Lens unit and coating liquid

Abstract

A lens unit according to the present invention has a first lens, a second lens that is opposite from the first lens, and a spacer for keeping the interval between the first lens and the second lens constant. The first lens and the second lens each have a set of surfaces that are opposite from each other. Each surface has a middle region that includes a lens surface functioning as a lens and is provided with a functional film on the lens surface, and a peripheral region at the periphery of the middle region. The spacer is positioned at the peripheral regions.

Description

Lens unit and coating liquid

[0001] The present invention relates to a lens unit and a coating liquid.

[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] Incidentally, Patent Document 1 describes that the above-mentioned anti-reflection film is formed on a lens. In recent years, lenses have been used for a variety of purposes, for example, in lens units for photography in smartphones, tablet PCs, and the like. Such lens units are housed inside a housing and are therefore less susceptible to external influences, such as direct contact with hands. Therefore, it is not a problem if the above-mentioned anti-reflection film peels off easily, and therefore films with low adhesive strength to the lens are generally used.

[0008] However, there is still a problem that the coating easily peels off from the lens during the manufacturing stage before the lens unit is installed in a smartphone, etc. This problem can occur not only with anti-reflection coatings but also when various functional coatings are formed on lenses.

[0009] The present invention has been made to solve the above problems, and has an object to provide a lens unit and a coating liquid that can prevent peeling of a functional film during the manufacturing stage.

[0010] Item 1. A lens unit having a first lens, a second lens facing the first lens, and a spacer for maintaining a constant distance between the first lens and the second lens, wherein the first lens and the second lens each have a pair of opposing surfaces, each of the surfaces including a lens surface that functions as a lens, and having a central region on the lens surface where a functional film is provided, and a peripheral region around the central region, and the spacer is disposed in the peripheral region.

[0011] Item 2. The lens unit according to Item 1, wherein each of the lenses has a center thickness of 1 mm or less.

[0012] Item 3. The lens unit according to Item 1 or 2, wherein each of the lenses has an outer diameter of 20 mm or less.

[0013] Item 4. The lens unit according to any one of items 1 to 3, which is built into a mobile device.

[0014] Item 5. The lens unit according to any one of Items 1 to 4, wherein at least one surface included in the first lens and the second lens includes an axisymmetric concave curved surface and a convex curved surface.

[0015] Item 6. The lens unit according to any one of Items 1 to 5, wherein the functional film is an anti-reflection film.

[0016] Item 7. The lens unit according to Item 6, wherein the anti-reflection film is a film made of an inorganic material having a fine uneven structure on the surface.

[0017] Item 8. The lens unit according to Item 7, wherein the inorganic substance is an oxide.

[0018] Item 9. The lens unit according to Item 8, wherein the oxide is aluminum oxide.

[0019] Item 10. The lens unit according to any one of Items 6 to 9, wherein the antireflection film contains functional fine particles and a binder.

[0020] Item 11. The lens unit according to Item 10, wherein the fine particle layer in which the functional fine particles are aligned in the surface direction is a two-layer laminate.

[0021] Item 12. The lens unit according to Item 10 or 11, wherein the functional fine particles have a particle size of 55±10 nm.

[0022] Item 13. The lens unit according to any one of Items 10 to 12, 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 14. A coating liquid for an antireflection coating formed on at least one surface of at least one lens included in the lens unit according to any one of Items 1 to 13, the coating liquid comprising: a plurality of functional fine particles having a refractive index lower than that of the lens surface of the lens; a binder component that is a precursor of a binder that can fix the functional fine particles together in the antireflection coating and can fix the antireflection coating and the lens; and at least one solvent that has a boiling point lower than that of the binder component.

[0024] Item 15. The coating liquid according to Item 14, wherein the solvent includes a solvent having a boiling point of 60° C. or higher and 140° C. or lower.

[0025] Item 16. The coating liquid according to Item 14 or 15, 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.

[0026] Item 17. The coating liquid according to any one of Items 14 to 16, wherein the particle size variation of the functional fine particles is within ±10%.

[0027] Item 18. The coating liquid according to any one of Items 14 to 17, wherein a total mass ratio of the functional fine particles and the binder component to the coating liquid is 20% or less.

[0028] Item 19. 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.

[0029] The present invention is advantageous from the viewpoint of anti-reflection performance.

[0030] 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 photograph of a cross-section of an anti-reflection film taken by an SEM. Fig. 4 is a cross-sectional view showing an example of a nozzle used for spray coating. Fig. 5 is a view showing lenses before coating that are arranged on an installation surface. Fig. 6 is a cross-sectional view showing a lens after a coating liquid composition has been applied.

[0031] An embodiment of an imaging unit including a lens unit according to the present invention will be described below with reference to the drawings. First, the imaging unit and the anti-reflection film (optical thin film) will be described below, followed by a description of the coating liquid. Note that FIG. 1 is a formal schematic diagram used only to explain the various parts and features included in the imaging unit, and does not represent a practical imaging unit in terms of the number of lenses, the shape, size, spacing, and arrangement of each lens, or the spacing between the imaging element and other components. Furthermore, while FIG. 1 uses a case in which three lenses (L1, L2, and L3) are arranged at the sizes, shapes, and spacings shown in the figure for illustrative purposes, it should be noted that this does not limit the scope of the present invention.

[0032] 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.

[0033] 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.

[0034] 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. A black light-shielding film 14 is provided on the first lens L1 to shield the area of ​​the first upper lens surface 10A from light, excluding the lens surface. Similarly, the first lower lens surface 20A is provided with a black light-shielding film 14 on 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 light-shielding film 14 is formed from the lens surface to the vicinity of the spacer 12, which will be described later, and is separated from the spacer 12.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Alternatively, a housing may be provided to house the photographing 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The black light-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.

[0049] The black material as described above is dissolved and dispersed in a solvent, and then a known additive such as a photopolymerization initiator is added to form a liquid black light-shielding film composition. The black light-shielding film composition is then patterned on a 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.

[0050] 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.

[0051] 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.

[0052] Furthermore, the areas (central areas) where the anti-reflection coating is formed on each of the lenses L1 to L3 are the lens surfaces 10A, 10B, 20A, 20B, 30A, and 30B. Therefore, the anti-reflection coating is not formed on the areas (peripheral areas) outside the lens surfaces 10A, 10B, 20A, 20B, 30A, and 30B on each of the lenses L1 to L3. Therefore, the anti-reflection coating is not formed on the areas where the spacer 12 is fixed.

[0053] 2. Coating Liquid for Anti-Reflection Film In the present embodiment, the coating liquid composition constituting the coating liquid contains at least functional fine particles, a binder precursor (binder component), and a solvent. Each material constituting the coating liquid composition will be described below.

[0054] <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.

[0055] 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.

[0056] 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.

[0057] The variation in particle size of the fine particles is preferably ±20% or less, more preferably ±10% or less. 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 particle sizes of 50 arbitrarily selected fine particles by the average particle size.

[0058] 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).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] <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.

[0063] 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 nSi(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. 2 is 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] <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.

[0068] 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.

[0069] <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.

[0070] 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.

[0071] 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.

[0072] The particulate adhesion inhibitor may be a polymer, especially a thermoplastic polymer. The particulate adhesion inhibitor may be a dispersant.

[0073] <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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] <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.

[0079] 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.

[0080] <2-7. Solvent> The solvent may be composed of a single type of solvent, but preferably contains 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. 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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).

[0085] 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.

[0086] <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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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°.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 4. Method for Forming an Antireflection 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 applied by methods such as spin coating, so spray coating is suitable.

[0099] 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.

[0100] First, as described above, the black light-shielding film 14 is formed on the substrate 3. After the coating liquid composition is applied to the substrate 3, it is baked, whereby the solvent evaporates and a binder is produced from the binder precursor, forming an anti-reflection film. The baking temperature is lower than the boiling point of the solvent, for example, 80 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.

[0101] 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.

[0102] 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.

[0103] At least a portion of the particle adhesion inhibitor or dispersant contained in the formed anti-reflective coating may then be removed. Removal of the particle adhesion inhibitor or dispersant can be achieved by various treatments of the anti-reflective coating. Examples of such treatments include plasma treatment, corona treatment, UV cleaning, high-temperature treatment, organic cleaning, acid cleaning, and alkaline cleaning. Plasma treatment can be achieved by irradiating the anti-reflective coating with an oxidizing active species, such as oxygen plasma. Figure 3 shows an example of an anti-reflective coating formed by the above-described method, showing a cross-section of the anti-reflective coating formed by stacking two layers of hollow particles, photographed with an SEM. However, the anti-reflective coatings shown in Figures 2 and 3 are merely examples, and multiple layers of anti-reflective coatings can be stacked. In this case, the refractive index of the anti-reflective layer closest to the lens is close to that of the lens, and the refractive index of the outermost anti-reflective coating can be gradually reduced toward the outermost layer, as described above, to 1.10 to 1.35.

[0104] 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.

[0105] 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 outside 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 can be used as such a nozzle.

[0106] 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.

[0107] 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.

[0108] 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)

[0109] 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.

[0110] (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.

[0111] 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.

[0112] 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.

[0113] (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.

[0114] (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.

[0115] 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).

[0116] (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.

[0117] 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.

[0118] 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. While such anti-reflection films have issues with abrasion resistance and peel resistance, the lens unit described above is provided inside a housing (or inside a spacer) and is almost never exposed to external contact, so even if the above-mentioned problems do occur, they are thought to have little effect. In other words, although the above-mentioned problems do exist, they are hardly affected by them, and therefore good optical properties (low refractive index) can be maintained.

[0119] (2) Since the ratio of the 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, and an anti-reflection film that is easily deformed can be formed.

[0120] (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.

[0121] (4) Because the anti-reflection film is not formed in the area of ​​the lens module where the spacer is fixed, the spacer and the anti-reflection film do not come into contact with each other during the manufacturing of the imaging unit. This prevents the anti-reflection film from coming off due to contact between the spacer and the anti-reflection film. This prevents the generation of dust due to the anti-reflection film coming off.

[0122] 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.

[0123] (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, for example, a 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.

[0124] (2) In the above embodiment, the area where the anti-reflection coating is formed is the surface of each lens surface 10A, 10B, 20A, 20B, 30A, and 30B, but is not limited to this. For example, the anti-reflection coating 2 may be formed in an area outside each lens surface. However, the anti-reflection coating 2 is not formed in the area where the spacer is fixed in each lens module. That is, in the lenses L1 to L3 of the present invention, it is sufficient that the anti-reflection coating is formed in at least the area including the lens surface (the central area), and the spacer 12 is fixed to the area outside that where the anti-reflection coating 2 is not formed.

[0125] (3) The anti-reflection coating 2 does not have to be a film containing hollow particles as described above, and various configurations are possible. For example, the anti-reflection coating can be formed of an aluminum oxide film having an uneven surface. This point will be described in detail.

[0126] First, an Al2O3 film is formed in the central region of the lens module by ALD. When forming the Al2O3 film 14 by ALD, an Al2O3 film is formed by repeatedly supplying an Al-containing gas and an oxidizer sequentially to form thin unit films of Al2O3, i.e., by alternately supplying the Al-containing gas and the oxidizer, an Al2O3 film with a predetermined thickness is obtained. Specifically, a substrate is placed in a processing chamber, heated to a predetermined temperature, and the processing chamber is evacuated to a predetermined vacuum level. In this state, one cycle for forming a unit film is repeated multiple times: "supply of Al-containing gas → purging of the processing chamber → supply of oxidizer → purging of the processing chamber."

[0127] The Al-containing gas is not particularly limited and may be any commonly used gas, such as trimethylaluminum (TMA): Al(CH). The oxidizing agent may be, for example, H2O, O3, or O2 plasma.

[0128] The thickness of the Al2O3 film in this case is preferably a thickness that allows a desired anti-reflection structure to be obtained by the hydrothermal treatment described below. From this point of view, the thickness is preferably 100 nm or less, and more preferably 10 to 50 nm.

[0129] Next, the Al2O3 film is subjected to a hydrothermal treatment to form fine irregularities on the Al2O3 film. This results in a finely irregular anti-reflection film. The depth of the fine irregularities (the height of the convex portions) is preferably, for example, 100 to 500 nm. The fine protrusions and recesses are preferably formed at a pitch of, for example, approximately 100 nm. This allows for a pitch shorter than the wavelength of the irradiated light, and the fine irregularities are needle- or spindle-shaped, resulting in a continuous change in refractive index along the depth direction, thereby achieving anti-reflection functionality. The fine irregularities are needle- or spindle-shaped, resulting in a continuous change in refractive index along the depth direction, thereby achieving anti-reflection functionality. However, this poses challenges in terms of abrasion resistance and peel resistance. However, since the lens unit described above is installed inside a housing (or a spacer) and is virtually unaffected by external contact, it is believed that even if such issues exist, they will have little impact. The depth of the Al2O3 fine irregularities can be measured using conventional methods. The depth of the Al2O3 fine irregularities can be calculated, for example, by observing the cross section of the film with a scanning electron microscope (SEM) and analyzing the field of view with fluorescent X-rays (SEM-EDX method), mapping each element (including Al, for example) in the thickness direction of the film, and measuring the thickness of the layer in which that specific element (e.g., Al) is continuously contained.

[0130] The hydrothermal treatment method is not particularly limited, but can be performed by, for example, immersing the film in hot water or a high-temperature alkaline aqueous solution, or by exposing the film to water vapor. The immersion time depends on the thickness of the AlO film, but is preferably about 1 second to 30 minutes, more preferably 10 seconds to 10 minutes. In the case of exposing the film to water vapor, the treatment time is preferably 1 minute to 24 hours.

[0131] Although Al2O3 is shown as an example of the film material, this is not limiting. The film material is made of an inorganic material that can be formed by the ALD method. Examples of inorganic materials include oxides, nitrides, sulfides, and elemental metals. Specific examples of oxides include Al2O3, CoO, Er2O3, Fe2O3, Ga2O3, HfO2, ITO, In2O3, MgO, Nb2O5, NiO, SiO2, SnO2, Ta2O5, TiO2, WO3, ZnO, Al-doped ZnO, and ZrO2. Specific examples of nitrides include AlN, CoNx, FeNx, Hf3N4, HfSiON, NbN, NiNx, TiN, and WN. Specific examples of elemental metals include Co, Ni, Pt, and Ru. Specific examples of sulfides include ZnS. In consideration of film stability and handling, an oxide film is particularly preferable, and in consideration of film functionality, an Al2O3 film is particularly preferable.

[0132] (4) The functional film formed on the lens unit of the present invention may be a film other than the anti-reflection film described above, and various functional films such as an anti-fogging film, a water-repellent film, an anti-static film, an anti-fouling film, a heat-resistant film, and a hard coat film may be applied.

[0133] 2 anti-reflection film 21 fine particles 31 binder L1 first lens L2 second lens L3 third lens

Claims

1. A lens unit having a first lens, a second lens facing the first lens, and a spacer for maintaining a constant distance between the first lens and the second lens, wherein the first lens and the second lens each have a pair of opposing surfaces, each of the surfaces including a lens surface that functions as a lens, and each of the lens surfaces has a central region where a functional film is provided on the central region, and a peripheral region surrounding the central region, and the spacer is disposed in the peripheral region.

2. The lens unit of claim 1, wherein each of said lenses has a center thickness of 1 mm or less.

3. The lens unit according to claim 1, wherein each of said lenses has an outer diameter of 20 mm or less.

4. The lens unit of claim 1, which is incorporated into a mobile device.

5. The lens unit according to claim 1, wherein at least one surface included in the first lens and the second lens includes an axisymmetric concave curved surface and a convex curved surface.

6. The lens unit according to claim 1, wherein the functional film is an anti-reflection film.

7. The lens unit according to claim 6, wherein the anti-reflection film is a film made of an inorganic material having a fine uneven structure on the surface.

8. The lens unit according to claim 7, wherein the inorganic material is an oxide.

9. The lens unit according to claim 8, wherein the oxide is aluminum oxide.

10. The lens unit according to claim 6, wherein the anti-reflection film contains functional fine particles and a binder.

11. The lens unit according to claim 10, wherein the fine particle layer in which the functional fine particles are aligned in the surface direction is a laminate of two layers.

12. The lens unit according to claim 10, wherein the functional fine particles have a particle size of 55±10 nm.

13. The lens unit according to claim 10, wherein R>5r, where R is the diameter of the functional fine particles and r is the cross-sectional diameter of the binder.

14. A coating liquid for an anti-reflection coating formed on at least one surface of at least one lens included in the lens unit described in claim 1, comprising: a plurality of functional fine particles having a refractive index lower than that of the lens surface of said lens; a binder component that is a binder precursor and is capable of fixing said functional fine particles together in said anti-reflection coating and of fixing said anti-reflection coating and said lens; and at least one solvent having a boiling point lower than that of said binder component.

15. The coating liquid according to claim 14, wherein the solvent includes a solvent having a boiling point of 60°C or higher and 140°C or lower.

16. The coating liquid according to claim 14, 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.

17. The coating solution according to claim 14, wherein the particle size variation of the functional fine particles is within ±10%.

18. The coating liquid according to claim 14, wherein the total mass ratio of the functional fine particles and the binder component to the coating liquid is 20% or less.

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