Water-based ink and preparing method thereof

Details Water-based ink and preparing method thereof Water-based ink and preparing method thereof

2002-02-01

2004-11-30

Shosho, Callie (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S201000, C524S548000, C524S593000

Reexamination Certificate

active

06825247

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a water-based ink and preparing method thereof.
BACKGROUND OF THE INVENTION
In recent years, recording materials employed in printers, printing presses, markers, and writing means have been demanded to be free from organic solvents and to be comprised of water. Widely employed as water-based recording materials are ones which are mainly comprised of an aqueous water-soluble dye solution and of a dispersion of fine pigment particles.
Recording materials employing water-soluble dyes are prepared as described below and then employed. Added to an aqueous solution as a main component, comprising water-soluble dyes which are classified into acidic dyes, direct dyes, and food dyes, are moisture retention agents such as glycols and alkanolamines, surface active agents to control surface tension, alcohols, and resins utilized as binders. These recording materials, employing water-soluble dyes, are most commonly employed due to their high reliability for minimized clogging at writing tips or recording systems. However, such recording materials tend to result in bleeding on recording sheets, such as paper, due to the fact that the employed dyes are water-soluble. Further, since it is required to increase an apparent drying rate, said recording materials are prepared so as to rapidly penetrate into said recording paper sheet. As a result, inevitably, recording quality can be degraded due to ink bleeding. Further, naturally, water resistance is inferior due to use of water-soluble dyes. Still further, it is difficult to assume that water-soluble dyes, which are simply penetrated into a paper sheet, dried and held, are subjected to “dying”. As a result, the resulting light-fastness is very inferior. In order to overcome said drawbacks, in recent years, several methods have been proposed such as described in Japanese Patent Publication Open to Public Inspection No. 2000-281947, in a two-liquid system using a cationic polymer, by utilizing an interaction between the cationic polymer and the dye, bleeding is minimized by enhancing dyeability so that the resulting fastness is enhanced. However, it is difficult to state that light-fastness is improved while maintaining the color reproduction obtained by water-soluble dyes.
As methods to overcome problems of recording materials comprised of water-soluble dyes as noted above, the addition of fine resinous particles in the form such as an emulsion or a latex has been investigated over a long period. Japanese Patent Publication Open to Public Inspection No. 55-18418 proposes an ink jet recording material in which a latex is added which is “one type of a colloid composition prepared by dispersing a component such as rubber and resins into water in the form of fine particles (having a particle diameter of about 0.01 to several &mgr;m) employing an emulsifier.” Exemplified as preferably employed latexes are synthetic rubber based latexes such as a styrene-butadiene copolymer latex, an acrylonitrile-butadiene copolymer latex, a polychloroprene latex, a vinylpyridine-styrene-butadiene latex, a butyl rubber latex, a polybutadiene latex, a polyisoprene latex, a polysulfide rubber latex, and synthetic resin based latexes such as an acryl ester based latex, a styrene-butadiene resin latex, a vinyl acetate based latex, a vinyl chloride based latex, and a vinylidene chloride based latex.
In said proposal, the diameter of latex particles, which can be added, is limited to the range of 0.01 to several &mgr;m. However, particles, which have a diameter of less than 0.2 &mgr;m, result in insufficient minimization of ink bleeding on recording paper sheets, and is not capable of providing high quality recording. On the other hand, when the particle diameter exceeds 1.0 &mgr;m, nozzles are frequently clogged whereby it is difficult to use it from the aspect of reliability. Accordingly, the range of the particle diameter, which is practically usable, is considered to be in the range of about 0.2 to about 1.0 &mgr;m. When such fine resinous particles are added to ink, it is necessary to pay particular attention to sedimentation or floating of particles due to the difference in specific gravity between said particle and the medium. In the case of said water-based ink, it is difficult that the specific gravity of said medium is far apart from 1.0. In fine particles having a diameter of no more than 0.2 &mgr;m, since gravity effects are larger compared to the diffusion force of particles due to Brownian movement, in such a region, it is necessary that the difference between the specific gravity of particles and the specific gravity of the medium is commonly adjusted to no more than 0.1, and is preferably adjusted to no more than about 0.07.
The specific gravity of synthetic rubber based latexes, exemplified in said patent publication, is in the range of about 0.9 to about 1.0 and meets to some extent the conditions described above. However, since most of said synthetic rubber comprises unsaturated double bonds in its molecule, problems with light-fastness as well as weather resistance are exhibited. Further, when said unsaturated bonds are decreased by carrying out vulcanization, fixing particles onto a recording paper is hindered resulting in problems with appearance quality of the recording. Furthermore, since the glass transition temperature of said synthetic rubber based latexes is relatively low, they tend to form a film at room temperature. As a result, when they are dried at the tip of ink jet nozzles, nozzles tend to be clogged. When once clogged, it is very difficult to remove clogging because dried latexes are flexible and adhesive. The synthetic resin latexes exemplified in said patent publication exhibit a specific gravity of at least 1.1, and specifically, the specific gravity of synthetic resins, comprising a halogen element, approaches nearly 1.3 to 1.5. As a result, all particles with their diameter in said range, which exhibits minimized bleeding effects, are prone to sedimentation.
Further, it is generally understood that most emulsifiers, which are employed during production of said latexes, tend to enhance the formation of bubbles in the ink and excessively decrease the surface tension of said ink, whereby many problems occur. Japanese Patent Publication Open to Public Inspection No. 54-146109 proposes a recording material employing a water-soluble dye to which fine vinyl polymer particles, which are swelled employing a solvent, as well as dyed with an oil dye, are added. Examples of preferably employed fine polymers particles mainly include fine acrylic acid ester or methacrylic acid ester based copolymer particles. Further, said patent publication states that a glass transition temperature of no more than 30° C. is an appropriate condition. It is self-evident that a film is formed when fine particles with such a low glass transition temperature, which are further swelled with a solvent, is dried at room temperature. As a result, it is easily assumed that when said ink is employed, nozzles will be frequently clogged. Japanese Patent Publication Open to Public Inspection No. 3-56573 proposes an image recording ink comprising a dye or a pigment together with 40 percent by weight of ultra-fine organic particles which have been subjected to internally three-dimensional cross-linking. Said fine cross-linked particles, which are added to said ink, are not capable of being fixed on a recording paper. As a result, it is clear that the fastness of said recorded images is inferior.
In order to overcome drawbacks of recording materials employing water-soluble dyes, it is proposed to employ carbon black or organic pigments in said recording materials. The water resistance of recording materials, which are comprised of such a pigment dispersion, is markedly improved. However, said pigments exhibit a relatively high specific gravity of 1.5 to 2.0. As a result, care is required to guard against the sedimentation of dispersed particles. In order to prepare a stable dispersion of said pigments having a relatively

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