JP2001049008A - Forward scattering polymer film having haze anisotropy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film useful in obtaining a light conducting plate desirable for a polarizable backlight material by selecting a film having a specific haze anisotropy wherein the haze value varies, depending on the direction of the oscillation of a linearly polarized light incident vertically on the surface. SOLUTION: This film has a haze anisotropy satisfying formula II Hmax/ Hmin>=1.05, wherein the haze value H(%)=DF/TT×100 (formula I). In formulae I and II, DF is a diffused light transmittance; TT is a whole light transmittance; Hmax is a haze value W in the direction (scattering axis) in which the haze is the largest; and Hmin is a haze value in the direction (transmission axis) in which the haze is the smallest. It is preferable that this film is an oriented film of a crystalline polymer, more pref. of a polyester, or an oriented film made of a polymer in which a liq. crystal is dispersed and which satisfies formula III regarding a specific linearly polarized light. In formula III, n1A-B are refractive indices of the polymer and the liq. crystal obtd. with a linearly polarized light in a specific direction, and n2A-B are refractive indices of the polymer and the liq. crystal obtd. with a linearly polarized light at a right angle to the former polarized light, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forward-scattering polymer film having a haze anisotropy, and more particularly, to a haze anisotropy having a haze value that varies depending on the vibration direction of incident polarized light and its scattering direction. Is a forward scattered polymer film. The end-incidence type light guide plate in which this film is adhered to the light exit surface can be used as a polarizing surface light source device, thereby utilizing light in an image display device using linearly polarized light such as a general-purpose liquid crystal display device. Efficiency can be improved.

[0002]

2. Description of the Related Art Liquid crystal display devices have the characteristics of being thin and lightweight, and having low power consumption due to low voltage driving, and are rapidly growing as leading image information display devices.

A liquid crystal display device generally uses twisted liquid crystal for two.
It is composed of a cell held by two substrates, and polarizing plates arranged on both sides thereof with their polarization axes orthogonal to each other. As the polarizing plate, for example, a dichroic polarizing plate using an oriented dichroic dye such as a PVA-iodine system is used. This dichroic polarizing plate selectively absorbs only one linearly polarized light component out of the mutually orthogonally polarized light components and transmits only the other linearly polarized light component, thereby converting non-polarized light into linearly polarized light. .

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 the converted light rotates in the liquid crystal cell along the twist of the liquid crystal molecules, it is observed as display light without being absorbed by the polarizing plate in front of the liquid crystal cell (observer side). When a voltage is applied to the liquid crystal cell, the liquid crystal molecules are arranged in the direction of the electric field and twisting is eliminated, so that polarized light transmitted through the liquid crystal cell is absorbed by the observer-side polarizing plate.

The light utilization efficiency of a liquid crystal display device is mainly regulated by the light transmittance of a polarizing plate, the aperture ratio of a liquid crystal panel, and the light transmittance of a color filter. When the light utilization efficiency is low, the contrast (relative luminance) of the image light is reduced, and the display quality is reduced. On the other hand, if the output of the backlight light source is increased, the contrast of the video light is increased, but the power consumption is increased, and there is a problem that the driving time is reduced particularly when used as a portable device.

In order to increase the contrast of image light,
There is also a method of condensing light using a prism sheet, etc.,
In this case, the contrast in the front direction is improved, but the brightness is significantly reduced at other angles, which is contrary to the recent trend of widening the viewing angle.

What is most restricted in terms of light use efficiency is the light transmittance of the polarizing plate. In the process of extracting linearly polarized light from the light source light (non-polarized light) with a polarizing plate, theoretically 50
% Or more is lost. So we convert the light from the light source into linearly polarized light,
If the vibrating surface of the linearly polarized light can be made to coincide with the vibrating surface of the linearly polarized light transmitted through the polarizing plate, the light use efficiency is significantly improved.

For example, US Pat. No. 3,610,729 discloses a method in which an optical film in which two types of films are laminated in a multilayer is used to separate only one linearly polarized light and reflect and reuse the orthogonally polarized linearly polarized light. Is disclosed. Also E
P606940A2, DJBroer, JAMMvan.Haaren,
GNMol, F. Leenhouts; Asia Display '95, 735 (1995)
Discloses a method of selectively transmitting only one circularly polarized light by using a cholesteric liquid crystal and a quarter-wave plate and reflecting and reusing the other to enhance light use efficiency.

Although these methods are effective in terms of the efficiency of conversion into polarized light and the efficiency of use of light, they are difficult to manufacture due to the requirement of a strict high-order structure, and are therefore expensive. .

[0010] WO92 / 22838, FMWeber; S
ID 93 DIGEST, 669 (1993) discloses a method of performing polarization separation using a Brewster angle. Although these systems can be manufactured relatively inexpensively, the polarization conversion efficiency is insufficient, the angle dependence of the polarized light emission angle is large, and the type of linearly polarized light obtained is limited.

JP-A-6-331824, JP-A-9
Japanese Patent Application Laid-Open No. 292530/1990 discloses a method in which a layer having refractive index anisotropy is used for a light guide plate, and polarization separation is performed utilizing the difference in refractive index at the interface depending on the polarization direction. These methods also have insufficient polarization conversion efficiencies, and therefore do not have high light utilization efficiency. There is also a problem that the refractive index anisotropy is limited by the material.

OAAphonin, et al .; Liq. Cryst.,
15, 3, 395 (1993), OAAphonin; Liq. Cryst., 19, 4,
469 (1995), JP-A-8-76114, JP-A-9-114
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 polarizer. WO9
7/32222, WO97 / 32224,
WO97 / 32226, WO97 / 32227, USP 5,867,316, H. Yagt, et a
l .; Adv. Mater., 10, 2, 934 (1998), M. Miyatake, et.
al .; IDW'98, 247 (1998) discloses a method in which an incompatible polymer blend film is stretched to obtain a scattering-type polarizing plate.

Japanese Patent Application Laid-Open No. 9-297204 discloses that
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 for expressing anisotropic scattering is disclosed. It is described that when a polarizing plate is rotated on this element, it becomes darkest when the polarization axis and the scattering axis (stretching direction) coincide, and becomes brightest when it is orthogonal (coincides with the transmission axis).

These techniques involve a method of separating polarized light by transmitting polarized light in a direction (transmission axis) having a matched refractive index by stretching or the like and back-scattering polarized light in a direction (scattering axis) having a mismatched refractive index. And a so-called scattering type polarizing plate is used. The principle of the polarization separation is fundamentally different from the light source device targeted in the present invention. In addition, in the case of these techniques, since it is necessary to back-scatter the polarized light in the scattering axis direction without forward scattering, it is necessary to increase the scattering factor and perform multiple scattering. 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.However, in the case of this scattering polarizer, since the amount of dissipated light due to scattering is large, the reuse light efficiency is low and the polarization degree is low. Low luminance improvement rate.

WO 97/32222 describes an optical film (scattering type polarizing film) which performs polarization separation by utilizing transmission / non-transmission by scattering. With this optical film, linearly polarized light in the direction of the scattering axis is made non-transmitting by back scattering, and linearly polarized light in the direction of the transmitting axis is transmitted to perform polarization separation. Therefore, in order to further increase the polarization separation ability, it is necessary to make the difference in transmittance as large as possible. Ideally, TTmax≫TTmin〜0. It is described that this optical film has a diffuse reflectance of 30% or more in a scattering axis direction.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel forward scattering polymer film having haze anisotropy, and to provide a light guide plate suitable as a polarizing backlight material. An object of the present invention is to provide a forward scattering polymer film having haze anisotropy.

[0017]

The present invention is achieved by a forward-scattering polymer film having a haze value H that differs depending on the vibration direction of linearly polarized light perpendicularly incident on the surface and that satisfies the following formula (2). . (Where the haze value H is

[0018]

H (%) = DF / TT × 100 (1) where DF is the diffuse light transmittance and TT is the total light transmittance. )

[0019]

Hmax / Hmin ≧ 1.05 (2) (where Hmax is the direction of the largest haze (scattering axis))
Hmin indicates the haze value in the smallest direction (transmission axis).)

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The forward scattering polymer film of the present invention is a film in which the haze value H differs depending on the vibration direction of linearly polarized light, the haze in the direction of the largest haze (scattering axis) is Hmax, and the direction of the smallest is Hmax. When the haze of (transmission axis) is Hmin, the following equation (2)

[0021]

The haze anisotropic film, wherein Hmax / Hmin ≧ 1.05 (2). Here, the haze is defined by the following equation (1)

[0022]

H (%) = DF / TT × 100 (1) Where DF is the diffuse light transmittance, T
T is the total light transmittance. That is, haze indicates the ratio of diffuse transmitted light to transmitted light, and the larger the value, the more easily light is scattered. Haze anisotropy in the present invention,
When linearly polarized light is used as the incident light, this refers to a phenomenon in which the effect of scattering differs depending on the vibration direction of the linearly polarized light.

In the forward scattering polymer film of the present invention, when the haze is measured by rotating the plane of polarization of linearly polarized light in the plane, the highest haze value is Hmax and the lowest value is Hmax.
When it is set to min, the following formula (2-
1)

[0024]

Hmax / Hmin ≧ 1.20 (2-1) It is ideal that Hmin〜0.

The polymer film of the present invention has forward scattering properties. When the total light transmittance of the scattering axis is TTmin and the total light transmittance of the transmission axis is TTmax, the following equation (8) is used.

[0026]

[Expression 18] 1 ≦ TTmax / TTmin ≦ 2 (8) This is the difference from the scattering type polarizing plate. In the case of a scattering type polarizing plate, the larger the difference in transmittance is, the better. However, the smaller the difference is, the more preferred the film of the present invention is.
-1)

[0027]

It is preferable that 1 ≦ TTmax / TTmin ≦ 1.5 (8-1), and ideally, the following equation (8-2)

[0028]

TTmax = TTmin〜100% (8-2)

The film of the present invention has a high transmittance. When the total light transmittance of the scattering axis is TTmin and the total light transmittance of the transmission axis is TTmax, the following equation (9) is used.

[0030]

It is preferable that (TTmax + TTmin) / 2 ≧ 70 (%) (9) More preferably, the following formula (9-
1)

[0031]

(TTmax + TTmin) / 2 ≧ 80 (%) (9-1)

In the above film satisfying these conditions, the scattering efficiency greatly varies depending on the direction of polarization, but since the scattering is mainly forward scattering, the total amount of transmitted light is not affected by the polarization plane. In other words, the film has a low backscattering property not only in the transmission axis but also in the scattering axis direction.

In these respects, the forward scattering film of the present invention is different in characteristics from a so-called scattering polarizing film. That is, since the haze anisotropic film of the present invention utilizes linearly polarized light in the scattering axis direction, the transmittance T in the scattering axis direction is used.
It is preferable that Tmin is rather large as described above,
Ideally, TTmax = TTmin 100%. In other words, in the direction of the scattering axis, the larger the haze value H representing the degree of scattering is, the more preferable it is. However, it is preferable that the scattering is not forward scattering but scattered forward to reduce the transmittance.

According to the present invention, the light guide made of a transparent medium having excellent transparency, such as an acrylic resin, can be obtained by attaching the above-mentioned forward scattering polymer film to the surface of the light guide via an adhesive. Surprisingly, even though unpolarized light from the light source is incident, light containing a large amount of linearly polarized light component in one vibration direction is emitted, and the vibration direction is the scattering axis of the polymer film, That is, it was found that the haze coincided with the maximum direction. The present invention has been made based on such findings.

The light guide can convert the light incident from the light source through the end face into linearly polarized light having a one-way component and emit the light to the outside of the light guide.

The principle of the polarization separation estimated by the present inventors will be described below. When light enters the light guide 13 as shown in FIG. 3 from its end face at an angle smaller than the total reflection angle, this light travels while repeating reflection at the interface between the light guide plate and air. There is no emission from other sources.

Here, as shown in FIGS. 1 and 2 below, the film 2 of the present invention is attached to the surface of the transparent medium 1 via an adhesive layer to constitute a part of the light guide 13. In this method, suitable polarization can be arbitrarily selected by changing the direction in which the film 2 is attached. Here, for example, the haze anisotropy has an electric field vibration plane perpendicular to the paper surface. A case where the haze is high with respect to linearly polarized light and low with respect to linearly polarized light having a vibration plane of an electric field parallel to the paper surface will be described (FIG. 4). In the drawing, reference numeral 3 denotes a reflection plate, and 4 denotes a light source.

In the present invention, desired linearly polarized light can be arbitrarily selected by changing the direction of anisotropy in the in-plane direction of the forward scattering polymer film 2. Here, as an example, the haze anisotropy is high in FIG. 4 with respect to linearly polarized light having a plane of vibration of an electric field perpendicular to the plane of the paper, and is high with respect to linearly polarized light having a plane of vibration of an electric field parallel to the plane of FIG. Is described below. The polarized component perpendicular to the paper surface of the unpolarized light traveling in the light guide is scattered by the scattering anisotropy factor 8 in the polymer film 2. A part of the scattered light is incident on the interface between the polymer film and the air at an angle deeper than the critical angle, so that the scattered light is emitted as polarized light from the light guide 13 without being totally reflected. On the other hand, the polarized light component parallel to the paper is hardly scattered by the scattering anisotropy factor 8. Therefore, as before, the light enters the interface between the polymer film and air at an angle smaller than the critical angle, and is thus totally reflected and propagates 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 it becomes possible to separate specific linearly polarized light from unpolarized light. The polarized light that has not been emitted is depolarized by the birefringence of the transparent medium 1 or the polymer film 2 and is reused again as unpolarized light.

As described above, the light source device obtains polarized light by utilizing the principle of scattering the polarized light in the direction of high haze (scattering axis), changing the incident angle, and breaking the total reflection of the light guide to emit the light. Things. Therefore, the scattering direction does not matter whether it is 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 forward scattering polymer film itself. Also, the polarized light in the direction of low haze (transmission axis), which was not used, does not change its incident angle to the interface, so that it is repeatedly confined in the light guide plate by total reflection on the surface of the light guide, so that there is no fear of dissipation. Further, the polarized light is depolarized by the strong birefringence of the forward scattering polymer film itself, and is reused. Therefore, such a light source device has a very high light use efficiency.

In the above description, for the sake of simplicity, the case where the haze is high for linearly polarized light having an oscillating plane of an electric field perpendicular to the paper and low for haze with respect to linearly polarized light having an oscillating plane of an electric field parallel to the paper Explained. However, the feature of the present invention is that the haze of the haze anisotropic polymer film is high (scattering axis).
Is always emitted. Therefore, as shown in Examples 16 to 21 described later, by changing the direction of the scattering axis in the haze anisotropic layer, the direction of the linearly polarized light to be emitted can be freely selected. Is required, for example, TN (Twi
The present invention can also be applied to a (sted Nematic) type liquid crystal display device.

The above-mentioned haze anisotropic polymer film has an exit surface (the opposite surface to the reflector) of the light guide from which polarized light is emitted.
(FIG. 1), on the side opposite to the exit surface (on the side where the reflector is placed) (FIG. 2), or a combination of both. When both are combined, the haze maximum direction of the haze anisotropic polymer film placed on the exit surface side and the haze anisotropic polymer placed on the opposite surface side of the exit surface and on the exit surface side of the reflector It should match that of the film.

As described above, according to the present invention, light emitted from the light guide is scattered by linearly polarized light in a certain oscillation direction.
It is preferably due to forward scattering, and hardly emits linearly polarized light in a vibration direction other than the one vibration direction.
Further, basically, the emitted light is scattered light by the polymer film, and is not non-scattered light of the polymer film.
This point is significantly different from the system described in WO97 / 32222, JP-A-8-76114, and JP-A-9-297204, in which the obtained linearly polarized light in one oscillation direction is mainly based on non-scattered light. Is a point. Where the polymer film is

[0043]

TTmax >> TTmin or the following equation

[0044]

When (TTmax + TTmin) / 2 <70% is satisfied, it indicates that the transmittance of the film itself is low, and that much backscattering occurs. In this case, a sufficient polarization separation effect is recognized in the vertical direction (0 ° direction) of the light guide plate, but the light emitted at a large angle has a long optical path traveling in the film, so that it is backscattered by multiple scattering or the like. It becomes difficult to emit necessary polarized light, and the amount of light is lost.

The light-scattering plate and light source device having the above characteristics can be provided by attaching the forward scattering polymer film of the present invention to at least one surface of a transparent medium via an adhesive layer. It is important that the film is integrated with a transparent medium by an adhesive layer or the like and an air layer is not sandwiched between them.

The thickness of such a film is 0.1 μm.
m to 200 μm, preferably 5 to 100 μm.

The forward-scattering polymer film having haze anisotropy is not particularly limited. For example, (i) a crystalline polymer oriented film, (ii) a liquid crystal-dispersed polymer film, and (iii) 2 And (iv) an oriented film made of a polymer containing a transparent filler in an amount of 1 ppm to 30% by weight.

The oriented film (i) can be usually obtained by stretching a film composed of a crystalline polymer. When a crystalline or semi-crystalline polymer film in the amorphous state is strongly stretched in the uniaxial direction, the polymer chains are oriented and crystallized, and the refractive index and the fibril structure of the oriented crystal and the other amorphous Haze anisotropy is exhibited due to the difference in refractive index from the portion. For example, in the case of a polymer film having a positive birefringence such as polyethylene terephthalate (PET), the haze is high with respect to linearly polarized light having a plane of vibration of an electric field in the stretching direction, and the haze with respect to linearly polarized light perpendicular to the direction. Is low.

Here, it is preferable that the oriented film is strongly stretched in one uniaxial direction. Accordingly, for example, in addition to a so-called uniaxially stretched film, a biaxially stretched film having an equal width uniaxial stretching and a stretching ratio of 1.5 or more in length and width is included.

The stretching ratio in the high stretching ratio direction is preferably 1.5 times or more. The suitable stretching ratio varies depending on conditions such as the type of polymer, the stretching temperature, and the stretching speed. For example, in the case of a polyester film, it is preferably 3 times or more.

The crystalline polymer oriented film is not particularly limited, but may be a substantially transparent film such as a polyester film such as polyethylene terephthalate or polyethylene naphthalate, a syndiotactic polystyrene film, a polyethylene film or a polypropylene film. Alternatively, a film made of a translucent crystalline polymer can be used. Particularly, a polyethylene terephthalate film or a polyethylene naphthalate film is preferable because the difference in the refractive index between the crystalline portion and the amorphous portion is large.

In the polymer film (ii), liquid crystal is dispersed in the polymer film, and the following formula (3) is obtained for a specific linearly polarized light.

[0053]

Equation 25] | n1 _A -n1 _B | <0.02 and | n2 _A -n2 _B |> a film satisfying 0.02 (3).

Here, n1 _A and n1 _B are each independently the refractive index of the polymer A and the liquid crystal B with respect to the linearly polarized light in a specific direction, and n2 _A and n2 _B are each independently orthogonal to the linearly polarized light. A for linearly polarized light in different directions
And the refractive index of the liquid crystal B. This film can be usually obtained by stretching a film in which liquid crystal is dispersed in a polymer. Such a polymer film has the following formula (3-1)

[0055]

Equation 26] | n1 _A -n1 _B | <0.01 and | n2 _A -n2 _B |> preferably satisfies 0.01 (3-1).

When a liquid crystal having positive birefringence and a polymer matrix having positive birefringence are used, this film generally has a high haze with respect to linearly polarized light having a vibration plane of an electric field parallel to the stretching direction. Film. The liquid crystal molecules having anisotropy in refractive index are oriented by stretching, and have anisotropy in haze due to the difference in refractive index from the polymer matrix.

It is preferable that n1 _A and n1 _B substantially match. The difference between n2 _A and n2 _B is larger is preferable. That is, the polymer film is n1 _A ≒ n1 _B against specific linearly polarized light, and to linearly polarized light orthogonal thereto, a film satisfying n2 _A ≠ n2 _B.
That is, the oriented film has a matrix A in the plane.
There is a direction in which the refractive index of B and the domain B coincide with each other, thereby expressing haze anisotropy.

It is preferable that the film is stretched and oriented in one uniaxial direction. Accordingly, for example, in addition to a so-called uniaxially stretched film, a biaxially stretched film having an equal width uniaxial stretching and a stretching ratio of 1.5 or more in length and width is included. The stretch ratio in the high stretch ratio direction is preferably 1.5 times or more.

Examples of the material for the polymer film include polyester and polyvinyl alcohol.

The oriented film (iii) is a transparent polymer C
A film comprising a resin composition containing 99.9 to 50% by weight and 0.1 to 50% by weight of a transparent polymer D substantially incompatible with the polymer, wherein the polymer chains are oriented by stretching or the like. And for a specific linearly polarized light:

[0061]

Equation 27] | n1 _C -n1 _D | <0.02 and | n2 _C -n2 _D |> a film satisfying 0.02 (4).

Here, n1 _C and n1 _D are independently the refractive indexes of the polymers C and D with respect to linearly polarized light in a specific direction. Further, n2 _C and n2 _D are each independently a polymer C for linearly polarized light in a direction orthogonal to the linearly polarized light.
And D are the refractive indices.

It is preferable that n1 _C and n1 _D substantially match. The difference between n2 _C and n2 _D are larger are preferred. That is, the film is n1 _C ≒ n1 _D against specific linearly polarized light, and to linearly polarized light orthogonal thereto, a film satisfying n2 _C ≠ n2 _D. Such an oriented film has the following formula (4-1)

[0064]

[Number 28] | n1 _C -n1 _D | <0.01 and | n2 _C -n2 _D |> 0.01 It is preferable to satisfy (4-1).

The above film has a matrix C in the plane.
There exists a direction in which the refractive index of D and the domain D coincide with each other, thereby expressing haze anisotropy.

It is preferable that the film is strongly stretched and oriented in one uniaxial direction. Accordingly, for example, in addition to a so-called uniaxially stretched film, a biaxially stretched film having an equal width uniaxial stretching and a stretching ratio of 1.5 or more in length and width is included. The stretch ratio in the high stretch ratio direction is preferably 1.5 times or more.

The blend amount of D with respect to the polymer C is 0.1 to 50% by weight. If the amount is less than 0.1% by weight, the resulting haze is not sufficiently anisotropic. Preferably it is 1 to 49% by weight, more preferably 1 to 30% by weight.

In the oriented film, polymer D is dispersed in the matrix of polymer C in an island shape. The form of the polymer D is generally an elliptic sphere having a major axis in the stretching direction, and the average diameter is preferably 0.4 to 400 μm. If the average diameter is less than 0.4 μm, no optical effect may be produced, and if it is more than 400 μm, the haze anisotropy may be insufficient. More preferably, it is 1 to 50 μm.

The polymers C and D are not particularly limited as long as they are transparent polymers. When the glass transition temperatures of the polymers C and D are Tg _C and Tg _D , the following formula (5) is obtained.

[0070]

(29) The relationship of Tg _C > Tg _D (5) is satisfied. This indicates that the polymer D dispersed in the polymer C can also be stretched at the stretching temperature of the matrix resin C. More preferably, the following formula (5-1)

[0071]

[Mathematical formula-see original document] Tg_C> Tg_D+ 20 ° C (5-1) is satisfied. At this time, the matrix resin C can be stretched.
When stretched under the following conditions, the dispersion resin D is flow stretched.
And n1_C≒ n1_DWhen stretching that satisfies the condition of | n2 _C-N
2_DIs more preferred. Stretching temperature is usually
Tg_CHigher Tg_C+ 50 ° or less.

The method for preparing the oriented film is not particularly limited, and examples thereof include a method of stretching a blend film obtained by forming the resin composition by a melt film forming method or a solution casting method.

The polymer C is not particularly limited, but a transparent polymer having a relatively high Tg is preferable. For example, polyethylene terephthalate, polyester such as polynaphthalene terephthalate, polyether sulfone, polycarbonate, polyester carbonate, polysulfone,
Polyarylate can be mentioned.

As the polymer D, a transparent polymer having a lower Tg than that of the polymer C is selected. For example, polymers C and D are
The following formula (5-2)

[0075]

It is preferable to satisfy 250 ° C.> Tg _C > Tg _D + 10 ° C.> 50 ° C. (5-2).

As the polymer D, for example, polyester,
Polycarbonate, acrylic, styrene and their
Preferable examples include polymers. And Takaita
The film of the resin composition composed of the daughters C and D was stretched.
At time, as described above, n1 _C≒ n1_DAnd n2_C≠ n
2_DOf polymers C and D that can satisfy the condition of
You can choose a combination.

The film (iv) contains 1 p of transparent filler.
It is a film in which polymer chains are oriented by stretching a polymer film dispersed in a range of pm to 30% by weight. And,
Equation (6) below for a specific linearly polarized light

[0078]

Equation 32] | n1 _E -n1 _F | <0.02 and | n2 _E -n2 _F |> a film satisfying 0.02 (6).

Here, n1 _E and n1 _F are each independently the refractive index of the polymer E and the filler F with respect to linearly polarized light in a specific direction. Also each n2 _E and n2 _F independently is the refractive index of the polymer E and the filler F against linearly polarized light in a direction perpendicular to the linearly polarized light.

Here, it is preferable that n1 _E and n1 _F substantially coincide with each other. The difference between n2 _E and n2 _F are larger are preferred. That is, the film is n1 _E ≒ n1 _F against specific linearly polarized light, and to linearly polarized light orthogonal thereto, a film satisfying n2 _E ≠ n2 _F. Such an oriented film has the following formula (6-1)

[0081]

| N1 _E -n1 _F | <0.01 and | n1 _E -n1 _F |> 0.01 It is preferable to satisfy (6-1).

The above film has a matrix E in the plane.
There is a direction in which the refractive index of F and domain F coincide with each other, whereby haze anisotropy is developed. That is, this film has a refractive index difference between the filler F and the matrix E depending on the direction, thereby expressing haze anisotropy.

As the polymer E, for example, PET, PEN
And the like.

As the filler F, one that satisfies the above formula (6) and is optically transparent is required. For example, inorganic oxides such as silicon oxide and silicone, clay minerals such as kaolin, and high-grade materials such as cross-linked polystyrene. And molecular compounds. The size of the filler is 0.1 to 30 μm.
m is preferred. The shape of the filler is not particularly limited, such as a sphere or a rod.

The blend amount of the filler F with respect to the polymer E is 1 ppm to 30% by weight. If the amount is less than 1 ppm, the resulting haze is not sufficiently anisotropic, and 30%
In the case described above, haze anisotropy becomes insufficient due to multiple scattering. It is preferably at most 10% by weight.

It is preferable that the film is stretched strongly in one uniaxial direction. Accordingly, for example, in addition to a so-called uniaxially stretched film, a biaxially stretched film having an equal width uniaxial stretching and a stretching ratio of 1.5 times or more in length and width is included. The stretch ratio in the high stretch ratio direction is preferably 1.5 times or more. The suitable stretching ratio varies depending on conditions such as the type of polymer, stretching temperature, stretching speed, and the like. For example, in the case of a polyester film, it is preferably 2 times or more.

The thickness of the forward scattering film in the present invention is 0.1 μm to 200 μm, preferably 10 μm to 200 μm.
100 μm.

The material of the adhesive layer for attaching the film to a transparent medium is not particularly limited, and a material having a refractive index close to that of the transparent medium and the film is preferable. For example, it can be formed using a transparent adhesive such as an acrylic resin which is basically transparent for optical use. As the thickness of such an adhesive layer, 0.1 μm to 100 μm, preferably 1 to 50 μm
It is.

In consideration of the effect of polarized light separation due to interfacial reflection, the haze-anisotropic polymer film can be used by laminating multiple layers via an adhesive layer. At this time, the direction of the haze anisotropy of these films, specifically, the scattering axis is preferably aligned.

Thus, according to the present invention, by using the forward-scattering polymer film of the present invention, it is possible to affix, via an adhesive, to one surface of a transparent medium having an end face for receiving light from a light source. Accordingly, it is possible to provide a light guide having characteristics that mainly scatter and emit linearly polarized light in one oscillation direction, and hardly emit linearly polarized light in other oscillation directions other than the one oscillation direction.

Further, according to the present invention, the forward scattering polymer film is used, which is made of a transparent medium, has an end face through which light from a light source can be incident, and one surface is a light emitting surface. A light guide having two opposing surfaces,
Mainly scatters and emits linearly polarized light in one oscillation direction,
It is possible to provide a light guide having characteristics that hardly emit transmitted light and linearly polarized light in other vibration directions other than the one vibration direction.

Further, according to the present invention, the above light guide is used as a constituent element by using the above-mentioned forward scattering polymer film.
A light source device suitable for a liquid crystal display element can be provided. Such a light source device always has a high haze direction (scattering axis direction) regardless of the installation direction of the forward scattering polymer film.
In this case, linearly polarized light having an electric field vibration surface can be selectively emitted. In this respect, the above-mentioned WO 97/32222,
76114 and the method described in JP-A-9-297204 are essentially different from each other. The fact that the vibration plane of the obtained linearly polarized light is shifted by 90 degrees is described in Examples and Comparative Examples 3 to 5 described later. It is clear from the description. Further, by using such a light source device as a backlight of a liquid crystal display device, the liquid crystal display device can have high contrast and low power consumption. By making the polarization axis of the polarized light emitted from the light source device coincide with the polarization axis of the dichroic polarizing plate, the utilization efficiency of the light source light can be improved.

[0093]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

1. The glass transition temperature (Tg) was measured at 10 ° C. using a DSC2920 Modulated DSC manufactured by TA Instruments.
/ Min was measured at a heating rate.

2. The weight average molecular weight was dissolved in methylene chloride and the flow rate was 1 ml / ml using TSK-gel G2000H as a column.
Measured in seconds by the GPC method.

3. The haze value and total light transmittance were measured using a digital turbidity meter NDH-20D (De
gital Haze Meter NDH-20D), a polarizing plate was provided on the incident light side, and polarized light was made incident perpendicularly to the film surface for measurement. The case of measuring the linearly polarized light having a plane of vibration of the electric field as the incident light in the MD direction H _MD, was HTD the case of measuring the linear polarization as the incident light having the vibration plane of the electric field in the TD direction. In the following examples, HMD = Hma
x, H _TD = Hmin. The transmittance when the polarized light in the MD direction was incident was TTmin, and the total light transmittance when the polarized light in the TD direction was incident was TTmax. Where MD is Machine Direction and TD is Transvers Direc
is an option.

4. The refractive index is ATAGO Co., Ltd.
LTD) Abbe refractometer 2-T (ATAGO abbe refractom)
eter 2-T).

5. Luminance was measured using a luminance meter (MINOLT A Co., LTD) LS-110 (Luminan
ce meter LS-110)). A polarizing plate is placed on the light emitting surface (film setting surface) of the light guide plate, and while rotating the polarizing plate, the brightness of the polarized light coming out of the light emitting surface is measured, and the degree of polarization is calculated from the brightness by the following equation (7). Calculated.

[0099]

(34) degree of polarization δ (%) = (maximum luminance−minimum luminance) / (maximum luminance + minimum luminance) × 100 (7)

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.

6. The average diameter of the island-shaped polymer dispersed in the polymer is measured by Lasertec Corpo.
ration) Real-time scanning laser microscope 1LM
21D (Real Time Scanning Laser Microscope 1LM21
It measured using D).

7. The polymers used are as follows. (1) Polyethylene terephthalate (PE) manufactured by Teijin Limited
T) ;, Tg = 75 ° C (2) Polyethylene naphthalate (PE) manufactured by Teijin Limited
N) ;, Tg = 118 ° C. (3) Polyvinyl alcohol (PVA); Kuraray Co., Ltd.
Manufactured by "PVA-117", Tg = 70 ° C. (4) Polyester carbonate (PEC); Polyester carbonate having a structure represented by the following formula

[0103]

Embedded image

Weight average molecular weight 200,000, Tg = 162 ° C. (5) Polycarbonate (PC); Panlite “C-1400” manufactured by Teijin Chemicals Limited, Tg = 155 ° C. (6) Polystyrene (PSt); Denki Kagaku Kogyo (stock)
(Denki Kagaku Kogyo KK) “Denka styrol”, Tg = 90 ° C

[Synthesis Example 1] 83 parts by weight of a styrene monomer and 20 parts by weight of methyl methacrylate (monomer) were added to TH
The resultant was dissolved in 50 parts by weight of F, 0.2 parts by weight of benzoyl peroxide was added as a reaction initiator, and the mixture was reacted at 90 ° C. for 8 hours.
After the completion of the reaction, the reaction solution was diluted by adding THF, and then poured into methanol to reprecipitate the product. The product was recovered by filtration and dried. The refractive index of the obtained copolymer was 1.572, and Tg was 102 ° C.

[Synthesis Example 2] A copolymer was produced in the same manner as in Synthesis Example 1 except that 77 parts by weight of the styrene monomer and 26 parts by weight of methyl methacrylate were used. The refractive index of the obtained copolymer was 1.564, and Tg was 103 ° C.

[Example 1] Spherical silicon oxide (Nippon Shokubai Co., Ltd.) as an additive to PET
d.) 0.15% by weight of Seahorse KE-E30) was added and kneaded and extruded to produce a film. This film was uniaxially stretched 3.6 times at 100 ° C.
A μm stretched film was obtained. The haze value and light transmittance of this film were measured.

The uniaxially stretched film was treated with an adhesive (“SK Dyne” 1811L manufactured by Soken Chemical Co., Ltd.) for 80 minutes.
The light guide plate was adhered to the upper surface of an acrylic plate measuring 80 mm x 2 mm. The thickness of the adhesive layer was 2 μm. Then figure
As shown in FIG. 1, a rod-shaped light source lamp (cold cathode tube) having a tube diameter of 3 mm, a tube length of 100 mm, and a center luminance of 10,000 cd / m ² was mounted on an end face of the light guide plate through which light was incident. At this time, the length direction of the cold cathode tube was made parallel to the MD direction of the attached film. A portion of the light source lamp not facing the light guide plate, an end surface of the light guide plate other than the light incident surface, and a surface opposite to the film installation surface, which is an emission surface of the light guide plate, were covered with an aluminum vapor-deposited film.

Using the surface light source device thus prepared, the luminance was measured to obtain the degree of polarization. Table 1 and Table 2 show the measurement results.
It was shown to.

Example 2 The same procedure as in Example 1 was carried out except that the uniaxial stretching ratio was set to 4.0. The results are shown in Tables 1 and 2.

Example 3 A film was produced without adding additives to PET, and was uniaxially stretched 3.0 times at 100 ° C. to obtain a stretched film having a thickness of 55 μm. It was evaluated similarly.

Example 4 A kneaded extruded film was prepared in the same manner as in Example 1 except that spherical silica was used as an additive at 40 ppm. This film was increased 4.0 times at 145 ° C.
The film was axially stretched to obtain a stretched film having a thickness of 75 μm. The results are shown in Tables 1 and 2.

Example 5 A film was produced in the same manner as in Example 3 except that no additive was added. The thickness of the produced film was 75 μm. The results are shown in Tables 1 and 2.

Example 6 A film was produced in the same manner as in Example 5 except that the stretching ratio was changed to 3.6 times. The thickness of the produced film was 55 μm. The results are shown in Tables 1 and 2.

Example 7 A solution prepared by heating and dissolving 10 parts by weight of PVA in 90 parts by weight of water was mixed with a liquid crystal (BL03 manufactured by Merck & Co., Ltd.).
6) 1 part by weight was added and dispersed using a homogenizer. This dispersion solution was cast on a polycarbonate film as a support. This was dried at 60 ° C.
After heat treatment at 0 ° C. for 1 minute, the film was peeled off from the polycarbonate film. This film was uniaxially stretched 5 times at 110 ° C. to obtain a stretched film having a thickness of 43 μm. The haze value, light transmittance and degree of polarization of this film were determined in the same manner as in Example 1. Further, the refractive index of the liquid crystal component in the MD direction n1 _MD, the refractive index of the PVA n2
_MD, the refractive index of the liquid crystal component in the TD direction n1 _TD, PVA
The refractive index was determined as n2 _TD . The results are shown in Tables 1 and 2.

Example 8 A film was prepared in the same manner as in Example 7, except that the liquid crystal was changed to 2 parts by weight. This film was uniaxially stretched 6 times at 110 ° C. to obtain a stretched film having a thickness of 74 μm. About this stretched film, Example 5
Was evaluated in the same way as

Example 9 Copolymer synthesized in Synthesis Example 1
10 parts by weight and 90 parts by weight of PEC are mixed with methylene chloride 600
Dissolve in parts by weight, cast this on a glass plate and dry
The film was dried. 190 ° C.
The film was uniaxially stretched to 2.0 times. About this stretched film
The haze value, light transmittance and degree of polarization were determined in the same manner as in Example 1.
I did. Furthermore, about this stretched film,
The refractive index of the copolymer in n1_{M D}, The refractive index of PEC
Two_MD, The refractive index of the copolymer in the TD direction is n1_TD, PE
The refractive index of C is n2_TDAnd the refractive index was measured. Table 1 shows the results
And Table 2.

Example 10 The copolymer was adjusted to 5 parts by weight,
A stretched film was obtained in the same manner as in Example 9 except that the PEC was changed to 95 parts by weight. The results are shown in Tables 1 and 2.

Example 11 The amount of the copolymer was 1 part by weight,
A stretched film was obtained in the same manner as in Example 9 except that the amount of PEC was changed to 99 parts by weight. The results are shown in Tables 1 and 2.

[Example 12] Copolymer polymerized in Synthesis Example 2
5 parts by weight and 95 parts by weight of PC are 400 weight parts of methylene chloride.
After dissolving in an amount, cast it on a glass plate and dry it.
The film was dried. At 180 ° C
The film was uniaxially stretched 1.75 times. Using this stretched film,
The haze value, light transmittance, degree of polarization, and refractive index were determined as described above.
Was. In addition, about this stretched film, in the MD direction
The refractive index of the copolymer_MDThe refractive index of PC is n2_MD,
The refractive index of the copolymer in the TD direction is n1_TDPC squatting
N2_{T D}And

Example 13 The copolymer was 1 part by weight,
Example 12 was carried out in the same manner as in Example 12, except that 99 parts by weight of PC was used.

Example 14 10 parts by weight of PSt and P
EN 90 parts by weight was melt-kneaded at 300 ° C. using a twin-screw extruder kneader PCM-30 manufactured by Ikegai Corp. to produce a film. 13
The film was uniaxially stretched 5 times at 0 ° C. at a speed of 1 cm / sec to prepare a stretched film. Using this stretched film, the haze value, light transmittance, degree of polarization, and refractive index were determined in the same manner as described above. In the MD direction, the refractive index of PSt is n1 _MD , PEN
Is the refractive index of n2 _MD , and the refractive index of PSt in the TD direction is n
The refractive index of 1 _TD and PEN was n2 _TD . The results are shown in Tables 1 and 2.

[Example 15] 5 parts by weight of PSt, PEN
Was carried out in the same manner as in Example 14, except that 95 parts by weight was used.

[0124]

[Table 1]

[0125]

[Table 2]

Example 16 For the film obtained in Example 2, the polarizing plate was rotated at intervals of 15 degrees, and the front luminance emitted from the film was measured. FIG. 5 shows the profile.

[Examples 17 and 18] The luminance was measured in the same manner as in Example 16 except that the MD direction of the film was 45 degrees (Example 17) and 90 degrees (Example 18) with the cold cathode tube.

Example 19 The front luminance of the film obtained in Example 5 was measured in the same manner as in Example 16. FIG. 5 shows the profile.

[Examples 20 and 21] The MD direction of the film was 45 ° (Example 20) and 90 ° (Example 2)
The luminance was measured in the same manner as in Example 19 except that 1) was used.

[Comparative Example 1] With respect to the acrylic light guide plate used in Example 1, the degree of polarization of emitted light was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 The degree of polarization of emitted light was measured in the same manner as in Example 1 for a film obtained by uniaxially stretching PC at 1.75 times at 180 ° C. The results are shown in Table 1.

[0132]

According to the present invention, the edge-incidence type light guide plate using the haze-anisotropic forward-scattering polymer film can be used as a polarizing surface light source device. As described above, the light use efficiency of the image display device using linearly polarized light can be improved.

[Brief description of the drawings]

FIG. 1 is an example of a basic configuration of a light source device using a forward scattering polymer film of the present invention.

FIG. 2 is an example of a basic configuration of a light source device using the forward scattering polymer film of the present invention.

FIG. 3 is a view for explaining a light guide using the forward scattering polymer film of the present invention.

FIG. 4 is a diagram illustrating a polarization separation mechanism according to the present invention.

FIG. 5 shows polarization profiles in Examples 16 to 21.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transparent medium 2 forward scattering polymer film 3 reflector 4 light source lamp 5 lamp reflector 6 light traveling direction 7 linearly polarized light 8 scattering anisotropy factor 10 light source 11 transparent medium 12 forward scattering polymer film 13 light guide plate

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shinichiro Kim 4-3-2 Asahigaoka, Hino-shi, Tokyo Teijin Limited, Tokyo Research Center (72) Inventor Kazuo Yawata 4-2-2 Asahigaoka, Hino-shi, Tokyo No. Teijin Co., Ltd. Tokyo Research Center F-term (reference) 2H042 BA08 BA20 2H091 FA07Z FA31Z FA41Z FB02 FC08 FC09 JA01 LA03 LA12 LA17 4F071 AA15 AA20 AA22 AA29 AA33 AA43 AA45 AA46 AA48 AA50 AA64 AA31 AF30 AB30 AF30

Claims (15)

[Claims] 1. A forward-scattering polymer film having a haze value H which varies depending on the vibration direction of linearly polarized light perpendicularly incident on the surface and which has a haze anisotropy satisfying the following formula (2).
(Here, the value H of the haze is expressed by the following equation: H (%) = DF / TT × 100 (1), where DF is the diffused light transmittance and TT is the total light transmittance.) Hmax / Hmin ≧ 1.05 (2) (where Hmax is the direction of the largest haze (scattering axis))
Hmin indicates the haze value in the smallest direction (transmission axis).) 2. When the total light transmittance of the scattering axis is TTmin and the total light transmittance of the transmission axis is TTmax, the following expression (8) is satisfied: 1 ≦ TTmax / TTmin ≦ 2 (8) 2. The forward scattering polymer film according to 1. 3. The forward scattering polymer film according to claim 1, which further satisfies the following expression (9): (TTmax + TTmin) / 2 ≧ 70 (9) 4. The forward scattering polymer film according to claim 1, which is an oriented film of a crystalline polymer. 5. The forward scattering polymer film according to claim 4, wherein the crystalline polymer is a polyester. 6., a polymer A liquid crystal B is dispersed, and the following expression for specific linearly polarized light (3) [Equation 5] | n1 _A -n1 _B | <0.02 and | n2 _A -n2 _B |> 0.02 (3) The forward-scattering polymer film according to any one of claims 1 to 3, which is an oriented film satisfying (3). (Here, n1 _A and n1 _B are independently the refractive indexes of the polymer A and the liquid crystal B with respect to linearly polarized light in a specific direction, and n2 _A and n2 B
2 _B is independently the refractive index of the polymer A and the liquid crystal B with respect to the linearly polarized light in the direction orthogonal to the linearly polarized light. ) 7. Transparent polymer C 99.9 to 50% by weight and transparent polymer D0.1 substantially incompatible with said polymer
A resin composition consisting of 50 wt%, and the following formula (4) [6] against specific linearly polarized light | n1 _C -n1 _D | <0.02 and | n2 _C -n2 _D |> The forward scattering polymer film according to claim 6, which is an oriented film satisfying 0.02 (4). (Here, n1 _C and n1 _D are each independently the refractive index of the polymer C and D with respect to the linearly polarized light in a specific direction, and n2 _C and n2 _D are each independently a straight line in a direction orthogonal to the linearly polarized light. Polymer C for polarized light
And D are the refractive indices. ) 8. The forward scattering polymer film according to claim 7, wherein the polymer C is at least one selected from the group consisting of polyester, polycarbonate, and polyester carbonate. 9. The forward-scattering polymer film according to claim 7, wherein polymer D having an average diameter of 0.4 to 400 μm is dispersed in the form of islands in the sea of the matrix made of polymer C. . 10. The forward scattering polymer film according to claim 7, wherein the polymers C and D satisfy the following formula (5): Tg _C > Tg _D (5) (Here, Tg _C and Tg _D are the glass transition temperatures of polymers C and D, respectively.) 11. The forward scattering according to claim 10, wherein the polymers C and D satisfy the following formula (5-1): 250 ° C.> Tg _C > Tg _D + 10 ° C.> 50 ° C. (5-1) Polymer film.
(Here, Tg _C and Tg _D are macromolecules C and D, respectively.
Is the glass transition temperature. ) 12. A polymer E comprising a transparent filler in an amount of 1 ppm to 30% by weight and having the following formula (6) for a specific linearly polarized light: | n1 _E −n1 _F | <0. 02 And | n2 _E -n2 _F |> 0.02 front scattering polymer film according to any one of claims 1 to 3 is a film satisfying (6). (Where n1 _E and n1
_F is independently the refractive index of the polymer E and the filler F with respect to linearly polarized light in a specific direction, and n2 _E and n2 _F
Are independently the refractive indexes of the polymer E and the filler F with respect to the linearly polarized light in the direction orthogonal to the linearly polarized light. ) 13. The forward scattering polymer film according to claim 12, wherein the polymer is a polyester. 14. By sticking, via an adhesive, to one surface of a transparent medium having an end face for receiving light from a light source, linearly polarized light in one oscillation direction is mainly scattered and emitted, and the one oscillation is performed. The forward-scattering polymer film according to any one of claims 1 to 13, which can constitute a part of a light guide having a characteristic of hardly emitting linearly polarized light in a vibration direction other than the direction. 15. A forward scattering height that satisfies the following expression (2): Hmax / Hmin ≧ 1.05 (2) and the following expression (8): 1 ≦ TTmax / TTmin ≦ 2 (8) The use of a molecular film in contact with the surface of a transparent medium constituting the light guide through an adhesive layer in order to mainly scatter linearly polarized light in one vibration direction and to emit the light from the light guide. (Here, Hmax is the value of the haze in the direction of the largest haze, Hmin is the value of the haze in the direction of the smallest haze, and the value of the haze is the following equation (1) when linearly polarized light is incident light. H (%) = DF / TT × 100 (1) where DF is the diffuse light transmittance, TT is the total light transmittance, and TTmax is the total light transmittance in the direction of the smallest haze. And TTmin is the total light transmittance in the direction of the largest haze.)