JP2990760B2 - Optical film manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an optical film that selectively shows transmissivity and reflectivity according to the wavelength of light.

[Conventional technology]

Conventionally, optical members such as diffraction gratings, prisms and color filters have been widely used as means for selectively obtaining light components in a specific wavelength range from light such as white light in which a plurality of light components having different wavelengths are different from each other. ing.

However, while diffraction gratings and prisms can separate and decompose white light with high accuracy according to wavelength, optical systems using these optical members require a sufficiently long optical path length and slit. However, there is a disadvantage that the configuration of the entire optical system is complicated and a large occupied space is required, and it is difficult to configure a small optical device.

In addition, the color filter absorbs a light component of a part of the wavelength of the incident light by a dye such as a dye therein, thereby transmitting light corresponding to a complementary color thereof.
Since light absorption is used, it is difficult to use light in all wavelength ranges of incident light. For this reason, it is difficult to use it for separating light having a single wavelength and high energy density such as laser light, and there is a problem that light absorbed by the dye is converted into heat in the filter.

[Problems to be solved by the invention]

In recent years, mica whose surface is coated with titanium dioxide has been proposed as having a function of transmitting visible light and infrared light by scattering light components in the ultraviolet region of white light due to the thickness of the titanium dioxide. For example, it is used as a component of a sunscreen cream.

As described above, a film-shaped optical member having fine particles dispersed in a light-transmitting medium and having a function of selectively indicating transmissivity and reflectivity according to the wavelength of light is realized. It would be very useful if you could.

The present inventors have found that by dispersing submicron-order particles having a uniform particle diameter in a film, a separation function based on this light selective transmittance can be obtained.

However, in order to selectively exhibit transmissivity and reflectivity in accordance with the wavelength of light with high precision, the uniformity of the particle diameter of the fine particles is high, and the fine particles are uniformly distributed in the film matrix. It needs to be distributed and dense. However, at present, a technique for obtaining an optical film satisfying such requirements has not yet been established.

The present invention is based on the above-mentioned current technology, and in a film-like matrix made of a light-transmitting polymer, fine particles having high uniformity of particle diameter and high precision of average particle diameter are dispersed at high density. To provide a method for producing an optical film, which selectively exhibits transmittance and reflectivity according to the wavelength of light and can therefore easily and inexpensively produce an optical film useful as an optical device for separating light. With the goal.

[Means to solve the problem]

In the method for producing an optical film according to the present invention, a composite particle including a core portion and a shell portion formed of a light-transmitting polymer having a film-forming property and a refractive index different from that of the core portion is formed into a film. Thus, the micromolecules formed by the core portion are dispersed in the film-shaped matrix formed by the shell portion.

 Hereinafter, the present invention will be described specifically.

In the present invention, as shown in FIG.
A composite particle 3 having a core-shell structure comprising a core portion 1 and a shell portion 2, wherein the refractive index of the core portion 1 is different from that of the shell portion 2, and the polymer forming the shell portion 2 is translucent. By using the composite particles 3 having a film-forming property and subjecting the composite particles 3 to a film-forming treatment, the polymers of the shell portions 2 are joined or bound to each other to form an integral film, as shown in FIG. Thus, the optical film F in which the fine particles 5 of the core portion 1 are dispersed in the film matrix 4 of the shell portion 2 is obtained.

The particles forming the core of the composite particles are not particularly limited. Accordingly, polymer particles, polymer particles coated with ceramics such as metal or metal oxide, metal particles, ceramic particles such as metal oxides, and others can be used for the core portion. The shell portion of the composite particle is not particularly limited as long as it is a light-transmitting polymer and the polymer has a film-forming property.

It is necessary that the core portion and the shell portion in the composite particles have different refractive indices, but the portion having a higher refractive index is not limited among the core portion and the shell portion. May have a rate.

The difference between the refractive index of the core portion and the refractive index of the shell portion (Δ
The size of n) is not particularly limited, and if the difference is at least a certain size, desired characteristics that selectively show transmissivity and reflectivity according to the wavelength of light can be obtained. In practice, Δn is preferably 0.01 or more, and more preferably 0.02 or more.

In order to realize a state in which the refractive index difference Δn is larger, for example, polymer particles whose surfaces are coated with ceramics represented by metals or metal oxides such as titanium oxide, metal It is effective to use ceramic particles such as particles and metal oxides.

In the composite particles as described above, since the shell portion is a polymer, particles for forming the core portion are used as seed particles, and a polymer is synthesized by a so-called seed polymerization method so as to cover the seed particles. By forming the shell portion by means of a shell, it can be produced very advantageously. That is, in the seed polymerization method, particles having a required particle size, particle size distribution, and other properties can be used as they are as seed particles, so that a required core portion is formed. And the like can be controlled with a large degree of freedom, so that composite particles in a desired state can be easily produced.

In addition, since the seed polymerization method can be generally performed in an aqueous dispersion medium, there is no need to use an organic solvent, and thus there are no various problems associated with the use of an organic solvent.

When the core portion is formed of a polymer, the polymer and the polymer forming the shell portion include, for example, polymers obtained by polymerizing or copolymerizing one or more of the following monomers. A combination that satisfies the necessary conditions may be selected and used. Here, the core portion and the shell portion are preferably a combination of polymers having low compatibility with each other, and specific examples thereof include aromatic vinyl compounds: for example, styrene, α-methylstyrene, and p-methylstyrene. Chlorostyrene, styrenesulfonic acid, ethylstyrene, divinylstyrene, etc., aliphatic diene compounds: 1,3-butadiene, isoprene, 1,4-hexadiene, etc., ethylenically unsaturated carboxylic acid ester compounds: methyl acrylate, Methyl methacrylate, butyl acrylate, glycidyl methacrylate, lauryl acrylate, etc. Halogen unsaturated compounds: for example, vinyl chloride, vinylidene chloride, vinyl bromide, etc. Organic vinyl compounds: for example, vinyl acetate, vinyl stearate, etc. Dicarboxylic acid compounds: Le acid, methacrylic acid, itaconic acid, and anhydrides or monoalkyl esters of these dicarboxylic acids, monoamide compounds: such as acrylamide, and methacrylic amide, nitrile compound: for example, acrylonitrile.

In the case where the seed polymerization method is used, the seed particles forming the core portion are preferably those that do not swell in polymerization for forming the shell portion and those that do not change in particle size. From such a viewpoint, as the seed particles for the core portion, for example, polymer particles highly crosslinked with divinylbenzene or the like can be preferably mentioned.

The glass transition point Tg of the polymer forming the core portion is preferably high, specifically, 40 ° C. or higher, particularly preferably 100 ° C. or higher.

On the other hand, the glass transition point Tg of the polymer forming the shell portion
Is preferably low in order to obtain a good film-forming property, and specifically, is preferably 80 ° C. or lower, particularly preferably 60 ° C. to −60 ° C.

However, the glass transition point Tg of the polymer forming the core portion
Is preferably 10 ° C. or higher than the polymer forming the shell portion.

In the composite particles according to the present invention, it is preferable that the center of the core part is present at the center of the whole particle, but this is not essential, and the center of the core part is present in one side of the composite particle. However, there is no particular problem.

In the present invention, the diameter of the core portion of the composite particles is not particularly limited, but is usually preferably from 0.03 to 2 μm, more preferably from 0.05 to 1 μm, further preferably from 0.1 to 0.6 μm.
m is preferable.

The particle size distribution of the particles forming the core portion, that is, the state of the particle size distribution of the seed particles when the seed polymerization method is used is not particularly limited. But,
In the obtained optical film, in order to clarify the boundary between the wavelength region exhibiting high transmittance and the wavelength region exhibiting high reflectivity, the variation ratio (CV value) in the distribution should be 15% or less. Preferably, it is more preferably within 7%.

Further, in the present invention, it is also possible to produce an optical film by forming a film obtained by mixing two or more kinds of composite particles having different particle diameters of particles forming a core portion. According to this optical film, it is possible to control the selectivity of the transmittance and the reflectivity depending on the wavelength of the light stepwise at a plurality of boundaries.

The volume ratio between the core portion and the shell portion of the composite particle in the present invention is not particularly limited as long as the film can be formed by the shell portion, but preferably the volume ratio of the core portion / shell portion is preferable. Is 10/4 ~ 10/30, especially 10/10
1010/20 is preferred.

The above composite particles are formed by a normal method using the film forming property of the shell portion, whereby fine particles by the core portion are present in a dispersed state in the film-like matrix by the shell portion of the composite particle. Thus, an optical film obtained by the method of the present invention is obtained.

As a specific film forming means, the composite particles may be dispersed in an appropriate dispersion medium, the dispersion may be cast to form a film, and the dispersion medium may be dried and removed. Here, as the dispersion medium, any one that has solubility in the shell portion of the composite particles or one that is insoluble can be used.

The thickness of the optical film obtained by the method of the present invention,
The thickness is not particularly limited as long as the fine particles by the core portion are buried in the film matrix, and is not particularly limited, but is usually about 0.05 to 100 μm, and preferably 0.1 to 10 μm.

The optical film according to the present invention can be colored as required. For this purpose, for example, composite particles in which a dye such as a dye is added to a shell portion are used.

Further, the composite particles of the present invention may be mixed with other general latex particles, or a polymer may be dissolved in a dispersion of the composite particles before use.

[Function of the invention]

The optical film obtained by the method of the present invention has a core
Composite particles having a shell structure, the shell of which is obtained from a translucent polymer having a film-forming property, since fine particles having different refractive indices are dispersed in a film-like matrix, With respect to the incident light, an effect of selectively exhibiting transmissivity and reflectivity according to the wavelength can be obtained, so that the light can be separated according to the wavelength.

In addition, the shell portion of the composite particles has a function of preventing secondary aggregation of the fine particles in the core portion, in addition to the function as a film forming material.

The light separation performance of the optical film obtained by the method of the present invention is as good as, for example, that of colloidal gold arranged on a glass plate. Moreover, the light transmitted through the optical film has a straight traveling property.

The optical film according to the present invention can be used as an ultraviolet cut film, a color filter, and the like. In particular, in a color filter using an optical film obtained by the method of the present invention, unlike conventional color filters, since the hues of reflected light and transmitted light are different, the contrast of the hue by turning on and off the light is large, and thus excellent visibility It is useful as a display material.

Further, it can be used as an optical material for selectively transmitting and reflecting light having different wavelengths of excitation light and emission light with respect to a fluorescent material, a nonlinear optical material, and the like. It is also possible to use the obtained optical film in combination with a color filter.

〔Example〕

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

Example 1 1190.5 g of an emulsion containing 250 g (dry weight) of polymer particles highly crosslinked with divinylbenzene having a particle size of 0.1 μm and a particle size distribution variation coefficient of 9%, composed of 20 parts by weight of dinylbenzene and 80 parts by weight of styrene. Was placed in a separable flask equipped with a condenser, and the temperature was raised to 75 ° C. by a water bath while stirring with a stirring blade.

Next, 30 g of a 10% by weight aqueous solution of ammonium persulfate was added as a reaction initiator to this emulsion, and immediately thereafter, 190 g of methyl methacrylate and 300 g of butyl acrylate were added.
And a monomer dispersion obtained by dispersing 30 g of methacrylic acid in 300 g of water with the emulsifier dodecylbenzenesulfonic acid is added dropwise over 3 hours while maintaining the reaction temperature at 75 ° C., whereby the crosslinked polymer particles are obtained. Was used as seed particles to perform seed polymerization.

After the dropping of the monomer dispersion liquid is completed, it is 75
Stirring was continued at a temperature of ° C. to promote the reaction, and then the reaction system was cooled by a water bath to terminate the polymerization reaction, thereby producing a latex of composite particles having a core-shell structure.

 The properties of the composite particles are as follows.

Refractive index of core part: 1.599 Refractive index of shell part: 1.488 Glass transition point Tg of core part: 128 ° C. Glass transition point Tg of shell part: −23.3 ° C. Volume ratio of core part to shell part: 25:42 The latex of the composite particles was dropped on a flat glass plate surface and dried at room temperature to obtain a particle size of 0.
An optical film according to the present invention having a thickness of 0.3 μm in which 1 μm fine particles were dispersed was prepared.

The surface reflection light of this optical film is bluish,
When viewed through the optical film, a yellow scene was clearly seen through the optical film, and it was confirmed that light transmitted through the optical film went straight.

200nm to 1500nm measured for this optical film
The transmittance of light in the wavelength range up to 400 nm is shown in FIG.
FIG. 4 shows the reflectance of light in the wavelength range up to 00 nm.

As is clear from FIG. 3, the transmittance of this optical film sharply increases near 300 nm, and almost 10% near 500 nm.
On the other hand, while reaching nearly 0%, as is clear from FIG. 4, the reflectance decreases as the wavelength becomes longer, and the transmittance and the reflectance according to the wavelength of light have a complementary relationship.

Example 2 Except for using polymer particles highly crosslinked with divinylbenzene having a particle size of 0.2 μm comprising 15 parts by weight of divinylbenzene and 85 parts by weight of styrene and a coefficient of variation in particle size distribution of 5% as seed particles, Polymerization was performed in the same manner as in Example 1 to produce a composite particle latex.

 The properties of the composite particles are as follows.

Refractive index of core part: 1.598 Refractive index of shell part: 1.488 Glass transition point Tg of core part: 122 ° C Glass transition point Tg of shell part: −23.3 ° C Volume ratio of core part and shell part: 25:45 By forming a film using the latex of particles in the same manner as in Example 1, an optical film having a thickness of 0.3 μm in which fine particles having a particle size of 0.2 μm were dispersed was obtained.

The surface reflected light of the optical film is green, and when viewed through the optical film, a red scene is clearly seen through the optical film, whereby it is confirmed that light transmitted through the optical film goes straight. Was.

200nm to 1500nm measured for this optical film
Fig. 5 shows the transmittance of light in the wavelength range up to
FIG. 6 shows the reflectance of light in the wavelength range up to 00 nm.

As is clear from FIG. 5, the transmittance of this optical film rises from around 550 nm and is about 90% or more at 1000 nm or more, while as can be seen from FIG. 6, it is about 70% reflection up to 530 nm. At the same time, the reflectance decreased with the increase of the transmittance, and the reflectance of the transmittance according to the wavelength of light was complementary to that of the first embodiment.

Comparative Example 1 Polymer particles of 2-ethylhexyl polymethacrylate having an average particle diameter of 0.1 μm and a coefficient of variation in particle diameter distribution of 5% were used as seed particles, and a monomer dispersion containing methyl methacrylate as a monomer was used. Was subjected to a polymerization treatment in the same manner as in Example 1 to produce a latex of composite particles.

 The properties of the composite particles are as follows.

Refractive index of the core part: 1.465 Refractive index of the shell part: 1.489 Glass transition point Tg of the core part: −85 ° C. Glass transition point Tg of the shell part: 105 ° C. Volume ratio of the core part and the shell part: 25:42 It was impossible to form a film of the composite particle latex at room temperature. Then, when the latex of the composite particles was formed into a film at a temperature of 110 ° C., the shape of the fine particles was lost, the film became cloudy, and the effect of selectively separating white light was not recognized.

〔The invention's effect〕

The production method of the present invention is to form a specific composite particle having a core-shell structure, thereby dispersing fine particles by a core portion in a film-like matrix by a shell portion. It is easy to control the particle size and its distribution, and the film can be formed by utilizing the film forming property of the shell portion. Can be easily obtained in a state where the fine particles are dispersed at a high density. Therefore, according to the present invention, in a film-like matrix made of a light-transmitting polymer, fine particles having high uniformity of particle size and high accuracy of average particle size exist in a dispersed state at high density, and the wavelength of light Thus, it is possible to provide an optical film which is selectively used as a light separating optical device such as a filter, and which is easy to manufacture and low in cost.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing the structure of the composite particles used in the present invention, and FIG. 2 is an explanatory view schematically showing the structure of an optical film obtained by the method of the present invention. FIG. 4, FIG. 5 and FIG. 6 are characteristic curves showing the relationship between the wavelength of light and the transmittance and reflectance of the films obtained in Examples 1 and 2, respectively. 1 core part 2 shell part 3 composite particle 4 film matrix 5 fine particle F optical film

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 5/20

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein said shell portion is formed by forming a composite particle comprising a core portion and a shell portion formed of a translucent polymer having a film-forming property and a refractive index different from said core portion. A method for producing an optical film, comprising dispersing the fine particles of the core portion in a film-like matrix according to (1).