JP2008051985A - Near infrared ray absorbing filter - Google Patents

Near infrared ray absorbing filter Download PDF

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JP2008051985A
JP2008051985A JP2006227251A JP2006227251A JP2008051985A JP 2008051985 A JP2008051985 A JP 2008051985A JP 2006227251 A JP2006227251 A JP 2006227251A JP 2006227251 A JP2006227251 A JP 2006227251A JP 2008051985 A JP2008051985 A JP 2008051985A
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film layer
infrared
transmittance
near infrared
organic film
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Kazutoshi Mukai
和俊 迎
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Nidec Copal Corp
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<P>PROBLEM TO BE SOLVED: To provide a near infrared ray absorbing filter which can attain thickness reduction and which has high transmittance in a visible region. <P>SOLUTION: The near infrared ray absorbing filter has a transparent substrate 1, an organic film layer 2 which is formed on one side or both sides of the transparent substrate 1 and absorbs near infrared rays and inorganic film layers 3,4 for intercepting the near infrared rays. The organic film layer 2 is made to have ≥90% transmittance in the visible region and 20% to 60% transmittance in the near infrared region. The organic film layer 2 is consisting of a polymer composition containing at least one kind of near infrared ray absorbing dyestuff. The inorganic film layers 3,4 comprise a multilayer film constituted by alternatively laminating a dielectric film of a low refractive index and a dielectric film of a high refractive index. By combining the organic film layer 2 containing the near infrared ray absorbing dyestuff and the inorganic film layers 3,4 comprising the optical multilayer film, thickness reduction is attained and transmittance in the visible region is made high. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、可視域で高い光透過率を持つ一方、近赤外域の光を遮断する近赤外線吸収フィルタに関する。   The present invention relates to a near-infrared absorption filter that has a high light transmittance in the visible range and blocks light in the near-infrared range.

動画撮影や静止画撮影を行うため、カラーＣＣＤイメージセンサを含む撮像装置（デジタルカメラやビデオカメラ）が開発されている。これらの撮像装置で用いるカラーＣＣＤイメージセンサは、その感度が可視域を超えて近赤外領域まで及ぶ。この為、カラーＣＣＤイメージセンサで撮影した画像は、可視域のみに感度を有する人間が見る実像と異なる。そこで従来の撮像装置は近赤外線吸収フィルタが組み込まれており、近赤外線を遮断することで、人間の目に映る像と同じ撮像が得られるようにしている。この様に近赤外線吸収フィルタを組み込むことで、人が見るイメージと異なった映像化を防ぐことが出来る。この様な用途に用いる近赤外線吸収フィルタは以下の特許文献１〜３に開示されている。
特開平１１‐２０９１４４号公報 特開２０００‐００７８７０公報 特開２００２‐３０３７２０公報 An imaging device (digital camera or video camera) including a color CCD image sensor has been developed to perform moving image shooting and still image shooting. The color CCD image sensor used in these imaging devices has a sensitivity that extends from the visible region to the near infrared region. For this reason, the image photographed by the color CCD image sensor is different from a real image seen by a human having sensitivity only in the visible range. Therefore, a conventional imaging device incorporates a near-infrared absorption filter, and by capturing near-infrared rays, the same imaging as an image seen by human eyes can be obtained. By incorporating a near-infrared absorption filter in this way, it is possible to prevent visualization different from the image seen by humans. The near-infrared absorption filters used for such applications are disclosed in the following Patent Documents 1 to 3.
JP-A-11-209144 JP 2000-007870 A JP 2002-303720 A

特許文献１は近赤外吸収フィルタ用ガラス及びそれを用いた近赤外線吸収フィルタを開示している。この近赤外吸収フィルタ用ガラスは、金属イオンを含有しており、その近赤外線領域における吸収作用を利用している。また特許文献２は、近赤外線吸収用の樹脂組成物を開示している。この樹脂組成物は、置換または未置換のアミノ基と、銅イオンを含む金属イオン成分とがアクリル系樹脂中に含有されている。この樹脂組成物は同じく金属イオンの近赤外線に対する吸収作用を利用して、近赤外線吸収フィルタを作ることが出来る。特許文献３は近赤外線吸収フィルタを開示している。このフィルタは、近赤外線吸収色素をバインダ樹脂に分散した組成物を含む塗布液を基材上に塗布乾燥して作成する。例えばポリエステルなどのバインダ樹脂に近赤外線吸収色素を分散させ、ポリエステルフィルム基材上に積層することで、近赤外線吸収フィルタを作成している。   Patent Document 1 discloses a near infrared absorption filter glass and a near infrared absorption filter using the same. This near-infrared absorption filter glass contains metal ions and utilizes the absorption action in the near-infrared region. Patent Document 2 discloses a resin composition for absorbing near infrared rays. In this resin composition, a substituted or unsubstituted amino group and a metal ion component containing copper ions are contained in an acrylic resin. This resin composition can also make a near-infrared absorption filter by utilizing the absorption action of metal ions for near-infrared rays. Patent document 3 is disclosing the near-infrared absorption filter. This filter is prepared by applying and drying a coating solution containing a composition in which a near infrared absorbing dye is dispersed in a binder resin on a substrate. For example, a near-infrared absorbing filter is prepared by dispersing a near-infrared absorbing pigment in a binder resin such as polyester and laminating the polyester on a polyester film substrate.

特許文献１はガラス製赤外線吸収フィルタを開示し、特許文献２は樹脂製赤外線吸収フィルタを開示している。いずれも金属イオンの近赤外線に対する吸収作用を利用している。しかしながら、金属イオンの近赤外線に対する吸収作用はそれほど強くなく、実用レベルまで近赤外線の透過率を下げるためには、ある程度厚みが必要になる。現在最も薄いフィルタで、厚みｔ＝０．３５ｍｍ程度である。さらにこのフィルタに近赤外線カットコートや反射防止コートを付加すると、実際の厚みがもっと大きくなる。この様に厚みの大きな赤外線吸収フィルタは、カラーＣＣＤイメージセンサを利用した撮像装置の薄型化の障害となる。特に、撮像装置を携帯電話機などに組み込む場合、薄型化は必須であるにもかかわらず、赤外線吸収フィルタの厚みが薄型化を阻害している。またガラス製や樹脂製のフィルタは製造工程や実使用段階で樹脂及びガラスの割れや欠けなどの発生があり、不具合が生じる上に、自由な形状に加工することも出来ない。   Patent Document 1 discloses a glass infrared absorption filter, and Patent Document 2 discloses a resin infrared absorption filter. Both utilize the absorption effect of metal ions on near infrared rays. However, the absorption effect of metal ions on near infrared rays is not so strong, and in order to reduce the transmittance of near infrared rays to a practical level, some thickness is required. It is the thinnest filter at present and has a thickness t = 0.35 mm. Furthermore, if a near-infrared cut coat or an antireflection coat is added to this filter, the actual thickness will be further increased. Such a thick infrared absorption filter is an obstacle to thinning an imaging apparatus using a color CCD image sensor. In particular, when the imaging device is incorporated in a mobile phone or the like, the thickness of the infrared absorption filter hinders the reduction in thickness even though the reduction in thickness is essential. Further, a glass or resin filter may cause cracking or chipping of the resin or glass in the manufacturing process or the actual use stage, resulting in problems and being unable to be processed into a free shape.

特許文献３に記載された近赤外線吸収フィルタは近赤外線吸収色素を利用している。しかしながら近赤外線吸収色素は近赤外領域のみならず可視域でも多少の吸収を有するため、実用レベルまで近赤外域の吸収率を高めると、可視域での吸収率も大きくなり、透過率が８０％を下回ってしまう。近赤外線吸収フィルタの可視域の透過率が８０％を下回ると、カラーＣＣＤイメージセンサを含む撮像装置の撮像性能を低下させてしまうという課題がある。   The near-infrared absorbing filter described in Patent Document 3 uses a near-infrared absorbing dye. However, since the near-infrared absorbing dye has some absorption not only in the near-infrared region but also in the visible region, increasing the absorption factor in the near-infrared region to a practical level increases the absorption factor in the visible region, and the transmittance is 80. It will be less than%. When the transmittance of the near-infrared absorbing filter in the visible region is less than 80%, there is a problem that the imaging performance of the imaging device including the color CCD image sensor is deteriorated.

上述した従来の技術の課題に鑑み、本発明は薄型化が可能で且つ可視域での透過率が高い近赤外線吸収フィルタを提供することを目的とする。かかる目的を達成するために以下の手段を講じた。即ち本発明は、透明基板と、その片面または両面に形成された、近赤外線に吸収を持つ有機膜層及び近赤外線を遮断する無機膜層とを有する近赤外線吸収フィルタにおいて、前記有機膜層はその可視域での透過率を９０％以上にし、近赤外域での透過率を２０％〜６０％にしたことを特徴とする。   In view of the above-described problems of the conventional technology, an object of the present invention is to provide a near-infrared absorption filter that can be thinned and has high transmittance in the visible region. In order to achieve this purpose, the following measures were taken. That is, the present invention relates to a near-infrared absorption filter having a transparent substrate, an organic film layer that absorbs near-infrared rays, and an inorganic film layer that blocks near-infrared rays formed on one or both sides of the transparent substrate. The transmittance in the visible region is 90% or more, and the transmittance in the near infrared region is 20% to 60%.

好ましくは、前記有機膜層は、近赤外線吸収色素が少なくとも１種類含有されているポリマー組成物からなる。この場合、前記ポリマー組成物は、ポリエステル樹脂、ポリアクリル樹脂、またはポリイミド樹脂から選ばれたプラスチックス樹脂が好ましい。又前記無機膜層は、低屈折率の誘電体膜と高屈折率の誘電体膜を交互に重ねた多層膜からなる。   Preferably, the organic film layer is made of a polymer composition containing at least one near infrared absorbing dye. In this case, the polymer composition is preferably a plastic resin selected from a polyester resin, a polyacrylic resin, or a polyimide resin. The inorganic film layer is formed of a multilayer film in which a low refractive index dielectric film and a high refractive index dielectric film are alternately stacked.

本発明にかかる近赤外線吸収フィルタは、透明基板の片面または両面に、近赤外線に吸収を持つ有機膜層及び近赤外線を遮断する無機膜層が形成されている。有機膜層はその可視域での透過率を９０％以上に設定する一方、近赤外域の透過率を２０％〜６０％に設定している。この様な有機膜層は近赤外線吸収色素を少なくとも１種類含有したポリマー組成物からなる。一方無機膜層は、低屈折率の誘電体膜と高屈折率の誘電体膜を交互に重ねた光学多層膜からなり、多重反射による光干渉を利用して近赤外線を選択的に遮断する一方、可視光線を選択的に透過している。この様に、本発明は近赤外線吸収色素を含有した有機膜層と光学多層膜からなる無機膜層とを組み合わせることで、薄型化を達成すると共に、可視域での透過率を高くしている。本発明の近赤外線吸収フィルタは、例えば厚みｔ＝０．１ｍｍのポリエステルフィルム基材上に作成可能であり、カラーＣＣＤイメージセンサを含む撮像装置の薄型化が実現できる。またフィルタの割れや欠けなどの発生もなく、形状も自由に選択できる。さらに本発明の近赤外線吸収フィルタは、近赤外域の透過率を実用レベルの５％以下にまで下げることが出来る。この場合でも可視域における透過率は９０％以上を保つことが可能であり、カラーＣＣＤイメージセンサを含む撮像装置の撮像性能を低下させることなく、薄型化を実現できる。   In the near-infrared absorbing filter according to the present invention, an organic film layer that absorbs near-infrared rays and an inorganic film layer that blocks near-infrared rays are formed on one or both sides of a transparent substrate. The organic film layer has a transmittance in the visible region set to 90% or more, while a transmittance in the near infrared region is set to 20% to 60%. Such an organic film layer is made of a polymer composition containing at least one kind of near-infrared absorbing dye. On the other hand, the inorganic film layer is composed of an optical multilayer film in which low-refractive index dielectric films and high-refractive index dielectric films are alternately stacked, and selectively blocks near-infrared rays using optical interference caused by multiple reflections. , Selectively transmits visible light. Thus, the present invention achieves a reduction in thickness and increases the transmittance in the visible region by combining an organic film layer containing a near-infrared absorbing dye and an inorganic film layer composed of an optical multilayer film. . The near-infrared absorption filter of the present invention can be formed on a polyester film substrate having a thickness t = 0.1 mm, for example, and can realize a thin imaging device including a color CCD image sensor. Moreover, there is no generation | occurrence | production of the crack of a filter, a chip, etc., and a shape can be selected freely. Furthermore, the near-infrared absorption filter of the present invention can reduce the near-infrared transmittance to 5% or less of the practical level. Even in this case, the transmittance in the visible range can be maintained at 90% or more, and a reduction in thickness can be realized without deteriorating the imaging performance of the imaging device including the color CCD image sensor.

なお、本発明のように有機膜層と無機膜層とを組み合わせることなく、無機膜層のみでも所望の光学特性（可視域における高い透過率と近赤外域における高い吸収率）を得ることは可能である。しかしながら無機膜層単独の場合光学多層膜の積層数が多くなり、無機膜層が相当厚くなってしまう。膜厚が大きくなると、０．１ｍｍ程度の基板では膜の剥離やクラック（ひび割れ）が生じる。これは無機膜層の膜応力や無機膜層と基材フィルムとの間の熱膨張係数の違いなどが原因である。これに対し本発明では、有機膜層を併用することで、ある程度近赤外素子域での透過率を抑えることが出来、無機膜層に要求される光学特性（近赤外素子域における低い透過率）を軽減できるため、無機膜層を構成する光学多層膜の層数を少なく出来、結果的に膜厚が薄くて済む。   In addition, it is possible to obtain desired optical characteristics (high transmittance in the visible region and high absorption in the near infrared region) with only the inorganic film layer without combining the organic film layer and the inorganic film layer as in the present invention. It is. However, when the inorganic film layer alone is used, the number of laminated optical multilayer films increases, and the inorganic film layer becomes considerably thick. When the film thickness is increased, peeling or cracking (cracking) of the film occurs on a substrate of about 0.1 mm. This is due to the difference in the film stress of the inorganic film layer and the difference in thermal expansion coefficient between the inorganic film layer and the base film. In contrast, in the present invention, by using the organic film layer in combination, the transmittance in the near-infrared element region can be suppressed to some extent, and the optical characteristics required for the inorganic film layer (low transmission in the near-infrared element region) Therefore, the number of layers of the optical multilayer film constituting the inorganic film layer can be reduced, and as a result, the film thickness can be reduced.

逆に、有機膜層単独で赤外線吸収フィルタを作成すると、近赤外素子域だけでなく可視域の透過率も低下してしまう。即ち有機膜層に含まれる近赤外線吸収色素は、近赤外線だけでなく可視光も多少吸収してしまう。本発明では有機膜層に無機膜層を併用することで、有機膜層自体は近赤外域の透過率を２０％〜６０％程度にすればよく、これに応じて可視域での透過率を９０％以上確保できる。以上により、例えば厚みが０．１ｍｍ程度のＰＥＴフィルム基材上においても、膜剥離やクラックがなく、且つ近赤外線の阻止域での透過率が低く、可視域での透過率が高い近赤外線吸収膜を成膜することが可能になる。   On the other hand, when an infrared absorption filter is formed with an organic film layer alone, not only the near-infrared element region but also the visible region transmittance is lowered. That is, the near-infrared absorbing dye contained in the organic film layer absorbs not only near-infrared rays but also visible light to some extent. In the present invention, by using an inorganic film layer in combination with the organic film layer, the organic film layer itself may have a near-infrared transmittance of about 20% to 60%, and the transmittance in the visible range can be increased accordingly. 90% or more can be secured. As described above, for example, even on a PET film substrate having a thickness of about 0.1 mm, there is no film peeling or cracking, low transmittance in the near infrared blocking region, and high near infrared absorption in the visible region. A film can be formed.

以下図面を参照して本発明の実施形態を詳細に説明する。図１は本発明にかかる近赤外線吸収フィルタの層構成を示す模式的な断面図である。図示する様に、本発明にかかる近赤外線吸収フィルタは、透明基板１と、その片面または両面に形成された有機膜層２および無機膜層３，４とで構成されている。図示の実施形態は、透明基板１の片面に有機膜層２が形成されており、さらに透明基板１の両面に無機膜層３，４が形成されている。但し本発明はこれに限られるものではない。例えば透明基板１の上面に有機膜層２を形成する一方、透明基板１の下面に無機膜層を形成するものであっても良い。あるいは、透明基板１の上面に有機膜層及び無機膜層を形成し、透明基板の下面にも同様に有機膜層及び無機膜層を形成しても良い。成膜の順番についても、図１の実施形態は先に有機膜層を形成しその後無機膜層を形成しているが、逆であっても良い。   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a layer configuration of a near-infrared absorption filter according to the present invention. As illustrated, the near-infrared absorption filter according to the present invention includes a transparent substrate 1 and an organic film layer 2 and inorganic film layers 3 and 4 formed on one or both sides thereof. In the illustrated embodiment, the organic film layer 2 is formed on one surface of the transparent substrate 1, and the inorganic film layers 3 and 4 are formed on both surfaces of the transparent substrate 1. However, the present invention is not limited to this. For example, the organic film layer 2 may be formed on the upper surface of the transparent substrate 1 while the inorganic film layer may be formed on the lower surface of the transparent substrate 1. Alternatively, the organic film layer and the inorganic film layer may be formed on the upper surface of the transparent substrate 1, and the organic film layer and the inorganic film layer may be similarly formed on the lower surface of the transparent substrate. Regarding the order of film formation, the embodiment of FIG. 1 forms the organic film layer first and then forms the inorganic film layer, but it may be reversed.

有機膜層２は近赤外線に吸収を持つ。無機膜層３，４はそれぞれ近赤外線を遮断する。特徴事項として、有機膜層２は、その可視域での透過率を９０％以上にし、近赤外域の透過率を２０％〜６０％に設定している。特に可視域での透過率を９０％以上と高く確保することで、撮像装置などに近赤外線吸収フィルタを適用した場合、撮像性能を損なわないようにしている。この有機膜層２は近赤外線吸収色素が少なくとも１種類含有されているポリマー組成物からなる。このポリマー組成物は、例えばポリエステル樹脂、ポリアクリル樹脂またはポリイミド樹脂等のプラスチック樹脂を使うことが出来る。   The organic film layer 2 has absorption in the near infrared. The inorganic film layers 3 and 4 each block near infrared rays. As a characteristic matter, the organic film layer 2 has a transmittance in the visible region of 90% or more and a transmittance in the near infrared region of 20% to 60%. In particular, the transmittance in the visible region is ensured to be as high as 90% or more so that the imaging performance is not impaired when a near-infrared absorption filter is applied to an imaging device or the like. The organic film layer 2 is made of a polymer composition containing at least one kind of near infrared absorbing dye. For this polymer composition, for example, a plastic resin such as a polyester resin, a polyacrylic resin, or a polyimide resin can be used.

図２は、図１に示した近赤外線吸収フィルタに含まれる無機膜層３，４の具体的な構成を表す模式的な断面図である。図示する様に、無機膜層３，４はいずれも低屈折率の誘電体膜と高屈折率の誘電体膜を交互に重ねた多層膜からなる。図示の実施形態は、低屈折率の誘電体膜としてＳｉＯ２膜を用いており、その屈折率ｎ＝１．４５である。一方高屈折率の誘電体膜はＴｉＯ２膜からなり、その屈折率ｎ＝２．３０である。但し本発明はこれに限られるものではなく、様々な屈折率を有する無機膜を、低屈折率誘電体膜と高屈折率誘電体膜とで使い分け、図示の多層膜を形成することが出来る。無機膜層３，４を構成する光学多層膜は膜の層数及び個々の誘電体膜の厚みを適切に設定することで、多重干渉を利用して、選択的に可視光を透過する一方近赤外光を遮断することが可能である。 FIG. 2 is a schematic cross-sectional view showing a specific configuration of the inorganic film layers 3 and 4 included in the near-infrared absorption filter shown in FIG. As shown in the drawing, each of the inorganic film layers 3 and 4 is formed of a multilayer film in which a low refractive index dielectric film and a high refractive index dielectric film are alternately stacked. In the illustrated embodiment, a SiO 2 film is used as the dielectric film having a low refractive index, and the refractive index n = 1.45. On the other hand, the high refractive index dielectric film is made of a TiO 2 film and has a refractive index n = 2.30. However, the present invention is not limited to this, and an inorganic film having various refractive indexes can be selectively used as a low refractive index dielectric film and a high refractive index dielectric film to form the illustrated multilayer film. The optical multilayer film constituting the inorganic film layers 3 and 4 can selectively transmit visible light using multiple interference by appropriately setting the number of film layers and the thickness of each dielectric film. It is possible to block infrared light.

図１に示した近赤外線吸収フィルタの製造方法の実施例を詳細に説明する。まず最初に透明基板１を用意する。この透明基板は例えばポリエステルフィルム基材からなり、その厚みは、ｔ＝０．１ｍｍである。但し本発明はこれに限られるものではなく、透明基板１は他の透明樹脂フィルム機材を用いることが出来、厚みｔも適切に設定する。   An embodiment of the method for manufacturing the near-infrared absorbing filter shown in FIG. 1 will be described in detail. First, the transparent substrate 1 is prepared. This transparent substrate consists of a polyester film base material, for example, and the thickness is t = 0.1 mm. However, the present invention is not limited to this, and the transparent substrate 1 can use other transparent resin film materials, and the thickness t is also set appropriately.

続いて透明基板１の片面側に有機膜層２を成膜する。本実施例では適切な塗剤を作成し、透明基板１の片面にコーティングした。塗剤（塗布液）は、アクリル樹脂バインダと近赤外線吸収色素を適切な割合で混合し、溶解可能な溶媒に均一に溶かして調製する。具体的には、アクリルバインダ（株式会社日本触媒製ハルスハイブリッドＩＲ−Ｇ２０５）１０ｇと、波長８２６ｎｍ〜８５０ｎｍに吸収を有する近赤外線吸収色素ＳＤＡ６１０４（Ｈ．Ｗ．ＳＡＮＤＳ ＣＯＲＰ．）７４．２ｍｇと、波長７２６ｎｍ〜７５０ｎｍに吸収を有する近赤外線吸収色素ＳＤＡ６８２５（Ｈ．Ｗ．ＳＡＮＤＳ ＣＯＲＰ．）２３．２ｍｇとを、シクロヘキサン４０ｍｌに溶かして、所望の塗布液を作成した。   Subsequently, an organic film layer 2 is formed on one side of the transparent substrate 1. In this example, an appropriate coating agent was prepared and coated on one side of the transparent substrate 1. The coating agent (coating solution) is prepared by mixing an acrylic resin binder and a near-infrared absorbing pigment in an appropriate ratio and uniformly dissolving in a soluble solvent. Specifically, 10 g of acrylic binder (Halus Hybrid IR-G205 manufactured by Nippon Shokubai Co., Ltd.), 74.2 mg of near infrared absorbing dye SDA6104 (HW SANDS CORP.) Having absorption at wavelengths of 826 nm to 850 nm, wavelength A near-infrared absorbing dye SDA6825 (HW SANDS CORP.) 23.2 mg having absorption at 726 nm to 750 nm was dissolved in 40 ml of cyclohexane to prepare a desired coating solution.

この塗布液を１．０μｍの厚みとなるようにコーティングして、透明基板１の上に有機膜層２を形成した。   This coating solution was coated to a thickness of 1.0 μm to form an organic film layer 2 on the transparent substrate 1.

コーティング手段は、塗工機、またはスピンコータなどの薄膜塗工装置を用いるか、スプレーやディッピングなどの手法を用いることが出来る。スピンコータは、基板１を回転させ中央に塗布液を滴下して、遠心力により均一な膜厚に塗工を行う。塗工機は、基板１の上に塗布液を落としながらヘッドによって均一な膜厚に塗工を行う。あるいは基板の下側に毛細管現象を利用して塗布液を引き上げながらコーティングする方法もある。ディッピングは、塗布液に基板を浸し、引き上げることによって均一な膜厚に塗工を行う。これら全てのコーティング方法において、溶媒が蒸発して樹脂バインダが固まることにより、有機膜層２を形成することが基本となっている。   As the coating means, a coating machine, a thin film coating apparatus such as a spin coater, or a technique such as spraying or dipping can be used. The spin coater rotates the substrate 1 to drop the coating solution at the center, and performs coating to a uniform film thickness by centrifugal force. The coating machine applies a uniform film thickness with the head while dropping the coating solution onto the substrate 1. Alternatively, there is a method of coating the lower side of the substrate while pulling up the coating solution by utilizing capillary action. In dipping, the substrate is immersed in a coating solution and then pulled up to perform a uniform film thickness. In all these coating methods, the organic film layer 2 is basically formed by evaporating the solvent and solidifying the resin binder.

図３Ａは、上述のようにして作成された有機膜層２の分光光学特性を示すグラフである。このグラフは横軸に波長（ｎｍ）を取り、縦軸に透過率（％）を取ってある。グラフから明らかなように、この有機膜層２は可視域（４００〜７００ｎｍの波長領域）において、透過率が平均で９０％以上となっている。一方近赤外域（７００〜９００ｎｍ）の波長領域で、透過率が４０％程度に調整されている。この様な分光特性が得られるように、有機膜層２の膜厚と、塗布液の組成を決める。塗布液の組成は、主として樹脂バインダに対する近赤外線吸収色素の添加量で決まる。この有機膜層２は可視域で９０％以上と高い透過率を有することが特徴となっている。その分、近赤外域における透過率は４０％を中心にして±２０％の範囲に収まればよい。図３Ｂは、有機膜層２の透過率を近赤外域で上限の６０％に調整した場合と下限の２０％に調整した場合の光学特性カーブを示すグラフである。   FIG. 3A is a graph showing the spectral optical characteristics of the organic film layer 2 produced as described above. In this graph, the horizontal axis represents wavelength (nm) and the vertical axis represents transmittance (%). As is apparent from the graph, the organic film layer 2 has an average transmittance of 90% or more in the visible region (wavelength region of 400 to 700 nm). On the other hand, the transmittance is adjusted to about 40% in the wavelength region of the near infrared region (700 to 900 nm). In order to obtain such spectral characteristics, the film thickness of the organic film layer 2 and the composition of the coating solution are determined. The composition of the coating solution is mainly determined by the amount of the near infrared absorbing dye added to the resin binder. The organic film layer 2 is characterized by having a high transmittance of 90% or more in the visible region. Accordingly, the transmittance in the near infrared region may be within a range of ± 20% centering on 40%. FIG. 3B is a graph showing optical characteristic curves when the transmittance of the organic film layer 2 is adjusted to the upper limit of 60% and the lower limit of 20% in the near infrared region.

次に無機膜層３の成膜を詳細に説明する。本実施例では、先に形成された有機膜層２の上に重ねて無機膜層３を真空蒸着法によって形成している。なお本発明はこれに限られるものではなく、真空蒸着法に代えてイオンプレーティング法、イオンアシスト法、スパッタ法などのＰＶＤ手法を利用することが出来る。まず屈折率がｎ＝１．４５のＳｉＯ２膜を真空蒸着で所定の厚みに成膜する。続いて屈折率がｎ＝２．３０のＴｉＯ２膜を同じく真空蒸着法で所定の厚みに成膜する。この様な低屈折率光学膜と高屈折率光学膜を交互に１１層まで積層して、所望の無機膜層３を形成している。１１層で総厚は１０８８ｎｍとなる。 Next, the formation of the inorganic film layer 3 will be described in detail. In the present embodiment, the inorganic film layer 3 is formed by vacuum deposition on the organic film layer 2 previously formed. The present invention is not limited to this, and PVD techniques such as an ion plating method, an ion assist method, and a sputtering method can be used instead of the vacuum deposition method. First, a SiO 2 film having a refractive index n = 1.45 is formed to a predetermined thickness by vacuum deposition. Subsequently, a TiO 2 film having a refractive index n = 2.30 is formed to a predetermined thickness by the same vacuum deposition method. Such a low refractive index optical film and a high refractive index optical film are alternately laminated up to 11 layers to form a desired inorganic film layer 3. With 11 layers, the total thickness is 1088 nm.

無機膜層４も、無機膜層３と同様の手法で透明基板１の反対側の面に形成する。この無機膜層４はＳｉＯ２膜とＴｉＯ２膜を所定の厚みで交互に１３層重ねたもので、１３層の総厚は１５９１ｎｍである。 The inorganic film layer 4 is also formed on the opposite surface of the transparent substrate 1 in the same manner as the inorganic film layer 3. This inorganic film layer 4 is formed by alternately stacking 13 layers of SiO 2 and TiO 2 with a predetermined thickness, and the total thickness of 13 layers is 1591 nm.

図４は、このようにして作成した無機膜層３及び無機膜層４の分光特性を示すグラフである。図３のグラフと同様に、横軸に波長（ｎｍ）を取り、縦軸に透過率（％）を取ってある。無機膜層３は低屈折率誘電体膜と高屈折率誘電体膜を積層した光学多層膜で、各層の屈折率や膜厚及び積層数を適宜調整することで、所望の分光特性が得られる。無機膜層３は可視域で９０％程度の透過率となる一方、７００〜８５０ｎｍの波長領域で１０％程度の透過率となっている。一方、無機膜層４は８００ｎｍ以下の波長域で比較的高い透過率を示す一方、８５０ｎｍ以上の波長域で、透過率が１０％以下となっている。これらの無機膜層３，４は近赤外域で１０％程度の透過率である。これを５％程度の透過率まで下げるためには、積層数を増やさなければならない。しながら、無機膜層を構成する誘電体膜の積層数を増やすと、クラックなどの問題が生じる。本発明では、無機膜層を構成する誘電体膜の積層数が１０層程度で、その分透過率が１０％程度になっている。   FIG. 4 is a graph showing the spectral characteristics of the inorganic film layer 3 and the inorganic film layer 4 thus prepared. Similar to the graph of FIG. 3, the horizontal axis represents wavelength (nm) and the vertical axis represents transmittance (%). The inorganic film layer 3 is an optical multilayer film in which a low-refractive index dielectric film and a high-refractive index dielectric film are stacked. . The inorganic film layer 3 has a transmittance of about 90% in the visible region, and a transmittance of about 10% in the wavelength region of 700 to 850 nm. On the other hand, the inorganic film layer 4 shows a relatively high transmittance in the wavelength region of 800 nm or less, while the transmittance is 10% or less in the wavelength region of 850 nm or more. These inorganic film layers 3 and 4 have a transmittance of about 10% in the near infrared region. In order to reduce the transmittance to about 5%, the number of stacked layers must be increased. However, when the number of laminated dielectric films constituting the inorganic film layer is increased, problems such as cracks occur. In the present invention, the number of laminated dielectric films constituting the inorganic film layer is about 10, and the transmittance is correspondingly about 10%.

図５は、最終的に得られた近赤外線吸収フィルタの分光特性を示すグラフである。換言すると、有機膜層２と無機膜層３，４を重ねた積層の分光特性である。グラフから明らかなように、本発明の近赤外線吸収フィルタは可視域で９０％を超える高い透過率を有する一方、近赤外域の透過率は５％以下で十分に実用的なレベルで近赤外線をカットしている。この様な実用的に優れた分光特性は、本発明にしたがって有機膜層と無機膜層を組み合わせたことで実現している。有機膜層は可視域で高い透過率を有するように調製されており、これによって可視域で高い透明性が得られる。一方近赤外域では無機膜層が呈する若干高めの透過率１０％をこれに有機膜層を重ねることで、実用的な５％まで下げている。   FIG. 5 is a graph showing the spectral characteristics of the near-infrared absorption filter finally obtained. In other words, the spectral characteristics of a laminate in which the organic film layer 2 and the inorganic film layers 3 and 4 are stacked. As is apparent from the graph, the near-infrared absorption filter of the present invention has a high transmittance exceeding 90% in the visible region, while the transmittance in the near-infrared region is 5% or less and the near-infrared filter is sufficiently practical. It is cut. Such practically excellent spectral characteristics are realized by combining an organic film layer and an inorganic film layer according to the present invention. The organic film layer is prepared so as to have a high transmittance in the visible range, whereby high transparency is obtained in the visible range. On the other hand, in the near infrared region, the slightly higher transmittance of 10% exhibited by the inorganic film layer is reduced to a practical 5% by overlapping the organic film layer thereon.

本発明にかかる近赤外線吸収フィルタの基本的な構成を示す模式的な断面図である。It is typical sectional drawing which shows the basic composition of the near-infrared absorption filter concerning this invention. 同じく本発明にかかる近赤外線吸収フィルタの実施形態を示す断面図である。It is sectional drawing which similarly shows embodiment of the near-infrared absorption filter concerning this invention. 有機膜層の分光特性を示すグラフである。It is a graph which shows the spectral characteristic of an organic film layer. 同じく有機膜層の分光特性を示すグラフである。It is a graph which similarly shows the spectral characteristic of an organic film layer. 無機膜層の分光特性を示すグラフである。It is a graph which shows the spectral characteristic of an inorganic film layer. 本発明にかかる近赤外線吸収フィルタの分光特性を示すグラフである。It is a graph which shows the spectral characteristic of the near-infrared absorption filter concerning this invention.

符号の説明Explanation of symbols

１・・・透明基板、２・・・有機膜層、３・・・無機膜層、４・・・無機膜層
DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2 ... Organic film layer, 3 ... Inorganic film layer, 4 ... Inorganic film layer

Claims (4)

透明基板と、その片面または両面に形成された、近赤外線に吸収を持つ有機膜層及び近赤外線を遮断する無機膜層とを有する近赤外線吸収フィルタにおいて、
前記有機膜層はその可視域での透過率を９０％以上にし、近赤外域での透過率を２０％〜６０％にしたことを特徴とする近赤外線吸収フィルタ。 In a near-infrared absorbing filter having a transparent substrate, an organic film layer that absorbs near-infrared rays, and an inorganic film layer that blocks near-infrared rays, formed on one or both sides thereof,
The near-infrared absorbing filter, wherein the organic film layer has a transmittance in the visible region of 90% or more and a transmittance in the near-infrared region of 20% to 60%. 前記有機膜層は、近赤外線吸収色素が少なくとも１種類含有されているポリマー組成物からなることを特徴とする請求項１記載の近赤外線吸収フィルタ。   The near-infrared absorption filter according to claim 1, wherein the organic film layer is made of a polymer composition containing at least one kind of near-infrared absorbing dye. 前記ポリマー組成物は、ポリエステル樹脂、ポリアクリル樹脂、またはポリイミド樹脂から選ばれたプラスチックス樹脂であることを特徴とする請求項２記載の近赤外線吸収フィルタ。   The near-infrared absorbing filter according to claim 2, wherein the polymer composition is a plastic resin selected from a polyester resin, a polyacrylic resin, or a polyimide resin. 前記無機膜層は、低屈折率の誘電体膜と高屈折率の誘電体膜を交互に重ねた多層膜からなることを特徴とする請求項１記載の近赤外線吸収フィルタ。
The near-infrared absorption filter according to claim 1, wherein the inorganic film layer is formed of a multilayer film in which a low refractive index dielectric film and a high refractive index dielectric film are alternately stacked.
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