JP6200798B2 - Liquid crystal display device and head-up display device - Google Patents

Description

  The present invention relates to a head-up display device and a liquid crystal display device used therein.

  2. Description of the Related Art A head-up display (HUD) device that displays a virtual image (display image) by projecting display light from a liquid crystal display device onto a windshield of a vehicle or the like is known. In this head-up display device, for example, display light transmitted through a liquid crystal display device by illumination light from a backlight is reflected by a reflecting mirror (or concave mirror), and the reflected light is projected onto a display member such as a windshield or a combiner. Thus, the driver visually recognizes the virtual image displayed on the display member. Thereby, the driver can read information without moving the visual field from the driving state.

  In the head-up display device, due to its structure, a part of the external light (external light) such as sunlight (particularly the light component parallel to the light path of the backlight and opposite) is used in the liquid crystal used in the head-up display device. The display device may be irradiated. In this case, an unnecessary image that should not be displayed is displayed on the windshield by the external light reflected by the display surface of the liquid crystal display device. As a result, the display characteristics of the liquid crystal display device are significantly deteriorated.

JP 2011-247997 A

  The present invention provides a liquid crystal display device and a head-up display device that can suppress display characteristics from being deteriorated due to external light and can suppress a decrease in contrast.

  A liquid crystal display device according to one embodiment of the present invention is a liquid crystal display device in which a normal of a display surface is tilted by a tilt angle with respect to an optical path of external light, and includes a first substrate disposed to face a light source unit, A second substrate disposed opposite to the first substrate, a liquid crystal layer sandwiched between the first and second substrates, a first prism formed on the first substrate and formed of a triangular prism, and the second And a second prism made of a triangular prism. The first prism refracts light from the light source unit so that light transmitted through the liquid crystal layer is substantially perpendicular to the display surface, and the second prism transmits light transmitted through the liquid crystal layer. The light transmitted through the liquid crystal layer is refracted so as to be inclined by the tilt angle with respect to the display surface.

  A liquid crystal display device according to an aspect of the present invention is a liquid crystal display device in which a normal of a display surface is tilted by a tilt angle with respect to an optical path of external light, and a light source unit disposed in parallel with the display surface A first substrate disposed opposite to the light source unit, a second substrate disposed opposite to the first substrate, a liquid crystal layer sandwiched between the first and second substrates, and the second substrate. And a prism made of a triangular prism. The prism refracts light transmitted through the liquid crystal layer so that the light transmitted through the liquid crystal layer is inclined by the tilt angle with respect to the display surface.

  A head-up display device according to an aspect of the present invention includes the liquid crystal display device according to the above aspect and a reflecting mirror that reflects light transmitted through the liquid crystal display device toward a display member. .

  According to the present invention, it is possible to provide a liquid crystal display device and a head-up display device that can suppress display characteristics from being deteriorated due to external light and can suppress a decrease in contrast.

Sectional drawing of the head-up display apparatus which concerns on a comparative example. Sectional drawing of the head-up display apparatus which concerns on another comparative example. Sectional drawing of the liquid crystal display device which concerns on a comparative example. 4A and 4B illustrate contrast of a liquid crystal display device. The graph which shows an example of the relationship between the angle in a liquid crystal, and the contrast of a liquid crystal display device. 1 is a cross-sectional view of a head-up display device according to a first embodiment of the present invention. 1 is a cross-sectional view of a liquid crystal display device according to a first embodiment. Sectional drawing which shows the more specific structural example of a liquid crystal display device. The perspective view of a triangular prism. The figure which shows an example of incident angle (theta) and inclination-angle (alpha) of a prism. Sectional drawing of the liquid crystal display device which concerns on 2nd Embodiment of this invention. The perspective view of a prism sheet. Sectional drawing of the liquid crystal display device which concerns on the modification 1 of 2nd Embodiment. Sectional drawing of the liquid crystal display device which concerns on the modification 2 of 2nd Embodiment. Sectional drawing of the head-up display apparatus which concerns on 3rd Embodiment of this invention. Sectional drawing of the liquid crystal display device which concerns on 3rd Embodiment. Sectional drawing of the liquid crystal display device and light source part which concern on 4th Embodiment of this invention. The top view of a light source part. Sectional drawing of the liquid crystal display device and light source part which concern on the modification of 4th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. However, it should be noted that the drawings are schematic or conceptual, and the dimensions and ratios of the drawings are not necessarily the same as the actual ones. Further, even when the same portion is represented between the drawings, the dimensional relationship and ratio may be represented differently. In particular, the following embodiments exemplify an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention depends on the shape, structure, arrangement, etc. of components. Is not specified. In the following description, elements having the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

[Comparative example]
First, a comparative example will be described. FIG. 1 is a cross-sectional view of a head-up display device 10 according to a comparative example. The head-up display device 10 includes a liquid crystal display device 11, a light source unit 12, and a reflecting mirror 13.

  The illumination light emitted from the light source unit 12 is transmitted through the liquid crystal display device 11 and is optically modulated. The display light transmitted through the liquid crystal display device 11 is reflected by the reflecting mirror 13 and applied to the display member 14. A virtual image (display image) 16 obtained by irradiation of display light on the display member 14 is visually recognized by the driver 15. Accordingly, the driver 15 can observe the virtual image 16 displayed in front of the driver's seat in a superimposed manner with the scenery.

  On the other hand, part of the external light is transmitted through the display member 14, reflected by the reflecting mirror 13, and irradiated on the liquid crystal display device 11. External light refers to various light incident from the outside of the display member 14 (on the side opposite to the side where the liquid crystal display device 11 is disposed), for example, light from the outside such as sunlight. At this time, as shown in the comparative example of FIG. 1, when the display surface of the liquid crystal display device 11 and the emission surface of the light source unit 12 (surface from which illumination light is emitted) are parallel, the light is reflected by the liquid crystal display device 11. The irradiation light follows an optical path opposite to that of outside light and is projected onto the display member 14. For this reason, an unnecessary image that should not be displayed is generated, and the display quality of the display image visually recognized by the driver 15 is deteriorated. The display surface of the liquid crystal display device 11 is a surface on which an image light-modulated by the liquid crystal display device 11 is displayed.

  FIG. 2 is a cross-sectional view of a head-up display device 10 according to another comparative example. The display surface (substrate surface) of the liquid crystal display device 11 is inclined with respect to the emission surface of the light source unit 12 by a predetermined tilt angle θ. In other words, the perpendicular of the display surface of the liquid crystal display device 11 is inclined by a predetermined tilt angle θ with respect to the optical path of the light source unit 12 (or the optical path of external light). Thereby, the reflected light from which the external light is reflected by the liquid crystal display device 11 is not reflected in the same direction as the display light of the liquid crystal display device 11, and the optical path of the light source unit 12 as shown by the broken line in FIG. Is reflected in the direction of angle 2θ. As a result, it is possible to suppress the display characteristics from being deteriorated due to the reflected light of the liquid crystal display device 11.

  FIG. 3 is a cross-sectional view of the liquid crystal display device 11 according to the comparative example. The liquid crystal display device 11 includes a pair of substrates 20 and 21, a liquid crystal layer 22, a sealing material 29 that seals the liquid crystal layer 22, and a pair of polarizing plates 30 and 31.

  The illumination light from the light source unit 12 enters the polarizing plate 30 at an incident angle θ and is refracted at a refraction angle φ. Subsequently, the light transmitted through the liquid crystal layer 22 enters the polarizing plate 31 at an angle φ and is refracted at an angle θ. The refractive index of air is about 1. For example, the refractive indexes of the substrates 20 and 21 made of glass are about 1.5. The refractive indexes of the liquid crystal layer 22, the polarizing plates 30, 31, and the color filter (not shown) are substantially the same as those of the substrates 20, 21, and are about 1.5. Therefore, it is considered that light transmitted between the polarizing plates 30 and 31 hardly refracts, and refraction of light transmitted between the polarizing plates 30 and 31 is not considered.

  Thus, light having an angle φ is incident on the liquid crystal layer 22 with respect to the normal of the surface of the substrate 20 (substrate surface). When the refractive indexes of the substrates 20 and 21, the liquid crystal layer 22, the polarizing plates 30 and 31, and the color filter are all n, the angle φ is expressed by the following formula according to Snell's law.

φ = sin ⁻¹ (sin θ / n) (1)

FIG. 4 is a diagram for explaining the contrast (contrast ratio) of the liquid crystal display device 11. In FIG. 4, the relationship between the incident angle θ of the light incident on the polarizing plate 30, the angle φ with respect to the normal of the substrate surface in the light transmitted through the liquid crystal layer 22 (inside liquid crystal angle φ), and the contrast of the liquid crystal display device 11 An example is shown. FIG. 5 is a graph showing an example of the relationship between the in-liquid crystal angle φ and the contrast of the liquid crystal display device 11.

  As shown in FIGS. 4 and 5, in the case of normal incidence (θ = 0), that is, when light perpendicular to the substrate surface is transmitted through the liquid crystal layer 22, the contrast is about 1325. As the incident angle θ increases, the contrast decreases. For example, when the incident angle θ = 22.0 °, the contrast decreases to about 183, and the contrast decreases by 86% compared to the normal incidence.

  In view of the above consideration, embodiments of the present invention will be described below.

[First Embodiment]
FIG. 6 is a cross-sectional view of the head-up display device 10 according to the first embodiment of the present invention. The head-up display device 10 includes a liquid crystal display device 11, a light source unit 12, and a reflecting mirror 13.

  The light source unit 12 is composed of a light source having a surface shape (surface light source), for example, and supplies illumination light to the liquid crystal display device 11. As the light emitting element included in the light source unit 12, for example, a white light emitting diode (LED) is used. The liquid crystal display device 11 transmits illumination light from the light source unit 12 and performs light modulation. Then, the liquid crystal display device 11 displays an image indicating driving information such as vehicle speed.

  The reflecting mirror 13 is composed of a plane mirror or a concave mirror. The reflecting mirror 13 reflects the display light from the liquid crystal display device 11 toward the display member 14. When a concave mirror is used as the reflecting mirror 13, the concave mirror expands display light from the liquid crystal display device 11 at a predetermined magnification.

  If the inclination of the display member 14 with respect to the vertical line (gravity direction) is β, the reflection angle at the reflecting mirror (for example, a plane mirror) 13 is (90 ° −2θ), that is, the angle between the incident light and the reflected light at the plane mirror 13 is ( 180 ° −4θ). Further, the reflection angle at the display member 14 is β, that is, the angle formed between the incident light and the reflected light at the display member 14 is 2β.

  The display member 14 is used for projecting display light emitted from the liquid crystal display device 11, and displays the display light as a virtual image 16 by reflecting the display light to the driver. The display member 14 is, for example, a vehicle windshield. The display member 14 may be a translucent screen (combiner) provided exclusively for the head-up display device 10. For example, the combiner is used on a dashboard of a vehicle, mounted on a rearview mirror disposed in front of the driver 15, or mounted on a sun visor installed on an upper portion of a windshield. The combiner is made of, for example, a plate-shaped synthetic resin base material having a curved surface, and a vapor deposition film made of titanium oxide, silicon oxide or the like is applied to the surface of the base material, and this vapor deposition film provides a semi-transmissive function. Prepare.

  Similar to the comparative example, the display surface (substrate surface) of the liquid crystal display device 11 is inclined by a predetermined tilt angle θ with respect to the emission surface of the light source unit 12 (surface from which illumination light is emitted). In other words, the perpendicular of the substrate surface of the liquid crystal display device 11 is inclined by a predetermined tilt angle θ with respect to the optical path of the light source unit 12 (or the optical path of external light). Thereby, the reflected light from which the external light is reflected by the liquid crystal display device 11 follows the optical path indicated by the broken line in FIG. 6 and is not reflected in the same direction as the display light of the liquid crystal display device 11. As a result, it is possible to reduce the deterioration of display characteristics due to the reflected light of the liquid crystal display device 11. The magnitude of the tilt angle θ is appropriately determined according to the angle β of the display member 14, the distance between the display member 14 and the reflecting mirror 13, the distance between the reflecting mirror 13 and the liquid crystal display device 11, the enlargement ratio of the reflecting mirror 13, and the like. Is set. In the present embodiment, the tilt angle θ is, for example, not less than 10 ° and not more than 30 °.

  FIG. 7 is a cross-sectional view of the liquid crystal display device 11 according to the first embodiment. The liquid crystal display device 11 includes a pair of substrates 20 and 21, a liquid crystal layer 22, a sealing material 29 that seals the liquid crystal layer 22, a pair of polarizing plates 30 and 31, and a pair of triangular prisms 40 and 41. . The configuration and function of the triangular prisms 40 and 41 will be described later.

  FIG. 8 is a cross-sectional view showing a more specific configuration example of the liquid crystal display device 11. FIG. 8 shows details of the liquid crystal display device 11 excluding the members between the polarizing plates 30 and 31, that is, the prisms 40 and 41.

  The liquid crystal display device 11 includes a TFT substrate 20 on which a switching transistor and a pixel electrode are formed, a color filter substrate (CF substrate) 21 on which a color filter and a common electrode are formed and opposed to the TFT substrate 20, and a TFT substrate. 20 and a liquid crystal layer 22 sandwiched between the CF substrate 21. The TFT substrate 20 and the CF substrate 21 are each composed of a transparent substrate (for example, a glass substrate). The CF substrate 21 is disposed so as to face the light source unit 12, and illumination light from the light source unit 12 enters the liquid crystal display device 11 from the CF substrate 21 side. The surface of the TFT substrate 20 opposite to the light source unit 12 is the display surface of the liquid crystal display device 11.

  The liquid crystal layer 22 is composed of a liquid crystal material sealed with a sealing material 29 that bonds between the TFT substrate 20 and the CF substrate 21. In the liquid crystal material, the alignment of the liquid crystal molecules is manipulated according to the electric field applied between the TFT substrate 20 and the CF substrate 21, and the optical characteristics change. For example, a VA (Vertical Alignment) mode is used as the liquid crystal mode, but other liquid crystal modes such as a TN (Twisted Nematic) mode and a homogeneous mode may be used.

  A plurality of switching transistors 23 are provided on the TFT substrate 20 on the liquid crystal layer 22 side. As the switching transistor 23, for example, a thin film transistor (TFT) is used. The switching transistor 23 includes a gate electrode electrically connected to a scanning line (not shown), a gate insulating film provided on the gate electrode, and a semiconductor layer (for example, an amorphous silicon layer) provided on the gate insulating film. And a source electrode and a drain electrode provided on the semiconductor layer so as to be separated from each other. The source electrode is electrically connected to a signal line (not shown).

  An insulating layer 24 is provided on the switching transistor 23. A plurality of pixel electrodes 25 are provided on the insulating layer 24. A contact plug 26 electrically connected to the pixel electrode 25 is provided in the insulating layer 24 and on the drain electrode of the switching transistor 23.

  A color filter 27 is provided on the CF substrate 21 on the liquid crystal layer 22 side. The color filter 27 includes a plurality of coloring filters (coloring members), and specifically includes a plurality of red filters 27-R, a plurality of green filters 27-G, and a plurality of blue filters 27-B. A general color filter is composed of three primary colors of light, red (R), green (G), and blue (B). A set of three colors R, G, and B adjacent to each other is a display unit (referred to as a pixel or a pixel), and any single color portion of R, G, or B in one pixel is a subpixel (subpixel). This is a minimum drive unit called a pixel. The switching transistor 23 and the pixel electrode 25 are provided for each subpixel.

  A black matrix (light shielding film) BM for light shielding is provided at the boundary part of the red filter 27-R, the green filter 27-G, and the blue filter 27-B and the boundary part of the pixel (subpixel). That is, the black matrix BM is formed in a mesh shape. The black matrix BM is provided, for example, to shield unnecessary light between the coloring members and improve contrast.

  A common electrode 28 is provided on the color filter 27 and the black matrix BM. The common electrode 28 is formed in a planar shape over the entire display area of the liquid crystal display device 11.

  The polarizing plates 30 and 31 are provided so as to sandwich the TFT substrate 20 and the CF substrate 21. The polarizing plates 30 and 31 have a transmission axis and an absorption axis orthogonal to each other in a plane orthogonal to the light traveling direction. The polarizing plates 30 and 31 transmit linearly polarized light having a vibration surface parallel to the transmission axis and absorbing linearly polarized light having a vibration surface parallel to the absorption axis among light having vibration surfaces in random directions. The polarizing plates 30 and 31 are arranged so that their transmission axes are orthogonal to each other, that is, in an orthogonal Nicol state.

  The pixel electrode 25, the contact plug 26, and the common electrode 28 are made of transparent electrodes, and for example, ITO (indium tin oxide) is used. As the insulating layer 24, a transparent insulating material is used, for example, silicon nitride (SiN).

  Here, in this embodiment, as shown in FIG. 7, the liquid crystal display device 11 includes triangular prisms 40 and 41. The triangular prism 40 is provided on the surface of the polarizing plate 30 opposite to the TFT substrate 20, and the triangular prism 41 is provided on the surface of the polarizing plate 31 opposite to the CF substrate 21. The triangular prisms 40 and 41 are triangular prisms. FIG. 9 is a perspective view of the triangular prism 40. The triangular prism 41 has the same shape as the triangular prism 40. The triangular prisms 40 and 41 are made of polycarbonate, acrylic resin, glass, or the like.

  The triangular prism 40 has an inclination angle α, and the inclination angle α of the triangular prism 40 is an angle formed between the surface in contact with the polarizing plate 30 and the inclined surface 40a. Similarly, the inclination angle α of the triangular prism 41 is an angle formed between the surface in contact with the polarizing plate 31 and the inclined surface 41a. The triangular prisms 40 and 41 are arranged point-symmetrically (180 ° rotationally symmetric) so that the inclined surfaces 40a and 41a are parallel to each other. In FIG. 7, the triangular prisms 40 and 41 do not necessarily have a right-angle triangle in cross-sectional shape, and a right-angle triangle as long as the angle formed between the surface in contact with the polarizing plate and the inclined surface satisfies α. Not necessarily.

  Further, the size of the triangular prism 40 is set so that the area where the inclined surface 40 a is projected onto the polarizing plate 30 is equal to or larger than the effective display area of the liquid crystal display device 11. Similarly, the size of the triangular prism 41 is set so that the area where the inclined surface 41 a is projected onto the polarizing plate 31 is equal to or larger than the effective display area of the liquid crystal display device 11.

The inclination angle α of the triangular prisms 40 and 41 is set so that light incident on the liquid crystal display device 11 from the light source unit 12 is substantially perpendicular to the substrate surface in the liquid crystal layer 22. When the refractive index of the triangular prisms 40 and 41 is n _p , the inclination angle α of the triangular prisms 40 and 41 is expressed by the following equation.

sin (θ + α) = n _p · sin α
From the above formula,
α = tan ⁻¹ {sin θ / (n _p −cos θ)} (2)

Since the liquid crystal display device 11 includes the triangular prisms 40 and 41, the light emitted from the light source unit 12 and incident on the liquid crystal display device 11 at an angle θ with respect to the normal to the substrate surface follows the following optical path. That is, the light from the light source unit 12 enters the inclined surface 40a of the triangular prism 40 at an incident angle (θ + α) and is refracted at a refraction angle α. For this reason, the light transmitted through the liquid crystal layer 22 is substantially perpendicular to the substrate surface. Subsequently, the light transmitted through the liquid crystal layer 22 is refracted at the refraction angle (θ + α) on the inclined surface a of the triangular prism 41 and is emitted from the triangular prism 41. Therefore, the light emitted from the liquid crystal display device 11 is emitted at an angle θ with respect to the normal to the substrate surface.

  In addition, external light having the same direction as the light emitted from the liquid crystal display device 11 and opposite in direction is reflected on the inclined surface 41a of the triangular prism 41 in the direction of angle 2 (θ + α) with respect to the incident direction. For this reason, external light does not reach the driver 15.

  In the above description, the light transmitted through the liquid crystal layer 22 is made substantially perpendicular to the substrate surface. As shown in FIG. 5, when the light transmitted through the liquid crystal layer 22 is perpendicular to the substrate surface, the contrast of the liquid crystal display device 11 is maximized. However, if the contrast is 800 or more, a sufficiently high-definition or high-quality display is possible for the user viewing the liquid crystal display device 11. That is, the contrast, which is the visibility tolerance, is 800 or more when the liquid crystal internal angle φ is within the range of ± 5 ° (including both). Although FIG. 5 shows the positive-side liquid crystal angle φ, a graph symmetrical to that of FIG. 5 is obtained for the negative-side liquid crystal angle φ. Considering the visibility tolerance, the inclination angle α of the triangular prisms 40 and 41 is set to a range represented by the following expression.

n _p · sin (α−5 °) ≦ sin (θ + α) ≦ n _p · sin (α + 5 °)
From the above formula,
tan ⁻¹ {(sin θ−n _p · sin 5 °) / (n _p · cos 5 ° −cos θ)} ≦ α ≦
tan ⁻¹ {(sin θ + n _p · sin 5 °) / (n _p · cos 5 ° −cos θ)}
... Formula (3)

FIG. 10 is a diagram illustrating an example of the incident angle θ and the inclination angle α of the prism. Refractive index n _p = 1.5. Further, the minimum value and the maximum value of the inclination angle α shown in FIG. 10 are values of the inclination angle α in consideration of the visibility tolerance.

(effect)
As described above in detail, in the first embodiment, the perpendicular of the display surface (substrate surface) of the liquid crystal display device 11 is inclined by a predetermined tilt angle θ with respect to the optical path of the light source unit 12 (or the optical path of external light). Is set as follows. In addition, the liquid crystal display device 11 includes triangular prisms 40 and 41 on the incident side and the emission side, respectively, and the triangular prism 40 is configured so that the light transmitted through the liquid crystal layer 22 is substantially perpendicular to the display surface. The triangular prism 41 refracts the light transmitted through the liquid crystal layer 22 so that the light transmitted through the liquid crystal layer 22 is inclined by a tilt angle θ with respect to the display surface.

  Therefore, according to the first embodiment, it is possible to prevent the external light reflected by the liquid crystal display device 11 from being viewed by the driver 15 along the optical path in the opposite direction. Thereby, it can suppress that the display characteristic of the liquid crystal display device 11 deteriorates resulting from external light.

  Further, the light transmitted through the liquid crystal layer 22 travels in a direction substantially perpendicular to the substrate surface. Thereby, it can suppress that the contrast of the liquid crystal display device 11 falls.

[Second Embodiment]
When the triangular prism shown in FIG. 7 of the first embodiment is used, the thickness of the liquid crystal display device including the triangular prism becomes very large. When the thickness of the liquid crystal display device (vertical length in FIG. 7) is 2 cm and the inclination angle of the triangular prism is 29 °, the thickness increases by 2.2 cm (= 2 × 2 × tan 29 °). End up. Therefore, in the second embodiment, the thickness of the liquid crystal display device is reduced by arranging a plurality of triangular prisms having a thickness smaller than that of the triangular prism of the first embodiment.

  FIG. 11 is a cross-sectional view of the liquid crystal display device 11 according to the second embodiment of the present invention. The liquid crystal display device 11 includes prism sheets 40 and 41. FIG. 12 is a perspective view of the prism sheet 40. The prism sheet 41 also has the same shape as the prism sheet 40. The configuration other than the prism sheets 40 and 41 is the same as that of the first embodiment.

  The prism sheet 40 includes a base portion 40b and a plurality of triangular prism portions 40c. Each of the plurality of triangular prism portions 40c is formed of a triangular prism having a smaller size (thickness) than the triangular prism of the first embodiment, and is similar to the triangular prism of the first embodiment. The triangular prism portion 40c has an inclination angle α, and the inclination angle α of the triangular prism portion 40c is an angle formed between the surface in contact with the base portion 40b and the inclined surface 40a. The plurality of triangular prism portions 40c are arranged side by side in the same direction, that is, the inclined surfaces 40a are parallel to each other. Similar to the prism sheet 40, the prism sheet 41 includes a base portion 41b and a plurality of triangular prism portions 41c. The prism sheets 40 and 41 are arranged in point symmetry (180 ° rotational symmetry) so that the inclined surfaces 40a and 41a are parallel to each other.

  Even when the prism sheets 40 and 41 configured as described above are used, the same effect as the first embodiment can be obtained. If the number of triangular prism portions 40c is n, the thickness of the prism sheet 40 can be reduced to 1 / n (however, the base portion 40b is not considered) as compared with the triangular prism of the first embodiment. For example, if n = 100, the thickness of the liquid crystal display device (length in the vertical direction in FIG. 11) is 2 cm, and the inclination angle of the triangular prism portion is 29 °, the increase in thickness can be suppressed to 0.22 mm. it can.

(Modification 1)
FIG. 13 is a cross-sectional view of the liquid crystal display device 11 according to Modification 1 of the second embodiment. An absorption layer 42 is provided on a surface of the triangular prism portion 40c that is substantially perpendicular to the substrate surface (referred to as a vertical surface). The absorption layer 42 has a function of absorbing light incident on itself. Similarly, an absorption layer 42 is provided on the vertical surface of the triangular prism portion 41c.

  Effective light (light used for display) incident on the inclined surface 40a of the triangular prism portion 40c is refracted by the triangular prism portion 40c and travels substantially vertically through the liquid crystal layer 22. On the other hand, unnecessary light incident on the vertical surface of the triangular prism portion 40 c is hardly used for the display of the liquid crystal display device 11. The absorption layer 42 absorbs this unnecessary light. Thereby, it can suppress that the image quality of the liquid crystal display device 11 deteriorates. The absorbing layer 42 may be provided only on the prism sheet 40 to which the illumination light from the light source unit 12 is incident, and the absorbing layer 42 may not be provided on the prism sheet 41.

(Modification 2)
FIG. 14 is a cross-sectional view of a liquid crystal display device 11 according to Modification 2 of the second embodiment. A reflective layer 43 is provided between the vertical surface of the triangular prism portion 40 c and the absorption layer 42. Similarly, a reflective layer 43 is provided between the vertical surface of the triangular prism portion 41 c and the absorption layer 42. The reflective layer 43 has a function of reflecting light incident on itself.

  Of the light incident on the triangular prism portion 40 c, the light traveling toward the reflective layer 43 without going toward the liquid crystal layer 22 is reflected by the reflective layer 43 and passes through the liquid crystal layer 22 as indicated by the broken line in FIG. 14. That is, of the light incident on the triangular prism portion 40 c, the light traveling toward the reflective layer 43 is reused for display on the liquid crystal display device 11. As a result, a brighter display of the liquid crystal display device 11 becomes possible. The absorbing layer 42 and the reflecting layer 43 may be provided only on the prism sheet 40 to which the illumination light from the light source unit 12 is incident, and the absorbing layer 42 and the reflecting layer 43 may not be provided on the prism sheet 41.

[Third Embodiment]
FIG. 15 is a cross-sectional view of the head-up display device 10 according to the third embodiment of the present invention. The liquid crystal display device 11 is arranged such that the perpendicular of the display surface (substrate surface) of the liquid crystal display device 11 is inclined by a predetermined tilt angle θ with respect to the optical path of external light reflected by the reflecting mirror 13. Similarly, the light source unit 12 is arranged so that the perpendicular of the exit surface of the light source unit 12 is inclined by a predetermined tilt angle θ with respect to the optical path of the external light reflected by the reflecting mirror 13. That is, the substrate surface of the liquid crystal display device 11 and the emission surface of the light source unit 12 are arranged in parallel.

  FIG. 16 is a cross-sectional view of the liquid crystal display device 11 according to the third embodiment. The configuration of the liquid crystal display device 11 of the third embodiment is the same as that of the liquid crystal display device of the second embodiment except that the prism sheet 40 is omitted.

  Illumination light from the light source unit 12 enters the substrate surface of the liquid crystal display device 11 substantially perpendicularly. For this reason, the light transmitted through the liquid crystal layer 22 is substantially perpendicular to the substrate surface. Thereby, it can prevent that the contrast of the liquid crystal display device 11 falls.

  The prism sheet 41 refracts the light transmitted through the liquid crystal layer 22 by the refraction angle α on the inclined surface 41a of the triangular prism portion 41c. That is, the optical path of the light emitted from the liquid crystal display device 11 is the same as that in the first embodiment.

  In addition, external light having the same direction as the light emitted from the liquid crystal display device 11 and opposite in direction is reflected on the inclined surface 41a of the triangular prism portion 41c in the direction of the incident direction and the angle 2 (θ + α). For this reason, external light does not reach the driver 15 along the same optical path as the light emitted from the liquid crystal display device 11.

  As described above in detail, in the third embodiment, the prism sheet on the incident side of the liquid crystal display device 11 is eliminated, and the light source unit 12 is arranged in parallel with the liquid crystal display device 11. Thereby, since the number of prism sheets can be reduced to one, the liquid crystal display device 11 can be thinned, and the cost of the head-up display device 10 can be reduced. Other effects are the same as those of the first embodiment.

  The prism sheet 41 may be changed to the triangular prism 41 of the first embodiment. Further, the absorbing layer 42 and the reflecting layer 43 described in the second embodiment can be applied to the prism sheet 41 of the third embodiment.

[Fourth Embodiment]
FIG. 17 is a cross-sectional view of the liquid crystal display device 11 and the light source unit 12 according to the fourth embodiment of the present invention. The configuration other than the liquid crystal display device 11 and the light source unit 12 is the same as that of the third embodiment.

  In the liquid crystal display device 11, a reflective polarizing plate 50 is provided on the surface of the polarizing plate 30 opposite to the TFT substrate 20. A retardation plate (λ / 4 plate) 51 is provided on the surface of the reflective polarizing plate 50 opposite to the polarizing plate 30. Note that the plan view of the polarizing plate, the reflective polarizing plate, and the retardation plate in FIG. 17 shows the plane viewed from the light source unit 12 side. Further, in the plan view of FIG. 17, the angle of the transmission axis of the polarizing plate 30 with respect to the horizontal direction is expressed as γ. The angle γ can be arbitrarily set.

  The reflective polarizing plate 50 has a transmission axis and a reflection axis that are orthogonal to each other in a plane orthogonal to the traveling direction of light. The reflective polarizing plate 50 transmits linearly polarized light having a vibration surface parallel to the transmission axis, and reflects linearly polarized light having a vibration surface parallel to the reflection axis, among light having a vibration surface in a random direction. The transmission axis of the reflective polarizing plate 50 is set parallel to the transmission axis of the polarizing plate 30. Examples of the reflective polarizing plate 50 include DBEF (Dual Brightness Enhancement Film) manufactured by 3M Company, Asahi Kasei Wire Grid Polarizing Plate, and the like.

  The phase difference plate 51 has refractive index anisotropy, and has a slow axis and a fast axis that are orthogonal to each other in a plane that is orthogonal to the traveling direction of light. The phase difference plate 51 has a function of giving a predetermined retardation (a phase difference of λ / 4 when λ is a wavelength of light transmitted) between light of a predetermined wavelength that transmits the slow axis and the fast axis. have. That is, the phase difference plate 51 is composed of a λ / 4 plate. The slow axis of the phase difference plate 51 is set to make an angle of 45 ° with respect to the transmission axis of the reflective polarizing plate 50.

  FIG. 18 is a plan view of the light source unit 12 as viewed from the liquid crystal display device 11 side. The light source unit 12 includes a substrate 12A, a plurality of light emitting elements 12B, a reflective layer 12C, and a case 12D. A plurality of light emitting elements 12B are provided on the substrate 12A. Each light emitting element 12B is composed of, for example, a white LED. In FIG. 18, four light emitting elements 12B are shown as an example. However, the number of light emitting elements 12B can be arbitrarily designed, and the number of light emitting elements 12B may be one, or a plurality other than four. It may be. The substrate 12A is composed of a circuit board provided with wiring for supplying power to the light emitting element 12B. The surface of the substrate 12A is disposed in parallel with the surface of the TFT substrate 20 or the CF substrate 21 of the liquid crystal display device 11.

  A reflective layer 12C is provided in a region where the light emitting element 12B is not provided on the substrate 12A. That is, the reflective layer 12C has a plurality of openings each having substantially the same planar shape as the plurality of light emitting elements 12B. The reflection layer 12C reflects light incident from the liquid crystal display device 11 side again to the liquid crystal display device 11 side. On the substrate 12A, a case 12D surrounding the light emitting elements 12B and the reflective layer 12C is provided. The external shapes of the substrate 12A and the case 12D are, for example, rectangular.

  In the head-up display device 10 configured as described above, first, the illumination light emitted from the light source unit 12 passes through the phase difference plate 51 and reaches the reflective polarizing plate 50. The reflective polarizing plate 50 transmits light parallel to the transmission axis and reflects light parallel to the reflection axis. The light that has passed through the reflective polarizing plate 50 passes through the polarizing plate 30.

  On the other hand, the linearly polarized light reflected by the reflective polarizing plate 50 passes through the phase difference plate 51, is reflected by the reflection layer 12 </ b> C of the light source unit 12, and passes through the phase difference plate 51 again. That is, the linearly polarized light reflected by the reflective polarizing plate 50 passes through the phase difference plate 51 twice, and thus rotates 90 °. As a result, the linearly polarized light that has been transmitted through the retardation plate 51 twice is parallel to the transmission axis of the reflective polarizing plate 50, and therefore can be transmitted through the reflective polarizing plate 50 and the polarizing plate 30. Thereby, the light originally absorbed by the polarizing plate 30 can be reused as a display.

(Modification)
Next, a modification of the fourth embodiment will be described. FIG. 19 is a cross-sectional view of the liquid crystal display device 11 and the light source unit 12 according to a modification of the fourth embodiment. A diffusing member 52 is provided between the polarizing plate 30 and the reflective polarizing plate 50.

  The diffusing member 52 has a function of making the transmitted light uniform by diffusing (scattering) the transmitted light in a random direction. The diffusion member 52 is composed of a diffusion adhesive material, a diffusion film, a diffusion plate, or the like. When a diffusion adhesive material is used as the diffusion member 52, the diffusion adhesive material has a function of attaching the polarizing plate 30 and the reflective polarizing plate 50 in addition to the function of diffusing incident light.

  The diffusion member 52 has a function of making transmitted light and reflected light uniform by diffusing (scattering) light isotropically. By using the diffusing member 52, it becomes possible to reuse light further.

(effect)
As described above in detail, in the fourth embodiment, the light parallel to the absorption axis of the polarizing plate 30 is reflected to the light source unit 12 side by the reflective polarizing plate 50 before entering the polarizing plate 30. Furthermore, the reflection layer 12C is arranged so that the reflected light passes through the retardation plate 51 twice, so that the reflected light from the reflective polarizing plate 50 is parallel to the transmission axis of the polarizing plate 30.

  Therefore, according to the fourth embodiment, the light originally absorbed by the polarizing plate 30 can be reused as a display. Thereby, a brighter display of the liquid crystal display device 11 can be realized. Other effects are the same as those of the third embodiment.

  The present invention is not limited to the above embodiment, and can be embodied by modifying the constituent elements without departing from the scope of the invention. Further, the above embodiments include inventions at various stages, and are obtained by appropriately combining a plurality of constituent elements disclosed in one embodiment or by appropriately combining constituent elements disclosed in different embodiments. Various inventions can be configured. For example, even if some constituent elements are deleted from all the constituent elements disclosed in the embodiments, the problems to be solved by the invention can be solved and the effects of the invention can be obtained. Embodiments made can be extracted as inventions.

DESCRIPTION OF SYMBOLS 10 ... Head-up display apparatus, 11 ... Liquid crystal display device, 12 ... Light source part, 12A ... Board | substrate, 12B ... Light emitting element, 12C ... Reflective layer, 12D ... Case, 13 ... Reflector, 14 ... Display member, 15 ... Driver 16 ... Virtual image, 20 ... TFT substrate, 21 ... CF substrate, 22 ... Liquid crystal layer, 23 ... Switching transistor, 24 ... Insulating layer, 25 ... Pixel electrode, 26 ... Contact plug, 27 ... Color filter, 28 ... Common electrode, DESCRIPTION OF SYMBOLS 29 ... Sealing material, 30, 31 ... Polarizing plate, 40, 41 ... Prism sheet, 42 ... Absorbing layer, 43 ... Reflecting layer, 50 ... Reflective polarizing plate, 51 ... Retardation plate, 52 ... Diffusing member.

Claims (9)

A liquid crystal display device in which a normal of a display surface is inclined by a tilt angle with respect to an optical path of outside light,
A light source unit arranged in parallel with the display surface;
A first substrate disposed opposite to the light source unit;
A second substrate disposed opposite the first substrate;
A liquid crystal layer sandwiched between the first and second substrates;
A prism formed on the second substrate and made of a triangular prism;
Comprising
The liquid crystal display device, wherein the prism refracts light transmitted through the liquid crystal layer so that the light transmitted through the liquid crystal layer is inclined by the tilt angle with respect to the display surface. A first polarizing plate provided on the light source side of the first substrate;
A reflective polarizing plate that is provided on the light source unit side of the first polarizing plate and reflects a component parallel to the reflection axis of the light from the light source unit;
A retardation plate that is provided on the light source part side of the reflective polarizing plate and gives a phase difference of λ / 4 to light;
A second polarizing plate provided between the second substrate and the prism;
Further comprising
The liquid crystal display device according to claim 1, wherein a transmission axis of the reflective polarizing plate is parallel to a transmission axis of the first polarizing plate. The liquid crystal display device according to claim 2 , further comprising a diffusion member provided between the first polarizing plate and the reflective polarizing plate. The liquid crystal display device according to claim 2 , wherein the light source unit includes a first reflective layer that reflects light in a direction of the retardation plate. When the tilt angle is θ and the refractive index of the prism is n _p , the tilt angle α of the prism is
α = tan ⁻¹ {sin θ / (n _p −cos θ)}
The liquid crystal display device according to claim 1, wherein: 6. The liquid crystal display device according to claim 1 , wherein the prism includes a plurality of triangular prism portions each having an inclined surface arranged in parallel. The liquid crystal display device according to claim 6 , further comprising an absorption layer that is provided on one surface of each of the plurality of triangular prism portions and absorbs light. The liquid crystal display device according to claim 7 , further comprising a second reflective layer provided between the triangular prism portion and the absorbing layer and configured to reflect light. A liquid crystal display device according to any one of claims 1 to 8 ,
A reflecting mirror that reflects light transmitted through the liquid crystal display device toward a display member;
A head-up display device comprising:

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