JPH08122600A - Optical element holder and its production - Google Patents

Abstract

PURPOSE: To provide an optical element holder capable of satisfying high- accuracy optical characteristics without using intricate assembling stages at the time of fixing and assembling an optical element to a holding frame. CONSTITUTION: This optical element holder is formed by fixing and assembling the optical element 1, such as lens or prism, into the holding frame 2. The holder described above is provided with a clearance of >=0.5mm between the optical element 1 and the holding frame 2 and is provided with a water absorptive resin layer 3 which is formed by incorporating a highly water absorptive polymer having a water absorptive capacity of 5 to 1000cc per 1g and a grain size of <=50μm prior to water absorption therein at >=50vol.% and has hardness of <= JISA50 in the entire circumference of the clearance or a part thereof. Strains are absorbed by this water absorptive resin layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element holding device in which an optical element such as a lens or a prism is fixed to a holding frame such as a lens barrel or a holder for holding the optical element, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Generally, an optical element such as a lens is fixed to a holding frame by using an adhesive. However, due to a difference in thermal expansion coefficient between the optical element and the holding frame, optical distortion is caused by a change in operating environment conditions. Therefore, in the past, Japanese Patent Publication No. 3-60404, Japanese Unexamined Patent Publication No. 3-182708, Japanese Unexamined Patent Publication No. 62-21
In 8913, there is a proposal to prevent optical distortion with time.

In Japanese Patent Publication No. 3-60404, as shown in FIG. 2, the adhesive agent 13 for fixing the lens 11 to the lens barrel 12 is made to have rubber elasticity, and the force generated between the lens 11 and the lens barrel 12 is bonded. The invention of absorbing with agent 13 is disclosed.

In Japanese Patent Laid-Open No. 3-182708, there is shown in FIG.
As shown in FIG. 2, the lens 21 is provided with a cavity 24, and an elastically deformable stress absorbing portion 25 is integrally formed in the cavity 24. An adhesive 23 is applied to the tip of the stress absorbing portion 25 to attach the lens holder 22 to the lens holder 22. A locking invention is disclosed.

In Japanese Laid-Open Patent Publication No. 62-218913, as shown in FIG. 4, the outer surface 33a of the lens holding portion of the adhesive 33 is prevented from coming into contact with the lens barrel 32, and the lens barrel 32 is
There is disclosed an invention in which the lens 31 is fixed via an adhesive 33.

Further, in Japanese Utility Model Publication No. 63-33201, in order to prevent the occurrence of optical distortion after the adhesive is hardened, which tends to occur when the adhesive area of the adhesive is large, as shown in FIG. The holding frame 42 has an inner diameter larger than the inner diameter of the holding surface 42a that holds the lens 41 in the lens holding portion.
Disclosed is an invention in which an intermediate cylinder portion 44 having a length of ½ to 3/4 of the length is provided, and an adhesive 43 is interposed between the lens 41 and the holding surface 42a to fix the lens 41 to the holding frame 42. Has been done.

[0007]

However, Japanese Patent Publication No. 3-6
As described in Japanese Patent No. 0404, only by using the adhesive 13 having rubber elasticity, the level of optical distortion is improved to some extent, but as the durability / reliability condition in recent years becomes more severe, it occurs under that environment. Optical distortion tends to increase, and the level of achievement of conventional low optical distortion has become insufficient.

Further, as in JP-A-3-182708, a stress absorbing portion 25 is formed in the lens 21, and as in JP-B-63-33201, the holding surface 42a into which the adhesive 43 flows is regulated. Although providing the middle cylinder portion 44 for the holding frame 42 also improves the level of optical distortion, it is not sufficient for the optical characteristic specifications of recent high-precision optical systems, as described above, and the lens 21 And holding frame 4
Since 2 has a complicated shape, there is also a drawback that the machining cost of the mold, the machining cost of the holding frame and the like are additionally required.

Then, as disclosed in JP-A-62-218913, the outer peripheral surface 3 of the lens holding portion of the adhesive 33 is used.
In order to form the adhesive 33 layer so that 3a does not come into contact with the lens barrel 32, it is inevitable that a complicated bonding step is taken.
There was a problem that a significant improvement in optical distortion could not be expected despite the cost increase.

The present invention has been made in view of the above-mentioned problems of the prior art, and when fixing optical elements such as lenses and prisms to a holding frame to assemble, a complicated assembling process is not required, and it is inexpensive and highly accurate. It is an object of the present invention to provide an optical element holding device capable of satisfying various optical characteristics and a manufacturing method thereof.

[0011]

In order to solve the above-mentioned problems, the optical element holding device and its manufacturing method of the present invention are configured as follows. That is, according to the invention of claim 1, in an optical element holding device assembled by fixing optical elements such as lenses and prisms in a holding frame, a clearance of 0.5 mm or more is provided between the optical element and the holding frame. The water-absorbent resin layer having a hardness of JIS A50 or less, which has a water-absorbing capacity of 5 to 1000 cc per gram and contains 50% by volume or more of a super-water-absorbing polymer having a particle size before water absorption of 50 μm or less, is used for the clearance. It is provided on the whole circumference or part of it.

According to a second aspect of the present invention, in an optical element holding device assembled by fixing optical elements such as lenses and prisms in a holding frame, 0.5 m is provided between the optical element and the holding frame.
5 to 1000 per gram with clearance of m or more
JIS in which a water-absorbing polymer having a water absorption capacity of cc and a particle size before water absorption of 50 μm or less is used and the water-absorbing polymer which has already absorbed water is contained in an amount of approximately 100% by volume.
A water-absorbent resin layer having a hardness of A50 or less was provided on all or part of the clearance.

According to a third aspect of the present invention, in the structure of the first or second aspect, the water-absorbent resin layer is adhered to either the optical element or the holding frame, or either the optical element or the holding frame. It was configured so that it was not adhered to.

According to a fourth aspect of the present invention, in a method of manufacturing an optical element holding device in which optical elements such as lenses and prisms are fixed and assembled in a holding frame, the distance between the optical element and the holding frame is 0.5 mm or more. After providing a clearance and providing a water-absorbent resin layer containing 50% by volume or more of the super absorbent polymer in the adhesive on the entire circumference or a part of the clearance,
The water absorbent resin layer was formed by curing.

According to a fifth aspect of the present invention, in a method of manufacturing an optical element holding device in which optical elements such as lenses and prisms are fixed and assembled in a holding frame, the distance between the optical element and the holding frame is 0.5 mm or more. After providing a clearance and providing a packing layer in which at least a superabsorbent polymer and a water-soluble polymer are mixed in all or part of the clearance, the water-soluble polymer in the packing layer is removed and at the same time, a high water absorption is achieved. Water-absorbing polymer content of approximately 10
It was constructed by forming a 0% by volume water-absorbent resin layer.

That is, the optical element holding device and the method for manufacturing the same according to the present invention are configured such that the water absorbing resin layer is provided on all or a part between the optical element and the holding frame.

The optical element used in the present invention is
Any of glass, plastic, inorganic crystals, metal plates and combinations thereof can be used. The holding frame that holds the optical element may be made of plastic, metal, FRP, or the like.

Further, the superabsorbent polymer used in the present invention is such as used in paper diapers, sanitary products, soil conditioners, etc., having a water absorption capacity of 5 to 1000 cc / g, and a particle size before water absorption. Is a powder of 50 μm or less, and when it absorbs water, it expands in volume to form a gel. Examples of the material to be used include a polymerizable monomer that is water-soluble or becomes water-soluble by hydrolysis such as starch and cellulose, such as acrylic acid, methacrylic acid, an acrylic acid salt, and methacrylic acid. Acid salts, acrylic acid esters, methacrylic acid esters, acrylic acid amides, methacrylic acid amides, acrylonitrile, methacrylonitrile, maleic acid, sulfonated styrene, vinyl pyridine, etc. Hydrophilic polymer obtained by hydrolysis according to, three-dimensionally polymerized by a crosslinking agent, polyethylene oxide, polypropylene oxide, polyvinylpyrrolidone, sulfonated polystyrene, polyvinylpydiline, polyacrylate, poly Acrylic acid amide, polymer Krill salts, that three-dimensionally polymerized by a hydrophilic polymer crosslinking agent such as polymethacrylic acid amides, etc. are used. Commercially available products include PX-402A manufactured by Showa Denko KK, Sunwet IM-300 manufactured by Sanyo Kasei Co., Ltd., AquaKeep 10HS manufactured by Iron and Steel Chemical Co., Ltd., and the like.

Examples of the cross-linking agent include di- or tri- (meth) acrylic acid esters of polyols such as ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol and polyoxypropylene glycol; the above-mentioned polyols. And unsaturated polyesters obtained by reacting with unsaturated acids such as maleic acid; bisacrylamides such as N, N-methylene-bisacrylamide; di-esters obtained by reacting polyepoxide with (meth) acrylic acid Or tri- (meth) acrylic acid ester; di- (meth) acrylic acid carbamyl ester obtained by reacting polyisocyanate such as tolylene diisocyanate, hexamethylene diisocyanate and the like with hydroxyethyl (meth) acrylate Allylated den Emissions; allylated cellulose. In some cases, methylolation (meta)
Bifunctional compounds or calcium oxides that can be crosslinked under certain reaction conditions, such as acrylamide, glyoxal, phthalic acid, adipic acid, ethylene glycol, etc.
A polyvalent metal salt such as zinc diacetate can also be used.

The water-absorbent resin layer may contain an adhesive resin having high elasticity as a binder component in addition to the superabsorbent polymer. Materials used include polyurethane, polyester, polystyrene, polyethylene, soft polyvinyl chloride, styrene-acrylonitrile copolymer, modified phenol resin, modified epoxy resin, acrylic resin, ABS resin, cellulose acetate, ethylene-
A soft resin such as vinyl acetate copolymer, polyamide, nitrile-butadiene rubber, chloroprene rubber or silicone rubber, rubber or elastomer is used. Further, a water-soluble polymer such as polyvinylpyrrolidone, polyvinyl alcohol or polyacrylamide may be used.

The water-absorbent resin layer may be formed by mixing a binder component with highly water-absorbent polymer powder in the clearance between the optical element and the holding frame and curing it to form a water-absorbent resin layer. After that, the super absorbent polymer is made to absorb water to form a water absorbent resin layer that has already absorbed water, or the binder component is a water-soluble polymer and a mixture of the super absorbent polymer is used as the clearance between the optical element and the holding frame. After it is filled and fixed in water, the water-soluble polymer is dissolved and removed with water, and at the same time, the water-absorbent resin is also made to absorb water.
You may form a water absorption resin layer of volume%.

[0022]

[Action]

(Advantageous Effects of Claims 1 and 4) The optical element and its holding frame itself, or the adhesive for fixing the optical element and the holding frame, expands and contracts under the environment of use due to the influence of temperature and humidity. The difference causes strain from each interface to the inside. This residual strain impairs the optical characteristics as the optical strain of the optical element. When the water absorbing resin layer is formed between the optical element and the holding frame thereof, the residual strain is alleviated by using the water absorbing resin layer as a cushioning material, and the optical element Prevent it from occurring as distortion. In particular, when the water absorbing resin layer has a hardness of JIS A50 or less, the elasticity is high, so that the stress relaxation effect becomes remarkable. If the hardness of the water-absorbent resin layer exceeds JIS A50, the water-absorbent resin cannot expand even if water is absorbed, and the stress relaxation effect cannot be obtained. JIS A5
If it is 0 or less, JIS A0 can be applied, but actually, the hardness of the water-absorbent resin layer may be selected in consideration of the balance between the clearance between the optical element and the holding frame and the required holding strength. In order to absorb water quickly and uniformly, the clearance must be at least 0.5 mm or more. This value is the volume expansion ratio or hardness after absorption of water, and the particle size of the absorbent resin before curing. It is also necessary to change it depending on the mixing ratio and viscosity when mixed in the binder.

The content of the highly water-absorbent polymer in the water-absorbent resin layer depends on the particle size before water absorption, the volume expansion coefficient during water absorption, the hardness of the water-absorbent resin, etc., but is required to be 50% by volume or more.
When it is less than 50% by volume, the water absorbing effect of the water absorbing resin layer by the highly water absorbing polymer is hardly exhibited. Also, regarding the water absorption capacity, the same factor is taken into consideration, and it is 5
It is selected within the range of up to 1000 cc, but if it is less than 5 cc, it has almost no effect, and conversely, if it has a water absorption capacity of more than 1000 cc, uniform water absorption and expansion during water absorption are difficult to occur, and reproducibility is difficult. Further, the particle diameter of the superabsorbent polymer before water absorption is preferably 50 μm or less so that the water can be sufficiently and immediately absorbed from the outside to the inside of the superabsorbent polymer during water absorption. If the particle size exceeds 50 μm, it depends on the material,
When it comes into contact with water, gelation occurs only in the contact portion, which hinders the uniform permeation of water, resulting in a so-called “mamako” phenomenon in which a rapid water absorption rate cannot be obtained.

(Operation of Claim 3) When the water-absorbent resin layer is adhered to both the optical element and the holding frame, the buffer function of the water-absorbent resin layer tends to be insufficient, and either one (preferably the holding frame) is provided. It is preferable that it is adhered only to or not adhered to either. This is because the water-absorbent resin layer
This is because even at the adhesive interface with an optical element or holding frame that is a different material, distortion occurs due to mutual expansion and contraction during curing of the water-absorbent resin layer and during use environment, and this strain easily propagates through the adhesive interface. . At the non-bonded interface, the propagation of this strain is blocked and does not adversely affect the optical element.

(Functions of Claims 2 and 5) A binder in which a water-absorbent polymer is used and a superabsorbent polymer is mixed therein is filled in a clearance between the optical element and the holding frame,
When the water-soluble polymer is dissolved and removed with water or hot water, the superabsorbent polymer also absorbs and swells at the same time, and the clearance is swollen with water and the gelated superabsorbent polymer is filled, making the optical element and the holding frame elastic. To fix.

According to the invention of the method for manufacturing an optical element holding device of claims 4 and 5, the optical element and the holding frame are not specially worked, and a complicated assembling step is not taken. By providing a water-absorbent resin layer between the optical element holding frame and the holding frame, the strain generated during the assembly of the optical element holding device and the usage environment is mitigated, and the optical element holding device is stabilized without deteriorating the optical characteristics of the optical element. can do.

[0027]

[Embodiment 1] Hereinafter, each embodiment of the present invention will be described in detail with reference to FIG. FIG. 5 is a central longitudinal sectional view showing an embodiment of the optical element holding device according to the present invention. 2 in the figure
Is a lens barrel for holding the held lens 1, a concave portion 4 for accommodating the held lens 1 having a larger diameter than the held lens 1 is formed inside, and the held lens 1 is provided below the concave portion 4.
Is provided, and a chamfered portion 7 formed to be larger than the lens chamfered portion 6 formed at the outer peripheral upper end of the held lens 1 is provided at the inner peripheral upper end of the concave portion 4.

In the concave portion 4 of the lens barrel 2, the held lens 1 having a diameter of 30 mm is dropped from the upper portion and placed on the step portion 5, and the transparent silicone rubber adhesive "SE917" is used.
6 "(manufactured by Toray Dow Corning Silicone) and 80% by volume of super absorbent polymer powder" Sanwet IM-1000U "(manufactured by Sanyo Kasei Kogyo Co., Ltd.), which has been sieved to a particle size of 50 μm or less. The silicone rubber adhesive containing the super absorbent polymer is applied to the chamfered portion 7 of the lens barrel 2 to fill the clearance between the held lens 1 and the lens barrel 2, and the mixture is kept at 25 ° C. and 80% RH for 24 hours. The water absorbing resin layer 3 is formed by curing, and the held lens 1 is bonded and held to the lens barrel 2. The hardness of the water absorbent resin layer 3 was JIS A30. Before the lens 1 is dropped into the lens barrel 2, a fluorine-based release agent is thinly applied in advance to the outer peripheral surface of the lens 1 having a thickness of 6 mm so that the adhesive can be quickly removed from the lens 1 after curing. The interface is peeled off.

As means for fixing and holding the lens 1 on the lens barrel 2, the lens 1 is dropped into the lens barrel 2 and then the chamfered portion 7 is dispensed with a silicone rubber adhesive containing the super absorbent polymer (not shown). ) Or the like, and pour it over the entire circumference of the clearance between the lens 1 and the lens barrel 2. In the case of this example, the clearance was set to 0.8 mm.

When the adhesive is applied to the water-absorbent resin layer and the adhesive in the water-absorbent resin layer is gradually hardened by application of water in the air, the superabsorbent polymer in the water-absorbent resin layer also begins to absorb water, resulting in a clearance between the lens 1 and the lens barrel 2. It absorbs more water while gradually expanding and hardening. Then, the water absorption by the superabsorbent polymer is stopped when it absorbs water, expands, and balances with the cohesive force of the adhesive. Therefore, the core of the lens 1 is taken out from the lens barrel 2 with a bell chuck jig or the like, and the silicone rubber adhesive containing the superabsorbent polymer is applied while maintaining this state,
It is necessary to absorb the water.

In this embodiment, the water-absorbent resin layer 3 is formed on the entire circumference of the clearance. However, depending on the holding strength of the lens 1, the clearance and the viscosity of the adhesive, the water-absorbent resin layer may be applied only at three locations. 3 can be formed independently, and it is not always necessary to provide the water absorbing resin layer 3 that is continuous over the entire circumference of the clearance.

Further, in the present embodiment, the release agent is applied only to the outer peripheral surface of the lens 1 in advance. However, the release agent is applied to the inner peripheral side surface of the concave portion 4 of the lens barrel 2 so that the lens 1 and the mirror 1 It is also possible to implement it so that the water absorbing resin layer 3 does not adhere to both of the cylinders 2.

In the lens holding device manufactured as described above, the optical distortion could be suppressed to almost zero even in the initial stage and the lapse of time without forming a complicated shape or taking a complicated process.

[0034]

Example 2 In this example, polyvinyl alcohol was used in place of the silicone rubber adhesive used as the binder component of the water absorbent resin layer 3 in Example 1, and the polyvinyl alcohol had the same high water absorption as in Example 1. Assembled in the same manner as in Example 1 except that the water-soluble resin layer 3 was formed by mixing the water-soluble polymer in the same ratio as in Example 1, filling the clearance with a paste diluted with acetone, and evaporating and curing the paste to form the water-absorbent resin layer 3. It was It should be noted that in this embodiment as well, FIG.
Shall be explained.

The polyvinyl alcohol used in this example is water-soluble, and the hardness of the water-absorbent resin layer 3 after curing is JIS.
It was A43. The clearance between the lens barrel 2 and the lens 1 used was 0.5 mm.

In order to apply the water-absorbent resin before curing, it is effective to apply the water-absorbing resin to the chamfered portion 7 as in this embodiment, or to provide injection holes from several positions on the side surface of the lens barrel 2 and inject from there. Is. In this case, the work efficiency is improved and effective when the entire circumference coating in the clearance is unnecessary.

In the optical element holding device manufactured as described above, similar to the first embodiment, the optical distortion could be suppressed to almost zero in the initial stage and the time course by a simple design and process.
Further, when the optical element holding device manufactured in this example was used for the outermost peripheral optical system of a waterproof product, polyvinyl alcohol was gradually dissolved and removed when water was applied to the optical system, and the mixed high The water-absorbent polymer also begins to absorb water and expands, filling the clearance between the lens barrel 2 and the lens 1, and the polyvinyl alcohol is lost, so that the lens barrel 2 and the lens 1 are not bonded, but water penetrates further into the interior. I was able to prevent it. In this state, even if the product is not splashed with water, the water in the water-absorbent resin layer 3 does not drain, and the lens 1 does not cause optical distortion.
Was able to hold.

[0038]

Example 3 In this example, an ultraviolet curable water-soluble adhesive “3046” (manufactured by ThreeBond Co.) was used in place of the polyvinyl alcohol used in Example 2, except that the water absorbing resin layer 3 was formed. Assembled as in Example 2. However, the clearance between the optical element 1 and the lens barrel 2 was 0.8 mm. Note that this embodiment will be described with reference to FIG.

In this example, a mixture of 80% by volume of super-water-absorbing polymer powder in UV curable water-soluble adhesive "3046" was applied to the clearance between the optical element 1 and the lens barrel 2. After irradiating ultraviolet rays to cure and bond temporarily, sprinkle a 30 ° C warm water shower mainly on the clearance mixture to absorb and swell the superabsorbent polymer while dissolving and removing the cured water-soluble adhesive. . When the superabsorbent polymer has absorbed sufficient moisture, the hot water shower is stopped, the excess moisture is dried and removed, and the absorbed water-absorbent resin layer 3 containing almost 100% by volume of the superabsorbent polymer has a hardness J.
Formed by IS A20.

In the lens holding device manufactured as described above, as described in the second embodiment, the holding state of the lens 1 until the water is splashed from the outside and the highly water-absorbent polymer of the water-absorbent resin layer when the water is splashed Although the temperature characteristics and the like change depending on the holding state of the lens 1 after swelling, as in this embodiment, the water-absorbent resin layer 3 is formed only from the water-absorbed superabsorbent polymer from the beginning, and the lens 1 If is fixed to the lens barrel 2, the initial optical characteristics are maintained and stable performance is obtained. Further, it goes without saying that the same effect as that of the first embodiment can be obtained.

[0041]

According to the present invention, the following effects can be obtained. According to the first and second aspects of the present invention, when the optical element such as the lens or the prism is fixed to the holding frame to be assembled, only the water absorbing resin layer is provided between the optical element and the holding frame to assemble the optical element holding device. Since the water-absorbent resin layer can absorb the strain generated at the time of use or when the use environment changes, a complicated assembling process is not required, and therefore, inexpensive and highly accurate optical characteristics can be obtained even in the initial stage. It is possible to obtain a satisfying optical element holding device. According to the invention of claim 3, in addition to the effects of claims 1 and 2, the propagation of the generated strain can be blocked at the interface between the optical element not bonded to the water-absorbent resin layer and the holding frame. . Claims 4 and 5
According to the invention, when fixing and assembling optical elements such as lenses and prisms to the holding frame, the water-absorbent resin layer can be easily provided between the optical element and the holding frame, so that the initial and time Moreover, it is possible to manufacture an optical element holding device that satisfies highly accurate optical characteristics.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view showing each embodiment of an optical element holding device according to the present invention.

FIG. 2 is a central longitudinal sectional view showing a conventional optical element holding device.

FIG. 3 is a central vertical sectional view showing a conventional optical element holding device.

FIG. 4 is a central vertical cross-sectional view showing a conventional optical element holding device.

FIG. 5 is a central longitudinal cross-sectional view showing a conventional optical element holding device.

[Explanation of symbols]

 1 lens 2 lens barrel 3 water-absorbent resin layer

Claims (5)

[Claims] 1. An optical element holding device in which optical elements such as lenses and prisms are fixed and assembled in a holding frame, and a clearance of 0.5 mm or more is provided between the optical element and the holding frame to provide 5 per 1 g. A water-absorbing resin layer having a water-absorbing capacity of up to 1000 cc and a super-water-absorbing polymer having a particle size before water absorption of 50 μm or less in an amount of 50 vol% or more and having a hardness of JIS A50 or less, is provided around the entire circumference or one of the clearances An optical element holding device, characterized in that it is provided in a section. 2. In an optical element holding device assembled by fixing optical elements such as lenses and prisms in a holding frame, a clearance of 0.5 mm or more is provided between the optical element and the holding frame, and 5 g per 1 g. From a hardness of JIS A50 or less in which a water-absorbing polymer having a water absorption capacity of up to 1000 cc and a particle size before water absorption of 50 μm or less is used, and the water-absorbing polymer that has already absorbed water is contained in almost 100 volume% An optical element holding device, wherein a water-absorbent resin layer is provided on the entire circumference or a part of the clearance. 3. The water-absorbent resin layer is adhered to either the optical element or the holding frame, or is not adhered to either the optical element or the holding frame. Optical element holding device. 4. A method of manufacturing an optical element holding device in which optical elements such as lenses and prisms are fixed and assembled in a holding frame, and a clearance of 0.5 mm or more is provided between the optical element and the holding frame to bond the optical elements. A water-absorbent resin layer containing a super-water-absorbent polymer in an amount of 50% by volume or more is provided on the entire circumference or a part of the clearance, and then the water-absorbent resin layer is cured. Production method. 5. A method of manufacturing an optical element holding device in which optical elements such as lenses and prisms are fixed and assembled in a holding frame, and a clearance of 0.5 mm or more is provided between the optical element and the holding frame. After providing the filling layer in which at least the superabsorbent polymer and the water-soluble polymer are mixed in the entire circumference or part of the clearance, the water-soluble polymer in the filling layer is removed and at the same time the superabsorbent polymer absorbs water. And a water-absorbent resin layer having a high water-absorbent polymer content of about 100% by volume is formed.