Aqueous ink composition

An aqueous ink composition is provided which includes an aqueous mixture containing at least a coloring agent, a pigment dispersant, a water-soluble organic solvent and water, and an organic white pigment of an alkylene-bis-melamine derivative represented by the general formula (1): ##STR1## wherein R represents a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms or an alicyclic group; R1, R2, R3 and R4 are the same or different, each representing a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms; R1 and R2, or R3 and R4 may form a heterocyclic group together with a nitrogen atom; and X represents a lower alkylene group having 2 to 3 carbon atoms. The aqueous ink composition is particularly useful for writing instruments of direct ink supply type and of wick type.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to aqueous ink compositions for use in 
writing instruments such as of direct ink supply type or of wick type. 
More particularly, the present invention relates to aqueous ink 
compositions capable of exhibiting their intrinsic deep colors such as 
navy blue, violet, green and brown even on black paper for use in writing 
instruments of direct ink supply type having an ink container tube 
directly connected therewith and/or provided with an ink flow adjusting 
mechanism, through which ink container tube the ink remaining therein is 
visible, and further to aqueous ink compositions free from clogging at a 
writing tip even after prolonged use and excellent in concealing power for 
use in writing instruments of wick type. 
2. Related Arts 
Writing instruments of so-called direct ink supply type have a transparent 
ink container adapted to be directly charged with ink for storage and a 
ball-point tip, felt tip or the like writing tip. Writing instruments of 
wick type have a wick formed of a bundle of fibers with its periphery 
covered with a resin or the like and impregnated with ink, from which the 
ink is supplied to a ball-point tip, felt tip or the like writing tip 
through capillarity. 
It has been a conventional practice to prepare an aqueous ink composition 
for use in such writing instruments by adding a water-soluble organic 
solvent of a polyvalent alcohol or a derivative thereof to an aqueous 
solution containing a water-soluble dye or a water-dispersible pigment. 
However, a conventional aqueous ink composition prepared by adding thereto 
a certain pigment for impartation of a deep color fails to exhibit its 
intrinsic color on black paper because the color of the ink is assimilated 
with the black of the paper. An ink composition of a deep color applied to 
a transparent ink container tube of a refill for the writing instruments 
of direct ink supply type exhibits a deeper color in the container tube 
than that it exhibits on paper. Specifically, an ink composition of navy 
blue, violet, green, brown or the like looks almost black in the container 
tube, making it impossible to visually recognize the color thereof through 
the transparent ink container tube. Attempts have been made to overcome 
the aforesaid drawbacks by adding titanium oxide to an ink composition. 
However, the ink composition containing titanium oxide suffers from 
clogging at the writing tip of a writing instrument, because titanium 
oxide has a high specific gravity and cannot be rendered into fine 
particles. Thus, a satisfactory solution to the problem is yet to be 
found. 
For application to the writing instruments of wick type, there has been 
proposed an aqueous ink composition to which titanium oxide is added to 
impart thereto concealing power. If a writing instrument charged with such 
ink composition is allowed to stand with its writing tip oriented downward 
for a long time, however, titanium oxide having a high specific gravity 
precipitates into the writing tip to cause clogging and thus the 
instrument is disabled for use. To solve this problem, Japanese Unexamined 
Patent Publications No. 63-145380 (1988), No. 63-145382 (1988) and No. 
2-133479 (1990) disclose aqueous pigment ink compositions containing 
titanium oxide along with a hollow resin emulsion called "plastic 
pigment", all of which have a reduced concealing power compared with that 
of an ink composition not containing the hollow resin emulsion. 
It is, therefore, an object of the present invention to provide an aqueous 
ink composition which assures long-tern stability in dispersibility while 
maintaining an excellent concealing power, and is free from clogging at a 
writing tip even after a long-term storage, and the color of which can be 
recognized through a transparent ink container. 
SUMMARY OF THE INVENTION 
As a result of intensive study to solve the foregoing problem, the present 
inventors have found that the problems associated with the conventional 
ink compositions can be solved by providing an aqueous ink composition 
including an organic white pigment of an alkylene-bis-melamine derivative 
represented by the following general formula (1) and an aqueous ink 
mixture containing at least a coloring agent, a pigment dispersant, a 
water-soluble organic solvent and water. 
In accordance with the present invention, there is provided an aqueous ink 
composition comprising an aqueous ink mixture containing a coloring agent, 
a pigment dispersant, a water-soluble organic solvent and water, and an 
organic white pigment of an alkylene-bis-melamine derivative represented 
by the general formula (1): 
##STR2## 
wherein R represents a hydrogen atom, a lower alkyl group having 1 to 4 
carbon atoms or an alicyclic group; R1, R2, R3 and R4 are the same or 
different, each representing a hydrogen atom or a lower alkyl group having 
1 to 4 carbon atoms; R1 and R2, or R3 and R4 may form a heterocyclic group 
together with a nitrogen atom; and X represents a lower alkylene group 
having 2 to 3 carbon atoms. 
The aqueous ink composition is particularly useful for writing instruments 
of direct ink supply type and of wick type.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will hereinafter be described in detail. 
Applicable to the present invention as an organic white pigment is a 
compound of the general formula (1) wherein R is a substituent selected 
from the group consisting of a hydrogen atom, methyl group, ethyl group, 
propyl group and butyl group. R1, R2, R3 and R4 may be the same or 
different and each represent a hydrogen atom, methyl group, ethyl group, 
propyl group or butyl group. R1 and R2, or R3 and R4 may form together 
with a nitrogen atom a heterocyclic group such as a piperidyl group and 
morpholino group. X may be an ethylene group or propylene group. 
The content of the organic white pigment of the general formula (1) is 
preferably 1% by weight to 20% by weight with respect to the total amount 
of the aqueous ink composition for a writing instrument of direct ink 
supply type. If the content thereof is less than 1% by weight, the 
resultant ink composition does not have a satisfactory coloration effect. 
If the content exceeds 20% by weight, the resultant ink composition, which 
may sometimes contain a pseudo-plasticity formation agent when used in a 
writing instrument of direct ink supply type, has an excessively high 
viscosity and, hence, deteriorates writing smoothness. For use in the 
writing instrument of wick type, the pseudo-plasticity formation agent is 
rarely added to an ink composition unlike that for use in the writing 
instrument of direct ink supply type, and therefore, the content of the 
organic white pigment is preferably 1% by weight to 40% by weight, more 
preferably 5% by weight to 25% by weight with respect to the total amount 
of the aqueous ink composition. If the content thereof is less than 1% by 
weight, the resultant ink composition does not exhibit a satisfactory 
concealing power. If the content thereof exceeds 40% by weight, the 
resultant ink composition has an increased viscosity and, hence, 
deteriorates writing smoothness. 
Of the aforesaid organic white pigments represented by the general formula 
(1), a known organic white pigment of ethylene-bis-melamine represented by 
the following formula (2) is preferable, which is available from Hakkol 
Chemical Inc. under a trade name of SHIGENOX-OWP. 
##STR3## 
The pigment for use in the aqueous ink composition of the present invention 
may be any of various kinds of known pigments. Examples of pigments 
include organic pigments such as azo-type, condensed polyazo-type, 
phthalocyanine-type, quinacridone-type, anthraquinone-type, 
dioxazine-type, indigo-type, thioindigo-type, perinone-type and 
perylene-type pigments; inorganic pigments such as carbon black; and 
colored resin emulsions such as prepared by coloring an aqueous dispersion 
of fine polymer particles of an average particle diameter of 0.1 to 1 um 
obtained by emulsion polymerization of one or more resins selected from 
styrene resins, acrylic resins, acrylonitrile resins, 
polymethylmethacrylate resins and polyvinyl chloride resins with a basic 
dye or fluorescent basic dye and/or a fluorescent brightener. These may be 
used either alone or as a mixture. To enhance the concealing power of the 
aqueous ink composition for the writing instruments of wick type, titanium 
oxide may be added as a pigment in combination with the aforesaid organic 
white pigment. 
The amount of the pigment to be used is preferably in the range between 1% 
and 30% by weight, more preferably between 3% and 20% by weight with 
respect to the total amount of the aqueous ink composition. When the 
colored resin emulsion is used, the amount thereof is preferably in the 
range between 10% and 50% by weight with respect to the total amount of 
the aqueous ink composition. If the amount thereof is less than the 
aforesaid range, the ink density on paper is undesirably reduced. On the 
other hand, if the amount thereof is greater than the aforesaid range, the 
resultant ink has an increased viscosity and, hence, deteriorates writing 
smoothness. 
If a pigment or a fluorescent colored resin emulsion is used as a coloring 
agent in the present invention, a pigment dispersant is used. The pigment 
dispersant comprises at least one selected from generally used 
water-soluble resins, surface active agents and the like. Although the 
water-soluble resins maybe selected from natural resins, semisynthetic 
resins or synthetic resins, the synthetic resins are the most preferable 
in terms of fungi- and rot-resistance and viscosity characteristics of the 
ink for writing instruments. Examples of such synthetic resins include 
water-soluble acrylic resins, cross linked acrylic resins, water-soluble 
maleic acid resins, water-soluble styrene resins, water-soluble 
styrene-acrylic resins, water-soluble styrene-maleic acid resins, 
polyvinyl pyrrolidone, polyvinyl alcohol and water-soluble urethane 
resins. In particular, an alkali or ammonia salt or amine of 
.alpha.-methylstyrene-acrylic acid copolymer is preferable as the pigment 
dispersant. The surface-active agent for use in the present invention is 
any one selected from anionic surface-active agents, cationic 
surface-active agents, nonionic surface-active agents and ampholytic 
surface-active agents. The content of such a dispersant is preferably in 
the range between 0.05 parts and 2 parts by weight with respect to 1 part 
by weight of the pigment. Particularly for use in the ink composition for 
the writing instruments of wick type, the content thereof is preferably in 
the range between 0.2 parts and 0.5 parts by weight. If the content is 
less than the aforesaid range, the dispersion stability of the pigment is 
reduced. On the other hand, if the content is greater than the aforesaid 
range, the resultant ink composition has an increased viscosity and, 
hence, deteriorates writing smoothness. 
For use in the writing instruments of direct ink supply, it may be 
desirable that the aqueous ink composition contains a water-soluble dye. 
The water-soluble dye may be any one of dyes conventionally used for an 
aqueous ink, such as acid dyes including C. I. acid red 87, C. I. acid 
orange 56, C. I. acid violet 49 and C. I. acid blue 9; direct dyes 
including C. I. direct yellow 50 and C. I. direct black 19; and basic dyes 
including C. I. basic blue 9, C. I. basic red 1 and C. I. basic yellow 35. 
These may be used either alone or in combination. The amount of such a 
water-soluble dye to be used is preferably in the range between 0.1% and 
30% by weight, more preferably between 1% and 20% by weight with respect 
to the total amount of the aqueous ink composition. 
Examples of water-soluble organic solvents include polyvalent alcohols such 
as ethylene glycol, diethylene glycol, propylene glycol and glycerin; 
glycol ethers such as propylene glycol monomethyl ether; and glycol ether 
esters such as propylene glycol monomethyl ether acetate. These may be 
used either alone or as a mixture. The content of such water-soluble 
organic solvent is preferably in the range between 1% and 40% by weight 
with respect to the total amount of the ink composition. If the content 
thereof is less than the aforesaid range, the resultant ink dries too fast 
at a writing tip, leading to an unclear line drawn on paper. On the other 
hand, if the content is greater than the aforesaid range, the resultant 
ink dries too slow on paper. 
As required, the ink composition may contain an appropriate pH adjuster, 
lubricant, rust-preventive agent, antiseptic agent, antifungal agent and 
the like. 
For use in the writing instruments of direct ink supply type, it is 
desirable that the ink composition may contain a pseudo-plasticity 
formation agent, which is not particularly an essential ingredient, 
because the writing instrument of this type comprises an ink container 
tube adapted to be directly charged with ink. Usable as the 
pseudo-plasticity formation agent are natural polysaccharides and 
semisynthetic cellulosic polymers selected from generally used 
water-soluble polymers. More specifically, exemplary natural 
polysaccharides include guar gum, locust bean gum, weran gum, rhamzan gum, 
xanthan gum and the like, which have polymeric structure such as obtained 
by polymerization of monosaccharides such as glucose, galactose, rhamnose, 
and a glucuronic acid salt. Among these, weran gum and xanthan gum are 
particularly preferable. 
Examples of specific pH adjusters for use in the present invention include 
caustic soda, sodium carbonate, alkanolamine and ammonia. The pH of the 
ink composition is preferably in the range between 8 and 10 in terms of 
the solubility of the dispersant or the dispersibility of the pigment, but 
is not particularly limited to this range. 
Usable as the lubricant are alkali and amine salts of N-acyl amino 
acid-based, ether carboxylic acid-based and N-acyl tauric acid-based 
active agents, alkali and alkanolamine salts of fatty acids, and 
phosphate-based surface-active agent. 
Examples of specific rust-preventive agents usable in the present invention 
include benzotriazole, derivatives thereof and dicyclohexylammonium 
nitrate. Examples of specific antiseptic agents are potassium sorbate, 
sodium benzoate, pentachlorephenyl sodium, sodium dihydroacetate and 
1,2-benzisothiazoline-3-on. Among these, 1,2-benzisothiazoline-3-on is 
particularly preferable. 
For the application to the writing instrument of direct ink supply type, 
exemplary forms of an ink container particularly appreciating the effects 
of the ink composition of the present invention are as follows: 
(1) An ink container to be installed in the main body of the writing 
instrument comprising a transparent ink container tube of refill type made 
of a plastic material or the like which is adapted to be directly charged 
with an ink imparted with pseudo-plasticity and is clogged with a 
beck-flow preventing material at the tail end thereof, and a pen tip 
attached at the leading end of the ink container tube and having a 
ball-point tip formed of German silver or stainless steel as fitted 
therein; 
(2) An ink container comprising a transparent ink container pipe made of a 
plastic material or the like which is adapted to be directly charged with 
ink, a ink flow adjusting mechanism such as of bellows type or valve type 
fittingly attached to the ink container pipe, and a writing tip such as a 
fiber-bundle tip, nib or hall-point tip made of German silver or stainless 
steel which is fittingly attached at the leading end of the ink flow 
adjusting mechanism; 
(3) An ink container comprising a transparent ink container pipe made of a 
plastic material or the like which is adapted to be directly charged with 
ink, and a pen tip attached at the leading end of the ink container pipe 
and having a writing tip such as a ball-point tip fitted therein. The ink 
container is adapted to adjust the ink flow by way of a ball fitted in the 
ball-point tip by pressure applied to the interior of the ink container 
pipe when a cap of the writing instrument is fitted around the main body 
thereof; and 
(4) An ink container having the same structure as the aforesaid ink 
container (1) or (2) in which the interior of the ink container tube or 
ink container pipe is sealed off from the exterior, and the beck-flow 
preventing material is adapted to move toward the pen tip according to 
consumption of the ink. The beck-flow preventing material is prepared by 
gelating a base material such as polybutene with a gelling agent or the 
like. Alternatively, a rubber or an elastomer presenting a similar effect 
may be used as the base material. 
The excellent concealing power of the aqueous ink composition of the 
present invention and its coloration ability on black paper are 
attributable to crystalline particles of the organic white pigment 
contained therein, unlike the case where a resin emulsion is employed as a 
coloring agent. This is because the crystalline particles irregularly 
reflect light rays imparted with a color by a deep color pigment contained 
in the ink composition on the paper. Further, where the aqueous ink 
composition is charged in a transparent ink container tube to be installed 
in the writing instrument of direct ink supply type, the intrinsic color 
of the ink composition remaining in the ink container tube can be visually 
observed through the ink container. This is based on the same principle as 
the above, i.e., the light of the intrinsic color of the ink composition 
is irregularly reflected by the organic white pigment. Further, the 
aqueous ink composition ensures long-term stability because the organic 
white pigment has a specific gravity (1.4) lower than that of titanium 
oxide (3.9) and hence is less liable to precipitate. 
Accordingly, even if a dye is used as a coloring agent in combination with 
the organic white pigment, the organic white pigment can be properly 
dispersed. In particular, the effectiveness of the organic white pigment 
is remarkable where the aqueous ink composition contains a dye or 
fluorescent colored resin emulsion as a coloring agent and, hence, 
requires high dispersibility. Further, the combinational use of the 
organic white pigment and fluorescent colored resin emulsion enhances a 
fluorescent coloration effect to produce a vivid fluorescent color on 
black paper. In addition, the enhanced fluorescent coloration effect 
allows for obvious color recognition of the ink composition in the ink 
container 
EXAMPLES 
The present invention will be further detailed byway of examples thereof. 
Ink compositions in the following Examples 1 to 4 are adapted for use in a 
ball-pointpen which comprises an ink container pipe formed of 
polypropylene or the like and adapted to be directly charged with ink, a 
ball-point tip made of German silver or stainless steel, and an ink flow 
adjusting mechanism of bellows type provided at the tail end of the 
ball-point tip. Ink compositions in the following Examples 5 to 8 are 
adapted for use in a refill-type ball-point pen which comprises an ink 
container having an ink container tube of polypropylene or the like 
adapted to be directly charged with an ink (same as an oil ink ball-point 
pen) and clogged with a back-flow preventing material at the tail end 
thereof, and a pen tip attached at the leading end of the ink container 
tube and having a ball-point tip formed of German silver or stainless 
steel as fitted therein. The ink compositions of Examples 1 to 8 can be 
applied to writing instruments of direct ink supply type which are 
preferably used as an aqueous ink ball-point pen. 
EXAMPLE 1 
______________________________________ 
Copper phthalocyanine blue 
10.0 parts 
Ethylene-bis-melamine 1.0 part 
Sodium salt of styrene-maleic acid copolymer 
3.0 parts 
(dispereant) 
Glycerin 5.0 parts 
Propylene glycol 20.0 parts 
Nonionic active agent 0.5 parts 
(NOIGEN P available from Daiichi Irxiustrial 
Chemical, Inc.) 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I Japan 
Co., Ltd. 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Water 59.5 parts 
______________________________________ 
Copper phthalocyanine blue, ethylene-bis-melamine, sodium salt of 
styrene-maleic acid copolymer and water were first mixed together for 
dispersion for one hour by means of a sand mill. The remaining ingredients 
were then added to the dispersion and dissolved therein by stirring. After 
adjusted to pH 8 by caustic soda, the resultant dispersion was filtered to 
obtain a blue ink. 
EXAMPLE 2 
______________________________________ 
Copper phthalocyanine green 
10.0 parts 
Ethylene-bis-melamine 3.0 parts 
Sodium salt of styrene-acrylic acid copolymer 
3.0 parts 
(dispersant) 
Glycerin 10.0 parts 
Propylene glycol 15.0 parts 
Nonionic active agent 0.3 parts 
(NOIGEN EA112 available from Daiichi 
Industrial Chemical, Inc.) 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Water 57.7 parts 
______________________________________ 
Copper phthalocyanine green, ethylene-bis-melamine, sodium salt of 
styrene-acrylic acid copolymer and water were first mixed together for 
dispersion for one hour by means of a sand mill. The remaining ingredients 
were then added to the dispersion and dissolved therein by stirring. After 
adjusted to pH 8 by caustic soda, the resultant dispersion was filtered to 
obtain a green ink. 
EXAMPLE 3 
______________________________________ 
Dioxazine violet 5.0 parts 
Ethylene-bis-melamine 1.0 part 
Sodium salt of styrene-acrylic acid copolymer 
1.0 part 
(dispersant) 
Glycerin 5.0 parts 
Propylene glycol 20.0 parts 
Anionic active agent 0.3 parts 
(ECTD-3NEX available from Japan Surfactant 
Co., Ltd.) 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Water 66.7 parts 
______________________________________ 
Dioxazine violet, ethylene-bis-melamine, sodium salt of styrene-acrylic 
acid copolymer and water were first mixed together for dispersion for one 
hour by means of a sand mill. The remaining ingredients were then added to 
the dispersion and dissolved therein by stirring. After adjusted to pH 8 
by caustic soda, the resultant dispersion was filtered to obtain a violet 
ink. 
EXAMPLE 4 
______________________________________ 
Water blue #9 (food color blue No. 1) 
6.0 parts 
Ethylene-bis-melamine 10.0 parts 
Sodium salt of styrene-maleic acid copolymer 
2.0 parts 
(dispersant) 
Glycerin 5.0 parts 
Propylene glycol 15.0 parts 
Anionic active agent 0.3 parts 
(ECTD-3NEX available from Japan Surfactant 
Co., Ltd.) 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Water 60.7 parts 
______________________________________ 
Ethylene-bis-melamine, sodium salt of styrene-maleic acid copolymer and 
water were first mixed together for dispersion for one hour by means of a 
sand mill. The remaining ingredients were then added to the dispersion and 
dissolved therein by stirring. After adjusted to pH 8 by caustic soda, the 
resultant dispersion was filtered to obtain a blue ink. 
EXAMPLE 5 
______________________________________ 
Copper phthalocyanine blue 
4.0 parts 
Ethylene-bis-melamine 1.0 part 
Sodium salt of styrene-acrylic acid copolymer 
1.0 part 
(dispersant) 
Crosslinked acrylic resin 
4.0 parts 
(3% aqueous solution of CARBOPOL (available 
from B. F. Goodrich, Inc.) neutralized with 
equivalent NaOH) 
Propylene glycol 10.0 parts 
Glycerin 5.0 parts 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Xanthan gum 0.3 parts 
(pseudo-plasticity formation agent, KELZAN 
available from Sansho Co., Ltd.) 
Water 73.7 parts 
______________________________________ 
Xanthan gum was added little by little to 30 parts of water to avoid 
formation of undissolved lump of xanthan gum and completely dissolved 
therein by stirring. A mixture of copper phthalocyanine blue, 
ethylene-bis-melamine, sodium salt of styrene-acrylic acid copolymer and 
43.7 parts of water was stirred for dispersion for one hour by means of a 
sand mill. The remaining ingredients were added to the dispersion and 
dissolved therein by stirring. Then, the dispersion was added to the 
xanthane gum solution, and dispersed by stirring for one hour. After 
adjusted to pH 8by caustic soda, the resultant dispersion was filtered to 
obtain a blue ink. 
EXAMPLE 6 
______________________________________ 
Copper phthalocyanine green 
4.0 parts 
Ethylene-bis-melamine 2.5 parts 
Sodium salt of styrene-acrylic acid copolymer 
1.0 part 
(dispersant) 
Propylene glycol 10.0 parts 
Glycerin 5.0 parts 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Xanthan gum 0.3 parts 
(pseudo-plasticity formation agent, KELZAN 
available from Sansho Co., Ltd) 
Water 76.2 parts 
______________________________________ 
Xanthan gum was added little by little to 30 parts of water to avoid 
formation of undissolved lump of xanthan gum and completely dissolved 
therein by stirring. A mixture of copper phthalocyanine green, 
ethylene-bis-melamine, sodium salt of styrene-acrylic acid copolymer and 
46.2 parts of water was stirred for dispersion for one hour by means of a 
sand mill. The remaining ingredients were added to the dispersion and 
dissolved therein by stirring. Then, the dispersion was added to the 
xanthane gum solution, and dispersed by stirring for one hour. After 
adjusted to pH 8 by caustic soda, the resultant dispersion was filtered to 
obtain a green ink. 
EXAMPLE 7 
______________________________________ 
Quinacridone red 4.0 parts 
Ethylene-bis-melamine 2.0 parts 
Sodium salt of styrene-acrylic acid copolymer 
1.0 part 
(dispersant) 
Glycerin 5.0 parts 
Propylene glycol 10.0 parts 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Potassium oleate 0.1 parts 
Weran gum 0.3 parts 
(pseudo-plasticity formation agent available 
from Sanhso Co., Ltd.) 
Water 76.6 parts 
______________________________________ 
Weran gum was added little by little to 30 parts of water to avoid 
formation of undissolved lump of weran gum and completely dissolved 
therein by stirring. A mixture of quinacridone red, ethylene-bis-melamine, 
sodium salt of styrene-acrylic acid copolymer and 46.6 parts of water was 
stirred for dispersion for one hour by means of a sand mill. The remaining 
ingredients were added to the dispersion and dissolved therein by 
stirring. Then, the dispersion was added to the weran gum solution, and 
dispersed by stirring for one hour. After adjusted to pH 8 by caustic 
soda, the resultant dispersion was filtered to obtain a pink ink. 
EXAMPLE 8 
______________________________________ 
Dioxazine violet 3.0 parts 
Ethylene-bis-melamine 5.0 parts 
Sodium salt of styrene-acrylic acid copolymer 
2.0 parts 
(dispersant) 
Propylene glycol 10.0 parts 
Glycerin 5.0 parts 
Antiseptic agent 0.5 parts 
(PROXEL XL-2 available from I. C. I. Japan 
Co., Ltd.) 
Benzotriazole (rust-preventive agent) 
0.5 parts 
Xanthan gum 0.3 parts 
(pseudo-plasticity formation agent, CHELZAN 
available from Sansho Co., Ltd.) 
Water 73.7 parts 
______________________________________ 
Xanthan gum was added little by little to 30 parts of water to avoid 
formation of undissolved lump of Xanthan gum and completely dissolved 
therein by stirring. A mixture of dioxazine violet, ethylene-bis-melamine, 
sodium salt of styrene-acrylic acid copolymer and 43.7 parts of water was 
stirred for dispersion for one hour by means of a sand mill. The remaining 
ingredients were added to the dispersion and dissolved therein by 
stirring. The dispersion was added to the xanthane gum solution, and 
dispersed by stirring for one hour. After adjusted to pH 8 by caustic 
soda, the resultant dispersion was filtered to obtain a violet ink. 
COMATIVE EXAMPLE 1 
A blue ink was prepared in substantially the same manner as described in 
Example 1, except that ethylene-bis-melamine was replaced with the 
equivalent amount of titanium oxide. 
COMATIVE EXAMPLE 2 
A green ink was prepared in substantially the same manner as described in 
Example 2, except that ethylene-bis-melamine was replaced with the 
equivalent amount of titanium oxide. 
COMATIVE EXAMPLE 3 
A blue ink was prepared in substantially the same manner as described in 
Example 1, except that ethylene-bis-melamine was replaced with the 
equivalent amount of ion-exchanged water. 
COMATIVE EXAMPLE 4 
A green ink was prepared in substantially the same manner as described in 
Example 2, except that ethylene-bis-melamine was replaced with the 
equivalent amount of ion-exchanged water. 
COMATIVE EXAMPLE 5 
A blue ink was prepared in substantially the same manner as described in 
Example 5, except that ethylene-bis-melamine was replaced with the 
equivalent amount of titanium oxide. 
COMATIVE EXAMPLE 6 
A green ink was prepared in substantially the same manner as described in 
Example 6, except that ethylene-bis-melamine was replaced with the 
equivalent amount of titanium oxide. 
COMATIVE EXAMPLE 7 
A blue ink was prepared in substantially the same manner as described in 
Example 5, except that ethylene-bis-melamine was replaced with the 
equivalent amount of ion-exchanged water. 
COMATIVE EXAMPLE 8 
A green ink was prepared in substantially the same manner as described in 
Example 6, except that ethylene-bis-melamine was replaced with the 
equivalent amount of ion-exchanged water. 
Each of the aqueous ink compositions prepared in Examples 1 to 4 and 
Comparative Examples 1 to 4 was directly filled in an ink container pipe 
made of polypropyrene. Then, a pen tip including a ball-point tip made of 
German silver or stainless steel and an ultra hard ball having a diameter 
of 0.6 mm was attached to the ink container pipe. The pen tip was provided 
with an ink flow adjusting device of bellows type fitted at the tail end 
of thereof. Thus, an aqueous ink ball-point pen (writing instrument of 
direct ink supply type) was prepared. 
Each of the aqueous ink compositions prepared in Examples 5 to 8 and 
Comparative Examples 5 to 8 was directly filled in a refill including a 
polypropyrene container tube, and a pen tip and a ball-point tip pressedly 
fitted therein. After clogged with a back-flow preventing material at the 
tail end thereof, the refill was centrifuged for deaeration. Thus, an 
aqueous ink ball-point pen of refill type (writing instrument of direct 
ink supply type) was prepared. 
These aqueous ink ball-point pens (writing instrument of direct ink supply 
type) were subject to the following tests. Visual inspections were carried 
out first to determine if characters written on black paper with the 
respective ball-point pens could be visually recognized under natural 
light (indoor in the daytime), and then to determine if the colors of the 
ink compositions contained in the respective ball-point pens could be 
recognized under natural light (indoor in the daytime). The ball-point 
pens respectively containing the aqueous ink compositions prepared in 
Examples 1 to 8 and Comparative Examples 1 to 8 with caps being attached 
thereto were allowed to stand for one month in a thermostatic chamber at a 
temperature of 50.degree. C. with the pen tips thereof oriented downward. 
Thereafter, using a spiral-type writing tester, lines of 100 m were drawn 
with the respective ball-point pens under conditions of writing 
angle=65.degree.C., load=100 g, and writing speed=7 cm/sec to observe a 
change in the ink flow before and after the ball-point pens were kept in 
the thermostatic chamber. The test results are shown in Table 1. 
TABLE 1 
______________________________________ 
Visual Change in writing 
color characteristics before 
Recognizability 
of ink and after storage in 50.degree. C. 
Ink on black paper 
container 
thermostat for 1 month 
______________________________________ 
Ex. 1 Recognizable 
Blue No change, excellent 
Ex. 2 Recognizable 
Green No change, excellent 
Ex. 3 Recognizable 
Violet No change, excellent 
Ex. 4 Recognizable 
Blue No change, excellent 
Ex. 5 Recognizable 
Blue No change, excellent 
Ex. 6 Recognizable 
Green No change, excellent 
Ex. 7 Recognizable 
Pink No change, excellent 
Ex. 8 Recognizable 
Violet No change, excellent 
Comp. Recognizable 
Blue Disabled after storage 
Ex. 1 in 50.degree. C. thermostat 
Comp. Recognizable 
Green Dinabled after storage 
Ex. 2 in 50.degree. C. thermostat 
Comp. Unrecognizable 
Black No change, excellent 
Ex. 3 
Comp. Unrecognizable 
Black No change, excellent 
Ex. 4 
Comp. Recognizable 
Blue Disabled after storage 
Ex. 5 in 50.degree. C. thermostat 
Comp. Recognizable 
Green Disabled after storage 
Ex. 6 in 50.degree. C. thermostat 
Comp. Unrecognizable 
Black No change, excellent 
Ex. 7 
Comp. Unrecognizable 
Black No change, excellent 
Ex. 8 
______________________________________ 
As for recognizibility on black paper shown in Table 1, "recognizable" 
means that the ink on the black paper exhibited the intrinsic color 
thereof whereby the characters written on the black paper could be 
visually recognized. On the other hand, "unrecognizable" means that the 
intrinsic color of the ink was assimilated with the black of the paper 
whereby the characters written on the black paper could not be visually 
recognized. As for visual color shown in Table 1, "black" means that the 
intrinsic color of the ink could not be visually recognized through the 
ink container, while a color other than black means that the intrinsic 
color of the ink could be visually recognized through the ink container. 
As for change in writing characteristics shown in Table 1, "no change, 
excellent" means that the ink flow was substantially the same before and 
after the bell-point pen was stored in the thermostat chamber at a 
temperature of 50.degree. C. for one month, whereas "disabled after 
storage in 50.degree. C. thermostatic" means that the ball-point pen did 
not exhibit the normal writing characteristics after the storage. 
As can be understood from the foregoing, the aqueous ink composition 
according to the present invention can exhibit the intrinsic color thereof 
even on black paper, thereby allowing for obvious recognition of the 
intrinsic color thereof. Further, the present invention allows a deep 
color ink composition to be visually recognized through the transparent 
ink container tube or ink container pipe (refill-type) of the ink 
container. Yet further, the ink composition of the present invention 
advantageously assures a long-term stability and is free from 
deterioration in writing characteristics. 
Next, aqueous ink compositions for use in a writing instrument of wick type 
were examined. The writing instrument comprised a wick formed of a bundle 
of fibers with its periphery covered with a resin and impregnated with an 
ink composition, from which the ink composition was supplied to a pen tip 
having a hall-point tip or a felt tip through capillarity. Such aqueous 
ink compositions were prepared in Examples 11 to 15. 
EXAMPLE 11 
______________________________________ 
Copper phthalocyanine blue 
6.0 parts 
Titanium oxide 6.0 parts 
Ethylene-bis-melamine 8.0 parts 
Dispersent resin 18.0 parts 
(JOHNCRYL J-62 available from Johnson, Inc.) 
Propylene glycol 3.0 parts 
Anionic active agent 1.0 part 
(NEOCOL YSK available from Daiichi Industrial 
Chemical, Inc.) 
Antiseptic agent 0.1 parts 
(PROXEL XL-2 available from I.C.I. Japan 
Co., Ltd.) 
Antifungal agent 0.2 parts 
(COATIDE H available from Takeda Chemical 
Industries, Ltd.) 
Water 57.7 parts 
______________________________________ 
Copper phthalocyanine blue, titanium oxide and ethylene-bis-melamine were 
dispersed in a mixture consisting of 6 parts of the dispersant resin and 
18 parts of water for one hour by means of a sand mill. Then, the 
remaining ingredients were added to the dispersion and dissolved therein 
by stirring. A blue ink was obtained after the resultant dispersion was 
adjusted to pH 8 by an ammonia solution. 
EXAMPLE 12 
______________________________________ 
Copper phthalocyanine green 
5.0 parts 
Titanium oxide 8.0 parts 
Ethylene-bis-melamine 8.0 parts 
Dispersant resin 18.0 parts 
(JOHNCRYL J-62 available from Johnson, Inc.) 
Propylene glycol 3.0 parts 
Anionic active agent 1.0 part 
(NEOCOL YSK available frm Daiichi Industrial 
Chemical, Inc.) 
Antiseptic agent 0.1 parts 
(PROXEL XL-2 available from I.C.I. Japan 
Co., Ltd.) 
Antifungal agent 0.2 parts 
(COATIDE B available from Takeda Chemical 
Industries, Ltd.) 
Water 56.7 parts 
______________________________________ 
Copper phthalocyanine green, titanium oxide and ethylene-bis-melamine were 
dispersed in a mixture consisting of 6 parts of the dispersant resin and 
18 parts of water for one hour by means of a sand mill. Then, the 
remaining ingredients were added to the dispersion and dissolved therein 
by stirring. A green ink was obtained after the resultant dispersion was 
adjusted to pH 9 by an ammonia solution. 
EXAMPLE 13 
______________________________________ 
Quinacridone red 7.0 parts 
Titanium oxide 4.0 parts 
Ethylene-bis-melamine 6.0 parts 
Dispersant resin 18.0 parts 
(JOHNCRYL J-62 available frcm Johnson, Inc.) 
Propylene glycol 3.0 parts 
Anionic active agent 1.0 part 
(NEOCOL YSK available from Daiichi Industrial 
Chemical, Inc.) 
Antiseptic agent 0.1 parts 
(PROXEL XL-2 available from I.C.I. Japan 
Co., Ltd.) 
Antifungal agent 0.2 parts 
(COATIDE H available from Takeda Chemical 
Industries, Ltd.) 
Water 60.7 parts 
______________________________________ 
Quinacridone red, titanium oxide and ethylene-bis-melamine were dispersed 
in a mixture consisting of 6 parts of the dispersant resin and 18 parts of 
water for one hour by means of a sand mill. The mining ingredients were 
then added to the dispersion and dissolved therein by stirring. A pink ink 
was obtained after the resultant dispersion was adjusted to pH 10 by an 
ammonia solution. 
EXAMPLE 14 
______________________________________ 
Dioxazine violet 4.0 parts 
Titanium oxide 7.0 parts 
Ethylene-bis-melamine 10.0 parts 
Dispersant resin 24.0 parts 
(JOHNCRYL J-62 available from Johnson, Inc.) 
Propylene glycol 3.0 parts 
Anionic active agent 1.0 part 
(NEOCOL YSK available from Daiichi Industrial 
Chemical, Inc.) 
Antiseptic agent 0.1 parts 
(PROXEL XL-2 available from I.C.I. Japan 
Co., Ltd.) 
Antifungal agent 0.2 parts 
(COATIDE B available frcm Takeda Chemical 
Industries, Ltd.) 
Water 50.7 parts 
______________________________________ 
Dioxazine violet, titanium oxide and ethylene-bis-melamine were dispersed 
in a mixture consisting of 6 parts of the dispersant resin and 18 parts of 
water for one hour by means of a sand mill. The remaining ingredients were 
then added to the dispersion and dissolved therein by stirring. A violet 
ink was obtained after the resultant dispersion was adjusted to pH 8 by an 
ammonia solution. 
EXAMPLE 15 
______________________________________ 
Titanium oxide 10.0 parts 
Ethylene-bis-melamine 20.0 parts 
Dispersant resin 18.0 parts 
(JOHNCRYL J-62 available from Johnson, Inc.) 
Propylene glycol 3.0 parts 
Anionic active agent 1.0 part 
(NEOCOL YSK available from Daiichi Industrial 
Chemical, Inc.) 
Antiseptic agent 0.1 parts 
(PROXEL XL-2 available from I.C.I. Japan 
Co., Ltd.) 
Antifungal agent 0.2 parts 
(COATIDE H available from Takeda Chemical 
Industries, Ltd.) 
Water 50.7 parts 
______________________________________ 
Titanium oxide and ethylene-bis-melamine were dispersed in a mixture 
consisting of 6 parts of the dispersant resin and 18 parts of water for 
one hour by means of a sand mill. The remaining ingredients were then 
added to the dispersion and dissolved therein by stirring. A white ink was 
obtained after the resultant dispersion was adjusted to pH 9 by an ammonia 
solution. 
COMATIVE EXAMPLE 11 
A blue ink was prepared in substantially the same manner as described in 
Example 11, except that ethylene-bis-melamine was replaced with the 
equivalent amount of hollow resin particles (GRANDOIL PP2000S available 
from Dainippon Ink & Chemicals, Inc.). 
COMATIVE EXAMPLE 12 
A green ink was prepared in substantially the same manner as described in 
Example 12, except that ethylene-bis-melamine was replaced with the 
equivalent amount of hollow resin particles (GRANDOIL PP2000S available 
from Dainippon Ink & Chemicals, Inc.). 
COMATIVE EXAMPLE 13 
A pink ink was prepared in substantially the same manner as described in 
Example 13, except that ethylene-bis-melamine was replaced with the 
equivalent amount of hollow resin particles (GRANDOLL PP2000S available 
from Dainippon Ink & Chemicals, Inc.). 
The aqueous ink compositions prepared in Examples 11 to 15 and Comparative 
Examples 11 to 13 were each impregnated in the wick of the wick-type 
writing instrument to be subjected to the following tests. The concealing 
power of each ink composition was evaluated by visually inspecting lines 
drawn on art paper having black lines printed thereon with a writing 
instrument containing the ink composition. An ink composition completely 
concealing the black lines was evaluated as "acceptable", while an ink 
composition which did not completely conceal the black lines was evaluated 
as "unacceptable". For evaluation of the long-term stability of the ink 
compositions, the writing instruments were allowed to stand with the pen 
tips thereof oriented upward or downward at the temperature of 50.degree. 
C. for one month. The ink density on paper was observed before and after 
the one-month storage at a temperature of 50.degree. C., and the 
difference between the initial density and that after the one-month 
storage was examined by comparison. An ink composition which did not 
present a noticeable difference was evaluated as "no change", whereas an 
ink composition which presented a noticeable difference was evaluated as 
"some change". The results are shown in Table 2. 
TABLE 2 
______________________________________ 
Change in ink density before and 
Concealing 
after one-month storage at 50.degree. C. 
Ink Power Pen tip upward 
Pen tip downward 
______________________________________ 
Ex. 11 Acceptable No change No change 
Ex. 12 Acceptable No change No change 
Ex. 13 Acceptable No change No change 
Ex. 14 Acceptable No change No change 
Ex. 15 Acceptable No change No change 
Comp. Ex. 11 
Unacceptable 
Some change Some change 
Comp. Ex. 12 
Unacceptable 
Some change Some change 
Comp. Ex. 13 
Unacceptable 
Some change Some change 
______________________________________ 
As is apparent from Table 2, the aqueous ink compositions of the present 
invention for use in the wick-type writing instruments are also excellent 
in concealing power and long-term, stability. 
For application to the writing instruments of direct ink supply type, the 
content of the organic white pigment is preferably 1% by weight to 20% by 
weight with respect to the total amount of the ink composition. If the 
content is less than 1% by weight, the resultant ink composition does not 
exhibit a satisfactory coloration effect. On the other hand, if the 
content exceeds 20% by weight, the resultant ink composition has an 
excessive viscosity, resulting in deterioration in writing smoothness. 
This is because ink compositions for use in the writing instruments of 
direct ink supply type may contain a pseudo-plasticity formation agent. 
Unlike the ink compositions for the writing instruments of direct ink 
supply type, an ink composition for use in the wick-type writing 
instrument rarely includes the pseudo-plasticity formation agent and, 
therefore, the content thereof is preferably 1% by weight to 40% by 
weight, more preferably 5% by weight to 25% by weight with respect to the 
total amount of the ink composition. If the content is less than 1% by 
weight, the resultant ink composition does not present a satisfactory 
concealing power. If the content exceeds 40% by weight, the resultant ink 
composition has an increased viscosity, resulting in deterioration in 
writing smoothness. 
Though the aforesaid examples employ the organic white pigment of 
ethylene-bis-melamine which is one of exemplary alkylene-bis-melamine 
derivatives represented by the general formula (1), the following 
compounds may exhibit substantially the same effects as in the aforesaid 
examples: a compound wherein R is replaced with a lower alkyl group having 
1 to 4 carbon atoms or an alicyclic group, instead of a hydrogen atom; a 
compound wherein R1, R2, R3 and R4 are the same or different, each 
representing a hydrogen atom or a lower alkyl group having 1 to 4 carbon 
atoms; an alkylene-bis-melamine derivative wherein R1 and R2, or R3 and R4 
fore a heterocyclic group together with a nitrogen atom; and a 
propylene-bis-melamine wherein X represents a lower alkylene group having 
3 carbon atoms and the derivatives thereof.