JP2001030273A - Manufacture of mold roll, mold roll, and manufacture of lens sheet using the roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method for a mold roll, with which a lens sheet is molded and which can be easily manufactured at a low cost. SOLUTION: Firstly, a molding pattern corresponding to the lens pattern of a lenticular lens sheet (a pattern arranging a plurality of semispherical lenses in a lattice) is processed at the process 101 by working the roll surface of a tubular mold roll base material as a production object. Next, a development processing is applied to the roll surface of the mold roll base material and the material in the unexposed region of a photosensitive material and PVA coated on the roll surface of the mold roll base material are removed by a washing treatment and finally dried. After that, the surface of the worked pattern is made smooth by applying, an etch to the roll surface of the mold roll base material so as to form a final molding pattern at the process 103. Finally, the surface of the roll surface of the mold roll base material is chromized at the process 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a mold roll used for molding a lens sheet,
The present invention relates to a method of manufacturing a mold roll capable of easily and inexpensively manufacturing a mold roll used for molding a lens sheet, a mold roll manufactured by the method, and a method of manufacturing a lens sheet using the same.

[0002]

2. Description of the Related Art As a lens sheet used for a transmission screen or the like, a lens sheet in which a plurality of hemispherical lenses are arranged in a lattice shape (fly eye shape) is known. In such a lens sheet, the lens group arranged in a fly-eye shape is generally molded by a mold having a molding pattern corresponding to the outer shape. Conventionally,
Such a mold pattern is made by engraving the surface of a mold member, combining a plurality of parts corresponding to each part of the mold pattern, or the like.

[0003]

However, all of the above-mentioned conventional mold making methods for making a mold are for making a mold member for sheet-fed molding, such as a mold roll for continuous leaf molding. When making a plate, there is a problem that the plate processing becomes difficult and the processing time is long, so that the processing cost is increased, and as a result, an inexpensive lens sheet cannot be manufactured. .

The present invention has been made in view of the above points, and a method of manufacturing a mold roll for easily and inexpensively manufacturing a mold roll used for molding a lens sheet. An object of the present invention is to provide a manufactured mold roll and a method for manufacturing a lens sheet using the same.

[0005]

According to a first aspect of the present invention, there is provided a method of manufacturing a mold roll used for molding a lens sheet, comprising: forming a lens pattern on a lens sheet by processing a roll surface of a cylindrical member; A method for producing a mold roll, comprising the steps of: making a plate corresponding to a molding pattern, and performing a corrosion treatment on the roll surface of the tubular member to smooth the surface of the molding pattern. provide.

[0006] In the above-mentioned first solution,
It is preferable that the lens sheet has a lens pattern in which a plurality of hemispherical lenses are arranged in a lattice, and the molding pattern has an inverse shape of the lens pattern. Further, it is preferable that the roll surface of the cylindrical member is processed by a laser beam to form a plate having a molding pattern corresponding to the lens pattern of the lens sheet.

According to a second aspect of the present invention, there is provided a mold roll having a molding pattern corresponding to a lens pattern of a lens sheet, comprising a cylindrical member having a roll surface, wherein the cylindrical member has a roll surface. The plate has a mold pattern corresponding to the lens pattern of the lens sheet,
A mold roll characterized in that the surface of the molding pattern is smoothened by a corrosion treatment.

[0008] In the above-mentioned second solution,
It is preferable that the lens sheet has a lens pattern in which a plurality of hemispherical lenses are arranged in a lattice, and the molding pattern has an inverse shape of the lens pattern.

According to a third aspect of the present invention, there is provided a mold roll in which a molding pattern corresponding to a lens pattern of a lens sheet is formed on a roll surface of a cylindrical member.
A step of preparing a mold roll in which the surface of the molding pattern is smoothened by a corrosion treatment, and a step of applying a radiation-curable resin on the roll surface of the mold roll,
The roll surface and the film-shaped substrate are brought into contact with the radiation-curable resin interposed therebetween, and the radiation-curable resin is irradiated with radiation from the light-emitting side of the substrate to cure the radiation-curable resin. Forming a plurality of light incident lenses corresponding to the molding pattern of the roll surface on the light incident side of the material, and disposing a photosensitive material on the light exit side of the substrate on which the plurality of light incident lenses are formed Exposing the photosensitive material from the light incident side of the base material through each of the light incident lenses; developing the photosensitive material to form a light emitting part and light absorption on the light emitting side surface of the base material Forming a lens part.

According to the first to third solutions of the present invention, after the roll surface of the cylindrical member to be manufactured is processed to form a plate-shaped molding pattern corresponding to the lens pattern of the lens sheet, then the cylindrical member is formed. Since the surface of the molding pattern is smoothed by performing a corrosion treatment on the roll surface to form the final molding pattern, a lens pattern such as a lens pattern in which a plurality of hemispherical lenses are arranged in a lattice shape (fly-eye shape). A mold roll used for molding can be easily and inexpensively manufactured, so that a lenticular lens sheet can be manufactured at low cost.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 9 are views for explaining an embodiment of the present invention. In the present embodiment, a case where a lenticular lens sheet in which a plurality of hemispherical lenses are arranged in a lattice shape (fly shape) will be described as an example.

In the present embodiment, first, a mold roll used for forming a lenticular lens sheet is manufactured.
Next, a lenticular lens sheet is manufactured by a radiation curing method and a photolithography method using the manufactured mold roll.

[0013] Production of the mold roll First, FIGS. 1 to 5, a method for manufacturing the mold roller according to the present embodiment.

As shown in FIG. 1, first, a roll surface of a cylindrical mold roll base material (cylindrical member) to be manufactured is processed to form a lens pattern of a lenticular lens sheet (a plurality of hemispherical lenses are formed by a lattice). The plate making a molding pattern corresponding to the pattern arranged in the shape (step 101).

More specifically, as shown in FIG. 2, the roll surface 3a of the mold roll base material 3 'is processed by a laser beam to form a mold pattern corresponding to the lens pattern of the lenticular lens sheet.

At this time, as the mold roll base material 3 ',
An iron core roll having a copper plating layer with a thickness of about 30 μm to 3 mm formed by performing a copper plating process on the roll surface can be used. If the thickness of the copper plating layer is smaller than necessary, the surface accuracy after the copper plating decreases, and if the thickness is larger than necessary, the processing time of the copper plating increases. It is preferable to select an optimal thickness. Here, as an example, as an example, the thickness of a film-shaped base material (hereinafter referred to as “film base material”) of a finally manufactured lenticular lens sheet (here, 100 mm) is used.
μ) and the thickness of the copper plating layer
mm.

Then, the iron core roll (die roll base material 3 ') subjected to the copper plating process in this manner is mounted on a laser plate making machine. Here, the processing pattern formed on the roll surface 3a of the mold roll base material 3 'is the image processing device 3
2 and transmitted to the laser exposure machine 31 via the optical fiber 33, thereby setting the exposure conditions of the laser exposure machine 31. Here, the surface layer of the roll surface 3a of the mold roll base material 3 'is coated with a 4 μm-thick photosensitive material before exposure by the laser exposure device 31, and the photosensitive material is further coated on the surface layer of the photosensitive material. PVA to prevent volatilization
(Polyvinyl acetate).

Thereafter, while rotating the mold roll base material 3 'at a predetermined rotational speed, the exposure head 31a of the laser exposing machine 31 is axially moved relative to the roll surface 3a of the mold roll base material 3'. To expose the roll surface 3a of the mold roll base material 3 '. At this time, the processing pattern created by the image processing device 32 is sequentially transmitted to the laser exposure machine 31 via the optical fiber 33, and the laser light emitted from the exposure head 31a is turned on / off, so that the mold roll is formed. A desired processing pattern is formed on the roll surface 3a of the substrate 3 '. Here, as an example, the rotation speed of the mold roll base material 3 ′ is set to 700 rpm (revolution per revolution).
minute), a hexane pattern of 100 μ pitch was formed on the roll surface 3a of the mold roll base material 3 ′.

FIGS. 3 (a) and 3 (b) are views showing the appearance of the surface of the mold roll base material 3 'after laser plate making. FIG. 3 (a) shows the roll of the mold roll base material 3'. FIG. 3B is a plan view showing the surface 3a, and FIG. 3B is a cross-sectional view taken along the line IIIb-IIIb in FIG.

Next, the mold roll base material 3 'is thus prepared.
After forming a processing pattern on the roll surface 3a, the roll surface 3a of the mold roll base material 3 'is subjected to development processing,
Next, of the photosensitive material coated on the roll surface 3a of the mold roll base material 3 ', the material in the unexposed area and the PVA are removed by a washing treatment, and finally, the material is dried (Step 10).
2). Here, as an example, an aqueous solution of sodium carbonate having a concentration of 0.5% was used as a developing solution, and water was used as a cleaning solution.

In this manner, the mold roll base material 3 '
The processed pattern formed on the roll surface 3a is a state where the photosensitive material slightly remains in the unexposed region of the roll surface 3a and the copper plating layer is exposed in the exposed region.

Thereafter, the roll surface 3 of the mold roll base material 3 '
A is subjected to a corrosion treatment (etching treatment) to smooth the surface of the processed pattern, and a final molded pattern is formed (step 103).

More specifically, as shown in FIG. 4, the surface of the processing pattern formed on the roll surface 3a of the mold roll base material 3 'by the corrosive liquid ejected by a shower method from the corrosive liquid ejecting section 34. Corrode. Here, as an example, hydrochloric acid having a concentration of 5% was used as a corrosive liquid, the corrosive time was set to 20 seconds, and a molding pattern having a plate depth of about 30 μ was obtained.

The plate depth of the molding pattern is appropriately set according to the thickness of the film substrate of the lenticular lens sheet to be finally manufactured, and changes the concentration of the corrosive liquid, the corrosive time, and the like. This can be adjusted as appropriate.

FIGS. 5A, 5B and 5C are views showing the appearance of the surface of the mold roll base material 3 'after the corrosion treatment.
5 (a) is a plan view showing the roll surface 3a of the mold roll base material 3 'when the degree of the corrosion treatment is weak, and FIGS. 5 (b) and 5 (c) show the case where the degree of the corrosion treatment is strong. It is the top view which shows the roll surface 3a of the type | mold roll base material 3 ', and sectional drawing along the Vc-Vc line.

After the corrosion treatment is performed as described above, a washing treatment is sequentially performed in the order of water → dilute sulfuric acid → water → solvent → water → dilute sulfuric acid → water to remove the photosensitive material. Here, as an example, a mixed solution of MEK (methyl ethyl ketone), toluene and methanol (MEK: toluene:
Methanol = 4: 2: 4) was used.

Finally, the roll surface 3 of the mold roll base material 3 '
A chrome plating is applied to the surface of a (step 104).

By the steps 101 to 104 described above, a mold roll having a shape opposite to the lens pattern of the lenticular lens sheet as a molding pattern is manufactured.

Manufacturing of a lenticular lens sheet Next, a method of manufacturing a lenticular lens sheet by a radiation curing technique and a photolithography technique using a mold roll manufactured by the above-described method will be described with reference to FIGS. .

(First Example) First, referring to FIGS. 6 and 7,
A first example of a method for manufacturing a lenticular lens sheet according to the present embodiment will be described.

In this case, in the manufacturing apparatus as shown in FIG. 6, a mold roll manufactured by the above-described method is installed as the mold roll 3.

First, in step (A), the radiation curable resin 22 (for example, HRF manufactured by Inktec Co., Ltd.) is applied onto the roll surface 3a of the mold roll 3 by the nozzle coating device 4.
2535) is applied, and the nip roll 5 is used for the mold roll 3 on which the radiation-curable resin 22 is applied.
The film substrate 21 (for example, A-4100, manufactured by Toyobo Co., Ltd., thickness 188 μm) supplied from the paper feed roll 2 is nipped. Thereafter, in a state where the surface of the film substrate 21 (the surface to which the radiation-curable resin 22 is applied) is in contact with the mold roll 3, radiation is irradiated from the rear surface side of the film substrate 21 by the radiation lamp 6. The radiation-curable resin 22 is cured to form a plurality of light-entering lenses 22A corresponding to the molding pattern of the roll surface 3a of the mold roll 3 on the light-incident side surface of the film substrate 21. The film substrate 21 on which the light incident lens 22A is formed in this manner is released from the mold roll 3 by the release roll 7, and is conveyed to the next step.

Next, in step (B), the light incident lens 2
The dry film (negative-type photosensitive material) 24 for negative resist supplied by the paper feed roll 10 (for example, Nichi-Morton Co., Ltd .: NCP-) is applied to the light emitting side surface of the film substrate 21 on which the 2A is formed. 315) is laminated by the pressing roll 11 to form a negative resist layer on the light emitting side surface of the film substrate 21.

Then, in this step (B), the exposure light (parallel light) emitted from the exposure device 14 is applied to the film substrate 21, and each of the input light provided on the light entrance side of the film substrate 21 is irradiated. Film substrate 21 via optical lens A22
The negative type resist layer formed on the surface on the light emission side is exposed.

Thereafter, in the step (C), the exposed negative resist layer provided on the light-emitting side surface of the film substrate 21 is developed by the developing / washing unit 15, and then the developed negative resist is developed. After the negative resist material in the unexposed area (uncured area) of the layer is washed and removed, the layer is dried by the drying unit 16.

Then, in the step (D), a colored ink (coloring material) 23 such as black ink is applied to the surface on the light emitting side of the film substrate 21 by the colored ink coating device 17 and subjected to wiping processing. And drying by the drying unit 18. As a result, a colored ink layer 23A is formed in a region between the negative resist layers 24A left on the light-emitting side surface of the film base 21, and each light-entering lens 22A of the light-emitting side surface of the film base 21 is formed. A light-emitting portion (negative resist layer 24A) is formed in the light-collecting region, and a light-absorbing portion (colored ink layer 23A) is formed in a region other than the light-collecting region.

By the above-described steps (A) to (D), the lenticular lens sheet 2 as shown in FIG.
0, ie, the light incident lens 2 on the light incident side of the film substrate 21
The lenticular lens sheet 20 in which the light-emitting portion 24A and the light-absorbing portion 23A are formed on the light-emitting side of the film substrate 21 with the light-emitting portion 24A and the light-absorbing portion 23A formed on the light-emitting side of the film substrate 21 is formed. It can be manufactured continuously.

In the first manufacturing example described above,
A dry film for a negative resist is used as a negative resist material, and this is laminated on the light emitting side surface of the film substrate 21. However, the present invention is not limited to this.
The wet-type negative resist resin may be coated on the light-emitting side surface of the film substrate 21.

Second Example Next, referring to FIGS. 8 and 9,
A second example of the method for manufacturing a lenticular lens sheet according to the present embodiment will be described. The second manufacturing example is the same as the second manufacturing example shown in FIGS. 6 and 7 except that a light absorbing portion is formed on the light-emitting side surface of the film substrate using a light-shielding positive resist material. This is substantially the same as the production example of Example 1.
In the second manufacturing example, the same parts as those in the first manufacturing example shown in FIGS. 6 and 7 are denoted by the same reference numerals, and detailed description is omitted.

As shown in FIG. 8, first, in the step (A), a plurality of light incident lenses 22A are formed on the light incident side surface of the film substrate 21 by the same method as in the above-mentioned first production example.
Is molded.

Next, in the step (B), the light incident lens 2
The resist resin coating device 12 applies a positive resist resin (positive photosensitive material) 25 colored black or the like to the light emitting side surface of the film substrate 21 on which the 2A is formed.
(For example, Line Rex manufactured by Fuji Rex Co., Ltd.), and after wiping, dried by the drying unit 13 to form a light-shielding positive resist layer on the light-emitting side surface of the film substrate 21. .

Then, in this step (B), the exposure light (parallel light) emitted from the exposure device 14 is applied to the film substrate 21, and each of the input light provided on the light entrance side of the film substrate 21 is irradiated. The positive type resist layer formed on the light emitting side surface of the film substrate 21 is exposed through the optical lens 22.

Thereafter, in the step (C), the exposed positive resist layer provided on the light-emitting side surface of the film substrate 21 is developed by the developing / washing unit 15, and then the developed positive resist layer is developed. The positive resist material in the exposed area (uncured area) of the layer is washed and removed, and then dried by the drying unit 16. This allows
Only the positive resist material in the unexposed area (cured area) is left as the protruding part 25A, and the light emitting part 25 is provided on the light condensing area of each light incident lens 22A on the light emitting side surface of the film substrate 21.
B is formed, and a light absorbing portion (projection 25A) is formed in a region other than the light collecting region.

The lenticular lens sheet 2 shown in FIG. 9 is obtained by the above-described steps (A) to (C).
0, ie, the light incident lens 2 on the light incident side of the film substrate 21
The lenticular lens sheet 20 in which the light-emitting portion 25B and the light-absorbing portion 25A are formed on the light-emitting side of the film substrate 21 with the light-emitting portion 25B and the light-absorbing portion 25A formed on the light-emitting side of the film substrate 21 is formed. It can be manufactured continuously.

In the second manufacturing example described above,
A wet positive resist resin is used as the positive resist material, and this is coated on the light-emitting side surface of the film substrate 21. However, the present invention is not limited to this. Lumber 2
Alternatively, the surface on the light-emitting side may be laminated.

In the above-described second manufacturing example,
Although a light-shielding positive resist material is used as the positive resist material, the invention is not limited thereto, and a light-transmitting positive resist material may be used. Here, when a translucent positive resist material is used, for example, in the step (B), the positive resist layer formed of the translucent positive resist resin is exposed to light, C)
In the developed positive resist layer, the positive resist material in the exposed region (uncured region) of the developed positive resist layer is removed by washing, and the positive resist material in the unexposed region is left as a protrusion, and the remaining protrusion is By fixing a coloring ink (coloring material) such as a black ink on the upper surface, a light-emitting portion is formed in a light-collecting area of each light-entering lens on the light-emitting side surface of the film substrate 21 and a light-emitting portion other than the light-collecting area It is preferable to form a light absorbing portion in the region.

As described above, according to the present embodiment, the roll surface 3 of the cylindrical member (the mold roll base material 3 ′) to be manufactured.
After a is processed to form a mold pattern corresponding to the lens pattern of the lenticular lens sheet, a corrosion treatment is applied to the roll surface 3a of the mold roll base material 3 'to make the surface of the mold pattern smooth to final molding. Since the pattern is formed, the mold roll 3 used for molding a lens pattern in which a plurality of hemispherical lenses are arranged in a lattice shape (fly-eye shape) can be easily and inexpensively manufactured. Therefore, the lenticular lens sheet 20 can be manufactured at low cost.

In the above-described embodiment, the roll surface 3a of the mold roll base material 3 'is processed by a laser beam to form a mold pattern corresponding to the lens pattern of the lenticular lens sheet. Any existing method used for a coating roll, an anilox roll, or the like can be adopted as long as a molding pattern corresponding to a lens pattern of a lenticular lens sheet can be made endlessly.

[0049]

As described above, according to the present invention, after the roll surface of the cylindrical member to be manufactured is processed to form a plate to form a molding pattern corresponding to the lens pattern of the lens sheet, the roll of the cylindrical member is rolled. Since the surface is subjected to corrosion treatment and the surface of the molding pattern is smoothed to form the final molding pattern, it is suitable for molding lens patterns, etc., in which a plurality of hemispherical lenses are arranged in a grid (fly-eye shape). The mold roll to be used can be manufactured easily and inexpensively, so that the lenticular lens sheet can be manufactured inexpensively.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an embodiment of a method for manufacturing a mold roll according to the present invention.

FIG. 2 is a diagram schematically showing a laser plate making process.

FIG. 3 is a diagram showing a state of a surface of a mold roll base material after laser plate making.

FIG. 4 is a view schematically showing a corrosion treatment step.

FIG. 5 is a view showing a state of a surface of a mold roll base material after a corrosion treatment.

FIG. 6 is a diagram illustrating a first example of a method for manufacturing a lens sheet according to the present invention.

FIG. 7 is a view showing an example of a lens sheet manufactured by the manufacturing method shown in FIG.

FIG. 8 is a view for explaining a second example of the method for manufacturing a lens sheet according to the present invention.

FIG. 9 is a view showing an example of a lens sheet manufactured by the manufacturing method shown in FIG.

[Explanation of symbols]

2 Feed Roll (for Film Base) 3 Die Roll 3a Roll Surface 4 Nozzle Coating Device 5 Nip Roll 6 Radiation Lamp 7 Release Roll 10 Feed Roll (for Dry Film for Negative Resist) 11 Press Roll 12 Resist Resin Coating device 13 Drying unit 14 Exposure device 15 Developing / Washing unit 16, 18 Drying unit 17 Colored ink coating device 20 Lenticular lens sheet 21 Film base 22 Radiation curable resin 22A Light incident lens 23 Colored ink (colored material) 23A Colored ink layer (light absorbing part) 24 Dry film for negative resist (photosensitive material) 24A Negative resist layer (light emitting part) 25 Colored positive resist resin (photosensitive material) 25A Projecting part (light absorbing part) 25B Light emitting Unit 31 laser exposure machine 31a exposure head 32 image processing Device 33 optical fiber 34 corrosive liquid discharge portion

Claims (9)

[Claims] 1. A method for manufacturing a mold roll used for molding a lens sheet, comprising: a step of processing a roll surface of a cylindrical member to make a plate forming a molding pattern corresponding to a lens pattern of the lens sheet; Subjecting the roll surface to a corrosion treatment to smooth the surface of the molding pattern. 2. The lens sheet according to claim 1, wherein said lens sheet has a lens pattern formed by arranging a plurality of hemispherical lenses in a lattice, and said molding pattern has an inverted shape of said lens pattern. 2. The method for producing a mold roll according to 1. 3. The die roll manufacturing method according to claim 1, wherein the roll surface of the cylindrical member is processed by a laser beam to form a mold pattern corresponding to a lens pattern of a lens sheet. Method. 4. A mold roll having a molding pattern corresponding to a lens pattern of a lens sheet, comprising: a cylindrical member having a roll surface, wherein the roll surface of the cylindrical member corresponds to a lens pattern of a lens sheet. A mold roll characterized in that a molding pattern to be formed is made into a plate, and the surface of the molding pattern is smoothened by a corrosion treatment. 5. The lens sheet according to claim 1, wherein the lens sheet has a lens pattern formed by arranging a plurality of hemispherical lenses in a lattice, and the molding pattern has an inverse shape of the lens pattern. 4. The mold roll according to 4. 6. A mold roll in which a molding pattern corresponding to a lens pattern of a lens sheet is made on a roll surface of a cylindrical member, wherein the surface of the molding pattern is smoothened by a corrosion treatment. A step of preparing a roll, a step of applying a radiation-curable resin on the roll surface of the mold roll, and a step of applying the roll surface and the film-shaped substrate with the radiation-curable resin interposed therebetween. A plurality of light-entering lenses corresponding to the molding pattern of the roll surface are formed on the light-entering side of the substrate by contacting and irradiating radiation from the light-emitting side of the substrate to cure the radiation-curable resin. And a step of disposing a photosensitive material on the light exit side of the substrate on which the plurality of light incident lenses have been formed; and applying the photosensitive material from the light incident side of the substrate via each of the light incident lenses. Exposure work And a step of developing the photosensitive material to form a light-emitting portion and a light-absorbing portion on the light-emitting side surface of the base material. 7. The photosensitive material is a negative photosensitive material. The negative photosensitive material is developed to remove the material in the unexposed area and to color the unexposed area from which the material has been removed. By applying a material, a light-emitting portion is formed in the light-collecting region of each of the light-entering lenses on the light-emitting side surface of the base material, and a light-absorbing portion is formed in a region other than the light-collecting region. The method for producing a lens sheet according to claim 6, wherein: 8. The light-shielding positive-type photosensitive material is developed, and the light-shielding positive-type photosensitive material is developed to remove the material in an exposed area, so that the light-exiting side of the base material is removed. 7. The method for manufacturing a lens sheet according to claim 6, wherein a light-emitting portion is formed in a converging region of each of the light-entering lenses on the surface of the lens, and a light absorbing portion is formed in a region other than the converging region. . 9. The light-sensitive material is a light-transmitting positive-type photosensitive material. The light-transmitting positive-type photosensitive material is developed to remove the material in the exposed region and to remove the material in the unexposed region. By leaving the mold photosensitive material as a protruding portion and fixing the coloring material on the remaining protruding portion, a light emitting portion is formed in the light collecting area of each of the light incident lenses on the light emitting side surface of the base material. 7. The method according to claim 6, wherein a light absorbing portion is formed in a region other than the light collecting region.