JP6602056B2 - Optical element manufacturing method, mold, lens array, image forming apparatus, and image reading apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus, a method for manufacturing an optical element used in an image forming apparatus, a mold, and a lens array.

  The optical functional surfaces of optical elements used in digital cameras, laser printers, etc. are configured with curved surfaces, and high-precision processing is required not only for spherical surfaces but also for surface shapes with a change in curvature (aspherical shapes). The In recent years, an image forming apparatus and an image reading apparatus using a lens array optical system in which a lens array having a small diameter and a free-form surface is formed in units of several hundreds have been developed as optical elements used in LED printers and the like.

  As this lens array optical system, an image forming apparatus and an image reading apparatus are known that are held together with an array light source (LED or the like), a line sensor, or the like by a housing and incorporated as a unit. According to these apparatuses, it is possible to reduce the size and cost of the apparatus by using the lens array optical system.

  However, it is known that the lens array optical system causes unevenness in the amount of imaged light and the imaged performance depending on the pitch between lenses in which a plurality of lenses are arranged.

  Patent Document 1 discloses an optical system that eliminates unevenness in the amount of imaging light and imaging performance as shown in FIG. This lens array optical system is an optical system using two lens arrays 101 and 102 in which a plurality of lenses having continuous curved surfaces are arranged on the same line. In the lens array, the arrangement direction of a plurality of lenses is the longitudinal direction (Y direction in FIG. 9), and the direction perpendicular to the optical axis direction (X direction in FIG. 9) and the longitudinal direction is the short direction (FIG. 9). In the Z direction). The lens in the short direction is divided into two vertically (111a, 111b) along a line parallel to the longitudinal direction and passing through the optical axis of each lens. There has been proposed a lens array optical system that suppresses periodic unevenness by shifting the pitch, which is the distance between the optical axes of the lenses of the lens array, by 1/2 between the upper and lower lenses. The optical axis of the time-divided lens 111a is K1a, and the optical axis of 111b is K1b. Further, it has been proposed that the lens arrays 101 and 102 are manufactured using a mold. Specifically, a transfer surface of a lens array (a plurality of lenses arranged) is engraved (processed) in a mirror piece that is a part of a mold. At that time, the specular piece is divided into two parts, and after the lens transfer surface is processed, the divided specular pieces are assembled in the mold in a shifted state. It is disclosed that a lens array (optical element) is manufactured by transferring this.

JP2014-077964

  However, when the divided divided pieces disclosed in Patent Document 1 are combined to form a pair of specular pieces, the combined portions are not continuous surfaces, and a linear dividing line is formed. When a continuous lens surface straddling the dividing line is cut, the frequency of occurrence of minute scratches (chipping) on the diamond tool may increase. This is because, for example, the split surface, which is the mating surface of the split pieces, is processed with high precision by grinding, but at this time, abrasive grains remain on the split surfaces or when the split pieces are combined, Foreign matter may get caught. It has been found that when these contact with the diamond tool, chipping is likely to occur in the diamond tool.

  Therefore, the present invention provides a mold that suppresses chipping that occurs when a transfer surface of a continuous lens straddling a dividing line is cut using the divided pieces divided within the optically effective surface as a pair of mirror surface pieces. Also provided are a method for manufacturing an optical element having a plurality of stable high-quality lens surfaces with no scratches on the lens surface, and a lens array.

The optical element manufacturing method of the present invention is an optical element manufacturing method for manufacturing an optical element by transferring the transfer surface with a mirror piece in which a plurality of transfer surfaces of a lens are processed in the longitudinal direction, and the mirror surface piece Is composed of a first divided piece and a second divided piece arranged adjacent to each other, and after processing a groove in a boundary portion of the first divided piece and the second divided piece,
A plurality of shapes for transferring the lens are processed so as to straddle the first divided piece and the second divided piece, and the first divided piece and the second divided piece are relatively moved in the longitudinal direction. The lens is fixed so that the shape of transferring the lens is shifted by shifting, and the shape of transferring the shifted lens is transferred to manufacture an optical element.

The mold according to the present invention is a mold having a mirror surface piece in which a plurality of transfer surfaces of a lens are processed in the longitudinal direction, and the mirror surface piece includes an adjacent first divided piece and a second divided piece, A transfer surface of a plurality of lenses having a groove at the boundary between the first divided piece and the second divided piece and processed so as to straddle the first divided piece and the second divided piece, The groove is fixed in a state shifted in the longitudinal direction, and the width of the opening of the groove is 5 μm or more, and is 20% or less of the width of the shape to which the lens is transferred .

The lens array of the present invention is a lens array in which two rows in which a plurality of lenses are arranged at a predetermined pitch in the longitudinal direction are arranged in parallel in a direction perpendicular to the optical axis of the lens, and the two rows The positions of the optical axes of the plurality of lenses in the first row, which is one of the rows, and the positions of the optical axes of the plurality of lenses in the second row, which is the other of the two rows, The protrusions are arranged to be shifted in the longitudinal direction, and a protrusion is formed between the first row and the second row , and the width of the protrusion is not less than 5 μm, and is perpendicular to the longitudinal direction. It is characterized by being 20% or less of the width of the lens .
An image forming apparatus according to the present invention includes the lens array.
An image reading apparatus according to the present invention includes the lens array.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of an optical element which has a several high-quality lens surface without a crack in a lens surface, and a lens array can be provided.

  In addition, since the possibility of tool chipping can be greatly suppressed, cutting can be performed continuously without changing the tool, and thus a mold that can greatly improve the productivity of the lens array mirror piece can be provided.

The figure explaining embodiment of this invention The figure explaining embodiment of this invention The figure explaining embodiment of this invention The figure explaining embodiment of this invention The figure explaining embodiment of this invention Processed surface observation image of the embodiment of the present invention The figure explaining the comparative example with this invention Processed surface observation image of comparative example with the present invention The figure explaining the optical system using the conventional lens array

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a view for explaining a processing apparatus for cutting a specular piece which is a part of a mold used in a method for manufacturing an optical element (lens array) having a plurality of lens surfaces according to the present invention. In FIG. 1, 50 is an NC machine tool. Reference numeral 53 denotes an X linear motion table that moves straight in the X direction. Reference numeral 54 denotes a Y linear motion table that moves straight in the Y direction. A C table 56 that rotates around the Z direction is provided on the Y linear movement table. Reference numeral 21 denotes a work, which is mounted on the C table 56. Reference numeral 55 denotes a Z column 55 that moves straight in the Z direction, to which a grooving tool 11 is attached. The Z column 55 is also equipped with a tool rotating spindle 52 and other independently operated tool driving units. For example, a tool 10 for processing a curved surface having an arc contour shape can be attached to the tool rotating spindle 52.

  Each linear motion table and rotary table of the machine tool 50 are supported by hydrostatic bearings. By moving to XYZ and fly-cut processing by the rotary tool spindle 52, high-precision freedom such as molds for optical elements such as lenses and mirrors. Curved surface processing is possible.

  Further, a rotary table may be further provided on the Z column 55, and fly cutting can be performed by attaching a tool on the rotary table instead of the tool rotary spindle 52. In the present embodiment, the work 21 is mounted on the C table 55, and the curved surface processing tool 10 and the groove processing tool 11 are mounted on the Z column 55. However, the present invention is not limited to this. For example, the workpiece 21 may be attached to, for example, a rotary table on the Z column 55, and the curved surface processing tool 10 or the groove processing tool 11 may be attached to the C table 55.

  An optical element (lens array) having a plurality of lens surfaces of the present invention is shown in FIG. FIG. 2A shows an optical element in the case where the protrusions to be formed are tapered. In FIG. 2A, there are two rows having a plurality of lenses in the longitudinal direction (M direction), and tapered protrusions 222A and 222B are formed between the rows. In FIG. 2A, when a row having a plurality of lenses in two rows is designated as row A and row B, the plurality of lenses in row A is indicated as 221A, and the plurality of lenses in row B is indicated as 221B. Moreover, the uneven | corrugated | grooved part 223 is formed between the lenses of the several lens of each row | line | column. The lenses in the A and B rows have shapes in which the optical axes of the lenses are shifted by a half pitch in the longitudinal direction (M direction) with the protrusions 222A and 222B as boundaries. The half pitch is half of the distance between the optical axes OA of the lenses 221A. Alternatively, it is half the distance between the optical axes OB of the lenses 221B. That is, the lenses in the A and B rows are arranged so that the optical axis OB of the lens 221B is positioned at half the distance between the optical axes OA of the lenses 221A. The heights of the protrusions 222A and 222B from the lens surface are uniform. Thereby, since the width of the optical effective area can be kept uniform, the variation in the amount of light in the lens can be suppressed, and the optical characteristics can be kept uniform.

  FIG. 2B shows the optical element in the case where the formed protrusion has a rectangular shape. In FIG. 2B, there are two rows having a plurality of lenses in the longitudinal direction (M direction), and a rectangular protrusion 232 is formed between the rows. In FIG. 2B, when a row having a plurality of lenses in two rows is designated as row A and row B, the lenses in row A are indicated as 231A, and the lenses in row B are indicated as 231B. In addition, an uneven portion 233 is formed between the lenses of the plurality of lenses in each row. The lenses in rows A and B have a shape in which the optical axis of each lens is shifted by a half pitch in the longitudinal direction (M direction) with the protrusion 232 as a boundary. The half pitch is half of the distance between the optical axes OA of the lenses 231A. Alternatively, it is half of the distance between the optical axes OB of the lenses 231B. That is, the lenses in the A and B rows are arranged so that the optical axis OB of the lens 231B is positioned at a half of the distance between the optical axes OA of the lenses 231A. When the protrusion has a rectangular shape, the height of the protrusion 232 is constant from the surface perpendicular to the optical axis, unlike the case of the taper shape. Even if the height from the surface perpendicular to the optical axis is constant, the width of the optical effective range is uniform, and variation in the amount of light in the lens can be suppressed, and the optical characteristics can be kept uniform.

  Next, a method for processing a mirror piece that is a part of a mold used in the method for manufacturing an optical element (lens array) having a plurality of lens surfaces according to the present invention will be described.

  First, the first divided piece and the second divided piece obtained by dividing the mirror piece are arranged adjacent to each other, and a groove is formed in a portion (boundary portion) 23 where the divided surfaces of the first divided piece and the second divided piece are combined. (Relief groove machining) is performed.

  FIG. 3 is a view for explaining a method of processing the relief groove. 22a and 22b are a first divided piece and a second divided piece obtained by dividing the mirror piece, and the first divided piece and the second divided piece are arranged adjacent to each other. The divided surfaces of the first divided piece 22a and the second divided piece 22b are combined and held by a holder (not shown). In the surface to be processed, a portion (boundary portion) 23 where the divided surfaces are combined is not a continuous surface, but a linear boundary portion is formed.

  FIG. 3A shows a triangular relief groove 100a which is a V-shaped (V-shaped) groove. A grooving tool 11 having a V-shaped (V-shaped) cutting edge is directly attached to the Z-axis column 55 (see FIG. 1), and the XYZ linear motion stage is controlled to form a grooving tool 11 and a workpiece. Processing is performed while relatively moving the mirror surface pieces (22a, 22b). Data for processing a transfer surface of a lens array (a plurality of lenses arranged in advance) is stored in advance in a storage means (not shown) of the NC machine tool 50. As will be described later, a plurality of lenses are manufactured by pressing and transferring a resin or the like to a processed surface (transfer surface). Since the transfer surface is uneven at the boundary 23 for each of the plurality of lenses that are transferred and molded, if the triangular relief groove 100a is processed to the same depth, the opening width of the groove changes. For this reason, the locus 35a at the time of cutting forming the triangular relief groove 100a is moved following the unevenness of the lens to be transferred on the boundary portion 23. As a result, the opening width of the groove becomes uniform, so that the optically effective surface of the plurality of molded lenses can be made uniform, there is little change in the amount of light in the lens, and deterioration of optical performance can be suppressed as much as possible. Become.

  FIG. 3B shows a rectangular relief groove 100b that is a rectangular groove. If the shape of the groove is rectangular, the groove width is constant even if the shape of the lens to be transferred at the boundary portion 23 is uneven. Like the processing locus 35a of the triangular relief groove 100a in FIG. In other words, since it is only necessary to perform processing with a straight processing locus 35b with a cutting depth of the same depth by a groove processing tool having a rectangular cutting edge, the processing time can be significantly reduced.

  Next, a plurality of lens transfer surfaces are processed so as to straddle the first divided piece and the second divided piece with respect to the mirror piece having a groove formed at the boundary between the first divided piece and the second divided piece. To do.

  FIG. 4 is a diagram for explaining the cutting process of the transfer surface of the lens with respect to the mirror piece (work) 21 by a pair of divided pieces formed with a groove (triangular relief groove) 100a. A fly-cut process is performed with the tool 10 for processing a curved surface having an arc contour shape attached to the tool rotating spindle 52. In FIG. 4, 20 is a free-form surface that is a transfer surface of the lens having a center line K in the longitudinal direction of the lens. This free-form surface 20 extends in a direction (longitudinal direction of the lens array) M (the same direction as the Y direction in FIG. 4) and a vertical direction (X direction in FIG. 4) in which the groove 100a is formed at the boundary between the divided pieces. , A plurality of (for example, 250) processing is shown. By this processing, a mirror piece which is a part of a mold for forming a lens array (optical element) is manufactured. The free-form surface machining is performed by controlling the XYZ linear motion stage in the direction of the arrow indicated by 30a so that the machining point follows the shape in the X direction at an arbitrary Y position on each free-form surface 20, and a curved surface machining tool 10 and the mirror surface piece 21 which is a workpiece are relatively moved (scanning processing). The scanning process is sequentially repeated even at a position in the short direction shifted by an arbitrary pitch in the Y direction. When the processing of one transfer surface (free curved surface) is finished, the same processing is performed on the adjacent transfer surface (free curved surface). This is repeated for the number of lenses. That is, a plurality of transfer surfaces (free curved surfaces) of the lens are processed so as to straddle the first divided piece and the second divided piece.

  FIG. 5A shows the mirror surface piece (22a, 22b) in which a triangular relief groove is formed in the boundary portion 23 as shown in FIG. 3A while the boundary portion 23 is being processed by the tool 10 for curved surface processing. The X direction cross section of is shown in the schematic diagram. FIG. 5B shows a partially enlarged view thereof. A gap ε is inevitably generated in the boundary portion 23, and the remaining abrasive grains 112 when the divided pieces are ground and the foreign material 113 sandwiched when the divided pieces are combined are sandwiched there. By forming the triangular relief groove 100a, it is possible to avoid the possibility that the remaining abrasive grains 112, foreign matter 113, and the like come into contact with the curved surface processing tool 10 even when the curved surface processing tool 10 cuts over the boundary portion 23. . Further, even if burrs or returns (not shown) occur in the divided portion, the possibility of contact with the curved surface processing tool 10 can be reduced. Thereby, the chipping which arises in the ridgeline of the curved surface processing tool 10 can be suppressed significantly. Accordingly, it is possible to continuously obtain a stable high-quality specular piece without any scratch on the shape (free curved surface 20) to which each lens of the lens array is transferred. Even in the optical element transferred by the mirror piece, uniform optical performance can be provided. At this time, the width H of the opening is preferably 5 μm or more. Further, it is preferably 20% or less of the width of the shape (free curved surface) for transferring the lens (the length of the center line K in the longitudinal direction of the lens (see FIG. 4)). Since the groove does not have the light condensing performance as a lens, the light amount is lost by the ratio of the width of the opening to the width of the lens shape. If it is longer than 20%, the light amount is insufficient, and it is difficult to obtain good optical performance. In the present embodiment, for example, the width Z of the groove opening is 0.6 mm with respect to the lens-shaped width of 3.0 mm.

  In addition, since the possibility of tool chipping can be greatly suppressed, cutting can be performed continuously without changing the tool, so that the productivity of the mirror piece can be greatly improved.

  In the relief groove processing of the present embodiment, the triangular relief groove has been illustrated as one triangular relief groove. However, when the desired groove width is increased, the groove width may be increased by cutting deeper, but a plurality of grooves may be provided. May be formed to widen the groove width.

  In addition, the tool rotation spindle processing for processing the transfer surface (free curved surface) of the present embodiment is not limited in the processing scanning direction (longitudinal direction) and the sub-scanning direction (short direction). Even if the workpiece 21 is rotated by 90 °, the same free-form surface can be obtained even if the machining scanning direction (longitudinal direction) and the sub-scanning direction (short direction) are switched by 90 °. In that case, it is possible to perform cutting in either direction by using a tool having a minimum R of the free curved surface in the sub-scanning direction for feeding the pitch for cutting.

  In addition, as a processing method of the transfer surface (free curved surface), a processing mode using a tool rotating spindle has been described. However, as another machining method, the curved surface machining tool 10 is attached to a rotary scanning unit that can be operated in synchronization with the NC machine tool 50 by providing a rotary table on the Z column 55. May be. Then, the rotary scanning rotary table and the linear motion three table may be synchronized to perform the copying process to the shape of the transfer surface (free curved surface) 20.

  Similarly to the curved surface processing tool 10, the grooving tool 11 can be attached to the rotary scanning unit and processed by performing the same operation as the processing of the free curved surface 10.

  Further, the groove processing and the processing of the lens transfer surface (free curved surface) 20 can be performed independently and continuously.

  Specifically, the curved surface processing tool 10 is attached to a tool rotating spindle 52, and the tool rotating spindle 52 is attached to a Z column 55 of the NC machine tool 50. A free-form surface is machined with three linear stages and a spindle. For free-form surface machining, the machining point is calculated so that the transfer surface (free-form surface) is in contact with the surface drawn by rotating the contour curve of the cutting edge of the tool 10 for curved surface processing around the rotation center of the tool rotation spindle 52. Then, the transfer surface (free curved surface) is cut by operating the three linear motion stages.

  Next, the relief groove machining tool 11 is directly attached to the Z column at a position where it does not interfere with the curved surface machining tool 10 or the workpiece 21 during curved surface machining. As a result, the processing of the lens transfer surface (free curved surface) and the groove processing can be performed independently. Further, by storing the coordinates of each tool and the workpiece, the processing of the lens transfer surface (free curved surface) and the groove processing can be performed independently and continuously.

  Next, a method for manufacturing an optical element using a first divided piece and a second divided piece, which have been processed with a plurality of transfer surfaces of the lens after groove processing (relief groove processing), will be described. To do.

  First, after grooving (relief grooving), the first divided piece and the second divided piece obtained by machining a plurality of transfer surfaces of the lens are relatively shifted while being adjacently arranged. By shifting, the optical axis of the lens (sometimes simply referred to as the optical axis) transferred by the transfer surface of the lens is shifted in the direction perpendicular to the optical axis direction with the groove portion as a boundary. The amount of deviation is preferably half the length (pitch) between the optical axes of adjacent lenses. In this shifted state (the lens transfer surface is in a shifted shape), the lens is fixed in the mold, and the transferred lens transfer surface is transferred to resin, glass, etc. Array).

  The manufactured optical element (lens array) has two rows having a plurality of lenses in the longitudinal direction, and a protrusion is formed between the rows.

  And when the projection part formed is a taper shape, the height from the lens surface of a projection part is uniform so that the width | variety of an optical effective area | region may become uniform. Thereby, the width of the optical effective area can be kept uniform, variation in the amount of light in the lens can be suppressed, and the optical characteristics can be kept uniform.

  In addition, when the protrusion has a rectangular shape, the height of the protrusion does not need to be constant from the lens surface. That is, the height from the plane perpendicular to the optical axis can be made constant. Even if the height from the surface perpendicular to the optical axis is constant, the width of the optical effective range is uniform, and variation in the amount of light in the lens can be suppressed, and the optical characteristics can be kept uniform.

  Next, examples will be described.

(Example)
First, a trajectory for scanning following the shape of the free-form surface 20 shown in FIG. 4 was calculated. Next, a grooving tool 11 having a V-shaped cutting edge was directly attached to the Z-axis column of the apparatus shown in FIG. 1, and grooving was performed by XYZ linear motion three-axis control.

  Here, a grooving tool 11 having a V-shaped cutting edge having a tip angle of 60 ° was used, and a triangular relief groove having an opening angle of 60 ° was machined. The target value of the width of the triangular relief groove was ± 0.3 mm based on the dividing line, and 20% of the optical effective width was regarded as the relief groove. Thirty triangular relief grooves were formed at a pitch of 10 μm. At this time, the opening angle of the triangular relief grooves was 60 °, the triangular relief grooves were 10 μm pitch, and the processing depth was 18.6 μm.

  Next, the free curved surface 20 which is a shape to transfer the lens was processed. The free-form surface 20 was 0.9 mm × 3.0 mm and 250 linearly arranged. The length pitch between the optical axes in the shape of transferring a plurality of lenses was 0.9 mm, and the width of the free curved surface in the orthogonal direction (length of the optical axis) was 3.0 mm. The minimum R in the machining scanning direction and the sub-scanning direction of the free-form surface was 0.6 mm, and the cutting edge R of the tool used was a tool having a smaller cutting edge R of 0.4 mm.

  By the above method, triangular relief grooves were provided, and 330 free-form surfaces 20 were continuously processed. As a comparison object, a free curved surface was processed without providing a triangular relief groove at the 331rd.

  A triangular relief groove was provided to observe the surface of the 301st processed surface among the 330 processed continuously. For surface observation, scratches on the lens surface were observed with a differential interference microscope.

  The observation results are shown in FIG. FIG. 6 is an enlarged photograph of one of the 330 processed surfaces (free curved surface 20 and triangular relief groove 100a) that has been continuously processed by providing triangular relief grooves. In FIG. 6, even if the number of tools is 300 after cutting a very large number of free-form surfaces, the contour of the curved-surface processing tool 10 is formed over the entire free-form surface by forming relief grooves on the dividing lines of the mating surfaces. There was no chipping on the ridgeline. Therefore, neither the processing surface nor the processing surface streak due to tool chipping was observed. Therefore, it turned out that chipping of a tool can be suppressed and a good cutting mirror surface can be obtained by the present invention.

(Comparative example)
In the same manner as in the example, the processing was performed using a free curved surface without a relief groove as a comparative example.

  The surface of the 90th processed surface of 330 processed continuously was observed without providing a triangular relief groove. For surface observation, scratches on the lens surface were observed with a differential interference microscope.

  FIG. 8 shows an enlarged photograph as a result of observing the surface of the 90th processed surface among 330 continuously processed without providing triangular relief grooves. In FIG. 8, reference numeral 23 denotes a boundary portion. Reference numeral 20 denotes a shape (free curved surface) to which a lens as a processing surface is transferred.

  As shown in this processed surface observation image, a lot of chipping occurs on the contour ridgeline of the curved surface processing tool 10, and this is also transferred to the processing surface as a streak 40 on the processing surface by the tool chipping (free curved surface 20). You can see that The effect of the present invention could be confirmed from the fact that a large number of chippings occurred even when the number of free-form surfaces was 90 and 1/3 or less.

  Possible causes of chipping are as follows.

  FIG. 7A is a schematic diagram of the tool 10 and the free-form surface 20 for processing the boundary 23 when no escape groove is formed in the boundary of the split piece, and FIG. 7B is an enlarged view of the boundary. Show. As shown in FIG. 7, a small mating surface error (gap error) ε such as a burr 111 at the boundary, a remaining abrasive 112 when the boundary is ground, and a foreign object 113 sandwiched when the divided pieces are combined. Is sandwiched in the gap. For this reason, it is considered that the possibility that the curved machining tool 10 comes into contact with these tools increases and chipping that occurs on the ridgeline of the curved machining tool 10 suddenly occurs and cannot be controlled.

DESCRIPTION OF SYMBOLS 10 Tool for curved surface processing 11 Tool for groove processing 20 Free curved surface 21 Work piece 22a, 22b Dividing piece 23 Boundary part

Claims (12)

An optical element manufacturing method for manufacturing an optical element by transferring the transfer surface by a mirror piece in which a plurality of transfer surfaces of a lens are processed in a longitudinal direction,
The specular piece is composed of a first divided piece and a second divided piece arranged adjacent to each other,
After processing a groove at the boundary between the first divided piece and the second divided piece,
A plurality of shapes for transferring the lens so as to straddle the first divided piece and the second divided piece,
Fixing the shape of transferring the lens by shifting the first divided piece and the second divided piece relative to each other in the longitudinal direction;
A method of manufacturing an optical element, wherein an optical element is manufactured by transferring a shape for transferring the lens having the shifted shape.   The method of manufacturing an optical element according to claim 1, wherein the groove has a V shape.   The method for manufacturing an optical element according to claim 1, wherein the groove has a rectangular shape. 4. The method of manufacturing an optical element according to claim 1, wherein the width of the opening of the groove is 5 μm or more and 20% or less of the width of the shape to which the lens is transferred. A mold having a mirror piece in which a plurality of transfer surfaces of a lens are processed in the longitudinal direction,
The specular piece is composed of a first divided piece and a second divided piece adjacent to each other,
A boundary portion between the first divided piece and the second divided piece has a groove,
The transfer surfaces of a plurality of lenses processed so as to straddle the first divided piece and the second divided piece are fixed in a state shifted in the longitudinal direction ,
The width of the opening of the groove is 5 μm or more and 20% or less of the width of the shape to which the lens is transferred .   The mold according to claim 5, wherein the groove has a V shape.   The mold according to claim 5, wherein the groove has a rectangular shape. A lens array in which two columns in which a plurality of lenses are arranged at a predetermined pitch in the longitudinal direction are arranged in parallel in a direction perpendicular to the optical axis of the lens,
The positions of the optical axes of the plurality of lenses in the first row, which is one of the two rows, and the optical axes of the plurality of lenses in the second row, which is the other of the two rows. The position is shifted in the longitudinal direction,
A protrusion is formed between the first row and the second row ,
The width of the protrusion is 5 μm or more, and is 20% or less of the width of the lens in the direction perpendicular to the longitudinal direction .   The lens array according to claim 8, wherein the protrusion has a tapered shape.   The lens array according to claim 8, wherein the protrusion has a rectangular shape.   An image forming apparatus comprising the lens array according to claim 8.   An image reading apparatus comprising the lens array according to claim 8.