JPH0343780A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To uniformize the contrast of the images over the entire surface of the screen by refracting the light from a light source in the optimum visual field angle direction where the contrast increases with respect to the normal of the liquid crystal display element by an optical path refracting means. CONSTITUTION:The ray 28 entering at an incident angle theta with the normal within one plane inclusive of the normal perpendicular to the liquid crystal layer of the liquid crystal display element 7 and the optimum visual field angle direction where the contrast is maximized is so refracted by the incident side optical path refracting means 25, such as prism, as to emit near the max. visual field angle direction to the above-mentioned normal at the angle (theta+alpha) larger than the angle position of the max. visual field angle direction and the ray 27 entering at an incident angle -theta is so refracted as to emit at the angle (-theta+alpha) on the side opposite to the max. visual field angle direction to the normal and near the normal. The exit light is again refracted by the optical path refracting means 26 on the exit side of the liquid crystal display element 7 to the direction where the exit light is nearly parallel with the incident light. The contrast is uniformized over the entire screen surface in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a projection type liquid crystal display device, and more specifically, to a projection type liquid crystal display device, in which an image displayed by a liquid crystal display element is projected and displayed on a screen. The present invention relates to a liquid crystal display device.

Conventional technology FIG. 6 is a simplified cross-sectional view of the prior art.

Light 51 emitted from the light source 50 passes through the liquid crystal display element 7 at an angle of -0 towards the liquid crystal display element 52, is magnified by the projection lens 53, and is irradiated onto the edge 55 of the screen 54. Light 56 from the light source 50 passes through the liquid crystal display element 52 at an angle θ, is magnified by the projection lens 53, and is irradiated onto the edge 57 of the screen 54. The liquid crystal display element 7 is a twisted nematic (abbreviated as TN) liquid crystal display element, and therefore has viewing angle dependence such that it is easy to see from the direction in which it is formed, that is, has a large contrast, and is difficult to see from other directions. As a method for controlling the alignment of liquid crystal molecules, in -i, the alignment film 59 on the glass substrate 58 shown in FIG. 7 is rubbed using cotton cloth or the like. At this time, the liquid crystal molecules 60 produce a pretilt angle that is inclined by an angle δ with respect to the rubbing direction 61, and when the head 60a of the liquid crystal molecule 60 is one side of the viewer, the contrast is maximum and the This pretilt angle δ, which is easy to change, is
This is the biggest cause of visual angle dependence.

A direction 62 in which the liquid crystal molecules 60 have a pretilt angle δ corresponds to a rubbing direction 61.

When power is applied to the liquid crystal molecules 60, the liquid crystal molecules 60 rise in the pretilted direction, so I! When illuminated, the optical rotation is easily eliminated, and the terminal direction of the vector becomes most visible.

Therefore, when the liquid crystal display element 52 in FIG. 6 is viewed from the upper side of FIG.
When viewed from Perh et al., it shows a state of high contrast.

Such viewing angle dependence of the liquid crystal display element 520 is shown in FIG. The contrast is greatly different at viewing angles of θ and -θ with respect to the normal line perpendicular to the pair of glass substrates of the liquid crystal display element 52, and therefore has viewing angle dependence. Therefore, the contrast of the screen 55 where light passes through the liquid crystal display element 52 at an angle of -0 and the contrast at the end portion 57 of the screen 54 where light passes through the liquid crystal display element 52 at an angle θ are significantly different. Therefore, the display quality is poor.

In this Figure 8, if this angle -θ is (-θ
+α), and when the angle θ is (θPα〉),
It can be seen that the contrast at the ends 55, 57 of the screen 54 is approximately equal. Note that the contrast here refers to maximum light transmittance/minimum light transmittance.

Problems to be Solved by the Invention An object of the present invention is to provide a projection type liquid crystal display device that can make the contrast uniform over the entire screen.

Means for Solving the Problems The present invention provides a projection type liquid crystal display device in which light from a light source is projected through a liquid crystal display element. The means includes a plane 20 that intersects a normal line 21 perpendicular to the liquid crystal layer of the liquid crystal display element and an optimum viewing angle direction 19 in which the contrast is maximized.
(a) A ray incident at an incident angle θ with respect to the normal line 21 is placed at an angle (θ ”~α), and (b) the light ray incident at an incident angle −θ with respect to the normal line 21 is refracted so as to exit at a direction of maximum viewing angle 19 with respect to the normal line 21, Normal 2
Another 19 optical path refracting means are provided on the output side of the liquid crystal display element, and this output side optical path refraction means refracts the light from the liquid crystal display element at an angle of (-θ+α) toward 1.
This is a projection type liquid crystal display device characterized in that the emitted light is refracted in a direction substantially parallel to the incident light.

Function According to the present invention, the incident side optical path bending means of the liquid crystal display element is, for example, a prism, and the incident side optical path bending means changes the contrast of the light from the light source with respect to the normal line of the liquid crystal display element. Refract in the direction of increasing viewing angle. As a result, the contrast on the screen can be made almost the same, and uniform contrast can be obtained on the screen.

Another 19 optical path refracting means are provided on the output side of the liquid crystal display element, thereby refracting the light from the liquid crystal display element in a direction in which the emitted light is approximately parallel to the incident light. As a result, the optical path of the light emitted from the liquid crystal display element is corrected by the amount refracted by the optical path refracting means on the incident side, and the presence of the optical path refracting means on the incident side and the output side does not adversely affect the design of the optical system. do not have.

Embodiment FIG. 1 is a simplified sectional view of an embodiment of the present invention.
FIG. 2 is a sectional view showing the entire i-precept of the liquid crystal display device. Referring to these drawings, the present projection type liquid crystal display device 1 includes a projector 2 and a screen 11. On the projector 2, the light from the light source 3 is directed forward (to the right in FIGS. 1 and 2) by the reflecting mirror 10 and is focused by the condensing lens 4, and is condensed by the heat ray absorption filter 53! The heat ray is cut off by 31 after passing through J, passes through the first (W tip plate 6), becomes linearly polarized light, then passes through the liquid crystal display element 7, and undergoes optical rotation modulation according to the displayed content. Next, the second polarizing plate 8 forms a brightness pattern according to the display content, and the image is magnified by the projection lens 9 and irradiated onto the external screen 11.

The screen 11 is made up of a sheet material 12 made of vinyl chloride, for example, and a reflective sheet 13 made of aluminum or the like that covers the surface of the sheet material 12. The image projected onto the screen 11 from the projector 2 is reflected by the reflective sheet 13. and observed.

According to the present invention, prisms 25 and 26 are interposed between the liquid crystal display element 7, and therefore between the first and second polarizing plates 6 and 8, as optical path bending means on the incident side and the output side. The prisms 25 and 26 are right triangular pillars, with their hypotenuses facing the light source 10 and the projection lens 9, and having an apex angle of β.
are arranged at the top and bottom in FIG. The remaining corners of this prism 25,26 are designated by the reference γ.

FIG. 3 is an exploded perspective view of the liquid crystal display element 7. FIG.

The alignment film on one glass substrate 15 is formed in a rubbing direction 16.
The alignment films of the other 19 opposing glass substrates 17 are rubbed in the rubbing direction 18, and these rubbing directions 16° 18 are perpendicular to each other. It is a nematic type and uses a counterclockwise rotating liquid crystal. The liquid crystal molecule 60 has a pretilt angle δ and the head 60 a of the liquid crystal molecule 60
is raised, and the maximum contrast is obtained in the Ik311 viewing angle direction 19 of 45° with respect to the rubbing direction 16.18. This top 3! ! A virtual plane 20 is assumed along the viewing angle direction 19 .

FIG. 4 is a front view of the @imaginary plane 20 seen from the arrow 21a in FIG. In this plane 20, with respect to the pair of parallel glass substrates 15, 17, and therefore the normal 21 perpendicular to the liquid crystal layer, +θ is taken in the optimum viewing angle direction 19, and ~θ is taken in the direction away from the optimum viewing angle direction 19. to wear. Using the incident side prism 25, the angle -θ of the light to the liquid crystal display element 7 is set as (-θ+α), and the angle θ is set as (θ+α).
>.

That is, the prism 25 has an incident angle of (a) with respect to the normal line 21 within a plane 20 that includes a normal line 21 perpendicular to the liquid crystal layer of the liquid crystal display element and an optimum viewing angle direction 19 where the contrast is maximum. The incident light ray at θ is located near the maximum viewing angle direction 19 with respect to the normal 21, and at an angle (θ
(b) A ray incident at an incident angle -θ with respect to the normal 21 is refracted so as to exit at the normal 21 on the opposite side of the maximum viewing angle direction 19 with respect to the normal 21. It is refracted so that it exits at an angle rR (-θ+α).

For example, the F number of the projection lens 9 is 3.5, and the focal length is 1.
50 mm, the projection magnification is 40 times, and the size of the liquid crystal display element is 3 inches square. The liquid crystal display element uses a twisted nematic liquid crystal display element, and moreover, as shown in Figure 1! 3 and 2 are arranged to provide high contrast when viewed from above. ¥r of liquid crystal display element 7
The angle β of the triangular prism 25.26 placed after rI is 10
°, γ is 80°.

For example, the angle from the light source 10 to the triangular prism 25 is -16° (
The light 27 incident at an angle of -θ) passes through the triangular prism and then enters the liquid crystal display element 7 at an angle of -10° (-θ+α) (for example, α=6°). After passing through the liquid crystal display element 7 and the triangular prism 26, the light 27 enters the projection lens 9 at the same angle as the angle at which it entered the triangular prism 25, and finally the screen 1.
1 at position 24.

16” (=θ
) After passing through the triangular prism 25, the light 28 enters the liquid crystal display element 7 at an angle of 22" (=θ+α). After passing through the liquid crystal display element 7, the light 28 also passes through the triangular prism 26. By doing so, the light 28 enters the projection lens 9 at the same angle as the angle at which it entered the triangular prism 25.
and the position 23 on M r &scree〉'11
is irradiated.

FIG. 5 shows the contrast change with respect to the incident angle. Since the light 27 is incident on the liquid crystal display element 7 at an angle of -10 degrees and the light 28 is incident on the liquid crystal display element 7 at an angle of 22 degrees, the contrast is almost the same as shown in FIG. Therefore, the contrast at positions 23 and 24 on the screen 11 will be approximately the same, and a uniform contrast will be obtained on the screen 11.

A similar effect can be obtained by changing the arrangement of the triangular prisms even when the liquid crystal display element 7 has a high contrast when viewed from below by 1%.

Refraction angle by prism 25.26 -θ+α.

θ+α is chosen to be about 2° to 30°. The light incident on the prism 25 may be parallel to the optical axis 14.

The prism 26 on the output side may be omitted.

Effects of the invention in which other configurations for refracting the optical path may be used in place of the prisms 25 and 26 As described above, according to the present invention, the optical path refracting means is provided on the incident side of the liquid crystal display element. This increases the contrast of the light from the light source with respect to the normal to the liquid crystal display element! &
Since the light is refracted in the direction of an appropriate viewing angle, the contrast can be made almost uniform over the entire surface of the image on the screen. In addition, 19 more optical path refracting means are provided on the output side of the liquid crystal display element to compensate for changes in the optical path caused by the above-mentioned input side optical path refracting means, making it easy to design the optical system. This prevents adverse effects caused by changes in the optical path due to

[Brief explanation of drawings]

FIG. 1 is a simplified cross-sectional view of an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the overall configuration of a projection type liquid crystal display device according to an embodiment of the present invention, and FIG. 3 is a liquid crystal display element 7. An exploded perspective view of
4 is a front view of the virtual plane 20 seen from the arrow 21 in FIG. 3, FIG. 5 is a diagram showing the relationship between the angle of incidence on the liquid crystal display element 7 and the contrast, and FIG. 6 is a simplified version of the prior art. FIG. 7 is a diagram showing the pretilt angle δ of the liquid crystal molecules 60 in the orientation wA59 of the liquid crystal display element, and FIG. 8 is a diagram showing the relationship between the incident angle and the contrast to the liquid crystal display element in the prior art. be.

Claims (1)

[Scope of Claims] In a projection type liquid crystal display device that projects light from a light source through a liquid crystal display element, an optical path refracting means is provided on the incident side of the liquid crystal display element, and this optical path refracting means on the incident side is configured to display a liquid crystal display. A plane 20 that includes a normal 21 perpendicular to the liquid crystal layer of the device and an optimum viewing angle direction 19 where the contrast is maximum.
(a) A ray of light incident at an incident angle θ with respect to the normal 21 is directed toward the maximum viewing angle direction 19 and at an angle (
(b) the normal line 2
A ray incident at an angle of incidence -θ with respect to 1 is expressed as its normal 21
On the side opposite to the maximum viewing angle direction 19, the light is refracted so as to exit at an angle (-θ+α) toward the normal 21, and another optical path refracting means is provided on the exit side of the liquid crystal display element, and this exit The side optical path refracting means converts the light from the liquid crystal display element into
A projection type liquid crystal display device characterized in that the emitted light is refracted in a direction substantially parallel to the incident light.