Ink stock solution and ink composition

1. An ink stock solution comprising at least a dye and a colorless planar compound having more than ten delocalization π electrons in one molecule, wherein the concentration of the dye in the ink stock solution is more than 10 mass % and not more than 50 mass %.

2. The ink stock solution as claimed in claim 1 , wherein the dye is a compound represented by formula (C):

wherein X 1 , X 2 , X 3 , X 4 , Y 1 , Y 2 , Y 3 and Y 4 each independently represents a carbon atom or a nitrogen atom; A 1 represents an atomic group necessary to form an aromatic ring or a heterocyclic ring together with X 1 and Y 1, A 2 represents an atomic group necessary to form an aromatic ring or a heterocyclic ring together with X 2 and Y 2, A 3 represents an atomic group necessary to form an aromatic ring or a heterocyclic ring together with X 3 and Y 3 , A 4 represents an atomic group necessary to form an aromatic ring or a heterocyclic ring together with X 4 and Y 4 , each of A 1 to A 4 may have a substituent, at least one of A 1 to A 4 , or at least one of the substituents of A 1 to A 4 has a substituent for imparting solubility; and M represents a hydrogen atom, a metallic element, a metallic oxide, a metallic hydroxide, or a metal halide.

3. The ink stock solution as claimed in claim 2 , wherein the compound represented by formula (C) is represented by formula (C-d):

wherein G 1 represents —SO-Z, —SO 2 -Z, —SO 2 NV 1 V 2 , —CONV 1 V 2, —CO 2 Z, —COZ, or a sulfo group, G 2 represents —SO-Z, —SO 2 -Z, —SO 2 NV 1 V 2 , —CONV 1 V 2, —CO 2 Z, —COZ, or a sulfo group, G 3 represents —SO-Z, —SO 2 -Z, —SO 2 NV 1 V 2 , —CONV 1 V 2 , —CO 2 Z, —COZ, or a sulfo group, and G 4 represents —SO-Z, —SO 2 -Z, —SO 2 NV 1 V 2 , —CONV 1 V 2 , —CO 2 Z, —COZ, or a sulfo group, Z, which is the same or different, each represents an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group, or a heterocyclic group; V 1 and V 2 , which is the same or different, each represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group, or a heterocyclic group; M has the same meaning as M in formula (C); and t 11 , t 12 , t 13 and t 14 each represents 1 or 2.

4. The ink stock solution as claimed in claim 1 , wherein the planar compound is represented by formula (1):

A 10 -X 10 -L 10 -(Y 10 —B 10 )   (1)

wherein A 10 , L 10 , B 10 each independently represents an aromatic group, which is a monocyclic ring or a condensed ring; X 10 and Y 10 each independently represents a divalent linking group; n represents 0 or 1; provided that the compound represented by formula (1) contains at least one ionic hydrophilic group selected from a sulfo group, a carboxyl group, a phenolic hydroxyl group, and a phosphono group.

5. The ink stock solution as claimed in claim 1 , which has a content of the planar compound of from 0.1 to 10 mass%.

6. The ink stock solution as claimed in claim 1 , which has a coefficient of viscosity of from 1 to 10 mPa·s.

7. The ink stock solution as claimed in claim 1 , which contains an antiseptic.

8. The ink stock solution as claimed in claim 1 , which contains a pH adjustor.

9. An ink composition manufactured with the ink stock solution as described in claim 1 .

10. The ink stock solution as claimed in claim 1 , wherein X 10 and Y 10 each independently represents a divalent group selected from the group consisting of an alkylene group, an alkenylene group, —CO—,—SO m , —NR—, —O—, or a divalent group combining these linking groups, wherein

m represents 0, 1 or 2; and

R represents a hydrogen atom, an alkyl group, an aryl group, or a heterocyclic group.