JP5070891B2 - Optical sheet and backlight unit and display using the same - Google Patents

Description

  The present invention relates to an improvement of an optical sheet used for illumination light path control in a display backlight unit mainly using a liquid crystal display element, and a backlight unit and a display (display device) on which the sheet is mounted. About.

A display typified by a liquid crystal display device (LCD) is remarkably widespread in a type including a light source necessary for recognizing provided information. In a battery-powered device such as a laptop computer, the power consumed by the light source occupies a substantial portion of the power consumed by the entire battery-powered device.
Thus, reducing the total power required to provide a given brightness increases battery life, which is particularly desirable for battery powered devices.

  A brightness enhancement film (BEF) which is a registered trademark of 3M Corporation of the United States is widely used as an optical sheet for solving this problem.

BEF is a film in which unit prisms 72 having a triangular cross section are periodically arranged in one direction on a member 70 as shown in FIG.
The prism 72 has a size (pitch) larger than the wavelength of light.
BEF collects light from “off-axis” and redirects this light “on-axis” or “recycle” towards the viewer. To do.

  When using the display (when observing), the BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally the normal direction (direction F shown in FIG. 1) side with respect to the display screen.

  When the repetitive array structure of the prisms 72 is arranged in only one direction, only the direction change or recycling in the parallel direction is possible, and in order to control the luminance of the display light in the horizontal and vertical directions, the prism groups are arranged in parallel. Two sheets are stacked and combined so that the directions are substantially orthogonal to each other.

The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption.
As patent documents disclosing that a brightness control member having a repetitive array structure of prisms 72 typified by BEF is adopted for a display, many are known as exemplified in Patent Documents 1 to 3. ing.

In the optical sheet using the BEF as a brightness control member as described above, the light P from the light source 20 is finally emitted at a controlled angle φ by the refraction action x as shown in FIG. Thus, it is possible to control to increase the intensity of light in the visual direction F of the viewer.
However, at the same time, the light component due to the reflection / refraction action y is unnecessarily emitted in the lateral direction without proceeding in the visual direction F of the viewer.

Therefore, the light intensity distribution emitted from the optical sheet using the BEF as shown in FIGS. 1 and 2 corresponds to the visual direction F of the viewer, that is, the visual direction F as shown by the curve B indicated by the dotted line in FIG. Although the light intensity at the angle of 0 ° (corresponding to the on-axis direction) is the highest, as shown as a small light intensity peak around ± 90 ° shown on the horizontal axis in the figure, the light emitted from the horizontal direction is also wasted There is a problem that it increases.
A curve B in FIG. 3 is a light intensity distribution in the case of only one prism sheet, and a curve indicated by “vertical distribution” in the drawing corresponds to a direction in which the prisms 72 are arranged in parallel, and is indicated by “horizontal distribution”. The curved line corresponds to the longitudinal direction of the prism 72.
In general, a usage form in which two prism sheets are used in combination so that the directions in which the prisms 72 are arranged in parallel is substantially orthogonal.
A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution having no light intensity peak around ± 90 ° is more desirable.
In addition, if only the on-axis brightness is excessively increased, the width of the peaks in the graph (especially in the vertical distribution curve) becomes extremely narrow and the viewing area is extremely limited. Therefore, it is necessary to newly use a light diffusing film which is a separate member from the prism sheet, which is accompanied by an increase in the number of members.

  In order to overcome such drawbacks, there is a backlight unit 40 using an optical film 38 having a repetitive array structure of unit lenses instead of a prism as shown in FIGS. 4 and 5 (Patent Document 4). .

A lens 44 for guiding the light traveling in the optical film 38 to the liquid crystal panel 42 is provided on the surface of the transparent base 39 of the optical film 38 on the liquid crystal panel side. As shown in the perspective view of FIG. 4, the lens 44 has a plurality of unit lenses repeatedly forming an array structure.
Further, on the other surface, a reflector 48 having a stripe pattern having an opening 46 in the vicinity of the focal plane of the lens 44 is provided.

The reflecting material 48 is obtained by mixing a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive with a predetermined pattern (when the unit lens is a semi-cylindrical convex cylindrical lens group, each unit lens Is formed in a stripe shape having an opening corresponding to 1: 1).
In FIG. 5, reference numeral 21 denotes a lamp house, reference numeral 23 denotes a cold cathode tube, and reference numeral 27 denotes a reflector.

A curve A shown in FIG. 3 is an explanatory diagram showing an optical path control characteristic of the backlight when the optical sheet of FIGS. 4 and 5 is applied to the backlight unit.
Of the light emitted from the diffusion film 32, only the light that has passed through the opening 46 enters the lens 44 and is emitted after being condensed in a certain direction by the lens 44.
Then, the light enters the polarizing plate 49 and only light having a predetermined polarization component is guided to the liquid crystal panel 42.

  On the other hand, the light that could not pass through the opening 46 is reflected by the reflecting material 48, returned to the diffusion plate 26 side, and guided to the reflecting plate 27. Then, the light is incident on the diffusion plate 26 again by being reflected by the reflection plate 27 and is diffused again on the diffusion plate 26. As shown in FIG. 5, the light is squeezed into a predetermined angle φ and emitted by the lens 44.

In the backlight unit 40 using such an optical film 38, the size and the position of the opening 46 of the optical film 38 are adjusted to increase the light use efficiency, and the light is emitted from the lens 44 in the front direction S. Can be controlled to increase the proportion of light emitted.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A

  In a display having a large screen such as a monitor for a liquid crystal TV or a personal computer instead of a display having a relatively small screen such as a mobile phone or a mobile terminal, in order to make the luminance distribution in the screen uniform. It is preferable to adopt a direct backlight unit in which a light source is housed in a lamp house behind the screen, rather than a backlight unit using an edge light to a light guide plate.

As shown in FIG. 6, the backlight unit in the liquid crystal display device is in the form of a laminated structure of each element, and a diffusion film or DBEF80 / prism sheet or optical film 81 / diffusion film 82 / diffusion plate 83 is used as a light source. It is arranged on 84 lamp houses 85 accommodated. These laminated structures are designed so that uneven light from a light source is first converted into diffused light with a strong diffusion function, and then a desired luminance distribution is obtained with an optical element.
Hereinafter, the light control functions such as the diffusion film or DBEF 80, the prism sheet or optical film 81, and the diffusion film 82 are collectively referred to as an optical member.

  Among optical members, prisms and lenses having a high light collecting function use the refraction function of unit prisms and unit lenses, and have an effect of increasing on-axis luminance by reducing off-axis luminance. These optical members are usually mass-produced using molds designed and produced in a shape that exhibits desired optical characteristics. Therefore, when a plurality of optical characteristics are required, a plurality of molds must be prepared, which takes time and cost. However, the customer's demand for optical properties is different, and a plurality of molds must be prepared because of slight differences.

  In order to solve the above problem, the present invention includes a second optical element that increases the off-axis brightness of the optical sheet and does not impair the image on the display, and is adjusted by adjusting the second optical element. An object is to produce optical sheets having different optical characteristics from a single mold.

A first surface that has one surface in the thickness direction and the other surface; the light incident from the one surface on the other surface is controlled in at least one of its emission direction, range, color, and luminance distribution; In the optical sheet on which one optical element is formed, the light incident on the first optical element is previously converted into diffused light on the light source side. The diffused light is incident on the first optical element through a different optical path to provide a second optical element that increases off-axis brightness, and the first optical element is changed by changing the area of the second optical element. The distribution of the entire emitted light can be changed without deformation. However, when the off-axis brightness partially increases, it is recognized as unevenness. As a result of trial and error, the present inventor has succeeded in providing an optical sheet that defines the area of the second optical element, is not recognized as unevenness by increasing or decreasing the number, and can change the luminance distribution.
In the present invention, an optical member that controls at least one of the light emission direction, range, color, and luminance distribution is referred to as a first optical element.
In the embodiment described later, the first optical element also has a light collecting function.
Further, off-axis luminance is luminance in a direction that does not coincide with the visual direction of the viewer, and generally refers to luminance other than the normal line direction (F direction shown in FIG. 1) side with respect to the display screen.
That is, the invention described in claim 1 has one surface in the thickness direction and the other surface, and a lens portion or a plurality of prisms each including a convex cylindrical lens group or a hemispherical convex lens group are arranged in parallel on the other surface. In the optical sheet in which the first optical element made of the formed prism sheet is formed , a reflective layer as a second optical element is provided on the one surface, and the reflective layer is the lens section or the prism sheet. A light reflecting portion located in the non-condensing region and a light transmitting portion located in the remaining region, and the light reflecting portion is provided with a number of openings that allow light to pass therethrough. and said that you are.
Further, an invention according to claim 2, wherein the size of the aperture is an optical sheet according to claim 1, characterized in that the maximum diameter less than 3mm.
The invention of claim 3, wherein is an optical sheet of claim 1, wherein a large number of light transmitting particles is provided on the light transmitting portion of the part.
The invention according to claim 4 is the optical sheet according to claim 3 , characterized in that the size of the particles bonded to the one surface is a maximum diameter of 3 mm or less .

The invention of claim 5, wherein comprises a light source, disposed on the light emission side of the light source, for display, characterized in that it comprises at least an optical sheet according to any one of the 請 Motomeko 1-4 It is a backlight unit.
The invention of claim 6 wherein comprises a surface light source composed of a d Jjiraito formula source and the light guide plate, disposed on the light emitting side of the surface light source, an optical sheet according to any one of the 請 Motomeko 1-4 Is a backlight unit for a display.
According to a seventh aspect of the present invention, there is provided an image display element in which a display pattern is defined in accordance with transmission / non-transmission or transparency / scattering state in pixel units, and a rear panel disposed on the image display element. A display device comprising the display backlight unit according to claim 5 .

  According to the present invention, the first optical element that controls at least one of the direction, the range, the color, and the luminance distribution is formed on the opposite surface when the light incident from the substantially flat surface is emitted. In the optical sheet thus formed, it is possible to provide an optical sheet in which the distribution of emitted light is adjusted without changing the shape of the first optical element and without recognizing unevenness.

  Embodiments of the present invention will be described below. There are roughly two methods for carrying out the present invention.

FIG. 7 is a side view showing a prism and a lens sheet used as an optical element.
FIG. 8 is a side view showing a lens sheet with a reflective layer used as an optical element.

That is, the optical sheet 88 according to the embodiment is configured by disposing the first optical element 90 on the light exit surface side on the base sheet 91. As the material of the base material sheet 91, PET (polyethylene terephthalate), acrylic sheet, PC (polycarbonate) sheet or the like well known in the technical field is used. The optical element is made using a thermoplastic or UV curable resin.
That is, in the present embodiment, light is incident on one surface 88A of the optical sheet 88 and light is emitted from the other surface 88B. A first optical element 90 that controls at least one of the emission direction, range, color, and luminance distribution of light incident from the one surface 88A is formed on the other surface 88B.

  Alternatively, there is a method in which the first optical element 90 and the base material 91 are formed at a time by extrusion or injection molding.

  Further, when a lens is used for the first optical element 90, a reflective layer 92 may be provided on the incident surface side as shown in FIG. The presence or absence of the reflective layer 92 is determined depending on which of the necessary light collecting function and cost is taken.

  In the case of providing the reflective layer 92, it is preferable to use a white pigment and a metal vapor deposition layer that have high reflectivity and low light absorption. As the white pigment, titanium dioxide, barium sulfate, and magnesium oxide well known in the art are used, and as the metal deposition layer, silver or the like is used.

  The reflective layer 92 can also be formed by a transfer method using a UV curable adhesive. A UV curable adhesive material is bonded to the surface opposite to the lens in advance, UV is irradiated from the lens side, and then the reflective layer 92 is bonded to the uncured portion. With this method, the lens and the reflective layer 92 can be easily arranged in a 1: 1 correspondence. More specifically, as shown in FIGS. 4, 5, 11, and 12, the light reflecting portion 92 </ b> B (48) located in the non-condensing region of the lens unit and the remaining region (non-condensing of the lens unit). It is possible to easily form the reflective layer 92 including the light transmitting portion 92A (46) located in the region.

  The reflective layer 92 is formed by integrating and molding the first optical element 90, the base material 91, and the lens sheet with irregularities on the other surface by extrusion or injection molding, and then using the irregularities. It is also possible to create the pattern by applying an ink exhibiting light reflectivity in a pattern.

As a first creation method for creating the second optical element, as shown in FIG. 9 and FIG. 10, a resin or glass translucent member (on the other surface 88A) of the substrate 91 in FIG. And particles) 93 are arranged without air gaps. That is, there is a method in which the light source side of the translucent member 93 is arranged on the member 91 disposed on the light source side of the optical sheet 88 without any air gap. The shape of the translucent member 93 may be a fixed shape or an indefinite shape, but the maximum diameter of each contact surface with the base material 91 must be within 3 mm. Examples of the translucent member 93 include a method of attaching translucent particles to the base material 91 and a method of forming the optical element 90 and the base material 91 simultaneously by extrusion or injection molding.
That is, a large number of particles 93 made of a translucent material that emits incident light as diffused light toward the other surface 88B are provided on one surface 88A.
In this case, the second optical element is composed of a large number of translucent members (particles) 93.

  A configuration in which a hard coat layer, a diffusion layer, or a PET, PC, or acrylic sheet on which these layers are formed is disposed on the incident surface 88A of the substrate 91 is also within the scope of the optical sheet of the present invention. In this case, the translucent member 93 must be disposed on these coat layers without air gaps.

As a second production method for producing the second optical element, there is a method of eliminating a part of the reflective layer 92 as shown in FIGS. That is, a method of providing a large number of openings 92C in the light reflecting portion 92B of the reflective layer 92 can be mentioned. At this time, the maximum diameter of the opening 92C must be within 3 mm. As a method of providing the opening 92C, in the case of the transfer method, a pattern that is partially transferred at the time of transfer is previously attached to the base material, and the transfer is performed with particles that inhibit transfer at the time of transfer. Examples thereof include a method in which the adhesion between the foil transfer material and the substrate is partially changed, or conversely, the adhesive force of the UV curable adhesive is partially changed. Alternatively, a method of removing a part of the light reflecting portion 92B after forming the reflective layer 92 can be used.
In FIG. 11, reference numeral 83 denotes a diffusion plate.

In addition, in the case of extrusion or injection molding, a surface treatment that repels only a part of the ink is performed in advance, or an uneven shape that prevents a part of the ink from being applied is formed, or the light reflection is performed after the reflective layer 92 is formed. A method of removing a part of the portion 92B is exemplified.
In this case, the second optical element is composed of a large number of openings 92C.
Furthermore, as a third production method for producing the second optical element, as shown in FIGS. 12A and 12B, a light transmitting portion 92A of the reflective layer 92 is provided with a large number of light transmitting materials such as resin and glass. A method of arranging the member (particle) 93 is also mentioned. The size and shape of the translucent member (particle) 93 are the same as in the first production method. In this case, for example, after the patterned reflective layer 92 is formed, the light transmissive portion 92A is formed. The method of attaching the translucent member (particle | grains) 93 etc. are mentioned. In this case, the refractive index of the translucent member (particle) 93 is preferably close to that of the upper and lower sheets, that is, is preferably close to the refractive indexes of the base material 91 and the diffusion plate 83.
In this case, the second optical element is composed of a large number of translucent members (particles) 93.

When an optical sheet prepared as in the present invention is applied to a liquid crystal display device, a display in which the optical performance can be controlled by subsequent processing even in the same shape of the first optical element and the display screen is not uneven is provided. be able to.
(Example)

  FIG. 13 shows an embodiment of the present invention and its performance.

  As a first optical element, a cylindrical lens was made of UV curable acrylic resin on a PET substrate. Alternatively, prisms were formed on a PET substrate with UV curable acrylic resin.

  A UV curable adhesive was applied to the back surface of the prism sheet, and glass beads or resin beads having a diameter of 5 mm were dispersed as particles 93 made of a translucent material, followed by curing with UV. The maximum diameter of the surface of the contact portion between the beads and the prism sheet was adjusted by the time from spreading to curing, and adjusted to include those adjusted to 3 mm or less and those larger than 3 mm. The application amount was also varied, and the number of beads per area was counted after the sample was prepared.

  The cylindrical lens sheet was formed with a white reflective layer as disclosed in JP-A-2005-37694. When transferring, an organic filler or an inorganic filler was sprayed on the transfer foil to create an opening 92C in the light reflecting portion 92B. By changing the size of the filler, the size of the opening 92C was adjusted to 3 mm or less and the size adjusted to include a size larger than 3 mm. A difference was also applied to the amount of application, and the number of openings 92C per area was counted after the sample was prepared.

  The prepared sheet was integrated with the member on the light source side with an adhesive or an adhesive. As the light source member, the diffusion film 82 or the diffusion plate 83 shown in FIG. 6 was used. When integrated with the diffusion plate 83, the diffusion film 82 is omitted from the configuration of FIG. Commercially available diffusion films 82 and diffusion plates 83 were used.

  The sample prepared as described above was incorporated into a liquid crystal display, and the brightness and image display state were confirmed. The luminance is expressed as a ratio by comparing the state in which the prepared optical sheet is incorporated with the state in which only the optical sheet is removed as a reference. As for the one integrated with the diffusion plate, the configuration in which the optical sheet and the diffusion film 82 are removed is referred to, and the ratio is similarly expressed by the ratio. FIG. 13 shows the determination result. Regardless of the optical sheet, if the size of the second optical element exceeds 3 mm, the image is recognized as luminance unevenness. Those within 3 mm were not recognized as luminance unevenness. Further, when the number of the second optical elements is increased, the half-value angle is widened and the luminance is lowered, and the overall optical characteristics can be adjusted. Moreover, the difference by the kind of used bead was not seen.

  The combination used this time is an example of an optical sheet, and the present invention is not limited to such a configuration.

  As described above, according to the present invention, the emitted light is emitted from the optical sheet so as to partially increase the off-axis luminance, so that the optical shape can be changed without changing the shape of the first optical element. It becomes possible to provide an optical sheet with adjustable characteristics.

Explanatory drawing which shows "BEF" which is an optical sheet which concerns on a prior art. Explanatory drawing which shows the optical path control characteristic of the backlight by BEF. The graph which shows the optical path control characteristic of the backlight by BEF. The perspective view which shows the optical sheet | seat of FIG. Explanatory drawing which shows the optical path control characteristic of the backlight by the optical sheet of FIG. Explanatory drawing which shows an example of a backlight. The side view of an optical sheet. The side view of an optical sheet with a reflection layer. The side view which shows an example of an Example. The side view which shows an example of an Example. (A) is a cross-sectional plan view of the reflective layer, (B) is a BB cross-sectional view of (A). (A), (B) is sectional drawing of a reflection layer, respectively. The figure which shows an Example and a result.

Explanation of symbols

  20 ... Light source, 23 ... Light source, 26 ... Diffusion plate, 27 ... Reflection plate, 38 ... Optical sheet, 40 ... Backlight unit, 42 ... Liquid crystal panel, 44 ... Lens portion, 46 ... Opening portion 48... Reflective material having a striped pattern, 70... Member, 72... Unit prism, 80 .. diffusion film or DBEF, 81 ... prism sheet or optical film, 82. ...... Diffusion plate, 84 .. Light source, 85... Lamp house, 90 .. Optical element, 91 .. Base material, 92 .. Reflection layer, 92 A .. Light transmission part, 92 B .. Light reflection part, 92 C. ... openings, 93 ... particles.

Claims (7)

Having one surface in the thickness direction and the other surface;
In the optical sheet in which the first optical element composed of a prism sheet in which a lens portion composed of a convex cylindrical lens group or a hemispherical convex lens group or a plurality of prisms is formed in parallel is formed on the other surface,
A reflective layer as a second optical element is provided on the one surface;
The reflective layer includes a light reflecting portion located in a non-condensing region of the lens portion or the prism sheet, and a light transmitting portion located in the remaining region,
The light reflecting portion is provided with a large number of openings capable of transmitting light.
An optical sheet characterized by that. The size of the opening, the optical sheet of claim 1, wherein a is less than or equal to the maximum diameter 3 mm. The optical sheet of claim 1, wherein a large number of light transmitting particles is provided on the light transmitting portion of the part. The optical sheet according to claim 3, wherein a size of the particles bonded to the one surface is a maximum diameter of 3 mm or less . And a light source,
Disposed on the light emission side of said light source comprises at least an optical sheet according to any one of the 請 Motomeko 1 to 4,
A backlight unit for displays. A surface light source composed of a d Jjiraito formula source and the light guide plate,
Disposed on the light emitting side of the surface light source comprises at least an optical sheet according to any one of the 請 Motomeko 1 to 4,
A backlight unit for displays. An image display element in which a display pattern is defined in accordance with transmission / non-transmission or transparency / scattering in pixel units ;
Wherein disposed on the rear surface of the image display device comprises a backlight unit for a display of 請 Motomeko 5 or 6 wherein,
A display device characterized by that.

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