JP2007010863A - Retardation film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film provided with high retardation stability, and to provide a manufacturing method of the retardation film. <P>SOLUTION: The retardation film is made of a thermoplastic resin and is at least a uniaxially stretched film, wherein a glass transition temperature of the thermoplastic resin falls into the range of 100 to 180°C and an endothermic quantity at the glass transition temperature falls into the range of 0.01 to 5.0 J/g. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a retardation film having excellent dimensional stability and environmental stability of optical properties, such as a liquid crystal display device, a light emitting element, an antiglare film, an optical recording device, and a polarizing beam splitter, and its production. Regarding the method.

  In recent years, the progress of liquid crystal display devices has been remarkable, and the application of liquid crystal display devices has been changed from small ones such as calculators, watches, mobile phones, digital cameras, etc. to PDA, car navigation, POS systems, and other medium types, as well as personal computer liquid crystal monitors, liquid crystals The products are applied to a wide variety of products such as large-sized liquid crystal display devices such as televisions, and there is an increasing demand for improving the quality and function of members used in the liquid crystal display devices. Of course, the environmental resistance requirements for the materials used in them are becoming stricter. In this liquid crystal display device, a retardation film is usually used for improving display quality such as color compensation of liquid crystal, expansion of viewing angle, and improvement of contrast. For this retardation film, polycarbonate or the like has been widely used as a polymer material. Recently, however, a resin called amorphous polyolefin has attracted attention as a material for the retardation film. Amorphous polyolefin is a polyolefin which has an alicyclic structure and is made amorphous by increasing heat resistance, and is characterized by excellent dimensional stability due to high transparency and low water absorption. Furthermore, since it does not contain an aromatic component, the photoelastic constant is extremely low.

Such amorphous polyolefins can be broadly classified into two in terms of structure. One is obtained by ring-opening polymerization of a cyclic olefin, and then hydrogenating the double bond of the main chain produced. Product names “ZEONEEX”, “ZEONOR”, JSR (manufactured by Nippon Zeon Co., Ltd.) Resins such as “ARTON” manufactured by Co., Ltd. are already on the market. The other is obtained by copolymerizing cyclic olefin with ethylene and vinyl, and is commercially available under the trade name “APEL” manufactured by Mitsui Chemicals, Inc., and the product name “TOPAS” manufactured by TICONA. Etc. These have been studied as retardation films, such as retardation characteristics, production methods, and incorporation into liquid crystal display devices (see, for example, Patent Documents 1 to 9).
However, although such amorphous polyolefin has a characteristic that is excellent in dimensional stability because of its low water absorption, it has an alicyclic structure to improve heat resistance, but is mainly composed of an olefin skeleton. The glass transition temperature is as low as about 130 to 160 ° C., and there remains a problem in the retardation stability in durability, particularly heat resistance.

JP-A-4-245202 JP-A-5-002108 Japanese Patent No. 3273046 JP-A-6-59121 JP-A-8-43812 Japanese Patent No. 3470567 JP 2001-042130 A JP 2003-306557 A Japanese Patent No. 3497894

  When examining a retardation film having high retardation stability, for example, when focusing on the above-mentioned amorphous polyolefin, in order to increase the heat resistance of the amorphous polyolefin and improve the retardation stability, In the case of such an alicyclic structure, if the ratio is too large, the mechanical strength of the film made of amorphous polyolefin is reduced. Thus, it becomes a material that is easily broken, and it is difficult to handle it as a retardation film. On the other hand, if the heat resistance of the amorphous polyolefin is low, changes in optical properties such as retardation changes become prominent in terms of environmental resistance, and the properties as a retardation film cannot be satisfactorily maintained. . For this reason, in the case of using amorphous polyolefin as a retardation film, a technique for imparting retardation stability to a material having appropriate mechanical strength is indispensable.

  The objective of this invention is providing the retardation film which provided high retardation stability, and its manufacturing method.

  In order to solve the above-mentioned problems, the present inventors have intensively studied a polymer material for a retardation film, a production method, and the like. As a result, it has been found that by providing a retardation film made of a thermoplastic resin having a glass transition point temperature in a specific range and an endothermic amount at the glass transition point having a specific amount, high retardation stability is imparted. . In addition, a film made of a thermoplastic resin and stretched in at least a uniaxial direction is subjected to a heat treatment (hereinafter sometimes referred to as an annealing treatment) for 1 minute to 1000 hours in a temperature range of 90 ° C. to (glass transition point −5 ° C.). Thus, the inventors have found that such a retardation film can be produced effectively, and have reached the present invention.

That is, the present invention can be achieved by the following [1] to [9].
[1] A film made of a thermoplastic resin and oriented in at least a uniaxial direction, wherein the glass transition temperature of the thermoplastic resin is in the range of 100 to 180 ° C., and the endothermic amount at the glass transition temperature is 0. Retardation film characterized by being in a range of 01 to 5.0 J / g.
[2] The retardation film of [1], wherein the thermoplastic resin is an amorphous polyolefin.
[3] The amorphous polyolefin is a copolymer of i) ethylene and norbornene, and ii) the meso-type and racemo-type abundance ratio of the meso-type and racemo-type abundance in terms of the stereoregularity of the two-chain site (dyad) of norbornene units. Type] / [Lacemo type]> 4 retardation film of the above [2].
[4] A film comprising a thermoplastic resin and at least uniaxially stretched at a temperature of 90 ° C. to (glass transition point −5 ° C.) within a range of 1 minute to 1000 hours. A method for producing a phase difference film.
[5] A circularly polarizing film comprising a polarizing film and the retardation film of any one of [1] to [3].
[6] A light emitting device using the circularly polarizing film of [5].
[7] An elliptically polarizing film comprising a polarizing film and the retardation film of any one of [1] to [3].
[8] A liquid crystal display element using the retardation film of any one of [1] to [3].
[9] An optical device using the retardation film of any one of [1] to [3].

The present inventors have found a method for annealing within an appropriate temperature and time range, in addition to increasing the heat resistance of the polymer material, in order to increase the retardation stability of the retardation film. Moreover, as a physical property of the retardation film which consists of a thermoplastic resin which has retardation stability, the glass transition point temperature needs to be 100-180 degreeC, and the endothermic amount in a glass transition point should be 0.01-5.0 J / g. I found. Thereby, the retardation film excellent in dimensional stability and retardation stability was able to be provided.
As described above, since the retardation film of the present invention has high retardation stability, it has excellent moisture and heat resistance characteristics in which dimensions and retardation values do not change even under high temperature and high humidity conditions.

  According to the present invention, a film made of a thermoplastic resin such as amorphous polyolefin and oriented in at least a uniaxial direction, the glass transition temperature of the thermoplastic resin being in the range of 100 to 180 ° C., the glass transition With the retardation film having an endothermic amount in the range of 0.01 to 5.0 J / g, a retardation film having excellent dimensional stability and retardation stability can be obtained. In addition, such a retardation film has realized a method of subjecting a film stretched at least in a uniaxial direction to a heat treatment (annealing treatment) under specific temperature and time conditions.

  The retardation film thus obtained can be combined with a polarizing plate to provide a circularly polarizing film, an elliptically polarizing film, and a viewing angle widening polarizing film. Also, an anti-transmissive reflective liquid crystal display device and a transmissive liquid crystal display device can be provided. In combination with the above, it is possible to increase the luminance of the liquid crystal display device and to provide a liquid crystal display device that does not impair the screen quality under an environment in a wide temperature and humidity range.

〔Thermoplastic resin〕
In the present invention, a retardation film is formed by processing a thermoplastic resin into a film and performing molecular orientation by performing an operation such as stretching. What is necessary is just to use what can form the orientation film excellent in transparency as a thermoplastic resin used for this invention, As specific examples, polyolefins, such as polyethylene and a polypropylene, aromatic vinyl polymers, such as a polystyrene, polymethylmethacrylate Such as poly (meth) acrylates, polyphenylene oxide, polycarbonates, polyvinyl chloride, polyethylene terephthalate, polyarylate, polyethersulfone, polyethylene naphthalate, polymethylpentene-1, alicyclic polyolefins (eg, dicyclopentadiene) -Opening (co) polymers of cyclic olefins such as polyolefins and norbornene-based polyolefins, their hydrogenated (co) polymers, and saturated copolymers of cyclic olefins with unsaturated double bond-containing compounds For example, a copolymer of an alicyclic (meth) acrylate such as tricyclodecanyl methacrylate, cyclohexyl methacrylate or isobornyl methacrylate and a (meth) acrylate ester such as methyl methacrylate, polysulfone, polyetherimide, Examples thereof include thermoplastic resins such as crystalline polyamide, polyphenylene ether, and hydrogenated polymers of cyclic olefins, cyclopentadiene, and cationic (co) polymers of aromatic vinyl compounds. These may be either a blend polymer, a copolymer, or a mixture of a copolymer and a blend polymer. Among these, polycarbonates and amorphous polyolefins can be exemplified as those having preferable optical characteristics as a retardation film.

  The thermoplastic resin in the present invention refers to all synthetic polymer compounds such as synthetic resins and synthetic rubbers obtained by synthesis such as monomer addition polymerization or polycondensation, and polysaccharides such as cellulose and starch obtained from natural products. In addition, proteins such as gelatin and keratin, mineral-derived substances such as asbestos and mica, natural polymer compounds such as enzymes and nucleic acids, and derivatives from natural polymer compounds are also included.

  In addition, it is important that the thermoplastic resin has sufficient mechanical properties to be processed or handled as a retardation film. Therefore, the weight average molecular weight of the thermoplastic resin is preferably 1000 to 500000, more preferably 3000 to 100000, and most preferably 5000 to 50000. The retardation film of the present invention has a certain degree of environmental resistance because the glass transition temperature of the thermoplastic resin is 100 ° C. or higher and 180 ° C. or lower. The glass transition temperature is preferably 110 ° C. or higher and 180 ° C. or lower, and more preferably 120 ° C. or higher and 180 ° C. or lower. When the glass transition temperature exceeds 180 ° C., the mechanical strength of the film becomes too strong, the film is easily broken, and it is difficult to use it as a retardation film. Further, the film stretching process itself becomes difficult.

  The thermoplastic resin preferably has a low water absorption rate. If the water absorption rate exceeds 0.2%, the effect of volume change due to moisture absorption is large, so that the optical characteristics of the retardation film cannot be kept uniform, and the image quality of the liquid crystal display element can be kept good. difficult. For this reason, the water absorption rate of the thermoplastic resin is preferably 0.2% or less, more preferably 0.15% or less, and most preferably 0.1% or less.

  As a specific resin of the thermoplastic resin, amorphous polyolefin is particularly preferable in various points such as heat resistance, mechanical properties, and transparency.

[Amorphous polyolefin]
The amorphous polyolefin in the present invention is a copolymer obtained by vinyl-type polymerization of ethylene and norbornene, and consists of repeating units (A) and (B) shown below.

Furthermore, in the present invention, the glass transition temperature (Tg) of such a copolymer is in the range of 100 ° C to 180 ° C. In this copolymer, the composition of the repeating units (A) and (B) and the glass transition temperature are substantially correlated, and the molar ratio is in the range of (A) / (B) = 61/39 to 40/60. Preferably there is. A more preferable glass transition temperature range is from 120 ° C. to 160 ° C., and a molar ratio (A) / (B) = 57/43 to 46/54. Such a composition can be determined by ¹³ C-NMR measurement.

[式（Ｃ）中、ｎは０または１であり、ｍは０または正の整数であり、ｐは０または１であり、Ｒ^１〜Ｒ^２０は同一または異なり、水素原子、ハロゲン原子、または炭素数１〜１２の飽和あるいは不飽和脂肪族炭化水素基であり、また、Ｒ^１７とＲ^１８とで、あるいはＲ^１９とＲ^２０とでアルキリデン基を形成していてもよく、また、Ｒ^１７またはＲ^１８と、Ｒ^１９またはＲ^２０とが環を形成していてもよく、かつ該環が二重結合を有していてもよい。]、
プロピレン、１−ブテン、１−ヘキセン、４−メチル−１−ペンテン、１−オクテン、１−デセン、１−ドデセン、１−テトラデセン、１−ヘキサデセン、１−オクタデセン等の炭素数３〜１８のα−オレフィン、シクロブテン、シクロペンテン、シクロペンテン、シクロヘキセン、３−メチルシクロヘキセン、シクロオクテン等のシクロオレフィン等を挙げることが出来る。この中で炭素数３〜１８のα−オレフィンは共重合の際の分子量調節剤として用いることが出来、中でも１−ヘキセンが好適に用いられる。かかるその他のビニルモノマーは単独であるいは２種類以上組み合わせて用いてもよく、またその繰り返し単位が全体の１０モル％以下が好ましく、より好ましくは５モル％以下である。 Moreover, the said copolymer may contain the repeating unit which consists of other copolymerizable vinyl monomers other than said (A) and (B) in the range which does not impair the objective of this invention. Specifically, as this other vinyl monomer, a cyclic olefin represented by the following formula (C),

[In the formula (C), n is 0 or 1, m is 0 or a positive integer, p is 0 or 1, and R ^{1 to} R ²⁰ are the same or different and each represents a hydrogen atom, a halogen atom, or A saturated or unsaturated aliphatic hydrocarbon group having 1 to 12 carbon atoms, and R ¹⁷ and R ¹⁸ , or R ¹⁹ and R ²⁰ may form an alkylidene group, and R ¹⁷ Alternatively, R ¹⁸ and R ¹⁹ or R ²⁰ may form a ring, and the ring may have a double bond. ],
C3-C18 α such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, etc. -Cycloolefins such as olefin, cyclobutene, cyclopentene, cyclopentene, cyclohexene, 3-methylcyclohexene, cyclooctene and the like. Among these, an α-olefin having 3 to 18 carbon atoms can be used as a molecular weight regulator in the copolymerization, and 1-hexene is preferably used among them. Such other vinyl monomers may be used alone or in combination of two or more, and the repeating unit is preferably 10 mol% or less, more preferably 5 mol% or less of the whole.

  The molecular weight of the copolymer of ethylene and norbornene is a reduced viscosity ηsp / c measured in a cyclohexane solution having a temperature of 30 ° C. and a concentration of 0.5 g / dL, and is in the range of 0.1 to 10 dL / g. More preferably, it is 3 to 3 dL / g. If the reduced viscosity ηsp / c is less than 0.1, the film becomes brittle, and if it is more than 10, the melt viscosity becomes too high, making it difficult to melt the film.

  In the present invention, one type of copolymer may be used as it is, or two or more types of copolymers having different compositions and molecular weights may be blended and used. In the case of such a blend, the above preferred composition and molecular weight indicate the entire blend. When using such a blend, it is preferable to use a copolymer having a close copolymer composition from the viewpoint of compatibility. When the composition is too far, phase separation may occur due to blending, and the film may be whitened during film formation or stretching orientation.

In general, an ethylene-norbornene copolymer depends on a polymerization method, a catalyst to be used, a composition, and the like, but in any case, a chain site of a norbornene component exists to some extent. Regarding the stereoregularity at the two-chain site (hereinafter referred to as NN dyad) of the norbornene component of the vinyl polymerization type, a repeating unit (meso type) represented by the following formula (D) and a repeating unit represented by the following formula (E) ( It is known that there are two stereoisomers of the racemo type).

Regarding the stereoregularity of the copolymer in the present invention, those having a meso-type and racemo-type abundance ratio of [meso-type] / [racemo-type]> 4 (molar ratio) can be preferably used. More preferably, [Meso type] / [Lacemo type]> 6. There is no restriction | limiting in particular about the upper limit of a ratio, and it is suitable and preferable for the expression of birefringence, so that it is high. The abundance ratio of the NN dyad stereoisomer here is determined by ¹³ C-NMR from a reference (Macromol. Rapid Commun. 20, 279 (1999)) analyzing the stereoregularity of the ethylene-norbornene copolymer. In the present invention, in ¹³ C-NMR measured with a heavy orthodichlorobenzene solvent, [meso type] / [racemo type] = [peak area of 28.3 ppm of ¹³ C-NMR spectrum] / [ ¹³ C -It is calculated by 29.7 ppm peak area of NMR spectrum. The smaller the ratio is 4 or less, that is, the greater the ratio of the racemo type, the lower the birefringence develops. Of course, the thickness of the film is increased, the stretching ratio is increased, the stretching temperature is lowered, and the stretching is performed. In some cases, a desired retardation value can be obtained by this means, but it is not preferable from the viewpoints of thinning and productivity.

In the analysis by ¹³ C-NMR, the abundance ratio (molar fraction) of the NN dyad relative to the total amount of norbornene component, that is, how much the norbornene component forms a chain structure can be obtained. It is in the range of ~ 0.6. The molar fraction referred herein, ^[13 C-NMR peak area ⁺ 13 C-NMR peak area of 29.7ppm of the spectrum of 28.3ppm spectrum] / [peak area of one carbon atom of total norbornene component ] Is calculated.

で表される。ここで、上記式（Ｆ）中、Ｍはチタン、ジルコニウムまたはハフニウムよりなる群より選ばれる金属であり、Ｒ^２４とＲ^２５は同一もしくは異なり、水素原子、ハロゲン原子、炭素数１〜１２の飽和あるいは不飽和炭化水素基、炭素数１〜１２のアルコキシ基、または炭素数６〜１２のアリールオキシ基であり、Ｒ^２２とＲ^２３は同一もしくは異なっていて、中心金属Ｍと共にサンドイッチ構造を形成することのできる単環状あるいは多環状炭化水素基であり、Ｒ^２１はＲ^２２基とＲ^２３基を連結するブリッジであって、下記式群 Preferred examples of the method for producing the ethylene-norbornene copolymer include a method of copolymerizing ethylene and norbornene using a metallocene catalyst. The metallocene used in this case is represented by the following formula (F)

It is represented by Here, in the above formula (F), M is a metal selected from the group consisting of titanium, zirconium or hafnium, and R ²⁴ and R ²⁵ are the same or different and are a hydrogen atom, a halogen atom, or a C 1-12 saturated. Alternatively, it is an unsaturated hydrocarbon group, an alkoxy group having 1 to 12 carbon atoms, or an aryloxy group having 6 to 12 carbon atoms, and R ²² and R ²³ are the same or different and form a sandwich structure with the central metal M. A monocyclic or polycyclic hydrocarbon group, wherein R ²¹ is a bridge connecting R ²² group and R ²³ group,

であり、このときＲ^２６〜Ｒ^２９は同一または異なっていて、水素原子、ハロゲン原子、炭素数１〜１２の飽和あるいは不飽和炭化水素基、炭素数１〜１２のアルコキシ基、または炭素数６〜１２のアリールオキシ基であるか、あるいはＲ^２６とＲ^２７またはＲ^２８とＲ^２９とが環を形成していていもよい。

In this case, R ^{26 to} R ²⁹ are the same or different and are a hydrogen atom, a halogen atom, a saturated or unsaturated hydrocarbon group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or 6 carbon atoms. Or an aryloxy group of ˜12, or R ²⁶ and R ²⁷ or R ²⁸ and R ²⁹ may form a ring.

Wherein, R ²² and R ²³ is a ligand, if the same has C2 symmetry with respect to the central metal M, to be different from preferably has a C1 symmetry. R ²² and R ²³ are preferably a cyclopentadienyl group, an indenyl group, an alkyl or aryl substituent thereof, and the central metal M is most preferably zirconium in terms of catalytic activity. R ²⁴ and R ²⁵ may be the same or different, but are preferably an alkyl group having 1 to 6 carbon atoms or a halogen atom, particularly a chlorine atom. R ^{26 to} R ²⁹ are preferably a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group, and as R ²¹ , a lower alkylene group such as a methylene group, an ethylene group, or a propylene group, an alkylidene group such as isopropylidene, Preferred examples include substituted alkylene groups such as diphenylmethylene, silylene groups, and substituted silylene groups such as dimethylsilylene and diphenylsilylene.

  Specific preferred metallocenes include isopropylidene- (cyclopentadienyl) (1-indenyl) zirconium dichloride, isopropylidene-[(3-methyl) cyclopentadienyl] (1-indenyl) zirconium dichloride, dimethylsilylene- (Cyclopentadienyl) (1-indenyl) zirconium dichloride, dimethylsilylene-bis (1-indenyl) zirconium dichloride, diphenylsilylene-bis (1-indenyl) zirconium dichloride, ethylene-bis (1-indenyl) zirconium dichloride, isopropyl Examples thereof include redene-bis (1-indenyl) zirconium dichloride. These may be used alone or in combination of two or more. As the metallocene promoter, a known catalyst such as methylaluminoxane, which is an organoaluminum oxy compound, or a combination of an ionic boron compound and an alkylaluminum compound can be used.

  By using such a metallocene catalyst, the desired copolymer can be polymerized by a known polymerization method using a hydrocarbon solvent such as toluene, xylene, cyclohexane, etc. It can be isolated by removing the solvent after removing it by washing by reprecipitation in a solvent, or by adsorbing the catalyst to the adsorbent, adding some additive to agglomerate and depositing, etc. .

  When producing (synthesizing) the above copolymer, known antioxidants such as Irganox 1010 and 1076 (manufactured by Ciba Geigy), lubricants, plasticizers, surfactants, UV absorbers, antistatic agents Additives such as may be added.

[Phase difference film]
The retardation film of the present invention is a film having a retardation due to the orientation of molecular chains of a polymer at least in a uniaxial direction. The retardation film may be an optical uniaxial or biaxial film.
The retardation film of the present invention can be produced by forming the thermoplastic resin described above into a film and then stretching it.

  As a specific film forming method, for example, an unstretched film of a thermoplastic resin is produced by a known method such as a solution casting method, a melt extrusion method, a hot pressing method, a calendering method, and then by uniaxial or biaxial stretching described later. It can be stretched to form a film. Of these, the melt extrusion method is preferable from the viewpoint of productivity and economy, and from the viewpoint of solvent-free environment. In the melt extrusion method, a method in which a resin is extruded to a cooling roll using a T die is preferably used. The resin temperature at the time of extrusion is determined in consideration of the fluidity and thermal stability of the resin. For example, in the case of the ethylene-norbornene copolymer as a thermoplastic resin, it is preferable to carry out in the range of 220 ° C to 300 ° C. If it is lower than 220 ° C., the melt viscosity of the resin becomes too high, and if it exceeds 300 ° C., there is a concern that the transparency and homogeneity of the film are impaired due to degradation and gelation of the resin. More preferably, it is in the range of 220 ° C to 280 ° C. In order to suppress oxidative degradation of the resin during melt extrusion, it is preferable to add an antioxidant. When the copolymer is formed into a film by a solution casting method, a hydrocarbon solvent such as toluene, xylene, cyclohexane, decalin or the like is preferably used. In the production of an unstretched film by these methods, it is preferable to reduce the thickness unevenness as much as possible. This is because if the thickness unevenness is large at this time, the retardation unevenness of the retardation film obtained in the subsequent stretching step is likely to increase. The thickness unevenness is preferably ± 8% or less, more preferably ± 5% or less with respect to the average thickness. The thickness at the unstretched film stage is determined in consideration of a desired retardation value and thickness in the stretched retardation film, but is in the range of 30 to 400 μm, more preferably in the range of 40 to 300 μm.

  The retardation film of the present invention can be obtained by uniaxially or biaxially stretching the unstretched film thus obtained. As the stretching method, for example, known methods such as longitudinal uniaxial stretching between rolls, lateral uniaxial stretching using a tenter, simultaneous biaxial stretching combining them, and sequential biaxial stretching can be used. Moreover, although it is preferable from a point of productivity to perform continuously, you may carry out by a batch type. The stretching temperature is preferably in the vicinity of the glass transition point of the thermoplastic resin used. For example, in the case of an ethylene-norbornene copolymer, the glass transition point temperature (Tg) is (Tg-20 ° C.) to (Tg + 30 ° C.). Within the range, preferably within the range of (Tg-10 ° C) to (Tg + 20 ° C). Although the draw ratio is determined by the target retardation value, it is 1.05 to 4 times, more preferably 1.1 to 3 times for each of the length and width.

As one of the preferable retardation films obtained in the present invention, the in-plane retardations R (550) and Rth (550) at a wavelength of 550 nm are in the ranges of the following formulas (1) and (2), and the thickness is Is a retardation film having a thickness of 10 to 150 μm.
0 nm <R (550) <300 nm (1)
50 nm <Rth (550) <400 nm (2)
Here, the phase differences R and Rth are defined by the following formulas (3) and (4), and are characteristics representing the phase delay of light transmitted in the direction perpendicular to the film.
R = (nx−ny) × d (3)
Rth = {(nx + ny) / 2−nz} × d (4)
In the formula, nx is the refractive index of the slow axis (the axis with the highest refractive index) in the film plane, ny is the refractive index in the direction perpendicular to nx in the film plane, and nz is the x-axis and y-axis. It is the refractive index in the vertical thickness direction, and d is the thickness. In the formula, R (550) and Rth (550) are an in-plane retardation value and a thickness direction retardation value at a wavelength of 550 nm, respectively.

  The thickness of the retardation film is preferably 10 to 150 μm, more preferably 30 to 120 μm, and still more preferably 30 to 100 μm. Such a retardation film can be prepared by uniaxial stretching or biaxial stretching, and is suitably used for λ / 4 plates, λ / 2 plates, λ plates, and the like.

  Next, the endothermic amount in the vicinity of the glass transition point of the retardation film made of the thermoplastic resin in the present invention will be described. This is an endothermic peak prominently observed during a relaxation phenomenon (generally referred to as enthalpy relaxation) that occurs in an amorphous state in a polymer caused by annealing a thermoplastic resin at a temperature below the glass transition temperature. The endothermic amount that appears in the vicinity of the glass transition point caused by the amorphous relaxation of this thermoplastic resin is shown. The endothermic amount at the glass transition point is specifically the part shown in 2 of the chart (FIG. 1) obtained by measuring by DSC, and the part surrounded by the straight line 1 extending the base line after passing through the endothermic point. It is defined by the area of 1 and the unit is J / g. The endothermic amount in the vicinity of the glass transition point of this retardation film represents the degree of amorphous relaxation reduction. If the endothermic amount is less than 0.01 J / g, the amorphous relaxation reduction is insufficient. In the retardation film, the retardation stability is insufficient. On the other hand, in order to exceed the endothermic amount of 5 J / g near the glass transition point, an annealing treatment is actually required for a long time, which is a problem in the processing process. The endothermic amount in the vicinity of the glass transition point is more preferably 0.01 to 4 J / g, and further preferably 0.01 to 3 J / g.

  In the retardation film of the present invention, known antioxidants such as Irganox 1010 and 1076 (manufactured by Ciba Geigy), lubricants, plasticizers, surfactants, ultraviolet absorbers, antistatic agents, etc. Additives may be included.

[Annealing method of retardation film]
The retardation film of the present invention can be obtained by an annealing method. As a specific method, it means that a film made of a thermoplastic resin and stretched at least in a uniaxial direction is subjected to a heat treatment for 1 minute to 1000 hours in a temperature range of 90 ° C. to (glass transition point −5) ° C. . This is to effectively promote amorphous relaxation by the above-mentioned enthalpy relaxation in a retardation film made of a thermoplastic resin. An annealing process at a temperature lower than 90 ° C. requires a long time to obtain enthalpy relaxation, which is a problem in the processing process. (Glass transition temperature -5) In the annealing process at a temperature higher than ° C., the orientation of the polymer molecular chain of the retardation film itself is relaxed, the retardation value is greatly reduced, and the optical properties are satisfactorily maintained. I can't.

  Moreover, it is difficult for the annealing treatment for less than 1 minute to obtain a uniform annealing effect on the film. An annealing process exceeding 1000 hours results in a thermal acceleration test of the thermoplastic resin itself, which may cause yellowing or plasticization of the film and cannot be used as a retardation film. The annealing treatment condition is preferably an annealing treatment in a temperature range of 95 ° C. to (glass transition point −7) ° C. for 5 minutes to 500 hours, more preferably 100 ° C. to (glass transition point −10) ° C. In the temperature range of 10 minutes to 100 hours.

  Examples of the environment in which the annealing method is performed include a method of holding a roll of retardation film uniformly in an oven, or a method of transporting the roll in the oven at a predetermined temperature and time, etc. Any method can be used as long as the retardation film is uniformly and evenly heated.

[Retardation film, circularly polarizing film, elliptically polarizing film, and liquid crystal display element or optical device using them]
The retardation film of the present invention can be used for various wave plates such as a quarter wave plate.
Here, as the retardation film, the quarter-wave plate is excellent in image quality by using, for example, a reflective liquid crystal display device in which only one polarizing film is used and the back electrode is also used as a reflective electrode. It is possible to obtain a reflective display device. It is also possible to use this retardation film on the back side with respect to the observer of the guest-host type liquid crystal layer. In these cases, the role of the retardation film is to convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light in the visible light region. Moreover, it can use similarly as an element which converts the circularly polarized light of the reflective polarizing film comprised from the cholesteric liquid crystal etc. which reflect only either one of right and left circularly polarized light into linearly polarized light.

  In addition, the retardation film of the present invention is bonded to a polarizing film through an adhesive layer or an adhesive layer to form a circularly polarizing film or an elliptically polarizing film. Also, a certain material is coated on the retardation film to be wet heat resistant. The solvent resistance may be improved.

  Two or more retardation films of the present invention are laminated, or the retardation film of the present invention and another optical film (transparent film, transparent conductive film, retardation film, polarizing film, optical compensation plate, etc.). By laminating, for example, it is possible to obtain a retardation film or an optical film suitable for various uses such as producing ideal λ / 4 plates and λ / 2 plates in a wide wavelength range.

  In addition, by using such a retardation film in a liquid crystal display device, particularly a polarizing film single reflection type liquid crystal display device, a display device having excellent image quality can be obtained. This reflective liquid crystal display device is composed of a polarizing film, a retardation film, a substrate with a transparent electrode, a liquid crystal layer, a substrate with a scattering reflection electrode, a polarizing film, a scattering plate, a retardation film, and a transparent electrode. A substrate, a liquid crystal layer, a substrate with a mirror reflective electrode, a polarizing film, a retardation film, a substrate with a transparent electrode, a liquid crystal layer, a substrate with a transparent electrode, and a reflective layer. . Further, the quarter-wave plate can be used in a liquid crystal display device having both a transmission type and a reflection type. Examples of the configuration of the liquid crystal display device include a polarizing film, a retardation film, a substrate with a transparent electrode, a liquid crystal layer, a substrate with a reflection / transmission electrode, a retardation film, a polarizing film, and a backlight system. Furthermore, for example, in a reflective polarizing film that reflects only one of the left and right circularly polarized light made of cholesteric liquid crystal, excellent linearly polarized light can be obtained if it is used as an element that converts circularly polarized light into linearly polarized light.

  Furthermore, the retardation film of the present invention can also be used as a quarter-wave plate used in an optical head of an optical recording apparatus. In particular, since such a retardation film can give a phase difference of a quarter wavelength with respect to multiple wavelengths, it contributes to reducing the number of retardation plates in an optical head using a plurality of laser light sources. be able to.

  Further, as an optical member in a liquid crystal projector or the like, for example, the retardation film of the present invention may be used for a polarization conversion element, a polarization beam splitter, or the like as a quarter wavelength plate or a quarter wavelength plate.

  In addition, organic or inorganic electroluminescent elements, which are light emitting elements, use a metal electrode on the back side of the light emitting layer. However, since this metal electrode reflects light, the contrast is significantly reduced in the presence of external light. Sexuality decreases. In order to prevent this, the retardation film of the present invention and a polarizing film may be combined to form a circularly polarizing film, which may be used as an antireflection film. Since this circularly polarizing film uses the retardation film of the present invention capable of setting the phase difference to a quarter wavelength in a wide wavelength range of visible light, reflection can be prevented at a wide wavelength range. It is possible to provide an element with less coloration and excellent visibility. Moreover, you may use as a touch panel and may be used for CRT and PDP.

  Furthermore, the retardation film of the present invention can be used as an image quality improving film for improving the color tone and widening the viewing angle of a transmissive liquid crystal display device. Examples of the liquid crystal display device include a twisted nematic mode, a vertical alignment mode, an OCB (Optically Compensated Bend) alignment mode, an in-plane switching mode, and the like.

  The retardation film of the present invention may be used simultaneously with an optical compensation film such as another retardation film or a viewing angle widening film (for example, a discotic liquid crystal layer or a polymer liquid crystal layer is oriented in the film thickness direction of the film). Viewing angle expansion film, etc.). Further, the retardation film of the present invention may be used for a liquid crystal display device using a ferroelectric liquid crystal or an antiferroelectric liquid crystal.

Examples of the present invention will be described below, but the present invention is not limited thereto. Moreover, the material characteristic value etc. which are described in this specification were obtained by the following evaluation methods.
(1) Glass transition temperature (Tg): A differential scanning calorimeter (DSC) Q10 manufactured by TA Instruments was used, and the temperature rising rate was measured at 20 ° C./min.
(2) Measurement of water absorption rate: Measurement was performed in accordance with American Industrial Standard ASTM D570.
(3) Endothermic amount at the glass transition point: A differential scanning calorimeter (DSC) Q10 manufactured by TA Instruments was used, and the heating rate was 20 ° C./min and the measurement temperature range was 30 to 300 ° C. For measuring the endothermic amount at the glass transition point, the portion 1 shown in FIG. 1 was calculated.
(4) Measurement of R value and Rth value The phase difference R value, which is the product of birefringence Δn and film thickness d, and the phase difference K value perpendicular to the in-plane direction are the product name “KOBRA21” manufactured by Oji Scientific Instruments. -ADH ". The R value is measured in a state where the incident light beam is perpendicular to the surface of the film, and R = Δn · d = (nx−ny) · d and Rth = ((nx + ny) / 2−nz) · d. The unit of R value and Rth value is nm. Here, nx, ny, and nz are defined as follows.
nx: Refractive index in the main stretching direction in the film plane ny: Refractive index in the direction perpendicular to the main stretching direction in the film plane nz: Refractive index in the normal direction of the film surface (in the case of uniaxial stretching in the main stretching direction) (In the case of biaxial stretching, it means the direction of stretching so that the degree of orientation increases, and the chemical structure indicates the orientation direction of the polymer main chain.)
(5) Total light transmittance and haze value of the film: Measured using a turbidimeter NDH-2000 type manufactured by Nippon Denshoku Industries Co., Ltd.
(6) Film thickness: Measured with an electronic micro film thickness meter manufactured by Anritsu Corporation.

[Example 1]
As a thermoplastic resin, trade name “TOPAS” 6013 manufactured by TICONA (cycloolefin copolymer obtained by copolymerizing ethylene and norbornene with a metallocene catalyst, [meso type] / [rasemo type] = 0.36 / 0.04 = 9, The abundance ratio (molar fraction) of NN dyad is 0.40, the molar ratio of ethylene component to norbornene component is (A) / (B) = 50/50, and reduced viscosity ηsp / c is 0.80 dL / g) did. The thermoplastic resin pellets were melt-extruded from a T-die having a width of 15 cm using a twin-screw melt extruder (TEX30SS-42BW-3V manufactured by Nippon Steel Works), and continuously formed with a cooling roller to form a film. . Film forming conditions were a cylinder temperature of 260 ° C., a T die temperature of 270 ° C., a cooling roller temperature of 145 ° C., and a film forming speed of 1 m / min. This film was excellent in transparency and homogeneity, and had good surface properties. The average thickness was 120 μm except for the 2.5 cm width at both ends of the film. The glass transition temperature (Tg) was 138 ° C., the total light transmittance was 91.5%, and the haze was 0.3%. The film was stretched using a batch-type biaxial stretching apparatus in which the film end was fixed with a chuck. Stretching conditions were a stretching temperature of 148 ° C., a stretching ratio of 2.0 times, a stretching speed of 50% / mm, and longitudinal uniaxial stretching with the transverse direction being free. The film thickness after stretching was 75 μm. At this time, the endothermic amount of the obtained film at the glass transition point was not observed.

  The film was placed in an oven at 120 ° C. and held for 3 minutes for annealing. After the annealing treatment, the retardation values of the film were retardation values R (550) = 138 nm and Rth (550) = 71 nm. The endothermic amount at the glass transition point of the annealed film was 0.2 J / g.

  The annealed film was held for 60 hours at 90 ° C. and 90 ° C. DRY for 1000 hours as a heat and humidity resistance test. However, the change in retardation was not observed before and after the wet heat resistance test, and it was confirmed that the retardation film was excellent in environmental resistance.

[Example 2]
In the same manner as in Example 1, an unstretched film having an average thickness of 140 μm was obtained using a product name “TOPAS” 6013 manufactured by TICONA as a thermoplastic resin. The film had a glass transition temperature of 138 ° C., a total light transmittance of 91.1%, and a haze of 0.3%. The film was stretched using a batch-type biaxial stretching apparatus in which the film end was fixed with a chuck. Stretching conditions were a stretching temperature of 148 ° C., a longitudinal stretching ratio of 1.5 times, a transverse stretching ratio of 2.0 times, and a longitudinal and transverse sequential biaxial stretching at a stretching speed of 50% / mm. The film thickness after stretching was 56 μm. At this time, the endothermic amount at the glass transition point of the obtained film was not observed.

  The film was placed in an oven at 125 ° C. and held for 1 minute for annealing. After the annealing treatment, the retardation values of the film were retardation values R (550) = 52 nm and Rth (550) = 141 nm. The endothermic amount at the glass transition point of the film after the annealing treatment was measured to be 0.5 J / g.

  The film after the annealing treatment was held at 60 ° C. 90% and 90 ° C. DRY 1000 hours as a moisture and heat resistance test. However, the change in retardation was not observed before and after the wet heat resistance test, and it was confirmed that the retardation film was excellent in environmental resistance.

[Comparative Example 1]
In the same manner as in Example 1, an unstretched film having an average thickness of 140 μm was obtained using a product name “TOPAS” 6013 manufactured by TICONA as a thermoplastic resin. The film had a glass transition temperature of 138 ° C., a total light transmittance of 91.0%, and a haze of 0.4%. The film was stretched using a batch-type biaxial stretching apparatus in which the film end was fixed with a chuck. Stretching conditions were a stretching temperature of 148 ° C., a stretching ratio of 2.0 times, a stretching speed of 50% / mm, and longitudinal uniaxial stretching with the transverse direction being free. The film thickness at the center of the film after stretching was 77 μm, the retardation value R (550) = 139 nm, and Rth (550) = 72 nm. Thereby, the endothermic quantity in the glass transition point of the obtained film was not seen.

  The film was held at 60 ° C. for 90% and 90 ° C. DRY for 1000 hours as a moisture and heat resistance test. At this time, before and after the wet heat resistance test, the phase difference value R (550) = 133 nm and Rth (550) = 66 nm at 60 ° C. and 90%, and the phase difference value R (550) = 127 nm and Rth at 90 ° C. DRY. (550) = 63 nm. As a result, before and after the wet heat resistance test, a maximum 11 nm decrease in R (550) and a maximum 9 nm decrease in Rth (550) are observed, and the retardation film has a problem of deterioration of optical properties in environmental resistance. It was confirmed that.

[Comparative Example 2]
In the same manner as in Example 1, an unstretched film having an average thickness of 140 μm was obtained using a product name “TOPAS” 6013 manufactured by TICONA as a thermoplastic resin. The film had a glass transition temperature of 138 ° C., a total light transmittance of 91.1%, and a haze of 0.3%. The film was stretched using a batch-type biaxial stretching apparatus in which the film end was fixed with a chuck. Stretching conditions were a stretching temperature of 148 ° C., a longitudinal stretching ratio of 1.5 times, a transverse stretching ratio of 2.0 times, and a longitudinal and transverse sequential biaxial stretching at a stretching speed of 50% / mm. The film thickness after stretching was 56 μm retardation value R (550) = 44 nm and Rth (550) = 145 nm. At this time, the endothermic amount at the glass transition point of the obtained film was not observed.

  The film was held at 60 ° C. for 90% and 90 ° C. DRY for 1000 hours as a moisture and heat resistance test. At this time, before and after the wet heat resistance test, at 60 ° C. and 90%, the retardation value R (550) = 40 nm and Rth (550) = 138 m, and at 90 ° C. DRY, the retardation value R (550) = 37 nm and Rth. (550) = 122 m. As a result, before and after the wet heat resistance test, it was observed that the retardation value of the film was reduced by a maximum of 7 nm for R (550) and a maximum decrease of 23 nm for Rth (550). It was confirmed that this was a retardation film.

  The retardation film of the present invention can be preferably used in optical elements such as a liquid crystal display device, a light emitting element, an antiglare film, an optical recording apparatus, and a polarizing beam splitter that require environmental resistance.

The schematic diagram which defined the endothermic amount of the glass transition point temperature vicinity obtained with a differential scanning calorimeter.

Explanation of symbols

1: Line obtained by extending the base line after the glass transition point 2: Endothermic amount (J / g)

Claims (9)

  A film made of a thermoplastic resin and oriented in at least a uniaxial direction, wherein the glass transition temperature of the thermoplastic resin is in the range of 100 to 180 ° C., and the endothermic amount at the glass transition temperature is 0.01 to 5 A retardation film having a thickness of 0.0 J / g.   The retardation film according to claim 1, wherein the thermoplastic resin is an amorphous polyolefin.   The amorphous polyolefin is a copolymer of i) ethylene and norbornene, and ii) the meso-type and racemo-type abundance ratio of the meso-type and racemo-type in terms of stereoregularity of the two-chain sites (dyads) of norbornene units. The retardation film according to claim 2, wherein [Rasemo type]> 4.   A retardation film comprising a thermoplastic resin and a film stretched at least in a uniaxial direction at a temperature of 90 ° C. to (glass transition point −5 ° C.) within a range of 1 minute to 1000 hours. Production method.   The circularly-polarizing film which consists of a polarizing film and the retardation film in any one of Claims 1-3.   A light-emitting element using the circularly polarizing film according to claim 5.   An elliptically polarizing film comprising a polarizing film and the retardation film according to claim 1.   A liquid crystal display element using the retardation film according to claim 1.   An optical device using the retardation film according to claim 1.

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