Ink for thermal ink jet recording and thermal ink jet recording method using the same

An ink for thermal ink jet recording comprising water, a coloring material, (a) 2,2'-thiodiethanol, and (b) C.sub.n H.sub.2n+1 O(CH.sub.2 CH.sub.2 O).sub.m H, wherein n represents an integer of 3 to 6 and m represents an integer of 1 to 3; and the content of the component (a) is 3 to 20% by weight based on the ink and the content of the component (b) is from 1 to 20% by weight based on the ink.

FIELD OF THE INVENTION 
The present invention relates to an ink for thermal ink jet recording and a 
thermal ink jet recording method for recording on a recorded material by a 
thermal ink jet recording apparatus. 
BACKGROUND OF THE INVENTION 
In the principle of an ink jet recording system, a liquid or a molten solid 
ink is jetted from nozzles, slits, porous films, etc., to perform 
recording on papers, cloths, films, etc. As a system of jetting an ink, 
there are proposed various kinds of systems such as a so-called charge 
control system of jetting an ink by utilizing an electrostatic attraction 
force, a so-called drop-on-demand system (pressure pulse system) of 
jetting an ink by utilizing a vibration pressure of a piezo element, a 
so-called thermal ink jet system of jetting an ink by utilizing a pressure 
generated by forming and growing bubbles by applying a heat at a high 
temperature etc., and by these systems, very high precise images can be 
obtained. 
As an ink being used for such an ink jet recording system, solutions or 
dispersions formed by dissolving or dispersing various water-soluble dyes 
or pigments in a liquid medium composed of water or a water-soluble 
organic solvent are known and used. 
For the inks described above, various improvements have been investigated. 
In regard to the ink being used for an ink jet printer, following 6 points; 
(1) the ink has a good quick drying property on a paper, 
(2) the ink gives uniform images having a high resolving power and a high 
density on a paper without causing blotting and fog, 
(3) the ink does not cause clogging of the tips of nozzles by drying and 
always shows a good jetting stability, 
(4) in a thermal ink jet system, the ink does not cause scorching on a 
heater or the ink does not cause a so-called heater trouble in which a 
material always in contact with the ink is eroded with the ink and finally 
a working electrode which is a part of the heater is short-circuited to 
make the heater unworkable, 
(5) the ink has a good long storage stability, and 
(6) even when continuous printing is carried out, the ink does not cause an 
image disturbance and an image defect, are investigated and for meeting 
these requirements, many attempts have been proposed. 
Improvements of the quick drying property of the ink on papers are 
disclosed in JP-B-60-34992 (the term "JP-B" as used herein means an 
"examined published Japanese patent application"), JP-A-62-11781 (the term 
"JP-A" as used herein means an "unexamined published Japanese patent 
application"), and JP-B-62-13388 and they propose that the permeability of 
the ink into papers is improved by the addition of surface active agents 
or polyhydric alcohol derivatives. 
However, in the improvements described in the foregoing patent 
publications, the drying property of images is improved by greatly 
improving the permeability of the ink into plain papers but at the same 
time there is a problem that the occurrence of an image blotting is 
increased. Also, when such an improvement is applied to a thermal ink jet 
system, there is a problem that scorching occurs on the heater. 
On the other hand, with regard to the improvement of the quality of prints, 
the use of 2,2'-thiodiethanol has been variously proposed. For example, in 
JP-B-61-55546, it is disclosed to combine a specific dye and a solvent 
containing 2,2'-thiodiethanol. Also, in JP-A-1-263169, it is disclosed to 
combine Direct Black 168 and a specific solvent containing 
2,2'-thiodiethanol. 
However, when 2,2'-thiodiethanol is used, in particular, at continuous 
printing at a high-frequency, there are faults that images are disturbed 
and image defects are liable to occur, and also when 2,2'-thiodiethanol is 
used for a thermal ink jet system, there is a fault that a heater trouble 
is liable to occur. 
As described above, conventionally used thermal ink jet recording inks do 
not satisfy all the required factors and hence the development of inks 
suitable for a thermal ink jet recording system has been demanded. 
SUMMARY OF THE INVENTION 
The present invention has been made under the present circumstances as 
described above. 
An object of the present invention is to provide a thermal ink jet 
recording method which does not cause clogging of the tips of nozzles by 
drying of an ink, does not cause scorching on a heater, does not cause a 
heater trouble, and does not cause ink leakage from the head. 
Another object of the present invention is to provide a thermal ink jet 
recording method showing a good quick drying property of an ink on a plain 
paper and capable of obtaining uniform images having no blotting in the 
case of forming the images by a thermal ink jet recording system and also 
capable of obtaining images forming an image disturbance and an image 
defect even in the case of continuous printing, in particular, in the case 
of continuous printing at a high-frequency. 
As the result of various investigations, the inventors have discovered that 
the above objects can be attained by using an ink for use in a thermal ink 
jet system comprising water, a coloring material, 
(a) 2,2'-thiodiethanol, and 
(b) C.sub.n H.sub.2n+1 O(CH.sub.2 CH.sub.2 O).sub.m H (wherein n is an 
integer of from 3 to 6, m is an integer of from 1 to 3) as the 
indispensable components, wherein the content of component (a) is from 3 
to 20% by weight and the content of component (b) is from 1 to 20% by 
weight both based on the ink, and have accomplished the present invention 
based on the discovery. 
That is, the present invention is a thermal ink jet recording method of 
carrying out recording by acting a heat energy to an ink to heat the ink 
drops and jetting the ink drops onto a recorded material, which comprises 
using the ink described above. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention is described in detail. 
First, the ink being used in the present invention is explained. The ink 
contains water, a coloring material, the foregoing component (a), and the 
foregoing component (b) as the indispensable components together with 
optional components such as a surface active agent, a pH controlling 
agent, etc. 
The content of 2,2'-thiodiethanol which is the foregoing component (a) is 
required to be from 3 to 20% by weight, and is preferably in the range of 
from 4 to 18% by weight. If the content of the component (a) is less than 
3% by weight, clogging at the tips of nozzles occur and blotting is liable 
to occur on the paper, while the content of the component (a) is larger 
than 20% by weight, in particular, in the case of printing at a high 
speed, the disturbance and the defect of images caused by the disturbance 
of jetting are undesirably liable to occur. 
The component (b) is shown by the following formula; 
EQU C.sub.n H.sub.2n+1 O(CH.sub.2 CH.sub.2 O).sub.m H 
wherein n is required to be in the range of an integer of from 3 to 6. If n 
is less than 3, the effect of permeation of the ink into a plain paper is 
not sufficiently obtained and if n is over 6, the compatibility with water 
becomes insufficient. Also, m is required to be in the range of from 1 to 
3. If the value of m is over 3, the compatibility with water is too good 
to give the sufficient effect of the permeation into a paper. 
Examples of the component (b) include C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 
O).sub.2 H, C.sub.4 H.sub.9 O(CH.sub.2 CH.sub.2 O).sub.3 H, and C.sub.6 
H.sub.13 O(CH.sub.2 CH.sub.2 O).sub.2 H. 
The compounds shown by the above formula may be used singly or as a mixture 
of two or more kinds thereof as the ink component. The content of the 
compound in the ink is required to be from 1 to 20% by weight for 
accelerating the permeation of the ink into papers, is particularly 
preferably from 3 to 10% by weight. If the content is less than 1% by 
weight, the effect thereof is not sufficiently obtained, while if the 
content is over 20% by weight, the lines or images formed are liable to 
become excessively thick and further the jetting stability is reduced and 
thus the image defect is liable to form. 
The ink being used in the present invention can contain, if necessary, 
known various moisture-retaining agents. As such a moisture-retaining 
agent, polyhydric alcohols such as ethylene glycol, diethylene glycol, 
propylene glycol, polyethylene glycol, triethylene glycol, hexylene 
glycol, glycerin, 1,2,6-hexanetriol, 1,5-pentanediol, etc.; basic solvents 
such as pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 
triethanolamine, etc.; and alcohols such as ethanol, isopropyl alcohol, 
butyl alcohol, benzyl alcohol, etc., can be used. Of these compounds, 
ethylene glycol, diethylene glycol, and glycerin are particularly 
preferred and they can be used as a mixture thereof. 
In the present invention, as the foregoing coloring materials, oil-soluble 
dyes containing various dyes, pigments, colored polymers, waxes, etc., can 
be used but the use of water-soluble dyes, particularly, acidic dyes and 
direct dyes are preferred. 
Examples of the acidic dyes and direct dyes include, there are Basacid 
Black X34 Liquid (trade name, made by BASF A.G.), Special Black SP Liquid 
and Special Black HF (trade names, made by Bayer A.G.), C.I. Direct 
Black-4, -9, -11, -17, -19, -22, -32, -80, -151, -154, -168, -171, and 
-194; C.I. Direct Blue-1, -2, -6, -8, -22, -34, -70, -71, -76, -78, -86, 
-142, -199, -200, -201, -202, -203, -207, -218, -236, and -287; C.I. 
Direct Red-1, -2, -4, -8, -9, -11, -13, -15, -20, -28, -31, -33, -37, -39, 
-51, -59, -62, -63, -73, -75, -80, -81, -83, -87, -90, -94, -95, -99, 
-101, -110, and -189; C.I. Direct Yellow-1, - 2, -4, -8, -11, -12, -26, 
-27, -28, -33, -34, -41, -44, -48, -86, -87, -88, -135, -142, and -144; 
C.I. Food Black-1 and -2; C.I. Acid Black-1, -2, -7, -16, -24, -26, -28, 
-31, -48, -52, -63, -107, -112, -118, -119, -121, -172, -194 and -208; 
C.I. Acid Blue-1, -7, -9, -15, -22, -23, -27, -29, -40, -43, -55, -59, 
-62, -78, -80, -81, -90, -102, -104, -111, -185, and -254; C.I. Acid 
Red-1, -4, -8, -13, -14, -15, -18, -21, -26, -35, -37, -249, and -257; 
C.I. Acid Yellow-1, -3, -4, -7, -11, -12, -13, -14, -19, -23, -25, -34, 
-38, -41, -42, -44, -53, -55, -61, -71, -76, and -79, etc. 
These dyes can be used singly or as a mixture thereof and in addition to 
the four primary colors of cyan, magenta, yellow, and black, they may be 
toned into custom colors such as red, blue, green, etc. 
The content of the dye(s) is in the range of from 0.3 to 10% by weight, and 
preferably from 1 to 8% by weight to the total amount of the ink. 
Also, the ink of the present invention may contain so-called surface active 
agents, dispersing agents, inclusive compounds, etc., for further 
stabilizing the dissolved or dispersed state of the coloring material. 
As the surface active compound, nonionic surface active agents, anionic 
surface active agents, cationic surface active agents, or amphoteric 
surface active agents may be used. 
Examples of the nonionic surface active agent include polyoxyethylene 
nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene 
dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty 
acid ester, sorbitan fatty acid ester, a polyoxyethylene/polyoxypropylene 
block copolymer, polyoxyethylene sorbitan fatty acid ester, and fatty acid 
alkylolamide. Examples of the anionic surface active agent, include an 
alkybenzenesulfonate, an alkylphenylsulfonate, an 
alkylnaphthalenesulfonate, a formarine condensation product of an 
alkylnaphthalenesulfonate, a high fatty acid salt, a sulfuric acid ester 
salt of a higher fatty acid ester, a sulfonate of a higher fatty acid 
ester, a sulfuric acid salt of a higher alcohol ether, a sulfonate of a 
higher alcohol ether, an alkylcarboxylate of a higher alkyl sulfonamide, a 
sulfosuccinate, and an ester salt. Examples of cationic surface active 
agent, include a primary amine, a secondary amine, a tertiary amine, and a 
quaternary ammonium salt. Examples of the amphoteric surface active agent, 
there betaine, sulfobetaine, and sulfate betaine. Of these surface active 
agents, the anionic surface active agents are preferably used. 
As other surface active agents, an acrylic acid/methacrylic acid/maleic 
acid copolymer, an acrylate/methacrylate/maleate series water-soluble 
polymer, polyethyleneimine, polyamines, polyvinylpyrrolidone, polyethylene 
glycol, cellulose derivatives, cyclodextrin, macrocyclic amines, crown 
ethers, urea, acetamide, etc., can be used. 
The ink in this invention can further contain, if necessary, a pH 
controlling agent, an antifoggant, a viscosity controlling agent, an 
electric conductivity imparting agent, etc. 
Then, a thermal ink jet recording method using the foregoing ink is 
explained. The thermal ink jet recording method is a recording method 
utilizing a film boiling phenomenon and a heater is equipped in the 
recording head. As the material for the recording head, silicon, 
polyimide, an epoxy resin, etc., is used and silicon is preferably used. 
Also, at printing, the heating temperature by the heater is at least 
150.degree. C. Furthermore, the frequency at driving is preferably from 2 
KHz to 15 KHz, more preferably 5 KHz or more. In the present 
specification, high frequency driving corresponds to high speed printing. 
In the case of using a conventional ink for high speed printing, the ink 
oozes from a nozzle to stain the vicinity of the tip of the nozzle and to 
cause a printing defect. On the other hand, the foregoing trouble can be 
prevented. 
Then, the present invention is further described in more detail by the 
following examples.

EXAMPLES 1 TO 9 AND COMATIVE EXAMPLES 1 to 5 
Each components shown in Table 1 (Examples 1 to 9) and Table 2 (Comparative 
Examples 1 to 5) was used together with an ion-exchanged water as a 
balance in the total amount of 100% by weight and the mixture was 
sufficiently mixed to dissolve the components. After filtering the 
solution obtained with a filter of 0.2 .mu.m under pressure, the solution 
was subjected to a degassing treatment by using a vacuum pump to provide 
each of inks. On each of the inks thus prepared, the following tests were 
applied and the results obtained are shown in Table 3 below. 
(1) Ink Surface Tension: 
The ink surface tension was measured using a Wilhelmy's tensiometer under 
the circumstances of 20.degree. C. and 50% RH. 
(2) Ink Viscosity: 
The viscosity was measured at a shear rate of 1,400 s.sup.-1 under the 
circumstances of 20.degree. C. and 50% RH. 
(3) Print Test (Image quality): 
By using an ink jet printer (thermal ink jet system, 300 dpi) as a trial 
product, the print test of each ink was carried out using an FX-L paper 
(uncoated plain paper; trade name, made by Fuji Xerox Co., Ltd.). The 
evaluation was visually carried out by the following standards. 
.smallcircle.: A Chinese character of 5 points is readable. 
.DELTA.: Chinese character of 8 points is readable. 
.times.: A Chinese character of 10 points is unreadable. 
Also, about fine scattering of the ink, the presence or absence of the 
generation thereof was determined around a solid image at which fine 
scattering is relatively liable to occur. 
(4) Dry Time Test: 
An FX-L paper (made by Fuji Xerox Co., Ltd.) as a plain paper and a coated 
paper for ink jet (made by Xerox Corporation) were used. A solid black 
image of 51 mm.times.10 mm was printed on the FX-L paper, the coated paper 
for ink jet was superposed on the printed FX-L paper and a pressure was 
applied thereto from above. In this case, the time until the ink on the 
printed FX-L paper was not transferred onto the side of the coated paper 
for ink jet was defined as the dry time and the dry time was evaluated by 
the following standards. 
.smallcircle.: Shorter than 30 seconds. 
.DELTA.: From 30 seconds to 60 seconds. 
.times.: Longer than 60 seconds. 
(5) Image Defect Test: 
A printing test was carried out in an atmosphere of 20.degree. C. and 50% 
RH, the continuous run test of 300 prints at 3 kHz, 5 kHz, and 7 kHz, 
respectively was carried out, the presence of the occurrence of the heater 
trouble, blank area of images, bending of lines, and the distortion of 
images were observed to determine the presence or absence of the image 
defects. (In addition, in Table 3, .times. means that the defects were 
observed, .DELTA. means that the detects were partially observed, and 
.smallcircle. means that the defects were not observed.). 
At the same time, the dot diameters were measured and the occurrence of 
scorching on the head was evaluated by the following standards. 
.smallcircle.: The change of the dot diameter was less than .+-.10%. 
.DELTA.: The change of the dot diameter was less than .+-.15%. 
.times.: The change of the dot diameter was more than .+-.15%. 
(6) Clogging Test: 
After allowing to stand each ink for a prescribed time in an atmosphere of 
10.degree. C. and 15% RH and an atmosphere of 30.degree. C. and 85% RH, 
the print test was carried out and the evaluation was carried out by the 
following standards. 
.smallcircle.: Printable after allowing to stand for 300 seconds. 
.DELTA.: Printable after allowing to stand for 180 seconds. 
.times.: Unprintable after allowing to stand for 180 seconds. 
The results obtained are shown in Table 3 below. 
TABLE 1 
__________________________________________________________________________ 
2,2'-thiodi- Moisture 
ethanol 
C.sub.n H.sub.2n+1 O(CH.sub.2 CH.sub.2 O).sub.m 
H Retaining Agent 
Other 
Dye (wt. %) (wt. %) 
(wt. %) (wt. %) Additive 
__________________________________________________________________________ 
Example 1 
C.I. Food Black #2 
5 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
-- -- 
(3 wt. %) (5) 
Example 2 
C.I. Food Black #2 
6 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
Diethylene glycol 
-- 
(3 wt. %) (10) (15) 
Example 3 
C.I. Food Black #2 
8 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.3 
Glycerin Isopropyl alcohol 
(3 wt. %) (8) (10) (3 wt. %) 
Example 4 
C.I. Food Black #2 
6 C.sub.4 H.sub.9 O(CH.sub.2 CH.sub.2 O).sub.3 
Glycerin C.sub.18 H.sub.35 
O(CH.sub.2 CH.sub.2 
O).sub.15 H 
(3 wt. %) (8) (5) (0.1 wt. %) 
Example 5 
C.I. Direct Black 168 
7 C.sub.4 H.sub.9 O(CH.sub.2 CH.sub.2 O).sub.2 
Ethylene glycol 
-- 
(4 wt. %) (4) (10) 
Example 6 
C.I. Direct Blue 199 
6 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
Diethylene glycol 
-- 
(3 wt. %) (10) (5) 
Example 7 
C.I. Acid Red 257 
4 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
Glycerin -- 
(2.5 wt. %) (15) (5) 
Example 8 
Basacid Black X34 Liquid 
3 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
Glycerin -- 
(10 wt. %) (5) (5) 
Example 9 
Bayscript Black SP Liquid 
3 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
Diethylene glycol 
-- 
(10 wt. %) (4) (5) 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
2,2'-thiodi- Moisture 
ethanol 
C.sub.n H.sub.2n+1 O(CH.sub.2 CH.sub.2 O).sub.m 
Retaining Agent 
Other 
Dye (wt. %) 
(wt. %) 
(wt. %) (wt. %) Additive 
__________________________________________________________________________ 
comparative 
C.I. Direct Black 168 
10 Diethylene glycol 
-- 
Example 1 
(4 wt. %) (0) (5) 
Comparative 
C.I. Direct Black 168 
25 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
-- -- 
Example 2 
(2.5 wt. %) (3) 
Comparative 
C.I. Food Black #2 
2 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.2 
Ethylene glycol 
-- 
Example 3 
(3 wt. %) (10) (5) 
Comparative 
C.I. Direct Blue 199 
16 C.sub.3 H.sub.7 O(CH.sub.2 CH.sub.2 O).sub.4 
Diethylene glycol 
-- 
Example 4 
(2 wt. %) (10) (5) 
Comparative 
C.I. Direct Black 154 
5 C.sub.4 H.sub.9 O(CH.sub.2 CH.sub.2 O).sub.1 
Glycerin -- 
Example 5 
(3 wt. %) (10) (5) 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Thermal ink jet 
Ink surface 
Ink system test 
tension 
viscosity 
Image 
Dry 
Image Defect 
Dot diameter 
Heater 
Clogging 
(mN/m) 
(mPas) 
quality 
time 
3 kHz 
5 kHz 
7 kHz 
change trouble 
Test 
__________________________________________________________________________ 
Example 1 
40 1.7 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 2 
36 2.3 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 3 
37 2.8 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 4 
37 2.1 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 5 
41 2.2 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 6 
35 2.1 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 7 
33 2.8 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 8 
41 1.7 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 9 
41 1.5 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Comparative 
60 1.5 .largecircle. 
X .largecircle. 
.DELTA. 
X .largecircle. 
X .largecircle. 
Example 1 
Comparative 
44 2.9 .DELTA. 
X .largecircle. 
X X .largecircle. 
X .largecircle. 
Example 2 
Comparative 
34 1.9 X .largecircle. 
.largecircle. 
.largecircle. 
.DELTA. 
X .largecircle. 
X 
Example 3 
Comparative 
39 3.1 .largecircle. 
X .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example 4 
Comparative 
31 2.1 .largecircle. 
.largecircle. 
X X X X .largecircle. 
.largecircle. 
Example 5 
__________________________________________________________________________ 
Since the thermal ink jet recording method of the present invention uses 
the ink composed of the components described above, scorching onto the 
heater does not occur and a heat trouble does not occur. Also, clogging of 
nozzle tips by drying of the ink does not cause and link leakage from the 
heads of the nozzles does not occur. Furthermore, according to the thermal 
ink jet recording method of the present invention, the drying property of 
the ink is good even on a plain paper and uniform images having no ink 
leakage can be obtained and at continuous printing, in particular, at 
continuous printing by a high frequency, images having neither image 
turbidity and nor image defect can be formed. 
While the invention has been described in detail and with reference to 
specific embodiment thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.