Optical element

An optical element formed by stacking each of two resin layers on a glass substrate, wherein when the second resin layer of the two resin layers counting from the glass substrate is formed, an external circumferential part of the second resin layer is formed so as to be located inward of the outer circumferential part of the first resin layer, which is located closer to the glass substrate than the second resin layer.

TECHNICAL FIELD

The present invention relates to an optical element, and to a method for manufacturing the same.

TECHNICAL BACKGROUND

Molding processes are frequently employed in the manufacture of optical elements (for example, see Patent Document 1). For example, in the case of a molding process for a phase Fresnel lens, which is a bonded-multilayer diffractive optical element, a first resin material is packed into a gap between a disk-shaped glass substrate and a molding die positioned in proximity to the glass substrate, and a first resin layer having a diffraction grating is molded. Then, a molding die is pressed against a second resin material having a different refractive index than the first resin material, which has been dripped onto the first resin layer, and a second resin layer is molded. Consequently, a bonded-multilayer diffractive optical element be molded.

PRIOR ARTS LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, during formation of multiple layers by the method mentioned above, when the outside diameter of the second layer is greater than the outside diameter of the first layer, there is a tendency for gases to get trapped inside the external circumferential part of the second layer which protrudes out from, the first layer, creating a risk of air bubbles becoming incorporated into the optical element, and of degraded appearance.

With the foregoing in view, it is an object of the present invention to provide a method for manufacturing an optical element that prevents incorporation of air bubbles, and an optical element manufactured thereby.

Means to Solve the Problems

To achieve this object, the method for manufacturing an optical element provides a method for manufacturing an optical element by stacking and molding individual layers of a plurality of layers on a base material, wherein when those among the plurality of layers constituting the second and subsequent layers as counted from the base material are to be molded, the molding is conducted in such a way that the external circumferential part of the layer to be molded is located inward from the external circumferential part of the layer located closer towards the base material than the layer.

In the above method, in preferred practice, the plurality of layers constitutes two layers, and during molding of the layer constituting the second of the two layers as counted, from the base material, the molding is conducted in such a way that the external circumferential part, of the second layer is located inward from the external circumferential part of the first layer, which is located closer towards the base material than the second layer.

In the above manufacturing method, the first layer and the second layer are respectively molded from a resin material, and the viscosity of the resin material employed during molding of the second layer can be 3000 to 7000 mPa·s.

Additionally, in the above manufacturing method, in preferred practice, the first layer, which has a diffraction grating, is molded onto the base material, the second layer is stacked and molded onto the first layer so as to become bonded to the diffraction grating, and the resin material employed during molding of the first layer having a viscosity of 200 to 800 mPa·s.

Additionally, in the above manufacturing method, each of the layers is respectively molded from a resin material, and the viscosity of the resin material employed during molding of at least any one of the plurality of layers can be 3000 to 7000 mPa·s.

Additionally, in the above manufacturing method, each of the layers preferably has a thickness of 50 to 400 μm.

The optical element according to a first invention is manufactured by the aforementioned method for manufacturing an optical element.

The optical element according to a second invention is provided with a base material, and with a plurality of layers stacked and molded onto the base material, the external circumferential part of those among the plurality of layers constituting the second and subsequent layers as counted from the base material, being located inward from the external circumferential part of the layer located closer towards the base material than the layer.

In the second optical element, in preferred practice, the plurality of layers constitutes two layers, the external circumferential part of the layer constituting the second of the two layers, as counted from the base material, being located inward from the external circumferential part of the first layer, which is located closer towards the base material than the second layer.

Additionally, in the second optical element, the first layer and the second layer are respectively molded from a resin material, and the viscosity of the resin material employed during molding of the second layer can be 3000 to 7000 mPa·s.

Additionally, in the second optical element, in preferred practice, the first layer, which has a diffraction grating, is molded onto the base material, the second layer is stacked and molded onto the first layer so as to become bonded, to the diffraction grating, and the resin material employed during molding of the first layer having a viscosity of 200 to 800 mPa·s.

Additionally, in the second optical element, each of the plurality of layers is respectively molded from a resin material, and the viscosity of the resin material employed during molding of at least any one of the plurality of layers can be 3000 to 7000 mPa·s.

Additionally, in the second optical element, each of the plurality of layers preferably has a thickness of 50 to 400 μm, respectively.

Advantageous Effects of the Invention

According to the present invention, incorporation of air bubbles info an optical element can be prevented.

DESCRIPTION OF THE EMBODIMENTS

The preferred embodiments of the present invention are described below, making reference to the accompanying drawings. As an example of the optical element in a first embodiment, a phase Fresnel lens (hereinbelow designated as “PF lens1”), which is a bonded-multilayer diffractive optical element, is shown inFIG. 2. The PF lens1of the first embodiment is constituted by a glass substrate2, a first resin layer4molded onto the glass substrate2, and a second resin layer6stacked and molded onto the first resin layer4. The glass substrate2is molded into a disk shape from a transparent glass material, and a primer layer3of a silane coupling agent is formed on a one face of the glass substrate2(the face to be joined to the first resin layer4).

The resin layer4, which is the first layer counting from the glass substrate2, is formed to disk shape front a transparent resin material, and a diffraction grating5in which a plurality of ring zones are arrayed in concentric circles is formed on a one face of the first resin layer4(the face to be joined to the second resin layer6). The diameter of the first resin layer4is slightly smaller than the diameter of the glass substrate2(and is larger than the effective diameter of the PF lens1), with the external circumferential part of the first resin layer4being located inward of the external circumferential part of the glass substrate2. Also, the thickness of the first resin layer4is 50 μm to 400 μm, for example. For simplicity in description in the drawings, the diffraction grating5is depicted as having a reduced number of ring zones; however, the actual number of ring zones would be sufficiently great as to be serviceable. Also, in the drawings, hatching is omitted in cross sectional views, for simplicity in description.

The resin layer6, which is the second layer counting from the glass substrate2, is molded to disk shape from a transparent resin material having a different refractive index than the first resin layer4. The diameter of the second resin layer6is slightly smaller than the diameter of the first resin layer4(and is larger than the effective diameter of the PF lens1), with the external circumferential part of the second resin layer6being located inward of the external circumferential part of the first, resin layer4. Also, the thickness of the second resin layer6is 50 μm to 400 μm, for example.

The method for manufacturing the PF lens1constituted in the above manner is described with reference to the flowchart shown inFIG. 3. Firstly, the first resin layer4is molded and joined onto the glass substrate2(Step S101). During molding of the first resin layer4, as shown inFIG. 1A, a liquid mixture of a silane coupling agent/ethyl alcohol/water (the water being made moderately acidic with acetic acid or the like) is applied by spin coating over the entire surface of a one face of the glass substrate2, and baked to form a primer layer3. A first molding die (mold)10having a predetermined diffraction grating is positioned adjacently to the one face of the glass substrate2on which the primer layer3has been formed, and as shown inFIG. 1B, an uncured resin4afor molding the first resin layer4is packed into the gap between them. In this state, the resin4ais irradiated with ultraviolet light at a predetermined exposure (for example, 2000-4000 mJ/cm2) from the other face of the glass substrate2, curing the uncured resin4a, which is then released from the mold.

Consequently, the first resin layer4having the diffraction grating5is molded through transfer of the grating shape of the first molding die10to the resin4a, and the first resin layer4is joined to the one face of the glass substrate2via the primer layer3. The resin material (resin4a) employed for the first resin layer4is an ultraviolet-curing resin having a viscosity of 200 mPa·s to 800 mPa·s in the uncured state. During molding, the resin4ais packed in such a way that the external circumferential part of the first resin layer4is located inward of the external circumferential part of the glass substrate2.

Next, the second resin layer6is stacked and molded onto the first resin layer4, becoming joined thereto (Step S102). During molding of the second resin layer6, as shown inFIG. 1C, an uncured resin6afor molding the second resin layer6is dripped onto the first resin layer4; and as shown inFIG. 1D, a molding die (mold)12is placed against the dripped resin6a, then cured with ultraviolet in the same manner as the first layer, and released from the mold. The surface (transfer surface) of the second molding die12is formed to a flat surface. The surface (transfer surface) of the second molding die12is determined according to the shape of the second resin layer6, and may be a spherical face or aspherical face.

As shown inFIG. 1E, the second resin layer6is molded in such a way as to bond to the diffraction grating5at the other face, and the second resin layer6is joined to the one face of the first resin layer4. The resin material (resin6a) employed for the second resin layer6is an ultraviolet-curing resin having a viscosity, in the uncured state, of 3000 mPa·s to 7000 mPa·s. During molding, the second molding die12is brought into contact against the resin6ain such a way that the external circumferential part of the second resin layer6is located inward of the external circumferential part of the first resin layer4. In this way, the PF lens1in which the two resin layers4,6are molded onto the glass substrate2is manufactured.

As a result, according to the first embodiment, because the external circumferential part, of the second resin layer8is located inward of the external circumferential part, of the first resin layer4which is located closer to the glass substrate2than the second resin layer6, during molding, the external circumferential part of the resin6aof the second layer does not protrude out from the first resin layer4so that gases become entrained inside, and air bubbles can be prevented from being incorporated into the PF lens1.

The viscosity of the resin material (resin6a) employed during molding of the second resin layer6is 3000 mPa·s to 7000 mPa·s, and in cases in which a resin material of such relatively high viscosity is employed for the second resin layer6, when the external circumferential part of the resin material6aof the second layer protrudes out from the first resin layer4during molding, gases would tend to became entrained therein. Therefore, incorporation of air bubbles into the PF lens1can be effectively prevented. The range of viscosity of the resin material (resin6a) employed during molding of the second resin layer6can be from 4600 mPa·s to 5400 mPa·s.

The viscosity of the resin material, (resin4a) employed during molding of the first resin layer4is 200 mPa·s to 800 mPa·s, and by employing a resin material of lower viscosity than the second resin layer6for the first resin layer4, incorporation of air bubbles into the first resin layer4can be prevented. The range of viscosity of the resin material (resin4a) employed during molding of the first resin layer4can be from 400 mPa·s to 600 mPa·s.

The thicknesses of the first resin layer4and the second resin layer6are respectively from 50 μm to 400 μm, and the two resin layers can be molded, as appropriate, within this range of thickness for each layer.

Next, a second embodiment of a PF lens is described while referring toFIG. 4. The PF lens21of the second embodiment is constituted by a first glass substrate22, a first resin layer24molded onto the first glass substrate22, a second resin layer26stacked and molded onto the first resin layer24, and a second glass substrate28stacked onto and joined to the second resin layer26. The first glass substrate22is molded to disk shape from a transparent glass material, and a primer layer23of a silane coupling agent is formed on a one face of the first glass substrate22(the face to be joined to the first resin layer24).

The resin layer24, which is the first layer counting from the first glass substrate22, is formed into disk shape from a transparent resin material, and a diffraction grating25in which a plurality of ring zones are arrayed in concentric circles is formed on a one face of the first resin layer24(the face to be joined to the second resin layer26). The diameter of the first resin layer24is slightly smaller than the diameter of the first glass substrate22(and is larger than the effective diameter of the PF lens21), with the external circumferential part of the first resin layer24being located inward of the external circumferential part of the first glass substrate22. Also, the thickness of the first resin layer24is 50 μm to 400 μm, for example.

The resin layer26, which is the second layer counting from the first glass substrate22, is molded to disk shape from a transparent resin material having a different refractive index than the first resin layer24. The diameter of the second resin layer26is slightly smaller than the diameter of the first resin layer24(and is larger than the effective diameter of the PF lens21), with the external circumferential part of the second resin layer26being located inward of the external circumferential part of the first resin layer24. Also, the thickness of the second resin layer26is 50 μm to 400 μm, for example.

The second glass substrate28is molded to disk shape from a transparent glass material, and a primer layer29of a silane coupling agent is formed on the other face of the second glass substrate28(the face to be joined to the second resin layer26).

The method for manufacturing the PF lens21constituted in the above manner is now described. The flow of the manufacturing method of the PF lens21according to the second embodiment is similar to that in the case of the first embodiment, and the description will employ the flowchart shown inFIG. 3. Firstly, the first resin layer24is molded and joined onto the first glass substrate22(Step S101). During molding of the first resin layer24onto the first glass substrate22, as shown inFIG. 5A, a liquid mixture of a silane coupling agent/ethyl alcohol/water (the water being made moderately acidic with acetic acid or the like) is applied by spin coating over the entire surface of a one face of the first glass substrate22, and baked to form a primer layer23. A molding die (mold)30having a predetermined diffraction grating is positioned adjacently to the one face of the first glass substrate22onto which the primer layer23has been formed, and as shown inFIG. 5B, an uncured resin24afor molding the first resin layer24is packed into the gap between them. In this state, the resin24ais irradiated with ultraviolet light for a predetermined duration (for example, two minutes) from the other face of the first glass substrate22, curing the uncured resin24a, which is then released from the mold.

Consequently, the first resin layer24having the diffraction grating25is molded through transfer of the grating shape of the molding die30to the resin24a, and the first resin layer24is joined to the one face of the glass substrate22via the primer layer23. The resin material (resin24a) employed for the first resin layer24is an ultraviolet-curing resin having a viscosity of 200 mPa·s to 800 mPa·s in the uncured state. During molding, the resin24ais packed in such a way that the external circumferential part of the first resin layer24is located inward of the external circumferential part of the first glass substrate22.

Next, the second resin layer26is stacked and molded onto the first resin layer24, becoming joined thereto (Step S102). During molding of the second resin layer26, as shown inFIG. 5C, an uncured resin26afor molding the second resin layer26is dripped onto the first resin layer24; and as shown inFIG. 5D, the second glass substrate28is placed against the dripped resin26a, then cured with ultraviolet in the same manner as the first layer. At this time, the primer layer29has been formed on the other face of the second glass substrate28in the same manner as for the first glass substrate22, and through contact of this primer layer29against the resin26a, molding of the second resin layer26and joining of the second glass substrate28to the second resin layer26can be accomplished simultaneously.

Consequently, the second resin layer26is molded in such a way as to bond to the diffraction grating25at the other face, as well as joining the second resin layer26to the one face of the first resin layer24, while simultaneously joining the second glass substrate28to the one face of the second resin layer26via the primer layer29. The resin material (resin26a) employed for the second resin layer26is an ultraviolet-curing resin having a viscosity, in the uncured state, of 3000 mPa·s to 7000 mPa·s. During molding, the second glass substrate28is brought into contact against the resin26ain such a way that the external circumferential part of the second resin layer26is located inward of the external circumferential part of the first resin layer24. In this way, the PF lens21of two molded resin layers24,26between the two glass substrates22,28is manufactured.

As a result, according to the second embodiment, advantageous effects comparable to those in the case of the first embodiment can be obtained. Moreover, according to the second embodiment, the second glass substrate28, on which the primer layer29has been formed, is brought into contact against the resin26awhile molding the second resin layer26, whereby molding of the second resin layer26and joining of the second glass substrate28to the second resin layer26can be accomplished simultaneously. Therefore, in the case of manufacture of the PF lens21by molding of the two resin layers24,26between the two glass substrates22,28, the need to mold the second resin layer with a molding die is obviated, and the production process of the PF lens21can be simplified.

In the second embodiment mentioned above, the second resin layer26is molded while the second glass substrate28on which the primer layer29has been formed is brought into contact against the resin26a; however, there is no limitation to this. For example, in the same manner as in the first embodiment as shown inFIGS. 1A to 1E, after molding the two resin layers4,6over the (first) glass substrate2, an adhesive9could be used to stack and adhere (join) the second glass substrate8onto the second resin layer6as shown inFIG. 1F. Consequently, because the second glass substrate8is adhered by the adhesive9, in the case of manufacture to a PF lens41in which the two resin layers4,6are molded between the two glass substrates2,8, the need to form a primer layer on the second glass substrate8is obviated, and the PF lens41manufacturing process can be simplified.

Additionally, whereas in the embodiments mentioned above, only two resin layers are molded over the (first) glass substrate, such an arrangement is not provided by way of limitation; it would be acceptable, for example, to mold three or more layers, applying the present invention during stacking and molding of each layer of the plurality of layers on the base material. In this case, the viscosity of the resin material employed during molding of at least any one of the plurality of layers can be one having a viscosity of 3000 mPa·s to 7000 mPa·s. The viscosity of the resin can be 4600 mPa·s to 5400 mPa·s.

In the embodiments mentioned above, a glass substrate is employed as the base material, but such an arrangement is not provided by way of limitation; a substrate of plastic or the like, for example, could also foe employed, as long as the material is transparent.

In the embodiments mentioned above, the glass substrate, the first resin layer, and the second layer are each molded to disk shape, but such an arrangement is not provided by way of limitation; at least any one face (the first or other face) of the glass substrate, the first resin layer, and the second resin layer may be a spherical face or an aspherical face. Additionally, after the first resin layer and the second resin layer have been formed on the glass substrate, the external circumferential parts may be cut to effect finishing the desired shape. In a case in which the second resin layer has an aspherical face, the thickness of the second resin layer can be from 50 μm to 1000 μm.

While the embodiments mentioned above describe the example of a PF lens, which is a type of diffractive optical element, such an arrangement is not provided by way of limitation; the invention is applicable sis well to ordinary Fresnel lenses, aspherical lenses, microlens arrays, and the like.

EXPLANATION OF NUMERALS AND CHARACTERS

4: first resin layer

6: second resin layer

24: first resin layer

26: second resin layer