JP2002148415A - Reflected light diffusing film for liquid crystal display and light reflecting sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflected light diffusing film for a liquid crystal display having a high reflectance and little unevenness in luminance and to provide a light reflecting sheet. SOLUTION: The reflected light diffusing film has a polyester resin film containing microvoids as the substrate, the total light transmittance of the substrate film is 10 to <40% and the difference between the average reflectance of the substrate film in the wavelength range of 400-700 nm and that of the substrate film at the time when a metallic lustrous surface is disposed on the rear face of the film is >=5%. The light reflecting sheet is obtained by overlapping the substrate film and a plastic film with a stack metallic thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection light diffusion film for a liquid crystal display. More specifically, the present invention relates to a reflected light diffusion film for a liquid crystal display in a liquid crystal display device having an illumination mechanism from the back of a liquid crystal display such as a liquid crystal monitor or a liquid crystal television.

[0002]

2. Description of the Related Art A backlight system in which a cold cathode ray tube is used as a light source and a light source is arranged on the back of the display, or a transparent light guide plate is arranged on the back of the display and a light source is applied from the side of the light guide plate for illumination of a liquid crystal display. A side light method for supplying light is used.

[0003] In particular, in the sidelight method, uniform brightness can be easily obtained by illuminating light from halftone printing on one side of the light guide plate.
Further, since the light source is arranged at the edge of the light guide plate, the lighting unit can be made thin. Here, in order to prevent the illumination light from leaking to the rear surface, a member having excellent light reflection characteristics is installed on the rear surface of the light guide plate.

A light reflecting member is disclosed in Japanese Patent Publication No. 8-1617.
Also, a foamed white polyester film as described in JP-A No. 5 (1993) -105 is used. The reflection film according to the publication has a large number of fine cavities and obtains light reflection characteristics of the cavities. However, the film thickness is 188μ
However, there is a problem in that a small display is inconsistent with thinning and that it is difficult to follow a light guide plate having a curvature. In addition, there is a problem that light absorption inside the foamed white film is large compared to the surface of the metallic glossy reflection plate, and sufficient reflection performance cannot be obtained.

Further, as a light reflecting member, Japanese Patent Application Laid-Open No. 5-301 is used.
No. 318 is also used. However, although the silver reflective sheet has a high total reflectance of light, it tends to cause luminance unevenness on the screen. If a layer containing an inorganic pigment is provided on the surface as a countermeasure, the luminance itself tends to decrease.

[0006] High total reflectance of light, less uneven brightness,
At the present time, a thin, light-reflecting member with good curved surface followability has not been developed, and there is a strong demand from liquid crystal display manufacturers.

That is, the present invention is to solve the above-mentioned conventional problems and to provide a reflection light diffusion film and a light reflection sheet for a liquid crystal display having a high reflectance and less luminance unevenness.

[0008]

That is, the present invention has the following configuration.

A first aspect of the present invention is a reflected light diffusing film based on a polyester resin film containing fine cavities, wherein the base film has a total light transmittance of 10% or more and less than 40%. , Wavelength 400-700nm
The difference between the average reflectance of the base film and the average reflectance when a metallic glossy surface is arranged on the back surface of the film is 5
% Of the reflected light diffusion film for a liquid crystal display.

A second invention is the reflected light diffusion film for a liquid crystal display according to the first invention, wherein the thickness of the base film is 25 to 100 μm.

A third invention is the reflected light diffusion film for a liquid crystal display according to the first or second invention, wherein the content of the inorganic particles in the base film is 10% by weight or less. .

According to a fourth aspect of the present invention, there is provided a light reflecting sheet comprising the substrate film according to the first, second, or third aspect and a plastic film on which a metal thin film is laminated. .

According to a fifth aspect of the present invention, there is provided a light reflection sheet comprising a base material film according to the first, second, or third aspect, and a metal thin film laminated on one surface of the base film.

In a sixth aspect of the present invention, the metal thin film is any one of silver, an alloy containing silver, and a laminated film of silver and another metal.
The light reflecting sheet according to the fourth or fifth invention, which is a seed.

In the present invention, the total light transmittance of the substrate film needs to be 10% or more and less than 40%. When the total light transmittance is less than 10%, the excellent light reflectance of the metallic glossy surface cannot be utilized, and the luminance becomes insufficient.
On the other hand, when the total light transmittance is 40% or more, the light diffusion effect is insufficient and the vertical luminance is reduced.

In the present invention, the base film 400
It is necessary that the difference between the average reflectance at ~ 700 nm and the average reflectance when a metallic glossy surface is arranged on the back surface of the base film is 5% or more. If the difference in reflectance is less than 5%, the excellent light reflectance of the metallic glossy surface cannot be utilized.
If the difference in reflectance is 30% or more, the effect of diffusing light is insufficient, and the vertical luminance tends to decrease. Therefore, the upper limit of the difference in average reflectance is preferably less than 30%.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The polyester resin film containing fine cavities (hereinafter abbreviated as a base film) in the present invention comprises a polyester resin (a) and a thermoplastic resin (b) incompatible with the polyester resin (a). It is a film obtained by stretching the resin composition containing at least one direction.

Examples of the polyester resin (a) include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid or esters thereof, and glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol and neopentyl glycol. Are obtained by polycondensation of an aromatic dicarboxylic acid and a glycol directly, or by subjecting a polyester to a transesterification reaction of an aromatic dicarboxylic acid alkyl ester with a glycol. It can also be produced by a method of condensing or polycondensing a diglycol ester of an aromatic dicarboxylic acid.

Representative examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene-2,6-naphthalate. These polyesters may be homopolymers or copolymers obtained by copolymerizing the third component. Of course, in the present invention, the ethylene terephthalate unit and the butylene terephthalate unit are used. Alternatively, the proportion occupied by ethylene-2,6-naphthalate units is preferably at least 70 mol%, more preferably at least 80 mol%, particularly preferably at least 90 mol%.

The thermoplastic resin (b) which is incompatible with the polyester resin (a) is essentially incompatible with the base polyester resin, and is dispersed in the polyester resin in the form of particles. Any resin may be used as long as it is a thermoplastic resin that forms a cavity by peeling off at the interface with the polyester resin during film stretching. For example, polystyrene-based resins, polyolefin-based resins, polyacryl-based resins, polycarbonate-based resins, polysulfone-based resins, cellulose-based resins and the like can be mentioned. These can be used alone, or if necessary, two or more can be used as a mixture. Alternatively, they can be copolymerized to impart an appropriate affinity to the polyester.

Among them, polystyrene resins and polyolefin resins such as polymethylpentene and polypropylene are recommended as preferable.

The preferred blending amount of the thermoplastic resin incompatible with the polyester resin (a) varies depending on the void content and the stretching conditions required for the finally obtained film. 3% by weight based on resin composition
It is at least 40% by weight and more preferably in the range of 5 to 30% by weight. If it is less than 3% by weight, the void content generated in the stretching step becomes insufficient, and it becomes difficult to obtain sufficient reflection performance. On the other hand, when the content is 40% by weight or more, not only the stretchability is remarkably reduced, but also the heat resistance, the strength or the stiffness (stiffness) may be impaired.

Further, the thermoplastic resin (b) comprises (1) a thermoplastic resin (b1) incompatible with the polyester resin (a), and (2) the polyester resin (a) and the thermoplastic resin (b). A thermoplastic resin which is incompatible with both of the thermoplastic resins (b1) and has a higher surface tension (surface energy) than the thermoplastic resin (b1), and is 100 weight parts of the thermoplastic resin (b1) 0.01 to 2 parts
It contains the thermoplastic resin (b2) contained in 0 parts by weight.

That is, the thermoplastic resin of the above (b2) has a cavity generating effect similarly to the above (b1) in that it is a thermoplastic resin incompatible with the polyester resin (a). However, while (b1) mainly exerts a cavity-forming effect, (b2) also has the property of a thermoplastic resin incompatible with (b1), and (b1)
By mixing (b2) having a higher surface tension than (1) with (b1) at a specific ratio, a “dispersion effect” of finely dispersing the thermoplastic resin incompatible with the polyester in the raw material resin is obtained. It exerts an effect effectively, and has an action of uniformly forming fine cavities. Therefore, in the following description, (b1) will be referred to as a cavity-expressing agent in order to particularly distinguish these (b1) and (b2) from the aspect of action,
(B2) will be referred to as a dispersible resin.

The properties of the dispersible resin (b2) used in the present invention are preferably "a thermoplastic resin having a larger surface tension than that of the cavity-forming agent (b1)", and its content is 100% by weight of the cavity-forming agent (b1). 0.01 to 20 parts by weight per part by weight is preferred. The lower limit of the content of the dispersible resin (b2) is 0.0
The amount is more preferably 2 parts by weight, particularly preferably 0.1 part by weight. On the other hand, the upper limit of the content of the dispersible resin (b2) is
It is more preferably 15 parts by weight, particularly preferably 10 parts by weight.

When the content of the dispersible resin (b2) is less than 0.01 part by weight, the effect of finely dispersing the cavity-forming agent (b1) cannot be exhibited effectively. On the other hand, if it exceeds 20 parts by weight, the dispersible resin (b2) will cover most of the cavity developing agent (b1). As a result, an improperly-sized one is formed, for example, a cavity having a short length is formed for the thickness.

When the content of the dispersing resin (b2) with respect to the cavity-forming agent (b1) is within the above range, the dispersing resin (b2) having a high surface tension can be used for the cavity-forming agent (b2) having a lower surface tension. Even if b1) is covered, it is partially covered or thinly and uniformly covered (the shape to be covered is not limited to these, and depending on the type of resin used, for example, a portion covered like a mesh and not covered) Various cases, such as a case where the portions are present periodically or a combination thereof, are considered), so that the adhesion to the polyester is not substantially affected.

Accordingly, the fine dispersing effect of the dispersible resin (b2) can be effectively exhibited, and the cavity-forming agent (b1) can be finely dispersed in the polyester-based resin. In contrast, many long cavities can be obtained. As described above, by setting the properties and the content of the dispersible resin used in the present invention within the above-mentioned ranges, the function as a dispersant can be exhibited. Examples of the combination of the cavity generating agent (b1) and the dispersible resin (b2) include, for example, the following.

When a polyolefin resin such as a polymethylpentene resin, a polypropylene resin, a cyclic olefin polymer, or a silicone resin is used as the cavity developing agent (b1), polystyrene is used as the dispersible resin (b2). A resin, a polycarbonate resin, a polyacrylic resin, a polyphenylene ether resin, a polyolefin resin modified with a maleimide or a carboxylic acid, a polystyrene resin, or the like is used.

When a polystyrene resin is used as the cavity-forming agent (b1), a polycarbonate resin, polyacrylic resin, polyphenylene ether-based resin, maleimide, carboxylic acid or the like is used as the dispersible resin (b2). A modified polyolefin resin is used. These dispersible resins (b2) can be used alone, or if necessary, two or more can be used in combination.

The preferred blending amount of the incompatible resin (b1) and the dispersible resin (b2) in the polyester resin also varies depending on the amount of voids required in the finally obtained film and the stretching conditions. But usually 3 to 30% by weight, more preferably 5 to 30% by weight based on the total resin composition.
It is selected from the range of 25% by weight. If it is less than 3% by weight,
The void content generated in the stretching step becomes insufficient, and it becomes difficult to obtain sufficient reflectance and light scattering in the visible light region. On the other hand, if it exceeds 30% by weight, not only the stretchability is remarkably reduced, but also the strength or stiffness (stiffness) may be impaired.

In the present invention, the content of the inorganic particles in the base film is preferably set to 10% by weight or less. If it exceeds 10% by weight, light scattering in the substrate film becomes too strong, and light energy absorption tends to increase.

The base film may be a single layer, but by laminating a polyester layer having substantially no voids on one side, the adhesion is improved when the polymer resin layer is provided on the layer having no voids. Further improve. This is a protective layer that prevents lubricants and low molecular weight substances contained in polystyrene, polypropylene, etc. from bleeding out from the inside of the film to the surface during film production and inhibiting adhesion to the polymer resin layer. This is because it plays a role.

In this case, if necessary, inorganic particles may be contained in the polyester layer having no voids in order to improve the slipperiness and winding property during film formation. However, it is preferable that the content of the inorganic particles in the entire laminated film including the void-containing polyester layer and the polyester layer not containing voids does not exceed 10% by weight.

However, in the present invention, if necessary, additives such as a fluorescent whitening agent, an antistatic agent and an ultraviolet absorber may be contained in an appropriate amount.

The thickness of the reflection light diffusing film for a liquid crystal display of the present invention is not particularly limited, but is 25 to 100 μm.
Is preferred. If the thickness is less than 25 μm, the light diffusivity tends to be insufficient. On the other hand, if it exceeds 100 μm, the high reflectivity of the metal surface cannot be sufficiently utilized. In addition, it is difficult to cope with a thin liquid crystal display and to make a reflected light diffusion film follow a back surface of a light guide plate having a curvature and to overlap it.

The reflected light diffusing film for a liquid crystal display of the present invention can be provided with a coating layer as required.
The type of resin that forms the coating layer is an oxidation polymerization type ink or U type.
There is no particular limitation as long as it has good adhesiveness to both or any of the V-curable inks. For example, polyester-based resins, polyurethane-based resins, and resin mixtures thereof are preferable because of their excellent adhesiveness.

The coating layer is applied to at least one side of the polyester film at an arbitrary stage during the production of the film. The coating layer can be applied by any known method. Examples include a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire barber coating method, a pipe doctor method, an impregnation coating method, a curtain coating method, and the like. These methods can be performed alone or in combination.

The step of coating the coating layer may be a normal coating step, that is, a step of coating a base film that has been biaxially stretched and heat-set, or may be a coating step during the manufacturing process of the film.

The reflective light diffusing film of the present invention can be used as a light reflecting sheet by disposing a metallic glossy surface on one side. The glossy metal surface can be obtained by forming a thin metal film on a plastic film by a method such as sputtering, vacuum deposition, ion plating, or ionization deposition. Further, a glossy surface of a metal plate may be used. As the type of the metal thin film, silver, an alloy containing silver, or a laminated film of silver and another metal is preferable, and it is more preferable to form a corrosion-resistant metal layer on the outermost layer of the metal thin film layer.

The thickness of the metal thin film layer is preferably 300 ° or more. If it is less than 300 °, the light reflectance tends to be insufficient. Although there is no particular upper limit for the thickness, usually about 1000 ° is often used.

The structure of the light reflecting sheet may be a structure in which the base material sheet of the present invention is laminated with a plastic film in which a metal thin film is laminated, or a structure in which a metal thin film layer is laminated on one surface of the base film of the present invention. May be.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and all modifications that do not impair the effects of the present invention can be made by the present invention. Included in the technical scope.

[0044]

<Example><Total light transmittance measurement method>
Using a haze meter (TC-H3P, manufactured by Tokyo Denshoku Co., Ltd.), five points were measured, and the average T2 value was determined.

<Method of Measuring Reflectance> The reflectance was measured by attaching an integrating sphere to a spectrophotometer (Spectrophotmeter U-3500, manufactured by Hitachi), and forming a base film (reflected light diffusion film) and a metallic glossy surface on one side of the base film. (Light reflecting sheet) with a wavelength of 400 to 700 nm
The reflectance was measured every m steps. At this time, the reflectance of alumina white plate (manufactured by Hitachi Instrument Service Co., Ltd., 210-0740) was set to 100%.
And

<Luminance Measurement Method> The reflection sheet, which is standardly mounted on the light source light guide plate type 15-inch backlight unit (equipped with two lamps on the long side), is removed, and the sample and the reflection material are inserted. The backlight is turned on (lamp type: Φ2.4 × length 310 mm, applied voltage: 12 V, applied current: 0.86 A / line), and the display screen is divided into three equal parts vertically and horizontally and divided into nine sections. The luminance at the center of each section was measured using a luminance meter (manufactured by Minolta, CS-100), and the average luminance and luminance unevenness were determined. The luminance unevenness was obtained by the following equation. Brightness unevenness (%) = ((maximum value−minimum value) / average luminance) ×
100

Example 1 A film material A comprising the following composition was vacuum-dried at 180 ° C. for 3 hours, and then charged into a twin screw extruder.
After being melted and extruded from a T-die at 290 ° C., an unstretched sheet was obtained by solidifying and tightly contacting a cooling rotating metal roll while applying static electricity. Next, the unstretched sheet was longitudinally stretched 3.1 times at 80 ° C. by a roll stretching machine, and then transversely stretched 2.6 times at 125 ° C. by a tenter, and further 220 ° C. by a tenter. And stretched transversely 1.4 times.

Thereafter, a 4% relaxation treatment in the width direction was performed at 235 ° C. to obtain a 50 μm-thick void-containing biaxially stretched polyester film (reflection light diffusion film) having a large number of voids inside the film. . Next, a biaxially stretched polyester film obtained by laminating the obtained void-containing biaxially stretched polyester film and a silver thin film layer (silver film thickness: 1)
000Å, film thickness: 12 μm)
A light reflection sheet was used. Table 1 shows the obtained results.

Film raw material A (1) Polyethylene terephthalate resin (intrinsic viscosity:
0.62 dl / g): 74% by weight (2) General-purpose polystyrene resin (PS) (manufactured by Mitsui Toatsu Chemicals, T575-57U): 25% by weight (3) Maleimide-modified polystyrene resin (M-PS) (Mitsui Tohatsu Chemical's NH1200): 1% by weight

Example 2 Example 1 was repeated except that the film raw material A and the film raw material B comprising the following composition were mixed at a ratio of A / B = 92 parts by weight / 8 parts by weight. Similarly, a cavity-containing biaxially stretched polyester film (reflected light diffusion film) having a thickness of 50 μm was obtained. Next, the obtained cavity-containing biaxially stretched polyester film and a biaxially stretched polyester film (silver film thickness: 1000 °, film thickness: 12 μm) having a silver thin film layer laminated thereon were laminated to form a light reflecting sheet. Table 1 shows the obtained results.

Film raw material B (1) Polyethylene terephthalate resin (intrinsic viscosity:
(0.62 dl / g): 50% by weight (2) Anatase type titanium dioxide particles (manufactured by Fuji Titanium Co., Ltd., TA-300; average particle size 0.35 μm): 50% by weight

Comparative Example 1 The procedure of Example 1 was repeated, except that the amount of resin discharged from the extruder was increased to adjust the thickness of the unstretched sheet so that the final film thickness was 188 μm.
An 88 μm void-containing biaxially stretched polyester film (reflective light diffusion film) was obtained. Next, a biaxially stretched polyester film obtained by laminating the obtained void-containing biaxially stretched polyester film and a silver thin film layer (silver film thickness: 100
0 °, film thickness: 12 μm) to obtain a light reflecting sheet. Table 1 shows the obtained results.

Comparative Example 2 In Example 1, as the film raw material, the raw material A and the raw material B comprising the following composition were used, and A / B = 76 parts by weight / 24
A cavity-containing biaxially stretched polyester film (reflective light diffusion film) having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the raw materials mixed in a ratio of parts by weight were used. Next, the obtained cavity-containing biaxially stretched polyester film and a biaxially stretched polyester film (silver film thickness: 1000 °, film thickness: 12 μm) having a silver thin film layer laminated thereon were laminated to form a light reflecting sheet. Table 1 shows the obtained results.
Shown in

Comparative Example 3 The procedure of Example 2 was repeated, except that the amount of resin discharged from the extruder was reduced and the thickness of the unstretched sheet was adjusted so that the final film thickness was 20 μm.
A μm void-containing biaxially stretched polyester film (reflective light diffusion film) was obtained. Next, a biaxially stretched polyester film obtained by laminating the obtained void-containing biaxially stretched polyester film and a silver thin film layer (silver film thickness: 1000 °,
(Film thickness: 12 μm) to obtain a light reflecting sheet. Table 1 shows the obtained results.

Comparative Example 4 Polyethylene terephthalate resin (intrinsic viscosity: 0.62
dl / g) and a film raw material D composed of the following composition were separately charged into two twin screw extruders, and laminated in a T-die.
It was melt-extruded at 290 ° C from a die, and was adhered and solidified on a cooling rotating metal roll while applying static electricity to obtain an unstretched sheet. Next, the unstretched sheet was longitudinally stretched 3.1 times at 80 ° C. by a roll stretching machine, and then transversely stretched 2.6 times at 125 ° C. with a tenter, and further 220 ° C. with a tenter. And stretched transversely 1.4 times.

Thereafter, a relaxation treatment of 4% in the width direction is performed at 235 ° C., so that the layer (c
Layer) and a mat-like void-containing biaxially stretched polyester-based laminated film having a constitution of a layer (d layer) composed of raw material D on one side thereof. The thickness of each layer is c layer / d layer = 40 μm
m / 10 μm. Next, a biaxially stretched polyester film obtained by laminating the obtained void-containing biaxially stretched polyester-based laminated film and a silver thin film layer (silver film thickness: 1000
Å, film thickness: 12 μm) to obtain a light reflecting sheet. Table 1 shows the obtained results.

Raw Material D (1) Polyethylene terephthalate resin (intrinsic viscosity:
(0.62 dl / g): 90% by weight (2) Zeolite particles (AMT-08 manufactured by Mizusawa Chemical Co., Ltd.);
Average particle size 0.6 μm): 10% by weight

Comparative Example 5 A metallic silver target was coated on the surface of a biaxially stretched polyethylene terephthalate film (Cosmoshine A4140, manufactured by Toyobo Co., Ltd.) having a thickness of 50 μm with an argon gas pressure of 0.
At 4 Pa, a 1000 ° silver thin film was formed by DC magnetron sputtering to obtain a light reflecting sheet. Table 1 shows the obtained results.

Comparative Example 6 The procedure of Example 1 was repeated except that the raw material of the film was changed to the raw material B, and the thickness of the unstretched sheet was adjusted by reducing the resin discharge amount of the extruder so that the final film thickness became 25 μm. As in Example 1, the thickness was 25 μm,
A cavity-containing biaxially stretched polyester film containing 50% by weight of titanium dioxide particles was obtained. Next, a biaxially stretched polyester film obtained by laminating the obtained void-containing biaxially stretched polyester film and a silver thin film layer (silver film thickness: 10
00 °, film thickness: 12 μm) to obtain a light reflecting sheet. Table 1 shows the obtained results.

[0060]

[Table 1]

[0061]

As described above, the reflected light diffusing film for a liquid crystal display of the present invention is a polyester resin film containing many fine cavities, and has a total light transmittance of 10% or more and 40% or more. Is less than
When a light reflecting sheet having a metallic glossy surface provided on the film is used, excellent light reflectance of the metallic glossy surface can be utilized, and vertical luminance due to a light diffusion effect is excellent, and luminance unevenness is small.

Further, at a wavelength of 400 to 700 nm,
The difference between the average reflectance of the film and the average reflectance between the film and the light reflective sheet when the metal reflective surface is arranged on the back surface of the film is 5% or more. There is an advantage that it is excellent.

Further, the reflected light diffusing film of the present invention
While maintaining the above performance, the film thickness is 25-100μ
m, so that it can be superimposed on the back surface of the light guide plate by following a light guide plate provided with a curved surface or a thin display.

Therefore, it is suitable for a liquid crystal display used as a member of a liquid crystal display device having a backlight mechanism such as a liquid crystal monitor for a stationary computer or a liquid crystal television, and particularly, a reflected light diffusion film for a thin liquid crystal display. is there.

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Claims (6)

[Claims] 1. A reflected light diffusion film based on a polyester resin film containing fine cavities, wherein the base film has a total light transmittance of 10% or more and less than 40%, and has a wavelength of 400 to 700 nm. A reflected light diffusion film for a liquid crystal display, wherein a difference between an average reflectance of a base film and an average reflectance when a metallic glossy surface is provided on the back surface of the film is 5% or more. 2. The method according to claim 1, wherein said base film has a thickness of 25 to 100.
2. The reflection light diffusion film for a liquid crystal display according to claim 1, wherein the thickness of the reflection light diffusion film is μm. 3. The reflection light diffusion film for a liquid crystal display according to claim 1, wherein the content of the inorganic particles in the base film is 10% by weight or less. 4. A light reflection sheet comprising a substrate film according to claim 1, and a plastic film on which a metal thin film is laminated. 5. A light reflecting sheet comprising a metal thin film laminated on one surface of the base film according to claim 1. 6. The light reflection sheet according to claim 4, wherein the metal thin film is any one of silver, an alloy containing silver, and a laminated film of silver and another metal.