Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-03-22
2003-11-11
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860
Reexamination Certificate
active
06645284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink composition for a water based ballpoint pen which is improved in a drawn line-drying property and a water based ballpoint pen using the same.
2. Description of the Related Art
A drawn line-drying property of a water based ballpoint pen depends largely on a penetrability of the ink into paper, an evaporation-drying speed of the ink and an ink discharge amount per unit area. In particular, a level of the drawn line-drying property endowed is different according to the ink discharge amount per unit area, and an ink discharge amount (less than 4.5×10
−3
mg/mm
2
) in writing with a water based ballpoint pen which has so far been usually used has made it possible to maintain a drawn line-drying property required in conventional inks without particularly trying to elevate a penetrability of the ink into paper and an evaporation-drying speed of the ink. However, when trying to make a ball diameter larger than &phgr;0.7 mm in order to obtain a thick line in a water based ballpoint pen or obtain a dense line, the ink discharge amount in writing has reached 4.5×10
−3
to 10.0×10
−3
mg/mm
2
in many cases, and it has been impossible to obtain a drawn line-drying property of such an extent as endurable in practical use without raising either of a penetrability of the ink into paper and an ink-drying speed.
However, in the case of a water based ballpoint pen, a rise in an evaporation-drying speed of the ink brings about a problem connecting directly with clogging of the ink at the pen tip caused by dry-up, and therefore it is not realistic to easily elevate the ink-drying speed. Further, it is considered to set a large clearance in the vicinity of a ball in a ballpoint pen tip as a countermeasure for clogging. In this method, however, new problems such as straight flow and blowing-off are caused in a certain case, and a tendency thereof is markedly shown particularly in a water based ballpoint pen using an ink having a low viscosity (1 to 10 mPa·s).
Accordingly, a method for elevating a penetrability of an ink into paper has so far usually been employed as a measure for obtaining a satisfactory drawn line-drying property. A method in which a large amount of a surfactant is added to an ink to reduce a surface tension of the ink has so far been taken as means for raising a penetrability of the ink into paper. In this case, however, feathering takes place a lot depending on the kind of a face of paper to be written, and a phenomenon in which an ink penetrates into a back side of a paper face (hereinafter called ┌strike-through┘) is caused in many cases. Further, a surface tension of the ink to the ballpoint pen tip is reduced to a large extent, and a problem on quality (straight flow, blowing-off and the like) originating in a change in the environment in storage of the pen over a long period of time has so far been caused.
Further, it is considered to blend an ink with an alcohol base solvent having a relatively high surface tension such as cyclohexanol as a method for solving the problems described above. In this case, however, the ink blended therewith gives out an offensive smell which is intrinsic to an alcohol base solvent to lower a product value of the water based ballpoint pen, and a small solubility of the solvent into water is likely to deteriorate a solubility of the other components contained in the ink when moisture is evaporated from the pen tip during long-term storage or in opening the pen tip.
SUMMARY OF THE INVENTION
The present invention provides an ink composition for a water based ballpoint pen which satisfies all of no change in the ink composition even in storage over a long period of time, a good strike-through property and an excellent drawn line-drying property at the same time.
Intensive researches repeated by the present inventors in light of the existing situations described above have resulted in finding that the object described above can be achieved by blending an ink composition with a specific amount of a drawn line-drying property-improving agent comprising a specific compound, and they have completed the present invention based on this finding. That is, the present invention comprises the following items (1) to (5).
(1) An ink composition for a water based ballpoint pen comprising at least water and a colorant, characterized by further comprising at least one drawn line-drying property-improving agent selected from butyl cellosolve and butyl carbitol in a proportion of 0.1 to 2.5% by weight based on the whole amount of the composition and having a surface tension of 16 to 45 mN/m.
(2) The ink composition for a water based ballpoint pen as described in the above item (1), wherein the viscosity is 1 to 10 mPa·s (25° C.), and the surface tension is 25 to 45 mN/m.
(3) The ink composition for a water based ballpoint pen as described in the above item (1), characterized by having a viscosity of 100 to 4000 mPa·s (25° C.) at a shear rate of 3.84 s
1−
and a surface tension of 16 to 38 mN/m and having a pseudo-plasticity.
(4) The ink composition for a water based ballpoint pen as described in any of the above items (1) to (3), wherein a blending amount of a pigment as the colorant is 0.05 to 30% by weight based on the whole amount of the composition; 5.0 to 40.0% by weight of a water-soluble organic solvent based on the whole amount of the composition is further added; and the pH is 7.0 to 10.0.
(5) A water based ballpoint pen which contains the ink composition for a water based ballpoint pen as described in any of the above items (1) to (4) and is equipped with a ball tip having a ball diameter of exceeding 0.7 mm and 1.5 mm or less and which has an ink discharge amount per unit area of 4.5×10
−3
to 10.0×10
−3
mg/mm
2
.
The water based ink composition of the present invention can maintain a quick drawn line-drying property and a high surface tension and therefore can hold a high writing level such as an inhibition in straight flow and blowing-off from the pen tip. It is such an excellent ink composition capable of satisfying all the performances described above that the strike-through resistance can be improved as well particularly in a water based ballpoint pen in which a ball having a ball diameter exceeding 0.7 mm is used to set a discharge amount of an ink so that it is 4.5×10
−3
to 10.0×10
−3
mg/mm
2
.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Butyl cellosolve used as the drawn line-drying property-improving agent in the ink composition for a water based ballpoint pen of the present invention is a compound represented by the following chemical formula (I):
CH
3
(CH
2
)
3
—OCH
2
CH
2
OH (I)
and butyl carbitol is a compound represented by the following chemical formula (II):
CH
3
(CH
2
)
3
—(OCH
2
CH
2
)
2
OH (II)
Butyl cellosolve represented by the chemical formula (I) described above and butyl carbitol represented by the chemical formula (II) described above are publicly known substances. Butyl cellosolve can be synthesized by reacting ethylene oxide with 1-butanol under applied pressure, and butyl carbitol is obtained as a by-product thereof.
A blending amount of the drawn line-drying property-improving agent in the ink composition of the present invention can be set to 0.1 to 2.5% by weight, preferably 0.1 to 1.7% by weight and more preferably 0.5 to 1.0% by weight based on the whole amount of the composition. If it is less than 0.1% by weight, the satisfactory drawn line-drying property which is the object of the present invention is not obtained. On the other hand, if it exceeds 2.5% by weight, problems such as a reduction in the strike-through resistance and a surface tension of the ink are brought about, or when a pigment which is the colorant is a phthalocyanine base or a naphthol base, coagulation is caused, though a reason therefore is not clear, in the ink to make writing impossible in a certain case. This tendency is the case
Bell Mark L.
Darby & Darby
Faison Veronica F.
Mitsubishi Pencil Kabushiki Kaisha
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