Thermal electrostatic ink-jet recording apparatus

Disclosed is a thermal electrostatic ink-jet recording apparatus comprising a head body provided with an ink chamber, electrodes for selectively applying heat, in response to image signals to each of discrete ink unit areas corresponding to pel density, and electrodes for producing a predetermined electrostatic field between an ink surface and a recording sheet so as to jet the heated ink unit areas by applying the electrostatic field, in which electric current is passed through an organic resistance film to heat the ink.

FIELD OF THE INVENTION 
The present invention relates to an ink-jet recording apparatus, and, more 
particularly, relates to an improvement in an ink-jet recording apparatus 
wherein ink is jetted by use of both thermal and electrostatic energies. 
BACKGROUND OF THE INVENTION 
Conventional ink-jet recording devices have jet-openings, or orifices, 
arranged to correspond to the desired pel density. Such devices have ink 
contained in a chamber communicating with the openings or orifices, and 
employ pressure pulses which are selectively applied to jet the ink from 
the corresponding jet-openings onto paper. 
In apparatus of this type, it is necessary to set the volume ratio of each 
orifice at a relatively high value in order to maintain the ink jetting 
capability of the orifice. Thus, it is difficult to miniaturize the ink 
jetting devices. Also, it is necessary to set the pitch, or interval 
between adjacent jet-openings, at a relatively high value, so that the 
image recording density cannot be high. Further, recording speed is 
lowered because mechanical scanning is employed to apply the pressure 
pulses used to jet the ink. 
In order to solve such problems, various structures, such as the following, 
have been proposed. A first system, the magnetic ink-jet system, provides 
magnetic ink in the vicinity of an array of magnetic electrodes, and ink 
jetting is accomplished at a corresponding image density by use of a 
magnetic field applied to the meniscus of the ink. The magnetic ink is 
then jetted toward a recording sheet by use of a patterned electric field 
formed between the electrode array and an electrode disposed opposite the 
array on the other side of a recording sheet (Japanese Patent Unexamined 
Publication No. 37163/1981). 
In addition to the aforesaid methods, the so-called plane ink jet method is 
also well known. This method, involves arranging ink in a slitlike 
inkholder in parallel to an electrode array, and jetting the ink in 
accordance with an electric field pattern formed between an electrode 
facing the electrode array so that ink droplets selectively impact upon an 
intervening recording paper. Since no minute orifice for storing ink is 
required in this method, ink clogging can be prevented. However, a high 
voltage must be applied to jet the ink droplets which makes it necessary 
to drive the electrode array on a time division basis to prevent a voltage 
leak across the adjoining or neighboring electrodes. Consequently, the 
recording speed is limited. 
Another system, the thermal bubble-jet system, uses apparatus wherein heat 
is rapidly applied to the ink to cause film-surface boiling. The ink is 
then jetted from an orifice by the pressure increase caused by the rapid 
growth of bubbles within the orifice (Japanese Patent Unexamined 
Publication No. 1611664/1980). 
In the ink-jet recording systems described above, high-density recording 
can be made, and because electrical scanning can be carried out, 
high-speed recording can be achieved in most systems. However, in the 
magnetic ink-jet system, it is necessary to use ink containing magnetic 
powder which causes the ink to be black and makes it difficult to 
reproduce a color picture by superimposing several colors of ink to form 
an image. The plane scanning ink-jet system is disadvantageous in that it 
is necessary to apply a high voltage to jet the ink. Therefore, time 
division driving of the electrode array is required to prevent voltage 
leakage between adjacent electrodes. This is unsuitable for high-speed 
recording. Furthermore, in the apparatus using the thermal bubble-jet 
system, it is necessary to apply heat rapidly to cause film-surface 
boiling, resulting in thermal deterioration of the protective layer 
applied to the resistance heaters used to heat the ink. 
The present invention provides a thermal electrostatic ink-jet recording 
apparatus in which thermal energy, corresponding to image information, is 
selectively applied to the recording ink in an electric field and the 
heated ink portions are jetted toward a recording sheet by use of a 
predetermined electrostatic field. 
In apparatus of this latter type, magnetic ink used in the magnetic ink-jet 
system is not required. Accordingly, not only can color imaging be easily 
attained by superimposing several kinds of ink during printing, but also 
voltage leakage in the vicinity of the electrode array can be effectively 
prevented because the extremely high intensity electric field required in 
the plane ink-jet system (in which ink is jetted only by an electrostatic 
field) is not required for jetting ink. Furthermore, the quantity of 
thermal energy can be reduced because the very large thermal energy 
required in the bubble-jet method (in which ink is jetted only by thermal 
energy) is not required for jetting ink. Accordingly, thermal 
deterioration of ink can be effectively prevented, and high-speed, 
high-density recording can be accomplished while effectively eliminating 
the above defects in conventional apparatuses. 
In such a thermal electrostatic ink-jet recording apparatus, an exothermic 
array, composed of a plurality of electrical resistance heating elements 
that are disposed at intervals corresponding to pel density, is used as 
means for applying thermal energy to the ink. The array of heaters is 
provided at an edge portion of the ink-jet recording head in the vicinity 
of an orifice in the ink reservoir located in the head body, so that ink 
within the ink reservoir is indirectly heated. In this case, an insulating 
substrate constituting one side wall of the ink reservoir is subjected to 
a photolithographic process or the like to form the array of heating 
elements. 
While the thermal electrostatic ink-jet printer above has been found to be 
very effective, it is difficult in producing the exothermic array to 
arrange the heating elements in the vicinity of the orifice side end 
portion of the insulating substrate while maintaining the array in a 
plane. Generally, it is required that the exothermic array be arranged a 
certain distance apart from the the edge portion of the insulating 
substrate, and then the end portion of the substrate is cut so as to 
properly position the exothermic array relative to the edge portion of the 
insulating substrate. Further, in order to keep recording image quality 
good it is necessary to stabilize the jetting of the ink. Formation of a 
stable ink meniscus is one of the means for stabilizing the jetting of the 
ink. In the conventional apparatus, however, it happens that the surface 
of the end portion is rough because the end portion of the head body is 
cut, as described above. Therefore, it is necessary to polish the surface 
of the end portion to make the surface satisfactorily smooth. In short, a 
problem exists in that the process of producing the head body is 
troublesome and sometimes not effective. 
Furthermore, since the exothermic array is attached or fixed onto the 
insulating substrate, the heat from the heating resistors naturally 
escapes toward the insulating substrate, resulting in a problem that the 
efficiency of heat transmission to the ink becomes correspondingly poor. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the present invention is to solve the problems described 
above. 
Another object of the present invention is to provide a thermal 
electrostatic ink-jet recording apparatus which is easier and more 
efficient to produce, as well as providing greater efficiency of thermal 
transmission to ink, while at the same time utilizing the innate 
advantages in the thermal electrostatic ink-jet system. 
In order to attain the above objects, according to one aspect of the 
present invention, the thermal electrostatic inkjet recording apparatus 
comprises a recording head body having an orifice side and a back side; 
first and second spaced apart wall members in the body defining an ink 
chamber for accommodating ink therein, the first wall member being on the 
orifice side and the second wall member being on the back side of the head 
body, and one of the wall members comprising an electrically conductive 
organic resistance film; orifice means in one of the wall members in flow 
communication with the chamber for jetting ink therefrom; thermal energy 
applying means for applying thermal energy to selected portions of the ink 
adjacent the orifice means in response to image signals, including a 
plurality of spaced apart electrical current conducting electrodes in 
contact with the film to pass an electric current through the film and 
thereby heat selected areas of the ink in response to image signals; and 
electrostatic field applying means for applying an electrostatic field 
between the ink and a recording sheet to jet the ink from the orifice 
means. 
In one embodiment of the apparatus described above, the said first wall 
member comprises the organic resistance film which has an ink-jet orifice 
means for jetting the ink contained in the head body from the side 
opposite a recording sheet. In this case, the ink-jet orifice means may be 
constituted by holes in the film corresponding pel density or by a slit 
having a pre-determined width. The construction using the holes is 
advantageous for precisely defining the ink-jet orifice into ink unit 
areas corresponding to image elements, and the construction using a slit 
is advantageous for preventing blockage with ink. 
An organic resistance film material capable of producing heat by electrical 
current conduction is employed in the thermal energy applying means. It is 
necessary that electrical signals corresponding to image information, or 
image signals, are selectively applied to the respective 
current-conduction electrodes provided on the unit orifice edge portions 
of the ink-jet orifice means in the organic resistance material 
corresponding to the ink unit areas, so that the respective edge portions 
function as heating portions. In this case, in order to provide greater 
efficiency of thermal transmission to ink, it is preferable that a portion 
of each of the current conduction electrodes, other than the ink-jet 
orifice edge portion, is insulated from the organic resistance film. 
Further, the electrostatic field producing means may be freely modified in 
any manner as long as such means can produce an electrostatic field of 
such a magnitude that heated ink between the surface thereof and the 
recording sheet can be jetted onto the recording sheet. 
Furthermore, the ink used in the practice of the present invention may be 
freely selected as long as the ink can be brought into a state in which 
the ink can be jetted when a predetermined level of thermal energy is 
applied. 
In order to satisfactorily jet the ink, it is necessary to lower the 
viscosity and surface tension of the ink to such values that the ink can 
be jetted by the action of the electrostatic field, and it is necessary 
that the ink have a suitable conductivity. 
The organic resistance film constituting the recording sheet side portion 
of the head body is made of a suitably selected, electrically conductive 
resin material that contains suitable electrically conductive powder, 
usually in the range from about 20 to about 80 weight percent, and has a 
volume resistivity of about 0.01 to 10.sup.4 ohms/cm. The resin material 
may be selected from the group of aromatic polyamide, polyimide, 
polysulfone, polyphenylene oxide, polycarbonate and polyester polymers and 
various kinds of fluorinated polymers. The electrically conductive powder 
may be selected from the group of metal fine powders such as Ni, Cu, Ag or 
the like; metal oxides such as SnO.sub.2, ZnO, Fe.sub.2 O.sub.3 and the 
like; carbon; and the like. 
As mentioned above, when an electrical signal corresponding to image 
information is applied to selected one or ones of the current-conduction 
electrodes, the unit opening edge portion or portions of the organic 
resistance film are directly electrically heated, so that the ink unit 
area or areas facing the orifice side unit opening edge portion or 
portions are heated. As the result, the viscosity and surface tension of 
the thus heated ink unit area or areas are lowered, and the conductivity 
thereof is increased. Accordingly, the heated ink unit area or areas are 
brought to a condition where it is possible to jet the ink, and then the 
heated ink in such unit area or areas is jetted toward the recording sheet 
by the electrostatic attraction force resulting from the electric field 
acting on the ink surface. The end portion of the resultant projecting ink 
column or columns come into contact with the recording sheet, so that an 
ink dot or dots can be formed by the transfer of ink to the recording 
sheet. 
In another embodiment of the present invention, the organic resistance film 
is in the second wall member on the back side of the head body opposite 
the orifice side. The ink-jet orifice means is located in the first wall 
member on the orifice side opposite a recording sheet. The current 
conduction electrodes are provided on the second wall member at locations 
corresponding to the ink unit area to heat selected areas of the organic 
resistance film corresponding to the respective ink unit areas in response 
to image signals. The operation of the above-described second embodiment 
of the invention is the same as previously described.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 through 3 show a first embodiment of the inkjet recording apparatus 
according to the present invention. The apparatus has a head body 1 
provided with an ink chamber 2 acting as an ink reservoir, a thermal 
energy applying means 4, for applying a predetermined level of energy 
thermal to the ink 3, and an electrostatic field producing means 6 for 
producing a predetermined electrostatic field between a surface of the ink 
3 and a recording sheet 5. 
In this first embodiment, the head body 1 includes a second wall member 11 
made of an insulating material such as a ceramic, e.g., alumina, or the 
like, and a first wall member formed of an electrically conductive organic 
resistance plate or film 12, both members 11, 12 defining the box-like ink 
chamber 2. The organic resistance film 12, may be, for example, a 
conductive polyimide film of a thickness of about 30 .mu.m, containing 48% 
by weight of carbon in polyimide and having a volume resistivity of about 
1 ohm/cm. The organic resistance film 12 is provided with ink-jet orifice 
means through which ink is jetted from the recorder head onto a recording 
sheet. For example, holes 13 may be formed at a spacing corresponding to a 
selected pel density (for example, six holes per millimeter with a hole 
size of 100 .mu.m). 
The ink 3 is supplied into the the ink chamber 2 with appropriate pressure 
by an ink supply means (not shown), so that each of the holes 13 is filled 
with the ink 3 by capillary action. In this embodiment, the ink 3 supplied 
into the ink chamber 2, may for example, be a conductive ink having a 
volume resistivity not larger than about 10.sup.7 ohms/cm is used, and the 
viscosity of the ink 3 is established so as to have a value which is 
within a range from about 20 to about 300 cps at ordinary temperature 
(20.degree. C.) but which is reduced substantially when heated (for 
example at 200.degree. C.). 
The ink-jet orifice means is constituted by a series of holes, or a slit, 
in one of the wall members for jetting the ink, and may also include 
corresponding openings in the electrodes, insulating layers, etc., through 
which the ink is jetted. 
The thermal energy applying means 4 is constituted by the organic 
resistance film 12, one or more pairs of current-conduction electrodes 14 
(see pair 14a and 14b) provided on opposite sides of film 12 adjacent the 
edge portions of each of the holes 13 in the organic resistance film 12, a 
switching element 15 interposed between each pair of current-conduction 
electrodes 14 for the purpose of performing switching operation 
corresponding to electrical image signals, and a current-conduction 
electric power source 16 connected in series to each of the switching 
elements 15. In this first embodiment, each of the current-conduction 
electrodes 14 is constituted by an annular portion 17 having an outer 
diameter of about 150 .mu.m and disposed around the hole 13, and a linear 
portion 18 extending from the annular portion 17. The annular portions 17, 
are provided in pairs on opposite sides of the film 12, and directly 
contact the surfaces of the organic resistance film 12. The linear 
portions 18, are also provided in pairs and are separated from the organic 
resistance film 12 by an insulating layer 19, made of SiO.sub.2 or the 
like. A second insulating film 20 of about 10 .mu.m thick is made of 
SiO.sub.2 or the like, and is provided to cover the sheet side surface of 
the organic resistance film 12 and electrodes 14. 
The production of the current-conduction electrodes 14 and the insulating 
film 20 is described more in detail. For example, the process of 
production comprises the steps of forming an insulating layer 19 by 
sputtering SiO.sub.2 or the like on the opposite surfaces of the organic 
resistance film 12 except the areas adjacent the holes 13, depositing a 
metal layer through evaporation with metal such as Cr, Cu, Al, Au, or the 
like, onto the insulating layer 19, forming the metal layer into 
current-conduction electrodes 14 of the above-described pattern through a 
photolithographic process, forming an insulating film 20 through 
sputtering, and simultaneously forming the holes 13 through all of the 
above layers by means of a laser, microdrill, plasma processing, or the 
like. 
The electrostatic field producing means 6 is constituted by electrically 
conductive layers 21 employing the respective current-conduction 
electrodes 14b, a roll-like electrostatic induction electrode 22 disposed 
at a predetermined distance apart from the surface of the ink 3 and 
functioning as a surface for supporting the recording sheet 5, and an 
electrostatic induction electric power source 23 connected to each of the 
conductive layers 21 and the electrostatic induction electrode 22 for the 
purpose of forming an electrostatic field from the surface of the ink 3 to 
the electrostatic induction electrode 22. In this embodiment the 
electrostatic control pulse to be applied to the electrostatic induction 
electrode 22 from the electrostatic induction electric power source 23 is 
generated in synchronism with the drive pulse for the thermal energy 
applying means. 
In the first embodiment, the ink-jet recording apparatus according to the 
present invention operates as follows. When the switching elements 15 are 
selectively turned on corresponding to image signals, or information of an 
image to be recorded, a current a flows through film 12 adjacent the edge 
portion of the hole 13 through the associated conduction electrodes 14 in 
pairs as shown in FIG. 2. The edge portions defining the hole 13 is 
directly heated by the current a, so that thermal energy Q is applied to 
the ink unit area M facing the hole 13 to heat the ink unit area M to the 
desired temperature. As the result, in the heated ink unit area M, the 
viscosity and surface tension of the ink 3 are reduced and the 
conductivity is increased. When an electrostatic control pulse is applied 
to the electrostatic induction electrode 22 of the electrostatic induction 
producing means 6 in synchronism with the drive pulse for the thermal 
energy applying means 4, an electrostatic field S of a predetermined 
strength is formed between the ink 3 facing the conductive layer 21 and 
the electrostatic induction electrode 22. Due to the electrostatic field 
S, the heated ink unit area M is jetted toward the recording sheet 5 
positioned in front of the electrostatic induction electrode 22. At this 
time, a protruding end portion of an ink column 3a caused by the jetting 
operation of the ink as shown by the dashed line of FIG. 2 touches the 
recording sheet 5, so that the ink 3 is transferred to the recording sheet 
5. Thus, an ink dot D is formed on the recording sheet 5. 
The process of the recording operation in the first embodiment has several 
advantages. First, because the edge portion defining the hole 13 is 
directly heated by electric power, the ink unit area M facing the through 
hole 13 can be directly heated. Secondly, because the organic resistance 
film 12 acting as a heating material has no substrate for supporting an 
array of heating elements, the thermal energy generated from the organic 
resistance film 12 does not escape toward the substrate. Thirdly, because 
the edge portion of the hole 13 is defined as a cylindrical surface, the 
heating area can be relatively enlarged compared with a heating resistance 
material disposed in a plane. In view of these advantages, the 
transmission efficiency of heat to the ink unit area M is improved 
compared with a system using an exothermic array. 
To establish the superiority of the recording system of the present 
invention, several experiments were conducted. An electrostatic control 
pulse of 1000 V/300 .mu.m for 0.5 ms was generated in synchronism with a 
drive pulse of 7 V for 0.5 ms, corresponding to image signals. As the 
result, the recording operation could be made stably with the repeated 
frequency kept at 500 Hz. Furthermore, it was found that the thermal 
energy electric power was about 0.1 W per dot. 
The process of producing the heat body unit U of the first embodiment of 
the ink-jet recording apparatus is as follows. The ink-jet holes 13 are 
formed through the organic resistance film 12. The power electrodes 14 are 
arranged at the edge portions of each of the respective holes 13. The 
outer surface of the organic resistance film 12 is coated with the 
insulating film 20. The organic resistance film 12 constructed as 
described above is joined onto the box-like base member 11 with an 
adhesive. In the head body unit U, the edge portion of each of the holes 
13 of the organic resistance film 12 functions as a heating portion. 
Accordingly, the conventional process of cutting a substrate for arranging 
exothermic resistance materials at the edge portion is no longer 
necessary. 
The surface roughness of the organic resistance film 12 may be reduced to a 
very small value in the production process. The surface roughness of the 
insulating film 20 positioned on the organic resistance film 12 can be 
likewise reduced. Consequently, the step of polishing the edge surface of 
the head body 1 can be omitted, and the number of steps necessary to 
produce the head body unit U is reduced compared wtih the prior art 
process. As a result, the efficiency of the production process can be 
improved. Furthermore, because the surface roughness of the edge surface 
of the head body 1 can be satisfactorily reduced, the meniscus of ink in 
the ink unit area M facing the through hole 13 can be maintained in a 
stable condition. 
In this first embodiment, the organic resistance film 12 is formed of 
polyimide or other suitable organic resin film having adequate strength 
and elasticity. Accordingly, if the organic resistance film 12 is expanded 
by heat or deformed by a shock or a load, the deformation can be absorbed 
to a certain extent due to its elasticity. In the case where the organic 
resistance film 12 is joined to the stiff base member 11 acting as one 
member of the head body 1, a satisfactory seal and adherence therebetween 
can be maintained. 
Furthermore, because the insulating film 20 is provided on the outer 
surface of the organic resistance film 12, electric discharge between the 
current-conduction electrode 14 and the electrostatic induction electrode 
22 can be effectively prevented from occurring, and at the same time, the 
distance between meniscus of the ink within the hole 13 and the 
electrostatic induction electrode 22 can be maintained by the thickness of 
the insulating film 20. Accordingly, the intensity of electrostatic field 
S acting on the meniscus of ink becomes large enough so that the induction 
of electrical charge on the meniscus of ink can be easily achieved. 
Although the holes 13 are used as orifices for jetting the ink in the first 
embodiment, the invention is not limited thereto. For example, the 
invention may be modified as shown in FIG. 4. This modification is 
characterized in that a slit 25 having a width corresponding to the size 
of an image element is provided in the organic resistance film 12, and 
pairs of spaced apart current-conduction electrodes 26 (specifically 26a 
and 26b) and pairs of spaced apart current-conduction electrodes 27 
(specifically 27a and 27b) are provided at the opposite edge portions of 
respective unit jet orifices 25a of the slit 25, each arranged to provide 
ink unit areas M corresponding to pel density. In short, in the 
modification, the edge portions of each of the unit jet-openings 25a are 
electrically heated through the associated current-conduction electrodes 
26 and 27. In the modification, separate orifices directly defining each 
of the ink unit areas M are not necessary, so that clogging of small 
orifices by dried ink can be effectively prevented compared with the 
first-described embodiment. 
Although the first embodiment described the use of an organic resistance 
film made of a conductive polyimide resin film having predetermined 
conductivity and volume resistivity, the invention is not limited to this, 
and other suitable films may be used, for example, an organic resistance 
film made of a resin film about 20 .mu.m thick where the resin film 
contains 40% by weight of carbon in polycarbonate resin and has a volume 
resistivity of 30 ohms/cm, or an organic resistance film made of an about 
50 .mu.m polyester resin film containing about 20% by weight of SnO.sub.2 
and having a volume resistivity of about 3.times.10.sup.3 ohms/cm. In such 
cases, the same result can be attained. 
Other than that described above, various modifications of the first 
embodiment may be made. For example, it is not necessary that each of the 
holes 13 be formed linearly but they may be in a zigzag or inclined 
pattern. Further, the array of the current-conduction electrodes 14 on one 
side may be replaced by a common electrode, and the conductive layer 21 of 
the electrostatic field producing means 6 may be provided separately from 
the one side current-conduction electrode 14b. 
FIGS. 5 and 6 show a second embodiment of the ink-jet recording apparatus 
of the present invention. The apparatus has a head body 101 provided with 
an ink chamber 102, a thermal energy applying means 104 for applying a 
thermal signal to ink 103 provided within the ink chamber 102, and an 
electrostatic field producing means 106 for producing a predetermined 
electrostatic field between a surface of the ink 103 and a recording sheet 
105. 
In this second embodiment, the head body 101 is constituted by a first wall 
member 111 disposed on the recording sheet side of the head body, a second 
wall member 112 spaced apart from and opposite the first wall member 111, 
and a spacer member 113 interposed between the two wall members 111 and 
112 to determine the size of the ink chamber 102 which, for example, has a 
200 .mu.m thickness, a 300 .mu.m width and a uniform depth. In the head 
body 101, each of the first wall member 111 and the spacer member 113 is 
made of an insulating material such as glass, ceramic or the like. A slit 
114 having a width of 100 .mu.m, for example, corresponding to an image 
element is longitudinally formed in the top defining member 111. For 
example, the slit 114 is formed using an etching process with fluoro-acid 
or the like with a metal mask applied to a portion of the first wall 
member 111 other than that portion where the slit is to be formed. The 
second wall member 112 is made of an organic resistance film A. For 
example, a 30 .mu.m thick conductive polyimide resin film containing about 
48% by weight of carbon and having a volume resistivity of about 10 
ohms/cm may be used as the organic resistance film. 
The ink 103 is pressure-fed by an ink supply means (not shown) into the ink 
chamber 102 through an ink supply passage 115, so that the slit 114 is 
filled with the ink 103 by capillary action. In this embodiment, the ink 
103 supplied to the ink chamber 102 may be conductive and have a volume 
resistivity not larger than 10.sup.7 ohms/cm. The viscosity of the ink 3 
is established so as to have a value that is within a range from about 20 
to about 300 cps at ordinary temperature (20.degree. C.) but which is 
reduced substantially when heated (for example, at 200.degree. C.). 
The thermal energy applying means 104 is constituted by the organic 
resistance film A forming the second wall member 112, an array of 
spaced-apart current-conduction electrodes 121 each having a width of 50 
.mu.m and a length of 100 .mu.m and being disposed corresponding to pel 
density (for example, 8 lines per miilimeter) on the outside surface of a 
belt-like portion 112A of the second wall member 112 along the slit 114, a 
common return electrode 122 on the inside surface of the second wall 
member 112, switching elements 123 connected to the respective 
current-conduction electrodes 121 and the return electrode 122 for the 
purpose of performing switching operations corresponding to image signals, 
and a current-conduction electric power source 124 connected in series to 
each of the switching elements 123. In this second embodiment, an 
insulating film 125 made SiO.sub.2 or the like is provided between the 
second wall member 112 and portions of the respective current-conduction 
electrodes 121. Those portions of the electrodes 121 which are not 
opposite slot 114 are insulated from the belt-like portion 112a of the 
second wall member 112 since the insulating film 125 separates the 
electrodes from the film and limits contact between each of the 
current-conduction electrodes 121 and the organic resistance film A to 
locally heat the portion of film A opposite slit 114. 
The process of producing the current-conducting electrodes 121 and 
insulating film 125 will now be described in more detail. The process 
employed may comprise the steps of forming the insulating film 125 on one 
side surface of the organic resistance film A by sputtering, depositing a 
metal layer onto the organic resistance film A and the insulating film 125 
through evaporation with metal such as Cr, Cu, Al, Au, or the like, 
forming the metal layer into current-conduction electrodes 121 of the 
above-described pattern through a photolithographic process applied to the 
metal layer, and depositing a conductive metal layer through evaporation 
onto the opposite side surface of the organic resistance film A to form 
the return electrode 122. 
The electrostatic field producing means 106 is constituted by a conductive 
layer 131 which also serves as the return electrode 122, a roll-like 
electrostatic induction electrode 132 which is disposed at a predetermined 
distance apart from the surface of the ink 103 and which also functions as 
a surface for supporting the recording sheet 105, and an electrostatic 
induction electric power source 133 which is connected to the conductive 
layer 131 and the electrostatic induction electrode 132 for the purpose of 
forming an electrostatic field from the surface of the ink 103 to the 
electrostatic induction electrode 132. In this second embodiment, the 
electrostatic control pulse applied to the electrostatic induction 
electrode 132 from the electrostatic induction electric source 133 is 
generated in synchronism with the drive pulse for the thermal energy 
applying means 104. 
In the second embodiment of the invention, the ink-jet recording apparatus 
operates as follows. When a selected one of the switching elements 123 
turns on in response to an electrical signal corresponding to an image to 
be recorded, a current a flows in a part of the organic resistance film A 
between the corresponding current-conduction electrode 121 and the return 
electrode 122 as shown in FIG. 7. A part of the organic resistance film A 
electrically energized is heated to the desired temperature, so that a 
predetermined level of thermal energy Q is applied to the corresponding 
ink unit area M. Thus, the ink unit area M is heated. As a result, in the 
heated ink unit area M, the viscosity and the surface tension of the ink 
103 are reduced and the conductivity is increased. When the electrostatic 
control pulse is applied to the electrostatic induction electrode 132 of 
the electrostatic induction producing means 106 in synchronism with the 
drive pulse for the thermal energy applying means 104, an electrostatic 
field S having a predetermined strength is established between the ink 103 
facing the conductive layer 131 and the electrostatic induction electrode 
132. Due to the electrostatic field S, the ink in the heated ink unit area 
M is jetted toward the recording sheet 105 passing in front of the 
electrostatic induction electrode 132. At this time, a protruding end 
portion of an ink column 103a caused by the jetting operation of the ink 
as shown by the virtual line of Fig. 7 touches the recording sheet 5, so 
that the ink 103 is transferred to the recording sheet 105. Thus, an ink 
dot D is formed on the recording sheet 105. 
In the recording operation in the second embodiment, the organic resistance 
film A has no member equivalent to a substrate for supporting an 
exothermic array. Accordingly, there is no possibility of the thermal 
energy generated from the organic resistance film A leaking to the 
substrate. Accordingly, the transmission efficiency of heat to the ink 
unit area M is improved compared with the conventional system using an 
exothermic array. 
To establish the excellent results of this recording operation system, an 
experiment was conducted with an electrostatic control pulse of 1000 V/300 
.mu.m for 0.5 ms, which was generated in synchronism with the drive pulse 
of 5 V for 1.0 ms, corresponding to picture information. As a result, 
recording operations could be made stably at a frequency of 500 Hz. 
Furthermore, it was found that the electric power for the thermal energy 
was about 0.1 W per dot. For comparison, a recording experiment was 
carried out in the same manner with use of a conventional system using an 
exothermic array. The thermal energy electric power required was about 0.5 
W per dot. Accordingly, it is apparent from the results of the two 
experiments that the ink-jet recording apparatus of this embodiment is 
improved in thermal transmission efficiency. 
The head body unit U of the second embodiment, of the ink-jet recording 
apparatus can be produced using a process as follows. The ink-jet slit 114 
is formed in the first wall member 111, while the current-conduction 
electrodes 112 and the return electrode 122 are formed on the organic 
resistance film A which serves as the second wall member 112. Both the 
constructed wall members 111 and 112 are attached to each other through 
the spacer member 113 with an epoxy adhesive or the like. In the thus 
constructed head body unit U, the belt-like portion 112A of the second 
wall member 112 functions as a heating element, so that the conventional 
step of cutting a substrate for arranging resistance heating elements at 
the edge portion thereof can be omitted. Furthermore, the roughness of the 
outside surface of the top defining member 111 can be reduced, so that the 
step of polishing the edge surface of the head body 101 can be omitted. 
Accordingly, the number of steps in the process of producing the head body 
unit U can be reduced compared with the prior art process. As a result, 
the production process can be improved. Furthermore, because the surface 
roughness of the edge surface of the head body 101 can be reduced, the 
meniscus of ink in the ink unit area M facing the slit 114 can be 
maintained in a stable condition. 
In this second embodiment, the organic resistance film A constituting the 
second wall member 112 is made of a polyimide film having adequate 
strength and elasticity. Accordingly, if the organic resistance film A 
expands with heat or is deformed by a shock and/or a load, the deformation 
can be absorbed to a certain extent owing to its elasticity. As the 
result, when the stiff spacer member 113 and the second wall member 112 
constituting the head body 101 are joined to each other with the adhesive, 
the seal and the adherence therebetween can be well maintained, and 
therefore the tightness of the ink chamber 102 can be maintained. 
Although the second embodiment has been described as using an organic 
resistance film A made of a conductive polyimide film having predetermined 
conductivity and volume resistivity, the invention is not limited thereto, 
and, for example, the organic resistance film may be made of any suitable 
resin, for example, the polycarbonate resin film may be made about 20 
.mu.m thick contain 40% by weight of carbon and have a volume resistivity 
of 30 ohm/cm. The organic resistance film may be made of a polyester resin 
film of about 50 .mu.m thick containing 20% by weight SnO.sub.2 and having 
a volume resistivity of 3.times.10.sup.3 ohm/cm. In either case, the same 
result can be attained. 
Although the second embodiment has been described with the slit 114 used to 
form jet-orifices for jetting ink, the invention is not limited thereto, 
and holes corresponding to pel density may be used such as described for 
the first embodiment. Alternatively, the positional relation between the 
current-conduction electrodes 121 and the return electrode 122 may be 
reversed, or the return electrode may be formed with the same pattern as 
the current-conduction electrodes 121. Further alternatively, the 
conductive layer 131 of the electrostatic field producing means 106 and 
the return electrode 122 of the thermal signal applying means 104 may be 
separate electrodes. 
As described above, the ink-jet recording apparatus according to the 
present invention has the following benefits, while using the innate 
advantages in the thermal electrostatic ink-jet system. First, because 
orifices for jetting ink are provided in the organic resistance film 
constituting a part of the head body, and the edge portions of the 
orifices are selectively, electrically heated so as to directly heat the 
ink unit area, a direct thermal transmission path is provided. Therefore, 
thermal energy losses to the substrate can be reduced so that the thermal 
transmission efficiency to ink can be improved compared with the 
conventional system in which a heating element array is provided on a 
substrate. 
Secondly, in producing the head body unit, not only can the orifice edge 
portion of the organic resistance film constituting the head body be 
easily constructed as a heating portion, but also the end surface of the 
head body can be made smooth with no polishing step required. Accordingly, 
compared with the conventional system in which a heating element array is 
provided on a substrate with the intention of stabilizing the recording 
operation, the production steps can be reduced, and the efficiency of 
producing the head body unit can be improved. 
Thirdly, the second wall member of the head body is made of an organic 
resistance film which is selectively electrically heated so that the ink 
unit area is directly heated. Accordingly, compared with the conventional 
system in which an array of heating elements is provided on a substrate, 
the loss in thermal energy transmitted to the substrate or the like can be 
reduced to improve the thermal transmission to ink.