Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-06-07
2002-05-14
Jagannathan, Wasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C524S102000, C524S428000, C524S497000
Reexamination Certificate
active
06387984
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous ink composition for ball-point pens. More specifically, the present invention relates to the improvement of stability to dispersibility and concealing power of an aqueous ink composition for ball-point pens wherein a titanium oxide is contained as a white pigment.
BACKGROUND ART
With regard to a conventional aqueous ink composition, for example, an aqueous ink composition with high viscosity comprising a coloring agent, water, a water-soluble organic solvent, a viscosity modifier and spherical fine particles of polymer has been disclosed in the Japanese Examined Patent Publication No.5-46389. And an aqueous ink composition comprising alkylene-bis-melamine derivatives as a white pigment is disclosed in Japanese Unexamined Patent Publication No.8-48930.
However, in case that a ball-point pen with an ink container tube charged with a conventional aqueous ink composition with high viscosity comprising, for example, the titanium oxide and spherical fine particles of polymer is allowed to stand with its writing tip oriented downward for a long time (for storage, and the like), the titanium oxide contained in the mentioned aqueous ink composition precipitates and non-uniformity of the density of the ink composition arises inside the ink container. This non-uniformity of the density of the ink composition causes clogging at the writing tip and then, the writing characteristic deteriorates. Inside the ink container, the ink composition separates into various layers (such as a layer including the titanium oxide, a layer without the titanium oxide and the like). Thus, with a ball-point pen comprising a transparent or semitransparent ink container, the outward appearance deteriorates.
On the other hand, when the mentioned ball-point pen is allowed to stand with its writing tip oriented upward for a long time (for storage, and the like), the titanium oxide contained in the mentioned aqueous ink composition precipitates at the opposite end of the ink container to the writing tip, so that the titanium oxide has difficulty in flowing out during writing. As a result, its writing portion has poor color development (particularly, that of white color and the like) and the lowered concealing power.
Conventional aqueous ink composition for ball-point pens has the above mentioned disadvantages. Therefore, when a ball-point pen with such an aqueous ink composition (the conventional aqueous ink composition comprising the titanium oxide and spherical fine particles of polymer) is displayed at a shop with its writing tip oriented downward for a long time, the precipitation of the titanium oxide causes a clogging of the ink. On the other hand, when displayed with its writing tip oriented upward, the precipitation of the titanium oxide causes the fall of the color development and concealing power of its writing portion and the value of the ball-point pen as a merchandise lowers. Accordingly, the aqueous ink composition containing the spherical fine particles of polymer has disadvantages in that the stability to the dispersibility is low because of the easy precipitation of the titanium oxide and therefore, the concealing power and the outflow of the ink from the writing tip are not satisfactory.
DISCLOSURE OF THE INVENTION
As a result of intensive study to solve foregoing problems, the present inventor has found that when the aqueous ink composition with high viscosity, wherein flat-shaped resin particles are added instead of spherical resin particles to an aqueous ink composition containing the titanium oxide and the viscosity modifier, is applied to an aqueous ball-point pen, the precipitation of the titanium oxide can be restrained or prevented even after the mentioned ball-point pen is allowed to stand for a long term, and at the same time, the writing characteristic is excellent and its writing portion has high concealing power.
The present invention directs an aqueous ink for ball-point pens containing the flat-shaped resin particles in the aqueous ink composition which contains the titanium oxide as a white pigment and the viscosity modifier.
In addition to the titanium oxide, it is preferable in the present invention to add alkylene-bis-melamine derivatives as a white pigment represented by the formula(1).
(wherein R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alicyclic group; R
1
, R
2
, R
3
and R
4
are the same or different groups, each of which representing a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R
1
and R
2
and/or R
3
and R
4
may form a heterocyclic group together with nitrogen atom; and X represents an alkylene group having 2 to 3 carbon atoms.)
The object of the invention is to provide an aqueous ink composition for ball-point pens with high concealing power and an excellent ink flow, wherein a precipitation of a titanium oxide in the ink container tube can be prevented even if the titanium oxide is used as a white pigment.
BEST MODE FOR CARRYING OUT THE INVENTION
As above mentioned, Japanese Examined Patent Publication No.5-46389 discloses an aqueous ink composition with high viscosity comprising spherical particles of polymer. Generally, an aqueous ink composition having high viscosity with the viscosity modifier has better stability to dispersibility than does an aqueous ink composition without the viscosity modifier due to the effect of the viscosity modifier or its high viscosity itself. However, in case of preparing an aqueous ink composition using a pigment with a high specific gravity such as the titanium oxide and the like, the precipitation of the pigment (the titanium oxide) is difficult to be prevented with the help of the viscosity modifier alone, and therefore, the stability to the dispersibility of ink composition is low. Moreover, the spherical resin particles (the spherical particles of polymer) are not capable of preventing the precipitation of the titanium oxide and thus, the stability to the dispersibility of the ink composition does not improve sufficiently.
The inventor has noted that the spherical particles of polymer cannot capture the titanium oxide for preventing its precipitation because of their spherical shape. Therefore, in the present invention, the ink composition is prepared with the titanium oxide together with the flat-shaped resin particles.
The flat-shaped resin particles has a low specific gravity (the specific gravity of titanium oxide is about 4; the specific gravity of the flat-shaped resin particles is about 0.7 to about 1.5) and flat-shaped shape, so that they are capable of capturing or covering the titanium oxide easily. Namely, the upper side of the flat-shaped resin particles is suitable for capturing the titanium oxide. And it is easy for the flat-shaped resin particles not only to capture the titanium oxide with its upper side, but also to cover an entire particle of the titanium oxide. As a result, the total specific gravity of the combination of the titanium oxide and the flat-shaped resin particles becomes lower than that of the titanium oxide alone. It seems that during the storage of an aqueous ball-point pen, the precipitation of the titanium oxide can be prevented or restrained owing presumably to this low specific gravity. The flat-shaped resin particles have an excellent stability to the dispersibility because of their low specific gravity and seldom precipitates during the storage. Therefore the flat-shaped resin particles are capable of preventing or restraining the precipitation of the titanium oxide and hence, prevent the non-uniformity of the density (the difference of the density of the ink at the writing tip and at the opposite end of the ink container) from arising inside the ink container tube. Thus, with the use of the present ink composition, the clogging of the ink composition at the writing tip can be prevented even if the ball-point pen is allowed to stand with its writing tip oriented downward. On the other hand, the deterioration of the color development and the concealing power can be prevented eve
Jagannathan Wasu
Sakura Color Products Corporation
Shosho Callie E
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