1. Field of the Invention
The present invention relates to a guanidine compound and a heat sensitive recording material and particularly, to a novel guanidine compound, and a novel heat sensitive recording material which can develop color at high image density by the inclusion of a diazonium salt compound and a coupler as color developing components and of the above-described guanidine compound as a base.
2. Description of the Related Art
Diazonium salt compounds form an azo dye by reacting with a compound called a coupler such as a phenolic derivative and the like, and at the same time, have photo-sensitivity and are decomposed by irradiation with light to lose the activity thereof. Therefore, diazonium salt compounds have been used for a long time as light recording materials typified by diazo copy (cf. xe2x80x9cBasics of Photographic Technology (shashin kogaku no kiso)xe2x80x94the chapter on non-silver salt photography (higinen shashin hen)xe2x80x94xe2x80x9d published by Japan Photographic Society (nippon shashin gakkai), corona corp., (1982) pp 89 to 117 and 182 to 201).
Further, diazonium salt compounds have recently been used for recording materials for which require fixation of an image by utilizing the fact that they are decomposed by light to lose their activity. Typical examples include light fixation type heat sensitive recording materials in which a diazonium salt compound and a coupler are heated according to image signals and allowed to react to form an image which is then fixed by irradiation with light (Koji Sato et al., Image Electron Society Bulletin (gazo denshi gakkai shi), vol. 11, No 4 (1982), pp 290 to 296, and the like).
In these heat sensitive recording materials, it is necessary for the diazonium salt and coupler to react immediately to develop color when heated, and conventionally organic salts such as tertiary amines, piperidines, piperazines, amidines, formamidines, pyridines, guanidines, morpholines and the like are added for the purpose of promoting the coupling reaction of the diazonium salt compound with the coupler. Among these, triphenylguanidine whose conjugated acid has a pKa of 7 has been mainly used for the guanidines.
However, when the reactivity of a diazonium salt compound with a coupler is low, a stronger base is required.
On the other hand, a multicolor heat sensitive recording material can be obtained by laminating heat sensitive recording layers developing different hues. The layer structure is not particularly restricted, and one example is a multicolor heat sensitive recording material in which a double heat sensitive recording layer comprising a combination of two kinds of diazonium salt compounds having different photo-sensitive wavelengths and couplers which develop different hues by reacting when heated with the respective diazonium salt compounds is laminated with a heat sensitive recording layer comprising a combination of an electron donative colorless dye with an electron receptive compound.
When a strong base as described above is used in the diazo heat sensitive recording layer of this type of multicolor heat sensitive recording material, it is necessary for the strong base to be superior in diffusion resistance so as not to influence other layers.
In view of the above circumstances, an object of the present invention is to provide a novel guanidine compound which is strongly basic and superior in diffusion resistance, and a novel diazo heat sensitive recording material which can develop color at high image density by the inclusion of a diazonium salt compound and a coupler as color developing components and of the guanidine compound as a base.
After intensive research into the structure of a guanidine compound in order to attain the above-described objective, the present inventors discovered the following facts (1) and (2), thus completing the present invention.
(1): Basicity increases by the substitution of an alkyl group for at least one of the three phenyl groups in triphenylguanidine owing to the substituent effect of the alkyl group.
(2): By forming bis type structure, the diffusion of a base into other layers can be prevented, and when a multi-layer structure is adopted, the color developing density in the layer which includes the base does not decrease and a deleterious influence is not exerted on other layers.
Namely, the first guanidine compound of the present invention is represented by the following general formula (1): 
(in general formula (1), R1 and R2 represent an alkyl group or aryl group. R1 and R2 may be the same or different. R3 and R4 represent a hydrogen atom, alkyl group or halogen atom. R3 and R4 may be the same or different. X represents a divalent connecting group.).
The second guanidine compound of the present invention is represented by the following general formula (2): 
(in general formula (2), R1 and R2 represent an alkyl group or aryl group. R1 and R2 may be the same or different. R3 represents a hydrogen atom, alkyl group or halogen atom.).
The third guanidine compound of the present invention is represented by the following general formula (3): 
(in general formula (3), R5 and R6 represent a hydrogen atom, alkyl group or halogen atom. R5 and R6 may be the same or different. X represents an alkylene group.).
The first heat sensitive recording material of the present invention is a material comprising a substrate supporting thereon a heat sensitive recording layer comprising a diazonium salt compound, a coupler which reacts with the diazonium salt compound and develops color when heated, and a base, wherein the heat sensitive recording layer includes as the base at least one guanidine compound represented by general formula (1) according to the above-described first invention.
The second heat sensitive recording material of the present invention is a material comprising a substrate supporting thereon a heat sensitive recording layer comprising a diazonium salt compound, a coupler which reacts with the diazonium salt compound and develops color when heated, and a base, wherein the heat sensitive recording layer includes as the base at least one guanidine compound represented by general formula (2) according to the above-described second invention.
The third heat sensitive recording material of the present invention is a material comprising a substrate supporting thereon a heat sensitive recording layer comprising a diazonium salt compound, a coupler which reacts with the diazonium salt compound and develops color when heated, and a base, wherein the heat sensitive recording layer includes as the base at least one guanidine compound represented by general formula (3) according to the above-described third invention.
The fourth heat sensitive recording material of the present invention is a material comprising a substrate supporting thereon a heat sensitive recording layer comprising a diazonium salt compound, a coupler which reacts with the diazonium salt compound and develops color when heated, and a base, wherein the heat sensitive recording layer includes as the base at least one guanidine compound represented by general formula (4): 
(in general formula (4), R7 and R8 represent an alkyl group. R7 and R8 may be the same or different. X represents a divalent connecting group.).
It is preferable that a heat sensitive recording material of the present invention comprises as the above-described coupler at least one pyrrolo [1,2-a] pyrimidine compound represented by the following general formula (5): 
(in general formula (5), R9 to R12 represents a hydrogen atom, halogen atom, aryl group, alkyl group, cyano group, acyl group, substituted carbamoyl group, alkoxycarbonyl group, aryloxycarbonyl group, acyloxy group, alkoxy group, aryloxy group, alkylthio group, arylthio group, substituted sulfamoyl group, alkylsulfonyl group, arylsulfonyl group, alkylphosphoryl group, arylphosphoryl group or substituted amino group.).
In a heat sensitive recording material of the present invention, it is preferable to use a diazonium salt compound having a maximum absorption wavelength xcexmax of 450 nm or less in view of the hue and light fixation properties thereof, and it is more preferable to use at least one diazonium salt compound selected from compounds represented by the following general formula (6), compounds represented by the following general formula (7) and compounds represented by the following general formula (8): 
(in general formula (6), Ar represents a substituted or unsubstituted aryl group. Each of R13 to R14 represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. R13 to R14 maybe the same or different. Xxe2x88x92 represents an acid anion.), 
(in general formula (7), each of R16, R17 and R18 represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. R16, R17 and R18 may be the same or different. Y represents a hydrogen atom or xe2x80x94OR15 group. R15 represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Xxe2x88x92 represents an acid anion.), 
(in general formula (8), each of R19 and R20 represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Xxe2x88x92 represents an acid anion.)