JP2008257215A - Optical device, optical low-pass filter, and solid-state imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device which hardly deteriorates quality and performance thereof even when continuously being exposed to both of high-temperature and high-humidity environment and normal environment, and to provide an optical low-pass filter and a solid-state imaging apparatus. <P>SOLUTION: The optical low-pass filter comprises a first birefringent plate, an IR-cut glass, a 1/4 retardation film, a second birefringent plate and a tacky adhesive agent as a bonding layer for bonding the members. The tacky adhesive agent primarily contains a tacky adhesive agent main agent polymer composed of a monomer including many hydrophilic groups to improve permeability of water within the tacky adhesive agent. In addition, by selecting a mixing weight ratio of the pressure sensitive adhesive main agent polymer, the permeability of water can be further improved. As a result, such an optical device and an optical component that, under the high-temperature and high-humidity environment, hardly cause white turbidity by causing the tacky adhesive agent to contain water sufficiently up to the saturated state and, under the normal environment, can release water in the tacky adhesive agent from the outer circumferential part of the optical element to the air and can recover the optical characteristics in a short time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical element, an optical low-pass filter, and a solid-state imaging device, and more particularly to an optical element in which members constituting the optical element are joined by an adhesive.

  The above-described optical element is, for example, an optical low pass filter (OLPF). This optical low-pass filter has a structure as shown in Patent Document 1. More specifically, as shown in FIG. 11, the optical low-pass filter 110 includes two birefringent plates 150 in which a retardation film 170, which is a kind of transmissive optical film, is made of quartz, which is a kind of transmissive optical substrate. , 180. The members constituting the optical low-pass filter 110 (the birefringent plate 150, the IR cut glass 160, the retardation film 170, and the birefringent plate 180) are joined by a joining layer 190, respectively. Note that some optical low-pass filters 110 are configured by integrally bonding an IR cut glass 160. The outer peripheral end of the optical low-pass filter 110 has a sealing material 200. The sealing material 200 has a shape formed continuously from the end portion of the bonding layer 190, a shape covering the entire end portion of the optical low-pass filter 110, and the like.

  For optical elements such as the optical low-pass filter 110, quality reliability such as a high temperature environment test, a low temperature environment test, a temperature impact test repeatedly repeating high and low temperatures, and a high humidity environment test is required as an essential condition. Therefore, the adhesive layer 190 shown in FIG. 11 tends to employ a pressure-sensitive adhesive suitable for temperature impact properties rather than an adhesive. More specifically, in order to prevent the birefringent plates 150 and 180 made of quartz and the retardation film 170 from being separated from each other due to a difference in volume shrinkage due to a temperature change, the difference in volume shrinkage is preferably made by using a viscous function. An adhesive that can be absorbed is used. In order to prevent moisture from penetrating into the adhesive layer, a sealing material 200 is formed on the end of the adhesive or on the outer periphery of the optical element.

JP 2006-309151 A JP 2004-258165 A

  However, the use of pressure-sensitive adhesives can solve problems caused by temperature changes and improve the reliability of temperature impact. However, in high-humidity environmental tests, pressure-sensitive adhesives absorb water and become cloudy, and optical elements are usually used. Even after returning to the environment (hereinafter referred to as a low humidity environment as a normal environment), the optical properties deteriorated, such as the cloudiness continued for a long time. This has been a problem in commercialization of optical elements in which the bonding layer 190 is changed from a conventional adhesive to a pressure-sensitive adhesive.

  In general, it is said that the above problem can be solved if moisture does not penetrate into the pressure-sensitive adhesive, and it has been common knowledge to provide the sealing material 200 on the outer peripheral portion of the optical element (Patent Document 1 and Patent Document 2). However, even if these methods are used, it cannot be improved to the extent that white turbidity can be prevented. That is, even if the sealing layer is provided on the outer peripheral portion of the optical element, when the optical element is exposed to a high humidity environment for a long time, moisture gradually passes through the sealing layer and penetrates into the pressure-sensitive adhesive material and becomes white turbid. And when the above-mentioned white turbid optical element was returned to a normal environment, there was a problem that white turbidity at the center of the substrate continued for a long time. That is, the outer peripheral sealing layer is effective for exposure to a high-humidity environment for a short time, but is not effective for a long time. Furthermore, an optical element having a sealing layer on the outer peripheral portion has a disadvantage that the recovery of transparency when it is returned to the normal environment is delayed.

  In order to obtain a suitable viscosity capable of absorbing the difference in expansion of the substrate due to temperature change, it is preferable to use an adhesive having a low crosslinking density. However, a pressure-sensitive adhesive having a low crosslinking density cannot prevent moisture penetration and becomes cloudy, resulting in deterioration of optical quality. Furthermore, when exposed to a high humidity environment for a long time, it becomes cloudy and cannot be recovered in a short time even if it is returned to a normal environment. For this reason, in order to commercialize optical elements that can satisfy both temperature shock resistance and high humidity environmental tests, it is difficult to cause white turbidity due to moisture without increasing the crosslink density, or even when white turbidity due to moisture occurs. There was a demand for a pressure-sensitive adhesive that can be recovered in a short time.

  The present invention is exposed to both a high humidity environment and a normal environment as needed. For example, even when used in an outdoor environment, the quality and performance are not easily deteriorated, or once it is deteriorated, it is recovered in a short time. An object is to provide an optical element, an optical low-pass filter, and a solid-state imaging device.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
Application Example 1 An optical element according to this application example is an optical element including a transmissive optical film, a transmissive optical substrate, and an adhesive, and the optical element is an optical element of the transmissive optical film. The transparent optical substrate is bonded to both surfaces using the pressure-sensitive adhesive, and the pressure-sensitive adhesive has an open-air structure in which an end portion of the pressure-sensitive adhesive is in direct contact with the outside air, and the pressure-sensitive adhesive is an alkoxyalkyl ester of acrylic acid or methacrylic acid. It consists of the polymer which has as a main component 1 or more types of monomers chosen from alkoxyalkyl ester.

According to this configuration, by using the pressure-sensitive adhesive mainly composed of the above-described polymer, the bonding layer using the pressure-sensitive adhesive has improved moisture permeability into the pressure-sensitive adhesive in a high-humidity environment. Absorbs moisture until it reaches saturation. In the conventional pressure-sensitive adhesive, the water permeability into the pressure-sensitive adhesive is insufficient, and as a result, a large number of dispersed bulky water is generated. Light scattering occurs on the surface of the massive water generated inside the conventional pressure-sensitive adhesive, which tends to cause white turbidity. Inside the pressure-sensitive adhesive according to the present invention, water easily penetrates and diffuses between the molecules of the pressure-sensitive adhesive, and it is difficult to generate massive water. Therefore, it is considered that the generation of massive moisture having a surface that causes light scattering is less likely to cause white turbidity. In the pressure-sensitive adhesive according to the present invention, it can be confirmed that the water permeability and diffusion are improved as compared with the conventional pressure-sensitive adhesive because the amount of water absorbed in the pressure-sensitive adhesive is larger than that of the conventional pressure-sensitive adhesive.
In addition, when the pressure-sensitive adhesive that has absorbed moisture up to the saturated state is returned to the normal environment, the moisture permeability is high, so that the moisture of the pressure-sensitive adhesive at the center of the optical element easily moves to the edge, It moves to the part and is released to the outside air. Since the moisture permeability of conventional pressure-sensitive adhesives is insufficient, the movement of moisture inside the pressure-sensitive adhesive is slow, and thus the release of moisture from the outside into the outside takes time. Deterioration of optical properties due to moisture is likely to occur. In the optical element using the pressure-sensitive adhesive according to the present invention, the pressure-sensitive adhesive has high penetrability, and further has a structure in which the outside air is released without sealing the end portion. It can recover quickly.
The transmissive optical film is a film that transmits light, and the wavelength and transmittance of light that can be transmitted are not limited. The transmissive optical substrate is a substrate through which light is transmitted, and the wavelength and transmittance of light that can be transmitted are not limited.

Application Example 2 In the optical element according to this application example, at least a part of the end portion of the adhesive material protrudes from the outer peripheral portion of the transmissive optical substrate.
Since at least a part of the end portion of the pressure-sensitive adhesive protrudes, the surface area in contact with the outside air can be ensured larger than before, and moisture can be discharged from the end portion to the outside air more efficiently. Therefore, since the removal of moisture can be performed more efficiently when the optical element that has absorbed moisture in a superhumid environment in a high humidity environment is moved to the normal environment, the deterioration of optical characteristics can be recovered in a short time.

Application Example 3 An optical low-pass filter according to this application example uses the optical element of the above application example.
According to this configuration, even if left in a high humidity environment for a long time, it is difficult to become cloudy, and when returning to a normal environment, moisture inside the adhesive that constitutes the optical element can be released in a short time, and information on incident light An optical low-pass filter that suppresses changes such as retardation without degrading (for example, image information) can be provided.

Application Example 4 A solid-state imaging device according to this application example uses the optical element of the above application example.
According to this configuration, even when left in a high humidity environment for a long time, it is difficult to become cloudy, and when returning to a normal environment, moisture inside the adhesive constituting the optical element can be released in a short time, and information on the incident image It is possible to provide a solid-state imaging device capable of receiving image information close to a normal state without degrading the image quality.

Application Example 5 In the optical element according to this application example, at least one of the transparent optical substrates is any one of quartz, lithium niobate, and calcite.
According to this configuration, it is preferable when materials having different linear expansion coefficients are bonded together, such as bonding of an inorganic material such as a quartz substrate and a transparent optical film of an organic material. By using the above-mentioned pressure-sensitive adhesive, the difference in volume shrinkage can be absorbed by a suitable viscosity, and further, it can be recovered in a short time from the deterioration of optical characteristics.

Application Example 6 In the optical element according to this application example, at least one of the transmissive optical substrates is either optical glass or IR absorbing glass.
According to this configuration, materials having different linear expansion coefficients can be bonded to each other, and even when left in a high humidity environment for a long time, it is difficult to become cloudy, and deterioration of optical properties due to moisture can be eliminated in a short time under a normal environment. Glass having functions such as dust prevention and IR cut can be laminated, and an optical element with these functions can be provided.

Application Example 7 In the optical element according to this application example, the transmissive optical film is an organic polymer material.
According to this configuration, a phase difference characteristic can be easily obtained by a uniaxial stretching method or the like, and for example, a member that is joined as a part of the low-pass filter and has a function of changing linearly polarized light into circularly polarized light can be obtained at low cost.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing the structure of an optical low-pass filter 11 as an optical element. Hereinafter, the structure of the optical low-pass filter 11 will be described with reference to FIG.

  As shown in FIG. 1, the optical low-pass filter 11 is used, for example, in a digital still camera, a digital video camera, or the like to suppress the generation of pseudo signals such as moire. The optical low-pass filter 11 is disposed between a light receiving lens 13 that forms an image of light 12 (incident light) and a solid-state imaging device 14 that converts the captured optical image into an electric signal and takes it in. The solid-state image sensor 14 is a CCD or CMOS. The optical low-pass filter 11 disposed adjacent to the solid-state imaging device 14 has a first birefringent plate 15 as a transmissive optical substrate, an IR cut glass 16, and a quarter position as a transmissive optical film. Phase difference film 17, a second birefringent plate 18 as a transmissive optical substrate, and these members (first birefringent plate 15, IR cut glass 16, 1/4 phase difference film 17, second birefringent plate 18) And an adhesive 19 for bonding.

  The first birefringent plate 15 is a rectangular crystal substrate and is disposed on the light receiving lens 13 side in the optical low-pass filter 11. The first birefringent plate 15 is used to separate the light 12 into an ordinary ray and an extraordinary ray. The first birefringent plate is cut so that the normal line of the main surface is at a predetermined angle with respect to the crystal optical axis (Z axis) of the crystal in order to obtain a desired separation width.

  The IR cut glass 16 is disposed between the first birefringent plate 15 and the quarter retardation film 17 and is used for cutting the infrared component.

  The quarter retardation film 17 is disposed between the IR cut glass 16 and the second birefringent plate 18. The quarter retardation film 17 is, for example, a resin material made of an organic polymer material formed by a uniaxial stretching method. The resin material used here is, for example, a polycarbonate resin. Polycarbonate resins have high heat resistance, low water absorption, and excellent durability and transparency. Furthermore, when the polycarbonate-based resin is mixed with a compound having optical anisotropy, it is possible to provide wavelength dispersion characteristics in which the phase difference increases as the wavelength of the incident light 12 increases. / 4 wavelength plate.

  Such a quarter retardation film 17 can function as a quarter wavelength plate by appropriately setting the film thickness in consideration of the birefringence (flexural anisotropy) of the resin material. It has become. In other words, the quarter retardation film 17 can change the polarization state of the light 12 separated into two points by the first birefringent plate 15 from linearly polarized light to circularly polarized light.

  The second birefringent plate 18 is a rectangular crystal substrate similar to the first birefringent plate 15, and is disposed on the solid-state imaging device 14 side in the optical low-pass filter 11. The second birefringent plate 18 is used to further separate the two lights converted into the circularly polarized light by the quarter retardation film 17 into four linearly polarized lights (four-point separation). Similarly to the first birefringent plate 15, the second birefringent plate 18 is such that the normal line of the principal surface is at a predetermined angle with respect to the crystal optical axis (Z axis) of the crystal in order to obtain a desired separation width. So that it is cut.

As a material having birefringence used for the first birefringent plate 15 and the second birefringent plate 18, in addition to the quartz substrate, lithium niobate, chili nitrate, calcite, rutile, KDP (KH ₂ PO ₄ ), ADP (NH ₄ H ₂ PO ₄ ) and the like are mentioned, and quartz, lithium niobate, and calcite are preferable from the viewpoint of strength and cost. If the optical low-pass filter is not a four-point separation type, a glass material may be used as the transmissive optical substrate.

  An antireflection film (AR) for improving the transmittance of visible light is formed on the surface of the first birefringent plate 15 on the side of the light receiving lens 13 and on the surface of the second birefringent plate 18 on the side of the solid-state imaging device 14. Film), an ultraviolet cut film and an infrared cut film (UV-IR cut film) for preventing the incidence of ultraviolet rays and infrared rays on the solid-state imaging device 14 (both not shown) may be provided. .

  As described above, the optical low-pass filter 11 including the adhesive 19 is required to maintain its original performance in various environmental changes. Therefore, it is necessary to satisfy various environmental reliability tests. Specifically, the high temperature environment test is 85 ° C., the low temperature environment test is −40 ° C., the temperature impact test is −40 ° C. (low temperature) and 85 ° C. (high temperature), and the high temperature and high humidity environment test is 90%, 60 ° C. A test is conducted. In particular, the pressure-sensitive adhesive 19 maintains a suitable viscosity and hardly becomes cloudy in a high-temperature and high-humidity environment. When the environment is changed from a high-temperature and high-humidity environment to a normal environment, the adhesive 19 recovers in a short time from the deteriorated optical characteristics. Is required.

  The pressure-sensitive adhesive 19 is a pressure-sensitive adhesive composition obtained by curing a pressure-sensitive adhesive main component polymer mainly composed of an acrylic acid alkoxyalkyl ester or a methacrylic acid alkoxyalkyl ester with a crosslinking agent. Furthermore, in order to improve adhesion to an object to be bonded and to prevent floating during a durability test, a low molecular weight polymer obtained by copolymerizing an amino group or amide group-containing monomer can be blended.

  The adhesive main component polymer is obtained by copolymerizing a carboxyl group-containing monomer with one or more monomers selected from an alkoxyalkyl ester of acrylic acid or an alkoxyalkyl methacrylate as a main component. It can also be set as the copolymer which added the monomer which can be copolymerized.

  Examples of the alkoxyalkyl ester of acrylic acid or alkoxyalkyl methacrylate as the main component include 2-methoxyethyl acrylate, 2-methoxypropyl acrylate, 2-methoxybutyl acrylate, 2-ethoxyethyl acrylate, 3-acrylic acid 3- Examples include ethoxypropyl, 2-methoxyethyl methacrylate, 2-methoxypropyl methacrylate, 2-methoxybutyl methacrylate, 2-ethoxyethyl methacrylate, 3-ethoxypropyl methacrylate, 4-ethoxybutyl methacrylate, and the like. Can do.

  Examples of the carboxyl group-containing monomer copolymerized with the monomer include acrylic acid, methacrylic acid, maleic acid, and fumaric acid.

  Furthermore, as copolymerizable monomers, acrylic acid alkyl ester, methacrylic acid alkyl ester, acrylic acid aryl ester, methacrylic acid aryl ester, hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, and epoxy group containing allyl glycidyl ether, etc. Monomers and the like.

  If the mixing ratio of the alkoxyalkyl ester of acrylic acid or alkoxyalkyl methacrylate monomer as the main component is too low, white turbidity tends to occur in a high temperature and high humidity environment, so the mixing ratio is 60% or more and 100% or less.

  Moreover, since the durability in a high temperature, high humidity environment will be inferior if the molecular weight of the adhesive main agent polymer obtained by copolymerization is too low, it is preferable that the weight average molecular weight is 600,000 or more.

  As the crosslinking agent, general materials such as isocyanate, epoxy compound and metal chelate can be used. The appropriate blending amount of the cross-linking agent varies depending on the cross-linking agent to be used. If the amount added is less than necessary, the cohesive force of the pressure-sensitive adhesive 19 is insufficient, and the durability is hindered.

  Low molecular weight polymers added as necessary to improve adhesion to the object to be bonded are mainly composed of monomers such as alkyl methacrylate and cycloalkyl methacrylate, and aminoethyl acrylate and amino methacrylate It is a polymer obtained by copolymerizing an amino group-containing monomer such as ethyl or an amide group-containing monomer such as acrylamide or methacrylamide. The weight average molecular weight of this low molecular weight polymer is preferably about 50,000 or less, and if it is more than that, the compatibility with the adhesive main agent polymer tends to be poor.

  In addition, it is possible to maintain the decrease in the adhesive strength of the pressure-sensitive adhesive 19 caused by having many hydrophilic properties (hydrophilic groups) by copolymerizing a low molecular weight monomer.

  FIG. 2 is a chart showing the relationship between the weight mixing ratio of the pressure sensitive adhesive main agent polymer and the amount of water absorption in the pressure sensitive adhesive, and the relationship between the weight mixing ratio of the pressure sensitive adhesive main agent polymer and the HAZE value (cloudiness). FIG. 3 is a graph showing the relationship between the weight mixing ratio of the pressure-sensitive adhesive main agent polymer and the amount of water absorption in two types of pressure-sensitive adhesives. FIG. 4 is a graph showing the relationship between the elapsed time when the high-humidity environment is changed to the normal environment (low-humidity environment) and the HAZE value for each weight mixing ratio of the adhesive main agent polymer. Hereinafter, the relationship between the weight mixing ratio of the adhesive main agent polymer and the amount of water absorption of the present embodiment, and the relationship between the weight mixing ratio of the adhesive main agent polymer and the HAZE value will be described.

  The HAZE value was measured using a single beam haze computer, HZ-1, manufactured by Suga Test Instruments Co., Ltd. In addition, the amount of water absorption was measured by measuring the change in weight before and after leaving an adhesive between two glass substrates (50 mm x 50 mm) in an environment of 60 ° C and 90% for 1000 hours. Was calculated.

  First, measurement conditions for obtaining the above characteristics will be described with reference to FIG. The sample used for the measurement is configured such that a pressure-sensitive adhesive 19 is sandwiched between 10 cm × 10 cm polycarbonate films (for example, a thickness of 80 μm). The thickness of the adhesive 19 is two types of 40 μm and 10 μm.

  The weight mixing ratio of the main adhesive polymer is the ratio of the weight of the main adhesive polymer to the weight of the adhesive 19. The chart shown in FIG. 1 shows the characteristics when the weight mixing ratio of the main adhesive polymer is changed to 50%, 55%, and 60%.

  The high humidity environment is, for example, an environment in which the temperature is 60 ° C. and the humidity is 90%, and the sample is held in this for 1000 hours.

  The amount of water absorption (g) is the amount of water absorbed by the adhesive 19 in the high humidity environment described above.

  The HAZE value is the cloudiness level (white turbidity level), and the smaller this value, the higher the transparency. Here, the HAZE value is measured immediately after putting a sample held in a high humidity environment for 1000 hours into the normal environment, 5 minutes later and 10 minutes later.

  FIG. 3 is a graph showing the relationship between the weight mixing ratio of the above-mentioned adhesive main agent polymer and the amount of water absorption, the horizontal axis indicates the weight mixing ratio (wt%) of the adhesive main agent polymer, and the vertical axis indicates the water absorption amount (g). Is shown. A solid line A shown in FIG. 3 indicates characteristics when the thickness of the pressure-sensitive adhesive 19 is 40 μm. A solid line B indicates characteristics when the thickness of the pressure-sensitive adhesive 19 is 10 μm. In the experiment, acrylic acid alkoxyalkyl ester was used as the main adhesive polymer. (The same applies to the following examples)

  In the graph shown in FIG. 3, it can be seen that the water absorption amount increases abruptly when the weight mixing ratio of the pressure sensitive adhesive main agent polymer is around 55% to around 60%. The two types of pressure-sensitive adhesives 19 (solid line A and solid line B) have the same tendency.

  FIG. 4 is a graph showing the relationship between the elapsed time (minutes) and the HAZE value when the above-mentioned high humidity environment is changed to the normal environment, the horizontal axis indicates the elapsed time (minutes), and the vertical axis indicates the HAZE value. Is shown. Each solid line CL shown in FIG. 4 shows the characteristics when the weight mixing ratio of the pressure-sensitive adhesive main agent polymer is changed from 45% to 68% at a predetermined interval.

  In the graph shown in FIG. 4, the HAZE value is close to approximately 0 immediately after changing from the high humidity environment to the normal environment by changing the weight mixing ratio of the adhesive main agent polymer from 60% to 68%. Specifically, as shown in the chart of FIG. 2, by setting the weight mixing ratio of the adhesive main agent polymer to 60%, a value of 0.04 that can be judged as high transparency immediately after changing the environment is shown.

  As described above, by making the weight mixing ratio of the pressure-sensitive adhesive main component polymer constituting the pressure-sensitive adhesive 19 60% or more and 100 or less, it becomes possible to improve the hydrophilicity by including many hydrophilic groups of the pressure-sensitive adhesive 19, As shown in FIG. 3, even if the pressure-sensitive adhesive 19 contains a lot of moisture in a high humidity environment, as shown in FIG. 4, high transparency can be maintained immediately after changing to the normal environment. Furthermore, since the crosslink density is not high, it is possible to suppress a decrease in the viscoelastic function. Therefore, when the adhesive 19 is used for the optical low-pass filter 11 and the environment is changed, the adhesive 19 is not peeled off and the solid-state image sensor 14 receives light without degrading image information (light). Can do. Conventionally, what requires about 10 to 20 minutes from the cloudy state (cloudy state) to high transparency can be made nearly transparent immediately after the environment is changed.

Further, the pressure-sensitive adhesive 19 is constituted using the above components, and the hydrophilicity is improved by adding a large amount of hydrophilic groups, whereby the vapor permeability indicating the degree of moisture permeation is, for example, 350 to 400 in the past. What is about (g / m ² · 24 hr) can be changed to about 550 (g / m ² · 24 hr), and the pressure-sensitive adhesive 19 can be very easily permeable to moisture.

  As described above in detail, according to the optical low-pass filter 11 of the first embodiment, the following effects can be obtained.

(1) According to the first embodiment, since the pressure-sensitive adhesive 19 mainly composed of the pressure-sensitive adhesive main polymer containing many hydrophilic groups described above is used, the hydrophilicity inside the pressure-sensitive adhesive 19 can be improved. It is possible to blend with water by promoting penetration and diffusion. Therefore, when moisture enters the pressure-sensitive adhesive 19, the moisture can easily penetrate and diffuse, and the moisture can penetrate and diffuse to the extent that light is not scattered. Furthermore, since the weight mixing ratio of the pressure-sensitive adhesive main agent polymer is selected as described above, the crosslinking density connecting the molecules does not become too high, and the pressure-sensitive adhesive force of the pressure-sensitive adhesive 19 can be ensured. As a result, even if it is in a state where moisture easily enters, the moisture penetrates and diffuses, so that the pressure-sensitive adhesive 19 is not easily clouded. As a result, even if a change occurs in the environment, the adhesive 19 constituting the optical low-pass filter 11 is suppressed from becoming clouded, so that incident light (for example, image information) is deteriorated. Thus, the optical low-pass filter 11 that can suppress the generation of pseudo signals such as moire can be provided.
Furthermore, by using a pressure-sensitive adhesive that is very permeable to moisture and having a structure in which the end of the pressure-sensitive adhesive can be in direct contact with the atmosphere, moisture can be released in a shorter time. The effect on the structure of the end of this adhesive and the release of moisture will be described later.

(Second Embodiment)
FIG. 5 is a schematic cross-sectional view showing the structure of the solid-state imaging device of the second embodiment. Hereinafter, the structure of the solid-state imaging device will be described with reference to FIG. Note that the solid-state imaging device of the second embodiment is different from the above-described first embodiment in that the optical low-pass filter is used as a cover of the solid-state imaging device. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified here.

  A solid-state imaging device 21 illustrated in FIG. 5 is provided in, for example, a digital still camera or a digital video camera, and includes a solid-state imaging device 14, a package 22, and a cover 23.

  The solid-state imaging device 14 is, for example, a CCD or CMOS as described above, and is enclosed in the package 22 (bottom). The solid-state imaging device 14 has a plurality of pixels, and the pixels are regularly arranged at a constant pitch.

  The package 22 is used for housing the solid-state imaging device 14 and is formed in a concave shape having an opening on the light receiving lens side (not shown). The package 22 is provided with an external connection wiring (not shown) for electrically connecting the inside and the outside of the package 22 through, for example, a side wall. The solid-state imaging device 14 is electrically connected to external connection wiring via a bonding wire (not shown).

  The cover 23 is used to prevent dust and the like from adhering to the solid-state image sensor 14 and is closed so as to cover the opening of the package 22. As described above, the cover 23 has the function of the optical low-pass filter 11, and is the same as the first embodiment, the first birefringent plate 15, the IR cut glass 16, and the quarter retardation film 17. And a second birefringent plate 18 and an adhesive 19 that joins these members (first birefringent plate 15, IR cut glass 16, 1/4 retardation film 17, second birefringent plate 18). . The configuration and components of the adhesive 19 are the same as those in the first embodiment.

  As described above in detail, according to the solid-state imaging device 21 of the second embodiment, in addition to the effect (1) of the first embodiment described above, the following effects can be obtained.

  (2) According to the second embodiment, even if a change occurs in the environment, as described above, the adhesive 19 constituting the cover 23 of the solid-state imaging device 21 is less likely to become cloudy, and even if it becomes cloudy, in a short time Since it can be recovered, it is possible to provide the solid-state imaging device 21 that can receive the light 12 close to the normal state without deteriorating the incident light 12 (for example, image information).

(Third embodiment)
FIG. 6 is a schematic cross-sectional view showing the structure of an optical low-pass filter having a convex end of the adhesive. Hereinafter, the structure of the optical low-pass filter will be described as a third embodiment with reference to FIG. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified here.

  The difference between the optical element shown in FIG. 6 and the optical element shown in FIG. 1 is the shape of the end of the adhesive 19. The edge part of the adhesive 19 shown in FIG. 6 protrudes from the outer periphery of the optical element in a bowl shape. In addition, this protrusion part may be along the outer peripheral part of a translucent base material. That is, the shape may be various as long as the area where the end of the adhesive 19 is in contact with the atmosphere can be increased. Note that FIG. 6 is created without any dimensional ratio, and the edge wrinkles are emphasized, and are different from the actual shape dimensions. That is, what is necessary is just to protrude about 0.1 mm-about 1 mm or more from the outer peripheral part of the adjacent translucent base material. Moreover, all the edge parts of an adhesive do not need to protrude, and a part of edge part should just protrude as mentioned above.

  As shown in FIG. 11, a sealing layer is formed in the shape of the pressure-sensitive adhesive end portion in the prior art. Using the pressure-sensitive adhesive of the present application, end portions of this pressure-sensitive adhesive were prepared in three different shapes, and the change with time of the retardation was evaluated. In addition, the retardation measurement used KOBRA-21ADH by Oji Scientific Instruments. The size of the test piece was 20 mm × 30 mm, and the measurement position was the center of the optical surface of the optical low-pass filter. A pressure-sensitive adhesive having a pressure-sensitive adhesive main polymer of 60% and a thickness of 10 μm was used. Two optical glasses (BK7) and one retardation film were joined with this adhesive to prepare a test piece. The end portions of the pressure-sensitive adhesive were prepared in three levels: a level with a sealing layer, a level without a sealing layer, a level without a sealing layer and a hook-shaped level on the end surface. A pressure-sensitive adhesive having a pressure-sensitive adhesive main polymer of 60% is not easily clouded by itself, but supersaturated water deteriorates retardation.

  FIG. 7 shows the change over time in the increase of moisture in a high humidity environment. The broken line S represents a sample with a sealing layer, and the solid R line represents a sample without a sealing layer. The conditions of the high humidity environment were 60 ° C. and 90% RH. When left for a short time, the sealing layer formed at the edge of the adhesive prevents moisture penetration. However, if the elapsed time is close to 500 hours, it penetrates until the moisture is saturated even if the sealing layer is present. Resulting in. That is, the sealing layer is not useful when left in a high humidity environment for a long time.

  FIG. 8 shows the change over time in the change in the amount of moisture when a sample that has been left in a high-humidity environment for 500 hours and has absorbed moisture until it is saturated is left in the normal environment. In other words, we evaluated how much moisture could be released into the atmosphere in a normal environment. Normal environmental conditions were 25 ° C. and 20% RH. The S broken line indicates a sample without a sealing layer, the R solid line indicates a sealing layer, and the P dotted line indicates a sample with a protruding end of an adhesive. It can be seen that when there is a sealing layer, the release of moisture in a normal environment is delayed. And when there is no sealing layer and the pressure-sensitive adhesive end is convex, the release of moisture is further accelerated. This can be considered because the surface area of the end portion of the pressure-sensitive adhesive that comes into contact with the outside air has increased.

  FIG. 9 is a graph showing the relationship between the elapsed time after moving from the high-humidity environment to the normal environment and the retardation value, depending on the weight mixing ratio of the main adhesive polymer. The initial retardation (phase difference value) before entering the high-humidity environment was 147 nm. The end of the adhesive was convex. The high humidity environment conditions were 60 ° and 90% RH, the standing time was 500 hours, and the normal environment conditions were 25 ° C. and 20% RH. If the pressure-sensitive adhesive has a weight mixing ratio of the pressure-sensitive adhesive main component polymer, the retardation is recovered in a short time. From the result of this graph, it can be seen that only the broken line I with a weight mixing ratio of the main adhesive polymer of 60% and the solid K line with 65% recovered the initial retardation. Therefore, the weight mixing ratio of the adhesive main component polymer is preferably 60% or more for the recovery of retardation in a normal environment.

  FIG. 10 is a graph showing the relationship between the elapsed time after moving from a high-humidity environment to a normal environment and the retardation value depending on the shape of the end of the adhesive and the presence or absence of the sealing layer. The initial retardation (phase difference value) before entering the high-humidity environment was 147 nm. The high humidity environment condition was 60 ° C. and 90% RH, the standing time was 500 hours, and the normal environment condition was 25 ° C. and 20% RH. In addition, the adhesive used the sample whose weight mixing ratio of the adhesion main ingredient polymer is 60%. The broken line S indicates that there is no sealing layer, the solid R line indicates that there is a sealing layer, and the dotted P line indicates a sample in which the adhesive end has a convex shape. It can be seen that when there is a sealing layer, it takes a long time to recover the retardation in a normal environment. Further, when there is no sealing layer and the pressure-sensitive adhesive end is convex, the recovery of retardation is further accelerated.

  From the above, if an adhesive with a weight mixing ratio of the adhesive main component polymer of 60% or more is used and the end of the adhesive is shaped so that moisture can be easily released, the optical element returned to the normal environment is optically affected by the influence of moisture. The deterioration of characteristics can be recovered in a short time.

  In addition, embodiment is not limited above, It can also implement with the following forms.

  (Modification 1) As described above, the optical low-pass filter and the solid-state imaging device are exemplified as the one using the adhesive 19, but the present invention is not limited thereto. For example, the optical head device, the liquid crystal display device, and the copying machine You may make it use for.

1 is a schematic cross-sectional view showing the structure of an optical low-pass filter according to a first embodiment. The graph which shows the relationship between the weight mixing ratio of an adhesive main ingredient polymer, and the amount of water absorption, and the relationship between the weight mixing ratio of an adhesive main agent polymer, and a HAZE value. The graph which shows the relationship between the weight mixing ratio of an adhesion main ingredient polymer, and water absorption. The graph which shows the relationship between the elapsed time after moving to a normal environment from a humid environment, and a HAZE value. FIG. 6 is a schematic cross-sectional view illustrating a structure of a solid-state imaging device according to a second embodiment. The schematic cross section which shows the structure of the optical low-pass filter which concerns on 3rd Embodiment. The graph which shows the relationship between the presence or absence of sealing of an adhesive edge part, and a moisture content. The graph which shows the relationship between the elapsed time after moving to a normal environment from a high-humidity environment, and the dehydration amount by the difference in the shape of an adhesive edge part. The graph which shows the relationship between the elapsed time after moving from a high-humidity environment to a normal environment, and the retardation value by the weight mixing ratio of an adhesive main ingredient polymer. The graph which shows the relationship between the elapsed time after moving from a high-humidity environment to a normal environment, and a retardation value by the difference in the shape of an adhesive edge part. FIG. 6 is a schematic cross-sectional view showing the structure of a conventional optical low-pass filter.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Optical low-pass filter, 12 ... Light, 13 ... Light receiving lens, 14 ... Solid-state image sensor, 15 ... 1st birefringent plate as a transmissive optical board, 16 ... IR cut glass, 17 ... 1 as a transmissive optical film / 4 retardation film, 18 ... second birefringent plate as a transmissive optical substrate, 19 ... adhesive, 21 ... solid-state imaging device, 22 ... package, 23 ... cover.

Claims (7)

An optical element composed of a transmissive optical film, a transmissive optical substrate, and an adhesive,
Using the adhesive, bonding the transmissive optical substrate to the transmissive optical film,
And the end of the pressure-sensitive adhesive is a structure of open air that directly contacts the open air,
The pressure-sensitive adhesive is composed of a polymer mainly composed of one or more monomers selected from an alkoxyalkyl ester of acrylic acid or an alkoxyalkyl ester of methacrylic acid, and the weight mixing ratio of the polymer is from 60% to 100%. A featured optical element.   The optical element according to claim 1, wherein at least a part of an end portion of the adhesive material protrudes from an outer peripheral portion of the transmissive optical substrate.   The optical element according to claim 1, wherein at least one of the transmissive optical substrates is one of quartz, lithium niobate, and calcite.   The optical element according to claim 1, wherein at least one of the transmissive optical substrates is either optical glass or IR absorbing glass.   The optical element according to claim 1, wherein the transmissive optical film is made of an organic polymer material.   An optical low-pass filter using the optical element according to any one of claims 1 to 5.   A solid-state imaging device using the optical element according to any one of claims 1 to 5.