JP2005153498A - Method for production of phase retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a phase retardation film, which has a high retardation and a uniform optical axis in parallel to the width direction. <P>SOLUTION: The method comprises an uniaxial extension of a substantially non-oriented non-crystalline long resin film in a width direction by a tenter under such temperature condition that a film temperature T<SB>n</SB>(°C) at an appropriate position of the film for 5 seconds after starting of extension, a film temperature T<SB>n+1</SB>(°C) for 5 seconds before termination of extension and a glass transition temperature T<SB>g</SB>(°C) of the non-crystalline resin are satisfied with the following formula (1)formula (1): T<SB>g</SB><T<SB>n+1</SB><T<SB>n</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a retardation film having a high retardation value used in a liquid crystal display device.

  In recent years, a liquid crystal display device has been frequently used instead of a cathode ray tube type CRT. A liquid crystal display device realizes display by utilizing the electro-optical characteristics of liquid crystal molecules, but since liquid crystals inherently have optical anisotropy, optical distortion caused by birefringence and visual direction Visual dependency such as the coloration of the display occurs due to the modulation by. In order to eliminate such drawbacks, a retardation plate is widely used as a light compensation film, and generally has a retardation (phase difference) value in the range of 50 to 800 nm when a 550 nm light beam is incident. Is used.

  The retardation film is generally produced by uniaxially stretching a thermoplastic resin film. However, if the film temperature or stretching speed during uniaxial stretching varies or is inappropriate, the retardation film has a desired retardation value. Various stretching methods have been studied because a retardation film cannot be obtained, the molecular main chain of the thermoplastic resin is not oriented in a certain direction, and the optical axis varies, resulting in display unevenness. Yes.

  As the uniaxial stretching method, a so-called longitudinal uniaxial stretching method in which a long thermoplastic resin film is stretched in the longitudinal direction (MD), and a thermoplastic resin film is stretched in a width direction (TD) orthogonal to the longitudinal direction. The so-called transverse uniaxial stretching method can be roughly classified.

  As a longitudinal uniaxial stretching method, a long thermoplastic resin film wound around a roll shaft is unwound at a predetermined speed in a temperature environment near the glass transition temperature of the thermoplastic resin, and a different roll with a higher peripheral speed is used. An example is a roll-to-roll stretching method in which a stretching force is applied in the longitudinal direction of the thermoplastic resin film by winding and the molecular main chain of the thermoplastic resin is stretched in the longitudinal direction to obtain a retardation film.

  Also, as a different method of longitudinal uniaxial stretching, both ends of the thermoplastic resin film are gripped by clips, and the longitudinal speed of the clip is changed in a temperature environment near the glass transition temperature of the thermoplastic resin. And a tenter stretching method for obtaining a retardation film by stretching the molecular main chain of the thermoplastic resin in the longitudinal direction by gradually increasing the distance in the longitudinal direction.

  As the horizontal uniaxial stretching method, the both ends of the thermoplastic resin film are gripped with clips, and the clips are run on side rails that are installed so as to gradually widen on both sides of the thermoplastic resin film. There is a tenter stretching method in which a retardation film is obtained by stretching a molecular main chain of a thermoplastic resin in the width direction through a step, a thermal relaxation step, and a cooling step.

  The horizontal uniaxial stretching method by the tenter stretching method has the advantages that the stretch distance of the thermoplastic resin film is short compared to the longitudinal uniaxial stretching method, so that it is easy to control and there is no variation in stretching, but it is unique to the tenter stretching method. As a phenomenon, the stretching of the center portion of the thermoplastic resin film is not synchronized with the end portion of the thermoplastic resin film, leading or delayed, and as a result, the molecular main chain orientation of the thermoplastic resin in the width direction takes a bow-shaped distribution. The so-called Boeing phenomenon is known.

  The bowing phenomenon is a very inconvenient phenomenon in producing a retardation film having a uniform optical axis by aligning the molecular main chain of a thermoplastic resin in a certain direction. Generally, after stretching, the obtained stretched film is heated. Control was performed by providing a so-called thermal relaxation process. However, the method of controlling in the thermal relaxation step has a drawback that the retardation value obtained in the stretching step also decreases at the same time.

  As a method of eliminating or mitigating the above bowing phenomenon, when a thermoplastic resin film is sequentially biaxially stretched or laterally stretched, it is a method for producing an optical compensation film, characterized in that the lateral stretching step is multistaged, A method for producing an optical compensation film in which a rail opening angle of a transverse stretching machine used in the transverse stretching step is within 5 degrees has been proposed (see Patent Document 1).

  However, in the above manufacturing method, since the rail opening angle of the transverse stretching machine is within 5 degrees, in order to obtain an optical compensation film having a high stretch ratio, a long widening step is required, and as a result, a long heating furnace is required. Not practical.

  In addition, the longer width-expanding step means that the thermoplastic resin film is continuously heated for a long time in a temperature environment near the glass transition temperature of the thermoplastic resin, and the development of retardation due to stretching and the relaxation of orientation due to heating. It was difficult to obtain an optical compensation film that competed and had a desired retardation.

Therefore, it is still difficult to obtain a retardation film having a high retardation by suppressing variations in the optical axis by suppressing the bowing phenomenon and making the molecular main chain of the thermoplastic resin uniform in the width direction of the thermoplastic resin film. Met.
JP 2002-148437 A

  The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a method for producing a retardation film having a high retardation, a parallel and uniform optical axis in the width direction. To do.

The method for producing a retardation film of the present invention is a method for producing a retardation film in which a substantially non-oriented long amorphous resin film is uniaxially stretched in the width direction by a tenter, and for 5 seconds after the start of stretching. The film temperature T _n (° C.) at an arbitrary point, the film temperature T _{n + 1} (° C.) at an arbitrary point for 5 seconds before stretching, and the glass transition temperature Tg (° C.) of the amorphous resin satisfy the following formula (1). It is characterized by uniaxial stretching under the temperature conditions.
Tg <T _{n + 1} <T _n (1)

  The amorphous resin used in the present invention has characteristics suitable as an optical member, such as excellent transparency, heat resistance and matching with liquid crystal, low intrinsic birefringence, and low photoelastic coefficient. However, the resin is not particularly limited as long as it is a resin having substantially no crystallinity, but a cyclic olefin resin and a maleimide resin are particularly preferably used.

  The cyclic olefin-based resin is a hydrocarbon resin having an alicyclic structure in the main chain or side chain, and examples thereof include norbornene-based resins, cyclic conjugated diene resins, and vinyl alicyclic hydrocarbon-based resins. The norbornene-based resin is particularly suitable because it is excellent in transparency, heat resistance and matching with liquid crystal, has a low intrinsic birefringence, and a small photoelastic coefficient.

The norbornene-based resin includes, for example, (i) a ring-opening (co) polymer or addition (co) polymer of a norbornene monomer, (ro) an addition (co) polymer of a norbornene monomer, (ha) a norbornene monomer And addition copolymers of α-olefin and conjugated diene, and derivatives thereof. These norbornene resins may be used alone or in combination of two or more.
In the case where an unsaturated bond remains in the structure, it is desirable that the structure is saturated by hydrogenation.

  The norbornene-based monomer constituting the norbornene-based resin is not particularly limited as long as it is a monomer having a norbornene ring. For example, a bicyclic body such as norbornene and norbornadiene; Tetracycles such as cyclododecene; pentacycles such as cyclopentadiene trimer, heptacycles such as tetracyclopentadiene; alkyls such as methyl, ethyl, propyl and butyl, alkenyls such as vinyl, ethylidene, etc. Substituents such as aryl such as alkylidene, phenyl, tolyl, naphthyl; and further, ester groups, ether groups, cyano groups, halogen groups, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carboxylic acid groups, amino groups, hydroxyl groups free of these, Silyl group, epoxy group, acrylic group, methacryl group, etc. Groups containing elements other than carbon and hydrogen, and substituted and the like having a so-called polar group.

  Among these norbornene monomers, those which are easily available, excellent in reactivity, and excellent in heat resistance of the obtained optical compensation film are preferable, and therefore polycyclic norbornene monomers having three or more rings are preferable. Ring, tetracycle and pentacycle norbornene monomers are more preferred. In addition, a norbornene-type monomer may be used independently and 2 or more types may be used together.

  When the number average molecular weight of the norbornene resin decreases, the mechanical strength of the obtained retardation film decreases, and when the number average molecular weight increases, the expression of retardation of the retardation film decreases. It is preferably 5,000 to 50,000, more preferably 8,000 to 30,000, as measured by association chromatography.

  The norbornene resin is marketed, for example, under the trade name “Zeonor” series from ZEON CORPORATION, the product name “ARTON” series from JSR, and the product name “APEL” series from Mitsui Chemicals.

Examples of the maleimide resin include maleimide / olefin copolymers comprising the following component (1) and component (2). For example, the maleimide resin can be obtained by radical copolymerization reaction of maleimides and olefins. it can.
Examples of compounds that give component (1) include maleimide, N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn-butylmaleimide, Ni-butylmaleimide , Ns-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide, N-cyclohexylmaleimide, and other maleimides N-methylmaleimide is particularly preferable from the viewpoints of heat resistance, mechanical properties, and transparency. Furthermore, these compounds can be used alone or in combination of two or more.

  Examples of the compound that provides the constituent component (2) include olefins such as isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, and 2-methyl-1-hexene. Isobutene is particularly preferable from the viewpoints of properties and transparency. Moreover, these compounds can be used 1 type or in combination of 2 or more types. The content of the constituent component (1) is preferably 40 to 60 mol%, and more preferably 45 to 55 mol% of the entire copolymer.

  For the polymerization of these monomers, any of known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be employed. The precipitation polymerization method is particularly preferred from the viewpoint of the transparency and color tone of the obtained film.

  The maleimide / olefin copolymer described above can also be obtained by post-amidating a resin obtained by copolymerization of maleic anhydride and olefins with ammonia or alkylamine.

  In order to improve ultraviolet resistance, heat resistance, weather resistance, smoothness, etc. within the range that does not deteriorate the function of the retardation film, the amorphous resin is benzophenone, benzotriazole, salicylic acid ester, cyanoacrylate. UV absorbers such as acrylonitrile and acrylonitrile; antioxidants such as phenol and phosphorus; lactone and phenol based thermal degradation inhibitors; aliphatic alcohol esters, polyhydric alcohol partial esters, partial ethers, etc. Lubricant: An amine-based antistatic agent or the like may be added.

  The amorphous resin film used in the present invention is a substantially non-oriented film. “Substantially non-oriented” means that the retardation remaining in the plane based on the orientation at the time of film formation is extremely small, preferably 10 nm or less, and more preferably 5 nm or less.

  The thickness of the amorphous resin film is not particularly limited, but if it is thin, it is difficult to obtain a desired retardation, and if it is thick, the thickness of the liquid crystal panel is generally large when used in a liquid crystal display device. 30-200 micrometers is preferable, More preferably, it is 40-150 micrometers.

  The method for producing the amorphous resin film is not particularly limited. For example, the amorphous resin is supplied to the extruder and melted and kneaded, and the film is formed from a mold attached to the tip of the extruder. A melt extrusion method for forming a long resin film, casting a solution of an amorphous resin film in an organic solvent on a drum, endless belt, etc., and evaporating the organic solvent, Any conventionally known molding method such as a solution casting method for forming a long resin film may be employed.

  In the case where the thickness of the amorphous resin film is 80 μm or more, it is difficult to sufficiently evaporate and remove the organic solvent by the solution casting method.

  In the method for producing a retardation film of the present invention, the substantially non-oriented amorphous resin film is uniaxially stretched in the width direction (hereinafter referred to as “lateral uniaxial stretching”) with a tenter.

  The transverse uniaxial stretching by the tenter may be any conventionally known lateral uniaxial tenter stretching method. For example, the both ends of the amorphous resin film in the width direction are held by the tenter clip, and the width direction of the tenter clip The method of extending | stretching and widening a resin film in the width direction by gradually separating the space | interval of this is mentioned.

  This horizontal uniaxial tenter stretching method reduces the preheating step of preheating the amorphous resin film, the stretching step of stretching and widening the amorphous resin film in the width direction, and the bowing of the stretched amorphous resin film. It is preferable to comprise a thermal relaxation step for aligning the orientation and a cooling step for fixing the orientation of the amorphous resin film.

  If the temperature of the amorphous resin film in the stretching process is low, the film may be cut during stretching or the tenter clip may be detached. Conversely, if the temperature is too high, orientation relaxation occurs and the desired retardation value is obtained. “Amorphous resin glass transition temperature Tg” to “Amorphous resin glass transition temperature Tg + 20 ° C.”, more preferably “Amorphous resin glass transition temperature Tg + 2 ° C.” to “Amorphous resin glass transition temperature Tg + 10 ° C.”.

In addition, the temperature of the amorphous resin film in the stretching process is as follows: film temperature T _n ° C at an arbitrary point for 5 seconds after the start of stretching, film temperature T _{n + 1} (° C.) at an arbitrary point for 5 seconds before the end of stretching, and the amorphous The glass transition temperature Tg (° C.) of the conductive resin must satisfy the following formula (1).
Tg <T _{n + 1} <T _n (1)

  In particular, if the temperature of the amorphous resin film increases in the second half of the stretching process, the retardation value decreases and it becomes difficult to correct the bowing phenomenon, so the temperature of the resin film is stretched from the stretching start point side. It is preferable that the temperature distribution always decreases toward the end point.

  In this way, by setting the temperature of the amorphous resin film in the stretching step, the orientation stress of the resin film immediately before the end of stretching is increased, and at the same time, the temperature of the resin film immediately before the end of stretching is kept low, thereby highly oriented. In the latter half of the stretching process, the lowering of the retardation due to thermal relaxation is suppressed, and the central portion that precedes the convex shape with respect to the length direction of the resin film is caused by the back tension generated toward the film supply port side. The main alignment axis can be corrected to be flat in the width direction.

  When the strain rate in the stretching step is reduced, the retardation value is lowered by thermal relaxation, the control effect of the bowing phenomenon is lowered, and when the strain rate is increased, the amorphous resin film is broken, so 50 to 1000% / min. Preferably, it is 200 to 500% / min.

  Although the strain rate may be constant or may change throughout the stretching process, it is preferable to maintain the stretching stress in the latter half of the stretching process immediately before the end of stretching, so that the strain in the latter half of the stretching process is maintained. The speed is preferably 400 to 1000% / min faster than the first half.

  In addition, if the stretching time from the start of stretching to the end of stretching is shortened, a decrease in the retardation value due to thermal relaxation can be suppressed, and a high stretching strain can be secured in a short stretching region, resulting in a high retardation. 20 seconds or less is preferable because the main orientation axis can be corrected flat in the width direction by the back tension generated toward the film supply port side. However, if the stretching time is too short, the amorphous resin film may be cut or the tenter clip may come off, so the time is more preferably 5 to 20 seconds.

  The stretching ratio of the amorphous resin film may be appropriately determined depending on the compensation retardation amount of the obtained retardation film, but if the stretching ratio is low, the orientation direction may not be uniform, and conversely too high. Since the central part of the amorphous resin film is loosened, the retardation value varies in the width direction, and the main orientation axis and thickness are not uniform, 1.2 to 3 times is preferable, more preferably 1.5. ~ 2.5 times.

  In the preheating step, the amorphous resin film is heated to near the temperature at which it can be stretched, and may be heated to near the stretching temperature set in the stretching step.

  The thermal relaxation process is a process for reducing the bowing of the stretched amorphous resin film and aligning the orientation. If the temperature of this process is too high, the retardation value decreases. Is not more than the temperature at the end of stretching, and is preferably set within the range of “glass transition temperature Tg of amorphous resin” to “glass transition temperature Tg of amorphous resin + 10 ° C.”.

  The cooling step is a step for fixing the orientation formed in the amorphous resin film by rapidly cooling the amorphous resin film, and the cooling temperature is “the glass transition temperature Tg-50 of the amorphous resin”. "C" to "Glass transition temperature Tg-5 ° C of amorphous resin" is preferable.

In the retardation film obtained by the method for producing a retardation film of the present invention, the molecular main chain orientation angle θ (°) with respect to the width direction of the film preferably satisfies the following formula (2).
| Θ | <1 ° (2)

  When the molecular main chain orientation angle θ falls within the above range, the molecular main chain is uniformly oriented and the optical axis is stabilized. Therefore, when laminated on a liquid crystal panel, there is no display unevenness and a high-quality image display can be obtained. .

In addition, the retardation film obtained by the method for producing a retardation film of the present invention preferably has an in-plane retardation Re defined by the following formula (3) of 100 nm or more.
_{Re (nm) = (n x} -n y) × d ··· (3)
Incidentally, wherein, n _x represents a refractive index in the direction indicated by the refractive index maximum phase difference film plane, n _y represents a refractive index in the direction perpendicular to the direction indicating the largest phase difference film plane , D represents the thickness (nm) of the retardation film.

  When the value of retardation Re is small, birefringence when passing through the liquid crystal cannot be compensated when laminated on the liquid crystal panel, and the commercial value as a retardation film is lowered. Therefore, the value of retardation Re is in the above range. Is preferred.

  The retardation film obtained in the present invention can be further stretched in the length direction to obtain a biaxial retardation film. However, when the retardation Re value of the retardation film decreases, The retardation Rth (nm) in the thickness direction of the axial retardation film becomes difficult to develop, and the value of the retardation Re decreases by heating due to heating during stretching, so that the value of the retardation Re is 150 or more. Is preferred.

  Examples of the stretching method in the length direction for obtaining the biaxial retardation film include longitudinal uniaxial stretching methods such as the above-described inter-roll stretching method and tenter method.

  The structure of the method for producing a retardation film of the present invention is as described above, and is an extremely effective method for obtaining a retardation film having a high retardation and a parallel and uniform optical axis in the width direction.

  When the retardation film obtained by this method is used in a liquid crystal display device, optical distortion based on the birefringence of the liquid crystal substance can be effectively compensated, display unevenness can be eliminated, and an excellent quality image display can be obtained. it can.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Examples 1-4, Comparative Examples 1-4)
Norbornene resin (trade name “ZEONOR 1420”, manufactured by Nippon Zeon Co., Ltd., glass transition temperature Tg = 142 ° C.) is supplied to a single screw extruder with a T-die, on a chromium plating roll at a melting temperature of 230 ° C. and a take-up speed of 20 m / min. Then, the film was continuously formed into a film and wound into a roll on a vinyl chloride resin core to obtain a substantially non-oriented norbornene resin film. The obtained norbornene resin film had a width of 300 mm and an average thickness of 100 μm.

The obtained norbornene resin film was continuously unwound and supplied to a horizontal uniaxial tenter stretching machine having a preheating zone, a stretching zone, and a cooling zone at a speed of 5 m / min. The film was stretched 2.0 times to obtain a retardation film.
The time required for stretching at this time is shown in Table 1.

  The temperature of the preheating zone was set to 150 ° C., and the temperature of the cooling zone was set to 140 ° C. The drawing zone was composed of a plurality of heating furnaces capable of adjusting the temperature. The heating furnace temperature on the preheating zone side was the highest, and the heating furnace temperature on the cooling zone side was the lowest.

The temperature of the norbornene resin film was measured at predetermined times tf and tr after the start of stretching shown in Table 1 and shown in Table 1. The temperature of the norbornene resin film at the predetermined time tf is a film temperature T _n at a point close to the stretching start point side, and the temperature of the norbornene resin film at the predetermined time tr is a film temperature T _{n + 1} at a point close to the stretching end point side. .

The width of the obtained retardation film was 570 mm excluding the tenter clip gripping part, but both ends in the width direction were excluded because they were not uniformly stretched, and the central part 400 mm was used as the product.
When the thickness was measured at intervals of 10 mm in the width direction, the average thickness was 48 μm. Further, the retardation value Re and molecular main chain orientation angle θ of the obtained retardation film were measured, and the results are shown in Table 1.

  The glass transition temperature Tg of the norbornene resin, the norbornene resin film temperature, the retardation value Re of the retardation film, and the molecular main chain orientation angle θ are measured as follows.

Glass transition temperature Tg of norbornene resin
Using a differential scanning calorimeter (trade name “DSC2920 Modulated DSC” manufactured by TA Instruments), the glass transition temperature at the final temperature rise was measured as the glass transition temperature of the present invention under the following temperature program conditions.
・ Raise the temperature from room temperature to 50 ° C. at 10 ° C./min and keep isothermal for 5 minutes, raise the temperature from 50 ° C. to 200 ° C. at 10 ° C./min and keep isothermal at 200 ° C. for 5 minutes, from 200 ° C. to −50 The temperature was lowered to 10 ° C / min and kept isothermally at -50 ° C for 5 minutes, and the temperature was raised from -50 ° C to 200 ° C at 10 ° C / min and kept isothermally at 200 ° C for 5 minutes.

Measurement method of norbornene resin film temperature A two-wire radiation thermometer (trade name “micratherm”, manufactured by Rand Co., Ltd.) was installed at a predetermined position on the film center line, and measured at a measurement distance of 100 mm from the lower surface of the norbornene resin film during running .

Measuring method of retardation value Re of retardation film Automatic birefringence measuring device (manufactured by Oji Scientific Instruments Co., Ltd., trade name “KOBRA-21ADH”), measured every 10 mm interval in the width direction of retardation film, average The value was defined as a retardation value Re.

Measuring method of molecular main chain orientation angle θ of retardation film Using width direction of retardation film as reference axis, automatic birefringence measuring device (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments Co., Ltd.) Measurement was performed at 10 mm intervals, and the average of the absolute values of the orientation angles (angles formed between the slow axis and the reference axis) at each position was defined as the molecular main chain orientation angle θ.

Claims (6)

A method for producing a retardation film in which a substantially non-oriented long amorphous resin film is uniaxially stretched in the width direction by a tenter, and a film temperature T _n (° C.) at an arbitrary point for 5 seconds after stretching starts The film temperature T _{n + 1} (° C.) at an arbitrary point for 5 seconds before the end of stretching and the glass transition temperature Tg (° C.) of the amorphous resin are uniaxially stretched under temperature conditions satisfying the following formula (1): A method for producing a retardation film.
Tg <T _{n + 1} <T _n (1)   2. The method for producing a retardation film according to claim 1, wherein the required time for uniaxial stretching is 20 seconds or less. 3. The method for producing a retardation film according to claim 1, wherein the molecular main chain orientation angle [theta] ([deg.]) With respect to the width direction of the film satisfies the following formula (2).
| Θ | <1 ° (2)   In-plane retardation Re is 150 nm or more, The manufacturing method of the retardation film of any one of Claims 1-3 characterized by the above-mentioned.   The method for producing a retardation film according to claim 1, wherein the amorphous resin is a cyclic olefin resin or a maleimide resin.   6. The method for producing a retardation film according to claim 5, wherein the cyclic olefin resin is a norbornene resin.