JP2005049764A - Light scattering film and liquid crystal display device mounting the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film capable of suppressing a deterioration in contrast of a liquid crystal display device and forming the liquid crystal display device having an excellent viewing angle, and to provide the liquid crystal display device using the optical film. <P>SOLUTION: A light scattering film which changes the scattering characteristic according to the incident direction of light and has such a scattering property that scattering haze on the center of a screen is ≤50 and the scattering haze on the surrounding part is larger than the scattering haze on the center part by 5 to 20 is used on the observer side of a liquid crystal display element of the liquid crystal display device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical film that can form a liquid crystal display device that suppresses a decrease in contrast of the liquid crystal display device and has an excellent viewing angle, and more particularly to a liquid crystal display device that uses a twist-aligned liquid crystal element and a discotic liquid crystal. The present invention relates to a liquid crystal display device having a wide viewing zone by compensating for a viewing angle other than the direction and using a diffusion film having an incident angle dependency for the downward direction.

  With the widespread use of liquid crystal display devices (LCD) in televisions, personal computer monitors, etc., it is desired to increase the viewing angle and increase the contrast. The phase difference is compensated by the phase difference plate due to the birefringence of the liquid crystal as in the case of achieving a black-and-white display by expanding the viewing angle for good viewing in the commonly used TN (twisted nematic) type and color compensation in the STN-LCD. Thus, proposals have been made to improve the visual characteristics.

  As such a retardation compensation film, for example, as disclosed in Patent Document 1 to Patent Document 3, a discotic liquid crystal film is used and a film that compensates birefringence with liquid crystal is known.

However, the conventional compensator cannot sufficiently cope with the phase difference characteristics of the liquid crystal, and sufficiently compensates for birefringence in directions other than one direction, but sufficiently compensates for birefringence in one direction. Cannot be satisfied, and the improvement of the visual characteristics is not satisfactory.
For example, as shown in Table 2 of Patent Document 2, the viewing angle can be expanded only to 45 degrees in one direction.

  Therefore, in a liquid crystal display device using a discotic liquid crystal that compensates for such birefringence, the notebook PC or the like is obliquely above, so the upper viewing area is given priority from the front, and the lower viewing area. Was insufficient. Conventionally, this uncompensated direction of birefringence has come to the direction of the lower edge, which is a direction that is hardly observed on a monitor. Therefore, in such a liquid crystal display device, the viewing angle in the direction of the lower edge is usually obtained only up to about 30 degrees. At angles deeper than 30 degrees, gradation inversion occurs, and the visibility of the image is significantly deteriorated.

  However, recently, with the spread of liquid crystal televisions and the like, there is an increasing need for observing the screen from the lower side, for example.

  There are things that use only conventional diffusion films for such problems, but such diffusion films have poor central visibility and are usually at angles deeper than 30 degrees such as liquid crystal televisions (TN series). Enlarging the field of view is insufficient.

  In particular, various displays such as FA, navigation, tablet PC, monitor and the like using LCD have recently become widespread. Of these, as TVs have recently increased in size, products with a size of 30 inches or more have been developed for LCDs. When used in normal homes, they should be placed on a table or lie down, and viewed from below. There are cases. In addition, in the case of FA, an unspecified number of people view with advertisements and the like, so that it is desired to have a wide viewing area in the downward direction. At the same time, simple scattering increases the apparent contrast, but increases text and image blur.

Furthermore, when a human sees a display, he focuses with a perpendicular line down the center. At this time, the peripheral portion is angled and viewed in an oblique direction, so the focal length and angle are different between the center and the periphery. For this reason, when the focus is viewed at the center, the peripheral portion is easily blurred.
JP-A-6-214116 JP-A-6-222213 JP-A-6-265728.

  Therefore, the present invention uses a film that compensates for the phase difference and an anisotropic scattering film that scatters only the light in the downward direction, particularly by lowering the haze at the center and increasing the haze at the periphery. An object of the present invention is to provide a light scattering film that realizes a screen display in which the peripheral portion is easy to see by correcting the deviation of the focal length and the angle, and a liquid crystal display device that can uniformly see the entire surface using this film.

  The invention according to claim 1 is a light scattering film characterized in that the scattering characteristics vary depending on the direction of light incident on the viewer side of the liquid crystal element, and the light scattering film has different scattering properties at the center and the periphery of the screen. is there.

  The invention according to claim 2 is characterized in that the scattering haze at the central portion is 50 or less, whereas the haze at the peripheral portion is 5 to 20 larger than the central portion haze. It is a film.

  The invention according to claim 3 is characterized in that the maximum scattering angle in the vicinity of the center is 0 to 40 degrees, and the maximum scattering angle in the peripheral portion is 20 to 50 degrees. It is.

  Invention of Claim 4 is a light-scattering film in any one of Claim 1 to 3 whose haze of the said light-scattering film is the range of 20-70.

  The invention according to claim 5 is a liquid crystal display device characterized in that the light scattering film according to any one of claims 1 to 4 is disposed on the viewer side of the liquid crystal display element.

  The invention according to claim 6 is the liquid crystal display device according to claim 5, wherein the liquid crystal display element has a retardation film on both sides and a polarizing plate on the outside.

  According to the liquid crystal display device of the present invention, the light coming from the illumination unit is incident on the polarizing plate, and a wide viewing angle can be obtained by transmitting the light compensated for polarization by the liquid crystal element and the two discotic liquid crystal films. it can.

  In addition, in the direction not compensated by these two discotic liquid crystal films, in the diffusion film disposed on the viewer side of the exit side polarizing plate, the region where the contrast is not reversed, the region where the contrast is not reversed. By diffusing the light, it is possible to suppress a decrease in contrast in a region that is not compensated by the discotic liquid crystal.

  And it becomes possible to raise visibility by raising the resolution of a front image more by making center part haze low, and setting peripheral part haze high. Moreover, even if the apparent haze is the same by setting the maximum scattering angle to be smaller in the peripheral part than in the central part, the visibility is improved in the same way as the haze is higher in the peripheral part than in the central part.

  On the other hand, since the scattering film of the present invention has different scattering properties depending on the incident angle, it hardly scatters light in the region where the polarization is compensated by the discotic liquid crystal film. Therefore, it is possible to scatter light only in a region where the viewing angle is to be widened without incurring much blurring or lowering of luminance, so that a sufficient contrast can be obtained even though it is a twist-aligned liquid crystal cell. A wide viewing angle can be realized by increasing the observation angle range where the gradation is not inverted.

  In the two discotic liquid crystal films, the product of the refractive index anisotropy Δn ′ of each liquid crystal and the film thickness d ′ is the product of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the film thickness d. The birefringence effect of the discotic liquid crystal film does not adversely affect the display.

  According to the liquid crystal display device of the present invention, the light coming from the illumination unit is incident on the polarizing plate, and a wide viewing angle can be obtained by transmitting the light compensated for polarization by the liquid crystal element and the two discotic liquid crystal films. it can.

  In addition, in the direction not compensated by these two discotic liquid crystal films, in the diffusion film disposed on the viewer side of the exit side polarizing plate, the region where the contrast is not reversed, the region where the contrast is not reversed. By diffusing the light, it is possible to suppress a decrease in contrast in a region that is not compensated by the discotic liquid crystal.

  And it becomes possible to raise visibility by raising the resolution of a front image more by making center part haze low, and setting peripheral part haze high. Moreover, even if the apparent haze is the same by setting the maximum scattering angle to be smaller in the peripheral part than in the central part, the visibility is improved in the same way as the haze is higher in the peripheral part than in the central part.

  On the other hand, since the scattering film of the present invention has different scattering properties depending on the incident angle, it hardly scatters light in the region where the polarization is compensated by the discotic liquid crystal film. Therefore, it is possible to scatter light only in a region where the viewing angle is to be widened without incurring much blurring or lowering of luminance, so that a sufficient contrast can be obtained even though it is a twist-aligned liquid crystal cell. A wide viewing angle can be realized by increasing the observation angle range where the gradation is not inverted.

  In the two discotic liquid crystal films, the product of the refractive index anisotropy Δn ′ of each liquid crystal and the film thickness d ′ is the product of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the film thickness d. The birefringence effect of the discotic liquid crystal film does not adversely affect the display.

<Structure>
The liquid crystal display device used in the present invention includes a liquid crystal display element including a substrate having a pair of electrodes and a liquid crystal layer sandwiched between the substrates, and two discotic liquid crystal films on both sides of the liquid crystal display element. The polarizing plate is further disposed on the outer side, and the light-scattering film whose scattering characteristics change depending on the incident direction of light is provided on the viewer side of the exit-side polarizing plate.
Usually, an illumination member such as a backlight is added to such a configuration.

  A liquid crystal display element has a liquid crystal layer interposed between a pair of transparent substrates made of glass or the like. Electrodes are formed inside both substrates of the liquid crystal display element, and an alignment film is formed thereon. Is provided. Note that the pair of substrates are bonded via a frame-shaped sealing material, and the liquid crystal is sealed in a region surrounded by the sealing material on both substrates.

  This liquid crystal is a nematic liquid crystal having positive dielectric anisotropy, and the liquid crystal molecules are twisted between the substrates, with the alignment direction in the vicinity of each substrate being restricted by the alignment film.

Among the polarizing plates, the polarizing plate in the incident direction is provided with its absorption axis substantially parallel to the alignment direction of the liquid crystal molecules in the vicinity of the incident side substrate of the liquid crystal element, and the polarizing plate on the exit side absorbs the absorption. The axis is provided substantially parallel to the alignment direction of the liquid crystal molecules in the vicinity of the emission side substrate of the liquid crystal element, and the TN type liquid crystal display system is constituted by the liquid crystal element and these polarizing plates.
<Liquid crystal display device>
In the liquid crystal display device of the present invention, the retardation compensation film is a special discotic liquid crystal film composed of a polymer liquid crystal whose molecular shape is a disk shape, and the disk-shaped molecule is transferred from one surface of the film to the other. They are oriented sequentially so as to rise almost vertically from the state of lying down almost horizontally toward the surface. The direction along the central axis of these discotic molecular orientation changes (the direction parallel to the film surface in the discotic molecular diameter direction) is the slow axis, and the direction orthogonal thereto is the fast axis.

  For example, in a twist type liquid crystal in which a liquid crystal cell has a twist angle of approximately 90 degrees, one discotic liquid crystal film has its slow axis as the orientation direction of liquid crystal molecules in the vicinity of one substrate of the liquid crystal display element. It is preferable that the orientation direction of the other discotic liquid crystal is substantially parallel to the orientation direction of the liquid crystal molecules in the vicinity of the other liquid crystal.

  Therefore, in a twist type liquid crystal display device, these two discotic liquid crystal films are arranged so that the planes in which the alignment states of the disc-like molecules are the same are brought together, and the respective slow axes are substantially perpendicular to each other, so that the liquid crystal It is desirable to arrange on both sides of the display element.

  In the two discotic liquid crystal films, the product of the refractive index anisotropy Δn ′ of each liquid crystal and the film thickness d ′ is the product of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the film thickness d. It is desirable that it is almost the same. In this way, the birefringence effect of the discotic liquid crystal film does not adversely affect the display.

  As the scattering film used in the liquid crystal display device of the present invention, a cylindrical fine layer having a different refractive index has a sea-island structure and is in a cylindrical shape with respect to the thickness direction. . FIG. 1 and FIG. 2 show a plan view (a) and a sectional view (b) of such a film. When light is incident in a direction parallel to the boundary surface of the layered regions having different refractive indexes of the film, the light is scattered due to the difference in the refractive index of the boundary. On the other hand, light incident at an angle close to the perpendicular to the boundary surface of the layered regions having different refractive indices has a property of being transmitted as it is because there is no scattering at the boundary.

Furthermore, in the present invention, the vicinity of the center is designed with a haze of 50 or less, giving priority to the elimination of contrast and character blur (unclearness) in the front, and the outer peripheral part is designed to be 5 to 20 larger than the center part.
The angle at which the scattering property is generated is not particularly specified, but it is preferably in the range of 10 to 40 degrees at the center and 5 to 20 degrees larger at the periphery than the center.
<Viewing area expansion effect>
With the liquid crystal display device having such a configuration, the twist type liquid crystal display device and the configuration of only the discotic liquid crystal have conventionally had a contrast of about 45 ° and the image is very difficult to see. According to the configuration of the present invention, a configuration in which such a film is added can suppress a decrease in contrast even from 45 to 60 °, and a liquid crystal display device having a wide viewing area can be realized.

  At this time, if the scattering property (haze) of the film is increased, a more effective film can be obtained. However, if the haze is high, the contrast at the front will be reduced.

As a result of various experiments, when the eyes are placed in the center of the screen and observed at around 45 degrees below, the haze near the center is more easily less than about 50, and the peripheral part has an angle with the eyes and the focal length is different. It is easier to see when the haze is 5 to 20 degrees higher than the center. On the other hand, in the case of using a light diffusion film of 70 or less at the haze center, even if a liquid crystal with a high front contrast is used, the backscattering is increased, so that a practically sufficient contrast cannot be obtained. In addition, blurring when observing an image from the front also increases, and satisfactory image quality cannot be obtained. Thus, in view of the image quality at the front, it is reasonable to set the haze to 70 or less, preferably 50 or less, and the peripheral part is 50 to 20 higher than the central part, with the eye centered. If the angle is different from the center,
In addition, it is good because the focal length does not match.

In addition, in a case where it is not supposed to be observed from below, for example, a personal liquid crystal display, etc., if the application gives priority to the image quality at the front and does not place importance on the image quality observed from below, A light diffusion film having a low haze can also be used. When such a light diffusion film was used, the image quality from the lower direction was not good, but the front image quality was better. With respect to what was assumed to be used in this way, a good one having a haze of 50 or less was obtained. Even in this case, the peripheral image quality was improved by raising the peripheral portion by about 5 to 20 from the central portion.
<Film structure>
Next, the structure of the light scattering film 1 of the present invention will be described in detail. As described above, in the light scattering film 1 of the present invention, portions having different refractive indexes are distributed in irregular shapes and thicknesses, thereby forming a light and shade pattern having a high and low refractive index.

  If the difference in refractive index is too small, the scattering property is deteriorated. On the other hand, if the difference is too large, light scattering occurs regardless of the incident angle of light. It becomes difficult to have. Therefore, light scattering does not occur only by the difference in refractive index on the surface, and it is necessary that the refractive index difference is optimal so as to have sufficient scattering properties due to the thickness of the film.

  The light scattering film of the present invention is appropriately selected in the range of refractive index difference of 0.001 to 0.2 so that the above conditions are met, and the film thickness is similarly in the range of 1000 μm to 1 μm depending on the refractive index difference. Is selected as appropriate.

  For example, in a film having an average refractive index of 1.52 and a thickness of 20 μm, a portion having a refractive index of 1.56 (refractive index difference of 0.04) is distributed to form a shading pattern. A light scattering film with sufficient scattering properties and incident angle selectivity could be obtained.

  Since the refractive index difference that can be recorded is limited by the production method and recording material, the light scattering of the present invention can be achieved by making the film thinner if it has a large refractive index difference and thicker if it has a small refractive index difference. It is possible to realize a film.

  The sizes of the portions having different refractive indexes are random and non-regular in order to cause light scattering, but the average size is in the range of 0.1 μm to 300 μm in diameter in order to have the necessary scattering properties. Of these, it is appropriately selected according to the required scattering property for each application.

  As an example, by using a light and shade pattern consisting of high and low refractive indexes having an average size of 12 μm, a scattering property having a scattering spread of about ± 40 degrees was obtained.

  In addition, the distribution of portions having different refractive indexes on the film surface is random and non-regular in order to cause light scattering, but in order to have the necessary scattering properties, the average refractive index of the entire film is set to <n. When>, the probability distribution exhibits a normal distribution centered on <n>. Alternatively, it may be distributed according to a probability distribution that takes a maximum value at the minimum value nmin of the refractive index n and monotonically decreases to the maximum value nmax of the refractive index exponentially, or a probability distribution that monotonously increases.

<Production means>
FIG. 3 is an explanatory view showing an example of an optical system for producing a light scattering film using a random mask pattern. The ultraviolet light emitted from the UV light source 15 is converted into parallel light 17 by the collimating optical system 16 and irradiated on the mask original plate 18. The mask original plate 18 includes a glass substrate 20 and a chrome pattern which is a random pattern.

  The mask original plate 18 having a random pattern used in FIG. 3 was obtained by etching the black and white pattern data produced from the random number calculation using a computer as the metal chromium pattern 21 on the glass substrate 20 by a so-called photolithography technique. . Of course, the method for producing the mask original plate is not limited to the above-described method, and a similar mask can be produced even if produced by a photographic technique using a squirrel plate.

  In the production of the original plate, in the case of the present invention, the density of the speckle pattern is intentionally adjusted between the central portion and the peripheral portion. As this method, for example, it is possible to make the UV irradiation amount strong at the center and weak at the peripheral part at the time of original plate photographing. In addition to this, it is also possible to take a picture with the resist thickness on the chromium layer 21 of the mask blank being thin at the central portion and thick at the peripheral portion. In addition, this technique can also insert partial characters and patterns into the original plate in a pattern, and the arrangement can be freely set. For example, it is possible to produce a scattering film containing characters and patterns that are not conventional. An example is shown in FIG.

  On the other hand, with respect to the method for producing a scattering film from the original plate, the photosensitive material 19 is disposed in close contact with the surface opposite to the UV irradiation side of the mask original plate 18, and the pattern of the mask original plate 18 is exposed to the exposure material 19. To do. At this time, the UV parallel light 17 and the mask original plate 18 are inclined at a predetermined angle α as shown in the figure, so that the pattern exposure is performed at a predetermined angle in the photosensitive material 19. Since this angle corresponds to the inclination angle of the portion having a different refractive index in the light scattering film (that is, the incident angle-dependent scattering peak angle θ), the angle is 0 to 60 degrees depending on the application. It is appropriately selected within a range of degree.

  The photosensitive material 19 used here is a photosensitive material that can be recorded in the form of a change in refractive index between the exposed portion and the unexposed portion of UV light, and has a higher resolving power than the gray pattern to be recorded. The material must be capable of recording a pattern in the thickness direction.

  As such a recording material, a photosensitive material for volume holograms can be used, a silver salt photosensitive material for holograms manufactured by Agfa (trade name 8E56 dry plate), a photosensitive material H for holograms manufactured by DuPont (trade name RF film), or Bichromated gelatin, manufactured by Polaroid (trade name DMP-128 recording material), etc. can be used.

(Specific example 1)
Polaroid product name DMP128 was used as the recording material, and the change in image quality was observed when the maximum scattering angle was changed between the central part and the peripheral part.

  Table 1 shows the results of the effect on the image quality due to the difference in haze between the central part and the peripheral part when the maximum scattering angle is 40 degrees.

(Specific example 2)
Table 2 shows the results of an experiment on how the image quality changes depending on the difference in the maximum scattering angle between the central part and the peripheral part when the same recording material as in Example 1 is used and the haze is fixed at 50.

It is explanatory drawing which shows one example of the light-scattering film which concerns on this invention, (a) Sectional drawing, (b) Plan view. BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing of the liquid crystal display device using the light-scattering film of this invention. Explanatory drawing which shows one example of the optical system which produces the light-scattering film shown in FIG. 1 using a random mask pattern. The top view which shows the structure from which optical performance (haze, a maximum scattering angle) differs in the center and periphery of a diffusion film from which scattering property differs with the incident angle in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Diffusion film 1a ... High refractive index area | region 1b in a diffusion film ... Low refractive index area | region 2a, 2b in a diffusion film ... Polarizing plate 3a, 3b ... Discotic liquid crystal 4 ... Liquid crystal element 6a ... Normal incident light to a diffusion film 6b: Light emitted perpendicularly to the diffusion film 6a: Light incident obliquely on the diffusion film 6b: Light emitted obliquely incident on the diffusion film 10: Illumination device 31: Photosensitive material 32 ... Mask master 33 ... UV parallel light 34 ... UV light source

Claims (6)

  A light scattering film, characterized in that the scattering characteristics vary depending on the direction of light incident on the viewer side of the liquid crystal element and have different scattering properties at the center and the periphery of the screen.   2. The light scattering film according to claim 1, wherein the central portion has a scattering haze of 50 or less, and the peripheral portion has a haze of 5 to 20 larger than that of the central portion.   The light scattering film according to claim 1, wherein the maximum scattering angle near the center is 0 to 40 degrees, and the maximum scattering angle in the peripheral portion is 20 to 50 degrees.   4. The light scattering film according to claim 1, wherein the light scattering film has a haze in the range of 20 to 70. 5.   5. A liquid crystal display device comprising the light scattering film according to claim 1 disposed on an observer side of a liquid crystal display element.   6. The liquid crystal display device according to claim 5, wherein the liquid crystal display element has a retardation film on both sides and a polarizing plate on the outer side.