KR101698226B1 - Optical film - Google Patents

Abstract

The present application relates to optical films. The exemplary optical film can be used as a reflection type polarizing plate capable of improving light utilization efficiency and brightness of a display device such as an LCD, for example.

Description

Optical film {Optical film}

The present invention relates to an optical film, a reflection type polarizing plate and a liquid crystal display device.

The liquid crystal display (LCD) may include a liquid crystal panel and a polarizing plate disposed on the upper side and the lower side of the liquid crystal panel, and may include various functional optical elements in addition to the polarizing plate.

In the LCD, an image can be displayed by changing the orientation of the liquid crystal for each pixel of the liquid crystal panel. Since the LCD is not a self-luminous device, a light source such as a backlight unit (BLU) is usually placed on the back surface of the lower polarizer of the liquid crystal panel, and the light emitted from the light source is transmitted through the panel to display an image .

The present application provides an optical film, a reflection type polarizing plate and a liquid crystal display device.

This application relates to an optical film. An exemplary optical film comprises a liquid crystal layer (hereinafter " CLC layer ") comprising a cholesteric aligned liquid crystal region. The optical film may further include a haze layer having a haze of about 40% to 60% at the top of the liquid crystal layer.

In the optical film, the CLC layer may be a single layer. Herein, the CLC layer may be formed as a single layer by laminating or adhering two or more CLC layers, or may exclude a CLC layer formed by coating the CLC composition a plurality of times.

The CLC layer may include a cholesteric liquid crystal region, and the liquid crystal region may include two or more types of liquid crystal regions having different center wavelengths of reflected light. In the present specification, a cholesteric liquid crystal or a cholesteric liquid crystal can be abbreviated as " CLC ". Referring to FIG. 1, the CLC has a helical structure in which a waveguide (n in FIG. 1) of liquid crystal molecules is layered and aligned along a spiral axis (X in FIG. 1). The distance (P in Fig. 1) until the waveguide of the liquid crystal molecules completes the rotation of 360 degrees in the structure of CLC is called " pitch ". As used herein, the term " liquid crystal region or CLC region " may mean a CLC region in which a CLC waveguide completes a 360 degree rotation. In this specification, each CLC region can be divided, for example, according to the central wavelength of reflected light of each CLC region.

CLC can selectively reflect circularly polarized light. The wavelength of the light reflected by the CLC depends on the refractive index and the pitch of the liquid crystal. The helical twist of the CLC waveguide causes spatially periodic deformation in the dielectric tensor of the material, which causes wavelength selective reflection of the light. Generally, in CLC, Bragg reflections occur when the wavelength λ of the light propagating along the helical axis falls within the category of the following general formula (1).

[Formula 1]

N _o P <λ <N _e P

In the above general formula 1, P represents the pitch of the CLC region, N _e represents the refractive index of CLC for light polarized parallel to the CLC waveguide, N _o represents the refractive index of CLC &Lt; / RTI &gt;

In addition, the center wavelength? ₀ in the wavelength range of the light reflected by the CLC, that is, the reflected light, can be approximated by the following general formula (2).

[Formula 2]

λ _o = 0.5 (N _o + N _e ) P

In the general formula (2), P, N _e and N _o are as defined in the general formula (1).

Further, the spectral width?? ₀ of the light reflected by the CLC can be approximated by the following general formula (3).

[Formula 3]

? ₀ = 2? _O (N _e -N _o ) / (N _o + N _e ) = P (N _e -N _o )

In the general formula 3, P, N _e and N _o are as defined in general formula

The CLC layer includes two or more kinds of CLC regions. In the two or more types of CLC regions, light that can be reflected, that is, the central wavelength of reflected light, is different from each other.

In one example, the CLC regions having different center wavelengths of reflected light may have different pitches from each other. According to one example, when two or more types of CLC regions are included in a CLC layer of a single layer, the selective reflection characteristic by the CLC layer can be utilized in a wide wavelength range while the CLC layer is made thin. In this specification, the CLC layer including the single layer and two or more types of CLC regions may be referred to as a broadband CLC layer.

The arrangement of the CLC regions having different center wavelengths of the reflected light in the CLC layer is not particularly limited. In one example, the CLC regions are disposed such that the center wavelength of the reflected light of each region sequentially lengthens or shortens from one side to the other of the CLC layers, or is arranged such that the central wavelength becomes longer and then shortens again, Or may be arranged so as to lengthen again, or may be arranged so as to vary the central wavelength irregularly. In one example, if the CLC contained in the CLC layer is the same kind of compound, the pitch of the CLC region may change so that each CLC region represents the center wavelength of the reflected light as described above.

In one exemplary CLC layer, a CLC region having a central wavelength of reflected light belonging to a red light region of visible light is disposed on one main surface side of the CLC layer, and a central wavelength of reflected light is arranged on the other main surface side of the CLC layer The CLC regions belonging to the blue light region may be arranged such that the central wavelengths of the reflected light of each CLC region sequentially change along the thickness direction of the CLC layer.

In this specification, the term &quot; thickness direction of the CLC layer &quot; may refer to a direction parallel to a virtual line connecting the one major surface of the CLC layer and the major surface opposite to the major surface. In one example, when the optical film further includes a base layer as described later, and the CLC layer is formed on one side of the base layer, the thickness direction of the CLC layer is such that the CLC layer is formed And may be a direction parallel to an imaginary line formed in a direction perpendicular to the surface of the substrate layer. In this specification, when defining the angle and using terms such as vertical, parallel, orthogonal, or horizontal, it means a substantial vertical, parallel, orthogonal, or horizontal range without impairing the desired effect. For example, it includes an error considering manufacturing error or variation. For example, each of the above cases may include an error within about +/- 15 degrees, an error within about +/- 10 degrees, or an error within about +/- 5 degrees.

2 is a schematic diagram schematically illustrating the CLC layer 2 in which the central wavelength of the reflected light from the main surface 21 side to the other main surface 22 side of the CLC layer 2 is red A CLC region 231 belonging to the category of light, a CLC region 232 belonging to the category of green light and a CLC region 233 belonging to the category of blue light are sequentially arranged.

In one example, the CLC layer comprises a first region having a central wavelength of reflected light of 400 nm to 500 nm, a second region having a central wavelength of reflected light of 500 nm to 600 nm, and a second region having a center wavelength of reflected light of 600 to 700 nm Region. &Lt; / RTI &gt; For example, the first to third regions may be arranged so that the center wavelength of the reflected light of each region sequentially changes along the thickness direction of the CLC layer, but the present invention is not limited thereto. The center wavelength of the reflected light in the CLC region can be measured according to a method known in the art.

In one example, the CLC layer may comprise a CLC region formed such that the helical axis of the waveguide of the liquid crystal molecules is not parallel to the thickness direction of the CLC layer. For example, the CLC layer may include a CLC region in which the helical axis is parallel to the thickness direction and a CLC region in which the helical axis is formed in a direction not parallel to the thickness direction.

The arrangement of the helical axes of the CLC region will be described below with reference to FIG.

Typically, the CLC region comprises a spirally-rotating CLC molecule, and the director of the CLC molecule, for example, the helical axis of the long axis of the CLC molecule, is aligned to be parallel to the thickness direction of the CLC layer. The CLC region is generally oriented such that the helical axis HA of the CLC is parallel to the thickness direction 31 of the CLC layer, as shown in Fig. In FIG. 3, the direction 32 perpendicular to the thickness direction 31 may mean, for example, the plane direction of the base layer as described above. In this specification, the CLC region in which the helical axis is oriented parallel to the thickness direction of the CLC layer as described above may be referred to as a planar oriented CLC region.

The direction of the helical axis of the waveguide of the CLC molecule may be aligned in a direction not parallel to the thickness direction of the CLC layer depending on the orientation condition of the CLC or the surface of the base layer on which the CLC is formed. For example, as shown in FIG. 3B, the helical axis HA of the CLC may be oriented in a direction perpendicular to the thickness direction 31 of the CLC layer, or may be oriented in a direction perpendicular to the thickness direction 31 of the CLC layer, (HA) may be oriented in a direction other than the direction perpendicular and parallel to the thickness direction 31 of the CLC layer. In this specification, the CLC region in which the helical axis is oriented perpendicular to the thickness direction of the CLC layer is referred to as a homeotropic oriented CLC region, and the helical axis is perpendicular and parallel to the thickness direction of the CLC layer The CLC region oriented in a direction other than one direction may be referred to as a focal conic oriented CLC region.

In a CLC layer formed in a conventional manner, the CLC region is oriented with the helical axis parallel to the thickness direction of the CLC layer. However, the CLC layer of the optical film may include a CLC region in which a helical axis is artificially formed in a direction other than the thickness direction of the CLC layer. The CLC region in which the helical axis is formed in a direction other than the direction parallel to the thickness direction of the CLC layer can control the haze characteristics of the optical film.

The amount, position or distribution state in the CLC layer of the homeotropic or focal-conical CLC region or the angle formed by the spiral axis in the thickness direction of the CLC layer in the focal-conic orientation is not particularly limited, Lt; / RTI &gt;

The homeotropic or focal-coked CLC region can be formed, for example, by adjusting the surface characteristics of the surface on which the CLC layer is formed, or by appropriately setting the orientation conditions of the CLC, as described later.

In one example, the CLC layer may comprise a liquid crystal polymer. An exemplary method for producing a CLC layer is a method of coating a composition comprising a polymerizable liquid crystal compound and a polymerizable or non-polymerizable chiral agent, The CLC layer may comprise a polymerized liquid crystal polymer.

One exemplary CLC layer may comprise a polymeric form of a compound represented by the following formula (1).

 [Chemical Formula 1]

Wherein A is a single bond, -COO- or -OCO-, and R ₁ to R ₁₀ are each independently selected from the group consisting of hydrogen, a halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group, -OQP, Wherein at least one of R ₁ to R ₁₀ is -OQP or a substituent of the following formula 2, Q is an alkylene group or an alkylidene group, P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, A methacryloyl group, an acryloyloxy group or a methacryloyloxy group.

(2)

In the formula 2 B is a single bond, -COO- or -OCO-, R ₁₁ to R ₁₅ are each independently hydrogen, halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group or -OQP provided that, R ₁₁ to At least one of R &lt; ₁₅ &gt; is -OQP, Q is an alkylene group or an alkylidene group, and P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, a methacryloyl group, Methacryloyloxy group.

In the above formula (2), "-" to the left of B means that B is directly connected to benzene of formula (1).

The term "single bond" in the above formulas (1) and (2) means a case where there is no separate atom in the part represented by A or B. For example, when A is a single bond in formula (I), benzene on both sides of A may be directly connected to form a biphenyl structure.

As the halogen in the formulas (1) and (2), chlorine, bromine or iodine and the like can be exemplified.

The alkyl group in the general formulas (1) and (2) is preferably a linear or branched alkyl group having from 1 to 20 carbon atoms, from 1 to 16 carbon atoms, from 1 to 12 carbon atoms, from 1 to 8 carbon atoms or from 1 to 4 carbon atoms or from 3 to 20 carbon atoms, A cycloalkyl group having 4 to 12 carbon atoms may be exemplified. In addition, the alkyl group may be optionally substituted by one or more substituents.

In the general formulas (1) and (2), an alkoxy group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms may be exemplified. The alkoxy group may be linear, branched or cyclic. In addition, the alkoxy group may be optionally substituted with one or more substituents.

The alkylene group or the alkylidene group in the formulas (1) and (2) may be an alkylene group or an alkylidene group having 1 to 12 carbon atoms, 4 to 10 carbon atoms, or 6 to 9 carbon atoms. The alkylene group or alkylidene group may be linear, branched or cyclic. The alkylene or alkylidene group may be optionally substituted by one or more substituents.

The alkenyl groups in the general formulas (1) and (2) include an alkenyl group having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms or 2 to 4 carbon atoms. The alkenyl group may be linear, branched or cyclic. In addition, the alkenyl group may be optionally substituted with one or more substituents.

Examples of the substituent which may be substituted in the above alkyl group, alkoxy group, alkenyl group, alkylene group or alkylidene group include alkyl group, alkoxy group, alkenyl group, epoxy group, cyano group, carboxyl group, acryloyl group, methacryloyl group, Acryloyloxy group, methacryloyloxy group, aryl group, and the like, but the present invention is not limited thereto.

In the general formulas (1) and (2), P may be an acryloyl group, a methacryloyl group, an acryloyloxy group or a methacryloyloxy group, or an acryloyloxy group or a methacryloyloxy group. In another example, acryloyloxy Time.

The -OQP or the moiety of formula 2 which may be present in at least one of the formulas 1 and 2 may for example be present at the position of R ₃ , R ₈ or R ₁₃ , for example 1 or 2 above Can exist. Further, substituents other than -OQP or the residue of the formula (2) in the compound of the formula (1) or the residue of the formula (2) include, for example, hydrogen, halogen, a straight or branched alkyl group of 1 to 4 carbon atoms, An alkyl group, a cyano group, an alkoxy group having 1 to 4 carbon atoms, a cyano group or a nitro group, preferably a chlorine, a straight or branched alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 4 to 12 carbon atoms, Or an alkoxy group or a cyano group.

The chiral agent that can be included in the CLC layer is not particularly limited as long as it can induce a desired spiral pitch without deteriorating liquid crystallinity, for example, nematic regularity. The chiral agent for causing the helical pitch in the liquid crystal needs to include at least the chirality in the molecular structure. Chiral agents include, for example, a compound having one or more asymmetric carbons, a compound having an asymmetric point on a heteroatom such as a chiral amine or a chiral sulfoxide, or a compound having an asymmetric carbon atom such as cumulene ) Or an axially asymmetric (optically active site) having an axial-reducing agent such as binaphthol. The chiral agent may be, for example, a low molecular weight compound having a molecular weight of 1,500 or less. As the chiral agent, a commercially available chiral nematic liquid crystal, for example, a chiral dopant liquid crystal S-811 available from Merck Co., Ltd. or LC756 manufactured by BASF may be used

The CLC layer may have a thickness of, for example, 3 占 퐉 to 8 占 퐉 or 4 占 퐉 to 6 占 퐉. By controlling the thickness of the CLC layer to the above range, the wide band CLC layer can be effectively implemented and, if necessary, the above-described homeotropic or focal-conicted CLC region can be effectively formed.

The optical film may include a haze layer present on the liquid crystal layer and having a haze of 40% to 60%. Fig. 4 shows a schematic diagram of an exemplary optical film 400 in which a liquid crystal layer 401 and a haze layer 402 are formed on the liquid crystal layer 401. In Fig. 4 illustrates a case where the haze layer 402 is directly formed on the upper portion of the liquid crystal layer 401. However, another layer may be formed between the haze layer 402 and the liquid crystal layer 401, for example, A quarter wavelength layer, an orientation layer, an adhesive layer, or an adhesive layer may be present.

The haze layer can exhibit the most suitable effect depending on the application to which the optical film is applied. For example, when the optical film is included in the reflective polarizer as described later, the haze layer can prevent the color characteristics of the display device including the polarizer, particularly the color change such as color inversion on the side have. In addition, the haze layer can improve the brightness of the display device by appropriately scattering and / or diffusing light. Further, the optical film can effectively reproduce the color coordinates of the light source by the haze layer. The haze of the haze layer can be measured according to the manufacturer's manual using a hazemeter such as HR-100 or HM-150 of Sephoon Co.,

The specific kind of the haze layer in the liquid crystal layer is not particularly limited as long as it represents the haze in the above range. That is, in this specification, the term haze layer may include all known layers capable of imparting appropriate haze to the optical film.

In one example, the haze layer may be a resin layer comprising particles. The particles may have different refractive indices from the resin layer. The resin layer containing particles having different refractive indices can impart the haze of the optical film by scattering and / or diffusing the incident light. Such a resin layer may be formed, for example, on a suitable film or sheet. 5 is a cross-sectional view of an exemplary optical film 500 and shows a case where a film or a sheet 501 and a resin layer 502 formed on one side thereof are used as the haze layer 402 in Fig. As the film or sheet described above, for example, a suitable type of plastic substrate layer used in a base layer described later can be selected and used.

In one example, the resin layer may include a room temperature curable, moisture curable, thermosetting, active energy ray curable or hybrid curable composition in a cured state. The term &quot; cured state &quot; may mean a state after the components contained in the composition have undergone a crosslinking reaction, a polymerization reaction, or the like. In addition, the room temperature curing type, moisture curing type, thermosetting type, active energy ray curing type or hybrid curing type composition may be prepared by irradiating the cured state with heat or an active energy ray in the presence of room temperature or moisture respectively, May refer to a composition in which more than two mechanisms act simultaneously or sequentially to cure. In the above, the active energy ray may mean, for example, an electromagnetic wave such as an ultraviolet ray or an electron ray.

The composition may include an acrylic compound, an epoxy compound, a urethane compound, a phenol compound, or a polyester compound. The &quot; compound &quot; may be a monomeric, oligomeric or polymeric compound. In this case, the resin layer may include an acrylic resin, an epoxy resin, a urethane resin, a phenol resin, or a polyester as a binder.

In one example, the resin layer may include an acrylic composition having excellent optical properties such as transparency and resistance to yellowing, for example, an active energy ray-curable acrylic composition in a cured state.

The active energy ray-curable acrylic composition may, for example, comprise an active energy ray polymerizable polymer component and a reactive diluent monomer.

Examples of the polymer component include polymers known as photopolymerizable oligomers, such as urethane acrylate, epoxy acrylate, ether acrylate or ester acrylate, or a mixture of monomers such as (meth) acrylic acid ester monomers and the like Can be illustrated. Examples of the (meth) acrylic acid ester monomer include alkyl (meth) acrylate, (meth) acrylate having an aromatic group, heterocyclic (meth) acrylate or alkoxy (meth) acrylate. Various polymer components are known in the art for making active energy ray curable compositions, and such compounds can be selected as needed.

Examples of the reactive diluting monomer that can be contained in the active energy ray-curable acrylic composition include monomers having one or more active energy ray-curable functional groups such as an acryloyl group or a methacryloyl group, , For example, the above (meth) acrylic acid ester monomers and multifunctional acrylates can be used.

The selection of the above-mentioned components for forming the active energy ray-curable acrylic composition, the blending ratio of the selected components and the like are not particularly limited and can be adjusted in consideration of the hardness and other physical properties of the desired resin layer.

In one example, the particles included in the resin layer may have a refractive index different from that of the resin layer. For example, the difference in refractive index between the particles and the resin layer may be 0.03 or less or 0.02 to 0.2. If the difference in refractive index is too small, it is difficult to cause haze. On the contrary, if the refractive index difference is excessively large, scattering in the resin layer occurs a lot and haze increases, but deterioration of light transmittance or contrast characteristics may be induced. And appropriate particles can be selected.

The shape of the particles contained in the resin layer is not particularly limited and may have, for example, spherical, elliptical, polyhedral, amorphous or other shapes. The particles may have an average diameter of 50 nm to 5,000 nm. In one example, as the particles, particles having irregularities on the surface can be used. Such particles may have a mean surface roughness (Rz) of, for example, 10 nm to 50 nm or 20 nm to 40 nm, and / or a maximum height of irregularities formed on the surface of about 100 nm to 500 nm or 200 nm to 400 nm, and the width between the irregularities may be 400 nm to 1,200 nm or 600 nm to 1,000 nm. Such particles are excellent in compatibility with the resin layer and in dispersibility therein.

As the particles, various inorganic or organic particles can be exemplified. Examples of the inorganic particles include silica, amorphous titania, amorphous zirconia, indium oxide, alumina, amorphous zinc oxide, amorphous cerium oxide, barium oxide, calcium carbonate, amorphous barium titanate, barium sulfate, Examples of the organic particles include crosslinked or non-crosslinked particles of an organic material such as an acrylic resin, a styrene resin, a urethane resin, a melamine resin, a benzoguanamine resin, an epoxy resin or a silicone resin, It is not.

The content of the particles in the resin layer is not particularly limited. For example, the content of the particles can be determined to such an extent that the optical film can exhibit the haze described above.

The resin layer may further contain an additive such as a polymerization initiator, an ultraviolet screening agent or an absorbent, an antistatic agent or a dispersant if necessary.

In one example, the optical film may further comprise a substrate layer, and a CLC layer may be formed on one side of the substrate layer. When the optical film further comprises a base layer and a CLC layer is formed on one side of the base layer, for example, as described above, the center wavelength of the reflected light is reflected on one main surface side of the CLC layer, And a CLC region having a center wavelength of reflected light belonging to the blue light region is arranged on the other main surface side so that the center wavelength of the reflected light of each CLC region sequentially changes along the thickness direction of the CLC layer, A CLC region belonging to the red light region or a CLC region belonging to the blue light region may be disposed on the main surface side of the CLC layer contacting the base layer. In another example, a CLC region having a center wavelength of the reflected light belonging to the red light region may be formed on the main surface side of the CLC layer contacting the base layer.

6 is a cross-sectional view showing an exemplary optical film 600. In the case where a CLC layer 401 is formed on one main surface of a base layer 601 and a haze layer 402 is formed thereon .

In one example, in order to form homeotropic or focal-conical oriented CLC regions, the side on which the CLC layer of the substrate layer is formed may be hydrophilic. In one example, the surface on which the CLC layer of the substrate layer is formed has a wetting angle to water of 0 to 50 degrees, 0 to 40 degrees, 0 to 30 degrees, 0 to 20 degrees, or 0 10 degrees to 50 degrees, 20 degrees to 50 degrees, and 30 degrees to 50 degrees. When the CLC layer is formed on the surface of the substrate layer having such a range of the wetting angle, the CLC regions that are homeotropic or focal-conical can be suitably formed. The method of measuring the wetting angle of the substrate layer with respect to water is not particularly limited and a wetting angle measurement method known in the art can be used. For example, by using a DSA100 device manufactured by KRUSS, Can be measured according to the manual.

In order to cause the substrate layer to have the wetting angle, a hydrophilic treatment may be performed on the surface of the base layer, or a base layer containing a hydrophilic functional group may be used as the base layer. In this field, various hydrophilization treatment methods capable of controlling the wetting angle of the substrate layer within the above-mentioned range, and a substrate layer having such a wetting angle as described above are variously known. As the hydrophilizing treatment, corona treatment, plasma treatment or alkali treatment can be exemplified. Thus, in one example, a corona treatment layer, a plasma treatment layer or an alkali treatment layer may be formed on the surface of the base layer.

As the base layer, various types of base layers may be used. In one example, the substrate layer may be an optically anisotropic substrate layer or a polarization element, such as an optically isotropic base layer, a retardation layer, or the like.

As the optically isotropic base layer, a transparent base layer such as a glass or transparent plastic base layer or the like may be used. The plastic substrate layer may be a cellulosic substrate layer such as a DAC (diacetyl cellulose) or TAC (triacetyl cellulose) substrate layer; A cycloolefin copolymer (COP) base layer such as a norbornene derivative resin base layer; An acrylic base layer such as PMMA (poly (methyl methacrylate) base layer, a polycarbonate base layer, an olefin base layer such as a PE (polyethylene) or a polypropylene (PB) base layer, a polyvinyl alcohol ether sulfone base layer, a polyetheretherketone (PEEK) base layer, a polyetherimide (PEI) base layer, a polyethylenenaphthatate (PEN) base layer, a polyester base layer such as a PET (polyethyleneterephtalate) base layer, a polyimide ) Base layer, a PAR (polyarylate) base layer, a fluororesin base layer, etc. The base layer may be, for example, in the form of a sheet or a film.

As the optically anisotropic base layer, for example, the phase retardation layer, for example, a 1/4 wavelength layer or a half wavelength layer or the like may be used. In the present specification, the term &quot; quarter wavelength layer &quot; means a phase delay element capable of phase-delaying incident light by 1/4 of its wavelength, and &quot; half wavelength layer &quot; And can be a phase delay element capable of delaying a phase by 1/2 of the wavelength. The retardation layer may be a liquid crystal polymer layer formed by aligning and polymerizing a polymerizable liquid crystal compound, or may be a plastic film imparted with birefringence by a stretching or shrinking process or the like.

As the polarizing element, a conventional element known in this field can be used. For example, as the polarizing element, an element manufactured by adsorbing and orienting a dichroic dye or the like on a polyvinyl alcohol resin can be used.

The substrate layer may be subjected to various surface treatments such as low reflection treatment, anti-reflection treatment, anti-glare treatment and / or high-resolution anti-glare treatment, if necessary.

The optical film may further include an orientation layer. The term &quot; orientation layer &quot; can refer to a layer exhibiting surface alignment properties that improve or provide alignment uniformity in the process of forming the CLC layer, or produce alignment of the liquid crystal waveguide. The alignment layer may be, for example, a resin film providing a plurality of patterned groove regions, a rubbing treatment film such as a photo alignment layer or rubbed polyimide, or the like. The alignment layer may be formed on the surface of the base layer 601, for example, the base layer 601 and the CLC layer 401 when the optical film includes the base layer 601 as shown in Fig. 6, As shown in FIG. In some cases, a method of imparting orientation to the substrate layer by simply rubbing or stretching the base layer without imparting a separate orientation layer, or imparting hydrophilicity to the surface may be used. For example, if the base layer has the above-mentioned range of the wetting angle, the base layer may exhibit the property that the orientation of the CLC or the position of the helical axis of the CLC region can be controlled within a desired range without the orientation layer.

The optical film may further comprise a quarter wavelength layer between the CLC layer and the haze layer. 7 is a schematic diagram of an exemplary optical film 700 that additionally includes a quarter wavelength layer 701 between the CLC layer 401 and the haze layer 402. As shown in FIG.

As the 1/4 wavelength layer, for example, a polymer film or a liquid crystal film may be used, and the above may be a single layer or a multilayer structure. Examples of the polymer film include polyolefins such as polycarbonate (PC), norbonene resin, polyvinyl alcohol (PVA), polystyrene (PS), poly (methyl methacrylate) (poly (arylate), PA (polyamide), PET (poly (ethylene terephthalate)) or PS (polysulfone). The polymer film may be stretched or shrunk under appropriate conditions to impart birefringence and used as the 1/4 wavelength layer.

In another example, as the 1/4 wavelength layer, a liquid crystal film may be used. Layer. When the 1/4 wavelength layer is a liquid crystal film, the optical film may further include an alignment layer for orienting the liquid crystal compound forming the liquid crystal film. For example, in the case of FIG. 7, an orientation layer may be further formed between the 1/4 wavelength layer 701 and the haze layer 402. In this field, a variety of liquid crystal films and orientation layers capable of serving as a quarter wavelength layer are known, and these elements can be used in all of the optical films.

In one example, the liquid crystal film having a quarter wavelength layer can be formed by aligning and polymerizing a polymerizable liquid crystal compound such as RM (Reactive Mesogen) from Merk or LC242 from BASF. As the alignment layer, for example, a known alignment layer such as a photo alignment layer or a rubbing alignment layer may be used.

The present application also relates to a method for producing an optical film. The manufacturing method may include forming a haze layer having a haze of 40% to 60% on a CLC layer including two or more types of CLC regions whose center wavelengths of reflected light are different from each other.

In one example, the formation of a CLC layer may include applying a CLC composition comprising a polymerizable liquid crystal compound, such as the compound of Formula 1 and a chiral agent, and polymerizing the liquid crystal compound.

As used herein, the term &quot; CLC composition &quot; may include any kind of composition that can be used to form a CLC layer comprising a liquid crystal region in a desired pattern. In one example, the composition may comprise a low molecular weight compound such as a CLC compound, a CLC polymer, or a monomer or oligomer capable of reacting to form a CLC polymer. In addition, the CLC composition may comprise one or more other additives, such as crosslinking agents, polymerization initiators, and the like. Polymerization initiators may be included in the CLC composition to initiate polymerization or crosslinking of monomers or other low molecular weight compounds. Suitable polymerization initiators include those capable of generating free radicals to initiate polymerization and crosslinking and to propagate. The free radical initiator may be selected, for example, depending on its stability or half life. Preferably, the free radical initiator does not generate additional color in the CLC layer by absorption or otherwise. Free radical initiators are typically thermal free radical initiators or photoinitiators. Thermally-free radical initiators include, for example, peroxide, persulfate or azonitrile compounds. Free radical initiators generate free radicals upon thermal degradation.

Photoinitiators can be activated by electromagnetic radiation or particle irradiation. Examples of suitable photoinitiators may include onium salt photoinitiators, organometallic photoinitiators, cationic metal salt photoinitiators, photodegradable organosilanes, latent sulfonic acids, phosphine oxides, cyclohexyl phenyl ketones, amine substituted acetophenones, and benzophenones have. In general, ultraviolet (UV) irradiation may be used to activate the photoinitiator, although other light sources may be used. The photoinitiator can be selected based on absorption of a specific wavelength of light.

The CLC composition typically can be part of a coating composition comprising at least one solvent. The coating composition may comprise, for example, dispersants, antioxidants and antiozonants. In addition, the coating composition may include various dyes and pigments to absorb ultraviolet, infrared or visible light, if desired. In some cases, it may be appropriate to add viscosity modifiers such as thickeners and fillers.

The CLC composition can be applied by various liquid coating methods. In some embodiments, after coating, the CLC composition is polymerized or converted into a CLC layer. This conversion can be accomplished by evaporation of the solvent, heating to align the CLC material, Crosslinking of the CLC composition; Or application of heat, such as, for example, actinic irradiation; Irradiation of light such as ultraviolet light, visible light or infrared light and irradiation of an electron beam, or a combination thereof, or curing of a CLC composition using a similar technique.

In one example, the CLC composition may comprise a compound of Formula 1, a photoinitiator, and a chiral agent.

The photoinitiator is used for initiating the polymerization or crosslinking of the compound of formula (1). As long as there is no problem in compatibility with the above compound, general components known in this field can be appropriately selected and used. Examples of the photoinitiator include 2-methyl-1- [4- (methylthio) phenyl] -2- (4-morpholinyl) phenyl-2- (4-morpholinyl) -1-propanone, 2-dimethoxy-1,2-diphenylethan-1- 1-hydroxy-cyclohexyl-phenyl-ketone, triarylsulfonium hexafluoroantimonate salts, and diphenyl (2,4,6-trimethyl Benzoyl) -phosphine oxide (diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide) may be used, but the present invention is not limited thereto. The CLC composition may include 0.1 to 10 parts by weight of the photoinitiator relative to 100 parts by weight of the compound of Formula 1. By controlling the content of the photoinitiator as described above, it is possible to induce effective polymerization and crosslinking of the liquid crystal compound and to prevent deterioration of physical properties due to the residual initiator after polymerization and crosslinking. Unless otherwise specified, the unit weight portion in the present specification may mean the weight ratio of each component.

As the chiral agent, for example, a compound of the above-mentioned kind can be used. The CLC composition may contain the chiral agent in an amount of 1 part by weight to 10 parts by weight based on 100 parts by weight of the compound of the formula (1). By controlling the content of chiral agent as described above, effective twisting of CLC can be induced.

The CLC composition may further comprise a solvent if desired. Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, tetrachloroethane, trichlorethylene, tetrachlorethylene and chlorobenzene; Aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene; Alcohols such as methanol, ethanol, propanol, isopropanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone; Cellosolve such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; And ethers such as diethylene glycol dimethyl ether (DEGDME) and dipropylene glycol dimethyl ether (DPGDME). The content of the solvent is not particularly limited and may be suitably selected in consideration of coating efficiency, drying efficiency, and the like.

In addition, the CLC composition may further comprise a surfactant. The surfactant is dispersed on the surface of the liquid crystal to make the surface even and stabilizes the liquid crystal alignment so that the surface of the film can be smoothly maintained after the formation of the CLC layer. As a result, the appearance quality can be improved.

As the surfactant, for example, a fluorocarbon surfactant and / or a silicon surfactant may be used. Fluorad FC4430 (TM), Fluorad FC4432 (TM), Fluorad FC4434 (TM) manufactured by 3M Company and Zonyl produced by Dupont Co., Ltd. can be used as the fluorocarbon surfactant, and silicone surfactants BYK 占 manufactured by BYK-Chemie, etc. may be used. The content of the surfactant is not particularly limited and may be suitably selected in consideration of coating efficiency, drying efficiency, and the like.

After the application of the CLC composition as described above, for example, the components of the composition may be polymerized to form a CLC layer in a state where CLC orientation of the liquid crystal compound is induced in the composition.

In one example, the CLC layer is formed by irradiating a coating layer of the CLC composition with a relatively weak ultraviolet ray to form a concentration gradient of the chiral agent, irradiating the coating layer on which the concentration gradient is formed with a relatively strong ultraviolet ray, And polymerizing the components of the composition. In this manner, a single-layer CLC layer including two or more types of CLC regions having different center wavelengths of reflected light can be effectively formed.

When irradiating the coating layer of the CLC composition with ultraviolet light having a relatively weak intensity at a predetermined temperature, it is possible to induce a concentration gradient of the chiral agent in the coating layer, that is, a change in the concentration of the chiral agent along the predetermined direction in the coating layer . In one example, the concentration gradient of the chiral agent may be formed along the thickness direction of the coating layer. The irradiation of ultraviolet rays having a concentration gradient of chiral agent can be performed at a temperature range of, for example, 40 캜 to 80 캜, 50 캜 to 70 캜 or about 60 캜. The irradiation of the ultraviolet ray for forming the concentration gradient may be performed by irradiating the ultraviolet ray of the ultraviolet ray A region with an amount of light of about 10 mJ / cm ² to 500 mJ / cm ² .

After the concentration gradient is formed in the same manner as described above, a CLC layer can be formed by irradiating ultraviolet ray in an amount sufficient to polymerize the components of the composition. By the ultraviolet ray irradiation, the coating layer can be fixed with different pitches of the liquid crystal according to the concentration gradient of the chiral agent to form the CLC region. The conditions of the irradiation of the strong ultraviolet ray are not particularly limited as long as the polymerization of the components of the composition is sufficiently carried out. In one example, the irradiation of the ultraviolet light can be performed by irradiating ultraviolet rays of the ultraviolet rays A to C at an amount of about 1 J / cm ² to 10 J / cm ² .

In one example, the application layer of the CLC composition may be formed on a suitable substrate layer. The substrate layer may be, for example, an optically isotropic or anisotropic substrate layer as described above, or a polarizing element or the like.

In one example, the surface of the base layer on which the application layer of the CLC composition is formed may be provided with an orientation. The orientation can be imparted, for example, by using a base layer of a hydrophilic surface as described above, by rubbing or stretching the base layer, or by forming an orientation layer on the surface of the base layer. The effect of forming the wide band CLC layer can be enhanced by giving the surface of the base layer with proper orientation. The manner of forming the alignment layer in the base layer is not particularly limited, and any suitable method known in the art can be used.

In one example, the application layer of the CLC composition is formed on the surface of the substrate layer with a wetting angle of 0 to 50 degrees, 0 to 40 degrees, 0 to 30 degrees, 0 to 20 degrees, or 0 to 10 degrees . As the base layer having such a wetting angle as described above, a substrate layer having been subjected to a suitable hydrophilizing treatment on its surface or a substrate layer having hydrophilic properties from the beginning including a hydrophilic functional group itself may be used. Examples of the hydrophilizing treatment include corona treatment, plasma treatment, alkali treatment, and the like. The treatment conditions are not particularly limited. In this field, various methods for imparting hydrophilicity to the substrate layer are known, and the hydrophilization treatment can be performed by employing the above-described method so that the substrate angle is represented by the wetting angle.

When the CLC layer is formed on the surface of the substrate layer having the wetting angle as described above, a CLC layer including the above described homeotropic or focal-conic CLC regions can be formed.

The method may comprise forming a haze layer on the CLC layer as described above. The method of forming the haze layer is not particularly limited. For example, when the resin layer described above is employed as the haze layer, the resin layer may be formed on a suitable film or sheet, and a film or sheet on which the resin layer is formed may be attached to the CLC layer, A method of directly forming a layer can be used.

The resin layer can be formed, for example, by coating a room temperature curing type, moisture curing type, thermosetting type, active energy ray curing type or hybrid curing type composition containing particles and curing the composition. The application and curing of the composition may be performed directly on the surface of the CLC layer or may be performed on one surface of the substrate layer on which the CLC layer is formed or on any other substrate layer. When the haze layer is performed on another arbitrary base layer, the base layer is adhered to the CLC layer, or the haze layer formed on the base layer is transferred to the CLC layer or another base layer of the optical film to form the haze layer .

The manufacturing method may further include forming a 1/4 wavelength layer between the CLC layer and the haze layer. The formation method of the 1/4 wavelength layer is not particularly limited and may be formed by disposing a 1/4 wavelength layer between the CLC layer and the haze layer at an appropriate time during the process.

In one example, a resin layer containing particles in the process of forming a haze layer and having a refractive index different from that of the resin layer is formed on one surface and a 1/4 wavelength layer is formed on the other surface It is also possible to simultaneously form the haze layer and the 1/4 wavelength layer by placing a 1/4 wavelength layer of the film or sheet on the CLC layer. That is, when the resin layer formed on the film or sheet is used as the haze layer, the resin layer is formed on one surface of the film or sheet, the 1/4 wavelength layer is formed on the other surface, A 1/4 wavelength layer and a haze layer can be obtained by laminating a sheet to a CLC layer or by using a polymer film or sheet serving as a 1/4 wavelength layer as a film or sheet on which the resin layer is formed and laminating it on a CLC layer .

The formation of the 1/4 wavelength layer on one side of the film or sheet may be achieved by, for example, (a) forming an orientation layer on a film or sheet, (b) applying a polymerizable liquid crystal compound on the orientation layer , Orientation and polymerization.

The method of laminating the thus formed film or sheet with the CLC layer is not particularly limited, and for example, a well-known method using an appropriate adhesive layer or an adhesive layer can be applied.

The present application also relates to a reflective polarizer. An exemplary reflective polarizer may comprise the optical film and the polarizing element. The polarizing element may be disposed above the haze layer of the optical film.

When used as a reflection type polarizing plate, the optical film may include the 1/4 wavelength layer between the haze layer and the CLC layer. 8 shows an exemplary reflection type polarizing plate 800 and shows a case where a polarizing element 801, a haze layer 402, a 1/4 wavelength layer 701 and a CLC layer 401 are sequentially formed.

The type of the polarizing element is not particularly limited. For example, a polyvinyl alcohol polarizing element or the like commonly used in a display device such as an LCD can be used.

The reflective polarizer includes a wide-band CLC layer and includes a haze layer exhibiting a suitable range of haze. Thus, the reflective polarizer can be applied to, for example, a display device such as an LCD to exhibit suitable luminance characteristics, It is possible to effectively reproduce and prevent the color reversal phenomenon which is problematic at the time of side observation.

The present application also relates to LCDs. An exemplary LCD may include the reflective polarizer.

In one example, the LCD may further include a liquid crystal panel and a light source disposed on one side of the liquid crystal panel, and the reflective polarizer may be disposed between the liquid crystal panel and the light source. In the case where the reflection type polarizing plate includes a quarter wavelength layer, the polarizing plate may be arranged such that the CLC layer of the optical film is located closer to the light source than the quarter wavelength layer.

9, the LCD 900 includes, for example, a liquid crystal panel 901 in which the upper polarizer plate 903 is disposed on one side and the reflective polarizer plate 902 is disposed on the other side; And a light source 905 disposed below the reflection type polarizing plate 902.

In this structure, the CLC layer of the reflective polarizer 902 transmits a part of the light emitted from the light source 904 to the quarter wavelength layer side, and the remaining light can be reflected to the light source 904 side. The light sent to the 1/4 wavelength layer can be converted into linearly polarized light by the 1/4 wavelength layer and transmitted to the upper liquid crystal panel 901 through the polarizing element. In this case, the light reflected by the CLC layer is reflected again inside the device, the polarization characteristics thereof are changed, and the polarized light is incident on the polarizer 902 again. This process can be repeated to improve the brightness characteristics of the device.

As long as the LCD includes the optical element, other parts, structures, and the like are not particularly limited, and all contents well known in this field can be appropriately applied.

The exemplary optical film of the present application can be used as a reflection type polarizing plate capable of improving light utilization efficiency and brightness of a display device such as an LCD, for example. The exemplary optical film can effectively reproduce the color of the incident light while minimizing the loss of brightness, thereby providing a display device with excellent image quality.

1 is an exemplary diagram for explaining CLC.
FIG. 2 is a diagram illustrating an exemplary arrangement of CLC regions in a CLC layer. FIG.
3 is an exemplary diagram for explaining the orientation of the CLC.
4 to 8 are views showing an exemplary optical film.
9 is a diagram showing an exemplary LCD.
10 and 11 are views showing the results of measurement of CIE color coordinates for the reflection type polarizing plate manufactured in Examples and Comparative Examples.

Hereinafter, the optical film will be specifically described with reference to Examples and Comparative Examples, but the scope of the film is not limited by the following examples.

Manufacturing example  One. CLC  Preparation of composition (A)

The CLC composition was prepared by dissolving RMM856, a CLC mixture available from Merck, in a mixed solvent of toluene and cyclohexanone (weight ratio = 7: 3 (toluene: cyclohexanone) to a solids content of about 40% The mixture was heated at 60 캜 for about 1 hour and cooled sufficiently to form a homogeneous solution.

Manufacturing example  2. (A) of the haze layer  Produce

10 g of urethane acrylate oligomer and 20 g of dipentaerythritol hexaacrylate (DPHA) were compounded in a mixed solvent of 30 g of methyl ethyl ketone and 38 g of toluene to prepare a composition for a binder. Thereafter, styrene resin-based particles having different refractive indices from those of the binder to be formed in the binder composition and having an average particle diameter of about 3,500 nm were blended. The blending ratio of the styrene resin-based particles was such that the final resin layer had a haze of about 50%. Thereafter, 2 g of the ultraviolet polymerization initiator was uniformly mixed to prepare a resin composition for forming a haze layer. Thereafter, the resin composition was coated on one surface of an optical TAC (triacetyl cellulose) film so as to have a dry thickness of about 2 탆, and irradiated with ultraviolet rays (300 mW / cm ² ) to form a haze layer having a haze of about 50% .

Example  One.

Manufacture of optical film

As a substrate layer, a substrate layer on which a hydrophilic surface was formed was prepared by performing corona treatment on one surface of a PET (poly (ethylene terephthalate), MRL38, Mitsubishi) base layer under conditions of 300 Watt for 5 seconds. The wetting angle of the PET base layer with respect to water was about 60 degrees, and the wetting angle of the hydrophilic surface with respect to water was adjusted to about 30 to 40 degrees by the ultraviolet ray irradiation. Next, the CLC composition (A) was directly coated on the hydrophilic surface of the base layer with a wire and dried at 100 DEG C for 2 minutes to form a liquid crystal layer having a thickness of about 5 mu m. Then, the coating layer dried at a temperature of about 60 ° C was irradiated with ultraviolet rays having a wavelength within the range of about 350 nm to 400 nm with an ultraviolet ray irradiation equipment (TLK40W / 10R, manufactured by Philips) to induce a concentration gradient of the chiral agent (amount of light: About 100 mJ / cm ² ). After the concentration gradient was induced, the coating layer was irradiated with ultraviolet ray to sufficiently cure the composition with ultraviolet ray irradiation equipment (Fusion UV, 400W) to form a CLC layer to prepare an optical film.

Production of Reflective Polarizer

A CLC layer of the prepared optical film was attached to a 1/4 wavelength layer to prepare a reflective polarizer. As the 1/4 wavelength layer, a general orientation layer and a liquid crystal layer capable of forming a 1/4 wavelength layer on the surface of the TAC film having the resin layer formed on one side of the Production Example 2 are not formed, Respectively. The prepared 1/4 wavelength layer was laminated on the CLC layer to prepare a reflective polarizer. 10 and 11 show the x and y characteristics of the CIE color coordinates measured for the produced reflection type polarizing plate. The CIE color coordinates were measured according to the manual of the manufacturer using the EZ Contrast equipment of Eldim Inc. for the light transmitted through the CLC layer side of the polarizing plate.

Comparative Example  One.

Except that a 1/4 wavelength layer prepared by sequentially forming an alignment layer and a liquid crystal layer on a TAC film having no resin layer on one side, which is the same as the TAC film used in Production Example 2, in the production of a reflective polarizer , A reflective polarizer was prepared in the same manner as in Example 1. FIGS. 10 and 11 show the x and y characteristics of the CIE color coordinates measured for the reflective polarizer produced in the comparative example, as compared with Example 1. FIG. From FIGS. 10 and 11, it can be confirmed that the reflective polarizer of Example 1 including the haze layer effectively reproduces the color coordinates of the light source in comparison with Comparative Example 1 while preventing the color reversal phenomenon on the side.

n: CLC waveguide
P: pitch
X: Spiral axis
2: CLC layer 21, 22: main surface of CLC layer
231, 232, 233: CLC area
HA: Spiral axis of CLC region
31: thickness direction of CLC layer
32: direction perpendicular to the thickness direction of the CLC layer
400, 500, 600, 700: optical film
401: CLC layer
402: haze layer
501: film or sheet
502: resin layer
601: substrate layer
701: quarter wavelength layer
800: reflective polarizer
801: Polarization element
900: liquid crystal display
903: upper polarizer plate
901: liquid crystal panel
902: reflective polarizer
904: Light source

Claims (18)

materials; A liquid crystal layer formed on one surface of the substrate and including at least two kinds of cholesteric aligned liquid crystal regions whose center wavelengths of reflected light are different from each other; And a haze layer having a haze of 40% to 60% at an upper portion of the liquid crystal layer, wherein the liquid crystal layer is a single layer and has a first region in which the center wavelength of reflected light is 400 nm to 500 nm, and a third region having a central wavelength of the reflected light of 600 to 700 nm, wherein the first to third regions are optical films having mutually different pitches,
The surface of the substrate on which the liquid crystal layer is formed is hydrophilic and has a wetting angle of 20 to 50 degrees,
Wherein the liquid crystal region includes a liquid crystal region formed so as not to be parallel to a liquid crystal region formed so that a helical axis of a waveguide of the cholesteric liquid crystal molecule is parallel to a thickness direction of the liquid crystal layer,
A 1/4 wavelength layer is further provided between the liquid crystal layer including the cholesteric liquid crystal region and the haze layer, and the 1/4 wavelength layer is an optical film which is a liquid crystal film attached to the liquid crystal layer .
delete delete The optical film according to claim 1, wherein the haze layer is a resin layer containing particles and the particles have a refractive index different from that of the resin layer. The optical film according to claim 4, wherein a difference in refractive index between the resin layer and the particles is 0.03 or less. The optical film according to claim 4, wherein the resin layer comprises an acrylic resin, an epoxy resin, a urethane resin, a phenol resin or a polyester. delete delete The optical film of claim 1, further comprising an orientation layer between the substrate and a liquid crystal layer comprising a cholesteric aligned liquid crystal region.
delete delete Forming a haze layer having a haze of 40% to 60% on a liquid crystal layer including two or more types of cholesteric aligned liquid crystal regions whose center wavelengths of reflected light are different from each other, wherein the liquid crystal layer is a single layer, A first region having a center wavelength of 400 nm to 500 nm, a second region having a center wavelength of reflected light of 500 nm to 600 nm and a third region having a central wavelength of reflected light of 600 to 700 nm, The method of claim 1, wherein the regions have different pitches from each other. The method of claim 12, wherein the liquid crystal layer, cholesteric ultraviolet rays of the ultraviolet region A in the cholesteric 40 ℃ to 80 ℃ the applied layer of the liquid crystal composition after irradiating with 10 mJ / cm ² to 500 mJ / cm ² ultraviolet ray A to the area C In an amount of 1 J / cm ² to 10 J / cm ² . delete The method as claimed in claim 12, wherein the step of forming a haze layer on the liquid crystal layer comprises the steps of forming a quarter-wave layer of a film or sheet having a haze layer on one side thereof and a quarter- Wherein the haze layer is a resin layer containing particles and the particles are disposed on the liquid crystal layer including the resin layer and the liquid crystal layer, Is a resin layer having a different refractive index. An optical film according to claim 1; And a polarizing element on top of the haze layer of the optical film. delete A liquid crystal display device comprising the reflective polarizer of claim 16.

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