JP4448359B2 - Backlight and method for preventing backlight failure - Google Patents

Description

  The present invention relates to a backlight that does not cause image defects over time.

  Backlights used in liquid crystal displays and electric signboards have been used significantly in line with the expansion of shipments of liquid crystal displays such as notebook computers and large liquid crystal televisions.

  As such a backlight, an edge light type or a direct type backlight is mainly used. Edge-light type backlights are used in notebook computers and the like because the thickness of the backlight itself can be reduced, and direct-type backlights are often used in large LCD TVs and the like.

  Such a backlight is an edge light type backlight, in addition to a light source and a light guide plate, a prism sheet, a light diffusion film, a light reflection film, a polarizing film, a reflective polarizing film, a retardation film, an electromagnetic wave Consists of optical members such as shield film. In direct type backlight, in addition to light source and light diffusion plate, prism sheet, light diffusion film, light reflection film, polarizing film, reflection type polarizing film, retardation It is comprised from optical members, such as a film and an electromagnetic wave shield film (refer patent document 1).

  In the liquid crystal display using the backlight as described above, image defects hardly occurred over time, except for the lighting failure of the light source.

JP-A-9-127314 (Claim 1, paragraph number 0034)

  However, with the increase in the size of the liquid crystal display, and in turn, the increase in the backlight, after several hours have passed since the liquid crystal display turned on, a phenomenon has been reported in which a portion where the image state differs from the surroundings locally occurs on the display. I'm starting.

  As a result of diligent research to solve the above problems, the present inventors have found that the cause of the image failure is that the optical member constituting the backlight is wavy and bent. It was.

That is, the backlight of the present invention includes a light source, a bent light diffusing plate made of a synthetic resin disposed on the light source, and one or more optical members disposed on the light diffusing plate. The backlight has an area of a light emission surface of 900 cm ² or more, and at least one of the optical members is obtained by the following methods (1) to (3): The measured stress is 12 g or less.
(1) A sample having a width of 2.54 cm and a length of 11 cm is taken from the optical member.
(2) The sample is bonded so that the ends of the sample overlap each other by 1 cm, and a cylindrical sample is prepared so that the circumference becomes 10 cm.
(3) Place the sample prepared in a cylindrical shape in a horizontal measuring device so that the bonded part is facing downward, and push it in 1 cm with a 0.3 cm diameter needle from the opposite side of the bonded part of the sample. Measure.

Further, the backlight of the present invention includes a bent light guide plate made of a synthetic resin, a light source disposed at at least one end of the light guide plate, and a light output surface and / or a light output surface of the light guide plate. A backlight having one or more optical members arranged on the opposite surface, wherein the backlight has an area of a light exit surface of 900 cm ² or more, and At least one of the optical members is characterized in that the stress measured by the methods (1) to (3) is 12 g or less.

  Hereinafter, “on the light exit surface of the light guide plate and / or on the surface opposite to the light exit surface” may be simply referred to as “on the light guide plate”. Hereinafter, the “stress measured by the methods (1) to (3)” may be referred to as “stress by circular indentation method”. FIG. 4 is an explanatory diagram of the circular push-in method.

  Since the backlight of the present invention is formed by using at least one optical member arranged on the light diffusion plate or the light guide plate that has a stress of 12 g or less by a circular indentation method, Deflection does not occur, and this causes no image defect on the liquid crystal display.

The backlight according to the present invention includes a light source, a light diffusion plate made of synthetic resin disposed on the light source, and one or more optical members disposed on the light diffusion plate. The backlight has an area of a light emitting surface of 900 cm ² or more, and at least one of the optical members has a stress by a circular indentation method of 12 g or less. (Hereinafter, also referred to as “direct-type backlight”). Further, the backlight of the present invention includes a light guide plate made of a synthetic resin, a light source disposed at least at one end of the light guide plate, a light exit surface of the light guide plate and / or a light exit surface opposite to the light exit surface. A backlight having one or more optical members disposed on a surface, wherein the backlight has an area of a light exit surface of 900 cm ² or more, and At least one type is characterized in that the stress by the circular indentation method is 12 g or less (hereinafter sometimes referred to as “edge-light type backlight”). Hereinafter, embodiments of the backlight of the present invention will be described.

  In the backlight of the present invention, at least one of the optical members arranged on the light diffusion plate or the light guide plate is used so that the stress caused by the circular indentation method is 12 g or less, so that the optical member is bent. It is what prevented. The reason why it is possible to prevent the optical member from being bent by such a configuration will be described together with the cause of the occurrence of the deflection.

  First, most of the light diffusing plate and the light guide plate are made of synthetic resin from the viewpoint of optical characteristics, weight, and the like. And synthetic resin tends to absorb moisture with high water vapor permeability. When such a light diffusing plate or light guide plate that easily absorbs moisture is left in a high humidity environment for a long time, the light diffusing plate or the light guide plate sufficiently absorbs moisture. Then, when the backlight is turned on in a state where the light diffusion plate and the light guide plate are sufficiently absorbed in this way, sudden moisture release is started by the heat of the light source. This moisture release does not occur uniformly in the light diffusion plate or the light guide plate, and is likely to occur in the vicinity of the light source of the light diffusion plate or the light guide plate. Insufficient and non-uniform moisture absorption occurs. In such a state, the part that has been dehumidified (near the light source) is in a state of being contracted and bent as compared with the part that has been absorbed. In summary, the cause of the deflection is considered to be partially non-uniform moisture absorption in the light diffusion plate or the light guide plate. FIG. 3 shows a state where the light diffusion plate is bent in the direct type backlight.

Here, in a state where only the light diffusing plate and the light guide plate are bent, local image defects are hardly seen on the display screen of the liquid crystal display. However, optical members such as a prism sheet, a light diffusing film, a light reflecting film, a polarizing film, a reflective polarizing film, a retardation film, and an electromagnetic wave shielding film are arranged on the light diffusing plate and the light guide plate where the deflection occurs. As a result, local image defects are extremely remarkable. That is, the optical member disposed on the light diffusion plate or the light guide plate tries to follow the bent shape of the light diffusion plate and the light guide plate, but cannot follow up, and causes deflection due to its own weight. And the local image defect becomes very remarkable by the deflection of the optical member. The deflection of the optical member becomes conspicuous with the increase in the area of the backlight due to the increase in the size of the liquid crystal display (the area of the light emission surface of the backlight is 900 cm ² or more), and consequently the area of the optical member. .

  Here, in the present invention, as the optical member disposed on the light diffusing plate or the light guide plate, an optical member whose stress by the circular indentation method is 12 g or less is used, so that the light diffusing plate or the light guide plate is bent. The optical member can follow, the deflection of the optical member is prevented, and the occurrence of local image defects of the liquid crystal display can be prevented.

  Note that once the deflection of the optical member occurs, it is difficult to make it completely flat as in the beginning. In other words, once the deflection of the optical member occurs, a video defect will occur permanently. Therefore, the present invention that can prevent the occurrence of deflection is extremely useful.

Next, embodiments of the direct type backlight and the edge light type backlight of the present invention will be further described. As described above, the direct type backlight of the present invention has a light exit surface area of 900 cm ² or more, and is disposed on the light source, the light diffusion plate disposed on the light source, and the light diffusion plate. And one or more optical members. In addition, as described above, the edge light type backlight of the present invention has an area of a light emitting surface of 900 cm ² or more, and includes a light guide plate, a light source disposed at at least one end of the light guide plate, It has 1 type, or 2 or more types of optical members arrange | positioned on the light emission surface of a light plate, and / or the surface on the opposite side to a light emission surface.

  As a light source of the direct type backlight and the edge light type backlight, a cold cathode tube is mainly used. Examples of the shape of the light source include linear and U-shaped backlights for direct type backlights, and linear and L-shaped backlights for edge light type backlights.

  The light diffusing plate constituting the direct type backlight is installed on the light source, has a role of erasing the pattern of the light source, and is mainly made of synthetic resin. Since such a light diffusing plate is used for erasing the pattern of the light source, the thickness needs to be as thick as 1 to 10 mm, in order to give a suitable viewing angle while improving the front luminance. It is different from the light diffusion film which is used and has a thickness of 12 to 350 μm.

  Synthetic resins constituting the light diffusion plate include polyester resins, acrylic resins, acrylic urethane resins, polyester acrylate resins, polyurethane acrylate resins, epoxy acrylate resins, urethane resins, epoxy resins, polycarbonate resins. , Cellulosic resin, Acetal resin, Polyethylene resin, Polystyrene resin, Polyamide resin, Polyimide resin, Melamine resin, Phenol resin, Silicone resin and other thermoplastic resins, Thermosetting resin, Ionizing radiation curing Resin. Among these, acrylic resins having excellent optical properties are preferably used.

  Fine particles are added to the light diffusing plate in order to impart light diffusibility. In addition to inorganic fine particles such as silica, clay, talc, calcium carbonate, calcium sulfate, barium sulfate, aluminum silicate, titanium oxide, synthetic zeolite, alumina, smectite, styrene resin, urethane resin, benzoguanamine resin, silicone resin, Organic fine particles made of acrylic resin and the like can be mentioned.

  The light guide plate constituting the edge light type backlight has a substantially flat plate shape formed so that at least one end portion is a light incident surface and one surface substantially orthogonal to the light incident surface is a light emission surface, It consists of a synthetic resin. Each surface of such a light guide plate may have a complicated surface shape instead of a uniform plane, or may be provided with diffusion printing such as a dot pattern. The thickness of the light guide plate is about 1 to 10 mm.

  As resin which comprises a light-guide plate, the thing similar to what was illustrated as resin which comprises a light-diffusion board can be used, and especially acrylic resin excellent in an optical characteristic is used suitably. Moreover, you may add an organic fine particle in a light-guide plate as needed. As the organic fine particles, those similar to those added to the light diffusion plate can be used.

  1 type or 2 types on the light diffusion plate of the direct type backlight and on the light emitting surface of the light guide plate of the edge light type backlight and / or on the surface opposite to the light emitting surface, depending on the purpose. The above optical members are arranged. Examples of such an optical member include a prism sheet, a light diffusing film, a light reflecting film, a polarizing film, a reflective polarizing film, a retardation film, and an electromagnetic shielding film.

  In the present invention, the circular indentation method is used as at least one of the optical members arranged on the light diffusion plate or the light guide plate, preferably as all kinds of the optical members arranged on the light diffusion plate or the light guide plate. Those having a stress of 12 g or less, preferably 10 g or less are used. The lower limit of the stress is preferably 1 g or more, and more preferably 2 g or more. By setting the stress to 12 g or less, the optical member can follow the deflection of the light diffusing plate or the light guide plate, the deflection of the optical member can be prevented, and local image defects can be prevented. it can. Further, by setting the stress to 1 g or more, it is possible to ensure handling at the time of working such as processing an optical member.

  In order to reduce the stress caused by the circular indentation method of the optical member to 12 g or less, for example, the main material constituting the optical member is made of a flexible material such as polycarbonate, polypropylene, polyurethane, polystyrene, polyvinyl chloride, cyclic polyolefin. That's fine. The optical member can be divided into those consisting only of a synthetic resin base material and those having a functional layer on the synthetic resin base material. It is preferable to use a material made of a material. For example, by forming a layer having a light diffusion function consisting of a binder resin and resin beads on a substrate made of polycarbonate, a light diffusion film having a stress of 12 g or less by a circular indentation method can be obtained, By forming a layer having a light reflection function from a binder resin and a white pigment on a substrate made of polyvinyl chloride, a light reflection film having a stress of 12 g or less by a circular indentation method can be obtained.

  In addition, you may have an optical member in other parts in direct type | mold backlight, such as the opposite side to the light diffusing plate of the light source of direct type | mold backlight. Moreover, you may have these optical members in other parts in an edge light type backlight, such as the circumference | surroundings of the light source of an edge light type backlight.

  FIG. 1 shows an embodiment of a direct backlight 1. As shown in the figure, the backlight 1 includes a plurality of light sources 13 disposed on a reflective film 12 housed in a chassis 11, and a light diffusion film 15 and a prism sheet 16 are disposed thereon via a light diffusion plate 14. Has been placed. Here, in the direct type backlight of the present invention, the optical member of the present invention having a stress by a circular indentation method of 12 g or less is used as the light diffusion film and / or the prism sheet.

  FIG. 2 shows an embodiment of the edge light type backlight 2. The backlight 2 has a configuration in which light sources 22 are provided at both ends of the light guide plate 21, and a light diffusion film 23 and a prism sheet 24 are disposed on the upper side of the light guide plate 21. The light source 22 is covered with a reflective film 25 except for a portion facing the light guide plate 21 so that light from the light source 22 is efficiently incident on the light guide plate 21. A reflective film 25 accommodated in the chassis 26 is provided below the light guide plate 21. Thereby, the light emitted to the side opposite to the light emitting surface side of the light guide plate 21 is returned to the light guide plate 21 again, so that the emitted light from the light emitting surface of the light guide plate 21 is increased. Here, in the edge light type backlight of the present invention, as at least one of a light diffusion film, a prism sheet, and a light reflection film (however, a reflection film on the surface opposite to the light exit surface of the light guide plate), The optical member of the present invention having a stress by a circular indentation method of 12 g or less is used.

Since the backlight of the present invention described above uses an optical member disposed on the light diffusion plate or the light guide plate having a stress of 12 g or less by the circular indentation method, the light diffusion plate or the light guide plate is used. Deflection of the optical member to be installed can also be prevented, and local image defects on the display can be prevented. Such an effect is extremely useful in a backlight having a large area where the area of the light emitting surface where the problem of deflection is likely to occur is 900 cm ² or more, as in the present invention. Since such a large-area backlight is widely used in direct type backlights, the present invention is particularly suitable for direct type backlights.

  The following examples further illustrate the present invention. “Parts” and “%” are based on weight unless otherwise specified.

[Example 1]
A light diffusion layer coating solution having the following formulation is applied and dried on one side of a synthetic resin base material (Panlite: Teijin Chemicals) made of polycarbonate with a thickness of 100 μm so that the thickness after drying is 12 μm. It formed and the optical member (light-diffusion film) was obtained. It was 10.6 g when the stress by the circular indentation method of the obtained optical member (light diffusion film) was measured.

<Light diffusion layer coating solution>
・ Acrylic polyol 10 parts (Acridic A-807: Dainippon Ink & Chemicals, Inc.)
-Polyisocyanate 2 parts (Takenate D110N: Mitsui Takeda Chemical Company)
・ 10 parts of acrylic resin particles (Techpolymer MBX-8: Sekisui Plastics Co., Ltd.)
・ Methyl ethyl ketone 18 parts ・ Butyl acetate 18 parts

Next, a light diffusing plate made of synthetic resin is disposed on the light source, and further, the optical member (light diffusing film) obtained in the above operation is disposed on the light diffusing plate, and the light emitting surface area is 2090 cm ² . A direct type backlight of the invention was obtained (size 26 type).

[Example 2]
A light diffusion layer similar to that of Example 1 was formed on one surface of a synthetic resin base material (Malphan: Mitsubishi Plastics) made of polyvinyl chloride having a thickness of 100 μm to obtain an optical member (light diffusion film). It was 7.1g when the stress by the circular indentation method of the obtained optical member (light-diffusion film) was measured.

Next, a light source is disposed at both ends of the light guide plate, and the optical member (light diffusion film) obtained in the above operation is disposed on the light exit surface of the light guide plate, and the area of the light exit surface is 993 cm ² . An edge light type backlight was obtained (size 18 type).

[Evaluation of deflection]
After the backlights obtained in Examples 1 and 2 were allowed to stand for 24 hours in an environment of 40 ° C. and 90% RH, Example 1 was a commercially available 26-type liquid crystal TV, and Example 2 was commercially available. Each was installed in a liquid crystal display for a desktop PC, the liquid crystal TV and the liquid crystal display were turned on, and the progress of the video state was observed. As a result, in all of Examples 1 and 2, no image defect occurred in the liquid crystal display no matter how many hours elapsed from lighting. Further, when the backlight optical member (light diffusion film) incorporated in the liquid crystal TV and the liquid crystal display was taken out, no deflection was observed.

[Comparative example]
On the other hand, as a comparative example, instead of the optical member (light diffusion film) used in Examples 1 and 2, the following optical member (light diffusion film) having a stress of 19.2 g by the circular indentation method was used. Deflection was evaluated in the same manner as in Examples 1 and 2. As a result, a phenomenon was observed in which a portion having a different video state from the surroundings locally occurred on the liquid crystal display after 3 hours had passed since the liquid crystal TV and the liquid crystal display were turned on. This local image defect part gradually became smaller with time, but did not disappear completely even after several days. Further, when the optical member (light diffusion film) incorporated in the liquid crystal TV and the liquid crystal display was taken out, deflection was observed.

<Optical member (light diffusion film) used in comparative example>
A light diffusion layer similar to that of Example 1 was formed on one surface of a synthetic resin base material (Lumirror T60: Toray Industries, Inc.) made of polyethylene terephthalate having a thickness of 100 μm to obtain an optical member (light diffusion film). It was 19.2g when the stress by the circular indentation method of the obtained light-diffusion film was measured.

Sectional view showing an example of backlight Sectional drawing which shows the other example of a backlight Diagram explaining the state of deflection Diagram explaining the circular indentation method

Explanation of symbols

1, 2, ... Backlight 14 ... Light diffusing plate

Claims (4)

A backlight comprising a light source, a bent light diffusing plate made of synthetic resin disposed on the light source, and one or more optical members disposed on the light diffusing plate. The backlight has an area of a light emitting surface of 900 cm ² or more, and at least one of the optical members has a stress measured by the following methods (1) to (3) of 12 g or less. Backlight characterized by that.
(1) A sample having a width of 2.54 cm and a length of 11 cm is taken from the optical member.
(2) The samples are bonded so that the ends of the sample overlap each other by 1 cm, and a cylindrical sample is prepared so that the circumference becomes 10 cm.
(3) Place the sample prepared in a cylindrical shape in a horizontal measuring device so that the bonded part is facing downward, and push it in 1 cm with a 0.3 cm diameter needle from the opposite side of the bonded part of the sample. Measure. A bent light guide plate made of synthetic resin, a light source disposed at least at one end of the light guide plate, and a light exit surface of the light guide plate and / or a surface opposite to the light exit surface. A backlight comprising one or more optical members, wherein the backlight has an area of a light exit surface of 900 cm ² or more, and at least one of the optical members is: (1) The backlight measured by the method of (3) is 12 g or less.
(1) A sample having a width of 2.54 cm and a length of 11 cm is taken from the optical member.
(2) The sample is bonded so that the ends of the sample overlap each other by 1 cm, and a cylindrical sample is prepared so that the circumference becomes 10 cm.
(3) Place the sample prepared in a cylindrical shape in a horizontal measuring device so that the bonded part is facing downward, and push it in 1 cm with a 0.3 cm diameter needle from the opposite side of the bonded part of the sample. Measure.   Prevention of image defects in a backlight comprising a light source, a light diffusion plate made of synthetic resin disposed on the light source, and one or more optical members disposed on the light diffusion plate A way to
  The backlight has a light exit surface area of 900 cm. ² That's it,
  At least one of the optical members has a stress measured by the following methods (1) to (3) of 12 g or less.
(1) A sample having a width of 2.54 cm and a length of 11 cm is taken from the optical member.
(2) The sample is bonded so that the ends of the sample overlap each other by 1 cm, and a cylindrical sample is prepared so that the circumference becomes 10 cm.
(3) Place the sample prepared in a cylindrical shape in a horizontal measuring device so that the bonded part is facing downward, and push it in 1 cm with a 0.3 cm diameter needle from the opposite side of the bonded part of the sample. Measure.   A light guide plate made of a synthetic resin, a light source arranged at least at one end of the light guide plate, and one or more types arranged on the light exit surface of the light guide plate and / or on the surface opposite to the light exit surface A method for preventing a video defect of a backlight having two or more optical members,
  The backlight has a light exit surface area of 900 cm. ² That's it,
  At least one of the optical members has a stress measured by the following methods (1) to (3) of 12 g or less.
(1) A sample having a width of 2.54 cm and a length of 11 cm is taken from the optical member.
(2) The sample is bonded so that the ends of the sample overlap each other by 1 cm, and a cylindrical sample is prepared so that the circumference becomes 10 cm.
(3) Place the sample prepared in a cylindrical shape in a horizontal measuring device so that the bonded part is facing downward, and push it in 1 cm with a 0.3 cm diameter needle from the opposite side of the bonded part of the sample. Measure.

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