JP2001172403A - Light-diffusing film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a light-diffusing film used for a transmission screen, a backlight for liquid crystal display, a lighting panel, or the like, excellent in optical isotropy, having high planarity and a smooth surface, scarcely curling, having good surface quality, and giving high productivity, and to provide a method for producing the same. SOLUTION: This method for producing the light-diffusing film comprises casting a dope containing fine particles on a support, peeling the film from the support, and drying, wherein the formed film has a haze of >=30%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing film or a light diffusing plate used for a backlight or a lighting panel of a liquid crystal display or a light diffusing plate or a light diffusing function used for a transmissive screen used for a transmissive projection television. The present invention relates to a polarizing plate protective film having the same.

[0002]

2. Description of the Related Art In a liquid crystal display device using a liquid crystal such as a liquid crystal television, a portable terminal, a personal computer or a word processor display, in order to make the displayed image easy to see,
An illumination panel is disposed behind the liquid crystal display panel, and light from the illumination panel is transmitted from the rear to the front of the liquid crystal display panel to perform display.

The backlight used here is required to irradiate the entire liquid crystal display screen uniformly.
In recent years, for a thin liquid crystal display device such as a notebook type personal computer, which is desired to be reduced in size and thickness, a sidelight type surface light source device in which light is incident on a liquid crystal display screen from a side surface is preferably used. I have. In general, the side light type surface light source device employs a light guide plate system in which a light guide plate capable of uniformly transmitting and diffusing light is used to uniformly irradiate the entire liquid crystal display screen. In this light guide plate system, a light guide plate, a light source disposed on an end face on which light on both sides of the light guide plate is incident, a reflection plate disposed on a back surface side of the light guide plate, and a surface of the light guide plate. It has a light diffusion film that scatters and diffuses light emitted from the light emitting surface to make the luminance of the irradiated surface uniform.

[0004] A milky white resin film is used as a light diffusion film applied to such a lighting panel.
This makes the light emitted from the light guide plate scattered light, makes the light from the light source uniform, and widens the light, thereby contributing to the improvement of the viewing angle of the display device.

In a transmission screen used for a transmission projection television or the like, a light diffusion film or a light diffusion plate is used for any member of the screen.
As a light diffusing plate used for such an application, a light diffusing plate described in JP-A-11-271510 has been proposed.

However, there has been a demand for a light diffusion film or a light diffusion plate having better optical isotropy, high flatness, a smooth surface, little curl, and good surface quality. Further, a method for producing a light diffusion film or a light diffusion plate having high productivity has been required.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a light-diffusing film or a light-diffusing plate (hereinafter referred to as a light-diffusing film) used for a transmission screen or a backlight of a liquid crystal display, a lighting panel, a touch panel, and the like. It is an object of the present invention to provide a light diffusion film having excellent optical isotropy, high flatness, a smooth surface, little curl, and good surface quality. Another object of the present invention is to provide a method for producing a light diffusion film having high productivity.

[0008]

The above object is achieved by the following means.

1. A method for producing a light-diffusing film, comprising casting a dope containing fine particles on a support, peeling the dope, and drying the film to form a film having a haze of 30% or more.

[0010] 2. A method for producing a light diffusion film, in which at least two or more dopes are used, and the dopes are simultaneously or sequentially cast on a support, peeled off and dried to produce a film having a haze of 30% or more. A method for producing a light diffusing film, characterized in that fine particles are added to at least one of a dope used on the support side (B side) and a dope used on the air side (A side).

3. A method for producing a light-diffusing film for producing a light-diffusing film having a haze of 30% or more, comprising using at least two or more dopes and simultaneously or sequentially casting the dope on a support, and drying after peeling. The dope used comprises at least one dope for forming the surface layer of the film and at least one dope for forming the internal region, and the at least one dope for forming the internal region contains fine particles. A method for producing a light-diffusing film.

4. The method for producing a light diffusing film according to any one of the above items 1 to 3, wherein the amount of the fine particles in the dope containing the fine particles is 1% by mass or more per solid content.

5. The concentration of the fine particles contained in the dope for forming the surface layer is 0 to 0.5% by mass per solid content, and the fine particles of at least one dope forming the internal region of the film sandwiched between these two types of dopes The method for producing a light diffusion film according to claim 3, wherein the concentration is 1% by mass or more per solid content.

6. A method for producing a light diffusion film, comprising stretching a resin film containing fine particles to produce a light diffusion film having a haze of 30% or more.

[0015] 7. By forming a biaxially stretched thermoplastic resin molded article containing fine particles so that the stretch ratio in one direction is 1.0 to 2.0 times and the stretch ratio in the other direction is 2.3 to 7.0 times, A method for producing a light diffusion film, comprising producing a light diffusion film having a haze of 30% or more.

8. The method for producing a light diffusion film according to any one of the above items 1 to 5, further comprising a stretching step.

9. 9. A light-diffusing film produced by the method described in any one of 1 to 8 above.

10. A light diffusion film characterized in that a plasticizer is contained in a light diffusion film having a haze of 30% or more containing fine particles.

11. The light-diffusing film as described in 9 or 10, wherein the light-diffusing film contains a plasticizer having a freezing point of 25 ° C. or lower.

[12] The light diffusing film according to any one of 9 to 11, further comprising an ultraviolet absorber.

13. 13. The light diffusion film according to any one of 9 to 12, wherein the light diffusion film contains a cellulose ester.

Hereinafter, the present invention will be described in detail. A light diffusion film used for a backlight of a liquid crystal display, a lighting panel or the like, or a part of a light diffusion plate used for a transmission type clean used for a transmission type projection television or a protective film for a polarizing plate has a light diffusion function. Light diffusion film (hereinafter, light diffusion plate is also included)
And JP-A-11-6905 and JP-A-1
Various light diffusing films have been proposed, such as JP-A-1-64611, JP-A-10-142406, JP-A-9-159837, JP-A-7-130002, and JP-A-11-271510. However, these light diffusion films have a complicated structure and it is difficult to obtain a light diffusion film having good optical properties and surface quality. Therefore, as a result of intensive studies to solve this problem, by stretching a resin film containing fine particles, it is possible to obtain a light diffusion film having less curl, good surface quality, and excellent optical characteristics. did it. If a large amount of fine particles are added, there are also problems such as deterioration of surface quality and loss of adhesion. However, when the solution casting method was used, the surface quality of the surface on the support side at the time of casting could be made particularly good, and no decrease in adhesiveness was observed. Further, a retardation in the film thickness direction of the film was low and an optically uniform light diffusion film could be obtained.

Further, when two or more dopes are used,
When casting the dope on the support, the amount of fine particles added to the surface layer on the side A (air side) and / or the side B (side of the support) is reduced so that the light diffusion property is provided inside the film. Thereby, a uniform light diffusion film having a better surface quality can be obtained, and a light diffusion film having both a light diffusion layer and a transparent resin layer can be obtained with excellent productivity and excellent quality according to the purpose. I was able to. In addition, by reducing the amount of fine particles added on the surface layer, not only the surface quality can be improved, but also the process contamination due to the drop of fine particles from the surface can be prevented, and higher productivity can be secured. It was done.

Further, when a large amount of fine particles are added to impart light diffusivity, the film becomes brittle. However, by adding a plasticizer, this problem can be solved. Preferably the amount of plasticizer is 1 to solid content
More preferably, it is 20% by mass and contains a plasticizer having a freezing point of 25 ° C. or lower. Furthermore, it was confirmed that by adding an ultraviolet absorber to the portion containing the fine particles, a higher ultraviolet absorbing ability could be obtained with the same addition amount.
This is because light containing ultraviolet light diffuses in the part containing fine particles,
Due to the irregular reflection, the light passes through a longer distance in the film than in a straight line, and it is considered that the apparent ultraviolet absorption capacity is increased. The ultraviolet absorber may be contained in the resin binder of the layer in which the fine particles are present, or the added fine particles themselves may have the ultraviolet absorbing ability, but it is more preferable that both have the ultraviolet absorbing ability. It is preferable that the difference in the refractive index between the fine particles to be added and the resin binder is 0.02 or more, since the light diffusibility can be increased with a small amount of added particles.

In the present invention, the surface layer refers to a region having a depth of 10 μm from the film surface toward the center, and the inside (or the internal region) of the film refers to a region excluding the surface layer.

The resin used in the light diffusing film of the present invention is not particularly limited. Examples thereof include polyethylene film, polypropylene film, cellophane, cellulose diacetate film, cellulose acetate butyrate film, cellulose acetate propionate film, and cellulose acetate. Phthalate films, films made of cellulose esters such as cellulose triacetate and cellulose nitrate or derivatives thereof, polyethylene terephthalate (PET) films,
Polyvinylidene chloride film, polyvinyl alcohol film, ethylene vinyl alcohol film, syndiotactic polystyrene film, polycarbonate film, norbornene resin film, polymethylpentene film, polyetherketone film, polyethersulfone film, polysulfone film,
Polyether ketone imide film, polyamide film, fluororesin film, nylon film, polymethyl methacrylate film, acrylic film or polyarylate film, and the like,
In the present invention, a cellulose triacetate film (TAC film), a cellulose ester film such as a cellulose acetate propionate film, and a polycarbonate (hereinafter abbreviated as PC) film, which can be formed by a casting method, are transparent, mechanical, TAC film and PC film are particularly preferable because they have no properties and no optical anisotropy. Among them, TAC film and PC film are preferably used because of ease of film formation and excellent workability.

In the cellulose ester film according to the present invention, the cellulose ester is preferably a lower fatty acid ester. The lower fatty acid in the lower fatty acid ester of the cellulose ester means a fatty acid having 6 or less carbon atoms, for example, cellulose acetate, cellulose propionate, cellulose butyrate and the like are preferred examples of the lower fatty acid ester of cellulose. .

Further, in addition to the above, Japanese Patent Application Laid-Open No. H10-458
04, 08-231761, U.S. Pat. No. 2,31
Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate described in JP-A-9,052 and the like can be used.

In the above description, a particularly preferred lower fatty acid ester of cellulose is cellulose triacetate.

Further, from the viewpoint of base strength, it is particularly preferable to use a polymerization degree of from 250 to 400 and an amount of bound acetic acid of from 54 to 62.5%, more preferably from 58 to 400%.
62.5% cellulose triacetate.

As the cellulose triacetate according to the present invention, either cellulose triacetate synthesized from cotton linter or cellulose triacetate synthesized from wood pulp can be used alone or in combination. If the releasability from the belt or drum becomes a problem, it is preferable to use a large amount of cellulose triacetate synthesized from cotton linter having good releasability from the belt or drum because the productivity is high.

When cellulose triacetate synthesized from wood pulp is used as a mixture, the ratio of cellulose triacetate synthesized from cotton linter is preferably 40% by mass or more, and the effect of releasability becomes remarkable. Is more preferable, and it is most preferable to use it alone.

Depending on the properties of the resin, a method of forming a film by a solution casting method and a method of extruding the resin in a molten state by melt extrusion molding using an extruder or the like are possible. In order to obtain high film thickness accuracy and surface quality, it is more preferable to form a film by a solution casting method.

The light diffusion film of the present invention has a thickness of 30 μm to 3 m.
A film having a thickness of about m is preferably used depending on the application. Although the required haze value varies depending on the application, according to the present invention, a light diffusion film having a haze value of 30% or more can be easily produced, and preferably a light diffusion film having a haze value of 50% or 70% or more can be produced. .

As the fine particles used in the light diffusion film of the present invention, the following inorganic substances and / or organic substances are used alone or in an appropriate combination.

For example, examples of the inorganic particles include silicon dioxide, titanium oxide, aluminum oxide, aluminum hydroxide, tin oxide, zinc oxide, calcium carbonate, barium sulfate, talc, kaolin, and calcium sulfate.
As the organic particles, acrylic resin, organic silicone resin, polystyrene, urea resin, formaldehyde condensate, polymethyl methacrylate resin, acrylic styrene resin, polymethyl methacrylate resin,
Silicone resin, polystyrene resin, polycarbonate resin, benzoguanamine resin, melamine resin, polyolefin resin, polyester resin, polyamide resin, polyimide resin, or polyfluoroethylene resin is used. However, the present invention is not particularly limited to these.

The fine particles of silicon dioxide according to the present invention include, for example, Aerosil R972, R972V, R97
4, R812, 200, 200V, 300, R202,
OX50, TT600 (all manufactured by Nippon Aerosil Co., Ltd.)
Commercially available products having trade names such as

As the fine particles of zirconium oxide according to the present invention, those commercially available under the trade names such as Aerosil R976 and R811 (all manufactured by Nippon Aerosil Co., Ltd.) can be used.

As the organic compound, for example, polymers such as silicone resin, fluorine resin and acrylic resin are preferable, and among them, silicone resin is preferably used.

Among the above-mentioned silicone resins, those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 1
Commercial products having trade names such as Nos. 45, 3120 and 240 (all manufactured by Toshiba Silicone Co., Ltd.) can be used.

The difference in the refractive index between the fine particles constituting the light diffusion film of the present invention and the resin in which the fine particles are dispersed is as follows:
0.02 or more is preferable. When the difference in refractive index is less than 0.02, the light diffusion effect is small, so the amount of added fine particles is increased, and the mechanical strength may be reduced.

The volume average particle diameter of these particles is 0.01 to 50 μm. Preferably 0.
Fine particles of 1 to 30 μm are used, and particularly preferably 1 to 30 μm.
Fine particles of 20 μm are used. Also, it is preferable to add fine particles having different average particle sizes at the same time in order to enhance light diffusivity. The proportion of the addition depends on the required light diffusivity, but it is desirable that the addition is made in an amount of 1 to 30% by mass per solid content. More preferably, the content is 5 to 15% by mass. When the addition amount is large, the mechanical properties of the film are reduced, and when the addition amount is small, it is difficult to obtain a sufficient light diffusing property.

The method for preparing the dispersion liquid of fine particles according to the present invention includes, for example, the following three methods, but is not particularly limited thereto.

(Preparation method A) After stirring and mixing the solvent and the fine particles, the mixture is dispersed with a disperser. This is used as a fine particle dispersion. The fine particle dispersion is added to the dope and stirred.

(Preparation method B) After stirring and mixing the solvent and the fine particles, the mixture is dispersed with a disperser. This is used as a fine particle dispersion. Separately, a small amount of resin is added to a solvent and dissolved by stirring. The fine particle dispersion is added thereto and stirred. This is used as a fine particle addition liquid. The fine particle addition liquid is sufficiently mixed with the dope liquid using an in-line mixer.

(Preparation method C) A small amount of resin is added to a solvent,
Stir to dissolve. Fine particles are added thereto and dispersed by a disperser. This is used as a fine particle addition liquid. The fine particle addition liquid is sufficiently mixed with the dope liquid using an in-line mixer.

Preparation method A is excellent in dispersibility of the fine particles, and preparation method C is excellent in that the fine particles are hard to re-aggregate. Preparation method B is a preferable preparation method because it is excellent in both the dispersibility of the fine particles and the difficulty of reaggregation of the fine particles.

(Dispersion Method) When the fine particles are mixed with a solvent and dispersed, the concentration of the fine particles is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and most preferably 15 to 20% by mass.

As the solvent used, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, and alcohols are used. Particularly, lower alcohols are preferable, and methyl alcohol, ethyl alcohol, propyl alcohol, and the like are used. Examples thereof include isopropyl alcohol and butyl alcohol, but are not particularly limited thereto.

As the disperser, an ordinary disperser can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers.

Examples of the media dispersing machine include a ball mill, a sand mill, a dyno mill and the like.

As the medialess disperser, there are an ultrasonic type, a centrifugal type, a high pressure type and the like. The high-pressure dispersing device is a device that creates a special condition such as a high shear or a high pressure state by allowing a composition in which fine particles and a solvent are mixed to pass through a thin tube at a high speed. When processing with a high-pressure dispersion device, for example,
When the maximum pressure condition inside the device is 10
It is preferably at least MPa. More preferably, 20
MPa or more. At that time, the maximum arrival speed is 100
Those which reach m / sec or more and those whose heat transfer rate reaches 418 kJ / hour or more are preferable.

The high-pressure dispersion apparatus as described above includes Micro
There is an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Fluidics Corporation or a Nanomizer manufactured by Nanomizer, and a homogenizer of the Manton-Gaulin type, such as a homogenizer manufactured by Izumi Food Machinery Co., Ltd., and a UHN- manufactured by Sanwa Machine Co., Ltd. 01 and the like.

When a dope containing fine particles for imparting light diffusing property is cast on a support to form a film, the surface in contact with the support becomes a film having a very smooth surface, especially the surface. A light diffusing film having a roughness Ra of 0.2 μm or less can be easily obtained. Thereby, the side in contact with the support can be used as the side where smoothness is required.

In the present invention, the surface layer refers to a region from the film surface to a depth of 10 μm in the center direction, and the inside (or the internal region) of the film refers to a region excluding the surface layer.

In order to produce a film having a haze of 30% or more, at least two or more kinds of dopes are used, and the dopes are simultaneously or sequentially cast on a support, dried and peeled off. Fine particles for imparting light diffusing property may be added to at least one of the dope used on the body side (side B) and the dope used on the air side (side A). By adding a large amount of fine particles to the dope used on the (B side) and reducing the amount of fine particles of the dope used on the air side (A side), not only the support side (B side) but also the air The surface on the side (side A) can also be a film having a smooth surface, which is preferable.

Further, more preferably, at least two or more dopes are used, and the dopes are simultaneously or successively cast on a support, and then separated and dried to produce a light-diffusing film. Is a dope used on the side of the support (B side) and a dope used on the air side (A side), and one or more types mainly forming an internal region of the film sandwiched between these two types of dopes. And at least one dope used for forming the internal region contains fine particles for imparting light diffusing property. In this case, at least one dope used for forming the internal region contains fine particles for imparting light diffusing property, and light having a smooth surface containing no fine particles on both surfaces is provided. A diffusion film is obtained.

The thickness of the cellulose ester laminated film of the present invention will be described. When the entire thickness of the light diffusion film is constant, the thinner the layer on the surface of the cellulose ester laminated film, the higher the haze, and the better the mechanical strength. Elution of the absorbent can be suppressed, resulting in excellent productivity. The film thickness of the surface layer that balances these is preferably 5 to 20 μm, more preferably 7 to 15 μm, and most preferably 10 to 20 μm.
μm.

If the film thickness of the whole cellulose ester film is too thin, the strength of the polarizing plate as a protective film is insufficient, and the dimensional stability of the polarizing plate and the storage stability under wet heat deteriorate. Alternatively, it becomes difficult to obtain a sufficient light diffusion effect. On the other hand, if the film thickness is large, the polarizing plate becomes thick, and it is difficult to reduce the thickness of the liquid crystal display. The film thickness of the cellulose ester laminated film that balances these is 30 to 1000 μm, preferably 40 to 500 μm, and more preferably 50 to 300 μm.
It is.

The polarizing plate can be manufactured by a general method. For example, in the case of the light-diffusing film of the present invention comprising a cellulose ester, there is a method in which an alkali treatment is performed, and both surfaces of a polarizing film produced by immersion stretching in an iodine solution are bonded using a completely saponified polyvinyl alcohol aqueous solution. . The alkali saponification treatment refers to a treatment in which the cellulose ester film is immersed in a high-temperature strong alkaline solution in order to improve the wettability of the aqueous adhesive at this time and improve the adhesiveness.

The polarizing film, which is a main component of the polarizing plate, is an element that transmits only light having a polarization plane in a certain direction, and a typical polarizing film currently known is a polyvinyl alcohol-based polarizing film. Are dyed polyvinyl alcohol-based films with iodine and dyed with dichroic dyes. These are formed by forming a film of an aqueous solution of polyvinyl alcohol, uniaxially stretching and dyeing the film, or dyeing the film and then uniaxially stretching the film, and preferably performing a durability treatment with a boron compound. The polarizing plate is formed by sandwiching the polarizing film with a light diffusing film of the present invention and another transparent plastic film which is a protective film for a polarizing plate and laminating them.

The method for producing the cellulose ester laminated film of the present invention will be described with reference to the process charts shown in FIGS.

FIG. 1 is a process diagram showing an example of an apparatus for producing a cellulose ester laminated film of the present invention.
Shows a sectional view of the slit die 6 of FIG.

A dope solution 1a is charged into a dope solution tank 1 for preparing a cellulose ester dope solution.
The fine particle addition liquid tank 2 is charged with the fine particle addition liquid 2a.

The dope solution 1a is sent to the in-line mixers 5a and 5b by the sending pumps 4b and 4c, and the fine particle addition solution 2a is sent to the in-line mixer 5a by the pump 4a.
a. Dope solution 1 with in-line mixer 5a
a and the fine particle addition liquid 2a are sufficiently mixed, and the slit die 6
To the slit 12.

Similarly, the dope solution 1 a and the ultraviolet absorber additive solution 3 a are sufficiently mixed by the in-line mixer 5 b and sent to the slit 13 of the slit die 6.

By means of the slit die 6, the middle layer is composed of a mixture of the dope solution 1a and the fine particle addition liquid 2a, and the upper and lower surface layers are composed of the dope solution 1a and the ultraviolet absorber addition liquid 3a.
Is co-cast from the casting port 11 in the state of a mixed solution of
It is cast on a casting belt 8 that moves more continuously. The cast cellulose ester dope layer consisting of three layers,
After drying, as a cellulose ester laminated film 10,
The roller 9 separates from the casting belt.

The method of co-casting according to the production method of the present invention will be described. Co-casting is a sequential multilayer casting method in which two or more layers are formed through different dies, and two or three or more layers are merged in a die having two or three or more slits. The method may be any of a simultaneous multilayer casting method and a multilayer casting method combining sequential multilayer casting and simultaneous multilayer casting.

In the present invention, the dope solution in which the resin is dissolved means that the resin such as cellulose ester is a solvent (solvent).
It is desirable that an additive such as a plasticizer be added to the dope solution, and of course, other additives can be added if necessary. The concentration of the resin in the dope solution is preferably from 10 to 30% by mass, and more preferably from 18 to 20% by mass.

The solvent used in the present invention may be used alone or in combination. However, it is preferable to use a mixture of a good solvent and a poor solvent from the viewpoint of production efficiency. More preferably, a mixture of a good solvent and a poor solvent is used. The ratio is such that the good solvent is 70 to 95% by mass and the poor solvent is 30 to 5% by mass.

The good solvent and the poor solvent used in the present invention are:
Those that dissolve the resin used alone are defined as good solvents, and those that swell or do not dissolve alone are defined as poor solvents. For this reason, the good solvent and the poor solvent vary depending on the amount of the bound carboxylic acid of the resin. For example, when acetone is used as the solvent, the solvent becomes a good solvent when the amount of bound acetic acid is 55% in the case of cellulose ester, and is poor when the amount of bound acetic acid is 60%. It becomes a solvent.

The good solvent used in the present invention includes organic halogen compounds such as methylene chloride and dioxolanes.

As the poor solvent used in the present invention, for example, methanol, ethanol, n-butanol, cyclohexane and the like are preferably used.

As a method for dissolving the cellulose ester in preparing the above-mentioned dope solution, a general method can be used, but a preferable method is to mix the cellulose ester with a poor solvent and wet or swell. Let
Further, a method of mixing with a good solvent is preferably used. At this time, under pressure, the method of heating at a temperature not lower than the boiling point of the solvent at room temperature and the solvent does not boil, and dissolving while stirring, in order to prevent the generation of a massive undissolved substance called gel or mamako, More preferred.

The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

The heating temperature after the addition of the solvent is preferably set to a temperature not lower than the boiling point of the solvent used and not causing the solvent to boil, for example, preferably not lower than 60 ° C. and not lower than 70 to 110 ° C. . The pressure is adjusted at the set temperature so that the solvent does not boil.

After the dissolution, it is taken out of the container while cooling, or is taken out of the container by a pump or the like, cooled by a heat exchanger or the like, and supplied to a film. The cooling temperature at this time may be cooled to room temperature, but it is more preferable to cool to a temperature 5 to 10 ° C. lower than the boiling point and perform casting at that temperature because the dope viscosity can be reduced.

For example, as described above, in the production of the cellulose ester laminated film having two or more layers according to the present invention, a dope solution in which cellulose ester is dissolved in a solvent, a solution in which fine particles and a small amount of cellulose ester are dissolved, are used. And a dope solution prepared by mixing and dispersing the dope with an in-line mixer and a dope solution in which the cellulose ester is dissolved (if necessary, an ultraviolet absorber added inline separately is added). Using a die slit having a slit, the dope solution containing fine particles is directly cast on a casting belt, and co-cast (casting step). After removing the portion (drying step on the casting belt), the film is peeled off from the casting belt, and the peeled film is dried (film drying step), thereby obtaining the film of the present invention. Diffusion film can be obtained.

As the support in the casting step, a support in which a belt-shaped or drum-shaped stainless steel is mirror-finished is preferably used. The temperature of the support in the casting step can be cast in a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, but casting on the support at 0 to 30 ° C. causes gelation of the dope. It is preferable because the separation time can be increased, and it is more preferable to cast on a support at 5 to 15 ° C. The peeling limit time is the limit of the casting speed at which a transparent and flat good film can be continuously obtained.
The time during which the cast dope remains on the support. It is preferable that the peeling limit time is short because the productivity is excellent.

The surface temperature of the support on the side to be cast (cast) is 10 to 55 ° C., the temperature of the solution is 25 to 60 ° C.
Further, the temperature of the solution is preferably higher than the temperature of the support by 0 ° C. or more, and more preferably 5 ° C. or more. The solution temperature and the support temperature are preferably higher as the drying speed of the solvent can be increased, but if the temperature is too high, foaming or
Flatness may be deteriorated.

A more preferred range of the temperature of the support is 20
~ 40 ° C, a more preferred range of solution temperature is 35-45.
° C.

Further, the temperature of the support at the time of peeling is 10 to 4
The temperature is preferably set to 0 ° C, more preferably 15 to 30 ° C, because the adhesion between the film and the support can be reduced.

In order for the cellulose ester film to exhibit good flatness at the time of production, the amount of residual solvent when peeled from the support is preferably from 10 to 80%, more preferably from 20 to 40%, or from 60 to 40%. 80%, particularly preferably 20 to 30%.

In the present invention, the amount of the residual solvent is defined by the following equation. Residual solvent amount = (mass before heat treatment−mass after heat treatment) /
(Mass after heat treatment) × 100% The heat treatment, which is the final measurement of the amount of residual solvent, means that the film is heated at 115 ° C. for 1 hour.

The peeling tension at the time of peeling the film from the support is usually 200 to 250 N (Newton) / m. However, the content of the ultraviolet absorber per unit mass of the cellulose ester is large, and The cellulose ester film of the present invention, which has been made thinner than before, is likely to have wrinkles at the time of peeling, so that the minimum tension that can be peeled off
Peeling is preferably performed at 170 N / m, more preferably at a minimum tension of 140 N / m.

In the drying step of the cellulose ester film, the film peeled off from the support is further dried to reduce the residual solvent amount to preferably 3% by mass or less, more preferably 0.5% by mass or less. is there.

In the film drying step, a method of drying while transporting a film by a roll hanging method or a pin tenter method is generally employed. For liquid crystal display members, it is preferable to dry while maintaining the width by a pin tenter method in order to improve dimensional stability. In particular, it is particularly preferable to maintain the width at a place where the amount of the residual solvent is large immediately after peeling off from the support, since the effect of improving the dimensional stability is further exhibited. The means for drying the film is not particularly limited, and is generally performed using hot air, infrared rays, a heating roll, a microwave, or the like.
It is preferable to use hot air in terms of simplicity. Drying temperature is 40
It is preferable that the temperature is gradually increased in three to five steps in the range of 150 to 150 ° C., and it is more preferable to perform in the range of 80 to 140 ° C. in order to improve dimensional stability.

A small amount of fine particles can be added to the dope used on the side of the support (B side) or the dope used on the air side (A side), which also has the effect of improving the slipperiness of the film surface. Be expected. The slip property is expressed by a coefficient of kinetic friction. The coefficient of kinetic friction is a coefficient of kinetic friction between the front and back surfaces of the film, and is defined by JIS-K-7125 (1).
When measured according to 987), it is preferably 2 or less, more preferably 1.5 or less, and
It is more preferably 0 or less, more preferably 0.5 or less. The dynamic friction coefficient can be reduced by increasing the amount of the matting agent added. In order to increase the slipperiness and prevent blocking by adding these particles, the volume average particle diameter is from 0.01 μm to 0.1 μm.
It is preferable to use 0.005 to 5% by mass of 5 μm particles.

For example, on the air side (A side), it is preferable that the addition amount of fine particles on the surface is small in order to maintain surface quality, and that the addition amount of fine particles on the surface is small in order to maintain adhesiveness. Is desirable. According to the present invention, a light diffusion film having a surface roughness Ra of 0.2 μm or less can be easily produced.

In the production of the light diffusing film of the present invention, it is preferable that the film is peeled after casting and then stretched in the lateral direction by means of a tenter or the like, thereby maintaining higher flatness. This makes it possible to obtain a light diffusion film that does not warp for a long time. The tenter is desirably applied with a residual solvent amount of 10 to 40% by mass. More preferably, the content is 15 to 35% by mass. The amount of residual solvent is determined from the change in mass before and after the film containing the solvent is treated at 115 ° C. for 1 hour and the mass of the film after the heat treatment according to the above-described formula.

The light-diffusing film produced by the method of the present invention is also excellent in optical isotropy. A light-diffusing film having a retardation (Rt) value in the film thickness direction of 100 nm or less is obtained, and a light-diffusing film of 50 nm or less. It is excellent in that a light diffusion film can be obtained, and a light diffusion film of 0 to 30 nm can be obtained. Further, the method of the present invention is also excellent in that a uniform retardation can be obtained.

The retardation (Rt) value is represented by the following equation. Rt = ((Nx + Ny) / 2−Nz) × d where Nx is the refractive index of the film in a direction parallel to the film forming direction, Ny is the refractive index of the film in a direction perpendicular to the film forming direction, and Nz is The refractive index of the film in the thickness direction, d, represents the thickness (nm) of the film, respectively.

For example, the retardation is measured by an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments)
Sample before alkali saponification treatment at 23 ° C., 5 ° C.
In an environment of 5% RH, a three-dimensional refractive index measurement is performed at a wavelength of 590 nm, and Nx, Ny, and Nz are measured, whereby the Rt value can be calculated.

It is preferable to add a plasticizer to the portion containing the fine particles, so that the film which becomes brittle due to the inclusion of the fine particles can be given flexibility and the adhesion is improved.

As a plasticizer, a phosphoric acid ester or a carboxylic acid ester is preferably used. Phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP), biphenyl-diphenyl phosphate, dimethylethyl phosphate. Representative carboxylic esters include phthalic esters and citric esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), and dioctyl phthalate (DO).
P) and diethylhexyl phthalate (DEHP),
Ethylphthalylethyl glycolate and the like are used. Examples of citrate esters include acetyltriethyl citrate (OACTE) and acetyltributyl citrate (OACTE).
ACTB) is used. Examples of other carboxylic esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic esters. Phthalate ester plasticizers (DMP,
DEP, DBP, DOP, DEHP) are preferably used, but not limited to these.

The amount of the plasticizer is preferably 1 to 20% by mass, more preferably 2 to 15% by mass in the film.
It is desirable to add it.

Further, a plasticizer having a freezing point of 25 ° C. or less is preferably used for imparting flexibility to the film and maintaining the adhesion between the resin and the fine particles.

Further, by incorporating an ultraviolet absorber into the light diffusion film of the present invention, a light diffusion film having a high ultraviolet absorbing ability can be obtained. This is thought to be due to scattering and diffusion in the light diffusion layer rather than passing through the transparent resin film linearly and passing through a longer distance. The addition amount can be reduced. More preferably, it is desirable that the added fine particles also have ultraviolet absorption.

The ultraviolet absorber useful in the present invention includes salicylic acid derivatives (UV-1), benzophenone derivatives (UV-2), and benzotriazole derivatives (UV-1).
3), acrylonitrile derivative (UV-4), benzoic acid derivative (UV-5), organometallic complex salt (UV-6), etc., and (UV-1) is phenyl salicylate, 4-t-butylphenyl, respectively. Salicylic acid, etc. (UV
-2) includes 2-dihydroxybenzophenone, 2
-Hydroxy-4-methoxybenzophenone and the like, (U
V-3) includes 2- (2'-hydroxy-5'-methylphenyl) -benzotriazole, 2- (2'-hydroxy-3'-5'-di-butylphenyl) -5-chlorobenzotriazole Etc., as (UV-4)
2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate, methyl-α-cyano-β- (p-methoxyphenyl) acrylate, and the like; (UV-5) includes resorcinol-monobenzoate, 2 ′, 4'-
Di-t-butylphenyl-3,5-t-butyl-4-hydroxybenzoate and the like (UV-6) include nickel bis-octylphenylsulfamide, ethyl-
Nickel salts of 3,5-di-t-butyl-4-hydroxybenzylphosphoric acid and the like can be mentioned.

The above-mentioned ultraviolet absorber preferably used in the present invention is preferably a benzotriazole-based ultraviolet absorber or a benzophenone-based ultraviolet absorber which has high transparency and is excellent in preventing deterioration of a polarizing plate or a liquid crystal element. Benzotriazole UV absorbers with less unwanted coloring are particularly preferred. Examples of the method of adding the ultraviolet absorbent additive liquid used in the present invention include the following methods.

(Addition Method A) As a method for preparing an ultraviolet absorber additive liquid, an ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride, or dioxolane, and then added directly to the dope composition.

(Addition method B) As a method for preparing an ultraviolet absorber additive liquid, an ultraviolet absorber and a small amount of a cellulose ester are dissolved in an organic solvent such as alcohol, methylene chloride, or dioxolane, and then added to the dope with an in-line mixer. .

The addition method B is preferable because the addition amount of the ultraviolet absorber can be easily adjusted, so that the productivity is excellent.

The amount of the ultraviolet absorber used is not uniform depending on the kind of the compound and the conditions of use, but is usually preferably 0.1 g to 2.0 g per 1 m ² of the light diffusion film,
g to 1.5 g are more preferable, and 0.5 g to 1.0 g are particularly preferable.

In another embodiment of the present invention, a method for forming a film by melt extrusion is also provided. That is, when a light diffusion film is produced by melt-extrusion molding of a thermoplastic resin such as polyester, a resin containing fine particles for imparting light diffusion property is stretched to produce a light diffusion film. It was possible to obtain a light diffusion film having good flatness. This will be specifically described below.

Polyester is also preferably used in the light diffusion film of the present invention. The polyester constituting the polyester film is not particularly limited,
It is preferable that the polyester is a film-forming polyester containing a dicarboxylic acid component and a diol component as main components.

The main dicarboxylic acid components include terephthalic acid, isophthalic acid, phthalic acid, 2-6 naphthalenedicarboxylic acid, 2-7 naphthalenedicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylether dicarboxylic acid, and diphenylethanedicarboxylic acid. , Cyclohexanedicarboxylic acid, diphenyldicarboxylic acid,
Examples thereof include diphenylthioether dicarboxylic acid, diphenyl ketone dicarboxylic acid, and phenylindane dicarboxylic acid. Further, as the diol component,
Ethylene glycol, propylene glycol, tetramethylene glycol, cyclohexane dimethanol, 2,
2-bis (4-hydroxyphenyl) propane, 2,2
-Bis (4-hydroxyethoxyphenyl) propane,
Bis (4-hydroxyphenyl) sulfone, bisphenol full orange hydroxyethyl ether, diethylene glycol, neopentyl glycol, hydroquinone, cyclohexanediol and the like can be mentioned.

Among polyesters containing these as main components, from the viewpoints of transparency, mechanical strength, dimensional stability, etc., terephthalic acid and / or 2-6 naphthalenedicarboxylic acid and diol component as dicarboxylic acid components
Polyesters containing ethylene glycol and / or diethylene glycol as the main constituent are preferred. Among them, polyethylene terephthalate or polyethylene 2-
Polyesters containing 6-naphthalate as a main component, copolymerized polyesters composed of terephthalic acid, 2-6-naphthalenedicarboxylic acid and ethylene glycol, and polyesters containing a mixture of two or more of these polyesters as a main component are preferable. . When the ethylene terephthalate unit (component) or the ethylene 2-6 naphthalene unit (component) is contained in an amount of 70% by mass or more with respect to the polyester, the resin itself is highly excellent in transparency, mechanical strength, dimensional stability, and the like. A film is obtained.

The polyester constituting the polyester film used in the light diffusing film of the present invention may be further copolymerized with other copolymer components as long as the effects of the present invention are not impaired. Polyester may be mixed. Examples of these include the above-mentioned dicarboxylic acid component and diol component, and polyesters composed thereof.

The polyester constituting the polyester film used for the light diffusion film of the present invention includes an aromatic dicarboxylic acid having a sulfonate group or an ester-forming derivative thereof, and a dicarboxylic acid having a polyoxyalkylene group or an ester-forming derivative thereof. And a diol having a polyoxyalkylene group. In terms of polymerization reactivity of polyester and transparency of film, 5
-Sodium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 4-sodium sulfophthalic acid, 4-
Sodium sulfo-2,6-naphthalenedicarboxylic acid and a compound obtained by substituting sodium with another metal (eg, potassium, lithium, etc.), an ammonium salt, a phosphonium salt, or an ester-forming derivative thereof, polyethylene glycol, polytetramethylene glycol , A polyethylene glycol-polypropylene glycol copolymer, and a compound in which a hydroxy group at both ends thereof is oxidized to form a carboxyl group are preferred. Also,
For the purpose of improving the heat resistance of the film, a bisphenol-based compound and a compound having a naphthalene ring or a cyclohexane ring can be copolymerized.

The above-mentioned fine particles can be added to the polyester used in the light diffusion film of the present invention in order to impart light diffusion. In particular, in the case of forming a film in a molten state, it is preferable to add and knead sufficiently fine particles to be added, since they dislike water.

The polyester used for the light diffusion film of the present invention may contain an antioxidant. In particular, when the polyester contains a compound having a polyoxyalkylene group, the effects of the object of the present invention are remarkable.
The type of the antioxidant to be contained is not particularly limited, and various antioxidants can be used. Examples thereof include antioxidants such as hindered phenol compounds, phosphite compounds, and thioether compounds. Can be. Above all, an antioxidant of a hindered phenol compound is preferred from the viewpoint of transparency.

The content of the antioxidant is usually from 0.01 to 2% by mass, preferably from 0.1 to 2% by mass, based on the polyester.
0.5% by mass.

The polyester film of the present invention may be provided with lubricity as required. The means for imparting lubricity is not particularly limited, but a method of adding external particles to the polyester to add inert inorganic particles, a method of depositing internal particles to precipitate a catalyst to be added during the synthesis of the polyester,
Alternatively, a method of applying a surfactant or the like to the film surface is generally used.

The method for synthesizing the polyester as a raw material for the polyester film of the present invention is not particularly limited, and it can be produced according to a conventionally known method for producing polyester. For example, a direct esterification method in which a dicarboxylic acid component is directly esterified with a diol component, first using a dialkyl ester as a dicarboxylic acid component, a transesterification reaction between the dialkyl ester and the diol component, and heating this under reduced pressure. A transesterification method in which polymerization is performed by removing an excess diol component can be used. At this time, if necessary, a transesterification catalyst or a polymerization reaction catalyst may be used, or a heat stabilizer may be added. In addition, in each process at the time of synthesis, an anti-coloring agent, an anti-oxidant, a crystal nucleating agent, a slipping agent, a stabilizer, an anti-blocking agent, an ultraviolet absorber, a viscosity modifier, an antifoaming agent, a clarifying agent, an antistatic agent, pH
Adjusters, dyes, pigments and the like may be added.

(Definition of glass transition temperature Tg, crystallization temperature Tc and melting point Tm in the present invention) 10 mg of a film or a pellet was placed in a nitrogen stream of 300 ml / min.
Melt at 0 ° C. and immediately quench in liquid nitrogen. This quenched sample was subjected to a differential scanning calorimeter (DSC8, manufactured by Rigaku Denki Co., Ltd.).
230) and in a nitrogen stream at 100 ml / min.
The temperature is raised at a rate of 10 ° C. per minute, and Tg, Tc and Tm are detected. Tg is the temperature at which the baseline begins to shift,
Tc was the peak temperature of the exothermic peak, and Tm was the peak temperature of the endothermic peak. The measurement start temperature is determined by the Tg to be measured.
The temperature is lower by at least 50 ° C.

Next, a method for producing the light diffusing film of the present invention using the polyester of the present invention will be described.

In the present invention, the polyester film is
It is preferable that the stretch ratio in one direction is 1.0 to 2.0 times, and the stretch ratio in the direction orthogonal thereto is 2.3 to 7.0 times, and the polyester film is biaxially stretched. A stretch ratio of 1.0 to 2.0 times in the longitudinal direction and a stretch ratio of 2.3 to 7.0 times in the transverse direction. It is a polyester film formed into a biaxially stretched film with a stretching ratio of 1.1 to 1.8 times and a lateral stretching ratio of 3.0 to 6.0 times.

The polyester film can be obtained by a conventionally known method and is not particularly limited, but can be obtained by the following method. The longitudinal direction refers to the film forming direction (longitudinal direction) of the film, and the lateral direction refers to the direction perpendicular to the film forming direction.

First, the raw material polyester is formed into pellets, dried with hot air or vacuum, and then fine particles for imparting light diffusivity are added, mixed and dispersed, melt-extruded, and formed into a sheet from a T-die. The sheet is extruded, brought into close contact with a cooling drum by an electrostatic application method or the like, and solidified by cooling to obtain an unstretched sheet. At this time, coextrusion may be performed so that the resin containing fine particles is sandwiched by the resin not containing fine particles.

Next, the obtained unstretched sheet is subjected to a heating operation such as a plurality of roll groups and / or an infrared heater from the glass transition temperature (Tg) of the polyester to Tg + 1.
This is a method in which the film is heated to a temperature within the range of 00 ° C. and longitudinally stretched in one or more stages. In the present invention, the stretching ratio in the longitudinal direction is 1.0 to
The range is preferably 2.0 times, more preferably 1.1 to 1.8 times.

Next, the polyester film stretched in the machine direction obtained as described above was subjected to Tg-Tm-20 ° C.
In the temperature range described above, the film is stretched in the transverse direction and then heat set. In the present invention, the stretching ratio in the transverse direction is preferably in the range of 2.3 to 7.0 times, more preferably 3.0 to 6.0.
It is more preferably in the range of 4.0 to 6.0 times.

In the case of lateral stretching, it is preferable to carry out lateral stretching while sequentially increasing the temperature in the range of 1 to 50 ° C. in the stretching region divided into two or more portions, since the distribution of physical properties in the width direction can be reduced.
Further, after the transverse stretching, the film is maintained at a temperature of not lower than the final transverse stretching temperature and at a temperature of not less than Tg-40 ° C. for 0.01 to 5 minutes.

The heat setting is performed at a temperature higher than the final transverse stretching temperature and in a temperature range of Tm-150 ° C. to Tm-25 ° C. for usually 0.5 to 300 seconds. The heat setting temperature is more preferably in the temperature range of Tm-140 ° C to Tm-60 ° C, and still more preferably in the temperature range of Tm-130 ° C to Tm-70 ° C. At this time, it is more preferable to heat-fix while sequentially increasing the temperature in the range of 1 to 100 ° C. in the two or more divided regions.

The heat-fixed film is usually cooled to Tg or less, cut off the clip holding portions at both ends of the film, and wound up. At this time, within a temperature range of not more than the final heat setting temperature and not less than Tg, 0.1 to 1 in the horizontal and / or vertical directions.
It is preferable to perform a 0% relaxation treatment. Further, it is preferable that the cooling is gradually performed from the final heat setting temperature to Tg at a cooling rate of 100 ° C. or less per second. The means for cooling and relaxing treatment is not particularly limited, and can be performed by a conventionally known means. In particular, it is preferable to perform these treatments while sequentially cooling in a plurality of temperature regions from the viewpoint of improving the dimensional stability of the film. The cooling rate is a value obtained by (Tl-Tg) / t, where Tl is the final heat setting temperature and t is the time required for the film to reach the Tg from the final heat setting temperature.

The most optimal conditions for the heat setting, cooling, and relaxation treatments differ depending on the polyester constituting the film. Therefore, the physical properties of the obtained biaxially stretched film are measured and adjusted appropriately so as to have preferable characteristics. It should just be determined by doing.

In the production of the film, a functional layer such as an antistatic layer, a slippery layer, an adhesive layer and a barrier layer may be provided before and / or after the stretching. At this time, various surface treatments such as a corona discharge treatment, a plasma treatment, and a chemical treatment can be performed as necessary. The clip gripping parts at both ends of the cut film are pulverized, or after granulation, depolymerization, repolymerization, etc., as necessary, as raw materials for the same type of film or different types. It may be reused as a film material.

The polyester film stretched and formed in only one direction of the present invention can be obtained by performing only one direction in the above-described biaxially stretched film formation. The stretching direction may be either the vertical direction or the horizontal direction, but more preferably, the film is stretched only in the horizontal direction. in this case,
The stretching ratio is preferably in the range of 2.3 to 7.0 times, more preferably in the range of 3.0 to 6.0 times, and still more preferably in the range of 4.0 to 6.0 times. Regarding the refractive index in the plane direction of the polyester film formed as described above, the difference nTD-nMD between the horizontal refractive index (nTD) and the vertical refractive index (nMD) is 0.03 or more. It is preferably 0.04 or more, more preferably 0.05 or more.

In the present invention, the heat shrinkage of the polyester film formed as described above at 80 ° C. for 30 minutes is preferably 5% or less in both the vertical and horizontal directions. More preferably, the heat shrinkage is 2% or less in both the vertical and horizontal directions,
More preferably, it is 1% or less.

The T of the polyester film used in the present invention
g is preferably 50 ° C. or higher, more preferably 60 ° C. or higher. Tg is determined as an average value of a temperature measured by a differential scanning calorimeter at which a baseline starts to be shifted and a temperature at which the baseline returns to a new baseline.

In the present invention, the surface of the light diffusion film is preferably conductive, and has a surface resistivity (23 ° C.,
(25% RH) is preferably 1 × 10 ¹² Ω / □ or less. More preferably, it is 1 × 10 ¹¹ Ω / □ or less, and further preferably, it is 1 × 10 ¹⁰ Ω / □ or less.

In the present invention, the method for imparting conductivity is not particularly limited, but it can be formed by incorporating a hygroscopic substance or a conductive substance. Examples of the substance imparting conductivity include a surfactant, a conductive polymer, and an inorganic metal oxide.

The surfactants that can be used include:
Any of anionic, cationic, amphoteric and nonionic may be used. Examples of the anionic surfactant include alkyl carboxylate, alkyl sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfate, alkyl phosphate, N-acyl-N-alkyltaurine Acid groups such as carboxy, sulfo, phospho, sulfate, and phosphate groups such as sulfosuccinates, sulfoalkylpolyoxyethylene alkylphenyl ethers, and polyoxyethylene alkyl phosphates. Is preferred.

Examples of the cationic surfactant include alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts such as pyridinium and imidazolium, and phosphonium or aliphatic or heterocyclic containing heterocyclic rings. Sulfonium salts and the like are preferred.

As the amphoteric surfactant, for example, amino acids, aminoalkylsulfonic acids, aminoalkylsulfuric acid or phosphoric acid esters, alkylbetaines, amine oxides and the like are preferable.

Examples of the nonionic surfactant include saponin (steroid type), alkylene oxide derivatives (eg, polyethylene glycol, polyethylene glycol / polypropylene glycol condensate, polyethylene glycol alkyl ethers or polyethylene glycol alkyl aryl ethers, polyethylene glycol ester) , Polyethylene glycol sorbitan esters, polyalkylene glycol alkylamines or amides, polyethylene oxide adducts of silicone), glycidol derivatives (eg, alkenyl succinic acid polycerides, alkylphenol polyglycerides),
Alkyl esters such as polyhydric alcohol fatty acid esters are preferred.

The conductive polymer is not particularly limited, and may be any of anionic, cationic, amphoteric and nonionic. Among them, preferred are anionic and cationic. More preferred are sulfonic acid-based and carboxylic acid-based polymers for anionic and tertiary amine-based and quaternary ammonium-based polymers or latex for cationic.

These conductive polymers include, for example, anionic polymers or latexes described in JP-B-52-25251, JP-A-51-29923 and JP-B-60-48024, and JP-B-57-18176 and JP-B-57-18176. 560
No. 59, 58-56856, U.S. Pat.
8,231 and the like.

The light-diffusing film of the present invention may be provided with a clear hard coat layer on the surface, if necessary, to improve the scratch resistance. For this reason, a coating composition containing an actinic ray-curable resin (for example, an ultraviolet-curable resin) or a thermosetting resin can be applied. May be coarse. However, since the light diffusion film of the present invention has excellent flatness and small surface roughness, even when a clear hard coat layer is provided, good flatness can be obtained on the surface.

Further, an antistatic agent may be added to the surface layer or the inside of the light diffusion film of the present invention, if necessary. Further, an antistatic layer, an antireflection layer and an easy-adhesion layer can be applied by coating.

The light diffusion film of the present invention can be subjected to corona discharge treatment or plasma discharge treatment to modify the surface, thereby improving the wettability of the adhesive layer or the like and further improving the adhesiveness. You can also.

The light-diffusing film of the present invention can be bonded to a lenticular sheet of a transmissive screen member via an adhesive and used. Can be provided.

The light diffusion film of the present invention can be used as a part of a polarizing plate protective film. The polarizing plate can be manufactured by a general method. For example, in the case of the light-diffusing film of the present invention comprising a cellulose ester, there is a method in which an alkali treatment is performed, and both surfaces of a polarizing film produced by immersion stretching in an iodine solution are bonded using a completely saponified polyvinyl alcohol aqueous solution. . The alkali saponification treatment refers to a treatment in which the cellulose ester film is immersed in a high-temperature strong alkaline solution in order to improve the wettability of the aqueous adhesive at this time and improve the adhesiveness.

The polarizing film, which is a main component of the polarizing plate, is an element that transmits only light having a polarization plane in a certain direction. As described above, a polyvinyl alcohol-based polarizing film is well known. And a transparent plastic film which is another protective film for a polarizing plate and a light diffusing film of the present invention, and are laminated to form a polarizing plate.

The light diffusing film of the present invention may be used by being bonded to a light guide plate used in a side light type surface light source device used as a backlight of a transmission type liquid crystal display device or an advertising board. it can. Further, it can be used not only in the sidelight system but also in a direct surface light source device, and can be used as a light diffusion film for various devices other than the liquid crystal display device.

[0146]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Each dope in which fine particles containing the components shown in Table 1 were dispersed was produced as follows.

First, the fine particles were added to and dispersed in 10 kg of ethanol. The remaining ethanol and the other components were put into a closed container, kept at 80 ° C. under pressure, completely dissolved with stirring, and then filtered. Further, an ethanol solution in which the fine particles were dispersed was added to the mixture, and the mixture was sufficiently mixed, and then filtered again.

[0149]

[Table 1]

The compounds used above are described below. CAP: Cellulose acetate propionate (acetyl substitution degree 1.9, propionyl substitution degree 0.8, number average molecular weight 100,000) TAC: Cellulose triacetate (average acetylation degree 61%) PC: polycarbonate resin (viscosity average molecular weight 4) UV absorber A1: Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 0.3 kg Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0.4 kg Tinuvin 117 (manufactured by Ciba Specialty Chemicals) )) 0.4 kg UV absorber A2: Tinuvin 326 (manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.1 kg Tinuvin 109 (manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.2 kg Tinuvin 117 (Ciba Specialty Chemicals Co., Ltd.) ) Made ) 0.2 kg UV absorber A3: Tinuvin 326 (manufactured by Ciba Specialty Chemicals KK) 0.3 kg Tinuvin 109 (manufactured by Ciba Specialty Chemicals KK) 0.5 kg Tinuvin 117 (manufactured by Ciba Specialty Chemicals KK) ) 0.5 kg Plasticizer B: Triphenyl phosphate 11 kg Plasticizer C: Triphenyl phosphate 8 kg Ethylphthalylethyl glycolate 3 kg Fine particles D: Polystyrene fine particles (average particle size 10 μm) 15 kg Fine particles E: Aerosil R972V (Nippon Aerosil (Nippon Aerosil) 0.1 kg Fine particles F: Aerosil R972V (manufactured by Nippon Aerosil Co., Ltd.) 10 kg Fine particles G: Polystyrene fine particles (average particle diameter 2 μm) 5 kg Polystyrene fine particles (average particle diameter 10 μm) 5 kg I kept cooled to 33 ° C., uniformly flow cast on a stainless steel band, and dried 5 minutes at 33 ° C..
After peeling from the stainless steel band, the tenter was used so that the residual solvent amount was 10 to 30% by mass and the stretching ratio was 1.01 to 1.05.

Further, drying was completed while being conveyed by a large number of rolls to obtain light diffusion films 1 to 5 in Table 2 (only the light diffusion film 1 was not subjected to tenter).

Similarly, using a belt casting apparatus, using a dope 2 and a dope 3 shown in Table 1, they are merged in a die having two slits and co-cast by a simultaneous multilayer casting method to form a two-layer structure. The liquid was placed on a stainless steel casting belt at a temperature of 33 ° C. and a width of 1500 mm from the belt side from the first layer (dope 2).
In the order of the second layer (dope 3), dope 2 is 30
The solution was uniformly cast on a stainless steel band so that the dope 3 became 0 μm and the dope 3 became 100 μm, and dried at 33 ° C. for 5 minutes. After peeling off from stainless steel band, residual solvent amount is 30
The tenter was performed such that the stretching ratio was 1.01 to 1.05 times at 10% by mass. Further, drying is completed while being conveyed by a number of rolls.
I got

Similarly, using a belt casting apparatus, the dope 2 shown in Table 1 is merged in a die having three slits so as to be sandwiched by the dope 3 to form a three-layer structure. Casting liquid at a temperature of 33 ° C and 1500mm
The first layer (dope 3), the second layer (dope 2), and the third layer (dope 3) are arranged in order from the belt side on a stainless steel casting belt from the belt side, and the dry film thickness of the dope 2 becomes 180 μm. 3 was uniformly cast on a stainless steel band so as to have a thickness of 10 μm, and dried at 33 ° C. for 5 minutes. After peeling from the stainless steel band, a tenter was performed so that the residual solvent amount was 30% by mass to 10% by mass and the stretching ratio was 1.01 to 1.05 times.

Further, drying was completed while being conveyed by a large number of rolls, and a light diffusion film 7 shown in Table 2 was obtained.

Comparative Example 1 A dope 7 containing the components shown in Table 1 was prepared in the same manner as described above. That is, the fine particles were added to and dispersed in 10 kg of ethanol. The other composition was put into a closed container, kept at 80 ° C. under pressure, completely dissolved with stirring, and filtered.

Further, an ethanol solution in which the fine particles were dispersed was added thereto, mixed well, and then filtered again. After cooling, the temperature was maintained at 33 ° C., the solution was uniformly cast on a stainless steel band, and dried at 33 ° C. for 5 minutes. After peeling off from the stainless steel band, the drying was terminated while being conveyed by more rolls, to obtain a film having a dry film thickness of 80 μm. The following composition was applied by reverse roll coating on the surface that was the stainless steel band side (surface B side) at the time of casting of this film, and a light diffusion layer having a dry film thickness of 10 μm was provided. It was set to 1.

(Coating composition) Diacetyl cellulose 1.0 kg Polystyrene particles (average particle size 10 μm) 0.3 kg Ethyl acetate 50 kg Acetone 32 kg Isopropyl alcohol 4 kg Regarding the samples 1 to 7 of the present invention obtained above and Comparative sample 1 The evaluation was performed according to the following method.

(A) Measurement of curl value After leaving a film sample for 48 hours in an environment of 23 ° C. and 55% RH, the film is cut into a longitudinal direction (film forming direction) of 2 mm and a width direction of 50 mm. In addition, a small piece of the film
After humidifying for 24 hours in an environment of 3 ± 2 ° C. and 55% RH, a radius of curvature corresponding to a circumference having a curve matching the film was confirmed using a curvature scale, and the radius of curvature (1/1) was determined.
m) was taken as the curl value of the film.

(B) Roll dirt After a light diffusion film of 10,000 m was prepared, the degree of dirt on the first roll in contact with the film peeled from the stainless steel band support was visually observed and evaluated according to the following ranks.

◎: The roll is not dirty at all ○: A very small part of the roll is slightly stained △: The roll is slightly stained entirely ×: The roll is completely stained ( c) Center line surface roughness (Ra) Optical interference type surface roughness measuring device (RST Pl manufactured by WYKO)
us), 0.2% for the A and B sides of each sample
Each Ra was measured for an area of mm × 0.3 mm.

A: Ra less than 0.05 μm O: Ra 0.05 to less than 0.2 μm Δ: Ra 0.2 μm or more (d) Ultraviolet transmittance Spectrophotometer U-3200
The spectral absorption spectrum of the film was measured by Hitachi (manufactured by Hitachi, Ltd.), and the transmittance at 380 nm was determined.

A: Transmittance of less than 6% O: Transmittance of 6% or more and less than 10% Δ: Transmittance of 10% or more (e) Measurement of haze (turbidity) Measured in accordance with ASTM-D1003-52 with one film sample. did.

Table 2 shows the obtained results. (F) Adhesion (cross-cut adhesion test) Adhesion was evaluated according to the cross-cut adhesion test described in 4.15 of JIS D0202. That is, JI
1 mm on the test surface by the method according to 6.15 of SK5400
Make 100 grids (10 × 10) in width, attach cellophane adhesive tape (18 mm width) described in JIS Z1522 completely on the grid, immediately keep one end of the tape perpendicular to the test surface, Then, the number of grids remaining without being completely removed was checked.

A: Not peeled at all B: Peeled area ratio was less than 10% C: Peeled area ratio was less than 10 to 30% D: Peeled area ratio was 30% Was more than

[0165]

[Table 2]

Example 2 Light diffusion film 8 using polyethylene terephthalate
Was prepared as follows.

To 100 parts by mass of dimethyl terephthalate, 65 parts by mass of ethylene glycol and 2 parts by mass of diethylene glycol, 0.05 parts by mass of magnesium acetate hydrate was added as a transesterification catalyst, and a transesterification reaction was carried out according to a conventional method. Antimony trioxide was added to the obtained product in an amount of 0.1 mL.
05 parts by mass and 0.03 parts by mass of trimethyl phosphate were added. Then, the temperature is gradually raised and reduced to 280
C., polymerization at 0.5 mmHg, intrinsic viscosity 0.70,
Melting point (Tm) 261 ° C, Glass transition temperature (Tg) 76 ° C
Of polyethylene terephthalate was obtained.

Further, the polyethylene terephthalate was vacuum-dried at 150 ° C. for 8 hours, and then, as fine particles, Tospearl 3120 manufactured by Toshiba Silicone Co., Ltd. (average particle size: 1)
2 μm) and Tospearl 120 (average particle size 2 μm) were added to each other so as to be 5% by mass, kneaded sufficiently, melt-extruded at 285 ° C. using an extruder, and electrostatically applied to a cooling drum at 30 ° C. Then, it was cooled and solidified to obtain an unstretched sheet. This unstretched sheet was stretched 1.2 times in the machine direction at 85 ° C. using a roll-type longitudinal stretching machine. The temperature difference between the front and back surfaces was within 5 ° C.

The obtained uniaxially stretched film was stretched 2.5 times in the transverse direction at 95 ° C. using a tenter type transverse stretching machine.
Next, heat treatment is performed at 70 ° C. for 2 seconds.
Heat set at 80 ° C. for 25 seconds. Next, at 150 ° C., the film is relaxed in the transverse (width) direction and wound up to a length of 15 mm in the transverse direction.
A light diffusion film 8 of biaxially stretched polyethylene terephthalate (PET) having a thickness of 00 mm and a thickness of 500 μm was produced.

Comparative Example 2 A PET film produced in the same manner as described in Example 2 except that no fine particles were added, was coated with the following coating composition so as to have a dry film thickness of 16 μm. A light diffusion film 2 for comparison was obtained.

(Coating composition) Polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.) 10 kg Polystyrene particles (average particle size: 10 μm) 4 kg Toluene 11 kg Methyl ethyl ketone 3 kg The above-described curl measurement, surface roughness measurement, and grid adhesion test ( Adhesion) and haze were measured. Table 3 shows the results.

[0172]

[Table 3]

Example 3 A polarizing plate was produced using the light diffusing film of the present invention, and evaluation as a polarizing plate was performed as follows.

One of the protective films for a polarizing plate was used as the light diffusion film 7 of the present invention or the comparative light diffusion film 1,
80 μm thick triacetyl cellulose film (Konica Cat KC8UVSF) as the other film
Was used to produce a polarizing plate.

As the polarizing film, a polyvinyl alcohol film having a thickness of 120 μm was coated with 1 kg of iodine and 2 k of potassium iodide.
g, 100 kg of an aqueous solution containing 4 kg of boric acid.
The film was stretched 4 times at a temperature of ° C.

The following 1. ~ 5. In the step (3), the polarizing film was bonded to the light diffusing film 7 of the present invention or the comparative light diffusing film 1 and a triacetyl cellulose film (Konica Cat KC8UVSF) having a thickness of 80 μm to produce a polarizing plate.

<Method of Manufacturing Polarizing Plate> Light-diffusing film 7 cut to 30 cm in longitudinal direction and 18 cm in width direction (or light-diffusing film 1 for comparison)
Sample at 60 ° C. in 2 mol / l sodium hydroxide solution
For 2 minutes, further washed with water and dried. An alkali treatment was also performed on a triacetylcellulose film (Konica Cat KC8UVSF) having a thickness of 80 μm by the same operation.

[0178] 2. The polarizing film having the same size as the protective film sample was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

[0179] 3. The above 2. The excess adhesive adhering to the polarizing film was lightly removed, and the above-mentioned 1. The light-diffusing film sample (or comparative light-diffusing film 1) was placed on the b-side of the light-diffusing film sample, and the above-mentioned 1. The triacetylcellulose film sample having a thickness of 80 μm prepared in the above was laminated and arranged so that the b-side was in contact with the adhesive.

4. 3. Use a hand roller as described in 3. Excess adhesive and air bubbles are removed from the end of the laminate of the polarizing film, the light diffusing film, and the triacetyl cellulose film, which are laminated in the step (1), and the laminate is laminated. Hand roller pressure is about 0.2 ~
0.3 MPa and the roller speed were about 2 m / min.

5. In a dryer at 80 ° C. Was left for 2 minutes. The polarizing plate using the light diffusion film 7 of the present invention thus produced and the comparative light diffusion film 1
About the polarizing plate using, when cut by a cutter, the peeling of the light diffusion layer occurred at the end in the polarizing plate using the comparative light diffusion film, but in the polarizing plate using the light diffusion film of the present invention. Peeling of the edge was not observed.

The polarizing plate is disposed between the liquid crystal portion of the liquid crystal display and the backlight, and is arranged such that the side on which the light diffusion film is bonded is the backlight side. And excellent display properties could be shown.

[0183]

The optical isotropy, the flatness is high, the surface is smooth, the curl is small, and the surface quality is good.
A light-diffusing film with high productivity and a production method thereof were obtained.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of an apparatus for producing a cellulose ester laminated film of the present invention.

FIG. 2 is a sectional view of a slit die used in the manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dope liquid tank 1a Dope liquid 2 Particle addition liquid tank 2a Particle addition liquid 3 Tank 3a Ultraviolet absorber addition liquid 4a Pump 4b Pump 4c Pump 4d Pump 5a In-line mixer 5b In-line mixer 6 Slit die 7 Drum 8 Casting belt 9 Roller 10 Cellulose ester laminated film 11 Casting port 12 Slit 13 Slit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiaki Shibue 1st Konica Stock Company, Sakura-cho, Hino-shi, Tokyo In-house (72) Inventor Toshiyuki 1st Konica Stock Exchange, 1st Sakura-cho, Hino-shi, Tokyo F-term (reference) 2H042 BA02 BA15 BA20 4F071 AA09 AA26 AA31 AA43 AA50 AA67 AC10 AD02 AE04 AE05 AE19 AF30Y AF35 AG34 AH19 BA02 BB02 BB08 BC02 4J002 AB021 BB012 BB031 BB121 BB171 BB221 BC031 BG021 BG021 BG021 CG001 CG002 CH091 CL001 CL002 CM041 CM042 CN031 CP032 DE096 DE106 DE136 DE146 DE236 DG046 DJ016 DJ036 DJ046 EE038 EH037 EH097 EH147 EJ068 ET008 EU178 EW047 EZ008 FD027 FD058 FD310 GF00 GP00 HA05

Claims (13)

[Claims] 1. A method for producing a light-diffusing film, comprising casting a dope containing fine particles on a support, peeling the dope, and drying the film to form a film having a haze of 30% or more. 2. Use of at least two or more dopes,
The dope is cast on a support at the same time or sequentially, and then peeled off and dried to produce a film having a haze of 30% or more. A method for producing a light diffusing film, comprising adding fine particles to at least one of a dope to be used and a dope used on the air side (A side). 3. Use of at least two or more dopes,
The dope used in the method for producing a light-diffusing film for producing a light-diffusing film having a haze of 30% or more is formed by simultaneously or sequentially casting the dope on a support, and then drying after peeling to form a surface layer of the film. A light-diffusing film comprising at least one dope for forming an internal region and at least one dope for forming an internal region, wherein at least one dope for forming the internal region contains fine particles. Manufacturing method. 4. The method for producing a light diffusing film according to claim 1, wherein the amount of the fine particles in the dope containing the fine particles is 1% by mass or more per solid content. . 5. The concentration of fine particles contained in a dope for forming a surface layer is 0 to 0.5% by mass per solid content,
4. The method for producing a light diffusing film according to claim 3, wherein the concentration of the fine particles of at least one dope forming the internal region of the film sandwiched between these two kinds of dopes is 1% by mass or more per solid content. . 6. A resin film containing fine particles is stretched,
A method for producing a light diffusion film, comprising producing a light diffusion film having a haze of 30% or more. 7. A biaxially stretched thermoplastic resin molded article containing fine particles, having a stretch ratio in one direction of 1.0 to 2.0 times and a stretch ratio in another direction of 2.3 to 7.0 times. A method for producing a light-diffusing film, comprising forming a light-diffusing film having a haze of 30% or more by forming a film. 8. The method for producing a light diffusing film according to claim 1, further comprising a stretching step. 9. A light-diffusing film produced by the method according to claim 1. 10. A light diffusion film comprising a light diffusion film containing fine particles and having a haze of 30% or more, wherein a plasticizer is contained. 11. The light-diffusing film according to claim 9, wherein a plasticizer having a freezing point of 25 ° C. or less is contained. 12. The light diffusion film according to claim 9, further comprising an ultraviolet absorbent. 13. The light diffusion film according to claim 9, wherein the light diffusion film contains a cellulose ester.