KR102502464B1 - Composite polarizing plate and liquid crystal display device - Google Patents

Abstract

It includes an absorption-type polarizer, a reflection-type polarizer, and a blue light transmission suppression layer that suppresses transmission of blue light within a wavelength range of 380 to 500 nm, wherein the blue light transmission suppression layer has an average transmittance over a wavelength range of 500 to 780 nm. A composite polarizing plate having an average transmittance of 80% or less over a wavelength range of 380 to 500 nm and a liquid crystal display device using the same is provided.

Description

Composite polarizing plate and liquid crystal display {COMPOSITE POLARIZING PLATE AND LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a composite polarizing plate including an absorption type polarizing plate and a reflection type polarizing plate, and a liquid crystal display device using the same.

A polarizing plate is widely used in liquid crystal display devices, particularly in recent years, various mobile devices (small and medium-sized liquid crystal display devices) such as smart phones and tablet terminals. As a polarizing plate, an absorption type polarizing plate obtained by bonding a protective film to one or both surfaces of a polarizer (linear polarizer) in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film is generally used.

With the development of liquid crystal display devices into mobile devices, thin film weight reduction and cost reduction of polarizing plates are increasingly required, and on the other hand, improvement in display quality of liquid crystal display devices is also required. One of the display qualities is contrast. The contrast of the display device is expressed by the following formula:

Contrast of display device = (luminance at white display)/(brightness at black display)

is defined as Higher contrast means that a clearer black and white image can be obtained, and is frequently used as one of the indicators of visibility in display devices. Another display quality is luminance (brightness of a display screen). [0003] Along with the high-definition of liquid crystal panels in recent years, the demand for high luminance of liquid crystal display devices is also high.

Patent documents related to high contrast and high luminance of liquid crystal display devices include, for example, Japanese Patent No. 5147014 and Japanese Unexamined Patent Publication No. 2001-228332.

As one of the methods for improving the contrast, there is a method of improving the polarization performance of the absorption type polarizing plate, that is, the single transmittance and polarization degree. However, if the contrast is increased by increasing the degree of polarization, the single transmittance and thus the luminance decrease, and conversely, when the single transmittance is increased to increase the luminance, the degree of polarization and thus the contrast decrease. Therefore, only the polarization performance of the absorption polarizing plate is controlled. It was difficult to aim at coexistence of high luminance and high contrast by doing it.

In Japanese Patent No. 5147014, it is proposed to establish a specific relationship between the light emission wavelength characteristics of a backlight and the wavelength dependence of single-piece contrast of a polarizer possessed by an absorption type polarizing plate in order to improve the contrast of a liquid crystal display device. It was not easy to aim at coexistence of high contrast.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 2001-228332, in order to increase the luminance of a liquid crystal display device, there is a technique of disposing a reflective polarizing plate (also referred to as a luminance enhancing film) between an absorption polarizing plate on the backlight side and a backlight. It is known in the past. However, when a reflective polarizer is combined with an absorbing polarizer having a high single transmittance as an absorption polarizer to increase luminance, there is a problem that light leakage in a black display is increased and contrast is lowered.

An object of the present invention is to provide a composite polarizing plate comprising an absorption type polarizing plate and a reflection type polarizing plate, capable of realizing a liquid crystal display device with high luminance and high contrast, and a liquid crystal display device using the same.

The present invention provides a composite polarizing plate and a liquid crystal display device shown below.

[1] comprising an absorption type polarizer, a reflection type polarizer, and a blue light transmission suppression layer for suppressing transmission of blue light within a wavelength range of 380 to 500 nm;

Wherein the blue light transmission suppression layer has an average transmittance of 90% or more over a wavelength range of 500 to 780 nm and an average transmittance of 80% or less over a wavelength range of 380 to 500 nm.

[2] The composite polarizing plate according to [1], wherein the absorption type polarizing plate has a visibility-corrected single transmittance of 42.6 to 44.0% and a visibility-corrected polarization degree of 99.5% or more.

[3] The composite polarizing plate according to [1] or [2], wherein an angle formed between a reflection axis of the reflective polarizing plate and an absorption axis of the absorbing polarizing plate is 0±4°.

[4] The composite polarizing plate according to any one of [1] to [3], wherein the absorption type polarizing plate includes a polarizer and a resin film laminated on at least one surface thereof.

[5] The absorption polarizer includes the polarizer, a cellulose acetate-based resin film laminated on one side of the polarizer through an adhesive layer, and a cyclic polyolefin-based resin film laminated on the other side through an adhesive layer. The composite polarizing plate described in [4].

[6] The absorption type polarizing plate includes the polarizer and a cellulose acetate-based resin film or a cyclic polyolefin-based resin film laminated on one side of the polarizer through an adhesive layer,

The composite polarizing plate according to [4], wherein the reflective polarizing plate is laminated on the other surface of the polarizer or on the surface of the cellulose acetate-based resin film or the cyclic polyolefin-based resin film via an adhesive layer.

[7] A backlight, the composite polarizing plate according to any one of [1] to [6], and a liquid crystal cell are included in this order,

The liquid crystal display device of claim 1 , wherein the composite polarizing plate is arranged so that the absorption type polarizing plate is closer to the liquid crystal cell side than the reflection type polarizing plate.

[8] In the light emission spectrum measured with the liquid crystal cell stacked on the backlight and the backlight turned on, the light emission intensities at the emission peak wavelengths of blue, green, yellow, and red are L(Bmax) and L, respectively. (Gmax), when L (Ymax) and L (Rmax), the following formula (1) or the following formula (2):

L(Bmax)/L(Ymax) > 1 (1)

L(Bmax)/L(Gmax)>1, and also L(Bmax)/L(Rmax)>1 (2)

The liquid crystal display device according to [7], which satisfies.

According to the composite polarizing plate of the present invention, a high-brightness and high-contrast liquid crystal display device can be realized.

1 is a schematic cross-sectional view showing an example of the layer configuration of a composite polarizing plate according to the present invention.
Fig. 2 is a schematic cross-sectional view showing another example of the layer structure of the composite polarizing plate according to the present invention.
Fig. 3 is a schematic cross-sectional view showing another example of the layer configuration of the composite polarizing plate according to the present invention.
Fig. 4 is a schematic cross-sectional view showing an example of the layer structure of the liquid crystal display device according to the present invention.
5 is a graph showing an example of an emission spectrum measured by laminating a liquid crystal cell on a CCFL type backlight.
6 is a graph showing an example of an emission spectrum measured by laminating a liquid crystal cell on a backlight of a high color rendering type LED.
7 is a graph showing an example of an emission spectrum measured by laminating a liquid crystal cell on a backlight of a simulated white type LED.

<Composite polarizer>

A composite polarizing plate according to the present invention includes an absorption type polarizing plate, a reflection type polarizing plate, and a blue light transmission suppression layer (blue light cut layer) that suppresses transmission of blue light in a wavelength range of 380 to 500 nm. The transmission suppression layer has an average transmittance of 90% or more over a wavelength range of 500 to 780 nm, and an average transmittance of 80% or less over a wavelength range of 380 to 500 nm. The composite polarizer exhibits luminance enhancement performance by a combination of an absorption type polarizer and a reflection type polarizer, and at the same time has a high average transmittance in a wavelength range of 500 to 780 nm, and a blue light transmission suppression layer that effectively suppresses the transmission of blue light. Since it is further provided, leakage of blue light (blue leak) is effectively suppressed, and thus both good luminance enhancing performance and contrast enhancing performance are obtained. Accordingly, the liquid crystal display device equipped with the composite polarizing plate according to the present invention can have both high luminance and high contrast.

(1) Configuration of composite polarizer

Referring to the drawings, examples of the layer structure of the composite polarizing plate according to the present invention are as follows.

1 is a schematic cross-sectional view showing an example of the layer configuration of a composite polarizing plate according to the present invention. The composite polarizer 1 shown in FIG. 1 includes an absorption type polarizer 100, a reflection type polarizer 200 stacked thereon, and a blue light transmission suppression layer (blue light cut layer) 300 stacked thereon. Include in this order In the composite polarizing plate 1, the absorption type polarizing plate 100 includes a polarizer 5, a first protective film 10 laminated on one side of the polarizer through a first adhesive layer 15, and the other side. A polarizing plate with double-sided protective films having a second protective film (20) laminated on the second adhesive layer (25). The reflective polarizing plate 200 may be stacked on the absorption type polarizing plate 100 through the first adhesive layer 41 . In the composite polarizing plate 1 , the blue light transmission suppressing layer 300 is directly formed on the outer surface of the reflective polarizing plate 200 .

Fig. 2 is a schematic cross-sectional view showing another example of the layer structure of the composite polarizing plate according to the present invention. The composite polarizing plate 2 shown in FIG. 2 uses a blue light transmission suppression film (blue light cut film) 350 having a blue light transmission suppression layer 300 on one side of a base film 301, It has the same layer configuration as the composite polarizing plate 1 shown in FIG. 1 except that it is laminated and bonded to the outer surface of the reflective polarizing plate 200 through the two pressure-sensitive adhesive layers 42 . In this way, by using the blue light transmission suppression film 350 and bonding it to the reflective polarizing plate 200 through an adhesive layer (or adhesive layer, etc.), contrast enhancing performance (blue leak suppression function) can be imparted to the composite polarizing plate. may be

As shown in Fig. 3 (a) and (b), the absorption type polarizing plate may be a polarizing plate with a single-sided protective film. That is, in the composite polarizing plate 3 shown in (a) of FIG. 3 , the absorption type polarizing plate 110 includes the polarizer 5 and a first layer laminated on one side of the polarizer 5 via the first adhesive layer 15. It is a polarizing plate with a single-sided protective film provided with the protective film (10). The reflective polarizing plate 200 is laminated on the surface of the polarizer 5 opposite to the first protective film 10 via the first pressure sensitive adhesive layer 41 . In addition, the blue light transmission suppression layer 300 is directly formed on the outer surface of the reflective polarizing plate 200 .

On the other hand, the absorption type polarizing plate 120 constituting the composite polarizing plate 4 shown in FIG. 3 (b) is also laminated with the polarizer 5 and the first adhesive layer 15 on one side thereof. Although the first protective film 10 is provided, the reflective polarizing plate 200 is laminated on the outer surface of the first protective film 10 via the first adhesive layer 41 . The blue light transmission suppression layer 300 is directly formed on the outer surface of the reflective polarizing plate 200 . Also in the composite polarizing plates 3 and 4 shown in (a) and (b) of FIG. 3 , a blue light transmission suppression film 350 may be used instead of the blue light transmission suppression layer 300 .

The composite polarizers 1, 2, 3, and 4 may be other optical functional layers (or films) laminated on the outer surface of the first protective film 10, the polarizer 5, and/or the blue light transmission suppression layer 300, or You may further have a pressure-sensitive adhesive layer, a separate film laminated on the outer surface of the pressure-sensitive adhesive layer (also referred to as a "peeling film"), a protection film, and the like. The optical function layer (or film) may be interposed not on the outermost surface of the composite polarizing plate but inside.

(2) Optical Characteristics of Absorptive Polarizer

The absorptive polarizers 100, 110, and 120 preferably have a visibility corrected single transmittance (Ty) of 42.6 to 44.0%, more preferably 42.9 to 44.0%, from the viewpoint of both luminance improvement performance and contrast enhancement performance. And, it is more preferable that it is 42.9 to 43.5%. When Ty is less than 42.6%, the transmittance is too low and it is difficult to obtain a sufficiently high luminance. When Ty exceeds 44.0%, the contrast tends to decrease.

From the viewpoint of improving contrast, the absorption type polarizers 100, 110, and 120 preferably have a visibility correction polarization degree (Py) of 99.5% or more, more preferably 99.9% or more, and even more preferably 99.95% or more. The method for measuring the visibility-corrected single transmittance (Ty) and the visibility-corrected polarization degree (Py) is as described in the following Examples.

(3) Polarizer

The polarizer 5 is an absorption type polarizer having a property of absorbing linearly polarized light having a vibration plane parallel to the absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis), A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film can be suitably used. The polarizer 5 is, for example, a step of uniaxially stretching a polyvinyl alcohol-based resin film; a step of adsorbing the dichroic dye by dyeing the polyvinyl alcohol-based resin film with the dichroic dye; treating the polyvinyl alcohol-based resin film to which the dichroic dye is adsorbed with an aqueous solution of boric acid; And it can manufacture by the method including the process of washing with water after the process by boric acid aqueous solution.

As the polyvinyl alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group. In this specification, "(meth)acryl" means at least one selected from acryl and methacryl. The same applies when referring to "(meth)acryloyl" or the like.

The degree of saponification of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The average degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000. The average degree of polymerization of polyvinyl alcohol-based resin can be determined in accordance with JIS K 6726.

What produced such a polyvinyl alcohol-type resin into a film is used as a raw film of the polarizer 5. A method for forming a polyvinyl alcohol-based resin into a film is not particularly limited, and a known method is employed. The thickness of the polyvinyl alcohol-based raw film is, for example, 150 μm or less, and preferably 100 μm or less (eg, 50 μm or less).

Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing of the dichroic dye, simultaneously with dyeing, or after dyeing. When performing uniaxial stretching after dyeing, you may perform this uniaxial stretching before boric acid treatment or during boric acid treatment. Moreover, you may perform uniaxial stretching in these several steps.

In uniaxial stretching, it may be uniaxially stretched between rolls having different circumferential speeds, or it may be uniaxially stretched using a hot roll. Further, uniaxial stretching may be dry stretching in which stretching is performed in the air, or wet stretching in which stretching is performed in a state where a polyvinyl alcohol-based resin film is swollen using a solvent or water. The draw ratio is usually about 3 to 8 times.

As a method for dyeing a polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of immersing the film in an aqueous solution containing the dichroic dye is employed. As the dichroic dye, iodine or a dichroic organic dye is used. In addition, the polyvinyl alcohol-based resin film is preferably immersed in water before dyeing.

As the dyeing treatment with iodine, a method in which a polyvinyl alcohol-based resin film is immersed in an aqueous solution containing iodine and potassium iodide is usually adopted. The content of iodine in this aqueous solution may be about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide may be about 0.5 to 20 parts by weight per 100 parts by weight of water. Also, the temperature of this aqueous solution may be about 20 to 40°C. On the other hand, as a dyeing treatment with a dichroic organic dye, a method in which a polyvinyl alcohol-based resin film is immersed in an aqueous solution containing a dichroic organic dye is usually adopted. The aqueous solution containing the dichroic organic dye may contain an inorganic salt such as sodium sulfate as a dyeing aid. The content of the dichroic organic dye in this aqueous solution may be about 1×10 ^-4 to 10 parts by weight per 100 parts by weight of water. The temperature of this aqueous solution may be about 20 to 80°C.

As the boric acid treatment after dyeing with the dichroic dye, a method in which the dyed polyvinyl alcohol-based resin film is immersed in an aqueous solution containing boric acid is usually employed. When using iodine as a dichroic dye, it is preferable that this aqueous solution containing boric acid contains potassium iodide. The amount of boric acid in the aqueous solution containing boric acid may be on the order of 2 to 15 parts by weight per 100 parts by weight of water. The amount of potassium iodide in this aqueous solution may be about 0.1 to 15 parts by weight per 100 parts by weight of water. The temperature of this aqueous solution may be 50°C or higher, for example, 50 to 85°C.

The polyvinyl alcohol-based resin film after boric acid treatment is usually washed with water. Water washing treatment can be performed, for example, by immersing the polyvinyl alcohol-type resin film treated with boric acid in water. The water temperature in the water washing treatment is usually about 5 to 40°C. A drying process is performed after water washing, and the polarizer 5 is obtained. The drying treatment can be performed using a hot air dryer or a far-infrared heater.

Moreover, as another example of the manufacturing method of the polarizer 5, the method of Unexamined-Japanese-Patent No. 2000-338329 or the method of Unexamined-Japanese-Patent No. 2012-159778 is mentioned, for example. In this method, after forming a resin layer by applying a solution containing a polyvinyl alcohol-based resin to the surface of a base film, the laminated film composed of the base film and the resin layer is stretched, followed by dyeing treatment, crosslinking treatment, etc. By carrying out, a polarizer layer is formed from the resin layer. This light-polarizing laminated film composed of a base film and a polarizer layer is a polarizing plate with a single-sided protective film having a protective film or the like on one side of the polarizer 5 by peeling off the base film after bonding a protective film or the like to the polarizer layer surface. can be done with When a protective film is further bonded to the surface of the polarizer layer exposed by peeling of the base film, it becomes a polarizing plate with double-sided protective films.

The thickness of the polarizer 5 can be 40 μm or less, preferably 30 μm or less (for example, 20 μm or less, more preferably 15 μm or less, more preferably 10 μm or less). According to the method described in Japanese Unexamined Patent Publication No. 2000-338329 or Japanese Unexamined Patent Publication No. 2012-159778, the thin film polarizer 5 can be manufactured more easily, and the thickness of the polarizer 5 can be reduced to, for example, 20 It becomes easier to set it as micrometer or less, Furthermore, 15 micrometer or less, and furthermore, 10 micrometer or less. The thickness of the polarizer 5 is 2 micrometers or more normally. Reducing the thickness of the polarizer 5 is advantageous for reducing the thickness of the composite polarizing plate and consequently the liquid crystal display device.

In the polarizer 5 obtained by the above method, as a specific method for adjusting the visibility corrected single transmittance (Ty) and the visibility corrected polarization degree (Py) within the above preferred numerical range, for example, in an aqueous solution used for dyeing treatment Methods of adjusting the concentration of the dichroic dye, the dyeing temperature, and the dyeing time, or adjusting the temperature and time in the drying treatment are exemplified.

(4) first and second protective films

The first and second protective films 10 and 20 may each be a resin film, specifically, a light-transmitting (preferably optically transparent) resin, such as a chain polyolefin-based resin (polypropylene-based resin). etc.), polyolefin-based resins such as cyclic polyolefin-based resins (norbornene-based resins, etc.); cellulose acetate-based resins such as triacetyl cellulose and diacetyl cellulose; polyester-based resin; polycarbonate-based resin; (meth)acrylic resin; polystyrene-based resin; Alternatively, it may be a film made of a thermoplastic resin such as a mixture or copolymer thereof. In the absorption type polarizing plate 100 with double-sided protective films, the first protective film 10 and the second protective film 20 may be protective films made of the same type of resin or different types of resins. .

The first and/or second protective films 10 and 20 may be protective films having an optical function such as a retardation film. For example, a retardation film having an arbitrary retardation value can be obtained by stretching the film made of the thermoplastic resin (eg, uniaxial stretching or biaxial stretching) or forming a liquid crystal layer or the like on the film.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resins and polypropylene resins, as well as copolymers composed of two or more types of chain olefins.

Cyclic polyolefin resin is a generic term for resins polymerized using cyclic olefins as polymerization units. Specific examples of cyclic polyolefin-based resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically random copolymers). ), graft polymers modified with unsaturated carboxylic acids or derivatives thereof, and hydrides thereof. Among them, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer as the cyclic olefin is preferably used.

The cellulose acetate-based resin is a partial or complete acetate ester product of cellulose, and examples thereof include triacetyl cellulose (TAC), diacetyl cellulose, and cellulose acetate propionate.

Polyester-based resins are resins other than the above cellulose acetate-based resins that have ester bonds, and are generally composed of polycondensates of polyhydric carboxylic acids or derivatives thereof and polyhydric alcohols. Dicarboxylic acids or derivatives thereof can be used as polyhydric carboxylic acids or derivatives thereof, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalene dicarboxylic acid. As the polyhydric alcohol, diols can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol.

Specific examples of the polyester-based resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexane dimethyl terephthalate, and polycyclohexane. Contains dimethylnaphthalate.

A polycarbonate-type resin consists of a polymer to which monomer units are bonded via a carbonate group. The polycarbonate-based resin may be a resin called a modified polycarbonate obtained by modifying a polymer skeleton, a copolymerized polycarbonate, or the like.

A (meth)acrylic resin is a resin that uses a compound having a (meth)acryloyl group as a main constituent monomer. Specific examples of the (meth)acrylic resin include poly(meth)acrylic acid esters such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-(meth)acrylic acid ester copolymer; methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer; methyl (meth)acrylate-styrene copolymers (such as MS resin); and copolymers of methyl methacrylate and a compound having an alicyclic hydrocarbon group (eg, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). Preferably, a polymer containing poly(meth)acrylic acid C _1-6 alkyl ester as a main component such as poly(meth)acrylate is used, more preferably, methyl methacrylate as a main component (50 to 100% by weight, Preferably 70 to 100% by weight) of methyl methacrylate-based resin is used.

On the surface of the first and/or second protective films 10 and 20 opposite to the polarizer 5, a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer is formed. You may.

The thickness of the first and second protective films 10 and 20 is preferably 90 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less, from the viewpoint of thinning the composite polarizing plate and the liquid crystal display device. am. The said thickness is usually 5 micrometers or more from a viewpoint of strength and handleability.

As an example of a preferred embodiment of the absorption type polarizing plate, for example, the first protective film 10 is a cyclic polyolefin-based resin film (norbornene-based resin film or the like), and the second protective film 20 is a cellulose acetate-based resin An absorption type polarizing plate 100 with a double-sided protective film, which is a film (such as a TAC film), and the first protective film 10 is a cyclic polyolefin-based resin film (such as a norbornene-based resin film) or a cellulose acetate-based resin film ( TAC film, etc.) and the absorption type polarizing plates 110 and 120 with a single-sided protective film. In these embodiments, the first protective film 10 may be a retardation film having an in-plane retardation value and/or a thickness direction retardation value according to the type of liquid crystal cell or the like.

It is also one of preferable embodiments to make the at least 1 protective film bonded to the polarizer 5 into a resin film with low moisture permeability. Thereby, deterioration of the optical characteristic of the polarizer 5 in a high-humidity environment or a high-temperature, high-humidity environment can be suppressed. The water vapor transmission rate of the protective film is preferably 400 g/m ² 24 hr or less, more preferably 300 g/m ² 24 hr or less, still more preferably 100 It is g/m ² ·24 hr or less, particularly preferably 50 g/m ² ·24 hr or less.

(5) first and second adhesive layers

As the adhesive forming the first and second adhesive layers 15 and 25, a water-based adhesive or an active energy ray-curable adhesive can be used. The adhesive forming the first adhesive layer 15 and the adhesive forming the second adhesive layer 25 may be of the same type or may be of different types.

Examples of the water-based adhesives include adhesives made of an aqueous polyvinyl alcohol-based resin solution, water-based two-component urethane emulsion adhesives, and the like. Among them, a water-based adhesive composed of a polyvinyl alcohol-based resin aqueous solution is preferably used.

As the polyvinyl alcohol-based resin, besides the vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl alcohol-based copolymer obtained by saponifying a copolymer of vinyl acetate and other monomers copolymerizable therewith , or modified polyvinyl alcohol-based polymers obtained by partially modifying their hydroxyl groups. The water-based adhesive may contain an additive such as a polyhydric aldehyde, a water-soluble epoxy compound, a melamine-based compound, a zirconia compound, or a zinc compound.

When using a water-based adhesive agent, after bonding the polarizer 5 and the protective film together, it is preferable to perform a drying process to be dried in order to remove water contained in the water-based adhesive agent. You may provide the curing process of curing at the temperature of about 20-45 degreeC after a drying process, for example.

The active energy ray-curable adhesive refers to an adhesive that is cured by irradiating active energy rays such as ultraviolet rays, and includes, for example, a polymerizable compound and a photopolymerization initiator, a photoreactive resin, a binder resin, and a photoreactive crosslinking agent. and the like including. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable (meth)acrylic monomers, and photocurable urethane monomers, and oligomers derived from photopolymerizable monomers. Examples of the photopolymerization initiator include substances that generate active species such as neutral radicals, anion radicals, and cation radicals when irradiated with active energy rays such as ultraviolet rays. As the active energy ray-curable adhesive containing a polymerizable compound and a photopolymerization initiator, one containing a photocurable epoxy-based monomer and a photocationic polymerization initiator can be preferably used.

When using an active energy ray-curable adhesive, after bonding polarizer 5 and a protective film, a drying process is performed as needed, and then the hardening process of hardening an active energy ray-curable adhesive by irradiating an active energy ray is performed. The light source of the active energy ray is not particularly limited, but an ultraviolet ray having a luminous distribution with a wavelength of 400 nm or less is preferable, and specifically, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultra-high pressure mercury lamp, a chemical lamp, a black light lamp, and a microwave excitation A mercury vapor lamp, a metal halide lamp, or the like can be used.

Prior to bonding of the polarizer 5 and the protective film using an adhesive, if necessary, surface activation treatment on the bonding surface of the polarizer 5 and / or the bonding surface of the protective film, such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame You may perform (flame) treatment, saponification treatment, etc.

(6) pressure-sensitive adhesive layer and other layers

On the outer surface of the first protective film 10 in the absorption type polarizers 100 and 110 or the outer surface of the polarizer 5 in the absorption type polarizer 120, a composite polarizer is applied to another member (for example, a liquid crystal display device). You may laminate|stack the adhesive layer for bonding to the liquid crystal cell in a case, or another optical film) (refer FIG. 4, for example). The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually made of a pressure-sensitive adhesive composition in which a (meth)acrylic resin, a styrene resin, a silicone resin, or the like is used as a base polymer, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. . Moreover, it can also be set as the adhesive layer which contains microparticles|fine-particles and shows light-scattering property. The thickness of the pressure-sensitive adhesive layer may be 1 to 40 μm, but it is preferable to form a thin layer within a range that does not impair workability and durability, and specifically, it is preferable to be 3 to 25 μm.

The method for forming the pressure-sensitive adhesive layer is not particularly limited, and the pressure-sensitive adhesive composition (pressure-sensitive adhesive solution) containing each component including the base polymer described above may be coated on the surface of a protective film or the like, and then dried to form an pressure-sensitive adhesive layer. After forming an adhesive layer on a film (release film), you may transfer this adhesive layer to the surface of a protective film etc. When forming the pressure-sensitive adhesive layer on the surface of the protective film or the like, surface activation treatment such as plasma treatment, corona treatment, or the like may be applied to the bonding surface of the protective film or the like and/or the bonding surface of the pressure-sensitive adhesive layer, if necessary.

The above description of the pressure-sensitive adhesive layer can also be applied to the first pressure-sensitive adhesive layer 41 shown in FIGS. 1 and 3 and the second pressure-sensitive adhesive layer 42 shown in FIG. 2 .

The polarizing plate may include a separate film laminated on the outer surface of the pressure-sensitive adhesive layer. The separation film may be a film made of polyethylene-based resins such as polyethylene, polypropylene-based resins such as polypropylene, and polyester-based resins such as polyethylene terephthalate. Especially, the stretched film of polyethylene terephthalate is preferable.

On the outer surface of the first protective film 10 in the absorption type polarizers 100 and 110 or the outer surface of the polarizer 5 in the absorption type polarizer 120, for example, through an adhesive layer or a pressure-sensitive adhesive layer, other than the absorption type polarizer You may laminate|stack the optical film which has the optical function of. As such an optical film, an optical compensation film in which a liquid crystalline compound is applied to the surface of a substrate and is aligned; and retardation films made of polycarbonate-based resins and cyclic polyolefin-based resins.

(7) Manufacturing method of absorption type polarizing plate

By attaching the first protective film 10 to one side of the polarizer 5 described above through the first adhesive layer 15 according to a conventional method, the single-side protective film attachment shown in (a) and (b) of FIG. Absorptive polarizers 110 and 120 may be obtained. In addition, when the second protective film 20 is bonded to the other side of the polarizer 5 through the second adhesive layer 25, the absorption type polarizing plate 100 with double-sided protective films shown in FIGS. 1 and 2 is obtained In the case of obtaining the absorption type polarizing plate 100, the first and second protective films 10 and 20 may be bonded simultaneously or sequentially.

It is not limited to the method of bonding a protective film to the polarizer 5 which consists of a single-piece|unit (single) film, As mentioned above, using the base film for supporting the polyvinyl alcohol-type resin layer and polarizer in a manufacturing process, an absorption type A polarizing plate may be produced. In this case, the absorption type polarizing plates 110 and 120 with a single-sided protective film are, for example, the following steps:

A resin layer forming step of obtaining a laminated film by coating a coating solution containing a polyvinyl alcohol-based resin on at least one surface of a base film and then drying it to form a polyvinyl alcohol-based resin layer;

A stretching step of obtaining a stretched film by uniaxially stretching the laminated film;

A dyeing step of obtaining a polarizing laminated film by dyeing the polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to form a polarizer 5;

1st bonding process of bonding the 1st protective film 10 on the polarizer 5 of a polarizing laminated film, and obtaining a bonding film,

Peeling step of peeling and removing the substrate film from the bonding film to obtain the absorption type polarizing plate 110, 120 with a single-sided protective film

It can be prepared by a method including in this order.

In the case of manufacturing the absorption type polarizing plate 100 with a double-sided protective film shown in FIGS. 1 and 2, the manufacturing method of the absorption type polarizing plate is, after the peeling step,

A second bonding step of bonding the second protective film 20 to the polarizer 5 side surface of the absorption type polarizers 110 and 120.

more includes

(8) a reflective polarizer, and lamination of the reflective polarizer to the absorption polarizer

The reflective polarizer 200 is a polarization conversion element having a function such as separating backlight light into transmitted polarized light and reflective polarized light or scattered polarized light. By disposing the reflective polarizer 200 on the absorption polarizers 100, 110, and 120, the efficiency of using backlight can be improved, and thus the luminance of the liquid crystal display can be improved. As the reflective polarizing plate 200, a commercially available one may be used. In the case of constructing a liquid crystal display device by laminating a composite polarizing plate on a liquid crystal cell, the reflective polarizing plate 200 is disposed on a surface opposite to the liquid crystal cell in the absorption type polarizing plates 100, 110, and 120.

The reflective polarizer 200 may be, for example, an anisotropic reflective polarizer. An example of an anisotropic reflective polarizer is an anisotropic multiple thin film that transmits linearly polarized light in one vibration direction and reflects linearly polarized light in the other vibration direction. -268505, etc.), and "APF" (manufactured by 3M, available from Sumitomo 3M Co., Ltd.). Another example of the anisotropic reflective polarizer is a composite of a cholesteric liquid crystal layer and a λ/4 plate, and a specific example thereof is "PCF" manufactured by Nitto Denko (Japanese Patent Laid-Open No. 11-231130, etc.). Another example of the anisotropic reflective polarizer is a reflective grid polarizer, and specific examples thereof include a metal lattice reflective polarizer that emits reflective polarized light even in the visible light region by performing microprocessing on metal (US Patent No. 6288840 specification, etc.); It is a film (Japanese Unexamined Patent Publication No. 8-184701) obtained by adding metal fine particles to a polymer matrix and stretching the film.

The thickness of the reflective polarizing plate 200 may be about 10 to 100 μm, but is preferably 10 to 50 μm from the viewpoint of thinning the composite polarizing plate and the liquid crystal display device. The reflective polarizer 200 may be stacked on the absorption type polarizers 100, 110, and 120 through the first adhesive layer 41, as shown in FIGS. 1 to 3 . However, it is also possible to bond using an adhesive. 1 and 2, the reflective polarizing plate 200 is laminated on the second protective film 20 via the first adhesive layer 41, and in FIG. 3(a), the reflective polarizing plate 200 ) is laminated on the polarizer 5 via the first pressure sensitive adhesive layer 41, and in FIG. It is laminated on the film 10. On the surface of the reflective polarizing plate 200 opposite to the pressure-sensitive adhesive layer 30, an optical functional layer such as a hard coat layer, an antiglare layer, a light diffusion layer, and a retardation layer having a retardation value of 1/4 wavelength (retardation film) is formed. may be arranged In addition, a protective film or a retardation film may be disposed between the reflective polarizing plate 200 and the blue light transmission suppression layer 300 .

The reflective polarizer 200 is placed on the absorption polarizer 100, 110, or 120 so that the angle α formed between the reflection axis and the absorption axis of the absorption polarizer 100, 110, or 120 is parallel or approximately parallel. It is preferable to laminate on. Parallel or substantially parallel means specifically that the angle α is 0±4°. When the angle α is within the above range, it is advantageous in terms of suppressing light leakage during black display and improving the contrast of the liquid crystal display device. The method for measuring the angle α is as described in the following embodiment section.

(9) Blue light transmission suppression layer

The blue light transmission suppression layer 300 is a layer that suppresses transmission of blue light within the wavelength range of 380 to 500 nm, and preferably suppresses transmission of blue light over the entire wavelength range. In order to impart good luminance enhancement performance to the composite polarizing plate, the blue light transmission suppression layer 300 has an average transmittance T(500-780) over a wavelength range of 500 to 780 nm of 90% or more, preferably 95% or more. am. In addition, in order to impart good contrast enhancement performance to the composite polarizing plate, the blue light transmission suppression layer 300 has an average transmittance T(380-500) over a wavelength range of 380 to 500 nm of 80% or less, preferably 75 less than % The average transmittance T (500-780) of the blue light transmission suppression layer 300 over the wavelength range of 500 to 780 nm is obtained by measuring the transmittance at each wavelength (5 nm pitch) using a spectrophotometer, It can be obtained by finding the average of these over the wavelength region of nm. The same applies to the average transmittance T (380-500) over the wavelength range of 380 to 500 nm.

As shown in FIG. 2 , the blue light transmission suppression layer 300 is introduced into the composite polarizing plate in the form of a blue light transmission suppression film 350 having the blue light transmission suppression layer 300 on one side of the base film 301. You may. However, the blue light transmission suppression layer 300 does not need to be laminated on the surface of the base film 301, and is, for example, a three-layer structure film having the blue light transmission suppression layer 300 as an inner layer of the base film 301. It may be formed inside, or the blue light transmission suppression layer 300 may be the base film 301 itself which has a blue light transmission suppression function.

The base film 301 can be formed of a thermoplastic resin having light transmission properties (preferably optically transparent), and the description relating to the protective film described above is cited for specific examples thereof. Among them, the base film 301 is preferably composed of a resin selected from the group consisting of cyclic polyolefin-based resins, polycarbonate-based resins, cellulose ester-based resins, polyester-based resins, and (meth)acrylic-based resins. .

The base film 301 may have retardation characteristics, and may be, for example, a retardation plate (retardation film) such as a λ/2 plate or a λ/4 plate. Preferably it is a λ/4 plate. A liquid crystal display device is constructed by imparting retardation characteristics to the base film 301 and laminating the composite polarizing plate on the outside of the reflective polarizing plate 200 (a liquid crystal cell) with the base film 301 (preferably a λ/4 plate). In this case, better luminance improvement performance can be imparted to the composite polarizing plate by arranging it on the liquid crystal cell (and on the side opposite to the absorption polarizing plate 100, 110, 120) in the reflective polarizing plate 200.

When the base film 301 is a λ/4 plate, the blue light transmission suppression film 350 has a direction in which the slow axis of the base film 301 is approximately counterclockwise with respect to the direction of the reflection axis of the reflective polarizing plate 200. It is arranged to tilt at 45° or approximately 135°. Approximately 45° means 45°±20°, and approximately 135° means 135°±20°. When the angle θ ₁ of the slow axis of the base film 301 with respect to the direction of the reflection axis of the reflective polarizing plate 200 is outside the above range, the effect of improving the luminance tends to be insufficient. The angle θ ₁ (relative to the direction of the reflection axis of the reflective polarizer 200, counterclockwise) is preferably in the range of 45±10° or 135±10°, more preferably 45±5° or 135°. It is within the range of ±5°. The base film 301, which is a retardation plate, is a stretched film composed of a resin selected from the group consisting of cyclic polyolefin-based resins, polycarbonate-based resins, cellulose ester-based resins, polyester-based resins, and (meth)acrylic-based resins. can

The thickness of the blue light transmission suppression layer 300 is, for example, 0.1 to 100 μm, and the thickness of the blue light transmission suppression film 350 composed of the blue light transmission suppression layer 300 and the base film 301 is, for example, 5 to 300 μm. am. As the blue light transmission suppression layer 300 and the blue light transmission suppression film 350, those having conventionally known structures can be used, and commercial products can also be used.

The blue light transmission suppression layer 300 and the blue light transmission suppression film 350 for suppressing the transmission of blue light suppress transmission by absorbing the blue light (absorption type) and suppress transmission by reflecting the blue light ( reflective type). In the present invention, any type can be used.

A disposition position of the blue light transmission suppression layer 300 or the blue light transmission suppression film 350 in the composite polarizing plate is not particularly limited. For example, as in the examples of FIGS. 1 to 3 , the absorption type polarizers 100 , 110 , and 120 , the reflection type polarizer 200 , the blue light transmission suppression layer 300 or the blue light transmission suppression film 350 are arranged in this order. To be disposed, the blue light transmission suppression layer 300 or the blue light transmission suppression film 350 may be disposed on the opposite side of the absorption type polarizers 100, 110, and 120 in the reflective polarizer 200, or in a position other than that ( For example, it may be disposed on the side opposite to the reflection type polarizer 200 in the absorption type polarizers 100, 110, and 120 or between the absorption type polarizers 100, 110, and 120 and the reflection type polarizer 200.

When the blue light transmission suppression layer 300 or the blue light transmission suppression film 350 is of a reflective type, in the case of constructing a liquid crystal display device by laminating a composite polarizing plate on a liquid crystal cell, the blue light transmission suppression layer 300 or the blue light transmission suppression film When 350 is disposed between the liquid crystal cell and the absorption type polarizers 100, 110 and 120 or between the absorption type polarizers 100, 110 and 120 and the reflection type polarizer 200, the blue light transmission suppression layer 300 or The blue light transmission suppression film 350 may serve as a polarization depolarization element. Therefore, in the case of the reflective type, the blue light transmission suppression layer 300 or the blue light transmission suppression film 350 is preferably disposed on the opposite side of the absorption type polarizers 100, 110, and 120 in the reflection type polarizer 200. .

(10) Characteristics of composite polarizer

According to the composite polarizing plate of the present invention, the luminance and contrast of a liquid crystal display device to which the same is applied can be increased. The luminance of a liquid crystal display device can be measured with a commercially available luminance meter or spectroradiometer. The luminance values measured by these measurement devices are corrected for visibility.

On the other hand, although the luminance and contrast of the liquid crystal display device can be evaluated by actually constructing the liquid crystal display device and directly measuring the luminance and contrast, the transmittance at each wavelength λ of the composite polarizing plate (T _x (λ) or T _y (λ)) is multiplied by the light emission intensity (P(λ)) of each wavelength λ in the "combination of liquid crystal cell and backlight", and the luminance (L) at the time of white display after luminous sensitivity correction is performed (= Equation (3) below) numerator of ), and the contrast (S _CR ) defined by the ratio of the luminance (L) at the time of white display and the luminance at the time of black display (= the denominator of Equation (3) below) may be evaluated as indicators, respectively. Luminance (L) and contrast (S _CR ) as these indicators may be values in the wavelength range of 380 to 780 nm, and are respectively L (380-780) and S _CR (380-780). The higher L(380-780) and S _CR (380-780), the higher the luminance and contrast of the liquid crystal display device.

S _CR (380-780) is the following formula (3):

is defined as The numerator on the right side in equation (3) is the integrated value of P(λ)·y(λ)·T _X (λ) at wavelengths of 380 to 780 nm, and the denominator is P(λ) at wavelengths of 380 to 780 nm. )·y(λ)·T It is the integrated value of _Y (λ). In the present invention, in the actual measurement of S _CR (380-780), these integrated values are respectively P(λ)·y(λ)·T _X (λ), P(λ)· It is obtained as the sum of y(λ)·T _Y (λ) measured at a pitch of 5 nm.

In the above formula (3), P(λ) is the luminous intensity measured in a state where a liquid crystal cell is stacked on a backlight and the backlight is turned on, and y(λ) is a 2-degree field color matching function [photopic time It is the non-visibility function in 所視). In addition, T _x (λ) and T _y (λ) are the following formulas (4) and (5), respectively:

T _X (λ)= 0.5×[Tp(λ) ² +Tc(λ) ² ]/100 (4)

T _Y (λ)=Tp(λ)×Tc(λ)/100 (5)

is indicated by

Tp(λ) in the above equations (4) and (5) is the transmittance (%) of the composite polarizer measured in terms of the relationship between linear polarized light and parallel Nicols of the incident wavelength λ nm, and Tc(λ) is the incident It is the transmittance (%) of the composite polarizer measured in relation to the linearly polarized light of wavelength λ nm and crossed Nicols. A spectrophotometer is used as a measuring device for Tp(λ) and Tc(λ). In order to more accurately evaluate the Tc(λ) value, it is necessary to use a spectrophotometer capable of measuring up to a higher absorbance range, and specifically, a spectrophotometer capable of measuring absorbances of about 7 to 8 is used. As such a spectrophotometer, Nippon Spectroscopy Co., Ltd. product spectrophotometer "V7100" etc. are mentioned. As a method of receiving linearly polarized light, a method using a polarizing prism made of calcite or the like is generally known, and the extinction ratio of the polarizing prism is set to 10 ^-5 or less.

When all of the constituent layers included in the composite polarizer (eg, a protective film of an absorption type polarizer, a base film of a blue light transmission suppression film, etc.) do not substantially have retardation characteristics (specifically, in-plane retardation at a wavelength of 590 nm ( _Re ) and thickness direction retardation value (R _th ) of 10 nm or less), or even if it has retardation characteristics, if its slow axis is parallel or orthogonal to the absorption axis of the polarizer, the composite polarizer as it is S _CR (380-780) can be used as a measurement sample. On the other hand, when layers having phase difference characteristics are disposed on both surfaces of the polarizer and their slow axes are neither parallel nor orthogonal to the absorption axis of the polarizer, Tp(λ) and Tc(λ) are determined by the phase difference. Since it becomes impossible to measure accurately, for example, if the protective film of the absorption polarizing plate has retardation characteristics, the protective film is peeled off from the absorption polarizing plate and the reflective polarizing plate and the blue light transmission suppression layer are laminated, or the absorption polarizing plate is laminated. A sample obtained by laminating a reflective polarizing plate and a blue light transmission suppression layer on the same polarizer as that contained in the type polarizing plate was used as a measurement sample.

The in-plane retardation value (R _e ) and the thickness direction retardation value (R _th ) are, respectively, the following formulas:

R _e =(n _x -n _y )×d

R _th =[(n _x +n _y )/2-n _z ]×d

is defined as In the formula, n _x is the refractive index in the slow axis direction (x-axis direction) within the film plane, n _y is the refractive index in the fast axis direction (y-axis direction orthogonal to the x-axis within the plane) within the film plane, and n _z is It is the refractive index in the film thickness direction (the z-axis direction perpendicular to the film plane), and d is the thickness of the film.

In the composite polarizing plate according to the present invention, from the viewpoint of the contrast of the liquid crystal display device, the S _CR (380-780) is preferably 30000 or more, and more preferably 40000 or more.

<Liquid crystal display device>

Referring to FIG. 4 showing an example of the layer configuration of the liquid crystal display device according to the present invention, the liquid crystal display device according to the present invention includes a backlight 60, the composite polarizing plate according to the present invention, and a liquid crystal cell 50. include in order FIG. 4 is an example of using the composite polarizing plate 1 shown in FIG. 1 as a composite polarizing plate. The composite polarizers 1, 2, 3, and 4 are usually used as rear-side (backlight-side) polarizers, and the absorption type polarizers 100, 110, and 120 are on the side of the liquid crystal cell 50 rather than the reflection type polarizer 200. are arranged so that Further, when the composite polarizers 1, 2, 3, and 4 include the absorption polarizers 100, 110, and 120, the reflection polarizer 200, and the blue light transmission suppression layer 300 in this order, blue light The transmission suppression layer 300 is on the backlight 60 side. The composite polarizing plates 1 , 2 , 3 , and 4 can be stacked on the liquid crystal cell 50 via the third pressure sensitive adhesive layer 43 . The drive system of the liquid crystal cell 50 may be any conventionally known system, but in-plane switching (IPS) and vertical alignment (VA) modes are preferable.

The liquid crystal display device usually further includes a front-side (visible-side) polarizer 70 stacked on a surface opposite to the surface on which the rear-side polarizer (composite polarizer related to the present invention) is stacked in the liquid crystal cell 50. . The front-side polarizing plate 70 may also be laminated on the liquid crystal cell 50 via an adhesive layer. A front-side polarizer 70, a liquid crystal cell 50, and a rear-side polarizer constitute a liquid crystal panel.

When the liquid crystal cell 50 is stacked on the backlight 60 without stacking the composite polarizing plate and the backlight 60 is turned on, the spectrum of light emitted through the liquid crystal cell 50 is not the same in all wavelengths, and is different for each wavelength. strength exists. This intensity is determined by the light emission spectrum from the backlight and the design of the color filter included in the liquid crystal cell 50 .

5 to 7 show examples of emission spectra measured in a state where a liquid crystal cell is stacked on a backlight and the backlight is turned on. 5 is an example of using a cold cathode fluorescent lamp (CCFL) for a backlight, FIG. 6 is an example of using a light emitting diode (LED) of a high color rendering type, and FIG. 7 is an example of using a simulated white type LED. example of using Since the design of the color filter of the liquid crystal cell is important for color production of the liquid crystal display device, there are differences in design between each company, but it is composed of three colors of red (R), green (G), and blue (B). many. Since the principle of light emission differs depending on the type of backlight, the shape of the light emission spectrum when a liquid crystal cell is laminated on a backlight is also characteristic to some extent.

The shape of the emission spectrum when a liquid crystal cell is stacked on a backlight is roughly divided into two types. One type is a type including three emission peaks of blue (B), green (G), and red (R), as shown in FIGS. 5 and 6 (hereinafter, also referred to as BGR type). Another type is a type including two emission peaks of blue (B) and yellow (Y), as shown in FIG. 7 (hereinafter, also referred to as BY type).

According to the composite polarizing plate according to the present invention, it is possible to realize a high-luminance and high-contrast liquid crystal display device in any type of emission spectrum, but the present invention is particularly effective in an emission spectrum with high emission intensity in the blue region. That is, when it is desired to obtain high luminance by relatively increasing the visibility correcting single transmittance (Ty) of the absorption type polarizer included in the composite polarizer, the absorbance in the blue region of the absorption type polarizer is generally low, and light in this wavelength range is used for black display. Since there is a tendency to cause light leakage (blue leak) in particular, according to the composite polarizing plate according to the present invention including the blue light transmission suppression layer, light leakage in the blue region with high emission intensity can be effectively suppressed. A liquid crystal display device having high luminance and high contrast can be provided.

In the luminescence spectrum measured with a liquid crystal cell stacked on a backlight and the backlight turned on, the luminescence spectrum having a high luminescence intensity in the blue region is, specifically, in the BY type, the following formula (1):

L(Bmax)/L(Ymax) > 1 (1)

, and in the BGR type, the following formula (2):

L(Bmax)/L(Gmax)>1, and also L(Bmax)/L(Rmax)>1 (2)

means to satisfy

In the above formulas (1) and (2), Bmax, Gmax, Ymax and Rmax represent the emission peak wavelengths of blue, green, yellow and red, respectively, and L(Bmax), L(Gmax), L(Ymax) and L (Rmax) represents the emission intensity at the emission peak wavelengths Bmax, Gmax, Ymax and Rmax, respectively.

For example, an LED backlight type, such as a mobile phone liquid crystal display, has clear peaks as shown in FIGS. 6 and 7 and is very easy to understand. In some cases, it is composed of a plurality of fine peaks. Therefore, Bmax is set as the emission peak wavelength of the peak having the largest integrated area among emission peaks having emission peak wavelengths between 380 and 500 nm. The peak wavelength is determined by performing an appropriate fitting method such as normal distribution approximation as necessary, without counting minute jumps such as noise as peaks. Similarly, Gmax and Ymax are the emission peak wavelengths of the peaks having the largest integrated area among emission peaks having an emission peak wavelength of 500 to 570 nm, and Rmax is an emission peak having an emission peak wavelength of 570 to 700 nm. It is the emission peak wavelength of the peak at which the integrated area is maximized.

In general, the emission spectrum measured in a state where a liquid crystal cell is laminated on a backlight and the backlight is turned on is the following formula (6) for the BY type:

(Ymax-550)<(550-Bmax) (6)

satisfies, and in the BGR type, the following formula (7):

(Rmax-550)<(550-Bmax) (7)

satisfies

"550" in the above equations (6) and (7) considers light at a wavelength of approximately 550 nm, to which the human eye has the highest sensitivity, and these equations represent red or yellow color when the luminance corrected for visibility is measured. This means that blue light is measured weakly compared to light. In a liquid crystal display device for mobile use such as a mobile phone or PDA using a white LED or the like for a backlight, since the peak on the long-wavelength side is restricted, in principle, in particular, equations (1) and (6) or equation (2) ) and (7). However, even in a large TV or the like using a CCFL type backlight, it is preferable to satisfy the above formula from the viewpoint of color production and the like.

Example

Hereinafter, Examples and Comparative Examples are disclosed to explain the present invention more specifically, but the present invention is not limited by these examples.

(Thickness of polarizer, protective film and reflective polarizer)

It was measured using a digital micrometer "MH-15M" manufactured by Nikon Co., Ltd.

(Average Transmittance of Blue Light Cut Film)

A spectrophotometer with an integrating sphere ["V7100" manufactured by Nippon Spectroscopy Co., Ltd., 2-degree field of view; C light source] was used to measure the transmittance at each wavelength (5 nm pitch). The average of these over the wavelength range of 380 to 500 nm is obtained, this is regarded as the average transmittance T (380-500) over the wavelength range of 380 to 500 nm, and the average of these over the wavelength range of 500 to 780 nm is obtained. , and this was taken as the average transmittance T (500-780) over the wavelength range of 500 to 780 nm. It can be said that the average transmittance of the blue light cut film is substantially equal to the average transmittance of the blue light transmission suppression layer it has.

(Visibility-corrected single transmittance and visibility-corrected polarization degree of absorption type polarizer)

The single transmittance and polarization degree are respectively expressed by the following formula:

Single transmittance (λ)=0.5×(Tp(λ)+Tc(λ))

Degree of polarization (λ)=100×(Tp(λ)-Tc(λ))/(Tp(λ)+Tc(λ))

is defined as Tp(λ) is the transmittance (%) of the absorption-type polarizer measured in terms of the relationship between linearly polarized light with an incident wavelength of λ nm and parallel Nicols, and Tc(λ) is the transmittance of linearly polarized light with an incident wavelength of λ nm and crossed Nicols. It is the transmittance (%) of the absorption type polarizer measured by the relationship.

Visibility correction single transmittance (Ty) and visibility correction polarization degree (Py) are corrected for visibility by the 2-degree field of view (C light source) of JIS Z 8701 with respect to the single transmittance (λ) and polarization degree (λ) obtained for each wavelength. was performed, and a spectrophotometer with an integrating sphere ["V7100" manufactured by Nippon Spectroscopy Co., Ltd., 2-degree field of view; C light source]. In addition, the measurement was performed with an absorption type polarizing plate alone. During the measurement, the incident light was set to be incident on the side opposite to the surface to be bonded to the reflective polarizing plate. Ty and Py were measured at a pitch of 5 nm in a wavelength range of 380 to 780 nm.

(The angle between the reflection axis of the reflective polarizer and the absorption axis of the absorption polarizer)

The angle α formed by the reflection axis of the reflective polarizing plate and the absorption axis of the absorbing polarizing plate separates the reflective polarizing plate and the absorbing polarizing plate from the composite polarizer, and taking the same side as the reference side, the reflection axis of the reflective polarizing plate, And the absorption axis of the absorption type polarizing plate was measured by the rotational analyzer method using an automatic birefringent meter "KOBRA-WPR" manufactured by Oji Instruments Co., Ltd., and the following formula (8):

α = (angle of reflection axis of reflective polarizer) - (angle of absorption axis of absorption type polarizer) (8)

calculated according to

<Example 1>

(1) Fabrication of polarizer

A polyvinyl alcohol film (average polymerization degree of about 2400, saponification degree of 99.9 mol% or more) with a thickness of 30 μm was uniaxially stretched about 4 times by dry stretching, and then placed in pure water at 40 ° C. for 40 seconds while maintaining a tension state. After immersion, dyeing treatment was performed by immersing in a dyeing aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.044/5.7/100 at 28°C for 30 seconds. Then, it was immersed for 120 second at 70 degreeC in boric acid aqueous solution whose weight ratio of potassium iodide/boric acid/water was 11.0/6.2/100. Then, after washing with pure water at 8°C for 15 seconds, drying at 60°C for 50 seconds and then at 75°C for 20 seconds while holding the tension at 300 N/m, iodine is adsorbed onto the polyvinyl alcohol film. An oriented polarizer having a thickness of 12 μm was obtained.

(2) Fabrication of Absorptive Polarizer

With respect to 100 parts by weight of water, 3 parts by weight of carboxyl group-modified polyvinyl alcohol [trade name “KL-318” obtained from Kuraray Co., Ltd.] was dissolved, and polyamide epoxy-based additive [Taoka, which is a water-soluble epoxy resin] was dissolved in the aqueous solution. A water-based adhesive was prepared by adding 1.5 parts by weight of "Sumirase Resin 650 (30)", a trade name obtained from Chemical Industry Co., Ltd., an aqueous solution having a solid content concentration of 30% by weight. This water-based adhesive was coated on one side of the polarizer obtained in (1) above, and a triacetyl cellulose (TAC) film with a thickness of 25 μm was used as a protective film by a nip roll [trade name manufactured by Konica Minolta Opto Co., Ltd.] KC2UA”, without retardation characteristics] through an adhesive layer, and at the same time, through an adhesive layer made of the same water-based adhesive on the other side, a norbornene-based resin film having an in-plane retardation value of 10 nm or less and a thickness of 23 μm [Nippon Product name "ZEONOR" manufactured by Zeon Co., Ltd.] was bonded. While maintaining the tension at 280 N/m, after 5 seconds from bonding, drying treatment was performed on the bonded product at 60°C for 220 seconds and then at 80°C for 125 seconds, and the visibility correction single transmittance (Ty) was 43.0% and the visibility An absorption type polarizing plate having a corrected degree of polarization (Py) of 99.99% was obtained. Thereafter, a sheet-like pressure-sensitive adhesive (trade name “#7” manufactured by Lintec Co., Ltd.) having a thickness of 25 μm was bonded to the outer surface of the norbornene-based resin film.

(3) Fabrication of composite polarizer

On the outer surface of the TAC film side of the absorption-type polarizing plate obtained in (2) above, a 25-μm-thick sheet-type adhesive [product name “#7” manufactured by Lintec Co., Ltd.] was applied to a 26-μm-thick reflective polarizing plate [manufactured by 3M Co., Ltd.] (trade name "APF", obtained from Sumitomo 3M Co., Ltd.) was bonded so that the angle α formed by the reflection axis of the reflective polarizing plate with respect to the absorption axis of the absorbing polarizing plate was 4° in the counterclockwise direction.

Subsequently, a blue light cut film A (trade name "EF-FLBL series", reflective type manufactured by ELECOM) was bonded to the outer surface of the reflective polarizing plate to obtain a composite polarizing plate. T(380-500) and T(500-780) of the blue light cut film A were 78.9% and 95.0%, respectively.

<Comparative Example 1>

Instead of the blue light cut film A, a composite polarizing plate was obtained in the same manner as in Example 1 except that blue light cut film B (trade name "LCD-140WBC" manufactured by Sanwa Supply Co., Ltd., absorption type) was used. T(380-500) and T(500-780) of the blue light cut film B were 73.8% and 79.7%, respectively.

<Comparative Example 2>

A composite polarizing plate was obtained in the same manner as in Example 1 except for not bonding the blue light cut film A.

<Example 2>

In the dyeing treatment of the polyvinyl alcohol film, a composite polarizing plate was obtained in the same manner as in Example 1 except for using a dyeing solution having a weight ratio of iodine/potassium iodide/water of 0.04/5.7/100. The visibility-corrected single transmittance (Ty) and the visibility-corrected polarization degree (Py) of the obtained absorption type polarizing plate were 43.5% and 99.97%, respectively.

<Comparative Example 3>

A composite polarizing plate was obtained in the same manner as in Example 2 except for using the blue light cut film B instead of the blue light cut film A.

<Comparative Example 4>

A composite polarizing plate was obtained in the same manner as in Example 2 except for not bonding the blue light cut film A.

[Evaluation of display quality of liquid crystal display device]

(1) Luminance

As described above, the luminance of the liquid crystal display device can be evaluated by luminance L (380-780). The larger L(380-780) is, the higher the luminance of the liquid crystal display is. L(380-780) has the same meaning as the molecule on the right side in the above formula (3), and Tp(λ) and Tc(λ) at a 5 nm pitch (dλ = 5 nm) in the wavelength range of 380 to 780 nm was measured by the method described above and obtained according to the above formulas (3) and (4). For P(λ), the emission spectrum (FIG. 7) of a VA-type liquid crystal cell laminated on the backlight 1 described below was used. The results are shown in Table 2.

(2) Contrast

As described above, the contrast of the liquid crystal display device can be evaluated by contrast S _CR (380-780). The higher the S _CR (380-780), the higher the contrast of the liquid crystal display. Tp(λ) and Tc(λ) were measured by the method described above at a 5 nm pitch (dλ = 5 nm) in the wavelength range of 380 to 780 nm, and S _CR ( 380-780). For P(λ) in the above formula (3), the emission spectrum (FIG. 7) of a VA-type liquid crystal cell laminated on the following backlight 1 was used. The results are shown in Table 2.

In addition, L'(380-780) and S _CR '(380- 780) was obtained. The results are shown in Table 2.

Backlight 1 is a simulated white type LED backlight. A VA-type liquid crystal cell was laminated on this, and the emission spectrum measured with backlight 1 turned on is shown in FIG. 7 . Backlight 2 is a high color rendering type LED backlight. A VA-type liquid crystal cell was laminated on this, and the emission spectrum measured with backlight 2 turned on is shown in FIG. 6 . For the measurement of the emission spectrum, a spectroradiometer "SR-UL1" manufactured by TOPCON was used. Emission spectral characteristics obtained from these emission spectra are summarized in Table 1 below.

Claims (8)

An absorption type polarizer, a reflection type polarizer, and a blue light transmission suppression layer for suppressing transmission of blue light in a wavelength range of 380 to 500 nm,
The blue light transmission suppression layer has an average transmittance of 90% or more over a wavelength range of 500 to 780 nm and an average transmittance of 80% or less over a wavelength range of 380 to 500 nm,
The composite polarizing plate of claim 1 , wherein the blue light transmission suppression layer is a layer that suppresses transmission of the blue light by reflecting the blue light. The composite polarizer according to claim 1, wherein the absorption type polarizer has a visibility corrected single transmittance of 42.6 to 44.0% and a visibility corrected polarization degree of 99.5% or more. The composite polarizer of claim 1 , wherein an angle between a reflection axis of the reflection type polarizer and an absorption axis of the absorption type polarizer is 0±4°. The composite polarizing plate according to claim 1, wherein the absorption type polarizing plate includes a polarizer and a resin film laminated on at least one surface of the polarizer. The method of claim 4, wherein the absorption type polarizing plate comprises: the polarizer, a cellulose acetate-based resin film laminated on one side of the polarizer through an adhesive layer, and a cyclic polyolefin-based resin laminated on the other side through an adhesive layer A composite polarizer comprising a film. The method of claim 4, wherein the absorption type polarizing plate includes the polarizer and a cellulose acetate-based resin film or a cyclic polyolefin-based resin film laminated on one side of the polarizer through an adhesive layer,
The reflective polarizing plate is laminated on the other surface of the polarizer or on the surface of the cellulose acetate-based resin film or the cyclic polyolefin-based resin film through an adhesive layer. A backlight, the composite polarizing plate according to any one of claims 1 to 6, and a liquid crystal cell are included in this order,
The liquid crystal display device of claim 1 , wherein the composite polarizing plate is arranged so that the absorption type polarizing plate is closer to the liquid crystal cell side than the reflection type polarizing plate. The method of claim 7, wherein the liquid crystal cell is stacked on the backlight, and in the emission spectrum measured in a state where the backlight is turned on, the emission intensity at the emission peak wavelengths of blue, green, yellow, and red is respectively L (Bmax ), when L (Gmax), L (Ymax) and L (Rmax), the following formula (1) or the following formula (2):
L(Bmax)/L(Ymax) > 1 (1)
L(Bmax)/L(Gmax)>1, and also L(Bmax)/L(Rmax)>1 (2)
A liquid crystal display device that satisfies

Images