high magnification stretching are performed as described above. It is considered that a component having a short relaxation time can be removed. (Film formation by high-temperature and high-magnification stretching makes it possible to create a product in a relaxed state with a relatively short relaxation time among the relaxed components of the stretched molecular chain, resulting in a long relaxation time. (It is estimated that the ingredients can be left in the film.)
By stretching the film of the alicyclic polyolefin resin under the above conditions, ΔRth of the stretched polyolefin film of the present invention can be made 2 or less.

  In the method for producing a stretched polyolefin film of the present invention, the take-up tension at the exit of the tenter stretching machine is preferably 200 N / m or less, and more preferably 180 N / m. By setting the take-up tension within the above range, it is considered that the film during transverse stretching can be easily relaxed particularly in the flow direction, and the components having a short relaxation time can be removed. The ΔRth of the polyolefin film can be 2 or less. The take-up tension can be adjusted by a take-up roll installed at the rear of the production line from the location where the film is stretched. The take-up roll is a well-known roll for taking up the film sent out from the tenter stretching machine, and is desirably usable for cooling. There may be one take-up roll or a plurality of take-up rolls. The take-up tension can be adjusted by known process control, for example, PID control. The control period is usually 3 to 30 minutes, preferably 5 to 15 minutes.

  In the method for producing a stretched polyolefin film of the present invention, the tension of the tenter chain described below is preferably 1960 N or less, and more preferably 1700 N or less. By setting the tenter chain tension within the above range, it is considered that the stretched film can be easily relaxed particularly in the width direction, and the component having a short relaxation time can be removed. The ΔRth of the film can be made 2 or less. The tenter chain tension can be adjusted by moving the position of the shaft fixing base of the sprocket on the film entrance side or the exit side of the tenter stretching machine. At this time, the tenter chain tension is increased when the distance between the inlet sprocket shaft and the outlet sprocket shaft is increased, and the tenter chain tension is relaxed when the distance is closer to each other. The preparation of the tenter chain tension can be carried out by known process control as in the adjustment of the take-up tension, and the control cycle is usually 3 to 30 minutes, preferably 5 to 15 minutes.

As shown in FIGS. 1 and 2, the tenter stretching machine is equipped with an oven 1 for heating the film, a plurality of pairs of left and right grips (not shown) for gripping both ends in the film width direction, and grips. The unit chain 8 (only a part of the unit chain (8a1 to 8a4 and 8b1 to 8b4) is shown in FIG. 2) and a pair of left and right guide rails 7 for guiding the travel of the unit chain (gripping tool) are provided. Yes. The unit chains are connected in a closed curve shape to form a pair of left and right connected bodies (hereinafter referred to as a tenter chain 2).
The tenter chains are respectively wound around sprockets 3 and 4 provided on the film entrance side and the exit side of the tenter stretching machine. As the sprocket rotates synchronously with an external drive device, the tenter chain moves on the guide rail (in the direction of the arrows in FIGS. 1 and 2). In the traveling process of the tenter chain, the gripping tool holds both ends in the film width direction on the film entrance side of the tenter stretching machine, and the film can be stretched by moving along the guide rail.
The oven can be divided into a plurality of blocks as necessary, and the atmospheric temperature of each block can be adjusted as necessary. Although the number of gripping tools depends on the length of the line, it is generally several hundreds on one side.

  In the method for producing a stretched polyolefin film of the present invention, the stretched film is preferably heat-treated for 24 hours or more at a temperature of Tg-30 ° C. or less of the alicyclic polyolefin resin film. By performing the heat treatment in the above-mentioned range, it is considered that components that can be easily relaxed can be removed more effectively, and ΔRth of the stretched polyolefin film of the present invention can be made 2 or less. Since such processing causes a decrease in Re and Rth, it must be processed with care, such as setting Re and Rth before processing higher than the target. The heat treatment can be performed by using a general constant temperature and humidity chamber.

  If necessary, the surface of the stretched polyolefin film of the present invention can be subjected to a surface treatment. Examples of the surface treatment include glow discharge treatment, corona discharge treatment, ultraviolet treatment, and flame treatment. By surface-treating, for example, when used as a polarizing plate protective film, adhesion with a polarizer can be improved.

  The polarizing plate of the present invention includes the stretched polyolefin film of the present invention on at least one surface of the polarizing film. The stretched polyolefin film of the present invention may be laminated on both sides of the polarizing film or on one side, and the number of laminations is not particularly limited, and two or more may be laminated. Moreover, as a lamination | stacking method, although it is not an essential method, it can laminate | stack using an adhesive agent. Another member may be interposed between the stretched polyolefin film and the polarizing film as long as the characteristics of the present invention are not impaired.

  For the polarizing film, a film made of a suitable vinyl alcohol polymer such as polypinyl alcohol or partially formalized polyvinyl alcohol, etc., dyeing treatment with a dichroic substance such as iodine or dichroic dye, 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 polarizing film is generally 5 to 80 μm, but is not limited thereto.

  Since the stretched polyolefin film of the present invention can be easily manufactured and highly compensated for birefringence, it can be used alone or in combination with other members as a retardation plate or a viewing angle compensation film. An EL display device, a plasma display device, an FED (field emission) display device, an SED (surface electric field) display device, or the like can be provided. Examples of the liquid crystal display device include an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, a continuous spin wheel alignment (CPA) mode, a hybrid alignment nematic (HAN) mode, Examples include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, and an optically compensated bend (OCB) mode. Among these, the viewing angle compensation effect is particularly large for the VA mode liquid crystal display device.

  In the liquid crystal display device, when forming the liquid crystal display device, 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 are arranged in one or more layers at appropriate positions. can do. Examples of 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
Measure 50 points in the plane using Mitutoyo Corporation Snap Gauge ID-C112BS, and use the average value as the thickness.
(2) Glass transition temperature Using DSC-6600 manufactured by Seiko Instruments Inc., measurement is performed at a sample weight of 10 mg and a temperature increase rate of 10 ° C / min.
(3) Re and Rth
Using KOBRA-21ADH manufactured by Oji Scientific Co., Ltd., five points near the center are measured in the width direction of the film, and the average value is taken as the measured value.
(4) Take-up tension In the configuration shown in Fig. 3, a free roll is installed between the tenter stretching machine and the take-up roll, and a load cell (LM-10PD, manufactured by Mitsubishi Electric Corporation) is attached to this free roll. The load N1 applied to the free roll from the film is measured. Further, a load N2 obtained by vector-decomposing N1 in the running direction of the film is obtained, and a value obtained by dividing N2 by the film width is taken as a take-up tension.
(5) Tenter chain tension Load cells (LM-10PD, manufactured by Mitsubishi Electric Corporation) are attached to the left and right sprockets of the tenter stretching machine, and the load N applied to the sprockets during film stretching is measured. The average value is calculated.
(6) Display characteristics of liquid crystal display device An image of a liquid crystal display device incorporating a stretched film is held in a thermostatic bath at 80 ° C. for 72 hours, and the image display before and after is visually observed and compared.

Example 1
After drying pellets of ZEONOR1420 (made by Nippon Zeon Co., Ltd.), which is a norbornene resin, at 100 ° C. for 5 hours, the pellets are fed to an extruder by a conventional method and melted at 250 ° C. By discharging, an unstretched film a-1 having a thickness of 150 μm was obtained. Subsequently, the unstretched film a-1 was stretched 1.2 times in the longitudinal direction at a temperature of 143 ° C. by a longitudinal stretching machine using a float system between rolls, and this was further used by a tenter method. The biaxially stretched film A-1 was obtained by stretching it 1.8 times in the transverse direction at a temperature of 150 ° C. while supplying the transverse stretching machine and adjusting the take-up tension and the tenter chain tension. Table 1 shows the physical properties and evaluation results of the obtained stretched film.
The stretched film A-1 and a polarizing plate having a transmission axis in the longitudinal direction (manufactured by Sanlitz, HLC2-5618S, thickness 180 μm) were laminated by a roll-to-roll method to obtain a roll of an optical element. At this time, lamination was performed so that the slow axis of the stretched film and the absorption axis of the polarizing plate were almost perpendicular. The optical element cut out from the wound body is replaced with a polarizing plate on the viewing side of a commercially available vertical alignment (VA) mode liquid crystal display device, and is incorporated so that the laminate is disposed on the liquid crystal cell side. ) The evaluation results are shown in Table 2.

(Comparative Example 1)
By the same means as in Example 1, an unstretched film b-2 having a thickness of 130 μm was obtained. Furthermore, a stretched film B-1 was obtained in the same manner as in Example 1 except that the production conditions during transverse stretching were changed. In addition, a VA mode liquid crystal display device (B) was obtained in the same manner as in Example 1. All evaluation results are shown in Tables 1 and 2.

From the results shown in Tables 1 and 2, the following can be understood.
The film of Example 1 produced by the method of the present invention has a small change in Rth even in a high temperature range, and a small change in Rth, so when confirming the display performance of a liquid crystal display device using this, Even in a high temperature range, there is no color change particularly when the screen is observed from an oblique direction, and the display characteristics are good.
On the other hand, a comparison was made in which transverse stretching was performed at a ratio lower than (longitudinal stretching ratio +0.3) times, the take-up tension exceeded 200 N / m, and the tenter chain tension exceeded 1960 N. The film of Example 1 has a large change in Re and Rth in the high temperature range, and when this is used for a liquid crystal display device, the display performance is poor in the high temperature range.

It is explanatory drawing of a tenter drawing machine. It is explanatory drawing of the tenter chain and guide rail of a tenter stretching machine. It is explanatory drawing of the measurement of the take-up tension of the film of a tenter drawing machine exit.

Explanation of symbols

1 Oven 2 Tenter chain (unit chain connection)
DESCRIPTION OF SYMBOLS 3 Entrance side sprocket 4 Outlet side sprocket 5 Film before stretching (film entrance side) 6 Film after stretching (film exit side) 7 Guide rail 8 Unit chain 9 Film gripped by gripping tool mounted on unit chain 10 Tenter Stretching machine 11 Free roll 12 Free roll (Load cell installed)
13 Stretched polyolefin film

Claims (7)

A film of an alicyclic polyolefin resin having a glass transition temperature of 130 to 150 ° C. and a molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of 1.2 to 3.5 is biaxially stretched to 80 ° C. A stretched polyolefin film having a value (ΔRth) represented by the following formula of 2 or less when exposed for 72 hours under the above conditions:
ΔRth = 100 × [Rth (before processing) −Rth (after processing)] / Rth (before processing) When the longitudinal draw ratio is Rm and the transverse draw ratio is Rt, the alicyclic polyolefin resin film is stretched longitudinally with a roll stretching machine at Rm <1.3, and then tenter-stretched with Rm + 0.3 <Rt. A method for producing a stretched polyolefin film, wherein the transverse stretching is performed by a machine. The method for producing a stretched polyolefin film according to claim 2, wherein the transverse stretching temperature is higher by 5 ° C or more than the longitudinal stretching temperature. The method for producing a stretched polyolefin film according to claim 2, wherein the take-up tension at the exit of the tenter stretching machine is 200 N / m or less. The method for producing a stretched polyolefin film according to claim 2, wherein the tenter chain tension of the tenter stretching machine is 1960 N or less. A polarizing plate comprising the stretched polyolefin film according to claim 1. A display device comprising the stretched polyolefin film according to claim 1.

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