JP2012027259A - Depolarizing film and method for manufacturing depolarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a depolarizing film capable of converting linear polarization into unpolarized light while suppressing haze to be low.SOLUTION: A depolarizing film 10 includes a liquid crystal layer 2 containing liquid crystal polymers 3 which are homogeneously aligned and form a schlieren-like composition, and has a haze value of less than 40%.

Description

  The present invention relates to a depolarizing film that converts polarized light into non-polarized light, and a method for producing the depolarizing film.

  In recent years, a liquid crystal display has been used not only indoors but also outdoors as a display device such as a mobile phone, a car navigation system, a digital camera, a game machine, and a clock as well as a liquid crystal TV. These liquid crystal displays have various driving methods such as TFT method, STN method, ECB method, IPS method, and VA method. In any of these methods, a polarizing film is provided on the surface of the liquid crystal display. The outgoing light is linearly polarized light.

  On the other hand, polarized glasses are often worn outdoors. At this time, since the light emitted from the liquid crystal display is linearly polarized light, if the absorption axis of the polarized glasses worn is close to the polarization axis of the linearly polarized light of the emitted light, the light emitted from the liquid crystal display is blocked by the polarized glasses. Therefore, there is a problem that the display content of the liquid crystal display cannot be visually recognized.

  In order to avoid this problem, a method has been proposed in which a depolarizing plate or a depolarizing filter having a spherulite structure is arranged on the outgoing light side of the liquid crystal display (Patent Document 2).

  Furthermore, liquid crystal compounds that are aligned vertically to the substrate and liquid crystal compounds that are aligned in parallel to the substrate and generate an in-plane retardation are mixed to depolarize the liquid crystal compound in all directions of the film. A film has been proposed (Patent Document 3).

Japanese Patent Laid-Open No. 10-10522 WO2007 / 119959 pamphlet JP 2009-251035 A

  However, the commercially available depolarizing plate of Patent Document 1 is composed of a quartz plate whose birefringence is strictly controlled, and is expensive and poor in productivity. Further, the depolarization filter of Patent Document 2 has difficulty in controlling the in-plane retardation and spherulite size, and it is difficult to achieve both the degree of depolarization and the parallel light transmittance. For example, if the parallel light transmittance decreases and light scattering occurs in the filter, the haze value increases. Such an increase in the haze value causes a reduction in the image quality of the display and causes the display content to appear blurred.

  In addition, in the depolarization film of Patent Document 3, when the film is viewed from the front, the liquid crystal alignment becomes a discontinuous singular point in the portion where the vertically aligned liquid crystal compound exists, and the phase difference disappears. Causes scattering. For this reason, the parallel light transmittance decreases and the haze increases.

  This invention is made | formed in view of the said situation, and it aims at providing the manufacturing method of the depolarization film which can convert linearly polarized light into non-polarized light, and a depolarization film, suppressing haze low. .

  The present invention provides a depolarizing film comprising a liquid crystal layer containing a liquid crystal polymer that is homogeneously aligned and forms a schlieren structure, and has a haze value of less than 40%.

  In the depolarizing film of the present invention, the liquid crystal polymer contained in the liquid crystal layer is homogeneously oriented and forms a schlieren-like structure. it can. In addition to this, in the present invention, since the liquid crystal polymer is homogeneously aligned, an optical singularity hardly exists and the haze value of the film is less than 40%. Therefore, in the present invention, light scattering by the film can be suppressed. Thus, the present invention can achieve both depolarization and suppression of haze. Such a depolarizing film is used for depolarizing linearly polarized light such as light emitted from a liquid crystal display or laser light.

  The homogeneous alignment refers to an alignment state in which the mesogen of the liquid crystal polymer is parallel to the substrate. The schlieren form means that the orientation direction of the liquid crystal polymer (the slow axis direction of the retardation) is entirely random in the film plane, but is locally isotropic and the orientation direction thereof. Is a state of continuously changing.

In the present invention, the ordinary refractive index of the liquid crystal polymer as n _o, when the extraordinary light refractive index of the liquid crystal polymer and n _e, it is preferable that n _o and n _e satisfies the following equation (1). If | n _e −n _o | is in such a range, it becomes easier to eliminate polarized light better and haze can be more effectively suppressed.
0.05 ≦ | n _e −n _o | ≦ 0.5 (1)

Further, in the present invention, when the thickness of the liquid crystal layer is d, and emitted from the light source to the highest optical wavelength of the luminance of the light incident on the liquid crystal layer lambda, n _o, ne, d and lambda is It is preferable to satisfy the following formula (2) or (3). Thereby, both depolarization and suppression of haze can be achieved more reliably.
λ / 8 ≦ | n _e −n _o | × d ≦ 7λ / 8 (2)
9λ / 8 ≦ | n _e −n _o | × d ≦ 15λ / 8 (3)

The present invention further relates to a method for producing a depolarizing film for obtaining the above depolarizing film, comprising: a coating step of applying a liquid crystal composition solution containing a liquid crystal polymer on a substrate; and a liquid crystal composition on the substrate. And a heat treatment step in which the liquid crystal polymer is homogeneously aligned on the substrate by heating at a temperature T ° C., and when the nematic-isotropic transition temperature of the liquid crystal composition is Ti ° C., T and Ti are represented by the following formula ( A method for producing a depolarizing film that satisfies 4) is provided.
Ti-40 ≦ T <Ti (4)

  According to the method for producing a depolarizing film of the present invention, it is possible to provide a depolarizing film capable of converting linearly polarized light into non-polarized light while keeping haze low. In addition, with such a manufacturing method, for example, it is not necessary to produce a quartz plate whose birefringence is strictly controlled as in the prior art, so that high productivity can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the depolarization film which can convert a linearly polarized light into a non-polarized light, and a depolarization film can be provided, suppressing a haze low.

It is a schematic cross section which shows the depolarization film which concerns on one Embodiment of this invention. In the depolarization film which concerns on one Embodiment of this invention, it is a schematic diagram which shows the schlieren-like structure | tissue which a liquid crystal polymer forms. It is a figure which shows the orientation state of a liquid crystal polymer when the depolarizing film of Example 1 under cross nicol is observed with a polarizing microscope (400 times). It is a figure which shows the orientation state of a liquid crystal polymer when the optical film of the comparative example 1 under cross nicol is observed with a polarizing microscope (400 times). It is a figure which shows the orientation state of a liquid crystal polymer when the optical film of the comparative example 2 under cross nicol is observed with a polarizing microscope (400 time).

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to the following embodiments.

[Depolarization film]
As shown in FIG. 1, the depolarizing film 10 includes a substrate 1 and a liquid crystal layer 2 including a liquid crystal polymer 3 formed on the substrate 1.

(Liquid crystal polymer)
The liquid crystal polymer 3 in the liquid crystal layer 2 has a nematic phase, is homogeneously oriented with respect to the substrate 1, and forms a schlieren-like structure. The liquid crystal polymer 3 may be a calamitic liquid crystal or a discotic liquid crystal as long as it has no absorption in the wavelength region where the depolarizing film is used. However, since the optical axis is easily homogeneously aligned, it is a calamitic liquid crystal. It is preferable. Note that the calamitic liquid crystal is rod-like liquid crystal, ordinary refractive index n _o, when the extraordinary refractive index was n _e, it refers to a n _e> n _o. In addition, the discotic liquid crystal is a disk-like liquid, refers to what is n _o> n _e.

  In the above schlieren-like structure, the alignment state of the liquid crystal polymer 3 is fixed by vitrification or crosslinking of the liquid crystal polymer. Examples of such a liquid crystal polymer include the following.

<Liquid crystal polymer that can fix the alignment state by vitrification>
First, examples of the liquid crystal polymer capable of fixing the alignment state by vitrification include those having a nematic phase at a glass transition temperature or higher, for example, an aromatic diol unit and an aromatic dicarboxylic acid unit, or an aromatic diol unit, The main component is a main chain type liquid crystalline polyester composed of an aromatic dicarboxylic acid unit and an aromatic hydroxycarboxylic acid unit. The glass transition temperature Tg of such a liquid crystal polymer is preferably 60 ≦ Tg ≦ 160 ° C., more preferably 70 ≦ Tg ≦ 140 ° C., and further preferably 80 ≦ Tg ≦ 120 ° C. . When Tg is higher than 160 ° C., the temperature necessary for aligning the liquid crystal polymer becomes too high, and there is a tendency that it is difficult to obtain an alignment state with little scattering. On the other hand, when Tg is less than 60 ° C., the heat resistance of the produced depolarizing film itself is lowered, and the liquid crystal alignment is likely to be disturbed at the use temperature, so that the depolarizing ability tends to be lowered.

  When the liquid crystal polymer does not have a glass transition temperature, even if the liquid crystal polymer can be temporarily aligned by heating to a predetermined temperature, the alignment state is maintained because crystallization occurs during the cooling process. Can not do it.

  Examples of structural units of the main-chain liquid crystalline polyester include the following (a) aromatic diol units, (b) aromatic dicarboxylic acid units, and (c) aromatic hydroxycarboxylic acid units. In particular, for vitrification, the main-chain liquid crystalline polyester preferably includes catechol as a structural unit and catechol in which a hydrogen atom is substituted with a halogen, alkyl, or oxyalkyl group. When a bending unit such as catechol is included as a constituent unit, the linearity of the molecule is lowered and the crystallinity is lowered. Thereby, main chain type liquid crystalline polyester becomes easy to vitrify.

In formulas (5) to (7), X represents F, Cl, Br or C _n H _{2n + 1} , and n and m represent an integer of 2 to 10.

Examples of the main-chain liquid crystalline polyester having such a structural unit include the following.

In formula (8), a = 10, b = 2 to 8, c = 2 to 8, and 9 <b + c <11.

In the formula (9), a + b = 10, b = 0.1 to 3, c = 2 to 8, d = 2 to 8, and c + d = 9 to 11.

In the formula (10), a = 0 to 10, b = 0 to 10, c = 1 to 9, c + d = 10, e = 0 to 5, f = 4 to 11, and e + f = 9 to 11.

In formula (11), a = 0 to 10, b = 0 to 10, c = 1 to 9, c + d = 10, e = 0.1 to 5, f = 4 to 11, and e + f = 9 to 11.

<Liquid crystal polymer that can fix the alignment state by cross-linking>
Examples of the liquid crystal polymer capable of fixing the alignment state by crosslinking include those having a nematic phase in a heat-treatable temperature range and capable of fixing the alignment state by light or thermal polymerization while maintaining the nematic phase. And a side chain type liquid crystalline poly (meth) acrylate having a crosslinking group in the side chain. In addition, (meth) acrylate means an acrylate or a corresponding methacrylate.

  Examples of such a crosslinking group include a radical polymerizable (meth) acryl group, a cationic polymerizable epoxy group, an oxetane group, and a vinyl ether group. Among these, it is preferable to use a cationic polymerizable crosslinking group. In particular, it is preferable to use a relatively stable oxetane group or vinyl ether group. Thereby, it becomes possible to synthesize a side chain type liquid crystalline poly (meth) acrylate having a crosslinking group more easily.

  The side chain type liquid crystalline poly (meth) acrylate having a crosslinking group in the side chain can be obtained by copolymerizing a structural unit having a polymer group and a structural unit having no polymer group.

Examples of the structural unit having a polymer group include the following structures.

In formula (12), Z represents the following formula.

In formulas (12) and (13), R ¹ , R ² , L ¹ and L ² represent the following formulas, and n and m each represent an integer of 0 to 10.

In the formula (12), ^{M 1} represents a following formula.

In this case, ^{L 3} and ^{L 4} and ^P 1 to P ³ are as formula.

In the formula (16), X represents F, Cl, Br, CH ₃ , OCH ₃ , t-C ₄ H ₉ or C ₂ H ₅ .

On the other hand, examples of the structural unit having no polymerization group include the following structures.

In formula (17), m and n each represent an integer of 1 to 10, and R ¹ and L ¹ represent the following formula.

In formula (17), M ² represents the following formula.

In this case, ^{L 2} and ^{L 3} and ^P 1 to P ³ are as formula.

In formula (20), X represents H, F, Cl, Br, C ₁ H _{21 + 1} , OC ₁ H _{21 + 1} or CN. However, l represents the integer of 1-10.

Specific examples of the side-chain liquid crystalline poly (meth) acrylate having these structural units include the following compounds.

In formula (21), X represents F, Cl, Br, C _n H _{2n + 1} , OC _n H _{2n + 1,} or CN. However, n represents the integer of 1-10.

Moreover, R < ¹ > -R < ⁵ > represents a following formula, m represents the integer of 1-10, l, o, p, and q represent the integer of 1-5. Then, a = 0 to 8, b = 0 to 7, c = 0.1 to 5, d = 0 to 2, and a + b + c + d = 10.

The following compounds are also specific examples of the side-chain liquid crystalline poly (meth) acrylate having the above structural units.

Wherein (23), X represents _{F, Cl, Br,} or _{C n H 2n + 1, OC} n H 2n + 1 or CN. However, n represents the integer of 1-10.

Moreover, R < ¹ > -R < ⁵ > represents a following formula, m represents the integer of 1-10, l, o, p, and q represent the integer of 1-5. Then, a = 0 to 8, b = 0 to 7, c = 0.1 to 5, d = 0 to 2, and a + b + c + d = 10.

Furthermore, the following examples are also given.

In formula (25), X represents F, Cl, Br, C _n H _{2n + 1} , OC _n H _{2n + 1,} or CN. However, n represents the integer of 1-10.

Moreover, R < ¹ > -R < ⁵ > represents a following formula, m represents the integer of 1-10, o, p, and q represent the integer of 1-5. Then, a = 0 to 8, b = 0 to 7, c = 0.1 to 5, d = 0 to 2, and a + b + c + d = 10.

  When the depolarizing film under crossed Nicols is observed with a polarizing microscope, such a liquid crystal polymer forms a schlieren-like structure as shown in FIG. 2 in the liquid crystal layer of the depolarizing film. That is, the dark field (quenching position) portion 4 existing so as to connect the dots is present in the film plane so as to form a random network pattern as a whole. Thereby, the depolarization film of this embodiment turns into a film which has phase difference, when it sees from a film front (direction perpendicular | vertical to the liquid-crystal layer surface).

  The slow axis direction of the phase difference, that is, the alignment direction of the liquid crystal polymer is in a random direction in the film plane and continuously changes. For example, when the phase difference of the liquid crystal layer is λ / 2, the linearly polarized light incident on the film in the vertical direction is the polarization of the incident light when the angle between the polarization direction and the slow axis direction of the phase difference is θ. The light is emitted as linearly polarized light whose polarization direction is rotated by 2θ from the direction. For this reason, when the slow axis direction of the phase difference is random in the plane, the polarization direction of the emitted linearly polarized light is also random in the plane. Even when the phase difference of the liquid crystal layer is not strictly λ / 2, the azimuth angle of the emitted elliptically polarized light is determined by the slow axis direction of the phase difference, and therefore the azimuth angle of the emitted elliptically polarized light is random in the plane.

  When the depolarizing film under crossed Nicols is observed with a polarizing microscope, in such a schlieren structure, when the depolarizing film is rotated in-plane, the dark field portion (that is, in the direction of the transmission axis or absorption axis of the polarizing plate) The position and shape of the portion where the liquid crystal polymer is aligned are randomly changed. Thereby, it can confirm that the orientation of the liquid crystal polymer in the liquid crystal layer is random and continuous in the plane.

  On the other hand, even when the liquid crystal polymer is randomly oriented, if it does not continuously change in the plane, a point where the orientation of the liquid crystal polymer becomes discontinuous appears. Such singular points continue to exist as dark field portions even when the film is rotated in-plane when observed with a polarizing microscope under crossed Nicols. At a singular point, the liquid crystal polymer is homeotropically aligned (orientated perpendicular to the substrate), so that light scattering occurs and haze increases.

  The haze value that can be used as the depolarizing film is less than 40%, preferably 20% or less, more preferably 15% or less, and still more preferably 10% or less. When the haze value is larger than 40%, the light transmitted through the depolarizing film diffuses, and the display content of the liquid crystal display looks unclear. The haze value is a value obtained by dividing the scattered light transmittance of the film by the total light transmittance, expressed as a percentage. For example, the haze value is measured by a measuring device such as a haze meter (manufactured by Gardner, Haze-gard plus). can do.

The birefringence of the liquid crystal polymer is preferably 0.05 ≦ | n _e −n _o | ≦ 0.5, and preferably 0.1 ≦ | n _e −n _o | ≦ 0.3. More preferred. When | n _e −n _o | (hereinafter referred to as Δn) is smaller than 0.05, it is necessary to increase the film thickness, and it becomes difficult to align the liquid crystal polymer, and the haze tends to increase. There is. On the other hand, if Δn is greater than 0.5, visible light tends to be absorbed.

  Here, the birefringence of the liquid crystal polymer is the same condition as when the liquid crystal polymer is produced as a depolarizing film, and when the liquid crystal polymer is aligned on a substrate having an alignment regulating force in the in-plane direction of the film. The birefringence of the liquid crystal layer can be measured by, for example, an Abbe refractometer.

  The retardation of the liquid crystal layer used as the depolarizing film of this embodiment is preferably (n + 1/8) λ ≦ Δnd ≦ (n + 7/8) λ, and (n + 1/4) λ ≦ Δnd ≦ (n + 3 / 4) More preferably, λ, and further preferably (n + 3/8) λ ≦ Δnd ≦ (n + 5/8) λ. Note that λ is the wavelength of the emitted light having the highest luminance among the light emitted from the light source and incident on the liquid crystal layer, and is usually 550 nm. N is 0 or 1. When the retardation of the liquid crystal layer is 0 <Δnd <λ / 8, 7λ / 8 <Δnd <9λ / 8, or 15λ / 8 <Δnd <2λ, linearly polarized light is easily converted to elliptically polarized light with a low ellipticity. Therefore, the degree of depolarization tends to be low. Further, when 2λ <Δnd, it is preferable to increase the film thickness d. However, in that case, the liquid crystal polymer becomes difficult to align sufficiently randomly and continuously, and the haze tends to increase.

(substrate)
It is preferable that the substrate 1 used for the depolarizing film 10 has an isotropic orientation in the plane of molecules constituting the substrate. This makes it easy for the liquid crystal polymer 3 to form a schlieren-like structure. As described above, the substrate 1 that is isotropic in the plane and has no orientation regulating force includes a polyvinyl alcohol film, a triacetyl cellulose film, a cyclopolyolefin film, a polycarbonate film, a poly (meth) acrylic film, and the like. It is done.

  On the other hand, stretched films such as polyethylene terephthalate film, polyethylene naphthalate film, and polyphenylene sulfide film have orientation ability in the stretched direction and cannot be used as a substrate as they are. However, by forming a film made of polyvinyl alcohol resin or polyimide resin on the film having the orientation ability, the substrate 1 having in-plane isotropy can be used for the depolarizing film of this embodiment. . That is, the liquid crystal layer 2 may be formed on a film made of polyvinyl alcohol resin or polyimide resin.

  The thickness of the substrate 1 is preferably 10 μm to 200 μm, more preferably 25 μm to 100 μm, and still more preferably 38 μm to 75 μm. If the thickness of the board | substrate 1 is in this range, the handleability in each process of coating, drying, heat processing, and bridge | crosslinking will improve.

[Method for producing depolarizing film]
The manufacturing method of the depolarizing film of this embodiment is described below.

  The manufacturing method of the depolarizing film of this embodiment comprises a preparation process, a coating process, a drying process, a heat treatment process, and a heat treatment process. In the preparation step, a liquid crystal composition solution containing a liquid crystal polymer is prepared. In the coating step, the liquid crystal composition solution is coated on an in-plane isotropic alignment substrate. In the drying step, the liquid crystal composition solution is dried so as to remove the solvent from the liquid crystal composition solution applied on the substrate. In the heat treatment step, the dried liquid crystal polymer is further heated to cause the liquid crystal polymer to be homogeneously oriented with respect to the substrate and to be oriented in a random direction within a plane parallel to the substrate surface. In the fixing step, the alignment state of the liquid crystal polymer on the substrate is fixed by vitrification or crosslinking of the liquid crystal polymer. In addition, it has the process of providing a protective layer on a liquid-crystal layer as needed, or transferring a liquid-crystal layer on the translucent board | substrate (it was excellent in the optical characteristic) which can be used as an optical film. Also good.

  In the preparation step, a liquid crystal composition solution containing a liquid crystal polymer and a solvent is prepared. The solvent may be any solvent that can dissolve the liquid crystal polymer and does not attack the substrate. Various solvents such as halogen, ester, ether, alcohol, ketone, amide, lactone, and sulfoxide are available. Any solvent can be used. Specifically, chloroform, tetrachloroethane, ethyl acetate, propylene glycol methyl ether, 2-propanol, methyl ethyl ketone, dimethylformamide, N-methylpyrrolidone, γ-butyrolactone, dimethylsulfoxide, and the like can be used.

  The content of the liquid crystal polymer in the liquid crystal composition solution is preferably 0.5 to 90% by mass and more preferably 1 to 70% by mass based on the total mass of the liquid crystal composition solution. Since such a liquid crystal composition solution has good fluidity, it can be suitably used in the coating process. In addition, when using the liquid crystal polymer which can fix an alignment state by bridge | crosslinking, a liquid-crystal composition solution is 0.1-10 mass% photoinitiator or thermal polymerization start based on the total mass of a liquid crystal polymer. Contains agents. At this time, as a subcomponent, at least one crosslinking agent having a polymer group that is the same as or copolymerizable with the polymer group possessed by the liquid crystal polymer or a photosensitizer may be appropriately contained.

Examples of such a crosslinking agent include compounds having a (meth) acryl group, a styrene group, an epoxy group, and a vinyl ether group, and the following structures are exemplified.

In formula (27), Z ¹ and Z ² represent the following formula.

In formula (28), R ¹ and R ² represent the following formula.

Furthermore, in formula (27), L ¹ , L ² and M ¹ represent the following formula.

At this time, ^{L 4} and ^{L 5} and ^P 1 to P ³ are as formula.

In the formula (31), X represents F, Cl, Br, CH ₃ , OCH ₃ , t-C ₄ H ₉ or C ₂ H ₅ .

  In addition, the liquid crystal composition solution may contain additives such as a surfactant or a leveling agent in order to increase the leveling property at the time of applying the liquid crystal composition solution. It is preferably 0.0001 to 10% by mass, more preferably 0.001 to 1% by mass based on the total mass of the solution.

  In the application step, the liquid crystal composition solution obtained in the preparation step is applied on a predetermined substrate. Examples of the coating method include a spin coating method, a gravure coating method, a dip coating method, a die coating method, and the like, and any method can be used as long as it can be applied uniformly by controlling the film thickness. In addition, since a favorable productivity can be achieved, a gravure coating method, a dip coating method, and a die coating method that can be continuously applied with a roll are preferable.

  In the drying step, the liquid crystal composition solution is dried so as to remove the solvent from the applied liquid crystal composition solution, thereby forming a precursor layer (a precursor of the liquid crystal layer) on the substrate. The drying conditions are set according to the type of solvent used, the concentration of the solution, etc., but the drying temperature is preferably 25 ° C. or higher and 120 ° C. or lower, and 30 ° C. or higher and 100 ° C. or lower. More preferably, it is 40 degreeC or more and 80 degrees C or less. The drying time is preferably from 10 seconds to 30 minutes, more preferably from 30 seconds to 20 minutes, and further preferably from 1 minute to 10 minutes. When the drying temperature is 25 ° C. or lower or the drying time is 10 seconds or shorter, the residual amount of the solvent contained in the liquid crystal composition tends to increase. On the other hand, when the drying temperature is 120 ° C. or higher, unevenness during drying tends to occur, and it tends to be difficult to produce a good precursor layer (liquid crystal layer). Moreover, when the drying time is 30 minutes or more, good productivity tends not to be expected. In addition, when continuous coating is performed in the coating process, drying is generally performed continuously. In that case, the drying temperature is initially set to a low temperature of about 25 ° C., and gradually about 120 ° C. It is preferable to dry the film while raising it until the unevenness can be effectively suppressed.

  In the heat treatment step, the precursor layer is further heat treated to impart a predetermined alignment state to the liquid crystal composition containing the liquid crystal polymer. Here, when the liquid crystal polymer can fix the alignment state by vitrification, the liquid crystal composition represents the liquid crystal polymer itself. On the other hand, in the case where the liquid crystal polymer can fix the alignment state by cross-linking, the object to be actually aligned is at least a reaction product of the liquid crystal polymer and the initiator. The thing containing an initiator etc. is represented. In this case, the liquid crystal composition may contain a crosslinking agent as necessary, but the crosslinking agent is not essential. As described above, what the liquid crystal composition represents varies depending on the type of liquid crystal polymer used, but the liquid crystal polymer contained in the liquid crystal composition is aligned by aligning the liquid crystal composition in any type. become.

  The predetermined alignment state imparted to the liquid crystal composition in the heat treatment step means an alignment state in which the liquid crystal composition forms a schlieren-like structure while having a homogeneous alignment and the haze value as a film is less than 40%. It is. In order to obtain such an alignment state, disclination lines and singular points where the alignment of the liquid crystal composition is inconsistent can be made as much as possible in order to reduce the haze while maintaining the fluidity of the liquid crystal composition. There is a need to reduce it. For that purpose, it is preferable to heat-treat the liquid crystal composition at a temperature T ° C. close to the nematic isotropic transition temperature.

  Specifically, the heat treatment temperature T ° C. is a temperature at which the liquid crystal composition is in a nematic state, and when the nematic isotropic transition temperature is Ti ° C., it is Ti-40 or more and less than Ti, preferably Ti— The temperature is 30 or more and less than Ti, more preferably Ti-20 or more and less than Ti. When T is less than Ti-40 ° C., the coalescence of domains is slow, so that a schlieren structure with a small pitch is formed, and the haze value is increased. Furthermore, if the temperature is lower than the temperature at which the liquid crystal polymer is in a nematic state, the fluidity of the liquid crystal composition is lowered, so that a predetermined alignment state cannot be obtained. Further, if T is Ti or more, the liquid crystal composition is in an isotropic state, so that a predetermined liquid crystal alignment cannot be obtained. That is, when the liquid crystal layer is cooled to room temperature in the immobilization step described later, the liquid crystal composition is suddenly aligned from the disordered isotropic phase, so that a schlieren structure with a small pitch is formed. Thereby, light scattering in the liquid crystal layer increases, and haze cannot be suppressed low.

  In addition, when a predetermined orientation state is realizable only by drying in a drying process, the following fixing process can be implemented without passing through the above-mentioned heat treatment process.

  In the fixing step, a predetermined alignment state of the liquid crystal composition obtained in the heat treatment step is fixed. If the liquid crystal composition has a glass transition point and vitrification occurs while maintaining the liquid crystal alignment when cooled to below the glass transition point, the alignment state can be fixed simply by cooling the liquid crystal layer after the heat treatment step. Can do. In addition, in order to ensure the heat resistance of a depolarizing film, it is preferable that the glass transition point of such a liquid crystal composition is 60 degreeC or more as mentioned above. However, even when the glass transition point is less than 60 ° C., desired heat resistance can be imparted to the depolarizing film by further fixing the orientation state by crosslinking. In this case, the liquid crystal composition solution may contain a liquid crystal composition having a structural unit having a crosslinkable polymer group and a polymerization initiator. Photopolymerization initiators are preferred because polymerization can be initiated regardless of the heat treatment temperature.

  On the other hand, when the liquid crystal composition does not have a glass transition point, after the liquid crystal composition is brought into a predetermined alignment state in the drying step or the heat treatment step, the liquid crystal composition is crosslinked while maintaining the state, A predetermined orientation state can be fixed. At this time, if it is cooled to a certain temperature after the heat treatment step, a crystal phase or a smectic phase appears at a low temperature, and the alignment state of the liquid crystal composition is disturbed. For this reason, it is necessary to start polymerization of the liquid crystal composition and fix the alignment state by cross-linking by applying an external stimulus such as light or heat to the liquid crystal layer in a temperature range showing a predetermined alignment state.

  In order to increase the strength of the surface of the liquid crystal layer, it is possible to provide a hard coat layer on the depolarizing film of this embodiment obtained by the above steps.

  In addition, when a transparent and isotropic substrate such as a polyvinyl alcohol film, a triacetyl cellulose film, a cyclopolyolefin film, a polycarbonate film, or a poly (meth) acrylic film is used as the substrate, the substrate and A laminate comprising a liquid crystal layer formed on a substrate can be used as it is as a depolarizing film.

  On the other hand, when an opaque film such as a polyethylene naphthalate film or a polyphenylene sulfide film formed of an isotropic alignment film made of polyvinyl alcohol resin or the like is used as a substrate, a liquid crystal composition solution is placed on the alignment film. It may be applied. Thereafter, the liquid crystal layer formed on the alignment film through a predetermined process can be transferred to another suitable substrate or the like via an adhesive or an adhesive. Similarly, when the substrate is too thick and unsuitable for use as a depolarizing film, the liquid crystal layer formed on the substrate is transferred to another suitable substrate via an adhesive or adhesive. can do.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1
[Preparation of liquid crystal composition solution]
<Preparation process>
100 mmol of terephthalic acid, 35 mmol of methylhydroquinone diacetate, 65 mmol of catechol diacetate and 60 mg of N-methylimidazole were mixed and subjected to polycondensation at 270 ° C. for 12 hours in a nitrogen atmosphere to obtain a reactive organism. The obtained reaction product was dissolved in tetrachloroethane and purified by reprecipitation with methanol to obtain a main-chain liquid crystalline polyester polymer represented by the following formula (27). In addition, when the logarithmic viscosity of this main chain type liquid crystalline polyester polymer was measured at 30 ° C. in a phenol / tetrachloroethane (60/40: mass ratio) mixed solvent using an Ubbelohde viscometer, 0.15 dl / g.

  20 parts by mass of the main chain type liquid crystalline polyester polymer obtained as described above and 0.01 parts by mass of a surfactant (manufactured by AGC Seimi Chemical Co., Surflon, S-386) were added to 79.99 parts by mass of N-methylpyrrolidone. After dissolving in an N-methylpyrrolidone solution, the insoluble matter was filtered with a PTFE (polytetrafluoroethylene) filter having a pore size of 0.45 μm to prepare a liquid crystal composition solution of Example 1.

  In order to measure the nematic isotropic transition temperature Ti of the liquid crystal composition, the liquid crystal composition solution of Example 1 was applied onto a soda glass using a spin coater to prepare an observation sample. While this observation sample was heated on a hot stage (manufactured by Mettler), the liquid crystal composition was observed with a polarizing microscope. As a result, the liquid crystal composition of Example 1 had a nematic phase, and the nematic isotropic transition temperature Ti was 265 ° C.

[Preparation of depolarized (optical) film]
2-Propanol / water (50% by mass / 50% by mass) of PVA (polyvinyl alcohol: manufactured by Nihon Acetate / Poval, JF-17) on a PPS (polyphenylene sulfide) film (Toray Industries, Torelina, thickness 60 μm) A 4 mass% solution was applied using a spin coater (application conditions: 400 rpm × 30 seconds). This was heat-treated for 30 minutes on a 55 ° C. hot plate and further for 5 minutes in an oven at 130 ° C. to form a PVA film (isotropic alignment film) having no alignment regulating force on the PPS film.

<Application process>
On the PVA film formed on the PPS film, the liquid crystal composition solution was applied using a spin coater (application conditions: 650 rpm × 30 seconds).

<Drying process>
The liquid crystal composition solution applied to the PVA film was dried on a hot plate at 55 ° C. for 10 minutes to form a precursor layer on the PVA film.

<Heat treatment process and immobilization process>
The precursor layer on the PVA film was heat-treated in an oven at 250 ° C. for 10 minutes, and then cooled to room temperature, thereby forming a vitrified liquid crystal layer on the PVA film.

Next, an ultraviolet curable adhesive (manufactured by Toagosei Co., Ltd., UV-3400) is applied on the liquid crystal layer to a thickness of 5 μm, and then a TAC film (triacetyl cellulose film: Fuji Film, T80-SZ, thickness). 80 μm) was laminated. The depolarization of Example 1 in which the PPS film and the PVA film were peeled off by irradiating 600 mJ / cm ² of ultraviolet light from the TAC film side, and then the PPS film and PVA film were peeled off to form a liquid crystal layer on the TAC film. A film was obtained.

(Example 2)
[Preparation of liquid crystal composition solution]
<Preparation process>
By mixing and polymerizing acrylic monomers having an oxetanyl group at a predetermined ratio, a side chain type liquid crystalline polyacrylate having an oxetanyl group represented by the following formula (28) (Mn = 8,000, Mw / Mw / Mn = 1.5) was obtained.
In addition, by using hydroxybenzoic acid as a starting compound, a compound obtained by bonding an oxetanyl group by Williamson's ether synthesis method and a predetermined diol are bonded using an acid chloride method to obtain the following formula (29 The crosslinking agent which has two oxetanyl groups represented by this was obtained.
Furthermore, a cross-linking agent having an oxetanyl group and an acrylic group represented by the following formula (30) was obtained by combining a site having an oxetanyl group and a site having an acrylic group by Williamson's ether synthesis method.

  0.8 parts by mass of a side-chain liquid crystalline polyacrylate having an oxetanyl group obtained as described above, 0.15 parts by mass of a crosslinking agent having two oxetanyl groups, and a crosslinking agent having an oxetanyl group and an acrylic group. 05 parts by mass and 0.001 part by mass of a surfactant (manufactured by AGC Seimi Chemical Co., Surflon, S-386) were dissolved in 9 parts by mass of N-methylpyrrolidone to obtain an N-methylpyrrolidone solution. After moving this solution to a dark place and adding 0.05 parts by mass of triallylsulfonium hexafluoroantimonate 50% propylene carbonate solution (manufactured by Aldrich), the insoluble matter was removed with a PTFE filter having a pore size of 0.45 μm. The liquid crystal composition solution of Example 2 was prepared by filtration.

  The nematic isotropic transition temperature Ti of the liquid crystal composition was measured in the same manner as in Example 1 except that the liquid crystal composition solution of Example 2 was used. As a result, the liquid crystal composition of Example 2 had a nematic phase, and the nematic isotropic transition temperature Ti was 180 ° C.

[Preparation of depolarized (optical) film]
<Application process>
On a non-stretched cyclopolyolefin film (Sekisui Chemical Co., Ltd., Essina, thickness 30 μm) subjected to corona treatment, the obtained liquid crystal composition solution was applied using a spin coater (application condition: 280 rpm × 20 seconds), A precursor layer was formed on the film.

(Drying process)
The precursor layer on the film was dried on a hot plate at 60 ° C. for 30 minutes.

(Heat treatment process and immobilization process)
While the precursor layer after drying is heat-treated in an oven at 150 ° C. for 5 minutes, it is irradiated with ultraviolet light with an integrated irradiation amount of 450 mJ / cm ² by a high-pressure mercury lamp in an air atmosphere, and the liquid crystalline polyacrylate in the precursor layer Was crosslinked. The precursor layer after heat treatment and ultraviolet irradiation was cooled to room temperature, whereby a depolarizing film of Example 2 in which a liquid crystal layer was formed on a cyclopolyolefin film was obtained.

(Comparative Example 1)
An optical film was produced in the same manner as in Example 1 except that the liquid crystal composition solution was directly applied onto the PPS film without forming the PVA film on the PPS film.

(Comparative Example 2)
An optical film was produced in the same manner as in Example 1 except that the heat treatment conditions in the oven were 190 ° C. and 10 minutes.

(Comparative Example 3)
An optical film was produced in the same manner as in Example 2 except that the heat treatment conditions in the oven were 120 ° C. and 10 minutes.

(Evaluation of liquid crystal polymer)
After the polyimide alignment film was formed on the high refractive index glass and rubbed, the liquid crystal composition solutions of Examples 1 and 2 were applied on the polyimide alignment film with a spin coater. The observation sample thus obtained was heat-treated on a hot plate at 55 ° C. for 10 minutes and further in an oven at 250 ° C. for 10 minutes to form a liquid crystal layer on the polyimide alignment film. Then, using an Abbe refractometer (Atago Co., Ltd. 4-T), it was determined the ordinary refractive index n _o and extraordinary refractive index n _e of the liquid crystal polymer of Example 1 and 2 (the liquid crystal layer), respectively below As shown in Table 1.

(Evaluation of depolarization (optical) film)

When the thickness of the liquid crystal layer of the depolarizing film obtained in Example 1 was measured using a stylus type film thickness meter (manufactured by ULVAC, DEKTAK-3030), it was d = 1300 nm. Therefore, the phase difference of the liquid crystal layer was calculated as Δnd = | n _e −n _o | × d = 277 nm≈λ / 2 (λ = 550 nm). Similarly, when the thickness of the liquid crystal layer of the depolarizing (optical) film of Example 2 was measured, d = 1800 nm. Therefore, the phase difference of the liquid crystal layer was calculated as Δnd = | n _e −n _o | × d = 277 nm≈λ / 2 (λ = 550 nm).

  Next, about the depolarization film obtained in Example 1, and the optical film obtained in Comparative Examples 1 and 2, a liquid crystal layer is formed under crossed Nicols using a polarizing microscope (manufactured by Olympus, BX-51). The alignment state of the liquid crystal polymer was observed at 400 times (objective lens: 40 times, eyepiece: 10 times). The results are shown in FIGS.

  In addition, the depolarization (optical) films obtained in the examples and comparative examples were placed on the incident side polarizing plate at 0 ° and 45 °, and under UV and visible near infrared spectrophotometers under crossed Nicols and paranicols. (Nippon Bunko V-570) was used to measure the light transmittance (λ = 550 nm) in each film. Furthermore, the haze value (diffuse transmittance / total light transmittance × 100) of each film was measured using a haze meter (manufactured by Gardner, Haze-gard plus). These results are shown in Table 2.

  In Examples 1 and 2, the liquid crystal polymer was homogeneously aligned and formed a suitable schlieren-like structure as shown in FIG. For this reason, the film has a low haze value and the transmittance of the film under crossed Nicols and paranicols is almost the same regardless of whether the incident polarization axis is 0 ° or 45 °. It was solved.

  In Comparative Example 1, as shown in FIG. 4, the liquid crystal polymer was aligned in a substantially uniform direction without forming a schlieren-like structure. For this reason, although the haze value of the film was low, when the incident-side polarization axis was 0 °, the transmittance of the film under crossed Nicols was significantly lower than the transmittance under paranicol. Further, when the incident-side polarization axis was 45 °, the transmittance of the film under para-Nicol was significantly lower than the transmittance of the film under cross-Nicol. Therefore, when the incident side polarization axis is 0 °, the linearly polarized light is emitted while maintaining almost the same polarization state, and when the incident side polarization axis is 45 °, the linearly polarized light is emitted by rotating by approximately 90 °. , It was found that the polarization was not eliminated.

  In Comparative Examples 2 and 3, the liquid crystal polymer formed a very fine schlieren structure as shown in FIG. For this reason, as in Examples 1 and 2, although the polarization was eliminated, light scattering occurred in the liquid crystal layer, the haze value was high, and the transmittance was low.

  The depolarizing film of the present invention can convert linearly polarized light such as light emitted from a liquid crystal display or laser light into non-polarized light close to natural light while suppressing haze to a low level. For example, the light emitted from a laser projector can be used to make it non-polarized light. Moreover, according to the manufacturing method of the depolarizing film of this invention, the depolarizing film provided with such a characteristic can be produced.

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Liquid crystal layer, 3 ... Liquid crystal polymer, 4 ... Dark field part, 10 ... Depolarization film.

Claims (4)

  A depolarizing film comprising a liquid crystal layer containing a liquid crystal polymer that is homogeneously aligned and forms a schlieren-like structure, and has a haze value of less than 40%. The ordinary refractive index of the liquid crystal polymer and n _o,
When the extraordinary refractive index of the liquid crystal polymer and n _e,
Wherein n _o and the n _e satisfies the following equation (1), depolarizing film according to claim 1, wherein.
0.05 ≦ | n _e −n _o | ≦ 0.5 (1) The thickness of the liquid crystal layer is d,
When the wavelength of light having the highest luminance among the light emitted from the light source and incident on the liquid crystal layer is λ,
The depolarizing film according to claim 2, wherein the n _o , the n _e , the d, and the λ satisfy the following formula (2) or (3).
λ / 8 ≦ | n _e −n _o | × d ≦ 7λ / 8 (2)
9λ / 8 ≦ | n _e −n _o | × d ≦ 15λ / 8 (3) A method for producing a depolarizing film for obtaining the depolarizing film according to any one of claims 1 to 3,
A coating step of coating a liquid crystal composition solution containing the liquid crystal polymer on a substrate;
A heat treatment step of heating the liquid crystal composition on the substrate at a temperature T ° C. to homogeneously align the liquid crystal polymer on the substrate,
A method for producing a depolarizing film, wherein the T and Ti satisfy the following formula (4) when the nematic-isotropic transition temperature of the liquid crystal composition is Ti ° C.
Ti-40 ≦ T <Ti (4)