JPH07333406A - Optical sheet - Google Patents

Abstract

PURPOSE:To obtain an optical sheet with which uniform illumination with high luminance and with decreased restrictions on a visual field angle is possible and a reduction of thickness is possible by composing this optical sheet of a microlens array specified in diameter, height and pitch. CONSTITUTION:This optical sheet consists of the microlens array which is 0.1 to 100mum in all of the diameter (a), the height (c) and the pitch (d). Namely, this fine lens assembly is curved by subjecting three-dimensional patterns of dotty or stripe patterns of 0.1 to 100mum, more preferably 0.1 to 50mum, further preferably 0.1 to 20mum in all of the diameter (a), width (b), the height (c) and the pitch (d) formed of a thermally flowable photoresist material on a substrate to fluidization under heating. The surface of the assembly is coated with a conductive metal and further a metallic layer is formed by electroforming thereon; thereafter, a stamper for producing a metallic sheet is obtd by being separated from the boundary between the resist layer and the conductive metallic layer. This optical sheet is formed and produced by using the stamper formed in the manner described above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sheet having a light collecting property.

[0002]

2. Description of the Related Art As a backlight for illuminating a liquid crystal display section of a personal computer from the back side, a side light (also called edge light) type is often used instead of the direct type until then, as the display section becomes thinner. I started to be seen. In the sidelight type backlight, the light from the lamp on the side surface is guided to the entire surface of the liquid crystal display unit by the light guide plate, and the function of the reflection plate on the back surface is added to illuminate the liquid crystal side. In order to use the light of the light source more effectively, various innovations and improvements have been made. For example, as the light guide plate, there is used an acrylic resin plate on the back surface of which dots are printed using ink containing a white pigment or a V-shaped parallel groove.

Further, a light-condensing sheet is used to further brighten the backlight without increasing the power consumption of the lamp. As a conventional light-condensing sheet, there is known a sheet of plastic such as polycarbonate in which prisms having an apex angle of 90 to 100 degrees are arrayed. This increases the brightness by collecting the light entering from the flat side of the sheet into a narrow range of angles by the prism when exiting from the sheet.
There is inconvenience that the viewing angle is narrow.

On the other hand, a microlens array corresponding to a pixel pitch is used for optical parallel transmission as a large-capacity information transmission means in a large-scale computer or communication equipment and a small CCD as an electronic eye of a camera-integrated video tape recorder. ing.

As a method of manufacturing a microlens array,
A method in which a resist pattern is formed on the surface of an optical glass substrate and then etched to form an array of cylindrical protrusions, and the resist layer is removed and heated to deform the protrusions into spherical shapes (Japanese Patent Laid-Open No. 58-58-58). 185445, JP-A-5-16490
No. 4), a method of forming a lens array by applying a photoresist pattern to a semiconductor material and performing Ar ⁺ ion etching (Journal of the elect).
rochemical soc. , Vol. 131, p
p. 2373-2380, 1984), etc. are known.

However, since the microlens array manufactured by these conventional manufacturing methods is made of an inorganic material, it is difficult to reduce flexibility and weight, and there is a problem that productivity is low.

On the other hand, glass, plastics, and metal are used as a method for manufacturing a micro Fresnel lens having a concentric circular shape with a large number of corners used for forming a spot such as a laser, having a diameter of 0.4 mm. A resist is applied to the smooth surface of a substrate such as a plate, a concentric pattern is applied to this to expose and develop it, and then concentric convexes and concaves are formed, and then a conductive layer is formed on the surface by a method such as sputtering or vapor deposition. Japanese Unexamined Patent Publication No. 60-103308 discloses a method for producing a micro Fresnel lens made of a synthetic resin by forming an electrode, electroforming nickel using this as an electrode, then peeling off the nickel layer, and using this as a stamper. ing.

However, this method is only shown in FIG.
The purpose of the present invention is to manufacture a single micro-Fresnel lens in which concavities and convexities with a large number of corners are concentrically provided, and to improve the brightness over the entire sheet surface. It does not produce an optical sheet of the necessary convex lenses and an assembly thereof.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide, as a backlight for a liquid crystal display unit, high-luminance and uniform illumination with a limited viewing angle and, if necessary, reduction in thickness. To provide a simple optical sheet.

[0010]

A first aspect of the present invention relates to an optical sheet comprising a microlens array having a diameter, a height and a pitch of 0.1 to 100 μm. The optical sheet has a diameter of a μm and a height of cμ.
m and pitch is dμm,

## EQU3 ## It is preferable that the relationship of d / 2 ≦ a ≦ d (1) and c ≧ a / 4 (2) is satisfied.

A second aspect of the present invention relates to an optical sheet comprising a bar-shaped (cylindrical) lens array whose width, height and pitch are all 0.1 to 100 μm. When the width of the optical sheet is b μm, the height is c μm, and the pitch is d μm,

## EQU4 ## It is preferable that the relationship of d / 2 ≦ b ≦ d (3) and c ≧ b / 4 (4) is satisfied.

In the fine lens assembly, for example, the diameter or width, the height, and the pitch of the heat-fluidizable photoresist material formed on the substrate are each 0.1 to 100 μm.
m, preferably 0.1 to 50 μm, more preferably 0.
A three-dimensional pattern (resist layer) having spots or stripes of 1 to 20 μm is made into a curved surface by heating and fluidizing, a conductive metal is coated on this surface, and a metal layer is further formed thereon by electroforming to form a resist. It can be manufactured by molding using a metal optical sheet manufacturing stamper obtained by separating from the interface between the layer and the conductive metal layer.
The sheet here includes a plate-like sheet. Any photoresist material can be used as long as it can be fluidized by heating, but a material that is melted and fluidized at 100 to 200 ° C. is preferable.

The lens diameter or width and pitch are set to 100
When the thickness is not more than μm, the intensity of the light incident on the sheet when it is emitted from the sheet can be made uniform over the entire surface of the sheet, and illumination with uniform brightness can be performed in a liquid crystal backlight or the like.

When the sheet of the present invention is used by being attached to a marking plate or the like, by setting the lens diameter or width and pitch to 100 μm or less, it is possible to obtain an image with fine texture and high resolution. It is also possible to make the uncomfortable lens itself invisible.

Further, by making the pitch smaller, it is possible to suppress the occurrence of moiré which is expected in a combination with a display device / display object having a synchronous pixel such as a liquid crystal cell or an optical display or a print poster. .

The manufacture of the stamper will be described with reference to FIG. (A) to (i) in FIG. 1 show an example of a stamper manufacturing process.

FIG. 1A is a sectional view of a base 1, such as a silicon wafer or a glass plate, for applying a photoresist forming solution to a base.

(B) A negative or positive photoresist forming solution is applied on a substrate 1 such as a silicon single crystal plate or a glass plate in spots or stripes to form a photoresist forming layer 2. (Resist coating step).

(C) A photomask 5 having a light-shielding layer 3 such as a chrome film on a glass plate 4 is placed on the resist forming layer 2 (b), and an ultraviolet ray, an electron beam, or the like as indicated by an arrow. Irradiating the active light of (exposure step). The light shielding layer, in the finally obtained fine lens aggregate,
Diameter (shown as a in FIG. 2) or width (shown as b in FIG. 4), height (shown as c in FIG. 3) and pitch (shown as d in FIG. 4).
Any of 0.1 to 100 μm, preferably 0.1 to 100 μm
The spots (shapes are arbitrary such as square, rectangle, circle, and ellipse) or striped patterns having a thickness of 50 μm, more preferably 0.1 to 20 μm.

(D) Since a positive type material was used as the photoresist forming material, the portion exposed to light was eluted by development. The part which was not exposed to light remained as it was, and became a resist layer 2 '(development and rinse steps). The thickness of the resist layer is preferably 0.1 to 100 μm. If a negative type is used, the part exposed to the light remains. The developing solution is selected depending on the resist material used.

(E) When the resist layer 2'is heated to a temperature at which it heat-flows, the resist layer 2'flows, and the surface tension thereof causes the resist layer 2'to project in a convex shape or a mountain range shape as shown in the figure. An upward convex lens shape group (corresponding to the shape of the microlens array) or a pattern of three-dimensional stripes (corresponding to the shape of the bar-shaped lens array) having a curved convex cross section is formed (heating convex shape). Process). The heating temperature depends on the material for forming the resist layer, but is usually 100 to 200 ° C.
Is.

(F) After cooling, the surface of the shape 2'corresponding to the microlens array or the shape 2'corresponding to the bar-shaped lens array is coated with a conductive metal such as silver or nickel by a film forming method such as vapor deposition or sputtering. Then, the conductive metal layer 6 is formed (film forming step). The thickness of the conductive metal layer 6 is usually 0.01 to 1 μm.

(G) A metal layer 7 of nickel, copper or the like is formed on the conductive metal layer 6 by electroforming (electroforming step). The thickness of the metal layer is usually 0.01 to 50 mm, but is not limited to this.

(H) The substrate 1 having the resist layer 2'and the laminated body composed of the conductive metal layer 6 / electroformed metal layer 7 are peeled off (peeling step). There is no limitation on the peeling means, and it can be peeled by hand.

(I) Next, the conductive metal layer 6 is usually
It is removed by pickling or the like (removing step of the conductive metal layer).
This step is not necessary in all cases, but when Ag is used as the conductive metal, stains may be transferred when used as a stamper, so it is preferable to remove it.

The fine lens assembly used in the present invention can be manufactured by transferring the uneven pattern of the stamper onto the synthetic resin layer, and the following three specific preferred methods are available.

The first is a thickness of a transparent thermoplastic resin, preferably a resin selected from the group consisting of polycarbonate, methylphthalate homopolymers or copolymers, polyethylene terephthalate, polystyrene and thermoplastic norbornene resins. It is a manufacturing method in which unevenness of the stamper is transferred to a resin sheet by a hot pressing method using the stamper on a resin sheet of 0.01 to 5 mm.

The second is a composition of a transparent thermoplastic resin, preferably a resin selected from the group consisting of polycarbonate, methyl phthalate homopolymers or copolymers, polyethylene terephthalate, polystyrene and thermoplastic norbornene resins. The method is a method of injection molding into a die having the stamper as a bottom surface.

Thirdly, a resin forming material consisting of a monomer or an oligomer and a photopolymerization initiator are injected into a mold having the stamper as a bottom surface, and then this is polymerized by irradiating light such as ultraviolet rays. It is a manufacturing method.

Examples of the resin molding monomer or oligomer include methyl methacrylate; ethylene glycol;
Monomers such as polyfunctional (meth) acrylate derivatives which are esters of polyols such as 1,3-propanediol and trimethylolpropane with acrylic acid or methacrylic acid; methacrylate oligomers, acrylate oligomers, oligomers of the polyfunctional derivatives. Examples thereof include oligomers. In particular, it is preferable to use a methyl methacrylate in which a polyfunctional (meth) acrylate derivative and optionally an oligomer of these monomers are added. Further, benzoyl peroxide, benzoin, benzoin ether, etc. are used as the photopolymerization initiator.

As a mode in which the optical sheet of the present invention is used as a light-condensing sheet in a liquid crystal lighting device, it can be used as one component of a liquid crystal backlight as shown in FIGS. There are no particular restrictions on the configuration of the lighting device. In FIG. 5, the light collecting sheet 12 is placed under the diffusion sheet 11, but the light collecting sheet may be placed on the diffusion sheet (see FIGS. 6 and 7). Of course, a plurality of light collecting sheets can be used.

The shape of the microlens array is preferably obtained by melting a quadrangular prism (square or rectangular prism) from the viewpoint of increasing the occupation area ratio of the elementary lenses in the light condensing sheet. Further, in the case of the bar-shaped lens array, the direction of light collection can be adjusted by stacking a plurality of sheets in a vertical and horizontal manner.

When reflected light is used in the optical sheet of the present invention, if it is attached to the surface of a warning display plate or the like, the incident light is reflected at various angles, so that the attention of a person can be sufficiently drawn. .

The embodiment of the present invention is as follows. (1) Diameter, height and pitch are all 0.1 to 10
An optical sheet comprising a microlens array assembly sheet of 0 μm. (2) Diameter, height and pitch are all 0.1 to 50
The optical sheet according to the above item (1), which has a thickness of μm. (3) Diameter, height and pitch are all 0.1 to 20
The optical sheet according to the above item (1), which has a thickness of μm. (4) The above item (1), which comprises a transparent thermoplastic resin,
The optical sheet according to (2) or (3). (5) The optical sheet as described in (1), (2) or (3) above, which comprises a photopolymerizable resin. (6) When the diameter is a μm, the height is c μm, and the pitch is d μm,

## EQU5 ## d / 2 ≦ a ≦ d (1) c ≧ a / 4 (2), which satisfies the relationship (1), (2),
The optical sheet according to (3), (4) or (5). (7) All of width, height and pitch are 0.1 to 10
An optical sheet comprising a bar-shaped lens array sheet of 0 μm. (8) All of width, height and pitch are 0.1 to 50
The optical sheet according to the above item (7), which has a thickness of μm. (9) All of width, height and pitch are 0.1 to 20
The optical sheet according to the above item (7), which has a thickness of μm. (10) The previous item (7) consisting of a transparent thermoplastic resin,
The optical sheet according to (8) or (9). (11) The optical sheet as described in (7), (8) or (9) above, which comprises a photopolymerizable resin. (12) When the width is b μm, the height is c μm, and the pitch is d μm,

## EQU6 ## d / 2 ≦ b ≦ d (3) c ≧ b / 4 (4), which satisfies the relationship (7), (8),
The optical sheet according to (9), (10) or (11). (13) (1), (2), (3), (4),
(5), (6), (7), (8), (9), (10),
A light-condensing sheet comprising the optical sheet according to (11) or (12).

[0035]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 1-1 Preparation of Master A novolac-based positive photoresist (ZPP320 manufactured by Zeon Corporation of Japan) was formed on a silicon wafer having a diameter of 4 inches.
0) was spin-coated and dried on a hot plate at 100 ° C. for 90 seconds to form a photoresist layer having a film thickness of 2.3 μm. Then, a photomask having a predetermined pattern was brought into close contact with the photoresist layer and irradiated with ultraviolet rays for about 7 seconds by an ultraviolet baking device (PLA501F manufactured by Canon Inc., equipped with a 250 W ultra-high pressure mercury lamp). After this,
It was developed for 90 seconds with a 2.38 wt% tetramethylammonium hydroxide aqueous solution, and then rinsed with pure water. The obtained pattern was formed by arranging substantially rectangular prisms each having a length and width of 4 μm and a height of 2.3 μm with a space of 0.5 μm in each of the length and width directions. Next, the silicon wafer having the above resist pattern is heated on a hot plate at 180 ° C. for 10 minutes,
A lenticular pattern having a desired curved surface was obtained.

1-2 Preparation of Stamper After a silver layer having a thickness of 2000 Å was provided on the master prepared in Example 1-1 by vapor deposition, the thickness of 1 mm was obtained in an electrolytic solution containing nickel sulfamate as a main component. Of nickel was electrodeposited. Then, after separating the nickel layer from the resist layer, the silver on the surface was removed with a chromic acid aqueous solution to obtain a stamper having a desired pattern.

1-3 Production of Optical Sheet Using the obtained stamper on the surface of the mold, a sheet of polycarbonate microlens array having a thickness of 1 mm was prepared by injection molding.

1-4 Use of Optical Sheet A light guide plate made of acrylic resin is arranged on the front surface of an illuminating device in which two 15-watt fluorescent lamps having a tube diameter of 15 mm are arranged in parallel with each other with a space of 12 mm. A milky white acrylic resin diffuser plate was placed in the above, and the microlens array sheet obtained in Example 1-3 was placed on the front surface thereof. As a result of measuring the luminance at 15 points at a position 35 cm vertically above this sheet, an average 18.0% improvement in luminance was observed as compared with the case where the sheet of the microlens array was not placed. In addition, the variation in luminance (relative standard deviation) was as small as 4%.

Example 2 2-1 Preparation of Master A cyclized polyisoprene negative resist (ZPN10 manufactured by Nippon Zeon Co., Ltd.) was formed on a 4-inch diameter silicon wafer.
3) is applied by spin coating, and it is 9 at 90 ° C on a hot plate.
After drying for 0 seconds, a photoresist layer having a film thickness of 2.5 μm was provided. Then, a photomask having a predetermined pattern was brought into close contact with the photoresist layer, and the ultraviolet baking apparatus used in Example 1-1 (with an optical filter UC-20).
UV irradiation for about 6 seconds. Then, a normal heptane / normal butyl acetate mixed solution (50/50% by volume)
Development was carried out for 1 minute, followed by rinsing with normal butyl acetate. The obtained pattern was such that substantially squares of 6 μm each in the vertical and horizontal directions were arrayed through spaces of 1.5 μm in each of the vertical and horizontal directions when viewed from above. Next, the silicon wafer having the above resist pattern was heated on a hot plate at 160 ° C. for 2 minutes to obtain a lens-shaped pattern having a desired curved surface.

2-2 Production of Stamper Example 1-using the master produced in Example 2-1
A stamper having a desired pattern was obtained in the same manner as in 2.

2-3 Production of Optical Sheet A mixture having the following composition was injected between a stamper and a polycarbonate sheet having a thickness of 0.25 mm, and ultraviolet rays were irradiated through the polycarbonate sheet to carry out a polymerization reaction. The resin that was combined with the polycarbonate sheet and cured was peeled from the stamper to obtain a microlens array sheet. Methyl methacrylate 81 parts by weight 1,6-hexanediol diacrylate 17 parts by weight Benzoin butyl ether 2 parts by weight

2-4 Utilization of Optical Sheet As in Example 1-4, except that the sheet obtained in 2-3 was used as the sheet of the microlens array and the upper 35
As a result of measuring the luminance at 15 points of 10 cm, an average of 11.
The brightness was improved by 4%. Further, the variation in brightness (relative standard deviation) was as small as 6%.

Comparative Example 1 A mold using a stamper in which concave-shaped hemispheres having a diameter of 2 mm and arranged vertically and horizontally with a pitch of 4 mm were prepared by machining.
A convex lens array was formed on a polycarbonate sheet in the same manner as in Example 2-3. As a result of measuring the luminance using this sheet in the same manner as in Example 1-4, it was found that the luminance was improved by 6% on average as compared with the case where the lens array sheet was not placed. Brightness variation (relative standard deviation) is 1
It was as large as 7%. Also, the shape of the lens was clearly visible.

[0045]

EFFECTS OF THE INVENTION 1) Since the present invention utilizes a curved surface generated by the surface tension of the resist by fluidizing by heating the resist layer, a fine and uniform curved surface can be easily formed. And the pitch is 100 μm or less, preferably 50 μm
Hereafter, it is possible to further preferably set the thickness to 20 μm, which makes it possible to further improve the in-plane uniformity of the luminance as compared with the conventional light-condensing sheet. 2) When the optical sheet of the present invention is used for reflected light, the accuracy of the lens assembly is high, and therefore the uniformity of reflection on the entire surface is excellent.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of stamper manufacturing steps (a) to (i) of the present invention.

FIG. 2 is a partial plan view of a microlens array which is an example of an optical sheet used in the present invention.

3 is a cross-sectional view of FIG.

FIG. 4 is a partial perspective view of a bar-shaped microlens array which is an example of an optical sheet used in the present invention.

FIG. 5 is a cross-sectional view showing one structural example of a liquid crystal lighting device of the present invention.

FIG. 6 is a sectional view showing a structure of a micro Fresnel lens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Photoresist forming layer 2'Resist layer 3 Light-shielding layer 4 Glass plate 5 Photomask 6 Conductive metal layer 7 Metal layer 11 Diffusion sheet 12 Condensing sheet 13 Light guide plate 14 Reflector 15 Fluorescent lamp or cold concealed tube 16 Reflector 17 Frame a Diameter b Width c Height d Pitch

Claims (4)

[Claims] 1. The diameter, height and pitch are all 0.1.
An optical sheet comprising a microlens array of -100 μm. 2. The diameter is a μm, the height is c μm, and the pitch is d.
The optical sheet according to claim 1, wherein, when μm, the following relationship is satisfied: d / 2 ≦ a ≦ d (1) c ≧ a / 4 (2) 3. The width, height and pitch are all 0.1.
An optical sheet comprising a bar-shaped lens array of -100 μm. 4. When the width is b μm, the height is c μm, and the pitch is d μm, the following relationship is satisfied: d / 2 ≦ b ≦ d (3) c ≧ b / 4 (4) The optical sheet according to claim 3, wherein