JP7715764B2 - Gradient index lens, rod lens array, image scanner, printer, inspection device, and glass composition - Google Patents

Description

The present invention relates to a gradient index lens, an optical product, an optical device, a glass composition for a gradient index lens, and a method for manufacturing a gradient index lens.

Conventionally, devices that use a Charge-Coupled Device (CCD) to observe defects on the surface of an object are known. For example, Patent Document 1 describes a surface defect detection device equipped with a light source, an illumination means, a focusing means, and an observation means. The observation means consists of an imaging lens and a CCD.

Patent Document 2 describes an inspection device suitable for visually inspecting the photosensitive drums of electrophotographic copiers and printers. This inspection device is equipped with a camera device that photographs the photosensitive drum using multiple one-dimensional CCD cameras arranged in a row.

On the other hand, contact image sensors (CIS) are also known as imaging sensors. CISs are equipped with a rod lens array, which typically uses gradient index lenses.

For example, Patent Documents 3 to 5 describe gradient index lenses. A gradient index lens or gradient index rod lens is a rod-shaped lens with a refractive index distribution in which the refractive index decreases continuously from the center to the periphery. In the gradient index lens described in Patent Document 3, the difference Δn between the refractive index at the peripheral surface of the lens and the refractive index at the central axis is 0.003 or greater. Patent Document 3 suggests that when Δn is less than 0.003, the aperture angle (2θ) becomes smaller than approximately 10°, which is undesirable. In other words, Patent Document 3 is thought to suggest that an aperture angle (θ) of less than 5° is undesirable.

In Patent Document 4, the aperture angle of the gradient index lens in the examples is approximately 10.1 to 12.9°. In Patent Document 5, the aperture angle of the gradient index lens in the examples is 10.1 to 12.0°.

Japanese Patent Application Publication No. 7-27709 Japanese Patent Application Laid-Open No. 2003-75906 Special Publication No. 51-21594 Japanese Patent Application Laid-Open No. 2005-289775 Japanese Patent Application Laid-Open No. 2008-230956

Patent Documents 1 and 2 do not mention the use of a gradient index lens. The gradient index lenses described in Patent Documents 3 to 5 have a large aperture angle. This is hardly advantageous from the perspective of achieving a large depth of field in a gradient index lens, and the gradient index lenses described in Patent Documents 3 to 5 are considered to have a small depth of field. If the depth of field of a gradient index lens is small, for example, when there is variation in the thickness of an object, some parts of the object are in focus and some are out of focus. Furthermore, if a product equipped with a gradient index lens can be used not only in general air conditioning but also in hot and humid environments, the value of the product can be increased.

In view of these circumstances, the present invention provides a gradient index lens that is less likely to produce in-focus and out-of-focus areas on an object even when the object has variations in thickness, and that can be used in high-temperature, high-humidity environments.

The present invention provides
A gradient index lens,
It has a depth of field of 1.5 to 3.0 mm,
the depth of field is determined by subtracting the minimum value from the maximum value of the working distance while maintaining a constant distance between the gradient index lens and the image formation position;
At the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines/mm is 30% or more,
An aperture angle of 3.5° to 5.5°;
Water resistance is grade 1 as determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06-2009.
A gradient index lens is provided.

The present invention provides
A rod lens array is provided which includes the above gradient index lenses arranged in one or more rows in the main scanning direction with their optical axes parallel to one another.

The present invention provides
The rod lens array described above;
a linear light receiving element;
A linear lighting device
Provide an image scanner.

The present invention provides
There are provided a printer including the rod lens array, and an inspection device including the rod lens array .

The present invention provides
Expressed in mole percent,
40%≦SiO ₂ ≦65%
1%≦TiO ₂ ≦10%
0.1%≦MgO≦22%
0.15%≦ZnO≦15%
0.5%≦Li2O _< 4%
2%≦Na ₂ O≦20%
0%≦B ₂ O ₃ ≦20%
0%≦ Al2O3 _{≦ 10} %
0%≦K ₂ O≦3%
0%≦Cs2O _≦ 3%
0%≦Y ₂ O ₃ ≦5%
0%≦ZrO ₂ ≦2%
0%≦Nb ₂ O ₅ ≦5%
0%≦ In2O3 _{≦ 5} %
0%≦La ₂ O ₃ ≦5%
0%≦Ta ₂ O ₅ ≦5%;
containing at least two selected from the group consisting of CaO, SrO, and BaO in an amount of 0.1 mol% or more and 15 mol% or less,
Expressed in mole percent,
2%≦MgO+ZnO,
0.07≦ZnO/(MgO+ZnO)≦0.93,
2.5%≦Li ₂ O+Na ₂ O<24%, and
The condition of 0%≦Y ₂ O ₃ +ZrO ₂ +Nb ₂ O ₅ +In ₂ O ₃ +La ₂ O ₃ +Ta ₂ O ₅ ≦11% is satisfied.
A glass composition is provided .

The gradient index lens described above is less likely to produce in-focus and out-of-focus areas on an object even when the object has varying thicknesses, and is applicable even in hot and humid environments.

FIG. 1 is a diagram for explaining a method for determining the depth of field of an example of a gradient index lens according to the present invention. FIG. 2 is a diagram showing the aperture angle of an example of a gradient index lens according to the present invention. FIG. 3A is a diagram showing an ion exchange process in an example of a method for manufacturing a gradient index lens according to the present invention. FIG. 3B is a graph conceptually showing the refractive index distribution in a gradient index lens. FIG. 4 is a perspective view showing an example of an optical product according to the present invention. FIG. 5 is a cross-sectional view showing an example of an optical device according to the present invention. FIG. 6 is a cross-sectional view showing another example of an optical device according to the present invention. FIG. 7 is a diagram showing yet another example of an optical apparatus according to the present invention. FIG. 8 is a diagram showing yet another example of an optical apparatus according to the present invention. FIG. 9 is a graph showing the relationship between the MTF value and the working distance of the gradient index lenses according to Example 2, Comparative Example 3, and Reference Example 1.

Image data collected during visual inspection of an object must have a resolution sufficient to identify defects on the object. When attempting to obtain high-resolution image data using a camera equipped with a linear CCD sensor, the effective width that can be captured by a single camera becomes smaller. This can make it difficult to capture the entire object with a single camera. For example, if the pixel size corresponding to the required resolution of the image data is 90 μm, the width of the area that can be captured by a camera equipped with a 4096-pixel linear CCD sensor is approximately 370 mm. In this case, to thoroughly inspect an object with a width of 1200 mm, four camera systems equipped with linear CCD sensors and camera lenses must be arranged in the width direction. Installing multiple camera systems equipped with linear CCD sensors increases the manufacturing costs of the device. Additionally, adjustment and maintenance of multiple camera systems is required each time the type of object is changed, increasing the running costs of the inspection.

Therefore, visual inspection of specimens using a CIS is considered. A CIS includes multiple one-dimensional light-receiving elements arranged on a substrate and a rod lens array. In a CIS, the rod lens array forms an erect, life-size image. Using a CIS, a one-dimensional image with a width of 1200 mm can be obtained with a single unit. A rod lens array, for example, is an array of multiple rod-shaped gradient index lenses. A gradient index lens has a refractive index distribution in its radial direction, with the refractive index varying from the center to the periphery in the radial direction of the lens. Compared to conventional camera systems equipped with a CCD sensor and lens, a CIS equipped with a rod lens array can reduce the distance between the image sensor and the object being imaged by approximately one-tenth, offering the advantage of compactness. However, a CIS has a small depth of field (DOF), a characteristic value that indicates the tolerance for the distance between the object being imaged and the lens. This can lead to the problem of in-focus and out-of-focus areas occurring on the specimen when the specimen's thickness varies. As a result, images of out-of-focus areas are not clear, which can lead to defects being overlooked or misidentified.

As mentioned above, the gradient index lenses described in Patent Documents 3 to 5 have large aperture angles, which is hardly advantageous from the perspective of increasing the DOF of the gradient index lens. Therefore, in order to achieve a desired range of DOF in a gradient index lens, the inventors thoroughly reviewed the conditions for the glass composition used to manufacture the gradient index lens. After extensive trial and error, the inventors finally discovered a gradient index lens that can achieve a desired range of DOF. The gradient index lens according to the present invention can be used not only in the technical field of visual inspection of specimens, but also throughout the technical field of image formation, such as image scanners, copiers, facsimiles, and printers.

Embodiments of the present invention will be described below with reference to the drawings. Please note that the following description relates to one example of the present invention, and the present invention is not limited to the following embodiments.

The gradient index lens 1b has a depth of field (DOF) of 1.5 to 3.0 mm. The DOF of the gradient index lens 1b is determined by subtracting the minimum value from the maximum value of the working distance. At the working distance of the gradient index lens 1b, the modulation transfer function (MTF) value at a spatial frequency of 6 lines/mm is 30% or greater.

As shown in FIG. 1 , the DOF of a gradient index lens 1b can be determined by, for example, arranging a lens array 10a, a line pattern 3, and a light-receiving element 2 at a predetermined interval along the optical axis and calculating the MTF value while varying the distance between the lens array 10a and the line pattern 3. The lens array 10a is configured by arranging multiple gradient index lenses 1b in a direction perpendicular to the optical axis. The line pattern 3 has black and white line pairs corresponding to a spatial frequency of 6 lines/mm. The light-receiving element 2 is, for example, a CCD sensor. For example, light emitted from a halogen lamp is passed through a color filter and a light diffuser plate and then irradiated onto the line pattern 3. The color filter may transmit light with a wavelength in the range of 500 to 600 nm, or may primarily transmit light with a wavelength of 530 nm. In this case, the MTF value can be determined as the reproduction ratio of the image (output image) obtained by focusing the image of the line pattern 3 (input image) on the light receiving element 2 by the lens array 10a, which has a predetermined spatial frequency consisting of bright and dark areas, before it is incident on the lens array 10a.

The distance D _max between the line pattern 3 and the light receiving element 2 (distance between the object point and the image point) at which the MTF value is maximized is determined. Then, the positive direction (ΔL>0) and negative direction (Δ
The line pattern 3 is moved to a position (ΔL<0) and the MTF value is calculated at each position. This allows the maximum and minimum values of the working distance to be calculated by setting the allowable range of a predetermined MTF value. As a result, the DOF of the gradient index lens 1b can be determined. Note that when ΔL>0, the distance between the line pattern 3 and the lens array 10a is the distance D _max
On the other hand, when ΔL<0, the distance between the line pattern 3 and the lens array 10a is smaller than the working distance corresponding to the distance _Dmax . When ΔL=0, the distance between the line pattern 3 and the lens array 10a is equal to the working distance corresponding to the distance _Dmax .

Since the gradient index lens 1b has a DOF within the above range, it is advantageous for obtaining image data suitable for visual inspection of objects with uneven thickness, steps, or irregularities. Therefore, the gradient index lens 1b can contribute to improving the accuracy of visual inspection of objects and raising the level of inspection standards.

The DOF of the gradient index lens 1b is preferably 1.5 mm or more, more preferably 1.8 mm or more, and even more preferably 2 mm or more. The DOF of the gradient index lens 1b is preferably 2.8 mm or less, and more preferably 2.5 mm or less.

The working distance corresponding to the object point-image point distance D _max at which the MTF value is maximum is, for example, 15
mm or more, and preferably 18 mm or more. When the object point-to-image point distance D _max is within this range, the DOF is in an appropriate range. By incorporating a rod lens array including such a gradient index lens 1b into an inspection device, it is possible to inspect objects with steps. In addition, the rod lens array can be kept at an appropriate distance from the object, making it easier to assemble the optical system.

The gradient index lens 1b has an aperture angle θ of, for example, 3 to 6°. This makes it easy to adjust the DOF of the gradient index lens 1b to a desired range. The aperture angle θ of the gradient index lens 1b is defined, for example, as shown in FIG. 2. The aperture angle θ is the maximum value of the angle between the optical axis and a ray that can be incident on one end of the optical axis of the gradient index lens 1b. In FIG. 2, F1 is the object plane, and F2 is the light receiving surface (imaging surface) of a light receiving element or the like. Z ₀ is the length of the gradient index lens 1b. _{L 0} is the object plane F when the MTF value is maximum.
where L _{i is the distance between the image plane F1 and the gradient index lens 1b, and L i} is the distance between the image plane F2 and the gradient index lens 1b when the MTF value is maximized. In FIG. 2, the lens array 10a forms a substantially erect, equal-magnification imaging system, and the distance L _i is substantially equal to the distance L _o . In FIG. 2, X _o is the field radius of the gradient index lens 1b. The aperture angle θ of the gradient index lens 1b can be determined, for example, according to the method described in the Examples. Note that in the methods described in the Examples, the aperture angle θ may be determined using the refractive index n _o at the center of the gradient index lens 1b instead of the refractive index N c of the glass fiber before ion exchange. N c or n _o can be determined using the V-block method described in Japanese Industrial Standards (JIS) B 7071-2:2018.

The aperture angle θ of the gradient index lens 1b may be 3.5° or more, or may be 3.7° or more. The aperture angle θ of the gradient index lens 1b is preferably 5.5° or less, and more preferably 5.2° or less.

The gradient index lens 1b may have a refractive index distribution constant (√A) of, for example, 0.130 to 0.230 mm ⁻¹ . √A denotes the square root of A. If the refractive index of the gradient index lens at radius r is n(r), then n(r)=n ₀ ×{1−(A/2)×r ² } holds in the paraxial region of the lens. If the refractive index distribution constant √A is within this range, the aperture angle θ of the gradient index lens 1b is likely to fall within a desired range. As a result, the DOF of the gradient index lens 1b is likely to be adjusted to a desired range.

The refractive index distribution constant of the refractive index gradient lens 1b may be 0.140 mm ⁻¹ or more, or may be 0.145 mm ⁻¹ or more. The refractive index distribution constant of the refractive index gradient lens 1b is preferably 0.210 mm ⁻¹ or less, and more preferably 0.205 mm ⁻¹ or less.

The imaging distance of an erect image in the gradient index lens 1b is, for example, 45 to 80 mm. This is advantageous from the perspective of adjusting the DOF of the gradient index lens 1b to a desired range.

The imaging distance of an erect image in the gradient index lens 1b may be 47 mm or more, 50 mm or more, 53 mm or more, or 54 mm or more. The imaging distance of an erect image in the gradient index lens 1b may be 75 mm or less, 70 mm or less, or 67 mm or less.

The gradient index lens 1b is typically a rod-shaped or fiber-shaped lens. The gradient index lens 1b has, for example, a refractive index distribution in the radial direction as shown in FIG. 3B. Here, the refractive index n ₀ at the origin in FIG. 3B means the refractive index at the central axis of the gradient index lens 1b. r represents the position in the radial direction of the gradient index lens 1b.

Gradient index lens 1b may, if necessary, have a structure that prevents incident light with an angle of incidence greater than the aperture angle from reflecting off the side surface of the lens and generating noise light (so-called white noise (stray light)). Such a structure may be, for example, a light-absorbing layer or a light-scattering layer provided on the side surface of the lens. For example, gradient index lens 1b may have a core-clad structure in which a colored layer that serves as a light-absorbing layer is disposed on the side surface of the lens, or a structure in which fine irregularities that serve as a light-scattering layer are formed on the side surface.

The gradient index lens 1b is typically a glass lens. The glass composition for the gradient index lens has the following components in mole percent: 40%≦SiO ₂ ≦65%, 0%≦TiO ₂ ≦10%, 0.1%≦MgO≦22%, 0.15%≦ZnO≦15%, 0.5%≦Li ₂ O<4%.
, 2%≦ _Na2O ≦20%, 0%≦ _{B2O3 ≦} 20%, 0%≦ _Al2O3 ≦10%, 0%≦ _{K2O ≦} 3%, 0%≦Cs2O≦3%, 0%≦ _Y2O3 ≦ ₅ %, 0%≦ZrO2 _≦ 2%, 0%≦ _Nb2O5 ≦5%, 0%≦ _{In2O3 ≦ 5} %, 0%≦ _La2O3 ≦5%, and 0%≦ _{Ta2O5 ≦} 5%. In addition, the glass composition for _a refractive index gradient lens contains at least two elements selected from the group consisting of CaO, SrO, and BaO, each in an amount _of 0.1 mol % to 15 mol %. Furthermore, the glass composition for a refractive index gradient lens contains, expressed in mol %, 2%≦MgO+
ZnO, 0.07≦ZnO/ ₍ MgO+ _ZnO )≦0.93, 2.5%≦ _Li2O + _Na2O <24% _{, and} 0%≦ _Y2O3 + _ZrO2 + _Nb2O5 + _In2O3 + _La2O3 +Ta ₂ O ₅ ≦
By using such a glass composition, a gradient index lens having a desired DOF can be obtained.

The gradient index lens 1b can be manufactured, for example, by subjecting a glass wire made of the above-mentioned glass composition to ion exchange treatment.

( _SiO2 )
_SiO2 is an essential component for forming the glass network structure. If the _SiO2 content is less than 40 mol%, the contents of other components necessary for developing the optical properties of a gradient index lens after ion exchange become relatively large, making devitrification more likely. Furthermore, if the content is less than 40 mol%, the chemical durability of the glass composition is significantly reduced. On the other hand, if the content exceeds 65 mol%, the contents of other components, such as alkali components for forming a refractive index distribution, refractive index increasing components, and physical property adjusting components, are limited, making it difficult to produce a practical glass composition. For this reason, the _SiO2 content is 40 mol% or more and 65 mol% or less.

( _TiO2 )
_TiO2 is an essential component that increases the refractive index of the glass composition. Increasing the refractive index of the base glass composition can increase the central refractive index of the gradient index lens obtained from the glass composition. Furthermore, increasing the _TiO2 content can bring the refractive index distribution in the gradient index lens closer to an ideal state, enabling the production of a gradient index lens with excellent resolution. When the _TiO2 content is 10 mol%, no reduction in image resolution is observed based on the resulting lens. However, when the TiO2 content is less than 1 mol%, the image resolution is clearly reduced, making it impossible to obtain a practical lens. On the other hand, when the TiO2 content exceeds 10 mol%, the coloring becomes strong, resulting in large chromatic aberration, making it impossible to obtain a practical lens. Therefore, to obtain a lens that can increase image resolution and has small chromatic aberration, the _TiO2 content is 1 mol% or more and 10 mol% or less. The _TiO2 content is preferably 2 mol% or more and 8 mol% or less.

(MgO)
MgO is an essential component that lowers the melting temperature of the glass composition and increases the refractive index difference (Δn) between the center and periphery of the lens after ion exchange. If the MgO content exceeds 22 mol%, devitrification is likely to occur. Furthermore, if the MgO content exceeds 22 mol%, the contents of other components are excessively reduced, making it impossible to obtain a practical glass composition. Therefore, the MgO content is 0.1 mol% or more and 22 mol% or less. From the viewpoint of achieving a sufficient refractive index difference, the MgO content is preferably 2 mol% or more. If the MgO content is 2 mol% or more, the content of alkaline earth metal oxides (CaO, SrO, BaO) can be more appropriately controlled to further reduce the mobility of alkali ions. That is, the MgO content is preferably 2 mol% or more and 22 mol% or less, more preferably 2% or more and 16% or less.

(ZnO, MgO+ZnO, ZnO/(MgO+ZnO))
ZnO has the effect of improving the weather resistance of the glass composition and the gradient index lens. In the glass composition according to the present invention, ZnO may be added to replace a portion of MgO. From the viewpoint of improving the weather resistance of the glass composition and the gradient index lens, the content of ZnO is 0.15 mol % or more and 15 mol % or less. In this case, the contents of MgO and ZnO are adjusted so that the total content of MgO and ZnO (MgO + ZnO) is 2 mol % or more. In addition, the ratio of the content of ZnO to the total content of MgO and ZnO (ZnO
The contents of MgO and ZnO are adjusted so that the ratio ZnO/(MgO+ZnO) satisfies the following relationship: 0.07≦ZnO/(MgO+ZnO)≦0.93. From the viewpoint of further improving the weather resistance of the glass composition and the gradient index lens, the ZnO content is preferably 3 mol% or more and 15 mol% or less. In this case, MgO+ZnO may be 6 mol% or more, and the condition 0.12≦ZnO/(MgO+ZnO)≦0.93 may be satisfied. From the viewpoint of devitrification resistance, the ZnO content is preferably 8 mol% or less. From the viewpoint of further improving the weather resistance of the glass composition and the gradient index lens, the ZnO content is more preferably 4 mol% or more and 15 mol% or less. In this case, MgO+ZnO may be 6 mol% or more, and the condition ZnO+ZnO may be 6 mol% or more and 22 mol% or less. The sum of MgO and ZnO may be 15 mol % or less. ZnO/(MgO and ZnO) is preferably 0.07 to 0.9, more preferably 0.25 to 0.85, even more preferably 0.25 to 0.8, and particularly preferably 0.3 to 0.8.

( _Li2O )
Li ₂ O is an essential component and is one of _the most important components for obtaining a gradient index lens by ion-exchanging the glass composition of the present invention.
It was previously thought that if the Li 2 O content was low, a sufficient concentration distribution, i.e., a sufficient refractive index distribution, could not be achieved by ion exchange, making it impossible to obtain an appropriate gradient index lens. However, the present inventors have newly discovered that even if a glass composition has a Li ₂ O content of 4 mol % or less, by performing ion exchange under specified conditions, a gradient index lens having an appropriate refractive index distribution and a large DOF can be produced. If the Li ₂ O content exceeds 4 mol %, the resulting gradient index lens is likely to have a large aperture angle and a small DOF. The Li ₂ O content is 0.5 mol % or more, preferably 0.7 mol % or more, and more preferably 1 mol % or more. Furthermore, the Li ₂ O content is 4 mol % or less, preferably 3.5 mol % or less, more preferably 3 mol % or less, and even more preferably 2 mol % or less.

One of the features of the gradient index lens 1b is that it contains less Li ₂ O than various prior art lenses. Previously, there were manufacturing process reasons that made it impossible to reduce the Li ₂ O content.
The present inventors have newly discovered that, by employing new techniques such as limiting the amount of glass wire processed per batch by ion exchange and reducing the initial Li content in the molten salt, it is possible to obtain a gradient index lens that has a smaller aperture angle than conventional lenses and that has practical resolution while suppressing lens aberrations such as field curvature.

( _Na2O )
During ion exchange, Na ₂ O facilitates the ion exchange between Li and the ion-exchange species (ions contained in the molten salt) that replace the Li ions through the so-called mixed alkali effect, thereby maintaining appropriate ion mobility. Maintaining appropriate ion mobility allows for the ion exchange rate to be adjusted appropriately, thereby adjusting the optical characteristics of the gradient index lens. If the Na ₂ O content in the glass composition is less than 2 mol%, the glass becomes hard during glass molding, making molding difficult. In addition, the melting temperature of the glass increases significantly, making lens fabrication difficult. Furthermore, it is difficult to fully achieve the effect of maintaining appropriate ion mobility. On the other hand, if the Na ₂ O content exceeds 20%, the chemical durability of the glass decreases, making it impractical. Therefore, the Na ₂ O content is 2 mol% or more, preferably 5 mol% or more, and more preferably 10 mol% or more. Furthermore, the Na ₂ O content is 20 mol% or less, preferably 17 mol% or less.

( _Li2O + _Na2O )
As described above, the sum of the Li ₂ O content and the Na ₂ O content in the glass composition (Li ₂
The content of Li2O+ _Na2O is 2.5 mol% or more and less than 24 mol%. When the content of _Li2O + _Na2O is within this range, a gradient index lens manufactured using this glass composition can provide an image with good resolution. The content of _Li2O + _Na2O is preferably 6 mol% or more, and more preferably 10 mol% or more.

( _Li2O / _Na2O )
When the ratio of the _{Li2O content to the Na2O content} ( _Li2O / _Na2O ) is large, the resolution of a gradient index lens manufactured using the glass composition may be improved. On the other hand, when the _Li2O / _Na2O ratio is excessively large (for example, 1.0 or more), the gradient index lens manufactured using the glass composition tends to have a large aperture angle and a small DOF. Therefore, the _Li2O / _Na2O ratio is, for example, 0.2 or less, preferably 0.15 or less, and more preferably 0.1 or less.

The above glass composition may further contain the following components:

( _{B2O3 )
B2O3} is an optional component that forms a glass network structure. _It promotes vitrification of the glass composition and adjusts its viscosity without substantially changing the resolving power and aperture angle θ of the resulting gradient index lens. It also slightly slows the ion exchange rate of the glass composition. While the contents of the above-mentioned essential components are within the ranges of the present invention, _B2O3 may be added when the contents of some components become relatively high in the composition, reducing the stability of the glass (e.g., making _it more susceptible to devitrification). Adding _B2O3 reduces the relatively high contents of some of the components without changing the ratio of the contents of the essential components. The content of _B2O3 that can be added without changing the resolving power and aperture angle of the resulting gradient index _lens is, for example, ₂₀ % mol or less. Therefore, _{the B2O3 content} is between 0% mol and 20 mol%. The content is preferably 0 mol % or more and 10 mol % or less, and when the glass composition contains B ₂ O ₃ , the content thereof is preferably 1 mol % or more and 10 mol % or less.

( _{Al2O3 )}
The glass composition for a refractive index gradient lens may contain Al ₂ O ₃ as an optional component, and the content thereof is from 0 mol % to 10 mol %.

(SiO ₂ +TiO ₂ +B ₂ O ₃ )
In the glass composition for a refractive index gradient lens, the total content of SiO ₂ , TiO ₂ , and B ₂ O ₃ (SiO ₂ + TiO ₂ + B ₂ O ₃ ) is, for example, 41 mol % or more and 70 mol % or less, and preferably 50 mol % or more and 70 mol % or less.

(Y ₂ O ₃ , ZrO ₂ , Nb ₂ O ₅ , In ₂ O ₃ , La ₂ O ₃ , Ta ₂ O ₅ )
The glass composition for a gradient index lens may contain at least one component selected from the group consisting of _Y2O3 , _ZrO2 , _Nb2O5 , _In2O3 , _La2O3 , and _Ta2O5 for the purposes of adjusting the refractive index of _the gradient index lens obtained after ion _exchange or improving weather resistance. The total content of these components is 0 mol% or more _and 11 mol% or less, and when the glass composition for _a gradient index lens _contains these components, the total content of these components is preferably 0.2 mol% or more and 6 mol% or less. Furthermore, the total content of these components and the content of ZnO is preferably 15 mol% or less.

( _{Y2O3 )}
The content of Y ₂ O ₃ is preferably 0 mol % or more and 5 mol % or less.

( _ZrO2 )
The content of ZrO ₂ is preferably 0 mol % or more and 2 mol % or less, and when the glass composition for a refractive index gradient lens contains ZrO ₂ , the content thereof is 0.2 mol % or more and 2 mol % or less.

The content of each of Nb ₂ O ₅ , In ₂ O ₃ , La ₂ O ₃ and Ta ₂ O ₅ is preferably 0 mol % or more and 5 mol % or less.

(K ₂ O, Cs ₂ O)
_K2O and _Cs2O are optional components that, like MgO, CaO, SrO, and BaO, have the effect of reducing the mobility of alkali ions due to the mixed alkali effect. The contents of _K2O and _Cs2O are each, for example, 0 mol% or more and 3 mol% or less. From the viewpoint of improving the water resistance of the glass composition for a refractive index gradient lens, the content of _Cs2O is preferably less than 2 mol%, more preferably 0 mol% or more and 1 mol% or less, and even more preferably 0.5 mol% or less. From the viewpoint of improving the water resistance of the glass composition for a refractive index gradient lens, it is desirable that the glass composition for a refractive index gradient lens is substantially free of _Cs2O . In this specification, "substantially free" means that the content of the component in question is less than 0.1 mol%.

(Other ingredients)
The glass composition for a refractive index gradient lens may contain _GeO2 as another component. The content of _GeO2 may be 0 mol% or more and 10 mol% or less. The glass composition for a refractive index gradient lens may also contain at least one additive selected from the group consisting of _SnO2 , _As2O3 , and _{Sb2O3 . SnO2 , As2O3} , and _S
The content of each of _{the b2O3} components may be 0 mol % or more and 1 mol % or less. The glass composition for a refractive index gradient lens may consist essentially of the above components. In this case, the content of each component contained in the glass composition and the relationship between the contents of each component (total and content ratio) satisfy the above-mentioned conditions. In this specification, "consisting essentially of" means that impurities of less than 0.1 mol % are allowed.

(PbO)
The glass composition for the gradient index lens is substantially free of lead (a typical compound is PbO), and the gradient index lens 1b is also substantially free of lead.

The glass composition for a gradient index lens may have a water resistance of Grade 1 as determined in accordance with, for example, Japan Optical Glass Industry Standard (JOGIS) 06-2009. In this case, the glass composition for a gradient index lens has high water resistance, and a gradient index lens manufactured using the glass composition for a gradient index lens also tends to have high water resistance. The glass for forming a gradient index lens may also have a water resistance of Grade 1 as determined in accordance with JOGIS 06-2009.

The glass composition for a gradient index lens contains an oxide of a first alkali metal element. The gradient index lens 1b can be produced, for example, by a method including the following steps (I) and (II).
(I) A glass wire 1a is formed from the above-mentioned glass composition for a refractive index gradient lens.
(II) A glass wire 1a is immersed in a molten salt S containing a second alkali metal element R different from the first alkali metal element Q contained in the glass composition for a refractive index gradient lens, and an ion exchange treatment is performed between the first alkali metal element Q in the glass wire 1a and the second alkali metal element R in the molten salt, thereby forming a refractive index gradient in the glass wire 1a.

In step (II), for example, as shown in FIG. 3A , the glass fiber wire 1 a is placed in the molten salt S in a container V and immersed in the molten salt S for a predetermined time. The molten salt S contains, for example, at least one of potassium nitrate and sodium nitrate. When the glass fiber wire 1 a is immersed in the molten salt S, cations of a first alkali metal element Q, such as Li (lithium), contained in the glass fiber wire 1 a dissolve in the molten salt S. Meanwhile, cations of a second alkali metal element R, such as K (potassium), contained in the molten salt S penetrate the glass fiber wire 1 a. By adjusting the temperature of the molten salt S and the immersion time of the glass fiber wire 1 a in the molten salt S, the ion exchange between the cations of the first alkali metal element Q and the cations of the second alkali metal element R can be appropriately controlled. A concentration distribution of specific monovalent cations occurs within the glass fiber wire 1 a, and a refractive index distribution, as shown in FIG. 3B , is formed in the glass fiber wire 1 a according to this concentration distribution. In this way, a gradient index lens 1b can be manufactured from the glass wire 1a.

The optical product according to the present invention is not limited to a specific product as long as it includes a gradient index lens 1b. For example, a specific lens array can be provided using the gradient index lens 1b. In this case, the lens array may have a zero-dimensional, one-dimensional, or two-dimensional arrangement of the gradient index lenses 1b. A zero-dimensional arrangement is, for example, a configuration in which a single gradient index lens 1b is arranged, and the desired effect is expected from an optical product consisting of a single gradient index lens 1b. A one-dimensional arrangement is a configuration in which multiple gradient index lenses 1b are arranged in a row in a specific direction. This specific direction is referred to as the main scanning direction, and the direction perpendicular to the main scanning direction and perpendicular to the optical axis is referred to as the sub-scanning direction. The multiple gradient index lenses 1b are arranged so that their optical axes are approximately parallel. A two-dimensional arrangement is a configuration in which, in addition to a one-dimensional arrangement, multiple lenses are arranged in a different direction. For example, a configuration in which multiple gradient index lenses 1b are arranged in two or more rows along the main scanning direction can be considered a two-dimensional arrangement. With lens array 10b, it is possible to obtain a wide range of erect, life-size images even if the diameter of each gradient index lens is small.

For example, the lens array 10b shown in FIG. 4 can be provided using gradient index lenses 1b. In the lens array 10b, multiple gradient index lenses 1b are arranged so that their optical axes are approximately parallel. In the lens array 10b, the multiple gradient index lenses 1b are arranged in two rows to form a two-dimensional array. In the lens array 10b, the multiple gradient index lenses 1b are arranged, for example, between a pair of fiber-reinforced plastic (FRP) substrates 5. Between the pair of FRP substrates 5, the spaces between the multiple gradient index lenses 1b and the spaces between the FRP substrates 5 and the gradient index lenses 1b are filled with black resin 7. This integrates the multiple gradient index lenses 1b between the pair of FRP substrates 5. Such a lens array 10b can be fabricated, for example, as follows. First, multiple gradient index lenses 1b are arranged approximately parallel on the surface of one FRP substrate 5, and the lenses are sandwiched between the other FRP substrate 5. The space between the pair of FRP substrates 5 is then filled with black resin 7 to integrate the entire structure. Furthermore, the end faces of the gradient index lens 1b are polished as necessary.

The lens array 10b can be modified in various ways, and the materials for each component of the lens array may be materials known in the art for manufacturing lens arrays. Furthermore, the arrangement of the multiple gradient index lenses 1b is not limited to two rows. The multiple gradient index lenses 1b may be arranged in a single row, or in three or more rows. By arranging the gradient index lenses 1b in multiple rows, a lens array that can accommodate a large area can be provided.

The gradient index lens 1b can be a plastic rod lens having the above-mentioned optical performance. Plastic rod lenses can be produced by methods such as copolymerization, sol-gel, and mutual diffusion. In particular, the mutual diffusion method involves concentrically stacking resins whose refractive index gradually decreases from the center to the periphery, and then mutual diffusion of materials between the layers so that the refractive index becomes continuous. After this process, the material is further heated and stretched to obtain a rod-shaped rod lens. Due to the characteristics of the material, plastic rod lenses are easy to handle and generally inexpensive, which can be advantageous in some cases.

Lens arrays equipped with gradient index lenses 1b have a large DOF and, in some cases, excellent weather resistance, making them suitable for a wide range of optical equipment, including scanners, copiers, facsimiles, printers, CISs, and line cameras. Furthermore, because lens arrays equipped with gradient index lenses 1b are particularly water-resistant (moisture-resistant), they can be applied to the above optical equipment in a variety of environments, including not only general air conditioning in offices, but also factories, storage warehouses, and logistics facilities exposed to high temperatures and humidity, such as transport trucks.

Using the lens array 10b, for example, a CIS scanner 100 as shown in FIG. 5 can be provided. The CIS scanner 100 includes, for example, the lens array 10b, a housing 11, a linear light receiving element 12, a linear illuminator 13, and a document table 14. The linear light receiving element 12 extends in the main scanning direction of the lens array 10b. In FIG. 5, the direction parallel to the X axis is the main scanning direction, and the direction parallel to the Y axis is the sub-scanning direction. The linear illuminator 13 extends in the main scanning direction of the lens array 10b. The document table 14 is formed of a glass plate. The glass plate constituting the document table 14 is arranged to cover the opening of the housing 11. The lens array 10b, the linear light receiving element 12, and the linear illuminator 13 are arranged inside the housing 11. Illumination light is linearly irradiated from the linear illuminator 13 onto a document P placed on the document table 14. Lens array 10b is arranged so that light reflected from the surface of document P is incident on linear light receiving elements 12. Two-dimensional image data of document P can be obtained by scanning the scanner mechanism including lens array 10b and linear light receiving elements 12 in the sub-scanning direction, or by transporting document P placed on document table 14 in the sub-scanning direction.

The lens array 10b is equipped with gradient index lenses 1b that have a large DOF, so the quality of the scanned image is likely to be good even in areas where parts of the original P are raised due to, for example, wrinkles or open pages.

The lens array 10b can be used to provide, for example, the scanner 300 shown in FIG. 6. The scanner 300 includes a housing 31, a linear light receiving element 32, a linear illumination device 33, a first spacer 34a, a second spacer 34b, and a substrate 35. In the scanner 300, the linear illumination device 33 is disposed outside the housing 31. For example, in the scanner 300, the lens array 10b is positioned and fixed relative to the housing 31 by the first spacer 34a and the second spacer 34b to appropriately adjust the optical alignment between the portion of the document P to be read and the linear light receiving element 32. The scanner 300 may also be used in a device for inspecting the appearance of an object, or may be used to obtain an image of the object (inspection target) instead of the document P. In this case, light emitted from the linear illumination device 33 is irradiated onto the object, and light reflected from the surface of the object is imaged on the linear light receiving element 32 by the imaging effect of the lens array 10b. The linear light-receiving element 32 can sequentially convert one-dimensional image information of the surface of the subject into electrical signals and output them.

The lens array 10b can be used to provide, for example, a printer 500 as shown in FIG. 7 . The printer 500 includes a writing head 51, a photosensitive drum 52, a charger 53, a developing unit 54, a transfer unit 55, a fixing unit 56, an erase lamp 57, a cleaner 58, and a paper feed cassette 59. The lens array 10b is disposed inside the writing head 51. The printer 500 is an electrophotographic printer. The writing head 51 includes the lens array 10b and a light-emitting element array (not shown). The lens array 10b forms an imaging optical system that exposes light emitted from the light-emitting element array onto the photosensitive drum 52. More specifically, the lens array 10b has its focal point located on the surface of the photosensitive drum 52, forming an erect, equal-magnification optical system. A photosensitive layer made of a photoconductive material (photoconductor) such as amorphous silicon is formed on the surface of the photosensitive drum 52. First, the surface of the rotating photosensitive drum 52 is uniformly charged by a charger 53. Next, a write head 51 irradiates the photosensitive layer of the photosensitive drum 52 with light of a dot image corresponding to the image to be formed. The charge in the irradiated areas of the photosensitive layer is neutralized, forming a latent image on the photosensitive layer. Next, a developer 54 applies toner to the photosensitive layer, and the toner adheres to the areas of the photosensitive layer where the latent image is formed, depending on the charge state of the photosensitive layer. Next, a transfer unit 55 transfers the adhered toner to paper fed from a cassette. The paper is then heated by a fuser 56, fixing the toner to the paper and forming an image. Meanwhile, after transfer, the charge on the photosensitive drum 52 is neutralized across the entire area by an eraser lamp 57, and then a cleaner 58 removes any toner remaining on the photosensitive layer.

Using the lens array 10b, for example, an inspection device 700 as shown in FIG. 8 can be provided. The inspection device 700 includes a CIS scanner 71, a linear illumination device 72, a controller 73, an output device 74, a conveyor device 75, and a conveyor control device 76. The lens array 10b is disposed inside the CIS scanner 71. The conveyor device 75 is, for example, a belt conveyor. The conveyor device 75 conveys specimens T, such as printed circuit boards, textiles, and paper. The conveyor control device 76 is a digital computer for controlling the conveyor device 75 and outputs a control signal to the conveyor device 75 to adjust the conveying speed of the conveyor device 75. The CIS scanner 71 and linear illumination device 72 are disposed, for example, above the conveyor device 75, and the specimens T pass directly below the CIS scanner 71 by the conveyor device 75. The CIS scanner 71 and linear illumination device 72 are disposed so as to obtain clear image data of the specimens T. The controller 73 is a digital computer that generates image data of the inspected object T. As the inspected object T passes directly beneath the CIS scanner 71, the controller 73 continuously acquires one-dimensional image information from the CIS scanner 71. In addition, the controller 73 acquires transport position information of the inspected object T from the transport control device 76. The controller 73 performs calculations based on the one-dimensional image information acquired from the CIS scanner 71 and the transport position information acquired from the transport control device 76 to generate two-dimensional image information. The generated two-dimensional image information is compared with information that characterizes defects such as foreign matter, cracks, and pinholes, pre-stored in the controller 73. The controller 73 thereby identifies the presence or absence of defects in the inspected object T, the number of defects, and their locations. The controller 73 may determine the quality of the inspected object T based on the comparison results. The output device 74 is, for example, a monitor, and displays the two-dimensional image information generated by the controller 73.

The present invention will be explained in more detail below using examples. Note that the present invention is not limited to the following examples.

(Preparation of Glass Composition and Fabrication of Gradient Index Lens)
Glass raw materials were mixed to obtain the compositions shown in Table 1, and the mixtures were melted to obtain glass melts (glass compositions) according to Examples 1 to 4, Comparative Examples 1 to 3, and Reference Example 1. The numerical values in Table 1 indicate mol %. The relationships between the mol % contents of predetermined components in each glass composition are shown in Table 2. Each glass melt was spun into a fiber, and the resulting glass fiber was cut to a predetermined length and the cut surface was polished. This resulted in glass strands according to each Example, Comparative Example, and Reference Example 1. Each glass strand had a diameter (filament diameter) of 560 μm. Next, each glass strand was immersed in a sodium nitrate molten salt heated to a temperature near the glass transition temperature of the glass composition constituting the glass strand, thereby performing an ion exchange treatment. This resulted in a refractive index distribution in each glass strand. The glass strands after the ion exchange treatment were then cut to a periodic length, and the cut end surfaces were polished to obtain refractive index distribution lenses according to each Example, Comparative Example, and Reference Example 1.

(Characteristics evaluation)
The gradient index lenses prepared as described above were cut to an appropriate length, and the cut surfaces of the resulting samples were mirror-polished. Next, a sheet bearing a grid pattern was placed in contact with one end surface of the sample, and an upright image of the pattern was observed from the other end surface of the sample to determine the periodic length P of each gradient index lens. Next, the refractive index distribution coefficient √A of each gradient index lens was determined based on the relationship √A = 2π/P. Next, the aperture angle θ of each gradient index lens was determined based on the refractive index distribution coefficient √A, the radius _r0 of the gradient index lens, and the refractive index Nc of the glass fiber before ion exchange treatment, as shown in Equation (1) below. The results are shown in Table 3. The refractive index Nc was 1.60, which could be considered the refractive index at the optical axis of each gradient index lens.
θ=sin ^-1 {√A・Nc・r ₀ } Formula (1)

The refractive index Nc was determined by evaluating the refractive index of the glass compositions of each Example, Comparative Example, and Reference Example 1. A rectangular parallelepiped sample with a cross-sectional area of 15 mm square was cut out of a glass matrix composed of the glass composition, and the refractive index Nc was evaluated according to the V-block method described in JIS B 7071-2:2018. In this method, the sample is placed on a V-block prism, and the deviation angle of the light beam bent by the sample when a dispersed light beam passes through it is measured. This method calculates the refractive index of the sample relative to the deviation angle value and the known refractive index of the V-block prism. A Shimadzu KPR-3000 was used for the evaluation.

(Water resistance evaluation)
The water resistance of each glass composition was evaluated in accordance with JOGIS 06-2009. A sample prepared from each glass composition was placed in boiling water for one hour to measure the weight loss rate, and the water resistance of each glass composition was evaluated according to the weight loss rate. JOGIS 06-2009 classifies water resistance into grades 1 to 6, and glass with a grade 1 water resistance can be said to have excellent weather resistance, particularly durability against moisture.

(DOF Measurement)
Each gradient index lens underwent a predetermined treatment (irregularity formation treatment) on its side surface to remove noise light. Then, a plurality of gradient index lenses were arranged two-dimensionally to produce a lens array in which a plurality of gradient index lenses were arranged in two rows, as shown in Figure 4. In this manner, lens arrays according to each Example, Comparative Example, and Reference Example 1 were obtained. A line pattern with six pairs of black and white lines spaced 1 mm apart was prepared. That is, this line pattern had a spatial frequency of 6 lines/mm. Light emitted from a halogen lamp was passed through a color filter (transmission center wavelength: 530 nm, full width at half maximum: 15 nm) and irradiated onto the line pattern. As shown in Figure 1, the line pattern, each lens array, and light-receiving element were positioned at the position where the MTF value was maximized. The distance between the lens array and the light-receiving element at this time was determined as the lens-to-imaging position distance L _o . The results are shown in Table 3. The line pattern was then moved in the optical axis direction, and the MTF value was determined at each position. The range of working distances where the MTF value was 30% or greater was identified from the relationship between ΔL and the MTF value. The depth of field (DOF) of each gradient index lens was then determined by subtracting the minimum value from the maximum value of the working distance. The results are shown in Table 3. Figure 9 also shows the relationship between the MTF value and ΔL for the lens arrays of Example 2, Comparative Example 3, and Reference Example 1.

As shown in Table 1, the DOF in the lens arrays equipped with the gradient index lenses according to each Example was in the range of 1.5 to 3.0 mm, suggesting that the gradient index lenses according to each Example had the desired DOF. In addition, the water resistance of the glass compositions according to each Example was Grade 1. On the other hand, the DOF in the lens arrays equipped with the gradient index lenses according to each Comparative Example was small. The DOF in the lens array equipped with the gradient index lenses according to Reference Example 1 was 2.4 mm. However, the water resistance of the glass composition according to Reference Example 1 was Grade 4,
It was suggested that the glass composition of Reference Example 1 was inferior in water resistance to the glass compositions of each Example.

1a Glass wire 1b Gradient index lens 2 Light receiving element 3 Line pattern 10a, 10b Lens array 100 CIS scanner 300 Scanner 500 Printer 700 Inspection device

Claims (7)

A gradient index lens,
It has a depth of field of 1.5 to 3.0 mm,
the depth of field is determined by subtracting the minimum value from the maximum value of the working distance while maintaining a constant distance between the gradient index lens and the image formation position;
At the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines/mm is 30% or more,
An aperture angle of 3.5° to 5.5°;
Water resistance is grade 1 as determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06-2009.
Gradient index lens. 10. A lens system comprising: the gradient index lenses according to claim 1, which are arranged in one or more rows in the main scanning direction so that their optical axes are parallel to one another;
Rod lens array. The rod lens array according to claim 2;
a linear light receiving element;
An image scanner comprising: a linear illumination device. A printer equipped with the rod lens array described in claim 2. An inspection device equipped with the rod lens array described in claim 2. A rod lens array for use in a visual inspection device,
The visual inspection device includes: a CIS scanner equipped with the rod lens array;
a transport device for transporting the inspection object;
a control device;
The visual inspection device forms two-dimensional image information of an inspection object by continuously acquiring one-dimensional image information of the inspection object conveyed by the conveying device,
The rod lens array according to claim 2 . Expressed in mole percent,
40%≦SiO ₂ ≦65%
1%≦TiO ₂ ≦10%
0.1%≦MgO≦22%
0.15%≦ZnO≦15%
0.5%≦ _Li2O <4%
2%≦Na ₂ O≦20%
0%≦B ₂ O ₃ ≦20%
0%≦ _{Al2O3 ≦} 10%
0%≦K ₂ O≦3%
0%≦ _Cs2O ≦3%
0%≦Y ₂ O ₃ ≦5%
0%≦ZrO ₂ ≦2%
0%≦Nb ₂ O ₅ ≦5%
0%≦ _{In2O3 ≦} 5%
0%≦La ₂ O ₃ ≦5%
0%≦Ta ₂ O ₅ ≦5%;
containing at least two selected from the group consisting of CaO, SrO, and BaO in an amount of 0.1 mol% or more and 15 mol% or less,
Expressed in mole percent,
2%≦MgO+ZnO,
0.07≦ZnO/(MgO+ZnO)≦0.93,
2.5%≦ _Li2O + _Na2O <24%,
The conditions _of Li2O /Na2O _≦ 0.2 and _{0 %} ≦ _Y2O3 + _{ZrO2+Nb2O5 + In2O3} + _La2O3 + _{Ta2O5 ≦} 11% _are satisfied _.
Glass composition.