Diimmonium compound and use thereof Number:7,521,006 from the United States Patent and Trademark Office (PTO) owispatent

Title: Diimmonium compound and use thereof

Abstract: Disclosed is a near-infrared absorbing compound which does not contain antimony or arsenic, and has excellent stability, especially excellent heat resistance, light resistance and moist heat resistance. Also disclosed are a near-infrared absorbing filter, which is produced by using the near-infrared absorbing compound, and has excellent resistance such as light resistance and heat resistance, an optical filter and an optical recording medium. Specifically disclosed are a diimmonium compound represented by the formula (1) below and a near-infrared absorbing filter obtained by using such a diimmonium compound. Further specifically disclosed are a near-infrared absorbing filter wherein an adhesive layer containing the diimmonium compound is arranged on a transparent supporting body, and an optical filter using such a near-infrared absorbing filter. ##STR00001## (In the formula (1), R.sub.1 to R.sub.8 independently represent a hydrogen atom or an optionally substituted aliphatic hydrocarbon residue; R.sub.9 to R.sub.11 independently represent an aliphatic hydrocarbon residue which may have a halogen atom; and rings A and B may further have a substituent).

Patent Number: 7,521,006 Issued on 04/21/2009 to Ikeda,   et al.

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Inventors:	Ikeda; Masaaki (Kita-ku, JP), Kurata; Takaaki (Kita-ku, JP), Kaneko; Syouichi (Saitama, JP), Segawa; Junichi (Kita-ku, JP)
Assignee:	Nippon Kayaku Kabushiki Kaisha (Tokyo, JP)
Appl. No.:	11/661,800
Filed:	September 2, 2005
PCT Filed:	September 02, 2005
PCT No.:	PCT/JP2005/016094
371(c)(1),(2),(4) Date:	April 16, 2007
PCT Pub. No.:	WO2006/028006
PCT Pub. Date:	March 16, 2006

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Foreign Application Priority Data

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Sep 06, 2004 [JP]			2004-258602
Apr 22, 2005 [JP]			2005-124368
Apr 26, 2005 [JP]			2005-127917

Current U.S. Class:	252/587 ; 313/479; 359/350; 359/359; 359/360; 359/885; 430/270.11; 524/236; 552/302; 558/388; 564/271
Current International Class:	F21V 9/04 (20060101)
Field of Search:	252/587 552/302 524/236 558/388 564/271 359/350,359,360,885 430/270.11 313/479

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References Cited [Referenced By]

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U.S. Patent Documents

3575871	April 1971	Susi et al.
4923390	May 1990	Oguchi et al.
5415957	May 1995	Okada et al.
5945209	August 1999	Okazaki et al.
6475590	November 2002	Kitayama et al.
6522463	February 2003	Shimomura et al.
2002/0033661	March 2002	Sugimachi et al.
2006/0073407	April 2006	Yamanobe et al.
2006/0091365	May 2006	Kitayama et al.

Foreign Patent Documents

	1 090 910		Apr., 2001		EP
	1 176 436		Jan., 2002		EP
	1 403 666		Mar., 2004		EP
	1 496 375		Jan., 2005		EP
	1 564 260		Aug., 2005		EP
	1 589 358		Oct., 2005		EP
	64-38490		Feb., 1989		JP
	10-180922		Jul., 1998		JP
	10-180947		Oct., 1998		JP
	2000-211239		Feb., 2000		JP
	2000-81511		Mar., 2000		JP
	2000-211239		Aug., 2000		JP
	2000-227515		Aug., 2000		JP
	2000-229931		Aug., 2000		JP
	2001-175185		Jun., 2001		JP
	2005-49848		Feb., 2005		JP
	173937		Dec., 1991		TW
	335435		Jul., 1998		TW
	454009		Sep., 2001		TW
	99/67200		Dec., 1999		WO
	03/005076		Jan., 2003		WO
	2004/048480		Jun., 2004		WO
	2004/068199		Aug., 2004		WO

Other References

The European Search Report dated Aug. 13, 2008. cited by other.

Primary Examiner: Douyon; Lorna M
Assistant Examiner: Ahvazi; Bijan
Attorney, Agent or Firm: Nields & Lemack

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Claims

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What is claimed is:

1. A diimmonium compound represented by the following Formula (1): ##STR00015## wherein R.sub.1 to R.sub.8 each independently represent a hydrogen atom or an aliphatic hydrocarbon residue which may have a substituent; R.sub.9 to R.sub.11 each independently represent an aliphatic hydrocarbon residue which may have a halogen atom; and rings (A) and (B) may independently have a further substituent.

2. The diimmonium compound according to claim 1, wherein the diimmonium compound shown by Formula (1) is a compound represented by the following Formula (2): ##STR00016## wherein R.sub.1 to R.sub.8 and R.sub.9 to R.sub.11 have the same meanings as described for Formula.

3. The diimmonium compound according to claim 1 or claim 2, wherein all of R.sub.9 to R.sub.11 in Formula (1) are aliphatic hydrocarbon residues having a fluorine atom.

4. The diimmonium compound according to claim 3, wherein the aliphatic hydrocarbon residue having a fluorine atom is a trifluoromethyl group.

5. The diimmonium compound according to claim 1, wherein all of R.sub.1 to R.sub.8 in Formula (1) are straight chain or branched chain alkyl groups.

6. The diimmonium compound according to claim 5, wherein the straight chain or branched chain alkyl group is a C.sub.1 to C.sub.6 straight chain or branched chain alkyl group.

7. The diimmonium compound according to claim 6, wherein the straight chain or branched chain alkyl group is a C.sub.2 to C.sub.5 straight chain or branched chain alkyl group.

8. The diimmonium compound according to claim 7, wherein the straight chain or branched chain alkyl group is an ethyl group, an n-propyl group, an n-butyl group, an iso-butyl group or an n-amyl group.

9. The diimmonium compound according to claim 1, wherein the substituents in aliphatic hydrocarbon residues which may have a substituent of R.sub.1 to R.sub.8 in Formula (1) or Formula (2) are each independently a halogen atom, a cyano group, a nitro group, a hydroxyl group, a carboxyl group, a carbonamide group, an alkoxycarbonyl group, an acyl group, an aryl group or an alkoxyl group.

10. The diimmonium compound according to claim 9, wherein all of R.sub.1 to R.sub.8 are alkyl groups substituted by a cyano group.

11. The diimmonium compound according to claim 10, wherein the alkyl group substituted by a cyano group is a cyanopropyl group.

12. A resin composition characterized by comprising the diimmonium compound according to claim 1 and a resin.

13. A near-infrared light absorbing filter characterized by having a layer comprising the diimmonium compound according to claim 1.

14. The near-infrared light absorbing filter according to claim 13, wherein the layer comprising the diimmonium compound is a sticking layer.

15. The near-infrared light absorbing filter according to claim 14, wherein the sticking layer comprises a rust-preventing agent.

16. The near-infrared light absorbing filter according to claim 15, wherein the rust-preventing agent is 1H-benzotriazole.

17. The near-infrared light absorbing filter according to claim 14, wherein the content of an organic acid in the sticking layer is 0.5 mass % or less with respect to the mass of the sticking layer.

18. The near-infrared light absorbing filter according to claim 14, characterized in that the sticking layer comprises a compound having the absorption maximum in a wavelength between 550 and 620 nm together with the diimmonium compound of Formula (1).

19. An optical filter for a plasma display panel characterized by comprising the near-infrared light absorbing filter according to claim 13 and an electromagnetic-wave-shielding layer.

20. A plasma display panel having the optical filter for a plasma display panel according to claim 19.

21. An optical information recording medium characterized by comprising a recording layer containing the diimmonium compound according to claim 1.

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Description

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TECHNICAL FIELD

The present invention relates to a compound having absorption in a near-infrared region and the use thereof. The present invention particularly relates to a diimmonium compound which is not a deleterious substance and is superior in heat resistance, light resistance and solubility, a near-infrared light absorbing filter using the diimmonium compound, and an optical filter and an optical information recording medium using the diimmonium compound.

BACKGROUND ART

A diimmonium compound as a near-infrared light absorbing material has been widely known (for instance, see Patent Documents 1 to 3), and has been widely used in a near-infrared light absorbing filter, a thermal insulation film, sunglasses and the like. However, among these compounds, the compounds having a hexafluoroantimonate ion, a hexafluoroarsenate ion or the like as a counter ion has been used for the reason of being comparatively superior in heat resistance, and above all, the compound having a hexafluoroantimonate ion as a counter ion has been used in many cases. However, a compound not containing these metals has been desired to be developed in the industrial field in which the use of heavy metals is regulated, particularly, in the field of electric material, because the compound containing antimony is categorized as a deleterious substance. As means for solving the problem, there is a method of using a perchlorate ion, a hexafluorophosphate ion and a fluoroborate ion as the counter ion, but these counter ions are insufficient, in consideration of heat resistance and resistance to moist heat. Furthermore, a compound using an organic counter ion such as naphthalenedisulfonic acid is proposed (for instance, see Patent Document 2), but a field in which the compound is practically usable is limited because molar absorptivity is low and the compound in itself takes on a green tinge. In addition, compounds using a trifluoromethanesulfonate ion, bis(trifluoromethane)sulfonic acid imide and the like have been known (for instance, see Patent Documents 1, 4 and 5), but it cannot be said that these compounds have sufficient heat resistance and resistance to moist heat, so that a more excellent compound has been demanded to be developed.

By the way, near-infrared light is used for a beam for remotely operating electrical machinery and apparatuses, so that machinery and apparatuses emitting near-infrared light may cause misoperation in electrical machinery and apparatuses installed in the periphery. It is therefore needed to install a filter having a function of shielding near-infrared light on the front surface of such machinery and apparatuses.

Among electrical machinery and apparatuses, a PDP (plasma display, panel) has been frequently used in large-sized televisions in recent years. The PDP generates visible light necessary for an image according to a principle of: applying voltage on a rare gas (such as neon and xenon) which is sealed in a cell sandwiched between two pieces of tabular glass to generate ultra-violet light; and making the generated ultra-violet light irradiate a luminous body coated on the surface of cell wall. However, the PDP also emits a harmful electromagnetic wave such as near-infrared light, an electromagnetic wave harmful to a human body and an orange beam (hereafter referred to as neon light) which is originated in neon gas and decreases red light, simultaneously with the emission of visible light. It is accordingly needed to equip the PDP with an optical filter which passes the useful visible light through itself but shields the harmful electromagnetic wave including the near-infrared light.

A near-infrared light absorbing filter to be used in an optical filter is produced by coating a compound which absorbs near-infrared light (a near-infrared light absorbing compound) on the surface of a transparent support or on the surface of a functional film such as a film for shielding an electromagnetic wave which is harmful to a human body (hereafter referred to as an electromagnetic-wave-shielding film) with the use of a polymer resin as a binder. There are many near-infrared light absorbing compounds in such a field of application, but a diimmonium compound or a combination thereof with another near-infrared light absorbing compound is often used because a diimmonium compound has a wide absorption wavelength region to the near-infrared light.

However, a conventional diimmonium compound has not only the disadvantage of the harmfulness as above described, but also has a problem on stability as has been pointed out that the diimmonium compound has insufficient stability on heat resistance and on resistance to moist heat in general, when a near-infrared light absorbing filter is prepared by coating the diimmonium compound on a resin film with the use of a resin as a binder.

Patent Document 6 discloses a technology for stabilizing a diiummonium compound by making a polymeric resin layer contain the diimmonium compound while controlling the amount of a solvent remaining in the resin layer to a specified ratio or smaller. The technology needs, however, some work of controlling the amount of the remaining solvent, so that a diimmonium compound has been desired to be developed which shows high heat resistance and resistance to moist heat when coated by a more general coating method and drying method. Patent Document 7 discloses an optical filter with near-infrared light absorptivity, which has a diimmonium compound with a bis(fluoroalkyl sulfonyl) imide anion or a tris(fluoroalkyl sulfonyl)carbanion contained in a coating layer of a transparent polymeric resin, and states that the diimmonium compound, particularly one having the bis(fluoroalkyl sulfonyl)imide anion, shows good heat resistance and resistance to moist heat with specific examples of the compound. However, the Patent Document does not describe the name of a specific compound, a specific production method, physical properties or an application example about the diimmonium compound having the tris(fluoroalkyl sulfonyl) carbanion. Further, there is a method of making a near-infrared light absorbing compound contained in a sticking layer for adhesively bonding a polymeric resin film to a support, as a method of making a near-infrared light absorbing compound held in a resin film. The method can make the near-infrared light absorbing compound contained in the sticking layer of a functional film such as an anti-reflection film and an electromagnetic-wave-shielding film which compose an optical filter, and accordingly has a great merit of cost reduction in comparison with the method of additionally forming a layer containing the near-infrared light absorbing compound, because one step can be eliminated from coating steps. However, the method has been considered to have a high technical hurdle because of aggravating heat resistance and resistance to moist heat more than the method of making the near-infrared light absorbing compound contained in a polymeric resin film or in a coating layer. Patent Document 1: Japanese Patent Publication (KOKOKU) No. 07-51555 (Page 2) Patent Document 2: Japanese Patent Laying Open (KOKAI) No. 10-316633 (Page 5) Patent Document 3: Japanese Patent Publication (KOKOKU) No. 43-25335 (Pages 7 to 14) Patent Document 4: International Publication Pamphlet WO2004/068199 Patent Document 5: International Publication Pamphlet WO2004/048480 Patent Document 6: Japanese Patent Laying Open (KOKAI) No. 2000-227515 Patent Document 7: Japanese Patent Laying Open (KOKAI) No. 2005-49848 (Pages 2 to 12)

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The present invention is developed under the above described situation. An object of the present invention is to provide a near-infrared light absorbing compound which does not contain a heavy metal such as antimony, and has more excellent stability, particularly, heat resistance, light resistance and resistance to moist heat; such a near-infrared light absorbing filter (particularly for a plasma display panel); and further a photorecording medium and a resin composition superior in atmospheric corrosion resistance. Another object of the present invention is to provide a particularly preferred embodiment of the near-infrared light absorbing filter using the diimmonium compound according to the present invention.

Means of Solving the Problems

As a result of making an extensive investigation for solving the above described problems, the present inventors found that a diimmonium compound having a particular structure solves the above described various problems, and arrived at the accomplishment of the present invention. Specifically, the present invention relates to: (1) a diimmonium compound represented by the following Formula (1):

##STR00002## (wherein R.sub.1 to R.sub.8 each independently represent a hydrogen atom or an aliphatic hydrocarbon residue which may have a substituent; R.sub.9 to R.sub.11 each independently represent an aliphatic hydrocarbon residue which may have a halogen atom; and rings (A) and (B) may independently have a further substituent); (2) the diimmonium compound according to the item (1), wherein the diimmonium compound shown by Formula (1) is a compound represented by the following Formula (2):

##STR00003## (wherein R.sub.1 to R.sub.8 and R.sub.9 to R.sub.11 have the same meanings as described for Formula (1)); (3) the diimmonium compound according to items (1) or (2), wherein all of R.sub.9 to R.sub.11 in Formula (1) are aliphatic hydrocarbon residues having a fluorine atom; (4) the diimmonium compound according to the item (3), wherein the aliphatic hydrocarbon residue having a fluorine atom is a trifluoromethyl group; (5) the diimmonium compound according to any one of items (1) to (4), wherein all of R.sub.1 to R.sub.8 in Formula (1) are straight chain or branched chain alkyl groups; (6) the diimmonium compound according to the item (5), wherein the straight chain or branched chain alkyl group is a C.sub.1 to C.sub.6 straight chain or branched chain alkyl group; (7) the diimmonium compound according to the item (6), wherein the straight chain or branched chain alkyl group is a C.sub.2 to C.sub.5 straight chain or branched chain alkyl group; (8) the diimmonium compound according to the item (7), wherein the straight chain or branched chain alkyl group is an ethyl group, an n-propyl group, an n-butyl group, an iso-butyl group or an n-amyl group; (9) the diimmonium compound according to any one of items (1) to (4), wherein the substituents in aliphatic hydrocarbon residues which may have a substituent of R.sub.1 to R.sub.8 in Formula (1) or Formula (2) are each independently a halogen atom, a cyano group, a nitro group, a hydroxyl group, a carboxyl group, a carbonamide group, an alkoxycarbonyl group, an acyl group, an aryl group or an alkoxyl group; (10) the diimmonium compound according to the item (9), wherein all of R.sub.1 to R.sub.8 are alkyl groups substituted by a cyano group; (11) the diimmonium compound according to the item (10), wherein the alkyl group substituted by a cyano group is a cyanopropyl group; (12) a resin composition characterized by comprising the diimmonium compound according to any one of items (1) to (11) and a resin; (13) a near-infrared light absorbing filter characterized by having a layer comprising the diimmonium compound according to any one of items (1) to (11); (14) the near-infrared light absorbing filter according to the item (13), wherein the layer comprising the diimmonium compound is a sticking layer; (15) the near-infrared light absorbing filter according to the item (14), wherein the sticking layer comprises a rust-preventing agent; (16) the near-infrared light absorbing filter according to the item (15), wherein the rust-preventing agent is 1H-benzotriazole; (17) the near-infrared light absorbing filter according to any one of items (14) to (16), wherein the content of an organic acid in the sticking layer is 0.5 mass % or less with respect to the mass of the sticking layer; (18) the near-infrared light absorbing filter according to any one of items (14) to (17), characterized in that the sticking layer comprises a compound having the absorption maximum in a wavelength between 550 and 620 nm together with the diimmonium compound of Formula (1); (19) an optical filter for a plasma display panel characterized by comprising the near-infrared light absorbing filter according to any one of items (13) to (18) and an electromagnetic-wave-shielding layer; (20) a plasma display panel having the optical filter for a plasma display panel according to the item (19); and (21) an optical information recording medium characterized by comprising a recording layer containing the diimmonium compound according to any one of items (1) to (11). Effect of the Invention

The diimmonium compound having near-infrared light absorbing properties according to the present invention is a compound which does not include antimony and arsenic, is not a deleterious substance, has molar absorptivity as high as 100,000 or higher, is superior in heat resistance and light resistance, and has high solubility. The diimmonium compound is particularly superior in heat resistance and resistance to moist heat to a conventional diimmonium compound containing a hexafluorophosphate ion, a perchlorate ion or a fluoroborate ion. Because of having such characteristics, the diimmonium compound according to the present invention can be preferably used as a material for absorbing near-infrared light such as in a near-infrared light absorbing filter, a thermal insulation film and sunglasses, and is particularly preferable for the near-infrared light absorbing filter for a plasma display.

A near-infrared light absorbing filter using a diimmonium compound according to the present invention adequately absorbs near-infrared light in a wavelength region of 700 to 1,100 nm. Particularly, when having the diimmonium compound contained in a sticking layer which is provided on a transparent support, the near-infrared light absorbing filter shows excellent heat resistance and resistance to moist heat, and does not cause the degradation of near-infrared light absorptivity, the discoloration of the layer and the degradation of surface quality. Accordingly, an optical filter for a PDP, which is formed by combining the near-infrared light absorbing filter and another functional film, shows excellent performance and can sufficiently cope with the above described problems.

Furthermore, an optical information recording medium according to the present invention can have greatly improved light resistance in comparison with an optical information recording medium containing a conventional diimmonium compound. In addition, the diimmonium compound according to the present invention has sufficient solubility in preparing the optical information recording medium, and has superior workability as well. In addition, when making the compound contained, for instance, in a thin film of an organic coloring matter, which is a recording layer of the optical information recording medium, the provided optical information recording medium shows remarkably improved durability and stability of light resistance in a re-recording operation.

BEST MODE FOR CARRYING OUT THE INVENTION

The diimmonium compound according to the present invention is a salt composed of one particular diimmonium cation and two particular anions as counter ions, and is represented by the following Formula (1).

##STR00004##

In Formula (1), R.sub.9 to R.sub.11 each independently represent an aliphatic hydrocarbon residue which may have a halogen atom. The aliphatic hydrocarbon residue includes saturated and unsaturated, straight chain, branched chain and cyclic alkyl groups of preferably having 1 to 36 carbon atoms; is more preferably saturated straight chain alkyl groups which may have a substituent and have 1 to 20 carbon atoms; and is most preferably the above alkyl group having 1 to 4 carbon atoms. The halogen atom is preferably a fluorine, chlorine, bromine or iodine atom; is more preferably a fluorine, chlorine or bromine atom; and is most preferably a fluorine atom. A specific example of the group includes: a saturated straight chain alkyl group such as a methyl group, a trifluoromethyl group, a difluoromethyl group, a monofluoromethyl group, a dichloromethyl group, a monochloromethyl group, a dibromomethyl group, a difluorochloromethyl group, an ethyl group, a pentafluoroethyl group, a tetrafluoroethyl group, a trifluoroethyl group, a trifluorochloroethyl group, a difluoroethyl group, a monofluoroethyl group, a trifluoroiodoethyl group, a propyl group, a heptafluoropropyl group, a hexafluoropropyl group, a pentafluoropropyl group, a tetrafluoropropyl group, a trifluoropropyl group, a difluoropropyl group, a monofluoropropyl group, a perfluorobutyl group, a perfluorohexyl group, a perfluorooctyl group and a perfluorooctylethyl group; an unsaturated alkyl group such as an allyl group, a tetrafluoroallyl group, a trifluorovinyl group and a perfluorobutylvinyl group; a branched chain alkyl group such as an isopropyl group, a pentafluoroisopropyl group, a heptafluoroisopropyl group, a perfluoro-3-methylbutyl group and a perfluoro-3-methylhexyl group; and a cyclic alkyl group such as a cyclohexyl group. In Formula (1), R.sub.9 to R.sub.11 are preferably all the same. Further, all of R.sub.9 and R.sub.10, R.sub.9 and R.sub.11 or R.sub.10 and R.sub.11 may be coupled to form a cyclic alkyl group.

It is particularly preferable that all of R.sub.9 to R.sub.11 are aliphatic hydrocarbon residues having a fluorine atom. A specific example of the residue includes a trifluoromethyl group, a difluoromethyl group, a monofluoromethyl group, a pentafluoroethyl group, a tetrafluoroethyl group, a trifluoroethyl group, a difluoroethyl group, a heptafluoropropyl group, a hexafluoropropyl group, a pentafluoropropyl group, a tetrafluoropropyl group, a trifluoropropyl group and a perfluorobutyl group; is preferably a trifluoromethyl group, a difluoromethyl group, a pentafluoroethyl group, a trifluoroethyl group, a heptafluoropropyl group, a tetrafluoropropyl group and a perfluorobutyl group; and more preferably is a trifluoromethyl group. In the above described respective groups, an alkyl moiety is straight chain unless otherwise specified.

In Formula (1), rings (A) and (B) may respectively have 1 to 4 substituents in positions other than 1-position and 4-position. The substituent that may be bonded includes, for instance, a halogen atom, a hydroxyl group, a lower alkoxy group, a cyano group and a lower alkyl group. The halogen atom includes, for instance, a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. The lower alkoxy group includes, for instance, a C1 to C5 alkoxy group such as a methoxy group and an ethoxy group, and the lower alkyl group includes, for instance, a C1 to C5 alkyl group such as a methyl group and an ethyl group. It is preferable in Formula (1) that any of rings (A) and (B) does not have a substituent in positions except 1-position and 4-position, or both of the rings (A) and (B) are substituted by a halogen atom (a chlorine atom, a bromine atom and a fluorine atom in particular), a methyl group or a cyano group.

When a ring (B) has a substituent, all of the four rings (B) preferably have the same substituents, and furthermore, the substituent is preferably bonded to an m-position with respect to a nitrogen atom bonded to the ring (A).

R.sub.1 to R.sub.8 each independently represent a hydrogen atom or an aliphatic hydrocarbon residue which may have a substituent. The aliphatic hydrocarbon residue means a group formed by eliminating one hydrogen atom from a saturated or unsaturated, straight chain, branched chain or cyclic aliphatic hydrocarbon. The number of carbon atoms is 1 to 36, and preferably is 1 to 20.

A specific example of a saturated aliphatic hydrocarbon residue or an unsaturated aliphatic hydrocarbon residue having no substituent group includes a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, an s-butyl group, a ter-butyl group, an n-pentyl group, an iso-pentyl group, a ter-pentyl group, an octyl group, a decyl group, a dodecyl group, an octadecyl group, an isopropyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, an allyl group, a propenyl group, a pentynyl group, a butenyl group, a hexenyl group, a hexadienyl group, an isopropenyl group, an isohexenyl group, a cyclohexenyl group, a cyclopentadienyl group, an ethynyl group, a propynyl group, a hexynyl group, an isohexynyl group and a cyclohexynyl group. Among those, a preferred residue includes a C1 to C5 saturated aliphatic straight chain or branched chain hydrocarbon residue or an unsaturated aliphatic hydrocarbon residue, such as a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, a ter-butyl group, an n-pentyl group, an iso-pentyl group, a ter-pentyl group, a vinyl group, an allyl group, a propenyl group and a pentynyl group.

In the present invention, all of R.sub.1 to R.sub.8 are preferably a straight chain or branched chain alkyl group, and more preferably are a (C2-C5) straight chain or branched chain alkyl group. A specific example of the particularly preferred straight chain or branched chain alkyl group includes an ethyl group, an n-propyl group, an n-butyl group, an iso-butyl group, and an n-amyl group.

An example of a substituent in an aliphatic hydrocarbon residue having a substituent includes, for instance: a halogen atom (such as F, Cl and Br), a hydroxyl group, an alkoxy group (such as a methoxy group, an ethoxy group and an isobutoxy group), an alkoxyalkoxy group (such as a methoxyethoxy group), an aryl group (such as a phenyl group and a naphthyl group; and the aryl group may further have a substituent), an aryloxy group (such as a phenoxy group), an acyloxy group (such as an acetyloxy group, a butyryloxy group, a hexylyloxy group and a benzoyloxy group; and the aryloxy group may further have a substituent), an amino group, an alkyl substituted amino group (such as a methylamino group and a dimethylamino group), a cyano group, a nitro group, a carboxyl group, a carbonamide group, an alkoxycarbonyl group (such as a methoxycarbonyl group and an ethoxycarbonyl group), an acyl group, an amide group (such as an acetamido group), a sulfonamide group (such as a methane sulfonamide group), and a sulfo group. Among those substituents, a preferred substituent is a halogen atom, a cyano group, a nitro group, a hydroxyl group, a carboxyl group, a carbonamide group, an alkoxycarbonyl group, an acyl group, an aryl group or an alkoxyl group.

A specific example of an aliphatic hydrocarbon residue having a substituent includes: a cyano substituted (C1-C6) alkyl group such as a cyanomethyl group, a 2-cyanoethyl group, a 3-cyanopropyl group, a 2-cyanopropyl group, a 4-cyanobutyl group, a 3-cyanobutyl group, a 2-cyanobutyl group, a 5-cyanopentyl group, a 4-cyanopentyl group, a 3-cyanopentyl group, a 2-cyanopentyl group and 3,4-dicyanobutyl group; an alkoxy substituted (C1-C6) alkyl group such as a methoxyethyl group, an ethoxyethyl group, a 3-methoxypropyl group, a 3-ethoxypropyl group, a 4-methoxybutyl group, a 4-ethoxybutyl group, a 5-ethoxypentyl group and a 5-methoxypentyl group; and fluorinated (C1-C8) alkyl group such as a trifluoromethyl group, a monofluoromethyl group, a pentafluoroethyl group, a tetrafluoroethyl group, a trifluoroethyl group, a heptafluoropropyl group, a perfluorobutyl group, a perfluorobutylethyl group, a perfluorohexyl group, a perfluorohexylethyl group, a perfluorooctyl group and a perfluorooctylethyl group.

A preferred example of an aliphatic hydrocarbon residue having a substituent includes an alkyl group substituted by a cyano group. An example of a preferred diiummonium compound includes: a diimmonium compound in which all of R.sub.1 to R.sub.8 are an alkyl group substituted by a cyano group; and a diimmonium compound in which at least one of R.sub.1 to R.sub.8 is an alkyl group substituted by a cyano group. Here, the specific example of the alkyl group substituted by a cyano group includes a cyanopropyl group.

In a diimmonium compound in Formula (1), R.sub.1 to R.sub.8 can be independent from each other. For instance, one amino group may be substituted by an unsubstituted straight chain alkyl group and a cyano substituted alkyl group; by an unsubstituted branched chain alkyl group and a cyano substituted alkyl group; or by an unsubstituted straight chain alkyl group and an unsubstituted branched chain alkyl group.

Among diimmonium compounds shown by Formula (1) in the present invention, a preferred example of the compound includes a compound shown by Formula (2).

##STR00005##

In Formula (2), R.sub.1 to R.sub.8 and R.sub.9 to R.sub.11 represent the same meaning as in the description for Formula (1).

A diimmonium compound shown by Formula (1) according to the present invention can be obtained by a method in conformance to a method described in Patent Document 3. Specifically, the product of Ullmann reaction between p-phenylenediamins and 1-chloro-4-nitrobenzenes is reduced to obtain a compound represented by the following Formula (3):

##STR00006## (In Formula (3), rings (A) and (B) have the same meanings as described for the above described Formula (1)).

Then the compound represented by Formula (3) is reacted with a halogenated compound corresponding to the desired R.sub.1 to R.sub.8 (for instance, n-C.sub.4H.sub.9Br when all of R.sub.1 to R.sub.8 are n-C.sub.4H.sub.9), in an organic solvent, preferably in a water-soluble polar solvent such as dimethylformamide (DMF), dimethyl imidazolidinone (DMI) and N-methylpyrrolidone (NMP) at 30 to 160.degree. C., preferably at 50 to 140.degree. C. to obtain a compound represented by the following Formula (4) in which all of substituents R.sub.1 to R.sub.8 are the same. Alternatively, when preparing a compound represented by the following Formula (4) (for instance, a precursor of a compound with a compound No. 19 which will be described later) other than a compound represented by Formula (4) in which all substituents R.sub.1 to R.sub.8 are the same, an n-butyl group is first introduced into four groups among R.sub.1 to R.sub.8 by reacting the compound represented by Formula (3) with a reagent (n-C.sub.4H.sub.9Br) of predetermined moles (for instance, 4 moles per one mole of the Formula (3)), and then the obtained compound is reacted with a reagent (iso-C.sub.4H.sub.9Br) necessary for introducing the remaining substituents (iso-butyl group) in an amount of necessary moles (for instance, 4 moles per one mole of an amine compound in the Formula (4)) to prepare the compound represented by Formula (4). Still alternatively, when preparing the other arbitrary compounds than the above described compounds, a similar method as in the method for preparing the compound in exemplified No. 19 is conducted.

##STR00007##

Then the compound shown by Formula (4) which has been obtained as described above, is subjected to an oxidation reaction by adding an oxidizing agent (such as silver salt) corresponding to the following Formula (5) in an amount of 2 equivalents in an organic solvent, preferably, in a water-soluble polar solvent such as DMF, DMI and NMP, at 0 to 100.degree. C., preferably at 5 to 70.degree. C. to obtain a diimmonium compound represented by the Formula (1). Alternatively, the compound shown by Formula (4) which has been obtained as described above is oxidized with an oxidizing agent such as silver nitrate, silver perchlorate and cupric chloride, and then is subjected to salt exchange by adding an acid or a salt having an anion shown by Formula (5) to the reacted liquid to obtain a diimmonium compound represented by the Formula (1). Still alternatively, an acid or an alkaline metal salt containing the anion shown by Formula (5) is added to the compound shown by Formula (4) which has been obtained as described above, and then the oxidizing agent of mineral acid such as the above described silver nitrate and silver perchlorate is added to the product to cause an oxidation reaction to obtain a diimmonium compound represented by the Formula (1).

##STR00008##

A specific example of a diimmonium compound according to the present invention shown by Formula (1) will be shown in the following Table 1. In the column concerning R.sub.1 to R.sub.8 of the table, n- is an abbreviation of "normal" and means a straight chain, i- is an abbreviation of "iso-" and means a branched chain, and cy means "cyclo". In the column concerning rings (A) and (B), the case when positions other than 1-position and 4-position are unsubstituted is expressed by "4H", and a substituted position is a position with respect to a nitrogen atom bonded to the ring (A). In addition, in the column concerning R.sub.1 to R.sub.8, when all of R.sub.1 to R.sub.8 are n-butyl groups, the formula is abbreviated as "4(n-C.sub.4H.sub.9, n-C.sub.4H.sub.9)", and, for instance, when one is an iso-pentyl group and the others are an n-butyl group, in other words, when one of four combinations of substituents is the iso-pentyl group and all of the other three combinations are the n-butyl groups, the formula is abbreviated as "3(n-C.sub.4H.sub.9, n-C.sub.4H.sub.9),(n-C.sub.4H.sub.9, i-C.sub.5H.sub.11)". In addition, in the column concerning R.sub.9 to R.sub.11, all of alkyl moieties having 3 or more carbon atoms are formed of a straight chain.

TABLE-US-00001 TABLE 1 Specific example of diimmonium compund Cpd (R.sub.1, R.sub.2)(R.sub.3, R.sub.4) No. (R.sub.5, R.sub.6)(R.sub.7, R.sub.8) A B R.sub.9 R.sub.10 R.sub.11 1 4 (n-C.sub.4H.sub.0, n-C.sub.4H.sub.9) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 2 4 (i-C.sub.4H.sub.9, i-C.sub.4H.sub.9) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 3 4 (C.sub.3H.sub.6CN, C.sub.3H.sub.6CN) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 4 4 (i-C.sub.5H.sub.11, i-C.sub.5H.sub.11) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 5 4 (n-C.sub.5H.sub.11, n-C.sub.5H.sub.11) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 6 4 (i-C.sub.5H.sub.11, n-C.sub.5H.sub.11) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 7 4 (C.sub.2H.sub.4OCH.sub.3, C.sub.2H.sub.4OCH.sub.3) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 8 4 (CH.sub.2CH.dbd.CH.sub.2, CH.sub.2CH.dbd.CH.sub.2) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 9 4 (C.sub.4H.sub.8CN, C.sub.4H.sub.8CN) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 10 4 (n-C.sub.3H.sub.7, i-C.sub.3H.sub.7) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 11 4 (i-C.sub.4H.sub.9, C.sub.3H.sub.0CN) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 12 4 (Cy-C.sub.6H.sub.11, n-C.sub.6H.sub.11) 4H 4H CF.sub.3 C.sub.2F.sub.5 CF.sub.3 13 4 (n-C.sub.4H.sub.9, n-C.sub.4H.sub.9) 4H 4H C.sub.2F.sub.5 C.sub.2F.sub.5 C.sub.2F.sub.5 14 4 (n-C.sub.4II.sub.0, n-C.sub.4II.sub.0) 4H 4H C.sub.3F.sub.7 C.sub.3F.sub.7 C.sub.3F.sub.7 15 4 (n-C.sub.4H.sub.9, n-C.sub.4H.sub.9) 4H 3-CH.sub.3 CF.sub.3 CF.sub.3 CF.sub.3 16 4 (CF.sub.3, CF.sub.3) 4H 3-Br CF.sub.3 CF.sub.3 CF.sub.3 17 4 (CF.sub.2CF.sub.3,CF.sub.2CF.sub.3) 4H 4H CF.sub.3 C.sub.2F.sub.5 CF.- sub.3 18 4 (n-C.sub.3F.sub.7, n-C.sub.3F.sub.7) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 19 4 (n-C.sub.4H.sub.9, i-C.sub.4H.sub.9) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 20 3 (n-C.sub.4H.sub.9, n-C.sub.4H.sub.9) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 1 (n-C.sub.4H.sub.9, i-C.sub.5H.sub.11) 21 4 (C.sub.2H.sub.5, C.sub.2H.sub.5) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 22 4 (C.sub.3H.sub.6CF.sub.3, C.sub.3H.sub.6CF.sub.3) 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 23 ##STR00009## 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 24 ##STR00010## 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 25 ##STR00011## 4H 4H CF.sub.3 CF.sub.3 CF.sub.3 26 4 (n-C.sub.3H.sub.7, n-C.sub.3H.sub.7) 4H 4II CF.sub.3 CF.sub.3 CF.sub.3

A resin composition according to the present invention contains a resin and a diimmonium compound shown in Formula (1) according to the present invention.

A specific example of a resin to be used in a resin composition according to the present invention includes: an addition polymer of a vinyl compound such as polyethylene, polystyrene, polyacrylic acid, polyacrylate, polyvinyl acetate, polyacrylonitrile, polyvinyl chloride and polyvinyl fluoride; polymethacrylic acid, polymethacrylate, polyvinylidene chloride, polyvinylidene fluoride, polyvinylidene cyanide, a copolymer of a vinyl compound or a fluorine-based compound such as vinylidene fluoride/trifluoroethylene copolymer, vinylidene fluoride/tetrafluoroethylene copolymer and vinylidene cyanide/vinyl acetate copolymer; a fluorine-containing resin such as polytrifluoroethylene, polytetrafluoroethylene and polyhexafluoropropylene; polyamide like nylon 6 and nylon 66, polyimide, polyurethane, polypeptide, a polyester such as polyethylene terephthalate; polycarbonate, a polyether such as polyoxymethylene; an epoxy resin, polyvinyl alcohol and polyvinylbutyral.

The method of producing a resin composition according to the present invention and the method of using the same is not limited in particular, but a method well-known in itself can be employed, for instance, as followings: (1) a method of kneading a resin with a diimmonium compound according to the present invention, heating it and molding it to produce a resin plate or a film; (2) a method of cast-polymerizing the diimmonium compound according to the present invention with a resin monomer or a prepolymer of the resin monomer in the presence of a polymerization catalyst to produce a resin plate or a film; (3) a method of preparing a paint containing the resin composition according to the present invention, and coating the paint onto a transparent resin plate, a transparent film or a transparent glass plate; (4) a method of producing a laminated resin plate, a laminated resin film or a laminated glass plate using a resin composition (sticking agent) containing a diiummonium compound according to the present invention and a resin (sticking material); and (5) a method of forming a sticking layer formed of a sticking agent containing the diimmonium compound according to the present invention on the surface of a transparent support (when the transparent support has the above described function, on the surface of the side which does not hinder the function), in a step of coating the sticking agent, and making the sticking layer retain the diimmonium compound.

The above described production method (1) ordinarily includes, though a treatment temperature and a film-forming (resin-plate-forming) condition vary according to a resin (base resin) to be used: a method of adding a diimmonium compound according to the present invention to a powder or a pellet of the base resin, heating and melting it at 150 to 350.degree. C., then molding it to produce a resin plate; or forming it into a film (into a resin plate) by using an extrusion machine. An amount of the diimmonium compound according to the present invention to be added to the base resin is ordinarily 0.01 to 30 mass %, preferably 0.03 to 15 mass % with respect to the total mass of the base resin, though the amount varies according to a thickness, absorption intensity and transmittance for visible light of the resin plate or the film to be produced.

The above described method (2) can employ a method of injecting a diimmonium compound according to the present invention, and a resin monomer or a prepolymer of the resin monomer into a mold (die) in the presence of a polymerization catalyst, and reacting them to cure the resin monomer or the prepolymer; or pouring the above substances into a die and solidifying them in the die into a hard product to mold them. Many resins can be molded with the method, but a specific example of the resin which can be applied to the molding method includes an acrylic resin, a diethylene glycol bis(allyl carbonate) resin, an epoxy resin, a phenol-formaldehyde resin, a polystyrene resin and a silicone resin. Among those, a method of bulk-polymerizing methyl methacrylate by casting is preferable, because it provides an acrylic sheet superior in hardness, heat resistance and chemical resistance. The concentration of the diiummonium compound according to the present invention in a resin varies according to the thickness, absorption intensity and transmittance for visible light of a resin plate or a film to be produced, but ordinarily is 0.01 to 30 mass %, preferably 0.03 to 15 mass % with respect to the total mass of the resin.

In the method, a well-known thermal radical polymerization initiator can be used as a polymerization catalyst. A specific example of the usable polymerization catalyst includes a peroxide such as benzoyl peroxide, p-chlorobenzoyl peroxide and diisopropyl peroxycarbonate; and an azo compound such as azobisisobutyronitrile. The content is normally 0.01 to 5 mass % with respect to the total mass of a mixture of a diimmonium compound and a resin monomer or a prepolymer of the resin monomer. A heating temperature in the thermal polymerization step is ordinarily 40 to 200.degree. C., and a polymerization period of time is ordinarily 30 minutes to 8 hours. In addition to a thermal polymerization method, a method of adding a photoinitiator or a sensitizer to the resin and photopolymerizing the resin can be adopted.

The above described method (3) includes a method of preparing paint by dissolving a diimmonium compound according to the present invention in a resin (binder) and an organic solvent; and a method of fine-graining the diimmonium compound according to the present invention in the presence of a resin and dispersing it in water to prepare a water-based paint. The former method can employ, for instance, an aliphatic ester resin, an acrylic resin, a melamine resin, a urethane resin, an aromatic ester resin, a polycarbonate resin, a polyvinyl resin, an aliphatic polyolefin resin, an aromatic polyolefin resin, a polyvinyl alcohol resin, a polyvinyl modified resin, or a copolymer resin thereof, as a binder. When a diimmonium compound according to the present invention is employed in the method and is dissolved in a resin to be used as a binder even having a glass transition temperature (Tg) of a comparatively low Tg such as 70.degree. C., the diimmonium compound does not cause denaturation, so that a coating layer superior in heat resistance and resistance to moist heat can be formed.

The former method also can use a halogen-based, alcohol-based, ketone-based, ester-based, aliphatic hydrocarbon-based, aromatic hydrocarbon-based or ether-based organic solvent, or a mixture thereof, as an organic solvent. The concentration of a diimmonium compound according to the present invention in a resin varies according to the thickness, absorption intensity and transmittance for visible light of a coating to be formed, but ordinarily is 0.1 to 30 mass % with respect to the total mass of the resin (binder).

A near-infrared light absorbing filter or the like can be obtained by applying a paint prepared as described above on a transparent resin film, a transparent resin plate or transparent glass with a spin coater, a bar coater, a roll coater, a spray gun or the like.

The above described method (4) can employ an adhesive for a resin such as a silicone resin, a urethane resin and an acrylic resin, or a well-known transparent adhesive for laminated glass such as a polyvinylbutyral adhesive and an ethylene-vinyl acetate adhesive, as a resin for a sticking material. A filter or the like is produced by adhesively bonding transparent resin plates with each other, a resin plate with a resin film, a resin plate with a glass plate, the resin films with each other, a resin film and a glass plate, and the glass plates with each other, with the use of the sticking agent which contains a diimmonium compound according to the present invention in an amount of 0.1-30 mass %.

In addition, in the above described methods (1) to (4), a normal additive to be used in molding a resin such as an ultraviolet absorbing agent and a plasticizing agent may be added in a kneading or mixing step.

The above described method (5) will be described later.

Thus obtained resin-molded article according to the present invention can be used in application fields such as a sheet or a film (near-infrared light absorbing filter) for absorbing near-infrared light, and a filter or a film required to cut infrared light such as a thermal insulation film, an optical article and sunglasses.

In the next place, a near-infrared light absorbing filter using a diimmonium compound according to the present invention will be described, which is the most characteristic use of the diimmonium compound according to the present invention.

A near-infrared light absorbing filter according to the present invention has only to have a layer containing a diimmonium compound according to the present invention, and accordingly may be the filter having a resin layer containing the diimmonium compound according to the present invention provided on a substrate, or may be a sheet, film, plate or layer of which the substrate in itself is formed of a resin composition (or a cured substance thereof) containing the diimmonium compound according to the present invention. The material for the substrate is not limited in particular as long as it can be generally used in a near-infrared light absorbing filter, but ordinarily a substrate of the above described resins or glass is employed. The thickness of the sheet, the film, the plate or the layer containing the diimmonium compound according to the present invention is ordinarily about 0.1 .mu.m to 10 mm, and is appropriately determined according to an intended cutting rate for near-infrared light. The content of the diimmonium compound according to the present invention is also appropriately determined according to the intended cutting rate for the near-infrared light, as described above. The substrate to be used has preferably as high transparency as possible after having been formed and worked into a plate, a film or the like.

A near-infrared light absorbing filter according to the present invention may contain only one of diimmonium compounds shown by Formula (1) according to the present invention as a near-infrared light absorbing compound; it may be produced, however, by concomitantly using two or more of the diimmonium compounds according to the present invention; or it may be produced by concomitantly using the diimmonium compound according to the present invention and a near-infrared light absorbing compound other than the diimmonium compounds according to the present invention. The near-infrared light absorbing compound other than the diimmonium compounds according to the present invention includes, for instance, an organic compound such as a phthalocyanine-based compound, a cyanine-based compound and a dithiol nickel complex; a copper compound such as metallic copper, copper sulfide and copper oxide; a metal mixture containing zinc oxide as a main component; and a metallic compound or a mixture thereof such as a tungsten compound, indium tin oxide (ITO), and antimony-doped tin oxide (ATO).

For the purpose of adjusting a color tone of a near-infrared light absorbing filter, the filter may also contain a coloring matter (coloring matter for color matching) showing absorption in a visible light region in such a range as not to hinder an effect of the present invention. Alternatively, it is possible to prepare a filter containing only the coloring matter for color matching and then affix the near-infrared light absorbing filter according to the present invention to it.

When such a near-infrared light absorbing filter is used in a front plate of a plasma display, the filter needs to have as high transmittance for visible light as possible, and needs to have a transmittance of at least 40%, preferably at least 50%. The near-infrared light absorbing filter cuts near-infrared light in a region of 700 to 1,100 nm, and shows average transmittance of ordinarily 50% or less, preferably 30% or less, more preferably 20% or less and particularly preferably 10% or less, for the near-infrared light in said region.

A near-infrared light absorbing filter according to the present invention is an excellent near-infrared light absorbing filter which shows an extremely high transmittance in a visible light region, is friendly to the environment because of containing no antimony or arsenic, and absorbs the near-infrared light in a wide region. The filter is also superior in stability to a conventional near-infrared light absorbing filter which does not contain antimony but contains a perchlorate ion, a hexafluorophosphate ion and a fluoroborate ion. Furthermore, a diimmonium compound according to the present invention has sufficient solubility in a solvent to be used when the near-infrared light absorbing filter is produced, so that the filter has excellent producibility as well. The near-infrared light absorbing filter according to the present invention particularly has extremely superior heat resistance, resistance to moist heat and light resistance, hardly causes a reaction such as a decomposition reaction due to heat, and accordingly does not cause scarcely any coloration in a visible light region.

A near-infrared light absorbing filter using a diimmonium compound shown by Formula (1) according to the present invention may be produced by any of the above described methods (1) to (5); but preferably by the methods (3), (4) and (5); and particularly preferably by the method (5) which is a method of forming a sticking layer formed of a sticking agent containing the diimmonium compound according to the present invention, on the surface of a transparent support (when the transparent support has the above described function, on the surface of the side which does not hinder the function), in a step of coating the sticking agent, and making the sticking layer retain the diimmonium compound, because the method (5) shows a merit of cost reduction due to the reduction in the number of coating steps.

In the next place, a near-infrared light absorbing filter produced by adding a diimmonium compound represented by the Formula (1) according to the present invention to a sticking layer will be described in detail.

A diimmonium compound used in the present invention and represented by the Formula (1) may be singly contained in a sticking layer, but may be contained concomitantly with one or more near-infrared light absorbing compounds other than the diimmonium compound represented by Formula (1). An example of other concomitantly-usable near-infrared light absorbing compounds includes: the above described compounds; a diimmonium compound other than the diimmonium compound represented by Formula (1) according to the present invention; a nitroso compound or a metal salt thereof; an organic compound such as a cyanine-based compound, a squalirium-based compound, a thiol nickel complex salt, a phthalocyanine-based compound, a naphthalocyanine-based compound, a triarylmethane-based compound, a naphthoquinone-based compound and an anthraquinone-based compound; and an inorganic compound such as antimony tin oxide, indium tin oxide and a hexaboride compound of a rare earth metal like lanthanum hexaboride. As a matter of course, the diimmonium compound of Formula (1) may be used singly, or may be used in a form of a mixture with other one or more diimmonium compounds of Formula (1). When the diimmonium compound of Formula (1) is concomitantly used with another near-infrared light absorbing compound, 40 to 100 mass % of the diimmonium compound of Formula (1) according to the present invention is preferably contained in the mixture to be used.

In the next place, a method for preparing a near-infrared light absorbing filter will be described which contains a diimmonium compound of Formula (1) in a sticking layer.

A type and thickness of a support to be used for a near-infrared light absorbing filter according to the present invention is not limited in particular, as long as it has high transparency, has no flaw, and is endurable for use as an optical film. A specific example thereof includes a film of a polymeric resin such as a polyester-based (hereafter referred to as PET) resin, a polycarbonate-based resin, a triacetate-based resin, a norbornene-based resin, an acrylic resin, a cellulosic resin, a polyolefin-based resin and a urethane-based resin. It is also possible to use a transparent support containing an ultraviolet absorbing material for absorbing ultraviolet light coming from the outside to stabilize a function of an inner member such as a film. The surface of the support may be subjected to corona discharge treatment, plasma treatment, glow discharge treatment, roughening treatment or chemical treatment, or may have a coating layer of an anchor coat agent or a primer thereon, in order to improve its adhesiveness to a coating agent. The support is more preferably such a film or a sheet as to possess one or more functions among, for instance, reflection-reducing properties, antiglare/antireflection properties, antistatic properties, an antifouling property, neon light absorbing properties, electromagnetic-wave-shielding properties, color-tone-adjusting properties and the like, because when a sticking layer with the near-infrared light absorbing capability is formed on the support, the obtained optical filter can simultaneously possess the function imparted to the transparent support and the near-infrared light absorbing capability, and because such a form is advantageous in a production process and provides an excellent filter.

In the next place, an example of using a support (film) imparted with the above described functions will be described.

A first example is a reflection-reducing film which inhibits the reflection of light coming from the outside by coating the surface of a transparent support such as PET with a low refractivity agent together with a polyme