Image recording ink

An ink which can cause a change in its adhesiveness by an electrochemical reaction is obtained by impregnating a crosslinked substance such as polyvinyl alcohol with a liquid dispersion medium comprising an organic solvent having a relative dielectric constant of 15 or larger at 25.degree. C. such as ethylene glycol. The ink shows little characteristic change due to drying, etc., and suitably retains its fluidity when left standing in the air for a long period. The ink is supplied with a pattern of energy to be provided with an adhesive pattern, which is then transferred to a recording medium such as plain paper, directly or by the medium of an intermediate transfer medium to form an ink pattern corresponding to the energy pattern applied.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to an ink adapted to an image recording 
method which retains various advantages of the conventional recording 
systems and yet realizes a low recording cost. 
In recent years, along with the rapid progress of information industries, 
various data processing systems have been developed, and accordingly 
various recording methods and recording apparatus have been developed and 
adopted for the respective data processing systems. Among these, 
representative recording systems capable of recording on plain paper 
include electrophotography and laser beam printing system developed 
therefrom, ink jetting, thermal transfer, and impact printing system using 
a wire dot printer or daisy-wheel printer. 
The impact printing system produces annoying noise and the application 
thereof to full- or multi-color recording is difficult. The 
electrophotography and the laser beam printing produce images at a high 
resolution, but the apparatus therefor are complicated and large in size 
thus requiring a large apparatus cost. The ink jet printing system 
requires only a small expendable cost but involves a process defect in 
that, because a thin nozzle is used for jetting a low-viscosity liquid ink 
therefrom, the nozzle is liable to be clogged with the ink solidified 
during a period of non-use. Further, as the ink for the ink jet system is 
low-viscosity ink, the ink is liable to spread after it is deposited on 
paper, thus resulting in blurring of images. 
Further, according to the thermal transfer method, a heat pattern was 
supplied to a solid ink layer formed on a sheet form support to form a 
fused ink pattern, which is then transferred to plain paper, etc., to form 
an image thereon. The thermal transfer method has advantages in that a 
relatively small apparatus is used and therefore only a small apparatus 
cost is required. However, an ink ribbon used in the thermal transfer 
method is composed by forming a solid ink layer on an expensive support 
and the ink ribbon is disposed of after use, so that the thermal transfer 
method involves a disadvantage in that it requires a high expendable cost. 
In order to remove the above disadvantage of the thermal transfer method, 
Japanese Patent Publication (JP-B) 59-40627 has proposed a thermal 
transfer system which does not necessitate the use of an ink ribbon used 
in the conventional thermal transfer method by coating a roller with a 
heat-fusible ink. More specifically, JP-B 59-40627 discloses a recording 
system wherein a roller is coated with a heat-fusible ink showing a 
plasticity and containing electroconductive powder. Heat generated by 
current-conduction from a recording electrode is supplied to the ink and 
the resultant fused ink is transferred to paper. However, the ink used in 
JP-B 59-40627 is plastic, so that an image formed by conduction-heating in 
the ink on the roller is liable to be deformed and disturbed. Further, the 
conductivity is provided by inclusion of a necessarily large amount of 
conductive powder, so that the color of the ink is constrained by the 
conductive powder generally colored in black. As a result, it is difficult 
to constitute and use an ink of a color other than black. 
U.S. Pat. No. 4,462,035 discloses an apparatus similar to that of the above 
JP-B 59-40627. In this apparatus, however, since a roller is coated with a 
heat-fusible ink, and heat generated by current-conduction is supplied to 
the ink to thereby effect recording as in the above JP-B 59-40627, a high 
electric power is required and it has been difficult to obtain a fine or 
precise image. 
In order to remove the above disadvantage of the thermal transfer method, 
our research group has proposed a novel recording method which has solved 
the above-mentioned problems and realized a low recording cost (Japanese 
Patent Application No. 175191/1986, corresponding to U.S. patent 
application Ser. No. 075,045). 
This recording method comprises: 
providing a fluid ink which is capable of forming a fluid layer, 
substantially non-adhesive and capable of being imparted with an 
adhesiveness on application of an energy, 
forming a layer of the fluid ink on an ink-carrying member, 
applying a pattern of the energy corresponding to a given image signal to 
the ink layer to form an adhesive pattern of the ink, and 
transferring the adhesive pattern of the ink to a transfer-receiving medium 
to form thereon an ink pattern corresponding to the energy pattern 
applied. 
In the above-mentioned new type of recording method, when a fluid ink 
having a crosslinked structure (i.e., one in a gel form, in a broad sense) 
is used, image deformation at an energy application position is 
considerably reduced because of the elastic property of the ink based on 
gel elasticity. 
The above-mentioned new type of recording method utilizes 
oxidation-reduction at an electrode as a recording mechanism, similarly as 
in the conventional electrolytic recording method. However, the 
above-mentioned recording method is novel and has various advantages as 
follows: 
(1) The new method is mainly based on the application of an adhesiveness 
(e.g., that due to sol-gel phase transition in the ink) caused by electric 
conduction, but is not based on color formation caused thereby. Therefore, 
it provides an image having higher stability and durability than that 
based on the chemical color formation. 
(2) In the new method, a paper preliminarily coated with a developer is not 
used, but the ink is ordinarily applied onto an ink-carrying member and 
used repeatedly while only a portion of the ink actually contributing to 
image formation is transferred to a transfer-receiving medium. 
Accordingly, the above new method may use plain paper as the 
transfer-receiving medium and only requires low running costs. 
(3) The new method only requires an application voltage and an application 
current which are much smaller than those in the conventional electrolytic 
recording method which requires an electric charge amount of one faraday 
in order to generate one chemical equivalent of the colored substance. For 
example, typically, the new method requires a voltage of about 10 V and a 
current of about 1 mA per one pixel (100 microns.times.100 microns) and 
may easily be applied to a high speed recording corresponding to a pulse 
duration of about 1 msec. 
(4) In view of the above point (3), the new method can effect a 
line-sequential recording on plain paper by using a line head having a 
highly fine electrode pattern (8 lines/mm-16 lines/mm) which cannot have 
been used in the conventional electrolyte recording method. 
Further, our research group has proposed, as an ink used for the 
above-mentioned new image recording method, an image recording ink 
comprising: a liquid dispersion medium, and a crosslinked substance 
impregnated with the liquid dispersion medium; the ink being capable of 
being imparted with an adhesiveness on application of an electric current; 
the ink containing an electrolyte capable of imparting a pH buffer action 
thereto (U.S. patent application Ser. No. 156,978 corresponding to 
Japanese Patent Application Nos. 36904/1987, 15241/1988 and 15242/1988). 
In order to further improve the practical characteristic (e.g., storage 
stability) of the fluid ink to be used in the above new image recording 
method while suitably retaining the image recording characteristic 
thereof, there has still been room for improvement with respect to a 
liquid dispersion medium as well as a crosslinked substance used in the 
ink. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an ink suitably used in 
the above new type of image recording method which has solved the 
above-mentioned problems of the conventional recording systems. 
Another object of the present invention is to provide a type of ink which 
can be used up without disposal as far as it has not been actually used 
for recording or without using an ink ribbon or ink sheet to be disposed 
after use as in the conventional thermal transfer system. 
A further object of the present invention is to provide an ink having a 
fluidity which is not attached or transferred to a transfer-receiving 
medium comprising an intermediate transfer medium or a recording medium 
(final transfer medium) when it only contacts such a medium, and which can 
be used without being applied as a thin solid ink layer on a support 
unlike a solid ink held on a conventional ink ribbon or ink donor film. 
A still further object of the present invention is to provide an ink which 
is excellent in a fluid layer-forming property, an extremely important 
factor in the above-mentioned novel image recording method utilizing the 
control of ink adhesiveness, and which can control its adhesiveness 
sharply, sensitively and stably under energy application. 
A still further object of the present invention is to provide an ink 
excellent in storage stability and stability of performances during 
successive use, i.e., an ink which shows very little characteristic change 
due to drying, etc., and suitably retains its fluidity, etc., when left 
standing in the air for a long period. 
A still further object of the present invention is to provide an ink 
capable of showing good transferability to an intermediate transfer medium 
or a recording medium under energy application. 
A still further object of the present invention is to provide an ink 
capable of providing an image with good printing quality and image quality 
on a recording medium. 
A still further object of the present invention is to provide an ink 
excellent in fixability to a recording medium. 
A still further object of the present invention is to provide an ink 
capable of showing good storability and having a long life without decay, 
deterioration, discoloration, separation, or decomposition. 
A still further object of the present invention is to provide an ink 
excellent in energy efficiency, which is capable of providing a good 
recorded image under the application of small quantity of energy. 
We have diligently studied on a liquid dispersion medium which is not only 
capable of imparting a suitable balance between adhesiveness and 
non-adhesiveness to a fluid ink, but also is capable of enhancing the 
storage stability thereof. As a result of earnest study, we have found 
that an organic solvent having a specific relative dielectric constant, in 
combination with a crosslinked substance retaining it, is not only 
advantageous to an inorganic solvent such as water in view of storage 
stability, but also provides a fluid ink capable of controlling its 
adhesiveness sensitively corresponding to electric conduction. 
The image recording ink according to the present invention is based on the 
above discovery and comprises: a liquid dispersion medium, and a 
crosslinked substance impregnated with the liquid dispersion medium, the 
ink being capable of causing a change in adhesiveness thereof by an 
electrochemical reaction, wherein the liquid dispersion medium comprises 
an organic solvent having a relative dielectric constant of 15 or larger 
at 25.degree. C. 
In the above image recording ink of the present invention, it is assumed 
that the above-mentioned organic solvent having a specific relative 
dielectric constant not only provides a suitable fluidity (or 
viscoelasticity) to the ink on the basis of the interaction with the 
crosslinked substance retaining it, but also provides a good energy 
efficiency to the fluid ink on the basis of the ionic conductivity 
thereof. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings, wherein like reference 
numerals denote like parts. In the following description, "%" and 
"part(s)" representing a quantitative proportion or ratio are by weight 
unless otherwise noted specifically.

DETAILED DESCRIPTION OF THE INVENTION 
The image recording ink according to the present invention comprises a 
liquid dispersion medium and a crosslinked substance impregnated 
therewith. 
In the present invention, it is possible to reduce the adhesiveness of the 
ink by electric conduction thereby to form an image. For example, it is 
possible to patternwise convert the ink of the present invention in a 
sol-state based on pH adjustment, etc., to a gel state under electric 
conduction. However, it is preferred that the ink of the present invention 
is one which is substantially non-adhesive and capable of being imparted 
with an adhesiveness under electric conduction, in order to suppress the 
quantity of a pattern energy or the ink consumed at the time of image 
formation. 
The term "adhesiveness" used herein is a selective one and refers to a 
property of the ink by which a portion of the ink contacting an object 
such as transfer-receiving medium is selectively separated or cut from the 
ink body to adhere to the object. Thus, the "adhesiveness" is not 
concerned with whether the ink body is glutinous or not. 
In the above-mentioned preferred embodiment of the present invention, the 
ink is one in the form of a gel, in a broad sense, which comprises a 
liquid dispersion medium (or vehicle) comprising an organic solvent with a 
specific relative dielectric constant, and a crosslinked substance such as 
a water-soluble (or hydrophilic) polymer impregnated with the liquid 
dispersion medium. 
Hereinbelow, the ink in such preferred embodiment will mainly be described. 
The above-mentioned "crosslinked substance" refers to a single substance 
which per se can assume a crosslinked structure, or a mixture of a 
substance capable of assuming a crosslinked structure with the aid of an 
additive (such as a crosslinking agent for providing a crosslinking ion 
such as borate ion), and the additive. Further, the term "cross-linked 
structure" refers to a three-dimensional structure having a cross-linkage 
or crosslinking bond. 
More specifically, the ink of the present invention may preferably be one 
satisfying the following properties. 
(1) Fluidity 
When measured by means of a rotational viscometer, e.g., Vismetron Model 
VS-A1, mfd. by Shibaura System K.K. with a stainless steel (SUS 27) rotor 
of about 3 mm in diameter at normal temperature (25.degree.), the ink of 
the present invention should preferably show a viscosity of 
1.0.times.10.sup.4 -2.0.times.10.sup.6 centipoises (cps), particularly 
1.0.times.10.sup.5 -1.0.times.10.sup.6 cps at a rotor speed of 0.3 rpm; 
and 5.0.times.10.sup.3 cps or more particularly 1.0.times.10.sup.4 
-4.0.times.10.sup.5 cps at a rotor speed of 1.5 rpm. 
Incidentally, the above-mentioned fluidity is preferred when the ink is 
used in an image recording apparatus as shown in FIG. 1, as described 
hereinafter, having an ink layer thickness-regulation means comprising a 
blade. If the method of conveying or carrying the ink is changed, the ink 
having a viscosity larger than the above range can suitably be used. 
If the fluidity (or fluid layer-forming property) of the ink is lower than 
the above range, smooth supply of the ink sometimes becomes difficult, or 
heating, etc., is sometimes required for the ink supply, in a case where a 
blade coating method is used as shown in FIG. 1. 
On the other hand, in a case where an ink layer is formed by coating, e.g., 
by means of an ink application roller as shown in a schematic sectional 
view of FIG. 2 (or in a schematic perspective view of FIG. 3), there may 
suitably be used an ink having a viscosity in a broader range than that 
mentioned above. In such case, it is preferred to measure the 
viscoelasticity of the ink rather than the viscosity thereof alone. More 
specifically, an ink is formed into a disk shape having a diameter of 25 
mm and a thickness of 2 mm, and a sine strain with an angular velocity of 
1 rad/sec is applied to the ink sample at 25.degree. C. by means of 
Rheometer RMS-800 (mfd. by Rheometrics Inc., U.S.A.). In such case, the 
ink of the present invention may preferably show a ratio (G"/G') of a loss 
elasticity modulus (G") to a storage elasticity modulus (G') of 0.1-10. 
Incidentally, it is possible to refer to a preceding application filed by 
our research group (Japanese Patent Application No. 131586/1987, 
corresponding to U.S. patent application Ser. No. 199,452), with respect 
to the detail of the viscoelasticity characteristics of the ink. 
(2) Non-adhesiveness (or liquid dispersion medium-retaining ability) 
On the surface of a sample fluid ink held in a container, an aluminum foil 
of 5 cm.times.5 cm in size is, after being accurately weighed, placed 
gently and is left standing as it is for 1 min. in an environment of a 
temperature of 25.degree. C. and a moisture of 60%. Then, the aluminum 
foil is gently peeled off from the surface of the fluid ink and then 
quickly weighed accurately to measure the increase in weight of the 
aluminum foil. Through the measurement, the ink of the present invention 
should preferably show substantially no transfer of its solid content 
(e.g., crosslinked substance) and a weight increase of the aluminum foil 
of less than 1000 mg, particularly on the order of 1-100 mg. In the above 
measurement, it is possible to separate the aluminum foil from the fluid 
ink body, if necessary, with the aid of a spatula. 
If the non-adhesiveness of the ink is insufficient in the light of the 
above standard, not only the liquid dispersion medium but also the 
crosslinked substance of the ink can transfer to a transfer-receiving 
medium to a practically non-negligible extent even under no energy 
application, thus resulting in a lower image quality. 
Further, in such case, a relatively large amount of the liquid dispersion 
medium is liable to transfer to the transfer-receiving medium and it is 
troublesome to remove the liquid dispersion medium. 
As described above, the ink according to the present invention may 
preferably be an ink in the form of a gel, in a broad sense, comprising a 
crosslinked substance impregnated with a liquid dispersion medium, more 
preferably, an ink in the form of a sludge obtained by dispersing 
particles having a particle size of preferably 0.1-100 microns, further 
preferably 1- 20 microns, in the above-mentioned gel ink. 
It is presumed that the ink of the present invention is not substantially 
transferred to a transfer-receiving medium because the liquid dispersion 
medium except for a minor portion thereof is well retained in the 
crosslinked structure. 
It is also presumed that when an energy such as electric energy is 
patternwise imparted to the gel ink, the crosslinked structure is changed 
thereby, so that the fluid ink is imparted with an adhesiveness in a 
pattern. 
In an image recording method using the ink of the present invention, when 
nearly 100% of the ink portion provided with adhesiveness is not 
transferred to a transfer-receiving medium or intermediate transfer 
medium, or a final transfer medium (i.e., a recording medium), i.e., when 
an ink which remains on an ink-carrying member or an intermediate transfer 
member described hereinbelow after a prescribed transfer thereof is not 
negligible in practice, it is preferred that the above-mentioned change in 
crosslinked structure, etc., is a reversible one. 
Further, it is preferred that the ink substantially retains the change in 
the crosslinked structure, etc., during the period from the time at which 
it is supplied with an energy as described below, to the time at which it 
is transferred to a transfer-receiving medium. 
In the ink of the present invention, the kind, amount, etc., of the 
crosslinked substance is not particularly limited as long as it can 
provide an ink having the above-mentioned characteristic, but the 
crosslinked substance may preferably comprise a hydrophilic (or 
water-soluble) high polymer or macromolecular substance, in view of the 
safety in the liquid dispersion medium to be combined therewith. 
Examples of such a hydrophilic high polymer include: plant polymers such as 
guar gum, locust bean gum, gum arabic, tragacanth, carrageenah, pectin, 
mannan, and starch; microorganism polymers such as xanthane gum, dextrin, 
succinoglucan, and curdran; animal polymers such as gelatin, casein, 
albumin, and collagen; cellulose polymers such as methyl cellulose, ethyl 
cellulose, and hydroxyethyl cellulose, starch polymers such as soluble 
starch, carboxymethyl starch, methyl starch; alginic acid polymers such as 
propylene glycol alginate, and alginic acid salts; other semi-synthetic 
polymers such as derivatives of polysaccharides; vinyl polymers such as 
polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, 
carboxyvinyl polymer, and polysodium acrylate; and other synthetic 
polymers such as polyethylene glycol, and ethylene oxide-propylene oxide 
block copolymer. These polymers may be used singly or in mixture of two or 
more species, as desired. Among these, guar gum or polyvinyl alcohol may 
particularly preferably be used, in view of a suitable balance between 
adhesiveness and non-adhesiveness. 
The above-mentioned hydrophilic polymer may preferably be used in a 
proportion of 0.2-50 parts, more preferably 0.5-20 parts, particularly 
preferably 0.5-5 parts, with respect to 100 parts of the liquid dispersion 
medium. 
The liquid dispersion medium constituting the image recording ink of the 
present invention in combination with the above crosslinked substance 
comprises an organic solvent (i.e., liquid organic compound) having a 
relative dielectric constant of 15 or above, preferably 30-200, at 
25.degree. C. 
If an organic solvent having a relative dielectric constant outside the 
above range is used, a recorded image of good quality cannot be obtained 
stably. More specifically, if an organic solvent having a relative 
dielectric constant of below 15 at 25.degree. C. is used, a change in the 
crosslinked structure does not occur sensitively, whereby there occurs 
only an insufficient change in adhesiveness or no change in the 
crosslinked structure. As a result, it is difficult to selectively 
transfer the ink to a transfer-receiving medium. 
Accordingly, such ink only provides a very unclear or not recorded image, 
whereby an image of good quality cannot be obtained. Incidentally, even if 
an image of a certain image quality is obtained, an excessive energy is 
required to lower the energy efficiency. Further, an electrode used for 
the image formation is liable to deteriorate, and the image recording 
apparatus cannot perform satisfactorily. 
The relative dielectric constant used herein is an important factor 
determining ionic conductivity in a solvent. Since the force (F) exerted 
between ions is represented by the following formula, a solvent having a 
high relative dielectric constant provides a high ionic conductivity: 
EQU F=Q.sub.1 .multidot.Q.sub.2 /(4.pi..epsilon..sub.0 .epsilon..sub.r 
r.sup.2)(I), 
wherein Q.sub.1 and Q.sub.2 respectively denote charges of the ions, 
.epsilon..sub.0 denotes a dielectric constant of empty space, 
.epsilon..sub.r denotes a relative dielectric constant, and r denotes the 
distance between the ions. 
Accordingly, when an electric energy is applied to an ink comprising a 
solvent having a relative dielectric constant of 15 or larger as a 
dispersion medium, an electrochemical reaction is sensitively caused to 
change the crosslinked, structure whereby selective transfer and recording 
may be effected. 
Examples of the organic solvent suitably used in the present invention may 
include: hydrophilic solvents such as N-methylacetamide, 
N-methylformamide, formamide, ethylene carbonate, acetamide, 
succinonitrile, dimethyl sulfoxide, sulfolane, glycerin, 1,2-ethanediol 
(ethylene glycol), furfuryl alcohol, N,N-dimethylacetamide, 
N,N-dimethylformamide, nitrobenzene, N-methylpyrrolidone, 1,2-propanediol 
(propylene glycol), diethylene glycol, 2-ethoxyethanol, 
hexamethylphosphoric triamide, 2-nitropropane, nitroethane, 
.gamma.-butyrolactone, propylene carbonate, triethylene glycol, 
1,2,6-hexanetriol, dipropylene glycol and hexylene glycol. As a matter of 
course, the organic solvent used in the present invention should not be 
restricted to these specific examples. 
Among these, polyhydric alcohols (particularly, glycol-type solvents), or 
derivatives thereof such as ether or ester derivatives may particularly 
preferably be used in view of the safety and/or chemical stability of the 
solvent per se. 
In the present invention, in order to suppress a change in the ink 
characteristic which can be caused by drying, etc. in the storage of the 
ink, the above-mentioned organic solvent having a relative dielectric 
constant of 15 or larger may preferably have a (saturation) vapor pressure 
of 21 mmHg or smaller, more preferably 13 mmHg or smaller, at 25.degree. 
C. 
In a case where an organic solvent having a vapor pressure of above 21 mmHg 
at 25.degree. C. is used for the dispersion medium of the ink, when the 
ink is left standing in the air for a period of about several months to 
one year, such solvent vaporizes and the ink viscosity increases, whereby 
the application thereof onto an ink-carrying member, etc., becomes 
difficult to some cases. 
In the present invention, the organic solvent having a relative dielectric 
constant of 15 may preferably be contained in the ink in an amount of 10 
-99 wt. %, more preferably 30-95 wt. %, based on the total weight of the 
ink. 
In the present invention, as the liquid dispersion medium, the organic 
solvent having a relative dielectric constant of 15 or larger may be used 
singly or as a mixture of two or more species. Further, as desired, such 
organic solvent may be used as a mixture with an inorganic solvent (such 
as water), or as a mixture with a liquid having a relative dielectric 
constant of below 15. 
When a mixture comprising the above-mentioned organic solvent is used as 
the liquid dispersion medium, this mixture per se may preferably have a 
relative dielectric constant of 15 or above. Further, the organic solvent 
having a relative dielectric constant of 15 or above may preferably be 
contained in an amount of 10 parts or more, more preferably 30 parts or 
more, particularly preferably 50 parts or more, in 100 parts of the 
above-mentioned mixture. 
In the present invention, there may particularly preferably be used a 
liquid dispersion medium comprising water, a glycol-type solvent 
(preferably having a relative dielectric constant of 20-45), and an 
organic solvent having a relative dielectric constant of 80 or larger 
(more preferably 140 or larger) at 25.degree. C. The water contained in 
the liquid dispersion medium suitably provides a film-forming property to 
the ink and facilitates a sensitive recording under low-energy 
application. Further, when the organic solvent having a relative 
dielectric constant of 80 or larger at 25.degree. C. is contained in the 
liquid dispersion medium, the electric conductivity of the ink may be 
increased and the ink may retain good sensitivity even when the water is 
vaporized. 
Preferred examples of the organic solvent having a relative dielectric 
constant of 80 or above used in the present invention may include: 
N-methylacetamide (relative dielectric constant at 25.degree. C. =191.3), 
N-methylformamide (ditto, 182.4), N-methylpropionamide (ditto, 172.2), 
ethylene carbonate (ditto, 89.6), etc. These organic solvents may be used 
singly or as a mixture of two or more species. In a case where a mixture 
of two or more species of the organic solvents is used, the entire mixture 
of the organic solvents may preferably have a relative dielectric constant 
of 80 or larger at 25.degree. C. 
On the other hand, preferred examples of the above-mentioned glycol-type 
solvent may include: propylene glycol, ethylene glycol, diethylene glycol, 
trimethylene glycol, dipropylene glycol, hexylene glycol, 
1,2,6-hexanetriol, tetraethylene glycol, polypropylene glycol, glycerin, 
etc. 
In such embodiment, the liquid dispersion medium may preferably comprise: 
10-35 parts (more preferably 15-25 parts) of water, 40-70 parts (more 
preferably 50-60 parts) of a glycol-type solvent, and 5-40 parts (more 
preferably 10-30 parts) of an organic solvent having a relative dielectric 
constant of 80 or above. Further, the liquid dispersion medium may more 
preferably comprise: 100-350 parts (particularly 200-300 parts) of a 
glycol-type solvent, and 40-120 parts (particularly 60-100 parts) of an 
organic solvent having a relative dielectric constant of 80 or above, per 
100 parts of water. 
If the amount of water is too small, the electric resistivity of the ink 
increases and the sensitivity thereof decreases to lower image density. On 
the other hand, if the amount of water is too large, non-selective 
transfer of the ink can occur. 
If the amount of the glycol-type solvent is too small, the viscosity of the 
ink increases and the application thereof onto an ink-carrying member 
becomes difficult in some cases. If the amount of the glycol-type solvent 
is too large, the ink viscosity decreases and the surface of the ink is 
liable to be disturbed by a recording electrode in contact therewith, 
thereby to invite a decrease in the resultant image quality. 
Further, if the amount of the organic solvent having a relative dielectric 
constant of 80 or larger is too small, sensitivity decrease in the ink due 
to water vaporization cannot be prevented sufficiently, and the resultant 
image density is lowered when the ink is used for a long period. If the 
amount of the above organic solvent is too large, the ink cannot be 
suitably applied onto an ink-carrying member. 
The crosslinked substance used in the present invention can form a 
crosslinked structure by itself e.g., based on its polymer characteristic, 
but can be used in combination with a crosslinking agent (or gelling 
agent) for more positively crosslinking the crosslinked substance in order 
to improve the ink characteristics when supplied with or not supplied with 
energy. 
A preferred class of the crosslinking agent may be ionic crosslinking 
agents, including: various salts such as CuSO.sub.4 ; boric acid source 
compounds capable of generating borate ions in water, such as borax and 
boric acid. When such an ionic crosslinking agent is used, it becomes easy 
to selectively provide the ink with an adhesiveness through an 
electrochemical reaction involving transfer of electrons or a pH change. 
As a result, the use of such an ionic crosslinking agent is preferred in 
order to suppress the consumption of pattern energy. The ionic 
crosslinking agent may preferably be used in a proportion of 0.05-3 parts, 
particularly 0.1-1.5 parts, per 100 parts of the crosslinked substance. 
Instead, a crosslink agent utilizing a crosslinking bond such as glyoxal or 
dialdehydebenzene can also be used. 
In the present invention, in order to adjust the pH of the ink, there may 
appropriately be added a strong or weak alkali such as NaOH, KOH and 
Na.sub.2 CO.sub.3, in a case where an alkaline component is used. 
Further, in order to adjust the conductivity of the ink at the time of 
energy application, a salt such as NaCl, LiCl, and KCl may be added 
thereto. 
Further, in order to adjust the viscoelasticity of the ink, fine powder 
filler such as silica and carbon black may appropriately be added thereto. 
The ink according to the present invention, on application of a pH change 
due to electric conduction, is at least partially subjected to a change in 
or destruction of the crosslinked structure to be reversibly converted 
into a sol state, whereby it is selectively imparted with an adhesiveness 
corresponding to the energy application pattern. 
According to our knowledge, e.g., when a polyvinyl alcohol crosslinked with 
borate ions is used as the crosslinked substance, the change in the 
crosslinked structure caused by a pH change may be considered as follows. 
Thus, when the borate ion bonded to the --OH group of the polyvinyl 
alcohol, 
##STR1## 
is subjected to an anodic reaction in the vicinity of an anode under 
electric conduction (or the addition of an electron acceptor such as 
hydrochloric acid), the pH of the ink is changed to the acidic side and 
electrons may be removed to destroy at least a part of the crosslinked 
structure, whereby the ink may be imparted with an adhesiveness 
selectively or imagewise. The reaction at this time may presumably be 
expressed by the following formula: 
##STR2## 
The above-mentioned sol-gel transition may be caused by a pH change, and 
the gelation is promoted along with a pH increase and the solation is 
promoted along with a pH decrease, while it varies depending on the 
polymerization degree or saponification degree of the polyvinyl alcohol, 
and the amount of the boric acid. 
The image recording ink according to the present invention preferably 
comprises a liquid dispersion medium and a crosslinked substance, as 
described above, and may further comprise, as desired, a colorant 
inclusive of dye, pigment and colored fine particles, a color forming 
compound capable of generating a color on electric conduction, an 
electrolyte providing a desired electroconductivity to the ink, or another 
additive such as an antifungal agent or an antiseptic. 
The colorant or coloring agent may be any of dyes and pigments generally 
used in the field of printing and recording, such as carbon black. Among 
these, a dye or pigment, particularly a pigment, having a relatively low 
affinity to the liquid dispersion medium is preferably used in order to 
suppress the coloring of a transfer-receiving medium, i.e., the 
intermediate transfer medium or a recording medium, due to the transfer 
thereto of the liquid dispersion medium under no electric conduction. The 
pigment or dye may preferably be used in a proportion of 0.1 part or more, 
more preferably 1-30 parts, particularly 1-10 parts, per 100 parts of the 
liquid dispersion medium. 
Further, the colorant may be in the form of fine colored particles, like a 
toner of various colors for electrophotography, obtained by dispersing a 
pigment or dye as described above in a natural or synthetic resin and 
forming the dispersion into fine particles. An ink containing such colored 
particles behaves like a dilatent liquid and is particularly preferred in 
respect of suppressing the transfer of the liquid dispersion medium to or 
coloring of the transfer-receiving medium under no electric conduction. 
The colored fine particles may preferably be used in a proportion of 1 part 
or more, further preferably 5-100 parts, particularly preferably 20-80 
parts, per 100 parts of the liquid dispersion medium. Generally speaking, 
it is preferred that colored particles having a large size are 
incorporated in a higher proportion in order to provide a better coloring 
characteristic. Incidentally, in the present invention, the above toner 
particles can be used regardless of the electrophotographic characteristic 
thereof such as chargeability. 
The colorant inclusive of the pigment or the colored fine particles may 
preferably have a particle size of 0.01-100 microns, particularly 0.01-20 
microns. 
If the particle size is below 0.01 micron, the colorant particles are not 
retained in the crosslinked structure but are transferred together with a 
minor portion of the liquid dispersion medium even when the ink contacts 
the intermediate transfer medium or the recording medium under no electric 
conduction, whereby an image fog is liable to result. On the other hand, 
if the particle size exceeds 100 microns, a resolution required for an 
ordinary image is not satisfied. 
The image recording ink according to the present invention may be obtained 
from the above components, for example, by uniformly mixing a liquid 
dispersion medium such as water, a crosslinked substance, and also an 
optional additive such as a crosslinking agent, a colorant, an 
electrolyte, etc., under heating as desired, to form a viscous solution or 
dispersion, which is then cooled to be converted into a gel. 
Incidentally, when colored particles such as toner particles are used as a 
colorant, it is preferred that a crosslinked substance and a liquid 
dispersion medium are first mixed under heating to form a uniform liquid, 
and then the colored particles are added thereto. In this case, it is 
further preferred that the addition of the colored particles is effected 
in the neighborhood of room temperature so as to avoid the agglomeration 
of the particles. 
Then, there is described a method of applying an electric current to the 
ink of the present invention. 
In a case where a pH change is imparted to the ink by using an electrode, 
the pH change does not diffuse three-dimensionally like heat, but 
selectively diffuses in the direction of the ink depth (i.e., in the 
direction of the current), whereby the clearness of the resultant ink 
pattern (e.g., sharpness and image quality) may be enhanced. 
Incidentally, when a recording is effected by using a pH change based on 
electric conduction, the anode material can be dissolved due to 
electrolysis. Accordingly, when the recording electrode is an anode, it is 
preferred to use an inert metal such as platinum, as the material for the 
recording electrode. In such case, however, fine or micro fabrication such 
as photolitho-etching is required. As a result, e.g., by using 
electron-beam deposition or sputtering, the production cost relatively 
tends to increase. 
On the other hand, in a case where the recording electrode is a cathode, 
the above-mentioned fine fabrication is not required whereby the 
production cost may preferably be reduced. As the ink which can be used in 
such cathodic recording, there may preferably be used an ink comprising a 
peptide compound such as a protein, and an aqueous dispersion medium, 
wherein the initial or unused pH value is higher than the isoelectric 
point of the peptide compound, e.g., by adding an aqueous alkaline 
solution thereto. 
Hereinbelow, there will be described an embodiment of the image recording 
method using the image recording ink of the present invention as described 
above. 
Referring to FIG. 1 which is a schematic sectional view taken across the 
thickness of a recording medium showing an embodiment of the recording 
apparatus used in such recording method, an ink-carrying roller 1 having a 
surface of stainless steel, etc., within an ink container 3 for holding 
therein an ink 2 of the present invention so that it rotates in the 
direction of an arrow A while carrying the ink 2. 
Above the ink-carrying roller 1 at an ink transfer position, there is 
disposed, with a certain gap from the surface (i.e., the ink-carrying 
face) of the ink-carrying roller 1, an intermediate transfer roller 4 as 
an intermediate transfer medium which is composed of, e.g., a cylinder of 
iron coated with a hard chromium plating, and rotates in the direction of 
an arrow B. The intermediate transfer roller 4 is disposed so that the 
surface thereof may contact a layer 2a of the ink 2 formed on the 
ink-carrying roller 1. 
On the other hand, at an ink pattern transfer position, a recording medium 
5 of, e.g., plain paper is disposed in contact with the surface of the 
intermediate transfer roller 4 (i.e., the surface on which an ink pattern 
is to be formed) and is conveyed in an arrow C direction. Further, so as 
to movably sandwich the recording medium 5 with the intermediate transfer 
roller 4, a platen roller 6 having a surface of silicone rubber, etc., and 
rotating in an arrow D direction is disposed opposite to the intermediate 
transfer roller 4. 
Above the ink-carrying roller 1 at a position upstream from the ink 
transfer position where the ink-carrying roller 1 and the intermediate 
transfer 4 are disposed opposite to each other, a recording electrode 7 as 
a means for applying an energy corresponding to a given signal is disposed 
with a certain spacing from the surface of the roller 1. The tip of the 
electrode 7 provided with an electrode element is disposed so that it can 
contact the layer 2a of the ink 2 formed on the ink-carrying roller 1. 
Then, there will be described the operation of the recording apparatus 
having the above-mentioned basic structure. 
Incidentally, in the present invention, it is possible to selectively 
transfer a portion of the ink 2 not supplied with an energy to the 
intermediate transfer roller 4, e.g., by imparting a pulse in a reverse 
direction to the recording electrode 7. Hereinbelow, however, there will 
be described a preferred embodiment wherein a portion of the ink 2 
supplied with an energy is selectively transferred to the intermediate 
transfer roller 4. 
Referring again to FIG. 1, the ink 2 in the ink container 3 is one 
according to the present invention which is substantially non-adhesive and 
can be imparted with an adhesiveness under electric conduction. The ink 2 
is carried on the ink-carrying roller 1 as in ink layer 2a and conveyed in 
an arrow E direction along with the rotation in the arrow A direction of 
the roller 1. 
The fluid ink 2 moved in this way is supplied with a pattern of voltage 
corresponding to an image signal from the recording electrode 7 at an 
energy application position where the ink 2 contacts the electrode 7. A 
current corresponding to the voltage flows between the recording electrode 
7 and the ink-carrying roller 1 through the ink 2, whereby the ink 2 is 
selectively imparted with an adhesiveness, e.g., because of a change in 
crosslinking structure through an electro-chemical reaction in the ink 2. 
A portion of the ink 2 selectively imparted with an adhesiveness is further 
moved in the arrow E direction to reach the ink transfer position where 
the intermediate transfer roller 4 contacts the ink 2, and the at least a 
portion of the ink 2 constituting the ink layer 2a is transferred onto the 
intermediate transfer roller 4 rotating in the arrow B direction, on the 
basis of the above-mentioned adhesiveness, thereby to form an ink pattern 
21 thereon. 
The ink pattern 21 is then conveyed along with the rotation in the arrow B 
direction of the intermediate transfer roller 4 to reach the ink 
pattern-transfer position where the roller 4 confronts the platen roller 6 
by the medium of the recording medium 5. At the ink pattern-transfer 
position, the ink pattern 21 formed on the intermediate transfer medium 4 
is transferred to the recording medium 5 under a pressure exerted by the 
platen 6 thereby to form a transferred image 22. 
Further, it is also possible to dispose a known fixing means (not shown) as 
by heating or pressing, downstream of the ink pattern-transfer position in 
order to ensure the fixation of a transfer-recorded image 22 formed on the 
recording medium 5. Further, the ink remaining on the intermediate 
transfer roller 4 after the transfer of the ink pattern 21 to the 
recording medium 5, may for example be removed, e.g., by a cleaning means 
8 including a blade 8a for scraping the ink in contact with the 
intermediate transfer roller 4. 
On the other hand, the remainder of the ink 2 not transferred onto the 
intermediate transfer roller 4 at the above-mentioned ink transfer 
position is further moved in the arrow E direction and is separated from 
the intermediate transfer roller 4 by gravity, etc., because of its 
non-adhesiveness to be returned into the ink container 3 and reused 
because of its fluidity. 
Incidentally, a somewhat negative shear force is applied at the point of 
separation between the intermediate transfer roller 4 and the ink layer 
2a. For this reason, it is preferred to make the peripheral speed of the 
intermediate transfer roller 4 smaller than (or equal to) the peripheral 
speed of the ink-carrying roller 1 so as to apply to the ink layer 2a a 
shear force based on the difference in peripheral speed, in respect to 
stabilization of separation of the ink layer 2a and the intermediate 
transfer roller 4. 
In a case where the ink 2 is in the form of a sludge ink, it is presumed 
that the ink is not substantially transferred to the intermediate transfer 
roller 4 because the particles contained therein are tightly aligned on 
the ink interface so that the contact of the dispersion medium to the 
intermediate transfer roller 4 is suppressed under no energy application. 
In an embodiment wherein the ink is electrochemically supplied with an 
adhesiveness, when a crosslinked substance comprising guar gum crosslinked 
with borate ions is used, the amount of current required for breaking at 
least a part of the crosslinked structure is only such an amount as 
required for causing transfer of electrons from crosslinking borate ions 
which are generally used in a considerably small amount, e.g., on the 
order of several hundred ppm of the ink. 
The above amount of current is almost 1/10 of the amount of current 
required by a thermal head, so that a low energy consumption recording may 
be effected by using such an electrochemical change. 
FIG. 4 shows an embodiment of the recording electrode 7. With reference to 
FIG. 4 which is an enlarged partial perspective view, the recording 
electrode 7 may be obtained by forming a plurality of electrode elements 
72 of a metal such as Cu on a substrate 71, and coating the electrode 
elements 72 except for the tip portions thereof contacting the ink with an 
insulating film 73 of polyimide, etc. The exposed tip portions of the 
electrode elements 72 may preferably be coated with a plating of Au, Pt, 
etc. In view of the durability, a Pt plating is preferred. 
In an embodiment already explained with reference to FIG. 1, a current is 
passed between the recording electrode 7 and the ink-carrying roller 1, 
but it is also possible that a current is passed between an adjacent pair 
of the plurality of electrode elements 72 on the recording electrode 7. 
In an embodiment shown in FIG. 2, an ink 2 is applied onto an ink-carrying 
roller 1 by a roller coating method. Referring to FIG. 2, there is 
provided an ink-holding member 3a being capable of holding therein an 
image recording ink 2. Below the ink-holding member 3a, i.e., on the side 
of an ink-supply part thereof through which the ink 2 can be flown, there 
is disposed an ink-application roller 11 for applying the ink 2 onto the 
ink-carrying roller 1, which is rotatable in the direction of an arrow F. 
The embodiment shown in FIG. 2 is substantially the same as that shown in 
FIG. 1 except that the image recording ink 2 is applied onto the 
ink-carrying roller 1 by means of the ink-holding member 3a and the ink 
application roller 11. 
As described hereinabove, in the present invention, an organic solvent 
having a specific relative dielectric constant is used as an liquid 
dispersion medium. However, such organic solvent, especially one 
compatible with water, can absorb moisture contained in the air under a 
certain storage condition for an ink. Herein, "organic solvent compatible 
with water" refers to one having a property such that 100 parts thereof is 
uniformly mixable with 30 parts or more of water at 25.degree. C. 
For example, in a case where the ink obtained in Example 12 appearing 
hereinafter, which comprised ethylene glycol as an organic solvent 
compatible with water, and polyvinyl alcohol as a crosslinked substance, 
was left open to the air (25.degree. C., 50% RH), the ink weight increased 
with the elapse of time as shown by a curve (a) in FIG. 5, and ink 
properties such as volume resistivity and viscoelasticity changed along 
therewith. When the ink was left standing in an airtight container, such 
phenomenon did not occur. 
On the other hand, when an ink obtained in Comparative Example 4 appearing 
hereinafter was left open to the air, it showed a change in the ink weight 
as shown by a curve (b) in FIG. 5, and after it was left standing for one 
week (168 hours), the weight was substantially the same as that of the 
solid content thereof. The reason for this may clearly be considered that 
the water content in the ink is lost due to drying. 
When the water content of the above-mentioned ink of Example 12, after 
being left standing in the air, was measured by using a Karl Fischer's 
reagent, it was found that substantially all of the above-mentioned weight 
increase was based on a water content. Accordingly, it was assumed that 
this weight increase was based on the absorption of water vapor in the 
air. 
Incidentally, the ink of Example 12 may cause no problem in practice when 
it has been subjected to sufficient aging operation in production process 
therefor, e.g., by leaving it open in a room for about four days. however, 
such aging time ordinarily becomes a time loss in the production process. 
Further, in a case where such ink is commercially handled, the 
above-mentioned aging cannot occur because the ink is ordinarily stored in 
an airtight container. 
Accordingly, in a case where the above-mentioned absorption of water 
content can cause a certain problem, it is preferred that in the 
production process for the ink, an organic solvent or a mixture of two or 
more species thereof having a low vapor pressure and a high dielectric 
constant may be selected as a dispersion medium, and the organic solvent 
is preliminarily mixed with an amount of water corresponding to an 
equilibrium water content. Such preliminary addition of water is preferred 
in order to considerably suppress a change in the ink characteristic based 
on moisture absorption or drying. 
The "equilibrium water content" used herein refers to the water content in 
a mixture of an organic solvent and water which has been left open to the 
air at constant temperature and humidity to reach a certain equilibrium 
state wherein the vaporization of the water content of the mixture is in 
equilibrium with the absorption of the moisture of the air into the 
mixture. 
As an example of the above equilibrium water content, FIG. 6 shows some 
data which are taken from "Glycols" published by Union Carbide Chemical 
Corp. Referring to FIG. 6, for example, with respect to 100 parts of 
ethylene glycol, the amount of absorbed water is about 25 parts and the 
equilibrium water content is about 20% at 50% RH (21.degree.-27.degree. 
C.). 
As shown in FIG. 6, the equilibrium water content considerably changes 
depending on humidity. In view of commercial handling, it is preferred 
that an ink for use in a recording apparatus is usable under a humidity 
condition of 30-70% RH, more preferably 10-90% RH. Accordingly, it is 
clearly preferred to preliminarily add a water content to an ink in order 
to prevent a characteristic change in the ink, as compared with in the 
case of no preliminary addition of water content to the ink. 
For the above reason, it is preferred that a water content is preliminarily 
added to 100 parts of a dispersion medium comprising an organic solvent in 
an amount which corresponds to one in the range of from an equilibrium 
water content at 25.degree. C. and 30% RH, to an equilibrium water content 
at 25.degree. C. and 70% RH. More specifically, as shown in the following 
Table 1, it is preferred to preliminarily add a water content to 100 parts 
of each organic solvent in an amount (parts) as described below. 
TABLE 1 
______________________________________ 
Organic solvent (100 parts) 
Water (parts) 
______________________________________ 
Ethylene glycol 12-60 
Glycerin 11-60 
Diethylene glycol 10-55 
Propylene glycol 9-50 
Triethylene glycol 7-40 
1,2,6-Hexanetriol 5-30 
Dipropylene glycol 4-25 
Hexylene glycol 2.5-10 
______________________________________ 
In the case of another organic solvent, or a mixed solvent, it is possible 
to consider a preferred water content in the same manner as described 
above. 
The above-mentioned equilibrium water content corresponds to a water 
content (parts) which is to be absorbed into 100 parts of an organic 
solvent when the organic solvent is left standing with an environment of 
constant temperature and humidity for a sufficiently long period. This 
equilibrium water content may be easily measured by means of a measurement 
system comprising an airtight container, as shown in FIG. 7. 
More specifically, referring to FIG. 7, about 0.1 liter of mixed solvent 17 
comprising 100 parts of an organic solvent (sample) and X parts of water 
is charged in an airtight container 16 (inner volume: about 1 liter) 
equipped with a hygrometer 15. Then, the remainder portion of the 
container 16 is filled with dry air 18, and the resultant system is left 
standing at 25.degree. C. until the indication of the hygrometer 15 
reaches an equilibrium. Thus, the humidity (Y %) at this time is measured. 
By using several species of the mixed solvents each comprising X parts of 
water and 100 parts of an organic solvent, the equilibrium water content 
corresponding to each water content (X) is measured, and the resultant 
values are interpolated to obtain the value of X (X.sub.30) corresponding 
to a humidity of 30% (Y.sub.30) and the value of X (X.sub.70) 
corresponding to a humidity of 70% (Y.sub.70). The thus obtained X.sub.30 
and X.sub.70 are used as equilibrium water contents at humidities of 30% 
and 70% respectively. 
In the ink according to the present invention, corresponding to the thus 
obtained X.sub.30 and X.sub.70, it is preferred to use as a liquid 
dispersion medium a mixture which has been obtained by preliminarily 
adding water to 100 parts of an organic solvent in an amount of x (parts) 
satisfying X.sub.30 23 x.ltoreq.X.sub.70. 
The thus prepared ink is stored and transported ordinarily in a state of 
being contained in an airtight container, and is commercially handled. In 
practice, the ink is opened in an environment of 25.degree. C., 50% RH, 
and the water content thereof (A) is measured by using a Karl Fischer's 
reagent, etc. Then, the ink is subjected to vacuum drying to measure the 
solid content (C) thereof, and the amount of a dispersion medium (B) is 
determined by the equation of B=100 - C. 
In this case, an actual ink may preferably satisfy the following formula: 
EQU X.sub.30 /(100+X.sub.30).ltoreq.A/B.ltoreq.X.sub.70 /(100+X.sub.70) 
Hereinbelow, the present invention will be explained with reference to 
Examples which however are not intended to restrict the scope of invention 
in any way. 
EXAMPLES 
Example 1 
Ethylene glycol: 30 parts 
(boiling point (b.p.)=198.degree. C., Relative dielectric constant 
(.epsilon..sub.r)=38.66 at 20.degree. C.) 
Polyvinyl alcohol: 3 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku Kogyo K.K.) 
Dye: 1.2 parts 
(Kayacion Red P-2B, mfd. by Nihon Kayaku K.K.) 
Silica: 4 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
The above components were sufficiently mixed under heating at 
60.degree.-70.degree. C., and to the resultant mixture, 20 drops of 
triethanolamine and 60 drops of a 20 wt. % ethylene glycol solution of 
sodium borate (Na.sub.2 B.sub.4 O.sub.7) were added. Thereafter, the 
resultant mixture was cooled to room temperature (25.degree. C.) thereby 
to obtain a gel ink having a fluidity according to the present invention. 
Then, by using the above-mentioned gel ink, image formation was effected by 
means of a recording apparatus as shown in FIG. 1. 
The gel ink was charged in an apparatus as shown in FIG. 1 wherein an 
ink-carrying roller 1 comprising a cylindrical roller of 40 mm in diameter 
having a surface of stainless steel with a surface roughness of 100 S and 
an intermediate transfer roller 4 comprising an iron cylindrical roller of 
40 mm in diameter having a surface coated with a hard chromium plating 
were disposed opposite to each other with a gap of 1 mm at an ink transfer 
position. The gel ink 2 obtained above was charged in the ink container 3. 
The ink-carrying roller 1 was rotated in the arrow A direction at about 15 
rpm to form thereon a layer 2a of the ink 2, whereby the fluid ink 2 
according to the present invention was uniformly applied onto the 
ink-carrying roller 1 and the surface of the applied ink layer 2a was very 
smooth. 
In contact with the thus formed ink layer 2a, the intermediate transfer 
roller 4 was rotated in the arrow B direction at about 15 rpm. In this 
instance, when electric energy was not supplied from a recording electrode 
7 to the ink layer 2a, the ink 2 was not substantially transferred to the 
intermediate transfer roller 4. The recording electrode 7 had a structure 
as shown in FIG. 4, wherein each electrode element 72 of copper was coated 
with an insulating film 73 of polyimide except for a tip thereof which was 
coated with gold plating in an area of 100.times.100 microns. 
On the other hand, when a pulse of 30 V and 2 msec was applied through the 
ink layer 2a between the recording electrode 7 as an anode and the 
ink-carrying roller 1 as a cathode to pass a current, the ink 2 was 
selectively transferred to the intermediate transfer roller 4 to form an 
ink pattern 21 thereon. 
At an ink image-transfer position, a platen roller 6 of a 20 mm-dia. iron 
cylindrical roller surfaces with 10 mm-thick silicone rubber layer was 
disposed opposite to the intermediate transfer roller 4 with a recording 
medium 5 of plain paper disposed therebetween moving in the arrow C 
direction. Further, the platen roller 6 was rotated in the arrow D 
direction at the same speed as the intermediate transfer roller 4 while 
exerting a slight pressure onto the recording medium 5. As a result, 
red-colored dot images (printed letter) 22 corresponding to the 
above-mentioned ink pattern 21 were formed on the recording medium 5. 
The transferred image 22 obtained on the recording medium 5 was a 
high-quality image having a sufficiently high image density without 
trailing, fog, or blurring, etc. 
Incidentally, the fluid ink 2 of the present invention was charged in a 
polymer cup (mfd. by Sanko Plastic K.K.) having a volume of 100 ml, and 
was left open in an atmospheric pressure at room temperature 
(22.degree.-27.degree. C.) and a humidity of 50% for 180 days to examine 
the effect of drying on the ink. As a result, there was substantially no 
change in the viscoelasticity of the ink due to drying, and it was found 
that the ink of the present invention was excellent in storage stability. 
Example 2 
An ink was prepared in the same manner as in Example 1 except that 
dimethylsulfoxide (b.p.=189.degree. C., .epsilon..sub.r =48.9) was used as 
an organic solvent instead of ethylene glycol used in Example 1. The thus 
prepared ink was subjected to image formation by using the same apparatus 
and method as in Example 1 to evaluate the resultant image, whereby good 
results substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was substantially no change in 
the viscoelasticity of the ink even after it was left for 180 days. 
Example 3 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 15 parts of ethylene glycol and 15 parts of N-methylformamide 
(b.p.=185.degree. C., .epsilon..sub.r =182.4) was used as an organic 
solvent instead of 30 parts of ethylene glycol used in Example 1. The thus 
prepared ink was subjected to image formation by using the same apparatus 
and method as in Example 1 to evaluate the resultant image, whereby good 
results substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, similarly as in Example 1, there was 
substantially no change in the viscoelasticity of the ink even after it 
was left for 180 days. 
Example 4 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 15 parts of ethylene glycol and 15 parts of formamide 
(b.p.=210.5.degree. C., .epsilon..sub.r =111.0) was used as an organic 
solvent instead of 30 parts of ethylene glycol used in Example 1. The thus 
prepared ink was subjected to image formation by using the same apparatus 
and method as in Example 1 to evaluate the resultant image, whereby good 
results substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was substantially no change in 
the viscoelasticity of the ink similarly as in Example 1. 
Example 5 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 20 parts of ethylene glycol and 10 parts of 
hexamethylphosphoric triamide (b.p.=233.degree. C., .epsilon..sub.r =29.6) 
was used as an organic solvent instead of 30 parts of ethylene glycol used 
in Example 1. The thus prepared ink was subjected to image formation by 
using the same apparatus and method as in Example 1 to evaluate the 
resultant image, whereby good results substantially the same as in Example 
1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was substantially no change in 
the viscoelasticity of the ink similarly as in Example 1. 
Example 6 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 20 parts of ethylene glycol and glycerin (b.p.=290.degree. C., 
.epsilon..sub.r =42.5) was used as an organic solvent instead of 30 parts 
of ethylene glycol used in Example 1. The thus prepared ink was subjected 
to image formation by using the same apparatus and method as in Example 1 
to evaluate the resultant image, whereby good results substantially the 
same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was substantially no change in 
the viscoelasticity of the ink similarly as in Example 1. 
Example 7 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 20 parts of ethylene glycol and 10 parts of water 
(b.p.=100.degree. C., .epsilon..sub.r =80.1) was used instead of 30 parts 
of ethylene glycol used in Example 1. The thus prepared ink was subjected 
to image formation by using the same apparatus and method as in Example 1 
to evaluate the resultant image, whereby good results substantially the 
same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was a slight increase in the 
ink viscosity, but the fluidity thereof was substantially retained so that 
the ink 2 could sufficiently be applied onto the ink-carrying roller 1 
shown in FIG. 1. 
Example 8 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 10 parts of water and 20 parts of N-methylformamide 
(b.p.=180.degree. C., .epsilon..sub.r = 182.4) was used instead of 30 
parts of ethylene glycol used in Example 1. The thus prepared ink was 
subjected to image formation by using the same apparatus and method as in 
Example 1 to evaluate the resultant image, whereby good results 
substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was a slight increase in the 
ink viscosity, but the fluidity thereof was substantially retained so that 
the ink 2 could sufficiently be applied onto the ink-carrying roller 1 
shown in FIG. 1. 
Example 9 
An ink was prepared in the same manner as in Example 1 except that a 
mixture of 13 parts of water and 17 parts of N-methylacetamide 
(b.p.=206.degree. C., .epsilon..sub.r =191.3 at 32.degree. C.) was used 
instead of 30 parts of ethylene glycol used in Example 1. The thus 
prepared ink was subjected to image formation by using the same apparatus 
and method as in Example 1 to evaluate the resultant image, whereby good 
results substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was a slight increase in the 
ink viscosity, but the fluidity thereof was substantially retained so that 
the ink 2 could sufficiently be applied onto the ink-carrying roller 1 
shown in FIG. 1. 
Example 10 
An ink was prepared in the same manner as in Example 1 except that 
formamide (b.p.=210.5.degree. C., .epsilon..sub.r =111.0 at 20.degree. C.) 
was used instead of ethylene glycol used in Example 1. The thus prepared 
ink was subjected to image formation by using the same apparatus and 
method as in Example 1 to evaluate the resultant image, whereby good 
results substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1. As a result, there was substantially no change in 
the viscoelasticity of the ink, similarly as in Example 1. 
Comparative Example 1 
An ink was prepared in the same manner as in Example 1 except that 30 parts 
of water was used instead of 30 parts of ethylene glycol used in Example 
1. The thus prepared ink was subjected to image formation by using the 
same apparatus and method as in Example 1 to evaluate the resultant image, 
whereby good results substantially the same as in Example 1 were obtained. 
Further, the above-mentioned ink was subjected to a drying test in the same 
manner as in Example 1, whereby the solvent was dried up and the ink was 
hardened. The resultant ink, as such, could not be used for image 
formation. 
Comparative Example 2 
Xylene: 30 parts 
(.epsilon..sub.r =2.266 at 20.degree. C., vapor pressure&lt;100 mmHg) 
Ethylene-vinyl acetate copolymer resin: 10 parts 
(Evaflex 45X, mfd. by Mitsui-Du Pont Polychemical K.K.) 
Pigment: 2 parts 
(Cromophtal Blue 4GNP, mfd. by Nihon Ciba-Geigy K.K.) 
The above components were sufficiently mixed under heating to obtain a gel 
ink having a fluidity. 
Image formation was attempted by applying the thus prepared ink to the 
image recording apparatus as shown in FIG. 1 in the same manner as in 
Example 1. However, the transferred image had much fog and soiling and was 
not suitable at all. 
Comparative Example 3 
An ink was prepared in the same manner as in Comparative Example 2 except 
that tetrahydrofuran (vapor pressure=176 mmHg at 25.degree. C., 
.epsilon..sub.r =7.58) was used instead of xylene. 
Image formation was attempted by applying the thus prepared ink to the 
image recording apparatus as shown in FIG. 1 in the same manner as in 
Comparative Example 1. However, the transferred image had much fog and 
soiling and was not suitable at all. Further, the ink was poor in storage 
stability because it was dried up in a short time. 
Example 11 
Ethylene glycol: 80 parts 
Water: 20 parts 
Polyvinyl alcohol 11 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku Kogyo K.K., average 
polymerization degree: 300, saponification degree: 88 mol %) 
Carbon black: 11 parts 
Silica: 11 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
NaCl: 6.6 parts 
The above components were sufficiently mixed at a high temperature 
(80.degree. C.) and then cooled. Then, 1.5 parts of borax (Na.sub.2 
B.sub.4 O.sub.7 .multidot.5H.sub.2 O) and 4.3 parts of 1N-NaOH were added 
to the resultant mixture, thereby to prepare a gel ink having a fluidity. 
When the thus prepared ink was left open in a room at 25.degree. C. and 50% 
RH, it should substantially no weight change as shown by a curve (C) in 
FIG. 5. Further, even after the ink was left standing for 450 hours, it 
showed substantially no change in apparent physical property thereof such 
as viscoelasticity as compared with the initial state. 
Separately, the same gel ink was stored in an airtight polyethylene bottle 
in the same room as described above. 
The thus obtained two species of inks, i.e., Ink (A) which had been left 
opening the room and Ink (B) which had been stored in the airtight bottle, 
were respectively subjected to image formation by means of an image 
recording apparatus as shown in FIG. 2. 
In FIG. 2, an ink-application roller 11 comprising a cylindrical roller of 
40 mm in diameter having a surface of stainless steel 304 of which surface 
had been ground with a grinder, and an ink-carrying roller 1 comprising a 
stainless steel 304 roller of 40 mm in diameter of which surface had been 
subjected to blasting treatment so as to provide a roughness of R.sub.Z 
=100 microns were disposed opposite to each other with a gap of d.sub.1 =2 
mm at an ink supply position. Further, an intermediate transfer roller 4 
comprising a stainless steel 304 roller of 40 mm in diameter, of which 
surface had been ground with a grinder, and the above-mentioned 
ink-carrying roller 1 were disposed opposite to each other with a gap of 
d.sub.2 =2 mm at an ink transfer position. Each of the two species of gel 
inks of (Ink (A) and Ink (B)) of the present invention obtained above was 
charged in an ink-holding member 3a. 
The ink-carrying roller 1 was rotated in the arrow A direction at about 20 
rpm, and the ink-application roller 11 was rotated in the arrow F 
direction at about 10 rpm to form a layer 2a of the ink 2 on the 
ink-carrying roller 1. As a result, the fluid ink 2 of the present 
invention could be uniformly applied onto the ink-carrying roller 1 and 
the surface of the ink layer applied onto the ink-carrying roller 1 was 
extremely smooth. 
Then, in contact with the layer 2a of the ink 2, the intermediate transfer 
roller 4 was rotated in the arrow B direction at about 20 rpm. In this 
instance, when electric energy was not supplied from a recording electrode 
7 to the ink layer 2a, the ink 2 was not substantially transferred to the 
intermediate transfer roller 4. The recording electrode 7 was disposed 
with a gap of d.sub.3 =1.7 mm from the surface of the ink-carrying roller 
1, at an energy application position. 
The recording electrode 7 had a structure wherein each electrode element of 
copper was coated with an insulating film except for a tip thereof which 
was coated with rhodium plating in an area of 100.times.100 microns. 
On the other hand, when a pulse of 25 V and 2 msec was applied through the 
ink layer 2a between the recording electrode 7 as an anode and the 
ink-carrying roller 1 as a cathode to pass a current, the ink 2 was 
selectively transferred to the intermediate transfer roller 4 to form an 
ink pattern 21 thereon. 
At an ink image-transfer position, a platen roller 6 of a 16 mm-dia. iron 
cylindrical roller surfaced with 2 mm-thick silicone rubber layer was 
disposed opposite to the intermediate transfer roller 4 with a recording 
medium 5 of plain paper disposed therebetween moving in the arrow C 
direction. Further, the platen roller 6 was rotated in the arrow D 
direction at the same speed as the intermediate transfer roller 4 while 
exerting a slight pressure onto the recording medium 5. As a result, black 
colored dot images (printed letter) 22 corresponding to the 
above-mentioned ink pattern 21 were formed on the recording medium 5. 
When any of the Ink (A) and the Ink (B) was used, the transferred image 22 
obtained on the recording medium 5 was a high-quality image having a 
sufficiently high image density without trailing, fog, or blurring, etc. 
Incidentally, with respect to the image forming apparatus as shown in FIG. 
2 used in this instance, it is possible to refer to a preceding patent 
application filed by our research group (Japanese Patent Application No. 
125970/1987). 
Comparative Example 4 
Water: 30 parts 
Polyvinyl alcohol: 3 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku Kogyo K.K.) 
Dye: 1.2 parts 
(Kayacion Red P-2B, mfd. by Nihon Kayaku K.K.) 
Silica: 4 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
The above components were sufficiently mixed under heating, and to the 
resultant mixture, 20 drops of 1N-NaOH and 60 drops of a 20 wt. % ethylene 
glycol solution of sodium borate (Na.sub.2 B.sub.4 O.sub.7) were added. 
Thereafter, the resultant mixture was cooled to room temperature 
(25.degree. C.) thereby to obtain a gel ink having a fluidity. 
Then, by using the above-mentioned gel ink, image formation was effected by 
means of a recording apparatus as shown in FIG. 2. As a result, a good 
transferred image 22 was obtained when a pulse of 10 V and 2 msec was 
used. 
On the other hand, when this ink was left open at 25.degree. C. and 50% RH, 
it showed a weight decrease as shown by a curve (b) in FIG. 5. Further, 
after being left standing for 20 hours, the ink could not be applied onto 
the ink-carrying roller 1, and could not be used. On the contrary, when 
the ink was stored in an airtight polymer bottle, the performance thereof 
was stable so as not to be changed from its original state, even after the 
ink was left standing for 450 hours. 
Example 12 
An ink containing substantially no water was prepared in the same manner as 
in Example 11 except that the mixture comprising 80 parts of ethylene 
glycol and 20 parts of water was replaced by 100 parts of ethylene glycol 
from which water content had been sufficiently removed, the borax 
(pentahydrate) was replaced by anhydrous borax, and the aqueous NaOH 
solution was replaced by 2.6 parts of triethanolamine. 
When the thus prepared ink was subjected to image formation, it provided an 
image substantially the same as in Example 11. Incidentally, in this 
instance, the recording voltage was required to be about 30 V. 
When the ink was left open in the air at 25.degree. C., 50% RH, it showed a 
weight change as shown by a curve (a) in FIG. 5. After being left standing 
for 100 hours, the ink showed a certain increase in adhesiveness, and it 
was liable to provide slight image fog. However, when 0.5 part of borax 
was added to such ink, the ink substantially recovered its initial state. 
On the other hand, when the ink was stored in an airtight polymer bottle, 
it provided a good image without problem even after being left standing 
for 450 hours. 
Comparative Example 5 
An ink was prepared in the same manner as in Example 11 except that 100 
parts of water was used alone and ethylene glycol was not used. 
The thus prepared ink provided a good image in the initial stage. However, 
when this ink was left open in the air at 25.degree. C. and 50% RH, after 
being left standing for 20 hours, the ink could not be applied onto the 
ink-carrying roller 1, and could not be used. On the contrary, when the 
ink was stored in an airtight polymer bottle, such phenomenon did not 
occur. 
Examples 13-15 
Inks were prepared in the same manner as in Example 11 except that the 
components shown in the following Table 2 were respectively used. 
TABLE 2 
______________________________________ 
Components Ex. 13 Ex. 14 Ex. 15 
______________________________________ 
Ethylene glycol 80 90 62 
(parts) 
Water 16 6 34 
Polyvinyl alcohol 20 20 20 
(Gohsenol GL-03, average 
polymerization degree: 300, 
saponification degree: 88 mol %) 
KCl 2 2 2 
Carbon black 3 3 3 
20 wt. % ethylene glycol 
4 4 4 
solution of borax 
1N-NaOH aqueous solution 
4 about about 
4 4 
______________________________________ 
In the ink obtained in the above Examples 13-15, water was contained in 
amounts of 25, 12 and 60 parts, respectively, per 100 parts of ethylene 
glycol. 
When the thus obtained inks of Examples 13-15 were respectively subjected 
to image formation in the same manner as in Example 11, they provided good 
images. Further, the voltage required for such image formation was as low 
as about 10 V, while the reason therefor was not necessarily clear. 
Even after these inks of Examples 13-15 were left open in a room 
(25.degree. C., 50% RH) for one week, they respectively provided good 
images in the image formation as described above, while the ink of Example 
14 was somewhat softened and that of Example 15 was somewhat hardened. 
Example 16 
An ink was prepared in the same manner as in Comparative Example 4 except 
that 30 parts of water was replaced by a mixture comprising 23 parts of 
ethylene glycol and 7 parts of water. The thus obtained ink was excellent 
in storage stability and image formation stability, even after being left 
open in the air. 
Examples 17-22 
Inks were prepared in the same manner as in Example 13 except that 
dispersion compositions shown in the following Table 3 were respectively 
used, instead of the mixture of 80 parts of ethylene glycol and 16 parts 
of water used in Example 13. 
TABLE 3 
______________________________________ 
Example 
Component 17 18 19 20 21 22 
______________________________________ 
Propylene glycol 
89 80 66 -- -- -- 
Diethylene glycol 
-- -- -- 91 80 65 
Water 11 20 34 9 20 35 
______________________________________ 
Incidentally, the amount of the 1N-NaOH aqueous solution was appropriately 
adjusted so that each ink showed a hardness (or fluidity) the same as that 
of the ink of Example 13, immediately after the production thereof. 
When the thus prepared inks were subjected to an image formation test and a 
storage stability test in the same manner as in Example 11, they 
respectively provided good results substantially the same as in Example 
11. 
Example 23 
Composition A 
Propylene glycol: 15 parts 
Water: 5 parts 
N-methylformamide: 6 parts 
(.epsilon..sub.r =182.4 at 25.degree. C.) 
Polyvinyl alcohol: 6 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku K.K.) 
Potassium iodide: 3.5 parts 
Carbon black: 2.5 parts 
(Stering SR, mfd. by Cabot Co., U.S.A.) 
Composition B 
Silica: 3 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
20 wt. % Propylene glycol solution of sodium tetraborade: 2.5 parts 
1N-NaOH aqueous solution: 0.5 part 
The above components in Composition A were uniformly mixed under heating at 
80.degree.-90.degree. C., and to the resultant mixture, the above 
components in Composition B were added and stirred thereby to prepare a 
gel ink having a volume resistivity of 230 .OMEGA..multidot.cm. 
The thus obtained ink was subjected to image formation by using a recording 
apparatus as shown in FIG. 2. Referring to FIG. 2, an ink-carrying roller 
1 of a stainless steel cylinder having an outside diameter of 40 mm was 
rotated in the arrow A direction, and the ink 2 was carried thereon. The 
ink 2 was formed into an ink layer 2a having a constant thickness by an 
ink application means 11 rotating in the arrow F direction. 
In this instance, the peripheral speed of the ink-carrying roller 1 was set 
to 20 mm/sec, that of the ink application roller 1 was set to 24 mm/sec, 
and the gap therebetween was set to 1.0 mm, so that the ink layer formed 
on the surface of the ink-carrying roller 1 had a thickness of about 1.2 
mm. 
An intermediate transfer roller 4 of a stainless steel cylinder having an 
outside diameter of 30 mm was disposed above the ink-carrying roller 1 
with a gap of about 1.0-1.2 mm from the surface of the ink-carrying roller 
1. The intermediate transfer roller was rotatable by a driving means (not 
shown) in the arrow B direction while being in contact with the ink layer 
2a formed on the ink-carrying roller 1. Further, a platinum electrode was 
used as a recording electrode 7 and a recording voltage of +25 V was used. 
Thus, the ink was evaluated in terms of an image density at the time at 
which the total weight of the ink remaining in the apparatus was decreased 
by 3.5 g from the initial ink weight (30 g). As a result, when the ink 
weight was decreased by 3.5 g, the image density was slightly decreased 
from the initial value thereof but the decrease was such that it 
substantially caused no problem in practice. 
Further, when 3.5 g of water was added to the ink which had shown the 
weight decrease of 3.5 g, the physical properties of the ink such as 
sensitivity were recovered to the initial state. Accordingly, it was 
considered that the most of the decrease of 3.5 g was based on the 
vaporization of water. 
Example 24 
Composition A 
Propylene glycol: 15 parts 
Water: 6 parts 
N-methylpropionamide: 5 parts 
(.epsilon..sub.r =172,2 at 25.degree. C.) 
Polyvinyl alcohol: 6 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku K.K.) 
Potassium iodide: 3.5 parts 
Carbon black: 2.5 parts 
(Stering SR, mfd. by Cabot Co., U.S.A.) 
Composition B 
Silica: 3 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
20 wt. %-Propylene glycol solution of sodium tetraborate: 2 parts 
1N-NaOH aqueous solution: 0.3 part 
An ink according to the present invention was prepared in the same manner 
as in Example 23 by using the above Compositions A and B. The thus 
prepared ink had a volume resistivity of 200 .OMEGA..multidot.cm. 
The above ink was evaluated in the same manner as in Example 23. As a 
result, when the ink weight was decreased by 3.5 g, the image density was 
slightly decreased from the initial value thereof but the decrease was 
such that it substantially caused no problem in practice. 
Example 25 
Composition A 
Propylene glycol: 13 parts 
Water: 6 parts 
N-methylacetamide: 7 parts 
(.epsilon..sub.r =191.3 at 25.degree. C.) 
Polyvinyl alcohol: 3 parts 
(Gohsenol GL-05, mfd. by Nihon Gosei Kagaku K.K.) 
Potassium iodide: 3.5 parts 
Carbon black: 2.5 parts 
(Stering SR, mfd. by Cabot Co., U.S.A.) 
Composition B 
Silica: 3 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
20 wt. %-Propylene glycol solution of sodium tetraborate: 2.3 parts 
1N-NaOH aqueous solution: 0.2 part 
An ink according to the present invention was prepared in the same manner 
as in Example 23 by using the above Compositions A and B. The thus 
prepared ink had a volume resistivity of 195 .OMEGA..multidot.cm. 
The above ink was evaluated in the same manner as in Example 23. As a 
result, when the ink weight was decreased by 3.5 g, the image density was 
slightly decreased from the initial value thereof but the decrease was 
such that it substantially caused no problem in practice. 
Example 26 
Composition A 
Ethylene glycol: 20 parts 
Water: 6 parts 
N-methylformamide: 6 parts 
(.epsilon..sub.r =182.4 at 25.degree. C.) 
Polyvinyl alcohol: 3 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku K.K.) 
Sodium chloride: 2 parts 
Carbon black: 3 parts 
(Stering SR, mfd. by Cabot Co., U.S.A.) 
Composition B 
Silica: 3 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
Sodium tetraborate: 0.4 part 
1N-NaOH aqueous solution: 2 parts 
An ink according to the present invention was prepared in the same manner 
as in Example 23 by using the above Compositions A and B. The thus 
prepared ink had a volume resistivity of 200 .OMEGA..multidot.cm. 
The above ink was evaluated in the same manner as in Example 23. As a 
result, when the ink weight was decreased by 3.5 g, the image density was 
slightly decreased from the initial value thereof but the decrease was 
such that it substantially caused no problem in practice. 
Example 27 
Composition A 
Propylene glycol: 15 parts 
Water: 6 parts 
Ethylene carbonate: 6 parts 
(.epsilon..sub.r =89.6 at 25.degree. C.) 
Polyvinyl alcohol: 6 parts 
(Gohsenol GL-03, mfd. by Nihon Gosei Kagaku K.K.) 
Potassium iodide: 3.5 parts 
Carbon black: 2.5 parts 
(Stering SR, mfd. by Cabot Co., U.S.A.) 
Composition B 
Silica: 3 parts 
(Aerosil 200, mfd. by Nihon Aerosil K.K.) 
20 wt. %-Propylene glycol solution of sodium tetraborate: 2 parts 
1N-NaOH aqueous solution: 0.3 part 
An ink according to the present invention was prepared in the same manner 
as in Example 23 by using the above Compositions A and B. The thus 
prepared ink had a volume resistivity of 220 .OMEGA..multidot.cm. 
The above ink was evaluated in the same manner as in Example 23. As a 
result, when the ink weight was decreased by 3.5 g, the image density was 
slightly decreased from the initial value thereof but the decrease was 
such that it substantially caused no problem in practice. 
As described hereinabove, the present invention provides many advantages as 
described below. 
(1) There is provided an ink which provides an image recording method 
capable of being easily effected at an extremely low recording cost than 
the thermal transfer recording method and free from plugging of a nozzle 
or blurring of recorded images as encountered in the ink-jet recording 
method. 
(2) There is provided an ink which is suitably used in a novel image 
recording method utilizing the control of ink adhesiveness, and has 
excellent storage stability such that it shows little characteristic 
change due to drying, etc., and suitably retains its fluidity when left 
standing in the air for a long period. 
(3) There is provided an ink which provides good sensitivity and a sharp 
change in its crosslinked structure due to energy application, and 
provides good selective transferability so that it can stably control its 
adhesiveness. 
(4) There is provided an ink excellent in energy efficiency, which is 
capable of providing a good recorded image under the application of small 
quantity of energy.