JP2007140011A - Method for manufacturing optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easy and stable manufacturing method of a film that is superior in optical characteristics, in particular, an optical film containing at least one kind of fine particles having optical anisotropy dispersed in a transparent polymer. <P>SOLUTION: The method for manufacturing an optical film includes at least steps of (a) adding a dispersant by 5 wt.% or higher, to fine particles having optical anisotropy and dispersing the particles in a solvent, to obtain a fine particle dispersion liquid; (b) dissolving a transparent polymer in the fine particle dispersion liquid to obtain a fine particle dispersion polymer solution; and (c) forming a film of the fine particle dispersion polymer solution by a solution flow casting method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for stably and efficiently producing an optical film in which at least one kind of fine particles having optical anisotropy is dispersed in a transparent polymer.

  In recent years, flat panel displays typified by liquid crystal displays, organic EL, PDP, etc. have the characteristics of thinness and light weight to meet market needs, and as the most important display devices in the multimedia society, from mobile phones to computer monitors, Widely used for notebook computers and televisions. In these flat panel displays, a number of polymer films are used, such as a polarizer protective film, a retardation film, a viewing angle compensation film, a transparent electrode film, a light diffusing film, a light reflecting film, an electromagnetic wave shielding film, It is used for display surface protection films. These polymer films are required to have very high transparency and excellent optical characteristics in order to improve the display characteristics of the display.

  On the other hand, polymer materials added with fine particles with optical anisotropy are interesting because new optical functions can be expected. Optical materials such as optical films and optical adhesives using optically anisotropic fine particles are proposed. (For example, refer to Patent Document 1 and Non-Patent Document 1). Moreover, the retardation film for liquid crystal displays using an optically anisotropic nanoparticle is disclosed (for example, refer patent documents 2-4).

JP-A-11-293116 Polymer Science Society Proceedings 2003 Vol. 52, no. 4, p748 JP 2005-156862 A JP 2005-156863 A JP 2005-156864 A

  However, in the methods proposed in Patent Documents 1 to 4, these fine particles are likely to be aggregated in the film production process, and the optical properties such as retardation and transparency of the film obtained by the aggregation of the fine particles are deteriorated. There were problems such as deterioration of surface properties. And in order to manufacture these optical films industrially, it was a big subject to suppress aggregation of fine particles.

  Accordingly, the present invention provides a method for producing an optical film having excellent optical properties, particularly suppressing aggregation of fine particles having optical anisotropy and efficiently dispersing fine particles having optical anisotropy in a transparent polymer. An object of the present invention is to provide a method for producing an optical film stably and efficiently.

  As a result of intensive studies in view of the above-mentioned problems, the present inventors suppressed the aggregation of the fine particles by using a specific amount of a dispersant for the fine particles having optical anisotropy when producing an optical film. As a result, it has been found that the method for producing an optical film having excellent dispersibility of the fine particles has been achieved, and the present invention has been completed.

That is, this invention relates to the manufacturing method of the optical film characterized by passing through the process of the following (a)-(c) at least.
Step (a): A step of adding 5% by weight or more of a dispersant to fine particles having optical anisotropy and dispersing in a solvent to obtain a fine particle dispersion.
(B) Step: a step of dissolving a transparent polymer in the fine particle dispersion to obtain a fine particle dispersed polymer solution.
(C) Step: A step of forming a film by forming the fine particle-dispersed polymer solution by a solution casting method to form a film.

  Hereinafter, the manufacturing method of the optical film of this invention is demonstrated in detail.

  The manufacturing method of the optical film of this invention is related with the manufacturing method of the optical film which passes through the process of said (a)-(c) at least.

  Step (a) is a step in which 5% by weight or more of a dispersant is added to fine particles having optical anisotropy and dispersed in a solvent to obtain a fine particle dispersion.

  Here, the fine particles having optical anisotropy are not particularly limited as long as they belong to the category of fine particles having optical anisotropy. Further, it is preferably a fine particle having a needle-like or spindle-like shape and having an aspect ratio expressed by length / diameter of 1.5 or more, particularly 5 or more, and an average particle diameter of 500 nm or less, particularly 300 nm or less. . When the aspect ratio is 1.5 or more, an optical film that easily exhibits functions such as retardation can be obtained. Moreover, when an average particle diameter is 500 nm or less, it is easy to obtain an optical film excellent in transparency.

  The fine particles having optical anisotropy are preferably one or more selected from the group consisting of minerals and ceramics, for example, and in particular when forming an optical film, fine particles having negative optical anisotropy are used. preferable. The fine particles having negative optical anisotropy are those in which the refractive index difference (ne-no) between the refractive index (ne) of extraordinary light and the refractive index (no) of ordinary light is negative (minus). Specific examples of the fine particles having negative optical anisotropy include at least one kind of fine particles selected from the group consisting of strontium carbonate, calcium carbonate, magnesium carbonate, cobalt carbonate, manganese carbonate, The fine particles are preferably surface-treated with an organic component in advance.

  The dispersant in the step (a) is a dispersion in which fine particles having optical anisotropy are efficiently dispersed in a solvent to form a stable fine particle dispersion. Examples of the dispersant include alkyl sulfates and ether sulfates. , Sulfonate, alkyl ether, alkylphenol, alcohol ester, fatty acid, fatty acid alcohol, fatty acid ester, phosphate ester, polyethylene glycol, polyglycerin ester, alkylammonium salt, alkylamine, alkyldiamine, alkylamine oxide, etc. Two or more types may be used in combination, and among them, fatty acid, fatty acid alcohol, fatty acid ester, and phosphate ester are preferable because of excellent dispersion characteristics of fine particles having optical anisotropy, and phosphate ester is particularly preferable. And as this dispersing agent, (brand name) PharmaM (made by Unichemical Co., Ltd.) can be obtained as a commercial item. The amount of the dispersant added is 5% by weight or more, particularly preferably 20% by weight or more, based on the fine particles having optical anisotropy. When the dispersant is less than 5% by weight, the effect of dispersing fine particles having optical anisotropy is reduced, and the optical film from which the fine particles can be aggregated is inferior in transparency.

  The solvent in the step (a) can be appropriately selected depending on the solubility of the dispersant and the transparent polymer in the step (b). For example, an alcohol solvent, an aromatic solvent, an ether solvent, One or more solvents selected from ketone solvents, ester solvents, chlorine solvents and the like are preferred.

  In the step (a), fine particles having optical anisotropy, a dispersant, and a solvent can be mixed and dispersed to obtain a fine particle dispersion. In this case, the fine particles having optical anisotropy generally form aggregates. In such a case, the aggregates need to be fine particles. In this case, it is preferable to use a ball mill, a bead mill, an impeller disperser, a thin film swirling mixer, and the like. Particularly, since a fine particle dispersion can be obtained in a short time, it is preferable to use a bead mill or a thin film swirling mixer. When using a bead mill, the size of the beads may be adjusted according to the size of the fine particle aggregate, and two or more types of beads having different particle diameters may be used, and dispersion may be promoted by changing from large beads to small beads. In particular, when the beads are changed from beads having a large particle size to beads having a small particle size, the particle size difference is preferably 1.5 times or more. Moreover, when using a thin film swirl mixer, it is preferable to set the outer peripheral speed of the rotating part of the stirrer to 10 m / second or more, particularly about 20 to 50 m / second.

  The fine particle dispersion obtained by the step (a) may contain, for example, a hindered phenolic antioxidant, a phosphorus antioxidant, other antioxidants, a hindered amine light stabilizer and an ultraviolet absorber. .

  The step (b) in the present invention is a step of dissolving the transparent polymer in the fine particle dispersion obtained in the above step (a) to obtain a fine particle dispersed polymer solution.

  As the transparent polymer used in the step (b), any polymer having practical properties as an optical film material may be used. For example, an acrylic resin, a styrene resin, a polycarbonate, a fluorene-based polymer may be used. Polycarbonate, polyarylate, polysulfone, polyethersulfone, polyimide, polyetherimide, polyethylene terephthalate, polyethylene naphthalate, fluorene polyester, polynorbornene resin, polycyclohexane and other cyclic polyolefin resins, maleimide copolymers, fumarate Acid ester resins, and the like. In particular, a transparent polymer having a glass transition temperature of 110 ° C. or higher, preferably 120 ° C. or higher, more preferably 130 ° C. or higher is preferable. Polycarbonate can be obtained, cyclic polyolefin resin, polyether sulfone, maleimide copolymer, fumaric ester resin is preferred.

  In addition, the amount of the transparent polymer added in the fine particle-dispersed polymer solution is controlled by the development of retardation based on the transparent polymer, and among them, an optical film having excellent retardation characteristics can be obtained. It is preferably 99.9 to 50% by weight, particularly 99 to 75% by weight, based on the total amount with the anisotropic fine particles. The viscosity of the fine particle-dispersed polymer solution may be appropriately selected depending on the desired thickness accuracy and surface smoothness of the optical film, and among them, an optical film having particularly excellent thickness accuracy and surface smoothness can be obtained. -30000 cps, more preferably 1000-10000 cps.

  The step (c) in the present invention is a step of forming an optical film by forming a film of the fine particle-dispersed polymer solution obtained in the step (b) by a solution casting method and forming a film.

  Here, the solution casting method can include a method generally known as a method of obtaining a film by evaporating a solvent by heating after a polymer solution is cast on a support substrate. In the present invention, a method of obtaining an optical film by casting a fine particle-dispersed polymer solution comprising fine particles having optical anisotropy and a transparent polymer on a support substrate and then evaporating the solvent by heating. Can be mentioned. Specifically, the fine particle dispersed polymer solution is continuously cast on a belt-shaped or drum-shaped support substrate. Examples of the supporting substrate at that time include a glass substrate, a metal substrate such as stainless steel and ferrotype, and a plastic substrate such as polyethylene terephthalate. Among them, an optical film having a high surface property and optical homogeneity is used. For industrial continuous film formation, a metal substrate or plastic substrate having a mirror-finished surface is preferably used. The cast fine particle-dispersed polymer solution is evaporated into a film in the drying process.

  The optical film thus obtained may be provided with a slitter to cut both ends, and the slitter at that time is not limited. Among them, even if it is a hard optical film, it is possible to efficiently cut the both ends by suppressing the occurrence of fine cracks on the fracture surface of the film. It is preferable to use a slitter called a shear cutter that presses and cuts. In addition, a winder for winding the obtained film may be used, and the winder at that time is not particularly limited, and among them, an accumulator facility for adjusting the balance between the take-up speed and the take-up speed It is preferable to use a winder having

  The optical film obtained by the production method of the present invention may be an uniaxially or biaxially stretched optical film as necessary in order to control the retardation. In this case, the stretching process is a process performed continuously after the process (c), or after winding the optical film once after the process (c), the optical film is used in a stretching apparatus to be stretched. And the like.

  Stretching can include free width uniaxial stretching that does not constrain the film width direction, constant width uniaxial stretching that constrains the film width direction, and biaxial stretching that controls the length direction and width direction of the film, What is necessary is just to select suitably in order to obtain the target phase difference. Examples of the uniaxial stretching method include a method of stretching with a tenter, a method of rolling and stretching with a calendar, a method of stretching between rolls, and the like. As a biaxial stretching method, for example, a method of stretching with a tenter, a tube shape There are methods such as inflating and stretching. As the stretching conditions, the film is less likely to have uneven thickness, and the resulting film is excellent in mechanical properties and optical properties. Therefore, the glass transition temperature of the optical film constituting material measured by DSC is −20 ° C. to + 40 ° C. Under the drawing temperature high temperature condition, the draw ratio is an important factor for controlling the magnitude of the retardation, and it is usually preferred to draw in the range of 1.1 to 3 times in order to express the desired retardation. The phase difference is adjusted according to the intended application, and for viewing angle compensation, it is preferably 20 nm or more, particularly 50 nm or more, more preferably 100 nm or more. Specifically, the circularly polarizing film is 100 nm to 200 nm, a half-wave film. Are preferably from 200 nm to 400 nm, for STN-LCD, and for viewing angle compensation of the brightness enhancement film, from 50 nm to 1000 nm.

  The present invention relates to a method for producing an optical film in which at least one kind of fine particles having optical anisotropy is dispersed in a transparent polymer, and the optical film has practical properties such as mechanical strength. Since birefringence is expressed by stretching orientation, it can be used as a retardation film.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measuring method of each physical property value is shown below.

~ Measurement of glass transition temperature ~
A differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd., trade name DSC2000) was used, and the temperature was 10 ° C./min. It measured at the temperature increase rate of.

~ Measurement of light transmittance ~
As an evaluation of transparency, light transmittance was measured in accordance with JIS K 7361-1 (1997 edition).

~ Measurement of refractive index ~
It was measured according to JIS K 7142 (1981 edition).

-Positive / negative judgment of birefringence-
Birefringence by the additive color determination method with a λ / 4 plate using a polarizing microscope described in Introduction to Polarizing Microscope of Polymer Materials (Hiroshi Hiroya, Agne Technology Center Edition, Chapter 5, pp 78-82, (2001)) The positive / negative judgment was performed.

-Measurement of three-dimensional refractive index, calculation of phase difference and orientation parameter-
The three-dimensional refractive index was measured by changing the elevation angle using a sample tilt type automatic birefringence meter (trade name KOBRA-WR, manufactured by Oji Scientific Instruments). Furthermore, the in-plane retardation Re and the out-of-plane retardation Rth of the film were calculated from the three-dimensional refractive index.

~ Stretching of film ~
This was carried out using a biaxial stretching apparatus (manufactured by Imoto Seisakusho, model 16A1).

Example 1
Aggregate 11% by weight of strontium carbonate fine particles (average particle size 0.26 μm, aspect ratio 1.7), phosphate ester dispersant (trade name Phosmer M, manufactured by Unichemical Co., Ltd.) 3% by weight, methylene chloride 86% by weight After stirring and roughly dispersing the mixture consisting of a stirring blade, a thin-film swirl mixer disperser (specialized trade name, (trade name) TK film mix) with an outer peripheral speed of the stirrer set to 50 m / sec was used. By stirring for 60 seconds, a dispersion liquid in which strontium carbonate fine particles were dispersed was obtained.

  Then, a mixture of 20% by weight of strontium carbonate fine particle dispersion, 20% by weight of polycarbonate (trade name Panlite L1250, manufactured by Teijin Ltd.) and 60% by weight of methylene chloride was mixed with a stirrer, and a strontium carbonate fine particle dispersed polycarbonate solution. Got.

  The obtained strontium carbonate fine particle-dispersed polycarbonate solution was cast on a 188 μm thick polyethylene terephthalate film and dried to prepare an 80 μm optical film.

  The obtained optical film had a glass transition temperature of 160 ° C. and a total light transmittance of 88%. The obtained optical film was stretched twice at 170 ° C. by a biaxial stretching apparatus (free width uniaxial stretching) to produce a retardation film. The three-dimensional refractive index (nx, ny, nz) of the obtained retardation film was measured. The in-plane retardation Re ((nx−ny) · d) in terms of 100 μm was −140 nm, and the out-of-plane retardation Rth (((nx + ny) / 2−nz) · d) was −75 nm. The relationship of the three-dimensional refractive index was ny <nx = nz.

Example 2
Aggregate 11% by weight of strontium carbonate fine particles (average particle size 0.26 μm, aspect ratio 1.7), phosphate ester dispersant (trade name Phosmer M, manufactured by Unichemical Co., Ltd.) 3% by weight, methylene chloride 86% by weight The mixture consisting of was roughly dispersed by stirring with a stirring blade, and then dispersed for 20 minutes with a bead mill (trade name: Viscomill manufactured by Imex Co., Ltd.) to obtain a dispersion in which strontium carbonate fine particles were dispersed. In the case of dispersion by a bead mill, dispersion was performed for 10 minutes using zirconia beads having a particle diameter of 1.5 mm, and then each dispersion was performed for 10 minutes using zirconia beads having a particle diameter of 0.8 mm. The zirconia beads were separated.

  A mixture of 20% by weight of a strontium carbonate fine particle dispersion, 20% by weight of polycarbonate (manufactured by Teijin Ltd., trade name Panlite L1250), and 60% by weight of methylene chloride was made into a bead mill (trade name, manufactured by Imex Corporation). (Viscomil) for 10 minutes to obtain a strontium carbonate fine particle-dispersed polycarbonate solution. At that time, mixing was performed using zirconia beads having a particle diameter of 0.8 mm, and then the zirconia beads were separated.

  The obtained strontium carbonate fine particle-dispersed polycarbonate solution was cast on a 188 μm thick polyethylene terephthalate film and dried to prepare an 80 μm optical film.

  The obtained optical film had a glass transition temperature of 160 ° C. and a total light transmittance of 87%. The obtained optical film was stretched twice at 170 ° C. by a biaxial stretching apparatus (free width uniaxial stretching) to produce a retardation film. The three-dimensional refractive index (nx, ny, nz) of the obtained retardation film was measured. The obtained retardation film has an in-plane retardation Re ((nx−ny) · d) of −120 nm and an out-of-plane retardation Rth (((nx + ny) / 2−nz) · d) of −60 nm. there were. The relationship of the three-dimensional refractive index was nx <ny = nz.

Example 3
An optical film and a retardation film were prepared in the same manner as in Example 2 except that N-methylmaleimide / isobutene copolymer was used instead of polycarbonate (trade name Panlite L1250, manufactured by Teijin Limited). It was.

  The obtained optical film had a thickness of 100 μm, a glass transition temperature of 160 ° C., and a total light transmittance of 91%.

  The in-plane retardation Re ((nx−ny) · d) in terms of 100 μm of the retardation film is −125 nm, and the out-of-plane retardation Rth (((nx + ny) / 2−nz) · d) is −88 nm. The relationship of the three-dimensional refractive index was nx <ny = nz.

Comparative Example 1
A mixture of 12% by weight of aggregates of strontium carbonate fine particles (average particle size 0.26 μm, aspect ratio 1.7) and 88% by weight of methylene chloride was stirred and roughly dispersed with a stirring blade, and then bead mill (manufactured by IMEX Co., Ltd.). (Trade name) Viscomil) for 120 minutes to obtain a dispersion in which strontium carbonate fine particles are dispersed. In addition, after dispersion for 60 minutes using zirconia beads having a particle diameter of 1.5 mm, the dispersion was performed for 60 minutes using zirconia beads having a particle diameter of 0.8 mm, respectively, The zirconia beads were separated.

  A mixture of 20% by weight of a strontium carbonate fine particle dispersion, 20% by weight of polycarbonate (manufactured by Teijin Ltd., trade name Panlite L1250), and 60% by weight of methylene chloride was made into a bead mill (trade name, manufactured by Imex Corporation). Viscomil) for 60 minutes to obtain a strontium carbonate fine particle-dispersed polycarbonate solution. At that time, mixing was performed using zirconia beads having a particle diameter of 0.8 mm, and then the zirconia beads were separated. In addition, the dispersibility of the strontium carbonate fine particles in the obtained strontium carbonate fine particle-dispersed polycarbonate solution was poor, and the reagglomerates could be confirmed visually.

  The obtained strontium carbonate fine particle-dispersed polycarbonate solution was cast on a 188 μm thick polyethylene terephthalate film and dried to prepare an 80 μm film.

  The obtained film had a glass transition temperature of 160 ° C. and a total light transmittance of 80%, and strontium carbonate fine particle aggregates could be visually confirmed.

  The obtained film was stretched twice at 170 ° C. by a biaxial stretching apparatus (free width uniaxial stretching) to produce a stretched film. The three-dimensional refractive index (nx, ny, nz) of the obtained stretched film was measured. The obtained stretched film has an in-plane retardation Re ((nx−ny) · d) of −10 nm and an out-of-plane retardation Rth (((nx + ny) / 2−nz) · d) of −25 nm. Both were low. The relationship of the three-dimensional refractive index was nx <ny = nz.

Claims (9)

The manufacturing method of the optical film characterized by passing through the process of the following (a)-(c) at least.
Step (a): A step of adding 5% by weight or more of a dispersant to fine particles having optical anisotropy and dispersing in a solvent to obtain a fine particle dispersion.
(B) Step: a step of dissolving a transparent polymer in the fine particle dispersion to obtain a fine particle dispersed polymer solution.
(C) Step: A step of forming a film by forming the fine particle-dispersed polymer solution by a solution casting method to form a film. In step (a), 5% by weight or more of a dispersant is added to the fine particle aggregate having optical anisotropy, and the fine particle having optical anisotropy is obtained by a bead mill using beads having two or more different particle diameters. 2. The method for producing an optical film according to claim 1, which is a step of dispersing in a solvent to obtain a fine particle dispersion. (A) The fine particle which has optical anisotropy with the thin film swirl mixer which the process added the dispersing agent 5weight% or more with respect to the fine particle aggregate which has optical anisotropy, and was set to 10 m / sec or more of stirrer outer peripheral speeds. The method for producing an optical film according to claim 1, wherein the method is a step of dispersing in a solvent to obtain a fine particle dispersion. The fine particles having optical anisotropy have a rod-like, needle-like or spindle-like shape, and are fine particles having an aspect ratio of 1.5 or more and an average particle diameter of 500 nm or less. The manufacturing method of the optical film of description. 5. The optical film according to claim 1, wherein the fine particles having optical anisotropy are fine particles having one or more kinds of negative optical anisotropy selected from the group consisting of minerals and ceramics. Method. 6. The fine particles having negative optical anisotropy are at least one kind of fine particles selected from the group consisting of strontium carbonate, calcium carbonate, magnesium carbonate, cobalt carbonate, and manganese carbonate. Manufacturing method of optical film. The method for producing an optical film according to claim 1, wherein the dispersant is at least one dispersant selected from the group consisting of fatty acids, fatty acid alcohols, fatty acid esters, and phosphate esters. The method for producing an optical film according to claim 1, wherein the dispersant is at least one type of dispersant containing a phosphate ester. The transparent polymer is at least one kind of transparent polymer selected from the group consisting of polycarbonate, polyethersulfone, cyclic polyolefin, maleimide copolymer and fumarate ester resin. Item 9. A method for producing an optical film according to Item 1-8.