Image-forming material

1. An image-forming material comprising a perimidine-based squarylium dye represented by the following formula (I):

2. The image-forming material as claimed in claim 1 , wherein the perimidine-based squarylium dye is present in a state of crystalline particles showing diffraction peaks at least at angles 9.9°, 13.2°, 19.9°, 20.8° and 23.0° corresponding to 2θ±0.2° in powder X-ray diffraction spectrum measured under irradiation with X-ray of 1.5405 Å from a Cu target, wherein θ is Bragg angle.

3. The image-forming material as claimed in claim 1 , wherein the perimidine-based squarylium dye is present in a state of crystalline particles having a median diameter d50 in a range of 10 nm to 300 nm.

4. The image-forming material as claimed in claim 1 , wherein a content of the perimidine-based squarylium dye is from 0.05% to 3% by weight.

5. The image-forming material as claimed in claim 1 , which is an electrophotographic toner, an ink for inkjet printer, or an ink for letterpress, offset, flexographic, gravure or silk-screen printing.

6. The image-forming material as claimed in claim 1 , which satisfies conditions given by the following expressions (II) and (III):

0≦ΔE≦16   (II)

(100 −R )≧75   (III)

wherein ΔE represents a color difference defined by the following expression (IV) in CIE1976L*a*b* color specification system,

Δ E =√{square root over (( L 1 −L 2 ) 2 +( a 1 −a 2 ) 2 +( b 1 −b 2 ) 2 )}{square root over (( L 1 −L 2 ) 2 +( a 1 −a 2 ) 2 +( b 1 −b 2 ) 2 )}{square root over (( L 1 −L 2 ) 2 +( a 1 −a 2 ) 2 +( b 1 −b 2 ) 2 )}  (IV)

wherein L 1 , a 1 and b 1 respectively represent an L-value, an a-value and a b-value of a recording medium surface before image formation, and L 2 , a 2 and b 2 respectively represent an L-value, an a-value and a b-value of an image area at the time of formation of a fixed image in an adhesion amount of 4 g/m 2 on the recording medium surface by using the image-forming material, and R represents a reflectivity-in-percent of the image area when an infrared ray with a wavelength of 850 nm strikes thereon.