Coating solution, antireflection film, and method for manufacturing lens

Abstract

Provided is a coating solution for forming at least one layer of an antireflection film on a lens unit including a plurality of resin lenses, wherein the lenses have an outer diameter of 20 mm or less. The coating solution contains: a plurality of functional fine particles having a refractive index smaller than that of each of the lenses; a binder component which is a precursor of a binder that can fix the functional fine particles in the antireflection film and fix the antireflection film and the lenses together; and at least one first solvent having a boiling point lower than that of the binder component.

Description

Coating liquid, anti-reflection film, and lens manufacturing method

[0001] The present invention relates to a coating liquid, an anti-reflection film, and a method for manufacturing a lens.

[0002] Conventionally, techniques for preventing or reducing light reflection from the surface of an article have been known.

[0003] For example, Patent Document 1 describes a substrate having a coating formed on its surface, the coating including predetermined hollow spherical silica-based particles and a matrix for forming a coating. These silica-based particles have pores inside their shells, and a solvent or gas is contained within the pores. Because the silica-based particles have a low refractive index, the coating also has a low refractive index, resulting in excellent anti-reflection properties.

[0004] Patent Document 2 describes an anti-reflection film having, from the lower layer side, a hard coat layer, a high refractive index layer, and a low refractive index layer on the surface of an organic film. The high refractive index layer is a synthetic resin thin film containing fine particles of a metal oxide such as ZrO. The synthetic resin is a UV- or electron beam-curable synthetic resin.

[0005] Patent Document 3 describes an antireflection laminate including a coating film formed by one-coat coating using a coating composition in which low refractive index particles and medium to high refractive index particles are dispersed in a binder resin. Silica particles treated with a fluorine-based compound are used as the low refractive index particles. As a result, due to the difference in specific gravity, the low refractive index particles are unevenly distributed in the upper to middle parts of the coating film, and the medium to high refractive index particles are unevenly distributed in the middle to lower parts.

[0006] Japanese Patent Application Laid-Open No. 2001-233611 Japanese Patent Application Laid-Open No. 2001-350001 Japanese Patent Application Laid-Open No. 2007-272132

[0007] The techniques described in Patent Documents 1 to 3 need to be reconsidered from the viewpoint of antireflection performance. An object of the present invention is to provide a novel coating liquid, an antireflection film, and a method for manufacturing a lens that are advantageous from the viewpoint of antireflection performance.

[0008] Item 1. A coating liquid for forming at least one layer of an anti-reflection coating on a lens unit including a plurality of resin lenses, the lenses having an outer diameter of 20 mm or less, the coating liquid containing: a plurality of functional fine particles having a refractive index smaller than that of each of the lenses; a binder component that is a binder precursor and is capable of fixing the functional fine particles together in the anti-reflection coating and fixing the anti-reflection coating and the lenses together; and at least one first solvent having a boiling point lower than that of the binder component.

[0009] Item 2. The coating solution according to Item 1, wherein the lens unit includes a lens having a center thickness of 1 mm or less.

[0010] Item 3. The coating liquid according to Item 1 or 2, wherein the lens unit is built into a portable device.

[0011] Item 4. The coating liquid according to any one of Items 1 to 3, wherein the lens unit includes a lens having at least one surface including an axially symmetric concave curved surface and a convex curved surface.

[0012] Item 5. The coating liquid according to any one of Items 1 to 4, wherein the first solvent includes a solvent having a boiling point of 60° C. or higher and 140° C. or lower.

[0013] Item 6. The coating liquid according to Item 5, further comprising a second solvent, the second solvent having a boiling point higher than 150° C. and a surface energy of 30 dyne / cm or more.

[0014] Item 7. The coating liquid according to any one of Items 1 to 6, wherein a mass ratio of the functional fine particles to the total of the functional fine particles and the binder component is 80% or more.

[0015] Item 8. The coating liquid according to any one of Items 1 to 7, wherein the particle size variation of the functional fine particles is within ±20%.

[0016] Item 9. The coating liquid according to any one of Items 1 to 8, wherein a total mass ratio of the functional fine particles and the binder component to the coating liquid is 20% or less.

[0017] Item 10. The coating solution according to any one of Items 1 to 9, wherein the number of the functional fine particles is √3S / 2R or more when formed into a film on the lens, where S is the surface area of ​​the lens onto which the coating solution is applied, and R is the diameter of the functional fine particles.

[0018] Item 11. The coating liquid according to Item 10, wherein R is 55±10 nm, and the number of the functional fine particles is √3S / R or less.

[0019] Item 12. The coating liquid according to any one of Items 1 to 11, wherein the binder component is mainly composed of a composition having Si—O—R (R represents an alkyl group having 1 to 4 carbon atoms).

[0020] Item 13. The coating liquid according to any one of Items 1 to 12, wherein the solvent includes a first solvent and a second solvent, and the boiling point of the second solvent is higher than the boiling point of the first solvent.

[0021] Item 14. An anti-reflection film formed by applying the coating liquid according to any one of items 1 to 13 to each of the lenses and then baking the applied coating liquid at a temperature lower than the boiling point of the solvent.

[0022] Item 15. The anti-reflection film according to Item 14, wherein R>5r, where R is the diameter of the functional fine particles and r is the cross-sectional diameter of the binder.

[0023] Item 16. The anti-reflection coating according to Item 14 or 15, wherein the functional fine particles are stacked on the lens in a square closest-packed manner.

[0024] Item 17. The antireflection film according to Item 16, having a refractive index of 1.16 or less.

[0025] Item 18. An anti-reflection film formed using the coating liquid according to any one of items 1 to 13, and having a refractive index n of 1.16 or less.

[0026] Item 19. An anti-reflection film formed using the coating liquid according to any one of items 1 to 13, wherein when baked at a temperature lower than the boiling point of the solvent, the functional fine particles are laminated in two layers.

[0027] Item 20. An optical thin film on a light control member, comprising: fine particles and a binder that fixes the fine particles; a ratio of the binder to the fine particles is 0.5 or less by mass; and the number of defects is 5 or less.

[0028] Item 21. A method for manufacturing a lens, comprising: applying a coating liquid onto a surface of the lens substrate, the coating liquid including a plurality of functional fine particles having a refractive index lower than that of a lens substrate, a binder component that is a precursor of a binder capable of binding the functional fine particles, and a first solvent having a boiling point lower than that of the binder component; and heating the coating liquid to form an anti-reflection film.

[0029] Item 22. The method for manufacturing a lens according to Item 21, wherein the lens substrate has at least one surface including an axially symmetric concave curved surface and a convex curved surface.

[0030] Item 23. The method for manufacturing a lens according to Item 21 or 22, wherein the coating liquid further contains a second solvent having a higher boiling point than the first solvent.

[0031] Item 24. The method for manufacturing a lens according to any one of Items 21 to 23, wherein the coating liquid further contains at least one selected from a fine particle adhesion inhibitor and a dispersant.

[0032] Item 25. The method for manufacturing a lens according to Item 24, further comprising subjecting the formed antireflection coating to at least one treatment selected from plasma treatment, corona treatment, UV cleaning, high-temperature treatment, organic cleaning, acid cleaning, and alkali cleaning.

[0033] The present invention is advantageous from the viewpoint of anti-reflection performance.

[0034] FIG. 1 is a cross-sectional view of an imaging unit to which an anti-reflection film according to the present invention is applied. FIG. 2 is a cross-sectional view of an anti-reflection film. FIG. 3 is a cross-sectional view showing another example of an anti-reflection film. FIG. 4 is a cross-sectional view showing an example of a nozzle used for spray coating. FIG. 5 is a view showing lenses arranged on an installation surface before coating. FIG. 6 is a cross-sectional view showing lenses after a coating liquid composition has been applied. FIG. 7 is a cross-sectional view showing another example of an anti-reflection film. FIG. 8 is a photograph taken by SEM of a cross section of the anti-reflection film formed in Example 1.

[0035] An embodiment of a coating liquid for an anti-reflection coating according to the present invention will be described below. In this embodiment, the application of this coating liquid to lenses included in an imaging unit will be described with reference to the drawings. First, the imaging unit and the anti-reflection coating (optical thin film) will be described below, followed by a description of the coating liquid. Note that FIG. 1 is a schematic diagram for illustrating the components and features included in the imaging unit, and does not accurately depict the number, shape, size, and arrangement of lenses, the distance between each component, and other aspects of the actual configuration. Furthermore, for the sake of convenience, FIG. 1 illustrates three lenses (L1, L2, and L3), but it should be noted that the present invention is not limited to this and may include a greater or lesser number of lenses.

[0036] 1 is a cross-sectional view of an imaging unit according to this embodiment. This imaging unit is provided in a device (sometimes referred to as a mobile device) such as a smartphone, tablet PC, or notebook PC, and includes a lens unit 100, an imaging element (here, a solid-state imaging element) D, and a sensor substrate W on which the solid-state imaging element D is provided.

[0037] Lens unit 100 is made up of three or more lenses L1, L2, and L3 (hereinafter referred to as the first to third lenses) stacked in this order from the light incident side (upper side in FIG. 1) via spacers 12. As shown in the figure, the surface of each lens is curved.

[0038] The first lens L1 has a first upper lens surface 10A and a first lower lens surface 10B. More specifically, the first lens L1 has a convex first upper lens surface 10A formed on its upper surface, and a concave first lower lens surface 20A formed on its lower surface. The first lens L1 is provided with a black light-shielding film 14 for the purpose of blocking light from the area of ​​the first upper lens surface 10A excluding the lens surface. Similarly, the first lower lens surface 20A is provided with a black light-shielding film 14 in the area excluding the lens surface. The shape of the pattern of the black light-shielding film 14 is not limited, as long as the black light-shielding film 14 is formed in a pattern that has openings at the portions that intersect with the optical axes of the two lenses 10A and 10B. Similar black light-shielding films 14 are also provided on the second and third lenses L2 and L3. However, the black shielding film 14 is formed from the lens surface to the vicinity of the spacer 12 described later, but is formed from the lens surface to the vicinity of the spacer 12 described later and is separated from the spacer 12 .

[0039] The second lens L2 has a second upper lens surface 20A and a second lower lens surface 20B. More specifically, the upper surface of the second lens L2 is formed with a second upper lens surface 10B having a concave lens surface, and the lower surface is formed with a second lower lens surface 20B having a convex lens surface. A black light-shielding film 14 is provided on the light incident side surface of the second lens L2, in a region excluding the lens surface of second upper lens surface 10B, i.e., on the lens edge. In the example shown in FIG. 1 , the black light-shielding film 14 is not provided on the lower surface of the second lens L2, but a patterned black light-shielding film 14 may be provided on a region excluding the lens surface of second lower lens surface 20B.

[0040] The third lens L3 has a third upper lens surface 30A and a third lower lens surface 30B. More specifically, the upper surface of the third lens L3 is formed with a third upper lens surface 30A having a curved lens surface such as an aspherical surface, and the lower surface is formed with a third lower lens surface 30B having a similar curved lens surface such as an aspherical surface. The third upper lens surface 30A has a convex surface symmetrical with respect to the optical axis on the image side (upper side of the drawing) in a region close to the optical axis, and a concave surface symmetrical with respect to the optical axis on the image side in its peripheral portion. Meanwhile, the third lower lens surface 30B has the opposite shape to the third upper lens surface 30A. With a lens having such a shape, the peripheral portion is concave, so the coating liquid described below tends to accumulate in this area, preventing a uniform film from being formed, which may result in an ineffective reflection effect. In contrast, as described below, a uniform film can be formed by using a solvent with a surface energy of 30 dyne / cm or more, for example. The aspherical shape of the third lens L3 shown in FIG. 1 is an example, and other shapes may be used.

[0041] Furthermore, a black light-shielding film 14 is provided on both surfaces of the third lens L3 in the area excluding the lens surfaces of the lenses 30A and 30B.

[0042] The six lens surfaces 10A, 10B, 10C, 20A, 20B, 30A, and 30B are all formed to have shapes that are rotationally symmetrical about the optical axis center. Lenses L1, L2, and L3 are supported by spacers 12 so that the optical axes of all lens surfaces 10A, 10B, 10C, 20A, 20B, 30A, and 30B coincide. Note that the lenses are arranged so that their optical axes approximately coincide, and the schematic diagram in FIG. 1 shows a cross section including the optical axis.

[0043] In addition, a sensor substrate W is disposed below the spacer 12. Therefore, the sensor substrate W is disposed with a gap between it and the third lens L3. The sensor substrate W is formed by cutting a wafer made of a semiconductor material such as silicon into a generally rectangular shape in a plan view. The solid-state imaging element D is provided near the center of the sensor substrate W. The solid-state imaging element D may be, for example, a CCD image sensor or a CMOS image sensor, which may be formed into a chip and then bonded onto a semiconductor substrate on which wiring and the like are formed. Alternatively, the solid-state imaging element D may be formed by subjecting the sensor substrate W to well-known film-forming processes, photolithography processes, etching processes, impurity doping processes, and the like, and then forming electrodes, insulating films, wiring, and the like on the sensor substrate W.

[0044] The spacer 12 is formed in a cylindrical shape, and three annular grooves 121 are formed on its inner peripheral surface at intervals in the axial direction. The outer peripheral edges of the lenses L1, L2, and L3 are fitted into each groove 121, thereby holding the lenses L1, L2, and L3 at intervals on the spacer 12. The spacer 12 may also be a member shaped to surround the solid-state imaging element D. By surrounding the solid-state imaging element D with the spacer 12 and isolating it from the outside, it is possible to block light other than light transmitted through the lenses from entering the solid-state imaging element D. Furthermore, by sealing the solid-state imaging element D from the outside, it is possible to prevent dust from adhering to the solid-state imaging element D.

[0045] With the above-described configuration, the spacer 12 is designed so that the lens surfaces 10A, 10B, 20A, 20B, 30A, and 30B of the lenses L1, L2, and L3 form a subject image on the solid-state image sensor D.

[0046] The configuration of the spacer 12 is not particularly limited, and its shape is not particularly limited and can be modified as appropriate as long as it can maintain a predetermined distance between the lenses L1, L2, and L3 or between the lens L3 and the sensor substrate W. The spacer 12 can be bonded to the outside of the lens area (area that functions as a lens) of each of the lenses L1, L2, and L3, but in addition to attaching each lens to one spacer as described above, spacers may also be attached between the lenses L1, L2, and L3 to form gaps.

[0047] Alternatively, a housing may be provided to house the imaging unit, and the lens may be held by this housing. In this case, the housing is used as a spacer. Alternatively, the outer periphery of the lens itself, outside the lens area, may be made thicker and used as a spacer. Furthermore, the thickness outside the lens area may be combined with a light-shielding film to function as a spacer.

[0048] An infrared cut filter or cover glass may be interposed between the lens module and the sensor substrate W. In this case, the position of each filter or cover glass is determined by a spacer or a housing. When there are three or more lenses, the sensor substrate can be placed outside the lowest lens.

[0049] The imaging unit configured as described above is reflow mounted on a circuit board (not shown) built into a smartphone, etc. Solder paste is printed on the circuit board in advance at the position where the imaging unit will be mounted, the imaging unit is placed thereon, and the circuit board including the imaging unit is subjected to a heating process such as irradiation with infrared rays or blowing hot air, thereby welding the imaging unit to the circuit board.

[0050] Each of the lenses L1, L2, and L3 can be formed from a resin, such as an ultraviolet-curable resin, a thermosetting resin, or a thermoplastic resin. However, taking into consideration the reflow mounting of the imaging unit described above, a resin with a relatively high glass transition point of, for example, 110° C. or higher is preferred, and a resin with a glass transition point of 250° C. or higher is even more preferred.

[0051] Specific examples of resins that can be used include acrylic (methacrylic) resins, styrene resins, polycarbonate resins, polyolefin resins, cycloolefin resins, epoxy resins, polyethylene resins, polypropylene resins, ABS resins, polyamide resins, polyacetal resins, and polyethylene terephthalate resins.

[0052] The black shielding film 14 contains a black material. The black material may be a colorant, metal particles, or metal-containing particles. The colorant may be, for example, a black pigment or a dye. The metal particles or metal-containing particles may be, for example, at least one selected from copper, silver, gold, platinum, tin, and alloys thereof.

[0053] The black material as described above is dissolved and dispersed in a solvent, and then known additives such as a photopolymerization initiator are added to form a liquid black light-shielding film composition. The black light-shielding film composition is then patterned on the lens module by a known method to form the black light-shielding film 14 as described above. In addition to the patterning as described above, a film-like black light-shielding film 14 may also be used.

[0054] The refractive index n of each lens at the D line (wavelength 589.3 nm) SB is, for example, 1.20 to 2.50, may be 1.30 to 2.30, or may be 1.35 to 2.00.

[0055] The thickness (center thickness) (H1, H2, H3) of each of the lenses L1, L2, and L3 on the optical axis is preferably 1 mm or less, more preferably 0.5 mm or less, and the outer diameter K of each lens is preferably 20 mm or less, more preferably 10 mm or less.

[0056] 2. Coating Liquid for Anti-Reflection Film In the present embodiment, the coating liquid composition constituting the coating liquid contains at least fine particles, a binder precursor (binder component), and a solvent. Each material constituting the coating liquid composition will be described below.

[0057] <2-1. Fine Particles> The fine particles (functional fine particles) may be inorganic fine particles or organic fine particles. Examples of inorganic fine particles include oxide fine particles and halide fine particles, and particularly oxide fine particles. Examples of oxide fine particles include silica fine particles, alumina fine particles, zirconia fine particles, and titania fine particles. The oxide fine particles may contain oxides of multiple elements, such as aluminosilicate fine particles. Examples of halide fine particles include chloride fine particles and fluoride fine particles. Examples of fluoride fine particles include magnesium fluoride fine particles and calcium fluoride fine particles. The organic fine particles may be resin fine particles. Examples of resins contained in the resin fine particles include (meth)acrylic resins, styrene resins, and urethane resins. However, when a treatment typified by plasma irradiation (plasma treatment), which will be described later, is applied to the film, it is desirable that the fine particles be inorganic fine particles.

[0058] As the fine particles, for example, hollow fine particles can be used. Hollow fine particles are advantageous in reducing the refractive index of the anti-reflection film. As the hollow fine particles, for example, hollow silica fine particles and hollow magnesium fluoride fine particles can be used. In addition, the fine particles may have voids formed therein, for example, fine particles whose voids are exposed to the outside. Also, porous fine particles may be used.

[0059] The average particle size of the microparticles is, for example, in the range of 10 to 300 nm, 10 to 200 nm, 10 to 150 nm, or in some cases 10 to 100 nm. The average particle size may be in the range of 15 to 100 nm, further 20 to 100 nm, or 30 to 100 nm. The average particle size may be in the range of 30 to 80 nm. The average particle size of the microparticles can be measured using a transmission electron microscope or a scanning electron microscope. This measurement is performed by calculating the average value of the maximum particle size of each of 50 randomly selected microparticles. The average particle size described here is based on the so-called primary particle size.

[0060] The variation in particle size of the fine particles is preferably ±20% or less, more preferably ±10% or less. Furthermore, the variation in particle size of 80% or more of the total fine particles is preferably within ±10%. The variation in average particle size of the fine particles can be measured using a transmission electron microscope or a scanning electron microscope, and can be calculated by dividing the difference between the maximum and minimum values ​​of the maximum particle size of each of 50 arbitrarily selected fine particles by the average particle size.

[0061] The refractive index of the particles is the refractive index n of the lens. SB The refractive index of a microparticle is smaller than the refractive index of the material constituting the microparticle's outer shell, for example, 1.10 to 1.40, preferably 1.15 to 1.40, and more preferably 1.17 to 1.35. The refractive index of a microparticle is not the refractive index of the material constituting the microparticle's outer shell, but the actual refractive index of the microparticle, including the effect of the hollow portion a. The refractive index of a microparticle at a specific wavelength may be widely known, or it can be determined by, for example, an effective medium approximation method using the Bruggemann equation, using representative or average values ​​of the approximate spherical size of the microparticle, the material and thickness of the microparticle's outer shell, etc. Here, unless otherwise specified, the refractive index of the microparticle and all other refractive index values ​​referred to in this specification refer to the refractive index at the D line (589.3 nm).

[0062] The number of functional fine particles contained in the anti-reflection coating 2 can be, for example, √3S / 2R or more, where S is the surface area of ​​the lens to which the coating liquid is applied, and R is the diameter of the fine particles. The diameter R of the fine particles is the value of the average particle diameter of the fine particles mentioned above.

[0063] This allows the anti-reflection coating 2 to be formed in multiple layers, as will be described later. To achieve a low refractive index, the fine particles are prone to peeling, but if the fine particles are arranged in a single layer, the optical properties (anti-reflection function) will be impaired when the fine particles peel off. In contrast, if the fine particles are stacked in multiple layers, the effect on the optical properties can be minimized even if one fine particle peels off.

[0064] When the particle diameter R is 55±10 nm, the number of particles can be √3S / R or less. This allows the particles to form two layers after film formation, and the film thickness is 90 to 130 nm due to the particle diameter range. In this range, an anti-reflection effect can be obtained in the visible light band due to optical interference.

[0065] <2-2. Binder and Its Precursor> The binder functions to bind fine particles to each other and to the underlying structure, such as the substrate (in this embodiment, the lens). The binder fixes fine particles in the anti-reflection coating and improves the abrasion resistance of the coating. The binder is added as a precursor to the coating liquid composition. The binder includes, for example, an oxide component, more specifically, a metal oxide component. The binder precursor that supplies the metal oxide component may be a metal alkoxide. The metal alkoxide provides the metal oxide component using a technique known as the sol-gel method. For example, silicon alkoxide provides the silica component through a hydrolysis reaction and a condensation polymerization reaction. The metal alkoxide is not limited to silicon alkoxide, but may also be aluminum alkoxide, zirconium alkoxide, titanium alkoxide, niobium alkoxide, tantalum alkoxide, etc. Furthermore, the boiling point of the binder precursor (binder component) is higher than the boiling point of the solvent described below.

[0066] The binder may contain an organic component together with a metal oxide component. The organic component may be a component derived from a metal alkoxide, more specifically, a component derived from an organic group bonded to a metal atom constituting the metal alkoxide. That is, the binder may be an inorganic-organic composite containing a metal oxide component and an organic component. The binder that is an inorganic-organic composite may be, for example, R 2 n Si(OR 1 ) 4-n where R 1 is an alkyl group having 1 to 4 carbon atoms, and R 2 is an organic group that provides an organic component to the binder, and n is 1 or 2, especially 1. 2is not particularly limited, and may be an aliphatic group or an aromatic group, and may contain a heteroatom. 2 may be a hydrocarbon group having 1 to 10 carbon atoms, particularly an alkyl group having 1 to 10 carbon atoms, and more particularly an alkyl group having 1 to 4 carbon atoms. Silicon alkoxides (trialkoxysilanes) in which n is 1 provide binders called silsesquioxanes.

[0067] When the binder precursor is primarily composed of Si—O—R as described above, the organic components volatilize after the anti-reflection film is formed, leaving fewer organic components in the film, although the detailed mechanism is not yet understood. As a result, fogging of the lens can be suppressed.

[0068] The binder may be supplied from only one precursor, or from two or more precursors. An example of a combination of two precursors is an alkyltrialkoxysilane and a tetraalkoxysilane. Again, the number of carbon atoms in the alkyl group is not particularly limited, and the alkyl group contained in the alkoxy group may have, for example, 1 to 4 carbon atoms, while the alkyl group bonded to the silicon atom may have, for example, 1 to 10 carbon atoms, particularly 1 to 4 carbon atoms. Tetraalkoxysilane corresponds to a compound in which n=0 in the above general formula.

[0069] The metal alkoxide such as silicon alkoxide may be contained in the coating liquid composition as a hydrolyzate. The hydrolyzate may be a partial hydrolyzate in which hydrolysis has progressed partially. The binder precursor may be a metal alkoxide or a hydrolyzate thereof, particularly an alkoxysilane or a hydrolyzate thereof.

[0070] <2-3. Ratio of binder precursor and fine particles> All ratios shown below are based on mass. Furthermore, these ratios are calculated based on the components supplied to the film, not the precursor. Therefore, for example, R 1 The ratio of the fine particles to the solid content (binder precursor and fine particles) in the coating solution is preferably 80% or more, more preferably 90% or more, and particularly preferably 95% or more. This reduces the amount of binder between the fine particles, making it possible to form a flexible anti-reflection film.

[0071] The total mass ratio of the functional fine particles and binder precursor to the coating solution is preferably 20% or less, more preferably 10% or less, which increases the amount of solvent in the coating solution and makes it easier to form a porous structure in the anti-reflection coating.

[0072] <2-4. Agent for suppressing adhesion of fine particles> It is desirable to add an agent for suppressing adhesion of fine particles to the coating liquid composition.

[0073] The particle adhesion inhibitor may have a boiling point of, for example, 300°C or higher, or even 400°C or higher. The boiling point of the particle adhesion inhibitor is desirably higher than the curing temperature of the binder precursor. The curing temperature of the binder precursor is the maximum temperature in the heating process applied to produce the binder from the binder precursor. Furthermore, the particle adhesion inhibitor desirably has a boiling point higher than that of the solvent. When the coating liquid composition contains multiple types of compounds as solvents, the particle adhesion inhibitor may have a boiling point higher than the boiling points of all of the compounds contained as solvents. Furthermore, as described below, when the coating liquid composition contains a first solvent and a second solvent and the boiling point of the second solvent is higher than the boiling point of the first solvent, the boiling point of the particle adhesion inhibitor may be higher than the boiling point of the second solvent.

[0074] The particulate adhesion inhibitor may have a viscosity of, for example, 1000 mPa·s or more, 1200 mPa·s or more, 1400 mPa·s or more, 1600 mPa·s or more, or even 1800 mPa·s or more. When the coating liquid composition contains multiple compounds as solvents, the particulate adhesion inhibitor may have a viscosity higher than the viscosity of all of the compounds contained as solvents. The relatively high viscosity of the particulate adhesion inhibitor is particularly useful when applying the coating liquid composition to a curved surface. When the coating liquid composition contains a first solvent and a second solvent, and the viscosity of the second solvent is higher than the viscosity of the first solvent, the viscosity of the particulate adhesion inhibitor may be higher than the viscosity of the second solvent. The viscosity can be measured at room temperature (25°C) using a vibration viscometer (e.g., manufactured by Sekonic Corporation, probe: PR-10L, controller: VM-10A). When the particulate adhesion inhibitor contains a solvent, the viscosity measurement is performed after removing the solvent.

[0075] The particulate adhesion inhibitor may be a polymer, especially a thermoplastic polymer. The particulate adhesion inhibitor may be a dispersant.

[0076] <2-5. Dispersant> It is desirable to add at least one dispersant selected from the group consisting of anionic polymer dispersants and polymer dispersants to the coating liquid composition. The dispersant can function as a particulate adhesion inhibitor. The dispersant can have the boiling point exemplified for the particulate adhesion inhibitor. The dispersant can have the viscosity exemplified for the particulate adhesion inhibitor.

[0077] The anionic polymer dispersant has an anionic group, such as a carboxylate group or a sulfonate group. The anionic polymer dispersant has a polymeric molecular structure, i.e., a molecular structure containing repeating units. The anionic polymer dispersant may be a homopolymer or a copolymer. It is desirable that the anionic polymer dispersant have an anionic group in the repeating unit.

[0078] Examples of anionic polymer dispersants include polyacrylates, polystyrene sulfonates, styrene-maleic anhydride copolymers, olefin-maleic anhydride copolymers, acrylamide acrylate copolymers, alginates, and carboxymethylcellulose salts. Examples of the salts include alkali metal salts such as sodium salts and potassium salts. Carboxylic acids derived from maleic anhydride may also exist as sodium salts.

[0079] The polymer dispersant has an average molecular weight of 2000 or more, which is relatively larger than the low-molecular-weight dispersants that are general-purpose surfactants, and acts effectively on fine particles. The molecular weight of the polymer dispersant may be 3000 or more, 4000 or more, 5000 or more, 6000 or more, 7000 or more, 8000 or more, 9000 or more, or even 10,000 or more. The upper limit of the molecular weight is not particularly limited, but is, for example, 200,000 or less, or even 100,000 or less. The polymer dispersant may be anionic, nonionic, or cationic, but is preferably anionic or nonionic.

[0080] Examples of anionic polymer dispersants are the same as those of anionic polymer dispersants. Examples of nonionic polymer dispersants include polyvinyl alcohol, polyethylene glycol, and polyacrylamide. Examples of cationic polymer dispersants include polyethyleneimine and polyvinylimidazoline.

[0081] <2-6. Amount of fine particle adhesion inhibitor> The amount of fine particle adhesion inhibitor or dispersant added relative to the fine particles may be 0.4 or more, 0.5 or more, 2 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or even 10 or more by mass. The upper limit of this ratio is not particularly limited, and may be 1,000 or less, particularly 100 or less. Examples of this ratio are 4 or more and 100 or less, 6 or more and 100 or less, 8 or more and 100 or less, and further 10 or more and 100 or less.

[0082] The particle adhesion inhibitor or dispersant, like the binder, can maintain the spacing between particles. When the particle adhesion inhibitor or dispersant is included, the ratio of the total amount of the binder and the particle adhesion inhibitor or dispersant to the particle is desirably 0.5 or more. This ratio is also expressed on a mass basis. This ratio may be 0.8 or more, 1.0 or more, 1.1 or more, 1.2 or more, 1.5 or more, 1.7 or more, or even 1.8 or more. The upper limit of this ratio is not particularly limited and may be 1000 or less, particularly 100 or less. Examples of this ratio are 0.5 or more and 100 or less, and 1.0 or more and 100 or less.

[0083] <2-7. Solvent> The solvent may be composed of a single type of solvent, but it is desirable to include two or more solvents with different boiling points. The solvent may include a first solvent and a second solvent, both of which are organic solvents, particularly polar organic solvents. When mainly using two types of solvents (first solvent and second solvent), the boiling point of the first solvent is preferably 60 to 150°C, more preferably 80 to 140°C, and particularly preferably 90 to 130°C. The boiling point of the second solvent is preferably higher than 150°C, more preferably 165°C or higher, and particularly preferably 170°C or higher. The boiling point of the second solvent may be 280°C or lower. An example of the boiling point of the second solvent is 150 to 280°C. When a particulate adhesion inhibitor or dispersant is included, the boiling point of the second solvent may be lower than the boiling point of the particulate adhesion inhibitor or dispersant. The difference in boiling point between the first solvent and the second solvent may be, for example, 50 to 100°C.

[0084] The first solvent and the second solvent are preferably blended so that the ratio of the second solvent to the first solvent is less than 1, 0.8 or less, preferably 0.6 or less, and particularly preferably 0.4 or less, by mass. The lower limit of this ratio may be 0.03 or more, 0.05 or more, or even 0.07 or more. This ratio is, for example, 0.03 or more and 0.8 or less, 0.05 or more and 0.5 or less, or even 0.07 or more and 0.4 or less. These ratios are determined for coating liquid compositions to be applied to curved surfaces by spray coating, particularly spray coating.

[0085] It is preferable to select a combination of solvents with excellent compatibility as the first and second solvents, which can be easily achieved, for example, by using alkoxy group-containing alcohols as both the first and second solvents.

[0086] As will be described later, the boiling point and surface energy of the solvent contained in the coating liquid composition are important when forming a film. The first solvent has a lower boiling point than the second solvent, so when forming a film by spray coating, as described later, it volatilizes before reaching the lens. On the other hand, the second solvent has a higher boiling point than the first solvent. When ejected from a nozzle by spray coating, it reaches the lens and adheres to the lens as droplets. The droplets that adhere to the lens then spread across the lens surface to form a film. In this case, if the surface energy of the second solvent is not high, the liquid will not spread sufficiently, which may cause defects such as color unevenness. Therefore, it can be said that the boiling point and surface energy of the second solvent are important properties. Specifically, the surface energy of the second solvent is preferably 30 dyne / cm or more, 35 dyne / cm or more, 40 dyne / cm or more, 45 dyne / cm or more, or even 70 dyne / cm or more.

[0087] Solvents with high boiling points can be broadly divided into (A) solvents with high molecular weights and high boiling points, and (B) solvents with smaller molecular weights than (A) but strong hydrogen bonds. Solvents in (B) have high surface energy and are suitable for spreading the liquid over the lens surface. A typical example of (A) solvent is butoxyethanol (boiling point 171°C, surface energy 24.8 dyne / cm), and a typical example of (B) solvent is propylene glycol 400 (boiling point 188°C, surface energy 71.6 dyne / cm).

[0088] The surface energy of a solvent can be measured by any ordinary method, for example, by a method in which a platinum ring is placed horizontally on the liquid surface using a lubrication method, and then pulled up and measured with a balance the force that balances the surface tension acting on the ring at the moment it begins to fall from the liquid surface.

[0089] <2-8. Other Components> The coating liquid composition may further contain a thickener, a thixotropy imparting agent, a surfactant, a crosslinking agent, a leveling agent, etc. The leveling agent is effective in improving the wetting of fine particles. The coating liquid composition may further contain a leveling agent. As the leveling agent, a surfactant with a low molecular weight, specifically an average molecular weight of less than 2000, is suitable.

[0090] 3. Anti-Reflection Film Fig. 2 is a cross-sectional view of an anti-reflection film laminated on a lens. As shown in Fig. 2, the anti-reflection film 2 is an example of a film provided on a substrate 3 (each of the above-mentioned lenses). The anti-reflection film 2 is formed of two layers of fine particles 21 fixed with a binder 31. Furthermore, both the fine particles 21 and the substrate 3 are fixed with the binder 31.

[0091] As described above, the coating liquid according to this embodiment has a low mass of solids relative to the solvent and a low mass ratio of binder to fine particles, which allows the anti-reflection coating 2 to have a porous structure. For example, such a porous structure preferably has a porosity of 50% or more.

[0092] The anti-reflection film 2 has a refractive index n of 1.10 to 1.35. L1 and a thickness t of 80 nm to 150 nm L1 With this configuration, the anti-reflection film 2 can exhibit high anti-reflection performance. L1 is the refractive index at the D line (wavelength 589.3 nm). In Fig. 2, for the sake of convenience, the substrate 3 is depicted as flat, but in reality it is a lens having a curved surface.

[0093] In the anti-reflection coating 2, for example, in a reflection spectrum showing the wavelength when light having a wavelength of 300 nm to 1200 nm is incident at an incident angle of 5° and the reflectance for that wavelength, the minimum reflectance r min 300-1200 can be less than 1%. min 300-1200is preferably 0.5% or less, and more preferably 0.2% or less. Unless otherwise specified, the reflectance of an anti-reflection film or the like is the reflectance determined from the reflection spectrum when light having a wavelength of 300 nm to 1200 nm is incident at an incident angle of 5°.

[0094] In the anti-reflection film 2, the minimum reflectance r in the wavelength range of 400 nm to 800 nm min 400-800 is not limited to a specific value. min 400-800 is, for example, 0.5% or less. In this case, the anti-reflection film 2 is more likely to exhibit high anti-reflection performance. min 400-800 is preferably 0.2% or less.

[0095] In the anti-reflection film 2, the range λ in which the reflectance is 2.5% or less in the wavelength range of 300 nm to 1200 nm range / 2.5 is not limited to a specific value. range / 2.5 is, for example, 400 nm or more. This allows the anti-reflection film 2 to more easily exhibit high anti-reflection performance. range / 2.5 The wavelength may be 450 nm or more, or 500 nm or more. Hereinafter, unless otherwise specified, the wavelength and wavelength range corresponding to a predetermined reflectance also refer to the wavelength determined from the reflectance spectrum.

[0096] In the anti-reflection film 2, the range λ in which the reflectance is 1.0% or less in the wavelength range of 300 nm to 1200 nm range / 1.0 is not limited to a specific value. range / 1.0 is, for example, 250 nm or more. This allows the anti-reflection film 2 to more easily exhibit high anti-reflection performance. range / 1.0 may be 300 nm or more, 350 nm or more, or 400 nm or more.

[0097] Refractive index n of the substrate (lens) sb and the refractive index of the anti-reflection film is n1, it is possible to adjust the optical thickness of the anti-reflection film to 1 / 4 of the predetermined wavelength λ. sb -n1 2The smaller the absolute value of the value, the smaller the reflectance at the wavelength λ corresponding to that refractive index. Therefore, from the viewpoint of reducing reflectance, it may be desirable for the antireflection coating 2 to have a low effective refractive index. When a low refractive index is required for the antireflection coating, it is advantageous for the antireflection coating to contain hollow fine particles.

[0098] 2, the substrate (lens) 3 and the anti-reflection coating 2 are in direct contact with each other, but this is not limiting and another film may be interposed between the substrate 3 and the anti-reflection coating 2. An example of such another film is polyvinyl butyral resin (PVB). Furthermore, although the surface of the anti-reflection coating 2 is exposed, this is not limiting and the surface of the anti-reflection coating 2 may be covered with another layer.

[0099] Furthermore, when R is the diameter of the fine particles and r is the cross-sectional diameter of the binder, it is preferable that R>5r (see Figure 2). This reduces the amount of binder, allowing the anti-reflection film to have a porous structure. The cross-sectional diameter r of the binder may be determined by measuring the maximum thickness of the portion where the fine particles are connected when observing the cross-section of the film with a transmission electron microscope or a scanning electron microscope, as shown in the schematic diagram of Figure 2. In this case, the thicknesses of the portions where the fine particles are connected that are recognizable within the observation field may be measured, and the average value of these may be used as the value of r.

[0100] The arrangement of the particles in each of the layers 21 and 22 is not particularly limited, but may be, for example, square closest packing, which allows the void ratio to be 50% or more.

[0101] 4. Method for Forming an Anti-Reflection Film The coating liquid composition of this embodiment can be subjected to various coating processes, but is suitable for application by spray coating. Spray coating is a well-known coating process in which a coating liquid composition is sprayed from a spray nozzle. The lens targeted in this embodiment is small, and the coating liquid composition cannot be uniformly applied by methods such as spin coating, so spray coating is suitable.

[0102] Antireflection films formed by spray coating using a coating liquid composition containing fine particles, a binder precursor, and a solvent are more susceptible to micro-defects than optical thin films formed by other coating processes. One cause of this is believed to be the adhesion of aggregates of fine particles. By using the above-described coating liquid composition, the occurrence of micro-defects is reduced and, in some cases, eliminated. Spray coating itself is a coating method that is highly suitable for mass production and can be applied to curved surfaces, and it is also a coating process that can continuously form films on multiple substrates.

[0103] First, as described above, the black light-shielding film 14 is formed on the substrate 3. Next, the coating liquid composition is applied to the substrate 3, and then baked, whereby the solvent evaporates, a binder is produced from the binder precursor, and an anti-reflection film is formed. The baking temperature is lower than the boiling point of the solvent, for example, 85 to 110°C, and the baking time can be, for example, 5 to 400 minutes. Because the lens according to this embodiment is made of resin, the baking temperature cannot be high, so the temperature range described above is used.

[0104] As described above, when the coating liquid composition contains the first solvent and the second solvent, when the coating liquid composition is applied to the substrate 3 by spray coating, it is possible to reduce unevenness in the thickness of the anti-reflection film formed, although the detailed mechanism is unknown.

[0105] After the coating liquid composition is applied to the substrate, the coating liquid composition spreads over the curved substrate 3 due to the action of the second solvent. The second solvent then evaporates during the baking process. Furthermore, the binder can be prevented from evaporating during the baking process. That is, by incorporating a metal alkoxide, which is a binder precursor, as a hydrolyzate, the binder precursor contained in the coating liquid composition can be prevented from evaporating during the baking process. This improves the controllability of the formation of the anti-reflective film.

[0106] At least a portion of the particulate adhesion inhibitor or dispersant contained in the formed antireflective film may then be removed. Specifically, the particulate adhesion inhibitor or dispersant can be removed by various treatments of the antireflective film. Examples of such treatments include plasma treatment, corona treatment, UV cleaning, high-temperature treatment, organic cleaning, acid cleaning, and alkali cleaning. Plasma treatment can be performed by irradiating the antireflective film with an oxidizing active species, such as oxygen plasma.

[0107] There are various methods for spray coating, and one example will be shown below. Fig. 4 is a cross-sectional view showing an example of a spray nozzle used for spray coating. As shown in Fig. 4, this spray nozzle has a storage section 91 that stores a coating liquid composition, and an annular liquid flow path 93 is formed extending from this storage section 91 to a nozzle outlet 92. This liquid flow path 93 is provided with an air swirler (not shown) for swirling the coating liquid composition within the liquid flow path 93. Therefore, the coating liquid composition that passes through the liquid flow path 93 and is discharged from the outlet 92 is discharged downward while swirling.

[0108] Additionally, an annular air flow path 94 extending toward the nozzle outlet 92 is formed outside the container 91 and the liquid flow path 93. This air flow path 94 is provided with an air swirler (not shown) for swirling the coating liquid composition within the air flow path 94. As a result, the air flowing through the air flow path 94 becomes a swirling flow, and merges with the liquid flow path 93 from the outside of the liquid flow path 93 near the outlet 92. As a result, the coating liquid composition is pressed against the outside of the liquid flow path 93 by the swirling air flow, and reaches the outlet 92 in the form of a thin film. The coating liquid composition is then discharged downward from the outlet 92 while swirling. The coating liquid composition discharged from the outlet 92 via the air flow path 94 swirls, its outer diameter increasing as it travels downward, and is applied to the lens to be coated. For example, a nozzle manufactured by Shimada Appli Co., Ltd. can be used as such a nozzle.

[0109] The height of the discharge port 92 of the spray nozzle 9 configured as described above from the lens to be coated is preferably 25 mm to 35 mm. The amount of the coating liquid composition discharged per unit time is preferably 0.1 ml / min to 0.3 ml / min. The amount of the liquid discharged per unit time may be determined by collecting the liquid discharged from the spray nozzle for 1 minute and measuring its volume.

[0110] As shown in FIG. 4, for example, in region N1, which is 25 to 35 mm away from the discharge port 92, the swirling flow of the coating liquid composition is strong because it is close to the discharge port 92. Therefore, the droplets that make up the mist in the swirling flow are swept inward by the swirling flow. Furthermore, droplets that have fallen outside the swirling flow are repelled further outward by the swirling flow. In other words, the repelled droplets do not adhere to the lens. Note that the droplets that adhere to the lens spread over the lens surface and form a film. Therefore, when a lens is placed in this region N1 and the coating liquid composition is applied, an appropriate coating film is formed.

[0111] On the other hand, in the region N2, which is 45 to 55 mm away from the discharge port 92, the swirling flow of the coating liquid composition weakens because it is far from the discharge port 92. Therefore, the droplets that make up the mist in the swirling flow are not prevented from flowing to the outside of the swirling flow. And, because the swirling flow is weak, the droplets that have flowed to the outside of the swirling flow are not repelled farther outward, and there is a possibility that they will adhere to the lens. Therefore, if a lens is placed in this region N2 and the coating liquid composition is applied, the uncontrolled droplets will adhere to the lens as scattering marks, which may result in a defective product. It should be noted that such scattering marks (the number of defects is preferably 5 or less)

[0112] As shown in FIG. 5 , when spray coating a lens L, multiple lenses L (e.g., 5 to 20 mm in diameter) are arranged in a grid pattern on a mounting surface (e.g., a stage or pallet) with front-to-back and left-to-right spacing of 5 to 30 mm, and the spray nozzle 9 is moved sequentially over each lens to perform coating. That is, the coating liquid composition is continuously applied to multiple lenses L. Therefore, particularly if the height of the spray nozzle 9 is outside the above-mentioned range or the amount of coating is small, the following problems may occur. Note that the spacing and arrangement of the lenses L are not as crucial as the height of the spray nozzle 9 and the appropriate amount of coating, and therefore the arrangement does not have to be grid-like and is arbitrary. That is, while the lens diameter and spacing described above are merely examples, the inventors have confirmed that, at least within these ranges, appropriate film formation is possible within the preferred ranges of the spray nozzle outlet height and discharge amount described above.

[0113] (a) When the amount of coating liquid composition applied is appropriate and the height of the spray nozzle is high (for example, when the distance between the spray nozzle 9 and the lens L is 35 mm or more), the coating area of ​​the coating liquid composition ejected from the spray nozzle 9 becomes large. Therefore, when the coating liquid composition is continuously applied to multiple lenses L, droplets of the coating liquid composition described above may adhere to the lenses L before application. When the droplets thus adhered dry, they form scattered marks, and the coating liquid composition is applied onto these marks, so the finished lens L exhibits uneven color discoloration such as color unevenness. Similarly, when droplets adhere to the lens L after application, similar discoloration occurs.

[0114] However, if the height of the spray nozzle 9 is increased to 60 mm or more, the solvent becomes more likely to volatilize. As a result, the amount of liquid that reaches the lens is reduced, and the amount of liquid that flows to the center of the concave surface is also reduced. As a result, although splash marks are observed, color unevenness is unlikely to occur.

[0115] To prevent such discoloration, for example, the following measures can be taken: (1) Adding a certain amount of a microparticle adhesion inhibitor to the coating liquid composition prevents drying and reduces uneven discoloration even if some of the liquid composition adheres to the surface of the lens L before coating. (2) Setting the distance between the outlet 92 of the spray nozzle 9 and the lens L to the appropriate distance described above reduces uneven discoloration.

[0116] (b) When the amount of coating liquid composition applied is appropriate and the height of the spray nozzle is low (for example, when the distance between the spray nozzle 9 and the lens L is 25 mm or less), the thickness of the coating liquid composition applied to the lens L may become thick. This is for the following reason.

[0117] (1) Because the distance between the spray nozzle 9 and the lens L is small, the area coated with the coating liquid composition is narrow. If the discharge amount is constant, when the area of ​​the coated area is small, the film thickness immediately after application (immediately after the coating liquid composition adheres to the lens L) becomes thick. (2) Because the distance between the spray nozzle 9 and the lens L is small, the solvent contained in the coating liquid composition does not volatilize sufficiently. This causes the film thickness immediately after application to be thick.

[0118] In particular, since substrates such as lenses are curved, when a coating liquid composition is applied to the concave surface of lens L, for example, as shown in FIG. 6, the excess coating may flow toward the bottom of the concave surface before drying, resulting in an unacceptable deviation in film thickness. This may result in an inability to obtain appropriate refractive index and reflective performance, and may also cause appearance problems, such as uneven color due to uneven reflection. On the other hand, when a coating liquid composition is applied to the convex surface of lens L, the excess coating may flow toward the periphery of the convex surface before drying, resulting in an unacceptable deviation in film thickness. The above phenomenon may occur when a large amount of coating liquid composition is applied in the above-mentioned (a).

[0119] (c) When the amount of coating liquid composition to be applied is small (for example, when the amount of application is 0.1 ml / min or less), the nozzle structure makes it impossible to control the discharge of such a small amount of liquid, and therefore coating is not possible.

[0120] If the height of the spray nozzle 9 is high when the amount of binder is small, droplets of the coating liquid composition will scatter around, resulting in a defective anti-reflection film formed on the lens L. On the other hand, to solve this problem, it has been considered desirable to add a particle aggregation inhibitor (at least one dispersant selected from the group consisting of anionic polymer dispersants and polymer dispersants), but by optimizing the height of the spray nozzle 9, it is possible to produce a defect-free film without adding the aggregation inhibitor.

[0121] 5. Features The coating liquid according to this embodiment can provide the following effects. (1) Because it contains fine particles such as hollow fine particles having voids, it is possible to form an anti-reflection film with a porous structure. This makes it possible to achieve a low refractive index. (2) Because the ratio of fine particles to the solid content (binder precursor and fine particles) in the coating liquid is low, the amount of binder between the fine particles 21 is small, making it possible to form a flexible anti-reflection film. As a result, even when a film is formed on a material with a large thermal expansion coefficient, such as a resin lens, the anti-reflection film is less likely to crack before and after a heat resistance test.

[0122] (3) Because the total mass ratio of the fine particles and binder precursor to the coating solution is low, the amount of solvent in the coating solution is large. This makes it easier to form a porous structure in the anti-reflection coating 2. In other words, voids are more likely to form between adjacent fine particles, making it possible to achieve a low refractive index.

[0123] 6. Modifications Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. Note that the following modifications can be combined as appropriate.

[0124] (1) The lens unit on which the anti-reflection film of the present invention is laminated is not particularly limited, and FIG. 1 is merely one example. That is, the lens unit covered by the present invention may be any lens unit in which multiple resin lenses each having an outer diameter of 20 mm or less are stacked. Furthermore, the shape and number of each lens and the form of the black light-shielding film are not particularly limited, and can be configured appropriately according to requirements. For example, the curved surface constituting the surface of at least one of the lenses may have at least one inflection point.

[0125] (2) The antireflection film may be configured with multiple layers. For example, as shown in Fig. 3, a second antireflection film 4 may be provided between the above-described antireflection film (hereinafter referred to as a first antireflection film 2) and a substrate (lens) 3. This second antireflection film 4 has a plurality of hollow fine particles 21 dispersed within a layer formed of a binder 41.

[0126] The refractive index of the second antireflection film 4 is larger than the refractive index of the first antireflection film 2 and can be set to, for example, 1.30 to 1.25. The thickness of the second antireflection film 4 can be set to, for example, 5 nm to 150 nm.

[0127] The hollow fine particles 21 and the binder 41 may be the same as those used in the first antireflection coating 2. However, the number of hollow fine particles 21 in the second antireflection coating 4 is set to be smaller than that in the first antireflection coating 2. This allows the refractive index of the second antireflection coating 4 to be higher than that of the first antireflection coating 2.

[0128] To form the above-described reflective film, first, the second antireflection film 4 is formed on the substrate 3, and then the first antireflection film 2 is formed. The second antireflection film 4 can also be formed by spray coating, similar to the first antireflection film 2.

[0129] (3) In the example of FIG. 3, the antireflection coating is formed in two layers, but it can also be formed in three or more layers as shown in FIG. 7. In the example of FIG. 7, five antireflection coating layers are formed. Hereinafter, these will be referred to as first to fifth antireflection coatings 2, 5, 6, 7, and 8. The second antireflection coating 5 has roughly one layer of hollow particles 21 connected by a binder 31, similar to the first antireflection coating 2. However, the number of hollow particles 21 is fewer than that of the first antireflection coating 2. The third antireflection coating 6 has multiple hollow particles 21 dispersed in a layer formed with a binder 61. The number of hollow particles 21 is fewer than that of the second antireflection coating. In addition, voids 62 are also formed in the third antireflection coating 6.

[0130] In the fourth antireflection coating 7, a plurality of hollow fine particles 21 are dispersed in a layer formed from a binder 61. The number of hollow fine particles 21 is smaller than that in the third antireflection coating 6. The fifth antireflection coating 8 is a layer formed from a binder 71 and does not contain hollow fine particles.

[0131] As described above, the number of hollow fine particles contained gradually decreases from the first antireflection coating 2 to the fifth antireflection coating. As a result, the refractive index gradually increases from the first antireflection coating 2 to the fifth antireflection coating. More specifically, in this modification, it is preferable that the refractive index of the first antireflection coating 2 is close to that of air, and that of the fifth antireflection coating 8 is close to that of the lens.

[0132] The binder and hollow fine particles contained in each layer can be made of, for example, the same material as that contained in the first antireflection coating 2. To form the above-described reflective coating, first, the fifth, fourth, third, second, and first antireflection coatings are formed on the substrate (lens) in this order by spray coating or the like.

[0133] When a plurality of antireflection films are formed as shown in FIGS. 3 and 7, the antireflection performance can be improved.

[0134] The coating liquid and anti-reflection film according to the examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0135] (Formation of anti-reflective coating) A binder mixture was prepared by mixing tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and 0.3% formic acid in a mass ratio of 8.7:3.7:7.6. This mixture was mixed with fine particles, a dispersant, a leveling agent, a low-boiling point solvent, and a high-boiling point solvent to obtain coating liquid compositions according to Examples 1 to 7, as shown in Table 1. Table 2 shows the solid content in the coating liquid composition and the ratio of fine particles to the solid content. The solid content is the total mass of the binder mixture and the fine particles.

[0136] Next, the coating liquid composition was applied to the surface of the lens by spray coating. Subsequently, the glass plate coated with the coating liquid composition was air-dried for 10 minutes and then heated in an oven set at 85°C for 10 minutes to obtain an anti-reflection film. The film thickness of the formed anti-reflection film was in the range of 50 nm to 350 nm.

[0137] The lenses were made of cycloolefin resin (refractive index = 1.530 at the wavelength of the D line (wavelength 589.3 nm)), and were convex lenses with an outer diameter of 13 mm, a thickness of 0.5 mm, and an angle of 50 degrees near the outer periphery. Here, 100 lenses were arranged in a grid pattern with 13 mm intervals.

[0138] The raw materials used are as follows: (i) Fine particles: hollow silica fine particles, Balloonsil (registered trademark) Nano (Toyota Chemical Industries, average particle size 55 nm) (ii) Binder precursor: tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), 0.3% aqueous solution of orthosilicate (manufactured by Tama Chemical Industries, Ltd.) (iii) Fine particle contact inhibitor (dispersant): Styrene maleic anhydride copolymer BYK-2013 (manufactured by BYK) 2-propanol (special grade manufactured by Kanto Chemical Industry Co., Ltd.) boiling point 82 ° C, surface energy 20.8 dyne / cm 2 Methanol boiling point 64 ° C, surface energy 22.6 dyne / cm 2 Acrylic copolymer FLOWRENE DOPA-35 (manufactured by Kyoeisha Chemical Co., Ltd.) (iv) Low boiling point solvent (first solvent): 1M2P (1-methoxy-2-propanol), boiling point 120 ° C, surface energy 25.6 dyne / cm 2 (manufactured by Tokyo Chemical Industry Co., Ltd.) (v-1) High boiling point solvent (second solvent): (indicated as PG in the table) Propylene glycol 400 (manufactured by Fujifilm Wako Co., Ltd.), boiling point 188°C, surface energy 71.6 dyne / cm (v-2) High boiling point solvent (second solvent): (indicated as BE in the table) Butoxyethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (boiling point 171°C, surface energy 24.8 dyne / cm) (vi) Leveling agent: Polyether-modified silicone, KP-341 (manufactured by Shin-Etsu Silicones Co., Ltd.)

[0139] KP-341 (polyether-modified silicone) is a surfactant suitable as a leveling agent, and its average molecular weight corresponds to less than 2,000.

[0140] (The unit is g)

[0141]

[0142] (Measurement of refractive index) The refractive index was measured using an Olympus USPM to measure the spectral reflectance of the film in the visible light range, and the film configuration was simulated and fitted using optical film design software (TFCalc, manufactured by Hulinks Co., Ltd.) from this spectral reflectance data to obtain the refractive index at the wavelength of the D line (wavelength 589.3 nm). The refractive index of the antireflection films formed in Examples 1 to 7 was all 1.16. Therefore, it was found that antireflection films with low refractive indexes could be formed by this example.

[0143] The cross section of the anti-reflection film of Example 1 was observed using an SEM, and the result is shown in Fig. 8. As shown in Fig. 5, this anti-reflection film had two layers of fine particles stacked together, and many voids were observed.

[0144] (Study on Nozzle Conditions) The above-mentioned spray nozzle manufactured by Shimazu Appli Co., Ltd. was used to study the application of the coating liquid compositions of Examples 1 and 5 onto a lens. A 7 mm diameter lens made of cycloolefin resin (refractive index at the wavelength of D line (wavelength 589.3 nm) = 1.530) was used as the coating target, and the coating liquid composition was applied to the concave surface of the lens. Also, here, as described above, 100 lenses were arranged in a grid pattern with 13 mm intervals, and the coating liquid composition was continuously applied. The following A to D were set as nozzle conditions.

[0145] A: Nozzle height 60 mm, discharge rate 0.2 ml / min B: Nozzle height 30 mm, discharge rate 0.2 ml / min C: Nozzle height 10 mm, discharge rate 0.2 ml / min D: Nozzle height 30 mm, discharge rate 0.4 ml / min The discharge rate per unit time was determined by collecting the liquid discharged from the spray nozzle for 1 minute using the same method and conditions and measuring its volume.

[0146] Then, under each of the above conditions, the coating liquid composition was applied to a lens from a spray nozzle, and the appearance of each lens after drying was confirmed. In addition, the refractive index of each lens was measured. The appearance of the lens was evaluated as follows: (i) Defects The number of defects (the number of the above-mentioned scattered marks) was measured in Examples 1 and 5. The number of defects was measured using a 20x objective lens on a laser microscope (OPTELICS HYBRID L7) manufactured by Lasertec Corporation, and the number of defects was counted by visual inspection of the image obtained. The evaluation was as follows: ◎ 5 or less ○ 20 or less △ 50 or less × 50 or more

[0147] (ii) Color unevenness ◎ The color of the reflection is uniform (there are no discolored areas of φ0.1 mm or more) △ The color of the reflection is uneven (there are discolored areas of φ0.1 mm or more)

[0148] The results are shown in Table 3. Under condition A, the spray nozzle was quite high, which caused defects due to splash marks as described above, but the solvent was easily volatile, which reduced the amount of liquid reaching the lens and reduced color unevenness. Under condition C, almost no defects were observed, but slight color unevenness was observed, which is thought to be due to the unevenness of the film described above. Under condition D, the spray nozzle was at an appropriate height, but the discharge volume was large, which is thought to have caused unevenness of the film, and slight color unevenness was observed.

[0149] On the other hand, under Condition B, in which the nozzle height and discharge amount were appropriate, good film formation was achieved without defects or color unevenness in Examples 1 and 5. Furthermore, although the solid content of the coating liquid composition differs between Examples 1 and 5, there was no difference in this test. However, in Example 8, a second solvent with a lower surface energy than Examples 1 and 5 was used, so the droplets spread less well than in Examples 1 and 5, and the color unevenness was non-uniform.

[0150] 2 Anti-reflection film 21 Fine particles 31 Binder

Claims

1. A coating liquid for forming at least one layer of anti-reflection coating on a lens unit including a plurality of resin lenses, the lenses having an outer diameter of 20 mm or less, the coating liquid containing: a plurality of functional fine particles having a refractive index smaller than that of each of the lenses; a binder component which is a binder precursor and is capable of fixing the functional fine particles together in the anti-reflection coating and fixing the anti-reflection coating and the lenses together; and at least one first solvent having a boiling point lower than that of the binder component.

2. The coating solution of claim 1, wherein the lens unit includes a lens having a center thickness of 1 mm or less.

3. The coating solution according to claim 1, wherein the lens unit is built into a portable device.

4. The coating solution of claim 1, wherein the lens unit comprises a lens having at least one surface including an axisymmetric concave curved surface and a convex curved surface.

5. The coating liquid according to claim 1, wherein the first solvent contains a solvent having a boiling point of 60°C or higher and 140°C or lower.

6. The coating liquid according to claim 5, further comprising a second solvent, the second solvent having a boiling point higher than 150°C and a surface energy of 30 dyne / cm or more.

7. The coating liquid according to claim 1, wherein the mass ratio of the functional fine particles to the total of the functional fine particles and the binder component is 80% or more.

8. The coating solution according to claim 1, wherein the particle size variation of the functional fine particles is within ±20%.

9. The coating liquid according to claim 1, wherein the total mass ratio of the functional fine particles and the binder component to the coating liquid is 20% or less.

10. The coating solution according to claim 1, wherein the number of the functional fine particles when formed into a film on the lens is equal to or greater than √3S / 2R, where S is the surface area of ​​the lens onto which the coating solution is applied, and R is the diameter of the functional fine particles.

11. The coating liquid according to claim 10, wherein R is 55±10 nm, and the number of the functional fine particles is √3S / R or less.

12. The coating liquid according to claim 1, wherein the binder component is primarily composed of a composition having Si—O—R (R represents an alkyl group having 1 to 4 carbon atoms).

13. The coating liquid according to claim 1, wherein the solvent comprises a first solvent and a second solvent, and the boiling point of the second solvent is higher than the boiling point of the first solvent.

14. An anti-reflection film formed by applying the coating liquid according to claim 1 to each of the lenses and then baking the applied liquid at a temperature lower than the boiling point of the solvent.

15. The anti-reflection coating according to claim 14, wherein R>5r, where R is the diameter of the functional fine particles and r is the cross-sectional diameter of the binder.

16. The anti-reflection coating according to claim 14, wherein the functional particles are stacked on the lens in a square closest packing pattern.

17. The anti-reflective coating according to claim 14, having a refractive index of 1.16 or less.

18. An anti-reflection film formed using the coating liquid according to claim 1 or 2, having a refractive index n of 1.16 or less.

19. An anti-reflection film formed using the coating liquid according to claim 1 or 2, in which the functional fine particles are laminated in two layers when baked at a temperature lower than the boiling point of the solvent.

20. A method for manufacturing a lens, comprising: applying a coating liquid onto a surface of the lens substrate, the coating liquid including a plurality of functional fine particles having a refractive index lower than that of a lens substrate, a binder component that is a precursor of a binder capable of binding the functional fine particles, and a first solvent having a boiling point lower than that of the binder component; and heating the coating liquid to form an anti-reflection film.

21. The method of manufacturing a lens according to claim 20, wherein the lens substrate has at least one surface including an axisymmetric concave curved surface and a convex curved surface.

22. The method for manufacturing a lens according to claim 20, wherein the coating solution further contains a second solvent having a higher boiling point than the first solvent.

23. The method for manufacturing a lens according to claim 20, wherein the coating liquid further contains at least one selected from a fine particle adhesion inhibitor and a dispersant.

24. The method for manufacturing a lens according to claim 23, further comprising subjecting the formed anti-reflection coating to at least one treatment selected from plasma treatment, corona treatment, UV cleaning, high-temperature treatment, organic cleaning, acid cleaning, and alkali cleaning.

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