Patent Application
20100027123
The present invention relates to an anti-reflection coating for a visible light range suitable for exchange lens units and imaging devices, an optical member having such an anti-reflection coating, and an exchange lens unit and an imaging device comprising such an optical member.
A high-performance, single-focus or zoom lens unit widely used in single-lens reflex cameras, video cameras, etc. generally has about 10-40 lenses in a lens barrel. In a wide-angle lens unit for producing wide images, light has a large incident angle in its peripheral region. These lenses are provided with multilayer anti-reflection coatings comprising dielectric layers having various refractive indices different from that of a substrate, the dielectric layers being as thick as 1/2λ or 1/4λ, wherein λ is a center wavelength, to utilize an interference effect.
In addition, lenses may be tarnished or scratched in their production processes. Tarnish includes blue tarnish and white tarnish. The blue tarnish is a thin film formed by basic components in optical glass dissolved into dew attached to a surface of the optical glass left in the air, or water during a grinding step. The white tarnish is white blot generated by the chemical reaction of components eluted from glass.
Japanese Patent 3509804 discloses an optical member comprising a thin, multilayer optical coating formed on an optical substrate, at least one layer in the coating being an alkaline earth metal fluoride layer formed by a wet process. However, the alkaline earth metal fluoride layer has as high a refractive index as about 1.39.
JP 2005-352303 A and JP 2006-3562 A disclose an anti-reflection coating comprising pluralities of layers each having a physical thickness of 15-200 nm, which are formed on a substrate such that their refractive indices decrease gradually from the substrate side, the refractive index difference between adjacent layers and between the innermost layer and the substrate being 0.02-0.2, and the outermost layer being a silica aerogel layer. However, the silica aerogel layer has low scratch resistance and durability.
JP 2006-130889 A discloses a thin, mesoporous silica coating having nano-sized pores, a refractive index of 1.05-1.3, and as high transmittance as 90% or more in a wavelength range from visible light to near infrared light. This thin, mesoporous silica coating is formed by coating a solution comprising a surfactant, a silica-forming material such as tetraethoxysilane, water, an organic solvent, and acid or alkali onto a substrate to form an organic-inorganic composite coating, drying this coating, and photo-oxidizing it to remove organic components.
Japanese Patent 3668126 discloses a method for forming a porous silica coating having a low refractive index, by preparing a solution comprising a ceramic precursor such as tetraethoxysilane, a catalyst, a surfactant and a solvent, coating the solution onto a substrate, and removing the solvent and the surfactant.
However, because the thin, mesoporous silica coating of JP 2006-130889 A and the porous silica coating of Japanese Patent 3668126 are formed by hydrolysis and polycondensation for forming a thin silicate network around surfactant micelle, the hydrolysis and polycondensation takes a long period of time, and the resultant coating is not uniform.
JP 5-85778 A discloses an optical member comprising an anti-reflection coating having pluralities of dielectric layers formed on an optical substrate having high transmittance, the innermost layer being made of SiOx (1≦x≦2) and having a thickness nd of 0.25λ0 or more, wherein λ0 is a designed wavelength. Although this structure makes tarnish and scratches on the optical substrate surface less discernable, it fails to prevent tarnish.
Accordingly, an object of the present invention is to provide a uniform anti-reflection coating formed on a glass substrate having a low or medium refractive index, which has excellent transmittance as well as excellent scratch resistance and tarnish-preventing effect, without suffering flare and ghost, and an optical member having such an anti-reflection coating, and an exchange lens unit and an imaging device comprising such an optical member.
As a result of intensive research in view of the above object, the inventors have found that an anti-reflection coating having the following layer structure formed on a glass substrate having a low or medium refractive index has excellent anti-reflection performance, scratch resistance, durability and uniformity, as well as good effects of preventing flare, ghost and tarnish. The present invention has been completed based on such finding.
The anti-reflection coating of the present invention comprises first to seventh layers formed on a substrate in this order, the substrate having a refractive index of 1.45-1.72, the first layer being an alumina-based, dense layer having an optical thickness of 25.0-250.0 nm, the second layer being a dense layer having a refractive index of 1.95-2.23 and an optical thickness of 27.5-52.5 nm, the third layer being a dense layer having a refractive index of 1.33-1.50 and an optical thickness of 37.5-54.0 nm, the fourth layer being a dense layer having a refractive index of 2.04-2.24 and an optical thickness of 45.0-62.5 nm, the fifth layer being a dense layer having a refractive index of 1.33-1.50 and an optical thickness of 77.5-102.5 nm, the sixth layer being a dense layer having a refractive index of 1.85-2.40 and an optical thickness of 16.0-26.5 nm, the seventh layer is a porous layer of nanometer-sized, mesoporous silica particles having a refractive index of 1.09-1.19 and an optical thickness of 112.5-162.5 nm, in a wavelength range of 400-700 nm.
The nanometer-sized, mesoporous silica particles preferably have an average diameter of 200 nm or less.
The nanometer-sized, mesoporous silica particles preferably have a hexagonal structure.
The pore diameter distribution of the seventh layer preferably has two peaks. One peak is in a range of 2-10 nm attributed to pores in particles, and another peak is in a range of 5-200 nm attributed to pores among particles. The volume ratio of the pores in particles to the pores among particles is preferably 1/15 to 1/1.
The seventh layer preferably has porosity of 55-80%.
The first layer preferably has a refractive index of 1.58-1.71.
The second, fourth and sixth layers are preferably made of at least one selected from the group consisting of Ta2O5, TiO2, Nb2O5, ZrO2, HfO2, CeO2, SnO2, In2O3, ZnO, Y2O3 and Pr6O11, and the third and fifth layers are preferably made of at least one selected from the group consisting of MgF2, SiO2 and Al2O3.
The anti-reflection coating preferably has reflectance of 0.3% or less to light in a wavelength range of 450-600 nm at an incident angle of 0°.
The anti-reflection coating preferably further comprises a fluororesin layer of 0.4-100 nm in thickness having water repellency or water/oil repellency on the seventh layer.
The first to sixth layers are preferably formed by a vacuum vapor deposition method. The seventh layer is preferably formed by a sol-gel method.
The seventh layer is preferably formed by (i) aging a mixture solution comprising a solvent, an acid catalyst, alkoxysilane, a cationic surfactant and a nonionic surfactant, thereby causing the hydrolysis and polycondensation of the alkoxysilane; (ii) adding a base catalyst to the resultant silicate-containing acidic sol, to prepare a sol containing nanometer-sized, mesoporous silica particles containing the cationic surfactant in pores and covered with the nonionic surfactant; (iii) applying the sol to the sixth layer; (iv) drying the resultant coating to remove the solvent; and (v) baking the coating to remove the cationic surfactant and the nonionic surfactant.
The optical member of the present invention comprises the above anti-reflection coating.
The exchange lens unit of the present invention comprises the above optical member.
The imaging device of the present invention comprises the above optical member.
[1] Substrate
The anti-reflection coating 1 of the present invention formed on a substrate 3 is shown in
The refractive index of the substrate 3 in a wavelength range of 400-700 nm is 1.45-1.72, preferably 1.51-1.60. The substrate 3 with a refractive index in this range has improved optical performance in a visible wavelength range, enabling the size reduction of exchange lens units.
[2] Anti-Reflection Coating
(1) Structure of Anti-Reflection Coating
The anti-reflection coating 1 formed on a substrate 3 comprises first to seventh layers each made of a predetermined material and having a predetermined refractive index and optical thickness [refractive index (n)×physical thickness (d)]. Namely, the anti-reflection coating 1 of the present invention comprises a first layer 11 which is an alumina-based, dense layer having an optical thickness of 25.0-250.0 nm, a second layer 12 which is a dense layer having a refractive index of 1.95-2.23 and an optical thickness of 27.5-52.5 nm, a third layer 13 which is a dense layer having a refractive index of 1.33-1.50 and an optical thickness of 37.5-54.0 nm, a fourth layer 14 which is a dense layer having a refractive index of 2.04-2.24 and an optical thickness of 45.0-62.5 nm, a fifth layer 15 which is a dense layer having a refractive index of 1.33-1.50 and an optical thickness of 77.5-102.5 nm, a sixth layer 16 which is a dense layer having a refractive index of 1.85-2.40 and an optical thickness of 16.0-26.5 nm, and a seventh layer 17 which is a porous layer of nanometer-sized, mesoporous silica particles having a refractive index of 1.09-1.19 and an optical thickness of 112.5-162.5 nm, in a wavelength range of 400-700 nm.
The reflectance of the anti-reflection coating 1 to light in a wavelength range of 450-600 nm at an incident of 0° is preferably 0.3% or less, more preferably 0.25% or less.
(2) First Layer
The first layer 11 in the anti-reflection coating 1 is an alumina-based dense layer. The first layer 11 is preferably formed only by alumina (aluminum oxide). Alumina preferably has purity of 99% or more.
The refractive index of the alumina-based, first layer (alumina layer) 11 is preferably 1.58-1.71, more preferably 1.60-1.70. The first layer 11 preferably has an optical thickness of 120.0-210.0 nm. Alumina has high adhesion, high transmittance in a wide wavelength range, high hardness, excellent wear resistance, and good cost performance. Because alumina has excellent steam-shielding properties, the alumina-based dense layer formed as the first layer can prevent tarnish on the substrate surface.
(3) Second to Sixth Layers
The second layer 12, the fourth layer 14 and the sixth layer 16 are preferably dense layers made of at least one selected from the group consisting of Ta2O5, TiO2, Nb2O5, ZrO2, HfO2, CeO2, SnO2, In2O3, ZnO, Y2O3 and Pr6O11, and the third layer 13 and the fifth layer 15 are preferably dense layers made of at least one selected from the group consisting of MgF2, SiO2 and Al2O3. The second layer 12 preferably has a refractive index of 2.00-2.15 and an optical thickness of 30.0-51.0 nm, the third layer 13 preferably has a refractive index of 1.35-1.48 and an optical thickness of 42.0-53.0 nm, the fourth layer 14 preferably has a refractive index of 2.05-2.15 and an optical thickness of 40.0-60.5 nm, the fifth layer 15 preferably has a refractive index of 1.35-1.47 and an optical thickness of 85.0-95.0 nm, the sixth layer 16 preferably has a refractive index of 1.95-2.30 and an optical thickness of 20.0-25.5 nm.
(4) Seventh Layer
The seventh layer 17 is formed by nanometer-sized, mesoporous silica particles, having a low refractive index and an excellent anti-reflection function. The seventh layer (mesoporous silica layer) 17 preferably has a refractive index of 1.09-1.19 and an optical thickness of 130-155 nm. In the seventh layer 17, pores among particles are preferably 5-100 nm in diameter, and the porosity is preferably 55-80%, more preferably 56.5-79.0%. Unlike conventional silica aerogel, the nanometer-sized, mesoporous silica particles have a hexagonal structure with meso-pores arranged regularly and uniformly. Accordingly, they have high strength and porosity, low refractive index, and excellent scratch resistance. The nanometer-sized, mesoporous silica particles constituting the seventh layer 17 are not restricted to a hexagonal structure, but may have a cubic or ramera structure.
As shown in
A first peak on the smaller pore diameter side is attributed to the diameters of pores in particles, and a second peak on the larger pore diameter side is attributed to the diameters of pores among particles. The mesoporous silica layer 17 preferably has a pore diameter distribution having the first peak in a range of 2-10 nm and the second peak in a range of 5-200 nm.
A ratio of the total volume V1 of pores in particles to the total volume V2 of pores among particles is preferably 1/15 to 1/1. The mesoporous silica layer 17 having this ratio V1/V2 within the above range has as small refractive index as 1.19 or less. The ratio V1/V2 is more preferably 1/10 or more and less than 1/1.5. The total volumes V1 and V2 are determined by the following method. In
The mesoporous silica layer 17 is preferably formed by a wet method such as a sol-gel method, etc. The mesoporous silica layer 17 may be hydrophobidized to have excellent moisture resistance and durability.
(5) Fluororesin Layer
The anti-reflection coating of the present invention may have a fluororesin layer having water repellency or water/oil repellency on the outermost layer. The anti-reflection coating 2 shown in
The fluororesins are not particularly restricted as long as they are colorless and highly transparent. They are preferably fluorine-containing organic compounds, or organic-inorganic hybrid polymers.
The fluorine-containing organic compounds include fluororesins and fluorinated pitch (for instance, CFn, wherein n is 1.1-1.6). Specific examples of the fluororesins include fluorine-containing olefinic polymers or copolymers, such as polytetrafluoroethylene (PTFE), tetraethylene-hexafluoropropylene copolymers (PFEP), ethylene-tetrafluoroethylene copolymers (PETFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), ethylene-chlorotrifluoroethylene copolymers (PECTFE), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymers (PEPE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), etc. Commercially available fluororesins include, for instance, “OPSTAR” available from JSR Corporation, and “CYTOP” available from Asahi Glass Co., Ltd.
The fluorine-containing organic-inorganic hybrid polymers may be organic silicon polymers having fluorocarbon groups, which may be polymers obtained by the hydrolysis of silane compounds having fluorocarbon groups. The silane compounds having fluorocarbon groups may be compounds represented by the following formula (I):
CF3(CF2)a(CH2)2SiRbXc (1),
wherein R is an alkyl group, X is an alkoxyl group or a halogen atom, a is an integer of 0-7, b is an integer of 0-2, c is an integer of 1-3, and b+c=3. Specific examples of the compounds represented by the formula (I) include CF3(CH2)2Si(OCH3)3, CF3(CH2)2SiCl3, CF3(CF2)5(CH2)2Si(OCH3)3, CF3(CF2)5(CH2)2SiCl3, CF3(CF2)7(CH2)2Si(OCH3)3, CF3(CF2)7(CH2)2SiCl3, CF3(CF2)7(CH2)2SiCH3(OCH3)2, CF3(CF2)7(CH2)2SiCH3Cl2, etc. Examples of commercially available organic silicon polymers include Novec EGC-1720 available from Sumitomo 3M Ltd., XC98-B2472 available from GE Toshiba Silicone Co., Ltd., X71-130 available from Shin-Etsu Chemical Co., Ltd., etc.
The fluororesin layer 28 is as thick as preferably 0.4-100 nm, more preferably 10-80 nm. When the thickness of the fluororesin layer 28 is less than 0.4 nm, sufficient water/oil repellency cannot be obtained. On the other hand, with the fluororesin layer thicker than 100 nm, the anti-reflection coating has deteriorated transparency and degraded optical properties. The refractive index of the fluororesin layer 28 is preferably 1.5 or less, more preferably 1.45 or less. Although the fluororesin layer 28 may be formed by a vacuum vapor deposition method, it is preferably formed by a wet method such as a sol-gel method.
[3] Formation Method of Anti-Reflection Coating
(1) Formation Method of First to Sixth Layers
The first to sixth layers 11-16 are preferably formed by a physical vapor deposition method, such as a vacuum vapor deposition method and a sputtering method. From the aspect of production cost and precision, the vacuum vapor deposition method is particularly preferable. The vacuum vapor deposition method may be a resistor-heating type or an electron beam type.
The electron-beam-type vacuum vapor deposition method will be explained below. A vacuum vapor deposition apparatus 30 shown in
In the vacuum vapor deposition method, the initial degree of vacuum is preferably 1.0×10−5 Torr to 1.0×10−6 Torr. When the degree of vacuum is less than 1.0×10−5 Torr, insufficient vapor deposition occurs. When the degree of vacuum is more than 1.0×10−6 Torr, it takes too much time for vapor deposition. To increase the precision of the formed layers, it is preferable to heat the substrates 3 during vapor deposition. The substrate temperature during vapor deposition may be properly determined based on the heat resistance of the substrates 3 and the vapor deposition speed, but it is preferably 60-250° C.
(2) Formation Method of Seventh Layer
The seventh layer (mesoporous silica layer) 17 is formed by (i) aging a mixture solution comprising a solvent, an acid catalyst, alkoxysilane, a cationic surfactant and a nonionic surfactant, thereby causing the hydrolysis and polycondensation of the alkoxysilane; (ii) adding a base catalyst to the resultant silicate-containing acidic sol, to prepare a sol containing nanometer-sized, mesoporous silica particles containing the cationic surfactant in pores and covered with the nonionic surfactant (surfactants-containing, nano-sized, mesoporous silica composite particles); (iii) applying this sol to the sixth layer 16; (iv) drying the resultant coating to remove the solvent; and (v) baking the coating to remove the cationic surfactant and the nonionic surfactant.
(a) Starting Materials
(a-1) Alkoxysilane
The alkoxysilane may be a monomer or an oligomer. The alkoxysilane monomer preferably has 3 or more alkoxy groups. The use of the alkoxysilane having 3 or more alkoxy groups as a starting material provides a mesoporous silica coating with excellent uniformity. Specific examples of the alkoxysilane monomers include methyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, etc. The alkoxysilane oligomers are preferably polycondensates of these monomers. The alkoxysilane oligomers can be obtained by the hydrolysis and polycondensation of the alkoxysilane monomers. Specific examples of the alkoxysilane oligomers include silsesquioxane represented by the general formula: RSiO1.5, wherein R represents an organic functional group.
(a-2) Surfactants
(i) Cationic Surfactants
Specific examples of the cationic surfactants include alkyl trimethyl ammonium halides, alkyl triethyl ammonium halides, dialkyl dimethyl ammonium halides, alkyl methyl ammonium halides, alkoxy trimethyl ammonium halides, etc. The alkyl trimethyl ammonium halides include lauryl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, stearyl trimethyl ammonium chloride, benzyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, etc. The alkyl trimethyl ammonium halides include n-hexadecyl trimethyl ammonium chloride, etc. The dialkyl dimethyl ammonium halides include distearyl dimethyl ammonium chloride, stearyl dimethylbenzyl ammonium chloride, etc. The alkyl methyl ammonium halides include dodecyl methyl ammonium chloride, cetyl methyl ammonium chloride, stearyl methyl ammonium chloride, benzyl methyl ammonium chloride, etc. The alkoxy trimethyl ammonium halides include octadesiloxypropyl trimethyl ammonium chloride, etc.
(ii) Nonionic Surfactants
The nonionic surfactants include block copolymers of ethylene oxide and propylene oxide, polyoxyethylene alkylethers, etc. The block copolymers of ethylene oxide and propylene oxide include, for instance, those represented by the formula of RO(C2H4O)a—(C3H6O)b—(C2H4O)cR, wherein a and c are respectively 10-120, b is 30-80, and R is a hydrogen atom or an alkyl group having 1-12 carbon atoms. The block copolymers are commercially available as, for instance, Pluronic (registered trademark of BASF). The polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, etc.
(a-3) Catalysts
(i) Acid Catalysts
Specific examples of the acid catalysts include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, etc. and organic acids such as formic acid, acetic acid, etc.
(ii) Base Catalysts
Specific examples of the base catalysts include ammonia, amines, NaOH and KOH. The preferred examples of the amines include alcohol amines and alkyl amines (methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine, etc.).
(a-4) Solvents
The solvent is preferably pure water.
(b) Formation Method
(b-1) Hydrolysis and Polycondensation Under Acidic Conditions
An acid catalyst is added to the solvent to prepare an acidic solution, to which a cationic surfactant and a nonionic surfactant are added to prepare a mixture solution. Alkoxysilane is added to this acidic mixture solution to cause hydrolysis and polycondensation. The acidic mixture solution preferably has pH of about 2. Because a silanol group of alkoxysilane has an isoelectric point of about pH 2, the silanol group is stable in the acidic mixture solution of about pH 2. A solvent/alkoxysilane molar ratio is preferably 30-300. When this molar ratio is less than 30, the degree of polymerization of alkoxysilane is too high. When it is more than 300, the degree of polymerization of alkoxysilane is too low.
A cationic surfactant/solvent molar ratio is preferably 1×10−4 to 3×10−3, to provide nanometer-sized, mesoporous silica particles with excellent regularity of meso-pores. This molar ratio is more preferably 1.5×10−4 to 2×10−3.
A cationic surfactant/alkoxysilane molar ratio is preferably 1×10−1 to 3×10−1. When this molar ratio is less than 1×10−1, the formation of the meso-structure (hexagonal arrangement) of nanometer-sized, mesoporous silica particles is insufficient. When it is more than 3×10−1, the nanometer-sized, mesoporous silica particles have too large diameters. This molar ratio is more preferably 1.5×10−1 to 2.5×10−1.
A nonionic surfactant/alkoxysilane molar ratio is preferably 5.0×10−3 to 4.0×10−2. When this molar ratio is less than 5.0×10−3, the mesoporous silica layer has a refractive index exceeding 1.19. When it is more than 4.0×10−2, the mesoporous silica layer 17 has a refractive index less than 1.09.
A cationic surfactant/nonionic surfactant molar ratio is preferably 5-35 to provide nanometer-sized, mesoporous silica particles with excellent regularity of meso-pores. This molar ratio is more preferably 6-30.
The alkoxysilane-containing solution is strongly stirred at 20-25° C. for 1-24 hours for aging. The hydrolysis and polycondensation proceed by aging, to form an acidic sol containing silicate oligomers.
(b-2) Hydrolysis and Polycondensation Under Basic Conditions
A base catalyst is added to the acidic sol to turn the solution basic, to further conduct the hydrolysis and polycondensation. The resultant basic sol preferably has pH of 9-12. A silicate skeleton is formed around a cationic surfactant micelle by the addition of the base catalyst, and grows with regular hexagonal arrangement, thereby forming composite particles of silica and the cationic surfactant. As the composite particles grow, effective charge on their surfaces decreases, so that the nonionic surfactant is adsorbed to their surfaces, resulting in a sol of nano-sized, mesoporous silica particles containing the cationic surfactant in pores and covered with the nonionic surfactant, whose shape is shown in
In the process of forming the surfactants-containing, nano-sized, mesoporous silica composite particles, its growth is suppressed by the adsorption of the nonionic surfactant. Accordingly, the surfactants-containing, nano-sized, mesoporous silica composite particles obtained by using two types of surfactants (a cationic surfactant and a nonionic surfactant) have an average diameter of 200 nm or less and excellent regularity of meso-pores.
(b-3) Coating
A sol containing the surfactants-containing, nano-sized, mesoporous silica composite particles is coated onto the sixth layer. The sol may be coated by a spin-coating method, a dip-coating method, a spray-coating method, a flow-coating method, a bar-coating method, a reverse-coating method, a flexographic printing method, a printing method, or their combination. The thickness of the resultant porous coating can be controlled, for instance, by the adjustment of a substrate-rotating speed in the spin-coating method, by the adjustment of pulling-up speed in the dipping method, or by the adjustment of a concentration in the coating solution. The substrate-rotating speed in the spin-coating method is preferably 500-10,000 rpm.
To provide the sol containing surfactants-containing, nano-sized, mesoporous silica composite particles with proper concentration and fluidity, a basic aqueous solution having the same pH as that of the sol may be added as a dispersing medium before coating. The percentage of the surfactants-containing, nano-sized, mesoporous silica composite particles in the coating solution is preferably 10-50% by mass to obtain a uniform porous layer.
(b-4) Drying
The solvent is evaporated from the coated sol. The drying conditions of the coating are not restricted, but may be properly selected depending on the heat resistance of the substrate 3 and the first to sixth layers, etc. The coating may be spontaneously dried, or heat-treated at a temperature of 50-200° C. for 15 minutes to 1 hour for accelerated drying.
(b-5) Baking
The dried coating is baked to remove the cationic surfactant and the nonionic surfactant, thereby forming a mesoporous silica layer 17. The baking temperature is preferably 300° C. to 500° C. When the baking temperature is lower than 300° C., baking is insufficient. When the baking temperature exceeds 500° C., the resultant anti-reflection coating 1 has a refractive index exceeding 1.19. The baking temperature is more preferably 350° C. to 450° C. The baking time is preferably 1-6 hours, more preferably 2-4 hours.
[4] Optical Member Comprising Anti-Reflection Coating
An optical member comprising the anti-reflection coating of the present invention having excellent anti-reflection performance and scratch resistance is suitable for exchange lens units for single-lens reflex cameras, and imaging devices for single-lens reflex cameras and video cameras.
The present invention will be explained in further detail by Examples below without intention of restricting the present invention thereto.
An anti-reflection coating 1 having the layer structure shown in Table 1 was produced by the following steps. The refractive index of each layer was measured with light having a wavelength of 550 nm.
[1] Formation of First to Sixth Layers
Using the apparatus shown in
[2] Formation of Seventh Layer
40 g of hydrochloric acid (0.01 N) having pH of 2 was mixed with 1.21 g (0.088 mol/L) of n-hexadecyltrimethylammonium chloride (available from Kanto Chemical Co. Ltd.), and 7.58 g (0.014 mol/L) of a block copolymer of HO(C2H4O)106—(C3H6O)70—(C2H4O)106H (“Pluronic F127” available from Sigma-Aldrich), stirred at 23° C. for 1 hour, mixed with 4.00 g (0.45 mol/L) of tetraethoxysilane (available from Kanto Chemical Co. Ltd.), stirred at 23° C. for 3 hours, mixed with 3.94 g (1.51 mol/L) of 28-%-by-mass ammonia water to adjust the pH to 11, and then stirred at 23° C. for 0.5 hours. The resultant composite solution of a surfactant and nano-sized, mesoporous silica particles was spin-coated on the sixth layer, dried at 80° C. for 0.5 hours, and then baked at 400° C. for 3 hours.
With the outermost layer in contact with air as a medium, the characteristics of the resultant anti-reflection coating were measured. A lens reflectance meter (“USPM-RU” available from Olympus Optical Co., Ltd.) was used for the measurement of refractive index and physical thickness. The seventh layer had a ratio V1/V2 of 1/2.1.
An anti-reflection coating having the layer structure shown in Table 2 was formed in the same manner as in Example 1 except for adding 2.14 g (0.004 mol/L) of the above block copolymer “Pluronic F127.” With the outermost layer in contact with air as a medium, the characteristics of the anti-reflection coating were measured in the same manner as in Example 1. The seventh layer had a ratio V1/V2 of 1/1.7. The outermost surface of the anti-reflection coating had excellent scratch resistance.
An anti-reflection coating having the layer structure shown in Table 3 was formed in the same manner as in Example 1 except for adding 4.32 g (0.008 mol/L) of the above block copolymer “Pluronic F127.” With the outermost layer in contact with air as a medium, the characteristics of the anti-reflection coating were measured in the same manner as in Example 1. The seventh layer had a ratio V1/V2 of 1/1.9. The outermost surface of the anti-reflection coating had excellent scratch resistance.
It was found from
Images taken with optical lenses obtained in Examples 1-3 did not suffer flare and ghost.
The seven-layer anti-reflection coating of the present invention formed on glass substrate having a low to medium refractive index has excellent anti-reflection performance to a visible light wavelength of 400-700 nm, as well as excellent flare- and ghost-preventing effect, tarnish-preventing effect, scratch resistance, durability and uniformity. Accordingly, it is suitable for exchange lens units for single-lens reflex cameras, etc. used outdoors.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2008-198209 filed on Jul. 31, 2008, which is expressly incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-198209 | Jul 2008 | JP | national |
