WO2025220693A1 - Lens unit and coating liquid - Google Patents

Abstract

A lens unit according to the present invention is for a portable device and is capable of condensing light from outside onto an imaging element. The lens unit comprises a plurality of lenses disposed at prescribed intervals. Each of the lenses has a pair of opposing surfaces, and each of the surfaces has a central region including a lens surface functioning as a lens, and a peripheral region surrounding the central region, the peripheral region including, in at least a portion of the surface, an uneven region in which projections/recesses are provided in which the height difference between the recesses and projections is 50 nm or greater. An anti-reflection film is provided on the surface of the central region and the uneven region in the peripheral region.

Description

Lens unit and coating liquid

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

Technologies for preventing or reducing light reflection from the surface of an article are known.

For example, Patent Document 1 describes a substrate on whose surface a coating containing specific hollow spherical silica-based microparticles and a matrix for forming a coating is formed. These silica-based microparticles have pores inside their outer shells, and the pores contain a solvent or gas. Because the silica-based microparticles have a low refractive index, the coating also has a low refractive index, resulting in excellent anti-reflection performance.

Patent Document 2 describes an anti-reflection film having, from the bottom layer, 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 _ZrO2 . The synthetic resin is a UV- or electron beam-curable synthetic resin.

Patent Document 3 describes an anti-reflection laminate including a coating film formed in one coat 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 and middle parts of the coating film, and the medium to high refractive index particles are unevenly distributed in the middle and lower parts.

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

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, such as in lens units for photography in smartphones, tablet PCs, etc. Such lens units are sometimes provided with a black light-blocking layer around the periphery of the lens surface to prevent unwanted light from entering from outside.

However, the inventors have confirmed that, depending on the surface properties of such a light-shielding layer, external light can be reflected by the light-shielding layer, and this reflected light can be seen from the subject side, resulting in an unattractive appearance.

The present invention has been made to solve the above problems, and aims to provide a lens unit and coating liquid that can suppress reflected light caused by a light-shielding layer.

Item 1. A lens unit for a mobile device capable of condensing external light onto an imaging element,
The lens unit includes a plurality of lenses arranged at predetermined intervals,
the lens has a pair of opposing surfaces;
Each of the faces has a central region including a lens surface that functions as a lens;
a peripheral region including an uneven region around the central region, in which unevenness having a height difference of 50 nm or more is provided on at least a part of the surface;
and
an anti-reflection film is provided on the surface of the concave-convex region of the central region and the peripheral region;
Lens unit.

Item 2. The concave-convex region of the peripheral region is formed by a light-shielding film containing a particulate pigment capable of blocking external light.
Item 1. The lens unit according to item 1.

Item 3. The portable device is housed in a transparent cover member and is built into the portable device.
Item 3. The lens unit according to item 1 or 2.

Item 4. The lens unit described in any one of items 1 to 3, wherein the lens unit includes a lens having a center thickness of 1 mm or less.

Item 5. The lens unit described in any one of Items 1 to 4, wherein the lens unit includes lenses each having an outer diameter of 20 mm or less.

Item 6. The lens unit described in any one of Items 1 to 5, wherein the lens unit includes a lens having at least one surface that includes an axially symmetric concave curved surface and a convex curved surface.

Item 7. The lens unit described in any one of items 1 to 6, wherein the anti-reflection film contains functional fine particles and a binder.

Item 8. The lens unit described in Item 7, wherein the fine particle layer in which the functional fine particles are aligned in the surface direction is a two-layer laminate.

Item 9. The lens unit described in Item 7 or 8, wherein the functional fine particles have a particle size of 55±10 nm.

Item 10. The lens unit according to Item 8, wherein R>5r.
Here, R is the diameter of the functional fine particles, and r is the cross-sectional diameter of the binder.

Item 11. A lens unit described in any one of Items 1 to 10, wherein the anti-reflection film is a film made of an inorganic material having a fine uneven structure on its surface.

Item 12. The lens unit described in Item 11, wherein the inorganic substance is an oxide.

Item 13. The lens unit described in Item 12, wherein the oxide is aluminum oxide.

Item 14. A coating liquid for an antireflection film 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, 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 in the anti-reflection film and fix the anti-reflection film and the lens together;
At least one solvent having a boiling point lower than that of the binder component;
A coating solution containing the above.

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.

Item 16. The coating liquid according to Item 14 or 15, wherein the mass ratio of the functional fine particles to the total of the functional fine particles and binder component is 80% or more.

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

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

Item 19. An optical thin film on a light control member,
The composition includes fine particles and a binder that fixes the fine particles,
the ratio of the binder to the fine particles is 0.5 or less by mass;
The number of defects is 5 or less,
Optical thin film.

The present invention is advantageous from the perspective of anti-reflection performance.

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. 1 is a photograph of a cross section of an anti-reflection film taken by an SEM. FIG. 1 is a cross-sectional view showing an example of a nozzle used for spray coating. FIG. 10 is a diagram showing lenses before coating arranged on a mounting surface. FIG. 2 is a cross-sectional view showing a lens after a coating liquid composition has been applied. This is a photo taken from the outside of the smartphone's camera unit. FIG. 8 is an enlarged view of the area indicated by the square in FIG. 7, and is a photograph showing a case where an anti-reflection film is not formed on the black resist layer. FIG. 8 is an enlarged view of the area indicated by the square in FIG. 7, and is a photograph of the case where an anti-reflection film is formed on a black resist layer.

Below, one embodiment of an imaging unit including a lens unit according to the present invention will be described with reference to the drawings. First, the imaging unit and anti-reflection film (optical thin film) will be described, followed by a description of the coating liquid.

<1. Imaging unit>
FIG. 1 is a cross-sectional view of an imaging unit according to this embodiment. This imaging unit is installed in a device (sometimes referred to as a mobile device) such as a smartphone, tablet PC, or laptop 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 installed. Note that FIG. 1 is a schematic diagram for explaining the various parts 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. Also, for convenience of explanation, 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.

Lens unit 100 consists 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 (top side in Figure 1) via spacers 12. As shown in the figure, the surface of each lens is curved.

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 in the area excluding the lens surface. The shape of the pattern of the black light-shielding film 14 is not limited; it is sufficient that the black light-shielding film 14 is formed in a pattern that has openings where it intersects 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.

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 has a second upper lens surface 10B with a concave lens surface, and the lower surface has a second lower lens surface 20B with a convex lens surface. A black light-shielding film 14 is provided on the light-incident surface of the second lens L2, in the area excluding the lens surface of the 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 the area excluding the lens surface of the second lower lens surface 20B.

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 lens surface with a curved shape such as an aspherical surface, and the lower surface is formed with a third lower lens surface 30B having a lens surface with a curved shape such as an aspherical surface. The area of the third upper lens surface 30A close to the optical axis is convex on the image side (upper side of the drawing) and symmetrical about the optical axis, while the peripheral area is concave on the image side and symmetrical about the optical axis. On the other hand, the third lower lens surface 30B has the opposite shape to the third upper lens surface 30A. Because the peripheral area of a lens with this shape is concave, the coating liquid described below tends to accumulate in this area, preventing a uniform film from being formed, and there is a risk of not achieving an effective 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. Note that the aspherical shape of the third lens L3 shown in Figure 1 is just an example, and other shapes may also be used.

In addition, a black light-shielding film 14 is provided on both surfaces of the third lens L3, excluding the lens surfaces of each of the lenses 30A and 30B.

The six lens surfaces 10A, 10B, 10C, 20A, 20B, 30A, and 30B described above are all formed in shapes that are rotationally symmetrical about the center of the optical axis. Each lens L1, L2, and L3 is supported by a spacer 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 shown in Figure 1 shows a cross section including the optical axis.

Furthermore, a sensor substrate W is arranged below the spacer 12. Therefore, the sensor substrate W is arranged with a gap between it and the third lens L3. For example, the sensor substrate W is formed by cutting out a wafer made of a semiconductor material such as silicon into a generally rectangular shape in 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 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 formation processes, photolithography processes, etching processes, impurity addition processes, and the like, and forming electrodes, insulating films, wiring, and the like on the sensor substrate W.

The spacer 12 is cylindrical, with three annular grooves 121 formed on its inner surface at intervals in the axial direction. The outer periphery of each lens L1, L2, and L3 fits into each groove 121, thereby holding each lens L1, L2, and L3 at a distance on the spacer 12. The spacer 12 may also be a component 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 that passes through the lenses from entering the solid-state imaging element D. In this case, the spacer 12 corresponds to the cover member of the present invention, and prevents external light and dust from entering the lens unit. 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.

With the above 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 imaging device D.

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 outside the lens area (area that functions as a lens) of each lens L1, L2, and L3, but in addition to attaching each lens to a single spacer as described above, spacers can also be attached between each lens L1, L2, and L3 to form a gap.

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. In this case, the housing corresponds to the cover member of the present invention, and prevents external light and dust from entering the lens unit.

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

The imaging unit configured as described above is reflow mounted on a circuit board (not shown) built into a smartphone or similar device. Paste solder is printed on the circuit board in advance at the location where the imaging unit will be mounted, and the imaging unit is placed on top of it. The circuit board containing the imaging unit is then subjected to a heating process such as infrared irradiation or hot air blowing, and the imaging unit is welded to the circuit board.

Each of the lenses L1, L2, and L3 can be formed from resin. Examples of such resins that can be used include UV-curable resin, thermosetting resin, and thermoplastic resin. However, considering the reflow mounting of the imaging unit described above, resins with a relatively high glass transition point, such as 110°C or higher, are preferred, and those with a glass transition point of 250°C or higher are even more preferred.

Specific 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.

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

After dissolving and dispersing the black material described above in a solvent, 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 a lens module using a known method to form the black light-shielding film 14 described above. This type of black light-shielding film 14 generally has a height difference between the protrusions and recesses of 50 nm or more. In addition to the patterning described above, a film-like black light-shielding film 14 may also be used. The height of the protrusions and recesses in the light-shielding film can be measured using conventional methods. For example, the height of the protrusions and recesses in the light-shielding film can be calculated by observing the cross section of the film using a scanning electron microscope (SEM) and performing fluorescent X-ray analysis of the field of view (SEM-EDX method) to map each element in the thickness direction of the film, and measuring the thickness of the elements that make up the protrusions and recesses in the light-shielding film.

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

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, and more preferably 0.5 mm or less. Furthermore, the outer diameter K of each lens is preferably 20 mm or less, and more preferably 10 mm or less.

Furthermore, the area (central area) where the anti-reflection film is formed in each of the lenses L1 to L3 is the lens surface 10A, 10B, 20A, 20B, 30A, and 30B. The black light-shielding film 14 is formed in at least a portion of the area outside the central area (peripheral area). In this embodiment, the anti-reflection film is also formed on the black light-shielding film 14. The anti-reflection film formed on the lens surfaces 10A, 10B, 20A, 20B, 30A, and 30B and the anti-reflection film formed on the black light-shielding film 14 are the same and can be formed simultaneously, as described below. Note that the black light-shielding film 14 does not have to be formed over the entire peripheral area; it is sufficient to form the black light-shielding film 14 according to the required performance. In the peripheral area, the anti-reflection film is formed on the black light-shielding film 14, and it is not necessary to form it in other areas. In particular, it is preferable not to form the anti-reflection film in the area fixed to the spacer 12.

<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.

<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, 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 such as 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.

As the fine particles, for example, hollow fine particles can be used. Hollow fine particles are advantageous for lowering the refractive index of the anti-reflection film. As 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 inside, for example, fine particles whose voids are exposed to the outside. Porous fine particles are also possible.

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, or even 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 maximum particle size of 50 randomly selected microparticles. The average particle size mentioned here is based on the so-called primary particle size.

The variation in particle size of the microparticles is preferably ±20% or less, and more preferably ±10% or less. The variation in the average particle size of the microparticles 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 randomly selected microparticles by the average particle size.

The refractive index of the microparticle at the wavelength of the D line (589.3 nm) is smaller than the refractive index n _SB of the lens, and is, for example, 1.10 to 1.40, preferably 1.15 to 1.40, and more preferably 1.17 to 1.35. Note that the refractive index of the microparticle is not the refractive index of the material that forms 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 calculated by, for example, the effective medium approximation method using the Bruggemann equation, by obtaining representative or average values for the approximate spherical size of the microparticle, the material and thickness of the microparticle's outer shell, etc.

The number of functional microparticles 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 microparticles. Note that the diameter R of the microparticles is the average particle size of the microparticles mentioned above.

This allows the anti-reflection coating 2 to be formed in multiple layers, as described below. 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 impact on the optical properties can be minimized even if one fine particle peels off.

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 will be 90-130 nm due to the particle size range. Within this range, an anti-reflection effect can be achieved in the visible light band due to optical interference.

<2-2. Binder and its precursor>
The binder functions to bind the fine particles to each other and to the underlying structure, such as the substrate (in this embodiment, the lens). The binder fixes the 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. The boiling point of the binder precursor (binder component) is higher than the boiling point of the solvent described below.

The binder may contain an organic component in addition to the 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. An inorganic-organic composite binder may be provided, for example, from a silicon alkoxide represented by the formula R ² _n Si(OR ¹ ) _4-n . Here, R ¹ is an alkyl group having 1 to 4 carbon atoms, R ² is an organic group that provides the organic component to the binder, and n is 1 or 2, particularly 1. R ² is not particularly limited and may be an aliphatic group or an aromatic group, or may contain a heteroatom. ^{R 2} may be a hydrocarbon group having 1 to 10 carbon atoms, particularly an alkyl group having 1 to 10 carbon atoms, or even 1 to 4 carbon atoms. Silicon alkoxides (trialkoxysilanes) in which n is 1 provide binders called silsesquioxanes.

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

The binder may be supplied from only one type of precursor, but can also be supplied from two or more types of precursors. One example of a combination of two types of precursors is an alkyltrialkoxysilane and a tetraalkoxysilane. Here, too, the number of carbon atoms in the alkyl group is not particularly limited; for example, the alkyl group contained in the alkoxy group has 1 to 4 carbon atoms, and for example, the alkyl group bonded to the silicon atom has 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.

Metal alkoxides such as silicon alkoxides may be contained in the coating liquid composition as a hydrolysate. The hydrolysate may be a partial hydrolysate in which hydrolysis has progressed partially. The binder precursor may be a metal alkoxide or a hydrolysate thereof, in particular an alkoxysilane or a hydrolysate thereof.

<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, differences in ^R1 in the above general formula do not affect the ratio. The ratio of 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, allowing for the formation of a flexible anti-reflective coating.

Furthermore, the total mass ratio of the functional fine particles and binder precursor to the coating liquid is preferably 20% or less, and more preferably 10% or less. This increases the amount of solvent in the coating liquid, making it easier to create a porous structure in the anti-reflective coating.

<2-4. Fine particle contact inhibitor>
It is desirable to add a fine particle adhesion inhibitor to the coating liquid composition.

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. The particle adhesion inhibitor also desirably has a boiling point higher than that of the solvent. When the coating liquid composition contains multiple 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.

The particle 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 particle adhesion inhibitor may have a viscosity higher than the viscosity of all of the compounds contained as solvents. The relatively high viscosity of the particle 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 particle adhesion inhibitor may be higher than the viscosity of the second solvent. Viscosity can be measured at room temperature (25°C) using a vibration viscometer (e.g., Sekonic Corporation, probe: PR-10L, controller: VM-10A). When the particle adhesion inhibitor contains a solvent, the viscosity is measured after removing the solvent.

The particulate adhesion inhibitor may be a polymer, particularly a thermoplastic polymer. The particulate adhesion inhibitor may also be a dispersant.

<2-5. Dispersants>
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 a boiling point as exemplified for the particulate adhesion inhibitor. The dispersant can have a viscosity as exemplified for the particulate adhesion inhibitor.

Anionic polymer dispersants have anionic groups, such as carboxylate and sulfonate groups. Furthermore, anionic polymer dispersants have a polymeric molecular structure, i.e., a molecular structure containing repeating units. Anionic polymer dispersants may be either homopolymers or copolymers. It is desirable for anionic polymer dispersants to have anionic groups in the repeating units.

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 salts include alkali metal salts such as sodium salts and potassium salts. Carboxylic acids derived from maleic anhydride can also exist as sodium salts, etc.

Polymer dispersants have an average molecular weight of 2000 or more, which is relatively larger than the low-molecular-weight dispersants that are general-purpose surfactants, and they act effectively on fine particles. The molecular weight of polymer dispersants 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. There is no particular upper limit to the molecular weight, but it is, for example, 200,000 or less, or even 100,000 or less. Polymer dispersants may be anionic, nonionic, or cationic, but anionic or nonionic dispersants are preferable.

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.

<2-6. Amount of fine particle contact inhibitor>
The amount of the fine particle adhesion inhibitor or dispersant blended relative to the fine particles may be, on a mass basis, 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. 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 even 10 or more and 100 or less.

Like a binder, a particle adhesion inhibitor or dispersant can function to maintain the spacing between particles. When a particle adhesion inhibitor or dispersant is included, the ratio of the total amount of binder and particle adhesion inhibitor or dispersant to the amount of particles is desirably 0.5 or more. This ratio is also stated 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. There is no particular upper limit to this ratio, and it may be 1000 or less, and in particular 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.

<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. 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.

The first and second solvents 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 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 titrated into a coating liquid composition to be applied by spray coating, particularly to a curved surface by spray coating.

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

As will be described later, the boiling point and surface energy of the solvents 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 a film is formed by spray coating, as described below, it will volatilize before reaching the lens. On the other hand, the second solvent has a higher boiling point than the first solvent, so when it is ejected from the nozzle by spray coating, it reaches the lens and adheres to the lens as droplets. The droplets that adhere to the lens then spread over the lens surface and form a film. In this case, if the surface energy of the second solvent is not high, the liquid will not spread sufficiently, which can 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 should be 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.

High boiling point solvents can be broadly divided into (A) those with a high molecular weight and a high boiling point, and (B) those with a smaller molecular weight than (A) but with strong hydrogen bonds. (B) solvents have a 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).

In addition, any ordinary surface energy measurement method can be used to measure the surface energy of a solvent. For example, it can be measured using the lubrication method, where a platinum ring is placed horizontally on the liquid surface, then pulled up and the force that balances the surface tension acting on the ring at the moment it tries to fall off the liquid surface is measured using a balance.

<2-8. Other ingredients>
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 the 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.

<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.

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, allowing the anti-reflection coating 2 to have a porous structure. For such a porous structure, it is preferable that the porosity be 50% or more.

The antireflection coating 2 has a refractive index n _L1 of 1.10 to 1.35 and a thickness t _L1 of 80 nm to 150 nm. With this configuration, the antireflection coating 2 can exhibit high antireflection performance. The refractive index n _L1 is the refractive index at the D-line (wavelength 589.3 nm). Note that, for the sake of convenience, the substrate 3 is depicted as flat in FIG. 2, but in reality it is a lens having a curved surface.

In the antireflection coating 2, for example, in the reflection spectrum showing the wavelength and the reflectance for light with a wavelength of 300 nm to 1200 nm incident at an incident angle of 5°, the minimum reflectance r _min ^300-1200 within the wavelength range of 300 nm to 1200 nm can be 1% or less. The reflectance r _min ^300-1200 is preferably 0.5% or less, and more preferably 0.2% or less. Hereinafter, unless otherwise specified, the reflectance of an antireflection coating or the like refers to the reflectance determined from the reflection spectrum when light with a wavelength of 300 nm to 1200 nm is incident at an incident angle of 5°.

In the antireflection coating 2, the minimum reflectance r _min ^400-800 within the wavelength range of 400 nm to 800 nm is not limited to a specific value. The reflectance r _min ^400-800 is, for example, 0.5% or less. In this case, the antireflection coating 2 is more likely to exhibit high antireflection performance. The reflectance r _min ^400-800 is preferably 0.2% or less.

In the antireflection coating 2, the range λ _range/2.5 , within which the reflectance is 2.5% or less within the wavelength range of 300 nm to 1200 nm, is not limited to a specific value. The range λ _range /2.5 is, for example, 400 nm or greater. This allows the antireflection coating 2 to more easily exhibit high antireflection performance. The range λ _range/2.5 may be 450 nm or greater, or may be 500 nm or greater. Unless otherwise specified below, the wavelength and wavelength range corresponding to a given reflectance also refer to the wavelength determined from the reflection spectrum.

In the antireflection coating 2, the range λ _range/1.0 , in which the reflectance is 1.0% or less in the wavelength range of 300 nm to 1200 nm, is not limited to a specific value. The range λ _range /1.0 is, for example, 250 nm or more. This makes it easier for the antireflection coating 2 to exhibit high antireflection performance. The range λ _range/1.0 may be 300 nm or more, 350 nm or more, or 400 nm or more.

When the refractive index of the substrate (lens) is n _sb and the refractive index of the antireflection coating is n _L1 , it is possible to adjust the optical thickness of the antireflection coating to ¼ of a predetermined wavelength λ. In this case, the smaller the absolute value of n _sb -n _L1 ² , the lower the reflectance at the wavelength λ corresponding to that refractive index. For this reason, a low effective refractive index of the antireflection coating 2 may be desirable from the perspective of reducing reflectance. When a low refractive index is required for the antireflection coating, it is advantageous for the antireflection coating to contain hollow microparticles.

In the example of Figure 2, the substrate (lens) 3 and the anti-reflection coating 2 are in direct contact, but this is not limited thereto, 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, while the surface of the anti-reflection coating 2 is exposed, this is not limited thereto, and the surface of the anti-reflection coating 2 may be covered with another layer.

Furthermore, where 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 part where fine particles connect when observing the cross-section of the film with a transmission electron microscope or scanning electron microscope, as shown in the schematic diagram of Figure 2. In this case, the thickness of the part where recognizable fine particles connect within the observation field may be measured, and the average value of these may be used as the value of r.

Furthermore, the arrangement of the microparticles in each layer 21, 22 is not particularly limited, but can be, for example, square closest packing. This allows the porosity to be 50% or more.

4. Method for forming 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 applied by methods such as spin coating, so spray coating is suitable.

Anti-reflective coatings formed by spray coating using a coating liquid composition containing fine particles, a binder precursor, and a solvent are more likely to develop micro-defects than optical thin films formed by other coating processes. One cause of this is thought to be the adhesion of aggregates of fine particles. By using the coating liquid composition described above, 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 used on curved surfaces, and is also a coating process that can continuously form films on multiple substrates.

First, the black light-shielding film 14 is formed on the substrate 3 as described above. Then, a coating liquid composition is applied to the central and peripheral regions, including on the black light-shielding film 14, and then baked. This evaporates the solvent, produces a binder from the binder precursor, and forms 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.

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.

After the coating liquid composition has been applied to the substrate, the action of the second solvent causes the coating liquid composition to spread over the curved substrate 3. The second solvent then evaporates during the baking process. Furthermore, the binder can be made to barely evaporate during the baking process. In other words, by including a metal alkoxide, which is a binder precursor, as a hydrolyzate, the binder precursor contained in the coating liquid composition can be made to barely evaporate during the baking process. This increases the controllability of the formation of the anti-reflective film.

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, depicting a cross-section of an anti-reflective coating with 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 coating can be laminated. 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 layer can be gradually reduced toward the outermost layer, as described above, to 1.10 to 1.35.

There are various methods for spray coating, but one example is shown below. Figure 4 is a cross-sectional view showing an example of a spray nozzle used for spray coating. As shown in Figure 4, this spray nozzle has a storage section 91 that stores the coating liquid composition, and an annular liquid flow path 93 is formed that extends from this storage section 91 toward the nozzle's discharge 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 discharge outlet 92 is discharged downward while swirling.

Furthermore, an annular air flow path 94 extending toward the nozzle outlet 92 is formed outside the storage section 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. An example of such a nozzle that can be used is one manufactured by SHIMADA APPLI.

The discharge outlet 92 of the spray nozzle 9 configured as described above is preferably at a height of 25 mm to 35 mm from the lens to be coated. Furthermore, the amount of coating liquid composition discharged per unit time is preferably 0.1 ml/min to 0.3 ml/min. The amount of liquid discharged per unit time may also be determined by collecting the liquid discharged from the spray nozzle for one minute and measuring its volume.

As shown in Figure 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. As a result, the droplets that make up the mist within the swirling flow are swept inward by the swirling flow. Furthermore, droplets that fall outside the swirling flow are repelled further out by the swirling flow. In other words, the repelled droplets do not adhere to the lens. However, droplets that adhere to the lens spread over the lens surface and form a film. Therefore, if a lens is placed in this region N1 and the coating liquid composition is applied, an appropriate coating film will be formed.

On the other hand, in region N2, 45 to 55 mm away from the outlet 92, the swirling flow of the coating liquid composition weakens due to its distance from the outlet 92. As a result, the droplets that make up the mist within the swirling flow are not prevented from flowing to the outside of the swirling flow. Furthermore, because the swirling flow is weak, droplets that reach the outside of the swirling flow are not repelled farther and may end up adhering to the lens. Therefore, if a lens is placed in region N2 and the coating liquid composition is applied, uncontrolled droplets will adhere to the lens as scattered marks, potentially resulting in a defective product. Note that such scattered marks (the number of defects is preferably 5 or less)

As shown in Figure 5, when spray coating lenses L, multiple lenses L (e.g., 5-20 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 5-30 mm, and the spray nozzle 9 is moved over each lens in turn to apply the coating. In other words, the coating liquid composition is continuously applied to multiple lenses L. Therefore, the following problems may occur, particularly if the height of the spray nozzle 9 is outside the above-mentioned range or the amount of coating is small. Note that the spacing and arrangement of the lenses L are not as critical 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. In other words, while the lens diameter and spacing described above are 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.

(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)
In this case, the coating area of the coating liquid composition ejected from the spray nozzle 9 becomes wider. Therefore, when the coating liquid composition is continuously applied to a plurality of lenses L, droplets of the above-mentioned coating liquid composition may adhere to the lenses L before application. When the droplets thus adhered dry, they leave scattered marks, and the coating liquid composition is applied onto these marks, so that the completed lenses L exhibit uneven discoloration such as color unevenness. Similarly, when droplets adhere to the lenses L after application, similar discoloration occurs.

However, if the height of the spray nozzle 9 is increased further, such as to 60 mm or more, the solvent becomes more likely to volatilize. As a result, less liquid reaches the lens, and less liquid flows to the center of the concave surface. As a result, although splash marks can be observed, color unevenness is less likely to occur.

To prevent such discoloration, the following measures can be taken, for example.
(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) By setting the distance between the discharge port 92 of the spray nozzle 9 and the lens L to the appropriate distance described above, uneven discoloration can be reduced.

(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)
In this case, there is a possibility that the thickness of the coating liquid composition applied to the lens L will become thick. This is for the following reason.

(1) The area where the coating liquid composition is applied is narrow because the distance between the spray nozzle 9 and the lens L is small. If the discharge amount is constant, if the area of the applied area is small, the film thickness immediately after application (immediately after the coating liquid composition adheres to the lens L) will be thick.
(2) The solvent contained in the coating liquid composition does not evaporate sufficiently due to the small distance between the spray nozzle 9 and the lens L. This results in a thick film thickness immediately after coating.

In particular, because substrates such as lenses are curved, if a coating liquid composition is applied to the concave surface of lens L, for example, the excess coating may flow toward the bottom of the concave surface before drying, as shown in Figure 6, resulting in unacceptable deviations in film thickness. This may prevent appropriate refractive index and reflective performance from being achieved, and may also cause appearance problems, such as uneven color due to uneven reflection. On the other hand, if 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 unacceptable deviations in film thickness. The above phenomenon can occur if a large amount of coating liquid composition is applied in (a) above.

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

Furthermore, if the height of the spray nozzle 9 is high when there is little binder, droplets of the coating liquid composition will scatter around, resulting in a defective anti-reflection film formed on the lens L. Meanwhile, 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 above-mentioned aggregation inhibitor.

<5. Features>
The lens unit according to this embodiment has the following advantages.
(1) Because the anti-reflection coating contains fine particles such as hollow fine particles having voids, it is possible to form an anti-reflection coating with a porous structure, which allows a low refractive index to be achieved.
(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.

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

(4) By forming the black light-shielding film 14 as described above, it is possible to prevent light unnecessary for photography from entering the photographing unit. However, there is a problem in that light reflected by the black light-shielding film 14 is visible from the subject side when photographing. To explain in more detail, for example, materials such as pigments contained in the black light-shielding film 14 normally absorb light from outside, but if the film has a flat reflective surface, light may be reflected from that reflective surface. When the subject is a person, this reflected light is visible during photography and can be distracting. Therefore, in this embodiment, an anti-reflection film is formed on the black light-shielding film 14 as described above, thereby preventing such reflections.

An example is shown below. Figure 7 is a photograph of a smartphone's camera unit taken from the outside. Figures 8 and 9 are enlarged views of the area surrounded by a square in Figure 7. However, Figure 7 shows an example in which no anti-reflection film is formed on the black light-shielding film 14, while Figure 9 shows an example in which an anti-reflection film is formed on the black light-shielding film 14. As shown in Figure 8, when no anti-reflection film is formed, reflected light is observed on the periphery of the black light-shielding film 14. On the other hand, as shown in Figure 7, when an anti-reflection film is formed, reflected light on the periphery of the black light-shielding film 14 is suppressed. Therefore, by forming an anti-reflection film on the black light-shielding film 14, reflected light from the black light-shielding film 14 visible from outside the imaging unit can be suppressed, and the subject can be prevented from being bothered by reflected light. Note that in the examples of Figures 7 to 9, there are areas where reflection occurs on the periphery of the black light-shielding film 14, but this is just one example, and the inventor has confirmed that reflection can occur in any area of the black light-shielding film 14.

6. Modified Examples
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. The following modifications can be combined as appropriate.

(1) The lens unit on which the anti-reflection film of the present invention is laminated is not particularly limited, and Figure 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, number, spacer, and configuration of the lens module are not particularly limited. The curved surface that constitutes the lens surface of each lens may be formed so that there is at least one inflection point.

(2) In the above embodiment, a black light-shielding film 14 is formed to prevent light from entering the imaging unit. However, as long as it can block light, it may be formed of materials other than those mentioned above, or of a color other than black. For example, in addition to black pigment, colored organic pigments such as red, blue, yellow, green, white, and purple may be included as necessary. When colored organic pigments are used in combination, it is preferable to use 1 to 40% by mass of red pigment relative to the black pigment, and a preferred red pigment is Pigment Red 254. Examples of white pigments include titanium dioxide, magnesium oxide, barium sulfate, zirconium oxide, zinc oxide, and white lead, but titanium dioxide is preferred because of its excellent shielding properties and ease of industrial use. Pigments other than these black pigments can also be used.

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

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 Al-containing gas and an oxidizer are sequentially supplied to form thin unit films of _{Al2O3 .} This operation is repeated multiple times, i.e., the Al-containing gas and the oxidizer are alternately supplied, to form an _Al2O3 film with a predetermined thickness. Specifically, a substrate is placed in a processing chamber, the _substrate is heated to a predetermined temperature, and the processing chamber is evacuated to a predetermined vacuum level. In this state, one cycle of "supply of Al-containing gas → purging of the processing chamber → supply of oxidizer → purging of the processing chamber" is repeated multiple times to form a unit film.

The Al-containing gas is not particularly limited and may be any commonly used gas, such as trimethylaluminum (TMA): Al( _CH3 ) ₃ . As the oxidizing agent, for example, _H2O , _O3 , or _O2 plasma may be used.

The thickness of the Al ₂ O ₃ film at this time is preferably a thickness that allows a desired anti-reflection structure to be obtained by the hydrothermal treatment described below, and from this point of view, it is preferably 100 nm or less, more preferably 10 to 50 nm.

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 (height of the convexities) is preferably, for example, 100 to 500 nm. The fine convexities and concaves are preferably formed at a pitch of, for example, about 100 nm. This allows for a pitch shorter than the wavelength of the irradiated light, and the shape of the fine irregularities is needle-like or spindle-like, so the refractive index changes continuously in the depth direction, thereby achieving anti-reflection functionality. The depth of _{the Al2O3} fine irregularities can be measured by conventional methods. The depth of the Al ₂ O ₃ fine irregularities can be calculated, for example, by observing the cross section of the film with a SEM (scanning electron microscope) and analyzing the field of view with fluorescent X-rays (SEM-EDX method), thereby 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.

The hydrothermal treatment method is not particularly limited, but can be carried out by, for example, immersing in hot water or a high-temperature _alkaline aqueous solution, or by exposing to water vapor. The immersion time depends on the thickness of the _Al2O3 film, but is preferably about 1 second to 30 minutes, more preferably 10 seconds to 10 minutes. In the case of exposing to water vapor, the treatment time is preferably 1 minute to 24 hours.

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, WN, etc. Specific examples of metal elements include Co, Ni, Pt, Ru, etc. Specific examples of sulfides include ZnS _, etc. Considering the stability and handling of the film, an oxide film is particularly preferable. Furthermore, considering the functionality of the film, _{an Al2O3} film is particularly preferable.

(4) In the above embodiment, the anti-reflection film is formed on the surfaces of each lens 10A, 10B, 10C, 20A, 20B, 30A, and 30B and on the black light-shielding film 14. However, particularly in the peripheral region, the anti-reflection film may be formed in an area other than the black light-shielding film 14. However, it is preferable not to form the anti-reflection film 2 in the area where the spacer 12 is fixed in each lens module. This is because the spacer 12 and the anti-reflection film 2 do not come into contact with each other during the manufacture of the imaging unit. Therefore, peeling of the anti-reflection film 2 due to contact between the spacer 12 and the anti-reflection film 2 can be prevented. This makes it possible to prevent the generation of dust due to peeling of the anti-reflection film.

(5) In the above embodiment, an anti-reflection film is formed on the black light-shielding film 14, but reflection is not limited to the black light-shielding film 14, and it is believed that visible reflected light occurs in areas where the difference in height between the protrusions and recesses is 50 nm or more. Therefore, in the peripheral area, it is preferable to form an anti-reflection film in areas other than the black light-shielding film 14 where protrusions and recesses have a difference in height between the protrusions and recesses of 50 nm or more.

12 Spacer 14 Black light-shielding film 2 Anti-reflection film 21 Fine particles 31 Binder

Claims (18)

A lens unit for a mobile device capable of condensing external light onto an imaging element,
The lens unit includes a plurality of lenses arranged at predetermined intervals,
the lens has a pair of opposing surfaces;
Each of the faces has a central region including a lens surface that functions as a lens;
a peripheral region including an uneven region around the central region, in which unevenness having a height difference of 50 nm or more is provided on at least a part of the surface;
and
an anti-reflection film is provided on the surface of the concave-convex region of the central region and the peripheral region;
Lens unit. the concave-convex region of the peripheral region is formed by a light-shielding film containing a particulate pigment capable of blocking the external light;
The lens unit according to claim 1 . The portable device is housed in a cover member and is built into the portable device.
The lens unit according to claim 1 . The lens unit described in claim 1, wherein the lens unit includes a lens having a center thickness of 1 mm or less. The lens unit described in claim 1, wherein the lens unit includes a lens having an outer diameter of 20 mm or less. The lens unit of claim 1, wherein the lens unit includes a lens having at least one surface including an axially symmetric concave curved surface and a convex curved surface. The lens unit described in claim 1, wherein the anti-reflection film contains functional fine particles and a binder. The lens unit described in claim 7, wherein the microparticle layer in which the functional microparticles are aligned in the surface direction is a laminate of two layers. The lens unit described in claim 7, wherein the functional microparticles have a particle size of 55±10 nm. 9. The lens unit of claim 8, wherein R>5r.
Here, R is the diameter of the functional fine particles, and r is the cross-sectional diameter of the binder. The lens unit described in claim 1, wherein the anti-reflection film is a film made of an inorganic material having a fine uneven structure on its surface. The lens unit described in claim 11, wherein the inorganic material is an oxide. The lens unit of claim 12, wherein the oxide is aluminum oxide. A coating solution for an anti-reflection film formed on at least one surface of at least one lens included in the lens unit according to claim 1, 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 in the anti-reflection film and fix the anti-reflection film and the lens together;
At least one solvent having a boiling point lower than that of the binder component;
A coating solution containing the above. The coating liquid described in claim 14, wherein the solvent includes a solvent having a boiling point of 60°C or higher and 140°C or lower. 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 binder component is 80% or more. The coating solution described in claim 14, wherein the particle size variation of the functional fine particles is within ±10%. 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.