JP2951525B2 - Surface light source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Industrial applications]

The present invention relates to a film lens and a surface light source using the same, and is particularly useful for a backlight of a display device such as a liquid crystal display device, a lighting advertisement, a traffic sign, and the like.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view schematically showing a conventional example of a surface light source for a backlight of a liquid crystal display device. The surface light source 100 shown in FIG. 4 includes a light guide plate 1, a light reflection layer 2 formed on the back surface of the light guide plate 1, and a linear or point disposed adjacent to at least one side end of the light guide plate 1. A light source 3, a light guide plate 1, a film lens 4 provided on the surface opposite to the light reflection layer 2, a light source light reflection mirror 5, and the like.

The light guide plate 1 is made of a transparent parallel flat plate. Light is incident from a side end face, and the total internal reflection inside the flat plate is used.
The light is propagated throughout the light guide plate 1, and a part of the propagated light is diffused and reflected by a light-scattering light reflection layer 2 provided on the back surface of the light guide plate 1 to be less than a critical angle. Light is emitted from the surface of the light plate 1 (Japanese Utility Model Application Laid-Open No. 55-16220).
1).

However, with this configuration alone, the diffusion angle of the emitted light is too wide, so that the film lens 4 is arranged on the light guide plate 1 so that the emitted light is appropriately condensed.
The film lens 4 has projections (micro-unit lenses) on the front surface and a smooth rear surface.
The diffused radiated light can be uniformly and isotropically diffused in a desired angle range by utilizing the light converging function of the lens, with the lens surface facing up (see Japanese Utility Model Application Laid-Open No. 4-10720).
1, JP-A-5-119218, JP-A-5-127159
etc).

[0005]

As shown in FIG. 5, the conventional surface light source described above has two film lenses 4-1 and 4-1.
It is conceivable to control the diffusion angle in two directions (vertical direction, horizontal direction) by using 4-2 in combination such that the ridge lines are orthogonal.

However, the two film lenses 4-1 and 4
-2, the lower film lens 4
−1, a uniform interference fringe (e.g., Newton's ring) is generated between the unit lens 42 on the front surface and the smooth surface on the back surface of the upper film lens 4-2, thereby deteriorating the image quality. .

An object of the present invention is to provide a film lens which does not generate interference fringes having the same thickness even when the film lens is used by being overlapped with another film lens or the like, and a surface light source using the same.

[0008]

In order to solve the above-mentioned problems, a first aspect of the present invention is to provide a light guide comprising a light-transmitting flat plate,
A light source unit provided adjacent to both or one of the side end surfaces of the light guide, a light reflection layer formed on the back surface of the light guide, and stacked on a light emission surface of the light guide, A first film lens having a lens array in which micro unit lenses are arranged one-dimensionally or two-dimensionally is formed on a surface thereof, and a first film lens is laminated on the lens array of the first film lens. A second film lens laminated toward the front side of the film lens, wherein the second film lens forms a minute projection partially or entirely on a surface in contact with the lens surface; Is the longest wavelength of the visible light spectrum of the light source observing the film lens, λ _max , and the angular radius of the light source when the observer sees the light source through a reflecting surface on the film lens surface is Δθ. And when, (1) Δh ≧ λ _max / 2Δθ ^{2 The} microprojections have a non-periodic one-dimensional and two-dimensional array, and the width Δx of the microprojections is [Expression ² ] Δx ≦ 100 μm, and the average distance d between the adjacent minute projections satisfies the condition of Equation 3 with respect to the period P of the unit lens. d <2P is a surface light source characterized by the following.

[0009]

[0010]

According to the present invention, minute projections satisfying a predetermined condition are provided on the surface superimposed on the lens surface on which the minute unit lens is formed, so that the occurrence of interference fringes having the same thickness can be suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments will be described in more detail with reference to the drawings and the like. FIG. 1 is a perspective view showing an embodiment of a film lens according to the present invention, FIG. 2 is a schematic diagram illustrating the principle of the film lens according to the present invention, and FIG.
1 is a perspective view showing an embodiment of a surface light source using a film lens according to the present invention. In addition, parts performing the same functions as those of the above-described conventional example will be described with the same reference numerals. The film lens 4 of the first embodiment has a columnar body (FIG. 1).
A columnar lens group (a lenticular lens in a broad sense) is formed on the surface by arranging unit lenses 42 adjacent to each other with their ridge directions parallel to each other.

The film lens 4 has a minute projection 41 formed on the back surface. The height Δh of the minute projection 41 is
When the longest wavelength of the visible light spectrum of the light source for observing the film lens 4 is λ _max , and the angular radius of the light source when the observer views the light source through the reflection surface on the film lens surface is Δθ, The condition of [Equation 1] is satisfied. [Equation 1] The Δh ≧ λ _max / 2Δθ ^2, the microprojections 41 are one-dimensional and two-dimensional array is non-periodic, the width Δx of the microprojections 41, expression (2)
Satisfies the conditions. [Equation 2] Δx ≦ 100 μm

Further, the average distance d between the adjacent minute projections 41 satisfies the condition of [Equation 3] with respect to the period P of the unit lens 42. [Equation 3] d <2P

In the present embodiment, like the film lenses 4-1 and 4-2 shown in FIG. 1, two lenses having the same structure are stacked so that the ridges of the unit lenses 42 are orthogonal to each other. As shown in FIG. 3, the light guide plate 1, the reflection layer 2, the light source 3,
The surface light source 100 is used in combination with the light source light reflection plate 5 and the like.

Next, the height of the minute projections 41 formed on the back surface of the film lens 4 of the present embodiment and the conditions for eliminating the equal-thickness interference fringes on the laminated surface of the film lenses 4 and 4 will be described. In the present invention, as shown in FIG. 2, a minute projection 41 is provided on the back surface of the film lens 4-1 on the front surface side, and a gap H _(x) between the film lens 4-1 and the film lens 4-2 is provided. , Thereby suppressing the occurrence of equal thickness interference fringes (upper concept of Newton rings) due to interference between the light ray L ₁ reflected at the interface S ₁ and the light ray L ₂ reflected at the interface S _2. .

At this time, as the equal-thickness interference fringes, the full-thickness interference fringes are the same-thickness interference fringes of the minute projections 41 and the same-thickness interference fringes other than the minute projections 41 (peripheral portion). It is necessary to consider that. Of these, the microprojections 4
Regarding the interference fringes other than 1 (peripheral portion), the thickness H _(x) of the void layer (air layer) in this case is the minute protrusion 41.
Is the sum of the thickness h _(x) when the film lenses 4-1 and 4-2 are directly contacted and laminated, and the height Δh of the minute protrusion 41. That is, [Equation 4] H _(x) = h _(x) + Δh Here, since Δh> 0, even _if 0 ≦ h _(x) (that is, h _(x) → 0 and asymptotically approaches 0 ₎ [Equation 5] H _(x) ≧ Δh> 0, and H _(x) does not gradually approach 0.

The equal thickness interference fringes disappear as the thickness H of the gap increases. Therefore, the lower limit value of H at which the equal-thickness interference fringes disappear due to an increase in H is obtained, and this is substituted into [Equation 5] to obtain the conditions for eliminating the equal-thickness interference fringes around the microprojections 41.

Hereinafter, this condition will be calculated. `` Wave optics ''
(Hiroshi Kubota, published by Iwanami Shoten, 4th print on August 30, 1975) According to pages 87 to 89, when the light source has a spatial spread, the observer passes through the reflective surfaces S ₁ and S ₂ . The angle radius of the external light source 7 viewed (observing the film lens 4 from the outside) is Δθ [radian], and the wavelength of the light source light is λ.
[Μm], and when the thickness of the gap is H [μm], it is known that if [Equation 6] Δθ≪ (λ / 2H) ^1/2 , equal thickness interference fringes are recognized. Therefore, from Expression 6, when a condition under which the equal-thickness interference fringe is not visible (a condition under which no interference fringe is generated) is obtained for H _(x) , Expression 7 is obtained. H _(x) ≧ λ / 2Δθ ² . By substituting [Equation 7] into [Equation 5], the minute projection 4
It is derived that the height Δh of 1 should be as follows: Δh ≧ λ / 2Δθ ² [μm]

The above is a case of a monochromatic light source. However, for a light source having a normally used emission spectrum distribution,
Since [Equation 8] is directly proportional to λ, the light source spectrum (λ
_min ≦ λ ≦ λ _max ), the upper limit value λ of the spectrum distribution
_{If max} satisfies [Equation 8], it can be said that all the remaining λ satisfies [Equation 8]. Accordingly, the height of the conditions of the minute projection 41 on the light source having a equation (1) Δh ≧ λ _max / 2Δθ ² [μm] is the spectral distribution.

Now, when a specific numerical value of [Equation 1] is obtained,
Assuming that the surface of the film lens 4 is observed using white light of 0.38 μm ≦ λ ≦ 0.78 μm as the external light source 7,
Further, if the angular radius of the external light source 7 is normally set to 10 ° ≦ Δθ ≦ 120 °, that is, 0.175 [rad] ≦ Δθ ≦ 2.094 [rad] by indoor lighting or natural light from a window, Δ is the largest on the right side of [Equation 1], Δ
θ = 0.175 [rad] and λ _max = 0.78 [μ
[Equation 9] Δh ≧ 12.5 [μm] is obtained as a value corresponding to [m].

[Equation 8], [Equation 1], and [Equation 9] are minimum necessary conditions, but the following additional conditions are added. In other words, when the film lens 4 is made of an object that can be regarded as a completely rigid body, it is sufficient to support at least three projections that are not on the same straight line (form a vertex of a triangle). But,
When the film lens 4 is made of a thin and flexible object made of, for example, a synthetic resin, if the distance between the minute projections 41 is too large, the film lens 4 bends at the minute projection 41, and h _(x) Is that H _(x) is [Equation 8], [Equation 1],
The conditions of [Equation 9] and [Equation 5] are not satisfied.

Therefore, in this case, even if bending occurs,
The microprojections 41 on the back surface are provided with sufficient density so that the conditions of [Equation 8], [Equation 1], [Equation 9] and [Equation 5] are always satisfied. As a standard of the density of the minute projections 41, generally, the period P of the unit lens 42 of the lower film lens 4-2 is not more than twice, more preferably, not more than 1/2, two-dimensionally. Make it distributed. That is, the average distance d between the adjacent minute projections 41 may satisfy the condition of [Equation 3] with respect to the period P of the unit lens 42. [ Equation 3] d <2p Here, the condition of [Equation 3] will be further described with reference to FIG. For simplicity, among the small projections 41,
If the three nearest points A, B, and C form an equilateral triangle △ ABC, and the film lens 4 has only a linear (one-dimensional) array of the unit lenses 42, FIG. 16A and FIG. As shown, when the distance AB between the two micro projections is equal to the distance BC = the distance CA = 2P, the micro projections A and B are
When contacting 2-1 and 42-3, focusing only on the x-axis direction, it appears that there is a unit lens 42-2 that does not contact the minute projections in the middle of the minute projections A and B. However, when viewed two-dimensionally, the unit lens 42-2 is supported by the minute projections C separated in the y-axis direction. In this way, all the unit lenses 42 are not leaked and the minute projections 4
As shown in FIGS. 16 (C) and 16 (D), the film lens 4
The contact due to deflection between -1 and 4-2 is minimized. Also, experimentally, if d exceeds P starting from d = 2P, even if Δh and Δx satisfy the conditions of [Equation 1] and [Equation 2], the equal thickness interference fringes are visually observed. It has been confirmed that it will begin. Therefore, the condition of [Equation 3] is obtained. In this way, almost every two of the unit lenses 42 are supported by one minute projection 41, and the influence of bending is eliminated. However, if the average distance d is too small and the minute projections 41 are too dense, the diffusion angle of the emitted light becomes too wide, so it is preferable to select an appropriate range.

Next, the interference fringes having the same thickness of the minute projections 41 will be described. H _(x) → 0 (convergence) near the minute protrusion 41
Therefore, interference fringes of equal thickness are inevitable. As means for practically avoiding this, the distribution of the minute projections 41
This is to arrange them randomly without any periodicity in one dimension or two dimensions, and to make the width ΔX of the minute projections 41 invisible. By doing so, even if the interference fringes having the same thickness are generated, they are localized only in the region of the minute projections 41, and therefore are not visually recognized.

However, if the minute projections 41 are periodically arranged, the minute projections 41 and the unit lens 42 always contact at a certain period. The fringes are integrated and visually observed as interference fringes. The arrangement of the microprojections 41 is aperiodic, so that the interference fringes of the microprojections 41 are
When observed from a distance, the light and dark are randomly integrated and become zero,
It is no longer visible. Therefore, if the width ΔX of the minute projections 41 is usually about 100 μm or less, the object can be achieved in practical use. That is, it suffices to satisfy [Equation 2]. [Equation 2] Δx ≦ 100 μm

The fine projections 41 are preferably colorless and transparent, and the manufacturing method thereof is also the mechanical processing such as embossing (pressing), sandblasting or the like on the rear surface of the film lens 4 by hot pressing, or the transparent resin. A casting method or a method in which a coating material in which transparent fine particles are dispersed in a transparent binder is applied by spray coating, roll coating, or the like is used. 15-30 μm as transparent fine particles
m acrylic beads, polycarbonate beads and the like are preferably used. If the thickness is 15 μm or less, the transparency of the film lens is lost, and if it is 30 μm or more, the suitability for printing and coating is poor. The refractive index of the beads is preferably in the range of about 1.60 to 1.00, and the concentration of the beads is preferably 2 to 5% of the binder resin. The binder resin is transparent and has a refractive index of 1.60.
A range of about 1.00 to about 1.00 is used. Here, since the purpose is not to refract light, it is preferable to make the refractive index of the binder resin match that of the beads as much as possible. Examples of this resin include acrylic, polystyrene, polyester, and vinyl polymers. Also, in addition to acrylic beads, a method in which transparent fine particles such as calcium carbonate, silica, acrylic resin, etc. are dispersed in a transparent binder is applied, and a method of causing the fine particles to appear on the surface of the coating film, or No. 223883, U.S. Pat. No. 45
No. 76850, etc., may be used a method of molding an ultraviolet or electron beam curable resin liquid on a roll intaglio plate such that the surface becomes matte and has fine irregularities.

Further, the fine projections 41 can suppress the occurrence of interference fringes having the same thickness without losing the function of the film lens 4, and can be formed at random so that when they are combined with a liquid crystal cell, Moire generation can be prevented. Further, it is possible to make the reflection dots printed on the backlight acrylic plate less visible.

The present invention is not limited to the embodiments described above, but can be variously modified and changed, and they are also within the scope of the present invention. The lens sheet 4 of the present invention includes, for example,
As shown in FIG. 6, a columnar lens group (a lenticular lens in a broad sense) in which columnar unit lenses 42 are arranged adjacent to each other with their ridge lines parallel to each other, or as shown in FIG.
A fly's eye lens is used in which a large number of projecting unit lenses 42 each having an independent periphery such as a hemisphere are arranged in a two-dimensional direction.
Here, the sectional shape of the unit lens 42 is as shown in FIG.
A continuous smooth curve such as a circle, an ellipse, a cardioid, an egg shape of Rankin, a cycloid, or an involute curve as shown in FIG. Use the whole. These unit lenses 42 may be convex lenses as shown in FIG. 12 or concave lenses as shown in FIG. Among these, preferred are ease of design, manufacture, light collection, light diffusion characteristics (half value angle, low side lobe light (peak of brightness generated in an oblique direction), isotropic brightness within half value angle, It is a column or an elliptical column from the viewpoint of luminance in the normal direction). In particular, an ellipse having the long axis in the normal direction of the surface light source is preferable because of its high luminance. Long axis / short axis = 1.
The range of 27 to 1.85 is particularly good.

These film lenses 4 can be used in a single lens configuration. However, in order to control the light diffusion angles in two directions (vertical and horizontal directions) using a columnar lens, FIGS. As shown in the drawing, two film lenses 4-1 and 4-
2 may be stacked such that their ridges are orthogonal. In this case, the direction of the lens surfaces should be the same as shown in FIG. 15 for the best light transmission and the best. However, of course, the lenses of each film lens 4 face each other (lens surface). Is sandwiched between two film lenses 4,
The minute projection 41 is formed on one of the lens surfaces.) The film lens 4 may be obtained by integrally molding a light-transmitting base material as shown in FIG. 6, or as shown in FIG. The unit lens 42 may be formed on a light transmitting flat plate (or sheet) 44.

This film lens 4 is formed from a light-transmitting substrate. Here, as the translucent substrate, polymethyl methacrylate, a homo- or copolymer of acrylate or methacrylate such as polymethyl acrylate, polyethylene terephthalate, polyester such as polybutylene terephthalate, polycarbonate, polystyrene , A thermoplastic resin such as polymethylpentene, or an acrylate such as a polyfunctional urethane acrylate or polyester acrylate cross-linked by ultraviolet rays or electron beams,
Transparent resin such as unsaturated polyester, transparent ceramics such as transparent glass, and the like are used.

When this translucent substrate is used as the film lens 4, the total thickness is usually about 20 to 1000 μm.

As a method for forming a lens shape, for example, a known hot pressing method (described in Japanese Patent Application Laid-Open No. 56-157310), an ultraviolet-curable thermoplastic resin film, which is embossed with a roll embossing plate, A method of curing the film by irradiating ultraviolet rays (Japanese Unexamined Patent Publication No.
JP-A-156273), an ultraviolet or electron beam curable resin liquid is applied to a rotating roll intaglio engraved with a lens shape, and after filling into the concave portion, a transparent substrate film is coated on the roll intaglio via the resin liquid. A method in which a resin cured by irradiating an ultraviolet ray or an electron beam while being cured and a substrate film adhered thereto are released from the roll intaglio, and the lens shape of the roll intaglio is shaped into a cured resin layer (Japanese Patent Laid-Open No. Hei 3-223883). No. 4,576,850). of course,
These methods can be applied to the case where the minute projections 41 are formed.

The translucency required of the translucent substrate must be selected so as to transmit the diffused light at a minimum so as not to hinder the use of each application. ,
Depending on the application, it may be colored transparent or matte translucent. Here, the term “matte transparency” refers to the property of transmitting transmitted light almost uniformly and isotropically in all directions within a semi-solid angle, and is used synonymously with light isotropic diffusion. That is, matte transparency means that the angle between the surface of the transparent substrate and the normal direction is θ.
, The angle distribution I of transmitted light intensity when a parallel light beam is incident from the back surface (incident angle i = 0 °)
⁰ (θ) is a cos distribution [I ⁰ (θ) = I ⁰ _mD cos θ,
−90 ° ≦ θ ≦ 90 °], where θ is the angle between the normal N and I ⁰
_{The mD} means that the transmitted light intensity in the normal direction or a distribution similar thereto is obtained.

As shown in FIG. 1, the minute projections 41 are formed by the unit lens 42 of the film lens 4-1 and the film lens 4-.
It is an object of the present invention to suppress the occurrence of an equal-thickness interference fringe formed between the back surface of the light emitting device 2 and the back surface thereof.

If this purpose is achieved, the fine projections 4
Although 1 may have any uneven shape, the most preferable embodiments are shown in FIGS. 1, 6, and 6 in terms of obtaining a uniform luminance angle distribution within a desired diffusion angle and a uniform luminance distribution within a light source surface. 9, random irregularities (for example, a grain pattern, a satin pattern, etc.) are formed on the entire back surface of the film lens 4 as shown in FIG.

As shown in FIG. 11, the minute projections 41
It is also possible to use a pattern in which dot-like patterns such as halftone dots are distributed and arranged in a plane. However, since the pattern 41 is conspicuous in this case, the matting agent is applied to the film lens 4.
It is necessary to devise measures such as dispersing it in. Further, a smooth surface may be provided between the minute protrusion 41 and the adjacent minute protrusion 41, as shown in FIGS. 2 and 11. Particularly, when uniform emission of emitted light is intended, the minute protrusion 41 may be used. Thus, a fine projection or a rough surface (not shown) having a lower height can be formed. Of course, since such a low height of the fine projections or the rough surface satisfies [Equation 1], no interference fringes of equal thickness are generated.

The surface light source of the present invention has the structure shown in the perspective view of FIG. 3, FIG. 7 or FIG. A light guide plate 1; a linear or point light source 3 installed adjacent to at least one of its side edges; a light reflection layer 2 on the back surface of the light guide plate; And the film lens 4 as a minimum configuration. Usually, a light source light reflecting mirror 5, a housing (not shown) that houses the entire light source, and a light emitting surface is a window, a power supply (not shown), and the like are also attached thereto.

The opposite side of the light reflecting layer of the light guide plate 1 is a flat surface and has a surface roughness (10-point average roughness R according to JIS-B-0601).
(measured by z or the like) is finished to the wavelength of the light source light or less.
Usually the light source is visible light, the wavelength of which is 0.4-0.8
μm, the surface roughness is set to 0.4 μm or less. As a method of finishing to such a degree of roughness, known methods, for example, hot pressing on a mirror plate, injection molding using a mirror-like shape,
Casting molding, precision polishing performed with an optical lens or the like may be used.

The material of the light guide plate 1 is selected from the same translucent materials as those of the film lens. Usually, acrylic or polycarbonate resin is used. The thickness of the light guide plate is usually about 1 to 10 mm.

As the light source 3, a line light source such as a fluorescent lamp is preferable from the viewpoint of selling uniform brightness, but a point light source such as an incandescent lamp can also be used. The light source 3 is provided separately from the side end of the light guide plate as shown in FIG.
It is also possible to cut out a part of the side end and partially or entirely embed it in the light guide plate. The light source 3 can also be installed on the other side end of the light guide plate 1 from the viewpoint of improving the uniformity in the plane of high luminance and luminance. As the light source light reflecting mirror 5, a known one, for example, a parabolic column, a hyperbolic column, an elliptic column, or the like having a metal deposited on the inner surface of a plate is used.

The film lens 4-2 is placed on the smooth plane of the light guide plate 1. At this time, the film lens 4-2 is placed on the outer side (opposite side of the plane) with the minute projections 41 facing inward (flat side). In this case, the minute protrusion between the film lens 4-2 mounted on the light guide plate 1 and the smooth surface 10 of the light guide plate 1 has a height {h whose longest wavelength of the light source light spectrum of the light source 3 of the surface light source 3}. It is necessary to make it higher than _max . [Equation 10] Δh ≧ Λ _max The reason is that by allowing at least a part of the gap 9 having the wavelength A or more of the light source light, the light wavelength between the light guide plate 1 and the back surface of the film lens 4 is reduced. The above air layer (the refractive index is lower than that of the light guide plate 1) is partially formed. At the interface between the air layer and the smooth surface of the light guide plate 1, total reflection of light occurs, and the light is not emitted at that location, but is distributed farther (to the light source 3) of the light guide plate 1. Is done. In a portion where the light guide plate 1 and the minute protrusion 41 on the back surface of the film lens 4 are in direct contact, light is transmitted to the outside and emitted. Therefore, the amount of light output from the surface of the light guide plate 1 and the amount of light distributed to the entire light guide plate 1 are balanced, and a surface light source with uniform brightness over the entire surface is obtained. As can be seen from [Equation 1], under normal indoor use conditions, the condition of [Equation 1] and the condition of [Equation 10] have a common part. When the film lens of the present invention is used, [Equation 1] and [Equation 1]
0]. Next, the film lens 4-1 of the present invention is placed on the film lens 4-2 as shown in FIG.

The light reflecting layer 2 is a layer having a function of diffusing and reflecting light, and can be configured as follows. On one surface of the light guide plate layer, a white layer in which a pigment having high concealing property and high whiteness, for example, a powder of titanium dioxide, aluminum or the like is dispersed is formed by painting or the like. A metal thin film layer is formed by plating or vapor-depositing a metal such as aluminum, chromium, silver, or the like on the uneven pattern surface of the light guide plate having the matte fine unevenness formed by sand brightening, embossing, or the like. A metal thin film layer is formed on a white layer having a low concealing property and simply formed by coating a matte surface. It may be formed in a halftone dot-like white layer, and the area ratio may be increased as the distance from the light source increases, so that the attenuation of the light amount of the light source may be corrected.

Note that the surface light source 100 of the present invention is
FIG. 8 shows a configuration in the case of using as a backlight (back light source) of a transmission type display device such as D. That is, the transmission type display device 6 may be laminated on the lens surface (the side where the unit lens 42 is provided) of the film lens 4-1 of the surface light source 100 of the present invention. Further, the transmission type display device 6 may be stacked on the surface light source 100 as shown in FIG.

The diffusion angle is effective for evaluating the light distribution state of the surface light source. As the diffusion angle, for example, a half-value angle θ _H is used. This is because when the transmitted light luminance (or intensity) is a decreasing function I (θ) of the angle θ from the normal to the light emitting surface,
Twice the angle θ _{H such that} I (θ _H ) = I (θ) / 2, that is, 2
Defined as θ _H.

[Production Example] Material substrate: transparent biaxially stretched PET film (100 μm thick)
m), a transparent adhesive layer is applied so as to have a thickness of about 1 μm, and an ultraviolet-curable resin mainly containing a urethane acrylate prepolymer for forming a pattern of the unit lens 42 is applied thereon, After the resin coating is cured (solidified), the mold is released, so that an elliptic cylinder having a pitch of 110 μm and a unit lens shape of long axis length / short axis length = 1.85 is adjacent to the elliptic cylinder so that the ridge lines are parallel to each other. FIG. 12 arranged as
A film lens having a linear lens shape as described above is used. Microprojections were formed on the surface of the film lens opposite to the lens forming surface in the following manner. [Composition] Beads: Crosslinked acrylic resin having a particle size of 20 μm (MBX-20, manufactured by Sekisui Chemical Co., Ltd.) Binder: Chemical X-MD manufactured by Showa Ink Industry Co., Ltd.
Medium (mixture of vinyl chloride / vinyl acetate copolymer and acrylic) Antistatic agent: DEHYDAT 80 by Henkel Hakusui Co., Ltd.
X

Manufacturing Process An ink containing 3% of the above-mentioned beads for the above-mentioned binder resin and 20% of the above-mentioned antistatic agent for the above-mentioned binder resin is diluted with a solvent of MEK: toluene: IPA = 2: 2: 1. The viscosity was 17 seconds with a Zahn cup viscometer # 3.
This ink was applied to the non-lens surface of the above substrate by a gravure method (a gravure plate was a solid plate with an angle of 48 lines / cm set by an electronic engraving machine and heliocrissograph). Thereafter, the solvent was dried to solidify the coating film. On this coating film, microprojections having a height Δh = 15 to 20 μm were formed in a random arrangement at an average interval d = 150 μm.

[0046]

As described above, the film lens of the present invention is provided with the minute projections having a predetermined size distribution on the back surface (the surface opposite to the lens surface). There is an effect that the generation of the equal thickness interference fringes can be suppressed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a film lens according to the present invention.

FIG. 2 is a schematic diagram illustrating the principle of a film lens according to the present invention.

FIG. 3 is a perspective view showing one embodiment of a surface light source using a film lens according to the present invention.

FIG. 4 is a perspective view showing a conventional example of a surface light source for a backlight of a liquid crystal display device.

FIG. 5 is a perspective view showing another conventional example of a surface light source for a backlight of a liquid crystal display device.

FIG. 6 is a perspective view showing another embodiment of the film lens of the present invention (in the case where minute projections are directly formed on the back surface using a triangular prism type lenticular lens).

FIG. 7 is a perspective view showing another embodiment of the surface light source of the present invention.

FIG. 8 is a perspective view showing a case where the surface light source according to the example is used as a back light source of a liquid crystal display device.

FIG. 9 is a perspective view showing another embodiment of the film lens of the present invention (in the case where minute projections on the back surface are formed in another layer using a triangular prism type lenticular lens).

FIG. 10 is a perspective view showing another embodiment (when formed on a transparent substrate) of the film lens of the present invention.

FIG. 11 is a perspective view showing another embodiment of the film lens of the present invention (in the case where minute projections are partially formed).

FIG. 12 is a perspective view showing another embodiment (in the case of a convex lenticular cylindrical lenticular lens) of the film lens of the present invention.

FIG. 13 is a perspective view showing another embodiment (in the case of a concave lenticular cylindrical lenticular lens) of the film lens of the present invention.

FIG. 14 is a perspective view showing another embodiment of the film lens of the present invention (in the case of a protruding unit lens whose periphery is independent such as a hemisphere).

FIG. 15 shows another embodiment of the film lens of the present invention (when two film lenses are stacked so that their axes are orthogonal to each other).
FIG.

FIG. 16 is an explanatory diagram showing a relationship between a minute projection and a unit lens.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light guide plate 2 light reflection layer 3 light source (unit) 4, 4-1, 4-2 film lens 41 lens unit 42 minute projection 44 transparent flat plate 5 reflecting mirror 6 transmission type display device 7 external light source 100 surface light source 200 display device

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-3-120037 (JP, A) JP-A-5-313164 (JP, A) JP-A-5-313004 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G02B 5/02 G02B 3/00

Claims (1)

(57) [Claims] 1. A light guide comprising a light- transmitting flat plate, and a light guide provided adjacent to both or one of side end surfaces of the light guide.
Light source unit, a light reflecting layer formed on the back surface of the light guide, and a micro unit lens stacked on the light emission surface of the light guide.
One-dimensional or two-dimensional lens array is formed on the surface
A first film lens formed, and a lens array of the first film lens,
With the micro projections facing the front side of the first film lens
A second film lens that is laminated , wherein the second film lens has minute projections formed partially or entirely on a surface that is in contact with the lens surface, and the height Δh of the minute projections is When the longest wavelength of the visible light spectrum of the light source for observing the lens is λ _max , and when the angular radius of the light source is Δθ when the light source is viewed from the observer through the reflecting surface on the film lens surface,
The condition of [Equation 1] is satisfied, and [Equation 1] Δh ≧ λ _max / 2Δθ ^{2 The} one-dimensional and two-dimensional arrangement of the minute projections is aperiodic, and the width Δx of the minute projection is 2] Δx ≦ 100 μm, and the average distance d between the adjacent microprojections satisfies the condition of Equation 3 with respect to the period P of the unit lens. D <2P A surface light source characterized by the following: "