Erasable ink and water-base ballpoint pen using same

Details Erasable ink and water-base ballpoint pen using same Erasable ink and water-base ballpoint pen using same

1999-09-20

2001-10-23

Jagannathan, Vasu (Department: 1714)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C106S031320, C106S031330, C106S031640, C106S031650

Reexamination Certificate

active

06306930

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel species of erasable ink and a water-base ballpoint pen in which said ink is used.
BACKGROUND OF THE INVENTION
Erasable ink is characterized in that when letters, characters, figures or drawings are written or drawn on paper in such ink, the lines drawn can be erased with a rubber eraser. It is currently used in felt-tip pens and the like.
Such erasable inks are already known. There is known, for instance, an erasable ink composition characterized in that it comprises a resin having a film-forming temperature not higher than 0° C. or a glass transition temperature not higher than 0° C., spherical particles of a colored resin having a particle size of 1 to 20 &mgr;m and water and has an ink viscosity of 5 to 35 mPa•sec (Japanese Kokai Tokkyo Koho H05-279614).
In the case of said erasable ink composition, however, it is difficult to erase drawn lines completely and, from the erasability viewpoint, there is room for improvement. In particular, when writing is made with a great tool force, it is impossible to erase the drawn lines to the extent that they cannot be recognized any longer. This problem becomes more serious when such composition is used as ink for ballpoint pens with which the tool force tends to become high. Furthermore, when the ink composition mentioned above is to be used as ink for ballpoint pens, it tends to fail to flow out successfully, hence, as it is, such composition cannot be used in ballpoint pens.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an erasable ink composition which can be erased in a relatively easy manner even when writing has been made with a great tool force. Another object of the invention is to provide a water-base ballpoint pen in which said ink composition is used.
As the result of intensive investigations made by the present inventor in an attempt to solve the above problems of the prior art, it was found that the above objects can be accomplished by employing an ink composition containing a colorant whose particle size is controlled within a certain range. Based on this and other findings, the present invention has now been completed.
The present invention thus provides an erasable ink composition and a water-base ballpoint pen in which said ink composition is used, as specified below:
1. An erasable aqueous ink composition containing at least one colorant, characterized in that said colorant has a mean particle size of not less than 2 &mgr;m and that particles having a size of not more than 1.8 &mgr;m account for not more than 1.6% by weight of said colorant.
2. An erasable aqueous ink composition containing at least one colorant, characterized in that said colorant has a mean particle size of not more than 7 &mgr;m and that particles having a size of not less than 7 &mgr;m account for not more than 0.5% by weight of said colorant.
3. An erasable aqueous ink composition containing at least one colorant, characterized in that said colorant has a mean particle size of 2 to 7 &mgr;m, that particles having a size of not more than 1.8 &mgr;m account for not more than 1.6% by weight of said colorant and that particles having a size of not less than 7 &mgr;m account for not more than 0.5% by weight of said colorant.
4. A water-base ballpoint pen in which the ink composition specified above under any of paragraphs 1 to 3 is used.
DETAILED DESCRIPTION OF THE INVENTION
The colorant is not limited to any particular species on the condition that the particle size distribution conditions to be described later herein in more detail be met. Thus, those colorants which are used in known aqueous ink compositions or the like can be employed. For example, inorganic pigments such as titanium oxide, carbon black, ultramarine blue, cobalt blue, chromium oxide, iron oxide red and graphite as well as organic pigments such as C.I. pigment black 1, C.I. pigment green 7, C.I. pigment blue 15, C.I. pigment red 112 and C.I. pigment violet 19 can be used. In addition, fluorescent pigments, luminescent pigments and the like can also be used. Furthermore, the so-called colored resin beads can be used as the colorant in the practice of the present invention. As the colored resin beads, there may be mentioned, for example, resin beads (e.g. of an acrylic resin or a styrenic resin) containing a dye or pigment, resin beads colored with a dye etc. Further, in the practice of the present invention, toners for copying may also be used. These colorants may be used either singly or in combination of two or more of them. Among them, the use of colored resin beads is preferred.
In the practice of the present invention, it is necessary for these colorants to be controlled with respect to their particle size as follows. Thus, it is required that the colorant have a mean particle size of not less than 2 &mgr;m and particles having a size of not more than 1.8 &mgr;m account for not more than 1.6% by weight on the colorant basis, or that the colorant have a mean particle size of not more than 7 &mgr;m and particles having a size of not less than 7 &mgr;m account for not more than 0.5% by weight on the colorant basis.
In the practice of the present invention, it is particularly preferred that the colorant have a mean particle size of 2 to 7 &mgr;m (more preferably 2 to 5 &mgr;m), with particles having a size of not more than 1.8 &mgr;m accounting for not more than 1.6% by weight on the colorant basis and particles having a size of not less than 7 &mgr;m accounting for not more than 0.5% by weight, preferably not more than 0.1% by weight, on the colorant basis. This particle size control can be realized by any known classification technique such as spontaneous sedimentation, centrifugation or filter filtration.
The term “mean particle size” as used herein means the weight average particle size. Thus, the weight cumulative distribution is determined by the liquid phase precipitation method in the light transmission mode (measuring apparatus: Horiba Seisakusho model CAPA-700) and the particle size at 50 weight percent distribution is reported as the mean particle size. The precipitation is caused by centrifugation. The specific gravity of the colorant particles is calculated using the true specific gravity thereof.
The shape of the colorant(particle) is not critical but may be spherical, polyhedral, flaky or fibrous, for instance. In the practice of the present invention, however, a basically spherical form is preferred and, in particular, it is preferred that the shape be as close as possible to the true sphere.
The content of the colorant may be judiciously selected in consideration of the other components employed and, generally, it is about 1 to 40% by weight, preferably 3 to 20% by weight. When it is above 40% by weight, the viscosity will become excessively high, so that the ink will flow out with difficulty. When said content is less than 1% by weight, sufficient coloration may not be attained in some instances.
The erasable ink composition of the present invention may further contain a water-soluble polymer. If it is soluble in water, it may be a natural, synthetic or semisynthetic one for instance. Those known polymers which are used as gelling agents in gel ink compositions may also be used as they are. Such polymers may be used either singly or incombination. Among them, xanthan gum, carboxymethylcellulose, guar gum, pullulan, rhamsan gum, welan gum, succinoglucan and like polysaccharides are preferred, and those polysaccharides represented by the following general formula are more preferred.
(In the above formula, M represents an alkali metal selected from among sodium, potassium and lithium, and n is 1,000 to 3,000)
The polysaccharides represented by the above general formula can provide ink compositions with excellent thixotropic properties, stringiness and dischargeability, among others. As the polysaccharides giving such characteristics, commercial products, for example “rhamsan gum” (available from Sansho Corp.), can be used. This polysaccharide (rhamsan gum)

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