Method for forming a direct positive image

DETAILED DESCRIPTION OF THE INVENTION The nucleating agent represented by the foregoing general formula (N-I) is illustrated in detail below.
Specific examples of a heterocyclic ring completed by Z.
sup.
1 include quinolinium, benzimidazolium, pyridinium, thiazolium, selenazolium, imidazolium, tetrazolium, indolenium, pyrrolinium, acridinium, phenanthridinium, isoquinolinium and naphthopyridinium nuclei.
Z.
sup.
1 may be substituted by a substituent group, such as an alkyl group, an alkenyl group, an aralkyl group, an aryl group, an alkynyl group, a hydroxyl group, an alkoxy group, an aryloxy group, a halogen atom, an amino group, an alkylthio group, an arylthio group, an acyloxy group, an acylamino group, an aliphatic and aromatic sulfonyl group, an aliphatic and aromatic sulfonyloxy group, an aliphatic and aromatic sulfonylamino group, a carboxyl group, an acyl group, a carbamoyl group, a sulfamoyl group, a sulfo group, a cyano group, a ureido group, a urethane group (including an alkoxyamido group and a carbamoyloxy group), a carboxylate group (having a structure of ROCOO--), a hydrazino group, a hydrazono group, and an imino group.
As for the substituent groups by which Z.
sup.
1 may be substituted, at least one substituent is chosen from those cited above.
When Z.
sup.
1 has two or more of groups as substituents, these groups may be the same or different.
The substituent groups as set forth above may further be substituted by any of them.
The carbon number in an aryl moiety or an aralkyl moiety in the substituents is preferably from 6 to 20 and in an alkyl moiety in the substituents is preferably from 1 to 18.
Further, Z.
sup.
1 may contain a heterocyclic quaternary ammonium salt completed by Z.
sup.
1 via an appropriate linkage group L.
sup.
1.
Two Z.
sup.
1 groups may be the same or different.
In this case, the nucleating agent assumes, for example, a structure of a bis-compound.
Preferred examples of the heterocyclic nucleus completed by Z.
sup.
1 include quinolinium, benzimidazolium, pyridinium, acridinium, phenanthridinium, naphthopyridinium and isoquinolinium nuclei