JP2003021719A - Polarized light diffraction element and producing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a polarized light diffraction element whose adhesion force is strengthened. SOLUTION: In the polarized light diffraction element wherein the diffraction efficiency depends on the polarization direction and which has a first transparent substrate 1, a double refraction film 3 having a diffraction grating formed as a periodically rugged grating and adhering onto the first transparent substrate 1 via an adhesion layer 2, an overcoat layer 4 formed on the double refraction film and a second transparent substrate 5 adhering onto the overcoat layer 4 using the overcoat layer 4 as an adhesion layer, an adhesion strengthening part 6 is formed at least at a part on the periphery of the device as the part free from the adhesion layer and the double refraction film between the first and the second transparent substrates and the first and the second transparent substrates strongly adhere to each other by filling the adhesion strengthening part 6 with the material of the overcoat layer 4.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polarization diffraction element and a method for manufacturing the same.

[0002]

2. Description of the Related Art A polarization diffractive element is a diffractive element having different diffraction efficiency depending on the polarization direction. For example, in an optical pickup device, an optical path of a light beam directed from a light source to an optical disk and a return light beam from the optical disk are guided to a photodetection section. It is used to separate from the optical path.

As a birefringent polarization diffractive element, there has been proposed one in which a birefringent film having a periodic concave-convex grating is bonded on a transparent substrate and an isotropic overcoat layer is formed thereon ( Kahei 10-302291, JP 2000
-75130 publication).

The polarization diffraction elements described in these publications are
The structure can be manufactured at low cost by a simple process, and the material cost of the birefringent film material using the polymer birefringent material is relatively low, and mass production is easy.

Further, the one shown in FIG. 1 is intended to improve the above-mentioned polarization diffractive element to improve the flatness on both sides of the element to achieve good optical characteristics and mechanical strength. In the polarization diffraction element whose cross-sectional view is shown in FIG. 1, a birefringent film 3 having a periodic concavo-convex grating formed thereon is adhered by an adhesive layer 2 on a first transparent substrate 1 made of glass, plastic or the like, and the birefringent film 3 is formed. An isotropic overcoat layer 4 is formed on the upper side, and the second transparent substrate 5 is adhered using the overcoat layer 4 as an adhesive layer.

The polarization diffractive element having such a structure has a "mechanical strength as an element" at the time of use because both surfaces thereof are transparent substrates having high mechanical strength, and the productivity is high. However, there is a problem in terms of durability against environmental changes.

That is, since the birefringent film 3 and the transparent substrates 1 and 5 have different shrinkage rates and thermal expansion rates, internal stress is generated due to environmental changes such as temperature changes, and peeling easily occurs at the peripheral portion of the element. Generally, internal stress is easily generated on the joint surface of dissimilar materials, warpage and accompanying peeling of the adhesive surface are likely to occur, and peeling is also likely to occur when a shock is applied, so impact resistance is not sufficient. I want to.

As a countermeasure against this, it is effective to increase the adhesive strength by increasing the thickness of the overcoat layer which is the adhesive layer. However, when the adhesive layer is simply thickened, the adhesive itself generated when the adhesive is cured is generated. Since the effect of shrinkage of the adhesive becomes large, it becomes difficult to make the thickness of the adhesive layer uniform, and the amount of the adhesive used becomes large, resulting in poor production cost.

[0009]

In view of the above-mentioned circumstances, the present invention "controls the layer thickness of an overcoat layer which functions as an adhesive layer between a birefringent film having a diffraction grating and a second transparent substrate. It is an object to realize a polarization diffraction element which has an excellent thickness and is capable of strengthening the adhesive force, peeling off the adhesive surface and the like and having excellent impact resistance.

[0010]

The polarization diffractive element of the present invention is a "polarization diffractive element having a different diffraction efficiency depending on the polarization direction", and includes a first transparent substrate, a birefringent film, an overcoat layer, and 2 transparent substrates.

The "first and second transparent substrates" are made of a transparent material such as glass or plastic and have a parallel plate shape.

The "birefringent film" is adhered to the first transparent substrate via an adhesive layer, and a diffraction grating is formed as a periodic uneven grating on the surface opposite to the adhesive layer.

The "overcoat layer" is formed on the birefringent film (on the side where the periodic concavo-convex grating is formed) with an isotropic transparent material. This overcoat layer functions as an adhesive that bonds the birefringent film and the second transparent substrate.

The polarization diffraction element of the present invention has the following features. That is, the adhesion strengthening portion is formed on at least a part of the peripheral portion of the element. The “adhesion-strengthened portion” is formed between the first and second transparent substrates as “a portion having no adhesive layer and no birefringent film”. Then, by filling the adhesion strengthened portion with the material of the overcoat layer, the first and second transparent substrates are firmly bonded.

The adhesion-strengthening portion is formed as "at least a part of the element peripheral portion" as described above, but in order to realize sufficient strength, "adhesion-strengthening portion is equal to or more than half of the element peripheral portion". It is preferable (Claim 2), and more preferable is that "the entire periphery of the peripheral portion of the element is the adhesion strengthened portion" (Claim 3).

The polarization diffractive element according to claim 1 or 2 or 3 is characterized in that "the thickness of the transparent substrate is different from the portion where the adhesion strengthening portion of the first and / or second transparent substrate sandwiches the birefringent film. May have a step so as to reduce the thickness (claim 4), and the "adhesion strengthening portion of the first and / or the second transparent substrate may have an outer edge portion with respect to a portion sandwiching the birefringent film. It may have a taper so as to widen the width of the adhesion-strengthened portion "(claim 5). This claim 4
Alternatively, by adopting the method of 5, the adhesion area of the first and / or second transparent substrate in the adhesion strengthening portion increases, so that the adhesion force can be effectively increased.

A "spacer for controlling the thickness of the overcoat layer" can be provided in the overcoat layer of the polarization diffraction element according to any one of claims 1 to 5 (claim 6). The "spacer" can be made of a resin material (claim 7), and can be preferably made of "UV curable resin" (claim 8). The resin spacer can be formed by printing (claim 9).

The material of the overcoat layer in the polarization diffraction element according to any one of claims 1 to 9 is preferably an "acrylic or epoxy material" (claim 10).

The birefringent film in the polarization diffraction element according to any one of claims 1 to 10 is preferably a "polymer birefringent film" (claim 11), and particularly "polymer birefringence in which molecular chains are oriented". A "film" is preferable (claim 12), and as such a polymer birefringent film, "organic polymer film in which molecular chains are oriented by stretching" can be used (claim 13).

The manufacturing method of the present invention includes the above-mentioned claims 1 to 1.
A method for manufacturing a polarization diffraction element according to any one of 3 above, comprising a birefringent film bonding step, a mask pattern forming step, a grating forming step, a removing step, an overcoat layer forming step, and a curing / curing step. It has a bonding process and a dividing process.

In the "birefringence film forming step", the entire surface of the first transparent substrate having an area where a plurality of polarization diffraction elements can be arranged,
It is a step of adhering the birefringent film through an adhesive layer. The “mask pattern forming step” is a step of forming a mask pattern corresponding to a plurality of sets of diffraction gratings on the birefringent film by using a metal film.

The "grating formation step" is a step in which dry etching is performed through a mask pattern to remove the mask pattern to form a plurality of sets of diffraction gratings made of a periodic uneven grating.

The "removing step" is a step of removing the birefringent film portion and the adhesive layer portion excluding a plurality of sets of diffraction gratings.

The "overcoat layer forming step" is a step of forming an overcoat layer on the surface of the first transparent substrate exposed by the removing step and a plurality of sets of diffraction gratings formed by the birefringent film.

In the "curing / adhesion step", the second transparent substrate is arranged on the overcoat layer to cure the overcoat layer,
This is a step of adhering the second transparent substrate with the overcoat layer.

The "dividing step" is a step of separating the whole into groups of diffraction gratings to form a plurality of polarization diffraction elements.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments will be described below. In the embodiment shown in FIG. 2, the polarization diffraction element has a birefringent film 3 and an adhesive layer 2 on a first transparent substrate 1 as shown in the figure.
And the overcoat layer 4 is formed on the surface of the birefringent film 3 on the side where the diffraction grating is formed by the periodic concavo-convex grating, and the second transparent substrate 5 is arranged on the overcoat layer 4. In addition, as shown in the cross section shown in FIG. 2, the adhesion strengthening portion 6 has the “first adhesive strength” at least at a part (both ends in the drawing) of the peripheral portion of the element.
And the adhesive layer 2 and the birefringent film 3 between the second transparent substrates 1 and 5.
Formed by filling the adhesive strengthening portion 6 with the material of the overcoat layer 4 to form the first and second portions.
The transparent substrates 1 and 5 are firmly bonded together.

In the adhesion strengthening portion 6, since the birefringent film 3 does not exist between the transparent substrates 1 and 5, the "thickness of the material of the overcoat layer as an adhesive" that fills this portion becomes large, so that the adhesion is increased. Power improves. By thus strengthening the adhesion by the adhesion strengthening portion 6, the “birefringent film 3 and the second transparent substrate 5
The thickness of the overcoat layer 4 between the upper and lower transparent substrates 1 and 5 can be sufficiently reduced, and the thickness of the entire polarization diffraction element can be suppressed to a "thickness that can be easily controlled".
It is possible to improve productivity while achieving good parallelism.

In the embodiment shown in FIG. 2, the adhesion strengthening portion is formed only on the "end portion in the left-right direction of the drawing" of the polarization diffraction element, not on the end edge portion in the direction orthogonal to the drawing. Although the adhesion strengthening portion may be formed only in a part of the element peripheral portion, the adhesion strengthening portion is defined by a half circumference or more of the element peripheral portion (claim 2), and further, the entire circumference of the element peripheral portion is formed. It goes without saying that it is preferable to use the adhesion strengthened portion (claim 3).

In the embodiment shown in FIG. 3, the adhesion strengthening portion 6A is used.
In this portion, the first transparent substrate 1 has a “step with respect to the portion sandwiching the birefringent film 3 so as to reduce the thickness of the transparent substrate 1” (claim 4). .

In the embodiment shown in FIG. 4, the adhesion strengthening portion 6B is a portion of the adhesion strengthening portion 6B in which the first transparent substrate 1 "is directed toward the outer edge portion with respect to the portion sandwiching the birefringent film 3. Has a taper so as to widen the width (claim 5).

When the structure shown in FIGS. 3 and 4 is used, the adhesion area is "increased by the material of the overcoat layer" in the adhesion strengthening portion, so that the adhesion strength is further enhanced as compared with the embodiment shown in FIG. The effect of can be enhanced. Further, regardless of the presence or absence of the step or taper, by roughening the bonding surface in the bonding strengthened portion,
The effect of strengthening the adhesive strength can be obtained.

The embodiment of FIG. 5 has a configuration in which a spacer 7 for controlling the thickness of the overcoat layer 4 is provided in the overcoat layer 4 in the embodiment of FIG. 2 (claim 6). The spacer 7 is arranged outside the formation region of the “diffraction grating by the periodic uneven grating” of the birefringent film 3.

The spacer 7 is for "controlling the thickness of the overcoat layer 4 for adhering between the birefringent film 3 and the transparent substrate 5", and by providing this, "the thickness of the overcoat layer as an adhesive is provided. Can be made more uniform, the parallelism between the upper and lower transparent substrates 1 and 5 can be improved, and good performance as an optical element can be obtained.

The spacer 7 can be made of resin. A UV curable resin is suitable as this resin, and in the embodiment of FIG. 5 as well, the spacer 7 is made of a UV curable resin. Since the UV curable resin is cured by being irradiated with ultraviolet rays, the curing time can be shortened and the productivity becomes good.

The "thickness" of the spacer 7 is 1 when it is 1 μm or more.
The thickness is preferably 00 μm or less, and more preferably 5 μm or more and 50 μm or less.

A spacer having a thickness of 100 μm or more makes it difficult to obtain uniform thickness of the spacer itself.
If the spacer has a thickness of less than μm, the overcoat layer 4 may have a thickness of less than 1 μm, resulting in insufficient adhesion. Further, if the thickness of the spacer 7 is 100 μm or more, the amount of the overcoat agent to be filled increases, which causes a problem of lowering productivity.

The spacer 7 is preferably formed by "printing". Screen printing, intaglio printing, etc. are well known methods of "applying resin to a predetermined thickness",
Very good productivity.

In each of the above-mentioned embodiments, the material of the overcoat layer 4 is preferably acrylic or epoxy based from the viewpoint of easy control of properties such as viscosity and refractive index, adhesive strength and transparency. Item 10).

Considering that the birefringent film 3 can be manufactured in a required area in a large amount and at low cost, polycarbonate (PC), polyvinyl alcohol (PVA), polymethylmethacrylate (PMMA), polystyrene, polysulfone ( It is preferably a "polymer birefringent film" such as PSF), polyether sulfone (PES), and polyimide (claim 11), among which "polymer film with oriented molecular chains".
Is preferable (Claim 12), and from the viewpoint of productivity, “organic polymer film in which molecular chains are oriented by stretching” is particularly preferable (Claim 13).

[0041]

Example 1 Thickness: 10 on a transparent substrate having a thickness of 500 μm by a “adhesive layer having a thickness of 30 μm by an ultraviolet curable adhesive”.
The polymer birefringent film of 0 μm was laminated and integrated under reduced pressure, and then baked at 100 ° C. for 10 minutes while irradiating with ultraviolet rays to completely cure the adhesive layer (FIG. 6-
a: birefringent film bonding step).

Then, a periodic pattern (3.0 mm × 3.0 mm / 3.0 μm) formed of a metal thin film was formed on the polymer birefringent film.
m pitches) are formed (mask pattern forming step), dry etching is performed by using this periodic pattern as a mask, the metal mask is removed, and plural sets of periodic concave-convex lattice shapes are formed on the polymer birefringent film. (FIG. 6-b: Lattice forming step).

Next, the "polymer birefringent film and the adhesive layer" on the outer periphery of each set of the periodic concavo-convex lattice was physically removed by means of a dicing device or the like to form a portion to be an adhesion strengthening portion.
(FIG. 6-c: Removal step).

Further, an acrylic UV curable resin to be an overcoat layer was bottled on the side of the polymer birefringent film on which the periodic concavo-convex lattice was formed (overcoat layer forming step). Thickness on this acrylic UV curable resin: 50
Place a transparent substrate of 0 μm and apply appropriate pressure to fill the concave-convex lattice and the adhesion strengthened part with an overcoat agent (Fig. 6-d,
e) After irradiation with ultraviolet rays, baking was performed at 100 ° C. for 10 minutes to completely cure (curing / bonding step).

Thereafter, the whole is cut into "pieces of 5.0 mm x 5.0 mm size" by a dicing device, and a plurality of polarization diffraction elements having the structure shown in Fig. 2 are manufactured (Fig. 6-f: dividing step). ).

Example 2 In Example 1, a UV curable resin to be a spacer having a predetermined thickness was applied by screen printing to the periphery of each set of periodic concavo-convex grids and cured by irradiation with ultraviolet rays to a thickness of 1
Spacers of 0 ± 3 μm were formed. A plurality of polarization diffractive elements having the structure shown in FIG. 5 were manufactured by the same steps as in Example 1 except for the spacer formation.

Example 3 In the same process as in Example 1, a plurality of polarization diffractive elements having the structure as shown in FIG. 2 were prepared by using an epoxy-based ultraviolet curing resin for the overcoat layer.

Comparative Example 1 A polarization diffraction element having the structure shown in FIG. 1 was produced by the same steps as in Example 1. Comparative Example 2 A polarization diffraction element having the structure shown in FIG. 1 was produced by the same steps as in Example 2. That is, Comparative Examples 1 and 2 do not have an adhesion strengthening part.

Immediately after production and reliability test (under an environment of 70 ° C. and 95% RH) of the 5.0 mm × 5.0 mm size polarization diffraction element produced as in Examples 1 to 3 and Comparative Examples 1 and 2. Further, the appearance after standing for 200 hours) was visually evaluated, and when peeling was confirmed in the periphery, x was given, and when no peeling was confirmed, it was given ◯. The evaluation results are shown below.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 After fabrication ○ ○ ○ × × After reliability test ○ ○ ○ × × From these results, the polarization diffraction element according to the present invention has environmental resistance. It turns out to be excellent.

[0051]

As described above, according to the present invention, a novel polarization diffractive element and a method for manufacturing the same can be realized. In the polarization diffractive element of the present invention, since the adhesive strength between the transparent substrates is strengthened by the adhesion strengthening portion, peeling is less likely to occur, and the productivity and reliability are high while satisfying the function as the polarization diffractive element. Further, according to the manufacturing method of the present invention,
A plurality of polarization diffractive elements of the present invention can be manufactured at one time.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a conventional polarization diffractive element.

FIG. 2 is a diagram for explaining one embodiment of a polarization diffraction element.

FIG. 3 is a diagram for explaining one embodiment of the polarization diffraction element.

FIG. 4 is a diagram for explaining one embodiment of the polarization diffraction element.

FIG. 5 is a diagram for explaining one embodiment of the polarization diffraction element.

FIG. 6 is a drawing for explaining the manufacturing method of the polarization diffraction element.

[Explanation of symbols] 1 First transparent substrate 2 Adhesive layer 3 Birefringent film 4 Overcoat layer 5 Second transparent substrate 6 Adhesion strengthening part 7 Spacer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H049 AA03 AA33 AA37 AA57 AA64                       BA05 BA42 BA45 BA47 BB51                       BB62 BC01 BC21                 4F213 AC01 AD03 AD05 AD08 AG01                       AH73 WA15 WA53 WA58 WA67                       WA87 WA92 WB01                 5D119 AA35 AA38 JA22 NA05

Claims (14)

[Claims] 1. A polarization diffractive element having a different diffraction efficiency depending on the polarization direction, wherein a first transparent substrate and a diffraction grating are formed as a periodic concave-convex grating, and an adhesive layer is provided on the first transparent substrate. It has a birefringent film adhered thereto, an overcoat layer formed on the birefringent film, and a second transparent substrate adhered onto the overcoat layer using the overcoat layer as an adhesive. An adhesion strengthening portion is formed on at least a part of the peripheral portion of the element as a portion between the first and second transparent substrates without the adhesive layer and the birefringent film, and the adhesion strengthening portion is formed by the overcoat layer. A polarizing diffractive element characterized in that the first and second transparent substrates are firmly adhered by being filled with the material. 2. The polarization diffractive element according to claim 1, wherein the adhesion strengthening portion is at least half the circumference of the element. 3. The polarization diffraction element according to claim 2, wherein the entire periphery of the peripheral edge portion of the element is an adhesion strengthening portion. 4. The polarization diffraction element according to claim 1, 2 or 3, wherein the adhesion strengthening portion of the first and / or second transparent substrate has a thickness of the transparent substrate with respect to a portion sandwiching the birefringent film. A polarization diffractive element characterized by having a step so as to make the thickness thinner. 5. The polarization diffractive element according to claim 1, 2 or 3, wherein the adhesion-enhancing portion of the first and / or second transparent substrate faces the outer edge portion with respect to the portion sandwiching the birefringent film. A polarization diffraction element having a taper so as to widen the width of the adhesion strengthening portion. 6. The polarization diffraction element according to any one of claims 1 to 5, wherein the overcoat layer has a spacer for controlling the thickness of the overcoat layer. 7. The polarization diffraction element according to claim 6, wherein the spacer is made of resin. 8. The polarization diffraction element according to claim 7, wherein the resin material forming the spacer is a UV curable resin. 9. The polarization diffraction element according to claim 7 or 8, wherein the spacer made of a resin material is formed by printing. 10. The polarization diffraction element according to any one of claims 1 to 9, wherein the material of the overcoat layer is an acrylic or epoxy material. 11. The polarization diffractive element according to any one of claims 1 to 10, wherein the birefringent film on which the diffraction grating formed by the periodic uneven grating is formed is a polymer birefringent film. Polarization diffractive element. 12. The polarization diffraction element according to claim 11, wherein the birefringent film in which the diffraction grating is formed by a periodic concave-convex grating is a polymer birefringent film in which molecular chains are oriented. element. 13. The polarization diffraction element according to claim 12, wherein the polymer birefringent film is an organic polymer film in which molecular chains are oriented by stretching. 14. A method of manufacturing a polarization diffraction element according to any one of claims 1 to 13, wherein an adhesive layer is formed on the entire surface of the first transparent substrate having an area in which a plurality of polarization diffraction elements can be arranged. A birefringent film adhering step of adhering a birefringent film via a mask pattern forming step of forming a mask pattern corresponding to a plurality of sets of diffraction gratings by a metal film on the birefringent film; Through dry etching,
A step of removing the mask pattern to form a plurality of sets of diffraction gratings by a periodic concave-convex grating; a step of removing the birefringent film portion and the adhesive layer portion excluding the plurality of sets of diffraction gratings; A plurality of sets of diffraction gratings formed by a refraction film, an overcoat layer forming step of forming an overcoat layer on the surface of the first transparent substrate exposed by the removing step, and a second transparent substrate on the overcoat layer And a curing / bonding step of curing the above-mentioned overcoat layer and bonding the second transparent substrate with the above-mentioned overcoat layer, and a dividing step of separating the entire diffraction grating into a plurality of polarization diffraction elements. A method of manufacturing a polarization diffraction element, comprising: