Recording liquid

Abstract: A recording liquid excellent in print quality, light resistance, and water resistance which is characterized in that it contains an aqueous medium and at least one dye selected from the dyes represented by general formula [II]: (wherein R 1 and R 2 each represents H, CH 3 or OCH 3 ; X represents SO 3 M or COOM; and M represents an alkali metal, an ammonium group, or an organic amine salt.)

Description: The present invention relates to a recording liquid. More particularly, it relates to a recording liquid suitable for ink-jet recording. The so-called ink-jet recording method has come into practical use in which droplets of a recording liquid containing a water-soluble colorant, e.g., a direct dye or an acid dye, are issued from a minute ejection orifice to conduct recording. With respect to the recording liquid, it is required not only to be stably ejectable over a long time period and to rapidly fix to recording papers for general business use, e.g., paper for PPCs (plain-paper copiers) such as electrophotographic paper, and fanfold paper (continuous paper for computers, etc.), to give a print in which the printed characters are of good quality, that is, the printed characters are free of blurring and have clear contours, but also to be excellent in storage stability of the recording liquid. Therefore, solvents usable in the recording liquid are severely restricted. With respect to colorants for the recording liquid, on the other hand, they are required, for example, not only to have sufficient solubility in the solvents that are restricted as described above to thereby enable the recording liquid to be stably ejected over a long time period and be stable even in long-term storage and to give printed images having high density and excellent water resistance and light resistance, but also to be produced easily and free from any problem in safety. However, it has been difficult to satisfy these many requirements simultaneously. Although various techniques (e.g., JP-A-55-144067, JP-A-55-152747, JP-A-57-207660, JP-A-58-147470, JP-A-62-190269, JP-A-62-190271, JP-A-62-190272, JP-A-62-250082, JP-A-62-246975, JP-A-62-257971, JP-A-62-288659, JP-A-63-8463, JP-A-63-22867, JP-A-63-22874, JP-A-63-30567, JP-A-63-33484, JP-A-63-63764, JP-A-63-105079, JP-A-64-31877, JP-A-1-93389, JP-A-1-210464, JP-A-2-140270, JP-A-3-167270, JP-A-3-200882, etc.) have hence been proposed, a colorant has not been developed which sufficiently meets the performance requirements of the market and is easy to produce. (The term "JP-A" used herein means an "unexamined published Japanese patent application.) An object of the present invention is to provide a black recording liquid which is good in print quality when used in ink-jet recording, writing, etc. to conduct recording on plain paper, and which gives recorded images having high density and excellent in light resistance and, in particular, in water resistance and color tone of recorded-image, and has good stability in long-term storage. The present inventors have ascertained that the above object is accomplished when a specific dye is used as a recording liquid component, whereby the present invention has been accomplished. That is, the spirit of the present invention resides in a recording liquid characterized in that it contains an aqueous medium and at least one dye represented by general formula [II]: (wherein R 1 and R 2 each represents H, CH 3 , or OCH 3 ; X represents SO 3 M or COOM; and M represents an alkali metal, an ammonium group, or an organic amine salt.) The present invention will be explained below in detail. Examples of the alkali metal represented by M include Na, K, Li, etc. Examples of the organic amine salt represented by M include a group in which three or four hydrogen atoms of an ammonium group have been replaced by an alkyl group having 1 to 4 carbon atoms and/or a hydroxyalkyl group having 1 to 4 carbon atoms. Additionally, the organic amine salt may be a salt of a polyalkylenepolyamine such as tetraethylenepentamine or diethylenetriamine. Preferred as the polyalkylene group is a polyethylene group. The dyes of general formula [II] for use in this invention are each of a black color and suitable for use as a recording liquid. A mixture of two or more of these dyes may be used in this invention. In this case, two or more dyes which are identical to each other in general formula but different in substituent may be used, or two or more dyes that differ from each other in general formula may be used. Specific examples of the dyes represented by general formula [II] include the following: The azo dyes represented by general, formula [II] can be produced through diazotization and coupling step according to methods which themselves are known (see, for example, Shin Senryo Kagaku (New Industrial Chemistry) written by Yutaka Hosoda, published by Gihodo on Dec. 21, Showa-48 (1973) pp. 396-409). In the case of using the dyes of the above-described general formula [II] for a recording liquid, it is necessary to purify all these dyes after production. Effective means for purification include a method in which an alcohol, e.g., methanol or isopropanol, is added to an aqueous solution or suspension of a dye to crystallize out the dye, and a method in which a dye is suspended in and washed with dimethylformamide, N-methylpyrrolidone, etc. By these methods, the purity of the dye can be heightened and the inorganic salt can be removed. The content of the dyes of general formula [II] described above in the recording liquid is preferably 0.5 to 5% by weight, especially preferably 2 to 4% by weight, based on the total amount of the recording liquid. The solvent for use in the recording liquid of the present invention is preferably water and water containing a water-soluble organic solvent which, for example, includes a glycol solvent, e.g., ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (#200), and polyethylene glycol (#400); glycerol; a pyrrolidone solvent, e.g., N-methyl-pyrrolidone, N-ethyl-pyrrolidone, and 2-pyrrolidone; 1,3-dimethyl-imidazolidinone; ethylene glycol monoallyl ether; ethylene glycol monomethyl ether; diethylene glycol monomethyl ether; dimethyl sulfoxide; thiodiglycol; etc. These water-soluble organic solvents are used usually in an amount in the range of 5 to 50% by weight based on the total amount of the recording liquid. Water is usually used in an amount in the range of 45 to 93% by weight based on the total amount of the recording liquid. The property of quick drying after printing and print quality can be improved further by adding a compound selected from urea, thiourea, biuret, and semicarbazide to the recording liquid of this invention in an amount of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total amount of the liquid, or by adding a surfactant in an amount of 0.001 to 5.0% by weight based on the total amount of the recording liquid. The recording liquid of the present invention is used for ink-jet recording and in writing utensils and, when used in recording on plain paper, it gives recorded images excellent in printed-character density, light resistance, and water resistance. In addition, the recording liquid also has good storage stability. EXAMPLES The present invention will be explained below in more detail with respect to examples, but the invention is not construed as being limited thereto as long as it is within the spirit thereof. Dyes used in the reference examples are the following: Reference EXAMPLE 1 Water was added to 25 parts by weight of ethylene glycol monoallyl ether, 22 parts by weight of ethylene glycol, and 3.5 parts by weight of the dye of (I-1) specified hereinabove to regulate the total amount to 100 parts by weight. This composition was mixed sufficiently to dissolve the dye, filtered under pressure through a Teflon filter having a pore diameter of 1 µm, and then degassed with a vacuum pump and an ultrasonic cleaning machine to prepare a recording liquid. Using the recording liquid obtained, ink-jet recording was conducted on paper for electrophotography (manufactured by Fuji Xerox Co.) with an ink-jet printer (trade name HG-3000, manufactured by Epson Co.). Evaluations were conducted according to the following methods (a), (b), and (c), and the results thereof are shown. (a) Light Resistance of Recorded Image: Using a xenon fademeter (manufactured by Suga Shikenki Co.), the recording paper was irradiated for 100 hours. After the irradiation, little discoloration or fading was observed. (b) Water Resistance of Recorded Image: The recording paper was immersed in water for 5 minutes and the image was examined for blurring. The blurring of the image was slight and the decrease of density was also little. (c) Storage Stability of the Recording Liquid: The recording liquid was placed in sealed Teflon containers. After the recording liquid was stored for 1 month at 5°C and 60°C, it was examined for any change. Precipitation of an insoluble matter was not observed. Reference EXAMPLE 2 Water was added to 10 parts by weight of glycerol, 10 parts by weight of ethylene glycol, and 5 parts by weight of the dye of (I-2) specified hereinabove to regulate the total amount to 100 parts by weight. This composition was treated by the method described in Reference Example 1 to prepare a recording liquid, and the evaluations according to (a) to (c) in Example 1 were conducted. As a result, all the evaluations gave the similar satisfactory results as in Reference Example 1. Reference EXAMPLE 3 Water was added to 5 parts by weight of diethylene glycol monobutyl ether, 15 parts by weight of glycerol, and 2 parts by weight of the dye of (I-3) specified hereinabove to regulate the total amount to 100 parts by weight. This composition was treated by the method described in Reference Example 1 to prepare a recording liquid, and the evaluations according to (a) to (c) in Reference Example 1 were conducted. As a result, all the evaluations gave the similar satisfactory results as in Reference Example 1. EXAMPLE1 Water was added to 22 parts by weight of diethylene glycol and 2.5 parts by weight of the dye of (II-1) specified hereinabove to regulate the total amount to 100 parts by weight. This composition was mixed sufficiently to dissolve the dye, filtered under pressure through a Teflon filter having a pore diameter of 1 µm, and then degassed with a vacuum pump and an ultrasonic cleaning machine to prepare a recording liquid. Using the recording liquid obtained, the evaluations (a) to (c) in Reference Example 1 were conducted. As a result, all the evaluations gave the similar satisfactory results as in Reference Example 1. EXAMPLE 2 A recording liquid was prepared in the same manner as in Reference Example 2 except that 3 parts by weight of the dye of (II-2) specified hereinabove was used in place of 5 parts by weight of the above-specified dye of (I-2), and the evaluations according to (a) to (c) in Reference Example 1 were conducted. As a result, all the evaluations gave the similar satisfactory results as in Reference Example 1. EXAMPLE 3 A recording liquid was prepared in the same manner as in Reference Example 3 except that the dye of (II-3) specified hereinabove was used in place of the above-specified dye of (I-3), and the evaluations according to (a) to (c) in Reference Example 1 were conducted. As a result, all the evaluations gave the similar satisfactory results as in Reference Example 1. EXAMPLES 4 AND 5 Recording liquids were prepared by the method in Reference Example 1 using the same composition as in Example 1 except that each of the dyes of (II-4) and (II-5) specified hereinabove was used in place of the above-specified dye of (II-1) used in Example 1. The evaluations according to (a) to (c) in Reference Example 1 were conducted. As a result, all the evaluations gave the similar satisfactory results as in Reference Example 1. COMPARATIVE EXAMPLE 1 Recording liquids were prepared and evaluated in the same manner as above except that the dyes having the known structures of (1) to (4) shown below were used. The results are as shown in Table 3 given below. The recording liquids employing the known dyes had a problem in any of the evaluations, in contrast to the recording liquids of the present invention which were satisfactory in all the evaluations. (colorant described in JP-A-55-152747) (colorant described in JP-A-55-144,067) (colorant described in JP-A-3-200882) (colorant described in JP-A-3-200882) Comparative Colorant Recorded Image Recording Liquid (a) Light resistance (b) Water resistance (c) Storage stability Colorant of (1) good white ground stained, with considerable blurring good Colorant of (2) considerable discoloration and fading good insoluble matter precipitated Colorant of (3) good white ground stained, with considerable blurring good Colorant of (4) good white ground stained, with considerable blurring good

Claims: A recording liquid characterized by containing an aqueous medium and at least one dye selected from the dyes represented by general formula (II): (wherein R 1 and R 2 each represents H, CH 3 or OCH 3 ; X represents SO 3 M or COOM and M represents an alkali metal, an ammonium group, or an organic amine salt.) A recording liquid according to claim (1), wherein the dye represented by general formula [II] is contained in an amount of 0.5 to 5% by weight based on the total weight of the recording liquid. A recording liquid according to claim (1), wherein the aqueous medium comprises water and a water-soluble organic solvent selected from ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (#200), polyethylene glycol (#400), glycerol, N-methyl-pyrrolidone, N-ethyl-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-imidazolidinone, ethylene glycol monoallyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, dimethyl sulfoxide, and thiodiglycol. A recording liquid according to claim 3, wherein the content of water is in the range of 45 to 93% by weight and the content of the water-soluble organic solvent is 5 to 50% by weight, based on the total amount of the recording liquid. A recording liquid according to claim (1), 0.1 to 10% by weight of a compound selected from urea, thiourea, biuret, and semicarbazide; and/or 0.001 to 5.0% by weight of a surfactant are added to the recording liquid.

Inventors: SANO HIDEO, TAKIMOTO HIROSHI, YONEYAMA TOMIO, SANO, HIDEO, TAKIMOTO, HIROSHI, YONEYAMA, TOMIO
Applicants: MITSUBISHI CHEM IND, MITSUBISHI KASEI CORPORATION
Application year: 1992
Main classification: C09D11
IPC codes: C09D11