JPS6365035B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to inkjet recording methods, and more particularly to methods for improving multicolor inkjet recording. The inkjet recording method uses various recording liquid ejection methods (for example, an electrostatic suction method, a method that uses a piezoelectric element to apply mechanical vibration or displacement to the recording liquid, and a method that uses the pressure of heating the recording liquid to foam it and use the resulting pressure). etc)
This method generates small droplets of recording liquid (ink) and makes them fly, and some or all of them adhere to a recording material such as paper to perform recording, but it generates less noise and It is attracting attention as a recording method that allows high-speed printing and multicolor printing. Water-based recording liquids are mainly used for inkjet recording in view of safety and printability, while ordinary paper has conventionally been used as the recording material. When recording using liquid ink, it is generally necessary that the recording liquid does not bleed onto the recording paper and cause the print to become blurry, and that the recording liquid dries as quickly as possible after recording, resulting in unexpected damage. It is desirable not to contaminate the paper surface. Particularly in a multicolor inkjet recording system that uses recording liquids of two or more different colors, 1) the recording liquid is quickly absorbed into the recording material, and even if different color ink dots overlap, The recording liquid deposited later should not mix with the recording liquid deposited earlier, disturb the ink dots, or flow out. 2) The recording liquid droplets should not spread on the recording material and the diameter of the ink dots should not be larger than necessary. 3) The shape of the ink dot should be close to a perfect circle, and the surrounding area should be smooth. 4) The ink dot should have a high density and the area around the dot should not be blurred. 5) The color of the recording material should be white. 6) The color of the recording liquid does not change depending on the recording material; 7) There is little dimensional variation (e.g. wrinkles, spread) of the recording material before and after recording, etc. It is necessary to satisfy various requirements. However, in the past, it has been understood that satisfying these requirements depends greatly on the characteristics of the recording material and recording liquid used, but in reality, there are no inkjet recording methods that meet the above requirements. It is still not found. That is, for example, if we consider the relationship between the surface tension of the recording material and the recording liquid, when inkjet recording is performed using a recording material having a conventional recording layer, there is a second layer on the surface of this recording layer. As shown in the figure, since there are only small voids, when a recording liquid with a high surface tension is used, penetration into the voids is hindered and the absorption rate of the recording liquid becomes slow.
Therefore, if a recording liquid with a low surface tension is used to increase the absorption speed, there is the contradictory problem that the recording liquid spreads in the direction of the paper surface, making it impossible to obtain good printing characteristics, similar to when using non-coated paper. This problem could not be resolved. An object of the present invention is to satisfy all the problems that the prior art could not solve in the technical field mentioned above. Particularly, the present invention aims to satisfy the above-mentioned requirements in recording full-color images using a plurality of color recording liquids using an inkjet recording method. Another object of the present invention is to provide a novel inkjet recording method that can exhibit excellent recording characteristics over a wide range of recording liquid surface tensions. The above and other objects are achieved by the following invention. That is, the present invention provides an inkjet recording method in which recording is performed by forming small droplets of a recording liquid, and making the droplets adhere to a recording material having a coating layer provided on a base material. , the surface of the coating layer of the recording material is divided by irregularly shaped cracks, and the size of the divided portion is in the range of 10 μm × 10 μm to several hundred μm × several hundred μm; The surface tension of the recording liquid at 20°C is 30 to
This is an ink jet recording method characterized by being in the range of 60 dyne/cm. First, the recording material used in the method of the present invention will be explained based on the schematic diagram of FIG. In the figure, reference numeral 1 indicates a substrate made of a porous material such as paper or cloth, or a non-porous material such as a glass plate or resin film. Which one to select depends on the recording purpose and usage. 2 is a coating layer, and this layer mainly functions as a recording liquid receiving layer. This coating layer 2 is basically composed of a film-forming resin paint, but various surfactants and porous inorganic particles can also be mixed in the paint. Such surfactants and porous inorganic particles are components that can increase the absorption and capture rate of pigments (for example, dyes) in the ink in the coating layer 2, and are preferably used actively. As such a component, a white inorganic pigment that is porous and has ionicity on its particle surface is particularly effectively used. Specifically, natural zeolite, synthetic zeolite (for example, molecular sieve (manufactured by Union Carbide)), diatomaceous earth, synthetic mica (general formula:
M.Mg _2.5 (Si ₄ .O ₁₀ )F ₂ (wherein M is a hydrogen atom or a metal atom), etc. can be used. When manufacturing the recording material used in the method of the present invention, these particles (generally particles from several hundred microns to several microns) are mixed and dispersed in a resin coating, either singly or in combination, for coating. Make paint. As the resin suitable for use in this paint, any water-soluble or organic solvent-soluble resin can be used. For example, water-soluble resins include polyvinyl alcohol, starch, casein, gum arabic, SBR, gelatin, polyacrylamide, carboxymethyl cellulose, and sodium polyacrylate, and organic solvent-soluble resins include polyvinyl butyral, polyvinyl chloride, and polyacetic acid. Examples include vinyl, polyacrylonitrile, polymethyl methacrylate, polyvinyl formal, melamine resin, polyamide, phenolic resin, polyurethane, and alkyd resin. The mixing ratio of inorganic pigment particles and resin components in these paints is as follows:
Generally, the resin component is suitably used in an amount of 5 to 20 parts by weight per 100 parts by weight of the inorganic pigment particles. The coating layer 2 is generally formed on the substrate 1 by a known method (for example, a roll coating method, a rod bar coating method, a spray coating method, an air knife coating method).
Apply paint in an ^amount of about 1g/ ^m2 to 10g/m2.
Further, in practical terms, it is preferable to apply the coating at about 2 g/m ² to 5 g/m ² . After such a coating layer is provided, the coating layer is dried as soon as possible.
As shown in the partial enlarged view 2A, which is a partial enlarged view of a partial area 2a of the coating layer 2 produced in this way, there are irregularly shaped cracks 4 (the majority of these cracks are a fine scale-like coating (dye-trapping part) divided by
3 are closely arranged in a two-dimensional array. The size of each scale-like coating 3 is not particularly limited, but ranges from 10 μm x 10 μm to several hundred μm x
The width of the crack 4 is generally on the order of several hundred μm, and although the width of the crack 4 is not particularly limited, it is usually on the order of several μm. Incidentally, the individual size and shape of the scale-like coating 3, the width of the cracks 4, etc. can be adjusted to approximately the above-mentioned size by adjusting or controlling the composition of the coating material or film-forming conditions, especially the drying conditions after coating. It can be changed arbitrarily within the range. When ink adheres to this coating layer 2, the pigment (for example, dye) in the ink is selectively adsorbed to and captured in the area of the coating 3, while the solvent in the ink passes through the cracks 4 and then is captured. When a porous material is used as the substrate 1, the material is quickly absorbed into the substrate 1. When the above-mentioned recording material is used in this way, the coloring matter in the ink is captured almost in the outermost layer area of the recording paper, so that the coloring property is extremely good. Furthermore, since the solvent in the ink quickly migrates to the underlying substrate through the cracks, an apparent dry state is quickly achieved on the surface of the recording paper. Furthermore, the scale-like coating 3 is particularly effective in preventing ink dots from becoming unnecessarily large, dots with high concentration, and the periphery of the dots from becoming blurred. This is because the dye is intensively adsorbed. The quality of this adsorption ability is determined mainly by the surface physical properties and chemical properties (for example, ionicity) of the coating 3 itself, surfactant, and pigment particles. Therefore, the scale-like coating 3 in the coating layer 2
If the area occupied by the cracks 4 is extremely small, there is a disadvantage that the capture rate of the dye decreases, resulting in a decrease in color development and density of the dots.In addition, if the area occupied by the cracks 4 is extremely large, the ink may migrate to the substrate. When the amount increases, so-called ink bleed-through phenomenon occurs, and the shape of the dots deteriorates, among other disadvantages. Therefore, these aspects are preferably avoided. On the other hand, the recording liquid used in the method of the present invention consists of a recording agent such as a dye and a liquid medium component. Generally, when recording using a recording liquid, it is important to match the liquid physical properties of the recording material and the recording liquid, and in particular, select a recording liquid that has good wettability to the recording material. Must be used. That is, the critical surface tension of the recording material mentioned above is 40~
Since the surface tension is within the range of 50 dyn/cm, it is preferable to use a recording liquid having a surface tension close to this value. Therefore, the recording liquid used in the method of the present invention has a temperature of 30 to 60 dyn/cm, preferably 35 to 55 dyn/cm, at 20°C.
It is particularly preferable to have a surface tension in the range of 40 to 50 dyn/cm. When printing is performed using a recording liquid with a surface tension lower than this range, the wettability to the recording material is good, but the spread of the printed dots becomes large. On the other hand, when a recording liquid having a surface tension higher than the above-mentioned surface tension is used, the wettability to the recording material deteriorates, resulting in a decrease in ink absorbency and dot density, which is undesirable. As the liquid medium component of the recording liquid used in the method of the present invention, not only water alone but also preferably a mixture of water and various water-soluble organic solvents etc. are used within a range that satisfies the surface tension of the recording liquid. be done. Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol, each having 1 to 1 carbon atom. Alkyl alcohols of 4; amides such as dimethylformamide and dimethylacetamide; ketones or ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene 2 alkylene groups such as glycohol, propylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, etc.
Alkylene glycols containing ~6 carbon atoms; glycerin; lower alkyl ethers of polyhydric alcohols such as ethylene glycol methyl ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. It will be done. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred. Polyhydric alcohols are particularly preferable because they are highly effective as wetting and lubricating agents to prevent nozzle clogging caused by evaporation of water in the recording liquid and precipitation of the recording agent. In order to adjust the surface tension of the recording liquid containing such liquid medium components within the above range, a surface tension adjusting agent such as various cationic, anionic or nonionic surfactants, diethanolamine, triethanolamine, etc. may be added. I can do it. A solubilizer can also be added to the recording liquid. Typical solubilizers are nitrogen-containing heterocyclic ketones, and their intended action is to dramatically improve the solubility of the recording liquid in the liquid medium. For example, N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone are preferably used. A recording liquid prepared from such components has its own recording properties (signal response, stability of droplet formation, ejection stability, long-term continuous recording performance, ejection stability after a long period of recording interruption). ), has excellent storage stability and fixability to recording materials, but in order to further improve these properties, various additives may be further included. For example, viscosity regulators such as polyvinyl alcohol, celluloses, and water-soluble resins; PH regulators using buffer solutions can be mentioned. Further, in order to prepare a recording liquid used in an inkjet recording method of the type in which the recording liquid is charged, a resistivity adjusting agent such as inorganic salts such as lithium chloride, ammonium chloride, and sodium chloride is added. Note that when applied to an inkjet method in which the recording liquid is ejected by the action of thermal energy, the thermal properties (e.g., specific heat, coefficient of thermal expansion, thermal conductivity, etc.) may be adjusted. be. According to the method of the present invention, even if recording liquids of different colors are repeatedly deposited on the same spot within a short period of time, there is no phenomenon of recording liquid flowing out or seeping out, and images with high resolution, clarity, and excellent color development can be produced. is obtained. Moreover, even if recording liquids with a wide range of surface tensions are used depending on the recording liquid ejection method, recording purpose, etc., these excellent characteristics can always be exhibited, making the inkjet recording method suitable for full-color recording. It is excellent as such. Hereinafter, the method of the present invention will be explained in more detail with reference to Examples. Example 1 100 parts by weight of silica (Nipsil E150, trade name, manufactured by Nippon Silica Kogyo Co., Ltd., average particle diameter: 5 μm) and 20 parts by weight of polyvinyl alcohol were dispersed and dissolved in 500 parts by weight of water, and then dissolved in a ball mill. A slurry was obtained by grinding and mixing for 12 hours. This slurry was coated on one side of general high-quality paper (basis weight 60 g/m ² ) with a sizing degree of 35 seconds based on JIS P8122 so that the dry coating amount was 4 g/m ² . Next, this was dried by exposing it to hot air at 180° C. for 2 seconds to produce a recording material. FIG. 2 shows a scanning electron micrograph of the surface of the coating layer of the obtained recording material, magnified approximately 1000 times. An on-demand inkjet recording head (discharge orifice diameter 50 μm, piezo oscillator drive voltage 60 V,
Inkjet recording was performed using a recording device having a frequency of 4 KHz), and the recording characteristics were evaluated. Ink No. A: Surface tension is approximately 60 dyn/cm (composition) Ethylene glycol 30 parts by weight Water 70 CI Direct Blue 86 2 Ink No. B: Surface tension is approximately 55 dyn/cm (composition) Ethylene glycol 30 parts by weight Water 70 〃 Acetinol EH (10% water) 0.05 〃 (Surfactant, manufactured by Kawaken Huain Chemical Co., Ltd.) CI Direct Blue 86 2 〃 Ink No. C: Surface tension approximately 50 dyn/cm (composition) Ethylene glycol 30 parts by weight Water 70 〃 Acetinol EH (10% water) 0.07 〃 CI Direct Blue 86 2 〃 Ink No. D: Surface tension is approximately 45 dyn/cm (composition) Ethylene glycol 30 parts by weight Water 70 〃 Acetinol EH (10% water) 0.5 〃 CI Direct Blue 86 2 〃 Ink No. E: Surface tension is approximately 40 dyn/cm (composition) Ethylene glycol 30 parts by weight Water 70 〃 Acetinol EH (10% water) 1.1 〃 CI Direct Blue 86 2 〃 Ink No. F: Surface Tension is approximately 35 dyn/cm (composition) Propylene glycol monomethyl ether 30 parts by weight Water 70 Acetinol EH (10% water) 1.0 CI Direct Blue 86 2 Ink No. G: Surface tension is approximately 30 dyn/cm (composition) Propylene Glycol monomethyl ether 50 parts by weight Water 50 Acetinol EH (10% water) 0.1 CI Direct Blue 86 2 Table 1 shows the evaluation results of the recording properties of the recording material.
Each evaluation item in Table 1 was measured according to the following method. 1) To measure the dot density, measure the printed dots using a Sakura Microdensidometer PDM-5 (Konishi Roku Photo Industry Co., Ltd.).
Measured using a product manufactured by Co., Ltd. 2) The shape of the dots was determined by observing the printed dots with a stereomicroscope, and marking the dots almost circular as ○, those with a slightly distorted circular shape as △, and the irregularly shaped dots as ×. 3) The degree of bleeding was determined by measuring the diameter of the printed dot using a stereomicroscope, and was expressed as how many times larger the diameter of the printed dot was than that of the ink droplet. 4) Color clarity is determined by visually comparing the color clarity of the inkjet recorded images, with the best one being ◎ and the worst being ×, ◎, 〇, △, ×.
We ranked them by rank. 5) Ink absorption is determined by 1 printed with 3 dots overlapped.
After a few seconds, if there was no ink flowing out on the surface of the recording material and the image was clear, it was rated as ○, otherwise it was rated as ×. Examples 2 and 3 Diatomaceous earth (Celite White Mist, trade name, manufactured by John Manville, average particle size: 5.5 μm)
100 parts by weight and 15 parts by weight of sodium alginate were dispersed and dissolved in 500 parts by weight of water, and then pulverized and mixed in a ball mill for 15 hours to obtain a slurry. This slurry was coated on one side of general high-quality paper (basis weight 65 g/m ² ) with a sizing degree of 35 seconds based on JIS P8122 so that the dry coating amount was 4 g/m ² . Next, this was dried by exposing it to hot air at 110° C. for 1 minute (Example 2) and to hot air at 90° C. for 30 minutes (Example 3) to produce a recording material. Scanning electron micrographs of the surface of the coating layer of the obtained recording material at a magnification of about 1000 times are shown in FIG. 3 (Example 2) and FIG. 4 (Example 3). This recording material was evaluated in the same manner as in Example 1, and the results are shown in Table 2 (Example 2) and Table 3 (Example 3). Example 4 A recording liquid having the following composition and a surface tension of 54 dyn/cm at 20°C was used for the recording material used in Example 1, and thermal energy was applied to the recording liquid in the recording head. On-demand type multi-head that generates and records droplets (discharge orifice diameter 35μm, heating resistor resistance 150Ω, drive voltage
Full-color inkjet recording was performed by supplying the ink to a recording device having a voltage of 30 V and a frequency of 2 KHz. Yellow ink (composition) CI acid yellow 23 2 parts by weight Diethylene glycol 30 〃 Water 70 〃 Magenta ink (composition) CI acid red 92 2 parts by weight Diethylene glycol 30 〃 Water 70 〃 Cyan ink (composition) CI Direct Blue 86 2 parts by weight Diethylene glycol 30 〃 Water 70 〃 The obtained recorded image was clear and had a predetermined color tone, and the dot shape and ink absorbability were also good. Comparative Example 1 Inkjet recording characteristics were evaluated in the same manner as in Example 1 using commercially available art coat paper (trade name: SK Coat, manufactured by Sanyo Kokusaku Pulp Co., Ltd.) as a recording material. The results are shown in Table 4. In addition,
A scanning electron micrograph of the surface of the coating layer of this paper at a magnification of approximately 1000 times was as shown in FIG.

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【table】 [Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of the recording material used in the present invention, and FIGS.
The figure is a scanning electron micrograph of the surface of a recording layer of a recording material suitable for use in the method of the present invention, magnified approximately 1000 times. FIG. 5 is a scanning electron micrograph at the same magnification of the surface of a commercially available coated paper. In the figure, 1 is a substrate, 2 is a coating layer, 3 is a scale-like coating (dye trapping part), and 4 is a crack.

Claims (1)

[Claims] 1. In an inkjet recording method in which recording is performed by forming droplets of recording liquid and adhering these droplets to a recording material having a coating layer provided on a base material, the surface of the coating layer of the recording material is It is divided by irregularly shaped cracks, and the size of the divided part is 10 μm×
It is in the range of 10 μm to several hundred μm x several hundred μm, and the surface tension of the recording liquid at 20°C is
An inkjet recording method characterized in that the inkjet recording density is in the range of 30 to 60 dyne/cm.