JP4035982B2 - High wavelength dispersion retardation plate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a retardation plate used for a liquid crystal display device or the like.
[0002]
[Prior art]
The phase difference plate is generally used as an optical compensation layer of a super twisted nematic (STN) type liquid crystal display device. However, various applications as an optical compensation layer have been studied, and as a result, a phase difference having various optical characteristics. A board is needed. Particularly in liquid crystal display devices that require high-speed response, liquid crystals having a large birefringence wavelength dispersion characteristic are used. Therefore, the retardation plate in the optical compensation layer also has a birefringence wavelength dispersion characteristic in terms of matching with the liquid crystal. Larger ones are desired.
[0003]
The wavelength dispersion characteristic of birefringence can be expressed by the ratio R ₄₅₀ / R ₅₉₀ of the retardation R ₄₅₀ at a wavelength of ₄₅₀ nm and the retardation R ₅₉₀ at a wavelength of 590 nm, and this ratio is generally called a wavelength dispersion coefficient α. A retardation plate having a large birefringence wavelength dispersion characteristic, for example, a retardation plate having a wavelength dispersion coefficient α of 1.10 or more is composed of aromatic polyarylate, polysulfone, polyethersulfone, or the like. Although there is a phase difference plate, polysulfone and polyethersulfone are poorly soluble in chlorinated hydrocarbons such as methylene chloride, so the solvent is a raw material for obtaining a phase difference plate with high homogeneity. There is a problem that a cast film cannot be obtained.
[0004]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a retardation plate which is made of a polymer different from a known retardation plate and has a large birefringence wavelength dispersion characteristic. Another object of the present invention is to provide a retardation plate that has good solubility in a solvent and can be made into a highly uniform original film by a solvent casting method. As a result of diligent research, the present inventors have found that a retardation plate capable of solving the above-mentioned problems can be obtained by stretching a polymer obtained by copolymerizing specific three types of monomers at a composition ratio within a certain range. The headline, the present invention has been reached.
[0005]
[Means for Solving the Problems]
That is, the present invention includes the following components (A), (B) and (C):
(A) at least one acyclic olefin monomer selected from ethylene and an α-olefin compound having 3 to 20 carbon atoms;
(B) a copolymer of at least one cyclic olefin monomer selected from cyclic olefin compounds; and (C) a copolymer of at least one aromatic vinyl monomer selected from vinyl compounds having a cyclic unit consisting of aromatic hydrocarbons. The copolymer was polymerized at a copolymerization ratio of 5 to 40 mol% of the aromatic vinyl monomer (C) and 60 to 95 mol% of the total of the acyclic olefin monomer (A) and the cyclic olefin monomer (B). And a retardation plate having a wavelength dispersion coefficient α (= R ₄₅₀ / R ₅₉₀ ) expressed by a ratio of retardation R ₄₅₀ at a wavelength of ₄₅₀ nm and retardation R _{590 at} a wavelength of 590 nm of 1.1 or more. It is.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. A retardation plate in which a copolymer having a repeating unit composed of a monomer having a positive polarizability and a repeating unit composed of a monomer having a negative polarizability is stretched and oriented has the retardation derived from each repeating unit cancel each other. The retardation of the copolymer is a difference in retardation of components derived from the respective repeating units. Therefore, the wavelength dispersion characteristic of such a copolymer is determined by the wavelength dispersion characteristic of each repeating unit and the magnitude of retardation of the component derived from each repeating unit. That is, chromatic dispersion can be controlled by introducing repeating units having different polarizabilities and chromatic dispersions into the polymer.
[0007]
The role of the repeating unit derived from each of the acyclic olefin monomer (A), the cyclic olefin monomer (B), and the aromatic vinyl monomer (C) constituting the polymer to be the retardation plate of the present invention will be specifically described. Then, the repeating unit derived from the acyclic olefin monomer (A) has a role of imparting flexibility to the polymer, the polarizability is positive in the main chain direction of the polymer, and its wavelength dispersion coefficient α _A It is considered that 1.00. The repeating unit derived from the cyclic olefin monomer (B) has a role of improving the heat resistance of the polymer, and the polarizability is considered to be approximately positive in the main chain direction of the polymer, and its wavelength dispersion coefficient α _It is considered that _B ≈1.00. Furthermore, the repeating unit derived from the aromatic vinyl monomer (C) mainly has a role of improving the transparency of the polymer, the polarizability is negative in the main chain direction of the polymer, and its wavelength dispersion coefficient α _C It is considered that ≧ 1.00. By appropriately controlling the copolymerization ratio of these acyclic olefin monomers (A), cyclic olefin monomers (B) and aromatic vinyl monomers (C), flexibility, transparency, heat resistance, and wavelength dispersion characteristics A copolymer with excellent balance can be designed.
[0008]
The composition ratio of the repeating unit derived from the acyclic olefin monomer (A), the repeating unit derived from the cyclic olefin monomer (B), and the repeating unit derived from the aromatic vinyl monomer (C) in the copolymer is aromatic. The repeating unit derived from the vinyl monomer (C) is 5 to 40 mol%, and the total repeating unit derived from each of the acyclic olefin monomer (A) and the cyclic olefin monomer (B) is 60 to 95 mol%. The repeating unit derived from the cyclic olefin monomer (B) is preferably 20 mol% or more, and more preferably 40 mol% or more in consideration of flexibility and heat resistance. The repeating unit derived from the acyclic olefin monomer (A) is suitably present in an amount of 1 mol% or more. The retardation resulting from the repeating unit derived from the aromatic vinyl monomer (C) is larger than the retardation resulting from the repeating unit derived from each of the acyclic olefin monomer (A) and the cyclic olefin monomer (B), and the difference is smaller. When the retardation plate is used, the birefringence wavelength dispersion characteristic is increased.
[0009]
Furthermore, the aromatic vinyl monomer (C) has a function of controlling wavelength dispersion characteristics with respect to the retardation plate of the present invention. In order to increase the wavelength dispersion characteristics when a retardation plate is used, it is preferable that the aromatic vinyl monomer (C) is present in an amount of 9 mol% or more. And in order to obtain the copolymer whose wavelength dispersion coefficient (alpha) is 1.1 or more, the polymer which consists only of an acyclic olefin monomer (A), the polymer which consists only of a cyclic olefin monomer (B), and an aromatic vinyl monomer The polymers consisting of (C) only have wavelength dispersion coefficients α _A , α _B and α _C , respectively, and are derived from the acyclic olefin monomer (A), the cyclic olefin monomer (B) and the aromatic vinyl monomer (C), respectively. The retardation of the repeating unit at a wavelength of 590 nm is x, y and z, and the retardation at a wavelength of 590 nm of the retardation plate prepared from this copolymer is R, so that the following formulas (I) and (II) are satisfied. Any combination of x, y and z may be used.
[0010]
α _C z− (α _A x + α _B y) ≧ 1.1R (I)
z- (x + y) = R (II)
[0011]
Acyclic olefin monomers (A) and the cyclic olefin monomer employed in the present invention (B), since each of the homopolymers is the wavelength dispersion coefficient alpha _A and alpha _B approximately 1.00, the aromatic vinyl monomer ( An appropriate copolymerization ratio is determined by the wavelength dispersion coefficient α _C of the homopolymer of C). For example, when it is desired to obtain a retardation plate having a wavelength dispersion coefficient α of 1.20 and a retardation at a wavelength of 590 nm of 300 nm, if α _C = 1.10,
z: (x + y) = 2: 1
The copolymerization ratio is such that
x + y = 300 nm, z = 600 nm
It becomes. For example, if α _C = 1.07,
z: (x + y) = 2.86: 1.86
The copolymerization ratio is such that
x + y = 558 nm, z = 858 nm
It becomes. As can be seen from these examples, it is preferable that the difference between α _A and α _C and α _B and α _C is large because x, y, and z may be small.
[0012]
In consideration of the use environment, the retardation plate of the present invention is preferably a polymer having a glass transition temperature (Tg) of usually 100 ° C. or more and having heat resistance. The glass transition temperature is more preferably 140 ° C. or higher.
[0013]
Next, each monomer component constituting the copolymer will be described. The acyclic olefin monomer (A) is ethylene and / or an α-olefin compound having 3 to 20 carbon atoms. Examples of the α-olefin compound having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene and 1-hexadecene. , 1-octadecene, 1-eicosene-like linear α-olefin having 3 to 20 carbon atoms, 4-methyl-1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene Examples thereof include branched α-olefins having 4 to 20 carbon atoms. Among these, ethylene having 2 carbon atoms and propylene or 1-butene, which is a linear α-olefin having 3 or 4 carbon atoms, formed the polymer of the present invention into a film. In view of flexibility, ethylene is particularly preferable for the same reason. The above ethylene and α-olefin may be used alone or in combination of two or more.
[0014]
The cyclic olefin monomer (B) is a compound having a polymerizable carbon-carbon double bond in a carbocycle, and when copolymerized, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring in the main chain of the copolymer, It is a monomer capable of introducing an alicyclic ring such as a ring in which two or more of them are bonded. Specifically, bicyclo [2,2,1] hept-2-ene, usually called norbornene, 6-alkylbicyclo [2,2,1] hept-2-ene, 5,6-dialkylbicyclo Such as [2,2,1] hept-2-ene, 1-alkylbicyclo [2,2,1] hept-2-ene, 7-alkylbicyclo [2,2,1] hept-2-ene, Norbornene derivatives having an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group and butyl group, and tetracyclo [4,4,0,1 ^2,5 , also called dimethanooctahydronaphthalene 1 ^7,10 ] -3-dodecene, 8-alkyltetracyclo [4,4,0,1 ^2,5 , 1 ^7,10 ] -3-dodecene, 8,9-dialkyltetracyclo [4,4, 0,1 ^2,5, 1 ^7,10] -3-dodecene, such as, dimeta Dimethanooctahydronaphthalene derivatives in which an alkyl group having 3 or more carbon atoms is introduced into the 8-position and / or 9-position of octahydronaphthalene, and norbornene in which one or more halogens are introduced in one molecule Derivatives, dimethanooctahydronaphthalene derivatives in which halogen is introduced at the 8th and / or 9th position, and the like. These cyclic olefins may be used alone or in combination of two or more.
[0015]
The aromatic vinyl compound of component (C) is a compound in which an aromatic group is bonded to a vinyl group that forms a main chain by copolymerization with the acyclic olefin monomer (A) and the cyclic olefin monomer (B). Specific examples of the aromatic group include aromatic hydrocarbon groups having about 6 to 14 carbon atoms.
[0016]
The vinyl compound having an aromatic hydrocarbon group includes styrene and its derivatives. Styrene derivatives are compounds in which other groups are bonded to styrene, such as o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, o-ethylstyrene, p-ethyl. Alkyl styrene such as styrene, hydroxy styrene, t-butoxy styrene, vinyl benzoic acid, vinyl benzyl acetate, o-chloro styrene, p-chloro styrene, benzene nucleus of styrene with hydroxyl group, alkoxy group, carboxyl group, acyloxy Examples thereof include substituted styrene introduced with a group and halogen, and vinyl biphenyl compounds such as 4-vinyl biphenyl and 4-hydroxy-4'-vinyl biphenyl.
[0017]
Among these aromatic vinyl monomers (C), a monomer having a benzene ring unit is preferable from the viewpoint of wavelength dispersion characteristics, and for example, styrene and its derivatives are preferable. The above vinyl compounds having an aromatic group may be used alone or in combination of two or more.
[0018]
The retardation plate copolymer of the present invention is a repeating unit derived from the acyclic olefin monomer (A), a repeating unit derived from the cyclic olefin monomer (B), and a repetition derived from the aromatic vinyl monomer (C). Specifically, ethylene / norbornene / styrene copolymer, ethylene / dimethanooctahydronaphthalene / styrene copolymer, propylene / norbornene / styrene copolymer, propylene / dimethano Examples include octahydronaphthalene / styrene copolymer and ethylene / norbornene / t-butoxystyrene copolymer.
[0019]
The copolymerization type in the copolymer may be either a random type or a block type as long as the effects of the present invention are not hindered. However, the three types of constituent monomers each show a block property that forms a domain. Things can worsen transparency and should be avoided.
[0020]
The copolymer used for the retardation plate of the present invention is, for example, a copolymer of an acyclic olefin monomer (A), a cyclic olefin monomer (B), and an aromatic vinyl monomer (C) in the presence of a metallocene catalyst. It can manufacture by doing. At that time, by appropriately changing the polymerization conditions such as the amount of the acyclic olefin monomer (A), the cyclic olefin monomer (B) and the aromatic vinyl monomer (C), the polymerization temperature and the polymerization time, the copolymer composition and the molecular weight are changed. Different copolymers can be obtained. The copolymer may contain various additives such as an ultraviolet absorber, an antioxidant, a lubricant, an antistatic agent, an antibacterial agent, an antifogging agent, and a plasticizer as long as the effects of the present invention are not impaired. .
[0021]
The retardation plate of the present invention is usually produced by using the above-described copolymer as a film and further stretching. Although it does not specifically limit as a method to form in a film, For example, methods, such as a solvent cast method and a melt extrusion method, are employable. Further, the stretching method is not particularly limited, and examples thereof include lateral stretching by a tenter method and longitudinal stretching by roll-to-roll stretching.
[0022]
【Example】
Examples are shown below, but the present invention is not limited to these examples.
[0023]
Example 1
A copolymer obtained by copolymerizing ethylene, styrene, and norbornene at a molar ratio of 29:22:49 was formed into a film having a thickness of 100 μm by press molding. The obtained film was stretched uniaxially by 1.5 times at 160 ° C. using an autograph. As a result, a retardation plate with negative polarization, R ₅₉₀ = 12.3 nm, R ₄₅₀ = 14.1 nm, and α = 1.15 was obtained.
[0024]
Example 2
A copolymer obtained by copolymerizing ethylene, styrene, and norbornene at a molar ratio of 46:27:27 was formed into a film having a thickness of 100 μm by press molding. The obtained film was stretched uniaxially by 1.6 times at 80 ° C. using an autograph. As a result, a retardation plate with negative polarization, R ₅₉₀ = 126.0 nm, R ₄₅₀ = 142.7 nm, and α = 1.13 was obtained.
[0025]
Example 3
A copolymer obtained by copolymerizing ethylene, styrene, and norbornene at a molar ratio of 37:13:50 was formed into a film having a thickness of 90 μm by press molding. The obtained film was uniaxially stretched 1.8 times at 160 ° C. with an autograph. As a result, a retardation plate of R ₅₉₀ = 38.1 nm, R ₄₅₀ = 47.0 nm, α = 1.23 was obtained with negative polarization.
[0026]
Example 4
A copolymer obtained by copolymerizing ethylene, styrene, and norbornene at a molar ratio of 41: 9: 50 was formed into a film having a thickness of 90 μm by press molding. The obtained film was stretched uniaxially by 1.7 times at 160 ° C. using an autograph. As a result, a retardation plate of R ₅₉₀ = 2.7 nm, R ₄₅₀ = 7.1 nm, and α = 2.63 was obtained with negative polarization.
[0027]
【The invention's effect】
The retardation plate according to the present invention has a large birefringence wavelength dispersion characteristic, and can be effectively used as an optical compensation layer of a liquid crystal display device using a liquid crystal having a large birefringence wavelength dispersion characteristic. The terpolymer of acyclic olefin monomer / cyclic olefin monomer / aromatic vinyl monomer constituting the retardation plate is highly soluble in solvents such as methylene chloride. The raw film for this can be easily manufactured by the solvent casting method.

Claims (4)

Vinyl having a cyclic unit composed of at least one acyclic olefin monomer selected from ethylene and an α-olefin compound having 3 to 20 carbon atoms, at least one cyclic olefin monomer selected from cyclic olefin compounds, and aromatic hydrocarbons At least one aromatic vinyl monomer selected from the compounds was polymerized at a copolymerization ratio of 5 to 40 mol% of the aromatic vinyl monomer and 60 to 95 mol% of the total of the acyclic olefin monomer and the cyclic olefin monomer. A wavelength dispersion coefficient α (= R ₄₅₀ / R ₅₉₀ ) expressed by a ratio of retardation R ₄₅₀ at a wavelength of ₄₅₀ nm and retardation R ₅₉₀ at a wavelength of ₅₉₀ nm is 1.1 or more. Retardation plate. The phase difference plate according to claim 1, wherein the cyclic olefin monomer is 20 mol% or more. The phase difference plate according to claim 1 or 2, wherein the acyclic olefin monomer is ethylene, propylene or 1-butene. The retardation plate according to claim 1, wherein the aromatic vinyl monomer is styrene or a derivative thereof.