WO2011071065A1

WO2011071065A1 - Light diffusion film and backlight device comprising same

Info

Publication number: WO2011071065A1
Application number: PCT/JP2010/071981
Authority: WO
Inventors: 勝朗久世; 兼次河井; 一元今井; 章文安井
Original assignee: 東洋紡績株式会社
Priority date: 2009-12-10
Filing date: 2010-12-08
Publication date: 2011-06-16
Also published as: TW201128241A; KR20120130079A; JP5771963B2; CN102753999A; JP2011150303A; KR101711689B1; CN102753999B; TWI440898B

Abstract

Disclosed is a light diffusion film which exhibits good light diffusibility and good light resistance, while having excellent economic efficiency and excellent adhesion to other members. Specifically disclosed is a light diffusion film wherein an adhesive layer, which is mainly composed of a polyolefin resin containing a polar group, is arranged on at least one surface of a light diffusion layer, which is mainly composed of two kinds of polyolefin resins that are incompatible with each other, in such a manner that the adhesive layer forms the outermost surface of the light diffusion film. The light diffusion film is characterized in that the total light transmittance of the film is 66-100% and the haze of the film is 20-100%. A backlight device is configured by bonding the adhesive layer surface of the light diffusion film onto the base surface of the light exit surface of a backlight base unit.

Description

Light diffusion film and backlight device incorporating the same

The present invention relates to a light diffusing film excellent in light diffusibility and adhesiveness, and a backlight device incorporating the same.

The light diffusion film is widely used as a member of various lighting fixtures, display devices or screens. In this case, the light diffusing film may be used by being stuck with an adhesive or a pressure-sensitive adhesive for workability and shape stability, in addition to being used by simply overlapping with other members. For example, the light diffusing film is used by being attached to the surface of the light guide plate with an adhesive or an adhesive when incorporated in a planar light source device or a backlight device (see, for example, Patent Documents 1 to 3). However, this method requires a step of laminating an adhesive or the like, and has a problem that it is economically disadvantageous.

In Patent Document 1, a surface light diffusion type light diffusion film of a bead coating method is bonded to the surface of the light guide plate with a UV curable adhesive, but no mention is made of the brightness enhancement effect by the bonding.

In Patent Document 2, a directional light diffusing film is bonded to the light exiting surface of the light guide plate with a light diffusing adhesive containing fine particles. Not mentioned.

In Patent Document 3, a liquid resin made of acrylic acid prepolymer is applied to the surface of a light guide plate made of acrylic resin, a light diffusion film made of polycarbonate resin is laminated on the coated surface, and then the liquid resin is cured to be integrated. It has become. Patent Document 3 describes that air and foreign matters are prevented from being mixed at the interface between the light guide plate and the diffusion film, and light emission and reduction of diffusion due to this are suppressed. This method is described that the brightness is higher than when pasted with a double-sided adhesive tape, suggesting that the refractive index difference at the interface between the light guide plate and the light diffusion film affects the brightness. However, the effect is not clearly shown. In addition, the light diffusion film made of polycarbonate resin is shown to be a surface diffusion type light diffusion film utilizing the diffusion and scattering of light by the surface protrusions from the described figure, but its specific contents No optical properties are disclosed.

Also, in Patent Document 4, an optical film that has been processed to have a concavo-convex process so as to increase the surface area is bonded to the surface of the basic unit of the backlight device with an adhesive layer. The problem to be solved by the invention of Patent Document 4 is that “an optical sheet with an adhesive provided with an optical adhesive layer can be attached to an adherend that emits light to efficiently emit light. Although it is described in the example, it is shown in the example that the diffusion plate, the BEF, and the diffusion plate that were installed on the backlight used for luminance evaluation are mounted as they are. Only the comparison is made, and the effect of bonding in the same optical film is not disclosed.

Patent Document 5 discloses a light-scattering laminated film in which a transparent resin layer is laminated on at least one surface of a light-scattering layer composed of a continuous phase and a particulate dispersed phase having different refractive indexes. An unmodified polypropylene resin is used for the transparent resin layer, and the adhesiveness is insufficient.

Patent Document 6 discloses a light reflecting film provided with an adhesive layer, but does not provide an adhesive layer on a light diffusion film.

Japanese Patent Laid-Open No. 09-159837 JP 2005-50654 A Japanese Patent Laid-Open No. 06-324216 JP 2009-75595 A Japanese Patent Laid-Open No. 2002-1858 JP 2007-178998 A

An object of the present invention is to solve the above-mentioned problems of the prior art, a light diffusing film having excellent light diffusibility and light resistance, excellent economical efficiency, and excellent adhesion to other members. And a backlight device incorporating the same.

The present invention comprises the following configurations (1) to (9).
(1) An adhesive layer containing a polyolefin resin containing a polar group as a main component on at least one surface of a light diffusion layer containing two kinds of mutually incompatible polyolefin resins as a main component is the outermost surface. A light diffusing film, wherein the film has a total light transmittance of 66 to 100% and a haze of the film of 20 to 100%.
(2) The light diffusing film as described in (1), wherein the diffusivity in the main diffusion direction of the transmitted light measured at an incident angle of 0 degrees is 140 to 180 degrees.
(3) The light diffusion film as described in (1) or (2), wherein the inflection degree of light in the main diffusion direction is 1 to 100%.
(4) The two types of mutually incompatible polyolefin resins are composed of a polypropylene resin and a polyolefin resin containing ethylene and / or butene, according to any one of (1) to (3) Light diffusion film.
(5) The light diffusing film according to any one of (1) to (3), wherein the two types of mutually incompatible polyolefin resins are a cyclic polyolefin resin and a polyethylene resin.
(6) The light diffusion film as described in any one of (1) to (5), wherein the polyolefin resin containing a polar group contains a carboxyl group.
(7) A backlight device comprising a base material surface of a light exit surface of a basic unit of a backlight, and the adhesive layer surface of the light diffusing film according to any one of (1) to (6) bonded together.
(8) The backlight device according to (7), wherein the difference in refractive index between the substrate and the adhesive layer is −0.2 to +0.5.

The light diffusing film of the present invention is excellent in both light transmission and diffusing properties, has good light resistance, and has excellent adhesion to other members. For example, other members can be bonded by thermocompression bonding. It can be easily bonded, and is also economical. Therefore, it can be used suitably for various lighting devices, display devices and optical devices and devices such as screens. Further, by using the light diffusing film of the present invention for a backlight device, the light output efficiency of the backlight device can be increased, and the brightness of the backlight device can be increased. Furthermore, the economical efficiency of the backlight device can be improved by reducing the output of the light source of the backlight device and reducing the number of used optical films.

A transmitted light curve with respect to a light receiving angle measured at an incident angle of 0 degree of an automatic goniophotometer. The auxiliary figure of the inflection degree calculation method.

(Light diffusion film)
In the light diffusing film of the present invention, an adhesive layer containing a polyolefin resin containing a polar group as a main component is laminated on at least one surface of a light diffusing layer containing two kinds of mutually incompatible polyolefin resins as a main component. The total light transmittance of the film is 66 to 100%, and the haze of the film is 20 to 100%.

The light diffusion layer of the present invention contains two kinds of mutually incompatible polyolefin resins as main components. Here, a main component means that a content rate is 50 mass% or more, Preferably it is 70 mass% or more. Usually, a polyolefin resin does not have an aromatic ring and thus is not easily deteriorated by ultraviolet irradiation. Therefore, since yellowing by ultraviolet irradiation is suppressed, it is suitable as a constituent material for the light diffusion film.

The two types of incompatible polyolefin resins are not limited as long as they are a combination of resins that are incompatible with each other, but are preferably composed of a polypropylene resin and a polyolefin resin containing ethylene and / or butene.

The two types of mutually incompatible polyolefin resins are preferably composed of a cyclic polyolefin resin and a polyethylene resin.

The combination of the above two types enables stable control of optical characteristics by the light diffusion layer over a wide range. Moreover, said 2 types of combination is preferable also from the point of light resistance or economical efficiency. A nanocrystal structure control polyolefin elastomer resin may be further combined with the above two combinations.

The polyolefin resin is not limited as long as 70 mol% or more thereof is composed of an olefin monomer. The proportion of the olefin monomer is preferably 90 mol% or more, more preferably 95% or more, and further preferably 98% or more. Examples of polyolefin resins include polyethylene resins, polypropylene resins, polybutene resins, polyolefin resins such as cyclic polyolefin resins and polymethylpentene resins, and copolymers thereof. In addition, modified polyolefin resins in which functional groups such as carboxyl groups, ester groups, and hydroxyl groups are introduced into these resins are also preferably used. Moreover, you may be a copolymer of the monomer which does not have aromatic rings, such as acrylic acid, methacrylic acid, and these ester derivatives.

The polyethylene resin may be a single polymer or a copolymer. In the case of a copolymer, it is preferable that 50 mol% or more is an ethylene component. The density and polymerization method of the resin are not limited, but it is preferable to use a copolymer having a density of 0.909 or less. For example, a copolymer with octene is mentioned. The polymerization method may be either a metallocene catalyst method or a nonmetallocene catalyst method.

The polypropylene resin may be a single polymer or a copolymer. In the case of a copolymer, it is preferable that 50 mol% or more is a propylene component. The production method, molecular weight and the like of the resin are not limited, but those having high crystallinity are preferable from the viewpoint of heat resistance and the like. Specifically, the crystallinity is determined by the heat of fusion measured by a differential scanning calorimeter (DSC), and preferably has a heat of fusion of 65 J / g or more.

Examples of polyolefin resins containing ethylene and / or butene include homopolyethylene resins, homopolybutene resins, copolymers of these resins with other olefinic monomers, acrylic acid, methacrylic acid, and ester derivatives thereof. A copolymer etc. are mentioned. In the case of a copolymer with other olefinic monomers, any of random, block and graft copolymers may be used. Further, a dispersion such as EP rubber may be used. There are no particular limitations on the production method and molecular weight of the resin. For example, it is preferable to use the polyethylene resin or a copolymer of ethylene and butene.

Examples of the cyclic polyolefin-based resin include those having a cyclic polyolefin structure such as norbornene and tetracyclododecene. Specifically, (1) a resin obtained by hydrogenating a ring-opening (co) polymer of a norbornene-based monomer after performing polymer modification such as addition of maleic acid or cyclopentadiene, if necessary, (2) a norbornene-based polymer Examples thereof include resins obtained by addition-type polymerization of monomers, and (3) resins obtained by addition-type copolymerization of norbornene monomers and olefin monomers such as ethylene and α-olefin. The polymerization method and the hydrogenation method can be performed by conventional methods.

The nano-crystal structure control type polyolefin elastomer resin is a thermoplastic polyolefin-based elastomer in which the crystal / amorphous structure of the polymer is controlled in the nano order and the crystal has a network structure in the nano order. For example, manufactured by Mitsui Chemicals, Inc. Notio (registered trademark). The conventional polyolefin-based elastomer resin has a crystal size on the order of microns, whereas the nanocrystal structure control-type polyolefin-based elastomer resin has a feature that the crystal size is controlled on the order of nanometers. For this reason, it is often superior in transparency, heat resistance, flexibility, rubber elasticity and the like as compared with conventional polyolefin-based elastomer resins. Therefore, there are cases where the appearance of the resulting film can be improved by blending the nanocrystalline structure control polyolefin elastomer resin.

The blending ratio of the two mutually incompatible polyolefin resins is preferably 10/90 to 90/10, more preferably 20/80 to 80/20, and more preferably 30/70 to 70 / 30 is more preferable. At least two types of incompatible polyolefin-based resins may be blended in the film forming step, or may be blended in advance by a kneading method or the like.

In the present invention, two kinds of resins other than mutually incompatible polyolefin resins may be blended, and additives such as a compatibilizing agent and a dispersion diameter adjusting agent for improving the conformability of each resin are added. You may use together. Moreover, you may mix | blend additives, such as stabilizers, such as antioxidant and a ultraviolet absorber, and antistatic agent. Further, fine particles such as inorganic particles and polymer beads may be added as long as the above optical characteristics are not impaired.

The melt flow rate of the two kinds of mutually incompatible polyolefin resins is not particularly limited as long as the above optical characteristics are satisfied. Each resin is appropriately selected in the range of a melt flow rate measured at 230 ° C. of 0.1 to 100, preferably 0.2 to 50.

The adhesive layer of the present invention contains a polyolefin resin containing a polar group as a main component. Here, a main component means that a content rate is 10 mass% or more, Preferably it is 30 mass% or more. The polyolefin resin containing a polar group preferably contains at least one monomer of ethylene, propylene, butene, hexene, octene, methylpentene and cyclic olefin as the skeleton. It may be a homopolymer using one kind of the above monomer or a copolymer using two or more kinds.

As the polar group contained in the polyolefin resin, carboxyl group, sulfonic acid group, phosphonic acid group, hydroxyl group, glycidyl group, isocyanate group, amino group, imide group, oxazoline group, ester group, ether group, carboxylate metal base, Examples include sulfonic acid metal bases, phosphonic acid metal bases, tertiary amine bases, and quaternary amine bases. The polar group may be one kind or two or more kinds. The polar group preferably contains at least a carboxyl group.

The polar group may be introduced directly into the polymer chain of the polyolefin resin, or may be introduced into another resin, added to the polyolefin resin, and mixed. The polyolefin resin can also be used after being modified by reacting, for example, a carboxyl group or a hydroxyl group with a compound capable of reacting with these introduced into the terminal or inside of the molecular chain.

The polyolefin resin containing a polar group may be used alone or in combination of two or more. Moreover, the compound of the polyolefin resin which does not contain a polar group, and another kind of resin may be sufficient. By using a polyolefin resin containing a polar group, the adhesive layer of the present invention can be bonded by heat.

As long as the light diffusing film of the present invention is laminated on at least one surface of the light diffusing layer so that the adhesive layer is the outermost surface, the configuration and the manufacturing method are not limited.

The adhesive layer may be laminated on either one side or both sides of the light diffusion layer. The total thickness of the film is not limited, but is preferably 10 to 500 μm. The thickness of the adhesive layer is preferably 2 to 100 μm on one side.

Further, the ratio of the thickness of the light diffusion layer / adhesion layer in the light diffusion film is preferably 10/1 to 3/1, more preferably 6/1 to 4/1. By setting such a ratio of thickness, the smoothness of the adhesive layer can be sufficiently obtained.

The total light transmittance of the light diffusing film of the present invention is 66 to 100%, preferably 68% or more, more preferably 70% or more, and most preferably 100%. The upper limit of the total light transmittance is 100% in principle. If the total light transmittance is less than 66%, the utilization efficiency of the amount of light emitted from the light source decreases, which is not preferable.

The haze of the light diffusion film of the present invention is 20 to 100%, preferably 25% or more, and more preferably 30% or more. In principle, the upper limit of haze is 100%. When used as a light diffusion film for a backlight device, the haze of the film is preferably 72% or more, and more preferably 75% or more. If the haze is less than 20%, the light diffusibility is too low, and the effect of controlling the diffusivity is insufficient.

The light diffusion film of the present invention preferably has a diffusivity in the main diffusion direction of transmitted light of 140 to 180 degrees measured at an incident angle of 0 degree with a goniophotometer measured by the method described in the examples. . The diffusion degree is more preferably 145 to 180 degrees, and further preferably 150 to 180 degrees. By setting the diffusivity within this range, for example, when used as a light diffusion film for a backlight device, a remarkable brightness improvement effect is exhibited. If the diffusivity is less than 140 degrees, the light diffusibility is too low and the diffusivity control effect may be insufficient. On the other hand, the upper limit of the diffusion degree is theoretically 180 degrees.

The light diffusion film of the present invention preferably has a light inflection of 1 to 100% in the main diffusion direction measured by the method described in Examples. The inflection degree of light is more preferably 2 to 100%, further preferably 5 to 100%. By making the inflection degree of light within this range, for example, when it is used as a light diffusion film for a backlight device, a remarkable brightness improvement effect is exhibited.

The method for producing the light diffusing film is not particularly limited as long as the above optical characteristics are satisfied, but a method of forming a film by a melt extrusion method is preferable from the viewpoint of economy. In the present invention, the light diffusibility is imparted by blending the polyolefin resin of the film without containing the non-melting fine particles. Therefore, even if it is carried out by melt extrusion molding, Filtering filter clogging can be reduced, productivity is excellent, and the resulting film has high clarity.

As a method of laminating the light diffusing layer and the adhesive layer, for example, each layer is extruded by a plurality of separate extruders, and the layers are merged in a die to form a film, a so-called multilayer extrusion method, a light diffusing layer film and an adhesive layer film. A method of forming films separately and sticking them with an adhesive or a pressure-sensitive adhesive, a so-called extrusion laminating method in which an adhesive layer or a light diffusion layer is melt-extruded and laminated on a light diffusion layer film or an adhesive layer film, etc. Is mentioned. The multilayer extrusion method is preferable in terms of the adhesive force between the light diffusion layer and the adhesive layer.

The melt extrusion method is not particularly limited, and may be, for example, either a T-die method or an inflation method. Moreover, the film may be an unstretched film or may be subjected to a stretching process.

(Backlight device)
The backlight device of the present invention is formed by bonding the adhesive layer surface of the above-mentioned light diffusion film to the base material surface of the light exit surface of the basic unit of the backlight device.

The basic unit of the backlight device of the present invention is not particularly limited as long as it has a light emitting surface on at least one side. For example, any of an edge light system and a direct type may be used. Moreover, a double-sided light emission type may be used. The base material surface of the light exit surface of the basic unit of the backlight device is, for example, the light exit surface of the light guide plate in the case of the edge light system. In the case of a direct type, it refers to the upper substrate surface. In the case of the double-sided light emission type, it refers to the surfaces on both sides of the edge light type light guide plate.

Generally, in the backlight device, a reflective film or a reflector is used on the opposite surface of the light emitting surface for the purpose of increasing the luminance of the light emitting surface. Examples of the reflective film and the reflector include a diffusing type made of a white body, a highly directional film utilizing reflection by metallic luster, and a film having both characteristics.

In addition, in order to suppress the luminance attenuation due to the distance from the light source, the edge light type backlight device employs a method of applying a light emission pattern by printing, engraving, engraving, etc. It doesn't matter. Since the method of the present invention differs greatly from the conventional method in which various optical members are simply overlapped and installed, the light emission profile is greatly different. Therefore, the light emission pattern is designed to be compatible with the method of the present invention. preferable. In the method of the present invention, since the amount of emitted light at a short distance from the light source is increased, it is preferable to further increase the inclination of the light emission pattern.

The basic unit of the backlight device is preferably an edge light type light guide plate. As a result, the amount of light emitted to the surface of the backlight device due to a change in the critical angle of incident light propagating through the light guide plate is increased, and the brightness improvement effect is further increased. Further, since the backlight device can be made thinner than the direct type, it is easy to meet market demands for thin display devices and lighting devices.

The reason for the brightness improvement effect of the backlight device of the present invention is presumed as follows. That is, for example, when propagating through the light guide plate, light having an angle exceeding the critical angle is reflected at the interface between the light guide plate and the light diffusion film, and does not exit the surface of the light guide plate. When a conventionally widely used light diffusion film is simply superimposed on the surface of the light guide plate, an air layer exists between the light diffusion film and the substrate. Since the refractive index of air is significantly lower than the refractive index of the base material, the critical angle becomes small, so that the amount of light emitted to the surface of the base material becomes low, and as a result, the luminance decreases. Generally, the refractive index of the resin used for the light diffusion film is larger than that of air. Therefore, by bonding the light diffusion film, the critical angle of light propagating through the light guide plate is increased, so that the amount of light emitted to the surface of the light guide plate is increased, resulting in an improvement in luminance.

The above-mentioned brightness enhancement effect is first manifested by using the light diffusion film of the present invention. For example, a light diffusion component such as beads is applied to the surface of a conventionally used shaping method or transparent film. In a surface diffusion type light diffusion film utilizing the so-called surface unevenness light scattering effect obtained by processing, the effect is small. The light diffusion film of the present invention is a so-called internal diffusion film that imparts light diffusibility by light scattering by a light scatterer made of mutually incompatible resins existing inside the film, and is a surface diffusion type light diffusion. The light diffusing effect is greatly different from the film. In the case of a surface light diffusing film, light diffusibility is imparted by utilizing the scattering effect of surface irregularities, whereas light scattering is controlled by a light scattering layer on almost one surface. The light diffusing film of the present invention is a multilayer scattering type in which light scattering occurs throughout the film, and since this light scattering acts in a multilayer manner, the critical angle is widened to the surface of the light guide plate. The emitted light effectively acts to improve the luminance. Furthermore, in this invention, a brightness | luminance improves efficiently by limiting the optical characteristic of a light-diffusion film to the above ranges.

In the present invention, the method of bonding the adhesive layer surface of the light diffusion film and the substrate surface is not particularly limited as long as the air layer existing between the light diffusion film and the substrate is excluded. For example, it may be bonded with a pressure-sensitive adhesive or an adhesive, or may be bonded together with a liquid. Since a light-diffusion film has heat adhesiveness, the method of bonding both by the heat bonding method is preferable.

In the present invention, by adhering the light diffusing film and the base material, for example, there is also a secondary effect that a dimensional change due to an environmental change such as a temperature of the light diffusing film can be suppressed.

In the present invention, the difference in refractive index between the adhesive layer of the light diffusing film and the substrate is preferably −0.2 to +0.5. The difference in refractive index is more preferably −0.1 to +0.2, and most preferably 0. In general, the refractive index is displayed up to 3 digits after the decimal point. However, in the present invention, the refractive index may be evaluated by the difference in 1 digit after the decimal point (rounded off to 2 digits after the decimal point). In the present invention, the refractive index is measured by a regular method using a refractometer. For resins with literature values, literature values may be used. In the case of a mixture of resins, the value obtained by weighted averaging according to the composition ratio using the value of a single resin was used.

In the backlight device of the present invention, it is preferable to use only one light diffusion film. This is because the multilayer diffusion film has high brightness, uniformity of brightness, and disappearance of the light emission pattern, and thus it is not necessary to use an optical film such as a lens film or a brightness enhancement film. However, in combination with the lens film, it is possible to further increase the luminance and to further reduce the output of the lamp used in the backlight device.

The backlight device of the present invention can be used as a light source for a display device. Since the backlight device of the present invention has high luminance, when used as a light source for a display device, the brightness of the display device can be improved and the visibility of the display screen can be improved. When high brightness is not required, the amount of light of the backlight lamp can be reduced, so that the manufacturing cost and energy consumption of the display device can be reduced. The display device is not limited as long as the device has a function of transmitting some information by light emitted from the backlight device. For example, LCD display devices for transportation devices such as personal computers, TVs and vehicles can be mentioned. In addition, non-moving image display devices such as advertisements and information boards are listed.

Further, the backlight device of the present invention can be used as a light source for illumination. Since the backlight device of the present invention has high luminance, that is, high illuminance, the brightness of the lighting device can be improved as a light source for lighting. Similarly, when high illuminance is not required, the manufacturing cost and energy consumption of the lighting device can be reduced. The backlight device itself may be used as the illumination light source.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. These are all included in the technical scope of the present invention. The measurement / evaluation methods employed in the examples are as follows. In the examples, “parts” means “parts by mass” unless otherwise specified, and “%” means “% by mass” unless otherwise specified.

1. Total light transmittance and haze Measured in accordance with JIS-K-7136 using a haze meter “NDH-2000” manufactured by Nippon Denshoku Industries Co., Ltd.
Measured by fixing the winding direction of the film in the vertical and horizontal directions on the sample stage of the measuring device, using the average value of the measured values obtained in three measurements, and the average value of the measured values in both directions. Displayed asking for. The reason for this is that the parallel light transmittance may vary greatly depending on the vertical and horizontal directions of the film.
In addition, about the sample with which the contact bonding layer was laminated | stacked on the single side | surface, it incident and measured from the contact bonding layer side. When the adhesive layer was laminated on both surfaces and there was a difference in the surface roughness of both surfaces, the measurement was performed by entering light from the surface having the smaller surface roughness.

2. Diffusion degree of transmitted light in main diffusion direction Measurement was performed using an automatic variable angle photometer (GP-200: manufactured by Murakami Color Research Co., Ltd.).
Transmission measurement mode, light incident angle: 0 ° (angle that is perpendicular to the sample surface, up and down, right and left), light receiving angle: -90 ° to 90 ° (angle on the equator plane), filter: ND10 used, luminous flux Under the conditions of aperture: 10.5 mm (VS-1 3.0), light receiving aperture: 9.1 mm (VS-3 4.0), SENSITIVITY: 950, HIGH VOLTON: 600, and variable angle interval 0.1 degree, The frequency of the angle between the peak rising angle and the peak ending angle of the variable angle luminous intensity curve of the transmitted light obtained by moving the light receiver from 90 degrees to +90 was obtained (see FIG. 1). . With respect to the rising and ending angles of the peaks, these portions were observed with a magnifying glass of 10 times, and the most advanced angles at which the peak lines disappeared were defined as the respective angles.
The surface on which the light receiver is moved is defined as the equator plane.
The angle was measured while fixing the film so that the film winding direction was parallel to the vertical direction of the sample fixing table and the horizontal direction, and the value with the larger angle was defined as the diffusivity.
In addition, about the sample with which the contact bonding layer was laminated | stacked on the single side | surface, it incident and measured from the contact bonding layer side. When the adhesive layer was laminated on both surfaces and there was a difference in the surface roughness of both surfaces, the measurement was performed by entering light from the surface having the smaller surface roughness.
The film direction with the larger diffusivity was defined as the main diffusion direction.
In measuring, before measuring the sample, the light-up film (product registration) 100DX2 film, which is a light diffusion film manufactured by Kimoto Co., Ltd., the film winding direction is parallel to the vertical direction of the sample fixing base, and diffusion is performed. The sample was fixed to the sample fixing base so that the layer side was the light emission side, and the variable angle photometric measurement was performed under the same conditions as described above. In this measurement, if the height of the peak top of the variable angle light curve is more than 80% or less than 70% with respect to the full scale, this value becomes 70 to 80% with respect to the full scale. The numerical value of the SENSITIVITY or HIGH VOLTON dial was finely adjusted.

3. Inflection of light Measurement was performed using an automatic goniophotometer (GP-200: manufactured by Murakami Color Research Co., Ltd.).
Transmission measurement mode, light incident angle: 0 ° (angles perpendicular to the sample surface, up and down, right and left), light receiving angle: -90 ° to 90 ° (angle on the equator plane), filter: ND10 used, beam stop 10.5 mm (VS-1 3.0), light-receiving aperture: 9.1 mm (VS-3 4.0), and measurement with a variable angle interval of 0.1 degree. The peak height (H0) of transmitted light obtained by changing the settings of SENSITIVITY and HIGH VOLTON so that it is 40 to 90% (H0), and the incident angle of light is 60 ° (angle on the equator line) The height (H60) at an angle of 0 degree of the peak of transmitted light when measured under the same conditions as described above was obtained except for changing to. Inflection degree was calculated | required by the following formula using H60 and H0 calculated | required by this method. See FIG.
Inflection of light = H60 / H0 x 100 (%)
The surface on which the light receiver is moved is defined as the equator plane.
The inflection of light was determined by measurement in the main diffusion direction.

4). Adhesive strength between the light diffusion film and the base material A 3 mm thick and transparent acrylic plate (Mitsubishi Rayon Co., Ltd .: Acrylite) is set on the fixed base of the hot press machine. A sample is placed on top, and a silicone rubber sheet with a thickness of 3 mm (hardness HsA 50 °) is laid on the sample, and is pressed from above the silicone rubber sheet with a presser indenter whose surface temperature is set to 180 ° C. In addition, a pressing pressure of 49 N / cm ² was applied for 30 seconds. After thermocompression bonding, it is left for 30 minutes in an environment of 23 ° C and 65% relative humidity, and when it is peeled 180 degrees at a rate of 300 mm / min using “Tensilon” (UTM-IIIL) manufactured by Toyo Seiki Co., Ltd. The value was defined as adhesive strength.
Judgment of adhesive strength was carried out according to the following criteria.
Adhesive strength is 0.1 N / 15 mm or more: Good Adhesive strength is less than 0.1 N / 15 mm: Poor

5. Melt flow rate of thermoplastic resin It was measured under the condition of 2.16 kgf according to JIS-K-7210 A method.

6). Front luminance Example 1 to 5 and Comparative Examples 1 to 5, and the light diffusion film of Reference Example 1 bonded to a backlight unit are referred to as Examples 6 to 10, Comparative Examples 6 to 10, and Reference Example 2, respectively. The front luminance of was measured. The measuring method is as described in each example, comparative example, and reference example.

7). Disappearance of light emission pattern The opening in the front luminance measurement was observed with the naked eye in a state in which the backlight was turned on, and judged according to the following criteria.
The light guide plate mesh is not visible at all: Good The light guide plate mesh is faint: Somewhat poor The light guide plate mesh is clearly visible: Bad

Example 1
Using two melt extruders, 35 parts by mass of a cyclic polyolefin resin (TOPAS (TM) 6013S-04 Topas Advanced Polymers melt flow rate: 2.0 (230 ° C.)) was used in the first extruder. A block copolymer resin composed of ethylene and octene (INFUSE (TM) D9817.15 melt flow rate: 26 (230 ° C.) manufactured by Dow Chemical Co., Ltd.) is formed into a light diffusion layer of 65 parts by mass, and the second extruder Thus, an adhesive layer composed of a maleated polypropylene resin (Admer (TM) QF551, Mitsui Chemicals, Ltd., melt flow rate: 5.7 (190 ° C.)) as the adhesive resin forms both sides of the light diffusion layer. After the melt coextrusion by the T-die method, the light diffusion layer is cooled by cooling with a cooling roll with a mirror surface. A light diffusion film having a total thickness of 400 μm with an adhesive layer laminated on the surface was obtained, and the film was closely attached to the cooling roll during the cooling using a vacuum chamber (layer thickness structure (adhesion layer / light diffusion layer / The adhesive layer was 40/320/40 (μm).
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusion film obtained in this example was excellent in light diffusion characteristics and adhesiveness.

(Comparative Example 1)
In the method of Example 1, the resin of the adhesive layer formed by the second extruder was a cyclic polyolefin resin (TOPAS (TM) 6013S-04 Topas Advanced Polymers melt flow rate: 2.0 (230 ° C.)). A light diffusing film was obtained in the same manner as in Example 1 except that the above was changed.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusing film obtained in this Comparative Example was excellent in light diffusing properties, but was inferior in adhesiveness.

(Example 2)
In the method of Example 1, except that the total thickness of the light diffusing film is changed to 175 μm and the layer thickness configuration is changed to 25/125/25 (μm), the light diffusing film is formed in the same manner as in Example 1. Obtained.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusion film obtained in this example was excellent in light diffusion characteristics and adhesiveness.

(Comparative Example 2)
In the method of Example 2, the resin of the adhesive layer formed by the second extruder was a cyclic polyolefin resin (TOPAS (TM) 6013S-04 Topas Advanced Polymers melt flow rate: 2.0 (230 ° C.)). A light diffusing film was obtained in the same manner as in Example 2 except that the above was changed.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusing film obtained in this Comparative Example was excellent in light diffusing properties, but was inferior in adhesiveness.

(Example 3)
In the method of Example 1, the resin of the light diffusion layer formed by the first extruder was a cyclic polyolefin resin (TOPAS (TM) 6015 Topas Advanced Polymers melt flow rate: 0.41 (230 ° C.)). Block copolymer resin consisting of 50 parts by mass, ethylene and octene (INFUSE (TM) D9817.15 melt flow rate: 26 (230 ° C.) manufactured by Dow Chemical Co., Ltd.) Same as Example 1 except for changing to 50 parts by mass A light diffusion film was obtained by the method.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusion film obtained in this example was excellent in light diffusion characteristics and adhesiveness.

(Comparative Example 3)
Cyclic polyolefin resin (TOPAS (TM) 6015 manufactured by Topas Advanced Polymers, melt flow rate: 0.41 (230 ° C)), block copolymer resin composed of ethylene and octene (INFUSE (TM) manufactured by Dow Chemical Co., Ltd.) D9817.15 Melt flow rate: 26 (230 ° C.) 50 parts by mass was melt-mixed at a resin temperature of 250 ° C. using a PCM45 extruder manufactured by Ikekai Tekko Co., Ltd., extruded with a T-die, and a satin-finished cooling roll (Ra = A light diffusion film having a thickness of 400 μm was obtained by cooling at 0.55). The opposite surface of the cooling roll was a pressing roll whose surface was subjected to mold release treatment (Ra = 1.0).
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusing film obtained in this Comparative Example was excellent in light diffusing properties, but was inferior in adhesiveness.

Example 4
In the method of Example 3, except that the total thickness of the light diffusion film is changed to 200 μm and the layer thickness configuration is changed to 20/160/20 (μm), the light diffusion film is formed in the same manner as in Example 3. Obtained.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusion film obtained in this example was excellent in light diffusion characteristics and adhesiveness.

(Comparative Example 4)
In the method of Comparative Example 3, a light diffusing film was obtained in the same manner as in Comparative Example 3, except that the total thickness of the light diffusing film was changed to 200 μm and the layer thickness configuration was changed to 20/160/20 (μm). It was.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusing film obtained in this Comparative Example was excellent in light diffusing properties, but was inferior in adhesiveness.

(Example 5)
In the method of Example 1, the resin composition of the light diffusing layer was changed to a block copolymer resin (INFUSE (TM) manufactured by Dow Chemical Co., Ltd.) composed of 65 parts by mass of polypropylene resin (Sumitomo Chemical Co., Ltd., Sumitomo Nobrene FS2011DG3) and ethylene and octene. D9817.15 Melt flow rate: 26 (230 ° C.) An unstretched sheet was obtained in the same manner as in Example 1 except that the content was changed to 35 parts by mass. Subsequently, this unstretched sheet was stretched 4.5 times at a stretching temperature of 118 ° C. using the difference in roll peripheral speed of a longitudinal stretching machine, and then a corona treatment was performed on one side to obtain a light diffusion film having a thickness of 200 μm.
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusion film obtained in this example was excellent in light diffusion characteristics and adhesiveness.

(Comparative Example 5)
In the method of Example 5, the resin of the adhesive layer formed by the second extruder was changed from a polypropylene-based adhesive resin (Admer (TM) QF551, Mitsui Chemicals, melt flow rate: 5.7 (190 ° C.)). A light diffusion film was obtained in the same manner as in Example 5 except that the resin was changed to polypropylene resin (Sumitomo Chemical Co., Ltd., Sumitomo Noblen FS2011DG3).
Table 1 shows the characteristics of the obtained light diffusion film.
The light diffusing film obtained in this comparative example was excellent in light diffusing properties, but was inferior in adhesiveness.

(Examples 6 to 10 and Comparative Examples 6 to 10)
Near the center on the acrylic plate on the outgoing light side of a 19-inch light guide plate type (mesh type using a white reflective film) with three cold cathode tubes on each side of the long diameter side (lateral direction) An evaluation sample of 40 mm x 60 mm square (60 mm side is the horizontal direction) is placed on the surface, a silicone rubber sheet is placed on the surface, and the surface temperature is about 180 ° C from the surface of the silicone rubber sheet. Then, press and stick for about 1 minute, and install the black shading paper provided with a 30mm x 50mm square (50mm side is the horizontal direction) so that the center of the cutout part is the center of the evaluation sample The brightness was measured in a dark room. The black light-shielding paper was fixed so that the entire backlight unit was covered, and measurement was performed so that light did not leak.
Moreover, the backlight unit was installed horizontally and measured.
Luminance was measured using a Topcon Spectroradiometer SR-3A manufactured by Topcon Technohouse Co., Ltd. at a measurement angle of 2 degrees, at a distance of 40 cm from the backlight unit surface, and at the position where the center of the sample for evaluation was directly below. did.
The measurement was performed by installing the sample for evaluation so that the main diffusion direction was perpendicular to the longitudinal direction of the cold cathode tube.
The results obtained by using the light diffusing films of Examples 1 to 5 and Comparative Examples 1 to 5 as evaluation samples are shown in Table 2 as Examples 6 to 10 and Comparative Examples 6 to 10, respectively.

The light diffusion films of Examples 1 to 5 are adhered to the acrylic plate surface by an adhesive layer, air between the acrylic plate and the light diffusion film is excluded, and the difference in refractive index at the interface becomes small. Was expensive. In addition, since the optical characteristics of inflection and diffusivity are in a preferable range, the light emission pattern is excellent in disappearance.
On the other hand, the light diffusing films of Comparative Examples 1 to 5 have a weak adhesive force between the acrylic plate and the light diffusing film, and air between the two materials is not excluded, resulting in a large difference in the refractive index of the interface between the two members. Compared with the light diffusion films of Examples 1 to 5, the front luminance was remarkably inferior.

The light guide plate was placed in an oven at 80 ° C. and allowed to stand for 240 hours.
In the evaluation of dimensional stability, those maintaining the same dimensions and shape as those before warming were excellent and considered good. Also, those that curled or reduced in size due to the heating treatment were considered inferior and were judged to be defective. The results are shown in Table 2.
The light diffusing films obtained in Examples 1 to 5 were not deformed and maintained the same size and shape as before heating, but the light diffusing films obtained in Comparative Examples 1 to 5 were subjected to heating treatment. The light diffusing film curled and the dimensions were reduced.

(Reference Example 1)
Using two melt extruders, in the first extruder, 100 parts by mass of polypropylene resin WF836DG3 (Sumitomo Chemical Co., Ltd., Sumitomo Nobrene) was melted to form the base layer A, and in the second extruder, A light diffusion layer B is formed by melting and mixing 17 parts by mass of a polypropylene resin WF836DG3 (Sumitomo Chemical Co., Ltd., Sumitomo Nobrene) and 83 parts by mass of a propylene / ethylene copolymer HF3101C (Nippon Polypro Co., Ltd.). An unstretched sheet was obtained by performing melt coextrusion by a T-die method and cooling with a casting roll at 20 ° C. so that A and the light diffusion layer B were laminated. Next, this unstretched sheet was stretched 4.8 times at a stretching temperature of 120 ° C. using the difference in roll peripheral speed of a longitudinal stretching machine, and subsequently heated at 165 ° C. by a tenter-type stretching machine, and then stretched at 155 ° C. The film was stretched 9 times in the transverse direction at the temperature. Subsequently, heat setting was performed at 166 ° C. to obtain a light diffusion film in which the thickness of the base layer A / light diffusion layer B was 22.2 / 2.8 (μm), respectively. The corona treatment was performed on the surface of the base layer A immediately before winding.
Table 1 shows the characteristics of the obtained light diffusion film. Further, using the obtained light diffusion film, front luminance, dimensional stability, and light emission pattern disappearance were measured in the same manner as in Examples 6 to 10 and Comparative Examples 6 to 10. The results are shown in Table 2.
The light diffusion film of this reference example was inferior in dimensional stability because there was no adhesive layer. Also, it is indicated that high brightness cannot be obtained because the inflection and diffusion are low. Moreover, the disappearance of the light emission pattern was also inferior.

(Reference Example 2)
Near the center on the acrylic plate on the outgoing light side of a 19-inch light guide plate type (mesh type using a white reflective film) with three cold cathode tubes on each side of the long diameter side (lateral direction) The light diffusion film obtained in Reference Example 1 of 40 mm × 60 mm square (the 60 mm side is the horizontal direction) is attached to the part with an acrylic optical adhesive tape (double-sided separate film type), and the 30 mm × 50 mm square (the 50 mm side is horizontal) A black shading paper provided with a cutout portion in the direction) was placed so that the center of the cutout portion was the center portion of the evaluation sample, and the luminance was measured in a dark room. The black light-shielding paper was fixed so that the entire backlight unit was covered, and measurement was performed so that light did not leak.
Moreover, the backlight unit was installed horizontally and measured.
Luminance was measured using a Topcon Spectroradiometer SR-3A manufactured by Topcon Technohouse Co., Ltd. at a measurement angle of 2 degrees, at a distance of 40 cm from the backlight unit surface, and at the position where the center of the sample for evaluation was directly below. did.
The measurement was performed by installing the sample for evaluation so that the main diffusion direction was perpendicular to the longitudinal direction of the cold cathode tube.
Bonding was performed such that the layer A side of the light diffusion film was the adhesive tape side.
Further, the dimensional stability and the light emission pattern disappearance were measured in the same manner as in Examples 6 to 10 and Comparative Examples 6 to 10. The results are shown in Table 2.
The light diffusing film of this reference example has a lower degree of inflection and diffusion than the light diffusing films obtained in Examples 1 to 5, and therefore, unlike the light diffusing films obtained in Examples 1 to 5, It was shown that the brightness improvement effect by bonding was small. Moreover, the disappearance of the light emission pattern was also inferior.

The light diffusing film of the present invention has both excellent light transmissive and diffusive properties and good light resistance, and can be easily bonded to other members by thermocompression bonding. Therefore, it can be suitably used for various lighting devices, display devices, optical devices and devices such as screens. Furthermore, by using the light diffusing film of the present invention for a backlight device, it is possible to increase the brightness of the backlight device and to improve the economics of the backlight device.

Claims

The adhesive layer containing a polyolefin resin containing a polar group as a main component was laminated on at least one surface of a light diffusing layer containing two types of mutually incompatible polyolefin resins as a main component. A light diffusing film, characterized in that the total light transmittance of the film is 66 to 100%, and the haze of the film is 20 to 100%.
2. The light diffusing film according to claim 1, wherein the diffusivity in the main diffusion direction of the transmitted light measured at an incident angle of 0 degrees is 140 to 180 degrees.
3. The light diffusion film according to claim 1, wherein the inflection degree of light in the main diffusion direction is 1 to 100%.
The light diffusing film according to any one of claims 1 to 3, wherein the two mutually incompatible polyolefin resins comprise a polypropylene resin and a polyolefin resin containing ethylene and / or butene.
The light diffusing film according to any one of claims 1 to 3, wherein the two kinds of mutually incompatible polyolefin resins are a cyclic polyolefin resin and a polyethylene resin.
6. The light diffusing film according to claim 1, wherein the polyolefin resin containing a polar group contains a carboxyl group.
7. A backlight device comprising a light-diffusing film adhesive layer surface according to any one of claims 1 to 6 bonded to a base material surface of a light exit surface of a basic unit of a backlight.
The backlight device according to claim 7, wherein the difference in refractive index between the substrate and the adhesive layer is -0.2 to +0.5.