CN111033323B - Optical film, polarizing plate and liquid crystal display device - Google Patents

Abstract

The invention discloses an optical film for improving contrast ratio, a polarizing plate comprising the optical film, and a liquid crystal display device comprising the polarizing plate. An optical film for improving contrast ratio comprises: a protective layer; and a patterned layer formed on the protective layer. The patterned layer includes patterned portions formed on one surface thereof, and the patterned portions include embossed optical patterns and flat sections disposed between adjacent embossed optical patterns. The embossed optical pattern has a base angle of about 55 ° to about 90 ° and the patterned portion satisfies formula 1. The contrast ratio improving optical film further includes a gap filling layer directly adjoining one surface of the patterned layer. Formula 1 is as defined in the specification.

Description

Optical film, polarizing plate and liquid crystal display device

Technical Field

The present invention relates to an optical film for improving a contrast ratio, a polarizing plate including the optical film, and a liquid crystal display device including the optical film.

Background

The liquid crystal display device is operated to emit light through two polarizing plates after receiving light from the backlight unit. Therefore, the screen of the liquid crystal display device has lower characteristics in its lateral direction than in its front direction in terms of color quality, contrast ratio, and viewing angle.

Various attempts have been made to improve color quality, contrast ratio, and viewing angle at the side of the liquid crystal display device by modifying the liquid crystal panel or the liquid crystal structure. However, the improvement by modifying the liquid crystal panel is restrictive and requires a complicated process. In the VA-type liquid crystal display device, the drawback of a narrower viewing angle becomes apparent as the size of the liquid crystal display device increases. To solve this problem, a pattern structure for internal diffusion may be provided to widen a viewing angle, thereby improving visibility.

An optical film for improving a contrast ratio may be provided to the polarizing plate at the viewer side in order to improve the viewing angle. In addition, in the case of mounting the contrast ratio-improved optical Film on the polarizing plate, an Anti-Glare Film (Anti Glare Film) having surface roughness may be mounted on the contrast ratio-improved optical Film to provide an Anti-Glare effect with respect to external light. A typical anti-glare film is composed of a matrix and anti-glare particles (e.g., beads distributed on the matrix), and can adjust inner and outer haze based on a difference in refractive index between the matrix and the anti-glare particles while achieving diffusion and scattering of internal or external light.

However, in a structure in which an antiglare film is stacked on an optical film of improved contrast ratio, the improvement in visibility by the optical film of improved contrast ratio may be deteriorated due to additional internal diffusion of light that has passed through the antiglare film. In addition, the antiglare film includes a total of two base layers including a protective layer (base layer) for the antiglare film and a protective layer (base layer) for an optical film for improving a contrast ratio, thereby increasing the thickness of the polarizing plate.

An example of the background art is disclosed in Japanese unexamined patent publication No. 2006-251659.

Disclosure of Invention

Technical challenge

An object of the present invention is to provide an optical film with improved contrast ratio, which can achieve the effect of scattering external light by particles while maintaining the improvement of front and side visibility by a patterned layer and a gap filling layer.

It is another object of the present invention to provide an optical film for improving contrast ratio, which includes a patterned layer and anti-glare particles without encountering Moire phenomenon.

It is yet another object of the present invention to provide an optical film with an elongated structure that improves contrast ratio.

Technical solution

According to one embodiment of the present invention, an optical film for improving a contrast ratio includes: a protective layer; and a patterned layer formed on the protective layer, wherein the patterned layer includes a patterned portion formed on one surface thereof and including embossed optical patterns and flat sections disposed between adjacent embossed optical patterns, the embossed optical patterns have a base angle θ of about 55 ° to about 90 °, and the patterned portion satisfies formula 1, and wherein the contrast ratio-improving optical film further includes: a gap-fill layer directly adjacent to one surface of the patterned layer, the gap-fill layer comprising a matrix and first particles contained in the matrix, an absolute value of a difference in refractive index between the matrix and the first particles being in a range of 0 to 0.03, and a difference in refractive index between the patterned layer and the gap-fill layer being 0.06 or greater than 0.06.

Equation 1

1<P/W≤10

(in formula 1, P is the pitch of the patterned part (unit: micrometer) and W is the maximum width of the embossed optical pattern (unit: micrometer))

In one embodiment, the gap filling layer may include a surface roughness having a height of 1% to less than 20% of a particle diameter of the first particles.

In one embodiment, the maximum distance between the first surface corresponding to the top portion of the patterned layer and the uppermost surface of the gap-fill layer may be greater than 0-15 microns.

In one embodiment, the first particles may have an average particle diameter that is less than a width of the first surface corresponding to the top portion of the embossed optical pattern.

In one embodiment, the first particles may be present in the gap fill layer in an amount of 1 weight percent (wt%) to 50 wt%.

In one embodiment, the first particles may comprise antiglare particles.

In one embodiment, the ratio of the maximum width W of the embossed optical pattern to the width L of the flat section (W/L) may be in the range of 0.1 to 3.

In one embodiment, the first particles may be formed of at least one of polymethylmethacrylate, polystyrene, and a copolymer of polymethylmethacrylate and styrene.

In one embodiment, the patterned layer may be formed from a composition for a patterned layer, the composition including an aromatic-free based resin and high refractive index inorganic particles.

In one embodiment, the embossed optical pattern may comprise an optical pattern having a trapezoidal, rectangular or square cross-sectional shape.

In one embodiment, the patterned layer may have a higher refractive index than the gap fill layer.

In one embodiment, the gap filling layer may further include second particles having a higher refractive index than the first particles.

According to another embodiment of the present invention, a polarizing plate may include a polarizing film and an optical film for improving contrast ratio according to the present invention disposed on the polarizing film.

According to another embodiment of the present invention, a liquid crystal display device may include the polarizing plate according to the present invention.

Effects of the invention

The present invention provides an optical film with improved contrast ratio, which can achieve the effect of scattering external light by particles while maintaining the improvement of front visibility and side visibility by a patterned layer and a gap filling layer.

The present invention provides an optical film for improving contrast ratio, which includes a patterned layer and anti-glare particles without suffering from Mohs phenomenon.

The present invention provides an optical film having an elongated structure with an improved contrast ratio.

Drawings

Fig. 1 is a cross-sectional view of an optical film for improving contrast ratio according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

Detailed Description

Embodiments of the present invention will be described in detail with reference to the accompanying drawings to provide a thorough understanding of the invention to those skilled in the art. It is to be understood that the present invention may be embodied in various forms and is not limited to the following embodiments. In the drawings, portions irrelevant to the description will be omitted for clarity. Like components will be denoted by like reference numerals throughout this specification.

Spatially relative terms such as "upper" and "lower" are defined herein with reference to the accompanying drawings. Thus, it will be understood that the term "upper surface" may be used interchangeably with the term "lower surface" and that when an element such as a layer or film is referred to as being "disposed on" another element, it may be directly disposed on the other element or intervening elements may be present. On the other hand, when an element is referred to as being "directly on" another element, there are no intervening elements present therebetween.

Herein, the terms "horizontal direction" and "vertical direction" mean a longitudinal direction and a lateral direction of a rectangular screen of a liquid crystal display device, respectively. Herein, "side surface" refers to a region where θ is in the range of 0 ° to 60 ° in the spherical coordinate system represented by (Φ, θ), where with reference to the horizontal direction, the front side surface is represented by (0 ° ), the left end point is represented by (180 °, 90 °), and the right end point is represented by (0 °, 90 °).

Herein, the term "top part" refers to the highest part in the embossed optical pattern.

Herein, "aspect ratio" refers to a ratio of a maximum height of an optical pattern to a maximum width thereof (maximum height/maximum width).

In this context, "pitch" means the sum of the maximum width W of an embossed optical pattern and the width L of a flat section.

As used herein, "in-plane retardation (Re)" is a value measured at a wavelength of 550 nm,

and is represented by formula a:

Re＝(nx-ny)×d，

(in formula A, nx and ny are refractive indices in a slow axis and a fast axis of a corresponding protective layer or base layer, respectively, at a wavelength of 550 nm, and d is a thickness (unit: nm) of the protective layer or base layer).

Herein, the term "methacryl" refers to propenyl and/or methacryl.

Hereinafter, an optical film for improving a contrast ratio according to one embodiment of the present invention will be described with reference to fig. 1. Fig. 1 is a cross-sectional view of an optical film for improving contrast ratio according to an embodiment of the present invention.

Referring to fig. 1, the optical film 10 for improving contrast ratio includes a protective layer 100 and a patterned layer 210 formed on the protective layer 100, and may further include a gap filling layer 220 directly adjoining one surface of the patterned layer 210.

Protective layer

The protective layer 100 may be formed on one surface of the patterned layer 210, i.e., on a light incident surface thereof, to support the patterned layer 210. In one embodiment, the protective layer may be formed directly on the patterned layer to reduce the thickness of the optical film that improves the contrast ratio. As used herein, "directly formed" means without some adhesive layer, adhesion layer, or adhesion/adhesion layer interposed between the protective layer and the patterned layer. However, it should be understood that the present invention is not limited thereto.

The protective layer 100 may be optically transparent and may include a light incident surface and a light exiting surface opposite the light incident surface. The patterned layer 210 is formed on the light exit surface of the protective layer 100. The protective layer 100 may have a total transmittance of 90% or more than 90%, for example, 90% to 100% in a wavelength range of visible light. In this range of transmittance, the protective layer 100 allows incident light to pass therethrough to the patterned layer without affecting the incident light.

The protective layer 100 may be a protective film or a protective coating.

When the protective layer is a protective film, the protective layer may comprise an optically transparent resin film. The protective film may be formed by melting and extrusion molding of a resin. The resin may be further subjected to stretching as necessary. The optically transparent resin may include at least one selected from the following: cellulose ester containing triacetyl cellulose (TAC), cyclic polyolefin resin containing amorphous cycloolefin polymer (COP), polycarbonate resin, polyester resin containing polyethylene terephthalate (PET), polyether sulfone resin, polysulfone resin, polyamide resin, polyimide resin, acyclic polyolefin resin, polyacrylate resin containing polymethyl methacrylate, polyvinyl alcohol resin, polyvinyl chloride resin, and polyvinylidene chloride resin.

The protective film may be a non-stretched film, a retardation film obtained by stretching a resin by a certain method and having a retardation in a certain range, or an isotropic optical film. In one embodiment, the protective film may be an isotropic optical film having an in-plane retardation Re of 60 nm or less than 60 nm, specifically 0 nm to 60 nm, more specifically 40 nm to 60 nm. In this range of in-plane retardation, the protective film can provide good image quality through compensation for the viewing angle. Herein, the term "isotropic optical film" means a film having substantially the same nx, ny, and nz, and the expression "substantially the same" includes not only the case where nx, ny, and nz are identical, but also the case where there is an acceptable margin of error between nx, ny, and nz. In another embodiment, the protective film may be a retardation film having an in-plane retardation Re of 60 nm or more than 60 nm. For example, the protective film may have an in-plane retardation Re of 60 to 350 nanometers. Alternatively, the protective film may have an in-plane retardation Re of 8,000 nanometers or more than 8,000 nanometers, specifically 10,000 nanometers or more than 10,000 nanometers, more specifically 10,100 to 30,000 nanometers, more specifically 10,100 to 15,000 nanometers. Within this range, the protective film may prevent generation of a rainbow point while further diffusing light diffused through the contrast ratio-improving layer.

When the protective layer is a protective coating, the protective coating may be formed from an actinic radiation curable resin composition comprising an actinic radiation curable compound and a polymerization initiator. The actinic radiation-curable compound may include at least one of a cationically polymerizable curable compound, a radically polymerizable curable compound, a urethane resin, and a silicone resin. The cationically polymerizable curable compound may be an epoxy compound having at least one epoxy group, or an oxetane compound having at least one oxetane ring. The epoxy compound may comprise at least one of a hydrogenated epoxy compound, a chain aliphatic epoxy compound, a cycloaliphatic epoxy compound, and an aromatic epoxy compound.

Examples of the radical polymerizable curable compound may include a methacrylate monomer having at least one methacryloxy group, and a methacrylate oligomer obtained by reacting at least two functional group-containing compounds and having at least two methacryloxy groups. Examples of the methacrylate monomer may include a monofunctional methacrylate monomer having one methacryloxy group, a difunctional methacrylate monomer having two methacryloxy groups, and a multifunctional methacrylate monomer having three or more methacryloxy groups. Examples of methacrylate oligomers may include urethane methacrylate oligomers, polyester methacrylate oligomers, and epoxy methacrylate oligomers. The polymerization initiator can cure the actinic radiation curable compound. The polymerization initiator may include at least one of an optical cationic initiator (cationic initiator) and a photosensitizer (photosensizer). Such as the optical cationic initiator and the photosensitizer, any typical optical cationic initiator and any typical photosensitizer known in the art may be used.

Preferably, the protective layer 100 is a non-surface-treated protective film or a protective coating that has not been surface-treated. As will be described in detail below, since the gap filling layer has an anti-glare effect, the contrast ratio-improved optical film does not require surface treatment of the protective layer, thereby simplifying the manufacturing process of the contrast ratio-improved optical film without adversely affecting the optical function of the contrast ratio-improved optical film.

The protective layer 100 may have a refractive index of 1.4 to 1.7, preferably 1.45 to 1.65.

The protective layer 100 may have a thickness of 10 to 200 micrometers, specifically 20 to 200 micrometers. The protective layer 100 of the protective film type may have a thickness of 20 to 250 micrometers, preferably 30 to 200 micrometers, and the protective layer 100 of the protective coating type may have a thickness of 5 to 50 micrometers. In this thickness range, the protective layer 100 may be used for a polarizing plate.

The protective layer 100 may have a single-layer structure, as shown in fig. 1, or may have a multi-layer structure of at least two protective films or protective layers.

Patterned layer

The patterned layer 210 is formed on the light-exiting surface of the protective layer 100 to allow light emitted from the protective layer 210 to exit therethrough. The patterned layer 210 may include patterned portions formed on one surface of the patterned layer 210 and including embossed optical patterns 211 and flat sections 212 formed between adjacent embossed optical patterns 211. The patterned portion formed on one surface of the patterned layer 210 directly adjoins the gap-fill layer 220.

The embossed optical pattern 211 may be composed of a first surface 214 formed at a top portion thereof and at least one inclined surface 213 connected to the first surface 214. The patterned portion satisfies the following formula 1 and the embossed optical pattern 211 has a base angle θ of 55 ° to 90 °. The base angle θ means an angle defined between the inclined surface 213 of the embossed optical pattern 211 and an imaginary line extending from the maximum width W of the embossed optical pattern 211. Here, the inclined surface 213 means an inclined surface directly connected to the flat section 212 of the embossed optical pattern 211. Within this range, the patterned layer 210 may improve both the front contrast ratio and the side contrast ratio, may reduce a difference between the front contrast ratio and the side contrast ratio, and may increase the contrast ratio at the same side viewing angle and at the same front viewing angle. Specifically, the patterned portion may have a base angle θ of 70 ° to 90 ° and a value of P/W (ratio of P to W) of 1.2 to 8.

Equation 1

1＜P/W≤10，

(in formula 1, P is the pitch of the patterned portion (unit: micrometer) and W is the maximum width of the embossed optical pattern (unit: micrometer)).

Although fig. 1 shows a structure in which the embossed optical pattern has the same base angle θ at both sides thereof, the embossed optical pattern may have different base angles θ as needed as long as the base angle θ is in the range of 55 ° to 90 °. For example, the embossed optical pattern may have a base angle θ of 55 °, 56 °, 57 °, 58 °, 59 °, 60 °, 61 °, 62 °, 63 °, 64 °, 65 °, 66 °, 67 °, 68 °, 69 °, 70 °, 71 °, 72 °, 73 °, 74 °, 75 °, 76 °, 77 °, 78 °, 79 °, 80 °, 81 °, 82 °, 83 °, 84 °, 85 °, 86 °, 87 °, 88 °, 89 °, or 90 °. For example, the embossed optical pattern may have a ratio (P/W) of 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, 5, 6, 7, or 8.

The embossed optical pattern 211 may be an embossed optical pattern including a first surface 214 formed at a top portion thereof and at least one inclined surface 213 connected to the first surface 214. Although fig. 1 illustrates a trapezoidal optical pattern in which two adjacent inclined surfaces 213 are connected to each other via a first surface 214, it is to be understood that the present invention is not limited thereto. Alternatively the embossed optical pattern may have a rectangular or square cross-sectional shape.

The first surface 214 is formed at the top portion of the embossed optical pattern, and may improve the viewing angle and brightness by further diffusing light reaching the patterned layer 210 in the optical display device. Accordingly, the embossed optical pattern 211 may minimize loss of brightness through improvement of light diffusion. The first surface 214 is a flat surface and may facilitate the process of manufacturing an optical film with improved contrast ratio. Alternatively, the first surface 214 may have a fine roughness or a curved surface. In configurations where the first surface 214 is a curved surface, the embossed optical pattern may be implemented by a lenticular pattern. Referring to fig. 1, the embossed optical pattern has a trapezoidal cross section in which the first surface formed at the top portion is a flat surface and the inclined surface is a flat surface (e.g., a truncated prism pattern having a truncated triangular cross section, i.e., a truncated prism shape or a cut prism shape). Alternatively, the embossed optical pattern may have a shape in which the first surface is formed at a top portion thereof and the inclined surface is a curved surface (e.g., a contrast ratio improving layer having a truncated lenticular (cut lenticular) lens pattern or a truncated microlens (cut microlens) pattern). In addition, the embossed optical pattern may include a pattern having an N-sided polygonal cross-sectional shape (N is an integer of 3 to 20), including a rectangular or square cross-sectional shape.

The first surface 214 may be parallel to at least one of the flat section 212 and a lowermost surface of the patterned layer 210. Fig. 1 shows a structure in which the first surface 214 of the embossed optical pattern 211, the flat sections 212, and the lowermost surface of the patterned layer 210 are parallel to each other.

The first surface 214 may have a width a of 0.5 to 30 microns, specifically 1 to 15 microns. Within this range, the first surface 214 may be used in an optical display device and may improve contrast ratio.

The embossed optical pattern 211 may have an aspect ratio (H1/W) of 0.1 to 10, specifically 0.1 to 7.0, more specifically 0.1 to 5.0. Within this range, the optical display device may exhibit improved contrast ratio and viewing angle at its sides.

The embossed optical pattern 211 may have a maximum height H1 of 20 microns or less than 20 microns, specifically 15 microns or less than 15 microns, more specifically 10 microns or less than 10 microns. Within this range, the optical display device can exhibit improvements in contrast ratio, viewing angle, and brightness without suffering from the Mohs phenomenon and the like.

The embossed optical pattern 211 may have a maximum width W of 20 microns or less than 20 microns, specifically 15 microns or less than 15 microns, more specifically 10 microns or less than 10 microns. Within this range, the optical display device can exhibit improvements in contrast ratio, viewing angle, and brightness without suffering from the Mohs phenomenon and the like.

Although fig. 1 illustrates a structure in which adjacent optical patterns of the patterned part have the same base angle, the same width of the first surface, the same maximum height, and the same maximum width, the adjacent optical patterns may have different base angles, different widths of the first surface, different maximum heights, and different maximum widths.

Upon receiving light from the patterned layer 210, the flat section 212 emits light to the gap fill layer 220, thereby improving front side brightness.

The ratio (W/L) of the maximum width W of the embossed optical pattern 211 to the width L of the flat section 212 may be 9 or less than 9, specifically from 0.1 to 3, more specifically from 0.15 to 2. Within this range, the embossed optical pattern can reduce the difference between the front and side contrast ratios while improving the contrast ratio at the same side viewing angle and at the same front viewing angle. The flat section 212 may have a width L of 1 to 50 microns, specifically 1 to 20 microns. Within this range, the embossed optical pattern can improve front brightness.

The maximum width W of an embossed optical pattern 211 and the flat section 212 directly adjacent to the optical pattern form a pitch P. The pitch P may be in the range of 1 micron to 50 microns, specifically from 1 micron to 40 microns. Within this range, the embossed optical pattern can improve brightness and contrast ratio without causing Mohs phenomenon.

Although fig. 1 illustrates a structure in which adjacent optical patterns of the patterned portion have the same pitch and the same maximum width, it is understood that the adjacent optical patterns may have different pitches and different maximum widths.

Although not clearly shown in fig. 1, fig. 1 shows a structure in which the embossed optical pattern extends in a stripe shape. Alternatively, the embossed optical pattern may be formed in dots. As used herein, "dots" means that the embossed optical pattern is discrete. Preferably, the embossed optical pattern extends in a stripe shape to enlarge the viewing angle at the right and left sides.

The difference in refractive index between the patterned layer 210 and the gap filling layer 220 is 0.06 or more than 0.06, preferably 0.08 to 0.3, more preferably 0.08 to 0.2, and still more preferably 0.08 to 0.15. Within this range, the optical film improving the contrast ratio can ensure a good light diffusion effect compared to the reduction of the front CR. For example, the difference in refractive index between the patterned layer 210 and the gap filling layer 220 may be 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.25, or 0.3.

The patterned layer 210 may have a refractive index of 1.52 or greater than 1.52, specifically 1.55 to 1.70, more specifically 1.60 to 1.70. Accordingly, the optical film may maximize a light diffusion effect and may increase a difference in refractive index between the patterned layer and the gap filling layer with an increased refractive index.

The patterned layer 210 may be formed of a composition for a patterned layer including at least one of a thermosetting resin and a photocurable resin capable of providing a refractive index as set forth above.

For example, the patterned layer 210 may be formed of at least one of an aromatic-based resin and an aromatic-free resin (non-aromatic resin). The aromatic group-containing resin may include, for example, a fluorine-or naphthalene-containing resin, but is not limited thereto.

The patterned layer 210 may be formed of a composition for a patterned layer including at least one of a thermosetting resin and a photocurable resin capable of providing a refractive index as set forth above. For example, the composition for the patterned layer may include a bifunctional or higher methacrylic monomer.

Specifically, the methacrylic monomer may comprise at least one of: difunctional methacrylates such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, butanediol dimethacrylate, hexanediol dimethacrylate, tricyclodecane dimethanol dimethacrylate, nonanediol dimethacrylate, ethoxylated hexanediol dimethacrylate, propoxylated hexanediol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, tripropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, neopentyl glycol dimethacrylate, ethoxylated neopentyl glycol dimethacrylate, tripropylene glycol dimethacrylate, hydroxypivalic acid neopentyl glycol dimethacrylate, and the like; trifunctional methacrylates such as trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane trimethacrylate, propoxylated trimethylolpropane trimethacrylate, tris 2-hydroxyethyl isocyanurate trimethacrylate, glycerol trimethacrylate, pentaerythritol trimethacrylate, dipentaerythritol trimethacrylate, ditrimethylolpropane trimethacrylate, and the like; tetrafunctional methacrylates such as pentaerythritol tetramethacrylate, ditrimethylolpropane tetramethacrylate, dipentaerythritol tetramethacrylate, and the like; pentafunctional methacrylates such as dipentaerythritol pentamethacrylate, ditrimethylolpropane pentamethacrylate, and the like; and hexafunctional methacrylates such as dipentaerythritol hexamethacrylate, ditrimethylolpropane hexamethacrylate and the like.

The patterned layer may be formed of a composition for the patterned layer including at least one of a thermosetting resin and a photocurable resin and at least one of a thermosetting monomer and a photocurable monomer capable of providing the refractive index as set forth above. The at least one of a thermosetting resin and a photocurable resin and the at least one of a thermosetting monomer and a photocurable monomer may form a matrix of the patterned layer.

The patterned layer may be formed of a composition for the patterned layer, the composition including high refractive index inorganic particles, such as at least one of zirconium dioxide (zirconia) and titanium dioxide (titania). The composition for a patterned layer containing high-refractive-index inorganic particles can increase the refractive index of the patterned layer without containing an aromatic-group-containing resin, while improving the reliability of the light resistance of the patterned layer. The aromatic group-containing resin may suffer from deterioration in light-resistance reliability due to yellowing upon long-term exposure to external UV light. The high refractive index inorganic particles may be present in the patterned layer in an amount of 10 to 80 wt%, preferably 20 to 80 wt%, more preferably 20 to 75 wt%, and still more preferably 30 to 70 wt%. Within this range, the composition for the patterned layer may improve the reliability of the refractive index and the light resistance of the patterned layer.

The high refractive index inorganic particles have a higher refractive index than the matrix of the patterned layer and may have a refractive index of 1.8 or greater than 1.8, preferably 2.0 or greater than 2.0, for example 2.0 to 3.0. Within this range, the composition can easily ensure a desired refractive index of the patterned layer. Although the inorganic particles may include particles that have not been subjected to surface treatment, the surface treatment of the inorganic particles may improve compatibility with other components. The surface treatment may be performed on the inorganic particles over 5% to 50% of their total surface area. Preferably, the patterned layer includes zirconia, which makes it easier to adjust the refractive index of the patterned layer than the gap-fill layer, thereby further improving visibility.

The high refractive index inorganic particles may have an average particle diameter D50 of 1 nm to 80 nm, preferably 5 nm to 50 nm. The average particle diameter D50 of the inorganic particles can be measured by typical methods well known to those skilled in the art. Within this range of the average particle diameter, the high refractive index inorganic particles can ensure an increase in the refractive index of the high refractive index layer without light scattering.

The composition for the patterned layer may further include at least one of a photoinitiator and a thermal initiator that facilitate formation of the patterned layer by curing the composition. For example, the composition can include at least one of a phosphorus, triazine, acetophenone, benzophenone, thioxanthone, benzoin, oxime, and phenyl ketone initiator.

The composition for the patterned layer may further include typical additives such as a release agent, an antifoaming agent, a leveling agent, an antioxidant, a UV absorber, and a light stabilizer. The patterning layer composition used may be a solvent-free composition or may further comprise a solvent so as to allow easier formation of the patterning layer. The solvent may be selected from typical solvents in the art.

Gap filling layer

The gap filling layer 220 is directly formed on one surface of the patterned layer 210, and more particularly, directly formed on the light exit surface of the patterned layer 210. The gap filling layer 220 diffuses light received from the light exit surface of the patterned layer 210, thereby further improving the light diffusion effect.

The gap filling layer 220 may be a flattening layer that flattens the contrast ratio improving layer 200 by filling at least a portion of the gaps between adjacent embossed optical patterns 211 of the patterned layer 210.

In one embodiment, the gap filling layer 220 may completely fill the gaps between adjacent embossed optical patterns 211 of the patterned layer 210.

In one embodiment, the thickness of the gap filling layer 220 may be greater than the maximum height of the embossed optical patterns 211, so that the gap filling layer 220 may completely fill the gaps between adjacent embossed optical patterns 211 of the patterned layer 210 while covering the top portions of the embossed optical patterns 211.

The patterned layer 210 has a higher refractive index than the gap filling layer 220. The contrast ratio-improving layer 200 composed of the patterned layer 210 and the gap-fill layer 220 may improve the side contrast ratio by allowing light received through the light incident surface of the patterned layer 210 to exit the contrast ratio-improving layer 200 through diffusion of light, may minimize a decrease in the front contrast ratio while improving the side contrast ratio, may reduce a difference between the front contrast ratio and the side contrast ratio, and may improve the contrast ratio at the same side viewing angle and at the same front viewing angle.

The gap filling layer 220 may have a refractive index greater than 0 to 1.53, and particularly 1.43 to 1.525. In this range of the refractive index, the difference in refractive index between the gap filling layer and the patterned layer becomes large, thereby ensuring good visibility.

The gap filling layer 220 may include a matrix and first particles 230 included in the matrix. At least some of the first particles 230 are exposed on the surface of the gap filling layer 220 to form surface roughness and may have the same refractive index as the matrix. With this structure, the gap filling layer prevents light that has passed through the patterned layer 210 from scattering by the first particles without affecting the improvement of visibility, and can provide an antiglare effect through surface roughness formed by the first particles exposed on the surface of the gap filling layer while suppressing the mohs phenomenon. Some of the first particles 230 may be exposed on the surface of the gap filling layer 220, and other first particles 230 may be distributed between the embossed optical patterns.

Even in the structure in which the first particles are distributed between the embossed optical patterns, the first particles may have a minimum internal haze so as not to have an influence on the visibility improvement effect, as long as the absolute value of the difference in refractive index between the first particles and the matrix falls within the range of 0 to 0.03.

The first particles 230 may be present in the gap filling layer 220 in an amount of 1 wt% to 50 wt%, preferably 2 wt% to 40 wt%, and more preferably 2 wt% to 30 wt%. Within this range, the first particles form an external roughness to provide an effect of scattering external light.

In one embodiment, at least 1% and less than 20% of the particle diameter of the first particles included in the gap-fill layer may be exposed on the surface of the gap-fill layer, particularly, on the uppermost surface of the gap-fill layer, and the gap-fill resin may be disposed on the first particles to form the surface roughness. Within this range, the gap filling layer may ensure an antiglare effect while maintaining an improvement in contrast ratio to light emitted from the patterned layer.

In one embodiment, the maximum distance (also referred to as the "net thickness") between the first surface 214 corresponding to the top portion of the patterned layer 210 and the uppermost surface of the gap-fill layer 220 may be greater than 0 to 15 microns, preferably 5 to 10 microns. Within this range, the gap filling layer may ensure an antiglare effect while maintaining an improvement in contrast ratio to light emitted from the patterned layer. When the known antiglare film is mounted on an optical film improving a contrast ratio, light emitted from the patterned layer reaches the antiglare particles via the film constituting the antiglare film. According to the present invention, the clear thickness is set as above and the absolute value of the difference in refractive index between the matrix and the first particles in the gap-filling layer is set in the range of 0 to 0.03, whereby the antiglare effect is ensured via the surface roughness while maintaining the effect of improving the lateral visibility.

The first particles 230 may include particles that provide an antiglare effect by scattering light received from the matrix. The first particles may comprise spherical or amorphous particles, preferably spherical particles. With such particles, the first particles can improve the external morphology of the optical film by allowing uniform scattering of light on the surface of the gap-fill layer.

The first particles may have an average particle diameter D50 of 20 microns or less than 20 microns, preferably from 2 microns to 15 microns, more preferably from 2 microns to 10 microns. Within this range of the average particle diameter, the first particles may be contained in the gap-filling layer and the antiglare effect may be ensured.

The average particle diameter of the first particles may be less than the width of the first surface corresponding to the top portion of the embossed optical pattern, or the maximum width of the embossed optical pattern or flat section. In this case, the first particles can secure the antiglare effect without causing the mohs phenomenon.

The first particles 230 are particles having a refractive index set such that the absolute value of the difference in refractive index between the first particles 230 and the matrix is in the range of 0 to 0.03, whereby improvement in visibility at the lower side of the optical film is maintained. In addition, the first particles may provide an anti-glare effect with respect to light received from the patterned layer. In one embodiment, the first particles may have the same refractive index as the matrix or a different refractive index. For example, the absolute value of the difference in refractive indices may be about 0, 0.005, 0.01, 0.015, 0.02, 0.025, or 0.03.

The first particles are typical antiglare particles and may include at least one of organic particles, inorganic particles, and organic-inorganic hybrid particles. The organic particles may be formed of polymethylmethacrylate, polystyrene, or a copolymer of polymethylmethacrylate and styrene, but is not limited thereto. The inorganic particles may include silica, titania, zirconia, and alumina, but are not limited thereto. Preferably, the first particles are organic particles, more preferably polymethylmethacrylate particles, to improve compatibility with the matrix.

The first particles may have a refractive index of greater than 0 to 1.53, specifically 1.43 to 1.53, more specifically 1.43 to 1.525.

The matrix may support the gap filling layer such that the first particles are exposed on a surface of the gap filling layer. The matrix may be formed of a composition for a gap filling layer, which may ensure that an absolute value of a difference in refractive index between the first particles and the matrix is in a range of 0 to 0.03. The matrix can have a refractive index greater than 0 to 1.53, specifically 1.43 to 1.53, and still specifically 1.43 to 1.525.

The composition for the gap filling layer may include a photocurable compound, a methacrylic monomer, an initiator, and first particles.

The photocurable compound may include a UV curable group such as a methacrylate group or an epoxy group-containing compound (at least one of an oligomer and a resin). The photocurable compound may include at least one of a bifunctional or higher functional methacrylate oligomer and a resin formed therefrom. The photocurable compound may include at least one of a multifunctional methacrylate of a polyol and a methacrylate, and a multifunctional urethane methacrylate prepared from a hydroxy ester of a polyol, an isocyanate compound, and a methacrylic acid. The methacrylic monomer may comprise at least one of the methacrylic monomers described above in the description of the composition for the patterned layer. The initiator may comprise at least one of the initiators described above in the description of the composition for the patterned layer. The first particles are the same as those described above.

The composition for the gap filling layer may further include typical additives such as a dispersant, an antifoaming agent, a leveling agent, a slip agent, an antioxidant, a UV absorber, a light stabilizer, and an anti-fingerprint agent.

For example, the leveling agent can be a UV reactive silicone additive (e.g., UV 3500). For example, the dispersant may be a non-flocculating dispersant having a high molecular weight block copolymer (e.g., Disperbyk-2163). For example, the anti-fingerprint agent may be a UV curable fluorine-based acrylic compound (e.g., KY 12001203).

Although the composition for the gap filling layer may be a solvent-free composition, the composition for the gap filling layer may further include a solvent to facilitate formation of the gap filling layer. The solvent may be a typical solvent such as at least one of propylene glycol monomethyl ether acetate and methyl isobutyl ketone, but is not limited thereto.

The composition for the gap filling layer may further include second particles having a higher refractive index than the first particles 230. Therefore, once the composition for the gap-fill layer is cured, it is possible to ensure that the absolute value of the difference between the first particles and the matrix is in the range of more than 0 to 0.03.

The second particles may have a refractive index of 1.8 or more than 1.8, preferably 2.0 or more than 2.0, or 2.0 to 3.0. Within this range, the composition can easily secure the refractive index of the gap filling layer.

The second particles may comprise substantially the same particles as the high refractive index inorganic particles described above in the description of the patterned layer. Preferably, the second particles comprise zirconia. The second particles may have an average particle diameter D50 of 5 to 80 nanometers. The average particle diameter D50 of the second particles can be measured by typical methods well known to those of ordinary skill in the art. Within this range of the average particle diameter, the second particles may increase the refractive index of the high refractive index inorganic particles.

The second particles may be present in the composition for the gap-fill layer or in the gap-fill layer in an amount of 10 to 80 wt%, preferably 10 to 75 wt%, for example 15 to 70 wt%. Within this range, the second particles may maintain the hardness of the gap-fill layer while maintaining the dispersion of the second particles.

The gap fill layer 220 may have a maximum thickness of 30 microns or less than 30 microns, such as 20 microns or less than 20 microns. Within this range, the gap filling layer can prevent warpage such as curling from occurring.

In the contrast ratio-improving layer 200, the first particles 230 may be present in an amount of 1 to 50 wt%, preferably 2 to 40 wt%. Within this range, the first particles can secure the antiglare effect while maintaining the improvement in the contrast ratio.

The optical film 10 for improving the contrast ratio may have a haze of 0% to 35%. Within this range, the optical film improving the contrast ratio may be used for an optical display device.

Subsequently, a polarizing plate according to one embodiment of the present invention will be described with reference to fig. 2. Fig. 2 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

Referring to fig. 2, the polarizing plate 20 according to this embodiment includes a polarizing film 300 and a contrast ratio-improving film, which may include a contrast ratio-improving optical film according to an embodiment of the present invention.

An optical film improving the contrast ratio may be formed on the light exit surface of the polarizing film 300. The contrast-ratio-improved optical film diffuses polarized light that has passed through the polarizing film 300, thereby improving a front contrast ratio, a side contrast ratio, a viewing angle, and black visibility.

The polarizing film 300 may polarize and transmit light received from the liquid crystal panel toward the layer 200 improving the contrast ratio. The polarizing film 300 is formed on the light incident surface of the contrast ratio improving layer 200.

The polarizing film 300 may include a polarizer. Specifically, the polarizer may include a polyvinyl alcohol polarizer obtained by uniaxially stretching a polyvinyl alcohol film, or a polyalkenyl polarizer obtained by dehydrating a polyvinyl alcohol film. The polarizer may have a thickness of about 5 microns to about 40 microns. Within this range, the polarizing film 300 may be used for an optical display device.

The polarizing film 300 may include a polarizer and a protective layer formed on at least one surface of the polarizer (i.e., formed on a light incident surface of the polarizer). The protective layer protects the polarizer, thereby improving the reliability and mechanical strength of the polarizing plate. The protective layer may comprise at least one of an optically transparent protective film and an optically transparent protective coating. The protective layer is the same as described above.

The polarizing plate may be manufactured by a typical method. Specifically, the polarizing plate is manufactured by forming an optical film of improved contrast ratio by the above-described method, and then adhering the polarizing film to the optical film of improved contrast ratio via the first resin layer. The first resin layer exhibits good adhesive strength with respect to the polarizing film.

According to the present invention, a liquid crystal display device may include the polarizing plate according to the present invention. In one embodiment, the liquid crystal display device may include a polarizing plate at a viewer side with respect to the liquid crystal panel. Herein, the term "polarizing plate at the viewer side" refers to a polarizing plate placed on the side of the screen of the liquid crystal panel, that is, a polarizing plate placed on the side of the liquid crystal panel opposite to the light source.

In one embodiment, a liquid crystal display device may include a backlight unit, a first polarizing plate, a liquid crystal panel, and a second polarizing plate, each stacked in the stated order, wherein the second polarizing plate may include a polarizing plate according to the present invention. The liquid crystal panel may employ a Vertical Alignment (VA) mode, an IPS mode, a Patterned Vertical Alignment (PVA) mode, or a super-patterned vertical alignment (S-PVA) mode, but is not limited thereto. In another embodiment, the liquid crystal display device may include a polarizing plate at the light source side. Herein, the term "polarizing plate at the light source side" refers to a polarizing plate disposed at the light source side with respect to the liquid crystal panel. In still another embodiment, both the polarizing plate at the viewer side and the polarizing plate at the light source side with respect to the liquid crystal panel may include the polarizing plate according to the present invention.

Examples of the invention

Subsequently, the present invention will be described in more detail with reference to some examples. It should be noted, however, that these examples are provided for illustration only and should not be construed as limiting the invention in any way.

Preparation example 1: preparation of a composition for patterning a layer

A composition for a patterned layer was prepared by mixing 73 parts by weight of a solvent-free zirconia-containing solution HR-10-1 (Nippon Shokubai co., Ltd.), the average particle diameter D50: 11 nm of zirconia, a high refractive index compound containing 80% by weight of zirconia dispersed in benzyl acrylate, the refractive index: 1.67) with 22 parts by weight of trimethylpropane triacrylate, followed by adding 4.5 parts by weight of a starter (TPO LG, globalized capital inc (IGC co., Ltd.), and 0.5 part by weight of a release agent (BYK3500) to the mixture. The composition used for the patterned layer had a refractive index of 1.60. In the composition for the patterned layer, zirconia was present in an amount of 51 wt% by solid content.

Preparation example 2: composition for preparing gap filling layer

23 parts by weight of a photocurable compound (UP111, ATIS Co., Ltd., solids content: 70% by weight, solvent: PGME (propylene glycol methyl ether)), 8.4 parts by weight of SR833S (Sartomer Co., Ltd.), 8 parts by weight of HDDA (ATIS Co., Ltd.), 46 parts by weight of Propylene Glycol Monomethyl Ether Acetate (PGMEA), and 12 parts by weight of methyl isobutyl ketone (MIBK) were mixed and stirred. After completion of the stirring, 1.15 parts by weight of a starter (Omnirad 184, indian globalization capital Ltd.), 0.03 parts by weight of a UV reactive silicone additive (UV3500), 0.07 parts by weight of a dispersant (Disperbyk-2163, beck chemical Ltd (BYK co., Ltd.)) and 0.05 parts by weight of an anti-fingerprint agent (KY1203, Shin-Etsu co., Ltd.)) were added to the mixture, thereby preparing a solution.

Organic particles (MSX-105, refractive index: 1.495, polymethyl methacrylate particles, average particle diameter D50: 5.41 μm, monodisperse particles, water accumulating Co., Ltd.) were mixed with the solution, thereby preparing a solution for the gap-filling layer. The composition for the gap-filling layer contained 6 wt% of organic particles based on the solid content.

Preparation example 3: preparation of composition for gap filling layer

A solution was prepared by the same method as in preparation example 2.

Organic particles (MSX-2H, refractive index: 1.495, polymethyl methacrylate particles, average particle diameter D50: 2.7 μm, intermediate dispersed particles, water-retention Co., Ltd.) were mixed with the solution, thereby preparing a solution for a gap-filling layer. The composition for the gap filling layer contained 6 wt% of organic particles by solid content.

Preparation example 4: composition for preparing gap filling layer

24 parts by weight of a photocurable compound (UP111, ENGIS Co., Ltd., solid content: 70% by weight, solvent: PGME (propylene glycol methyl ether)), 17 parts by weight of a zirconium oxide-containing solvent-free solution HR-10-1 (Japanese catalyst Co., Ltd., average particle diameter of zirconium oxide D50: 11 nm), 46 parts by weight of PGMEA, and 12 parts by weight of MIBK were mixed and stirred. After completion of the stirring, 1.15 parts by weight of a starter (Omnirad 184, india globalized capital ltd), 0.03 parts by weight of a UV-reactive silicone additive (UV3500), 0.07 parts by weight of a dispersant (Disperbyk-2163, bibk chemical ltd) and 0.05 parts by weight of an anti-fingerprint agent (KY1203, shin-pass co., ltd.) were added to the mixture, thereby preparing a solution.

Organic particles (MSX-105, refractive index: 1.495, polymethyl methacrylate particles, average particle diameter D50: 5.41 μm, monodisperse particles, water-collecting Co., Ltd.) were mixed with the solution, thereby preparing a solution for a gap-filling layer. The composition for the gap-filling layer contained 6 wt% of organic particles based on the solid content.

Preparation example 5: composition for preparing gap filling layer

A solution was prepared by the same method as in preparation example 2.

Organic particles (SMX-5R, refractive index: 1.555, polymethyl methacrylate copolymer particles, average particle diameter D50: 5.0 μm, polydispersed particles, water-accumulating Co., Ltd.) were mixed with the solution, thereby preparing a solution for the gap-filling layer. The composition for the gap-filling layer contained 6 wt% of organic particles based on the solid content.

Preparation example 6: composition for preparing gap filling layer

A solution was prepared by the same method as in preparation example 2.

Organic particles (SBX-4, refractive index: 1.595, polystyrene particles, average particle diameter D50: 4.0 μm, polydispersed particles, water-collecting Co., Ltd.) were mixed with the solution, thereby preparing a solution for a gap-filling layer. The composition for the gap-filling layer contained 6 wt% of organic particles based on the solid content.

Preparation example 7: composition for preparing gap filling layer

A solution was prepared by the same method as in preparation example 2. Particles are not added to the composition for the gap filling layer.

Preparation example 8: composition for preparing gap filling layer

38.5 parts by weight of a photocurable compound (UP111, ENGIS Co., Ltd., solid content: 70% by weight, solvent: PGME (propylene glycol methyl ether)), 6.5 parts by weight of a zirconia-containing solvent-free solution HR-10-1 (Japanese catalyst, Ltd., zirconia average particle diameter D50: 11 nm, high refractive index compound containing 80% by weight of zirconia dispersed in benzyl acrylate, refractive index: 1.67), 42 parts by weight of PGMEA, and 12 parts by weight of MIBK were mixed and stirred. After completion of the stirring, 1.15 parts by weight of a starter (Omnirad 184, india globalized capital ltd), 0.03 parts by weight of a UV-reactive silicone additive (UV3500), 0.07 parts by weight of a dispersant (Disperbyk-2163, bibk chemical ltd) and 0.05 parts by weight of an anti-fingerprint agent (KY1203, shin-pass co., ltd.) were added to the mixture, thereby preparing a solution.

Organic particles (MSX-105, refractive index: 1.495, polymethyl methacrylate particles, average particle diameter D50: 5.41 μm, monodisperse particles, water-collecting Co., Ltd.) were mixed with the solution, thereby preparing a solution for a gap-filling layer. The composition for the gap-filling layer contained 6 wt% of organic particles and 16 wt% of zirconia in terms of solid content.

Preparation example 9: preparation of a composition for patterning a layer

A composition for a patterned layer was prepared by mixing 40 parts by weight of a zirconia-containing solvent-free solution HR-10-1 (japanese catalyst co., average particle diameter of zirconia D50: 11 nm, high refractive index compound containing 80 wt% zirconia dispersed in benzyl acrylate, refractive index: 1.67) with 60 parts by weight of trimethylpropane triacrylate, followed by adding 4.5 parts by weight of a starter (TPO LG, indian globalization capital ltd.) and 0.5 parts by weight of a release agent (BYK3500) to the mixture. The composition used for the patterned layer had a refractive index of 1.55. In the composition for the patterned layer, zirconia was present in an amount of 28 wt% based on the solid content.

Example 1

A coating layer serving as a protective layer was formed by coating the composition for a patterned layer prepared in preparation example 1 onto one surface of a polyethylene terephthalate film (SKC co., Ltd., thickness: 40 μm). An embossed optical pattern and flat sections are applied to a coating by using an optical film having an engraved prismatic pattern and flat sections formed thereon to form a patterned layer on the coating.

An optical film with an improved contrast ratio was formed by depositing the composition for a gap-fill layer prepared in preparation example 2 onto a patterned layer having #18, followed by drying at 80 ℃ for 2 minutes and photocuring. Details of the optical pattern and the flat sections formed on the contrast ratio-improving optical film are shown in table 1.

The polarizer was manufactured by stretching a polyvinyl alcohol film to 3 times its original length at 60 ℃ and adsorbing iodine to the stretched film, followed by stretching the film to 2.5 times the stretched length of the film in an iodine solution at 40 ℃. A polarizer is adhered to the other surface of the protective film of the optical film for improving the contrast ratio, thereby preparing a polarizing plate.

Example 2

An optical film and a polarizing plate for improving a contrast ratio were manufactured in the same manner as in example 1, except that the composition for a gap-filling layer prepared in preparation example 3 was used instead of the composition for a gap-filling layer prepared in preparation example 2.

Example 3

An optical film and a polarizing plate for improving a contrast ratio were manufactured in the same manner as in example 1, except that the composition for a gap-filling layer prepared in preparation example 8 was used instead of the composition for a gap-filling layer prepared in preparation example 2.

Comparative examples 1 to 4

An optical film and a polarizing plate for improving a contrast ratio were manufactured in the same manner as in example 1, except that the composition for a gap-filling layer as listed in table 2 was used instead of the composition for a gap-filling layer prepared in preparation example 2.

Comparative example 5

An optical film and a polarizing plate for improving a contrast ratio were manufactured in the same manner as in example 3, except that the composition for a gap-filling layer prepared in preparation example 9 was used instead of the composition for a gap-filling layer prepared in preparation example 1.

Reference example 1

A polarizing plate was manufactured in the same manner as in example 1. A polarizing plate was manufactured by adhering a polyethylene terephthalate film (SKC ltd., thickness: 40 μm) serving as a protective layer to one surface of a polarizer.

TABLE 1

The optical films and polarizing plates with improved contrast ratios prepared in examples and comparative examples were evaluated for the following characteristics, and the evaluation results are shown in table 2.

Haze and total transmittance of optical film for improving contrast ratio (unit:%): the haze and the transmittance were measured using NDH2000 (Nippon Denshok co., Ltd.)). DF (diffuse transmitted light), PT (parallel transmitted light), TT (total transmitted light), and haze were measured in a wavelength range of 400 nm to 700 nm using NDH 2000.

DF: the sum of the light emitted from the lamp and passing through the sample while diffusing in the sample

PT: summation of light emitted from a lamp and linearly passing through a sample

TT: sum of diffuse transmitted light and parallel transmitted light

Turbidity: haze values exhibited by samples

Haze (%) < DF (diffuse transmission)/TT (total transmission) x100

Side contrast ratio (unit:%) and viewing angle (unit: °): the polarizing plates prepared in examples and comparative examples were evaluated according to the side contrast ratio and the 1/2 viewing angle (upper and lower, right and left), and the evaluation results are shown in table 2. The side contrast ratio and the 1/2 viewing angle were evaluated using a liquid crystal display device manufactured by the following method.

Manufacturing the first polarizing plate

The first polarizer was manufactured by stretching a polyvinyl alcohol film to 3 times its original length at 60 ℃ and adsorbing iodine to the stretched film, followed by stretching the film to 2.5 times the stretched length of the film in an aqueous solution at 40 ℃. As the base layer, a triacetyl cellulose film (thickness: 80 μm) was bonded to both surfaces of the first polarizer using an adhesive (Z-200, Nippon Goshei co., Ltd.) for a polarizing plate, thereby manufacturing a polarizing plate. The manufactured polarizing plate was used as the first polarizing plate.

Manufacturing a module for a liquid crystal display

Each of the first polarizing plate, the liquid crystal panel (PVA mode), and the polarizing plates manufactured in examples and comparative examples was assembled in the stated order, thereby providing a module for a liquid crystal display device. Here, each of the polarizing plates prepared in examples and comparative examples was assembled as a polarizing plate at the viewer side such that the gap filling layer was placed at the outermost side of the module.

An LED light source, a light guide plate, and a module for a liquid crystal display device are assembled, thereby providing a liquid crystal display device including a single-sided edge type LED light source (the liquid crystal display device has the same configuration as a Samsung LED TV (model: UN32H5500), but in which each of the modules for a liquid crystal display device of examples and comparative examples is changed.

The brightness in each of the white and black modes at coordinates (0 °, 60 °) in the spherical coordinate system was measured using EZCONTRAST X88RC (EZXL-176R-F422a4, aldimum co. The side contrast ratio is calculated as the ratio of the luminance in the white mode to the luminance in the black mode at coordinates (0 °, 60 °) in a spherical coordinate system. The viewing angle of 1/2 was set to an angle at which the liquid crystal display device had a luminance corresponding to 1/2 front luminance in the white mode.

External light scattering: the external light scattering was evaluated based on 60 ° reflected gloss (gloss) measured using BYK Gardner (BYK Gardner) according to JIS Z8741 and ISO 2813. The 60 ° reflected gloss of less than 90 is evaluated as the presence of the external light scattering effect, and the 60 ° reflected gloss of 90 or more than 90 is evaluated as the absence of the external light scattering effect.

TABLE 2

Refractive index difference 1: absolute value of difference in refractive index between the matrix and the first particles in the gap-fill layer

Refractive index difference 2: refractive index of patterned layer-refractive index of gap filling layer

As shown in table 2, the polarizing plate according to the present invention achieves a high improvement in front and side visibility, exhibits a high side contrast ratio, and can secure an external light scattering effect.

In contrast, the polarizing plate of comparative example 1, in which the absolute value of the difference in refractive index between the matrix and the first particles is not within the range of the present invention and the difference in refractive index between the patterned layer and the gap filling layer is less than 0.06, and the polarizing plates of comparative examples 2 and 3, in which the absolute value of the difference in refractive index between the matrix and the first particles is not within the range of the present invention, exhibit no significant improvement in the front and side contrast ratios and a poor side contrast ratio, although the polarizing plates of comparative example 1 and the polarizing plates of comparative examples 2 and 3 have the effect of scattering external light.

The polarizing plate of comparative example 4 manufactured without particles does not have an external light scattering effect, and thus an additional film is required to impart an effect of scattering external light, thus failing to provide the effect of the present invention.

The polarizing plate of comparative example 5, in which the difference in refractive index between the matrix and the first particles is within the range of the present invention in absolute value, but the difference in refractive index between the patterned layer and the gap filling layer is not within the range of the present invention, had a poor side contrast ratio and a poor 1/2 left-right viewing angle.

It is to be understood that various modifications, changes, alterations, and equivalent embodiments may be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims (13)

1. An optical film for improving contrast ratio, comprising:

a protective layer including a light incident surface and a light exit surface opposite to the light incident surface; and

a patterned layer formed on the light exit surface of the protective layer to allow light emitted from the protective layer to exit therethrough,

wherein the patterned layer comprises patterned portions formed on one surface thereof, the patterned portions comprising embossed optical patterns and flat sections disposed between adjacent ones of the embossed optical patterns,

the embossed optical pattern has a base angle of 55 to 90,

the patterned portion satisfies formula 1, and

wherein the contrast ratio-improving optical film further comprises: a gap fill layer directly adjacent to the one surface of the patterned layer, the gap fill layer comprising a matrix and first particles contained in the matrix,

the absolute value of the difference in refractive index between the matrix and the first particles is in the range of 0 to 0.03, an

The difference in refractive index between the patterned layer and the gap filling layer is 0.06 or greater than 0.06,

equation 1

1<P/W≤10

In formula 1, P is a pitch of the patterned portion and W is a maximum width of the embossed optical pattern, and P and W are in units of micrometers,

wherein the patterned layer has a higher refractive index than the gap fill layer.

2. The contrast-ratio improving optical film according to claim 1, wherein the gap filling layer comprises a surface roughness having a height of 1% or more and less than 20% of a particle diameter of the first particles.

3. The contrast-ratio improving optical film according to claim 1, wherein a maximum distance between a first surface corresponding to a top portion of the patterned layer and an uppermost surface of the gap-fill layer is greater than 0 to 15 micrometers.

4. The contrast-ratio improving optical film according to claim 1, wherein the first particles have an average particle diameter that is smaller than a width of the first surface corresponding to a top portion of the embossed optical pattern.

5. The contrast-ratio improving optical film according to claim 1, wherein the first particles are present in the gap-fill layer in an amount of 1 to 50 wt%.

6. The contrast-ratio improving optical film according to claim 1, wherein the first particles comprise antiglare particles.

7. The contrast-ratio improving optical film according to claim 1, wherein a ratio W/L of the maximum width W of the embossed optical pattern to a width L of the flat section is in a range of 0.1 to 3.

8. The contrast-ratio improving optical film according to claim 1, wherein the first particles are formed of at least one of polymethyl methacrylate, polystyrene, and a copolymer of polymethyl methacrylate and styrene.

9. The contrast-ratio improving optical film according to claim 1, wherein the patterned layer is formed of a composition for the patterned layer, the composition comprising an aromatic-free base resin and high-refractive-index inorganic particles.

10. The contrast-ratio improving optical film according to claim 1, wherein the embossed optical pattern comprises an optical pattern having a trapezoidal, rectangular, or square cross-sectional shape.

11. The contrast-ratio improving optical film according to claim 1, wherein the gap filling layer further comprises second particles having a higher refractive index than the first particles.

12. A polarizing plate comprising:

a polarizing film; and

the contrast-ratio-improving optical film according to any one of claims 1 to 11, which is formed on a light exit surface of the polarizing film.

13. A liquid crystal display device comprising the polarizing plate according to claim 12.

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