JP4602604B2 - Polymer film having scattering anisotropy and surface light source device using the same - Google Patents

Description

【００７５】
＊） 凝集体としての粒径
【図面の簡単な説明】
【図１】本発明の散乱異方性を用いた偏光出射性面光源装置の概念図の一例である。
【図２】本発明の散乱異方性を用いた偏光出射性面光源装置の概念図の一例である。
【図３】従来の面光源装置の概念図である。
【図４】本発明の面光源装置における偏光変換の原理を説明する概念図である。
【図５】Ｎｘ＝１．５５、ｎｘ＝１．６８の場合の散乱パラメータαと散乱効率Ｑの関係（計算値）
【図６】Ｎｘ＝１．６０、ｎｘ＝１．８４の場合の散乱パラメータαと散乱効率Ｑの関係（計算値）
【図７】実施例１の接着層がパターニングされた面光源装置の概念図である。
【符号の説明】
１：導光体
２：散乱異方性層
３：反射板
４：冷陰極管
５：ランプリフレクター
６：非偏光光（自然偏光）
７：直線偏光の振動方向
８：異方散乱因子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer film having scattering anisotropy, and more particularly to a polymer film having scattering anisotropy with little in-plane color shift when used as a polarizing backlight.
[0002]
This film can be used as a polarizing surface light source device by using it as an end face incident type light guide plate in a backlight system of a liquid crystal display device, thereby using linearly polarized light as in a general-purpose liquid crystal display device. The light use efficiency in the image display device can be improved.
[0003]
[Prior art]
The liquid crystal display device is characterized by being thin and light and having low power consumption because it is driven at a low voltage, and is rapidly growing as a powerful image information display device.
[0004]
In general, a liquid crystal display element is composed of a cell in which twisted liquid crystal is held by two substrates, and a polarizing plate arranged on both sides thereof with polarization axes orthogonal to each other. As the polarizing plate, for example, a dichroic polarizing plate using an oriented dichroic dye such as PVA-iodine is used. This dichroic polarizing plate selectively absorbs only one linearly polarized light component among polarized light components orthogonal to each other and transmits only the other linearly polarized light component, thereby converting non-polarized light into linearly polarized light. .
[0005]
In a liquid crystal display device, first, non-polarized light emitted from a backlight is converted into linearly polarized light by a polarizing plate on the other side (backlight side) of the cell. Since this converted light rotates in the liquid crystal cell along the twist of the liquid crystal molecules, it is not absorbed by the polarizing plate in front of the liquid crystal cell (observer side) and is observed as display light. When a voltage is applied to the liquid crystal cell, the liquid crystal molecules are aligned in the direction of the electric field and are not twisted. Therefore, the polarized light transmitted through the liquid crystal cell is absorbed by the observer side polarizing plate.
[0006]
The light use efficiency of the liquid crystal display device is mainly regulated by (1) the light transmittance of the polarizing plate, (2) the aperture ratio of the liquid crystal panel, and (3) the light transmittance of the color filter. When the light use efficiency is low, the contrast (relative luminance) of the image light is low, and the display quality is deteriorated. On the other hand, if the output of the backlight light source is increased, the contrast of the image light increases, but the power consumption increases, and there arises a problem that the drive time is reduced particularly when used as a portable device.
[0007]
In order to increase the contrast of the image light, there is a method of condensing the light using a prism sheet or the like. In this case, although the contrast in the front direction is improved, the luminance is remarkably reduced at other angles, and the wide-range in recent years. This contradicts the flow of viewing angle.
[0008]
The light transmittance of the polarizing plate is the most regulated in terms of light utilization efficiency. In the process of extracting linearly polarized light from the light source light (unpolarized light) by the polarizing plate, theoretically 50% or more of the light is lost. Therefore, if the light source light is converted into linearly polarized light, and the vibration surface of the linearly polarized light can be matched with the vibration surface of the linearly polarized light transmitted through the polarizing plate, the light utilization efficiency is remarkably improved.
[0009]
For example, USP 3,610,729 discloses a method in which only one linearly polarized light is separated, and orthogonally polarized light in a perpendicular direction is reflected and reused using an optical film in which two types of films are laminated in multiple layers. ing. In addition, in EP606940A2, J. Broer, JAMMvan. Haaren, GNMol, F. Leenhouts; Asia Display '95, 735 (1995), by using a cholesteric liquid crystal and a quarter wave plate, only one circularly polarized light can be obtained. A method of increasing the light utilization efficiency by selectively transmitting and reflecting and reusing the other is disclosed.
[0010]
Although these methods are highly effective in terms of conversion efficiency to polarized light and light utilization efficiency, they are difficult to manufacture because they require a strict high-order structure, and are therefore expensive.
[0011]
Further, WO92 / 22838, F.M.Weber; SID 93 DIGEST, 669 (1993) discloses a method of performing polarization separation using a Brewster angle. Although these methods can be manufactured at a relatively low cost, the polarization conversion efficiency is insufficient, and the angle dependency of the polarization exit angle is large, and the types of linearly polarized light obtained are limited.
[0012]
In Japanese Patent Laid-Open Nos. 6-331824 and 9-292530, a layer having refractive index anisotropy is used for a light guide plate, and the difference in refractive index at the interface differs depending on the polarization direction. A method of performing is disclosed. These methods also have insufficient polarization conversion efficiency, and therefore the light utilization efficiency is not high. There is also a problem that the refractive index anisotropy is limited by the material.
[0013]
OAAphonin, et al .; Liq. Cryst., 15, 3, 395 (1993), OAAphonin; Liq. Cryst., 19, 4, 469 (1995), JP-A-8-76114, JP-A-9 Japanese Patent No. -274108 discloses a method in which an anisotropic scatterer in which a liquid crystal is oriented by stretching a composite of a polymer and a liquid crystal is used as a scattering type polarizing plate. Also, WO97 / 32222, WO97 / 32224, WO97 / 32226, WO97 / 32227, USP5,867,316, H. Yagt, et al .; Adv. Mater., 10, 2, 934 (1998), M. Miyatake, et al .; IDW'98, 247 (1998) discloses a method of making a scattering type polarizing plate by stretching an incompatible polymer blend film. Yes.
[0014]
JP-A-9-297204 discloses an anisotropic scattering element comprising a stretched film in which titanium oxide having an aspect ratio of 1 or more is arranged in one direction as a component that causes anisotropic scattering. It is described that when the polarizing plate is rotated on this element, it is darkest when the polarization axis coincides with the scattering axis (stretching direction) and brightest when it is orthogonal (coincidence with the transmission axis).
[0015]
These techniques used a method of transmitting polarized light in the direction (transmission axis) with the same refractive index by stretching or the like, and separating the polarized light by backscattering the polarized light in the direction with the mismatched refractive index (scattering axis). In other words, a so-called scattering-type polarizing plate is used. The principle of the polarization separation is fundamentally different from that of the light source device targeted in the present invention. In addition, in these techniques, it is necessary to back-scatter the polarized light in the scattering axis direction without forward scattering, so it is necessary to increase the scattering factor to cause multiple scattering, and as a result, the transmittance in the transmission axis direction is kept high. There is a problem that it becomes difficult. In order to improve the brightness, it is necessary to depolarize and reuse the backscattered light, but in the case of this scattering type polarizing plate, the amount of dissipated light due to scattering is large, so the reused light rate is low and the degree of polarization is reduced. The brightness improvement rate is low.
[0016]
WO97 / 32222, WO97 / 41484, and the like describe optical films (scattering polarizing films) that perform polarization separation using transmission / non-transmission due to scattering. With this optical film, the linearly polarized light in the scattering axis direction is made non-transmissive by backscattering, and the linearly polarized light in the transmission axis direction is transmitted to separate the polarized light. Therefore, in order to further increase the polarization separation ability, it is necessary to make the difference in transmittance as large as possible, and ideally, TTmax >> TTmin˜0. WO 97/32222 describes that the diffuse reflectance in the direction of the scattering axis is 30% or more.
[0017]
On the other hand, in order to solve these problems, WO00 / 16154 discloses a polarizing surface light source device using a film having scattering anisotropy. Since these polarizing surface light source devices have high polarization separation ability and polarization conversion ability, they are excellent in terms of effective use of light. However, since scattering is used for polarization separation, color unevenness in the surface of the surface light source may occur in some cases.
[0018]
[Problems to be solved by the invention]
The main object of the present invention is to provide a polymer film having scattering anisotropy that is suitable as a polarizing backlight material. In particular, when the film is attached to a light guide plate to form a polarizing backlight, An object of the present invention is to provide a polymer film having scattering anisotropy with small color unevenness.
[0019]
Another object of the present invention is to provide a polarized light emitting light guide, a polarized light emitting surface light source device, and a liquid crystal display device using the film.
[0020]
[Means for Solving the Problems]
In the polymer film containing a dispersed phase in a film having a crystalline polymer as a matrix, the present inventors have importantly controlled the refractive index of the polymer matrix and the dispersed phase, and the scattering parameter. It was found that the color shift in the surface light source can be reduced by selecting the polymer matrix and the dispersed phase so that the value of α falls within a certain range.
[0021]
  That is, the present invention is as follows.
1. A polymer film obtained by stretching a film made of a crystalline polymer compound, the film having a dispersed phase in a matrix of the polymer compound, and the following formulas (1) and (2)
          | Ny-z- (ny + nz) /2|≦0.05 (1)
          | Nx−Nx |> 0.05 (2)
(Here, in the matrix of the crystalline polymer compound, nx is the refractive index in the direction having the highest refractive index in the plane of the film, ny is the refractive index in the direction perpendicular to the x direction in the plane, and nz is the refractive index in the thickness direction. (In the dispersed phase, Ny-z is the average refractive index in the yz plane, and Nx is the refractive index in the x direction.)
Satisfied(However, the condition that satisfies the following formula (4) is excluded.
| Ny-Ny | = | nz-Nz | (4)
(Ny is the refractive index in the direction perpendicular to the x direction in the film plane in the dispersed phase, and Nz is the refractive index in the thickness direction in the dispersed phase.),
Further, the scattering parameter α is expressed by the following formula (3)
            10 ≦ α = π · d / λ ≦ 200 (3)
(Where d is the average particle size of the dispersed phase in the x direction)(However, 2.48 μm <d <24.2 μm is excluded), Λ is the wavelength of visible light. )
Scattering anisotropic polymer film satisfying the relationship.
[0022]
2. 2. The scattering anisotropic polymer film according to 1 above, wherein the ratio of the dispersed phase is 0.01 to 30 parts by weight with respect to 100 parts by weight of the matrix of the crystalline polymer compound.
[0023]
3. The scattering anisotropic polymer film according to the above 1 or 2, wherein the total light transmittance (TT) is 50% or more.
[0024]
4). The polymer film according to the above 1 to 3, comprising a dye in an amount of 0.1 ppm to 20 ppm.
[0025]
5. A polarized light-emitting light guide formed by attaching the scattering anisotropic polymer film of 1 to 4 to an end-face incident type light guide plate made of a transparent medium via an adhesive layer or an adhesive layer.
[0026]
6). 5. The polarized light emitting surface comprising the polarized light emitting light guide of 5 above, a light source mounted on an end surface of the light guide, and a regular reflection plate disposed on the opposite side of the light emitting surface of the light guide as main components. Light source device.
[0027]
7). 7. A liquid crystal display device comprising the polarized light emitting surface light source device according to 6 above.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The present invention relates to a polymer film having scattering anisotropy (hereinafter sometimes referred to as scattering anisotropy polymer film), and particularly to a polarizing surface light source device used by sticking the film to a light guide surface. Is preferred. First, the principle of the polarizing surface light source device of the present invention will be described.
[0029]
Here, the polarization backlight will be briefly described. When light enters the light guide as shown in FIG. 3 at a shallower angle from the end face, the light travels while being repeatedly reflected at the interface between the light guide plate and the air. It does not exit from.
[0030]
However, in the present invention, for example, as shown in FIGS. 1 and 2, a polymer film having scattering anisotropy as a scattering anisotropic layer is provided on the surface of the light guide. In the present invention, a desired linearly polarized light can be arbitrarily selected by changing the direction of anisotropy in the in-plane direction of the scattering anisotropic layer. Here, as an example, the anisotropy of scattering is large for the linearly polarized light having the vibration surface of the electric field perpendicular to the paper surface in FIG. 4 and scattered for the linearly polarized light having the vibration surface of the electric field parallel to the paper surface. The case where is small will be described. Of the non-polarized light traveling through the light guide, the polarized component perpendicular to the paper surface is scattered forward by the scattering anisotropy factor in the scattering anisotropic layer. A part of the scattered light is incident on the interface between the scattering anisotropic layer and the air at an angle deeper than the critical angle, and thus is not totally reflected and is emitted as polarized light from the light guide. On the other hand, the polarization component parallel to the paper surface hardly receives scattering due to the scattering anisotropy factor. Therefore, it is incident on the interface between the haze anisotropic layer and air at an angle shallower than the critical angle as before, and is totally reflected and transmitted through the light guide. Therefore, the light emitted from the upper surface or the lower surface in FIG. 4 is always linearly polarized light having a vibration plane of an electric field perpendicular to the paper surface, and specific linearly polarized light can be separated from unpolarized light. The polarized light that has not been emitted is depolarized by the birefringence of the light guide or the scattering anisotropic layer, and is reused as non-polarized light again.
[0031]
As described above, the light source device including the polymer film having scattering anisotropy of the present invention scatters polarized light in the scattering direction (scattering axis) to change the incident angle and break the total reflection of the light guide. Polarization is obtained by utilizing the principle of emission. Therefore, the scattering direction may be either forward scattering or backward scattering. Rather, it is preferable that the forward scattering property is high in order to maintain the high transmittance of the polymer film itself having such scattering anisotropy. In addition, polarized light in the direction of small scattering (transmission axis) that has not been used does not change the incident angle to the interface, so that the total reflection on the surface of the light guide body is repeatedly confined in the light guide plate, so there is no risk of dissipation. Furthermore, the polymer film itself having scattering anisotropy is depolarized by the strong birefringence and reused.
[0032]
  The polymer film having scattering anisotropy of the present invention is a film in which a crystalline polymer compound is usually stretched in a uniaxial direction. In the polymer matrix constituted by the crystalline polymer compound, the matrix and A large number of phases that are substantially incompatible are dispersed. In such a polymer film, the refractive index nx, ny, nz of the polymer matrix (where nx is the refractive index in the direction having the highest refractive index in the plane of the film, ny is the refractive index in the direction perpendicular to the x direction in the plane) , Nz is the refractive index in the thickness direction)
The average refractive index Nyz in the yz plane of the dispersed phase is expressed by the following formula (1)
          | Ny-z- (ny + nz) /2|≦0.05 (1)
And the refractive index Nx in the x direction of the dispersed phase is expressed by the following formula (2)
          | Nx−Nx |> 0.05 (2)
Satisfy(However, the condition that satisfies the following formula (4) is excluded.
| Ny-Ny | = | nz-Nz | (4)
(Ny is the refractive index in the direction perpendicular to the x direction in the film plane in the dispersed phase, and Nz is the refractive index in the thickness direction in the dispersed phase.).
  This polymer film strongly scatters linearly polarized light having a vibration plane in the x direction, and has a weak scattering against linearly polarized light having a vibration plane orthogonal to the x direction. In particular, scattering is weak for linearly polarized light having a vibration plane perpendicular to the x direction incident at a shallow angle with respect to the xy plane.
[0033]
In the above formula (1), when | Ny-z- (ny + nz) / 2 |> 0.05, the refractive index of the matrix and the dispersed phase is not sufficiently matched in the yz plane. The scattering of the scattering axis may increase and the degree of polarization may decrease.
[0034]
In the above formula (2), if | nx−Nx | ≦ 0.05, the scattering of the scattering axis becomes insufficient, and the output of the necessary polarized light is lowered. This is also the degree of polarization as a polarizing surface light source device. Will be reduced. However, if the value of | nx−Nx | is too large, the backscattering property is increased, so that the total light transmittance is lowered, which may lead to an undesirable result in terms of light extraction efficiency. Therefore, the above formula (2) is more preferably
0.05 <| nx−Nx | ≦ 0.25 (2) −1
It is.
[0035]
As described above, the polymer film having scattering anisotropy of the present invention has substantially the same refractive index of the matrix and the dispersed phase not in one direction in the film plane but in the yz plane and in the x direction. Due to the large difference in the refractive index of the disperse phase and the absolute value of the difference being greater than or equal to a specific value, for the polarized light that is obliquely incident on the in-plane of the film that exists most in the light transmitted through the light guide Exhibit high scattering anisotropy.
[0036]
  In the film having scattering anisotropy of the present invention, the film matrix and the dispersed phase of the polymer compound satisfy the following formula (3).
            10 ≦ α = π · d / λ ≦ 200 (3)
  Where d is the particle size of the dispersed phase(However, 2.48 μm <d <24.2 μm is excluded), Λ is the wavelength of visible light. α = π · d / λ is a scattering parameter.
In general, since the scattering efficiency Q has wavelength dependency, in a polarized light emitting surface light source device, when the end face incident type light guide plate is made to have scattering properties, the relationship between the refractive index and the particle size must be controlled. It is generally said that color deviation occurs in the emitted light as the distance from the object increases. For example, in the case of very small particles on the order of submicrons, light having a shorter wavelength is more likely to be scattered. Therefore, blue light is likely to be scattered near the light source, and as a result, the vicinity of the light source becomes bluish, and on the contrary, it becomes reddish as it moves away from the light source, resulting in a color shift within the plane of the surface light source (color shift). Result.
[0037]
As an example, calculation of the relationship between the scattering efficiency Q and the scattering parameter α when Nx = 1.55 and nx = 1.68 (FIG. 5) and when Nx = 1.60 and nx = 1.84 (FIG. 6). Results are shown. As is clear from this result, when Nx and nx are determined in this way, the scattering efficiency Q can be uniquely determined if the scattering parameter α is determined. However, since the scattering parameter α includes a term of the wavelength λ, even if Nx, nx, and d are constant, the value of the scattering parameter α changes in the visible light region 380 nm ≦ λ ≦ 780 nm. The degree of scattering differs and causes color misregistration. As the scattering parameter α is smaller, the rate of change of the scattering efficiency Q depending on the wavelength is larger. Therefore, it is preferable that α ≧ 10 in order to reduce color shift. On the other hand, as the scattering parameter α increases, the scattering value approaches a constant value, but optically, the geometrical optical effects such as refraction and reflection become larger than the electromagnetic scattering effect, and the use of the polarizing surface light source device of the present invention Is not preferred. Therefore, the value of the scattering parameter α is preferably α ≦ 200.
[0038]
In terms of calculation, it is impossible for Q to be constant at all wavelengths in the visible range regardless of the particle size d, but in reality, there is no problem because the particle size d is distributed with a certain degree of dispersion.
[0039]
The polymer film having scattering anisotropy of the present invention comprises an end face incident type light guide made of a transparent medium and having a light exit surface and an end face, and regular reflection disposed on the opposite side of the light exit surface of the light guide. A light source mounted on an end face of the plate and the light guide is a main component, and light is emitted from the film surface side by adhering the film to at least one surface of the light guide via an adhesive layer. In the polarized light emitting surface light source device, a light source device having excellent characteristics such that the in-plane variations Δx and Δy of the chromaticity coordinates x and y in the surface of the light source device are both small and hardly causes a color shift. Specifically, the in-plane variations Δx, Δy of the chromaticity coordinates x, y are
Δx ≦ 0.025
Δy ≦ 0.025
Meet. When Δx> 0.025 or Δy> 0.025, there is a difference in chromaticity within the surface light source, so that when used in a liquid crystal display device or the like, a color shift occurs in the display surface, which is not preferable.
[0040]
The polymer constituting the polymer matrix in the polymer film having scattering anisotropy of the present invention is preferably a crystalline or semi-crystalline transparent polymer in which the polymer chain is easily oriented when the film is stretched. In the case of an amorphous polymer, it is difficult to align the polymer chain when stretching the film, so it is difficult to obtain a large difference in refractive index from the dispersion layer, and thus it is difficult to obtain sufficient scattering anisotropy. Become.
[0041]
Such a crystalline polymer is not particularly limited, but is a crystal that is substantially transparent or translucent, such as a polyester film such as polyethylene terephthalate or polyethylene naphthalate, a syndiotactic polystyrene film, a polyethylene film, or a polypropylene film. And a film made of a functional polymer. A polyester film is preferred.
[0042]
The polymer film of the present invention is preferably an oriented film that is strongly stretched in either uniaxial direction. Accordingly, for example, in addition to a so-called uniaxially stretched film, a monoaxially stretched monoaxially stretched film and a biaxially stretched film having a longitudinal and lateral stretch ratio of 1.5 or more are included.
[0043]
The draw ratio in the high draw ratio direction is preferably 1.5 times or more. The suitable draw ratio varies depending on the polymer type, the draw temperature, the draw speed, and the like. For example, in the case of a polyester film, it is preferably 3 times or more.
[0044]
By the way, scattering type polarizing films have been disclosed in WO97 / 32222 and WO97 / 41484 as films using similar functions. These scattering-type polarizing films use a match / mismatch between the refractive index of the matrix and the dispersed phase in the film plane.
[0045]
On the other hand, in the polarizing surface light source device of the present invention, light is transmitted through a polymer film having scattering anisotropy at an angle shallower than the total reflection angle. The direction is important. In particular, the refractive index matching between the matrix and the dispersed phase in the yz plane is important.
[0046]
The scattering anisotropic film of the present invention has a total light transmittance TT.
TT> 50%
It is. When this film is used for a polarizing surface light source device, a polarization separation function can be obtained regardless of whether the scattering direction is forward scattering or backward scattering. However, in order to effectively utilize the obtained linearly polarized light, it is preferable that the total light transmittance is high. More preferably, TT> 60%, and still more preferably TT> 70%.
[0047]
By satisfying the condition of the total light transmittance, the scattering efficiency varies greatly depending on the polarization vibration direction. However, since the scattering is forward scattering, the total light transmittance is not affected by the polarization plane. Therefore, it is suitable as a film having scattering anisotropy for the polarizing backlight as described above.
[0048]
By the way, the film described in WO97 / 32222 which is a scattering type polarizer is an optical film which performs polarization separation using transmission / non-transmission due to scattering. Therefore, it is disclosed that the anisotropy of scattering with respect to light from a direction orthogonal to the film is fundamentally important, and a film that requires anisotropy against oblique incidence as in the present invention. Are fundamentally different. In addition, the optical film described in this publication works so that linearly polarized light in the scattering axis direction is made non-transmissive by backscattering, and linearly polarized light in the transmission axis direction is transmitted to perform polarization separation, and the polarization separation ability is further increased. In order to achieve this, the difference in transmittance between the two directions needs to be as large as possible, so the light transmittance in one direction is low. However, in the present invention, a decrease in light transmittance is not preferable, and it is preferable that the transmittance in both directions is high.
[0049]
In the present invention, the ratio of the dispersed phase to the polymer matrix is 0.01 to 30 parts by weight with respect to 100 parts by weight of the matrix. In the present invention, it is possible to control such as increasing the number of dispersed phases to scatter multiple times to raise the outgoing light in the front direction, or reducing the number of dispersed phases to reduce multiple scattering and obtain a sharp emission pattern. However, when the dispersed phase is more than 30 parts by weight, the polarization separation effect tends to decrease due to excessive multiple scattering, and when it is less than 0.01 part by weight, sufficient luminance as a surface light source device can be obtained. It becomes difficult.
[0050]
In the present invention, as the dispersed phase contained in the matrix of the polymer compound, for example,
(i) Fine particles having a primary particle diameter of 0.01 to 10 μm, or aggregates thereof
(ii) polymer compound
Can be mentioned.
[0051]
(I) The fine particles having a primary particle diameter of 0.01 to 10 μm or aggregates thereof are not particularly limited as long as they are basically transparent organic or inorganic fillers. The organic filler is preferably an organic filler that hardly causes voids when the film is stretched. The primary particle size of the fine particles of the present invention is 0.01 to 10 μm. Here, the primary particle size is the minimum unit size of particles. If the primary particle size is 0.01 or less, there is a high possibility that no optical effect will occur, and if it exceeds 10 μm, voids are likely to occur during stretching, which is not preferred.
[0052]
The dispersed phase in the present invention may be composed of primary particles alone or aggregates thereof. In particular, when the primary particles are fine particles of submicron order, they tend to be aggregates due to the influence of surface energy, and preferable optical characteristics can be obtained as the aggregates. In this case, the particle size d in the x direction is the average length (usually the long diameter) in the x direction as an aggregate.
[0053]
Examples of the fine particles used in the present invention include acrylic fine particles, styrene fine particles, silicone fine particles, styrene-butadiene rubber fine particles, acrylic-acrylic core-shell type fine particles, and acrylic-styrene-butadiene core-shell fine particles. In particular, the core-shell type fine particles are preferable because they have rubber elasticity and have less adverse effects such as generation of voids due to stretching.
[0054]
(ii) When the dispersed phase is a polymer compound, the polymer in the dispersed phase is dispersed in islands in the polymer matrix. The dispersed phase is generally an ellipsoid having a major axis in the stretching direction, and the average diameter is preferably 0.1 to 400 μm. When the average diameter is less than 0.1 μm, an optical action may not occur, and when it is greater than 400 μm, the scattering anisotropy may be insufficient. More preferably, it is 0.5-50 micrometers.
[0055]
The polymer compound used in the dispersed phase is basically transparent and is not limited as long as it is basically incompatible with the crystalline polymer compound used in the matrix. However, it is necessary to select the refractive index so as to satisfy the relationships of the above formulas (1) to (3).
[0056]
For example, when polyethylene naphthalate is used as the polymer matrix, examples of the polymer compound used in the dispersed phase include polystyrene, syndiotactic polystyrene, methacrylate-styrene copolymer, acrylonitrile-styrene copolymer, and the like. Moreover, when a matrix is a polyethylene terephthalate, acrylic resins, such as polymethylmethacrylate, a methacrylate-styrene copolymer etc. can be illustrated.
[0057]
In addition, since the scattering anisotropic film of the present invention is produced by stretching as described later, it is preferable that the polymer constituting the dispersed phase at the stretching temperature has some elasticity and can follow the stretching.
[0058]
The film having scattering anisotropy of the present invention can be added with a small amount of a dye or a pigment in order to compensate for burns during film formation and the color of the polymer. These are preferably contained in an amount of 0.1 ppm to 20 ppm with respect to the polymer matrix. In particular, when it exceeds 20 ppm, the coloring tends to be too large.
[0059]
As a method for producing a scattering anisotropic polymer film of the present invention, after weighing a predetermined amount of a material forming a dispersed phase with a crystalline polymer compound, for example, the fine particles or an aggregate thereof, or the polymer compound, For example, a method of melt-mixing and extrusion film formation can be mentioned. In order to enhance dispersibility, it is also preferable to use a master batch of high concentration in advance.
[0060]
After such melt film formation, stretching is performed uniaxially or biaxially. The stretching temperature varies depending on the crystalline polymer used in the matrix, but is, for example, about 80 ° C. to 120 ° C. for polyethylene terephthalate and about 90 ° C. to 150 ° C. for polyethylene naphthalate.
[0061]
The thickness of the scattering anisotropic film of the present invention is 0.1 μm to 200 μm, preferably 10 to 200 μm. When this film thickness is thin, the emission angle becomes sharper. On the other hand, when it is thick, the emission peak rises to the front due to multiple scattering.
[0062]
The scattering anisotropic film of the present invention is a polarized light which is a light guide having polarization separation ability by sticking to an exit surface or an opposite surface of an end-face incident type light guide plate made of a transparent medium via an adhesive layer or an adhesive layer. An emissive light guide is provided. Here, adhesion or adhesion means that an air layer is not substantially sandwiched between the light guide and the scattering anisotropic film. As an adhesion method, an adhesive such as a UV adhesive or an optical pressure-sensitive adhesive can be used. In order not to disturb the polarized light, it is preferable that the adhesive layer or the adhesive layer does not have birefringence. The thickness of this layer is 5 to 100 μm.
[0063]
Thus, according to the present invention, a polarized backlight having the polarized light-emitting light guide is provided. That is, using the above-described polarized light-emitting light guide, polarized light emission mainly comprising a light source mounted on the end face of the light guide and a specular reflection plate installed on the side opposite to the light-emitting face of the light guide. A sex surface light source device is provided. There is no restriction | limiting in particular as a light source, The cold cathode tube and light emitting diode which are used normally can be used. Moreover, there is no restriction | limiting in particular also in the end surface which installs a light source. Further, it is preferable that the specular reflector does not have birefringence in the sense that it does not disturb the polarization.
[0064]
Further, the polarized light emitting surface light source device of the present invention has a feature that polarized light is emitted only through the adhesion portion between the light guide and the scattering anisotropic film on the surface of the light guide. It is possible to measure the in-plane luminance uniformity by controlling the area and ratio. As a method of controlling the shape, area, and ratio of the bonding site, the adhesive itself is dipped, patterned by screen printing, etc., the light guide plate, or the film is processed by applying unevenness to the film, A method for controlling the contact position of the light guide plate is conceivable. FIG. 7 shows a conceptual diagram of a surface light source device in which an adhesive layer is patterned.
[0065]
【The invention's effect】
According to the present invention, by making the refractive index of the matrix and the dispersed phase substantially coincide with each other in the yz plane of the stretched polymer film having a dispersed phase, the scattering property having a high forward scattering property suitable as a polarizing surface light source device is obtained. An isotropic film can be obtained. Then, by controlling the value of the scattering parameter α, color misregistration can be reduced when it is attached to a light guide plate and used as a polarizing surface light source device. A polarizing surface light source device provided with this film can improve the luminance of a liquid crystal display that requires polarized light and can reduce power consumption.
[0066]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.
1. The total light transmittance was measured using a digital turbidimeter NDH-20D (Degital Haze Meter NDH-20D) manufactured by Nippon Denshoku Industries Co., Ltd.
2. The refractive index was measured using an Abbe refractometer 2-T manufactured by ATAGO Co., LTD.
3. The luminance was measured using a luminance meter LS-110 (MINumta Co., LTD) manufactured by MINOLTA Co., LTD. A polarizing plate was placed on the exit surface of the light guide plate, and while rotating the polarizing plate, the luminance of linearly polarized light emitted from the light guide plate was measured, and the degree of polarization was calculated from the luminance using the following formula.
Polarization degree δ (%) = (maximum luminance−minimum luminance) / (maximum luminance + minimum luminance) × 100
Here, the maximum luminance is the luminance at the position (angle) where the luminance is maximum when the polarizing plate is rotated in the plane, and the minimum luminance is the luminance at the position (angle) where the luminance is minimum.
4). Color misregistration is the in-plane chromaticity with each film attached to an 80x80x2mm acrylic light guide plate, the back side with a white scattering sheet, and two diffusion plates + prism sheets on the light guide plate and two diffusion plates placed on the cross. The coordinates are measured using MCPD7000 manufactured by Otsuka Electronics, and four points of 25 mm, 40 mm, 60 mm, and 75 mm are measured from the light source on the center line, and the difference between the maximum value and the minimum value of the x coordinate and y coordinate is Δx and Δy, respectively. Expressed as:
5. The polymers used are as follows.
(1) Polyethylene terephthalate (PET) manufactured by Teijin Limited
[0067]
[Example 1]
Using a uniaxial kneading extruder, 99.7 parts by weight of PET as a matrix polymer, 0.3 parts by weight of Sekisui Chemical's porous crosslinked acrylic fine particles MBP-8 and 4 ppm of Nippon Kayaku dye KaysetACR as components constituting the dispersed phase were used. The film was kneaded at 280 ° C., formed into a film by the melt extrusion method, and continuously uniaxially stretched 3.9 times at 80 ° C. in the TD direction to obtain a film having a thickness of 70 μm. The light transmittance of this film was measured.
[0068]
Next, this uniaxially stretched film was attached to the upper surface of an 80 mm × 80 mm × 2 mm acrylic plate (manufactured by Mitsubishi Rayon) using an adhesive (“SK Dyne” 1811L, manufactured by Soken Chemical Co., Ltd.) to obtain a light guide plate. The thickness of the adhesive layer was 20 μm. Next, as shown in FIG. 1, the tube diameter is 3 mm, the tube length is 100 mm, and the center luminance is 10,000 cd / m.²A rod-shaped light source lamp (cold cathode tube) was attached to the end face of the light guide plate through which light was incident. At this time, the length direction of the cold cathode tube and the stretching direction of the attached film were made parallel. Moreover, the part which is not facing the light-guide plate of a light source lamp, the end surfaces other than the light-incidence surface of a light-guide plate, and the surface opposite to the said film installation surface which is the output surface of a light-guide plate were coat | covered with the aluminum vapor deposition film.
[0069]
Luminance was measured using the surface light source device thus created to determine the degree of polarization. The measurement results are shown in the table.
[0070]
[Example 2]
97 parts by weight of PET as a matrix polymer and 3 parts by weight of core-shell fine particles W-300A manufactured by Mitsubishi Rayon as a component constituting the dispersed phase are kneaded at 280 ° C. using a uniaxial kneading extruder, and formed into a film by a melt extrusion method. Then, it was carried out in the same manner as in Example 1 except that a film having a thickness of 70 μm was obtained by continuously uniaxially stretching 4.5 times at 80 ° C. in the TD direction.
[0071]
[Example 3]
97 parts by weight of PET as a matrix polymer and 2.5 parts by weight of core-shell fine particles C132 manufactured by Mitsubishi Rayon as a component constituting the dispersed phase are kneaded at 280 ° C. using a uniaxial kneading extruder, and formed into a film by a melt extrusion method. Then, it was carried out in the same manner as in Example 1 except that a film having a thickness of 70 μm was obtained by continuously uniaxially stretching 4.5 times at 80 ° C. in the TD direction.
[0072]
[Example 4]
97.5 parts by weight of PET as a matrix polymer and 2.5 parts by weight of Kureha Chemical fine particle paraloid BTA712 as a component constituting a dispersed phase are kneaded at 280 ° C. using a uniaxial kneading extruder, and formed into a film by a melt extrusion method. Then, it was carried out in the same manner as in Example 1 except that a film having a thickness of 70 μm was obtained by continuously uniaxially stretching 4.5 times at 80 ° C. in the TD direction.
[0073]
[Comparative example]
Add 0.2 part by weight of silica particles with an average particle size of 0.3 μm to 99.8 double parts of PET, knead and form a film at 280 ° C. with a single-screw kneader, and continuously 4 times at 100 ° C. in the MD direction. Was uniaxially stretched. It implemented like Example 1 except having used this film.
[0074]
[Table 1]

[0075]
*) Particle size as aggregate
[Brief description of the drawings]
FIG. 1 is an example of a conceptual diagram of a polarized light emitting surface light source device using scattering anisotropy of the present invention.
FIG. 2 is an example of a conceptual diagram of a polarized light emitting surface light source device using scattering anisotropy of the present invention.
FIG. 3 is a conceptual diagram of a conventional surface light source device.
FIG. 4 is a conceptual diagram illustrating the principle of polarization conversion in the surface light source device of the present invention.
FIG. 5 shows the relationship between the scattering parameter α and the scattering efficiency Q when Nx = 1.55 and nx = 1.68 (calculated values).
FIG. 6 shows the relationship between the scattering parameter α and the scattering efficiency Q when Nx = 1.60 and nx = 1.84 (calculated values).
7 is a conceptual diagram of a surface light source device in which an adhesive layer of Example 1 is patterned. FIG.
[Explanation of symbols]
1: Light guide
2: Scattering anisotropic layer
3: Reflector
4: Cold cathode tube
5: Lamp reflector
6: Unpolarized light (naturally polarized light)
7: Vibration direction of linearly polarized light
8: Anisotropic scattering factor

Claims (7)

A polymer film obtained by stretching a film comprising a crystalline polymer compound, the film having a dispersed phase in a matrix of the polymer compound,
The following formulas (1) and (2)
| Ny-z- (ny + nz) /2|≦0.05 (1)
| Nx−Nx |> 0.05 (2)
(Here, in the matrix of the crystalline polymer compound, nx is the refractive index in the direction having the highest refractive index in the plane of the film, ny is the refractive index in the direction perpendicular to the x direction in the plane, and nz is the refractive index in the thickness direction. (In the dispersed phase, Ny-z is the average refractive index in the yz plane, and Nx is the refractive index in the x direction.)
(Except for the condition that satisfies the following formula (4))
| Ny-Ny | = | nz-Nz | (4)
(Ny is the refractive index in the direction perpendicular to the x direction in the film plane in the dispersed phase, and Nz is the refractive index in the thickness direction in the dispersed phase.)
Further, the scattering parameter α is expressed by the following formula (3)
10 ≦ α = π · d / λ ≦ 200 (3)
(Where d is the average particle size in the x direction of the dispersed phase (excluding 2.48 μm <d <24.2 μm) , and λ is the wavelength of visible light.)
Scattering anisotropic polymer film satisfying the relationship.   The scattering anisotropic polymer film according to claim 1, wherein the ratio of the dispersed phase is 0.01 to 30 parts by weight with respect to 100 parts by weight of the matrix of the crystalline polymer compound.   The scattering anisotropic polymer film according to claim 1 or 2, wherein the total light transmittance (TT) is 50% or more.   The polymer film according to any one of claims 1 to 3, comprising a dye in an amount of 0.1 ppm to 20 ppm.   A polarized light-emitting light guide body comprising a scattering anisotropic polymer film according to any one of claims 1 to 4 attached to an end-face incident type light guide plate made of a transparent medium via an adhesive layer or an adhesive layer.   6. A polarized light emitting light guide according to claim 5, a light source mounted on an end face of the light guide, and a regular reflection plate installed on the side opposite to the light emitting surface of the light guide. Sexual surface light source device.   A liquid crystal display device comprising the polarized light emitting surface light source device according to claim 6.

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