CN112789552B

CN112789552B - Display device using polarizing layer

Info

Publication number: CN112789552B
Application number: CN201980052657.3A
Authority: CN
Inventors: 中村大辅; 成田康明
Original assignee: Nippon Kayaku Co Ltd
Current assignee: Nippon Kayaku Co Ltd
Priority date: 2018-09-07
Filing date: 2019-09-02
Publication date: 2024-05-28
Anticipated expiration: 2039-09-02
Also published as: JP2020042111A; JP7214412B2; CN112789552A; KR20210055674A; WO2020050190A1; KR102800902B1

Abstract

A display device includes a dye-based polarizing layer and a backlight source, wherein the orthogonal transmittance (Tc) of the dye-based polarizing layer in the visible light range of 380 nm to 780 nm is greater than 1%, and within the orthogonal transmission wavelength range, the luminous intensity of the backlight source is less than 0.03, and the luminous intensity is normalized according to the maximum luminous intensity in the visible light range of 380 nm to 780 nm.

Description

Display device using polarizing layer

Technical Field

The present disclosure relates to a display device using a polarizing layer.

Background

The dye-based polarizing layer using an azo dye or the like having dichroism has higher durability in a high-temperature and high-humidity high-heat environment than an iodine-based polarizing layer using iodine, and is suitable for providing a display device that operates for a long period of time in such an environment without degradation of display performance. Dye-based polarizing layers are particularly useful in automotive and outdoor display devices operating in harsh use environments.

In recent years, with the gradual increase in optical performance of dichroic dyes, optical characteristics of dye-based polarizing layers have been improved, and display performance such as contrast of display devices such as liquid crystal display devices has also been continuously increased.

Disclosure of Invention

Problems to be solved by the invention

However, in order to obtain a desired polarization characteristic in the visible light range, a plurality of dyes must be used in combination for the dye-based polarizing layer. Wherein each dye generally has a wavelength range exhibiting a main polarization characteristic (main absorption band) and a wavelength range not having a polarization characteristic (sub-absorption band), respectively, in the visible light range. When a plurality of dyes are used in combination, the secondary absorption band of one dye overlaps with the primary absorption band of the other dye, and this becomes a major factor causing the deterioration of the overall polarization characteristics of the dye-based polarizing layer.

For example, in order to ensure white display brightness of a display device, a treatment of incorporating a dye is sometimes performed to improve single transmittance of a dye-based polarizing layer in the entire visible light range. However, when a dye is incorporated in order to improve single transmittance in the entire visible light range, transmittance in an orthogonal state (orthogonal transmittance) is sometimes increased, and in particular, the orthogonal transmittance in a wavelength range of 700nm or more is made larger than that in the case of using an iodine-based polarizing layer. Specifically, for example, when the dye species in which the secondary absorption band is in this wavelength range among the dyes to be incorporated is reduced in order to improve the single transmittance in the wavelength range of 380nm to 700nm, the absorbance at 700nm to 780nm contained in the main absorption band of the dye is reduced, so that the orthogonal transmittance in this wavelength range is increased.

In addition, the optical characteristics of the polarizing layer are generally evaluated based on the CIE1931 color space and using values obtained from a light source using natural light (sunlight) as standard light. In addition, a backlight used as a light source of a display device is generally a white LED, and has a different light emission luminance characteristic from natural light. Therefore, when a display device including a dye-based polarizing layer having the above-described characteristics, which also needs to have an optical design having polarizing properties on the long wavelength side at the same time, is evaluated according to the foregoing method, there is a lack of correlation between the obtained optical characteristic value and the visual evaluation result. In addition, since an iodine-based polarizing layer used for display device use has polarization characteristics in a wide range of visible light from 380nm to 780nm, the polarization characteristics of the polarizing layer are not taken into consideration in the optical design of the display device, and the light emission characteristics of the backlight are not taken into consideration.

It is therefore an object of the present disclosure to provide a display device that takes into account the polarization properties of the dye-based polarizing layer so that the overall device, including the dye-based polarizing layer and the backlight, obtains the desired optical properties.

Technical means for solving the problems

One aspect of the present invention is a display device including a dye-based polarizing layer and a backlight, wherein the dye-based polarizing layer has an orthogonal transmittance (Tc) of 1% or more in a visible light range of 380nm to 780nm inclusive in an orthogonal transmission wavelength range in which a light emission intensity of the backlight is 0.03 or less, and the light emission intensity is normalized according to a maximum light emission intensity in a visible light range of 380nm to 780nm inclusive.

Wherein the dye-based polarizing layer may have an orthogonal transmission wavelength range in which an orthogonal transmittance (Tc) is 1% or more over the entire wavelength range of 700nm or more and less than 750 nm.

The dye-based polarizing layer may have a single transmittance (Ts) of 33% or more over the entire wavelength range of the visible light range of 420nm to 780nm, and a visual acuity corrected orthogonal transmittance (Yc) of 0.01% or less over the wavelength range of 400nm to 700 nm.

In addition, a liquid crystal layer may be included.

Effects of the present disclosure

According to the present disclosure, a display device employing a dye-based polarizing layer can obtain desired optical characteristics.

Drawings

Fig. 1 is a structural view of a display device according to an embodiment of the present disclosure.

Fig. 2 is a diagram of a polarizing layer structure according to an embodiment of the present disclosure.

Fig. 3 shows an example of light source emission characteristics.

Fig. 4 shows the single transmittance of the polarizing layer.

Fig. 5 shows the orthogonal transmittance of the polarizing layers.

FIG. 6 is a schematic diagram of the structure of the optical design simulation.

Detailed Description

As shown in the schematic cross-sectional view of fig. 1, the structure of a display device 100 according to an embodiment of the present disclosure includes a polarizing layer 10, a first substrate 12, a color filter 14, a counter electrode 16, an alignment film 18, a liquid crystal layer 20, an alignment film 22, a display electrode 24, an interlayer insulating film 26, a second substrate 28, a polarizing layer 30, and a backlight 32. The display device 100 operates on the principle that light emitted from the backlight 32 passes through the color filter 14 and is output from the polarizing layer 10 side, as indicated by an arrow, to display an image. In addition, fig. 1 is a schematic diagram, and the size and thickness of each constituent device do not reflect actual values.

In the present embodiment, the display device 100 is described by taking a liquid crystal display device as an example, but any display device may be applied to the present disclosure as long as a polarizing layer and a backlight are used in combination.

In the present embodiment, the display device 100 is described by taking an active matrix liquid crystal display device as an example, but the application scope of the present disclosure is not limited thereto, and any display device may be applied to the present disclosure as long as the display device uses a polarizing layer in combination with a backlight.

The first substrate 12 is a transparent substrate such as glass. The first substrate 12 is used to realize image display by transmitting light therethrough, in addition to providing mechanical support for the display device 100. The first substrate 12 may be a flexible substrate made of a resin such as an epoxy resin, a polyimide resin, an acrylic resin, or a polycarbonate resin.

The polarizing layer 10 is formed on the display surface side of the first substrate 12. The polarizing layer 10 is formed so as to cover the substrate surface of the first substrate 12. The polarizing layer 10 contains a dyed polarizer obtained by dyeing a PVA (polyvinyl alcohol) based resin with a dichroic dye. The polarizing layer 10 is typically superimposed on the surface of the first substrate 12 by an adhesive layer.

The commonly used polarizers are iodine-based polarizers formed from materials obtained after dyeing the resin with iodine and iodine compounds. However, iodine and iodine compounds are not heat resistant and are modified under heating conditions of around 100 ℃. In contrast, polarizers employing dyes (dichroic dyes) are more heat resistant. Moreover, the polarizer is not easy to change with time when being used in a high-temperature state, and has good durability.

The color filter 14 is formed on the first substrate 12. The color filters 14 may be arranged in a matrix on the surface of the first substrate 12 in one-to-one correspondence with the pixels. The color filter 14 receives light emitted from a backlight 32 described below and allows only light of a specific wavelength range to pass therethrough. Specifically, for each pixel, a color filter 14 that allows transmission of any one of red (R), green (G), and blue (B) is provided.

The counter electrode 16 is formed on the color filter 14. The counter electrode 16 is, for example, a transparent electrode made of ITO (indium tin oxide) or the like.

An alignment film 18 is formed on the counter electrode 16. The alignment film 18 is made of a resin material such as polyimide. The orientation film 18 may be formed, for example, by: a 5wt% solution of N-methyl-2-pyrrolidone, which can form a polyimide resin, is printed on the counter electrode 16; after being heated and hardened at the temperature of 110-280 ℃, the cloth is rubbed (Rubbing) for orientation treatment. The orientation direction of the orientation film 18 is orthogonal to the orientation direction of an orientation film 22 described below.

Hereinafter, a structure and a manufacturing method of the second substrate 28 side will be described. The second substrate 28 is used to transmit light from the backlight 32 before it is incident on the color filter 14 or the like, in addition to providing mechanical support for the display device 100. The second substrate 28 may be a transparent substrate such as glass. The second substrate 28 may be a flexible substrate made of a resin such as an epoxy resin, a polyimide resin, an acrylic resin, or a polycarbonate resin.

A polarizing layer 30 is formed on the second substrate 28. The polarizing layer 30 contains a dyed polarizer obtained by dyeing a PVA (polyvinyl alcohol) based resin with a dichroic dye. The dye-based material contains, for example, an azo compound and/or a salt thereof. The polarizing layer 30 is typically superimposed on the surface of the second substrate 28 by an adhesive layer.

As mentioned above, the polarisations using dyes (dichroic dyes) are more heat resistant than those used. Moreover, the polarizer is not easy to change with time when being used in a high-temperature state, and has good durability.

A backlight 32 is disposed on the polarizing layer 30. The backlight 32 is configured as a light source containing output light. The light source may for example be a white LED.

Switching elements such as TFTs may be provided over the second substrate 28 in one-to-one correspondence with the pixels. Two TFTs are shown in fig. 1. A gate electrode 28a connected to the gate line is provided under (on the substrate) the substantially central position of the TFT. A gate insulating film 28b is formed on the gate electrode 28a so as to cover the gate electrode 28a, and a semiconductor layer 28c is formed on the gate insulating film 28b so as to cover the gate insulating film 28 b. The gate insulating film 28b is formed of an insulator such as SiO ₂. The semiconductor layer 28c is formed of amorphous silicon or polysilicon, and a channel region having almost no dopant is directly above the gate electrode 28a, and a source region and a drain region having conductivity due to doping are provided on both sides. A contact hole is formed over the drain region of the TFT, in which a metal (e.g., aluminum) drain electrode is disposed (electrically connected). A contact hole is formed over the source region in which a metal (e.g., aluminum) source electrode is disposed (electrically connected). The drain electrode is connected to a data line supplied with a data voltage.

The display electrode 24 is provided on the surface of the second substrate 28 on the TFT-forming side via the interlayer insulating film 26. The display electrode 24 is a separate electrode separated from each other in one-to-one correspondence with the pixels, and is a transparent electrode made of, for example, ITO (indium tin oxide) or the like. The display electrode 24 is connected to a source electrode formed on the second substrate 28.

An alignment film 22 is formed on the display electrode 24 to cover the display electrode 24. The alignment film 22 is made of a resin material such as polyimide. The orientation film 22 may be formed, for example, by: a 5wt% solution of N-methyl-2-pyrrolidone, which can form a polyimide resin, is printed on the display electrode 24; after being heated and hardened at 180-280 ℃, the friction cloth is used for friction orientation treatment.

The alignment films 18 and 22 face each other, and the liquid crystal layer 20 is sealed between the alignment films 18 and 22. The liquid crystal layer 20 is formed by: a spacer (not shown) is provided between the alignment films 18 and 22; injecting liquid crystal between the alignment films 18 and 22; the periphery is sealed with a sealing material (not shown).

The alignment of the liquid crystal layer 20 is controlled by the alignment films 18 and 22, and the initial (when no electric field is applied) alignment state of the liquid crystal layer 20 is determined by the alignment films 18 and 22. When a voltage is applied between the display electrode 24 and the counter electrode 16, an electric field will be generated between the display electrode 24 and the counter electrode 16, thereby controlling the orientation of the liquid crystal layer 20 and the transmission/non-transmission of light.

The relationship between the polarizing layer 10, the polarizing layer 30, and the backlight 32 in the display device 100 will be described below. Further, although the structures of the polarizing layers 10 and 30 and the wavelength range values will be described below, the present disclosure is not limited thereto.

As described above, in order to obtain desired polarization characteristics in the visible light range, the polarizing layer 10 and the polarizing layer 30, which are dye-based polarizing layers, are used in combination with a plurality of dyes. That is, in order to obtain polarization characteristics and waveform bands that are not inferior to those of iodine-based polarizers, dye-based polarizing layers generally have polarization characteristics over a wide region of the visible light range by using a plurality of dichroic dyes having different hues in combination.

Each of the dyes has a wavelength range (main absorption band) exhibiting a main polarization characteristic and a wavelength range (sub-absorption band) not exhibiting a polarization characteristic in a visible light range of 380nm to 780nm, respectively. Therefore, when a plurality of dyes are mixed, the secondary absorption band of a certain dye may overlap with the primary absorption band of other dyes, thereby becoming a major factor causing the deterioration of the overall polarization characteristics of the dye-based polarizing layer. It is particularly difficult to obtain a waveform band equivalent to that of an iodine-based polarizing plate for a design in which polarization characteristics at 550nm with high visual sensitivity are emphasized. Based on this, by narrowing the wavelength range of the dye-based polarizing layer having polarization characteristics to 380 to 780nm, the variety of dichroic dyes selectable in optical design can be increased, so that high performance can be more easily obtained by the use of dyes in combination. For example, the polarization characteristics of the polarization layer are preferably designed to cover at least a wavelength range of 400 to 700nm, and more preferably to cover a range having the emission spectrum luminance of the backlight 32 described below.

Hereinafter, the production of the polarizing layer 10 and the polarizing layer 30, which are dye-based polarizing layers, will be described. The two polarizing layers may have a structure in which a support film 42 (in fig. 2, a first support film 42a and a second support film 42b, respectively) is attached to one side or both sides of a polarizing film used as a polarizer. Although the polarizing film 40 may be used alone, a polarizing plate obtained by sandwiching the polarizing film 40 on both sides of the first support film 42a and the second support film 42b is preferably used. The reason is that the polarizing film 40 is generally obtained by uniaxially stretching a polyvinyl alcohol resin (PVA) film dyed with a dichroic colorant, and is a film-like substance, and thus if not sandwiched by the first and second support films 42a and 42b, it will be easily deformed under the influence of heat and moisture, and thus its polarizing characteristics may be impaired.

The polarizing film 40 may be a film having a function of converting natural light into linearly polarized light, or may be a film obtained by adsorbing a dichroic colorant to a PVA film and aligning the PVA film. When a dichroic dye such as an azo compound, an anthraquinone compound, or a tetrazine is used as the dichroic colorant, excellent optical durability can be obtained under high temperature conditions or high temperature and high humidity conditions, and the color tone adjustment is easy.

The dichroic dye used in the polarizing film 40 is preferably an azo compound dye from the viewpoints of optical characteristics and durability. The azo-based compound dye may be, for example, each of the following dyes.

(1) An azo compound represented by the formula (1) or a salt thereof disclosed in the publication of japanese international patent application publication No. WO2009/057676 (A1).

(Chemical formula 1)

(Wherein R ₁ represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a hydroxyl group, a sulfonic acid group or a carboxyl group, R ₂～R₅ each independently represents a hydrogen atom, a lower alkyl group, a lower alkoxy group or an acetamido group, and X represents a benzoylamino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent or a naphthotriazolyl group which may have a substituent, wherein m is 1 or 2, and n is 0 or 1.)

(2) An azo compound represented by the formula (2) or a salt thereof disclosed in Japanese International patent application publication No. WO2007/145210 (A1).

(Chemical formula 2)

(Wherein A represents a phenyl group having a substituent or a naphthyl group having 1 to 3 sulfonic acid groups, X represents-N=N-or-NHCO-, and R ₁～R₄ each independently represents a hydrogen atom, a lower alkyl group or a lower alkoxy group, wherein m=1 to 3, n=0 or 1.)

(3) The trisazo dye represented by the chemical formula (3) disclosed in Japanese International patent application publication No. WO2006/057214 (A1).

(Chemical formula 3)

( In the formula, R ₁ represents a sulfonic acid group, a carboxyl group or a lower alkoxy group, and R ₂ represents a sulfonic acid group, a carboxyl group, a lower alkyl group or a lower alkoxy group. However, R ₁ and R ₂ are not both sulfonic acid groups. R ₃～R₆ independently represents a hydrogen atom, a lower alkyl group or a lower alkoxy group, and R ₇ and R ₈ independently represent a hydrogen atom, an amino group, a hydroxyl group, a sulfonic group or a carboxyl group. )

(4) A metal-containing disazo compound represented by the formula (4) or a salt thereof disclosed in Japanese patent application laid-open No. 2004-251963.

(Chemical formula 4)

( Wherein M represents a transition metal selected from copper, nickel, zinc, iron; a ¹ represents a substitutable phenyl group or a substitutable naphthyl group; b ¹ represents a 1-naphthol group or 2-naphthol group which may be substituted, wherein the hydroxyl group in the naphthol group is positioned at the ortho position of the azo group and is complexed with the transition metal represented by M; r ¹ and R ² each independently represent hydrogen, lower alkyl, lower alkoxy, carboxyl, sulfo, sulfamoyl, N-alkylsulfamoyl, amino, amido, nitro or halogen. )

(5) Trisazo compound represented by the formula (5).

(Chemical formula 5)

(Wherein A ² and B ² each independently represent a substituted phenyl group or a substituted naphthyl group, and R ³ and R ⁴ each independently represent hydrogen, lower alkyl, lower alkoxy, carboxyl, sulfo, sulfamoyl, N-alkylsulfamoyl, amino, amido, nitro or halogen, wherein m is 0 or 1.)

(6) Japanese patent application laid-open No. JPH03-12606 discloses a water-soluble compound represented by the formula (6) or a copper complex salt compound thereof.

(Chemical formula 6)

(In the formula, A represents methyl-substituted phenyl or naphthyl, R represents amino, methylamino, ethylamino or phenylamino.)

(7) Japanese patent application laid-open No. JPH02-61988 discloses a water-soluble disazo compound represented by formula (7) or a copper complex salt compound thereof.

(Chemical formula 7)

(8) Other dyes such as c.i. direct yellow 12, c.i. direct yellow 28, c.i. direct yellow 44, c.i. direct yellow 142, c.i. direct orange 26, c.i. direct orange 39, c.i. direct orange 71, c.i. direct orange 107, c.i. direct red 2, c.i. direct red 31, c.i. direct red 79, c.i. direct red 81, c.i. direct red 117, c.i. direct red 247, c.i. direct green 80, c.i. direct green 59, c.i. direct blue 71, c.i. direct blue 78, c.i. direct blue 168, c.i. direct blue 202, c.i. direct violet 9, c.i. direct violet 51, c.i. direct brown 106, c.i. direct brown 223, and the like. In addition, in order to supplement polarization characteristics at each wavelength in the visible light range, it is preferable to dye PVA with two, three or more of the above dyes in combination to achieve a neutral gray tone. Thus, a liquid crystal display device having excellent display performance in terms of high contrast can be obtained. In addition, when three or more dyes including a blue-based dichroic dye are used in combination, the degree of yellowing can be adjusted to an optimum degree particularly when the polarizing film is provided on a display device by adjusting the amount of the blue-based dichroic dye used. In addition, the adjustment of neutral gray can be made easier by using a dichroic dye for the colorless polarizer.

Further, kayafect Violet P Liquid (japan chemical Co., ltd.), kayafect Yellow Y, kayafect Orange G, kayafect Blue KW, kayafect Blue Liquid 400, etc. are used as commercial dyes.

In addition, by obtaining a polarizing layer having a single transmittance of 33% or more and an orthogonal transmittance of 0.01% or less uniformly in a wavelength range of 400 to 700nm, a display device having excellent contrast can be obtained. The dyes used for the polarizing layer have, for example, maximum absorption wavelength (main absorption wavelength) and high dichroism in any one wavelength region among (1) 400 to 500nm, (2) 500 to 590nm and (3) 590 to 660nm, and have optical characteristics in which no sub-absorption (or less sub-absorption) is present in a wavelength region other than the wavelength region in which the maximum absorption wavelength is present, and are preferably combined with each other by using dyes having these characteristics in combination.

The dye having the characteristics related to the above (1) may be, for example, the following orange-based dye:

an azo compound or an azo compound salt represented by the formula (8) disclosed in International patent application publication No. WO2007/138980,

(Chemical formula 8)

(Wherein R1 and R2 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, and n is 1 or 2.)

The dye having the characteristics related to the above (2) may be, for example, the following red-based dye:

an azo compound represented by the formula (9) or a salt thereof disclosed in International patent application publication No. WO2016/186196,

(Chemical formula 9)

( In the formula, A is naphthyl with hydrogen atom, hydroxyl, sulfo and carbon number of 1-5 alkoxy and/or sulfo; at least one of R ₁～R₄ independently represents an alkyl group having 1 to 4 carbon atoms having a sulfo group or an alkoxy group having 1 to 4 carbon atoms. )

The dyes having the characteristics related to the above (3) may be, for example, the following blue-based dyes:

An azo compound represented by the formula (10) and/or a salt thereof disclosed in International patent application publication No. WO2012/108169,

(Chemical formula 10)

( In the formula, A represents a phenyl group which may have a substituent; r ₁～R₆ independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms and a sulfo group, a benzoylamino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, or a naphthotriazole group which may have a substituent. )

When the support film 42 is used for the polarizing plate, the support film 42 is attached to one or both sides of the polarizing film 40 by an adhesive layer. The support film 42 (the first support film 42a and the second support film 42 b) may be a cycloolefin resin film, a polyester resin film, an acrylic resin film, a polycarbonate resin film, a polysulfone resin film, an alicyclic polyimide resin film, a cellulose acetate resin film, or the like. From the viewpoint of easy adhesion to a polarizing film to obtain a polarizing plate, cellulose acetate resin is preferable, and triacetyl cellulose (TAC) is more preferable.

Alternatively, the retardation layer and the viewing angle compensation layer may be provided on the opposite side of the support film adhesive surface by an adhesive or the like, or these layers may be used as support films directly. Further, a surface functional layer 44 such as an antiglare layer, an antireflection layer, a hard coat layer, etc. may be provided on the surface of the support film on the viewing side of the display device.

The adhesive layer 46 is used to attach the polarizing layers to the first substrate 12 and the second substrate 28 of the display device. The adhesive layer 46 is disposed on the opposite side of the first support film 42a from the polarizing film 40. The adhesive layer 46 is formed by, for example, applying an adhesive formed by diluting the solid content of an acrylic or polyester adhesive with a solvent such as toluene or Methyl Ethyl Ketone (MEK) to a release film and drying the same. The binder is not particularly limited as long as it is an acrylic or polyester, and other binders may be used in addition to this. In addition, an additive such as a curing agent or a silane coupling agent may be incorporated into the adhesive to adjust the tightness with the object to be bonded or to obtain a characteristic of reducing peeling or foaming in terms of durability.

Subsequently, the adhesive formulated as described above is coated on a release film, and the solvent is volatilized through a drying step. In the drying step, a plurality of drying ovens, each set at a temperature range of 40 to 100 ℃, may be used to volatilize the solvent from the adhesive coated release film.

Wherein the coating amount is adjusted so that the thickness of the adhesive after drying is 1 μm or more and 30 μm or less, more preferably 5 μm or more and 25 μm or less. After that, the adhesive-coated side is directed toward the first carrier film 42a, and is attached.

The optical properties of the polarizing layer are generally evaluated by measuring the transmittance by a spectrophotometer at each wavelength of 5nm or 10nm in the wavelength range of 380 to 780 nm. The transmittance value in the visible light range is represented by a value obtained by performing a visual acuity correction according to JIS Z8719 (CIE 1931 color space). The above transmittance (Ys, hereinafter referred to as single transmittance in%) in the case of a single polarizing layer is calculated according to the following formula (1). Wherein S is standard light, y is a 2-degree view field color matching equation, and t is transmittance at each wavelength. Mathematical formula (1) is typically calculated automatically by a program provided with a commercially available spectrophotometer. The standard light S is light used when transmitted or irradiated by a C light source, a D65 light source, or the like having a spectrum similar to that of sunlight as a natural light source.

(Mathematics 1)

Hereinafter, another method for evaluating the optical characteristics of the polarizing layer will be described. The contrast (C) is expressed as a ratio (expression (2)) of the transmittance (Yp, hereinafter referred to as parallel transmittance, in%) when the polarization axes of the two sets of polarizing layers are parallel to the transmittance (Yc, hereinafter referred to as orthogonal transmittance, in%) when the polarization axes of the two sets of polarizing layers are orthogonal, wherein each transmittance is obtained by expression (1). C is a display performance evaluation index when the polarizing layer is provided on the liquid crystal display device, yp corresponds to a white display state of the display device, and Yc corresponds to a black display state of the display device.

(Mathematics 2)

C＝Yp/Yc···(2)

The degree of polarization P (in%) representing the polarization characteristics of the polarizing layer can be obtained according to the mathematical formula (3). Where Py depends on the transmittance of the polarizing layer, the lower the transmittance, the higher the resulting degree of polarization.

(Mathematics 3)

Further, the orientation and polarization performance of the colorant in the polarizing layer can be evaluated by the dichroic ratio Rd. Rd is expressed as the ratio of absorbance obtained by the absolute parallel transmittance Kz obtained when the absolute polarized light is incident on the polarizing layer and the absolute orthogonal transmittance Ky obtained when the absolute polarized light is orthogonal to the absorption axis of the polarizing plate, respectively (expression (4)). Wherein A ₀ is obtained according to formula (5), and A ₉₀ is obtained according to formula (6). Generally, the dichroic ratio Rd of the iodine-based polarizer is 50 to 60 or more, and the dichroic ratio Rd of the dye-based polarizer is 30 to 40 or more.

(Mathematics 4)

Rd＝A₀/A₉₀···(4)

(Mathematics 5)

A₀＝-log(Kz/100)···(5)

(Mathematics 6)

A₉₀＝-log(Ky/100)···(6)

Ky and Kz can be obtained from the mathematical formula (7) and the mathematical formula (8) by Ys and Yc, respectively.

(Mathematics 7)

(Mathematics 8)

Further, for example, calculation in the wavelength range of 400 to 700nm may be performed according to the formula (9). Since the human eye generally hardly perceives colors and light in the wavelength ranges of 400nm or less and 700nm or more, such calculation can be adopted in the case of a low-precision spectrophotometer or in the case of a simple evaluation without pursuing precision, but it is assumed that there is little difference from the evaluation result when calculated according to the formula (1).

(Mathematics 9)

LED backlights used in liquid crystal display devices and the like are generally so-called quasi-white light emitting elements obtained by applying a yellow-emitting fluorescent agent to a blue light emitting element, and have almost no luminance in a wavelength range of 700nm or more. Therefore, when the display brightness or the display contrast is actually evaluated in a state where the polarizing plate is provided on the display device, the condition is considered to be almost no brightness in a wavelength range of 700nm or more. For example, when the optical characteristics of a dye-based polarizing layer having no effective polarization characteristics in the wavelength range of 700nm or more are calculated by performing the visual acuity correction according to the expression (1), there is a possibility that the optical characteristic value obtained by the calculation may be different from the optical evaluation result when the polarizing layer is actually provided on a display device. In this case, the above-described difference can be conveniently eliminated by narrowing the range of the visual acuity correction calculation to, for example, a wavelength range of 380nm to 700nm or more and 400nm to 700nm or less.

The y component (color matching equation) in the formula (1) is processed so that the value in the wavelength range of 750nm or more to 780nm is approximately 0 with respect to the value at the wavelength of 555 nm. Therefore, in the optical design of the dye-based polarizing layer of the present disclosure, it may be disregarded whether or not there is polarization characteristic at a wavelength of 750nm or more.

In addition, the calculation of the visual acuity correction in evaluating the optical characteristics of the dye-based polarizing layer and the liquid crystal display device provided with the dye-based polarizing layer is preferably performed using the waveform band of the backlight 32 that is actually used as standard light. In this way, the structure actually provided behind the display device can obtain an optical characteristic evaluation result that is comparable to that obtained by evaluating only the film. In this case, S of the formula (1) may use a value after normalizing the light emission spectrum of the backlight actually used. In addition, although the above approach of narrowing the calculation range for the convenience of eliminating the difference may cause the obtained color tone values to lack accuracy, by this approach, an evaluation result accurately reflecting the backlight condition can be obtained. The above S is a value obtained by normalization when the luminance at the wavelength of the maximum luminance (maximum emission intensity) in the wavelength range of 380 to 780nm in the backlight emission spectrum is 1.

In a liquid crystal display device provided with a dye-based polarizing plate having excellent polarization characteristics in the visible light range, the luminance wavelength range of the backlight 32 used in the liquid crystal display device is preferably white light having luminance in the visible light range and does not have luminance in the wavelength range of 700nm or more. Specifically, the maximum brightness in the wavelength range of 700 to 780nm is preferably 0.03 or less, more preferably 0.01 or less.

Fig. 3 shows light emission luminance waveforms obtained by normalizing a wavelength range of 380nm to 780nm when a white LED is used as the backlight 32 and a C light source is used as the standard light source (indicated by a dotted line). The backlight 32b (shown by a broken line) is NS2W364G manufactured by nitenpyram chemical industry co. The backlight 32a (shown by a solid line) is NS2W364G-HG manufactured by nitenpyram chemical industry co. The normalized emission luminance values on the long wavelength side (660 nm to 740 nm) of the backlights 32a and 32b are shown in table 1.

The high color rendering property of the liquid crystal display device means that the transmission efficiency of each color filter is improved by associating the spectrum of each RGB color filter with the light emission spectrum of the backlight, thereby enriching the colors reproduced by the display.

(Table 1)

Backlight source	660nm	680nm	700nm	720nm	740nm
						32a	0.016	0.005	0.003	0.001	0.001
32b	0.076	0.049	0.030	0.017	0.011

As shown in fig. 3, in the case of the standard light source, there is an emission intensity in the entire visible wavelength range, whereas in the case of the backlight 32, there is almost no emission intensity at the long wavelength side. As shown in table 1, the luminance value of the backlight 32a is about one tenth of the luminance value of the backlight 32b in the wavelength range of 680 to 740nm, which means that the luminance of the backlight 32a in this wavelength range is sufficiently small. The backlight 32 of the present embodiment preferably has a normalized luminance value of not more than 0.03, more preferably not more than 0.01 in the wavelength range of not less than 700nm and not more than 780nm, as described above, and thus the backlight 32a is preferably used. In particular, when a backlight having a luminance value of 0.01 or less at a wavelength of 700nm or more and 780nm or less is used, a dye-based polarizing plate having no polarizing properties at a wavelength of 700nm or more can be obtained, and a high-contrast liquid crystal display device free from occurrence of white spots or mottle even in a black display state can be obtained.

Example 1

[ Production of polarizer ]

After swelling a polyvinyl alcohol resin film (VF-PE (thickness: 60 μm) manufactured by Coleus chemical Co., ltd.) in water at 30℃for 5 minutes, it was immersed in a dyeing liquid at 30℃of a dye described in International patent application No. WO2007/138980 (the dyeing liquid being 0.1 to 0.3 parts by weight based on 1000 parts by weight of water and 1 part by weight of sodium tripolyphosphate) for 5 minutes to perform dyeing treatment of the dye. Subsequently, the dyed film was stretched 4 to 6 times in an aqueous solution of boric acid having a weight percentage of 3% at 50 ℃ to have the maximum polarization characteristics, thereby obtaining a stretched film. After the stretching treatment, the stretched film was immersed in a 5% by weight aqueous boric acid solution at 50 ℃ for 2 minutes, washed with water, and then dried in air at 30 to 80 ℃ to obtain an orange-type polarizing film. The thickness of the resulting polarizing film was 20. Mu.m. The saponified TAC film (thickness 60 μm, containing an ultraviolet absorber) was laminated on both sides of the resulting polarizing film by a water-based adhesive containing polyvinyl alcohol (PVA). After that, 5 minutes of drying was performed at 70 ℃ to obtain a polarizing layer a.

In the same manner as in example 1, a red-based polarizing film was obtained from the dye described in International patent application No. WO2016/186196, example 1. The thickness of the resulting polarizing film was 20. Mu.m. After that, in the same manner, a polarizing layer B to which a TAC film was attached was obtained.

In the same manner as in example 1, a blue polarizing film was obtained with the dye described in international patent application example 36 of publication No. WO 2012/108169. The thickness of the resulting polarizing film was 20. Mu.m. After that, in the same manner, a polarizing layer C to which a TAC film was attached was obtained.

The single transmittance (Ts), the parallel transmittance (Tp), and the orthogonal transmittance (Tc) were measured for each wavelength in the visible light range of 380nm to 780nm by a spectrophotometer (U-4100 manufactured by Hitachi, inc.) for the polarizing layer A, the polarizing layer B, and the polarizing layer C. Table 2 shows the above measurement results and the dichroic ratio (Rd) measurement results at the maximum absorption wavelength (λmax).

(Table 2)

	λmax(nm)	Ts(％)	Tc(％)	Rd
					Polarizing layer A	465	43.92	0.32	42
Polarizing layer B	520	43.96	0.36	41
					Polarizing layer C	630	43.80	0.30	42

The optical characteristics of the dye-based polarizing layer having the features of the present disclosure are obtained by the following method. Based on the monochromatic spectral measurement results of the polarizing layers a, B, and C, computer calculations were performed by the following waveform synthesis method, and neutral gray optical design of the polarizing film was achieved by simulation. By optimizing the contribution ratio of the polarizing layer A, the polarizing layer B and the polarizing layer C to the waveform, the dye-based polarizing layer D with high polarization characteristics in the whole visible light range of 400-700 nm wavelength is obtained.

Fig. 4 and 5 show single transmittance and orthogonal transmittance waveforms of the polarization layer D, respectively. Table 3 shows the optical properties of the polarizing layer D. In the actual manufacturing process of the polarizing layer D, the dye used above may be optimally formulated so as to obtain a dye solution in a manner that the waveform of the polarizing layer D can be obtained, and then PVA may be dyed and stretched, thereby directly obtaining a polarizing layer equivalent to the polarizing layer D.

The polarizing layer D has an orthogonal transmission wavelength range in which the orthogonal transmittance (Tc) in the visible light range of 380nm to 780nm is 1% or more. The polarizing layer D also has the above orthogonal transmission wavelength range in which the orthogonal transmittance (Tc) is 1% or more in the entire wavelength range of 700nm to 740 nm. The polarizing layer D has a single transmittance (Ts) of 33% or more in the entire visible light wavelength range of 420nm to 780nm, and a visual acuity correction orthogonal transmittance (Yc) of 0.01% or less in the wavelength range of 400nm to 700 nm.

[ Waveform Synthesis method ]

(1) Based on the transmittance (Ts, tp, tc) at each wavelength, an absolute orthogonal transmittance Ky at each wavelength orthogonal to the polarizer absorption axis and an absolute parallel transmittance Kz at parallel to the polarizer absorption axis are obtained;

(2) Assuming that the contribution of the surface and internal reflectivity of the polarizing layer is about 4%, calculating the products of Ky and Kz and 0.96 ^-2, respectively;

(3) Converting the Ky and Kz obtained in (2) into absorbance, and multiplying by an arbitrary concentration value;

(4) The above (1) to (3) were performed for each of the polarizing layers a to C, and the sum of the obtained values was used as the absorbance of the synthetic polarizing layer D. By adjusting the arbitrary concentration value in (3), the waveform balance condition of the polarizing layer D can be optimized. Here, the dichroic ratio in the wavelength range of 400 to 700nm is adjusted to be maximum;

(5) Converting the absorbance of the polarizing layer D obtained in the step (4) into Ky and Kz, and respectively obtaining products of Ky and Kz and 0.96 ² according to the step (2);

(6) From the result of (5), the transmittance (Ts, tp, tc) of the polarizing layer D is obtained, and the single transmittance (Ys, yc) and the polarization degree Py of the polarizing layer are obtained from the above formula.

(Table 3)

[ Evaluation of luminance characteristics at the time of Black display ]

The front luminance (black display luminance) in the dark state was simulated by optical design simulation software (Shintech, inc. LCD MASTER). Fig. 6 is a schematic structural diagram of a simulation for carrying out the present evaluation. The polarizing layer 50 (front side), the liquid crystal cell 52, and the polarizing layer 54 (back side) are disposed in this order, and the polarizing layer 50 and the polarizing layer 54 are disposed to have the optical characteristics of the polarizing layer D. Wherein the polarization axis relationship of the polarization layer 50 and the polarization layer 54 is in an orthogonal relationship, and the liquid crystal 52 in the liquid crystal cell 52 is disposed to be horizontally aligned in a plane. The material of the liquid crystal 52 is ZLI-4792 manufactured by merck patent co.ltd, selected from a database of the software. The luminance calculation was performed using the orthogonal transmittance waveform obtained as described above and the normalized emission intensity waveform of the backlight 32a shown as standard light in fig. 3 (NS 2W364G-HG manufactured by riya chemical industries, ltd.). Table 4 shows the evaluation results.

(Table 4)

Example 2

The description of example 1 is repeated except that a normalized emission spectrum of NS2W364G (backlight 32 a) manufactured by dix chemical industries, ltd, was used as the standard light LED backlight. The evaluation results are shown in Table 4.

Comparative example 1

The description of example 1 is followed except that the optical data obtained by spectroscopic measurement using a commercially available high-contrast dye-based polarizing plate SHC-13U (Baolai technology Co., ltd.). The evaluation results are shown in Table 4.

Comparative example 2

The description of example 2 is followed except that the optical data obtained by spectroscopic measurement using a commercially available high-contrast dye-based polarizing plate SHC-13U (Baolai technology Co., ltd.). The evaluation results are shown in Table 4.

Comparative example 3

The description of example 1 is followed except that the optical data obtained by spectroscopic measurement using a commercially available high-contrast dye-based polarizer VHC-128U (Baolai technologies Co., ltd.). The evaluation results are shown in Table 4.

Comparative example 4

The description of example 2 is followed except that the optical data obtained by spectroscopic measurement using a commercially available high-contrast dye-based polarizer VHC-128U (Baolai technologies Co., ltd.). The evaluation results are shown in Table 4.

Comparative example 5

The description of example 1 was repeated except that the optical data obtained by spectroscopic measurement using a commercially available iodine-based polarizing film SKN-18243T (Baolai technologies Co., ltd.). The evaluation results are shown in Table 4.

Comparative example 6

The description of example 2 was repeated except that the optical data obtained by spectroscopic measurement using a commercially available iodine-based polarizing film SKN-18243T (Baolai technologies Co., ltd.). The evaluation results are shown in Table 4.

The results of table 3 are described below. In the visual acuity correction calculation of the C light source 2-degree field of view of the polarizing layer D, a difference is generated between the calculation results of the calculation case where the wavelength range is set to 380 to 780nm (case 1) and the calculation case where the wavelength range is set to 400 to 700nm (case 2). This difference is reflected in particular in the transmittance Yc value, i.e. the Yc ratio of the polarizing layer D (case 1/case 2) is greater than that of the other polarizing layers. Accordingly, the resulting dichroic ratio Rd values also differ. The reason for this is that in the calculation method using the C light source (natural light) as the standard light source, the polarizing layer D has almost no polarization characteristic at a wavelength of 700nm or more, and therefore cannot block light having a wavelength of 700nm or more from the standard light. In contrast, as is clear from the calculation result of case 2, the polarizing layer D has optical characteristics superior to those of the conventional dye-based polarizing layer. This means that in the configuration of the orthogonal transmission waveform of the polarizing layer D, the waveform characteristics of the light source luminance need to be taken into consideration. Therefore, in the design of a display device in which the polarizing layer D is actually used, by using a light source having almost no luminance at a wavelength of 700nm or more, high display performance can be achieved even when a dye-based polarizing layer is used.

In case 1 and case 2 calculations of the existing dye-based polarizing layers (SHC-13U and VHC-128U) and iodine-based polarizing layer (SKN-18243T) compared to polarizing layer D, there was hardly any difference in optical characteristics between the calculated values of the two. Among them, there is hardly any difference between the values of case 1 and case 2, especially in the case of SHC-13U. The reason for this is that among all dye-based polarizing layers, the polarizing layer has the lowest orthogonal transmittance at wavelengths of 700nm or more. Therefore, in the optical design of the dye-based polarizing layer, by providing such a cross-transmission waveform configuration, a polarized wavelength range equivalent to that of the iodine-based polarizing layer can be obtained.

The results of table 4 are described below. Examples 1 and 2 have lower black display luminance than the case of using the existing dye-based polarizing layers (comparative examples 1 to 4) and iodine-based polarizing layers (comparative examples 5 and 6). That is, in the display device using the LED light source of the backlight 32a or the backlight 32b, the polarizing layer D can realize a black display effect that is not inferior to that of the iodine-based polarizing layer. Among them, the calculation result of case 2 in table 3 is preferably taken as the optical characteristics of the polarizing layer D. Further, as is clear from the result of example 1 using the backlight 32a, by combining the characteristic that the normalized emission luminance at a wavelength of 700nm or more is 0.01 or less with the polarizing layer D, it is possible to realize a black display luminance 36% lower than that of the backlight 32 b. That is, black display performance of the display device can be improved.

In contrast, in comparative examples 1 to 6, the effect of improving the black display luminance value when the backlight 32a is used was only 2 to 17% as compared with the case of using the backlight 32b, and the effect of improving the black display performance as in examples 1 and 2 was hardly generated.

As is clear from the above results, according to the present invention, when improving the display performance of a display device using a dye-based polarizing layer, it is possible to obtain display performance comparable to that of a display device using an iodine-based polarizing layer by focusing on the light emission spectrum of a backlight used in the display device, in addition to optimizing the optical characteristics by using a dye in combination. That is, even in the dye-based polarizing layer having a cross transmittance (Tc) of 1.0% or more in the wavelength range of 700nm or more, the use of the dye-based polarizing layer in combination with a backlight having a normalized emission luminance of 0.03 or less, more preferably 0.01 or less in the wavelength range of 700nm or more can reduce the luminance at the time of black display and improve the display contrast.

In addition, in the optical design of the dye-based polarizing layer of the present embodiment, since it is not necessary to have polarization characteristics in the wavelength range of 700nm or more, the types of dyes to be incorporated can be reduced as compared with the prior art. Thus, the influence of inherent sub-absorption of the dye in the wavelength range of 400-700 nm can be reduced, and the single transmittance higher than that of the existing dye-based polarizing layer can be realized. Therefore, the present embodiment can improve not only the black display effect but also the brightness at the time of white display, thereby further improving the display contrast of the display device.

(Modification)

In the structure of the display device according to the embodiment of the present disclosure, by including a material that absorbs light having a wavelength of 700nm or more in any one of the layers from the light emitting side of the backlight 32 to the polarizing layer 10, or by additionally providing a layer that absorbs light having a wavelength in this range, light having a wavelength of 700nm or more emitted from the backlight 32 can be eliminated. In this way, even when a dye-based polarizing layer such as the polarizing layer D described above is used, a liquid crystal display device excellent in display performance can be obtained regardless of the light emission characteristics of the backlight 32.

Among these, for example, a commercially available "filter" that allows only light having a specific property to be transmitted but does not allow other light to be transmitted among incident light may be used. More specifically, it is preferable to use a short-pass filter that allows only light having a wavelength shorter than a certain wavelength to be transmitted. In this embodiment, for example, a short-pass filter having a wavelength selective ability in a wavelength range around 650 to 700nm can be used.

In addition, for example, a cyanine colorant having a maximum absorption wavelength of 700nm to 780nm may be used. In the case of using this material, it may be contained in the adhesive layer of the polarizing layer 10, or may be provided by being coated on any one of the layers from the exit side of the backlight 32 to the polarizing layer 10, or the like.

Claims

1. A display device, comprising

A dye-based polarizing layer formed by using a dye having the following characteristics in combination, and a backlight source: (1) Having a maximum absorption wavelength and dichroism in any one of wavelength regions of 400 to 500nm,500 to 590nm and 590 to 660nm, and (2) having a wavelength region which does not affect polarization characteristics in a wavelength region other than the wavelength region in which the maximum absorption wavelength is located,

Wherein the dye-based polarizing layer has an orthogonal transmittance (Tc) of 1% or more in a visible light range of 700nm to 780nm, a single transmittance (Ts) of 33% or more in the entire wavelength range of 420nm to 780nm, and a visual sensitivity corrected orthogonal transmittance (Yc) of 0.01% or less in a wavelength range of 400nm to 700nm,

In the orthogonal transmission wavelength range, the luminous intensity of the backlight is 0.03 or less, and the luminous intensity is normalized according to the maximum luminous intensity in the visible light range of 700nm to 780 nm.

2. The display device of claim 1, wherein,

The dye-based polarizing layer has an orthogonal transmittance (Tc) of 1% or more over the entire wavelength range of 700nm or more and less than 750 nm.

3. The display device according to claim 1, comprising a liquid crystal layer.

4. A display device as claimed in claim 2, comprising a liquid crystal layer.