In ink-jet recording, recording of images and text is performed by ejecting minute ink droplets based on various action principles to be deposited on recording materials such as paper. Ink-jet recording exhibits advantages such as relatively high speed, low noise, and easy realization of multicolor formation.
In recent years, since ink-jet recording enables simple and less expensive formation of images, it has been applied to various printing fields such as photography, various kinds of printing, marking, and special printing such as color filters. Specifically, by employing ink-jet recording apparatuses which eject minute ink droplets and control them, ink-jet inks which result in an improved range of color reproduction, durability, as well as ejection adaptability, and specialized paper sheets of which ink absorbability, color forming properties of colorants and surface glossiness are markedly improved, it has become possible to result in image quality comparable to conventional silver salt photography. Improvement in image quality of the current ink-jet recording systems have only been achieved by integration of ink-jet recording apparatuses, ink-jet inks, and recording materials.
In ink-jet printers employed for ink-jet recording, since recording is performed by depositing ink droplets from ink-jet heads on recording materials, the printers exhibit advantages such as easer downsizing of the recording device, capability of recording highly detailed images at a relatively high rate, lower running cost, and the ease of recording of color images.
Of late, in view of highly detailed image recording, the nozzle orifice size of ink-jet heads has decreased. However, when the nozzle orifice size decreases, ink clogging and decap at the nozzle section tend to occur. “Decap” indicates a phenomenon of clogging at the nozzles caused by evaporation of a solvent (such as water) contained in the ink. In order to minimize these problems, maintenance such as suction and wiping of the nozzle section is more frequently performed, resulting in necessity of longer maintenance time in addition to image printing time. Specifically, at present, since higher printing rates are demanded, an increase in time required for the above maintenance due to the decreased nozzle orifice size has become a major problem.
On the other hand, ink-jet printers are known which employ a serial printing system in which scanning is performed in such a manner that the ink-jet head moves in the direction which crosses the conveyances direction of recording materials and a line printing system in which the ink-jet head is fixed perpendicular to the conveyance direction of recording materials.
In ink-jet printers employing the above line printing system, fixed type parallel recording heads are employed which are arranged at a right angle to the conveying direction of recording materials, and in that system, recording is performed employing only secondary scanning while recording materials are conveyed in the conveying direction. While ink is ejected from the ink-jet heads and over-all one-line recording is continuously performed, paper is conveyed at a specified rate, whereby images are formed on the entire area of the recording material. This method makes it possible to easily achieve a high rate of printing. On the other hand, however, since ink heads are fixed, resulting in mechanism making it difficult to perform maintenance. As a result, as noted above, demand is increasing to reduce maintenance time, due to ink clogging and decap in the nozzle section as, short as possible.
On the contrary, in ink-jet printers employing the serial printing system (hereinafter occasionally referred to as the shuttle head system), while intermittently conveying the recording material, images are formed by moving ink-jet heads in the direction which crosses at right angles to the conveying direction of recording materials. In these serial system ink-jet printers, it is easy to perform maintenance, but has been difficult to consistently prepare highly detailed images. Further, since ink-jet heads are mechanically driven back and forth, there are drawbacks for enhancement of the printing rate.
Proposed as a method to minimize clogging due to ink and decap, which hinder an increase in printing rate and formation of highly detailed images is, for example, one in which formation of a network and aggregates in ink is minimized by incorporating anion oxides as a surface active agent in the ink (refer, for example, to Patent Document 1). However, employed as ink solvents, proposed in the above method, are those composed of water exhibiting a high vapor pressure as a main component. Subsequently, problems are inherent in which capability capable of minimizing decap is limited due to an increase in viscosity of ink liquid caused by water evaporation.
Further proposed is a method (refer, for example, to Patent Document 2), which selects ink constituting materials in such a manner that water, water-soluble organic solvents, and water-soluble dyes are employed so that even though components such as water, which have a relatively high vapor pressure, are evaporated, the resultant ink is not solidified and the variation ratio of viscosity of the ink liquid is within a factor of ten, compared to the initial viscosity. However, in this method, it becomes necessary to select dyes which are highly soluble in solvents which did not evaporate. As a result, diffusion of dyes after being printed on recording materials increases, resulting in bleeding.
Further, disclosed is ink in which specified latex polymers, 3-hexyl-2,5-diol, and 1,2-octane-diol are simultaneously used (refer, for example, to Patent Document 3). However, in this method, since an excessive added amount of 2-octanediol results in feathering, its amount is limited with in the range of 0.01–0.5 percent by weight. Due to that, currently, decap is not minimized as desired. Further, in this method, water at a relatively high vapor pressure is employed as a major solvent. As a result, problems are inherent in which decap minimizing effects are limited due to an increase in viscosity caused by water evaporation.
As noted above, currently, a method has not been discovered which simultaneously achieves formation of highly detailed images, high rate printing, and minimization of decap.
On the other hand, in ink-jet image recording systems which necessitate specialized paper sheets, problems occur in which recording materials are limited and the cost of recording materials increases. Specifically in offices, a system is increasingly demanded which is capable of performing full-color printing at a high rate without any limitation to recording materials (e.g., plain paper, coated paper, art paper, or double sided printing on plain paper).
Various studies have been conducted with regard to compositions of ink-jet inks capable of achieving higher speed printing, desired text reproduction on plain paper, resulting in no ink penetration to the back surface during printing (being the phenomena in which printed ink passes through the recording material and a printed image appears on the rear surface), no feathering, and no image bleeding, as well as resulting in quick penetration into the recording paper and rapid drying of the image.
As one of these methods, so-called water-based ink-jet inks are widely employed. When images are recorded on plain paper such as copy paper for electrophotography, high quality paper or medium quality paper, in addition to problems such as image penetration to the rear surface and feathering due to penetration, curling and cockling of images recorded on plain paper result in major problems.
In order to overcome the above drawbacks, an ink-jet recording method is disclosed (refer, for example, to Patent Document 4) which employs a penetration-improved ink by specifying the wetting time and the absorption coefficient of recording materials in the Bristow method. However, since colorants in the ink simultaneously penetrate into plain paper, this method results in problems, in which a decrease in image density as well as penetration to the rear surface is enhanced, resulting in unsuitability for both sided printing.
Further, ink-jet ink is disclosed (refer, for example, to Patent Document 5) which incorporates specified amide compounds, pyridine derivatives, imidazoline compounds or urea compounds as an anticurl agent. However, this method results in problems in which clogging of the nozzle of a recording head tend to occur due to drying of liquid ink.
Still further, proposed is an ink-jet recording method to minimize the above curling (refer, for example, to Patent Document 6), in which curling balance is optimized by providing a solution containing water on the side opposite the image printing surface. However, this method results in problems in which along with an increase in the adhered amount of ink as well as curl balance liquid onto plain paper, its strength is deteriorated, whereby jamming tends to occur during conveyance.
Still further, instead of using the water-based ink-jet ink, a solvent-based ink capable of achieving printing at a high rate has been studied. Namely, by employing an oil-based ink (being a solvent-based ink-jet ink), even though printed on plain paper, it is possible to achieve high speed printing due to quick penetration into recording materials, shorter drying time, and no curling of recording materials. However, problems occur in which text is not reproduced as desired and penetration to the rear surface results due to the fact that the solvent based ink easily penetrates plain paper.                (Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 11-172174        (Patent Document 2) JP-A No. 2000-95983        (Patent Document 3) JP-A No. 2000-239591        (Patent Document 4) JP-A No. 10-316915        (Patent Document 5) JP-A No. 9-176538        (Patent Document 6) JP-A No. 10-272828