Recording liquid

A recording liquid comprises C.I.Acid Red 8 as a recording agent for forming an image and a liquid medium comprising at least PA0 (a) a member selected from the group consisting of polyethylene glycol, polyethylene glycol mono methylether and a mixture thereof, PA0 (b) a member selected from the group consisting of diethylene glycol, sulfolane and a mixture thereof, PA0 (c) a member selected from the group consisting of N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and a mixture thereof, and PA0 (d) water.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a new recording liquid and, more particularly, to 
a recording liquid suitable for a recording system in which droplets of 
the recording liquid are jetted from a small jet (jet orifice) provided at 
a recording head and the image is printed on a surface of a recording 
material. 
2. Description of the prior art 
Writing materials (such as a fountain pen, felt pen and the like) which 
make records on recording materials such as paper and the like usually use 
an ink composed of various dyes dissolved in water or organic solvents. 
There are also known compositions composed of various dyes into water or 
other organic solvents and the like used in the ink jet recording system 
which records by jetting liquid within the recording head from the jet 
orifice with vibration by a piezo-oscillator or with electrostatic 
attractive force and the like by high voltage apply. But, compared with 
ink for writing materials such as a popular fountain pen, felt pen and the 
like, the recording liqiud for the ink jet requires more strict conditions 
as to many characteristics. 
Such the ink jet recording method is that the recording was carried out by 
jetting droplets of the recording liquid, the so-called ink, and adhering 
this jetting ink to a record-receiving member. The recording liquid is 
comprised of a recording agent (using dye or pigment) and a liquid medium 
(water, various organic solvents, or a mixture thereof) capable of solving 
or dispersing the recording agent, as basic components, and if desired, 
various additive agents are added. 
In such a recording method, there are various systems depending methods for 
generating droplets and methods for controlling the jet direction. An 
example of system is shown in FIG. 1. 
FIG. 1 shows an apparatus in which a recording signal is applied to a 
recording head part containing the piezo-oscillator and droplets of the 
recording liquid are generated to effect recording in response to the 
signal. In FIG. 1, the recording head is designated by 1, the 
piezo-oscillator by 2a an oscillating plate by 2b, an inlet of ink by 3, a 
liquid chamber in the head by 4 and a liquid jetting portion (jetting 
orifice) by 5. Recording liquid 7 is introduced into the liquid chamber 4 
from a storage tank 6 through a supply tube 8. In case of necessity, 
intermediate processing means 9 such as pump or filter may be provided in 
the supply tube 8. Recording signal S is converted into a pulse by signal 
processing means 10 such as a pulse converter and then applied to the 
piezo-oscillator 2a. Change in pressure on the recording liquid within the 
liquid chamber 4 caused by the signal results in droplets 11 of the 
recording liquid 7 being jetted through the jet orifice 5. Thus, an image 
is printed on the surface of the record-receiving member 12 with the 
droplets. 
There are known various apparatuses other than the above mentioned 
apparatus. For example, FIG. 2, shows a modified embodiment of that in 
FIG. 1. In the modified embodiment, a liquid chamber 4 is a nozzle form, 
and around provided with a cylindrical piezo-oscillator (in this 
apparatus, a mechanism generating droplets is essentially the same as that 
(shown in FIG. 1). There are known an apparatus in which charged droplets 
are continuously generated to use a portion of the droplets for recording, 
another apparatus in which heat energy corresponding to a recording signal 
is applied to a recording liquid in a chamber of a recording head to 
generate droplets by the heat energy, and the like. 
An embodiment is shown in FIGS. 3-a, 3-b and 4. 
A head 13 is manufactured by jointing a plate such as glass, cermics, 
plastics, and the like, having a groove 14 to a head-generating head 15 
used for a heat-sensitive recording process (A thin film head is shown in 
the Figs., however a heat-generating head is not restricted to this 
construction). The heat-generating head 15 is constituted of a protective 
film 16 made of silicon oxide and the like, aluminum electrodes 17-1 and 
17-2, a resistive heater layer 18 made of nichrome and the like, a 
heat-accumulating layer 19, and a substrate 20 having an excellent 
heat-releasing property such as alumina and the like. 
An ink 21 arrives at the jet orifice, so that a meniscus 23 is formed by a 
pressure P. 
When an electric signal is applied to electrodes 17-1 and 17-2, heat is 
rapidly generated at the region indicated by "n" in the heat generating 
head 15, and a bubble is formed in ink 21 contacting the "n" region. 
The pressure due to the formation of the bubble projects the meniscus 23 
and a recording droplet of ink 21 is ejected as a droplet 24 through an 
orifice 22 and projected to the record-receiving member 25. 
FIG. 4 is a schematic diagram of multi-head made of a plurality of heads as 
shown in FIG. 3-a. The multi-head is fabricated by adhering a glass plate 
27 provided with multi-groove 26 to the heat generating head 28 as 
illustrated in FIG. 3-a. 
FIG. 3-a is a schematic cross sectional view of the head 13 taken along the 
ink flow path while FIG. 3-b is a schematic cross sectional view of FIG. 
3-a taken along the A-B line. 
In the past, there are known the recording liquid in which various dyes and 
pigments were dissolved and dispersed in aqueous or nonaqueous solvent, 
for example, as shown in Japanese Patent Publication Nos. 8361/1975, 
40484/1976, 13126/1977, and 13127/1977, and Japanese Patent Laid Open No. 
95008/1975. Desirable conditions for such recording liquid are shown as 
follow. 
(1) Having a property of liquid (viscosity, surface tension, conductivity 
and the like) matched to jet conditions (actuation voltage of 
piezoelectric device, actuation frequency, shape and quality of material 
of the orifice, diameter of the orifice and the like). 
(2) Not clogging the minute jet orifice and hole of a capillary because 
long time storge property is very good. 
(3) Fixation to the record receiving members (paper, film and the like) can 
proceed rapidly, circumference of a dot is smooth, and the blur is little. 
(4) A color tone of the printed image is sharp and the density is high. 
(5) Water resisting property and light fastness of the printed image are 
excellent. 
(6) Not corroding materials for handling the recording liquid (vessel, 
joint tube, seal materials and the like). 
(7) Safety to a bad smell, toxicity, inflammability and the like is 
excellent. 
It is very difficult to satisfy above mentioned conditions at the same 
time. In this point, the above-mentioned prior art is not satisfactory. 
Since the recording liquid is composed basically of dye and the solvent, 
the above mentioned properties of recording liquid are determined by 
matching of dye to solvent. Therefore, it is very important in the field 
of the art to effect matching of dye to solvent compositions so as to have 
the above-mentioned properties in the recording liquid. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a recording liquid having 
a very good long time storage propety and not easily clogging the jet 
orifice. 
Another object of the present invention is to provide a recording liquid 
which has a wide allowance for changing of temperature and actuation 
condition. 
A further object of the present ivnetion is to provide a recording liquid 
capable of being rapidly fixed to record receiving members and producing 
sharp images. 
Still another object of the present invention is to provide a recording 
liquid having very good water resisting property and very good light 
fastness or the printed matter. 
A still further object of the present invention is to provide a recording 
liquid having high safety and not corroding materials for handling the 
recording liquid (vessel sealing materials and the like). 
According to the present invention, there is provided a recording liquid 
which comprises C.I.Acid Red 8 as a recording agent for forming an image 
and a liquid medium comprising at least 
(a) a member selected from the group consisting of polyethylene glycol, 
polyethylene glycol mono methyl ether and a mixture thereof; 
(b) a member selected from the group consisiting of diethylene glycol, 
sulfolane and a mixture thereof; 
(c) a member selected from the group consisting of n-methyl-2-pyrrolidone, 
1,3-dimethyl-2-imidazolidinone and a mixture thereof; and 
(d) water.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention, variation of the viscosity of the 
recording liquid corresponding to variation of an environment temperature 
is small, and the recording liquid is of small variation of the viscosity 
and the surface tension when the water content varies. 
Therefore, when the environment temperature varies to a great extent, a jet 
state is always kept constant, and moreover, increase in viscosity by 
evaporation of water from a tip of a nozzle neither causes any difficulty 
upon jetting again after stood nor clogging. 
The recording liquid according to the present invention is not subjected to 
change in the physical properties and precipitation of solid matters 
during storage, and various members can be as the record receiving members 
regardless of the kind of the material. The fixation can proceed rapidly 
and water resisting property, light fastness, wear resistance and 
resolution of the resulting image are excellent. The content of C.I.Acid 
Red 8 is determined depending upon the kind of the liquid medium and the 
properties which are required to the recording liquid. In general, it is, 
to total weight of the recording liquid, 0.1-20 wt %, preferably 0.5-15 wt 
% and more preferably 1-10 wt %. The dye can be used alone or in 
combination (i.e. the dye as the essential component may be used in 
combination with various dyes such as direct dye, acid dye and the like). 
Content of the liquid medium used in the present invention in the recording 
liquid is, in general, 1-30 wt % of polyethylene glycol, polyethylene 
glycol monomethyl ether, or a mixture thereof, 1-40 wt % of diethylene 
glycol, sulfolane or a mixture thereof, 1-40 wt % of 
N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone or a mixture 
thereof, and 10-90 wt % of water, and preferably, 5-20 wt % of 
polyethylene glycol, polyethylene glycol monomethyl ether or a mixture 
thereof, 5-30 wt % of diethylene glycol or sulfolane or a mixture thereof, 
5-30 wt % of N-methyl-2-pyrrolidone or 1,3-dimethyl-2-imidazolidinone or a 
mixture thereof and 10-70 wt % of water. 
The recording liquid prepared from such components according to the present 
invention has excellent and well-balanced recording properties (signal 
responsing property, stability of droplet formation, jet stability, long 
time continuous recording property, and jet stability after a long rest 
time of recording operation), storge stability, fixability to record 
receiving members, and light fastness, weatherability, and water resisting 
property of the recorded images. For further improving such properties, 
various known additives may be added. For example, there may be mentioned 
a viscosity controlling agent such as poly(vinyl alcohol), celluloses, 
water-soluble resins and the like, a surface tension controlling agent 
such as cationic surfactants, anionic surfactants, nonionic surfactants, 
diethanol amine, triethanol amine and the like, a pH controlling agent 
such as buffer solutions, and antifungal agent and the like. 
When the recording liquid is to be used for an ink jet recording system 
where the recording liquid is electrically charged, there may be added a 
specific resistance controlling agent such as lithium chloride, ammonium 
chloride, sodium chloride and the like inorganic salts. 
When the recording liquid is used for an ink jet system for jetting the 
recording liquid by means of thermal energy, the thermal physical 
properties such as specific heat, coefficient of thermal expansion, 
thermal conductivity and the like may be adjusted. 
The present invention is illustrated in the following Examples. 
EXAMPLE 1 
______________________________________ 
C.I. Acid Red 8 3 parts by weight 
Polyethylene glycol 15 parts by weight 
monomethyl ether (viscosity-average 
molecular weight: 
210-240) 
Diethylene glycol 15 parts by weight 
N--methyl-2-pyrrolidone 
15 parts by weight 
Water 52 parts by weight 
______________________________________ 
The above mentioned components were sufficiently mixed in a vessel and 
pressure-filtered by means of a Teflon filter of hole size of 1.mu., and 
the resulting product was deaerated by a vacuum pump. 
The resulting recording liquid was tested as to T.sub.1 -T.sub.5 (infra) by 
using a recording apparatus which comprises an on-demand type recoreing 
head (the jet orifice with a diameter of 50.mu., the piezo-oscillator 
actuation voltage of 60 V, a frequency of 4 KHz) capable of jettling the 
recording liquid with the piezo-oscillator. Good result was obtained in 
each of the tests. 
(T.sub.1) Long time storage property of the recording liquid: 
The above mentioned recording liquid was bottled and sealed in a glass 
vessel and stored for six months at -30.degree. C. or 60.degree. C. In 
each case there was not observed any insoluble matter precipitated, and 
physical properties and color of the liquid did not change either. 
(T.sub.2) Jet stability: 
A 24-hour continuous ejection of the recording liquid was effected in an 
atmosphere of a room temperature, 5.degree. C., or 40.degree. C. In each 
condition, a stable and high quality recording was accomplished 
throughout. 
(T.sub.3) Jet responsiveness: 
In one experiment, an intermittent ink jet at intervals of every two 
seconds was carried out. In the other, an ink jet after leaving alone for 
two months was carried out. In both experiments, stable and uniform 
recording was performed without clogging at the tip of orifice. 
(T.sub.4) Quality of recorded image: 
Recorded image was high in density and in sharpness. Reduction ratio of 
density measured after exposing the recorded image to a room light for 
three months was found to be less than 1%. When the recorded image was 
dipped in water for a minute, only a very slight blur of image was 
observed. 
(T.sub.5) Fixability to record receiving members: 
After 15 seconds of printing, the printed portion of the image recording 
materials listed in the following Table were rubbed with a finger to test 
image aberration and blur of the ink. No image aberration and blur of the 
ink were observed, and the recording liquid showed excellent fixability. 
______________________________________ 
Image Receiving 
Material Type Supplier 
______________________________________ 
Gin Kan Wood free paper 
Sanyo-Kokusaku 
(High class) Pulp Co., Ltd. 
Seven Star Wood free paper 
Hokuetsu Paper 
(High class) Mills Co., Ltd. 
Shiro Botan Middle class Honshu Paper 
Mfg. Co., Ltd. 
Toyo Roshi No. 4 
Non-sized paper 
Toyo Roshi Co., Ltd. 
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EXAMPLE 2 
______________________________________ 
Polyethylene glycol 10 parts by weight 
Monomethyl ether (viscosity-average 
molecular weight: 
210-240) 
Sulfolane 10 parts by weight 
N--methyl-2-pyrrolidone 
20 parts by weight 
C.I. Acid Red 8 3 parts by weight 
Water 57 parts by weight 
______________________________________ 
Recording liquid of the above mentioned composition was prepared by the 
same procedure as in Example 1. The resulting recording liquid was tested 
as to (T.sub.1)-(T.sub.5) as shown in Example 1 by using a recording 
apparatus having an on-demand type multi head (the jet orifice with a 
diameter of 35.mu., heating resistor of resistance value of 150.OMEGA., 
actuation voltage of 30 V, frequency of 2 KHz) which generates droplets 
for recording by applying heat energy to the recording liquid in the 
recording head. Excellent results were obtained in all cases. 
EXAMPLE 3 
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C.I. Acid Red 8 5 parts by weight 
Polyethylene glycol 10 parts by weight 
(viscosity-average 
molecular weight: 
300) 
Sulfolane 15 parts by weight 
1,3-dimethyl-2-imidazolidinone 
10 parts by weight 
Water 60 parts by weight 
______________________________________ 
Recording liquid of the above mentioned composition was prepared by the 
same procedure as in Example 1. The resulting recording liquid was filled 
in a felt pen and evaluated for water in a felt pen and evaluated for 
water resisting property of the composition written on a middle class 
paper and writing property when stood for 24 hours after the cap was 
removed from the pen. 
The recording liquid in this example was excellent for both water resisting 
property and writing property after allowing to stand. 
EXAMPLES 4-13 
The recording liquids of the composition as shown in Table 1 were prepared 
by the same procedure as in Example 1. The resulting recording liquids 
were tested as to (T.sub.1 -T.sub.5) as shown in Example 1. The number in 
parentheses in Table 1 denotes the component (weight) ratio. 
These recording liquids exhibited very good long time preservation 
property, recording property, fixability of a recording image, degree of 
sharpness and the like. 
______________________________________ 
Other liquid medium 
Example No. 
Dye composition 
______________________________________ 
4 C.I. Acid 
Polyethylene glycol 
(15) 
Red 8 monomethyl ether 
(3) (viscosity-average 
molecular weight: 210-240) 
Diethylene glycol (15) 
1,3-dimethyl-2- (15) 
imidazolidinone 
Water (52) 
5 C.I. Acid 
Polyethylene glycol 
(10) 
Red 8 (viscosity-average 
(3) molecular weight: 300) 
diethylene glycol (10) 
N--methyl-2-pyrrolidone 
(20) 
Water (57) 
6 C.I. Acid 
Polyethylene glycol 
(10) 
Red 8 monomethyl ether 
(3) (viscosity-average 
molecular weight: 210-240) 
Diethylene glycol (15) 
N--methyl-2-pyrrolidone 
(10) 
Water (62) 
7 C.I. Acid 
Polyethylene glycol 
(10) 
Red 8 (viscosity-average 
(3) molecular weight: 210-240) 
Sulfolane (10) 
Polyethyleneglycol (5) 
(viscosity-average 
molecular weight: 300) 
1,3-dimethyl-2- (10) 
imidazolidinone 
Water (62) 
8 C.I. Acid 
Polyethylene glycol 
(15) 
Red 8 (viscosity-average 
(4) molecular weight: 300) 
Diethylene glycol (10) 
N--methyl-2-pyrrolidone 
(15) 
Water (56) 
9 C.I. Acid 
Polyethylene glycol 
(15) 
Red 8 (viscosity-average 
(4) molecular weight: 300) 
Sulfolane (15) 
N--methyl-2-pyrrolidone 
(15) 
Water (51) 
10 C.I. Acid 
Polyethylene glycol 
(15) 
Red 8 monomethyl ether 
(3) (viscosity-average 
molecular weight: 210-240) 
Sulfolane (10) 
1,3-dimethyl-2- (15) 
imidazolidinone 
triethanolamine (1) 
Water (56) 
11 C.I. Acid 
Polyethylene glycol 
(15) 
Red 8 monomethyl ether 
(3) (viscosity-average 
molecular weight: 210-240) 
Diethylenen glycol (10) 
N--methyl-2-pyrrolidone 
(15) 
urea (1) 
Water (56) 
12 C.I. Acid 
Polyethylene glycol 
(10) 
Red 8 monomethyl ether 
(3) (viscosity-average 
molecular weight: 210-240) 
Diethyleneglycol (10) 
1,3-dimethyl-2- (10) 
imidazolidinone 
Urea (1) 
Acetynol EH (Kawaken Fine 
(0.1) 
chemicals Co., Ltd.) 
Water (65.9) 
13 C.I. Acid 
Polyethylene glycol 
(10) 
Red 8 monomethyl ether 
(4) (viscosity-average 
molecular weight: 210-240) 
Diethylene glycol (15) 
N--methyl-2-pyrrolidone 
(10) 
Polyethylene glycol 
(5) 
(viscosity-average 
molecular weight: 200) 
Triethanolamine (1) 
Acetynol EH (0.1) 
Water (54.9) 
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As explained above, the advantages of the recording liquid according to the 
present invention are as shown below. 
(1) Long time storage property of the liquid is very good and the jet 
orifice does not easily clog. 
(2) Allowance is wide for changing of temperature and actuation condition. 
(3) Fixation to the record receiving members can proceed rapidly and the 
resulting image is sharp. 
(4) Water resisting property and light fastness of the printed matter are 
very good. 
(5) The recording liquid has high safety and does not corrode materials for 
handling the recording liquid (vessel sealing materials and the like).