Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-06-11
2003-09-02
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031670
Reexamination Certificate
active
06613135
ABSTRACT:
This application is a national phase application under 35 U.S.C. §371 of International Application No. PCT/JP99/04740, filed Sep. 1, 1999, which was published in Japanese as International Publication No. WO 00/12638 on Mar. 9, 2000 and claims the benefit of Japanese Patent Application No. 10/246763, filed Sep. 1, 1998.
TECHNICAL FIELD
The present invention relates to a water based ink for a ballpoint pen, more specifically to a shear thinning water based ink for a ballpoint pen having advantages of a ballpoint pen using an oil based ink, that is, a pseudo-plastic water based ink for a ballpoint pen.
BACKGROUND ART
In general, inks for a ballpoint pen have so far been classified into a water based ink for a ballpoint pen which contains a solvent comprising a water based solvent such as water and has a low viscosity of 10 mPa·s or less and an oil based ink which contains a solvent comprising an oil based solvent such as mineral oil, polyhydric alcohol, a fatty acid and cellosolve and has an ink viscosity of 1000 to 20000 mPa·s.
A ballpoint pen using an oil based ink for a ballpoint pen has such structure that the ink stuck on a ball through an ink reservoir having a small diameter is transferred onto a paper surface by rotation of the ball and only the transferred portion of the ink is fed again from the reservoir to the ball.
On the other hand, a ballpoint pen using a water based ink for a ballpoint pen has such structure that the ink is fed to a ball surface and a paper surface by virtue of capillary action of a feed prepared by binding fine fibers.
While the water based ink for a ballpoint pen and the oil based ink for a ballpoint pen described above each have excellent advantages, they have various problems as well.
For example, in the water based ink for a ballpoint pen, capillary action is used in a principle for feeding the ink because of a low viscosity thereof, wherein a simple contact of the tip portion of the ballpoint pen with paper allows the capillary action to be exerted on the contact point thereof to feed the ink, and good lines can be written on a paper surface without applying so much writing pressure, so that splitting, starving and blobbing are not likely to take place. On the other hand, storing the ink directly in the ink reservoir allows the ink to leak due to vibration, impact and a rise in an external temperature to make the amount of the ink to be fed to the ball instable, and therefore the ballpoint pen requires a complicated structure having a feed prepared by binding fine fibers and has the problem that it is difficult to observe the amount of the ink.
On the other hand, an oil based ink for a ballpoint pen is characterized in that because of a high viscosity thereof, blobbing of the ink from the pen tip can be prevented and the ink can be stored directly in the ink reservoir having a small diameter, so that the structure of the ballpoint pen can be simplified and that the amount of the ink can be observed by using a transparent material for the ink reservoir. On the other hand, there are involved the problems that since the ink is transferred only on a paper surface come into contact with the rotating ball, splitting and starving are liable to be caused if the ball rotates unstably and that since the ink hardly penetrates into a paper surface, blobbing which causes stain with the untransferred ink is apt to be caused.
In recent years, in order to solve such problems, produced are water based inks for a ballpoint pen (hereinafter referred to as “a pseudo-plastic water based ink for a ballpoint pen”) in which a gelatinizer and a water soluble paste are added to a water-soluble ink to impart a specific viscosity characteristic to the ink.
A ballpoint pen using this pseudo-plastic water based ink for a ballpoint pen is reduced in an ink viscosity by shear force which is applied to the ink by rotation of the ball at the tip point when writing and can write as smoothly as a ballpoint pen using a water based ink to make good lines on a paper surface. Further, when the pen is not used for writing, blobbing of the ink from the pen tip can be prevented because the ink has a high viscosity. The ink can be stored directly in the ink reservoir, so that the structure thereof can be simplified, and the use of a transparent material for the ink reservoir makes it possible to observe the amount of the ink. Thus, the use of the pseudo-plastic water based ink for a ballpoint pen provides a-writing instrument having both characteristics of a ballpoint pen using a water based ink and a ballpoint pen using an oil based ink.
When producing such a pseudo-plastic water based ink for a ballpoint pen, a viscosity-controlling agent (thickener) has so far had to be blended as an essential component for an ink material. The viscosity-controlling agent is added in order to impart a pseudo-plasticity to the ink, and it is proposed to add, for example, polyacrylic acid salts, cross-linking type acrylic acid polymers, salts of a styrene-acrylic acid copolymer, salts of a styrene-maleic acid copolymer, nonionic polymers such as polyvinylpyrrolidone and polyethylene glycol, and polysaccharides such as xanthan gum, guar gum, casein, gum arabic, gelatin, carrageenan, alginic acid, tragacanth gum and locust bean gum.
However, these viscosity-controlling agents have caused the problems that they bring about scattering in the capability for providing a shear thinning property depending on a lot to exert influence on the writing property and they are inferior in compatibility with some colorants to cause a change in a viscosity of the ink in heating and aging and reduce the performances of the ballpoint pen and that they restrict the compounding of various materials such as a surfactant, an organic solvent, a dispersing resin for a pigment and the like which are compounded in addition to these viscosity-controlling agents into some kinds of the inks.
On the other hand, proposed in Japanese Patent Laid-Open No. Hei 9-302299 is a shear thinning ink for a ballpoint pen which comprises a colorant, a water-soluble organic solvent and a nonionic surfactant having an HLB value of 8 to 12 as an agent for providing a shear thinning property and which has a viscosity of 25 to 160 mpa s determined at a revolution of 100 rpm by an EM type rotational viscometer and a shear thinning index of 0.1 to 0.6.
However, all nonionic surfactants having an HLB alue of 8 to 12 do not always impart the shear thinning property, and while-exhibiting the shear thinning property in an aqueous solution, a thickening property is lost in many cases by blending a water-soluble organic solvent. Further, if a blending amount of the above surfactant is increased in order to impart the shear thinning property and a water-soluble organic solvent is blended into the system, feathering of the drawn lines is heavy to make the lines very indistinct.
Further, proposed in U.S. Pat. No. 2,662,882 is a pigment ink for a ballpoint pen which comprises a pigment, water, water-soluble saccharides and a polyglycerin fatty acid ester.
However, an ink using water-soluble saccharides as a main thickener is increased in a concentration of the water-soluble saccharides (thickener) by a portion of moisture evaporated from the pen tip with the passage of time, and a viscosity of the ink at the pen tip grows large, which brings about the problems that the inferior flowability is caused and the cap-off resistance is reduced.
The present invention has been made in light of the problems described above, and an object thereof is to provide a pseudo-plastic water based ink for a ballpoint pen which causes less scattering in a viscosity depending on a production lot and has satisfactory viscosity and pseudo-plasticity and which has good stability with the passage of time whatever colorants are used and provides good writing feeling and excellent cap-off resistance.
DISCLOSURE OF THE INVENTION
Intensive researches continued by the present inventors in order to solve the problems described above have resulted in finding that a pseudo-plastic water based i
Miyamoto Masaru
Miyazaki Shigeru
Takeuchi Yoji
Bell Mark L.
Darby & Darby
Faison Veronica F.
Mitsubishi Pencil Kabushiki Kaisha
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