Thin film low in refractive index and its manufacturing method

The present invention relates to a low refractive index thin film and a method for producing the same. More specifically, the outermost surface of the screen of a flat panel display represented by a liquid crystal display device, a plasma display panel, a polarizing plate surface, a protective material for a display such as a mobile phone, a transparent plastic lens, an optical lens, a cover of various instruments, etc. An optical thin film that is directly formed on the surface of a substrate such as a window glass of an automobile or a train, a solar cell panel, or an optical pickup lens, or is used on the surface of a film to be attached to the surface of a substrate to improve the visibility of an image. The present invention relates to a low refractive index thin film used as an optical functional thin film such as an antireflection film for preventing Frenel reflection caused by a difference in refractive index between a base material and air, and a method for producing the same.

Films having high light transmission and low reflection performance, that is, antireflection films, are widely used in various products such as display panels, display members such as displays, lenses, optical components such as eyeglasses, and solar cell panels. Antireflection films are also used during laser annealing and in photoresist steps for manufacturing thin film transistors and single crystal thin film silicon solar cells. This is because multiple interference of light due to reflection becomes a big problem in processing techniques such as laser annealing and exposure, and in solar cells and lenses.

With the development of vacuum technology in the 1930s, magnesium fluoride, which is one of the low-refractive index materials, was used to improve the transmittance of military telescopes for the anti-reflection treatment of optical parts and members. Is said to be the beginning of. By then, the basic principle of antireflection was widely known as an already established law in the field of optics, and the design theory of antireflection by multilayer films was established in the 1950s. The raw materials used for antireflection are a substance having a low refractive index such as a fluoride such as magnesium fluoride and an oxide such as silica, and a substance having a high refractive index such as titanium oxide. That is, magnesium fluoride is vapor-deposited on the glass, or a titanium oxide layer is vapor-deposited, and then a multilayer is formed by a vapor deposition method so that fluoride or silica has an optical film thickness on the upper layer.

Initially, it was only used for lenses and prisms used for special purposes such as military and academic, but due to advances in film formation technology and cost reduction, it has been applied to lenses for cameras and eyeglasses. In recent years, the spread of TVs, personal computers, and mobile terminals has been remarkable, and along with this, the improvement of visibility of display devices used for them has become stronger as a market demand, and technological development to meet such demand is one of the antireflection treatment efforts. It has become. Especially in recent years, mobile phones, which are often used outdoors, are required to reduce the difficulty of seeing the screen due to the reflection of outside light. On the other hand, large flat panel displays such as PDPs are used for interior lights and viewers. Anti-reflection treatment is standard to suppress reflection on the screen.

Since the basic principle of antireflection has already been established in the field of optics, the formation of an antireflection film poses a main problem in the development and selection of the film material to be used and the problem of the equipment for making the antireflection film.

Currently generally used methods for producing an antireflection film are a dry process such as vacuum deposition and sputtering, or a coating method using a sol-gel method or a polymer of a perfluororesin or a partially fluoropolymer. It is a wet process. In recent years, due to price demands, antireflection treatment of wet process instead of dry process has become mainstream.

The main material for forming a coating type antireflection film is a cyclized polymer of perfluoroallyl vinyl ether, which is a perfluoro resin, or a copolymer of tetrafluoroethylene and perfluorodimethyldioxol. As a partially fluorinated resin, there is a fluoroalkyl methacrylate resin obtained by polymerizing a monomer synthesized by a reaction of methacrylic acid or methacrylic acid chloride and a fluoroalkyl alcohol, and these are applied to a base material using a fluorosolve. If the fluorine content is increased, it can be expected that the refractive index will be lowered and the reflectance will also be lowered, but there is a problem that unevenness and loss due to shavings are likely to occur during coating (Characteristics of antireflection film. Optimal Design / Membrane Fabrication Technology , 2002, Technical Information Association).

Recently, ultrafine particles having a wavelength lower than the visible light wavelength have been attracting attention and put into practical use from the viewpoint of controlling the refractive index of transparent materials. Considering price, stability, toxicity, environmental impact, availability, processability, etc., high refractive index materials include titanium oxide, cerium oxide, tin oxide, indium oxide, zinc oxide, zirconia oxide, niobium oxide, etc. Silica and fluoride are typical low-refractive index materials. There is a method of mixing these with a binder resin and applying them (Japanese Patent Laid-Open Nos. 04-202366, 2001-163906, 2001-167637).

Compared to the large number of high-refractive index materials, low-refractive-index materials have the smallest silica of 1.46 to 1.48, except for fluoride. Therefore, as a stable material having a smaller refractive index, a material in which silica is hollowed out has been developed (Japanese Patent Laid-Open No. 2001-233611). It has a refractive index of about 1.34 to 1.40, and although the base is silica, it has a refractive index comparable to that of fluoride or fluororesin. By dispersing this in a binder and using it, it is possible to obtain a film having a refractive index comparable to that of a fluororesin while being a silica dispersion system (Japanese Patent Laid-Open No. 07-48527).

On the other hand, the antireflection film formed by coating needs to form a film thickness given by the formula [1/4 × λ / refractive index of layer] (nm) in order to realize it with a single layer. .. In this equation, λ is the wavelength at which the reflectance is minimized, and the antireflection film is usually around 100 nm in order to more effectively set the antireflection ability to around 550 nm, which is the center of human visual sensitivity. Therefore, the biggest challenge in the wet process is the control of the film thickness, which requires high accuracy.

For example, as shown in Fig. 1, a deviation of 5 nm leads to a deviation of 25 nm at the minimum reflectance wavelength, and this wavelength deviation causes a large change in the reflected color, which causes color unevenness and becomes a big problem in practical use. .. For this reason, there is no sufficient error with respect to a predetermined film thickness, and more uniform coating is required. Therefore, for example, a flexible base material such as a plastic film, a base material having a curved surface or unevenness, and a thin film base. It is very difficult to continuously coat and manufacture the material.

Further, even if a fluororesin or a mixture of fine particles and a binder resin is used, there is a limit to lowering the refractive index, and in order to satisfy the coatability, the refractive index must be about 1.40. Therefore, in order to reduce the reflectance, it is common to have a multilayer structure including a high refractive index layer. In the dry process, the minimum reflectance wavelength is generally brought close to 0% by laminating the optical film thickness of silica and titania in multiple layers using a vacuum deposition method or a sputtering method. Increased reflectance at wavelengths deviating from the designed wavelength, that is, wavelength dependence, causes the problem of coloring (Fig. 2).

In addition, if a multi-layer structure is used in the coating method, the uniformity of the film thickness of the base becomes strict, and there is a problem that the coating liquid to be laminated on the base is limited to those that do not invade the base layer. Is the limit. Therefore, the antireflection film currently produced by the wet method is inferior in characteristics to the dry process.

Since the single-layer antireflection film has a feature that it has less wavelength dependence, that is, less coloring than a multi-layer structure, it efficiently prevents reflection even in the ultraviolet to visible light region. Therefore, there is a demand for an ideal material having a refractive index lower than that of fluoride in this wavelength region and a manufacturing method for uniformly forming the material.

In order to achieve 0% reflectance with a single layer, the refractive index (n) of the antireflection film satisfying the following equation_c) Is required. (Macleod, Thin-Film Optical Filters, Elsevier, New York, 1969, or Kanahara et al., Applied Physics Selection Book 3 Thin Films, Shokabo, 1984).<maths num="1"><img file="JP4747653B2_D0001.tif" /></maths>

(n_cIs the refractive index of the antireflection film, n_sIs the refractive index of the substrate, n₀Is the refractive index of the atmosphere) For example, the refractive index of glass or plastic substrates used for displays in the visible region is about 1.52, and the most ideal value is about 1.22 to 1.25, which is the square root of the product of the refractive index of air 1. Value.

The film having such a refractive index is, for example, a porous film in which the refractive index is controlled by the concentration of pores contained in the silica film. Moreover, in order to be transparent, the diameter of the pores of the void is required to be 100 nm or less so as not to scatter light.

For example, the method of etching glass (Journal of Optical Society of America, 1976, 66, 515 and Journal of Non-crystal Solids 1982, 48, 177) and the method using the sol-gel method (Applied Optics, 1984, 23, 1418). And Journal of Non-crystal Solids 1997, 218, 113), vapor deposition method (Journal of Non-crystal Solids 1997, 218, 92), phase separation (Science, 1999, 283, 520) and optical society structure (Nature, 244, 281-282, 1973). And the Journal of Optical Society of America A, 1996, 13, 988) have been reported.

These methods are suitable for providing a material having a low refractive index of 1.3 or less, and a refractive index of about 1.25 can be achieved depending on the conditions, but there are problems such as difficulty in controlling the film thickness of the plastic film. It is not suitable for productively forming a 100 nm level thin film that is continuously uniform over a large area on such a flexible substrate.

On the other hand, as a method for forming a nanometer-scale thin film from a solution, an alternating lamination method has been proposed. The alternating lamination method is a method for forming an organic thin film, which was announced by G. Decher et al. In 1992 (Thin Solid Films, 210/211, p831 (1992)). In this method, the base material is alternately immersed in an aqueous solution of a polymer electrolyte (polycation) having a positive charge and a polymer electrolyte (polyanion) having a negative charge, so that the polycation is adsorbed on the substrate by electrostatic attraction. A composite film (alternate laminated film) is obtained by laminating a set of polyanions.

In the alternating laminating method, the film thickness to be formed can be adjusted by the number of laminating. For example, if film growth of about 10 nm is observed in each lamination, if you want to form 100 nm, you can repeat the lamination ten times.

In the alternating lamination method, the charge of the material formed on the substrate and the material having the opposite charge in the solution are attracted by the electrostatic attraction to grow the film, so that the adsorption proceeds and the charge is neutralized. When this occurs, no further adsorption will occur. Therefore, when a certain saturation point is reached, the film thickness does not increase any more. Since the adsorption film thickness at one time is thin, it has the excellent feature that the highly accurate film thickness can be controlled by the number of times of lamination, so it is an appropriate film formation method for nanometer-sized optical thin film formation. I can say. Furthermore, it is a low-cost and highly accurate thin film forming method that does not require vacuum equipment. In addition, it has a feature not found in other methods, such as the inside of a tubular base material, the inside of woven fibers and the inside of a foaming material, and the part where the solution permeates can be coated.

After forming an alternating laminated film of polyacrylic acid and polyallylamine hydrochloride on a substrate by Rubner et al., By immersing it in an acid solution such as hydrochloric acid whose pH was adjusted, the electrostatically adsorbed bond portion was partially absorbed. There is a report that it is cut to form a void structure (Langmuir 16, p5017-5023 (2000)), and an antireflection film applying this has been proposed (International Publication WO 03/082481 A1 (2003), and Nature Materials, Vol1 p59-63 (2002)).

Shiratori et al. Used this polymer porous membrane as a mold to precipitate metal oxides in the porous membrane by a chemical solution precipitation method, and then fired at 650 ° C to remove the polymer component, and only the oxide was porous. It forms a film (Japanese Patent Laid-Open No. 2003-301283).

On the other hand, Lvov et al. Reported a method of applying the alternating lamination method to fine particles and laminating a polymer electrolyte having a charge opposite to the surface charge of the fine particles by the alternating lamination method using each fine particle dispersion of silica, titania, and ceria. (Langmuir, Vol.13, (1997) p6195-6203). Using this method, silica fine particles having a negative surface charge and polycations such as polydiallyldimethylammonium chloride (PDDA) or polyethyleneimine (PEI) having the opposite charge are alternately laminated to form silica. It is possible to form a fine particle laminated thin film in which fine particles and polymer electrolytes are alternately laminated.

Hattori et al. Formed an alternating laminated film of two types of polymer electrolytes, PDDA as a polycation and sodium polystyrene sulfonate (PSS) as a polyanion, and after sufficiently increasing the positive charge density of the base material, about 110 to 130 nm. Silica or polymer fine particles with the same particle size and negative charge are arranged on the substrate to obtain an antireflection film with gaps between the fine particles (Advanced Material. 13, 51-54 (2001). )). Here, by increasing the number of times the PDDA and PSS as the base are laminated, the surface coverage of the fine particles tends to increase and the reflectance tends to decrease. In contrast, when the number of PDDA and PSS layers is small, the positive charge density on the surface of the glass base material is low, so that there are parts where fine particles are not adsorbed, that is, parts where the base material is exposed, and the reflectance decreases. Absent.

Similarly, in Japanese Patent Application Laid-Open No. 2002-361767, fine particles having a volume density of 40 to 80% are laminated multiple times using the methods known in Langmuir, Vol.13, (1997) p6195-6203. We are proposing a method for forming a laminated film. These methods are characterized in that the fine particles are packed at a high density, and further, a multi-layered antireflection film is produced by combining layers of high refraction fine particles, for example, titania fine particles.

Here, the volume density of the silica fine particles required to form a thin film having a refractive index of 1.22 to 1.30, which is a single layer and a sufficient antireflection film can be obtained by laminating silica fine particles having a refractive index of 1.48 to form voids, is , Drude's theory is approximately obtained as follows (thin film / optical device author Sadafumi Yoshida, Hiroyoshi Yajima Publishing Co., Ltd. 1994 Tokyo University Press).<maths num="2"><img file="JP4747653B2_D0002.tif" /></maths>

therefore <maths num="3"><img file="JP4747653B2_D0003.tif" /></maths>

(n_cIs the index of refraction of the thin film, n_SiO2Is silica refractive index = 1.48, n₀Is air refractive index = 1, ρ is the volume density of silica fine particles)<maths num="4"><img file="JP4747653B2_D0004.tif" /></maths>

That is, the volume density of the silica fine particles must be 41% to 58% (Fig. 3). However, the method of controlling the volume density to be low has not been shown in the fine particle laminated film by the alternating lamination method so far, and as a result, the silica volume density becomes higher than necessary by the known method, and as a result, a single layer is formed. It was difficult to obtain an ideal low refractive index thin film of 1.3 or less when using it as an antireflection film.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 04-202366</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2001-163906</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2001-167637</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2001-233611</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 07-48527</text></patcit><patcit num="6"><text>International release WO 03/082481 Pamphlet</text></patcit><patcit num="7"><text>Japanese Unexamined Patent Publication No. 2003-301283</text></patcit><patcit num="8"><text>JP-A-2002-361767</text></patcit><nplcit num="1"><text>"Anti-reflective coating characteristics and optimum design / membrane fabrication technology", 2002, Technical Information Association</text></nplcit><nplcit num="2"><text>Macleod, "Thin-Film Optical Filters", Elsevier, New York (1969)</text></nplcit><nplcit num="3"><text>Kanahara et al., "Applied Physics Selection Book 3 Thin Film", Shokabo, (1984).</text></nplcit><nplcit num="4"><text>Journal of Optical Society of America, 1976, 66, 515</text></nplcit><nplcit num="5"><text>Journal of Non-crystal Solids 1982, 48, 177</text></nplcit><nplcit num="6"><text>Applied Optics, 1984, 23, 1418</text></nplcit><nplcit num="7"><text>Journal of Non-crystal Solids 1997, 218, 113</text></nplcit><nplcit num="8"><text>Journal of Non-crystal Solids 1997, 218,92</text></nplcit><nplcit num="9"><text>Science, 1999,283,520</text></nplcit><nplcit num="10"><text>Nature, 244, 281-282, 1973</text></nplcit><nplcit num="11"><text>Journal of Optical Society of America A, 1996, 13, 988</text></nplcit><nplcit num="12"><text>Thin Solid Films, 210/211, p831 (1992)</text></nplcit><nplcit num="13"><text>Langmuir 16, p5017-5023 (2000)</text></nplcit><nplcit num="14"><text>Nature Materials, Vol1 p59-63 (2002)</text></nplcit><nplcit num="15"><text>Langmuir, Vol.13, (1997) p6195-6203</text></nplcit><nplcit num="16"><text>Advanced Material. 13, 51-54 (2001)</text></nplcit><nplcit num="17"><text>Sadafumi Yoshida, Hiroyoshi Yajima "Thin Film / Optical Device" University of Tokyo Press 1994</text></nplcit>

<p> The present invention has been made in view of the above problems, and a low refractive index thin film having a nanometer-sized void structure on a substrate can be produced at room temperature by a wet process, and the film thickness can be easily controlled. An object of the present invention is to provide a manufacturing method capable of obtaining a uniform optical functional thin film, and to provide a low refractive index thin film obtained by the method.</p>

<p> In order to achieve the above object, the surface potential of the fine particles in the fine particle dispersion is intended in the step of alternately immersing the base material in the fine particle dispersion and the polymer solution having an ionicity opposite to the surface charge of the fine particles. By reducing the volume of the particles, the surface of the base material is prevented from being densely filled with fine particles, thereby forming a fine particle laminated film having a low volume density occupied by the fine particles of the film and a high void ratio, and the fine particle laminated film thereof. The present invention relating to a manufacturing method is provided.</p><p> In producing a low refractive index thin film, the present inventors intentionally impregnate a dispersion liquid in which the surface potential of the fine particles is controlled, preferably an electrolyte, at a concentration of 0.01 to 0.25 mol / liter and intentionally set the surface potential of the fine particles. By lowering, the electrostatic attraction of the opposite charge formed on the surface of the base material to the surface is reduced, and the volume density occupied by the fine particles of the film is due to the effect of preventing the fine particles from being densely packed. In other words, it was found that a fine particle laminated film having a high void ratio was formed. If the surface potential is lowered too much, the dispersibility of the fine particles in the liquid will decrease, causing aggregation and precipitation.</p><p> As already explained as a background technique, in the conventional alternating lamination method, in order to suppress the aggregation of fine particles in the dispersion liquid, the pH is adjusted to the range of 9.5 to 11 or 2 to 3 to raise the zeta potential. I was intentionally trying to keep the surface potential of the fine particles high. It is well known in the art that particles tend to aggregate as their particle size becomes finer, and in that respect, the conventional method can be said to be an extremely natural method for handling a dispersion of fine particles. The present invention differs from the prior art in that it does not require complete dispersion of fine particles.</p><p> In the present invention, it is preferable that the fine particle dispersion contains the electrolyte at a concentration of 0.01 to 0.25 mol / liter. If it is less than 0.01 mol / liter, the electrostatic attraction with the substrate on which the polymer having the opposite charge is adsorbed becomes strong, resulting in a film densely packed with fine particles. On the other hand, if it is more than 0.25 mol / liter, the electrostatic attraction with the base material does not work, and the repulsive force between the fine particles of the dispersion liquid decreases, causing agglomeration, and the agglomerates of the fine particles precipitate to form fine particles. Not laminated on the substrate. By alternately immersing the fine particles in a polymer solution having an ionicity opposite to the surface charge of the fine particles, a fine particle laminated film in which the fine particles and the polymer are alternately laminated is formed on the base material.</p><p> The thin film formed by the present invention is a low refractive index thin film having a refractive index of 1.22 to 1.30. As explained as a background technique, the index of refraction of glass or plastic substrates in the visible region is about 1.48 to 1.52, which is closer to the value of the product of air with the index of refraction of 1, 1.22 to 1.25. preferable.</p><p> Further, the volume density of the fine particles in the fine particle laminated film is preferably a low refractive index thin film of 41 to 58%. As a result, a low refractive index film that cannot be realized by a conventional wet process can be formed, and the function as an antireflection film having higher performance can be achieved.</p><p> The average primary particle size of the fine particles contained in the fine particle dispersion is preferably 10 nm or more and 100 nm or less. In order to obtain transparency, a fine particle diameter in the range of 100 nm or less at which light is not scattered is preferable. Finer fine particles can be selected in order to control the film thickness with high accuracy in the alternating lamination, and fine particles having a large particle size can be used to reduce the number of steps, that is, the number of laminations. On the other hand, if it is less than 10 nm, it takes time for laminating and a dense film is obtained, which is not preferable.</p><p> It is preferable that the fine particles contained in the fine particle dispersion liquid in the low refractive index thin film according to any one of claims 1 to 4 are colloidal silica, polymer fine particles, porous fine particles, or hollow fine particles. In order to control the dispersibility of the fine particles, a surfactant is added to the fine particle dispersion liquid. Further, if the fine particles contained in the fine particle dispersion are polymer fine particles, there are many choices of monomers as starting materials, and it is easy to impart functions such as low refractive index, ionicity, light or thermosetting. Further, if the fine particles contained in the fine particle dispersion are porous fine particles or hollow fine particles, the refractive index can be further lowered. The refractive index of silica and polymer fine particles is relatively low, about 1.48 to 1.50, but porous or hollow fine particles have a lower refractive index due to the effect of averaging with the refractive index with air. Is. By forming a laminated film of these fine particles, a low refractive index thin film having a refractive index of 1.22 to 1.30 can be obtained.</p><p> In the present invention, in the low refractive index thin film according to any one of claims 1 to 5, it is more preferable that the fine particles contained in the fine particle dispersion have a beaded shape. As shown in FIG. 4, when the beads are in the shape of beads, due to steric obstacles, other beads-like fine particles and polymers having an opposite charge cannot occupy the space densely, and as a result, the porosity is higher. This is because a low refractive index film can be easily formed.</p><p> Further, the fine particles contained in the fine particle dispersion liquid in the low refractive index thin film according to any one of claims 1 to 6 have an ionic functional group, a thermosetting functional group or a photocurable functional group on the surface of the fine particles. With this, the mechanical strength of the film can be increased by applying heat or light energy after forming the fine particle laminated film. This is because when it is used as an antireflection film, it is directly exposed to the environment in which it is used, so that it is required to have a property of being scratch-resistant.</p><p> For the same reason, in the low refractive index thin film according to any one of claims 1 to 7, it is preferable that a transparent overcoat film having a film thickness of 20 nm or less is laminated on the fine particle laminated film. If the film thickness is larger than that, the antireflection function tends to be optically reduced.</p><p> In the method for producing a low refractive index thin film according to the present invention, which comprises alternately laminating fine particles and a polymer on a substrate, a fine particle dispersion containing an electrolyte at a concentration of 0.01 to 0.25 mol / liter. Provided is a method for producing a low refractive index thin film, which comprises alternately repeating a step of immersing the fine particles in a polymer solution having an ionicity opposite to the surface charge of the fine particles. As a result, it is possible to lower the surface potential of the fine particles, intentionally inhibit the dense lamination of the fine particles, and form a thin film having a lower refractive index than the fine particle laminated film obtained by the conventional alternating lamination method.</p><p> This is because the surface potential of the fine particles can be controlled by increasing the salt concentration in the fine particle dispersion. It is presumed that the surface potential of the fine particles can be further lowered by adding the electrolyte because the added ions are electrically neutralized by coordinating around the fine particles. It should be noted that the addition of the electrolyte also has the effect of increasing the film thickness obtained by one immersion because the fine particles aggregate into two or more in the dispersion liquid. Therefore, the number of immersions can be reduced and the process can be shortened.</p><p> In the fine particle dispersion, it is preferable that the fine particles are dispersed in water or a mixed solvent of water and an organic solvent. This is because it is usually difficult to dissolve the electrolyte without water, and it is difficult to control the surface potential.</p><p> In the method for producing a low refractive index thin film according to claim 9, the film thickness can be controlled at the nanometer level at normal temperature and pressure, and a high-performance antireflection film can be produced at low cost. The average primary particle size of the fine particles contained in the fine particle dispersion is preferably 10 nm or more and 100 nm or less, and more preferably the fine particles are colloidal silica, polymer fine particles, porous fine particles or hollow fine particles. Further, it is preferable that the fine particles contained in the fine particle dispersion have a beaded shape, and that the fine particles have an ionic functional group, a thermosetting functional group or a photocurable functional group on the surface of the fine particles. More preferred for some reason.</p>

<p> The low-refractive index thin film of the present invention provides a thin film having a low refractive index as a single-layer fine particle laminated film, and is excellent in imparting an antireflection function to a base material. Further, the method for producing a low refractive index thin film of the present invention is capable of controlling the film thickness at the nanometer level at normal temperature and pressure, and is excellent in producing a high-performance antireflection film at low cost.</p>

The present inventors have formed an alternating laminated film of fine particles and a polymer electrolyte formed on the base material by electrostatic attraction by alternately immersing the solid base material in a polymer electrolyte solution having an opposite charge to the fine particle dispersion liquid. Focusing on controlling the surface potential, which is a parameter that determines the dispersibility of fine particles, by lowering the surface potential, the stacking density of fine particles on the substrate is controlled, resulting in a high void ratio, resulting in optics. We have come up with the invention to form a low refractive electrode thin film, which is important as a functional film. Hereinafter, the method for controlling the surface potential of the present invention and the materials used will be sequentially described.

(1) Electric double layer Many of the particles dispersed in a liquid are positively or negatively charged. In an attempt to maintain electrical neutrality, ions having a sign opposite to that of the particle gather in the liquid on the surface of the particle. Such a group of ions gathers around the particle surface in a spherical shell shape, and the charged layer is surrounded by the oppositely charged layer. Such a state is expressed as an "electric double layer".

The ion distribution of the ion layer in the liquid is disturbed by thermal motion. Therefore, the concentration of the opposite charge is high near the surface and gradually decreases as the distance increases. Ions with the same charge as the particle show the opposite distribution, and in the region sufficiently distant from the particle, the positive ion charge and the negative ion charge cancel each other out, and the electrical neutrality is maintained. In contrast to the above-mentioned capacitor-type double layer, what is actually seen in a liquid is called a "diffusion electric double layer", and the ion distribution of the opposite charge gradually becomes blurred as it moves away from the surface. It is a double layer.

The ion distribution on the inner particle surface is called the "diffusion layer". Further, the diffusion layer does not always start immediately from the surface of the fine particles, and in many cases, some ions are strongly attracted to the surface and fixed, and this layer is called a "fixed layer".

Particles dispersed in a liquid are often charged, and the stability of the dispersed state of the particles often depends on the charged state. The particles can be presumed to move with a portion of the inside of the "fixed layer" and the "diffusive layer", and the surface on which this movement occurs is called the "slip surface".

If the potential in the region that is sufficiently distant from the particle and is electrically neutral is defined as zero, the "zeta potential" is defined as the potential of the "sliding surface" when measured with reference to this zero point. .. In the case of fine particles, as the absolute value of the zeta potential increases, the repulsive force between the particles becomes stronger and the stability of the particles becomes higher. Conversely, when the zeta potential approaches zero, the particles tend to aggregate. Therefore, the zeta potential is used as an index of the dispersion stability of dispersed particles (Ayao Kitahara, Kunio Furusawa, Masataka Ozaki, Hiroyuki Ohshima, "Zeta Potential Zeta Potential: Physical Chemistry of Fine Particle Interface", Scientist, 1995).

(2) Zeta potential measurement method When an electric field is applied from the outside to a system in which charged particles are dispersed, the particles migrate toward the electrodes, but the rate is proportional to the charge of the particles, so the zeta is measured by measuring the migration rate of the particles. The potential is required.

For example, the electrophoretic light scattering measurement method is also known as the laser Doppler method, which states that "when light or sound waves hit a moving object and are reflected or scattered, the frequency of the light or sound waves changes in proportion to the speed of the object." The effect is used to determine the migration rate of particles. When the electrophoresed particles are irradiated with laser light, the frequency of the scattered light from the particles shifts due to the Doppler effect. Since the shift amount is proportional to the migration speed of the particles, the migration speed of the particles can be known by measuring this shift amount.

Actually, when a sample dispersed in a medium (liquid) having a refractive index (n) is irradiated with a laser beam having a wavelength (λ) and detected at a scattering angle (θ), the migration speed (V) and the Doppler shift amount The relationship of (Δν) is expressed by the following equation.<maths num="5"><img file="JP4747653B2_D0005.tif" /></maths>

[n: Refractive index of medium (liquid), θ: Detection angle] The electrical mobility (U) can be obtained from the migration speed (V) and the electric field (E) obtained here.<maths num="6"><img file="JP4747653B2_D0006.tif" /></maths>

The electric mobility (U) to the zeta potential (ζ) can be obtained by using the following equation of Smoluchowski.<maths num="7"><img file="JP4747653B2_D0007.tif" /></maths>

[η: viscosity of medium (liquid), ε: dielectric constant of medium (liquid)] In this way, the zeta potential can be obtained by observing the scattered light from the moving particles. Since the zeta potential obtained in this way reflects the surface potential of the fine particles, increasing the zeta potential improves the dispersibility due to the electrostatic repulsive force between the fine particles, but when used in the alternating lamination method, it is used. If a base material having an opposite charge is present, the attractive force with the surface becomes large, so that it becomes difficult to form a film having a high void ratio, that is, the packed state becomes a dense film. Is not preferable. Therefore, by controlling the absolute value of the zeta potential to be low, it is possible to prevent fine particles from being densely packed and laminated on the surface of the base material, and more specifically, it can be suppressed within the range of 1 to 45 mV. preferable. If it is lower than 1 mV, the dispersibility of fine particles in the medium (liquid) deteriorates, precipitation occurs, and the charge approaches 0, so that no attractive force with the substrate is generated and adsorption does not occur, which is not preferable.

(3) Surface potential control method Considering that the method of controlling the surface potential is equivalent to controlling the zeta potential, it is necessary to consider the factors that give the zeta potential. When the thickness of the diffused electric double layer on the surface of fine particles is expressed by 1 / κ, this thickness is the distance at which the attractive force between the surface charge and the counter ion (electrolyte ion) balances with the thermal motion that tries to disturb it. is there. Here, κ is called the Debye-Huckel parameter, and in the case of an electrolyte with an ionic value z,<maths num="8"><img file="JP4747653B2_D0008.tif" /></maths>

It is represented by. Where (k) = Boltzmann constant, (ε)₀) = Permittivity of vacuum, (ε_r) = Relative permittivity of the medium (liquid), (T) = absolute temperature, (e) unit charge. (n) is the number density of the electrolyte and the unit is (m)^-3). (n) is Avogadro's number (N)_A), N = 1000N_A× Concentration (C). From this equation, focusing on the denominator, increasing the electrolyte concentration or valence z reduces the thickness of the diffused electric double layer, and further focusing on the numerator of this equation, increasing the temperature T activates the thermal motion. The diffused electric double layer means that it becomes thicker. That is, it means that the thickness of the electric double layer is reduced by adding the electrolyte.

The relationship between the surface potential and the electric double layer is related by the following relational expression. That is, the electric field σ / ε in the medium (liquid) due to the surface charge density σ._rε₀Therefore, when the distance of the thickness (1 / κ) of the electric double layer is separated, the electric field × distance = (σ / ε)_rε₀) × (1 / κ) = (σ / ε)_rε₀There is a potential difference of κ). From this, the surface potential (φ₀) Is expressed by the following equation.<maths num="9"><img file="JP4747653B2_D0009.tif" /></maths>

From this equation, in order to lower the surface potential and zeta potential of the fine particles, the parameter 1 / κ of the denominator Debye-Huckel is lowered (κ is increased), that is, the electric double layer is thinned, in other words, the electrolyte concentration is lowered. Raising and the permittivity of the solution (ε)_r) Is increased and the charge density of the molecule is decreased.

Permittivity of water (ε_r) Since a higher medium (liquid) is not common, it is difficult to increase the permittivity of the dispersion. Therefore, as a method of lowering the surface potential, it is preferable to add an electrolyte (increase the electrolyte concentration). The electrolyte is not limited as long as it is soluble in water, water, an alcohol mixed solvent, etc., but is a salt of an alkali metal, an alkaline earth metal, a quaternary ammonium ion, etc. and a halogen element, LiCl, KCl. , NaCl, MgCl₂, CaCl₂Etc. are used. In the present invention, the concentration of the electrolyte is preferably about 0.01 to 0.25 M (= mol / liter, the same applies hereinafter). If more than 0.25M of electrolyte is added, the surface potential drops too much and the dispersibility deteriorates, and fine particles precipitate due to aggregation and the like.

The surface potential can also be controlled by pH. This is because the degree of dissociation (ionization) of the dissociation group on the particle surface is affected by pH. For example, if the surface of fine particles has a carboxyl group (-COOH) or a surface hydroxyl group (-OH), it will be ionized when the pH is raised and the carboxylate anion (-COO) will be ionized.^-) Or hydroxide ion (-O^-), So the charge density σ increases. On the other hand, the amino group (-NH)₂If there is), lower the pH and ammonium ion (-NH)₃⁺) And the charge density increases. That is, there is an increase in charge density in the high pH region and the low pH region. Therefore, in the present invention, by setting the pH of the fine particle dispersion in the range of 3 to 9, the increase in charge density σ is suppressed for both anions and cations, and as a result, the surface potential and the zeta potential are controlled to be low. It is possible to prevent the fine particles from being densely packed and laminated on the surface of the base material.

(4) Fine particle material The fine particles dispersed in the fine particle dispersion aqueous solution used in the present invention are optically transparent fine particles, and the particle size of the fine particles is preferably 10 nm or more and 100 nm or less. If it is 10 nm or less, it takes too much time to grow the film, and if it is 100 nm or more, it is difficult to control the film thickness and it becomes easy to scatter light. Further, it is preferable that the variation in particle size is 10 nm or less. This is because the variation in the size of the adsorbed particles affects the variation in the film thickness, which may cause optical unevenness.

Examples of inorganic fine particles include magnesium fluoride (MgF).₂), Aluminum fluoride (AlF₃), Lithium fluoride (LiF), Sodium fluoride (NaF), Silica (SiO)₂), Aluminum oxide (Al₂O₃), Zirconia oxide (ZrO)₂), Titanium oxide (TiO₂), Niobium oxide (Nb)₂O₅), Indium tin oxide (ITO), zinc oxide (ZnO), tin oxide (SnO)₂), Celia (CeO)₂), Yttrium oxide (Y₂O₃), Bismuth oxide (Bi₂O₃), Etc., which can be used alone or in admixture of two or more. Among the above-mentioned inorganic fine particles, silica (SiO) in that the refractive index can be lowered.₂) Is preferable, and the water-dispersed colloidal silica (SiO) whose particle size is controlled to be 10 nm to 100 nm.₂) Is the most preferable. Examples of commercially available products of such inorganic fine particles include Snowtex and Snowtex UP (manufactured by Nissan Chemical Industries, Ltd.).

Further, polymer fine particles satisfying the condition of particle diameter of 10 nm to 100 nm can also be used, and examples thereof include polyethylene, acrylic polymer, polystyrene, silicon polymer, phenol resin, polyamide, and natural polymer. These can be used alone or in admixture of two or more. They are a solution spray method, a solvent removal method, an aqueous solution reaction method, an emulsion method, a suspension polymerization method, a dispersion polymerization method, an alkoxide hydrolysis method (sol-gel method), a hydrothermal reaction method, a chemical reduction method, and a liquid phase. It is synthesized by a manufacturing method such as a medium pulse laser ablation method. Examples of commercially available polymer fine particles include mist pearl (manufactured by Arakawa Chemical Industry Co., Ltd.) and the like.

Further, an ionic or reactive functional group may be added to the surface of these fine particles for the purpose of providing a bond between the fine particles. Typical examples include an amino group, a carboxyl group, a carbonyl group, an epoxy group, a phenol group, a mercapto group, a methacryl group, a polyether group and the like. The addition of these functional groups can be achieved, for example, by subjecting a silane coupling agent having a functional group to a condensation reaction with the surface hydroxyl groups of the fine particles.

In order to obtain a higher porosity, it is more preferable that the basic fine particles contain porous fine particles or a beaded particle shape as shown in FIG. Commercially available products include Snowtex PS or Snowtex UP series (manufactured by Nissan Chemical Industries, Ltd.) and Fine Cataloid F120 (manufactured by JGC Catalysts and Chemicals Co., Ltd.), including pearl necklace-shaped silica sol.

(5) Fine particle dispersion In the fine particle dispersion used in the present invention, the above-mentioned fine particles are dispersed in a medium (liquid) which is a mixed solvent such as water or a water-soluble organic solvent, and the electrolyte is in the range of 0.01 to 0.25 mol / liter. It was added. Examples of the water-soluble organic solvent include methanol, ethanol, propanol, acetone, dimethylformamide, acetonitrile and the like. Further, when preparing the fine particle dispersion liquid, a so-called dispersant can be used in order to improve the dispersibility. As such a dispersant, a surfactant, an ionic polymer, a nonionic polymer, or the like can be used. The amount of these dispersants used varies depending on the type of dispersant used, but is generally preferably about 0.1% (weight) or less, and if it is too large, gelation / separation may occur or in the dispersion liquid. The fine particles become electrically neutral, and a laminated film cannot be obtained.

The electrolyte that can be used may be one that dissolves in water, water, an alcohol mixed solvent, or the like and dissociates in a fine particle dispersion as described above, and is a salt of a strong acid and a strong base, or a salt of a strong acid and a weak base. , Weak acid and strong base salts. Of these, salts of strong acids and strong bases or weak bases are preferable in terms of dissociability, ionic strength, etc., and for example, LiCl, NaCl, KCl, MgCl.₂, CaCl₂Etc. can be exemplified.

Further, in the fine particle dispersion, the pH of the fine particle dispersion is preferably about 3 to 9. The pH can be adjusted with an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide or an acidic aqueous solution such as hydrochloric acid or sulfuric acid, and the pH can also be adjusted with a dispersant. For example, the pH can also be adjusted by using a strong acid and a weak base or a salt that is a combination of a weak acid and a strong base. When the pH of the fine particle dispersion is greater than 9 or less than 3, the electrostatic attraction with the substrate to which the polymer having the opposite charge is adsorbed becomes stronger, and the film is densely packed with fine particles. Or, the electrostatic attraction with the base material does not work, and the repulsive force between the fine particles of the dispersion liquid decreases, causing agglomeration, and the agglomerates of the fine particles precipitate and the fine particles are laminated on the base material. It tends not to be done.

The proportion of fine particles in the fine particle dispersion is usually preferably about 0.01 to 10% (weight), and the fine particles can be dispersed by a known method.

(6) Ionic polymer solution The ionic polymer solution used in the present invention is obtained by dissolving an ionic polymer having a charge opposite to or similar to the surface charge of fine particles in water or a mixed solvent of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent that can be used include methanol, ethanol, propanol, acetone, dimethylformamide, and acetonitrile. This ionic polymer solution is used for forming a fine particle laminated film and forming an underlayer.

As the ionic polymer, a polymer having a charged functional group in the main chain or the side chain can be used. In this case, the polyanion generally has a functional group capable of being negatively charged, such as sulfonic acid, sulfuric acid, and carboxylic acid. For example, polystyrene sulfonic acid (PSS), polyvinyl sulfuric acid (PVS), and dextran. Sulfuric acid, chondroitin sulfuric acid, polyacrylic acid (PAA), polymethacrylic acid (PMA), polymaleic acid, polyfumaric acid and the like are used. In addition, as the polycation, generally, one having a functional group capable of being positively charged such as a quaternary ammonium group and an amino group, for example, polyethyleneimine (PEI), polyallylamine hydrochloride (PAH), polydiallyldimethyl Ammonium chloride (PDDA), polyvinylpyridine (PVP), polylysine, polyacrylamide and copolymers containing at least one of them can be used. All of these ionic polymers are water-soluble or soluble in a mixed solution of water and an organic solvent, and the molecular weight of the ionic polymer cannot be unconditionally determined depending on the type of the ionic polymer used. However, in general, those of about 20,000 to 200,000 are preferable. The concentration of the ionic polymer in the solution is generally preferably about 0.01 to 10% (weight). The pH of the ionic polymer solution is not particularly limited.

(7) Base material As the base material, all solid base materials other than those extremely hydrophobic, water repellent, such as resins, semiconductors such as silicon, metals, inorganic oxides, etc., or those whose surface is coated with such a film. Can be adapted. The shape is not limited as long as it is a film, a sheet, a plate, a shape having a curved surface, a tubular shape, a thread shape, a fiber, a foam material, or the like, as long as it can be immersed and water can enter. A transparent base material is desirable in order for this low refractive index film to function as an antireflection film. It is also possible to add an antireflection function to the polarizing plate used for the LCD display.

Examples of the transparent substrate include polyethylene terephthalate, triacetyl cellulose, diacetyl cellulose, acetate butyrate cellulose, polyether sulfone, polyamide, polyimide, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, and polymethyl methacrylate. , Polycarbonate, polyurethane and other thermoplastic resins, glass substrates and the like are used. It also includes those in which the surface of the base material is coated with a transparent resin film or an inorganic film.

The fine particle laminated film of the present invention is formed on such a base material, and an adhesive is applied to the base material surface on the opposite side of the antireflection film (fine particle laminated film) formed on such a transparent base material. A layer is formed, and it can be attached to a glass substrate or the like on the display surface as an adherend so that the antireflection film faces the air. Further, a low refractive index film is formed on the temporary support, an adhesive layer or an adhesive layer for transfer is formed on the film, and the adherend is bonded so that the adhesive layer or the adhesive layer faces each other. The antireflection film can also be formed on the adherend by peeling off the temporary support.

(8) Method for producing fine particle laminated film First, the above-mentioned base materials are used as they are, or their surfaces are subjected to corona discharge treatment, glow discharge treatment, plasma treatment, ultraviolet irradiation, ozone treatment, chemical etching treatment with alkali or acid, silane coupling treatment, etc. Introduces a functional group having polarity to make the surface charge of the substrate negative or positive.

In addition, as a method of efficiently introducing electric charges to the surface of the base material, it is also possible to form an alternating laminated film of PDDA or PEI based on polycation, which is a strong electrolyte polymer, and PSS based on polyanion (Advanced). Material.13,51-54 (2001)). That is, a solid substrate having a charge on such a surface is alternately immersed in two types of polymer ion solutions (polycation and polyanion) to prepare a thin film of polymer ions on the solid substrate. If the surface charge is negative, it is first immersed in a cationic solution, then immersed in an anionic solution, which, if necessary, alternates to form an alternating laminate. The production conditions such as the concentration of the polymer ion solution to be used, the pH condition and the immersion time, and the number of repetitions are adjusted in a timely manner in the same manner as in (6) above according to the film thickness to be laminated. Further, it is preferable to wash away the excess solution by rinsing only the solvent before immersing in the solution having the opposite charge. The alternate laminated film of polymer ions serving as the base layer for forming the fine particle laminated film on such a base material has a film thickness of about 1 to 5 nm, and the number of times of lamination (combination of cation and anion is one). ) Is preferably about 2 to 5 times, which improves the uniformity of the fine particle laminated film to be laminated thereafter.

Next, such a solid substrate having a charge on the surface is alternately immersed in a fine particle dispersion and a polymer ion solution (polycation or polyanion) having a charge opposite to the surface charge of the fine particles, and the thin film of the fine particle laminated film is made into a solid substrate. Make on top. When the surface charge of the base material is the opposite of the surface charge of the fine particles, it is necessary to start by immersing it in the fine particle dispersion, and when it is the same as the surface charge of the fine particles, start by immersing it in the ionic polymer solution. The immersion in the fine particle dispersion and the ionic polymer solution is repeated until the desired film thickness is obtained. The final immersion is usually in an ionic polymer solution to ensure adsorption of the particulates. The immersion time is appropriately adjusted according to the types of fine particles and ionic polymers used and the film thickness to be laminated.

Rinse off excess medium (liquid) or solution by rinsing the medium (liquid) or solvent only after immersion in the fine particle dispersion or ionic polymer solution and before immersing in the fine particle dispersion or ionic polymer solution having an opposite charge. Is preferable. Water, alcohol, acetone, etc. are used for such rinsing, but ion-exchanged water (so-called ultrapure water) having a specific resistance value of 18 MΩ · cm or more is usually used from the viewpoint of removing excess ions. Used. Since it is electrostatically adsorbed, it does not peel off during this rinsing process. In addition, rinsing may be performed to prevent unadsorbed polymer ions or fine particles from being brought into a medium (liquid) or solution having an opposite charge. If this is not done, cations and anions may be mixed in the medium (liquid) or solution by bringing in, and fine particles may aggregate or precipitate. Moreover, you may perform drying before immersing in each solution. As a drying method, a known method such as blowing hot air, dry air, nitrogen or the like with an air knife, passing through an electric heating furnace, an infrared furnace, or the like can be used.

The film thickness formed by immersing in a fine particle dispersion or an ionic polymer solution can be determined by, for example, forming a laminated film on a crystal transducer and monitoring a change in its frequency, or obtaining a laminated film. Can be obtained by observing with an SEM (scanning electron microscope), TEM (transmission electron microscope), AFM (atomic force microscope), or the like.

In FIG. 5, a fine particle laminate was formed on the crystal transducer using Snowtex pss aqueous dispersion (STps-s) as the fine particle dispersion and polydiallyl dimethylammonium chloride (PDDA) as the polymer solution. It is a graph showing the total immersion time and the amount of change in frequency at the time, the upper curve is the case where NaCl is added as an electrolyte to make the sodium chloride concentration 0.25 mol / liter, and the lower curve is the electrolyte. Is not added (electrolyte concentration such as sodium chloride ion is less than 0.01 mol / liter). From this graph, in each case, there is a large frequency change when immersed in the fine particle dispersion (STps-s) and then saturated, and the subsequent immersion in the polymer solution (PDDA) is large. It can be seen that there is no change in frequency. From the results of SEM (scanning electron microscope) and the like, the change in frequency corresponds to a film thickness of 20 to 25 nm at 1000 Hz. That is, in FIG. 5, by immersing the fine particle dispersion and the ionic polymer solution once, when the electrolyte is added, it is about 30 to 36 nm, and when the electrolyte is not added, it is about 15 to 18 nm. It can be seen that the film thickness is obtained, and the film thickness formed when the electrolyte is added is about twice as large as that when the electrolyte is not added. That is, the film thickness obtained by immersing the fine particle dispersion liquid and the ionic polymer solution once varies depending on the presence or absence of the electrolyte, the size of the fine particles used, the fine particle concentration in the dispersion liquid, and the like. Since a film thickness of about 10 to 40 nm can be obtained, it can be seen that the film thickness of the fine particle laminated film can be controlled by the immersion time and the number of repetitions. It goes without saying that the addition of the electrolyte increases the film thickness formed at one time, so that the number of repetitions can be reduced by that amount and the process can be simplified.

As the manufacturing apparatus, an alternating laminating apparatus called a dipper may be used. A base material is attached to a robot arm that moves up, down, left, and right, and at a programmed time, the base material is soaked in a cationic solution, then in a rinse solution, then in an anionic solution, and then in a rinse solution. With this process as one cycle, the number of times of stacking can be automatically performed continuously. The program may be a combination using two or more kinds of cationic substances and anionic substances. For example, the first two layers can use a combination of polydimethyldiallyl ammonium chloride and sodium polystyrene sulfonate, and the following ten layers can use a combination of polydimethyldiallyl ammonium chloride and anionic silica sol.

Take out the roll-shaped film from the unwinding part, arrange the cationic solution water tank, rinse water tank, anionic water tank, and rinse water tank side by side in the middle, arrange this arrangement as many times as you want to stack, and finally dry it. A continuous film forming process on a film-like substrate that is arranged and provided with a take-up portion can also be used.

(9) Fine particle laminated film When the fine particle laminated film is produced in this way, a thin film having a low refractive index of 1.30 or less can be obtained. With the above method, it is easy to make 1.22 to 1.30. The refractive index is preferably 1.22 to 1.28, more preferably 1.25 to 1.27, and even more preferably 1.22 to 1.26, from the viewpoint of imparting an antireflection function on a glass or plastic substrate.

Further, the fine particle laminated film produced in this manner can be a low refractive index thin film having a volume density of 41 to 58%. The volume density is more preferably 41 to 55% and even more preferably 41 to 50% from the viewpoint of imparting an antireflection function on a glass or plastic base material.

Since such a fine particle laminated film is laminated with a certain void in the fine particle laminated film without the fine particles adhering to each other, the volume density referred to here is the volume of the void portion in the fine particle laminated film. The volume occupied by the fine particles themselves with respect to the total volume occupied by the fine particles themselves, which is the volume occupied by the fine particles themselves. Therefore, for example, when the fine particles are porous or hollow, the voids in the fine particles are the fine particle laminated film. It is included in the volume of the void inside. FIG. 3 is a graph showing the relationship between the volume density and the refractive index in the case of silica. That is, in the fine particle laminated film of the present invention, the desired refractive index is obtained by controlling the adsorption amount and adsorption density of the fine particles by containing the electrolyte in the fine particle dispersion and keeping the volume density of the fine particles within a predetermined range. Can be obtained. The preferable volume density varies depending on the refractive index of the fine particles themselves, but as described above, the volume density range of 41 to 58% is preferable when silica is used as the fine particles.

The volume density in the fine particle laminated film is calculated from the relationship between the weight of the laminated fine particles based on the change in frequency and the laminated film thickness measured by an electron microscope, for example, using a crystal oscillator. It can be roughly calculated. Further, if the film thickness of the fine particle laminated film is about 1 μm, it can be obtained by a method by gas adsorption such as obtaining the pore ratio and pore distribution of a normal porous substance.

However, in the present invention, the thickness of the fine particle laminated film as a whole is 80 to 120 nm, and considering the reflectance of a single layer, it is preferably about 90 to 110 nm, and it can be obtained by laminating an ionic polymer. Since the film thickness is about 1 nm or less, which is extremely thin compared to the film thickness (usually 10 to 40 nm) obtained by laminating fine particles, the fine particle laminated film can be measured without considering this ionic polymer. We decided to use the value ρ calculated by Drude's theoretical formula (Equation 2) from the refractive index, the refractive index of the substance itself (that is, the bulk) that constitutes the fine particles, and the refractive index of the air. The case where the fine particles are silica is as shown in FIG. 3, but the case where fine particles other than silica can be used can be obtained in the same manner.

Further, this fine particle laminated film has a void structure in which visible light is not scattered. A void structure in which visible light is not scattered is a structure in which visible light is not scattered uniformly over the plane. Structurally speaking, a void portion having a size exceeding 100 nm or a size exceeding 100 nm, which causes scattering, is used. It means that the fine particles of the above are not present, and characteristically speaking, it means that, for example, the haze value indicating the ratio of the transmitted light and the scattered light of the incident light is 1% or less. Specifically, it means that the haze value of a substrate with a fine particle laminated film formed on a transparent substrate having a haze value of 1% or less in accordance with either JIS K7105 or JIS K7136 is 2% or less. To do.

Furthermore, the feature of this fine particle laminated film is that the wavelength dependence of reflectance is small, and when a film thickness of 100 nm to 120 nm is formed on a glass substrate, the surface of 4% or less in the entire range of 400 nm to 800 nm, which is called the visible light region. The reflectance is obtained. The particles are stacked three-dimensionally with voids so that the particles make almost point contact with each other. The color changes depending on the film thickness, but when a film thickness of 100 nm to 120 nm is formed on a smooth transparent glass substrate, the reflected color shows dark purple. A haze value of 1.0% or less can be obtained.

FIG. 6 shows an antireflection film (indicated as glass with an AR film) utilizing the low refractive index of the fine particle laminated film produced on the glass substrate as described above, and the glass itself (indicated as glass) as the substrate. This is a comparison of anti-reflection performance, and it can be seen that there is a large difference between the two in terms of anti-reflection function.

(10) Overcoat film Since the fine particle laminated film has voids, it is vulnerable to mechanical strength and is good when used on a part that does not come into direct contact with the outside, but when used on a surface such as a display, the effect on the antireflection function is minimized. It is preferable to form and use an overcoat having a film thickness that limits the thickness. The film thickness is preferably 20 nm or less.

Examples of such a film material include resin compositions such as ionizing radiation curable resins, thermosetting resins, thermoplastic resins, and reactive silicone oils. Further, a method of immersing in a metal alkoxide solution and then drying to obtain a cured film of a metal oxide, a method of dipping in a solution of polysilazane and converting to silica to coat the silica film, a thin-film deposition method or a sputtering method. The inorganic oxide film may be formed at 20 nm or less by using a dry method such as. The refractive index of the overcoat film should be as low as possible, MgF₂Fluoride and silica (SiO)₂) Etc. are preferable. Further, the strength and the refractive index can be adjusted by using the resin composition as a binder and mixing fine particles of these inorganic materials.

Further, a coating may be applied to prevent scratches and to prevent stains such as water and oil and fat components. The film thickness of the coating should be 20 nm or less so as not to affect it optically. Typically, there are surface coating agents such as perfluorosilane fluorine compounds having an alkoxy group. Similar to the sol-gel reaction, silane compounds are networked by dehydration or polycondensation due to dealcohol by hydrolysis. When silica is used as the fine particles, silanol groups are present on the surface, so even if they are directly coated, intermolecular bonds are formed. In these, the alkoxy group first reacts with the silanol group on the surface to dealcoholize and immobilize, and then hydrolysis proceeds due to moisture in the air, etc., and then condensation forms a siloxane bond that is three-dimensionally bonded and is strong. It has excellent mechanical durability such as surface friction and abrasion. Further, since a hydrophobic group containing fluorine as a main component is present on the surface, it is preferable because it exhibits high water repellency.

When polymer fine particles or fine particles having no silanol group are laminated, it is preferable to perform coating after forming a silica film. Typical examples are Optool DSX (manufactured by Daikin), Durasurf DS5000 (manufactured by Harves), and Novec EGC-1720 (manufactured by Sumitomo 3M).

As a method for forming the overcoat film, a wet process such as roll coating, spin coating and dip coating, a dry process such as a thin film deposition method and a sputtering method, or a combination thereof can be used.

Hereinafter, the examples of the low refractive index film of the present invention will be described in more detail.

Example 1 As materials, polydialyldimethylammonium chloride (PDDA, average molecular weight 100,000, manufactured by Aldrich) which is a polycation, sodium polystyrene sulfonate (PSS, average molecular weight 70,000, manufactured by Aldrich) which is a polyanion, and silica as a fine particle dispersion. A fine particle aqueous dispersion (ST20, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, Snowtex 20, average particle size 20 nm) was used.

The pH of ST20 is adjusted to 10 to maintain dispersibility. Therefore, in this example, sodium chloride was added so as to be 0.25 mol / liter after adjusting the weight%. The pH was 10 with little change.

First, an alternating laminated film of PDDA and PSS is formed as a base layer for efficiently applying an electric charge to the base material. As solutions, prepare a 0.3% by weight PDDA aqueous solution and a 0.3% by weight PSS aqueous solution. Next, BK-5 glass substrate (manufactured by Matsunami, 25 mm x 75 mm x 0.7 mm thick) was immersed in (a) PDDA aqueous solution for 5 minutes, and then immersed in ultrapure water for rinsing (specific resistance 18 MΩ · cm) for 3 minutes. Immersion, (a) Immersion in PSS aqueous solution for 5 minutes, and immersion in ultrapure water for rinsing for 3 minutes. This cycle was repeated twice, with the process of performing the steps (a) and (b) in order as one cycle, and two layers of PDDA and PSS alternating laminated films were laminated on the glass substrate. By this step, the charge density on the surface of the substrate can be made uniform, and there is an effect that fine particles are evenly adsorbed.

Subsequently, the process of forming the fine particle laminated film will be described. As solutions, prepare a 0.3% by weight PDDA aqueous solution and 1% by weight, pH = 10, and ST20 aqueous dispersion having a sodium chloride concentration of 0.25 mol / liter. The zeta potential of the fine particle aqueous dispersion was measured and found to be -40 mV. By alternately immersing in these liquids, a fine particle laminated film in which PDDA and silica fine particles are alternately laminated is obtained. In the procedure, since the outermost surface of the above-mentioned base layer is PSS, first, it is immersed in the opposite charge cation (c) PDDA aqueous solution for 1 minute, and then immersed in ultrapure water for rinsing for 3 minutes, (d). Immerse in 1% by weight silica fine water dispersion ST20 for 1 minute, and then in ultrapure water for rinsing for 3 minutes. This cycle was repeated 5 times, with the step of performing the steps (c) and (d) in order as one cycle.

When the transmittance spectrum of this glass substrate was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.), the maximum transmittance was about 99%, and a black tape on the back surface so that reflection from the back surface could be ignored. The reflectance (surface reflectance) was 0.4% when the reflection spectrum was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.) by incident at 5 °. However, silicon was used as the standard mirror, and the refractive index and extinction coefficient of silicon in the literature values (DEAspnes and JBTheeten, J. Electrochem.Soc. Vol.127, p1359 (1980)) were cited. The absolute reflectance of the sample is calculated from the relative reflectance of the sample with respect to the standard mirror. Since the transmittance of the glass substrate of the base material used is 91% and the surface reflectance is 4%, it means that an antireflection film having excellent characteristics is formed on the glass substrate. The above zeta potential was measured using a DELSA 440SX (manufactured by Beckman Coulter) at a constant current value of 0.7 to 1.0 mA.

In the same process, a silicon wafer was used as a base material instead of a glass substrate, and the obtained fine particle laminated film was measured for refractive index and film thickness by an ellipsometer (DVA-36LA, manufactured by Mizojiri Optical Co., Ltd., light source 633 nm). The refractive index was 1.29 and the film thickness was 110 nm. The volume density obtained from the refractive index was 56%. The refractive index and film thickness of the ellipsometer were obtained by simulating the amplitude ratio of the P-polarized light component and the S-polarized light component of the reflected light and their phase difference by the program attached to the DVA-36LA device.

Example 2 In the same process as in Example 1, Snowtex PS-S (STps-s, pearl necklace-like silica sol) containing fine particle dispersion liquid containing beaded fine particles manufactured by Nissan Chemical Industries, Ltd., 1% by weight, pH A fine particle laminated film was prepared using an aqueous dispersion containing = 10 and a sodium chloride concentration of 0.25 mol / liter. The number of stacking cycles was four. The zeta potential of the fine particle dispersion was measured and found to be -23 mV. When the transmitted spectrum of the obtained glass substrate was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.), the maximum transmittance was about 99% and the surface reflectance was 0.1%.

A silicon wafer was used as a base material instead of a glass substrate, and the obtained fine particle laminated film was measured for refractive index and film thickness by an ellipsometer (manufactured by Mizojiri Optical Co., Ltd., light source 633 nm). As a result, the refractive index was 1.24 and the film thickness was 110 nm. The volume density obtained from the refractive index was 45%.

Example 3 To the STps-s fine particle dispersion (1% by weight) used in Example 2, sodium chloride was added so as to be 0.25 mol / liter, and the pH was adjusted to 9 using 1 M hydrogen chloride water. It was used as a fine particle dispersion and immersed in the fine particle dispersion three times in the same process as in Example 1 to prepare a fine particle laminated film. The zeta potential of the fine particle dispersion was measured and found to be -23 mV. When the transmitted spectrum of the obtained glass substrate was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.), the maximum transmittance was about 99% and the surface reflectance was 0.1%. The measurement results of the reflection spectrum of the obtained low refractive index thin film are shown in FIG.

A silicon wafer was used as a base material instead of a glass substrate, and the obtained fine particle laminated film was measured for refractive index and film thickness by an ellipsometer (manufactured by Mizojiri Optical Co., Ltd., light source 633 nm). As a result, the refractive index was 1.24 and the film thickness was 110 nm. The volume density obtained from the refractive index was 45%.

A scanning electron micrograph of the fine particle laminated film formed on the glass substrate is shown in FIG. This electron micrograph is taken when the obtained fine particle laminated film is cut vertically and the cross section is observed from an oblique direction of 45 °. The arrow () in the figure indicates the cross-sectional portion of the fine particle laminated film, and the portion above the arrow indicates the surface state of the fine particle laminated film. From this electron micrograph, it can be seen that in the fine particle laminated film, individual fine particles are in contact with each other through the voids, the fine particles are arranged along the glass substrate, and 10 to 15 particles are stacked.

Comparative example 1 In the same process as in Example 1, ST20 was used without adding sodium chloride to the fine particle dispersion. The zeta potential of this dispersion was measured and found to be -48 mV. When the transmitted spectrum of the obtained glass substrate was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.), the maximum transmittance was about 98% and the surface reflectance was 0.5%. The measurement results of the reflection spectrum of the obtained low refractive index thin film are shown in FIG.

A silicon wafer was used as a base material instead of a glass substrate, and the obtained fine particle laminated film was measured for refractive index and film thickness by an ellipsometer (manufactured by Mizojiri Optical Co., Ltd., light source 633 nm). As a result, the refractive index was 1.31 and the film thickness was 110 nm. The volume density obtained from the refractive index was 60%.

From the above results, it is possible to control the laminated state of the fine particles by adjusting the concentration of the electrolyte added to the fine particle dispersion in the range of 0.01 to 0.25 mol / liter, which results in low refractive index and high transmittance. It can be seen that a low refractive index thin film as an optical functional thin film can be obtained.

<figref num="1">FIG. 1 is a graph showing the relationship between the wavelength and the reflection spectrum when the film thickness of the antireflection film having a refractive index of 1.30 formed on the glass obtained by the simulation is changed. In the figure, the dotted line shows the case where the film thickness is 105 nm, the thick solid line shows the case where the film thickness is 110 nm, and the solid line shows the case where the film thickness is 115 nm.</figref><figref num="2">FIG. 2 is a graph showing the relationship between the wavelength and the reflection spectrum in the multilayer antireflection film and the single layer antireflection film formed on the glass obtained by the simulation. In the figure, the solid line is the case of an antireflection film in which a porous silica film having a refractive index of 1.30 is provided as a single layer, and the broken line is a titania having a refractive index of 2.2 and silica having a refractive index of 1.48. This is the case of an antireflection film having a four-layer structure formed on glass in the order of titania / silica.</figref><figref num="3">FIG. 3 is a graph showing the relationship between the refractive index obtained from the calculation and the volume density of silica.</figref><figref num="4">FIG. 4 is a schematic diagram showing the state of fine particles arranged in a beaded shape.</figref><figref num="5">FIG. 5 shows a change in the frequency of the crystal oscillator with respect to the immersion time when the fine particle dispersion liquid and the ionic polymer solution are alternately immersed in the crystal oscillator to form a fine particle laminated film, that is, the film thickness formed. It is a graph which shows the relationship with the change of.</figref><figref num="6">FIG. 6 shows an antireflection film (indicated as glass with an AR film in the figure) utilizing the low refractive index of the fine particle laminated film produced on the glass substrate of the present invention and the glass itself (in the figure, glass). It is the figure which compared the antireflection performance with the display).</figref><figref num="7">FIG. 7 is a graph showing the measurement results of the reflection spectrum of the low refractive index thin film obtained in Example 3.</figref><figref num="8">FIG. 8 is a scanning electron micrograph showing the cross-sectional state and the surface state of the low refractive index thin film obtained in Example 3.</figref><figref num="9">FIG. 9 is a graph showing the measurement results of the reflection spectrum of the low refractive index thin film obtained in Comparative Example 1.</figref>