JP2006039328A - Diffusion film for display and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a liquid crystal display device providing a distinct and clear picture as a television by realizing the improvement of the color purity of emitted light color and the enhancement of the uniformity of luminance inexpensively preferably without increasing new members. <P>SOLUTION: A color reproducing range is more improved by ≥5% by using the diffusion film containing at least dyestuff having selective absorption in a wavelength region from 440nm to 510nm and/or dyestuff having selective absorption in a wavelength region from 570nm to 605nm at least in any one of a diffusion layer, base material and a back coat layer for the liquid crystal display device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diffusion film for a display, particularly preferably a diffusion film for a liquid crystal display device and a liquid crystal display device using the same. More specifically, the present invention relates to a diffusion film for the purpose of improving the color reproducibility of a liquid crystal display device.

  In recent years, with the advancement of society, optoelectronic-related parts and devices have made remarkable progress. In particular, displays for displaying images are becoming increasingly popular for use in computer monitor devices in addition to conventional television receivers. In particular, the market demands for larger and thinner displays are increasing. In recent years, liquid crystal display devices (LCD) have attracted attention as a display that achieves thinning and energy saving. In particular, liquid crystal televisions using LCDs are attracting attention from the viewpoint of space and power saving, and LCD colorization technology is In recent years, it has made remarkable progress.

LCDs are mainly classified into two types depending on the display method. One is a transmissive liquid crystal display device and the other is a reflective liquid crystal display device. The transmissive LCD brightens the display screen with a light source (backlight) located behind the liquid crystal panel, and has a structure including at least a light source, a reflector, and a backlight unit including a light guide plate as necessary. . Examples of the light source of the backlight unit include incandescent bulbs, light emitting diodes (LEDs), electroluminescence (EL), fluorescent lamps, metal hydride lamps, etc. Among them, fluorescent lamps, particularly three-wavelength fluorescent tubes are preferably used. It has been. The three-wavelength fluorescent tube has an emission spectrum at the position of “three primary colors” of red, green, and blue.
On the other hand, a reflective LCD does not use a backlight, but reflects sunlight or light from indoor and outdoor lighting fixtures to brighten the display screen.

  In addition, many optical films or optical sheets are used in LCDs, particularly transmissive LCDs. Hereinafter, the film and the sheet are referred to as a film without distinction. Various films such as a diffusion film, a polarizing film, a lens film, a reflective film, and a reflective polarizing film are used as optical films used in LCDs. These optical films control light transmission and reflection, polarization, and the like. The functional material contained in the film may play an important role in the expression of this function. For example, the member which controlled the shape of the surface like a pigment | dye and a lens film is mentioned.

  Color filters are usually used to color LCDs. This color filter is divided into red, green, and blue parts, blocks unwanted wavelength parts of the light emitted from the backlight, and extracts the three primary colors of red, green, and blue as a single color, and color reproducibility. (Color purity) is determined.

  Conventionally, an LCD has been mainly used as a terminal of a computer device. However, in recent years, as the color of the LCD has progressed, the replacement of a television with a cathode ray tube has been rapidly progressing. In order to use an LCD as a television, it is necessary to compete with a cathode ray tube. Comparing LCDs and CRTs with full-color display, which is essential for current television, was not a problem with computer monitors, but LCDs are particularly inferior in red color compared to CRTs. The voice which points out is growing.

In order to solve this problem, it is necessary to increase the color purity of red, green, and blue emitted from the display as much as possible, particularly to increase the color purity of red. In order to improve color purity, the wavelength spectrum of each emission of red, green, and blue should be as sharp as possible, or unnecessary emission other than the above emission wavelengths should be reduced as much as possible. In both cases, complicated processing is required, and both are not easy in terms of technology and cost, and simpler color purity improvement technology is expected.
Up to now, as attempts to improve color purity, Japanese Patent Application Laid-Open No. 58-153904 (Patent Document 1), Japanese Patent Application Laid-Open No. 59-221943 (Patent Document 2), Japanese Patent Application Laid-Open No. 60-22102 (Patent Document). 3) Although there are reports in JP-A-60-65050 (Patent Document 4), JP-A-5-316329 (Patent Document 5), etc., it cannot be said that the effect is sufficient.

  In particular, in a transmissive LCD, the light emitted from the backlight includes unnecessary light emission that lowers the color purity existing in the vicinity of 480 nm and 585 nm. In the color filter, this unnecessary light emission cannot be sufficiently blocked, and sufficient color purity of green and red is not obtained.

As another method of suppressing unnecessary light emission that lowers the color purity, absorption of unnecessary light emission by a functional dye can be mentioned. This is a method of improving color purity by absorbing unnecessary light using a functional dye that absorbs only light having a wavelength at which unnecessary light emission exists. When the color purity is improved by the dye, it is sufficient that the dye has a uniform spread, and there is no need for complicated processing. Therefore, the improvement of color purity by the functional dye can be an easy and effective means for improving the color purity of the LCD. However, dyes are expensive and the impact on product cost may not be negligible. For this reason, a method for improving color purity with as little pigment as possible has been awaited.
JP 58-153904 A JP 59-221943 A JP 60-22102 A JP 60-65050 A JP-A-5-316329

  SUMMARY OF THE INVENTION An object of the present invention is to provide a display such as a liquid crystal display device that can improve the color purity of light emission color and improve the uniformity of luminance at a low cost and provide, for example, a clear and beautiful image as a television.

In order to solve the above problems, the present inventors have studied. As a result, it is necessary for the LCD structural mechanism using a reflective polarizing film, etc., to contain a dye in a diffusion film that allows light from the light source to reciprocate several times. Thus, the inventors have found that the same color reproduction range can be obtained and completed the present invention.
That is, the present invention
(1) containing a dye (a) having a selective absorption maximum in a wavelength region between 440 nm and 510 nm and / or a dye (b) having a selective absorption maximum in a wavelength region between 570 nm and 605 nm. A diffusion film for display characterized by
(2) Preferably, at least the substrate (A), the diffusion layer (B), and the backcoat layer (C) have a laminated structure in the order of (B) / (A) / (C), and the substrate (A) A diffusion film for display, characterized in that the dye (a) and / or the dye (b) is contained in at least one member of the diffusion layer (B) and the backcoat layer (C),
(3) A display diffusion film characterized in that an ultraviolet absorber is preferably contained in at least one member of the substrate (A), the diffusion layer (B) and the backcoat layer (C),
(4) Preferably, the display diffusion film is characterized in that the dye (a) and / or the dye (b) is a porphyrin compound,
(5) Preferably, the minimum value of light transmittance in the wavelength region of 440 nm to 510 nm is 10% to 85% and / or the minimum value of light transmittance in the wavelength region of 570 nm to 605 nm is 10% to 85%. Is a diffusion film for display.
These display diffusion films have a preferable feature that the color purity can be effectively improved.
The present invention also provides
(6) A liquid crystal display device using the display diffusion film,
(7) Preferably, the liquid crystal display device is characterized in that the display diffusion film has a configuration installed between a light source and a liquid crystal panel.
Since these liquid crystal display devices have excellent color purity, they can provide beautiful images.

  According to the present invention, it is possible to effectively remove light in an unnecessary wavelength region emitted from a light source, and it is possible to obtain the same effect with a smaller amount of dye than in the prior art. As a result, it is possible to improve hue and preferably improve luminance uniformity at low cost, and provide a clear image.

    The display diffusion film according to the present invention includes a dye (a) having a selective absorption maximum in a wavelength region between 440 nm and 510 nm and / or a dye having a selective absorption maximum in a wavelength region between 570 nm and 605 nm. (B) is contained.

By including the dye (a) having a selective absorption maximum in the wavelength region between 440 nm and 510 nm, it is possible to remove light that decreases the color purity of blue and / or green existing in the meantime. By including the dye (b) having a selective absorption maximum in the wavelength region between 570 nm and 605 nm, the light that decreases the color purity of green and / or red existing during this period is removed. An effect is obtained.
The dye used in the present invention is not limited to a known dye as long as it is a dye (a) having an absorption maximum in the wavelength region of 440 nm to 510 nm and / or a dye (b) having an absorption maximum in the wavelength region of 570 nm to 605 nm. It can be used without. Moreover, it is not limited to dyes and pigments. Specific examples of the dye (a) and the dye (b) include xanthene, squarylium, cyanine, oxonol, azo, pyromethene, and porphyrin compounds. Preferably, a porphyrin-type compound is mentioned.
Particularly preferably, as the dye (b) having an absorption maximum between wavelengths of 570 nm to 605 nm, the general formula (1)
The porphyrin-type compound represented by these is used suitably.

［式（１）中、Ａ^１〜Ａ^８は、各々独立に、水素原子、ハロゲン原子、ニトロ基、シアノ基、ヒドロキシ基、アミノ基、カルボキシル基、スルホン酸基、炭素数１〜２０のアルキル基、ハロゲノアルキル基、アルコキシ基、アリールオキシ基、モノアルキルアミノ基、ジアルキルアミノ基、アラルキル基、アリール基、ヘテロアリール基、アルキルチオ基、または、アリールチオ基を表し、Ａ^１とＡ^２、Ａ^３とＡ^４、Ａ^５とＡ^６、Ａ^７とＡ^８は各々独立に連結基を介して芳香族環を除く環を形成してもよく、Ｍは２個の水素原子、２価の金属原子、３価の１置換金属原子、４価２置換金属原子、またはオキシ金属原子を表す。］
Ａ^１〜Ａ^８の具体例としては、各々独立に水素原子：フッ素、塩素、臭素、ヨウ素のハロゲン原子：ニトロ基：シアノ基：ヒドロキシ基：アミノ基：カルボキシル基：スルホン酸基：炭素数１〜２０の直鎖、分岐または環状アルキル基：炭素数１〜２０のハロゲノアルキル基：炭素数１〜２０のアルコキシ基：炭素数２〜２０のアルコキシアルコキシ基：炭素数６〜２０のアリールオキシ基：炭素数２〜２０のジアルキル基：炭素数７〜２０のアラルキル基：炭素数６〜２０のアリール基：ヘテロアリール基：炭素数１〜２０のアリールチオ基等が挙げられる。

[In the formula (1), A ^{1 to} A ⁸ each independently represents a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydroxy group, an amino group, a carboxyl group, a sulfonic acid group, or an alkyl group having 1 to 20 carbon atoms. Represents a group, a halogenoalkyl group, an alkoxy group, an aryloxy group, a monoalkylamino group, a dialkylamino group, an aralkyl group, an aryl group, a heteroaryl group, an alkylthio group, or an arylthio group, and A ¹ and A ² , A ³ And A ⁴ , A ⁵ and A ⁶ , A ⁷ and A ⁸ may each independently form a ring excluding an aromatic ring via a linking group, and M is two hydrogen atoms, a divalent metal atom A trivalent monosubstituted metal atom, a tetravalent disubstituted metal atom, or an oxymetal atom is represented. ]
Specific examples of A ^{1 to} A ⁸ are each independently a hydrogen atom: a halogen atom of fluorine, chlorine, bromine, or iodine: a nitro group: a cyano group: a hydroxy group: an amino group: a carboxyl group: a sulfonic acid group: 1 carbon atom. -20 linear, branched or cyclic alkyl group: C1-C20 halogenoalkyl group: C1-C20 alkoxy group: C2-C20 alkoxyalkoxy group: C6-C20 aryloxy group : C2-C20 dialkyl group: C7-C20 aralkyl group: C6-C20 aryl group: Heteroaryl group: C1-C20 arylthio group etc. are mentioned.

Specific examples where A ¹ and A ² , A ³ and A ⁴ , A ⁵ and A ⁶ , or A ⁷ and A ⁸ form a ring via a linking group include —CH ₂ CH ₂ CH ₂ CH ₂ — , —CH ₂ CH ₂ CH (NO ₂ ) CH ₂ —, —CH ₂ CH (CH ₃ ) CH ₂ CH ₂ —, —CH ₂ CH (Cl) CH ₂ CH ₂ — etc. Can be mentioned.

Specific examples of the divalent metal represented by M include Cu, Zn, Fe, Co, Ni, Ru, Rh, Pd, Pt, Mn, Sn, Mg, Hg, Cd, Ba, Ti, Be, and Ca. Can be mentioned. Specific examples of the monosubstituted trivalent metal include Al-F, Al-Cl, Al-Br, Al-I, Ga-F, Ga-Cl, Ga-Br, In-I, Ti-F, _{Ti-Cl, Ti-Br,} Ti-I, Al-C 6 H 5, Al-C 6 H 4 (CH 3), In-C 6 H 5, In-C 6 H 4 (CH 3), Mn ( _{OH), Mn (OC 6 H} 5), Mn [OSi (CH 3) 3], Fe-Cl, include Ru-Cl, etc.. Specific examples of the disubstituted tetravalent metal include CrCl ₂ , SiF ₂ , SiCl ₂ , SiBr ₂ , SiI ₂ , SnF ₂ , SnCl ₂ , SnBr ₂ , SnI ₂ , ZnCl ₂ , GeF ₂ , GeCl ₂ , GeBr ₂ , GeI ₂ , TiF ₂ , TiCl ₂ , TiBr ₂ , Si (OH) ₂ , Sn (OH) ₂ , Ge (OH) ₂ , Zr (OH) ₂ , Mn (OH) ₂ , TiA ₂ , CrA ₂ , SiA ₂ , SnA ₂ , GeA ₂ [A represents an alkyl group, a phenyl group, a naphthyl group, a trialkylsilyl group, a dialkylalkoxy group, an alkylthio group, an arylthio group, and derivatives thereof. ], Si (OA ') ₂ , Cr (OA') ₂ , Ge (OA ') ₂ , Ti (OA') ₂ , Cr (OA ') ₂ [A' is an alkyl group, a phenyl group, a naphthyl group, A trialkylsilyl group, a dialkylalkoxysilyl group, an acyl group, a trialkyltin group, a trialkylgermanium group, and derivatives thereof are represented. ], Si (SA ") ₂ , Sn (SA") ₂ , Ge (SA ") ₂ [A" represents an alkyl group, a phenyl group, a naphthyl group, and derivatives thereof. ] Etc. are mentioned. Specific examples of the oxymetal include VO, MnO, TiO and the like. Among them, Pd, Cu, Ru, Pt, Ni, Co, Rh, Zn, VO, TiO, Si (Y) ₂ , Ge (Y) ₂ [Y is a halogen atom, an alkoxy group, a phenyl group, a naphthyl group, an acyloxy group. Represents a group, a hydroxy group, an alkyl group, an alkylthio group, a phenylthio group, a naphthylthio group, a trialkylsilyloxy group, a trialkyltinoxy group or a trialkylgermaniumoxy group. ] Is preferable. More preferred are Cu, VO, Ni, Pd, Pt, and Co.

  The porphyrin compound of the formula (1) is, for example, a porphyrin compound having a branched alkyl group as a substituent such as a tetra-t-butyl-tetraazaporphyrin complex or a tetra-neo-pentyl-tetraazaporphyrin complex. It is most preferable because it is relatively easy to produce, the solubility in a solvent is improved, the complex is stable, and the absorption characteristics are excellent. This is considered to be because the solubility in the solvent is increased due to the stericity of the complex as a result of adding a branched alkyl group such as a tertiary butyl group or a neo-pentyl group. For this reason, since it becomes easy to contain a pigment | dye in various materials, a pigment | dye can be disperse | distributed uniformly and it is advantageous when obtaining the diffusion film for displays which has a high function.

  The diffusion film for display of the present invention has a laminated structure in which the substrate (A), the diffusion layer (B), and the backcoat layer (C) are in the order of (B) / (A) / (C). Is preferred. In addition, it is preferable that the pigment (a) and the pigment (b) are contained in at least one of the above (A), (B), and (C) from the viewpoint of reducing the number of members. Of course, it is also possible to provide a dye-containing layer separately and laminate them.

Any known method can be employed as a method of incorporating the coloring matter into the member. As a specific example, there is a method in which a resin and a pigment are uniformly mixed and molded into a film or the like. In this method, the processing temperature, filming conditions, and the like differ depending on the type of resin mixed with the pigment, but usually, the pigment is added to the base resin powder and pellets, and 150 ° C. while taking into account the melting temperature of the resin. After heating and melting at ˜350 ° C., preferably kneading, molding is performed to produce plastic sheets and plastic particles that are preferably used to form a diffusion film described later. Further, an additive such as a plasticizer may be added for the purpose of facilitating molding.
The content of the dye varies depending on the absorption coefficient of the dye, the thickness of the polymer film, and the intended transmission characteristics, but is usually from several ppm (mass) ppm to several mass percent of the base resin.

The said method can be used conveniently when making a base material (A) contain a pigment | dye, or making it contain in the particle | grains in a diffusion layer (B) and a backcoat layer (C).
As another method, there is a method by casting. In the casting method, first, a dye is added and dissolved in a resin solution in which a resin or a resin monomer is dissolved in an organic solvent. Next, a plasticizer, a polymerization initiator, an antioxidant and the like are added as necessary, and the mixture is poured onto a mold having a required surface state. Next, a plastic plate or a polymer film is generally obtained by solvent evaporation, drying, or polymerization, solvent evaporation, and drying.
Said method can be used suitably as a method of producing the base material (A) containing a pigment | dye.

  As a method of coating the dye on the substrate (A), etc., a method of forming a paint by dissolving the dye in a binder resin and an organic solvent, and finely pulverizing the dye into an uncolored acrylic emulsion paint (particle size: 50 nm to 500 nm) The method of coating using the coating material obtained by the method etc. which disperse | distributed what was disperse | distributed and used as the acrylic emulsion type water-based coating material etc. is mentioned. These methods can also be suitably used when the dye is contained in the binder layer of the diffusion layer (B) and the backcoat layer (C).

The concentration of the dye varies depending on the absorption coefficient of the dye, the thickness of the coating, and the desired optical properties, but is preferably 0.001 to 30 weight percent. In addition, you may add antioxidant etc. in a coating material.
The coating material prepared by the above method is coated and dried on a substrate by a conventionally known coating method such as a bar coater, blade coater, spin coater, reverse coater, die coater, or spray, and a binder containing a pigment. Layers can be formed.

  If the base material (A) in this invention is a transparent material, there will be no restriction | limiting in particular, A transparent polymer film etc. will be used. Specifically, polysulfone (PSF), polyethersulfone (PES), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polycarbonate (PC), polyetheretherketone (PEEK), polypropylene (PP) , Triacetyl cellulose (TAC) and the like, but are not limited thereto.

The thickness of the substrate (A) is not particularly specified as long as it has a certain degree of mechanical strength, but is generally about 10 μm to 500 μm. When high transparency is required as in the present invention, the thickness is preferably 10 μm to 250 μm. Among these, 30 μm to 200 μm is most preferably used.
As the diffusion layer (B) in the present invention, any known diffusion layer can be used. Also, any known method can be applied as the formation method.
Preferable examples of the diffusion layer (B) of the present invention include a configuration in which spherical small particles are dispersed in a binder.

  As the binder, a resin can be suitably used. The resin is not particularly limited as long as it is a transparent resin. In general, a thermosetting resin is used. Specific examples include melamine resin, epoxy resin, phenol resin, acrylic resin, urethane resin, silicon resin, urea resin and the like.

The material used as the spherical small particles is preferably a transparent material, but is not particularly limited. Specific examples of the material for the small particles having transparency include acrylic resin, polystyrene, polyurethane, polyacrylonitrile and the like.
The particle size of the small particles is not particularly limited as long as it has a light diffusing effect and does not affect the coating of the binder layer, and about 0.1 μm to 100 μm is generally used. Preferably, it is 1 micrometer-50 micrometers.

  The content of the small particles in the binder layer is generally 20% by mass to 80% by mass with respect to the resin, but is not particularly limited as long as a sufficient light diffusion effect can be obtained. . Furthermore, 30 mass%-60 mass% is used suitably.

  The back coat layer (C) in the present invention prevents sticking between the diffusion film and an adjacent member such as a light guide plate when the diffusion film of the present invention is applied to a display device such as a liquid crystal display device. It is a layer preferably introduced for the purpose. Generally, it is composed of a binder and spherical small particles. As the binder, a resin is generally used. The binder resin is not particularly limited as long as it is a transparent resin. For example, the resin used in the diffusion layer (B) can be suitably used. In addition, the small spherical particles used in the diffusion layer (B) can also be preferably used.

  The preferred constitution of the diffusion film in the present invention is as follows: diffusion layer (B) containing pigment in binder / base material (A) / back coat layer (C), diffusion layer containing pigment in small particles (B) / Base material (A) / Back coat layer (C), Diffusion layer (B) / Base material containing dye (A) / Back coat layer (C), Diffusion layer (B) / Base material (A) / Binder A backcoat layer (C) containing a dye in the layer, a diffusion layer (B) / base material (A) / a backcoat layer (C) containing a dye in a small particle.

  An example of the diffusion film of the present invention is shown in FIG. This is because a coating layer containing a small particle of acrylic resin, an acrylic resin as a binder resin, and a tetraazaporphyrin complex as a pigment is applied onto a substrate 30 such as PET to form a diffusion layer 40 containing the pigment, The diffusion film 10 is obtained by applying a coating liquid containing an acrylic resin binder resin and acrylic resin small particles on the main surface opposite to the layer 40 to form the backcoat layer 20.

In the diffusion film of the present invention, it is preferable from the viewpoint of the durability of dyes and resins that the ultraviolet absorbing ability is imparted by containing an ultraviolet absorber or the like. This preferably used ultraviolet absorbent may be contained in one or more members constituting the diffusion film of the present invention, such as the base material (A), the diffusion layer (B), and the back coat layer (C). Of course, a mode in which the binder and the small particles constituting the preferred form of the above-described diffusion layer (B) have an ultraviolet absorbing ability may be used. Furthermore, when used in a display device such as a liquid crystal display device, it is also preferable that even if other members constituting the display device contain an ultraviolet absorber, these members are members having ultraviolet absorbing ability. It is.
Moreover, when using the diffusion film in this invention for a display apparatus etc., it is also a suitable aspect to make the light source side member of display apparatuses, such as a light-guide plate, contain an ultraviolet absorber.

The diffusion film of the present invention obtained as described above can be suitably used for various display devices. A preferred example is a liquid crystal display device. In particular, when the diffusion film of the present invention is arranged inside the liquid crystal display device, specifically between the liquid crystal panel and the backlight, compared to the case of using the diffusion film of the present invention as a color tone correction filter on the front surface of the liquid crystal display device, It is possible to reduce the amount of the dye used for obtaining the same color reproducibility. Specifically, it may be possible to reduce from about 1/2 to about 3/4.
The reason why the amount of dye to be used can be reduced is not clear, but it is considered that the following estimation is possible.

  The liquid crystal display device generally has a configuration of a reflector / light source / light guide plate / diffusion film / lens sheet / reflective polarizing film / polarizing film 1 / liquid crystal panel / polarizing film 2. In the case of the above configuration, the diffusion film is usually used by being incorporated in a backlight unit including a light source, a reflection plate, and a light guide plate. Here, considering the light transmission path, the light emitted from the light source passes through the light guide plate, the diffusion film, the lens sheet, the reflective polarizing film, and the polarizing film 1 (regular transmission). The reflective polarizing film has a function of transmitting light having a phase that is not absorbed by the polarizing film 1 and selectively reflecting light having a phase that is absorbed.

  Therefore, the light reflected by the reflective polarizing film is again transmitted (reversely transmitted) to the light source side, reflected by the reflecting plate, and again transmitted (regularly transmitted) through each sheet. Thus, between the light source in the backlight unit and the reflective polarizing film, the optical path length in the light diffusing film that did not pass through the polarizing reflective film is substantially increased, so that the dye absorption capacity is more effective. It becomes possible to use it.

  Examples of the film or sheet used between the light source and the reflective polarizing film include a light guide plate, a diffusion film, and a lens sheet. Even if these members other than the diffusion film contain a pigment, it is expected that the same effect as described above can be obtained. However, among these, it is considered preferable to contain a pigment in the diffusion film. The reason is as follows.

  A diffusion film generally has a relatively simple three-layer structure such as a diffusion layer, a base material, and a back coat layer, and does not have a complicated structure like a lens sheet. Is easy. Further, it is easy to incorporate a dye in any layer such as a diffusion layer, a base material, and a back coat, and the degree of freedom in product design is high. Although it is relatively easy to include a pigment in the light guide plate, it is considered advantageous to include a pigment in the diffusion film for the following reason.

  As described above, since the dye may be deteriorated by the ultraviolet rays, it is preferable that the light passing through the dye is one obtained by cutting the ultraviolet rays. It can be expected that the durability is further improved by imparting the ultraviolet ray cutting ability to the light source side more than the layer containing the dye. The light guide plate is the closest to the light source among the above-mentioned members, and it is preferable that the light guide plate itself has an ultraviolet ray cutting ability in order to contain the pigment, and there are cases where the structure is restricted. On the other hand, if the diffusion film can provide the light guide plate with ultraviolet absorption ability, it is not necessary to provide the diffusion film with ultraviolet absorption ability. Moreover, even when it is necessary to give the diffusion film ultraviolet absorption ability, if the multilayer structure of the diffusion film is used, it is possible to introduce the ultraviolet absorption ability relatively easily without increasing new processes. . Also, the positional relationship with the dye-containing layer has a high degree of freedom. For the above reasons, a configuration in which a diffusion film containing a pigment is disposed between the liquid crystal panel and the light source is a preferable embodiment for realizing a reduction in the amount of pigment to be used and high durability.

  In the diffusion film of the present invention, the minimum value of light transmittance in the wavelength region of 440 nm to 510 nm is 10% to 85% and / or the minimum value of light transmittance in the wavelength region of 570 nm to 605 nm is 10% to 85%. It is preferable in terms of luminance maintenance rate and color purity. The light transmittance of the diffusion film of the present invention can be measured using a conventional method. Specifically, a method of measuring light transmittance in the visible region using a spectrophotometer (U-3400) manufactured by Hitachi, Ltd. may be mentioned.

The liquid crystal display device using the diffusion film obtained as described above can remove unnecessary light emission emitted from the light source, and can provide a beautiful image with improved color purity, preferably over a long period of time. it can.
As the light source, a known light source can be used without limitation. For example, in the case of a transmissive LCD, incandescent bulbs, light emitting diodes (LEDs), electroluminescence (EL), fluorescent lamps, metal hydride lamps and the like can be mentioned. Among these, fluorescent lamps are preferably used as the light source. Fluorescent lamps are roughly classified into a hot cathode type and a cold cathode type depending on the electrode structure and lighting method, and the hot cathode type tends to be larger for both electrodes and inverters. The hot-cathode type is less efficient in the vicinity of the electrode that does not contribute to light emission and is more efficient. It exhibits luminous efficiency several times better than the cold-cathode type. The cold cathode type is more preferably used from the viewpoint of low power consumption and durability.

The diffusion film of the present invention can be used for each display device such as an optical filter of a plasma display panel in addition to the liquid crystal display device. The pigment used for the diffusion film of the present invention is a pigment from a member containing the pigment. Dye is collected by extraction with a highly soluble solvent or by removing materials other than the dye with a solvent that dissolves only the other materials that form the member, and this is collected by nuclear magnetic resonance (NMR) and infrared spectroscopy. The dye can be identified or quantified by a known method such as the method (IR). Moreover, the maximum absorption wavelength of these pigment | dyes may analyze the above-mentioned extracted pigment | dye with a spectroscope by a spectroscope, or the member itself containing a pigment | dye may be able to measure a maximum absorption wavelength with a spectroscope.
The present invention will be specifically described with reference to examples. In addition, this invention is not restrict | limited by a following example.

Example 1
A diffusion film having a cross-sectional configuration similar to that of FIG. 1 was produced by the following method.
As a base material, a transparent polyethylene terephthalate (PET) film [thickness 100 μm, manufactured by Teijin DuPont, Tetron (registered trademark) film] is used. On one main surface, transparent acrylic resin particles (particle diameter: 5 μm to 15 μm) Transparent acrylic resin (Mitsubishi Chemical Co., Ltd., Chemisnow) dispersed with 40 mass% (in solid content) and copper complex of tetraazaporphyrin (absorption maximum wavelength: 585 nm) in 500 mass% (in solid content). A solution of Rayon Co., Ltd. (Dianar HR) was applied to a dry thickness of 25 μm to form a diffusion layer. On the main surface of the PET film opposite to the diffusion layer, 5% by mass (in solid content) of transparent acrylic resin particles (manufactured by Soken Chemical Co., Ltd., Chemisnow) having an average particle size of 10 μm and an ultraviolet absorber (2- A solution of a transparent acrylic resin (Made by Mitsubishi Rayon Co., Ltd., Dainar HR) in which hydroxy-4-n-octhexoxybenzophenone) is blended and dispersed so that the transmittance at 380 nm is 5% or less is 5 μm in dry thickness Was applied to form a backcoat layer to obtain a diffusion film.
When the light transmittance in the visible region was measured for the obtained diffusion film with a spectrophotometer (U-3400) manufactured by Hitachi, Ltd., the absorption of light having a wavelength of 585 nm showed a minimum value, and the transmittance was 52%. Met.
The obtained diffusion film is disposed between a liquid crystal panel and a backlight device including a light source, a reflector, and a light guide plate so that the back coat layer is on the backlight unit side, thereby producing a liquid crystal display device. Using MINOLTA CS-1000, a chromaticity diagram representing the color reproduction range of RGB was obtained from red, green, and blue light emission. Table 1 shows the results of evaluating the area of a triangle composed of three RGB points.

(Example 2)
A diffusion film having a cross-sectional configuration similar to that of FIG. 1 was produced by the following method.
As a base material, a film [thickness: 100 μm] formed by adding 125 (mass) ppm of a tetraazaporphyrin copper complex (absorption maximum wavelength: 585 nm) to PET resin, heating and melting the film, and containing the dye Transparent acrylic resin (Mitsubishi Rayon (in solid content) in which 40% by mass (in solid content) of transparent acrylic resin particles (particle size: 5 μm to 15 μm, manufactured by Soken Chemical Co., Ltd., Chemisnow) is dispersed on one main surface of the PET substrate. Co., Ltd. (Dianar HR) solution was applied to a dry thickness of 25 μm to form a diffusion layer. On the main surface opposite to the diffusion layer, 5% by mass (in solid content) of transparent acrylic particles having an average particle diameter of 10 μm (manufactured by Soken Chemical Co., Ltd., Chemisnow) and an ultraviolet absorber (2-hydroxy-4-n) -Backcoat layer by applying a transparent acrylic resin (Mitsubishi Rayon Co., Ltd., Dainar HR) in which octhexoxybenzophenone) is blended and dispersed so that the transmittance at 380 nm is 5% or less to a dry thickness of 5 μm. And a diffusion film was obtained.
When the light transmittance in the visible region of the obtained diffusion film was measured, the absorption of light having a wavelength of 585 nm showed a minimum value, and the transmittance was 52%.
The obtained film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
A diffusion film having a cross-sectional configuration similar to that of FIG. 1 was produced by the following method.
As a base material, a polyethylene terephthalate (PET) film [thickness 100 μm, manufactured by Teijin DuPont, Tetron (registered trademark) film] is used, and transparent acrylic resin particles (particle size 5 μm to 15 μm on one main surface) A diffusion layer is formed by applying a solution of transparent acrylic resin (Mitsubishi Rayon Co., Ltd., Dainar HR) in which 30% by mass (in solid content) of Soken Chemical Co., Chemisnow is dispersed at a dry thickness of 25 μm. did. On the main surface of the PET film opposite to the diffusion layer, transparent acrylic resin particles (manufactured by Soken Chemical Co., Chemisnow) having a particle size of 10 μm and a copper complex of tetraazaporphyrin (absorption maximum wavelength: 585 nm) 2500 (mass) ) A solution of transparent acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., Dianar HR) in which ppm (in the solid content) was dispersed was applied at a dry thickness of 5 μm to prepare a diffusion film having a back coat layer.
When the light transmittance in the visible region of the obtained diffusion film was measured, the absorption of light having a wavelength of 585 nm showed a minimum value, and the transmittance was 52%.
Using the produced diffusion film, a liquid crystal display device was produced and evaluated in the same manner as in Example 1 except that a light guide plate having ultraviolet absorbing ability was used. The results are shown in Table 1.

Example 4
Except for using a copper complex of tetraazaporphyrin (absorption maximum wavelength: 585 nm) at 1500 (mass) ppm (in solids) and a porphyrin compound (absorption maximum wavelength: 495 nm) at 1000 (mass) ppm (in solids). A diffusion film was produced in the same manner as in Example 3.
When the light transmittance in the visible light region of the obtained diffusion film was measured, the absorption of light having wavelengths of 585 nm and 495 nm showed a minimum value, and the transmittances were 66% and 72%, respectively.
A liquid crystal display device was produced and evaluated in the same manner as in Example 3. The results are shown in Table 1.

(Comparative Example 1)
A diffusion film was prepared and evaluated in the same manner as in Example 1 except that a copper complex of tetraazaporphyrin was not used. The results are shown in Table 1.

(Example 5)
A diffusion film was produced in the same manner as in Example 3 except that 4150 ppm of tetraazaporphyrin copper complex was used. A liquid crystal display device was obtained and evaluated in the same manner as in Example 1 except that this was placed on the person side of the liquid crystal panel and the diffusion film produced in Comparative Example 1 was placed between the liquid crystal panel and the backlight unit. It was.
When the light transmittance in the visible region of the obtained diffusion film was measured, the absorption of light having a wavelength of 585 nm showed a minimum value, and the transmittance was 38%.
The results are shown in Table 1.

From the results of the above examples, an improvement in the color reproduction range of 10% or more was obtained in any case.
Comparing Example 3 and Example 5, the same color reproduction range was obtained by reducing the amount of dye used by installing the display diffusion film in the present invention between the light source and the liquid crystal panel. .

  The present invention can be suitably used for a diffusion film for a liquid crystal display device, can eliminate luminance unevenness, and can easily improve the color purity of the liquid crystal display device at low cost.

It is sectional drawing (schematic diagram) which shows an example of the diffusion film of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diffusion film 20 Backcoat layer 30 Base material 40 Diffusion layer containing pigment

Claims (7)

It contains a dye (a) having a selective absorption maximum in a wavelength region between 440 nm and 510 nm and / or a dye (b) having a selective absorption maximum in a wavelength region between 570 nm and 605 nm. Diffusion film for display. At least the substrate (A), the diffusion layer (B), and the backcoat layer (C) have a laminated structure in the order of (B) / (A) / (C), and the substrate (A) and the diffusion layer The diffusion film for a display according to claim 1, wherein the pigment (a) and / or the pigment (b) is contained in at least one member of (B) and the backcoat layer (C). The diffusion film for display according to claim 2, wherein an ultraviolet absorber is contained in at least one member of the substrate (A), the diffusion layer (B), and the backcoat layer (C). The diffusion film for display according to claim 1, wherein the pigment (a) and / or the pigment (b) is a porphyrin compound. The minimum value of light transmittance in the wavelength region of 440 nm to 510 nm is 10% to 85% and / or the minimum value of light transmittance in the wavelength region of 570 nm to 605 nm is 10% to 85%. 1. A diffusion film for display as described in 1. A liquid crystal display device using the display diffusion film according to claim 1. The liquid crystal display device according to claim 6, wherein the display diffusion film has a configuration installed between a light source and a liquid crystal panel.

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