JP2011145705A - Circularly polarized light isolating sheet, method of manufacturing the same, and liquid crystal display device using them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circularly polarized light isolating sheet which displays without coloring, even in the case of oblique observation and having proper selective reflection characteristic, a liquid crystal display device which includes the circularly polarized light isolating sheet; and to provide a method for manufacturing the circularly polarized light isolating sheet with high productivity, by forming a resin layer having cholesteric regularity having a wide selective reflection band in one layer. <P>SOLUTION: A photopolymerizable composition contains a photopolymerization initiator, having an average molar extinction coefficient of 2,000 M<SP>-1</SP>cm<SP>-1</SP>or more at a wavelength of 350-400 nm, and a photopolymerizable liquid crystal compound, having an average molar extinction coefficient of 1,500 M<SP>-1</SP>cm<SP>-1</SP>or more at a wavelength of 350-400 nm. The photopolymerizable composition is applied on a base material and a coating film is obtained; and a light having a wavelength of 350-400 nm at least is irradiated on the coating film to polymerize the photopolymerizable liquid crystal compound, thereby forming the resin layer with cholesteric regularity, the width of which has a selective reflection band of 150 nm or more, in one layer and the circularly polarized light isolating sheet is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a circularly polarized light separating sheet and a method for producing the same, and a liquid crystal display device using the same, and more specifically, a circularly polarized light separating sheet having a cholesteric regular resin layer having a wide selective reflection band and a method for producing the same. The present invention also relates to a liquid crystal display device using the same.

  The resin layer having cholesteric regularity has a characteristic of reflecting circularly polarized light in the rotation direction that coincides with the spiral rotation direction of the cholesteric regularity (hereinafter, this characteristic is referred to as “selective reflection characteristic”). The wavelength band showing this selective reflection characteristic depends on the period of cholesteric regularity. By widening the distribution width of the cholesteric regularity period, it is possible to widen the width of the wavelength band showing the selective reflection characteristics (hereinafter referred to as the selective reflection band).

If a circularly polarized light separating sheet comprising a resin layer having a cholesteric regularity with a selective reflection band in the visible light wavelength region can be formed, only the circularly polarized light of a specific wavelength is reflected from the incident natural light, and the remaining circularly polarized light is reflected. Can be transmitted. The reflected light can be reused by re-entering the resin layer with a reflector or the like.
A combination of the circularly polarized light separating sheet and the quarter wavelength plate can convert natural light into linearly polarized light with high efficiency. By aligning the direction of the linearly polarized light with the transmission direction of an absorption polarizer made of polyvinyl alcohol or the like provided in the liquid crystal display device, a high-brightness liquid crystal display device can be obtained.

  As a method of expanding the selective reflection band of a resin having cholesteric regularity (hereinafter referred to as cholesteric resin), a method of providing a plurality of cholesteric resin layers having different selective reflection bands, and gradually changing the period of the cholesteric resin layer in the thickness direction. A method of making the structure is known.

Patent Documents 1 to ³ photopolymerize a polymerizable mesogenic compound having a specific structure with a molar extinction coefficient at a wavelength of 365 nm of 50 to 500 dm ³ mol ⁻¹ cm ⁻¹ in the presence of a polymerizable chiral agent and a photopolymerization initiator. Thus, it is described that a broadband cholesteric liquid crystal film having a selective reflection band width of 200 nm or more is obtained. The broadband cholesteric liquid crystal film disclosed in the examples has a total liquid crystal layer thickness of 9 μm or more.

JP 2004-233987 A JP 2004-219522 A JP 2004-264322 A

However, according to the study by the present inventors, it has been found that the conventional broadband cholesteric liquid crystal film is colored in the display when observed from an oblique direction.
An object of the present invention is to provide a circularly polarized light separating sheet that can display without coloring even when observed obliquely and is excellent in selective reflection characteristics, and a liquid crystal display device including the circularly polarized light separating sheet.
Another object of the present invention is to provide a method for producing a circularly polarized light separating sheet with high productivity by forming a cholesteric resin layer having a wide selective reflection band in one layer.

As a result of intensive studies to achieve the above object, the present inventors polymerized a photopolymerizable liquid crystal compound in the presence of a photopolymerization initiator having an average molar extinction coefficient at a wavelength of 350 to 400 nm of 2000 M ⁻¹ cm ⁻¹ or more. The circularly polarized light separating sheet having a layer made of a resin having a cholesteric regularity obtained in this way can be displayed without being colored even when observed obliquely, and has excellent selective reflection characteristics. The present invention has been completed.

Thus, according to the present invention,
(1) Photopolymerization having an average molar extinction coefficient at a wavelength of 350 to 400 nm of 1500 M ⁻¹ cm ⁻¹ or less in the presence of a photopolymerization initiator having an average molar extinction coefficient at a wavelength of 350 to 400 nm of 2000 M ⁻¹ cm ⁻¹ or more. There is provided a circularly polarized light separating sheet comprising one or more resin layers having a cholesteric regularity in which one layer has a selective reflection band width of 150 nm or more.

Furthermore, as a preferable aspect,
(2) The circularly polarized light separating sheet, wherein the birefringence Δn of the photopolymerizable liquid crystal compound is 0.18 or more,
(3) The circularly polarized light separating sheet in which the total thickness of the resin layer is 7 μm or less, and / or (4) the circularly polarized light separating sheet in which the period of cholesteric regularity changes stepwise or continuously in the thickness direction. Is provided.

According to the present invention,
(5) A photopolymerizable composition containing a photopolymerization initiator having an average molar extinction coefficient at a wavelength of 350 to 400 nm of 2000 M ⁻¹ cm ⁻¹ or more and a photopolymerizable liquid crystal compound is applied onto a substrate and applied. A film is obtained, and the coating film is irradiated with light having a wavelength of at least 350 to 400 nm at an irradiation dose of more than 0 and 10 mJ / cm ² or less to polymerize the photopolymerizable liquid crystal compound to obtain a semi-cured film, and the semi-cured film Changing the period of cholesteric regularity, and then irradiating light with a wavelength of 350 to 400 nm for 10 mJ / cm ² or more to further cure the semi-cured film to form a resin layer having cholesteric regularity A method for producing a circularly polarized light separating sheet is provided.

According to the present invention,
(6) A polarizer A, a liquid crystal cell, a polarizer B, a quarter wavelength plate and a liquid crystal display device having the circularly polarized light separating sheet in this order, and / or (7) the polarizer B and a quarter wavelength plate The liquid crystal display device is provided.

  The circularly polarized light separating sheet of the present invention exhibits high selective reflection characteristics in the visible light region. In addition, the cholesteric resin layer can be thinned. Furthermore, the display is not colored even when observed from an oblique direction. Therefore, the circularly polarized light separating sheet of the present invention is suitable as a brightness enhancement film for liquid crystal display devices.

The reason why the circularly polarized light separating sheet of the present invention does not cause coloration in the display by observation from an oblique direction is not clear, but the mechanism is estimated as follows.
The resin layer having cholesteric regularity has a structure in which rod-like liquid crystal molecules are twisted and rotated in a spiral shape. Refractive index of the resin layer having cholesteric regularity is its value changes in a cycle, such as cholesteric regularity, in _{general, n x = n y> n} z (n x, n y in-plane direction of the principal refractive index, n _z has a relationship of main refractive index in the thickness direction).

  The circularly polarized light reflected by the resin layer having cholesteric regularity that changes in the thickness direction is reflected at different locations, that is, in the thickness direction, depending on the wavelength. For example, when a resin layer having a cholesteric regularity having a selective reflection band is laminated on each of 400 to 500 nm, 500 to 600 nm, and 600 to 700 nm, one circularly polarized light of 400 to 500 nm is incident on the resin layer. Reflected by the immediate layer, the other circularly polarized light is transmitted through the remaining resin layer. The circularly polarized light of 500 to 600 nm is reflected around the center of the resin layer, and the other circularly polarized light is transmitted through the remaining resin layer. The circularly polarized light of 600 to 700 nm is reflected by the layer immediately before exiting from the resin layer, and the other circularly polarized light is transmitted through the remaining resin layer. Thus, the distance that passes through the resin layer varies depending on the wavelength of the circularly polarized light. Since the distance passing through the resin layer is different, the amount of phase change at each wavelength is different. This difference in the amount of phase change is more noticeable in obliquely incident light.

  When a photopolymerization initiator having a specific molar extinction coefficient according to the present invention is used, the width of the cholesteric regularity period can be widened. Since the period of cholesteric regularity affects the selective reflection band, the width of the selective reflection band becomes wider as the period width increases. As a result, it is possible to reduce the total thickness d (number of layers and number of pitches of the helical structure) necessary to secure a selective reflection band having the same width. If the total thickness d can be reduced, the difference in phase change due to wavelength can be greatly reduced. According to the present invention, it is considered that such a mechanism can significantly suppress the phase change of obliquely incident light without degrading the selective reflection characteristic, and as a result, can suppress coloring of the display in oblique observation. It is done.

It is a figure which shows an example of distribution of the molar extinction coefficient of the photoinitiator used for this invention. It is a figure which shows the structural example of the liquid crystal display device of this invention. It is a figure which shows distribution of the molar extinction coefficient of the photoinitiator and photopolymerizable liquid crystal compound which were used in the Example and the comparative example. It is a figure which shows the light transmittance distribution of the band pass filter used by the present Example and the comparative example.

The circularly polarized light separating sheet of the present invention has cholesteric regularity obtained by polymerizing a photopolymerizable liquid crystal compound in the presence of a photopolymerization initiator having an average molar extinction coefficient at a wavelength of 350 to 400 nm of 2000 M ⁻¹ cm ⁻¹ or more. And a resin layer.

  The resin layer constituting the circularly polarized light separating sheet of the present invention has cholesteric regularity. The cholesteric regularity is a structure in which the angle of the molecular axis is shifted (twisted) one after another as it proceeds in the normal direction of the layer plane of a resin having cholesteric regularity (hereinafter referred to as cholesteric resin). Such a structure in which the direction of the molecular axis is twisted is called a helical structure. The normal line (helical axis) of the plane is preferably substantially parallel to the thickness direction of the cholesteric resin layer.

The cholesteric resin layer constituting the circularly polarized light separating sheet of the present invention may be one layer or two or more layers. In the case of two or more layers, at least one of the layers has a selective reflection bandwidth of 150 nm or more.
The total thickness d of the cholesteric resin layer is preferably 7 μm or less, more preferably 5 μm or less. When the total thickness d is smaller than the above thickness, the difference in the amount of phase change due to wavelength is reduced. The total thickness means the total thickness of each layer when the cholesteric resin layer is two or more layers, and the thickness when the cholesteric resin layer is one layer.

  The cholesteric resin layer used in the present invention is preferably a non-liquid crystalline resin layer. This is because the cholesteric regularity does not change depending on the ambient temperature, electric field, or the like when it is non-liquid crystalline. The non-liquid crystalline cholesteric resin layer can be obtained by including those having two or more polymerizable groups as a photopolymerizable liquid crystal compound described later. A photopolymerizable liquid crystal compound having two or more polymerizable groups introduces a crosslinked structure into the cholesteric resin, and a resin that does not produce liquid crystallinity is obtained. The cholesteric resin layer preferably has an average refractive index of 1.5 to 1.8.

To obtain a cholesteric resin layer, a photopolymerization initiator used in the present invention has an average molar absorption coefficient at a wavelength of 350~400nm is ^2000M -1 ^{cm -1} or more, preferably ^2500M -1 ^{cm -1} or more, more preferably it is of 2500~100000M ^-1 cm ^-1. When the average molar extinction coefficient at a wavelength of 350 to 400 nm is within the above range, the width of the selective reflection band of the circularly polarized light separating sheet of the present invention can be widened. If the average molar extinction coefficient at a wavelength of 350 to 400 nm is smaller than the above range, it becomes difficult to change the cycle of cholesteric regularity in the thickness direction, and the width of the selective reflection band of the circularly polarized light separating sheet may be reduced.
The molar extinction coefficient is calculated from the absorbance obtained by measuring a spectrophotometric spectrum of an acetonitrile solution having a concentration of 1.0 × 10 ⁻⁵ g / ml under the condition of an optical path length of 10 mm. The average molar extinction coefficient is the arithmetic average value of the molar extinction coefficient at each wavelength within a certain wavelength range.

The photopolymerization initiator is a compound capable of generating radicals and / or acids that polymerize ethylenically unsaturated groups with ultraviolet rays.
As photopolymerization initiators, 2- (4-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (4-methoxynaphthyl) -4,6-bis (trichloromethyl) -s -Triazine, 2- (4-ethoxynaphthyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (4-ethoxycarbonylnaphthyl) -4,6-bis (trichloromethyl) -s-triazine, Halomethylated triazine derivatives; halomethylated oxadiazole derivatives; 2- (2′-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (2′-chlorophenyl) -4,5-bis (3 ′) -Methoxyphenyl) imidazole dimer, 2- (2'-fluorophenyl) -4,5-diphenylimidazole dimer, 2- (2'-methoxyphenyl) Nyl) -4,5-diphenylimidazole dimer, (4′-methoxyphenyl) -4,5-diphenylimidazole dimer, and other imidazole derivatives; benzoin methyl ether, benzoin phenyl ether, benzoin isobutyl ether, benzoin isopropyl ether Benzoin alkyl ethers such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, 1-chloroanthraquinone, and the like; benzanthrone derivatives; benzophenone, Michler's ketone, 2-methylbenzophenone, 3-methylbenzophenone Benzophenone derivatives such as 4-methylbenzophenone, 2-chlorobenzophenone, 4-bromobenzophenone, 2-carboxybenzophenone;

  2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, α-hydroxy-2-methylphenylpropanone, 1-hydroxy-1-methylethyl- (p-isopropyl) Phenyl) ketone, 1-hydroxy-1- (p-dodecylphenyl) ketone, 2-methyl- (4 ′-(methylthio) phenyl) -2-morpholino-1-propanone, 1,1,1-trichloromethyl- ( acetophenone derivatives such as p-butylphenyl) ketone; thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. H Xanthone derivatives; benzoic acid ester derivatives such as ethyl p-dimethylaminobenzoate and ethyl p-diethylaminobenzoate; acridine derivatives such as 9-phenylacridine and 9- (p-methoxyphenyl) acridine; 9,10-dimethylbenzphenazine Phenazine derivatives such as;

  Di-cyclopentadienyl-Ti-di-chloride, di-cyclopentadienyl-Ti-bis-phenyl, di-cyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluoropheny -1-yl, di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,4,6-tri Fluorophen-1-yl, di-cyclopentadienyl-Ti-2,6-di-fluorophen-1-yl, di-cyclopentadienyl-Ti-2,4-di-fluorophen-1-yl Di-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,6-di-fluoro Feni-1-i , And titanocene derivatives such as di-cyclopentadienyl-Ti-2,6-di-fluoro-3- (pyr-1-yl) -phen-1-yl; oxime esters described in JP-A-2001-233842 Compounds, and oxime derivatives such as carbazole oxime compounds described in JP-A No. 2004-359639. These photopolymerization initiators are used alone or in combination.

  Among these, halomethylated triazine derivatives, halomethylated oxadiazole derivatives, imidazole derivatives, anthraquinone derivatives, benzanthrone derivatives, benzophenone derivatives, thioxanthone derivatives, acridine derivatives from the viewpoint of high average molar extinction coefficient at wavelengths of 350 to 400 nm , A phenazine derivative and an oxime derivative are preferable, and an oxime derivative is particularly preferable. In particular, as shown in FIG. 1, there is a main absorption (wavelength range where the molar extinction coefficient has a maximum value) between wavelengths 200 to 300 nm, and a secondary absorption (the molar extinction coefficient has a maximum value) between wavelengths 300 to 400 nm. A photopolymerization initiator having a wavelength range shown) is preferred.

  The amount of the photopolymerization initiator is preferably 0.01 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the photopolymerizable liquid crystal compound.

The photopolymerizable liquid crystal compound used in the present invention can obtain a resin having cholesteric regularity by polymerization.
Suitable photopolymerizable liquid crystal compound in the present invention, the average molar absorption coefficient at a wavelength of 350~400nm is ^1500M -1 ^{cm -1} or less, and more preferably from 0~1000M ^-1 cm ^-1. When the average molar extinction coefficient at a wavelength of 350 to 400 nm is within the above range, the width of the selective reflection band of the circularly polarized light separating sheet of the present invention can be widened. If the average molar extinction coefficient at a wavelength of 350 to 400 nm is larger than the above range, it is difficult to change the period of cholesteric regularity in the thickness direction because the photopolymerizable liquid crystal compound absorbs light at a wavelength of 350 to 400 nm too much. Thus, the width of the selective reflection band of the circularly polarized light separating sheet may be reduced.

Also among the suitable photopolymerizable liquid crystal compound to be used in the present invention, from the viewpoint of capable of widening the thin can and selective reflection band the total thickness of the cholesteric resin layer, the birefringence Δn (= n _e -n _o; n _e is the long axis direction of the refractive index of the photopolymerizable liquid crystal compound molecules, n _o is the refractive index along the short axis of the photopolymerizable liquid crystal compound molecules) thereof is preferably 0.18 or more, 0.18 to 0. 40 is more preferable, and 0.18 to 0.22 is particularly preferable. Δn can be measured by the Cellnamon method.
The photopolymerizable liquid crystal compound having Δn falling within the above range is preferably selected from rod-like photopolymerizable liquid crystal compounds. Note that Δn of the photopolymerizable liquid crystal compound can be increased by increasing the π-conjugated system of the mesogenic group. As the π-conjugated system increases, the ultraviolet absorption band of the photopolymerizable liquid crystal compound moves to the longer wavelength side. For example, the maximum absorption wavelength λmax of benzene is 260 nm, but for naphthalene and anthracene, λmax is 312 nm and 375 nm, respectively.

Examples of the rod-like photopolymerizable liquid crystal compound include a compound represented by the formula (1).
R1-B1-A1-B3-M-B4-A2-B2-R2 Formula (1)
In addition, although A1 and A2 in Formula (1) are a coupling group so that it may mention later, this coupling group is abbreviate | omitted and B1 and B3 or B4 and B2 may couple | bond together directly.

  In formula (1), R1 and R2 represent a polymerizable group. Specific examples of R1 and R2 that are polymerizable groups include (r-1) to (r-15) shown in Chemical Formula 1, but are not limited thereto.

  B1, B2, B3 and B4 each independently represent a single bond or a divalent linking group. Moreover, it is preferable that at least one of B3 and B4 is a group containing —O—CO—.

  A1 and A2 represent a linking group having 1 to 20 carbon atoms. Examples of the linking group here include a polymethylene group and a polyoxymethylene group. The number of carbons contained in the structural unit forming the linking group is appropriately determined depending on the chemical structure of the mesogenic group, etc. In general, in the case of a polymethylene group, the number of carbons is 1 to 20, preferably 2 to 12, In the case of a polyoxymethylene group, the carbon number is 1 to 10, preferably 1 to 3.

  M represents a mesogenic group. The material for forming the mesogenic group M is not particularly limited, but azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines Alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.

In the present invention, a chiral agent can be present when the photopolymerizable liquid crystal compound is polymerized.
As the chiral agent, those described in JP-A No. 2003-66214, JP-A No. 2003-313187, US Pat. No. 6,468,444, International Publication No. WO 98/00428 can be used as appropriate. A large HTP which is an index representing the efficiency of twisting the liquid crystal compound is preferable from the viewpoint of economy. HTP is represented by the formula (I): HTP = 1 / p · c. Here, p represents the pitch length of the helical structure, and c represents the concentration of the chiral agent. In order to avoid an unintended change in the phase transition temperature due to the addition of the chiral agent, it is preferable to use a chiral agent that exhibits liquid crystallinity.

In order to adjust the surface tension of the coating film obtained by coating the photopolymerizable composition containing the photopolymerization initiator and the photopolymerizable liquid crystal compound on a substrate, and to make the film thickness uniform, a surfactant is added. Can be used.
As the surfactant, a nonionic surfactant is particularly preferable, and an oligomer having a molecular weight of about several thousand is preferable. Examples of such a surfactant include KH-40 manufactured by Seimi Chemical Co., Ltd.

  Moreover, in order to control the orientation state of the air side surface of the cholesteric resin layer formed on the base material, an orientation adjusting agent can be used. Examples of the alignment modifier include polyvinyl alcohol, polyvinyl butyral, and modified products thereof.

  The cholesteric resin layer is obtained by polymerizing a photopolymerizable liquid crystal compound in the presence of the above-mentioned photopolymerization initiator and other compounding agents (chiral agent, surfactant, alignment regulator, etc.) added as necessary. can get.

  The method for producing a circularly polarized light separating sheet according to the present invention comprises dissolving the photopolymerizable liquid crystal compound and the photopolymerization initiator, and the chiral agent, the surfactant, the alignment regulator and the like added as necessary in a solvent. The obtained photopolymerizable composition is coated on a substrate and dried to obtain a coating film, and the coating film is irradiated with ultraviolet rays to polymerize the photopolymerizable liquid crystal compound to have cholesteric regularity. Forming a layer of resin.

  As a solvent used for the preparation of the photopolymerizable composition, an organic solvent is preferably used. Specific examples of the organic solvent include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. In particular, ketones are preferable in consideration of environmental load. Two or more organic solvents may be used in combination.

  The substrate used for obtaining the coating film is not particularly limited as long as it is an optically transparent substrate, but is preferably optically isotropic in order to avoid polarization change. Examples of such a substrate include a transparent resin film and a glass substrate, and a long transparent resin film is more preferable from the viewpoint of efficiently producing a liquid crystal layer. The transparent resin film may be a single-layer film or a multilayer film, but preferably has a thickness of 1 mm and a total light transmittance of 80% or more.

  The resin material of the transparent resin film includes an alicyclic structure-containing polymer resin, a chain olefin polymer such as polyethylene and polypropylene, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, and polyether. Examples include sulfone, amorphous polyolefin, modified acrylic polymer, and epoxy resin. These can be used alone or in combination of two or more. Among these, alicyclic structure-containing polymer resins are preferable from the viewpoints of transparency, low hygroscopicity, dimensional stability, lightness, and the like.

  The alicyclic structure-containing polymer resin has an alicyclic structure in the repeating unit of the polymer resin, and the polymer resin having an alicyclic structure in the main chain and an alicyclic structure in the side chain. Any polymer resin can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and a cycloalkane structure is preferable from the viewpoint of thermal stability. Although there is no restriction | limiting in particular in carbon number which comprises an alicyclic structure, Usually, 4-30 pieces, Preferably it is 5-20 pieces, More preferably, it is 6-15 pieces.

  The proportion of the repeating unit having an alicyclic structure in the alicyclic structure-containing polymer resin is appropriately selected according to the purpose of use, but is usually 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass. % Or more. When there are too few repeating units having an alicyclic structure, the heat resistance of the film may be reduced.

  Specifically, the alicyclic structure-containing polymer resin includes (1) a norbornene polymer, (2) a monocyclic olefin polymer, (3) a cyclic conjugated diene polymer, and (4) vinyl fat. Examples thereof include cyclic hydrocarbon polymers and hydrogenated products thereof. Among these, norbornene polymers and hydrogenated products thereof are more preferable from the viewpoints of transparency and moldability.

  Examples of the norbornene-based polymer include, for example, a ring-opening polymer of a norbornene-based monomer, a ring-opening copolymer of a norbornene-based monomer and another monomer capable of ring-opening copolymerization, and hydrogenated products thereof; Examples include addition polymers and addition copolymers with other monomers copolymerizable with norbornene-based monomers. Among these, from the viewpoint of transparency, a ring-opening polymer hydrogenated product of a norbornene-based monomer is most preferable. The polymer having the alicyclic structure is selected from known polymers disclosed in, for example, JP-A No. 2002-321302.

  The resin material of the transparent resin film suitable for the present invention has a glass transition temperature of preferably 80 ° C. or higher, more preferably 100 to 250 ° C. A transparent resin film made of a resin material having a glass transition temperature in such a range is excellent in durability without causing deformation or stress during use at high temperatures.

  The resin material of the transparent resin film suitable for the present invention has a molecular weight of gel permeation chromatography (hereinafter abbreviated as “GPC”) using cyclohexane (toluene when the resin material is not dissolved) as a solvent. The measured weight average molecular weight (Mw) in terms of polyisoprene (when the solvent is toluene, in terms of polystyrene) is usually 10,000 to 100,000, preferably 25,000 to 80,000, more preferably 25,000. ~ 50,000. When the weight average molecular weight is in such a range, the mechanical strength and moldability of the film are highly balanced and suitable.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the resin material of the transparent resin film suitable for the present invention is not particularly limited, but is usually 1 to 10, preferably 1 to 4, more preferably 1 The range is from 2 to 3.5.

  The resin material of the transparent resin film suitable for the present invention has a resin component (that is, an oligomer component) having a molecular weight of 2,000 or less, preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably. Is 2% by mass or less. When the amount of the oligomer component is within the above range, fine convex portions are hardly generated on the surface, the thickness unevenness is reduced, and the surface accuracy is improved. In order to reduce the amount of the oligomer component, the selection of the polymerization catalyst and the hydrogenation catalyst, the reaction conditions such as polymerization and hydrogenation, and the temperature conditions in the step of pelletizing the resin as a molding material may be optimized. . The amount of oligomer components can be measured by GPC as described above.

  The thickness of the substrate used in the present invention is not particularly limited, but the thickness is usually 1 to 1000 μm, preferably 5 to 300 μm, more preferably 30 to 100 μm, from the viewpoint of productivity, thinning, and weight reduction.

  The base material used in the present invention is preferably surface-treated. By performing the surface treatment, the adhesion between the base material and the alignment film described later can be enhanced. Examples of the surface treatment include glow discharge treatment, corona discharge treatment, ultraviolet treatment, and flame treatment. It is also preferable to provide an adhesive layer (undercoat layer) on the substrate in order to improve the adhesion between the substrate and the alignment film.

  In addition, the base material used in the present invention preferably has an alignment film on the base material surface in order to adjust the orientation direction of the helical structure of the cholesteric resin layer to be formed.

The alignment film used in the present invention is not particularly limited as long as the alignment direction of the cholesteric resin layer can be adjusted.
For the alignment film, for example, a coating liquid mainly composed of a resin such as polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, or polyetherimide is laminated on the base material in a film shape, dried, and then rubbed in one direction. It is obtained by doing. By rubbing the coating layer laminated in a film shape in one direction, it becomes possible to regulate the orientation of the resin layer having cholesteric regularity in one direction.

  The rubbing method is not particularly limited, and examples thereof include a method of rubbing the alignment film in a fixed direction with a roll made of a synthetic fiber such as nylon or a natural fiber such as cotton or a felt. In order to remove fine powder (foreign matter) generated during rubbing and to clean the surface of the alignment film, it is preferable to clean the formed alignment film with isopropyl alcohol or the like. In order to give the alignment layer a function of regulating the alignment of the resin layer having cholesteric regularity in one direction in the plane, there is a method of irradiating the surface of the alignment film with polarized ultraviolet rays in addition to rubbing.

  The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 1 μm.

  In order to obtain a coating film by applying a photopolymerizable composition on a substrate, a known method such as an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a bar coating method, or a die coating method is performed. .

The method of irradiating the coating film of the photopolymerizable composition with ultraviolet rays is not particularly limited, but it is preferable to irradiate light having a wavelength of at least 350 to 400 nm in order to easily obtain the circularly polarized light separating sheet of the present invention. In particular, when Δn of the photopolymerizable liquid crystal compound is 0.18 or more, the absorption edge of the ultraviolet light of the photopolymerizable liquid crystal compound extends to around 350 nm. It is preferable to irradiate only light of ˜400 nm. By irradiating light including this wavelength range, the polymerization of the photopolymerizable liquid crystal compound by the photopolymerization initiator is efficiently started over the entire thickness direction of the coating film. The amount of ultraviolet irradiation until the polymerization conversion rate of the photopolymerizable liquid crystal compound reaches 100% varies depending on the type of the photopolymerizable liquid crystal compound, but the amount of irradiation until the polymerization conversion rate reaches 100% has a wavelength of 350 to 400 nm. The total amount of light irradiation is usually 200 to 1500 mJ / cm ² .

In the present invention, in order to increase the width of the selective reflection band of the circularly polarized light separating sheet, the photopolymerizable liquid crystal compound is irradiated with ultraviolet rays at an irradiation dose such that the polymerization conversion rate does not become 100%, and then the helical structure. A method of changing the pitch (cycle of cholesteric regularity) and irradiating ultraviolet rays until the polymerization conversion rate becomes 100% is preferable.
Specifically, a photopolymerizable composition containing a photopolymerization initiator having an average molar extinction coefficient at a wavelength of 350 to 400 nm of 2000 M ⁻¹ cm ⁻¹ or more and a photopolymerizable liquid crystal compound is applied on a substrate. A coating film was obtained, and the coating film was irradiated with light having a wavelength of at least 350 to 400 nm at an irradiation dose of more than 0 and not more than 10 mJ / cm ² to polymerize the photopolymerizable liquid crystal compound to obtain a semi-cured film, and the semi-cured film The period of the cholesteric regularity of the film is changed, and then a light having a wavelength of 350 to 400 nm is irradiated with 10 mJ / cm ² or more to further cure the semi-cured film to form a resin layer having cholesteric regularity. The photopolymerizable liquid crystal compound used at this time preferably has an average molar extinction coefficient at a wavelength of 350 to 400 nm of 1500 M ⁻¹ cm ⁻¹ or less.

Since the average molar extinction coefficient of the photopolymerization initiator at a wavelength of 350 to 400 nm is within the above range, and the irradiation amount of light with a wavelength of 350 to 400 nm is within the above range, the circle of the present invention can be obtained in a short irradiation time. The width of the selective reflection band of the polarization separation sheet can be increased.
The irradiation time of light having a wavelength of 350 to 400 nm is preferably 0.1 to 10 seconds, more preferably 0.1 to 5 seconds, and further preferably 0.1 to 3 seconds. When the light irradiation time is in the above range, when the circularly polarized light separating sheet of the present invention is continuously manufactured, the length of the exposure process in the manufacturing process can be shortened or the line speed can be increased. Therefore, the productivity of the circularly polarized light separating sheet can be improved.

  Examples of the method of changing the cycle of cholesteric regularity include a method of heating within a temperature range showing a liquid crystal phase, a composition containing a photopolymerizable liquid crystal compound is further applied to a photopolymerized semi-cured film, and photopolymerization is further performed. And a method of applying a non-liquid crystalline compound to the photopolymerized semi-cured film. Among these, the method of heating within the temperature range showing the liquid crystal phase is preferable. The heating temperature can be appropriately selected depending on the type of the photopolymerizable liquid crystal compound, and is usually 65 to 115 ° C. The heating time is usually 0.001 to 20 minutes, preferably 0.001 to 10 minutes, more preferably 0.001 to 5 minutes.

  The circularly polarized light separating sheet of the present invention preferably includes a cholesteric resin layer exhibiting selective reflection characteristics over the entire wavelength region of visible light. Specifically, it is preferably a cholesteric resin layer that exhibits selective reflection characteristics for light in any wavelength region of blue (wavelength 410 to 470 nm), green (wavelength 520 to 580 nm), and red (wavelength 600 to 660 nm). .

  The wavelength exhibiting the selective reflection characteristic depends on the pitch of the helical structure in the cholesteric resin (= period of cholesteric regularity). The pitch of the helical structure is the helical axis direction until the molecular axis direction gradually shifts as it advances in the normal direction of the plane of the cholesteric resin layer in the helical structure and then returns to the original molecular axis direction again. Is the distance. By changing the pitch of the helical structure, the wavelength exhibiting selective reflection characteristics can be changed.

When the coating film of the photopolymerizable composition is irradiated with ultraviolet rays according to the production method of the present invention, a cholesteric resin layer in which the pitch of the helical structure is continuously changed in the thickness direction can be obtained.
Although the mechanism by which the resin layer whose pitch is continuously changed by ultraviolet irradiation is obtained is not known in detail, it is considered that the pitch is inclined by the following mechanism. The light receiving intensity of the ultraviolet ray irradiated to the layer containing the photopolymerizable liquid crystal compound, the chiral agent, and the polymerization initiator is strong on the surface (ultraviolet irradiation surface) side of the layer. In the layer, ultraviolet rays are absorbed by the polymerization initiator, so that the ultraviolet light receiving intensity decreases as the layer depth increases. Therefore, a difference in polymerization degree occurs as the depth of the layer increases from the surface of the layer (ultraviolet irradiation surface). Among the photopolymerizable liquid crystal compound and chiral agent, the concentration of the compound having a high degree of polymerization increases on the surface side of the layer, and the compound having a low degree of polymerization among the photopolymerizable liquid crystal compound and the chiral agent remaining as unreacted components diffuses. Move to the other side of the layer. Eventually, a concentration gradient is formed in which the concentration of the photopolymerizable liquid crystal compound or the chiral agent continuously changes in the depth direction of the layer. The amount of chiral agent affects the pitch size of the helical structure. In this way, a cholesteric resin layer in which the pitch of the helical structure is continuously changed in the thickness direction can be obtained.

  By the production method of the present invention, it is possible to obtain a circularly polarized light separating sheet that exhibits selective reflection characteristics over the entire visible light region with a single cholesteric resin layer, but if necessary, it can be shared by a plurality of cholesteric resin layers. A circularly polarized light separating sheet showing selective reflection characteristics over the entire visible light region can be obtained. When the circularly polarized light separating sheet is formed of a plurality of cholesteric resin layers, it usually becomes a cholesteric resin layer in which the period of cholesteric regularity changes stepwise in the thickness direction.

  When the circularly polarized light separating sheet is formed of a plurality of cholesteric resin layers, for example, a cholesteric resin layer having a helical structure pitch that exhibits a circularly polarized light separating function with light in the blue wavelength region, light in the green wavelength region A mode of laminating a cholesteric resin layer having a helical structure pitch that exhibits a circularly polarized light separating function and a cholesteric resin layer having a helical structure pitch that exhibits a circularly polarized light separating function with light in the red wavelength region, blue to green wavelength Of laminating a cholesteric resin layer having a helical structure pitch that exhibits a circularly polarized light separating function with light in the region and a cholesteric resin layer having a helical structure pitch that exhibits a circularly polarized light separating function with light in the green to red wavelength range Any aspect such as can be selected. Moreover, it is preferable to laminate | stack each cholesteric resin layer so that the rotation direction of the circularly polarized light to reflect may become the same. In order to obtain a liquid crystal display device having a wide viewing angle, it is preferable that the order of stacking the cholesteric resin layers be ascending or descending according to the pitch of the helical structure. Lamination of these cholesteric resin layers may be simply overlaid, or may be bonded via an adhesive or adhesive.

  In the circularly polarized light separating sheet of the present invention, the maximum wavelength of light with an incident angle of 0 degree at which the reflectance is 30% or more is preferably 700 nm or more, more preferably 730 nm or more. Further, the maximum wavelength of light with an incident angle of 60 degrees at which the reflectance is 30% or more is preferably 570 nm or more, more preferably 600 nm or more. When these maximum wavelengths are within the above range, coloring of the display when observed from an oblique direction can be eliminated.

  The circularly polarized light separating sheet of the present invention is attached to a liquid crystal display device having at least a polarizer A, a liquid crystal cell, and a polarizer B in combination with a quarter wavelength plate, and the polarizer A, the liquid crystal cell, the polarizer B, 1 The brightness of the liquid crystal display device can be improved by arranging the quarter-wave plate and the circularly polarized light separating sheet of the present invention in this order.

  Polarizers A and B used in the present invention are known polarizers used in liquid crystal display devices and the like. The polarizer used in the present invention transmits one of two linearly polarized light intersecting at right angles. For example, a hydrophilic polymer film such as a polyvinyl alcohol film or an ethylene vinyl acetate partially saponified film adsorbed a dichroic substance such as iodine or a dichroic dye and uniaxially stretched, the hydrophilic polymer film Examples include uniaxially stretched and dichroic substances adsorbed, and polyene oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Other examples include a polarizer having a function of separating polarized light such as grid polarizer and multilayer polarizer into reflected light and transmitted light. Of these, a linear polarizer containing polyvinyl alcohol is preferred.

Although the polarization degree of the polarizer used for this invention is not specifically limited, Preferably it is 98% or more, More preferably, it is 99% or more. The average thickness of the polarizer is preferably 5 to 80 μm.
The polarizing transmission axis of the polarizer A and the polarizing transmission axis of the polarizer B are usually arranged so as to sandwich the liquid crystal cell so as to be perpendicular to each other. Polarizer performance may change due to moisture absorption. In order to prevent this, a protective film is usually bonded to both sides of the polarizer A or B.

A liquid crystal cell is filled with a liquid crystal substance between two glass substrates provided with transparent electrodes facing each other with a gap of several μm, and a voltage is applied to this electrode to change the alignment state of the liquid crystal and pass through this. The amount of light to be controlled is controlled.
The liquid crystal cell is classified according to a method (operation mode) for changing the alignment state of the liquid crystal substance. For example, a TN (Twisted Nematic) type liquid crystal cell, a STN (Super Twisted Nematic) type liquid crystal cell, or a HAN (Hybrid Alignment Nematic) type. Examples include a liquid crystal cell, an IPS (In Plane Switching) type liquid crystal cell, a VA (Vertical Alignment) type liquid crystal cell, an MVA (Multiple Vertical Alignment) type liquid crystal cell, and an OCB (Optical Compensated Bend) type liquid crystal cell.

  The quarter-wave plate used in the present invention gives a quarter-wave phase difference to incident light. Since the phase difference differs depending on the wavelength of the incident light, the one that gives a phase difference of ¼ wavelength at the center wavelength of visible light, for example, around 550 nm is generally called a ¼ wavelength plate.

  In the present invention, a broadband quarter-wave plate can be used. The broadband ¼ wavelength plate gives a phase difference of almost ¼ wavelength at any wavelength in the visible light region including wavelengths of 410 to 660 nm. Almost 1/4 means 0.15 to 0.40, preferably 0.18 to 0.36, more preferably 0.20 to 0.30.

Further, a quarter wavelength plate having a phase compensation function can be used. A quarter wavelength plate having a phase compensation function gives a phase difference of a quarter wavelength near 550 nm, and has a retardation Rth (= thickness direction of less than 0 nm, preferably −2000 to −10 nm). (( _Nx + _ny ) / 2- _nz ) * d); _nx and _ny are in-plane main refractive indexes, _nz is a main refractive index in the normal direction, and d is a thickness) .

  As a broadband quarter-wave plate, for example, a half-wave plate that gives a half-wave phase difference near a wavelength of 550 nm and a quarter-wave plate that gives a quarter-wave phase difference near 550 nm are stacked. One having a D layer made of a material having a positive intrinsic birefringence value and an E layer made of a material having a negative intrinsic birefringence value, wherein the D layer and the E layer are molecularly oriented in the same direction. Can be mentioned. Further, a commercially available broadband retardation film WRF (manufactured by Teijin Ltd.) or the like can be used.

In the preferable liquid crystal display device of the present invention, the polarizer B and the quarter-wave plate are integrated.
There is no particular limitation on the method of integrating the polarizer, for example, the polarizer B and the quarter wavelength plate may be directly bonded, and the quarter wavelength plate may function as the protective film; Further, a quarter wave plate may be bonded together. When pasting, an adhesive or an adhesive may be used. The polarizing transmission axis of the polarizer B is arranged so as to be substantially parallel to the direction of linearly polarized light emitted from the quarter wavelength plate. That the angle formed between the polarization transmission axis and the direction of linearly polarized light is substantially parallel means that the angle is an angle of 0 to 3 °.

In the liquid crystal display device of the present invention, when the quarter wavelength plate is not provided with the phase compensation function as described above, the liquid crystal display device does not substantially have in-plane retardation and has a thickness direction letter. Deshon _{Rth (Rth = {(n x} + n y) / 2-n z} × d: _{wherein, n x,} n _y represents a principal refractive index in the plane direction, _{n z} is a main refractive index in the thickness direction D represents a film thickness)) is a phase compensation element in the range of −20 nm to −1000 nm, preferably −50 nm to −500 nm, between the circularly polarized light separating sheet of the present invention and the quarter wavelength plate. It is preferable to provide. At this time, it is preferable that the phase compensation element and the quarter-wave plate are integrated.
The phase compensation element having Rth in such a range has a function of compensating for the phase difference of light incident obliquely on the quarter wavelength plate.

The phase compensation element is mainly refractive indices _n x, _{n y} and _{n z is} required to satisfy the relation of _{n z> n x, n z} > n y, and _{n x} ≒ _{n y.} The main refractive index can be measured by an automatic birefringence meter [for example, “KOBRA series” manufactured by Oji Scientific Instruments Co., Ltd.]. Note that the _{n x} ≒ _{n y,} the refractive index difference is, usually within 0.0002, preferably 0.0001, more preferably within it within 0.00005.

Further, the phase compensation elements, the in-plane direction retardation _{Re (Re = (n x -n} y) × d:. N x, n y and d represent the same meaning as described above) is usually 20nm or less, Preferably it is 10 nm or less, More preferably, it is 5 nm or less.
A phase compensation element having such optical characteristics can be obtained by stretching and orientation of a film including a layer of a material having a negative intrinsic birefringence value.

  FIG. 2 is a diagram showing an example of the liquid crystal display device of the present invention. As shown in FIG. 2, a reflection plate 20, a cold cathode tube 19, a diffusion plate 18, a prism sheet (not shown), a circularly polarized light separating sheet 21 made of a cholesteric resin layer 17 formed on a substrate 16, and The phase compensation element 15, the quarter wavelength plate 14, the polarizer B 13, the liquid crystal cell 12, and the polarizer A 11 are arranged in this order. The light from the light source includes right polarized light and left polarized light. When the light is incident on the circularly polarized light separating sheet 21, the circularly polarized light separating sheet 21 is maintained while keeping the rotational direction of the circularly polarized light in one rotational direction (circularly polarized light rotated rightward in the drawing in the drawing). To Penetrate. The other circularly polarized light in the direction of rotation (circularly polarized light rotated counterclockwise toward the light traveling direction in the figure) is reflected by the circularly polarized light separating sheet (the reflected circularly polarized light remains rotated counterclockwise toward the light traveling direction). Is). The transmitted circularly polarized light is converted into linearly polarized light parallel to the transmission axis of the polarizer B by the quarter wavelength plate. On the other hand, the reflected circularly polarized light is reflected by a reflecting plate disposed behind the light source, and is incident on the circularly polarized light separating sheet again. In this way, the light emitted from the light source is effectively used, and the display brightness of the screen can be improved.

The diffusion plate is generally known as a plate having a function in which a particulate diffusion material is uniformly dispersed in a matrix such as a resin, thereby scattering and diffusing light. The prism sheet is generally known as a sheet having a function of narrowing light having a wide traveling direction due to scattering or the like in the normal direction of the sheet surface.
In FIG. 2, a diffusion sheet may be interposed between the phase compensation element and the circularly polarized light separating sheet. The diffusion sheet is generally laminated on a transparent film so that the particulate diffusion material is uniformly dispersed, and is known as a sheet having a function of scattering and diffusing light.

  In the present invention, it is preferable that the surface of the circularly polarized light separating sheet on the quarter wavelength plate side has light diffusibility. The light diffusibility is a property of scattering and diffusing light. In order to provide light diffusibility, for example, a method of laminating a particulate diffusing material on the surface of a circularly polarized light separating sheet so as to uniformly disperse, a method of uniformly dispersing a particulate diffusing material on a substrate, Or the method of bonding the said diffusion sheet to a circularly polarized light separation sheet etc. are mentioned.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not restrict | limited to the following Example. Parts and% are based on mass unless otherwise specified.

The evaluation methods performed in this example are as follows.
<Reflection band>
The collimated white light was incident on the circularly polarized light separation sheet at an incident angle of 0 degree, and the reflection spectrum was measured using a spectroscope: [S-2600] manufactured by Soma Optical Co., Ltd. The width of the selective reflection band was the half width of the maximum reflectance (that is, the difference between the maximum wavelength and the minimum wavelength that is ½ of the maximum reflectance).
<Film thickness measurement>
It measured using the surface shape measuring apparatus [DEKTAK6M] by ULVAC.
<Δn>
According to the Senalmon method, it measured using the microscope (The Eclipse E-600POL IF lens 546nm by Nikon).

  The light transmittance distributions of the bandpass filters A and B used in the examples and comparative examples are shown in FIG. The band pass filter A has a region with a light transmittance of 5% or more in the range of 300 to 345 nm and a bandwidth of 45 nm. The band pass filter B has a region with a light transmittance of 5% or more in the range of 350 to 400 nm and a bandwidth of 50 nm. That is, the two types of band-pass filters used in the examples and comparative examples have a bandwidth of about 50 nm in different wavelength ranges.

(¼ wavelength plate with phase compensation function (C))
A styrene-maleic anhydride copolymer (a material having a negative intrinsic birefringence value, Tg = 131 ° C.) and a norbornene-based polymer (“ZEONOR 1020”, manufactured by Nippon Zeon Co., Ltd., Tg = 105 ° C.) are coextruded. Molding was performed to obtain a multilayer film having a three-layer structure of norbornene polymer layer (thickness 50 μm) / styrene-maleic anhydride copolymer layer (thickness 200 μm) / norbornene polymer layer (thickness 50 μm).
Next, this multilayer film was successively biaxially stretched at 140 ° C. by 1.8 times in the vertical direction and 1.5 times in the horizontal direction to obtain a quarter-wave plate (C). The average thickness of the quarter-wave plate (C) 120 [mu] m, the main refractive indices _{n x} 1.5801, _{n y} is 1.5789, _{n z} was 1.5811. The in-plane retardation Re was 144 nm, and the thickness direction retardation Rth was -192 nm.

(Polarizing plate with phase compensation function (X))
The quarter wave plate (C) was bonded and integrated on one side of a polarizer B obtained by adsorbing iodine to polyvinyl alcohol. Further, a polarizing plate (X) was obtained by pasting and integrating a triacetyl cellulose film having an average thickness of 60 μm on the other side of the polarizer B.

(Polarizing plate (Y))
A polarizing plate (Y) was obtained by laminating and integrating a triacetyl cellulose film having an average thickness of 60 μm on both surfaces of a polarizer A obtained by adsorbing iodine to polyvinyl alcohol.

FIG. 3 is a diagram showing the distribution of the molar extinction coefficient of the photopolymerizable liquid crystal compound and the photopolymerization initiator used in the examples and comparative examples.
Curve A is the distribution of the molar extinction coefficient of photopolymerization initiator A (carbazole oxime photopolymerization initiator). Curve B is the distribution of molar extinction coefficient of photopolymerization initiator B (Irgacure 907, manufactured by Ciba Specialty Chemicals). Curve C is the molar extinction coefficient distribution of photopolymerizable liquid crystal compound C (Irgacure 369, manufactured by Ciba Specialty Chemicals). Curve X is the molar extinction coefficient distribution of the photopolymerizable liquid crystal compound X. Curve Y is the molar extinction coefficient distribution of the photopolymerizable liquid crystal compound Y.
Table 1 shows the average molar extinction coefficient of the photopolymerizable liquid crystal compound and photopolymerization initiator and the birefringence Δn of the photopolymerizable liquid crystal compound.

  One side of a ZEONOR film (manufactured by Nippon Zeon Co., Ltd., ZF14-100) is corona discharged, and then a 5% by weight aqueous solution of polyvinyl alcohol (Kuraray Co., Ltd., Poval MP203) is applied to the surface and dried at 100 ° C. for 3 minutes. The substrate was obtained by rubbing with a felt roll to form an alignment film.

Example 1
94.2 parts of photopolymerizable liquid crystal compound X having a birefringence Δn of 0.18 and a distribution of molar extinction coefficient indicated by curve X in FIG. 3, 5.8 parts of chiral agent (LC756 manufactured by BASF), FIG. 3.1 parts of photopolymerization initiator A having a molar extinction coefficient distribution indicated by curve A and 0.1 part of a surfactant (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) are added to methyl ethyl ketone so that the solid content is 40%. And then filtered through a polytetrafluoroethylene syringe filter having a pore diameter of 0.45 μm to obtain a polymerizable solution.
This polymerizable solution was applied to the surface of the base material on which the alignment film was provided and dried to form a coating film. The surface side on which the coating film was formed was irradiated with ultraviolet light having passed through the bandpass filter B at a wavelength of 350 to 400 nm for 1 second at 5 mW / cm ² . Thereafter, the coating film is left in an oven at 100 ° C. for 3 minutes, and then the ultraviolet light transmitted through the bandpass filter B is irradiated on the coating film forming surface side at a wavelength of 350 to 400 nm for 5 seconds at 40 mW / cm ^2. Was cured to obtain an optical element having a cholesteric resin layer (thickness: 3 μm). The thickness was controlled by adjusting the coating amount of the polymerizable solution. The selective reflection bandwidth of the obtained optical element was 170 nm. Note that a mercury xenon lamp (EXECURE 3000, 200 W manufactured by HOYA) was used for ultraviolet irradiation. Further, an ultraviolet illuminance meter (manufactured by Oak Manufacturing Co., Ltd., UV-M03) was used for measuring the irradiation amount.

Example 2
94.2 parts of photopolymerizable liquid crystal compound X was changed to 93.9 parts of photopolymerizable liquid crystal compound Y having a birefringence Δn of 0.20 and a molar extinction coefficient distribution shown by curve Y in FIG. A polymerizable solution was obtained in the same manner as in Example 1 except that the amount of the agent (LC756 manufactured by BASF) was changed to 6.1 parts.
This polymerizable solution was applied to the surface of the base material on which the alignment film was provided and dried to form a coating film. The surface side on which the coating film was formed was irradiated with ultraviolet light having passed through the bandpass filter B at a wavelength of 350 to 400 nm for 1 second at 5 mW / cm ² . Thereafter, the coating film is left in an oven at 100 ° C. for 3 minutes, and then the ultraviolet light transmitted through the bandpass filter B is irradiated on the coating film forming surface side at a wavelength of 350 to 400 nm for 5 seconds at 40 mW / cm ^2. Was cured to obtain an optical element having a cholesteric resin layer (thickness: 3 μm). The selective reflection bandwidth of the obtained optical element was 180 nm.

Comparative Example 1
The polymerizable solution obtained in Example 1 was applied to the surface of the base material on which the alignment film was provided and dried to form a coating film. A cholesteric resin layer (thickness 3 μm) is cured by irradiating UV light having passed through the bandpass filter B on the surface on which the coating film is formed at 200 mW / cm ² for 1 second as an irradiation amount of a wavelength of 350 to 400 nm to cure the coating film. An optical element having was obtained. The selective reflection bandwidth of the obtained optical element was 70 nm.

Comparative Example 2
The polymerizable solution obtained in Example 2 was applied to the surface of the base material provided with the alignment film and dried to form a coating film. A cholesteric resin layer (thickness 3 μm) is cured by irradiating UV light having passed through the bandpass filter B on the surface on which the coating film is formed at 200 mW / cm ² for 1 second as an irradiation amount of a wavelength of 350 to 400 nm to cure the coating film. An optical element having was obtained. The selective reflection bandwidth of the obtained optical element was 80 nm.

Comparative Example 3
An optical element was obtained in the same manner as in Example 1 except that the photopolymerization initiator B was used in place of the photopolymerization initiator A. The selective reflection bandwidth of the obtained optical element was 70 nm.

Comparative Example 4
An optical element was obtained in the same manner as in Example 1 except that the photopolymerization initiator C was used in place of the photopolymerization initiator A. The selective reflection bandwidth of the obtained optical element was 70 nm.

Comparative Example 5
The polymerizable solution obtained in Comparative Example 3 was applied to the surface of the base material provided with the alignment film and dried to form a coating film. The surface side on which the coating film was formed was irradiated with ultraviolet light having passed through the bandpass filter A at a wavelength of 300 to 345 nm at 5 mW / cm ² for 1 second. Thereafter, the coating film is left in an oven at 100 ° C. for 3 minutes, and then the ultraviolet light transmitted through the bandpass filter B is irradiated on the coating film forming surface side at a wavelength of 350 to 400 nm for 5 seconds at 40 mW / cm ^2. Was cured to obtain an optical element having a cholesteric resin layer (thickness: 3 μm). The selective reflection bandwidth of the obtained optical element was 70 nm.

Comparative Example 6
The polymerizable solution obtained in Example 1 was applied to the surface of the base material on which the alignment film was provided and dried to form a coating film. The surface side on which the coating film was formed was irradiated with ultraviolet light having passed through the bandpass filter A at a wavelength of 300 to 345 nm at 5 mW / cm ² for 1 second. Thereafter, the coating film is left in an oven at 100 ° C. for 3 minutes, and then the ultraviolet light transmitted through the bandpass filter B is irradiated on the coating film forming surface side at a wavelength of 350 to 400 nm for 5 seconds at 40 mW / cm ^2. Was cured to obtain an optical element having a cholesteric resin layer (thickness: 3 μm). The selective reflection bandwidth of the obtained optical element was 70 nm.

Example 3
The thickness of the 2 μm thick cholesteric resin layer was the same as in Example 1 except that the amount of the photopolymerizable liquid crystal compound X was changed to 93.4 parts and the amount of the chiral agent (LC756 manufactured by BASF) was changed to 6.6 parts. An optical element P1 was obtained. The selective reflection bandwidth of the obtained optical element P1 was 150 nm.
A cholesteric resin layer (thickness 3 μm) was prepared in the same manner as in Example 1, except that the amount of the photopolymerizable liquid crystal compound X was changed to 95.1 parts and the amount of the chiral agent (LC756 manufactured by BASF) was changed to 4.9 parts. ) Was obtained. The selective reflection bandwidth of the obtained optical element P2 was 190 nm.
In the optical elements P1 and P2, the pitch of the helical structure continuously changes from the surface on one side to the surface on the other side, and the average value of the pitch length of the helical structure in the optical element P2 However, it was confirmed by observation with an SEM that it was larger than that in the optical element P1.

  The side where the pitch of the helical structure of the cholesteric resin layer of the optical element P1 is large and the side of the optical element P2 where the pitch of the helical structure of the cholesteric resin layer is small are opposed to each other, and the cholesteric resin layer (total A circularly polarized light separating sheet having a thickness of 5 μm was obtained. The selective reflection bandwidth of this circularly polarized light separating sheet was 340 nm.

  The circularly polarized light separating sheet and the polarizing plate (X) were placed in this order on a backlight unit comprising a light reflecting plate, a cold cathode tube, a diffusing plate and a prism sheet to obtain a polarized light source device. At this time, the surface of the circularly polarized light separating sheet having a larger pitch in the helical structure (that is, the surface of the circularly polarized light separating sheet on the optical element P2 side) and the quarter wavelength plate (C) side of the polarizing plate (X) Face to face. This polarized light source device has an ergoscope measurement in all directions at polar angles of 0 ° to 70 °. The x component variation Δx is 0.028, the y component variation Δy is 0.030, and the front luminance ratio is Was 1.25. The polar angle means an angle when tilted from the front direction when observing the polarized light source device. Further, it is shown that the smaller the chromaticity variations Δx and Δy, the better. The front luminance ratio is a ratio to luminance in a polarized light source device in which only a polarizer is placed on the backlight unit.

  The circularly polarized light separating sheet, the polarizing plate (X), the liquid crystal cell, and the polarizing plate (Y) are placed in this order on a backlight unit composed of a light reflecting plate, a cold cathode tube, a diffusion plate and a prism sheet, and a liquid crystal A display device was obtained. Even when this liquid crystal display device was observed from an oblique direction, the color was the same as that observed from the front direction, and the screen was not colored.

Comparative Example 7
Optical having a cholesteric resin layer (thickness 2 μm) in the same manner as in Comparative Example 1 except that the amount of the photopolymerizable liquid crystal compound X was 92.6 parts and the amount of the chiral agent (LC756 manufactured by BASF) was 7.4 parts. Element P3 was obtained. The selective reflection bandwidth of the obtained optical element P3 was 65 nm.
Optical having a cholesteric resin layer (thickness 2 μm) in the same manner as in Comparative Example 1, except that the amount of the photopolymerizable liquid crystal compound X is 93.8 parts and the amount of the chiral agent (LC756 manufactured by BASF) is 6.2 parts. Element P4 was obtained. The selective reflection bandwidth of the obtained optical element P4 was 70 nm.
Optical having a cholesteric resin layer (thickness 2 μm) in the same manner as in Comparative Example 1 except that the amount of the photopolymerizable liquid crystal compound X is 94.7 parts and the amount of the chiral agent (LC756 manufactured by BASF) is 5.3 parts. Element P5 was obtained. The selective reflection bandwidth of the obtained optical element P5 was 80 nm.
Optical having a cholesteric resin layer (thickness 2 μm) in the same manner as in Comparative Example 1 except that the amount of the photopolymerizable liquid crystal compound X is 95.4 parts and the amount of the chiral agent (LC756 manufactured by BASF) is 4.6 parts. Element P6 was obtained. The selective reflection bandwidth of the obtained optical element P6 was 95 nm.

The obtained optical elements P3, P4, P5, and P6 were bonded in this order to obtain a circularly polarized light separating sheet having a cholesteric resin layer (total thickness: 8 μm). The selective reflection bandwidth of this circularly polarized light separating sheet was 310 nm.
In the same manner as in Example 3, a polarized light source device was obtained, and chromaticity variation and front luminance ratio were measured with an ergoscope. Δx was 0.047, Δy was 0.070, and the front luminance ratio was 1.21. Moreover, the liquid crystal display device was obtained similarly to Example 3, and the display performance was confirmed. When this liquid crystal display device was observed from an oblique direction, the hue was different from that observed from the front direction, and the screen was seen as yellow as a whole.

X: Photopolymerizable liquid crystal compound X
Y: Photopolymerizable liquid crystal compound Y
A: Photopolymerization initiator A
B: Photopolymerization initiator B
C: Photopolymerization initiator C
11: Polarizer A
12: Liquid crystal cell 13: Polarizer B
14: 1/4 wavelength plate 15: Phase compensation element 16: Base material 17: Cholesteric resin layer 18: Diffusion plate 19: Cold cathode tube 20: Light reflection plate 21: Circularly polarized light separation sheet

Claims (7)

The average molar extinction coefficient at a wavelength of 350 to 400 nm calculated from the absorbance obtained by measuring a spectrophotometric spectrum of an acetonitrile solution having a concentration of 1.0 × 10 ⁻⁵ g / ml under the condition of an optical path length of 10 mm is 2000 M ⁻¹ cm ^{−. In} the presence of ^one or more photopolymerization initiators, a photopolymerizable liquid crystal compound having an average molar extinction coefficient of 1500 M ⁻¹ cm ⁻¹ or less at a wavelength of 350 to 400 nm is polymerized to form a selective reflection band in one layer. A circularly polarized light separating sheet having one or more resin layers having a cholesteric regularity with a width of 150 nm or more.   The circularly polarized light separating sheet according to claim 1, wherein the photopolymerizable liquid crystal compound has a birefringence Δn of 0.18 or more.   The circularly polarized light separating sheet according to claim 1, wherein the total thickness of the resin layer is 7 μm or less.   The circularly polarized light separating sheet according to any one of claims 1 to 3, wherein a cycle of cholesteric regularity changes stepwise or continuously in the thickness direction. The average molar extinction coefficient at a wavelength of 350 to 400 nm calculated from the absorbance obtained by measuring a spectrophotometric spectrum of an acetonitrile solution having a concentration of 1.0 × 10 ⁻⁵ g / ml under the condition of an optical path length of 10 mm is 2000 M ⁻¹ cm ^−. Coating a photopolymerizable composition containing ^one or more photopolymerization initiators and a photopolymerizable liquid crystal compound on a substrate to obtain a coating film;
A semi-cured film is obtained by polymerizing the photopolymerizable liquid crystal compound by irradiating the coating film with light having a wavelength of 350 to 400 nm at an irradiation dose of more than 0 and 10 mJ / cm ² or less,
Changing the period of cholesteric regularity of the semi-cured film,
Next, a method for producing a circularly polarized light separating sheet, comprising irradiating light having a wavelength of 350 to 400 nm with 10 mJ / cm ² or more to further cure the semi-cured film to form a resin layer having cholesteric regularity. A liquid crystal display device comprising: a polarizer A, a liquid crystal cell, a polarizer B, a quarter-wave plate, and the circularly polarized light separating sheet according to claim 1 in this order.   The liquid crystal display device according to claim 6, wherein the polarizer B and the quarter-wave plate are integrated.

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