JP2001354792A - Optical interface film - Google Patents

Abstract

(57) [Summary] [PROBLEMS] As a new optical functional material having sufficient optical interface function even when used by bonding to an optical functional material such as a sidelight type backlight light guide plate, and having an optical interface function. A useful optical interface film is provided. SOLUTION: This film is a film containing bubbles inside a transparent resin, and the shape of the bubbles is long in the film surface direction and thin in the film thickness direction, and the average number of bubbles in the film thickness direction is 0. 0.8 to 4.0 optical interface films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interface film suitably used for a backlight of a liquid crystal display, a lighting device, and the like.

[0002]

2. Description of the Related Art In recent years, many displays using liquid crystal have been used as display devices for personal computers, televisions, mobile phones, and the like. Since these liquid crystal displays are not themselves luminous bodies, illuminated display is possible by irradiating light from behind using a backlight.

In order to improve the image quality of a liquid crystal display,
Since the entire surface of the backlight needs to emit light uniformly, a surface light source structure called a sidelight type (also called an edge light type) or a direct type is used. Above all, a sidelight type, that is, a type that irradiates light from a side end face to a screen, is applied to a thin liquid crystal display used for a notebook-type personal computer or the like in which thinning and miniaturization are desired.

[0004] The sidelight type backlight employs a light guide plate method in which light is transmitted only uniformly to the side of the light source and only the surrounding area becomes bright. For example, a light source such as a fluorescent tube or an LED is placed on a side surface of the light guide plate, and light is introduced into the light guide plate from the side surface of the light guide plate and propagates in the plane to form a planar light source.

However, the light guide plate alone has sufficient uniformity,
Since it is not possible to obtain directivity of light, it is necessary to adjust the output direction of the light flux emitted from the light guide plate by using a large number of optical functional film materials such as a diffusion film and a prism sheet, and as a result, The sidelight type backlight is usually composed of 3 to 5 film materials.

On the other hand, a film containing bubbles inside a transparent resin is known as an opaque white film.

[0007]

However, in order for a large number of films incorporated in a sidelight type backlight to exhibit a light diffusing function, it is necessary to arrange them in an overlapping manner with an air layer therebetween. They cannot be glued together. In order to insert an air layer between them and fix them, it is necessary for each film to have sufficient stiffness, so each film must be thick and the entire backlight must be thick. Absent. Further, a frame for holding each film is required, and it takes a lot of time and labor to assemble the film. In addition, a slight dimensional change causes a phenomenon in which the film is wavy, and the in-plane uniformity of luminance is likely to be impaired.

[0008] These problems have become serious problems especially in large-sized large-sized backlights corresponding to the recent demand for large-sized screens. As the generated heat also becomes higher in temperature, the film is more likely to be lifted.

[0009] On the other hand, small displays are often mounted mainly on portable devices, and therefore there is a strong need for thinner and lighter displays. For this reason, it is desired that the film be as thin as possible and the number of parts be reduced.

[0010] All of the above-mentioned problems are caused by the fact that the prior art requires an air layer to exist between the light guide plate and the diffusion film or prism sheet, and cannot be bonded to each other. . That is, if the diffusion film is adhered to the surface of the light guide plate, the function of the light guide plate, that is, the function of transmitting light to a point far from the light source is lost. This is because the function of the light guide plate is exhibited when the surface of the light guide plate, in other words, the interface between the light guide plate and the outside air exists as an optical interface.

Accordingly, the present invention solves the above-mentioned problems by providing a new optical function having an optical interface function, which can exhibit a sufficient optical interface function even when used by bonding to an optical function material such as a light guide plate. An object is to provide an optical interface film useful as a material.

[0012]

In order to achieve the above object, the present invention provides a film containing bubbles inside a transparent resin, wherein the shape of the bubbles is long in a film surface direction and is long in a film thickness direction. Is an optical interface film having a thin layer shape and an average number of bubbles in the film thickness direction of 0.8 to 4.0.

The present invention also provides a laminated film comprising at least two layers, an optical interface layer containing air bubbles in a transparent resin and a light transmitting layer substantially containing no air bubbles. The shape of the bubbles contained in the layer is long in the film surface direction and thin in the film thickness direction,
The optical interface film is characterized in that the average number of bubbles in the film thickness direction is 0.8 to 4.0.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The optical interface film of the present invention can exhibit the same function as the optical interface function exhibited by an optically planar interface even when installed without an air layer interposed. As described above, the structure for exhibiting the function is a new optical function material included in the film, and its operation will be described first.

First, in order to facilitate understanding of the present invention, a conventional backlight mechanism will be described.

In many sidelight type backlights,
A light guide plate in which a transparent resin such as an acrylic resin or a cyclic polyolefin resin is molded into a planar shape is used. The back surface of the light guide plate is provided with irregularities and printing dots that increase in density as the distance from the light source increases, but the surface is generally a smooth surface.

A light source such as a fluorescent tube is disposed at an end of the light guide plate, and a light beam is introduced into the light guide plate from a side end surface of the light guide plate. Due to the relationship between the refractive index of the transparent resin and the refractive index of the surrounding air, most of the light is totally reflected to satisfy the critical reflection condition, and propagates inside the light guide plate without being emitted to the outside.

Of the light beam propagating inside the light guide plate, the light beam that has reached the irregularities and print dots provided on the back surface of the light guide plate is:
Since the critical reflection condition is broken, the light is refracted or reflected and emitted out of the light guide plate. Therefore, by devising the shape and density of unevenness and printing dots, their distribution and arrangement, that is, coarsely near the light source and denser as the distance from the light source, uniform brightness is obtained in the plane. .

Therefore, in such a backlight, if another resin or film is adhered or adhered to the surface of the light guide plate which is formed smoothly, the above critical reflection condition is broken, and light is propagated inside the light guide plate. In this case, uniform brightness in the plane cannot be obtained.

That is, since the surface of the light guide plate needs to be smooth and an air layer is always required on the surface, it is impossible to bond another optical function film such as a light diffusion film to the light guide plate. Met.

For this reason, the conventional backlight has many problems as follows. For example, although a film thickness of about 5 μm to 20 μm is satisfactory for exerting the light diffusion function, the light diffusion film needs to have a thickness of 100 μm or more due to its need for self-supporting properties. . For this reason, in the related art, “thinness” which is one of the features of the liquid crystal display is impaired, and the light efficiency is reduced. Each of the light guide plate and the light diffusing film must be handled carefully so as not to damage the surface. A frame is required to fix the light guide plate and the light diffusion film. Therefore, much work is required, and the productivity of the backlight is reduced. Deformation of the film due to the heat of the light source causes uneven brightness of the backlight.

These problems can be solved at once if a light diffusion film or the like disposed directly above the light guide plate can be bonded to the light guide plate. In the light diffusion film of the present invention, bubbles exist inside the film, and the shape and number of the bubbles are optimized. Therefore, even if there is no air layer on the surface of the light guide plate, the light guide plate and the air It can exert the same optical effect as the interface.

The film of the present invention is roughly classified into two embodiments. That is, one is a film containing bubbles inside a transparent resin, and the shape of the bubbles is long in the film surface direction and thin in the film thickness direction, and the average number of bubbles in the film thickness direction is small. 0.8 to 4.0 optical interface films. The other is an optical interface layer containing bubbles inside a transparent resin, and a light transmitting layer containing substantially no bubbles.
A laminated film consisting of at least two layers,
The shape of the bubbles contained in the optical interface layer is long in the film surface direction and thin in the film thickness direction, and the average number of bubbles in the film thickness direction is 0.8 to 4.0. It is a characteristic optical interface film.

The layer containing bubbles therein is made of a transparent resin such as a polyester resin and a resin incompatible with the resin.
Alternatively, after forming a sheet by melt extrusion and forming a sheet with inorganic particles as a main component, stretching is performed at least in a uniaxial direction, preferably in a biaxial direction to form a void having an incompatible resin and / or inorganic particles as a core. Can be obtained. Also, when a transparent resin is melt-extruded, a foaming agent is added and melt-extruded to form a sheet, and then a bubble is generated by internal pressure due to gasification of the foaming agent by a subsequent heat treatment or the like. A method such as dissolving a gas such as carbon dioxide gas in a supercritical state when melt-extruding a resin and adopting a method in which when the sheet is extruded into the atmosphere to form a sheet, the dissolved gas is vaporized to generate air bubbles. You can also.

In the present invention, it is necessary that the shape of the bubbles is long in the film surface direction and thin in the film thickness direction. By using such bubbles, an optical interface effect is exhibited.

In order to generate laminar bubbles, the melt-extruded sheet as described above can be obtained by stretching it in at least one axial direction, preferably in a biaxial direction. Therefore, as the transparent resin used in the present invention, those having biaxial stretching properties are preferable, and examples thereof include polyester resins, polyolefin resins, and polystyrene resins, and polyester resins are particularly preferable from the viewpoint of heat resistance and transparency. It is preferably used.

As the polyester resin, polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, polyester having 1,4-cyclohexanedimethanol as a copolymer component, and copolymers thereof are used. it can. As the acid component and the diol component to be copolymerized, aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, sulfonic acid metal base-containing dicarboxylic acids, alkylene glycols having 3 to 25 carbon atoms, and polyalkylene glycols are used. However, the present invention is not limited to this. Of these, transparency,
Polyethylene terephthalate and polyethylene-2,6-naphthalate are particularly preferred from the viewpoints of economy, void formation, and the like.

In this case, the resin which is incompatible with the polyester resin, which is the core of the void, is a resin having a phase separation structure in a sheet state after kneading, and a typical example is a polyolefin resin. Can be used.
Specifically, low density to high density polyethylene, isotactic, atactic, syndiotactic polypropylene, polymethylpentene, polystyrene and the like can be used. These incompatible resins are dispersed and blended in the polyester resin, and polymethylpentene having high incompatibility and a high heat distortion temperature in forming bubbles (voids) is most preferable. The compounding ratio is usually 3% by weight or more and 30% by weight or less, preferably 5% by weight or more and 25% by weight or less, more preferably 7% by weight or more and 20% by weight or less, from the viewpoint that void formation and light transmittance are not hindered as much as possible. It is desirable that:

In a polyester film in which such an incompatible resin is dispersed and blended, fine layered air bubbles having the incompatible resin as a nucleus are formed by stretching, and the interface between the polyester resin and the air bubbles is reduced. It becomes an optical interface element, and even if the optical interface element is not continuous, by controlling the arrangement of the optical interface element, it exhibits an optical interface function substantially equivalent to the case where an air layer exists on the light guide plate surface. Can be.

In order to exhibit the optical interface function, it is necessary to arrange the layered bubbles such that the average number of bubbles in the film thickness direction is 0.8 to 4.0.

Here, the average number of bubbles in the film thickness direction is defined as that a photograph of a cross section of the film is taken at any 10 points of the film, and a straight line parallel to the film thickness direction is set at an arbitrary position at each measurement point. The number of bubbles intersecting the straight line when drawn over is counted and obtained as an average value.

When the average number of bubbles is less than 0.8, the optical interface effect is reduced. When the average number of bubbles exceeds 4.0, light reflection by the bubbles cannot be ignored and the light transmittance decreases. From this viewpoint, the preferable range of the average number of bubbles is 1.0 to 2.0.
Individual.

In order to control the average number of bubbles in this range, a method of controlling the thickness and composition of the entire film, or a structure in which a resin layer substantially containing no bubbles and a laminated bubble-containing layer are laminated. And a method of controlling the thickness and composition of the bubble-containing layer.

The total light transmittance of the optical interface film of the present invention is preferably 70% or more, more preferably 85% or more, from the viewpoint of brightness when used as a backlight. Further, the haze is preferably 15% or less, more preferably 5% or less, in that the optical function design is easy.

The preferred size of the void, when observed from the cross-sectional direction of the film, is such that the major axis is about 3 to 20 (μm) and the minor axis is about 0.01 to 3 (μm) in terms of the light diffusion effect. Degree, that is, the value obtained by dividing the major axis by the minor axis is 1
When it is 0 or more, the optical interface effect is preferably high. More preferably, the flatness is 20 or more. However, when the flatness exceeds 1000, delamination tends to occur, which is not preferable in some cases. In the present invention, since the bubbles are long in the film surface direction and thin in the film thickness direction, when determining the flatness of the bubbles, the diameter in the film surface direction is defined as the long diameter,
What is necessary is just to make the diameter of a film thickness direction a short diameter.

The voids to be formed preferably have an independent shape, and the void formation rate is 10% in the layer.
% To 60%, preferably 15% to 55% in terms of mechanical strength and productivity.

Various additives other than the above-mentioned constituents can be added to the layer as long as the effects of the present invention are not lost. Specifically, organic and inorganic fine particles, pigments, dyes, fluorescent whitening agents, antioxidants, heat-resistant agents, light-proofing agents, weathering agents, antistatic agents, release agents, and the like can be used. Among these, the addition of a fluorescent whitening agent is preferable in that a brighter backlight can be obtained. The fluorescent whitening agent is preferably added in an amount of about 0.01 to 1% by weight based on the above resin component.

In the present invention, it is preferable from the viewpoint of mechanical strength and handleability that one layer substantially free of bubbles is laminated on one side of the layer containing bubbles or two layers are laminated on both sides thereof. . As a material constituting the layer containing substantially no air bubbles, the above polyester resin is preferable, and polyethylene terephthalate and polyethylene-2,6-naphthalate are preferable. Particularly, a polyester resin obtained by copolymerizing 1,4-cyclohexanedimethanol is more preferable because it is more excellent in transparency and can reduce loss of scattered light. In this layer, various additives such as those described above as additives for the microbubble-containing layer can be used as long as the effects of the present invention are not lost.

An organic or inorganic additive may be added to the optical interface film of the present invention (a layer containing substantially no air bubbles in the case of a laminated film) in order to impart handling properties represented by slip properties. Although it is possible, it is preferable to use organic fine particles in consideration of the refractive index difference from the polyester resin in order to suppress the loss of light as much as possible. Further, by providing a layer having a smaller refractive index than the polyester resin on the surface, loss due to reflection on the light diffusion film surface can be reduced. Such a layer is preferably an acrylic resin layer, and is preferably provided by coating, particularly so-called in-line coating, which is applied in the process of producing the film of the present invention. The acrylic resin to be used is not particularly limited, but is preferably an acrylic copolymer containing alkyl methacrylate such as methyl methacrylate, acrylic acid and its alkyl ester, acrylamide, and the like as main components. Polymerized ones are preferred.

The thickness of the optical interface film of the present invention is not particularly limited.
The thickness is preferably 1 μm to 10 μm from the viewpoint of the optical interface effect.

The optical interface film of the present invention can exhibit a further effect by forming another optical functional layer on the surface. For example, it is preferable to form a light diffusion layer, a fine prism array layer, a reflective polarizing layer, a light guide layer, and the like by coating or the like, or to form the optical functional layer as a laminated film.

The light-diffusing layer is a layer formed by coating a resin containing acrylic beads or glass beads having a spherical shape of 2 μm to 20 μm with an average thickness of 1 μm to 20 μm to form irregularities on the surface, or a transparent material having a different refractive index. Is dispersed in a transparent resin. The fine prism array layer has a vertex angle of 50 to 120 degrees, preferably 80 degrees.
A layer in which fine triangular prisms of degrees to 100 degrees are arranged without gaps, such as a layer formed of an ultraviolet curable resin or the like or a layer formed of a thermoplastic resin composition. Furthermore, as the reflective polarizing layer, a layer in which several hundred layers having different refractive index anisotropy are alternately laminated, or a layer in which flat particles having refractive index anisotropy are dispersed in a layer having substantially no birefringence. And a layer in which substantially isotropic flat particles are dispersed in a layer having a refractive index anisotropy, or a combination thereof.

In order to form these layers on the surface of the optical interface film of the present invention, it is preferable to form an easy-adhesion layer on the surface of the optical interface film. Resins used, for example, acrylic resins, melamine resins, polyester resins, and mixtures thereof can be used.

The optical interface film of the present invention can be effectively used as a backlight member mainly in the field of using a liquid crystal display, but is also suitable for a front light for a reflective display, and further for an electric sign. It can be used for

[Evaluation Method of Characteristics] Average number of bubbles in the film thickness direction Using a transmission electron microscope HU-12 manufactured by Hitachi, Ltd., cross-section of the film at any 10 points of the film (if the cut surface is perpendicular to the film surface, Observe a photograph by observing the direction of the film (arbitrary as to the direction of the film) and draw a straight line parallel to the film thickness direction at any position in each photograph and over the entire length of the film. The number of air bubbles is determined, and the average value is obtained.

B. The major axis, minor axis, and flatness of the bubble The cross section of the film is observed in the same manner as in A above. However, the cut surface is perpendicular to the film surface and parallel to the longitudinal direction of the film, and the cut surface is perpendicular to the film surface and the bubble-containing layer is observed in a direction perpendicular to the longitudinal direction of the film. Measure the diameter. The measurement is performed for 30 bubbles (60 total) in each direction.
Find the average value. The flatness is obtained by calculating the value obtained by dividing the major axis by the minor axis for each bubble, and calculating the average value.

C. Void ratio From the image observed in B above, the void portion was determined by using an image analyzer to determine the total void area per unit cross-sectional area.
The void fraction was calculated. D. Total light transmittance and haze Total visible light transmittance and haze were measured using a fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.).

E. Backlight Luminance (Optical Interface Function) As a sidelight method, halftone printing was performed on an acrylic plate having a thickness of 3 mm, and the end face was illuminated with a 6 W fluorescent tube.
At this time, the fluorescent tube is covered with a reflector film except in the direction of the light guide plate so that light loss does not occur. To prevent loss of light, and used as a backlight for evaluation. In such an apparatus, a film to be evaluated is arranged on the upper surface of the light guide plate (the surface on which the halftone dots are not printed), and a luminance meter (LS-L manufactured by Minolta Ltd.)
110) was used to measure the luminance. Brightness is 200mm ×
Divide the area of 200mm into 5mm x 5mm by 16
The points were measured, and the difference between the average value, the maximum value, and the minimum value was determined.

[0049]

Hereinafter, the present invention will be described with reference to Examples.
The present invention is not necessarily limited to this.

(Example 1) A composite film forming apparatus capable of forming a film in which a thin layer is laminated on one side by combining a resin from one main extruder and a resin from one sub-extruder is used. In a sub-extruder, 85% by weight of polyethylene terephthalate resin (hereinafter abbreviated as PET), 12% by weight of a polymethylpentene resin (hereinafter abbreviated as PMP), and polyethylene glycol having a molecular weight of 2000
A raw material chip obtained by uniformly mixing 3 wt% of PET copolymerized by weight was supplied, and a polyethylene terephthalate resin was supplied to a main extruder. In addition, each feed material used was vacuum-dried at 150 ° C. for 4 hours in advance.

Both extruders were heated to about 285 ° C., melt-extruded by a predetermined method, cooled on a mirror-finished cast drum by an electrostatic application method, and then subjected to a sub / main thickness ratio of 1 /.
Ten laminated sheets were prepared. This sheet is stretched 3.5 times in the longitudinal direction at 85 ° C., guided into a tenter while continuously gripping the ends with clips, and stretched 3.6 times in the width direction at 105 ° C. through a preheating zone of 85 ° C. And then 225 ° C
At a temperature of 5 seconds to form a 25 μm-thick optical interface film (composite film).

Acrylic resin was used as a binder on the surface of the layer consisting of only PET of this composite film, and acrylic beads were added thereto (trade name “MB” manufactured by Sekisui Plastics Co., Ltd.).
X-15 ") was mixed with 30 parts by weight, and coated and cured by a roll coating method so as to have a coating amount of 15 g / m ² to form a light diffusion layer.

On the other hand, an adhesive coating solution in which an acrylate copolymer resin and a crosslinking agent (epoxy resin) are dissolved in a solvent is applied to the surface of a layer in which PMP is mixed with PET (bubble-containing layer), and dried to form an adhesive layer. Provided.

The adhesive layer of the adhesive light-diffusing film thus obtained was adhered to the surface of the light guide plate to prepare a backlight, and the luminance was evaluated. Table 1 shows the results.

The backlight produced by using the optical interface film of the present invention has high brightness and uniformity even though the light diffusion film is directly attached to the surface of the light guide plate, and has an effective optical interface function. It was one that contained it.

Example 2 In an extruder, 85% by weight of polyethylene terephthalate resin (hereinafter abbreviated as PET), 12% by weight of a polymethylpentene resin (hereinafter abbreviated as PMP), and polyethylene glycol having a molecular weight of 2,000 were used. A raw material chip obtained by uniformly mixing 10% by weight of copolymerized PET and 3% by weight was supplied. In addition, what was previously vacuum-dried at 150 degreeC for 4 hours was used for the feed material.

The extruder was heated to about 285 ° C., melt-extruded by a predetermined method, and cooled on a mirror-surface cast drum by an electrostatic application method to prepare an extruded sheet.

This sheet is stretched 4.8 times in the longitudinal direction at 85 ° C., guided into a tenter while continuously gripping the ends with clips, passed through a preheating zone of 85 ° C. and stretched in the width direction at 105 ° C. The film was stretched 0 times and heat-treated at a temperature of 225 ° C. for 5 seconds to form an optical interface film having a thickness of 3 μm.

A light diffusing layer was formed on the surface of this film in the same manner as in Example 1, and an adhesive layer was provided on the opposite surface in the same manner as in Example 1.

The adhesive layer of the adhesive light-diffusing film thus obtained was adhered to the surface of the light guide plate to prepare a backlight, and the luminance was evaluated. The results are shown in Table 1.

The backlight produced by using the optical interface film of the present invention has high brightness and uniformity even though the light diffusion film is directly attached to the surface of the light guide plate, and has an effective optical interface function. It was one that contained it.

Example 3 A laminated sheet was prepared in the same manner as in Example 1.

This sheet is stretched 2.8 times in the longitudinal direction at 85 ° C., guided into a tenter while continuously gripping the ends with clips, and passed through a preheating zone of 85 ° C. in the width direction at 100 ° C. 3. The film was stretched 0-fold and heat-treated at a temperature of 225 ° C. for 5 seconds to prepare an optical interface film (composite film) having a thickness of 25 μm.

A light-diffusing layer was formed on the surface of the layer composed of only PET of the composite film in the same manner as in Example 1.
Further, an adhesive layer was provided in the same manner as in Example 1.

The adhesive layer of the adhesive light-diffusing film thus obtained was attached to the surface of the light guide plate, a backlight was prepared, and the luminance was evaluated. Table 1 shows the results.

The backlight produced by using the optical interface film of the present invention has high brightness and uniformity even though the light diffusion film is directly attached to the surface of the light guide plate, and has an effective optical interface function. It was one that contained it.

(Comparative Example 1) A polyethylene terephthalate resin was supplied to an extruder. In addition, what was previously vacuum-dried at 150 degreeC for 4 hours was used for the feed material.

The extruder was heated to about 285 ° C., melt-extruded by a predetermined method, and cooled on a mirror-like cast drum by an electrostatic application method to produce an extruded sheet.

The sheet was stretched 3.5 times in the longitudinal direction at 85 ° C., guided into a tenter while continuously gripping the ends with clips, passed through a 85 ° C. preheating zone, and 105 ° C. in the width direction. The film was stretched 6 times and heat-treated at a temperature of 225 ° C. for 5 seconds to form a transparent film having a thickness of 25 μm.

A light diffusing layer was formed on the surface of this film in the same manner as in Example 1, and an adhesive layer was provided on the opposite side in the same manner as in Example 1.

The adhesive layer of the adhesive light-diffusing film thus obtained was attached to the surface of the light guide plate, and a backlight was prepared to evaluate the luminance. The results are shown in Table 1.

Since the obtained film does not substantially contain air bubbles, when this transparent film is used, the uniformity is lost only by locally increasing the luminance near the light source, and the uniformity is lost. Had been lost.

Comparative Example 2 A laminated sheet was prepared in the same manner as in Example 1 except that the sub / main thickness ratio of the laminated sheet was set to １ ／, a composite film was prepared, and the light diffusing layer was formed. Formed and further provided with an adhesive layer.

The adhesive layer of the adhesive light-diffusing film thus obtained was adhered to the surface of the light guide plate, and a backlight was prepared to evaluate the luminance. Table 1 shows the results.

This composite film did not have high luminance because the average number of bubbles in the thickness direction was too large.

Comparative Example 3 A laminated sheet was prepared in the same manner as in Example 1 except that the sub / main thickness ratio of the laminated sheet was 1/50, a composite film was prepared, and the light diffusing layer was formed. Formed and further provided with an adhesive layer.

The adhesive layer of the adhesive light-diffusing film thus obtained was adhered to the surface of the light guide plate to prepare a backlight, and the luminance was evaluated. Table 1 shows the results.

Since the average number of bubbles in the thickness direction of this composite film was too small, uniformity of luminance could not be obtained.

(Comparative Example 4) A light diffusing film was prepared in the same manner as in Comparative Example 1 except that the adhesive layer was not provided, but curling was observed due to a difference in dimensional change between the light diffusing layer and the PET film layer. This caused the backlight to fail.

Then, when the film was thickened, the curl was reduced to a negligible level when the film thickness was 125 μm.

A light diffusion film having a film thickness of 125 μm and having no adhesive layer was produced in the same manner as in Comparative Example 1.
When assembled into the backlight without bonding to the surface of the light guide plate, it was 10 times more than the backlight created in Example 1.
It became as thick as 0 μm. In addition, a separately prepared frame is required for fixing the light diffusion film, and it takes much time and effort.

For reference, when the brightness of this backlight was evaluated, it was good as shown in Table 1. However, there was a problem that the film was thick, a mounting frame was required, and time was required.

[0083]

[Table 1]

In Examples 1 and 3 and Comparative Examples 2 and 3,
Bubbles were measured for a layer of PETMG mixed with PETMG.

[0085]

When the optical interface film of the present invention is used for a backlight, a sufficient optical interface function can be exhibited even if another optical functional material is directly adhered to the light guide plate surface without an air layer. it can. This solves the problems of the backlight thickness, complicated structure, and high output, which were problems in the conventional backlight, and simplified the backlight with higher brightness, higher efficiency, and thinner structure. Can be achieved.

Continued on the front page F-term (reference) 2H042 BA01 BA02 BA03 BA12 BA15 BA20 4F074 AA26 AA65 AA66 AA76 CA01 CA03 CC02Y DA12 DA20 DA24 DA47 DA59 4F100 AK01A AK08 AK25 AK42 BA02 DE04H DJ06A EH17 EH172 JH38 EH462 JE38 GB

Claims (3)

[Claims] 1. A film containing bubbles inside a transparent resin, wherein the shape of the bubbles is long in the film surface direction and thin in the film thickness direction, and the average number of bubbles in the film thickness direction is small. 0.8 to 4.0 optical interface films. 2. A laminated film composed of at least two layers, an optical interface layer containing air bubbles inside a transparent resin and a light transmitting layer substantially containing no air bubbles, wherein the optical interface layer contains at least two layers. The optical interface, characterized in that the shape of the bubbles contained is long in the film surface direction and thin in the film thickness direction, and the average number of bubbles in the film thickness direction is 0.8 to 4.0. the film. 3. The air bubble having a flatness of 10 or more.
Or the optical interface film of 2.