JP5011653B2 - Low refractive index thin film and manufacturing method thereof - Google Patents

Description

  The present invention relates to a low refractive index thin film and a method for manufacturing the same. More specifically, the outermost surface of a flat panel display represented by a liquid crystal display device, a plasma display panel, a display protective material for a polarizing plate surface or a mobile phone, a transparent plastic lens, an optical lens, a cover for various instruments, Optical thin film that can be directly formed on the surface of substrates such as window glass for automobiles, trains, solar battery panels, optical pickup lenses, etc. 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 Fresnel reflection caused by a refractive index difference between a substrate and air, and a method for producing the same.

  A film having high light transmittance and low reflection performance, that is, an antireflection film, is widely used in various products such as display panels, display members such as displays, optical components such as lenses and glasses, and solar battery panels. An antireflection film is also used during laser annealing or a photoresist process for manufacturing a thin film transistor or a single crystal thin film silicon solar cell. This is because multiple interference of light due to reflection becomes a serious problem in processing techniques such as laser annealing and exposure, and solar cells and lenses.

  Anti-reflective treatment for optical parts and components has been put into practical use because of the development of vacuum technology in the 1930s, magnesium fluoride, one of the low-refractive-index materials, was used to improve the transmittance of military telescopes. It is said that the beginning of. Until then, the basic principle of antireflection has been widely known as a law already established in the field of optics, and the design theory of antireflection by a multilayer film has been 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 glass, or a titanium oxide layer is vapor-deposited, and then a multilayer is formed by vapor deposition so that fluoride or silica has an optical film thickness on the upper layer.

  Initially it was used only for lenses and prisms used for special purposes such as military and academic purposes, but it has been applied to cameras and lenses for glasses, etc. due to the progress of film formation technology and cost reduction. In recent years, TVs, personal computers, and mobile terminals have been widely used, and accordingly, the visibility of display devices used for them has become a strong market requirement, and technological development to meet such requirements is one of the anti-reflection treatment efforts. It has become. In particular, in recent years, mobile phones that are often used outdoors are required to reduce the difficulty of seeing the screen due to the reflection of external light. On the other hand, large flat panel displays such as PDPs are used for indoor lights and viewers. In order to suppress the reflection on the screen, an antireflection treatment is standard.

  Since the basic principle of antireflection has already been established in the optical field, the formation of antireflection films has major problems in the development of and selection of film materials to be used, as well as the problems of the equipment that produces them.

  Current methods of manufacturing an antireflection film are generally dry processes such as vacuum deposition and sputtering, or sol-gel methods and coating methods using polymers of perfluorinated resins and partially fluorinated monomers. It is a wet process. In recent years, the antireflection treatment of the wet process replacing the dry process has become the mainstream due to the demand of price.

  The main materials for forming the coating type antireflection film include resin materials such as perfluoroallyl vinyl ether perfluoropolymer and a copolymer of tetrafluoroethylene and perfluorodimethyldioxole. A partially fluorinated resin is a fluoroalkyl methacrylate resin obtained by polymerizing a monomer synthesized by the reaction of methacrylic acid or methacrylic acid chloride and fluoroalkyl alcohol, and these are applied to a substrate using a fluorine-based solvent. If the fluorine content is increased, the refractive index can be lowered and the reflectance can be expected to decrease. However, there is a problem that unevenness and missing due to repellency are likely to occur during coating (see “Characteristics of antireflection film”). "Optimum design and film fabrication technology", 2002, Technical Information Association).

  Recently, ultrafine particles having a wavelength shorter 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. In consideration of price, stability, toxicity, environmental impact, availability, workability, etc., high refractive index materials include titanium oxide, cerium oxide, tin oxide, indium oxide, zinc oxide, zirconia oxide, niobium oxide, etc. As a low refractive index material, silica or fluoride is typical. There are methods in which these are mixed with a binder resin and applied (Japanese Patent Laid-Open Nos. 04-202366, 2001-163906, and 2001-167737).

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

  On the other hand, when an antireflection film formed by coating is to be realized with a single layer, it is necessary to form a film thickness given by a calculation formula [1/4 × λ / layer refractive index] (nm). . In this equation, λ is a wavelength at which the reflectivity is minimum, and the antireflection film is usually around 100 nm in order to set the antireflection ability to around 550 nm, which is the center of human visibility more effectively. Therefore, the greatest problem in the wet process is the film thickness control that requires high accuracy.

  For example, as shown in FIG. 1, a deviation of 5 nm leads to a shift of 25 nm at the minimum reflectance wavelength, and the reflected color changes greatly due to the shift of this wavelength. . For this reason, there is no sufficient error with respect to the predetermined film thickness, and more uniform coating is required. For example, a flexible substrate such as a plastic film, a substrate having curved surfaces or irregularities, a thin film substrate, etc. It is very difficult to apply and manufacture the material continuously.

  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 the refractive index must be about 1.40 in order to satisfy the coating property. Therefore, in order to reduce the reflectivity, a multilayer structure including a high refractive index layer is generally used. In the dry process, the minimum reflectance wavelength is generally approached to 0% by laminating multiple optical film thicknesses of silica and titania using vacuum deposition or sputtering. An increase in reflectance at a wavelength deviated from the designed wavelength, that is, wavelength dependency occurs, and a coloring problem occurs (FIG. 2).

  In addition, when a multi-layer structure is used in the coating method, there is a problem that the uniformity of the base film thickness becomes strict, and the coating liquid laminated thereon is limited to one that does not attack the base layer. Up to is the limit. Therefore, the antireflection film currently produced by the wet method has inferior characteristics as compared with the dry process.

  A single-layer antireflection film has a feature that it has less wavelength dependency than a multi-layer structure, that is, less coloration, and thus efficiently prevents reflection in the ultraviolet to visible light region. Therefore, an ideal material having a refractive index equal to or lower than that of fluoride in this wavelength region and a manufacturing method for uniformly forming the material are required.

In order to achieve a reflectance of 0% with a single layer, the refractive index (n _c ) of the antireflection film satisfying the following formula is required. (Macleod, Thin-Film Optical Filters, Elsevier, New York, 1969, or Kanehara et al., Applied Physics Book 3, Thin Film, Yukabo, 1984).

(N _c is the refractive index of the antireflection film, n _s is the refractive index of the substrate, n ₀ is the refractive index of the atmosphere)
For example, a glass or plastic substrate, which is a transparent substrate used in a display, has a refractive index in the visible region of about 1.52, and 1.22 to 1.25 taking the square root of the product with the refractive index 1 of air. The value of the degree is the most ideal value.

  A film having such a refractive index is, for example, a porous film whose refractive index is controlled by the concentration of pores contained in the silica film. Moreover, in order to be transparent, it is required that the pore diameter of the gap is 100 nm or less that does not scatter light.

  For example, a method of etching glass (Journal of Optical Society of America, 1976, 66, 515 and Journal of Non-crystalline Solids 1982, 48, 177) or a method using a sol-gel method (Ap14, Op23, Apr. 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 moth-eye structure (24, Nature 28). -282, 1973 and Journal of Optical Society y of America A, 1996, 13, 988) and the like 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 is achieved depending on conditions, but there are problems such as difficulty in controlling the film thickness. In addition, it is not suitable for forming a uniform thin film having a uniform 100 nm level in a large area on a flexible substrate such as a plastic film with high productivity.

  On the other hand, an alternate lamination method has been proposed as a method for forming a nanometer-scale thin film from a solution. The alternate lamination method is described in G.H. This is a method of forming an organic thin film published in 1992 by Decher et al. (Thin Solid Films, 210/211, p831 (1992)). In this method, a polycation adsorbed on a substrate by electrostatic attraction by alternately immersing the base material in an aqueous solution of a polymer electrolyte having a positive charge (polycation) and a polymer electrolyte having a negative charge (polyanion). A combination of polyanions is laminated to obtain a composite film (alternate laminated film).

  In the alternate lamination method, the film thickness to be formed can be adjusted by the number of lamination. For example, if film growth of about 10 nm is observed in a single lamination, if it is desired to form 100 nm, the lamination may be repeated ten times.

  In the alternating layering method, the film is grown by attracting the charge of the material formed on the substrate and the material having the opposite charge in the solution by electrostatic attraction, so that the adsorption proceeds and the charge is neutralized. When this occurs, no further adsorption occurs. Therefore, when reaching a certain saturation point, the film thickness does not increase any more. Since the adsorption film thickness per one time is thin, it has an excellent feature that the film thickness with high accuracy can be controlled by the number of laminations. I can say that. 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 tube-shaped substrate, the inside of a textile fiber or foam material, and the like, which can be coated on a portion where the solution penetrates.

  Rubner et al. Produced an alternating laminated film of polyacrylic acid and polyallylamine hydrochloride on a substrate, and then immersed the substrate in an acid solution such as hydrochloric acid whose pH was adjusted to partially absorb the electrostatically adsorbed binding portion. There is a report that a void structure is formed by cutting (Langmuir 16, p5017-5023 (2000)), and an antireflection film using this structure 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, and after depositing a metal oxide into the porous membrane by a chemical solution deposition method, the polymer component was removed by baking at 650 ° C. A film is formed (Japanese Patent Laid-Open No. 2003-301283).

  On the other hand, Lvov et al. Applied an alternate lamination method to fine particles, and reported a method of laminating a polymer electrolyte having a charge opposite to the surface charge of the fine particles by using each fine particle dispersion of silica, titania and ceria. (Langmuir, Vol. 13, (1997) p6195-6203). By using this method, silica fine particles having a negative surface charge and polydiallyldimethylammonium chloride (PDDA) or polyethyleneimine (PEI), which are polycations 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 a polymer electrolyte 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 substrate, about 110 to 130 nm An antireflective film having a particle size of, and negatively charged silica or polymer fine particles arranged on a substrate and having a gap between the fine particles is obtained (Advanced Material. 13, 51-54 (2001). )). Here, the surface coverage of fine particles increases and the reflectance tends to decrease by increasing the number of layers of PDDA and PSS as the base. In contrast, when the number of layers of PDDA and PSS is small, the positive charge density on the surface of the glass substrate is low, so that a portion where fine particles are not adsorbed, that is, a portion where the substrate is exposed is generated, and the reflectance is lowered. Absent.

  Similarly, in Japanese Patent Laid-Open No. 2002-361767, Langmuir, Vol. 13, (1997) p6195-6203 proposes a method of laminating fine particles a plurality of times using a method known in the art to form a fine particle laminate film having a volume density of 40 to 80%. These methods are characterized in that fine particles are filled at a high density, and an antireflection film having a multilayer structure in which layers of fine particles having high refraction, for example, titania fine particles are combined, is produced.

Here, it is necessary for laminating silica fine particles having a refractive index of 1.48 to form voids, and to form a thin film having a refractive index of 1.22 to 1.30, which can provide a sufficient antireflection film with a single layer. The volume density of silica fine particles is approximately calculated from Drude's theory as follows (thin film / optical device authors Sadayoshi Yoshida, Hiroyoshi Yajima Publishing Co., Ltd., University of Tokyo, 1994).

therefore

( _Nc is the refractive index of the thin film, n _SiO2 is the silica refractive index = 1.48, n ₀ is the air refractive index = 1, and ρ is the volume density of the silica fine particles)

That is, the volume density of silica fine particles is required to be 41% to 58% (FIG. 3). However, in the fine particle laminated film by the conventional alternate lamination method, the method for controlling the volume density low is not shown. As a result, the known method increases the silica volume density more than necessary, resulting in a single layer Thus, it was difficult to obtain a low refractive index thin film having an ideal refractive index of 1.3 or less when an antireflection film was used.
Japanese Patent Laid-Open No. 04-202366 JP 2001-163906 A Japanese Patent Laid-Open No. 2001-167637 JP 2001-233611 A JP 07-48527 A International Publication WO03 / 082481 Pamphlet Japanese Patent Laid-Open No. 2003-301283 JP 2002-361767 A “Characteristics and Optimal Design / Film Fabrication Technology of Anti-Reflective Coating”, 2002 Macleod, “Thin-Film Optical Filters”, Elsevier, New York (1969) Kanehara et al., "Applied physics selection book 3 thin film", Hanafusa, (Showa 59). Journal of Optical Society of America, 1976, 66, 515 Journal of Non-crystal Solids 1982, 48, 177 Applied Optics, 1984, 23, 1418 Journal of Non-crystal Solids 1997, 218, 113 Journal of Non-crystal Solids 1997, 218, 92 Science, 1999, 283, 520 Nature, 244, 281-282, 1973 Journal of Optical Society of America A, 1996, 13, 988 Thin Solid Films, 210/211, p831 (1992) Langmuir 16, p5017-5023 (2000) Nature Materials, Vol1 p59-63 (2002) Langmuir, Vol. 13, (1997) p6195-6203 Advanced Material. 13, 51-54 (2001) Sadafumi Yoshida, Hiroyoshi Yajima “Thin Films and Optical Devices” The University of Tokyo Press 1994

  The present invention has been made in view of the above problems, and a low refractive index thin film having a nanometer-size void structure on a substrate can be produced by a normal temperature and wet process, and film thickness control is easy. In addition, an object of the present invention is to provide a production method capable of obtaining a uniform optical functional thin film and to provide a low refractive index thin film obtained by the method.

  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 substrate in the fine particle dispersion and a polymer solution having an ionicity opposite to the surface charge of the fine particles. The effect of preventing the fine particles from being densely filled on the surface of the base material is reduced, thereby forming a fine particle laminated film having a low volume density occupied by fine particles in the film and a high porosity, and the fine particle laminated film. The present invention relating to a manufacturing method is provided.

  In producing a low refractive index thin film, the inventors of the present invention controlled a dispersion in which the surface potential of the fine particles was controlled, preferably the absolute value of the zeta potential of the fine particles was in the range of 1 to 45 mV, and the surface potential of the fine particles was controlled. By deliberately decreasing, the electrostatic attraction to the surface of the opposite charge formed on the surface of the substrate as a result is reduced, and the fine particles of the film are prevented from being densely packed. It has been found that a fine particle laminated film having a low volume density, in other words, a high porosity can be formed. If the surface potential is lowered too much, the dispersibility of the fine particles in the liquid is reduced, causing aggregation and precipitation.

  As already described as the background art, in the conventional alternating lamination method, in order to suppress aggregation of the fine particles in the dispersion, the pH is adjusted to a range of 9.5 to 11 or 2 to 3, and the surface potential of the fine particles is adjusted. I was trying to keep the absolute value of the zeta potential high intentionally. It is well known in the art that particles are more likely to agglomerate as the particle size becomes smaller, and in that respect, the conventional method is a very natural method for handling fine particle dispersions, The present invention differs from the prior art in that it does not require complete fine particle dispersion.

  In the present invention, the absolute value of the zeta potential indicating the surface potential of the fine particles in the fine particle dispersion is preferably in the range of 1 to 45 mV. When the absolute value of the surface potential of the fine particles is larger than 45 mV, the electrostatic attractive force with the substrate on which the polymer having the opposite charge is adsorbed becomes strong, resulting in a film in which the fine particles are densely packed. On the other hand, if the absolute value is less than 1 mV, the electrostatic attraction with the substrate does not work, and the repulsive force between the fine particles of the dispersion is reduced to cause aggregation. It will not be laminated on the substrate. By alternately dipping 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 on the substrate is formed.

  The thin film formed according to the present invention is a low refractive index thin film having a refractive index of 1.22 to 1.30. As described in the background art, the refractive index in the visible region of the glass or plastic substrate is about 1.48 to 1.52, which is closer to the value obtained by taking the parallel root of the product with the refractive index 1 of air. .22 to 1.25 is more preferable.

  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%. Thereby, a low refractive index film that cannot be realized by a conventional wet process can be formed, and a function as an antireflection film having higher performance can be achieved.

  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 of 100 nm or less in which light is not scattered is preferable. Finer fine particles can be selected in order to accurately control the film thickness by alternate lamination, and fine particles having a large particle diameter can be used to reduce the number of steps, that is, the number of laminations. On the other hand, when the thickness is less than 10 nm, it takes a long time to laminate, and a dense film is not preferable.

  The fine particles contained in the fine particle dispersion in the low refractive index thin film according to any one of claims 1 to 4 are preferably colloidal silica, polymer fine particles, porous fine particles, or hollow fine particles. In order to control the dispersibility of the fine particles, those in which a surfactant is added to the fine particle dispersion are also included. 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. Furthermore, if the fine particles contained in the fine particle dispersion are porous fine particles or hollow fine particles, the refractive index can be further reduced. The refractive index of silica and polymer fine particles is about 1.48 to 1.50, which is relatively low. However, porous and hollow fine particles have a lower refractive index due to the averaging effect with the refractive index of air. This is because it becomes fine particles. By using 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.

  In the present invention, it is more preferable that the fine particles contained in the fine particle dispersion in the low refractive index thin film according to any one of claims 1 to 5 have a continuous shape in a bead shape. As shown in FIG. 4, when the beads are beaded, other beaded fine particles or a polymer having an opposite charge cannot occupy the space densely due to a steric hindrance, resulting in a higher porosity. This is because a low refractive index film can be easily formed.

  The fine particles contained in the fine particle dispersion 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 particle. If it has, the mechanical strength of the film can be increased by applying heat or light energy after the fine particle laminated film is formed. This is because, when used as an antireflection film, since it is directly exposed to the environment in which it is used, it is required to have a characteristic that is not easily damaged.

  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 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 lowered.

  In the method for producing a low refractive index thin film according to the present invention, in which fine particles and a polymer are alternately laminated on a substrate, the absolute value of the zeta potential of the fine particles is controlled within a range of 1 to 45 mV. There is provided a method for producing a low refractive index thin film characterized by alternately repeating a step of immersing in a fine particle dispersion and a step of immersing in a polymer solution having an ionicity opposite to the surface charge of the fine particles. As a result, the surface potential of the fine particles can be lowered, and the fine lamination of fine particles can be intentionally inhibited to form a thin film having a refractive index lower than that of the fine particle laminated film by the conventional alternating lamination method.

  In addition, the fine particle dispersion used in the method for producing a low refractive index thin film is intended to reduce the surface potential of the fine particles by controlling the pH of the fine particle dispersion in the range of 3 to 9, and to stack fine fine particles. Therefore, it is possible to form a fine particle laminate film having a lower refractive index than that of the conventional fine particle laminate film by the alternating lamination method.

  For the same reason, since the fine particle dispersion contains the electrolyte at a concentration of 0.01 to 0.25 mol / liter, fine particles having a lower refractive index than the conventional fine particle laminated film by the alternating lamination method. A laminated film can be formed. This is because the surface potential of the fine particles can also be controlled by increasing the salt concentration. The reason why the surface potential of the fine particles can be further lowered by adding the electrolyte is presumed to be that the added ions are coordinated around the fine particles and are electrically neutralized. In addition, since the fine particles are aggregated into two or more in the dispersion by adding the electrolyte, it is also recognized that the film thickness obtained by one immersion can be increased. Therefore, the number of immersions is reduced and the process can be shortened.

  In the fine particle dispersion, the fine particles are preferably dispersed in water or a mixed solvent of water and an organic solvent. This is because it is difficult to control the zeta potential with a dispersion medium having a low dielectric constant.

  In the method for producing a low refractive index thin film according to claim 9, the film thickness can be controlled at a 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 the fine particles are more preferably colloidal silica, polymer fine particles, porous fine particles, or hollow fine particles. Furthermore, the fine particles contained in the fine particle dispersion preferably have a bead-like shape, and the surface of the fine particles has an ionic functional group, a thermosetting functional group, or a photocurable functional group as described above. More preferred for reasons.

  The low refractive index thin film of the present invention provides a low refractive index thin film with a single-layer fine particle laminated film, and is excellent in imparting an antireflection function to a substrate. 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 room temperature and normal pressure, and is excellent in producing a high-performance antireflection film at low cost.

  In the alternating laminated film of fine particles and polymer electrolyte formed by electrostatic attraction on a substrate by alternately immersing a solid substrate in a polymer electrolyte solution having a charge opposite to that of the fine particle dispersion. Focusing on controlling the surface potential, which is a parameter that determines the dispersibility of fine particles, and by lowering the surface potential, the lamination density of fine particles on the base material is controlled, resulting in high porosity. It came to the invention which forms the low refractive index thin film 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 Most of the particles dispersed in the liquid are positively or negatively charged. In order to maintain neutrality electrically, ions having a sign opposite to that of the particles gather in the liquid on the particle surface. Such an ion group surrounds the particle surface and gathers in a spherical shell shape, and a layer having a charge is surrounded by a layer having an opposite charge. Such a state is expressed as “electric double layer”.

  The ion distribution of the ion layer in the liquid is disturbed due to thermal motion. Therefore, the concentration of the opposite charge is high near the surface, and gradually decreases as the distance increases. The ion having the same charge as the particle exhibits an opposite distribution, and in a region sufficiently away from the particle, the charge of the positive ion and the charge of the negative ion cancel each other, and the electrical neutrality is maintained. In contrast to the capacitor-type double layer, what is actually seen in the liquid is called a “diffusion electric double layer”, in which the oppositely charged ion distribution 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”. In addition, the diffusion layer does not always start immediately from the surface of the fine particles, and some ions are strongly attracted to the surface and are often fixed, and this layer is called a “fixed layer”.

  Particles dispersed in a liquid often have a charge, and the stability of the dispersed state of the particle often depends on the charged state. It can be assumed that the particles move with a “fixed layer” and a part inside the “diffusion layer”, and the surface where this movement occurs is called the “sliding surface”.

  When the potential of a region that is sufficiently far away 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 based on this zero point. . In the case of fine particles, if 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 is close to zero, the particles tend to aggregate. Therefore, the zeta potential is used as an index of dispersion stability of dispersed particles (Fumio Kitahara, Kunio Furusawa, Masataka Ozaki, Hiroyuki Oshima, “Zeta Potential Zeta Potential: Physical Chemistry of Fine Particle Interface”, Scientist, 1995).

(2) Zeta potential measurement method When an external electric field is applied to a system in which charged particles are dispersed, the particles migrate toward the electrode, but the velocity is proportional to the charge of the particles. The zeta potential is determined by measuring the migration speed.

  For example, the electrophoretic light scattering measurement method is also known as the laser Doppler method, and it is a Doppler that "the frequency of light or sound waves changes in proportion to the speed of the object when light or sound waves are reflected or scattered by moving objects." The migration speed of particles is obtained using the effect. When laser light is irradiated onto the electrophoretic particles, 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 determined by measuring the shift amount.

Actually, when a sample dispersed in a medium (liquid) having a refractive index (n) is irradiated with laser light having a wavelength (λ) and detected by a scattering angle (θ), the migration speed (V) and the Doppler shift amount The relationship (Δν) is expressed by the following equation.

[N: refractive index of medium (liquid), θ: detection angle]
The electric mobility (U) is obtained from the migration speed (V) and the electric field (E) obtained here.

The electric mobility (U) to the zeta potential (ζ) can be obtained by using the following Smoluchowski equation.

[Η: viscosity of medium (liquid), ε: dielectric constant of medium (liquid)]
In this way, the zeta potential is determined by observing scattered light from the migrating 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 electrostatic repulsion between the fine particles. In the presence of a substrate having a charge opposite to that, the attractive force with the surface increases, so that it is difficult to form a film with a high porosity, that is, the state of filling becomes a dense film. Is not preferred. 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 stacked on the surface of the base material, and more specifically, to suppress within a range of 1 to 45 mV. preferable. Further, if it is lower than 1 mV, the fine particle dispersibility of the medium (liquid) is deteriorated, precipitation occurs, and since the electric charge approaches 0, no attractive force is generated with the base material and adsorption is not preferable.

(3) Method for controlling surface potential If the method for controlling the surface potential is considered equivalent to controlling the zeta potential, it is necessary to consider the factors given to the zeta potential. When the thickness of the diffusion electric double layer on the surface of the fine particle is expressed by 1 / κ, this thickness is the distance that the attractive force between the surface charge and the counter ion (electrolyte ion) balances with the thermal motion trying to disturb it. is there. Here, κ is called a Debye-Huckel parameter, and in the case of an electrolyte with an ionic value z,

It is represented by Here, (k) = Boltzmann constant, (ε ₀ ) = dielectric constant of vacuum, (ε _r ) = dielectric constant of medium (liquid), (T) = absolute temperature, and (e) unit charge. (N) is the number density of the electrolyte, and the unit is (m ⁻³ ). When (n) is expressed by the Avogadro number (N _A ), n = 1000 N _A × concentration (C). From this equation, focusing on the denominator, increasing the electrolyte concentration or valence z decreases the thickness of the diffusion electric double layer, and further focusing on the numerator of this equation, the thermal motion becomes active as the temperature T is increased. It means that the diffusion electric double layer 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 _r ε ₀ is generated in the medium (liquid) by the surface charge density σ. Therefore, when the distance of the electric double layer thickness (1 / κ) is separated, the electric field × distance = (σ / ε A potential difference of _r ε ₀ ) × (1 / κ) = (σ / ε _r ε ₀ κ) is generated. From this, the surface potential (φ ₀ ) is expressed by the following equation.

From this equation, in order to lower the surface potential and the zeta potential of the fine particles, the Debye-Huckel parameter 1 / κ of the denominator is lowered (κ is increased), that is, the electric double layer is made thinner, in other words, the electrolyte concentration is reduced. It can be seen that it is sufficient to increase the dielectric constant (ε _r ) of the solution and decrease the charge density of the molecule.

Since a medium (liquid) higher than the dielectric constant (ε _r ) of water is not common, it is difficult to increase the dielectric constant of the dispersion. Therefore, as a method for lowering the surface potential, it is preferable to add an electrolyte (increase the electrolyte concentration). The electrolyte is not limited as long as it dissolves in water or water, a mixed solvent of alcohol, etc., but salts of alkali metals and alkaline earth metals, quaternary ammonium ions and the like and halogen elements, LiCl, KCl , NaCl, MgCl ₂ , CaCl ₂ or the like is 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 the electrolyte is added more than 0.25M, the surface potential is too low and the dispersibility is deteriorated, so that fine particles are precipitated due to aggregation or the like.

The surface potential can also be controlled by pH. This is because the degree of dissociation (ionization) of the dissociating group on the particle surface is affected by pH. For example, when there are carboxyl groups (—COOH) or surface hydroxyl groups (—OH) on the surface of the fine particles, ionization occurs as carboxylate anions (—COO ⁻ ) or hydroxide ions (—O ⁻ ) when the pH is raised. Therefore, the charge density σ increases. On the other hand, when there is an amino group (—NH ₂ ), when the pH is lowered, ammonium ions (—NH ₃ ⁺ ) are formed and the charge density is increased. 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 within the range of 3 to 9, the increase of the charge density σ is suppressed for both anions and cations, and as a result, the surface potential and further the zeta potential are controlled to be low. It is possible to prevent fine particles from being densely packed on the surface of the base material and stacking.

(4) Fine particle material The fine particles dispersed in the fine particle dispersed aqueous solution used in the present invention are optically transparent fine particles, and the particle diameter 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. Moreover, it is preferable that the dispersion | variation in a particle diameter is 10 nm or less. This is because the variation in the size of the adsorbed particles may affect the variation in the film thickness, resulting in optical unevenness.

Examples of the inorganic fine particles include magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), lithium fluoride (LiF), sodium fluoride (NaF), silica (SiO ₂ ), and aluminum oxide (Al ₂ O). ₃ ), zirconia oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), niobium oxide (Nb ₂ O ₅ ), indium tin oxide (ITO), zinc oxide (ZnO), tin oxide (SnO ₂ ), ceria (CeO) ₂ ), yttrium oxide (Y ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), and the like. These may be used alone or in admixture of two or more. Among the above inorganic fine particles, silica (SiO ₂ ) is preferable in that the refractive index can be lowered, and water-dispersed colloidal silica (SiO ₂ ) whose particle diameter is controlled to be 10 nm to 100 nm is most preferable. Examples of such commercially available inorganic fine particles include Snowtex and Snowtex UP (manufactured by Nissan Chemical Industries, Ltd.).

  In addition, polymer fine particles satisfying a particle diameter of 10 nm to 100 nm can 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. From liquid phase to solution spray method, solvent removal method, aqueous solution reaction method, emulsion method, suspension polymerization method, dispersion polymerization method, alkoxide hydrolysis method (sol-gel method), hydrothermal reaction method, chemical reduction method, liquid It is synthesized by a manufacturing method such as medium pulse laser ablation. Examples of commercially available polymer fine particles include Mist Pearl (manufactured by Arakawa Chemical Industries).

  Further, for the purpose of providing a bond between the fine particles, an ionic or reactive functional group may be added to the surface of these fine particles. Typical examples include amino groups, carboxyl groups, carbonyl groups, epoxy groups, phenol groups, mercapto groups, methacryl groups, polyether groups, 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 include porous fine particles or particles having a bead-like shape as shown in FIG. Examples of commercially available products include Snowtex PS or Snowtex UP series (manufactured by Nissan Chemical Industries, Ltd.) and Fine Cataloid F120 (manufactured by Catalyst Kasei Kogyo Co., Ltd.), and pearl necklace-like silica sol.

(5) Fine particle dispersion The fine particle dispersion used in the present invention is obtained by dispersing the above-mentioned fine particles in a medium (liquid) which is water or a mixed solvent such as water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include methanol, ethanol, propanol, acetone, dimethylformamide, acetonitrile and the like. The zeta potential indicating the surface potential of the fine particles in the fine particle dispersion is controlled to have an absolute value in the range of 1 to 45 mV, and the zeta potential is controlled by adjusting the pH of the fine particle dispersion as described above. Or by adding an electrolyte to the fine particle dispersion.

  Further, when preparing the fine particle dispersion, a so-called dispersant can be used in order to improve dispersibility. As such a dispersant, a surfactant, an ionic polymer, a nonionic polymer, or the like can be used. The amount of these dispersants to be used varies depending on the type of the dispersant to be used, but generally it is preferably about 0.1% (weight) or less. Among them, the fine particles become electrically neutral, and a laminated film cannot be obtained.

  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. The pH can also be adjusted with a dispersing agent. For example, the pH can also be adjusted by a salt of a strong acid and a weak base or 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, electrostatic attraction with the base material on which the polymer having the opposite charge is adsorbed becomes strong, and the film in which fine particles are densely packed In addition, electrostatic attraction with the substrate does not work, and the repulsive force between the fine particles of the dispersion decreases, causing agglomeration, and the fine particle agglomerates precipitate and the fine particles are laminated on the substrate. There is a tendency not to be.

  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. It is. Examples of water-soluble organic solvents that can be used include methanol, ethanol, propanol, acetone, dimethylformamide, acetonitrile, and the like. This ionic polymer solution is used for forming a fine particle laminated film, forming an underlayer, and the like.

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

(7) Substrate Any substrate other than those that are extremely hydrophobic or water-repellent, such as resins, semiconductors such as silicon, metals, inorganic oxides, or those whose surfaces are coated with such a film It can be applied to any solid substrate. The shape is not limited as long as it can be immersed in water, such as a film, a sheet, a plate, a curved surface, a cylinder, a thread, a fiber, or a foamed material. In order for this low refractive index film to function as an antireflection film, a transparent substrate is desirable. An antireflection function can also be imparted to the polarizing plate used in 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. A thermoplastic resin such as polycarbonate or polyurethane, a glass substrate, or the like is used. Also included are those in which the surface of the substrate is coated with a transparent resin film or inorganic film.

  The fine particle laminated film of the present invention is formed on such a substrate, and the pressure-sensitive adhesive is formed on the substrate surface opposite to the antireflection film (fine particle laminated film) formed on such a transparent substrate. A layer is formed, and it can be attached to a glass substrate or the like on the surface of a display as an adherend so that the antireflection film faces the air. In addition, a low refractive index film is formed on the temporary support, and an adhesive layer or adhesive layer for transfer is further formed on the temporary support so that the adherend and the adhesive layer or adhesive layer face each other. The antireflection film can be formed on the adherend by peeling off the temporary support.

(8) Method for producing fine particle laminated film First, the base materials as described above are used as they are, or the surfaces thereof are subjected to corona discharge treatment, glow discharge treatment, plasma treatment, ultraviolet irradiation, ozone treatment, chemistry with alkali or acid, etc. The surface charge of the base material is made negative or positive by introducing a functional group having a polarity by a chemical etching process, a silane coupling process or the like.

  In addition, as a method for efficiently introducing a charge onto the substrate surface, it is possible to form an alternating laminated film of polycation PDDA or PEI which is a strong electrolyte polymer and polyanion PSS (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 produce 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, and this is continued alternately to form an alternate laminated film. The concentration of the polymer ion solution to be used, pH conditions, and the manufacturing conditions such as the immersion time and the number of repetitions are adjusted in a timely manner in the same manner as in the above (6) depending on the film thickness to be laminated. Moreover, it is preferable to wash away the excess solution by rinsing with only the solvent before immersing in the solution having the opposite charge. The alternating film of polymer ions serving as an underlayer for forming the fine particle laminated film on such a substrate has a film thickness of about 1 to 5 nm, and the number of times of lamination (the combination of cation and anion is one time) ) Is preferably about 2 to 5 times, and this improves the uniformity of the fine particle laminated film 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 solid substrate. Prepare on. If the surface charge of the substrate is opposite to the surface charge of the fine particles, start with immersion in the fine particle dispersion, and if the same as the surface charge of the fine particles, start with immersion in the ionic polymer solution. The immersion in the fine particle dispersion and the ionic polymer solution is repeated until the film thickness is obtained. The final immersion is usually immersed in an ionic polymer solution to ensure the adsorption of the fine particles. The immersion time is appropriately adjusted according to the type of fine particles and ionic polymer used and the film thickness to be laminated.

  After immersing in the fine particle dispersion or ionic polymer solution, wash away excess medium (liquid) or solution by rinsing with the medium (liquid) or solvent only before immersing in the fine particle dispersion or ionic polymer solution having the opposite charge. Is preferred. Examples of such rinsing include water, alcohol, and acetone. Usually, ion-exchanged water (so-called ultrapure water) having a specific resistance of 18 MΩ · cm or more is used from the viewpoint of removing excess ions. Used. Since it is electrostatically adsorbed, it does not peel off in this rinsing step. Further, rinsing may be performed in order to prevent polymer ions or fine particles that are not adsorbed from being brought into the oppositely charged medium (liquid) or solution. If this is not done, cations and anions may be mixed in the medium (liquid) or solution by bringing it in, which may cause aggregation or precipitation of fine particles. Moreover, you may dry before immersing in each solution. As a drying method, a known method such as a method of blowing hot air, dry air, nitrogen or the like using an air knife, an electric heating furnace, or an infrared furnace can be used.

  The film thickness formed by immersing in the fine particle dispersion or the ionic polymer solution is, for example, that a laminated film is formed on a quartz resonator and the change in the frequency is monitored or the obtained laminated film is obtained. Can be determined by observing with an SEM (scanning electron microscope), TEM (transmission electron microscope), AFM (atomic force microscope), or the like.

  FIG. 5 shows a case where a fine particle laminated film is formed on a crystal resonator using a water dispersion (STps-s) of Snowtex PS-S as a fine particle dispersion and polydiallyldimethylammonium chloride (PDDA) as a polymer solution. When formed, it is a graph showing the total immersion time and the amount of change in frequency. The upper curve is the case where NaCl is added as the electrolyte to adjust the sodium chloride concentration to 0.25 mol / liter. This curve shows the result when no electrolyte is added (concentration of electrolyte such as sodium chloride ion is less than 0.01 mol / liter). From this graph, in any case, when immersed in the fine particle dispersion (STps-s), there is a large change in frequency and then saturation, and in the subsequent immersion in the polymer solution (PDDA), there is a large amount. 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 is such that 1000 Hz corresponds to a film thickness of 20 to 25 nm. That is, in FIG. 5, about 30 to 36 nm is obtained when the electrolyte is added by one immersion of the fine particle dispersion and the ionic polymer solution, and about 15 to 18 nm when the electrolyte is not added. It can be seen that the film thickness is obtained, and that the film thickness formed when the electrolyte is added is about twice as large as when the electrolyte is not added. That is, the film thickness obtained by immersing the fine particle dispersion once with the ionic polymer solution differs depending on the size of the fine particles used, the fine particle concentration in the dispersion, etc. in addition to the presence or absence of the electrolyte. Since a film thickness of about 10 to 40 nm is 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. In addition, since the film thickness formed at once will increase when electrolyte is added, it cannot be overemphasized that the number of repetitions can be reduced and the process can be simplified.

  As a manufacturing apparatus, an alternate stacking apparatus called a dipper may be used. A substrate is attached to a robot arm that moves vertically and horizontally, and at a programmed time, the substrate is immersed in a cationic solution, subsequently immersed in a rinse solution, subsequently immersed in an anionic solution, and then immersed in a rinse solution. This process is one cycle, and the number of times of lamination can be continuously and automatically performed. The program may be a combination of two or more kinds of cationic substances and anionic substances. For example, the first two layers can use a combination of polydimethyldiallylammonium chloride and sodium polystyrene sulfonate, and the next 10 layers can use a combination of polydimethyldiallylammonium chloride and anionic silica sol.

  Take out the film wound up in roll form from the unwinding part, arrange the cationic solution water tank, rinse water tank, anionic water tank, rinse water tank in the middle, arrange the number of times you want to stack this arrangement and finally dry the process etc. It is also possible to use a continuous film forming process on a film-like substrate which is arranged and provided with a winding part.

(9) Fine Particle Laminated Film When the fine particle laminated film is produced in this manner, a thin film having a low refractive index of 1.30 or less can be obtained. If it is said method, it is easy to make the thing of 1.22-1.30. The refractive index is preferably 1.22-1.28, more preferably 1.22-1.27, and even more preferably 1.22-1.26 from the viewpoint of imparting an antireflection function on glass or plastic substrates. .

  Moreover, the fine particle laminated film manufactured in this way can be a low refractive index thin film having a volume density of 41 to 58%. The volume density is preferably 41 to 55%, more preferably 41 to 50%, from the viewpoint of imparting an antireflection function on glass or a plastic substrate.

  Since such a fine particle laminated film is laminated with a certain gap without fine particles adhering to the fine particle laminated film, the volume density here is the volume of the void in the fine particle laminated film. The volume occupied by the fine particles themselves relative to the total volume occupied by the fine particles themselves is the volume occupied by the fine particles themselves. For example, in the case where 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 volume density and refractive index in the case of silica. That is, in the fine particle laminated film of the present invention, the amount of fine particles adsorbed and the density of adsorption are controlled by adjusting the zeta potential of the fine dispersed particles with the pH of the fine particle dispersion, and the volume density of the fine particles is within a predetermined range. Thus, a desired refractive index can be obtained. Although the preferred volume density varies depending on the refractive index of the fine particles used, as described above, when silica is used as the fine particles, a volume density range of 41 to 58% is preferred.

  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 the frequency and the laminated film thickness measured by an electron microscope, for example, using a crystal resonator. Can be roughly determined. Further, if the film thickness of the fine particle laminated film is about 1 μm, it can also be obtained by a gas adsorption method for obtaining the porosity and pore distribution of a normal porous material.

  However, in the present invention, the thickness of the fine particle laminated film is 80 to 120 nm as a whole, and considering the reflectance in a single layer, it is preferably about 90 to 110 nm, and can be obtained by laminating ionic polymers. Since the film thickness is about 1 nm or less and is extremely thin compared to the film thickness obtained by laminating fine particles (usually 10 to 40 nm), the measurement of the fine particle laminated film can be performed without considering this ionic polymer. 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) and the refractive index of air was used as the volume density. The case where the fine particles are silica is as shown in FIG. 3, but the same can be obtained when fine particles other than silica are used.

  Moreover, this fine particle laminated film has a void structure in which visible light is not scattered. A void structure that does not scatter visible light is one that is uniform and does not scatter visible light over the surface. Speaking structurally, a void portion having a size exceeding 100 nm or a size exceeding 100 nm causes scattering. In terms of characteristics, for example, the haze value indicating the ratio of transmitted light to scattered light and scattered 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 conforming to either JIS K7105 or JIS K7136 is 2% or less. To do.

  Furthermore, the feature of this fine particle laminated film is that the reflectance has little wavelength dependency, and when a film thickness of 100 nm to 120 nm is formed on a glass substrate, the surface is 4% or less in the entire range of 400 nm to 800 nm, which is called the visible light region. Reflectance is obtained. The method of collecting particles is three-dimensionally stacked with voids so that the particles are almost in point contact. Although the color varies depending on the film thickness, 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 is obtained.

  FIG. 6 shows an antireflection film (displayed as glass with an AR film) using the low refractive index property of the fine particle laminated film prepared on the glass substrate as described above and the glass itself (displayed as glass) as the substrate. Although the antireflection performance is compared, it can be seen that there is a large difference between the two regarding the antireflection function.

(10) Overcoat film Since the fine particle laminate film has voids, it is weak against mechanical strength and may be used in areas that do not directly touch the outside. It is preferable to form and use an overcoat having a thickness that minimizes the influence on the function. The film thickness is desirably 20 nm or less.

Examples of such film materials include resin compositions such as ionizing radiation curable resins, thermosetting resins, thermoplastic resins, and reactive silicone oils. In addition, after dipping in a metal alkoxide solution, drying to obtain a cured film of metal oxide, dipping into a solution of polysilazane and converting to silica, coating a silica film, vapor deposition or sputtering The inorganic oxide film may be formed to a thickness of 20 nm or less using a dry method such as the above. The refractive index of the overcoat film should be as low as possible, and fluorides such as MgF ₂ and silica (SiO ₂ ) are preferable. Further, the strength and refractive index can be adjusted by mixing fine particles of these inorganic materials with the resin composition as a binder.

  Furthermore, a coating may be applied to make it difficult to scratch and to prevent dirt such as water and oil and fat components. The film thickness of the coating needs to be 20 nm or less so as not to affect optically. Typically, there are surface coating agents such as perfluorosilanes fluorine compounds having an alkoxy group. As in the sol-gel reaction, the silane compound is networked by hydrolysis and polycondensation due to dehydration and dealcoholization. When silica is used for the fine particles, silanol groups are present on the surface, and therefore intermolecular bonding occurs even when directly coated. First, the alkoxy group reacts with the silanol group on the surface and is dealcoholized to be immobilized, and then the hydrolysis proceeds due to moisture in the air, resulting in the formation of a three-dimensionally bonded siloxane bond by condensation. And has excellent mechanical durability such as surface friction and wear. Moreover, since the hydrophobic group which has a fluorine as a main component exists on the surface, it shows high water repellency, and is preferable.

  When polymer fine particles or fine particles not having a silanol group are laminated, it is preferable to perform coating after forming a silica film. Representative examples include OPTOOL DSX (manufactured by Daikin), Durasurf DS5000 (manufactured by Harves), Novec EGC-1720 (manufactured by Sumitomo 3M), and the like.

  The overcoat film can be formed by a wet process such as roll coating, spin coating, or dip coating, a dry process such as vapor deposition or sputtering, or a combination thereof.

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

Example 1
As materials, polycation, polydiallyldimethylammonium chloride (PDDA, average molecular weight 100,000, manufactured by Aldrich) and polyanion, sodium polystyrene sulfonate (PSS, average molecular weight 70000, manufactured by Aldrich), silica as fine particle dispersion A fine particle aqueous dispersion (ST20, manufactured by Nissan Chemical Industries, colloidal silica, Snowtex 20, average particle size 20 nm) was used.

  In ST20, the pH is adjusted to 10 in order to maintain dispersibility. Therefore, in this embodiment, after adjusting the weight%, a 1 mol / liter aqueous solution of hydrogen chloride is dropped to adjust the pH to 9.

  First, an alternating layer film of PDDA and PSS is formed as a base layer for efficiently applying a charge to the substrate. As a solution, a 0.3 wt% PDDA aqueous solution and a 0.3 wt% PSS aqueous solution are prepared. Next, a BK-5 glass substrate (manufactured by Matsunami Co., Ltd., 25 mm × 75 mm × 0.7 mm thickness) was immersed in (a) PDDA aqueous solution for 5 minutes, and then rinsed with ultrapure water (specific resistance 18 MΩ · cm) for rinsing. Immersion for 5 minutes, (i) Immersion in an aqueous solution of PSS for 5 minutes, and immersion in ultrapure water for rinsing for 3 minutes. The step of sequentially performing the steps (a) and (b) was taken as one cycle, and this cycle was repeated twice to laminate two layers of alternating layers of PDDA and PSS on the glass substrate. By this step, the charge density on the substrate surface can be made uniform, and there is an effect that fine particles are adsorbed without unevenness.

  Subsequently, a film forming process of the fine particle laminated film will be described. As a solution, a 0.3 wt% PDDA aqueous solution and a 1 wt% ST20 aqueous dispersion with pH = 9 are prepared. The zeta potential of the fine particle aqueous dispersion was measured and found to be -45 mV. By alternately dipping in these solutions, a fine particle laminated film in which PDDA and silica fine particles are alternately laminated is obtained. Since the outermost surface of the above-mentioned underlayer is PSS, the procedure is as follows: First, immerse in an aqueous solution of PDDA, which is a cation of the opposite charge, for 1 minute, and immerse in ultrapure water for rinsing for 3 minutes After immersing in 1 wt% silica fine particle aqueous dispersion ST20 for 1 minute, it is immersed in rinsing ultrapure water for 3 minutes. The cycle of repeating steps (c) and (d) in this order was taken as one cycle, and this cycle was repeated 10 times.

  When the transmission spectrum of this glass substrate was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.), the maximum transmittance was about 99%, and the black tape on the back surface so that the reflection from the back surface could be ignored. When a reflection spectrum was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.) at 5 ° incidence, the reflectance (surface reflectance) was 0.4%. However, silicon was used as the standard mirror, and literature values (DE Aspes and JB Theeten, J. Electrochem. Soc. Vol. 127, p1359 (1980)) were used. 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 base glass substrate used was 91% and the surface reflectance was 4%, an antireflection film having excellent characteristics was formed on the glass substrate. The zeta potential was measured using DELSA 440SX (manufactured by Beckman Coulter, Inc.) at a constant current value of 0.7 to 1.0 mA.

  In the same process, a silicon wafer was used as the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured with an ellipsometer (DVA-36LA, manufactured by Mizoji Optical Co., Ltd., light source 633 nm). As a result, 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 obtained by the ellipsometer were obtained from the amplitude ratio of the P-polarized component and the S-polarized component of the reflected light and the phase difference thereof by simulation using a program attached to the DVA-36LA apparatus.

Example 2
Snowtex PS-S (STps-s, pearl necklace-like silica sol) containing 1% by weight of water dispersion containing a bead-like fine particle manufactured by Nissan Chemical Industries, Ltd. as a material in the same process as in Example 1. A fine particle laminated film was prepared by using a liquid (adjusted to pH = 9 using hydrogen chloride). The number of lamination cycles was 8 times. The zeta potential of the fine particle dispersion was measured and found to be -36 mV. When the transmission 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 0.2%.

  A silicon wafer was used as the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji Optical Co., Ltd., light source 633 nm). As a result, the refractive index was 1.26 to 1.27, and the film thickness was 110 nm. The volume density determined from the refractive index was 49 to 51%.

Example 3
Snowtex PS-S (STps-s, pearl necklace-like silica sol) containing 1% by weight of water dispersion containing a bead-like fine particle manufactured by Nissan Chemical Industries, Ltd. as a material in the same process as in Example 1. A fine particle laminated film was prepared using a liquid (adjusted to pH = 8 using hydrogen chloride). The number of lamination cycles was 8 times. The zeta potential of the fine particle dispersion was measured and found to be -32 mV. When the transmission 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 0.2%.

  A silicon wafer was used as the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji Optical Co., Ltd., light source 633 nm). As a result, the refractive index was 1.26 to 1.27, and the film thickness was 110 nm. The volume density determined from the refractive index was 49 to 51%.

Example 4
Snowtex PS-SO (STps-so, pearl necklace-like silica sol), an acidic silica sol solution containing bead-like fine particles manufactured by Nissan Chemical Industries, Ltd. as a material in the same process as in Example 1. A fine particle laminated film was prepared using a water-dispersed solution (pH = 3.5). The number of lamination cycles was three. The zeta potential of the fine particle dispersion was measured and found to be -23 mV. When the transmission 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 the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji 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 5
What added sodium chloride so that it might become 0.25 mol / l to the STps-s fine particle dispersion liquid (1 weight%) used for Example 2 was adjusted to pH = 9 using 1M hydrogen chloride water. Then, 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 produce a fine particle laminated film. The zeta potential of the fine particle dispersion was measured and found to be -23 mV. When the transmission 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 result of the reflection spectrum of the obtained low refractive index thin film is shown in FIG.

  A silicon wafer was used as the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji 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 obtained by cutting the obtained fine particle laminated film vertically and observing the cross section from an oblique direction of 45 °. An arrow (← →) in the figure indicates a cross-sectional portion of the fine particle laminated film, and a 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, the 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.

Example 6
As materials, polycation, polydiallyldimethylammonium chloride (PDDA, average molecular weight 100,000, manufactured by Aldrich) and polyanion, sodium polystyrene sulfonate (PSS, average molecular weight 70000, manufactured by Aldrich), silica as fine particle dispersion A fine particle aqueous dispersion (ST20, manufactured by Nissan Chemical Industries, colloidal silica, Snowtex 20, average particle size 20 nm) was used.

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

  First, an alternating layer film of PDDA and PSS is formed as a base layer for efficiently applying a charge to the substrate. As a solution, a 0.3 wt% PDDA aqueous solution and a 0.3 wt% PSS aqueous solution are prepared. Next, a BK-5 glass substrate (manufactured by Matsunami Co., Ltd., 25 mm × 75 mm × 0.7 mm thickness) was immersed in (a) PDDA aqueous solution for 5 minutes, and then rinsed with ultrapure water (specific resistance 18 MΩ · cm) for rinsing. Immersion for 5 minutes, (i) Immersion in an aqueous solution of PSS for 5 minutes, and immersion in ultrapure water for rinsing for 3 minutes. The step of sequentially performing the steps (a) and (b) was taken as one cycle, and this cycle was repeated twice to laminate two layers of alternating layers of PDDA and PSS on the glass substrate. By this step, the charge density on the substrate surface can be made uniform, and there is an effect that fine particles are adsorbed without unevenness.

  Subsequently, a film forming process of the fine particle laminated film will be described. As a solution, a ST20 aqueous dispersion having a 0.3 wt% PDDA aqueous solution and 1 wt%, pH = 10, and a sodium chloride concentration of 0.25 mol / liter is prepared. The zeta potential of the fine particle aqueous dispersion was measured and found to be -40 mV. By alternately dipping in these solutions, a fine particle laminated film in which PDDA and silica fine particles are alternately laminated is obtained. Since the outermost surface of the above-mentioned underlayer is PSS, the procedure is as follows: First, immerse in an aqueous solution of PDDA, which is a cation of the opposite charge, for 1 minute, and immerse in ultrapure water for rinsing for 3 minutes After immersing in 1 wt% silica fine particle aqueous dispersion ST20 for 1 minute, it is immersed in rinsing ultrapure water for 3 minutes. The cycle of repeating steps (c) and (d) in this order was taken as one cycle, and this cycle was repeated 5 times. When the transmission 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 0.4%.

  In the same process, a silicon wafer was used as the base material instead of the glass substrate, and the resulting fine particle laminated film was measured for refractive index and film thickness by an ellipsometer (manufactured by Mizoji Optical, light source 633 nm). .29, and the film thickness was 110 nm. The volume density determined from the refractive index was 56%.

Example 7
Snowtex PS-S (STps-s, pearl necklace-like silica sol) containing a bead-like fine particle manufactured by Nissan Chemical Industries, Ltd. as a material in the same process as in Example 6, 1% by weight, pH = 10, a fine particle laminated film was prepared by using an aqueous dispersion containing a sodium chloride concentration of 0.25 mol / liter. The number of lamination cycles was four. The zeta potential of the fine particle dispersion was measured and found to be -23 mV. When the transmission 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 the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji 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 8
Snowtex PS-S (STps-s, pearl necklace-like silica sol) containing a bead-like fine particle manufactured by Nissan Chemical Industries, Ltd. as a material in the same process as in Example 1, 1% by weight, pH A fine particle laminated film was prepared using a silica sol dispersion of = 10. The number of lamination cycles was 10 times. The zeta potential of the fine particle dispersion was measured and found to be -40 mV. When the transmission 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 0.2%.

  A silicon wafer was used as the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji Optical Co., Ltd., light source 633 nm). As a result, the refractive index was 1.28 and the film thickness was 110 nm. The volume density obtained from the refractive index was 54%.

Comparative Example 1
In the same process as in Example 1, the pH of the fine particle dispersion of ST20 was set to 10. When the zeta potential of this dispersion was measured, it was -48 mV. When the transmission 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 result of the reflection spectrum of the obtained low refractive index thin film is shown in FIG.

  A silicon wafer was used as the base material instead of the glass substrate, and the refractive index and film thickness of the obtained fine particle laminated film were measured by an ellipsometer (manufactured by Mizoji 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, by adjusting the absolute value of the zeta potential of the fine particles in the fine particle dispersion to be in the range of 1 to 45 mV, the lamination state of the fine particles can be controlled. It turns out that the low refractive index thin film as a high optical function thin film is obtained.

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

Claims (16)

The solid substrate is (A) a fine particle dispersion in which the absolute value of the zeta potential of the fine particles is controlled within the range of 1 to 45 mV, and (B) a polymer solution having ionicity opposite to the surface charge of the fine particles. A low refractive index thin film in which a fine particle laminate film in which fine particles and a polymer are alternately laminated is formed by alternately dipping, and the fine particle laminate film has a void structure that does not scatter visible light. A low refractive index thin film characterized by comprising:   The low refractive index thin film according to claim 1, wherein the refractive index is 1.22 to 1.30.   The low refractive index thin film according to claim 1, wherein the volume density of the fine particles in the fine particle laminated film is 41 to 58%.   4. The low refractive index thin film according to claim 1, wherein the average primary particle size of the fine particles contained in the fine particle dispersion of (A) is 10 nm or more and 100 nm or less.   5. The low refractive index thin film according to claim 1, wherein the fine particles contained in the fine particle dispersion (A) are colloidal silica, polymer fine particles, porous fine particles, or hollow fine particles.   The low refractive index thin film according to any one of claims 1 to 5, wherein the fine particles contained in the fine particle dispersion (A) have a bead-like shape.   The low refractive index thin film according to any one of claims 1 to 6, wherein the fine particles contained in the fine particle dispersion (A) have an ionic functional group or a thermal or photocurable functional group on the surface of the fine particles.   The low refractive index thin film according to any one of claims 1 to 7, wherein a transparent overcoat film having a thickness of 20 nm or less is laminated on the fine particle laminated film. A method for producing a low refractive index thin film characterized by alternately laminating fine particles and a polymer on a substrate, the production method comprising:
(I) a step of immersing in a fine particle dispersion in which the absolute value of the zeta potential of the fine particles is controlled within a range of 1 to 45 mV;
(II) A method for producing a thin film having a low refractive index, wherein the surface charge of the fine particles and the step of immersing in an ionic polymer solution having an opposite charge are repeated alternately.   The method for producing a low refractive index thin film according to claim 9, wherein the fine particle dispersion of (I) is controlled in the range of pH 3 to 9.   The method for producing a low refractive index thin film according to claim 9, wherein the fine particle dispersion of (I) contains an electrolyte having a concentration of 0.01 to 0.25 mol / liter.   10. The method for producing a low refractive index thin film according to claim 9, wherein the fine particle dispersion (I) has fine particles dispersed in water or a mixed solvent of water and an organic solvent.   The method for producing a low refractive index thin film according to claim 9, wherein the average primary particle size of the fine particles contained in the fine particle dispersion of (I) is 10 nm or more and 100 nm or less.   The method for producing a low refractive index thin film according to claim 9, wherein the fine particles contained in the fine particle dispersion (I) are colloidal silica, polymer fine particles, porous fine particles, or hollow fine particles.   The method for producing a low refractive index thin film according to claim 9, wherein the fine particles contained in the fine particle dispersion of (I) have a bead-like shape.   The method for producing a low refractive index thin film according to claim 9, wherein the fine particles contained in the fine particle dispersion of (I) have an ionic functional group or a heat or photocurable functional group on the surface of the fine particles.