Refractive index distribution type lens, rod lens array, image scanner, printer, inspection apparatus, and glass composition

Abstract

To provide a gradient index lens having a large depth of field.SOLUTION: A gradient index lens (1b) has a depth of field of 1.5 to 3.0 mm. The depth of field is determined by subtracting a minimum value from a maximum value of a working distance. At the working distance, a modulation transfer function (MTF) value at a spatial frequency of 6 lines / mm is 30% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a refractive index distribution lens, an optical product, an optical device, a glass composition for a refractive index distribution lens, and a method for manufacturing a refractive index distribution lens.

Background Art

[0002] Conventionally, an apparatus for observing defects on the surface of a subject using a Charge-Coupled Device (CCD) has been known. For example, Patent Document 1 describes a surface defect apparatus including a light source, an irradiation unit, a condensing unit, and an observation unit. The observation unit includes an imaging lens and a CCD.

[0003] Patent Document 2 describes an inspection apparatus suitable for the appearance inspection of a photoreceptor drum of an electrophotographic copying machine or printer. This inspection apparatus includes a camera device that photographs the photoreceptor drum with a plurality of one-dimensional CCD cameras arranged in a row.

[0004] On the other hand, a contact image sensor (CIS) is also known as an imaging sensor. The CIS includes a rod lens array. A refractive index distribution lens is usually used for the rod lens array.

[0005] For example, Patent Documents 3 to 5 describe refractive index distribution lenses. A refractive index distribution lens or a refractive index distribution rod lens is a rod-shaped lens having a refractive index distribution in which the refractive index continuously decreases from the center toward the outer periphery. In the refractive index distribution lens described in Patent Document 3, the difference Δn between the refractive index on the peripheral surface of the lens and the refractive index on the central axis is 0.003 or more. According to Patent Document 3, when Δn becomes smaller than 0.003, the opening angle (2θ) becomes smaller than about 10°, suggesting that this is not desirable. In other words, it is considered that Patent Document 3 suggests that an opening angle (θ) of less than 5° is not desirable.

[0006] In Patent Document 4, the aperture angle of the refractive index distribution type lens according to the example is about 10.1 to 12.9°. In Patent Document 5, the aperture angle of the refractive index distribution type lens according to the example is 10.1 to 12.0°.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] Patent Documents 1 and 2 do not describe the use of a refractive index distribution type lens. The refractive index distribution type lenses described in Patent Documents 3 to 5 have a large aperture angle. This is hardly advantageous from the viewpoint of realizing a large depth of field in the refractive index distribution type lens, and it is considered that the depth of field of the refractive index distribution type lenses described in Patent Documents 3 to 5 is small. When the depth of field of a refractive index distribution type lens is small, for example, when there are variations in the thickness of an object, there may be portions of the object that are in focus and portions that are out of focus. Also, if a product equipped with a refractive index distribution type lens can be applied not only to general air conditioning but also to a high-temperature and high-humidity environment, the value of that product can be enhanced.

[0009] In view of such circumstances, the present invention Provided is a refractive index distribution type lens in which, even when there are variations in the thickness of an object, portions of the object that are in focus and portions that are out of focus are less likely to occur, and which is applicable even in a high-temperature and high-humidity environment.

Means for Solving the Problems

[0010] The present invention A refractive index distribution type lens, having a depth of field of 1.5 to 3.0 mm, wherein the depth of field is determined by subtracting the minimum value from the maximum value of the working distance while keeping the distance between the refractive index distribution type lens and the imaging position constant, wherein, at the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines / mm is 30% or more, having an aperture angle of 3.5° to 5.5°, having a water resistance of grade 1 determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06-2009, Provide a refractive index distribution type lens.

[0011] The present invention is Provided is a rod lens array including the above refractive index distribution type lens, arranged in one row or two or more rows in the main scanning direction so that the optical axes are parallel.

[0012] The present invention is The above rod lens array, a linear light receiving element, and a linear lighting device, are provided An image scanner is provided.

[0013] The present invention is A printer including the above rod lens array and an inspection device including the above rod lens array are provided .

[0014] The present invention is Expressed in mol%, 40% ≦ SiO 2 ≦65% 1% ≦ TiO 2 ≦10% 0.1% ≦ MgO ≦ 22% 0.15% ≦ ZnO ≦ 15% 0.5% ≦ Li 2 O<4% 2% ≦ Na 2 O≦20% 0%≦B 2 O 3 ≦20% 0%≦Al 2 O 3 ≦10% 0%≦K 2 O≦3% 0% ≦ Cs 2 O≦3% 0%≦Y 2 O 3 ≦5% 0% ≦ ZrO 2 ≦2% 0% ≦ Nb 2 O 5 ≦5% 0% ≦ In 2 O 3≦5% 0% ≦ La 2 O 3 ≦5% 0% ≦ Ta 2 O 5 ≦ 5%, and includes at least two selected from the group consisting of CaO, SrO, and BaO, each containing 0.1 mol% or more and 15 mol% or less, Expressed in mol%, 2% ≦ MgO + ZnO, 0.07 ≦ ZnO / (MgO + ZnO) ≦ 0.93, 2.5% ≦ Li 2 O + Na 2 O < 24%, and 0%≦Y 2 O 3 + ZrO 2[[ID=3%]] + Nb 2 O 5 + In 2 O 3 + La 2 O 3 + Ta 2 O 5 ≦ 11% conditions are satisfied, A glass composition is provided 。

Advantages of the Invention

[0015] According to the above refractive index distribution type lens, even when there are variations in the thickness of an object, portions of the object that are in focus and portions that are out of focus are less likely to occur, and it is applicable even in a high-temperature and high-humidity environment.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Image data collected in the appearance inspection of a subject must have a resolution capable of identifying defects in the subject. When attempting to obtain high-resolution image data using a camera equipped with a one-dimensional CCD sensor, the effective width that can be imaged by one camera becomes small. For this reason, it may be difficult to image the entire subject with one camera. For example, when the pixel size corresponding to the resolution required in the image data is 90 μm, the width of the area that can be imaged by a camera equipped with a one-dimensional CCD sensor having 4096 pixels is approximately 370 mm. In this case, in order to inspect a subject having a width of 1200 mm without omission, it is necessary to arrange four camera systems equipped with one-dimensional CCD sensors and camera lenses in the width direction. Mounting a plurality of camera systems equipped with one-dimensional CCD sensors increases the manufacturing cost of the apparatus. In addition, every time the type of the subject is changed, adjustment and maintenance of a plurality of camera systems are required, and the running cost of the inspection also increases.

[0018] Therefore, it is conceivable to perform an appearance inspection of a subject using a CIS. The CIS includes a plurality of one-dimensional light-receiving elements arranged on a substrate and a rod lens array. In the CIS, the rod lens array forms an erect and life-size image. By using the CIS, a one-dimensional image with a width of 1200 mm can be obtained in one unit. The rod lens array is, for example, an array of a plurality of rod-shaped refractive index distribution type lenses. The refractive index distribution type lens has a refractive index distribution in its radial direction, and the refractive index changes from the center part toward the peripheral part in the radial direction of the refractive index distribution type lens. The CIS equipped with the rod lens array can reduce the distance between the imaging element and the object to be photographed to about one-tenth compared with a conventional camera system including a CCD sensor and a lens, which is advantageous in terms of miniaturization of the device. On the other hand, in the CIS, the depth of field (DOF), which is a characteristic value indicating the allowable range of the distance between the object to be photographed and the lens, is small. This causes a problem that when there is a variation in the thickness of the subject, a part in focus and a part out of focus occur in the subject. Therefore, the image of the out-of-focus part is not clear, and there is a possibility of overlooking defects and misidentifying defects.

[0019] As described above, the aperture angle of the refractive index distribution type lens described in Patent Documents 3 to 5 is large, and it is difficult to say that this is advantageous from the viewpoint of increasing the DOF of the refractive index distribution type lens. Therefore, the present inventors fundamentally reviewed the conditions of the glass composition used for manufacturing the refractive index distribution type lens in order to realize a DOF in a desired range in the refractive index distribution type lens. As a result of repeated extensive trial and error, the present inventors have finally found a refractive index distribution type lens that can realize a DOF in a desired range. The refractive index distribution type lens according to the present invention can be used not only in the technical field of appearance inspection of a subject but also in the entire technical field of image formation such as image scanners, copiers, facsimiles, and printers.

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following description relates to an example of the present invention, and the present invention is not limited to the following embodiments.

[0021] The refractive index distribution type lens 1b has a depth of field (DOF) of 1.5 to 3.0 mm. The DOF of the refractive index distribution type lens 1b is determined by subtracting the minimum value from the maximum value of the working distance. At the working distance of the refractive index distribution type lens 1b, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines / mm is 30% or more.

[0022] As shown in FIG. 1, the DOF of the refractive index distribution type lens 1b is, for example, such that the lens array 10a and the line pattern 3 and the light receiving element 2 are arranged at a predetermined interval in the optical axis direction, and the value of the MTF is obtained while varying the distance between the lens array 10a and the line pattern 3. The lens array 10a is configured by arranging a plurality of refractive index distribution type 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, the light emitted from a halogen lamp is irradiated onto the line pattern 3 after passing through a color filter and a light diffusing plate. The color filter may, for example, transmit light in the wavelength range of 500 to 600 nm, or may mainly transmit light with a wavelength of 530 nm. At this time, the value of the MTF can be determined as the reproduction rate of the image (output image) obtained by imaging on the light receiving element 2 by the lens array 10a with respect to the image (input image) of the line pattern 3 having a predetermined spatial frequency composed of bright and dark portions before entering the lens array 10a.

[0023] The distance (object point - imaging point distance) D between the line pattern 3 and the light receiving element 2 at which the value of the MTF is maximized max is determined. Then, the line pattern 3 is moved in the positive direction (ΔL>0) and the negative direction (Δ L<0) of the Z-axis parallel to the optical axis, and the value of the MTF is obtained at each position. Thereby, by setting the allowable range of the value of the predetermined MTF, the maximum value and the minimum value of the working distance can be obtained. As a result, the DOF of the refractive index distribution type 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 is greater than the operating distance corresponding thereto. On the other hand, when ΔL < 0, the distance between the line pattern 3 and the lens array 10a is smaller than the operating distance corresponding to the distance D max corresponding thereto. When ΔL = 0 the distance between the line pattern 3 and the lens array 10a is the operating distance corresponding to the distance D max corresponding thereto and is equal.

[0024] Since the DOF of the refractive index distribution type lens 1b is within the above range, for example, it is advantageous for obtaining image data suitable for the appearance inspection of a subject having a non-uniform thickness, step, or unevenness. Therefore, the refractive index distribution type lens 1b can contribute to improving the accuracy of the appearance inspection of the subject and enhancing the inspection standard.

[0025] The DOF of the refractive index distribution type lens 1b is desirably 1.5 mm or more, more desirably 1.8 mm or more, and even more desirably 2 mm or more. The DOF of the refractive index distribution type lens 1b is desirably 2.8 mm or less, more desirably 2.5 mm or less.

[0026] The operating distance corresponding to the object point - image forming point distance D at which the MTF value becomes maximum max is, for example, 15 mm or more, desirably 18 mm or more. When the object point - image forming point distance D max is within these ranges, the DOF becomes an appropriate range. By incorporating a rod lens array including such a refractive index distribution type lens 1b into an inspection apparatus, an object having a step can also be inspected.In addition, the rod lens array can maintain an appropriate distance from the object, and the assembly of the optical system can be facilitated.

[0027] The refractive index distribution lens 1b has, for example, an aperture angle θ of 3 to 6°. Thereby, the DOF of the refractive index distribution lens 1b is easily adjusted to a desired range. The aperture angle θ of the refractive index distribution lens 1b is defined, for example, as shown in FIG. 2. The aperture angle θ is the maximum value of the angle formed by the optical axis and a light ray that can be incident on one end of the optical axis of the refractive index distribution lens 1b. In FIG. 2, F1 is the object plane, and F2 is the light receiving surface (imaging surface) in a light receiving element or the like. Z0 is the length of the refractive index distribution lens 1b. L o is the distance between the object plane F 1 and the refractive index distribution lens 1b when the value of MTF is maximum, and L i is the distance between the imaging surface F2 and the refractive index distribution lens 1b when the value of MTF is maximum . In FIG. 2, the lens array 10a constitutes a substantially erect and same - magnification imaging system, and the distance L i is substantially equal to the distance L o . In FIG. 2, X0 is the field radius of the refractive index distribution lens 1b. The aperture angle θ of the refractive index distribution lens 1b can be determined, for example, according to the method described in the embodiment. Note that, in the method described in the embodiment , the aperture angle θ may be determined using the refractive index n0 at the center of the refractive index distribution lens 1b instead of the refractive index Nc of the glass preform before ion exchange. Nc or n0 can be obtained using the V - block method described in Japanese Industrial Standard (JIS) B 7071 - 2:2018.

[0028] The aperture angle θ of the refractive index distribution lens 1b may be 3.5° or more, and may be 3.7° or more. The aperture angle θ of the refractive index distribution lens 1b is desirably 5.5° or less, and more desirably 5.2° or less.

[0029] The refractive index distribution lens 1b may have, for example, a refractive index distribution constant (√A) of 0.130 to 0.230 mm -1 . Note that √A means the square root of A. Assuming that the refractive index at the radius r of the refractive index distribution lens is n(r), in the paraxial region of the lens, n(r)=n0×{1-(A / 2)×r2} holds. If the refractive index distribution constant √A is within such a range, the aperture angle θ of the refractive index distribution type lens 1b is likely to fall within a desired range. As a result, the DOF of the refractive index distribution type lens 1b is easily adjusted to a desired range.

[0030] The refractive index distribution constant of the refractive index distribution type lens 1b may be 0.140 mm -1 or more, and may be 0.145 mm -1 or more. The refractive index distribution constant of the refractive index distribution type lens 1b is desirably 0.210 mm -1 or less, and more desirably 0.205 mm -1 or less.

[0031] The image formation distance of the erect image in the refractive index distribution type lens 1b is, for example, 45 to 80 mm. This is advantageous from the viewpoint of adjusting the DOF of the refractive index distribution type lens 1b to a desired range.

[0032] The image formation distance of the erect image in the refractive index distribution type lens 1b may be 47 mm or more, may be 50 mm or more, may be 53 mm or more, may be 54 mm or more. The image formation distance of the erect image in the refractive index distribution type lens 1b may be 75 mm or less, may be 70 mm or less, may be 67 mm or less.

[0033] The refractive index distribution type lens 1b is typically a rod-shaped or fiber-shaped lens. The refractive index distribution type lens 1b has, for example, a refractive index distribution as shown in Fig. 3B in the radial direction here. Here, the refractive index n0 at the origin in Fig. 3B means the refractive index on the central axis of the refractive index distribution type lens 1b. r represents the position in the radial direction of the refractive index distribution type lens 1b. center axis.

[0034] The refractive index distribution lens 1b may have a structure that prevents incident light having an incident angle larger than the numerical aperture from being reflected on the side surface of the lens and generating noise light (so-called white noise (stray light)) as needed. Such a structure can be, for example, a light absorption layer or a light scattering layer provided on the side surface of the lens. For example, the refractive index distribution lens 1b may have a core-clad structure in which a colored layer serving as a light absorption layer is disposed on the side surface of the lens, or may have a structure in which fine uneven portions serving as a light scattering layer are formed on the side surface.

[0035] The refractive index distribution lens 1b is typically a glass lens. The glass composition for the refractive index distribution lens contains, in mol%, 40% ≦ SiO2 ≦ 65%, 0% ≦ TiO2 ≦ 10%, 0.1% ≦ MgO ≦ 22%, 0.15% ≦ ZnO ≦ 15%, 0.5% ≦ Li2O < 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 the refractive index distribution lens contains at least two selected from the group consisting of CaO, SrO, and BaO, each in an amount of 0.1 mol% or more and 15 mol% or less. Further, the glass composition for the refractive index distribution lens satisfies the conditions of 2% ≦ MgO + ZnO, 0.07 ≦ ZnO / (MgO + ZnO) ≦ 0.93, 2.5% ≦ Li2O + Na2O < 24%, and 0% ≦ Y2O3 + ZrO2 + Nb2O5 + In2O3 + La2O3 + Ta2O5 ≦ 11%. By using such a glass composition, a refractive index distribution lens having a desired DOF can be obtained.

[0036] The refractive index distribution lens 1b can be manufactured, for example, by subjecting a glass preform made of the above glass composition to an ion exchange treatment.

[0037] (SiO2) SiO2 is an essential component that forms the network structure of glass. When the content of SiO2 is less than 40 mol%, the content of other components necessary to exhibit the optical properties as a refractive index distribution type lens after ion exchange becomes relatively large, and devitrification is likely to occur. Also, when the content is less than 40 mol%, the chemical durability as a glass composition significantly decreases. On the other hand, when the content exceeds 65 mol%, the content of other components, such as alkali components for forming the refractive index distribution, refractive index increasing components, and physical property value adjusting components, is limited, and it becomes difficult to obtain a practical glass composition. Therefore, the content of SiO2 is 40 mol% or more and 65 mol% or less.

[0038] (TiO2) TiO2 is an essential component that has the effect of increasing the refractive index of the glass composition. By increasing the refractive index of the base glass composition, the central refractive index of the refractive index distribution type lens obtained from the glass composition can be increased. Also, by increasing the content of TiO2 , the refractive index distribution in the refractive index distribution type lens can be made closer to an ideal state, and it becomes possible to manufacture a refractive index distribution type lens with excellent resolution. When the content of TiO2 is 10 mol%, no decrease in the resolution of the image based on the obtained lens is observed. However, when the content is less than 1 mol%, the resolution of the image clearly decreases, and a practical lens cannot be obtained. On the other hand, when the content exceeds 10 mol%, the coloring becomes stronger, resulting in a large chromatic aberration, and a practical lens cannot be obtained. Therefore, in order to obtain a lens with high resolution and small chromatic aberration, the content of TiO2 is 1 mol% or more and 10 mo l% or less. The content of TiO2 is preferably 2 mol% or more and 8 mol% or less.

[0039] (MgO) MgO is an essential component that has the effect of lowering the melting temperature of the glass composition and increasing the refractive index difference (Δn) between the center and the periphery of the lens after ion exchange. When the content of MgO exceeds 22 mol%, devitrification is likely to occur. Also, when the content of MgO exceeds 22 mol%, the contents of other components decrease excessively, and a practical glass composition cannot be obtained. Therefore, the content of MgO is 0.1 mol% or more and 22 mol% or less. From the viewpoint of realizing a sufficient refractive index difference, the content of MgO is desirably 2 mol% or more. When the content of MgO is 2 mol% or more, the content of alkaline earth metal oxides (CaO, SrO, BaO) can be more appropriately controlled for the purpose of further reducing the mobility of alkali ions. That is, the content of MgO is desirably 2 mol% or more and 22 mol% or less, and more desirably 2% or more and 16% or less.

[0040] (ZnO, MgO + ZnO, ZnO / (MgO + ZnO)) ZnO has the effect of improving the weather resistance of the glass composition and the refractive index distribution type lens. In the glass composition according to the present invention, ZnO may be added to replace a part of MgO. From the viewpoint of enhancing the weather resistance of the glass composition and the refractive index distribution type lens, the content of ZnO is 0.15 mol% or more and 15 mol% or less. At this time, 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 content ratios of MgO and ZnO are adjusted such that 0.07 ≦ ZnO / (MgO + ZnO) ≦ 0.93. From the perspective of further enhancing the weather resistance of the glass composition and the refractive index distribution type lens, the content ratio of ZnO is desirably 3 mol% or more and 15 mol% or less. In this case, MgO + ZnO may be 6 mol% or more, and the condition of 0.12 ≦ ZnO / (MgO + ZnO) ≦ 0.93 can be satisfied. From the perspective of devitrification resistance, the content ratio of ZnO is desirably 8 mol% or less. From the perspective of further enhancing the weather resistance of the glass composition and the refractive index distribution type lens, the content ratio of ZnO is more desirably 4 mol% or more and 15 mol% or less. In this case, MgO + ZnO may be 6 mol% or more, and MgO + ZnO may be 6 mol% or more and 22 mol% or less. MgO + ZnO may be 15 mol% or less. Also, ZnO / (MgO + ZnO) is desirably 0.07 or more and 0.9 or less, more desirably 0.25 or more and 0.85 or less, further desirably 0.25 or more and 0.8 or less, and particularly desirably 0.3 or more and 0.8 or less.

[0041] (Li2O) Li2O is an essential component and is one of the most important components for obtaining a refractive index distribution type lens by ion-exchanging the glass composition of the present invention. Conventionally, it has been considered that when the content ratio of Li2O in the glass composition is low, a sufficient concentration distribution, that is, a sufficient refractive index distribution, cannot be expressed by ion-exchange, and an appropriate refractive index distribution type lens cannot be obtained. However, the present inventors have newly found that a refractive index distribution type lens having an appropriate refractive index distribution and a large DOF can be produced by performing ion-exchange under predetermined conditions even with a glass composition in which the content ratio of Li2O is 4 mol% or less. When the content ratio of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content ratio of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, and more desirably 1 mol% or more. Also, the content ratio of Li2O is 4 mol and the refractive index distribution type lens having a large DOF can be produced by performing ion-exchange under predetermined conditions even with a glass composition in which the content ratio of Li2O is 4 mol% or less. When the content ratio of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content ratio of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, and more desirably 1 mol% or more. Also, the content ratio of Li2O is 4 mol % or less. When the content ratio of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content ratio of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, and more desirably 1 mol% or more. Also, the content ratio of Li2O is 4 mol % or less. When the content ratio of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content ratio of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, and more desirably 1 mol% or more. Also, the content ratio of Li2O is 4 mol % or less. When the content ratio of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content ratio of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, and more desirably 1 mol% or more. Also, the content ratio of Li2O is 4 mol % or less. When the content ratio of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content ratio of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, and more desirably 1 mol% or more. Also, the content ratio of Li2O is 4 mol is less than or equal to 5 mol%, preferably less than or equal to 3.5 mol%, more preferably less than or equal to 3 mol%, and still more preferably less than or equal to 2 mol%.

[0042] One of the features of the refractive index distribution type lens 1b is that the Li2O content is less than that of various prior arts due to manufacturing process reasons where the Li2O content could not be reduced previously. The inventors of the present invention have newly found that by new devices such as limiting the throughput of glass blanks per batch by the ion exchange method and reducing the initial content of Li in the molten salt, while suppressing lens aberrations such as field curvature, a refractive index distribution type lens with a smaller numerical aperture than before and a practical resolution can be obtained.

[0043] (Na2O) During ion exchange, Na2O helps the ion exchange between Li and the ions of the ion exchange species that replace Li ions (ions contained in the molten salt) due to the so-called mixed alkali effect, and appropriately maintains the ion mobility. By appropriately maintaining the ion mobility, the ion exchange rate can be appropriately adjusted, and the optical properties of the refractive index distribution type lens can be adjusted. If the content of Na2O in the glass composition is less than 2 mol%, the glass becomes hard during glass forming, so the forming becomes difficult and the melting temperature of the glass rises significantly, making it difficult to produce the lens. In addition, it is difficult to sufficiently obtain the effect of appropriately maintaining the ion mobility. On the other hand, if the content of Na2O exceeds 20%, the chemical durability of the glass decreases, lacking practicality. Therefore, the content of Na2O is 2 mol% or more, preferably 5 mol% or more, more preferably 10 mol% or more. Also, the content of Na2O is 20 mol% or less, preferably 17 mol% or less.

[0044] (Li2O + Na2O) As described above, the total of the Li2O content and the Na2O content in the glass composition (Li2​ (Li2O + Na2O) is more than 2.5 mol% and less than 24 mol%. When Li2O + Na2O is within this range, an image with good resolution can be obtained by a refractive index distribution type lens manufactured using this glass composition. Li2O + Na2O is desirably 6 mol% or more, and more desirably 10 mol% or more. When (Li2O + Na2O) is within this range, an image with good resolution can be obtained by a refractive index distribution type lens manufactured using this glass composition. Li2O + Na2O is desirably 6 mol% or more, and more desirably 10 mol% or more.

[0045] (Li2O / Na2O) When the ratio of the content of Li2O to the content of Na2O (Li2O / Na2O) is large, the resolution of a refractive index distribution type lens manufactured using the glass composition may be improved. On the other hand, when Li2O / Na2O is excessively large (for example, 1.0 or more), the aperture angle of a refractive index distribution type lens manufactured using the glass composition becomes large, and its DOF tends to become small. For this reason, Li2O / Na2O is, for example, 0.2 or less, desirably 0.15 or less, and more desirably 0.1 or less.

[0046] The above glass composition may further contain the following components.

[0047] (B2O3) B2O3 is an optional component that forms the network structure of the glass, and has the effect of promoting the vitrification of the glass composition and adjusting its viscosity without substantially changing the resolution and aperture angle θ of the resulting refractive index distribution type lens. It also has the effect of slightly slowing down the ion exchange rate of the glass composition. B2O3 may be added, for example, when the content ratios of the above-described essential components are within the scope of the present invention, but when the content ratios of some components become relatively large when viewed as a composition and the stability as a glass decreases (for example, devitrification is likely to occur). By adding B2O3, the content ratios of the above-described relatively large components can be reduced without changing the ratio of the content ratios between the essential components. The content ratio of B2O3 that can be added without changing the resolution and aperture angle of the resulting refractive index distribution type lens is, for example, 20 mol% or less. Therefore, the content ratio of B2O3 is 0 mol% or more and 20 mol% or less. This content ratio is preferably 0 mol% or more and 10 mol% or less, and when the glass composition contains B2O3, its content ratio is preferably 1 mol% or more and 10 mol% or less.

[0048] (Al2O3) The glass composition for a refractive index distribution type lens may contain Al2O3 as an optional component, and its content ratio is 0 mol% or more and 10 mol% or less.

[0049] (SiO2+TiO2+B2O3) In the glass composition for a refractive index distribution type lens, the total content ratio of SiO2, TiO2, and B2O3 (SiO2+TiO2+B2O3) is, for example, 41 mol% or more and 70 mol% or less, and preferably 50 mol% or more and 70 mol% or less.

[0050] (Y2O3, ZrO2, Nb2O5, In2O3, La2O3, Ta2O5) The glass composition for a refractive index distribution type lens contains at least one component selected from the group consisting of Y2O3, ZrO2, Nb2O5, In2O3, La2O3, and Ta2O5 for the purpose of adjusting the refractive index of the refractive index distribution type lens obtained after ion exchange or improving the weather resistance. It may be. The total content of these components is 0 mol% or more and 11 mol% or less. When the glass composition for a refractive index distribution type lens contains these components, the total content of these components is desirably 0.2 mol% or more and 6 mol% or less. Also, it is desirable that the total of the content of these components and the content of ZnO is 15 mol% or less.

[0051] (Y2O3) The content of Y2O3 is desirably 0 mol% or more and 5 mol% or less.

[0052] (ZrO2) The content of ZrO2 is desirably 0 mol% or more and 2 mol% or less. When the glass composition for a refractive index distribution type lens contains ZrO2, its content is 0.2 mol% or more and 2 mol% or less. There is.

[0053] The content of each of Nb2O5, In2O3, La2O3, and Ta2O5 is desirably 0 mol% or more and 5 mol% or less.

[0054] (K2O, Cs2O) K2O and Cs2O are optional components that, due to the mixed alkali effect, have the effect of reducing the mobility of alkali ions, similar to MgO, CaO, SrO, and BaO. The content of each of K2O and Cs2O is, for example, 0 mol% or more and 3 mol% or less. From the viewpoint of enhancing the water resistance of the glass composition for a refractive index distribution type lens, the content of Cs2O is desirably less than 2 mol%, more desirably 0 mol% or more and 1 mol% or less, and even more desirably 0.5 mol% or less. From the viewpoint of enhancing the water resistance of the glass composition for a refractive index distribution type lens, it is desirable that the glass composition for a refractive index distribution type lens does not substantially contain Cs2O. In this specification, "does not substantially contain" means that the content of the component is less than 0.1 mol%.

[0055] (Other components) In the glass composition for a refractive index distribution type lens, as other components, it may contain GeO2. The content of GeO2 can be 0 mol% or more and 10 mol% or less. Also, the refractive index The glass composition for a refractive index distribution type lens may contain at least one selected from the group consisting of SnO2, As2O3, and Sb2O3 as additives. The content of each of SnO2, As2O3, and Sb2O3 can be 0 mol% or more and 1 mol% or less. The glass composition for a refractive index distribution type lens may consist essentially of the above components. In this case, the content of each component contained in the glass composition, as well as the relationship (total and content ratio) between the contents of each component, satisfy the above-mentioned respective conditions. In this specification, "consisting essentially of ~" means allowing impurities with a content of less than 0.1 mol%.

[0056] (PbO) The glass composition for a refractive index distribution type lens substantially does not contain lead (as a typical compound, PbO). Also, the refractive index distribution type lens 1b substantially does not contain lead.

[0057] In the glass composition for a refractive index distribution type lens, for example, the water resistance determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06 - 2009 is grade 1. In this case, the glass composition for a refractive index distribution type lens has high water resistance, and the refractive index distribution type lens manufactured using the glass composition for a refractive index distribution type lens also tends to have high water resistance. Also, in the glass forming the refractive index distribution type lens, the water resistance determined in accordance with JOGIS 06 - 2009 may be grade 1.

[0058] The glass composition for a refractive index distribution type lens contains an oxide of a first alkali metal element. The refractive index distribution type lens 1b can be manufactured, for example, by a method including the following steps (I) and (II). (I) A glass preform 1a made of the above glass composition for a refractive index distribution type lens is formed. (II) The glass preform 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 distribution type lens, and the first alkali metal element Q in the glass preform 1a and the second alkali metal element R in the molten salt are ion-exchanged to form a refractive index distribution in the glass preform 1a.

[0059] (II) In the step of (II), for example, as shown in FIG. 3A, the glass preform 1a is put into the molten salt S inside the container V, and the glass preform 1a is immersed in the molten salt S for a predetermined time. In the molten salt S, for example, at least one of potassium nitrate and sodium nitrate is melted. When the glass preform 1a is immersed in the molten salt S, for example, the cations of the first alkali metal element Q such as Li (lithium) contained in the glass preform 1a dissolve into the molten salt S. On the other hand, the cations of the second alkali metal element R such as K (potassium) in the molten salt S penetrate into the glass preform 1a. By adjusting the temperature of the molten salt S and the immersion time of the glass preform 1a 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. Inside the glass preform 1a, a concentration distribution of specific monovalent cations is generated, and according to this concentration distribution, a refractive index distribution as shown in FIG. 3B is formed in the glass preform 1a. Thereby, the refractive index distribution type lens 1b can be manufactured from the glass preform 1a.

[0060] The optical product according to the present invention is not limited to a specific product as long as it includes the refractive index distribution type lens 1b. Using the refractive index distribution type lens 1b, for example, a predetermined lens array can be provided. In this case, the lens array may have a 0-dimensional array, a 1-dimensional array, or a 2-dimensional array with respect to the arrangement of the refractive index distribution type lenses 1b. The 0-dimensional array is, for example, a configuration in which a single refractive index distribution type lens 1b is arranged, and a desired effect is expected from an optical product composed of a single refractive index distribution type lens 1b. The 1-dimensional array is a configuration in which a plurality of refractive index distribution type lenses 1b are arranged in a line in a specific direction. That specific direction is called the main scanning direction, and the direction perpendicular to the main scanning direction and perpendicular to the optical axis is called the sub-scanning direction. The plurality of refractive index distribution type lenses 1b are arranged so that their optical axes are substantially parallel. The 2-dimensional array is a configuration in which, in addition to the 1-dimensional array, a plurality of lenses are arranged in a direction different from it. For example, a configuration in which a plurality of refractive index distribution type lenses 1b are arranged in two or more rows along the main scanning direction may correspond to the 2-dimensional array. According to the lens array 10b, even if the diameter of each refractive index distribution type lens is small, a wide range of erect and same-magnification images can be obtained.

[0061] For example, using the refractive index distribution type lens 1b, a lens array 10b shown in FIG. 4 can be provided. In the lens array 10b, a plurality of refractive index distribution type lenses 1b are arranged such that their optical axes are substantially parallel. In the lens array 10b, the plurality of refractive index distribution type lenses 1b are arranged in two rows so as to form a two-dimensional array. In the lens array 10b, the plurality of refractive index distribution type lenses 1b are arranged, for example, between a pair of fiber reinforced plastic (FRP) substrates 5. Between the pair of FRP substrates 5, the space between the plurality of refractive index distribution type lenses 1b and the space between the FRP substrate 5 and the refractive index distribution type lens 1b are filled with a black resin 7. Thereby, between the pair of FRP substrates 5, the plurality of refractive index distribution type lenses 1b are integrated. Such a lens array 10b can be manufactured, for example, as follows. First, a plurality of refractive index distribution type lenses 1b are arranged substantially in parallel on the surface of one FRP substrate 5, and the lenses are sandwiched by the other FRP substrate 5. Then, the space between the pair of FRP substrates 5 is filled with the black resin 7 to integrate the whole. Further, the end faces of the refractive index distribution type lenses 1b are polished as necessary.

[0062] The lens array 10b can be changed from various viewpoints, and known materials in the production of the lens array may be used for the materials of each part constituting the lens array. Also, the arrangement of the plurality of refractive index distribution type lenses 1b is not limited to two rows. The plurality of refractive index distribution type lenses 1b may be arranged in a single row, or may be arranged in three or more rows. When arranging a large number of rows of the refractive index distribution type lenses 1b, a lens array capable of corresponding to a large area can be provided.

[0063] The refractive index distribution type lens 1b can be a plastic rod lens having the above optical performance. The plastic rod lens can be manufactured by methods such as copolymerization method, sol-gel method, and mutual diffusion method. Particularly in the mutual diffusion method, after laminating resins whose refractive index decreases stepwise from the center to the outer periphery in concentric circles, mutual diffusion of substances between layers is performed so that the refractive index becomes continuous. After performing such a process, further heat drawing is performed to form a rod-shaped rod A lens is obtained. Plastic rod lenses are easy to handle and generally inexpensive due to the characteristics of their material, and have advantages in some cases.

[0064] The lens array provided with the refractive index distribution type lens 1b has a large DOF, and in some cases, is excellent in weather resistance, and can be widely used in optical devices such as scanners, copiers, facsimiles, printers, CISs, and line cameras. Furthermore, since the lens array provided with the refractive index distribution type lens 1b is particularly excellent in water resistance (moisture resistance), it can be applied to the above optical devices and the like not only in general air-conditioned offices but also in various environments including factories, storage warehouses, or transportation trucks exposed to high-temperature and high-humidity conditions.

[0065] Using the lens array 10b, for example, the CIS scanner 100 shown in FIG. 5 can be provided. The CIS scanner 100 includes, for example, a lens array 10b, a housing 11, a line-shaped light receiving element 12, a line-shaped illumination device 13, and a document table 14. The line-shaped 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 line-shaped illumination device 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 forming the document table 14 is disposed so as to cover the opening of the housing 11. The lens array 10b, the line-shaped light receiving element 12, and the line-shaped illumination device 13 are disposed inside the housing 11. Linear illumination light is irradiated from the line-shaped illumination device 13 onto the document P placed on the document table 14. The lens array 10b is disposed so that the light reflected from the surface of the document P enters the line-shaped light receiving element 12. By scanning the scanner mechanism including the lens array 10b and the line-shaped light receiving element 12 in the sub-scanning direction or by conveying the document P placed on the document table 14 in the sub-scanning direction, two-dimensional image data regarding the document P can be obtained.

[0066] Since the lens array 10b includes the refractive index distribution lens 1b having a large DOF, for example, even in a portion where a part of the document P floats due to wrinkles or an open part, the quality of the read image is likely to be good.

[0067] Using the lens array 10b, for example, a scanner 300 shown in FIG. 6 can be provided. The scanner 300 includes a housing 31, a line-shaped light receiving element 32, a line-shaped illumination device 33, a first spacer 34a, a second spacer 34b, and a substrate 35. In the scanner 300, the line-shaped illumination device 33 is disposed outside the housing 31. For example, in the scanner 300, in order to appropriately adjust the optical arrangement between the portion of the document P to be read and the line-shaped light receiving element 32, the lens array 10b is positioned and fixed to the housing 31 by the first spacer 34a and the second spacer 34b. The scanner 300 may be applied to a device for inspecting the appearance of a subject, or may be used to obtain an image from a subject (object to be inspected) instead of the document P. In this case, the light beam emitted from the line-shaped illumination device 33 irradiates the subject, and the light reflected by the surface of the subject is imaged on the line-shaped light receiving element 32 by the imaging action of the lens array 10b. The line-shaped light receiving element 32 can sequentially convert the one-dimensional image information on the surface of the subject into an electrical signal and output it.

[0068] Using the lens array 10b, for example, a printer 500 shown in FIG. 7 can be provided. The printer 500 includes a writing head 51, a photosensitive drum 52, a charger 53, a developer 54, a transferrer 55, a fixing device 56, an erasing 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 constitutes an imaging optical system that exposes the light emitted from the light emitting element array onto the photosensitive drum 52. Specifically, the focal point of the lens array 10b is located on the surface of the photosensitive drum 52, and it constitutes an erect same-magnification optical system. On the surface of the photosensitive drum 52, there is a photoconductive material such as amorphous Si A photosensitive layer made of a material (photosensitive member) is formed. First, the surface of the rotating photosensitive drum 52 is uniformly charged by the charger 53. Next, the light of the dot image corresponding to the image to be formed is irradiated onto the photosensitive layer of the photosensitive drum 52 by the writing head 51, the charge in the area of the photosensitive layer irradiated with light is neutralized, and a latent image is formed in the photosensitive layer. Next, when toner is attached to the photosensitive layer by the developing device 54, the toner adheres to the portion where the latent image is formed in the photosensitive layer according to the charged state of the photosensitive layer. Next, the attached toner is transferred to the paper sent from the cassette by the transfer device 55, and then, when the paper is heated by the fixing device 56, the toner is fixed to the paper and an image is formed. On the other hand, the charge of the photosensitive drum 52 after the transfer is neutralized over the entire area by the erasing lamp 57, and then, the toner remaining on the photosensitive layer is removed by the cleaner 58.

[0069] Using the lens array 10b, for example, an inspection apparatus 700 shown in FIG. 8 can be provided. The inspection apparatus 700 includes a CIS scanner 71, a line-shaped illumination device 72, a controller 73, an output device 74, a transport device 75, and a transport control device 76. The lens array 10b is disposed inside the CIS scanner 71. The transport device 75 is, for example, a belt conveyor. The transport device 75 transports a subject T such as a printed circuit board, a textile, and paper. The transport control device 76 is a digital computer for controlling the transport device 75, and outputs a control signal for adjusting the transport speed of the transport device 75 toward the transport device 75. The CIS scanner 71 and the line-shaped illumination device 72 are disposed, for example, above the transport device 75, and the subject T passes directly under the CIS scanner 71 by the transport device 75. The CIS scanner 71 and the line-shaped illumination device 72 are arranged so that clear image data of the subject T can be obtained. The controller 73 is a digital computer for forming image data of the subject T. When the subject T passes directly under the CIS scanner 71, the controller 73 continuously acquires one-dimensional image information from the CIS scanner 71. In addition, the controller 73 acquires the transport position information of the subject T from the transport control device 76. The controller 73 performs a calculation process 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, and forms two-dimensional image information. The formed two-dimensional image information is compared with information stored in advance in the controller 73 that characterizes defects such as foreign matter, cracks, and pinholes. Thereby, the controller 73 specifies the presence or absence of defects, the number of defects, and the positions of the defects in the subject T. The controller 73 may determine the quality of the subject T based on this comparison result. The output device 74 is, for example, a monitor, and displays the two-dimensional image information formed by the controller 73.

Example

[0070] Hereinafter, the present invention will be described in more detail with reference to examples. Note that the present invention is not limited to the following examples.

[0071] (Preparation of Glass Composition and Fabrication of Refractive Index Distribution Type Lens) Glass raw materials were mixed so as to have the compositions shown in Table 1, and the mixture was melted to obtain molten glass (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%. Table 2 shows the relationship of the content ratios of predetermined components in each glass composition based on mol%. Each molten glass was spun and formed into a fiber shape, and the obtained glass fiber was cut to a predetermined length, and the cut surface was polished. Thereby, glass element wires according to each Example, each Comparative Example, and Reference Example 1 were obtained. The diameter (wire diameter) of each glass element wire was 560 μm. Next, each glass element wire was immersed in a molten sodium nitrate salt heated near the glass transition temperature of the glass composition constituting each glass element wire, and ion exchange treatment was performed. Thereby, a refractive index distribution was formed in each glass element wire. Thereafter, the glass element wire after the ion exchange treatment was cut into a period length, and the cut end face was polished to obtain refractive index distribution type lenses according to each Example, each Comparative Example, and Reference Example 1.

[0072] (Characteristic Evaluation) The cut surface of a sample obtained by cutting the refractive index distribution type lens produced as described above to an appropriate length was mirror-polished. Next, a sheet on which a lattice pattern was described was brought into contact with one end face of this sample, and the upright image of the pattern was observed from the other end face of the sample to determine the period length P of each refractive index distribution type lens. Next, based on the relationship of √A = 2π / P, the refractive index distribution coefficient √A of each refractive index distribution type lens was determined. Next, based on the values of the refractive index distribution coefficient √A, the radius r0 of the refractive index distribution type lens, and the refractive index Nc of the glass element wire before the ion exchange treatment, and the following relationship shown in Formula (1) below, the aperture angle θ of each refractive index distribution type lens was determined. The results are shown in Table 3. Note that the refractive index Nc was 1.60 and could be regarded as the refractive index on the optical axis of each refractive index distribution type lens. θ = sin -1 {√A·Nc·r0} Formula (1)

[0073] The refractive index Nc was determined by evaluating the refractive indices of the glass compositions according to each example, each comparative example, and Reference Example 1. A base glass made of the glass composition was cut out to prepare a rectangular parallelepiped sample having a cross-sectional area of 15 mm square, 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 deflection angle of the light ray bent by the sample when passing through the spectrally separated light ray is measured. This method is a method of calculating the refractive index of the sample relatively from the value of this deflection angle and the refractive index of a known V-block prism. KPR-3000 manufactured by Shimadzu Corporation was used for the evaluation.

[0074] (Water resistance evaluation) The water resistance of each glass composition was evaluated in accordance with JOGIS 06-2009. Samples prepared from each glass composition were placed in boiling water for 1 hour to measure the weight loss rate, and the water resistance of each glass composition was evaluated according to the weight loss rate. The water resistance in JOGIS 06-2009 is classified from Class 1 to Class 6, and it can be said that a glass with a water resistance of Class 1 has excellent durability against weathering, particularly against moisture.

[0075] (Measurement of DOF) For each refractive index distribution type lens, a predetermined process (concavo-convex formation process) was performed on its side surface for the purpose of removing noise light. Thereafter, a plurality of each refractive index distribution type lens were arranged two-dimensionally to prepare a lens array in which a plurality of refractive index distribution type lenses as shown in FIG. 4 were arranged in two rows. In this way, lens arrays according to each example, each comparative example, and Reference Example 1 were obtained. A line pattern having six sets of black-and-white line pairs at intervals of 1 mm was prepared. That is, this line pattern had a spatial frequency of 6 lines / mm. The 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 FIG. 1, the line pattern, each lens array, and the light receiving element were arranged at the position where the value of the MTF was maximum. At this time, the distance between the lens array and the light receiving element was defined as the lens-imaging position distance L oIt was determined that. The results are shown in Table 3. Then, while moving the line pattern in the optical axis direction, the MTF values were obtained at each position, and the range of the operating distance at which the MTF value becomes 30% or more was specified from the relationship between ΔL and the MTF value. Then, the depth of field (DOF) of each refractive index distribution type lens was determined by subtracting the minimum value from the maximum value of the operating distance. The results are shown in Table 3. In addition, FIG. 9 shows the relationship between the MTF value and ΔL in the lens arrays according to Example 2, Comparative Example 3, and Reference Example 1. While moving the line pattern in the optical axis direction, the MTF values were obtained at each position, and the range of the operating distance at which the MTF value becomes 30% or more was specified from the relationship between ΔL and the MTF value. Moreover, the depth of field (DOF) of each refractive index distribution type lens was determined by subtracting the minimum value from the maximum value of the operating distance. The results are shown in Table 3. In addition, FIG. 9 shows the relationship between the MTF value and ΔL in the lens arrays according to Example 2, Comparative Example 3, and Reference Example 1.

[0076] As shown in Table 1, the DOF in the lens array provided with the refractive index distribution type lens according to each example was in the range of 1.5 to 3.0 mm, suggesting that the refractive index distribution type lens according to each example had a desired DOF. In addition, the water resistance of the glass composition according to each example was Class 1. On the other hand, the DOF in the lens array provided with the refractive index distribution type lens according to each comparative example was small. The DOF in the lens array provided with the refractive index distribution type lens according to Reference Example 1 was 2.4 mm. However, the water resistance of the glass composition according to Reference Example 1 was Class 4, suggesting that the glass composition according to Reference Example 1 was inferior in terms of water resistance compared to the glass compositions according to each example.

[0077]

Table 1

[0078]

Table 2

[0079]

Table 3

Explanation of Signs

[0080] 1a Glass wire 1b Refractive index distribution type lens 2 Light receiving element 3 Line pattern 10a, 10b lens arrays 100 CIS scanners 300 scanners 500 printers 700 inspection devices

Claims

1. A refractive index distribution type lens, having a depth of field of 1.5 to 3.0 mm, wherein the depth of field is determined by subtracting the minimum value from the maximum value of the working distance while keeping the distance between the refractive index distribution type lens and the imaging position constant, wherein, at the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines / mm is 30% or more, having an aperture angle of 3.5° to 5.5°, and having a water resistance of Class 1 determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06-2009. Refractive index distribution type lens.

2. A rod lens array comprising the refractive index distribution type lens according to Claim 1, arranged in one row or two or more rows in the main scanning direction so that the optical axes are parallel. Rod lens array.

3. An image scanner comprising the rod lens array according to Claim 2, a line-shaped light receiving element, and a line-shaped lighting device. Image scanner.

4. A printer comprising the rod lens array according to Claim 2.

5. An inspection device comprising the rod lens array according to Claim 2.

6. A rod lens array used in an appearance inspection device, wherein the appearance inspection device includes a CIS scanner on which the rod lens array is mounted, a transport device for transporting an object to be inspected, and a control device, and is used in the appearance inspection device for forming two-dimensional image information of the object to be inspected by continuously acquiring one-dimensional image information of the object to be inspected transported by the transport device. Rod lens array according to Claim 2.

7. Expressed in mol%, 40% ≤ SiO 2 ≤ 65% 1% ≤ TiO 2 ≤ 10% 0.1% ≤ MgO ≤ 22% 0.15% ≤ ZnO ≤ 15% 0.5% ≤ Li 2 O < 4% 2% ≤ Na 2 O ≤ 20% 0% ≤ B 2 O 3 ≤ 20% 0% ≤ Al 2 O 3 ≤ 10% 0% ≤ K 2 O ≤ 3% 0% ≤ Cs 2 O ≤ 3% 0% ≤ Y 2 O 3 ≤ 5% 0% ≤ ZrO 2 ≤ 2% 0% ≤ Nb 2 O 5 ≤ 5% 0% ≤ In 2 O 3 ≤ 5% 0% ≤ La 2 O 3 ≤ 5% 0% ≤ Ta 2 O 5 ≤ 5%, inclusive, including at least two selected from the group consisting of CaO, SrO, and BaO, each in an amount of 0.1 mol% or more and 15 mol% or less, expressed in mol%, 2% ≤ MgO + ZnO, 0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93, 2.5% ≤ Li 2 O + Na 2 O < 24%, Li₂O / Na₂O ≤ 0.2, and 0% ≤ Y 2 O 3 + ZrO 2 + Nb 2 O 5 + In 2 O 3 + La 2 O 3 + Ta 2 O 5 satisfying the condition of ≤ 11% Glass composition.

Images