JP2006341475A - Porous film and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a porous film the thickness of which is controlled easily and which is excellent in mechanical characteristics including scratch resistance and used in an antireflection film etc., and the porous film obtained by the method. <P>SOLUTION: The porous film comprises a membrane (A) formed on a substrate. The hardness of the membrane (A) is at least 0.8 GPa and the volume density is 30-60%. The porous film is produced by a method in which a fine particle lamination film is prepared by alternately repeating a process for immersing it in a fine particle dispersion and a process for immersing it in a polymer solution having the ionicity of an opposite charge to the surface charge of the fine particles and a process for heating the fine particle lamination film at 450-600°C is included. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a porous film used for an antireflection film used in a solar cell, a camera, a video camera, a CD player, a VD player, a liquid crystal projection, a television, and the like, and a manufacturing method thereof.

  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.

  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.

As a conventional method for producing a glass with an antireflection film, a method of forming a silicon dioxide film on the glass surface by, for example, a precipitation method is known. If the glass substrate is immersed in an immersion liquid in which an aqueous solution of silicofluoric acid is saturated with SiO ₂ powder and then an aqueous boric acid solution is added, deposition of the SiO ₂ film on the glass surface starts.

  Specifically, the anti-reflective film is characterized by removing the extraneous glass layer on the surface in advance when both surfaces of the glass plate are treated with a silica supersaturated aqueous solution of hydrofluoric acid to form an anti-reflective layer on both surfaces. A manufacturing method of glass with a film is known (Japanese Patent Laid-Open No. 57-166337).

As another glass with an antireflection film, the uppermost layer on the air side of the glass substrate surface has fine irregularities of several tens to several hundreds of nm or pores having a diameter in the range of several tens to several hundreds of nm. And a mixed oxide of SiO ₂ or SiO ₂ and other oxides having a refractive index of 1.40 to 1.60 and a film thickness of 70 to 130 nm, and if necessary, an uppermost layer There is a glass with an antireflection film obtained by coating a silane compound containing a polyfluoroalkyl group on the surface (Japanese Patent Laid-Open No. 5-330856).

  Furthermore, in this glass with an antireflection film, a coating in which two kinds of precursor sols having different average molecular weights as the oxide raw material solution, for example, precursor sols having an average molecular weight of several thousand and several hundred thousand are mixed. There is also a glass with an antireflection film in which pores are specifically expressed on the surface by controlling the mixing ratio of the precursor sol when the solution is coated and thermoformed into a thin film (Japanese Patent Laid-Open No. 5-147976).

  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.

  M.M. 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).

  In addition, a method of forming a porous film by laminating fine particles has been proposed. Y. 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 an alternate lamination method using silica, titania, and ceria fine particle dispersions. (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.

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, conventional porous membranes have a problem that the mechanical strength is further lowered by increasing the porosity (porosity), that is, by reducing the volume density of silica. In other words, the fine particle laminated film formed by the conventional alternating lamination method has a problem that the fine particles are adsorbed mainly by a weak electrostatic attraction such as a hydrogen bond, so that the scratch resistance is inferior.
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 JP-A-57-166337 Japanese Patent Laid-Open No. 05-330856 JP 05-147976 A International Publication WO03 / 082481 Pamphlet Japanese Patent Laid-Open No. 2003-301283 “Characteristics and Optimal Design / Film Fabrication Technology of Antireflection Film”, 2002 Macleod, “Thin-Film Optical Filters”, Elsevier, New York (1969) Kanehara et al., "Applied physics selection book 3 thin film", Hanafusa, (Showa 59). Thin Solid Films, 210/211, p831 (1992) Langmuir 16, p5017-5023 (2000) Nature Materials, Vol1 p59-63 (2002) Langmuir, Vol. 13, (1997) p6195-6203 Sadashi 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 the production of a thin film having a nanometer-size void structure on a substrate can be performed at room temperature and in a wet process, the film thickness can be easily controlled, and An object of the present invention is to provide a method for producing a porous film excellent in mechanical properties such as scratch resistance and used for an antireflection film and the like, and to provide a porous film obtained by the method.

  The inventors of the present invention have made various studies in order to achieve the above object. As a result, in the step of alternately immersing the base material in the fine particle dispersion and the polymer solution having the ionicity opposite to the surface charge of the fine particles, the fine particles By controlling the surface potential of the fine particles in the dispersion to form a fine particle laminate film having a desired volume density, and then heat-treating this fine particle laminate film, it has excellent mechanical properties such as scratch resistance and reflection. The inventors have found that a porous film that can be used for a prevention film or the like is obtained, and have completed the present invention.

  That is, this invention is a porous film which has the thin film (A) formed on the base material, Comprising: The hardness of this thin film (A) is 0.8 GPa or more, and volume density is 30-60. %, And the Young's modulus of the thin film (A) is preferably 16 GPa or more. Thereby, it is possible to provide a functional film having excellent scratch resistance while being porous.

  In the porous film of the present invention, the thin film (A) is an aggregate of fine particles, and the thin film (A) is obtained by heat-treating the fine particle laminated film. The average particle diameter of the fine particles in the thin film (A) is 10 to 100 nm, and particularly when used as an optical functional film such as an antireflection film, the porous film is required to be transparent. The average particle size of the fine particles in the membrane is preferably 100 nm or less.

  Further, the present invention is an invention of a method for producing a porous membrane as described above, and the production method comprises producing a porous membrane characterized in that fine particles and a polymer are alternately laminated on a substrate. A method comprising the steps of immersing in a fine particle dispersion and alternately immersing in a polymer solution having an ionicity opposite to the surface charge of the fine particles to prepare a fine particle laminated film, This is a method for producing a porous film including a step of heating the fine particle laminated film at 450 to 600 ° C. By performing heat treatment at 450 to 600 ° C. for a certain time in this way, water and polymer contained in the fine particle laminated film are removed, and intermolecular force, Coulomb attractive force, and covalent bond can be formed between the fine particles, so that scratch resistance is provided. Good mechanical properties can be obtained.

  Furthermore, in this production method, the average primary particle diameter of the fine particles contained in the fine particle dispersion is preferably 10 to 100 nm, and in particular, fine particles in a range of 100 nm or less in which light is not scattered in order to obtain transparency. It is preferable to use a diameter. Moreover, it is more preferable that the fine particles contained in the fine particle dispersion are fine particles having a bead shape as shown in FIG. If it is beaded, other beaded fine particles and polymers with opposite charges cannot occupy space due to steric hindrance, and as a result, a low refractive index film with higher porosity can be easily formed. Because it can. The fine particles are selected according to the use of the porous film. For example, in the case of an antireflection film, a compound having a small refractive index such as silica, lithium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride is used. .

  The porous membrane of the present invention is excellent in mechanical properties such as scratch resistance. In addition, the method for producing a porous film of the present invention can produce a substrate with a porous film excellent in scratch resistance by simply heat-treating the fine particle laminated film formed by the alternating lamination method. It is possible to control the film thickness at the nanometer level, and it is a manufacturing method with excellent mass productivity. Furthermore, since the volume density and film thickness of the fine particle laminated film can be arbitrarily controlled by changing the lamination conditions and the number of laminations, it is easy to control the optical characteristics such as the reflectance spectrum.

  The inventors of the present invention have developed a fine particle laminate which is an alternating laminated film of fine particles and polymer electrolyte formed by electrostatic attraction on a substrate by alternately dipping in a polymer electrolyte solution having an opposite charge to the fine particle dispersion. The film was heat-treated at a predetermined temperature after the fine particle laminated film was formed, thereby leading to an invention to improve mechanical characteristics such as scratch resistance while maintaining optical characteristics. Further, the thin film (A) obtained by heat-treating the fine particle laminated film of the present invention has a volume density of 30 to 60% occupied by the fine particles in the thin film, and the thin film (A) having such a volume density and thus In order to form the fine particle laminated film, it is necessary to control the dispersion state of the fine particles in the fine particle dispersion used in the step of laminating the fine particles and the polymer. Hereafter, the manufacturing method of this invention and the material to be used are demonstrated sequentially.

(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 substrate, 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 reduce the surface potential and zeta potential of the fine particles, the Debye-Huckel parameter 1 / κ is decreased (κ is increased), that is, the electric double layer is thinned, 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 dispersion used in the present invention are selected depending on the use of the porous film. Generally, the fine particles are optically transparent fine particles having a fine particle size. It 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.

As the fine particles, inorganic fine particles can be used. For example, magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), lithium fluoride (LiF), sodium fluoride (NaF), silica (SiO ₂ ), 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 can be used, and these can be used alone or in admixture of two or more.

When the porous film is intended to be a porous film having a low refractive index such as a low reflection film, the bulk refractive index is relatively low at 1.48 in that the refractive index can be lowered among the above-mentioned inorganic fine particles. Silica (SiO ₂ ) is preferable, and water-dispersed colloidal silica (SiO ₂ ) having a particle diameter 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 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 Chemical Industries, Ltd.), and pearl necklace-like silica sol.

  Furthermore, the inorganic fine particles as described above are preferable in that the hydroxyl groups present on the particle surface are bonded by dehydration condensation, and the scratch resistance can be further improved.

(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 absolute value of the zeta potential indicating the surface potential of the fine particles in the fine particle dispersion is preferably controlled 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.

  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. 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 As the substrate, all other than glass, silicon and other semiconductors, metals, inorganic oxides, etc., which are extremely hydrophobic, water-repellent or those whose surface is 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 sheet, a plate, a curved surface, a cylinder, a thread, a fiber, and 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 be imparted to the polarizing plate used in the LCD display, and it can also be used as an antireflection film for a cover glass of a silicon solar cell. The base material in which the lens shape is formed in order to acquire a condensing property is also included.

  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.

(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 (6) above 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 with 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.

(9) Heat treatment Next, the fine particle multilayer film prepared as described above is subjected to a heat treatment at a temperature of 450 to 600 ° C, preferably 500 to 600 ° C, more preferably 550 to 600 ° C. The heating time is about 10 minutes to 2 hours, preferably 30 minutes to 1 hour. Of course, the relationship between the heating temperature and the heating time is relative, and when the processing temperature is lowered, it goes without saying that the object can be achieved by continuing the processing for a longer time. The atmosphere for the heat treatment is not limited, and may be an oxidizing atmosphere such as air, an inert atmosphere such as nitrogen, or a reducing atmosphere including hydrogen. There is no restriction | limiting also in the heating method, It can carry out using heating means thru | or a heating apparatus like an oven, an induction heating apparatus, and an infrared heater. The heat treatment of the fine particle laminate film removes water and polymer contained in the fine particle laminate film, and intermolecular force, Coulomb attractive force, and covalent bond occur between the fine particles, improving mechanical properties such as scratch resistance. It is done. By this step, the fine particle laminated film is converted into the thin film (A) in the present application. When the heating temperature is less than 450 ° C., condensation between the fine particles does not occur, so that sufficient film hardness cannot be obtained, and when the heating temperature is 600 ° C. or higher, the fine particles are melted and fused, so that the porous structure tends to disappear. In FIG. 6, the conceptual diagram which showed the mode of the coupling | bonding between the silica fine particles by heat processing temperature was shown.

(10) Porous film When the fine particle laminated film is prepared in this way and the resulting fine particle laminated film is heat-treated to produce a porous film, that is, the fine particles are contained in the thin film (A) prepared from the fine particle laminated film. A porous film having a volume density of about 30 to 60% is obtained. Moreover, the porous film whose thin film (A) has a hardness of 0.8 GPa or more is obtained. Further, a porous film having a Young's modulus of the thin film (A) of 16 GPa or more is obtained.

  Since a porous film is used as an antireflection film, when silica is used as the fine particles, a low refractive index thin film having a volume density of 30 to 60%, preferably 41 to 58% can be obtained. 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 from 1.22 to 1.28, more preferably from 1.22 to 1.27, further preferably from 1.22 to 1.26, from the viewpoint of imparting an antireflection function on a substrate such as glass. From 1.22 to 1.25 is most preferable, and the volume density is more preferably 41 to 55% and further preferably 41 to 50% from the same viewpoint.

  Since the thin film (A) obtained from such a fine particle laminated film is laminated with a certain gap without the fine particles adhering in the thin film (A), the volume density here is the thin film. (A) The volume occupied by the fine particles themselves relative to the total volume of the voids and the volume occupied by the fine particles themselves is the volume occupied by the fine particles themselves. For example, when the fine particles are porous or hollow, The voids in the fine particles are included in the volume of the voids in the thin film (A). FIG. 3 is a graph showing the relationship between volume density and refractive index in the case of silica. That is, in the thin film (A) 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 by adjusting the pH of the fine particle dispersion, etc. A desired refractive index can be obtained by setting the volume density within a predetermined range. The preferred volume density varies depending on the refractive index of the fine particles to be used. However, in the case of using silica as the fine particles for the purpose of an antireflection film having a low refractive index, the volume density ranges from 41 to 58%. Is preferable as described above.

  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 thickness of the thin film (A) is about 1 μm, it can 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 thin film (A) is about 10 to 200 nm as a whole, and particularly when used as an antireflection film, the film thickness is 80 to 120 nm, and the reflectance in a single layer. In consideration of the above, the film thickness is preferably about 90 to 110 nm, and the film thickness obtained by laminating the ionic polymer is about 1 nm or less, and the film thickness obtained by laminating fine particles (usually 10 to 40 nm) Therefore, without considering this ionic polymer, the measured refractive index of the fine particle laminated film, the refractive index of the substance constituting the fine particle itself (ie, bulk), and the refractive index of air The value ρ calculated by Drude's theoretical formula (Equation 2) 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.

  The thin film (A) needs to have a void structure that does not scatter visible light, particularly when used as an antireflection film having a low refractive index. 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, the haze value of the substrate with a thin film (A) formed on a transparent substrate having a haze value of 1% or less according to either JIS K7105 or JIS K7136 may be 2% or less. preferable.

  Further, the thin film (A) having such a low refractive index has a feature that the reflectance is less dependent on the wavelength, and when a film thickness of 100 nm to 120 nm is formed on a glass substrate, the visible light region is 400 nm to 800 nm. A surface reflectance of 4% or less is obtained over the entire range. The method of collecting particles in the fine particle laminated film 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.

(11) Measurement of hardness of porous membrane To measure the hardness of a thin film such as the thin film (A) that is a porous film, a nanoindenter is used. A triangular pyramid (Berkovic) indenter made of diamond chips is pushed into the thin film to a desired depth below the film thickness, and then the indenter is pulled up. The load on the indenter at that time is measured. FIG. 7 shows the state of contact between the Barkovic indenter and the sample. FIG. 8 shows an example of hot-fused quartz having a typical load-displacement curve of an elastic / plastic deformable material. By analyzing the load-displacement curve as described below, the hardness and Young's modulus of the thin film can be obtained.

Nip depth h _c is the indentation elastic peripheral surface of the contact point as shown in FIG. 7, it is that the shallower than the overall indentation depth h _t usual. That means

Here, P is the maximum weight, ε is a constant related to the shape of the indenter, 0.75 for Barcovic, and S is the contact rigidity between the indenter and the sample (the slope of the unloading curve in FIG. 8).

Next, the contact projection area A between the indenter and the sample is given by the following equation in consideration of the indentation depth h _c and the shape of the indenter.

Here, f (h _c ) is a correction term obtained from the curvature of the indenter.

From the contact projection area A and the maximum load P obtained from the above equation, the hardness H is calculated by the following equation.

Next, the Young's modulus can be obtained as follows. First, the stiffness modulus _Er of the indenter and the sample is determined by the following equation from the contact stiffness S determined from the load-displacement curve of FIG.

Then, samples of the modulus (Young's modulus) E _s is calculated by the following equation.

Here, E _i is the modulus of the indenter, ν _i is the Poisson ratio of the indenter, and ν _s is the Poisson ratio of the sample.

(12) Overcoat film The porous film may be used in a portion that does not directly touch the outside. For example, when it is used on the surface of a display or the like, the antifouling is used to prevent dirt such as water and oil components. In order to give the property and other functionality, an overcoat layer can be formed and used. The thickness of the overcoat layer needs to be 20 nm or less so as not to affect optically. A typical example is a method in which a fluoropolymer is applied as a solution and heat-treated at a temperature of 40 ° C. or higher for coating. As the fluorine-based polymer, for example, Teflon SF (manufactured by DuPont) can be used, and as the solvent, a fluorine-based solvent such as Fluorinert CF-75 (manufactured by 3M) can be used, and the concentration of the solution is 0. .1 to 5% by weight is preferred. Other overcoat agents include surface coating agents such as perfluorosilanes fluorine compounds having alkoxy groups. 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. Representative examples of such a coating agent 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 porous film of the present invention will be described in more detail with reference to examples of the porous film used for the antireflection film which is a low refractive index thin film using silica.

Example 1
As a material, polydiallyldimethylammonium chloride (PDDA, average molecular weight 100,000, manufactured by Aldrich) as a polycation and sodium polystyrene sulfonate (PSS, average molecular weight 70000, manufactured by Aldrich) as a polyanion, silica as a fine particle dispersion A fine particle aqueous dispersion (ST-PS-S, manufactured by Nissan Chemical Industries, colloidal silica, Snowtex PS-S, pearl necklace-like silica sol) was used.

  ST-PS-S has a pH adjusted to 10 in order to maintain dispersibility. Therefore, in this embodiment, after adjusting the weight concentration, 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. One side of the substrate is covered with a masking tape, and an alternate laminated film composed of a base layer and a fine particle laminated film is formed only on the other side of 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% ST-PS-S aqueous solution having pH = 9 are prepared. The zeta potential of the fine particle aqueous dispersion was measured and found to be -36 mV. The zeta potential was measured using DELSA 440SX (manufactured by Beckman Coulter) at a constant current value of 0.7 to 1.0 mA. 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 ST-PS-S 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 8 times.

  Next, the fine particle laminated film obtained using the muffle furnace (FP31 manufactured by Yamato Scientific Co., Ltd.) is subjected to heat treatment at 600 ° C. First, a slide stand (150 mm x 82 mm x 22 mm) made of stainless steel with a thickness of 0.5 mm is placed on the floor in the muffle furnace, and a stainless steel plate (150 mm x 200 mm) with a thickness of 3 mm is placed on the flute floor. It was placed parallel to the surface. This stainless steel plate with a thickness of 3 mm is not placed directly on the floor surface in the muffle furnace, but a slide stand for setting up the slide glass is sandwiched between them so that the heat conduction between the stainless steel plate and the floor surface in the muffle furnace is achieved. This is to prevent it. One hour after the muffle furnace temperature reached 600 ° C., the glass substrate on which the fine particle laminated film was formed was placed on the stainless steel plate so that the fine particle laminated film surface and the stainless steel plate were in contact with each other. One hour later, the glass substrate was taken out of the muffle furnace and quickly cooled with air.

  When the transmission spectrum of this glass substrate was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.), the maximum transmittance in the wavelength range of 400 to 800 nm was about 95%, and reflection from the back surface was also observed. Black tape was pasted on the back so that it could be ignored, and the reflection spectrum was measured with a visible ultraviolet spectrophotometer (manufactured by Hitachi, Ltd.) at 5 ° incidence. The reflectance (surface reflectance) was 0.2%. there were. However, silicon was used as the standard mirror, and literature values (DE Aspens 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 glass substrate of the base material used was 91% in the wavelength range of 400 to 800 nm and the surface reflectance was 4%, an antireflection film having excellent characteristics was formed on the glass substrate. It will be.

  In addition, a smooth glass substrate (25 mm × 75 mm × 0.7 mm thickness) was fixed to the bottom of the 500 g weight with an adhesive, and a surface opposite to the weight of the glass substrate and a thin film (A) were formed. The glass was bonded to the surface opposite to the thin film (A). Next, the glass with the thin film (A) fixed to the weight is placed on the steel wool (# 0000, manufactured by Nippon Steel Wool Co., Ltd.) fixed on the smooth surface so that the thin film (A) faces the steel wool. The glass with the thin film (A) fixed on the weight was reciprocated 20 times at a distance of 1 cm. By this operation, the thin film (A) was polished with steel wool with a load of 500 g. The surface of the steel wool-polished thin film (A) was observed and photographed at a magnification of 20 times with a metal microscope or the like, and the ratio of the area of the film that remained without being peeled and damaged (100 × residual) The area of the film divided by the area taken was determined as the “remaining film ratio”. The thin film (A) does not peel off even when polished with steel wool and does not have scratches. Therefore, the residual film ratio was 100%, and excellent scratch resistance was exhibited.

  Next, the hardness and Young's modulus of the film were measured as described above using a nanoindenter (manufactured by Toyo Technica). The number of measurement points was 10, the indentation speed was 5 nm / second, and the indentation limit depth was 100 nm. The hardness obtained was 0.88 GPa and the Young's modulus was 16 GPa.

  Furthermore, in the same process, a silicon wafer is used as a base material instead of a glass substrate, and the refractive index and film thickness of the obtained thin film (A) are measured with an ellipsometer (DVA-36LA, manufactured by Mizoji Optical Co., Ltd., light source 633 nm). did. 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%. 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.

Experimental example 1
In the same manner as in Example 1, a fine particle laminated film was prepared, and the fine particle laminated film was not heat-treated, and the fine particle laminated film was heated at 250, 400, 450, 500, and 550 ° C. for 1 hour. The thin film (A) thus obtained was subjected to “remaining film ratio” in the same manner as in Example 1. The results are shown in FIG.

  In the case where the heat treatment was not performed and the case where the heat treatment was performed at 250 ° C., the remaining film ratio was 20% or less. Further, when these were measured with a nanoindenter under the same conditions as in Example 1, the hardness was 0.17 GPa and the Young's modulus was 5 GPa.

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 is a conceptual diagram showing a state of bonding between silica fine particles according to the heat treatment temperature. FIG. 7 is a conceptual diagram showing a state of contact between the Berkovich indenter and the sample. FIG. 8 is a graph showing a typical load-displacement curve of an elastic / plastic deformable material, taking hot fused quartz as an example. FIG. 9 is a graph showing the relationship between the heat treatment temperature (1 hour) of the fine particle laminated film and the remaining film rate.

Claims (7)

  A porous film having a thin film (A) formed on a substrate, wherein the thin film (A) has a hardness of 0.8 GPa or more and a volume density of 30 to 60% .   The porous film according to claim 1, wherein the thin film (A) has a Young's modulus of 16 GPa or more.   The porous film according to claim 1, wherein the thin film (A) comprises an aggregate of fine particles.   The porous film according to claim 3, wherein the average particle diameter of the fine particles in the thin film (A) is 10 to 100 nm.   A method for producing a porous membrane characterized by alternately laminating fine particles and a polymer on a substrate, the production method being opposite to the step of immersing in a fine particle dispersion and the surface charge of the fine particles The process of preparing the fine particle laminated film by alternately repeating the step of immersing in the polymer solution having charge ionicity, and then heating the fine particle laminated film at 450 to 600 ° C. The manufacturing method of the porous membrane in any one.   The method for producing a porous film according to claim 5, wherein the average primary particle diameter of the fine particles in the fine particle dispersion is 10 to 100 nm. 6. The method for producing a porous film according to claim 5, wherein the fine particles in the fine particle dispersion are fine particles arranged in a bead shape.