JPS64434B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aqueous inkjet recording ink composition suitable for use in an inkjet printer, and more particularly to a yellow ink composition suitable for use in a color inkjet printer. One of the essential characteristics of an inkjet recording ink composition, that is, an inkjet ink, is that it has physical properties that allow it to be properly formed into particles and charged in the inkjet device used. Physical properties such as surface tension, density, viscosity, and specific conductivity must be appropriate. Another essential characteristic of inkjet ink is that when ink jetting is stopped, the ink dries at the tip of the nozzle, causing clogging.
The overfilter that the ink passes through before reaching the ink head should not become clogged. In the case of color inkjet printer inks, a further essential characteristic is that the magenta, cyan, and yellow inks have sufficiently satisfactory tones as the three primary colors, such as high brightness and density. It is something that we have. It is known that the above-mentioned essential properties of inkjet inks can be significantly controlled through the use of various additive modifiers. In particular, it is said that additive regulators make a large contribution to the first necessary characteristic mentioned above. It is recognized that the two properties listed below are almost completely dependent on the properties of the colorant itself, and therefore there is a natural limit to the improvement of these properties of ink by additive regulators. Are known. Based on this view, considerable progress has been made in the field of research and development of colorants themselves. According to a very recent report, for example, JP-A-55-7869 discloses a ``recording medium liquid containing a recording agent that does not crystallize or aggregate in the liquid''. This report concerns black ink. Various dyes, such as water-soluble dyes such as direct dyes, acid dyes, basic dyes, reactive dyes, and disperse dyes, or oil-based dyes have been reported as colorants for use in inkjet inks. Many of these dyes that have been discovered and reported so far have had problems in solubility when used as colorants in inkjet inks. That is, it had a solubility of about 3% by weight at most. Therefore, when used in an inkjet recording device, it is a direct cause of nozzle clogging and filter clogging. The black ink disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-7869 solves the above problem by using a dye with good solubility. As a color ink, it is desirable to use one that satisfies the color tones of the three primary colors and has as high brightness and density as possible, but some of the conventional dyes mentioned above have good color tones to a certain extent, but they have poor solubility. There was hardly anything to be satisfied with. In view of these points, the present inventors have developed a colorant that has good solubility, that is, does not cause clogging, and has a high tone as a color primary color. The present invention was achieved as a result of many years of research aimed at obtaining an ink with the following properties. An object of the present invention is to provide an aqueous yellow ink composition suitable for use in color inkjet printers, which has a sufficiently satisfactory color tone as a yellow primary color and has good solubility. Another object of the present invention is to provide an aqueous yellow ink composition that does not cause nozzle clogging or filter clogging. Other objects of the invention will become apparent from the following more detailed description of the invention. The present invention, which has achieved the above object, relates to an aqueous inkjet recording ink composition characterized by containing a colorant selected from a monoazopyrazolone derivative having the following general formula () and a biphenyldisazopyrazolone derivative having (). It is something. (In the formula, A ₁ is a hydroxyl group, and A ₂ to _{A 6} are each independently hydrogen, a hydroxyl group, a methyl group, an amino group, a sulfone group, or a carboxyl group. _{D 1} to _{D 4} are each independently a hydroxyl group, an amino group, It is a benzene ring or a naphthalene ring that can be substituted with a sulfonic group or a carboxyl group. Both the hydroxyl group and the carboxyl group may be in the form of a sodium salt or a potassium salt, and the sulfonic group may be in the form of a sodium salt. (Good.) The present invention will be further explained in detail as follows. The compounds having the above general formulas () and () are water-soluble dyes. Both can remain dissolved in water at room temperature to an extent exceeding 15% by weight. In the present invention, the term "dissolved state" refers to a state in which the solute (dye) is stably suspended without precipitation. In the present invention, "solubility" refers to the property of being able to take a dissolved state as defined above. Conventionally used yellow dyes generally had a solubility of 3% by weight, but among them, for example,

[expression] and is known to exhibit a solubility of about 5% by weight in water. However, even if these are used, when used at a dye content in the ink normally used in an inkjet printer (1/3 to 1/2 of the solubility limit of the dye used in the solvent used), for example, 2.5% by weight. When using ink with a dye concentration of It was impossible to continue continuous operation. Therefore, the reliability of the ink was low. On the other hand, the compounds having the above general formulas () and () used in the present invention have a fairly good solubility state and can remain dissolved in water to an extent exceeding 15% by weight. When a continuous injection test was conducted using a 0.5-1μ overfilter with a dye concentration of 2.5% by weight, there was almost no clogging of the filter, and even continuous injection for 3 months did not cause operation stoppage due to clogging. It is. The nozzle diameter of an ink jet head can vary over a wide range, for example from 7 to 50 microns, depending on the type of head used, but color ink jet heads usually have a nozzle diameter of 20 to 50 microns. When using nozzle diameters in this range, a reliable ink that does not cause nozzle clogging is one that has a solubility of at least 5% by weight, and
It does not cause filter clogging when treated with an overfilter of 0.5 to 1μ. The dyes having the general formulas () and () used in the present invention are those which fully satisfy the above requirements. That is, both have a solubility in water of more than 15% by weight, and do not cause clogging in filters with a diameter of 0.5 to 1 μm. Such physical properties of the dye used in the present invention are believed to be due to the substituents of the general formulas () and (). That is, hydroxyl group, amino group,
It is understood that hydrophilic groups such as sulfone groups or carboxyl groups impart the above-mentioned properties to the dyes of the present invention. The present inventors have confirmed that the solubility of dyes represented by general formulas () and () increases as the number of hydrophilic groups substituted increases, thereby reducing ink clogging. It is generally said that the preferred content of the dye in the ink is from about 1/3 to about 1/2 of the solubility limit of the dye used in the solvent used. That is, it is said that reliability of ink jetting can be obtained when used in this ratio. However, the above-mentioned conventional dye having a solubility of up to about 5% by weight is
Although the ink used at a concentration of ~3% by weight can withstand short-term use, clogging of the filter is difficult to avoid, and therefore, the reliability of ink jetting is low. The solubility of the dyes having the general formulas () and () used in the present invention can vary widely depending on the type and number of substituents as described above, but the solubility in water exceeds 15% by weight. It is something that you have. 1/3 to 1/3 of the solubility limit of this dye.
An inkjet recording ink composition having a concentration of 5 to 7.5% by weight, which is a ratio of 2, has an ink jetting reliability that is approximately the same as or higher than that of the above-mentioned conventional ink composition. However, in order to cause no or almost no clogging of the filter when using a 0.5-1 μm filter, the aqueous inkjet recording ink composition of the present invention should contain about 1 to about 100% of the dye having the above general formula (). 5
It is contained in a proportion of % by weight. Preferably about 2~
Contains about 4. Preferred examples of the coloring agents having the above general formulas () and () used in the present invention include those shown below. Specific examples of compounds of general formula () used in the present invention Specific examples of compounds of general formula () used in the present invention Compounds of the above general formulas () and () prepared by any conventional manufacturing technique can be used in the present invention. The inkjet ink of the present invention is an aqueous inkjet recording ink composition having a yellow hue and using a compound having the above general formulas () and () as a colorant and water as a liquid medium for dissolving the colorant. be. The aqueous inkjet recording ink composition of the present invention is compatible with the colorants of the general formulas () and () used, and can be applied to any conventional inkjet recording ink composition that can add the above-mentioned essential properties as an inkjet ink. Additional modifiers may also be included. Additive adjusting agents that can be used in the present invention include wetting agents, solubilizing agents, pH adjusting agents, etc. that are commonly used in inkjet inks. Aliphatic polyhydric alcohols such as ethylene glycol, diethylene glycol and triethylene glycol, and ethylene glycol methyl are used as wetting agents to prevent nozzle clogging due to ink drying, for example, when ink dries up while ink ejection is stopped. Ethers and aliphatic polyhydric alcohol alkyl ether derivatives such as ethylene glycol ethyl ether are preferably added in the present invention. As the dissolving agent, N-methyl-2-pyrrolidone, 2-pyrrolidone, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, etc. are preferred in the present invention. Preferred examples of the pH adjuster in the present invention include ethanolamine, diethynolamine, triethanolamine, propanolamine, and ammonium hydroxide or alkali metal hydroxide. The amount of each of the above additive regulators used in the present invention is appropriately determined depending on the desired amount of colorant, the desired type of additive regulator, etc.
Care should be taken to ensure that the addition amount falls within an appropriate range that can provide the ink properties described above to a sufficiently satisfactory degree. In the present invention, the preferred amount of the wetting agent added is 3 to 7 parts by weight per 1 part by weight of the colorant used. In the present invention, the preferable addition amounts of the solubilizing agent and the PH regulator are 0.1 to 5 parts by weight and 0.1 to 3 parts by weight, respectively, per 1 part by weight of the colorant used. The aqueous medium used in the present invention may be added with the above-mentioned additives in necessary amounts as desired; however, the present invention is not limited thereto; It goes without saying that additives can also be used as necessary. When the aqueous inkjet recording ink composition of the present invention is subjected to actual work, that is, when ink particles of the ink of the present invention are ejected from a nozzle to form an image on recording paper placed opposite to each other. , a high-density, clear image with good saturation, brightness, and hue was formed. The hue is yellow and this spectral characteristic is 500
It exhibited a reflection curve in the range of ~780 nm, and had a color tone that could be sufficiently applied as a color ink. As will be clarified in the following examples, the aqueous inkjet recording ink of the present invention has an unprecedented and innovative property that does not cause any nozzle clogging or filter clogging even after three months of continuous ejection tests. It is color ink. Examples of the invention are as follows. Example 1 The following ingredients

【table】
After thoroughly mixing and stirring the parts by weight in the above proportions,
Heat treated for hours. Thereafter, the mixture was allowed to stand at room temperature and filtered through a 0.5μ millibore filter to obtain an ink composition A of the present invention. When the obtained ink composition A was jetted using a JP type jetting tester manufactured by Ricoh, no stoppage of jetting due to filter clogging occurred even under a three-month continuous jetting test. The above injection test was conducted under the following conditions. Nozzle diameter: 40μ Filter diameter: 1μ When printed on plain paper, it showed a clear yellow color, and as a result of measuring it with a spectrophotometer, it was 500μ
A reflection curve spanning ~780 nm is shown. For comparison, the conventional

A continuous jetting test was conducted under the same conditions using an ink composition prepared under the same conditions except that [Formula] was used as the coloring agent. After about one month, the filter became clogged and operation became impossible. Ta. Example 2 The following ingredients

After thoroughly mixing and stirring [Table] in the above ratio, Example 1
Heat treatment was performed at 60°C for 8 hours in the same manner as above. Thereafter, the mixture was allowed to stand at room temperature and filtered through a 0.5μ Millipore filter to obtain an ink composition B of the present invention. The obtained ink composition B was subjected to the same continuous jetting test as in Example 1. Composition B also did not stop spraying due to filter clogging even after three months of continuous spraying. When printed on plain paper, it exhibited a clear yellow color, and measurements using a spectrophotometer showed a reflection curve extending from 500 to 780 nm. Example 3

[Table] were mixed and stirred at the above ratio, and then heated at 80°C for 2 hours. Thereafter, the mixture was allowed to stand at room temperature, and the resulting mixture was filtered through a 0.5μ Millipore filter to obtain an ink composition C of the present invention. When the obtained ink composition C was jetted using the jetting tester described above, jetting did not stop due to filter clogging even under a two-month continuous jetting test. When printed on plain paper, it exhibited a clear yellow color, and measurements using a spectrophotometer showed that it exhibited a reflection curve spanning from 520 to 780 nm. Example 4

【table】

[Table] were mixed and stirred at the above ratio, and then heated at 80°C for 2 hours. Thereafter, the mixture was allowed to stand at room temperature, and the resulting mixture was filtered through a 1μ Millipore filter to obtain an ink composition D of the present invention. When the obtained ink composition D was jetted using the jetting tester described above, jetting did not stop due to filter clogging even under a continuous jetting test for two months. When printed on plain paper, it exhibited a clear yellow color, and measurements using a spectrophotometer showed a reflection curve ranging from 490 to 780 nm. Example 5

【table】

[Table] were mixed and stirred at the above ratio, and then heated at 80°C for 2 hours. Thereafter, the mixture was allowed to stand at room temperature, and the resulting mixture was filtered through a 1μ Millipore filter to obtain an ink composition E of the present invention. When the resulting ink composition E was jetted using the jetting tester described above, jetting did not stop due to filter clogging even under a continuous jetting test for 2.5 months. When printed on plain paper, it exhibited a clear yellow color, and measurements using a spectrophotometer showed a reflection curve spanning from 510 to 760 nm. Example 6

【table】

[Table] were mixed and stirred at the above ratio, and then heated at 80°C for 3 hours. Thereafter, the mixture was allowed to stand at room temperature, and the resulting mixture was filtered through a 0.5μ Millipore filter to obtain an ink composition F of the present invention. When the resulting composition F was sprayed using the above-mentioned spray tester, spraying did not stop due to filter clogging even under a three-month continuous spraying test. When printed on plain paper, it exhibited a clear yellow color, and measurements using a spectrophotometer showed a reflection curve spanning from 500 to 760 nm.

Claims (1)

[Scope of Claims] 1. An aqueous inkjet recording ink composition comprising a colorant selected from a monoazopyrazolone derivative having the following general formula () and a biphenyldisazopyrazolone derivative having (). (In the formula, A ₁ is a hydroxyl group, and A ₂ to _{A 6} are each independently hydrogen, a hydroxyl group, a methyl group, an amino group, a sulfone group, or a carboxyl group. _{D 1} to _{D 4} are each independently a hydroxyl group, an amino group, It is a benzene ring or a naphthalene ring that can be substituted with a sulfonic group or a carboxyl group. Both the hydroxyl group and the carboxyl group may be in the form of a sodium salt or a potassium salt, and the sulfonic group may be in the form of a sodium salt. good.)