JP2006070119A - Optical liquid crystal film and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monolayer optical liquid crystal film, in which precise cutting and laminating technique are not required, capable of being produced at a low cost by a simple process and utilized for broadband retardation films, etc., in which the function is sufficiently exhibited for incident light in whole area of visible light and to provide a method for producing the film. <P>SOLUTION: The optical liquid crystal film is composed of a liquid crystalline polymer having a nematic phase in a liquid crystal state and becoming a glass state at a temperature not higher than a glass transition point and a styrene-based random copolymer as an amorphous polymer compatibilized with the liquid crystalline polymer. In the optical liquid crystal film, at least the liquid crystalline polymer is oriented in a prescribed direction and the compatible state between the liquid crystalline polymer and the styrene-based random copolymer is kept. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical liquid crystal film that can be used for a retardation film and the like, and a method for producing the same.

  Liquid crystalline polymers exhibit various liquid crystal phases based on their unique alignment structures, and these liquid crystal structures can be fixed, so that optical recording elements, nonlinear optical materials, liquid crystal alignment films, optical fibers, and optical elements for liquid crystal display elements Active researches are being made in various functional material fields such as. Since such liquid crystalline polymers exhibit various orientations, the materials obtained by fixing these molecular orientations exhibit various optical properties such as refractive index and birefringence, and the phase of light. Since the polarization state and the like can be controlled, a wide range of applications are considered as optical materials.

  Among such optical materials, the retardation used for reflective liquid crystal display devices, optical disk pickups, anti-glare films, etc. is used for so-called quarter-wave plates with a quarter wavelength, and for liquid crystal projectors. As a so-called half-wave plate whose retardation is ½ of the wavelength, it is desired that the function is sufficiently exhibited for all incident light in the visible light region.

  Under such circumstances, a so-called broadband retardation film that can exhibit its function with respect to all incident light in the visible light region has been developed. For example, JP-A-5-27118 (Patent Document 1), JP-A-5-100114 (Patent Document 2), JP-A-10-68816 (Patent Document 3), and JP-A-10-90521 (Patent Document 4) have different optical anisotropies. A laminated film composed of two polymer films is disclosed.

  However, in the retardation film formed by laminating two polymer films in this way, it is necessary to cut the two polymer films and bond them with an adhesive, so that precise cutting and bonding techniques are required. In addition, the manufacturing process becomes complicated, and there is a limit to the reduction in manufacturing cost and the weight reduction of the retardation film.

  Therefore, development of a technique for forming a retardation film that gives uniform retardation characteristics with respect to incident light in the entire visible light region using a single layer film instead of a laminated film has been studied, and Japanese Patent Laid-Open No. 2001-337222 (Patent Document) 5) includes a retardation plate obtained by orienting a film made of a polymer blend including at least one polymer having a positive intrinsic birefringence value and at least one polymer having a negative intrinsic birefringence value. It is disclosed.

However, in practice, liquid crystalline polymers are difficult to mix with other amorphous polymers and phase-separate, and even when blended with polymers having different refractive indexes, they become cloudy. It was extremely difficult to form a retardation film as a single layer film.
JP-A-5-27118 JP-A-5-100114 JP-A-10-68816 JP-A-10-90521 JP 2001-337222 A

  The present invention has been made in view of the above-described problems of the prior art, and can be manufactured at a low cost by a simple process without requiring a precise cutting and bonding technique, and can be applied to the entire visible light region. It is an object of the present invention to provide a single-layer optical liquid crystal film that can be used for a broadband retardation film and the like that sufficiently exhibit its function with respect to incident light, and a method for producing the same.

  As a result of intensive studies to achieve the above object, the present inventors have used a styrene random copolymer as the amorphous polymer, so that the compatibility between the liquid crystalline polymer and the amorphous polymer can be achieved. It became possible to obtain an optical liquid crystal film in which the state was maintained, and found that the above object was achieved, thereby completing the present invention.

  That is, the optical liquid crystal film of the present invention comprises a liquid crystalline polymer having a nematic phase in a liquid crystal state and in a glass state at a temperature below the glass transition point, and a styrene random copolymer as the amorphous polymer. An optical liquid crystal film comprising a combination, wherein at least the liquid crystalline polymer is oriented in a predetermined direction, and a compatible state between the liquid crystalline polymer and the styrene random copolymer is maintained. It is characterized by being.

Moreover, the method for producing the optical liquid crystal film of the present invention includes:
A liquid crystalline polymer having a nematic phase in the liquid crystal state and in a glass state at a temperature below the glass transition point, and a styrene random copolymer as an amorphous polymer compatible with the liquid crystalline polymer, A step of applying a solution containing
Aligning at least the liquid crystalline polymer in a predetermined direction at a temperature at which the liquid crystalline polymer exhibits a liquid crystal state;
The liquid crystalline polymer aligned in the predetermined direction is cooled to a glass state so that the alignment state and a compatible state with the styrene random copolymer are maintained, and the liquid crystalline polymer and the styrene A step of obtaining an optical liquid crystal film comprising a system random copolymer;
It is the method characterized by including.

  In the method for producing an optical liquid crystal film of the present invention, the liquid crystalline polymer aligned in the predetermined direction is 200 to 200 so that the alignment state and the compatible state with the styrene random copolymer are maintained. It is preferable to cool to a glass state at a temperature decrease rate of 9000 ° C./min.

  In the optical liquid crystal film and the method for producing the same of the present invention, the liquid crystalline polymer is preferably a main chain polyester liquid crystalline polymer.

  Further, it is preferable that the liquid crystalline polymer has a positive intrinsic birefringence value and the styrene random copolymer has a negative intrinsic birefringence value, whereby a low dispersion film is formed as the optical liquid crystal film. It can be suitably obtained.

The low dispersion film here refers to an optical liquid crystal film having a birefringence value (Δn) of 0.15 or less in a wavelength range of 500 to 800 nm, more preferably a birefringence value in a wavelength range of 500 to 800 nm. An optical liquid crystal film having a dispersion (| Δn ₅₀₀ −Δn ₈₀₀ |) of (Δn) of 0.03 or less (particularly preferably 0.01 or less).

  According to the present invention, precise cutting and pasting techniques are not required, and it can be produced at a low cost by a simple process, and its function is sufficiently exerted with respect to incident light in the entire visible light range. It is possible to provide a single-layer optical liquid crystal film that can be used for a wide-band retardation film and the like, and a method for producing the same.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the optical liquid crystal film of the present invention will be described. That is, the optical liquid crystal film of the present invention comprises a liquid crystalline polymer having a nematic phase in a liquid crystal state and in a glass state at a temperature below the glass transition point, and a styrene random copolymer as the amorphous polymer. An optical liquid crystal film comprising a combination, wherein at least the liquid crystalline polymer is oriented in a predetermined direction, and a compatible state between the liquid crystalline polymer and the styrene random copolymer is maintained. It is characterized by being.

  The liquid crystalline polymer used in the present invention is not particularly limited as long as it has a nematic phase in a liquid crystal state and becomes a glass state at a temperature below the glass transition point. For example, polyester, polyamide, polycarbonate, Examples include main chain type liquid crystalline polymers such as polyesterimide, and side chain type liquid crystalline polymers such as polyacrylate, polymethacrylate, polymalonate, and polysiloxane. Among these, from the viewpoints of ease of synthesis, transparency, orientation, glass transition point, and the like, a main chain type polyester liquid crystalline polymer is preferable.

  The structural unit of such a main-chain polyester-based liquid crystalline polymer is not particularly limited, but preferred examples include (a) units derived from dicarboxylic acids (hereinafter referred to as dicarboxylic acid units), ( b) units derived from diols (hereinafter referred to as diol units), (c) units derived from oxycarboxylic acids having a carboxyl group and a hydroxyl group simultaneously in one unit (hereinafter referred to as oxycarboxylic acid units), etc. Is mentioned. Such polyester structures include (a) + (b) type, (a) + (b) + (c) type, and (c) single type.

  Examples of the dicarboxylic acid unit (a) include the following.

(X is hydrogen, halogen (chlorine, bromine), C1-C4 alkyl group (methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, etc.), alkoxy group (methoxy group, Ethoxy group, prepoxy group, butoxy group and the like) or phenyl group, k is an integer of 0 to 2, and so on.

(* Indicates optically active carbon. The same applies hereinafter)
Moreover, as a diol unit of (b), the following are mentioned, for example.

  Furthermore, examples of the oxycarboxylic acid unit (c) include the following.

  The liquid crystalline polymer used in the present invention has a nematic phase in the liquid crystal state and is in a glass state at a temperature below the glass transition point. Therefore, when such an alignment structure of a liquid crystalline polymer is fixed, the polymer molecules are once aligned at a liquid crystal temperature and then cooled for fixing. In the case of a liquid crystalline polymer having a crystal phase, There is a possibility that the alignment state once obtained is destroyed. Therefore, it is preferable that the liquid crystalline polymer used in the present invention further includes a structural unit that suppresses crystallization, and in the case of a main-chain type polyester liquid crystalline polymer, further includes an ortho-substituted aromatic unit. It is preferable. The ortho-substituted aromatic unit here means a structural unit in which the bonds forming the main chain are ortho to each other. Specific examples of such ortho-substituted aromatic units include catechol units, salicylic acid units, phthalic acid units, and those having a substituent on the benzene ring of these groups, such as the following:

And the like are preferable, and among these, the following are particularly preferable.

  Furthermore, the liquid crystalline polymer used in the present invention may be an aromatic unit having a bulky substituent as shown below, or an aromatic unit having a fluorine or fluorine-containing substituent, instead of the above ortho-substituted aromatic unit. It may be included as a constituent component. By including such an aromatic unit, the obtained liquid crystalline polymer tends to be homeotropic. Examples of the aromatic unit having such a bulky substituent include the following.

(R represents an alkyl group having 3 to 12 carbon atoms, iPr represents isopropyl, and tBu represents tertiary butyl.)
Moreover, as an aromatic unit which has a fluorine or a fluorine-containing substituent, the following are mentioned, for example.

  The following liquid crystal polymers can be specifically exemplified as representative examples of the main-chain polyester liquid crystal polymer suitable for the present invention described above.

(Wherein, k, l and m are simply composition ratios (moles), k = 1 + m, 1 / m = 80/20 to 20/80, preferably 75 / 25-25 / 75)

(Wherein, k, l and m are simply composition ratios (moles), k = 1 + m, 1 / m = 80/20 to 20/80, preferably 75 / 25-25 / 75)

(Wherein, k, l and m are simply composition ratios (moles), k = 1 + m, 1 / m = 80/20 to 20/80, preferably 75 / 25-25 / 75)

(Wherein, k, l, m, n are simply composition ratios (moles), k = 1 + m + n, 1 / m = 80/20 to 20/80, preferably 75 / 25-25 / 75, l / n = 80 / 20-20 / 80, preferably 75 / 25-25 /
75)

(Wherein, k, l, m, and n are simply composition ratios (moles), k + 1 = m + n, k / 1 = 80/20 to 20/80, preferably 75 / 25-25 / 75, m / n = 80 / 20-20 / 80, preferably 75 / 25-25 /
75)

(Wherein, k, l and m are simply composition ratios (moles), k = 1 + m, 1 / m = 80/20 to 20/80, preferably 75 / 25-25 / 75)

(Wherein, k, l and m simply represent the composition ratio (mole), k / l = 80/20 to 20/80, preferably 75/25 to 25 / 75, l / m = 80/20 to 20/80, preferably 75/25 to 25/75)

(Wherein, k, l, m, and n are simply composition ratios (moles), k + 1 = m + n, k / 1 = 80/20 to 20/80, preferably 75 / 25-25 / 75, m / n = 80 / 20-20 / 80, preferably 75 / 25-25 /
75 and p is 2-12)

(Wherein, k, l and m are simply composition ratios (moles), k + 1 = m, k / l = 80/20 to 20/80, preferably 75 / 25-25 / 75, p is 2-12).

  The molecular weight of the liquid crystalline polymer used in the present invention is not particularly limited, but the logarithmic viscosity measured at 30 ° C. in various solvents, for example, a mixed solvent of phenol / tetrachloroethane (60/40 (weight ratio)). Is preferably about 0.05 to 3.0, and more preferably about 0.07 to 2.0. When the logarithmic viscosity is less than 0.05, the strength of the obtained liquid crystalline polymer tends to be weak. There is a tendency that problems such as an increase in time required for orientation occur.

  In addition, the glass transition point of the liquid crystalline polymer used in the present invention is not particularly limited, but it generally affects the stability of the orientation after fixing the orientation, so that the glass transition point is generally 0 ° C. or higher. It is preferable that it is 20 degreeC or more.

  In addition, the method for synthesizing the liquid crystalline polymer used in the present invention is not particularly limited, and it is synthesized by a polymerization method known in the art, for example, a melt polymerization method or an acid chloride method using a corresponding acid chloride of a dicarboxylic acid. Is done. When synthesized by the melt polymerization method, for example, the acetylated product of the corresponding dicarboxylic acid and the corresponding diol can be produced by polymerization under high temperature and high vacuum, and the molecular weight can be controlled by controlling the polymerization time or the charged composition. A liquid crystalline polymer can be obtained. In order to accelerate the polymerization reaction, a conventionally known metal salt such as sodium acetate can also be used. Furthermore, when using the solution polymerization method, a predetermined amount of dicarboxylic acid dichloride and diol are dissolved in a solvent, and heated in the presence of an acid acceptor such as pyridine or N-methylimidazole, thereby increasing the target liquid crystallinity. A molecule can be obtained.

  In the present invention, the liquid crystalline polymer preferably has a positive intrinsic birefringence value, and also in this respect, the above-mentioned main chain generally having a positive intrinsic birefringence value is preferable. Type polyester-based liquid crystalline polymer is preferred.

  The optical liquid crystal film of the present invention is obtained by blending the liquid crystalline polymer and a styrene random copolymer as an amorphous polymer. As will be described in detail later, the styrene random copolymer used in the present invention is compatible with the liquid crystalline polymer and maintains the compatible state even in a glass state. . In general, liquid crystal polymers are difficult to mix with other amorphous polymers, and phase separation in the glass state is a common recognition of those skilled in the art, and the styrenic random copolymer used in the present invention. It is a surprising fact discovered for the first time by the present inventors that some polymers maintain a compatible state with a liquid crystalline polymer even in a glass state.

  Such a styrenic random copolymer according to the present invention includes a styrene monomer and at least one monomer selected from the group consisting of acrylonitrile, maleic anhydride, methyl methacrylate, butadiene, acrylic acid, ethylene, and propylene. In particular, a random copolymer of a styrene monomer and an acrylonitrile monomer is particularly preferable from the viewpoint of compatibility with a liquid crystalline polymer and excellent transparency. In the present invention, the styrenic random copolymer preferably has a negative intrinsic birefringence value, and in this respect also a styrene monomer generally having a negative intrinsic birefringence value Random copolymers of acrylonitrile monomers are preferred.

  Further, the content of the styrene monomer in the styrene random copolymer according to the present invention is not particularly limited as long as the compatibility with the liquid crystalline polymer is ensured, but the content of the styrene-acrylonitrile copolymer is not particularly limited. In this case, the styrene content is preferably 80 to 98% by weight (acrylonitrile content is 2 to 20% by weight), and the styrene content is particularly preferably 90 to 97% by weight (acrylonitrile content is 3 to 10% by weight). preferable. When the styrene content is less than the lower limit, the compatibility with the liquid crystalline polymer tends to be insufficient, and when the content exceeds the upper limit, the compatibility with the liquid crystalline polymer is sufficient. It tends to be impossible to obtain.

  Furthermore, the blend ratio (by weight) of the liquid crystalline polymer and the styrene random copolymer in the optical liquid crystal film is not particularly limited as long as the compatibility of both polymers is ensured. When the latter is a styrene-acrylonitrile copolymer, a blend ratio (weight basis) of a liquid crystalline polymer (hereinafter sometimes referred to as “LCP”) and a styrene-acrylonitrile copolymer (hereinafter sometimes referred to as “SAN”). ) Is preferably LCP / SAN = 9/1 to 1/9, and more preferably LCP / SAN = 6/4 to 4/6. When the content of LCP is less than the lower limit, the compatibility tends to decrease, and when the content exceeds the upper limit, the compatibility tends to decrease.

  The optical liquid crystal film of the present invention is composed of the liquid crystalline polymer and the styrene random copolymer, and at least the liquid crystalline polymer is oriented in a predetermined direction, and the liquid crystalline polymer and the Even if the compatible state with the styrene random copolymer is in the glass state, it is maintained.

  Here, the method for aligning the liquid crystalline polymer in a predetermined direction is not particularly limited, and can be appropriately aligned in a predetermined direction by various methods described later. Also. The orientation of the liquid crystalline polymer is such that the alignment direction of the liquid crystalline polymer (major axis direction of the polymer molecule) is substantially parallel to the substrate surface. Although homeotropic alignment that is substantially perpendicular to the substrate surface may be used, homogeneous alignment is preferable from the viewpoint of obtaining an optical liquid crystal film that can be used for a retardation film or the like.

  Whether or not the liquid crystalline polymer and the styrene random copolymer maintain a compatible state in the optical liquid crystal film of the present invention is determined by differential scanning calorimetry (DSC), optical microscope observation, light scattering measurement, and the like. Can be confirmed. That is, if the compatible state of both polymers is maintained, the glass transition temperature (Tg) of both polymers is observed in differential scanning calorimetry, the phase separation structure is observed in optical microscope observation, and light scattering measurement. No light scattering should be observed at. The term “compatible state” as used herein refers not only to a state in which the liquid crystalline polymer and the styrene random copolymer are uniformly mixed at the molecular level, but also to both polymers or dispersoids. Including a state in which the polymer has a fine size of about 0.3 μm or less, which is smaller than the length of one wavelength of visible light, and in the observation with a polarizing microscope at a magnification of about 250 times, In the present invention, it is referred to as “compatible state” including a state in which the influence on permeability is substantially not confirmed.

  The film thickness of the optical liquid crystal film of the present invention is not particularly limited, but is preferably in the range of about 1 to 100 μm. When the film thickness is smaller than 1 μm, the desired optical effect due to the optical liquid crystal film tends not to be sufficiently obtained. On the other hand, when the film thickness exceeds 100 μm, the alignment effect by the alignment treatment described later tends to be insufficient. It is in.

  As described above, the optical liquid crystal film of the present invention described above is basically uniform and transparent because the liquid crystalline polymer and the styrenic random copolymer maintain a compatible state even in a glass state. Yes, in such an optical liquid crystal film, when a liquid crystalline polymer having a positive intrinsic birefringence value and a styrene random copolymer having a negative intrinsic birefringence value are used in combination, the birefringence wavelength of both polymers There is a tendency to add dispersion. Therefore, according to the optical liquid crystal film of the present invention, a single liquid crystalline polymer such as a low-dispersion film with reduced birefringence wavelength dispersion or an optical film in which the absolute value of birefringence increases on the long wavelength side is It becomes possible to obtain an optical liquid crystal film having a wavelength dispersion characteristic that has been difficult to realize. Therefore, the optical liquid crystal film of the present invention is a very useful optical material that can be used for a broadband phase difference film or the like that sufficiently functions for incident light in the entire visible light range. Furthermore, since the optical liquid crystal film of the present invention is a single layer optical liquid crystal film that realizes such wavelength dispersion characteristics with a single liquid crystalline polymer, the precision required for conventional laminated type optical liquid crystal films. It is possible to manufacture at a low cost by a simple process without requiring an appropriate cutting and bonding technique.

  Next, the manufacturing method of the optical liquid crystal film of the present invention will be described. That is, in the method for producing an optical liquid crystal film of the present invention, first, a solution containing the liquid crystalline polymer and the styrene random copolymer is prepared.

  The solvent used here is not particularly limited as long as it can dissolve the liquid crystalline polymer and the styrenic random copolymer. Polar solvents such as fluorinated hydrocarbons, mixed solvents of these with phenols, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, sulfolane, cyclohexane and the like can be used. The concentration of the solution is usually preferably in the range of 0.1 to 50% by weight and more preferably in the range of 5 to 20% by weight as the solid content concentration including the liquid crystalline polymer and the styrene random copolymer.

  Next, in the method for producing an optical liquid crystal film of the present invention, after the solution is applied on a substrate, at least the liquid crystalline polymer is oriented in a predetermined direction at a temperature at which the liquid crystalline polymer exhibits a liquid crystal state. The step of applying the solution onto the substrate and the step of aligning the liquid crystalline polymer may be performed in the same step, or the solution is applied onto the substrate and dried to obtain a film. Thereafter, the liquid crystalline polymer may be aligned by heating again.

  Here, the method for applying the solution onto the substrate is not particularly limited, and for example, a spin coating method, a roll coating method, a gravure coating method, a curtain coating method, a slot coating method, a dip-up method, or the like may be appropriately employed. it can.

  Further, the method for aligning the liquid crystalline polymer in a predetermined direction is not particularly limited, and a method for aligning using a substrate having an alignment regulating force such as a rubbing substrate, a method for aligning by applying a magnetic field, and light irradiation. A method of aligning and stretching, a method of stretching and aligning, and the like can be employed. For example, when orienting using a rubbing substrate, various conventionally known rubbing substrates can be used, and the polyimide layer is formed with excellent heat resistance, solvent resistance and peelability as well as excellent orientation. Examples thereof include a glass substrate, a directly rubbed polyimide, a polyether ether ketone, a polyphenylene sulfide, and a polyethylene terephthalate film.

  In the method for producing an optical liquid crystal film of the present invention, the liquid crystalline polymer is oriented in a predetermined direction at a temperature at which the liquid crystalline polymer exhibits a liquid crystal state, regardless of which orientation method is employed. The temperature at this time, that is, the temperature at which the liquid crystalline polymer exhibits a liquid crystal state differs depending on the characteristics of the liquid crystalline polymer used, but is above the glass transition point of the liquid crystalline polymer and isotropic phase-liquid crystal phase transition. Heat treatment is preferably performed at a temperature lower than the temperature. Such a temperature is generally preferably in the range of about 100 to 300 ° C, more preferably in the range of 150 to 200 ° C. The time required for such alignment treatment is not particularly limited and varies depending on the composition of the liquid crystalline polymer, the molecular weight, etc., and cannot be generally stated. However, when a rubbing substrate is used, the range is about 10 seconds to 100 minutes. The range of about 30 seconds to 60 minutes is more preferable.

  Prior to the above alignment treatment, the solvent may be removed in advance from the solution applied on the substrate by performing a drying treatment as necessary. The temperature during the drying treatment is not particularly limited, but is preferably about the temperature between (the boiling point of the solvent minus 50 ° C.) and (the boiling point of the solvent).

  Next, in the method for producing an optical liquid crystal film of the present invention, the alignment state of the liquid crystalline polymer subjected to the alignment treatment, and the compatibility state of the liquid crystalline polymer and the styrene random copolymer Is cooled to a glass state. That is, by cooling the liquid crystalline polymer in the alignment state to a temperature below its glass transition point, it can be fixed without impairing the alignment. Since the compatibility between the liquid crystalline polymer according to the present invention and the styrenic random copolymer is sufficiently high, when cooling to a temperature below the glass transition point in this way, the liquid crystalline polymer and the styrenic polymer are used. The compatible state with the random copolymer is also maintained as it is.

  Thus, although the cooling rate at the time of cooling to the temperature below a glass transition point is not restrict | limited, It is preferable to cool with the temperature decrease rate of 200-9000 degreeC / min. If the cooling rate is less than the lower limit, the compatible state tends to be difficult to maintain. On the other hand, the manufacturing process tends to be complicated even if the cooling rate exceeds the upper limit.

  By the method of the present invention described above, at least the liquid crystalline polymer is oriented in a predetermined direction, and the compatibility state between the liquid crystalline polymer and the styrene random copolymer is maintained. A liquid crystal film can be obtained efficiently and reliably.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Synthesis of liquid crystalline polymer)
The polymerization reaction was allowed to proceed for 12 hours at 270 ° C. in a nitrogen atmosphere using 50 mmol of terephthalic acid, 50 mmol of 2,6-naphthalenedicarboxylic acid, 40 mmol of methylhydroquinone diacetate, 60 mmol of catechol diacetate and 60 mg of N-methylimidazole. Next, the obtained reaction product was dissolved in tetrachloroethane, and then purified by reprecipitation with methanol to obtain 14.7 g of a liquid crystal polyester having a wholly aromatic main chain type.

  This liquid crystalline polyester had a logarithmic viscosity of 0.17, a nematic phase as a liquid crystal phase, an isotropic phase-liquid crystal phase transition temperature of 250 ° C. or higher, and a glass transition point of 115 ° C. The liquid crystalline polyester had a positive intrinsic birefringence value.

(Synthesis of styrene-acrylonitrile copolymer (SAN4, SAN5, SAN6, SAN7))
First, in a nitrogen atmosphere, styrene monomer (St) and acrylonitrile monomer (AN) have the following composition:
(St) (AN)
SAN4 98.6 1.4
SAN5 98.3 1.7
SAN6 98.0 2.0
SAN7 97.6 2.8
And azobisisobutyronitrile (A13N) as an initiator was mixed by 0.1 phr. The reason why the charged composition is different from the composition of the copolymer finally obtained is that the reactivity of the styrene monomer and the acrylonitrile monomer is different.

  Next, after maintaining the obtained mixed liquid at 60 ° C. for 2 hours using a thermostatic bath for a polymerization reaction, the reaction was stopped with methanol, and the remaining monomer and methanol were removed by drying to remove styrene. -Used as an acrylonitrile copolymer (SAN4, SAN5, SAN6, SAN7), respectively.

The molecular weight of the obtained styrene-acrylonitrile copolymer was evaluated using a gel permeation chromatograph (GPC), and the randomness was evaluated using a nuclear magnetic resonance method ( ¹ H-NMR). Further, when the acrylonitrile content in the molecule was confirmed by elemental analysis, it was confirmed that the acrylonitrile content (weight basis) in each styrene-acrylonitrile copolymer was consistent with the number after SAN. Furthermore, the styrene-acrylonitrile copolymer had a negative intrinsic birefringence value.

(Examples 1-7 and Comparative Examples 1-5)
Using the liquid crystalline polyester (LCP) synthesized above, the amorphous polymer shown below, and N-methyl-2-pyrrolidone (NMP) as a common solvent, an optical liquid crystal film is formed as follows. Obtained.
SAN4, SAN5, SAN6, SAN7: synthesized above SAN50: styrene-acrylonitrile copolymer having an acrylonitrile content of 50 wt% SAN74: styrene-acrylonitrile copolymer polystyrene having an acrylonitrile content of 74 wt% (PS): Asahi Kasei Corporation Product name: Stylon polycarbonate (PC): Mitsubishi Engineering Plastics Co., Ltd. Product name: Iupilon styrene-maleic anhydride copolymer (maleic anhydride content: 8 wt%, SMA8): Nova Chemical Co., Ltd., product Name: Dialer 7232.

  That is, first, a liquid crystalline polyester, an amorphous polymer, and N-methyl-2-pyrrolidone were mixed at the following mixing ratio (weight basis) to prepare an NMP solution.

LCP / Amorphous polymer / NMP
Example 1 5 / (SAN4) 5/90
Example 2 5 / (SAN5) 5/90
Example 3 7 / (SAN5) 3/90
Example 4 9 / (SAN5) 1/90
Example 5 5 / (SAN6) 5/90
Example 6 7 / (SAN6) 3/90
Example 7 5 / (SAN7) 5/90
Comparative Example 1 5 / (PS) 5/90
Comparative Example 2 5 / (SMA8) 5/90
Comparative Example 3 5 / (PC) 5/90
Comparative Example 4 5 / (SAN50) 5/90
Comparative Example 5 5 / (SAN74) 5/90.

  Next, each NMP solution obtained was spin cast (500 rpm, 30 s) at room temperature on a glass substrate that was rubbed in a direction parallel to the substrate surface with an imide film, and then at 200 ° C. for 10 minutes. By performing heat treatment, an optical liquid crystal film having a thickness of about 1 μm was obtained.

<Compatibility confirmation test 1: Observation under a polarizing microscope>
The optical liquid crystal films obtained in Examples 1 to 5 and 7 and Comparative Examples 1 to 5 were observed with a polarizing microscope using a sensitive color plate (retardation 530 nm) under crossed Nicols, and the liquid crystal in the optical liquid crystal film. The compatibility between the crystalline polyester and the amorphous polymer and the alignment state of the liquid crystalline polyester were evaluated. The obtained polarizing micrographs are shown in FIG. 1 (Example 1), FIG. 2 (Example 2), FIG. 3 (Example 3), FIG. 4 (Example 4), FIG. 5 (Example 5), and FIG. (Example 7), FIG. 7 (Comparative Example 1), FIG. 8 (Comparative Example 2), FIG. 9 (Comparative Example 3), FIG. 10 (Comparative Example 4) and FIG. 11 (Comparative Example 5).

  As is clear from the results shown in FIGS. 1 to 11, it is recognized that a phase separation structure is formed in all of the optical liquid crystal films obtained in Comparative Examples 1 to 5, and the compatibility with the liquid crystalline polyester is relatively good. Even when the obtained polystyrene was used (Comparative Example 1), a relatively small phase separation structure was formed. Moreover, even if it was a styrene- acrylonitrile copolymer, the comparatively big phase-separation structure was formed in the optical liquid crystal film obtained in Comparative Examples 4-5 with many acrylonitrile content.

  In contrast, when a styrene-acrylonitrile copolymer having a low acrylonitrile content was used (Examples 1 to 5 and 7), no phase separation structure was observed in any of the optical liquid crystal films, and liquid crystalline polyester and amorphous It was confirmed that the compatible state with the functional polymer was maintained. In addition, it was confirmed that the most uniform compatible state can be obtained when the mixing ratio (weight basis) of the liquid crystalline polyester and the amorphous polymer is 1: 1 (Examples 1, 2, 5, and 7). It was.

  Moreover, although it is colored because a sensitive color plate (phase difference 530 nm) is used, in the case of a sample having no birefringence, it should appear pink. However, when a styrene-acrylonitrile copolymer having a low acrylonitrile content was used (Examples 1 to 5 and 7), no pink color was observed in any of the optical liquid crystal films. That is, it was confirmed that the film was oriented. Further, since the entire optical liquid crystal film appeared to have the same color uniformly, it was confirmed that the liquid crystalline polyester was aligned by the rubbing effect on the substrate surface even in the optical liquid crystal film thus blended.

<Compatibility confirmation test 2: light scattering measurement>
When the liquid crystalline polyester and the amorphous polymer are phase-separated, they should appear white turbid due to the difference in refractive index between them, and in order to confirm the presence / absence of phase separation and the size of the phase separation structure, Example 1 Light scattering measurement was performed on the optical liquid crystal films obtained in 2, 5, 7, and Comparative Example 1. In this light scattering measurement, the light scattering measurement system shown in FIG. 12 was used, and the angle dependence of the transmitted scattered light intensity was measured with a photodiode attached to a goniometer. In the figure, 1 is a He-Ne laser (wavelength 632.8 nm), 2 is a pinhole, 3 is a mirror, 4 is a sample cell, 5 is a photodiode (goniometer), 6 is an XY amplifier, and 7 is a computer. , 8 is a copper block (hot plate), 9 is a heat insulating material, 10 and 11 are glass windows, and 12 is a heat control device.

The relationship between the scattering angle θ in the sample (optical liquid crystal film) and the scattering vector q is as follows:
q = (4π / λ) sin (θ / 2)
[In the formula, π represents the refractive index of the sample, and λ represents the wavelength of light in the sample. ]
It is represented by

  When the optical liquid crystal films obtained in Examples 1, 2, 5, and 7 and Comparative Example 1 were subjected to light scattering measurement after heat treatment at room temperature, the optics obtained in Examples 1, 2, 5, and 7 were measured. In the liquid crystal film, light scattering was not observed and it was transparent and the compatible state was maintained, whereas in the optical liquid crystal film obtained in Comparative Example 1, white turbidity due to light scattering was observed, and the phase separation structure Was formed.

  Furthermore, in Examples 1, 2, 5, 7 and Comparative Example 1, the samples immediately after spin casting were subjected to light scattering measurement in the heat treatment process at 200 ° C. over time. FIG. 13 (Example 1) and FIG. (Example 2), FIG. 15 (Example 5), FIG. 16 (Example 7), and FIG. 17 (Comparative Example 1).

  As is apparent from the results shown in FIGS. 13 to 17, when a styrene-acrylonitrile copolymer having a low acrylonitrile content was used (Examples 1, 2, 5, and 7), even when heat treatment was performed at 200 C for 1 hour, no light was produced. Since no scattering occurred, it was confirmed that the compatibility was very good. On the other hand, when polystyrene was used (Comparative Example 1), it was confirmed that a phase separation structure was formed by spinodal decomposition.

<Confirmation test for birefringence wavelength dispersion>
In a system in which a compatible state is maintained in the optical liquid crystal film, no phase separation structure is formed, and therefore there is no region having a difference in refractive index. Therefore, the optical liquid crystal film having transparency as described above can be considered for application to a retardation film by controlling the wavelength dispersion of the retardation, but in order to control the wavelength dispersion characteristics of the retardation, an optical It is required to control the alignment state of molecules in the liquid crystal film. In the blend of liquid crystalline polyester and amorphous polymer, the former has high orientation, so the latter molecular chain orientation is accompanied by the liquid crystalline polyester, and the wavelength dispersion of the retardation is different from that of the liquid crystalline polyester alone. The present inventors speculated that the characteristics were obtained.

  Therefore, birefringence wavelength dispersion was confirmed for the optical liquid crystal films obtained in Examples 1 to 3 and 5 to 7 as follows. That is, the wavelength dispersion of retardation (Re = Δn · d, Δn: birefringence, d: film thickness) of each optical liquid crystal film was measured using a birefringence wavelength dispersion measurement system based on the Senarmont method. Moreover, the film thickness of each optical liquid crystal film was measured using the confocal laser microscope.

  About each optical liquid crystal film obtained in Examples 1 to 3 and 5 to 7 and an optical liquid crystal film made of a liquid crystalline polyester (LCP) alone for comparison, retardation (Δn · d) wavelength dispersion and each optical The wavelength dispersion characteristic of birefringence (Δn) was obtained from the film thickness (d) of the liquid crystal film. The obtained results are shown in FIGS.

As apparent from the results shown in FIG. 18 and FIG. 19, the liquid crystalline polyester alone has a large birefringence value and wavelength dispersion, whereas an optical liquid crystal film obtained by using a styrene-acrylonitrile copolymer having a low acrylonitrile content ( In Examples 1 to 3 and 5 to 7), it was confirmed that the birefringence value was small and the chromatic dispersion was also small. That is, all of the optical liquid crystal films obtained in Examples 1 to 3 and 5 to 7 have a birefringence value (Δn) of 0.15 or less in a wavelength range of 500 to 800 nm and a wavelength of 500 to 800 nm. The dispersion (| Δn ₅₀₀ −Δn ₈₀₀ |) of the birefringence value (Δn) in the range was 0.03 or less.

Next, the optical liquid crystal film which consists of a liquid crystalline polyester (LCP) single-piece | unit, and each optical liquid crystal film obtained in Examples 5-6 calculated | required the graph which normalized the value of the retardation of each wavelength with the value of 590 nm. . The obtained result is shown in FIG. In a single polymer, the birefringence value can be expressed by Δn = f · Δn ₀ (f: orientation function, Δn ₀ intrinsic birefringence value), but the birefringence value changes depending on the degree of orientation. When comparing the characteristics of various samples, the degree of orientation must be the same. However, in the case of a sample in which a plurality of polymers are blended, it is difficult to make all the samples have the same degree of orientation. On the other hand, since the value normalized by the birefringence value at a specific wavelength does not contribute to the orientation function and consists only of the term of the intrinsic birefringence value, (Δn <λ) / Δn (590 nm) = Δn ₀ (λ) / Δn ₀ (590 nm)), it becomes possible to compare the wavelength dispersion characteristics of birefringence regardless of the degree of orientation.

  As is clear from the results shown in FIG. 20, it was confirmed that the optical liquid crystal films obtained in Examples 5 to 6 had a slightly smaller wavelength dispersion than the optical liquid crystal film made of a liquid crystalline polyester alone. . Moreover, in the optical liquid crystal film obtained in Examples 5-6, the difference by a composition was hardly confirmed.

  From the above results, in the optical liquid crystal films obtained in Examples 5 to 6, the birefringence value decreased due to the decrease in the content of the liquid crystalline polyester having a large birefringence value, and the styrene-acrylonitrile copolymer and The present inventors speculate that the orientation of the liquid crystalline polyester has been changed by blending, or that the wavelength dispersion has been reduced due to some orientation of the styrene-acrylonitrile copolymer.

<Orientation confirmation test>
For the optical liquid crystal film obtained in Example 2, the optical liquid crystal film composed of SAN5 alone for comparison, and the optical liquid crystal film composed of liquid crystalline polyester (LCP) alone, Fourier transform polarized infrared spectroscopy (polarized light FT- IR). The obtained results are shown in FIGS. In addition, instead of the glass substrate, a silicon wafer was used for the optical liquid crystal film for polarization FT-IR measurement.

FIG. 21 and FIG. 22 show the results of measurement without orientation of a sample obtained by casting SAN5 alone and LCP alone on a silicon wafer. From these figures, a peak peculiar to SAN5 appears around 3000 cm ^−1. confirmed. FIGS. 23 and 24 show the results obtained by measuring the IR polarization direction of the optical liquid crystal film in which the LCP / SAN5 blend is oriented at 0 ° and 90 °, respectively. In both cases, it was confirmed that a peak specific to SAN5 appeared. Further, FIG. 25 is a graph in which the difference between the spectrum at 0 ° shown in FIG. 23 and the spectrum at 90 ° shown in FIG. 24 is calculated. From this graph, there is no SAN-specific peak in the difference spectrum. It was confirmed that

  From the above results, it was confirmed that in the optical liquid crystal film obtained in Example 2, the styrene-acrylonitrile copolymer was almost isotropic, although the liquid crystalline polyester was oriented. It was. Further, when the same measurement was performed on the optical liquid crystal films obtained in other examples, almost the same results were obtained.

  As described above, according to the production method of the present invention, at least the liquid crystalline polymer is oriented in a predetermined direction, and the compatible state between the liquid crystalline polymer and the styrene random copolymer is maintained. It is possible to obtain the optical liquid crystal film of the present invention. Such an optical liquid crystal film of the present invention is uniform and transparent, such as a low dispersion film in which birefringence wavelength dispersion is reduced, and an optical film in which the absolute value of birefringence is increased on the long wavelength side. Application to an optical liquid crystal film having a wavelength dispersion characteristic, which has been difficult to realize with the liquid crystalline polymer, is possible. Therefore, the optical liquid crystal film of the present invention is a very useful optical material that can be used for a broadband phase difference film or the like that sufficiently functions for incident light in the entire visible light range.

2 is a polarizing micrograph of the optical liquid crystal film obtained in Example 1. FIG. 4 is a polarizing micrograph of the optical liquid crystal film obtained in Example 2. FIG. 4 is a polarization micrograph of the optical liquid crystal film obtained in Example 3. FIG. 4 is a polarizing microscope photograph of the optical liquid crystal film obtained in Example 4. FIG. 6 is a polarizing micrograph of the optical liquid crystal film obtained in Example 5. FIG. 6 is a polarizing micrograph of the optical liquid crystal film obtained in Example 7. FIG. 2 is a polarizing micrograph of the optical liquid crystal film obtained in Comparative Example 1. 4 is a polarizing micrograph of the optical liquid crystal film obtained in Comparative Example 2. 4 is a polarizing micrograph of an optical liquid crystal film obtained in Comparative Example 3. 6 is a polarizing micrograph of an optical liquid crystal film obtained in Comparative Example 4. 6 is a polarizing micrograph of an optical liquid crystal film obtained in Comparative Example 5. It is a schematic diagram which shows the structure of a light-scattering measurement system. 4 is a graph showing the results of light scattering measurement in the heat treatment process in Example 1. 6 is a graph showing the results of light scattering measurement in the heat treatment process in Example 2. 10 is a graph showing light scattering measurement results of a heat treatment process in Example 5. 5 is a polarizing micrograph of the optical liquid crystal film obtained in 5, 7, and 1. FIG. 2 is a polarizing micrograph of the optical liquid crystal film obtained in Example 1. FIG. 10 is a graph showing light scattering measurement results of a heat treatment process in Example 7. 10 is a graph showing the results of light scattering measurement in the heat treatment process in Comparative Example 1. It is a graph which shows the wavelength dispersion characteristic of the birefringence in the optical liquid crystal film obtained in Examples 5-6, and the optical liquid crystal film which consists of a LCP single-piece | unit. It is a graph which shows the wavelength dispersion characteristic of the birefringence in the optical liquid crystal film obtained in Examples 1-3 and 5-7. It is the graph which normalized the retardation value in the optical liquid crystal film obtained in Examples 5-6, and the optical liquid crystal film which consists of a LCP single-piece | unit. It is a graph which shows the result of the polarization FT-IR measurement in the sample which casted SAN5 simple substance on the silicon wafer. It is a graph which shows the result of the polarization FT-IR measurement in the sample which casted LCP simple substance on the silicon wafer. It is a graph which shows the result of the polarization FT-IR measurement (polarization direction 0 degree) in the optical liquid crystal film obtained in Example 2. It is a graph which shows the result of the polarization FT-IR measurement (polarization direction 90 degrees) in the optical liquid crystal film obtained in Example 2. It is a graph which shows the difference of the spectrum shown in FIG. 23, and the spectrum shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... He-Ne laser, 2 ... Pinhole, 3 ... Mirror, 4 ... Sample cell, 5 ... Photodiode (goniometer), 6 ... XY amplifier, 7 ... Computer, 8 ... Copper block (hot plate), 9 ... heat insulating material, 10, 11 ... glass window, 12 ... heat control device.

Claims (7)

  A liquid crystalline polymer having a nematic phase in the liquid crystal state and in a glass state at a temperature below the glass transition point, and a styrene random copolymer as an amorphous polymer compatible with the liquid crystalline polymer, An optical liquid crystal film comprising: at least the liquid crystalline polymer is oriented in a predetermined direction, and a compatible state between the liquid crystalline polymer and the styrene random copolymer is maintained. An optical liquid crystal film characterized by   2. The optical liquid crystal film according to claim 1, wherein the liquid crystal polymer is a main chain polyester liquid crystal polymer.   The liquid crystalline polymer has a positive intrinsic birefringence value, the styrene random copolymer has a negative intrinsic birefringence value, and the optical liquid crystal film is a low dispersion film. Item 3. The optical liquid crystal film according to Item 1 or 2. A liquid crystalline polymer having a nematic phase in the liquid crystal state and in a glass state at a temperature below the glass transition point, and a styrene random copolymer as an amorphous polymer compatible with the liquid crystalline polymer, A step of applying a solution containing
Aligning at least the liquid crystalline polymer in a predetermined direction at a temperature at which the liquid crystalline polymer exhibits a liquid crystal state;
The liquid crystalline polymer aligned in the predetermined direction is cooled to a glass state so that the alignment state and a compatible state with the styrene random copolymer are maintained, and the liquid crystalline polymer and the styrene A step of obtaining an optical liquid crystal film comprising a system random copolymer;
A method for producing an optical liquid crystal film, comprising:   The method for producing an optical liquid crystal film according to claim 4, wherein the liquid crystalline polymer is a main chain polyester liquid crystalline polymer.   The liquid crystalline polymer has a positive intrinsic birefringence value, the styrene random copolymer has a negative intrinsic birefringence value, and the optical liquid crystal film is a low dispersion film. The manufacturing method of the optical liquid-crystal film of Claim 4 or 5.   The liquid crystalline polymer aligned in the predetermined direction is cooled at a temperature decreasing rate of 200 to 9000 ° C./min so that the alignment state and the compatible state with the styrene random copolymer are maintained. The manufacturing method of the optical liquid-crystal film as described in any one of Claims 4-6 characterized by the above-mentioned.