JPH09304605A - Production of optical control sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical control sheet for a backlight unit having such light condensing ability that, it is very bright in the front direction and the screen thereof is prevented from glaring in the case where the sheet is used for the liquid crystal display element, by uniaxially orienting a resin sheet having a surface where plural lines of columnar projections having nearly triangular cross section are arranged in parallel so that its cross section may be sawtoothed in the columnar axis direction of the columnar projection. SOLUTION: The resin sheet having one surface where plural lines of columnar projections being nearly triangular are arranged in parallel so that its cross section may be sawtoothed is uniaxially oriented in the columnar axis direction of the columnar projection. The thickness of the resin sheet 2 is properly set according to a corresponding liquid crystal display device, and it is set to >=200μm, desirably, and 200 to 1000μm, more desirably. An angle formed by two inclined surfaces putting the top of the columnar projection having the nearly triangular cross section in between is set to 30 deg. to 150 deg., desirably, and 60 deg. to 120 deg., more desirably. The pitch of the columnar projection in the case of arranging the columnar projection having the nearly triangular cross section in parallel so that the cross section of the sheet 2 may be sawtoothed is set to 100 to 50μm, desirably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a light control sheet, and more particularly to a light control sheet used for a liquid crystal display element light source device constituting a liquid crystal display such as a personal computer or a word processor, a liquid crystal color television or the like.

[0002]

2. Description of the Related Art Since a liquid crystal display screen does not have a self-luminous property, it is necessary to illuminate from other sources in order to improve visibility.
Therefore, a light source unit (hereinafter referred to as "backlight unit") that illuminates light from the back surface of the liquid crystal display element has been devised.

The backlight unit had a structure in which a light source such as a fluorescent tube was arranged directly on the back surface of the liquid crystal display element at the beginning of its development, but recently, the thickness of all the units is reduced to reduce the size of the device. To achieve this, an edge light system is often used in which the light source is arranged on at least one side surface of the liquid crystal display element.

In the edge light type planar light source device, a fluorescent tube is disposed as a light source on one side surface of a transparent light guide plate.
A dot pattern of paint is formed on the back surface of the light guide plate. This dot pattern is a light-scattering print pattern formed on the back surface of the light guide plate in order to allow the light incident from the side fluorescent tube to be emitted uniformly from any position on the screen, and is called a pseudo light source. is there. A reflection plate is arranged on the rear side of the light guide plate.

The light beam emitted from the fluorescent tube is diffusely reflected by the dot pattern on the back surface of the light guide plate and is emitted forward from the front surface of the light guide plate. At this time, as shown in FIG.
Most of the light emitted from the light rays emitted from the light guide plate 7
The light is emitted in a direction largely deviated from the direction of the normal line 2 (the state of the emitted light pattern 73), and the distribution thereof is also extremely steep. Therefore, for a user who normally observes from the direction of the normal line of the light guide plate 72. The LCD screen becomes a very dark screen.

In order to solve this drawback, a light control sheet is arranged on the front surface of the light guide plate. As a conventional light control sheet, a transparent glass or plastic sheet containing an inorganic or organic light diffusing agent (JP-A-3-78).
No. 701) or the front surface of a transparent plastic sheet is matted or embossed so that the roughness Ra = 100 to 15
It is known that fine random irregularities of about 0 μm are formed (Japanese Patent Laid-Open No. 62-291618).

Further, as another light control sheet, one side is
A sheet (hereinafter, referred to as a "prism sheet") having a structure surface in which a large number of prism portions having a substantially triangular cross section or a plurality of peak portions having a convex arc shape at the apex are arranged in parallel is also proposed. There is. (JP-A-5-203950, etc.). The prism sheet is an optical functional sheet in which a large number of small prisms are arranged in parallel on one surface and has a function of refracting or reflecting a light ray incident on the prism.

[0008]

Among the conventional light control sheets described above, in the case of the light control sheet 74 using a light diffusing agent, as shown in FIG. 8, the fluorescent tube 7 is provided on one side surface of the light guide plate 72.
In the one-edge type with 1 arranged, many light rays are emitted in an unnecessary direction for the user (emission in an oblique direction), and the loss of light rays due to irregular reflection at the interface between the light control sheet 74 and the light guide plate 72 is also ignored. Can not. Therefore, when used for illuminating the liquid crystal display element, there is a problem that the amount of light emitted in the front direction is small (state of the emitted light pattern 75).

Further, when a prism sheet is used, FIG.
As shown in, the intensity distribution of the light rays of the prism sheet S at each emission angle, that is, in the emission light pattern 60, the emission of the light rays in the normal direction is significantly increased. However, in the conventional prism sheet, the pitch of the ridges (prisms) is 10
There is a problem that the roughness is as small as 0 to 200 μm, so that the light and shade of the light generated by the prism becomes so observable that the screen becomes glaring and glare.
With the above glare, the pitch of the ridges (prism) is 100μ.
If it can be made finer than m, it should disappear.

However, a casting method, a solvent casting method, which are conventionally known as a method for manufacturing a prism sheet,
In methods such as the monomer casting method, the profile extrusion method, the roll embossing method, the hot pressing method, and the injection molding method, it is necessary to make the pitch of the ridges (prisms) finer than 100 μm because of the surface tension of the molten resin. It was almost impossible and difficult as an industrial method.

In view of the above points, the present invention provides a light for a backlight unit which has a light-collecting property such that the front direction is sufficiently bright when used in a liquid crystal display element and does not cause glare on the screen. An object is to provide a method for manufacturing a control sheet.

[0012]

According to the present invention, a resin sheet having a plurality of columnar protrusions each having a substantially triangular cross section and arranged in parallel in a sawtooth cross section is uniaxially stretched in the axial direction of the columnar protrusions. The gist is a method of manufacturing a light control sheet characterized by the above.

The resin used for the resin sheet is not particularly limited as long as it can form a transparent sheet, but for example, a resin having good light transmittance such as polycarbonate or polymethylmethacrylate is suitable. Used for.

In the columnar protrusion having a substantially triangular cross section, one surface of the columnar portion of the triangular prism is brought into close contact with the resin sheet, and the apex composed of the apex angle portions sandwiched by the other two faces is directed outward. , Two surfaces other than the bottom surface of the columnar portion of the triangular prism may intersect to form a geometrically true triangular prism, but the top portion is slightly cut by one or more surfaces, and It is possible to form various columnar bodies from a trapezoidal cross section to a substantially triangular cross section having a convex arc-shaped top.

A method for producing a resin sheet in which a plurality of columnar protrusions each having a substantially triangular cross section are arranged in parallel on the above-mentioned one surface in a sawtooth cross section is not particularly limited. For example, the above-mentioned casting method and solvent casting are used. Methods, monomer casting method, profile extrusion method, roll embossing method, hot pressing method, injection molding method and the like.

The thickness of the resin sheet is appropriately set by the corresponding liquid crystal display device, but is preferably 200 μm.
m or more, and more preferably 200 to 1000 μm.
If the thickness is less than 200 μm, it becomes difficult to arrange a plurality of columnar protrusions having a substantially triangular cross section in parallel with each other in a sawtooth cross section for shaping.

The angle formed by the two slopes sandwiching the top of the columnar protrusion having a substantially triangular cross section is preferably 30 to 150.
The angle is more preferably 60 to 120 degrees. If the angle is less than 30 degrees, it is difficult to arrange the plurality of columnar projections having a substantially triangular cross section in parallel with each other in a sawtooth cross section, and if the angle exceeds 150 degrees, the light condensing ability is deteriorated. There is a fear.

The pitch of the pillar-shaped projections having the substantially triangular cross-section and arranged in parallel to each other in a sawtooth-shape is preferably 100 to 500 μm. The pitch is 100 μm
If it is less than 100 μm, it is difficult to uniformly form the columnar protrusions. If the pitch exceeds 500 μm, the pitch of the columnar protrusions obtained by uniaxially stretching in the next step is aimed at.
It cannot be made finer than μm.

The method of uniaxially stretching the resin sheet, in which a plurality of columnar protrusions each having a substantially triangular cross section are arranged parallel to each other in a sawtooth cross section on the one surface in the column axis direction of the columnar protrusions, is not particularly limited. However, for example, there are various continuous and intermittent methods such as longitudinal uniaxial stretching by a roll method, lateral uniaxial stretching by a tenter method, and uniaxial stretching by gripping two opposite sides of a sheet of a sheet. . Especially, the longitudinal uniaxial stretching by the roll method in the stretching section of 1 m or more can make the pitch of the columnar projections finer due to the large neck-in. In order to stabilize the shape of the columnar projections in the uniaxial stretching step, for example, a method of introducing the sheet to be stretched into the air into a heating furnace and uniaxially stretching is preferably used.

The stretching temperature for the uniaxial stretching is preferably (Tg-5 ° C) to (Tg +) of the resin constituting the sheet to be stretched.
30 ° C.). If the stretching temperature is lower than (Tg-5 ° C) of the resin forming the stretched sheet, the stretched sheet does not reach the appropriate temperature for stretching, so that the stretchable sheet easily breaks, and the stretching temperature constitutes the stretched sheet. Of resin (Tg + 30
C.), the stress associated with the deformation of the stretched sheet becomes small, and stretching unevenness is likely to occur.

Since the method for producing a light control sheet of the present invention is constructed as described above, a plurality of columnar protrusions having a substantially triangular cross section with the top facing outward are formed on one surface. A prism sheet having a pitch of 100 μm or less and arranged in parallel in a sawtooth cross section can be manufactured stably and efficiently. In addition, the light control sheet obtained by the manufacturing method of the present invention is such that the front direction of the liquid crystal display element is sufficiently bright regardless of whether the sheet is used in an edge single-lamp type or a dual-lamp type planar light emitting device. It is useful as a light control sheet for a backlight unit that has a light collecting property and does not cause glare on the screen.

[0022]

Embodiments of the present invention will be described below.

(Example 1) Polycarbonate resin was melt extruded from a T-die, and as shown in FIG. 1, in the circumferential direction, the groove depth was 80 μm, the apex angle of the columnar projections was 90 °, and the groove pitch was 160.
A resin sheet having a thickness of 200 μm and a plurality of columnar protrusions each having a substantially triangular cross section arranged parallel to each other in a sawtooth cross section on one surface while cooling while sandwiching between a cooling roll having a plurality of μm grooves and a pressing roll. Got As shown in FIG. 2, a plurality of columnar protrusions each having a substantially triangular cross section formed on one surface of the obtained resin sheet had a columnar protrusion height of 70 μm, an angle formed by two surfaces sandwiching the top portion of 90 °, and a radius of curvature of the top portion. The pitch was 20 μm and the pitch of the columnar protrusions was 160 μm.

Then, the obtained resin sheet was stretched at a stretching section of 2 m and a stretching temperature of 16 using a stretching device (not shown) equipped with nip rolls having different peripheral speeds on both sides of a hot air heating furnace.
A light control sheet was produced by longitudinally uniaxially stretching in the column axis direction of the columnar projections at 5 ° C. and a stretching ratio of 4 times. As shown in FIG. 3, the obtained light control sheet had a thickness of 100 μm, a height of columnar projections of 35 μm, an angle formed by two surfaces sandwiching the top portion of 90 °, a radius of curvature of the top portion of 10 μm, and a pitch of the columnar projections of 80 μm. .

Comparative Example 1 The unstretched resin sheet obtained in Example 1 was used as it was as a light control sheet.

(Comparative Example 2) The cooling roll shown in FIG. 1 of Example 1 was replaced with a groove depth of 40 μm and an apex angle 90 of the columnar protrusion.
And a thickness of 100 μm in the same manner as in Example 1 using a cooling roll having a plurality of grooves with a groove pitch of 80 μm engraved.
A resin sheet was obtained in which a plurality of columnar protrusions having a substantially triangular cross section were arranged in parallel on one surface in a sawtooth cross section. As shown in FIG. 4, a plurality of columnar protrusions having a substantially triangular cross section formed on one surface of the obtained resin sheet had a columnar protrusion height of 30 μm, an angle formed by two surfaces sandwiching the top portion of 90 °, and a radius of curvature of the top portion. 20 μm,
The pitch of the columnar protrusions was 80 μm. The obtained resin sheet was directly used as a light control sheet.

In order to evaluate the performance of the light control sheets obtained in Example 1 and Comparative Examples 1 and 2, the following brightness measurement and luminescent appearance observation test were performed. The results are shown in Table 1.

(Measurement of Luminance) In accordance with JIS C7614, luminance was measured in the normal direction. The edge-lamp type backlight device used for the measurement has a dot pattern 52 on the back surface of 3 mm (thickness) × 205 mm as shown in FIG.
A reflective plate 54 is provided from the back surface of the dot pattern 52 of the light guide plate 53 made of a polymethylmethacrylate plate of × 135 mm, and a light source composed of a fluorescent tube 51 having a thickness of 35 mm and a length of 135 mm is provided on the side of the light guide plate 53. The light emitted from the light source is evenly incident on the entire surface of the test light control sheet S. A liquid crystal display element 55 is arranged on the front side of the light control sheet S. The reflector 54 is made of an opaque polyethylene terephthalate film. In the single edge type backlight device having the above structure, the applied voltage was 12V.

(Observation of appearance of light emission) By visually observing the liquid crystal display screen, the presence or absence of glare on the screen, the glare state, and whether the dot pattern of the light guide plate can be seen through the liquid crystal display screen (defective) or not (normal) The appearance of light emission was evaluated. About the above-mentioned visibility of the dot pattern, about 50 from the screen
It was observed from a position separated by cm.

[0030]

[Table 1]

From the results of this evaluation test, it is clear that in the case of the light control sheet of Example 1, sufficient front luminance and a wide angle range are secured, no glare on the screen, and no dot pattern is visible. . On the other hand, in the case of the light control sheet of Comparative Example 1, the screen has streaky glare, and in the case of the light control sheet of Comparative Example 2, the luminance in the normal direction is small, the screen is dark, and the light guide plate The dot pattern of No. 2 was visible through the liquid crystal display screen, resulting in a defective light emitting appearance.

[0032]

Since the method for producing a light control sheet of the present invention is constructed as described above, a plurality of columnar protrusions each having a substantially triangular cross section are provided on one surface, and the columnar protrusion pitch is 100 μm or less. A prism sheet arranged in parallel in a sawtooth shape can be manufactured stably and efficiently. Further, the method for manufacturing a light control sheet of the present invention, when using this for edge-one-lamp type or two-lamp type planar light emitting device,
It is useful as a light control sheet for a backlight unit that has a light-collecting property such that the front direction of a liquid crystal display element is sufficiently bright and does not cause glare on the screen.

[0033]

[Brief description of drawings]

FIG. 1 is a partially cutaway cross-sectional view showing a transverse cross-sectional shape of a groove formed in a circumferential direction of a cooling roll surface of a T-die extrusion apparatus used in Example 1 of the present invention.

FIG. 2 is a partially cutaway side view showing a cross-sectional shape of columnar protrusions of the resin sheet before uniaxial stretching obtained in Example 1 of the present invention.

FIG. 3 is a partially cutaway side view showing a cross-sectional shape of columnar protrusions of the light control sheet obtained in Example 1 of the present invention.

FIG. 4 is a partially cutaway side view showing a cross-sectional shape of columnar protrusions of a resin sheet before uniaxial stretching obtained in Comparative Example 2 of the present invention.

FIG. 5 is a cross-sectional view showing a light source unit used in a performance evaluation test of a light control sheet.

FIG. 6 is a schematic diagram showing emission light characteristics when the light control sheet obtained by the method for manufacturing a light control sheet of the present invention is used.

FIG. 7 is a schematic diagram showing emission light characteristics of a light guide plate alone.

FIG. 8 is a schematic diagram showing emission light characteristics of a conventional light control sheet containing a light diffusing agent.

[Explanation of symbols]

 1 Cooling Roll 2 Resin Sheet 3, 30, S, 74 Light Control Sheet 5 Light Source Unit 51, 71 Fluorescent Tube 52 Dot Pattern 53, 72 Light Guide Plate 54 Reflector 55 Liquid Crystal Display Element 60, 73, 75 Emitted Light Pattern

Claims (1)

[Claims] 1. A light control sheet, comprising: a resin sheet having a plurality of columnar protrusions each having a substantially triangular cross section arranged in parallel on one surface in a sawtooth cross section, and uniaxially extending in a column axis direction of the columnar protrusions. Production method.