JP2004109624A - Low-refractive index thin film, manufacturing method therefor, and anti-reflection film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-refractive index thin film capable of structurally changing a refractive index without changing materials and a manufacturing method therefor and to provide an anti-reflection film provided with the low-refractive index thin film. <P>SOLUTION: A laminated film having charged layers having positive electric charge and charged layers having negative electric charge, alternately laminated is subjected to acid treatment or alkali treatment to form gaps in the laminated film, thus the low-refractive index thin film is obtained. A high-refractive index thin film is formed on a base material, and the low-refractive index thin film is formed on the high-refractive index thin film to obtain the anti-reflection film. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a low refractive index thin film, a method for producing the same, and an antireflection film.
[0002]
[Prior art]
In recent years, in order to prevent light from being reflected on the surface of window glasses such as various displays such as word processors, computers, and televisions, various optical lenses, optical articles, automobiles, and trains, an antireflection film is provided on the surface of these articles. Has been done.
For example, Patent Document 1 discloses a multilayer heterostructure film in which a high refractive index layer formed by a sol-gel method and a low refractive index layer formed by an alternate adsorption method are alternately laminated on a substrate. Has been described.
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-350015
[Problems to be solved by the invention]
The antireflection performance of an antireflection film can be improved by changing the refractive index of a layer constituting the antireflection film. However, in general, the refractive index of a layer is almost determined by a material. There has been a need for a method that can change the refractive index.
In particular, in the case of an antireflection film composed of a multilayer heterostructure film, if the refractive index difference between adjacent layers can be structurally changed, the allowable range of the refractive index of the material is widened, and the degree of freedom in optical design is increased. It is preferable because it is enlarged.
[0005]
The present invention has been made in view of the above circumstances, and a low-refractive-index thin film capable of structurally changing a refractive index without changing a material, a method of manufacturing the same, and an anti-reflection method including the low-refractive-index thin film It is intended to provide a membrane.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present inventors have conducted intensive studies and found that a low-refractive-index thin film formed by alternately laminating a positively charged layer and a negatively charged layer was formed. Through the treatment or alkali treatment, it has been found that voids can be formed in the low-refractive-index thin film, and that the voids can structurally reduce the refractive index of the low-refractive-index thin film, and have completed the present invention. Was.
That is, the method for producing a low-refractive-index thin film of the present invention is a method in which a charged layer having a positive charge and a charged layer having a negative charge are alternately stacked, and the stacked film is subjected to an acid treatment or an alkali treatment. A void is formed in the laminated film to obtain a low refractive index thin film.
[0007]
The laminated film is preferably formed by an alternate adsorption method.
It is preferable to use a weak electrolyte as at least one of the electrolyte constituting the positively charged layer and the electrolyte constituting the negatively charged layer.
According to the method for manufacturing a low refractive index thin film of the present invention, the refractive index of the low refractive index thin film can be set to 1.45 or less.
It is preferable that the diameter of the void in a planar shape is less than 200 nm and the depth is less than 200 nm.
The present invention also provides a low refractive index thin film obtained by the method for producing a low refractive index thin film of the present invention.
[0008]
The low-refractive-index thin film of the present invention has a planar film with a diameter of less than 200 nm and a depth of less than 200 nm in a stacked film in which a positively charged layer and a negatively charged layer are alternately stacked. Are formed in plurality.
It is preferable that at least one of the electrolyte constituting the positively charged layer and the electrolyte constituting the negatively charged layer is a weak electrolyte.
According to the present invention, a low refractive index thin film having a refractive index of 1.45 or less can be obtained.
[0009]
The antireflection film of the present invention is characterized by comprising the low refractive index thin film of the present invention.
In the antireflection film of the present invention, it is preferable that the low refractive index thin film is laminated on a layer having a higher refractive index than the low refractive index thin film.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The charged layer having a positive charge in the present invention can be formed using a material capable of forming a film, including an electrolyte or charged fine particles that can be positively charged in a solution. As a material of the charged layer having a positive charge, a positive polymer compound that can be positively charged by ionization in a solution can be used. For example, a high molecular compound having a functional group capable of taking a positive charge in a solution, such as a quaternary ammonium group or an amino group, having water solubility or water dispersibility, or a mixture of water and an organic solvent. Those having solubility or dispersibility in a mixed solvent can be used, and an organic polymer compound is preferably used. Specific examples of the positive electrolyte polymer include polypyrrole, polyaniline, polyparaphenylene (+), polyparaphenylenevinylene, polyethylimine, polyethyleneimine (PEI), polyallylamine hydrochloride (PAH), and poly (allylaminehydrochloride). Examples include diallyldimethylammonium chloride (PDDA), polyvinylpyridine (PVP), and polylysine.
[0011]
The charged layer having a negative charge in the present invention can be formed using a material having an ability to form a film containing an electrolyte or charged fine particles that can be negatively charged in a solution. As a material of the charged layer having a negative charge, a negative polymer compound that can be negatively charged by ionization in a solution can be used. For example, sulfonic acid, sulfuric acid, carboxylic acid, and the like, a high molecular compound having a functional group capable of taking a negative charge in a solution and having water solubility or water dispersibility, or a mixture of water and an organic solvent. Those having solubility or dispersibility in a mixed solvent can be used, and an organic polymer compound is preferably used. Specific examples of the negative electrolyte polymer include polystyrenesulfonic acid (PSS), polyvinyl sulfate (PVS), dextran sulfate, chondroitin sulfate, polyacrylic acid (PAA), polymethacrylic acid (PMA), polymaleic acid, and polyfumaric acid. Examples thereof include paraphenylene (-), polythiophene-3-acetic acid, and polyamic acid.
[0012]
Alternatively, as a material of the positively charged layer and the negatively charged layer in the present invention, conductive polymer, functional polymer ions such as poly (aniline-N-propanesulfonic acid) (PAN), Charged biopolymers such as various deoxyribonucleic acids (DNA), ribonucleic acids (RNA), and charged polysaccharides such as pectin can also be used.
Further, besides the water-soluble material, water-insoluble charged fine particles such as ferrite fine particles can also be used.
Further, it is also preferable to use, for example, a ruthenium complex monomer (Ru (bpy) 3 (PF6) 2) ²⁺ as a material for the positive charging film and the PAA as a material for the negative charging film, in addition to the polymer material.
[0013]
In order to manufacture the low refractive index thin film according to the present invention, first, a laminated film in which charged layers having positive charges and charged layers having negative charges are alternately laminated is formed. As a method for forming such a laminated film, an alternate adsorption method is particularly preferable. In addition to the alternate adsorption method, for example, a sol-gel method, a spin coating method, a Langmuir-Blodgett method, or the like is used. It is possible to form.
The alternate adsorption method is a method of forming a laminated film on a substrate by alternately immersing the substrate in a solution containing the material of the positively charged layer and a solution containing the material of the negatively charged layer. Can be used as appropriate. If the substrate surface is negatively charged, first form a positively charged layer on the substrate, and if the substrate surface is positively charged, first form a negatively charged layer on the substrate. To form It is optional whether the uppermost layer is a positive charging layer or a negative charging layer.
The number and thickness of the positively charged layer and the negatively charged layer constituting the laminated film are set according to the thickness required for optical design.
In the present invention, it is preferable to use a weak electrolyte as at least one of the electrolyte constituting the positively charged layer and the electrolyte constituting the negatively charged layer, since voids are easily formed in the laminated film as described later.
[0014]
In the case of the alternate adsorption method, it is preferable to control the pH of the solution containing the material of the positively charged layer and the pH of the solution containing the material of the negatively charged layer to optimal values. Here, the optimum value of the pH of the solution containing the material of the positively charged layer and the optimum value of the pH of the solution containing the material of the negatively charged layer are as follows. Is set to a value that does not dissociate.
[0015]
Next, an acid treatment or an alkali treatment is performed on the formed laminated film to form voids in the laminated film. Specifically, the treatment can be performed by immersing the laminated film in an alkaline solution or an acidic solution.
When the treatment is performed using an alkaline solution having a pH higher than the pH of the positively charged layer constituting the laminated film, voids can be formed in the positively charged layer and the pH can be higher than the pH of the negatively charged layer. When the treatment is performed using an acidic solution having a low pH, voids can be formed in the negatively charged layer. By performing both the acid treatment and the alkali treatment in an arbitrary order, voids can be formed in both the positively charged layer and the negatively charged layer constituting the laminated film.
Here, the pH of the positively charged layer and the pH of the negatively charged layer constituting the laminated film refer to the positively charged layer used in the alternating adsorption method when the laminated film is formed by the alternate adsorption method. PH of the solution containing the material of the negatively charged layer and the pH of the solution containing the material of the negatively charged layer. When the laminated film is formed by a method other than the alternate adsorption method, the equipotential point of the material used for the positively charged layer is Higher pH, lower than the isoelectric point of the material used for the negatively charged layer.
[0016]
The void formed by such an acid treatment or an alkali treatment may have a hollow structure through which air can enter, and may have a porous structure or a fibrous structure in which fiber bundles are gathered. Good.
The voids preferably have a diameter of less than 200 nm and a depth of less than 200 nm when the surface of the low-refractive-index thin film is viewed in a plan view, and are subjected to an acid treatment so that voids having a size in this range are formed. Alternatively, it is preferable to adjust the treatment conditions of the alkali treatment.
If the diameter of the void is less than 200 nm, light scattering can be effectively suppressed. The transmittance decreases as the light scattering increases.
In order to secure the strength of the thin film itself, it is preferable that the depth of the gap is less than 200 nm.
[0017]
In the present invention, the laminated film in which the positively charged layer and the negatively charged layer are alternately laminated, the positively charged electrolyte or charged fine particles, and the negatively charged electrolyte or charged fine particles are formed by an electric force. Since the bonding is performed, by performing the acid treatment or the alkali treatment, the electrolyte or the charged fine particles in the stacked film are easily dissociated and moved to form voids.
By forming such voids in the laminated film and changing the structure of the laminated film, the refractive index (bulk refractive index) of the entire low-refractive-index thin film is reduced by the refractive index of the laminated film before the void is formed. Rate can be lower. That is, when such voids are formed in the laminated film, a large number of fine air layers are mixed in the laminated film, and the refractive index of air is usually lower than the refractive index of the material constituting the laminated film. Therefore, the refractive index of the entire laminated film including the voids (the bulk refractive index of the low-refractive-index thin film) is reduced by the presence of the air layer. Thereby, for example, the refractive index of the low refractive index thin film can be reduced to 1.45 or less, preferably 1.4 or less, and more preferably 1.3 or less. It is preferable to appropriately set the refractive index of each layer constituting the antireflection film so that a good antireflection effect can be obtained at the center wavelength where the antireflection effect is to be obtained.
In addition, the low-refractive-index thin film in which the positively charged layer and the negatively charged layer are alternately laminated has a strong adhesive force between the layers because each layer is bonded by an electric force. It is not easily peeled off.
[0018]
In the present invention, the electrolyte constituting the positively charged layer and the electrolyte constituting the negatively charged layer may be a strong electrolyte or a weak electrolyte, but voids are more likely to be formed in the weak electrolyte. The reason for this is not clear, but it is presumed that the weak electrolyte is easily ionized and thus easily ionized to a deep part. Therefore, it is preferable to use a weak electrolyte as at least one of the electrolyte constituting the positively charged layer and the electrolyte constituting the negatively charged layer. Examples of the positively charged weak electrolyte include polyaniline and the like, and examples of the negatively charged weak electrolyte include polyacrylic acid and the like.
[0019]
The anti-reflection film of the present invention is characterized by comprising the low-refractive-index thin film of the present invention, that is, the laminated film having the voids formed therein.
When the low refractive index thin film of the present invention is directly provided on the surface of a CRT, a liquid crystal, a plasma display, a lens, or the like, an antireflection film can be formed alone. It may be configured to be stacked on a layer having a higher refractive index than a thin film.
[0020]
The thickness of each layer of the low-refractive-index thin film and the high-refractive-index thin film in the antireflection film of the present invention is set to be close to nd = λ / 4 (n is a refractive index of a central wavelength, d is a film thickness, and λ is a central wavelength). Preferably, it is designed to With such a design, the reflected light reflected on the surface of each layer and the reflected light reflected on the inner end face of each layer cancel each other, and the antireflection effect is efficiently exhibited.
The layer having a higher refractive index than the low-refractive-index thin film may be a base material, or a high-refractive-index thin film is formed on a base material, and a low-refractive-index thin film according to the present invention is formed thereon. May be. Further, an antifouling layer, an antistatic layer, a hard coat layer and the like may be optionally formed on the low refractive index thin film.
The substrate may be any material that is transparent in the visible light band, and is appropriately selected in consideration of haze, retardation value, and the like depending on the object for which antireflection is required. For example, glass, PC (polycarbonate) film, PET ( A polyethylene terephthalate) film or the like is preferably used. The shape is arbitrary, and direct coating on the surface of an existing display or the like is possible by the method of the present invention.
[0021]
The high refractive index thin film only needs to have a higher refractive index than the bulk refractive index of the low refractive index thin film formed thereon, and its material and manufacturing method are not particularly limited. For example, a thin film made of an inorganic material such as an ITO (Indium Tin Oxide) thin film or a TiO2 (titanium oxide) thin film can be used as the high refractive index thin film. Alternatively, a high-refractive-index thin film can be formed using a dispersion in which TiO2 is dispersed in an organic binder. As a manufacturing method, for example, a coating method or a sputtering method can be applied.
The thickness of the base material and the thickness of the high-refractive-index thin film are not particularly limited, but as described above, the thickness of the high-refractive-index thin film is, like the thickness of the low-refractive-index thin film, excellent in antireflection in the wavelength band used. It is preferable to set appropriately so as to obtain the effect.
[0022]
As a material of the antifouling layer, silicone, a photocatalyst, or the like can be used. Although the production method is not particularly limited, for example, a wet coat method or a vacuum deposition method can be used. By forming an antifouling layer as the uppermost layer of the antireflection film, dirt is less likely to be attached, and antifouling properties can be improved. This makes it difficult for dirt such as fingerprints to adhere. The thickness of the antifouling layer is set within a range that does not affect the optical characteristics of the antireflection film. For example, the thickness is preferably 50 nm or less, and more preferably 10 nm or less.
Further, a hard coat layer, an antistatic layer and the like can provide functions even if they are not the uppermost layer.
[0023]
In general, in an antireflection film having a configuration in which a low-refractive-index thin film is laminated on a high-refractive-index thin film, the larger the difference between the refractive index of the high-refractive-index thin film and the refractive index of the low-refractive-index thin film is, the more the antireflection film becomes. The reflectivity decreases. Therefore, according to the present invention, fine voids are formed in the low refractive index thin film, and the refractive index of the low refractive index thin film is reduced by the formation of the voids. Is improved. At the same time, as the refractive index of the low-refractive-index thin film decreases, the choice of materials for the high-refractive-index thin film becomes wider.
[0024]
Materials used as the conventional low refractive index layer include SiO ₂ (n = 1.45), MgF ₂ (n = 1.38), and fluororesin (n = 1.24 to 1.45). The refractive index is determined by the material, and the optical design for forming the antireflection film is limited.
Further, since fluororesin is very expensive, an antireflection film using it is very expensive.
Conventionally, an anti-reflection film having an anti-reflection performance that satisfies requirements with a limited low-refractive-index material cannot be realized with a single low-refractive-index layer, but is realized with an anti-reflection film having a multilayer structure. .
On the other hand, if the low refractive index thin film of the present invention is used, sufficient antireflection performance can be realized even with a single layer.
The refractive index of the low refractive index thin film of the present invention can be arbitrarily changed, the degree of freedom in optical design is increased, and a more sophisticated antireflection film can be formed.
The low-refractive-index thin film of the present invention has a lower refractive index than conventional low-refractive-index materials such as silica. it can. It is also possible to obtain a higher performance antireflection performance by using a multilayer structure or the like.
[0025]
【Example】
Hereinafter, the effects of the present invention will be clarified by showing specific examples.
(Example 1)
Polyallylamine hydrochloride (PAH, molecular weight = 55000) was prepared as a positive electrolyte polymer, and polyacrylic acid (PAA, molecular weight = 90000) was prepared as a negative electrolyte polymer. In each case, an aqueous solution having a concentration of 10 ⁻² mol / liter was prepared and stored in a reaction tank.
Separately, ultrapure water having a specific resistance of 18 MΩ · cm or more was prepared as pure water to be used for the rinsing bath.
Using a 100 μm thick polyethylene terephthalate (PET) substrate (manufactured by Teijin DuPont, trade name: Melinex), titanium oxide (trade name: Titania A-11) as a high refractive index material is used. Then, a high refractive index layer was prepared by setting λ = 550 nm and d = 75 nm so that nd = λ / 4 (n is the refractive index at the center wavelength, d is the film thickness, λ is the center wavelength). The refractive index of the high refractive index thin film is about 1.8. Then, the surface of the formed high refractive index thin film was subjected to a hydrophilic treatment by a potassium hydroxide aqueous solution treatment.
Next, the substrate on which the high-refractive-index thin film is formed is first immersed in a PAH solution (pH = 7.5) for 15 minutes to form a PAH film, which is then PAA solution (pH = 3. 5) The film was immersed in the film for 15 minutes to form a film made of PAA. In this way, a film made of PAH and a film made of PAA were alternately formed to form a laminated film having a total of eight layers and a thickness of about 90 nm.
Subsequently, the substrate on which the laminated film is formed is immersed in hydrochloric acid adjusted to a pH of about 2.5 for 2 minutes, and then washed with ultrapure water having a specific resistance of 18 MΩ · cm or more. Fine voids were formed to obtain a low refractive index thin film. Thus, an antireflection film having a configuration in which a high-refractive-index thin film and a low-refractive-index thin film were sequentially laminated on a substrate was obtained.
[0026]
FIG. 1 is a cross-sectional view of the obtained antireflection film. In the figure, reference numeral 1 denotes a substrate, 2 denotes a high refractive index thin film, 3 denotes a low refractive index thin film, and 4 denotes a void.
As shown in this figure, a large number of fine voids were formed in the low refractive index thin film, and the diameter of the voids in a planar shape was less than 200 nm. Further, the voids penetrating the low-refractive-index thin film had a depth of less than the thickness of the low-refractive-index thin film, that is, less than 110 nm. The thickness greater than 90 nm, which was previously laminated, means that the film swelled with air by being immersed in hydrochloric acid. That is, unlike the method of creating voids by mixing and evaporating the third component, the polymer is immersed in an acid or alkali to change the structure of the film and create voids. Unlike the method of removing the third component, this is a method of producing a new and contamination-free porous body since the third component does not remain.
[0027]
The antireflection effect of the obtained antireflection film was evaluated as follows. In other words, the surface of the base of the anti-reflection film is roughened using steel wool or the like, and then black ink is applied. The reflectance and minimum reflectance were measured. The measurement was performed using an ultraviolet-visible spectrometer V-570 manufactured by JASCO Corporation while measuring the regular reflectance at an incident angle of 5 ° while changing the wavelength of the incident light in the range of 350 nm to 800 nm in units of 2 nm. The highest reflectance and the lowest reflectance were read from the measurement chart obtained. The refractive index of the portion of the low-refractive-index thin film constituting the antireflection film was calculated from the reflectance waveform obtained by the above-described measuring method by a known optical interference method.
The obtained measurement chart is shown by a solid line in FIG. As a result, the highest reflectance in the wavelength range was 2.2%, and the lowest reflectance was 0.41%. The refractive index of the low refractive index thin film portion was 1.18, and the luminous average reflectance (Y value) of the antireflection film was 0.51.
Here, the luminosity average reflectance (Y value) is a Y value of a color stimulus value by the XYZ color system (CIE1931 color system) using the sensitivity of the human eye as a parameter at each wavelength, and this value is high. The lower the brightness, the lower the visible reflectance. Specifically, a data processing tool (color measurement software) attached to the spectrophotometer (the UV-visible spectrometer V-570) is used to calculate Y, which is one of the tristimulus values for the C light source, and The luminosity average reflectance (Y value) was used.
[0028]
(Comparative Example 1)
An antireflection film was formed in the same manner as in Example 1, except that the laminated film was not immersed in hydrochloric acid after formation.
The antireflection effect of the obtained antireflection film was evaluated in the same manner as in Example 1. The obtained measurement chart is shown by a solid line in FIG. As a result, the highest reflectance was 4.67% and the lowest reflectance was 0.3%. The refractive index of the low refractive index thin film portion was 1.483, and the luminosity average reflectance (Y value) of the antireflection film was 0.72.
[0029]
From the evaluation results of Example 1 and Comparative Example 1, the refractive index of the low-refractive-index thin film portion was lower and the Y value was lower in Example 1 in which the hydrochloric acid treatment was performed on the laminated film. Further, from the measurement data of FIG. 2, the reflectance is low on the low wavelength side and the high wavelength side from the center wavelength. From this, it was found that there was also an effect of lowering the reflectance in the entire visible light region. From the above results, it was confirmed that the performance was high as the antireflection film.
[0030]
【The invention's effect】
As described above, according to the present invention, it is possible to structurally reduce the refractive index of a thin film composed of a stacked film in which a charged layer having a positive charge and a charged layer having a negative charge are alternately stacked. Can be. Thereby, the antireflection performance of the antireflection film can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an antireflection film according to the present invention.
FIG. 2 is a measurement chart of reflectance according to an example and a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... High refractive index thin film, 3 ... Low refractive index thin film, 4 ... Void.

Claims (11)

A charged layer having a positive charge and a charged layer having a negative charge are alternately laminated, and the laminated film is subjected to an acid treatment or an alkali treatment to form a void in the laminated film to obtain a low refractive index thin film. A method for producing a low refractive index thin film, comprising: 2. The method according to claim 1, wherein the laminated film is formed by an alternate adsorption method. The low-electrode according to claim 1, wherein a weak electrolyte is used as at least one of an electrolyte constituting the positively charged layer and an electrolyte constituting the negatively charged layer. 4. A method for producing a refractive index thin film. 4. The method for producing a low-refractive-index thin film according to claim 1, wherein the low-refractive-index thin film has a refractive index of 1.45 or less. The method for producing a low-refractive-index thin film according to any one of claims 1 to 4, wherein a diameter of the void in a planar shape is less than 200 nm and a depth is less than 200 nm. A low refractive index thin film obtained by the method according to claim 1. A plurality of voids having a diameter of less than 200 nm and a depth of less than 200 nm in a planar shape are formed in a stacked film in which charged layers having positive charges and charged layers having negative charges are alternately stacked. A low refractive index thin film characterized by the following. The low-refractive-index thin film according to claim 7, wherein at least one of the electrolyte constituting the positively charged layer and the electrolyte constituting the negatively charged layer is a weak electrolyte. 9. The low refractive index thin film according to claim 7, wherein the low refractive index thin film has a refractive index of 1.45 or less. An antireflection film comprising the low-refractive-index thin film according to claim 6. The anti-reflection film according to claim 10, wherein the low-refractive-index thin film is laminated on a layer having a higher refractive index than the low-refractive-index thin film.

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