JPH0441193B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an inkjet recording ink. More specifically, the present invention relates to an inkjet recording ink whose base material is a water-based colored polymer obtained by dyeing a water-soluble polymer into which a specific hydrophilic group has been introduced with a basic dye. The ink used for inkjet recording includes
Various basic conditions are required, although they differ depending on the recording method. First, in order to be compatible with the method of generating ink droplets and the method of controlling the flight direction of ink droplets, the viscosity, surface tension, specific conductivity, etc. of the ink must be within appropriate ranges. For example, it is preferable that the flying speed of the ink is high in order to improve the print quality, but for this reason, the viscosity of the ink is desirably low, and is generally required to be 10 cps or less. In addition, the higher the surface tension, the better the driving frequency response for the generation of flying ink droplets, but conversely, if the surface tension is too high, the ink tends to get wet and have poor fixing properties on the paper. Generally, it can be said that a range of 40 to 65 dyne/cm is desirable. Further, the specific conductivity is desirably 1 mv/cm (25°C) or higher, and is adjusted with triethanolamine, cationic surfactant, etc. Conventionally, many proposals have been made as inkjet recording inks. For example, there are inks made by dissolving water-soluble dyes in water and adding wetting agents, preservatives, etc. However, in reality, inkjet recording inks that satisfy all of the above conditions cannot be obtained. Not yet. As a result of research into an inkjet recording ink that satisfies the various requirements that such an inkjet recording ink should have, the present inventors discovered that a water-soluble polymer having a specific hydrophilic group introduced therein was dyed with a basic dye. The present invention was completed based on the discovery that a water-based colored polymer exhibits excellent performance as a base material for inkjet recording inks. That is, the present invention provides an inkjet recording ink based on an aqueous colored polymer obtained by dyeing a water-soluble polymer containing at least 2×10 ^-5 gram equivalents/gram polymer of sulfonic acid groups with a basic dye. It is something to do. The polymer containing a sulfonic acid group used in the present invention can be produced by subsequently introducing a sulfonic acid group into a pre-produced polymer, or by polymerizing a radically polymerizable vinyl monomer containing a sulfonic acid group. Alternatively, there is a method of copolymerizing a radically polymerizable vinyl monomer containing a sulfonic acid group with another radically polymerizable vinyl monomer. As a method for later introducing a sulfonic acid group into a previously produced polymer, a conventionally known method for sulfonating a polymer by a sulfonation reaction can be employed. For example, there is a method of sulfonating polystyrene or styrene-maleic anhydride copolymer with sulfuric acid, sulfuric anhydride, etc. in a suitable organic solvent. Furthermore, as a method of polymerizing a radically polymerizable vinyl monomer containing a sulfonic acid group, or copolymerizing a radically polymerizable vinyl monomer containing a sulfonic acid group with another radically polymerizable vinyl monomer, Polymerization may be carried out using a common radical polymerization initiator in a solvent at a polymerization temperature of, for example, 10°C to 90°C. Examples of the radically polymerizable vinyl monomer containing a sulfonic acid group include vinyl sulfonic acid, methallyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid,
Examples include vinylbenzyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and their lithium salts, sodium salts, potassium salts, and ammonium salts. Furthermore, other vinyl monomers copolymerizable with such radically polymerizable hydrophilic vinyl monomers include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylamide, methacrylamide, methylolacrylamide, and methylolmethacrylamide. hydrophilic vinyl monomer, methyl acrylate,
Ethyl acrylate, n-butyl acrylate,
Hydrophobic monomers such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, and styrene can be mentioned. These monomers are heated in a solvent (e.g., water) using a common radical polymerization initiator, usually from 10°C to 90°C.
The radical polymerization initiator used is ammonium persulfate,
Examples include potassium persulfate, t-butyl hydroperoxide, and cumene hydroperoxide. Of course, redox polymerization initiators used in combination with conventionally known polymerization initiators and reducing agents such as sodium bisulfite, sodium thiosulfate, ferrous sulfate, etc. can also be used. In the present invention, the amount of sulfonic acid groups contained in the water-soluble polymer is at least 2 x 10 ^-5 gram equivalent/g polymer, preferably 1, in view of the sunlight fastness of the ink and the viscosity stability of the ink. If it contains at least ×10 ^-4 gram equivalent/gram polymer, it is possible to obtain satisfactory physical properties as a base material for the inkjet recording ink of the present invention. When a water-soluble polymer that meets the requirements of the present invention is obtained by a polymerization method so as to achieve such an introduction rate, the molecular weight of the resulting water-soluble polymer depends on the concentration of each monomer present in the polymerization system, the radical It depends on the amount of polymerization initiator used, polymerization temperature, etc. Although the monomer concentration can be freely selected, it is generally 3 to 50 wt%, usually 10 to 30 wt%. Polymerization at high concentrations is not preferred because the viscosity of the polymerization system becomes high and it becomes difficult to remove the heat of polymerization. Furthermore, polymerization at too low a concentration is not preferred for economic reasons. Furthermore, as the amount of radical polymerization initiator used increases, the molecular weight of the water-soluble polymer tends to decrease, and as the amount of radical polymerization initiator decreases, the molecular weight of the water-soluble polymer tends to increase. The molecular weight of the water-soluble polymer containing sulfonic acid groups thus obtained is an important factor as it affects the viscosity of the ink, but the average molecular weight is 5×
It may be 10 ^-5 or less, preferably 2×10 ^-5 or less. In view of the purpose of the present invention, the present invention is not limited in any way by the method of obtaining such a water-soluble polymer. The following is the dyeing of the obtained water-soluble polymer, which is described in the Dye Handbook (published by Maruzen), which is known as triphenylmethane, azo, methine, oxazine, or anthraquinone. Conventional basic dyes and cationic dyes shown in the classification may be used. Industrially, the easiest way to dye is to add an organic acid such as formic acid, acetic acid, or butyric acid to a water-soluble polymer solution.
It can be carried out by a dyeing method in which the pH is adjusted to 2 to 7, preferably 3 to 5, with an inorganic acid such as hydrochloric acid or sulfuric acid, and a dye solution is added. Such a dyeing method is not limited in view of the spirit of the present invention. When the thus obtained aqueous colored polymer of the present invention is used as an inkjet recording ink, conventionally known adjuvants such as glycerin, ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, triethanolamine, N -Methyl 2-
It may also be used with wetting agents such as pyrrolidone, 1,3-ditothylimidazoline, and anti-mildew agents such as sodium omazine and dioxin. The inkjet recording ink using the water-based colored polymer of the present invention has features that have not been seen before. First, the present invention improves sunlight fastness through the use of basic dyes and cationic dyes, which have a rich variety of colors and are distinctive for their vividness, and the presence of a water-soluble polymer, resulting in printing with clear color tones. became possible. Furthermore, the second effect is the viscosity stability of the ink. That is, due to the presence of a chemically stable polymer, the viscosity of the ink can be maintained stably for a long period of time. EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited by the Examples. Water-soluble polymer synthesis example 1 Add 50 parts of water to a nitrogen-substituted polymerization flask and add 90 parts of water.
The temperature was raised to ℃. A monomer aqueous solution was prepared by dissolving 244 parts of spinomer Nass (sodium p-styrene sulfonate, purity 82.0%, manufactured by Toyo Soda Kogyo) in 720 parts of water. A polymerization initiator aqueous solution was prepared by dissolving 10 parts of ammonium persulfate in 30 parts of water. A monomer aqueous solution and a polymerization initiator aqueous solution were each added to a polymerization flask over a period of 3 hours, and polymerization was carried out at 90°C.
Polymerization was further continued at 90°C for 2 hours and cooled to 25°C, but the viscosity of the solution at 25°C was 9.3 cps. When the amount of unreacted sodium p-styrene sulfonate was determined by the bromine addition method, the polymerization rate of the monomer was found to be 99.0 wt% or more. The polymer was purified by dropping an aqueous polymer solution into absolute ethanol to obtain a water-soluble polymer powder. The average molecular weight determined by gel permeation chromatography (hereinafter referred to as "GPC method") was w1.1×10 ⁴ . Water-soluble polymer synthesis example 2 40 parts of water was charged into a polymerization flask purged with nitrogen.
The temperature was raised to 70°C. A monomer aqueous solution was prepared by dissolving 117 parts of spinomer Nass (sodium p-styrene sulfonate, purity 82.0%, manufactured by Toyo Soda Kogyo) and 24 parts of acrylic acid in 400 parts of water. An aqueous polymerization initiator solution was prepared by dissolving 6 parts of ammonium persulfate in 20 parts of water. A monomer aqueous solution and a polymerization initiator aqueous solution were added over 3 hours and polymerized at 70°C. The polymer was further polymerized at 70°C for 2 hours and cooled to 25°C, and the viscosity of the solution at 25°C was 28 cps. The polymer was purified by dropping an aqueous polymer solution into acetone to obtain a water-soluble polymer powder. Analysis of sulfur in the polymer revealed that the polymer contained 3.86×10 ^-3 gram equivalent/gram polymer of sulfonic acid groups. Moreover, the average molecular weight by GPC method was w3.4×10 ⁴ . Water-soluble polymer synthesis example 3 Pour 50 parts of water into a nitrogen-substituted polymerization flask and add 90 parts of water.
The temperature was raised to ℃. 20 parts of 2-hydroxyethyl methacrylate and spinomer Nass (sodium p-styrene sulfonate, purity 82.0%, manufactured by Toyo Soda Kogyo)
An aqueous monomer solution was prepared by dissolving 220 parts in 700 parts of water. Next, 8 parts of ammonium persulfate was dissolved in 30 parts of water to prepare an aqueous polymerization initiator solution. A monomer aqueous solution and a polymerization initiator aqueous solution were each added to a polymerization flask over a period of 3 hours, and polymerization was carried out at 90°C.
After further polymerization for 2 hours, the mixture was cooled to 25°C. The solution viscosity at 25°C was 18 cps. The average molecular weight of the polymer obtained as a precipitate by treating an aqueous polymer solution with a large amount of acetone is Mw7×10 ³ by GPC method, and the sulfur analysis value shows that the polymer contains 4.37×10 ^-3 gram equivalent/g polymer of sulfone. Contains acid groups. Examples 1 to 3 A warm aqueous solution of 3.0 g of a basic dye (manufactured by Hodogaya Chemical), 100 g of water, and 1.0 g of acetic acid was gradually added to 100 g of a 20 wt% aqueous solution of the water-soluble polymer obtained in Synthesis Example-1. The mixture was stirred at 80°C for 60 minutes. After concentrating under reduced pressure using a rotary evaporator to about 1/2 volume, the concentrated solution was added dropwise to the ethanol from Step 2, and the colored polymer precipitate was separated using a glass filter, followed by drying under reduced pressure. An ink was prepared by dissolving 2.5 g of these colored polymer powders and 10 g of tetraethylene glycol in 37.5 g of water. The properties of the ink are as shown in Table 1, and the ink of the present invention could be used on Toyo Paper No. 131 without clogging. Also, ink is 5
℃, 25℃, and 50℃ for one month, the viscosity did not change over time and no precipitates were observed. Further, the ink of the present invention was applied to art paper with a 1 mil doctor blade, dried at room temperature, and then tested for sunlight fastness using a xenon arc fade meter, and found to have good sunlight fastness.

[Table] The inks of Examples 1 to 3 were further filtered through a 0.45μ membrane filter, and the inks were jet-recorded on high-quality paper from a nozzle with an inner diameter of 50μ at a particle generation frequency of 100KHz, and clear prints were obtained. Examples 4 to 6 Examples 1 to 6 using 100 g of a 20 wt% aqueous solution of the water soluble polymer obtained in Water-soluble Polymer Synthesis Example-2
The colored polymer aqueous solution obtained by performing the same operation as in 3 was dropped into the acetone in 2, and the precipitated colored polymer was separated with a glass filter and dried under reduced pressure. 1.0 g of these colored polymer powders and 12 g of diethylene glycol were dissolved in 37 g of water. Furthermore, the ink of the present invention was prepared by adjusting the pH to 6.5 using ethanolamine. The properties of the ink are shown in Table 2, and the ink of the present invention could be used on Toyo Paper No. 131 without clogging. Furthermore, when the ink was stored at 50°C for one month, the viscosity did not change over time and no precipitates were observed. Furthermore, after applying the ink of the present invention to art paper with a 1 mil doctor blade and drying it at room temperature,
When the sunlight fastness was examined using a xenon arc fade meter, it showed good sunlight fastness.

[Table] Examples 7 to 8 Examples 1 to 8 were carried out using 100 g of a 20 wt% aqueous solution of the water-soluble polymer obtained in Water-soluble Polymer Synthesis Example-3.
The colored polymer aqueous solution obtained by performing the same operation as in 3 was dropped into the acetone in 2, and the precipitated colored polymer was separated with a glass filter and dried under reduced pressure. The ink of the present invention was prepared by dissolving 4.0 g of these colored polymer powders and 10 g of diethylene glycol monobutyl ether in 36 g of water. The properties of the ink are shown in Table 3, and the ink of the present invention could be used on Toyo Paper No. 131 without clogging. Also, the ink has a temperature of 1 at 50℃.
After storage for months, there was no change in viscosity over time and no precipitates were observed. Furthermore, after applying the ink of the present invention to art paper with a 1 mil doctor blade and drying it at room temperature,
When the sunlight fastness was examined using a xenon arc fade meter, it showed good sunlight fastness.

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Claims (1)

[Claims] 1 At least 2x sulfonic acid groups in the polymer
An inkjet recording ink based on a water-based colored polymer obtained by dyeing a water-soluble polymer containing 10 ^-5 gram equivalent/g polymer or more with a basic dye.