Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-04-29
2004-08-03
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...
C524S556000, C524S557000, C106S031600, C106S031690, C106S031700
Reexamination Certificate
active
06770688
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a water based pigment ink composition for a ballpoint pen, more specifically to a water based pigment ink composition used for a free ink type ballpoint pen having structure in which an ink is stored directly in an ink reservoir having a small diameter without using an ink absorber and a feed to be fed to a pen tip.
BACKGROUND ART
In general, an ink for a ballpoint pen includes a water based ink of a low viscosity containing a solvent comprising water and a water soluble solvent and having an ink viscosity of 10 mpa.s or less and an oil based ink containing a solvent such as a polyhydric alcohol and Cellosolve and having an ink viscosity of 1000 to 20000 mpa.s.
A ballpoint pen using an oil based ink has structure in which the ink adhered on a ball at a pen tip through an ink reservoir having a small diameter is transferred on a paper surface by rotation of the ball and only the transferred portion of the ink is fed to the pen tip through the reservoir.
A ballpoint pen using a water based ink has structure in which an ink is fed to a ball surface and a paper surface by means of capillary action of a feed prepared by binding fine fibers.
The foregoing water based ink and oil based ink for a ballpoint pen each have excellent advantages. On the other hand, however, they have various problems as well.
For example, since the water based ink has a low viscosity, the ink is fed by making use of a principle of capillary action. When the point portion of the ballpoint pen simply contacts paper, the capillary action is exerted on the contact point 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 scarcely take place. On the other hand, the capillary action is exerted as well after transferring the ink on a paper surface to cause the drawn lines to feather, and storing the ink directly in the ink reservoir allows the ink to seep due to vibration or impact to make the amount of the ink to be fed to the ball unstable. Accordingly, complicated structure having a feed prepared by binding fine fibers is required. Further, there is a problem that it is difficult to confirm the amount of the ink reserved in the ballpoint pen.
On the other hand, the oil based ink is characterized by that because of a high viscosity thereof, the ink can be stored directly in the ink reservoir having a small diameter and the structure of the ballpoint pen can be simplified and that the remaining amount of the ink can be confirmed by using a transparent material for the ink reservoir and the ink transferred on a paper surface does not feather. On the other hand, there are problems that since the ink is transferred only on a paper surface contacted 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, several countermeasures for solving such problems are reported. For example, the problems of feathering and seepage of an ink have been investigated in Japanese Patent Application Laid-Open No. Sho 54-98826 to provide a water based ink for a ballpoint pen in which gelatinizers (benzyl sorbitol and benzylidene xylitol or derivatives thereof) or a water soluble paste is added to provide the ink with thixotropy. Further, provided are a water based ink for a ballpoint pen in which the viscosity is increased by a cross linking type acrylic resin in Japanese Patent Application Laid-Open No. Sho 57-49678 and a water based ink for a ballpoint pen in which the viscosity is increased by xanthane gum in U.S. Pat. No. 4545818. However, they have problems of splitting and of stain caused by blobbing, and therefore they are not sufficiently satisfactory.
Further, it is shown in U.S. Pat. No. 4671691 to store a water based ink in a barrel of a simplified free ink type pen such as an oil based ballpoint pen, and disclosed therein is a ballpoint pen comprising a water based ink in which a water dispersible rubber or resin is added to provide a shear thinning property and a thinning index thereof falls in a range of from 0.01 to 0.6, and a viscoelastlc follower. However, there are the defects that an ink subjected to shearing is not good in a flowing property and is slow in temporal viscosity recovery, so that a follow-up property of the ink in writing is inferior to bring about starving of the drawn lines and the ink seeps immediately after writing, and therefore the ballpoint pen is not sufficiently satisfactory.
Further, shown in Japanese Patent Application Laid-Open No. Hei 6-346014 is a water based ink for a ballpoint pen provided with thixotropy by a thickener comprising an emulsion to be thickened in alkaline. However, there are the problems that a settling action of a pigment can not be prevented only by an increase in the viscosity only with a swelling action of a carboxyl group contained in the thickener, so that the ink in the circumference of a rotary ball at the pen tip seeps and that the ink does not have a long term storing property. Accordingly, it is not sufficiently satisfactory.
An object of the present invention is to solve the problems on the conventional technologies described above and provide a water based ink composition which has a good follow-up property in writing and solves conventional defects such as splitting, poor water resistance and stain of drawn lines caused by blobbing and which does not cause seepage in the circumference of the rotary ball immediately after writing and is stable over a long period of time without settling of a pigment itself, wherein the water based ink composition can be filled in a ballpoint pen having structure in which an ink is stored directly in an ink reservoir to be fed to a pen tip, that is, a ballpoint pen having simplified free ink type structure as is the case with a ballpoint pen for a so-called oil based ink.
DISCLOSURE OF THE INVENTION
The present inventors have made researches in order to solve the problems described above, and as a result, they have come to complete a water based ink in which dispersibility of a pigment is kept stable over an extended period of time and a follow-up property of the ink in writing and quality of the drawn lines are excellent and which does not bring about seepage in the circumference of the rotary ball and can be stored in a ballpoint pen having simplified free ink type structure by using a thickener having a hydrophobic group and a hydrophilic group in a molecule which increases a viscosity by a steric hindrance resistance viscosity brought about by hydration swelling of the hydrophilic group in the thickener molecule and associative adsorption of the hydrophobic group and the hydrophilic group in the thickener molecule on the components contained in the ink composition instead of exerting a single thickening action brought about only by a steric hindrance resistance of the thickener molecule.
The water based ink composition of the present invention for a ballpoint pen is composed of an alkali-swelling associative thickener comprising a polymer having a carboxyl group as a hydrophilic group and a hydrophobic group, a pigment a polar solvent containing water, a pH controlling agent and other additives. Preferred is the water based ink composition for a ballpoint pen in which the alkali-swelling associative thickener described above is contained in a proportion of 0.1 to 8% by weight (polymer component) based on the ink composition and increases the ink viscosity by dissolving and swelling in an alkaline area in the polar solvent containing water to associate with the particle surface of the pigment. More preferred is the water based ink composition for a ballpoint pen in which the particle surface of the pigment is subjected to surface treatment with a pigment surface-treating agent.
BEST MODE FOR CARRYING OUT THE INVENTION
The alkali-swelling associative thickener used for the ink composi
Darby & Darby
Mitsubishi Pencil Kabushiki Kaisha
Shosho Callie
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