HK1108941B - Retardation film - Google Patents

Description

Phase difference film

Technical Field

The present invention relates to a retardation film. More specifically, the present invention relates to a retardation film using an amorphous polyolefin copolymer containing an ethylene unit and a norbornene unit.

Background

In recent years, liquid crystal display devices have been remarkably developed, and not only small and medium-sized liquid crystal display devices such as mobile phones and personal computer displays, but also large-sized liquid crystal display devices for televisions have been widely used. In liquid crystal display devices, a retardation film exhibiting birefringence is generally used in a polymer film for color compensation of liquid crystal, expansion of a viewing angle, improvement of contrast, and the like, and polycarbonate or the like has been used as a polymer material. As for the retardation film, recently, a resin called amorphous polyolefin has been attracting attention. The amorphous polyolefin refers to a polyolefin having an alicyclic structure, improved in heat resistance, and made amorphous, and is characterized by high transparency and excellent dimensional stability due to low water absorption. Further, since the liquid crystal display device does not contain an aromatic component and has a feature of having an extremely low photoelastic constant, excellent physical properties have been attracting attention as the liquid crystal display device for television and the like is increased in size.

The amorphous polyolefins may be classified into 2 types in general in structure. An amorphous polyolefin obtained by ring-opening polymerization of a cyclic olefin and hydrogenation of the double bond of the main chain formed has been marketed: trade names ZEONEX (registered trademark) and ZEONOR (registered trademark) manufactured by Zeon corporation, japan; a resin available under the trade name ARTON (registered trademark) manufactured by JSR corporation. Another example of the polyolefin is an amorphous polyolefin obtained by vinyl-copolymerizing a cyclic olefin and ethylene, and commercially available amorphous polyolefins include a trade name APEL (registered trademark) manufactured by mitsui chemical corporation and a trade name TOPAS (registered trademark) manufactured by TICONA corporation. Among them, the former ring-opening polymerization hydrogenated amorphous polyolefin has been studied more frequently as a retardation film for retardation characteristics, production methods, assembly in a liquid crystal display device, and the like (see Japanese patent laid-open Nos. 4-245202, 3273046, 6-59121, 8-43812, 3470567, and 306557).

On the other hand, the latter copolymer of a cyclic olefin and ethylene can be produced by 1-stage polymerization and is advantageous in terms of economy as compared with the former amorphous polyolefin, but the characteristics as a retardation film have been hitherto unknown basically. Among the reported examples using the above ring-opening polymerization hydrogenated resins, the vinyl copolymer resins collectively referred to as thermoplastic polyolefins, cyclic polyolefins, and the like are often described as preferable resins, but basically, no specific study has been made. There has been reported only one example of a retardation film obtained by stretching a sheet made of a copolymer of ethylene and tetracyclododecene to provide birefringence (see patent No. 3497894), and it is completely unknown what structure is suitable as a retardation film. For example, when an amorphous polyolefin is used as a retardation film, in addition to film formability and transparency, the expression of birefringence, that is, the tendency of birefringence to appear is an important characteristic. This is because amorphous polyolefins generally have an extremely low photoelastic constant and have intrinsic characteristics such as birefringence which are difficult to be expressed compared with aromatic polymers such as polycarbonate and polysulfone. Therefore, in order to obtain a retardation film having a desired retardation value, a film thickness must be made considerably thick for a resin which hardly exhibits birefringence even when the film is stretched, and as a result, it is not suitable as a member of a liquid crystal display device which is required to be thin and light.

However, in order to obtain a vinyl-type copolymer of ethylene and a cyclic olefin, although several methods are known, a method of performing polymerization using a ziegler-natta catalyst represented by a combination of a vanadium compound and an organoaluminum compound; or a method of carrying out polymerization using a metallocene catalyst comprising a metallocene which is a metal complex compound of titanium, zirconium, or the like and a cocatalyst such as MAO (methylaluminoxane) is practically used. Among them, for a Ziegler-Natta catalyst, control of composition or stereostructure is difficult in its polymerization mechanism, and thus it is known to provide an atactic polymer lacking stereoregularity by random copolymerization. On the other hand, the metallocene catalyst has a uniform active site and can be controlled variously. For example, it was confirmed that the stereoregularity of the obtained copolymer was different depending on the ligand of the metallocene (see macromol. rapidcommun.20, 279 (1999)). Further, it has been reported that such a difference has an influence on the mechanical properties and melt properties of the copolymer (see Japanese patent application laid-open Nos. Hei 8-507800, Hei 8-507801 and Hei 7-2953), but no study has been made on the difference in optical properties.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a retardation film which is extremely suitable for an amorphous polyolefin of the latter type, i.e., a copolymer of a cyclic olefin and ethylene, which is advantageous in terms of economy.

Another object of the present invention is to provide a non-oriented film used for the retardation film.

It is still another object of the present invention to provide a liquid crystal display device having the retardation film.

Further other objects and advantages of the present invention will become apparent from the following description.

According to the present invention, the above object and advantages of the present invention are achieved by the following retardation film:

a phase difference film, comprising:

(a) containing an ethylene unit and a norbornene unit,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) an amorphous polyolefin copolymer having a glass transition temperature in the range of 100 ℃ to 180 ℃.

According to the present invention, the above object and advantage 2 of the present invention are achieved by an unoriented film for producing the retardation film of the present invention.

Further, according to the present invention, the above object and advantage 3 of the present invention are achieved by a liquid crystal display element having the retardation film of the present invention.

Drawings

FIG. 1 is a diagram showing an ethylene-norbornene copolymer having a norbornene component of 44 mol% obtained in example 1¹³C-NMR spectrum chart.

FIG. 2 shows grade 6013 of TOPAS, trade name, made by TICONA corporation, used in examples 2 to 5¹³C-NMR spectrum chart.

FIG. 3 shows contents obtained in comparative example 1Method for producing ethylene-norbornene copolymer having norbornene component of 42 mol%¹³C-NMR spectrum chart.

FIG. 4 shows grade 5013 of TOPAS tradename manufactured by TICONA corporation used in comparative example 2¹³C-NMR spectrum chart.

Detailed Description

The present invention will be described in detail below.

The amorphous polyolefin used in the present invention refers to a copolymer obtained by vinyl polymerization of ethylene and norbornene, and examples thereof include a copolymer containing an ethylene repeating unit (a) and a norbornene repeating unit (B) represented by the following formula.

Wherein R is⁰¹And R⁰²Independently of each other, a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

Examples of the norbornene compound providing the norbornene repeating unit (B) include bicyclo [2.2.1]Hept-2-ene, 6-methylbicyclo [2.2.1 ]]Hept-2-ene, 5, 6-dimethylbicyclo [2.2.1 ]]Hept-2-ene, 6-ethylbicyclo [2.2.1 ]]Hept-2-ene and 6-butylbicyclo [2.2.1 ]]Hept-2-ene. Among them, R is preferred⁰¹And R⁰²Bicyclo [2.2.1 ] s all being hydrogen atoms]Hept-2-ene.

The amorphous polyolefin may contain a small amount of a repeating unit of another copolymerizable vinyl monomer in addition to the repeating units (a) and (B) within a range not to impair the object of the present invention. Specific examples of the other vinyl monomers include cyclic olefins 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, R¹～R²⁰The same or different, is a hydrogen atom, a halogen atom or a saturated or unsaturated aliphatic hydrocarbon group having 1 to 12 carbon atoms, and R can be substituted with¹⁷And R¹⁸Or from R¹⁹And R²⁰Form an alkylene radical, and furthermore, R¹⁷Or R¹⁸And R¹⁹Or R²⁰A ring can be formed and the ring can have a double bond.]Alpha-olefins having 3 to 18 carbon atoms such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene; cycloolefins such as cyclobutene, cyclopentene, cyclohexene, 3-methylcyclohexene, and cyclooctene. Among these, an α -olefin having 3 to 18 carbon atoms can be used as a molecular weight modifier in copolymerization, and among these, 1-hexene is preferably used. The other vinyl monomers may be used alone or in combination of at least 2, and the repeating units thereof are preferably 10 mol% or less, more preferably 5 mol% or less, of the total.

In general, in an ethylene-norbornene copolymer, although depending on a polymerization method, a catalyst used, a composition, and the like, a certain degree of linkage sites of norbornene units are present in any case. Regarding the stereoregularity of 2-linked sites of norbornene units of vinyl polymerization type (hereinafter referred to as NN diads), it is known that 2 stereoisomers of meso type and (E) racemic type as shown in the following formula (D) exist, and in the copolymer of the present invention, the stereoregularity is characterized by the following formulae (D) and (E):

(meso type)

(racemic form)

The ratio of the meso-2 linkage site to the rac-2 linkage site is 4 or more in terms of the ratio of the rac-2 linkage site to the meso-2 linkage site. Preferably, the above ratio is 6 or more. The upper limit of the contrast ratio is not particularly limited, and the higher the contrast ratio is, the more suitable the birefringence expression is, the more preferable the contrast ratio is. The existence ratio of NN diad stereoisomers referred to herein can be determined from reports on the resolution of stereoregularity of an ethylene-norbornene copolymer (see Macromol. Rapid Commun.20, 279(1999))¹³C-NMR. In the present invention, measured in a deuterated o-dichlorobenzene solvent¹³In C-NMR, the ratio of the meso type 2 linkage site/the racemic type 2 linkage site is equivalent to [2 ], [¹³Peak area of 28.3ppm in C-NMR spectrum]/[¹³Peak area of 29.7ppm in C-NMR spectrum]Is calculated. If the ratio is less than 4, that is, if the ratio of the racemic form is larger, a copolymer having poorer birefringence expression is formed, and needless to say, a desired retardation value is obtained by a method of stretching by increasing the thickness, increasing the stretching magnification, lowering the stretching temperature, or the like, but it is not preferable from the viewpoint of film formation, productivity, or the like.

Furthermore, based on¹³In the analysis of C-NMR, the ratio of NN diads to the total norbornene unit component (mole fraction), that is, how much chain structure the norbornene units form, can be determined, and the range of about 0.1 to 0.6 in the present invention. The mole fraction referred to herein is defined as¹³Peak area of 28.3ppm of C-NMR spectrum +¹³Peak area of 29.7ppm in C-NMR spectrum]/[ peak area of 1 part of carbon atom of Total norbornene component]And (4) calculating.

Further, in the present invention, the glass transition temperature (Tg) of the copolymer is in the range of 100 ℃ to 180 ℃. If the Tg is less than 100 ℃, the heat resistance stability is poor. On the other hand, if Tg is higher than 180 ℃, toughness of the film tends to be lowered, and melt viscosity of the copolymer is too high to make melt film formation of the film difficult, which is not preferable. The Tg is preferably in the range of 120 to 160 ℃ and more preferably 130 to 150 ℃.

The copolymer used in the present invention has a composition of the repeating units (a) and (B) and a glass transition temperature, and the molar ratio of (a)/(B) is preferably 61/39 to 40/60. More preferably, the glass transition temperature is in the range of 120 to 160 ℃ in a molar ratio (a)/(B) of 57/43 to 46/54. Said composition may be prepared by¹³And C-NMR measurement.

The molecular weight of the ethylene-norbornene copolymer used in the present invention is in the range of 0.1dL/g to 10dL/g, more preferably 0.3dL/g to 3dL/g, in terms of the reduced viscosity eta sp/c measured in a cyclohexane solution at a temperature of 30 ℃ and a concentration of 1.2 g/dL. If the reduced viscosity η sp/c is less than 0.1, the film becomes brittle, which is not preferable, and if it is more than 10, the melt viscosity becomes too high for melt film formation, for example, and melt film formation of the film becomes difficult.

In the present invention, 1 copolymer may be used as it is or at least 2 copolymers different in composition or molecular weight may be blended and used. For blends, the preferred compositions or molecular weights described above refer to the compositions or molecular weights in the blend population. When the blend is used, it is preferable to use a blend having a similar copolymerization composition from the viewpoint of compatibility. If the composition difference is too large, phase separation may occur due to blending, and the film may be whitened during film formation or during stretch orientation.

The method for producing the ethylene-norbornene copolymer used in the present invention is not particularly limited as long as the glass transition temperature and the stereoregularity of NN diads satisfy the above ranges. Specifically, a method of copolymerizing ethylene and norbornene using a metallocene catalyst is preferably exemplified. The metallocene used in this case is of the formula (F)

Shown. In the above formula (F), M is a metal selected from titanium, zirconium or hafnium, R²⁴And R²⁵The same or different, and is 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 an aryloxy group having 6 to 12 carbon atoms, R²²And R²³Identical or different, are monocyclic or polycyclic hydrocarbon radicals capable of forming, together with the central metal M, a sandwich structure, R²¹Is connected with R²²Group and R²³A bridging group of groups selected from the group consisting of:

at this time R²⁶～R²⁹The same or different, hydrogen atom, halogen atom, saturated or unsaturated hydrocarbon group with 1-12 carbon atoms, alkoxy group with 1-12 carbon atoms, or aryloxy group with 6-12 carbon atoms; or, R²⁶And R²⁷Or R²⁸And R²⁹A ring may be formed.

R as ligand²²And R²³Having C relative to the central metal M at the same time₂Symmetry with C when not simultaneously₁Symmetry. R²²And R²³Preferably cyclopentadienyl, indenyl, alkyl or aryl substituents thereof, most preferably the central metal M is zirconium from the viewpoint of catalytic activity. R²⁴And R²⁵The alkyl groups may be the same or different and are preferably an alkyl group having 1 to 6 carbon atoms or a halogen atom, particularly a chlorine atom. R²⁶～R²⁹Preferably a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a phenyl group as R²¹Preferable examples thereof include lower alkylene groups such as methylene, ethylene and propylene; alkylene groups such as isopropylidene (RCH ═ e); substituted alkylene groups such as diphenylmethylene; silicon methyleneOr substituted silylene such as dimethylsilylene, diphenylsilylene and the like.

Specific examples of the preferable metallocene 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, and isopropylidene-bis (1-indenyl) zirconium dichloride. They may be used alone or in combination of at least 2. Further, as the cocatalyst of the metallocene, a known cocatalyst of metallocene such as methylaluminoxane which is an organoaluminum oxy compound, or a combination of an ionic boron compound and an alkylaluminum compound can be used.

Using the metallocene catalyst, a desired copolymer can be obtained by a known polymerization method using a hydrocarbon solvent such as toluene, xylene, cyclohexane, etc., and the obtained copolymer is reprecipitated in a poor solvent such as alcohol and washed; or adsorbing the catalyst on an absorbent; or by filtering the solution by adding some additives to the solution to precipitate, and then removing the solvent by distillation.

The retardation film of the present invention can be produced by forming a film of the copolymer to obtain a generally unstretched unoriented film for stretching, and then stretching the film.

The unstretched film can be formed into a film by a known method such as a solution casting method, a melt extrusion method, a hot extrusion method, or a rolling method. Among them, the melt extrusion method is preferable in view of productivity, economy, or solvent-free environment. In the melt extrusion method, a method of extruding the resin to be conveyed to a cooling roll using a T-die is preferably used. The temperature at the time of extrusion is determined by the fluidity, thermal stability and the like of the copolymer, but it is preferable to perform the extrusion in the range of 220 to 300 ℃. When the temperature is lower than 220 ℃, the melt viscosity of the copolymer is too high, and when the temperature is higher than 300 ℃, the transparency and homogeneity of the film may be impaired due to decomposition degradation and gelation of the copolymer. More preferably in the range of 220 ℃ to 280 ℃.

When the copolymer is formed into a film by solution casting, a hydrocarbon solvent such as toluene, xylene, cyclohexane, or decalin is preferably used. In the production of an unstretched film by these methods, it is preferable to reduce variation in film thickness as little as possible. This is because, if the film thickness unevenness at this time is large, there is a high possibility that the retardation unevenness of the retardation film obtained in the subsequent stretching step is large. The film thickness unevenness is preferably ± 8% or less, more preferably ± 5% or less, with respect to the film thickness. The film thickness in the unstretched film stage is determined in consideration of a desired retardation value and film thickness of the retardation film after stretching, but is preferably in the range of 30 to 400 μm, more preferably in the range of 40 to 300 μm, and particularly preferably in the range of 40 to 250 μm.

The thus obtained unstretched film is subjected to stretch orientation to obtain the retardation film of the present invention. The stretching method is not particularly limited, and a uniaxially oriented film or a biaxially oriented film can be obtained by a known method such as longitudinal uniaxial stretching using inter-roll stretching, transverse uniaxial stretching using a tenter, or simultaneous biaxial stretching or sequential biaxial stretching combining these. The continuous operation is preferable in view of productivity, but may be carried out in a batch manner, and is not particularly limited. The stretching temperature is in the range of (Tg-20 ℃) to (Tg +30 ℃) relative to the glass transition temperature (Tg) of the ethylene-norbornene copolymer, and preferably in the range of (Tg-10 ℃) to (Tg +20 ℃). The stretching ratio is determined according to the intended retardation value, but is 1.05 to 4 times, more preferably 1.1 to 3 times, in the longitudinal and lateral directions, respectively.

Liquid crystal display devices include various types such as TN type, STN type, TFT type, transmission type, reflection type, and semi-transmission type, and various types such as TN type, Vertical Alignment (VA) type, OCB type, and IPS type have been developed. Although there are various characteristics of the retardation film required by the kind of the liquid crystal or the type to be used, the ethylene-norbornene copolymer of the present invention is excellent in the expression of birefringence, and thus it is possible to provide a retardation film having various characteristics as a film having a small thickness.

One of preferable retardation films obtained by the present invention is a film in-plane retardation R (550) at a wavelength of 550nm in the range of the following formula (1),

100nm＜R(550)＜800nm ...(1)

and a retardation film having a film thickness of 10 to 150 μm. The phase difference R is defined by the following formula (5) and is a characteristic representing the phase retardation of light transmitted in the direction perpendicular to the film.

R＝(nx-ny)×d ...(5)

Where nx is a refractive index of a phase retardation axis (axis having the highest refractive index) in the film plane, ny is a refractive index in a direction perpendicular to nx in the film plane, and d is a film thickness.

Among them, R (550) is more preferably 100nm to 600nm, and still more preferably 120nm to 600 nm. The thickness is more preferably 20 to 120 μm, and still more preferably 20 to 80 μm. The retardation film can be produced by uniaxial stretching or biaxial stretching, and is suitable for 1/4 λ sheet, 1/2 λ sheet, and the like.

Further, as another preferable retardation film, there may be mentioned a film in-plane retardation R (550) at a wavelength of 550nm and a film thickness direction retardation K (550) in the following formulae (2) and (3)

0nm＜R(550)＜100nm ...(2)

50nm＜K(550)＜400nm ...(3)

And a film thickness of 10 to 150 μm.

In the above formula, K (550) is a phase difference value in the film thickness direction at a wavelength of 550nm, and is defined by the following formula (4).

K＝{(nx+ny)/2-nz}×d ...(4)

In the above formula, nx and ny are refractive indices of x and y axes in the film plane, nz is a refractive index in the thickness direction perpendicular to the x and y axes, and d is the film thickness.

Wherein the definition of the phase difference R is the same as that described above. R (550) is more preferably 10 to 80nm, still more preferably 30 to 80 nm. Further, K (550) is more preferably 80nm to 250 nm. The thickness is more preferably 30 to 100 μm, and still more preferably 30 to 85 μm. The retardation film can be produced by biaxial stretching, has birefringence in the film thickness direction, and is particularly suitable for Vertical Alignment (VA) type optical compensation.

In general, as a structure for vertical alignment type optical compensation for a large liquid crystal display device such as a television, there are a 2-sheet structure in which an optical compensation film is sandwiched between both sides of a liquid crystal cell and a 1-sheet structure used only on either side of the liquid crystal cell. As the retardation film of the present invention used in the 2-plate structure, it is preferable that 30nm < R (550) < 80nm, 80nm < K (550) < 150nm and the film thickness is in the range of 30 μm to 85 μm. Further, when used in a 1-piece structure, it is preferable that 30nm < R (550) < 80nm, 150nm < K (550) < 250nm and the film thickness is in the range of 30 μm to 85 μm. The retardation film of the present invention is excellent in the expression of birefringence, and therefore can be suitably used as a retardation film having a 1-plate structure requiring a high K value. When a vertical alignment liquid crystal display element in which these retardation films are combined is used, the contrast and color tone are excellent not only from the front but also from the oblique surface, and a wide viewing angle is obtained.

In the retardation film of the present invention, in view of all of the above, the following embodiments (i), (ii) and (iii) are particularly preferable.

(i) A retardation film comprising (a) a film containing an ethylene unit and a norbornene unit,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) an amorphous polyolefin copolymer having a glass transition temperature in the range of 120 ℃ to 160 ℃, and

(d) the in-plane retardation R (550) of light having a wavelength of 550nm satisfies the following formula (1-1)

120nm＜R(550)＜600nm ...(1-1)

And the film thickness is in the range of 20 μm to 80 μm.

(ii) A retardation film comprising (a) a film containing an ethylene unit and a norbornene unit,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) an amorphous polyolefin copolymer having a glass transition temperature in the range of 120 ℃ to 160 ℃, and

(d) the retardation R (550) in the film plane based on light having a wavelength of 550nm satisfies the following formulae (2-1) and (3-1)

30nm＜R(550)＜80nm ...(2-1)

80nm＜K(550)＜150nm ...(3-1)

And the film thickness is in the range of 30 to 85 μm.

(iii) A retardation film comprising (a) a film containing an ethylene unit and a norbornene unit,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) an amorphous polyolefin copolymer having a glass transition temperature in the range of 120 ℃ to 160 ℃, and

(d) the retardation R (550) in the film plane based on light having a wavelength of 550nm satisfies the following formulae (2-1) and (3-2)

30nm＜R(550)＜80nm ...(2-1)

150nm＜K(550)＜250nm ...(3-2)

And the film thickness is in the range of 30 to 85 μm.

In addition, a retardation film is generally used by being laminated between a liquid crystal cell and a polarizing film, and there are generally another bonding method in which the retardation film is used by being bonded to a protective film of a PVA (polyvinyl alcohol) film containing iodine using TAC (triacetyl cellulose) and a direct bonding method in which the PVA film is directly laminated without a protective film. Any mode can be used for the retardation film of the present invention.

The retardation film of the present invention can be produced by either a continuous or batch process as described above, but it is preferable to conduct stretching continuously from an industrial viewpoint. When the stretching is continuously performed, the fed film is wound around a winding core, and the retardation film can be obtained in a state of being wound into a film roll. In the above case, in the present invention, any one of a retardation film in which the phase retardation axis is oriented in the film width direction and a retardation film in which the phase retardation axis is oriented in the film traveling direction can be produced. Preferable examples of the retardation film having a retardation axis in the width direction of the film include a transverse uniaxially oriented film obtained by transversely uniaxially stretching an unstretched film by a tenter; and a biaxially oriented film obtained by stretching in the machine direction and then stretching in the transverse direction to orient the phase retardation axis in the transverse direction. Further, as a retardation film having a retardation axis in the film running direction, there can be mentioned a longitudinally uniaxially oriented film obtained by longitudinally uniaxially stretching an unstretched film; a biaxially oriented film obtained by longitudinally stretching and then transversely stretching or transversely stretching and then longitudinally stretching, and finally longitudinally orienting the phase retardation axis. In the vertical alignment type of the large-sized liquid crystal display device, since the transmission axis of the polarizing plate and the phase retardation axis of the retardation film are used in parallel, the biaxial alignment film is preferably a retardation film having a phase retardation axis in the film width direction, which can be laminated with a polarizing plate film roll in a so-called roll-to-roll manner, from the viewpoint of productivity.

Examples

Although the present invention will be described in more detail with reference to examples below, the present invention is not limited to these examples.

The raw materials used in the examples and comparative examples are as follows.

Toluene (solvent) and norbornene were purified by distillation and dried sufficiently. For the metallocene, ethylene-bis (1-indenyl) zirconium dichloride was directly used as purchased from Aldrich. Isopropylidene- (9-fluorenyl) (cyclopentadienyl) zirconium dichloride is synthesized according to the literature [ J.A.Ewen et al, J.Am.chem.Soc., 110, 6255-.

As the aluminoxane, Polymethylaluminoxane (PMAO) was purchased from Tosoh Akzo Co., Ltd. to prepare a toluene solution having a concentration of 2M and used.

Triisobutylaluminum [ (iBu)3Al ] was purchased as a 1M n-hexane solution from Kanto chemical Co., Ltd and used as it was.

The physical properties of the examples and comparative examples were measured by the following methods.

(1) Glass transition temperature (Tg): the temperature was measured at a temperature rise rate of 20 ℃ per minute by using a model 2920 DSC manufactured by TAInstructions.

(2) Molecular weight of copolymer: the reduced viscosity eta sp/c (dL/g) at 30 ℃ in a cyclohexane solution having a concentration of 1.2g/dL was determined.

(3) Of copolymers¹³C-NMR measurement: an NMR apparatus of JNM-. alpha.400, manufactured by Japan Electron System, was used. Dissolved in deuterated o-dichlorobenzene solvent and measured at a temperature of 100 ℃. Tetramethylsilane was used as a chemical shift benchmark. For quantification, 150MHz was measured using reverse gated decoupling mode¹³C-NMR spectrum.

(4) Total light transmittance and haze value of film: the measurement was carried out by using a turbidimeter model NDH-2000 manufactured by Nippon Denshoku industries Co., Ltd.

(5) In-plane retardation value R of film and retardation value K in film thickness direction: the measurement was carried out using a spectroscopic ellipsometer M150 manufactured by Nippon spectral Co., Ltd. at a light wavelength of 550 nm. The in-plane phase difference value R is measured in a state where the incident light is perpendicular to the film surface. For the phase difference K in the film thickness direction, the angle between the incident light and the film surface was slightly changed, the phase difference at each angle was measured, the three-dimensional refractive indices nx, ny, nz were obtained by curve fitting using a known refractive index ellipsoid formula, and K was obtained by substituting K { (nx + ny)/2-nz } × d. In this case, the average refractive index of the film is required, and the refractive index is measured by using an Abbe refractometer (trade name "Abbe refractometer 2-T" manufactured by the company of アタゴ).

(6) Film thickness: measured with an electron microscope film thickness meter manufactured by アンリツ.

(7) Photoelastic constant of film: measured with a spectroscopic ellipsometer M150 manufactured by Nippon spectral Co., Ltd. Calculated from the change in retardation value when stress was applied to the film at a measurement wavelength of 550 nm.

Example 1

Copolymerization of ethylene and norbornene was carried out as follows using a stainless steel autoclave with stirring blades and a capacity of 500mL as a polymerization apparatus and ethylene-bis (1-indenyl) zirconium dichloride as a metallocene.

After the autoclave was purged with nitrogen, 100mL of toluene and 32g of norbornene were charged into the vessel, and 0.1mmol of triisobutylaluminum was added as a scavenger. Then, a metallocene-PMAO solution obtained by dissolving 30mg of ethylene-bis (1-indenyl) zirconium dichloride in 35mL of a 2M toluene solution of PMAO in advance under a nitrogen atmosphere and activating the solution by stirring at 25 ℃ for 10 minutes was added. After the temperature was subsequently raised to 40 ℃, 9.5g of ethylene was added to the vessel under pressure to initiate polymerization. After the polymerization was initiated for 2 hours, the reaction was returned to the nitrogen atmosphere, and a small amount of isopropyl alcohol was added to complete the reaction. The reaction mixture was released into a large amount of methanol made acidic with hydrochloric acid, and a precipitate was precipitated, filtered, washed repeatedly with acetone, methanol and water, and dried to obtain 20.3g of a resin.

The ethylene-norbornene copolymer thus obtained had a molecular weight of 0.92 as a reduced viscosity η sp/c. Further, Tg was 120 ℃. By passing¹³The spectrum obtained by C-NMR measurement is shown in FIG. 1. As is clear from FIG. 1, almost no racemic form of NN diad at 29.7ppm was observed, and only a substantially meso form at 28.3ppm was observed. The existence ratio (mole fraction) of NN diads with respect to the total norbornene component amount was 0.21. The molar ratio of the ethylene component to the norbornene component was (a)/(B) 56/44. This resin was dissolved in cyclohexane to prepare a 20 wt% solution, and a film having a film thickness of 58 μm was obtained by a solution casting method. The total light transmittance of the film was 91.1% and the haze was 1.1%.

The Tg, which is less affected by the residual solvent, was 107 ℃. The photoelastic constant of the film was determined to be-6.3X 10^-12Pa^-1. The film was stretched using a batch biaxial stretching apparatus in which the film ends were fixed by chucks. The film was stretched by uniaxial stretching in the machine direction under the conditions shown in table 1 while the transverse direction was allowed to be free, and the film thickness and retardation R (550) at the center of the stretched film were measured. The results are shown in Table 1.

Example 2

TOPAS (trade name) manufactured by TICONA corporation is a cycloolefin copolymer obtained by copolymerizing ethylene and norbornene using a metallocene catalyst. For grade 6013(Tg 140 ℃ C.)¹³C-NMR measurement. The spectrum is shown in FIG. 2. As shown in fig. 2, it was found that the meso diad/racemic diad was 0.36/0.04 was 9, and the presence ratio (mole fraction) of NN diads to the total norbornene component was 0.40. The molar ratio (a)/(B) of the ethylene component and the norbornene component was 50/50. The reduced viscosity eta sp/c was 0.80dL/g for molecular weight. Pellets thereof were melt-extruded from a T die having a width of 15cm using a biaxial melt extruder (TEX 30SS-42BW-3V, manufactured by Nippon Steel works Co., Ltd.), and the film was continuously taken up by a chill roll to form a film. At a cylinder temperature of 260 deg.C, a T-die temperature of 270 deg.C, and a chill roll temperature of 14 deg.CThe film was formed at 5 ℃ and a film forming speed of 1m/min, and the film was excellent in transparency, homogeneity and surface properties. The film thickness was 120 μm on average except for the portions of 2.5cm width at both ends of the film. Tg was 138 ℃, total light transmittance 91.5%, haze 0.3%. The photoelastic constant of the film was determined to be-6.1X 10^-12Pa^-1。

The film was uniaxially stretched in the machine direction in the same manner as in example 1. The stretching conditions and the results are shown in table 1.

Examples 3 and 4

Using the unstretched film of example 2, uniaxial stretching in the machine direction was carried out under other stretching conditions shown in Table 1. The results are shown in Table 1.

Example 5

For the film formation by melt extrusion performed in example 2, the slit width of the T-die was changed to obtain a molten film having an average film thickness of 190 μm. The Tg was likewise 138 ℃, the total light transmittance 91.4% and the haze 0.4%. This film was subjected to sequential biaxial stretching by a batch biaxial stretching apparatus used in example 2 in a machine direction of 1.5 times and a transverse direction of 2.0 times. The film thickness, R (550), K (550) at the center of the stretched film were measured. The results are shown in Table 1.

Example 6

For grades 6013 and 8007(Tg ═ 80 ℃) of TOPAS (trade name), the pellets were mixed at 6013/8007 ═ 80/20 (weight ratio) and mixed with a twin screw extruder to make a melt film of the blend. The same procedure as in example 2 was repeated except that the cooling roll temperature was decreased to 130 ℃. The total light transmittance of the film is 90.8%, the haze is 0.8, and the film is high in transparency and homogeneity. The film thickness was 180 μm on average except for the portions of 2.5cm width at both ends of the film. The photoelastic constant of the film was determined to be-6.0X 10^-12Pa^-1. Further, 125 ℃ was observed as one Tg, indicating that the two resins were compatible. By carrying out the membrane¹³After C-NMR measurement, meso diad/racemic diad were obtainedThe ratio (mole fraction) of the presence of NN diads to the total norbornene component was 0.36, where the set was 0.33/0.03 ═ 11. The molar ratio of the ethylene component to the norbornene component was (a)/(B) 53/47. The reduced viscosity eta sp/c was 0.88dL/g for molecular weight. The unstretched film was subjected to longitudinal uniaxial stretching under the conditions of table 1. The results are shown in Table 1. The film after stretching is also excellent in transparency.

Comparative example 1

Polymerization was carried out in the same manner as in example 1 except that the metallocene used in example 1 was replaced with isopropylidene- (9-fluorenyl) (cyclopentadienyl) zirconium dichloride, thereby obtaining an ethylene-norbornene copolymer. The molecular weight of the obtained ethylene-norbornene copolymer was 0.77 for the reduced viscosity η sp/c and 120 ℃ for Tg. By using¹³The spectrum obtained by C-NMR measurement is shown in FIG. 3. As shown in fig. 3, it was found that the meso diad/racemic diad was 0.02/0.32 and 0.0625, and the ratio of the NN diad present (molar fraction) to the total norbornene component was 0.34. The molar ratio of the ethylene component to the norbornene component was (a)/(B) 55/45. The reduced viscosity eta sp/c was 0.88dL/g for molecular weight. This resin was dissolved in cyclohexane to prepare a 20 wt% solution, and a film having a film thickness of 65 μm was obtained by a solution casting method. The total light transmittance of the film was 91.6% and the haze was 0.5%. The Tg, which is less affected by the residual solvent, was 105 ℃. The photoelastic constant of the film was-9.2X 10^-12Pa^-1. The unstretched film was subjected to longitudinal uniaxial stretching under the conditions of table 1. The results are shown in Table 1. The phase difference is extremely low.

Comparative example 2

Subjected to TOPAS (trade name) grade 5013(Tg 140 ℃ C.)¹³C-NMR measurement. The spectrum is shown in FIG. 4. As shown in fig. 4, it was found that the meso diad/racemic diad was 0.05/0.41 and 0.12, and the ratio of the presence of NN diads (mole fraction) to the total norbornene component was 0.46. The molar ratio of the ethylene component to the norbornene component was (a)/(B) 50/50. Ratio of molecular weightThe concentrated viscosity eta sp/c was 0.66 dL/g. The pellets were extruded under the same conditions as in example 2 to obtain a molten film. The film is excellent in transparency, homogeneity and surface properties. The film thickness was 82 μm on average except for the portions of 2.5cm width at both ends of the film. Tg of 137 ℃, total light transmittance of 90.7% and haze of 0.5%. The photoelastic constant of the film was-9.3X 10^-12Pa^-1. The unstretched film was subjected to longitudinal uniaxial stretching in the same manner as in example 1. The stretching conditions and the results are shown in table 1. The phase difference is extremely low.

TABLE 1

Example 7 (longitudinal uniaxially oriented film roll film)

After drying pellets of grade 6013 of TOPAS (trade name) at 100 ℃ for 4 hours, the pellets were melt-extruded from a T-die at a resin temperature of 270 ℃ using the same twin-screw extruder as used in example 2, passed through a cooling drum at a film-forming speed of 3m/min, and continuously wound up, thereby obtaining a roll of a melt-extruded film having a width of 300 mm. The film is excellent in transparency, surface properties and homogeneity. The thickness averaged 103 μm. The total light transmittance was 91.8% and the haze was 0.4%. The unstretched film was passed through a longitudinal stretcher having a zone length of 7m and stretched between rolls in a drying furnace, and subjected to longitudinal stretching at a speed of 5m/min at the entry side and a temperature of 140 ℃ by a factor of 2.0 to wind up a longitudinally uniaxially oriented film. The film properties are shown in table 2. A retardation film having a retardation axis in the film advancing direction of about lambda/2 is obtained.

Example 8 (transverse uniaxially oriented film roll film)

The unstretched film roll obtained in example 7 was transversely stretched using a tenter transverse stretcher having a total length of 15m and 3 zones including a preheating zone, a stretching zone, and a fixing-cooling zone. The film was stretched 2.7 times at a speed of 5m/min and a temperature of 142 ℃ and the transverse uniaxially oriented film was wound up. The film properties are shown in table 2. A retardation film having a retardation axis in the width direction of the film of about lambda/4 is obtained.

Example 9 (film roll for VA type used for 2-sheet Structure biaxially oriented in longitudinal → transverse)

A film was produced under the same conditions except that the film-forming speed of the melt extrusion in example 7 was changed to 2m/min, to obtain a film having a width of 300mm and an average thickness of 153 μm in a roll. The film is excellent in transparency, surface properties and homogeneity. The film was passed through a machine direction stretcher used in example 7 and subjected to machine direction stretching 1.5 times at an input side speed of 3.3 m/min. Then, the film was transversely stretched to 2.0 times at a speed of 5m/min by a transverse stretcher used in example 8 to obtain a biaxially oriented film. The stretching conditions and film properties are shown in table 2. A retardation film for large VA mode suitable for 2-sheet structure having a retardation axis in the film width direction was obtained.

Example 10 (film roll for VA type used for 1 sheet Structure biaxially oriented in longitudinal → transverse Direction)

A film was produced under the same conditions except that the film-forming speed of the melt extrusion in example 7 was changed to 1.4m/min, to obtain a film having a width of 300mm and an average thickness of 215 μm in a roll. The film is excellent in transparency, surface properties and homogeneity. The film was passed through the machine direction stretcher used in example 7, and subjected to machine direction stretching 2.0 times at a feed side speed of 2.5 m/min. Then, the film was transversely stretched 2.5 times at a speed of 5m/min by a transverse stretcher used in example 8 to obtain a biaxially oriented film. The stretching conditions and film properties are shown in table 2. A retardation film for large VA mode suitable for 1-sheet structure having a phase retardation axis in the film width direction was obtained.

Example 11(VA type liquid crystal display device)

The film produced in example 10 was attached to a polyvinyl alcohol polarizer with the phase retardation axis of the film aligned with the transmission axis of the polarizer. The laminate was bonded to one side of a liquid crystal cell for a TFT VA mode, with one side of the retardation film being the liquid crystal cell side, and a polarizing plate was bonded to the other side of the liquid crystal cell to form a crossed nicol display device. The display device shows no coloration even when viewed obliquely as compared with a non-retardation film, and has an excellent contrast.

TABLE 2

^aLet the direction of travel of the film be 0 degrees.

As described above, according to the present invention, a retardation film having a smaller thickness can be obtained by using the above-mentioned copolymer having a low photoelastic constant and excellent birefringence expression in the ethylene-cyclic olefin copolymer.

The retardation film has high moisture resistance and excellent dimensional stability, and can be effectively used for improving the viewing angle, improving the contrast, improving the liquid crystal display quality such as color compensation, etc., when incorporated in a liquid crystal display device, for example.

Claims (11)

1. A phase difference film comprising an amorphous polyolefin copolymer,

(a) the amorphous polyolefin copolymer contains ethylene units and norbornene units,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) the glass transition temperature of the amorphous polyolefin copolymer is in the range of 100 ℃ to 180 ℃.

2. The retardation film according to claim 1, wherein a retardation R (550) in a film plane based on light having a wavelength of 550nm satisfies the following formula (1):

100nm＜R(550)＜800nm ...(1)

and the film thickness is in the range of 10 μm to 150 μm.

3. The retardation film according to claim 1, wherein a retardation in a film plane R (550) and a retardation in a film thickness direction K (550) based on light having a wavelength of 550nm satisfy the following formulae (2) and (3), respectively:

0nm＜R(550)＜100nm ...(2)

50nm＜K(550)＜400nm ...(3)

and the film thickness is in the range of 10 μm to 150 μm.

4. The retardation film as claimed in any one of claims 1 to 3, which has a retardation axis in a film width direction and is in a state of being wound into a roll.

5. The retardation film as claimed in any one of claims 1 to 3, which has a retardation axis in the film running direction and is wound into a roll.

6. A phase difference film comprising an amorphous polyolefin copolymer,

(a) the amorphous polyolefin copolymer contains ethylene units and norbornene units,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) the glass transition temperature of the amorphous polyolefin copolymer is in the range of 120-160 ℃,

and is

(d) A retardation R (550) in the film plane based on light having a wavelength of 550nm satisfies the following formula (1-1):

120nm＜R(550)＜600nm ...(1-1)

and the film thickness is in the range of 20 μm to 80 μm.

7. A phase difference film comprising an amorphous polyolefin copolymer,

(a) the amorphous polyolefin copolymer contains ethylene units and norbornene units,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) the glass transition temperature of the amorphous polyolefin copolymer is in the range of 120-160 ℃,

and is

(d) A retardation R (550) in the film surface and a retardation K (550) in the film thickness direction based on light having a wavelength of 550nm satisfy the following expressions (2-1) and (3-1), respectively:

30nm＜R(550)＜80nm ...(2-1)

80nm＜K(550)＜150nm ...(3-1)

and the film thickness is in the range of 30 to 85 μm.

8. A phase difference film comprising an amorphous polyolefin copolymer,

(a) the amorphous polyolefin copolymer contains ethylene units and norbornene units,

(b) the norbornene unit has a 2-linked part, the stereoregularity of the 2-linked part is meso-type and racemic-type, and the ratio of the meso-type 2-linked part to the racemic-type 2-linked part is 4 or more, and

(c) the glass transition temperature of the amorphous polyolefin copolymer is in the range of 120-160 ℃,

and is

(d) A retardation R (550) in the film surface and a retardation K (550) in the film thickness direction based on light having a wavelength of 550nm satisfy the following expressions (2-1) and (3-2), respectively:

30nm＜R(550)＜80nm ...(2-1)

150nm＜K(550)＜250nm ...(3-2)

and the film thickness is in the range of 30 to 85 μm.

9. An unoriented film for producing the retardation film according to claim 1.

10. A liquid crystal display device comprising the retardation film according to claim 1.

11. The liquid crystal display element according to claim 10, which is a vertical alignment type.