Ink jet printer

In an ink jet printer, a belt-type preheating unit 2 pressingly heats a recording sheet 6 while transporting the recording sheet in a transport direction B on a belt. A suction transport device 3 is positioned downstream of the belt-type preheating unit 2 in the transport direction B. The suction transport means transports, on its transport belt, the recording sheet 6 heated by the belt-type preheating unit 2 in the transport direction B while fixing the recording sheet onto the transport belt by a vacuum suction. An ink jet print head, positioned confronting the suction transport device 3, records images by ejecting water-based ink onto the recording sheet which is being transported by the suction transport device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an ink jet printer. 
2. Description of the Related Art 
For safety reasons, the ink used in ink jet printer is usually a 
water-based ink. To prevent clogging of nozzles, water-based ink that 
evaporates slowly must be used. However, such ink also dries slowly after 
printing so that printed sheets are difficult to handle. Because 
water-based ink runs easily, there has been a problem of different color 
inks running together and mixing during color printing. Also, precision of 
printing drops when recording sheets wrinkle, expand, or stretch. Attempts 
have been made to reduce severity of these problems by improving the 
recording sheets. However, these methods require production of special 
sheets that are expensive. Recording devices for rapidly drying the ink on 
the printed sheets are described on page 35 in the February 1994 issue of 
Hewlett-Packard Journal (not prior art). Actual methods described include 
heating printed sheets directly after printing to dry the printed sheets. 
The printed sheets are heated by streams of hot air, by radiant heat, or 
by heated platen rollers. 
However, all these methods require detection of the temperature of the 
printed sheet and control of energization of the heat source. Safety 
measures such as for preventing overheating and generation of smoke and 
fire are necessary. Normally heating efficiency is low. However, power 
consumption is not always low. Generally a long waiting period is required 
for the heat source to heat up after the power is turned on until when 
printing is possible. 
SUMMARY OF THE INVENTION 
It is therefore an objective of the present invention to provide a method 
of drying ink on printed sheets and a high-speed ink jet printer wherein 
printing can be started quickly after turning on the power, wherein power 
consumption is low, wherein detection of the temperature of printed sheets 
and control of energization of the heat source are unnecessary, wherein 
measures for preventing generation of smoke and fire are unnecessary, and 
wherein safety measures can be reduced. It is a further objective of the 
present invention to provide an ink jet printer wherein feathering of 
printed characters is greatly reduced, wherein, in the case of color 
printing, running and mixing of different colored inks is prevented, 
wherein drops in printing precision caused by wrinkling, expanding, or 
stretching of recording sheets is prevented, and wherein print quality 
equal to print quality attained using high-quality specially produced 
recording sheets can be obtained using normal recording sheets. 
In order to attain the above objects and other objects, the present 
invention provides an ink jet printer for printing ink onto a recording 
sheet, the ink jet printer comprising: belt-type preheating means for 
pressingly heating a recording sheet while transporting the recording 
sheet in a transport direction; suction transport means, positioned 
downstream of the belt-type preheating means in the transport direction, 
the suction transport means including a transport belt, the suction 
transport means transporting, on the transport belt, the recording sheet 
heated by the belt-type preheating means in the transport direction while 
fixing the recording sheet onto the transport belt by a vacuum suction; 
and ink ejection means, positioned confronting the suction transport 
means, for recording images by ejecting water-based ink onto a recording 
sheet which is being transported by the suction transport means. The 
belt-type preheating means preferably includes: a preheater for heating 
the recording sheet, the preheater having a heat source for generating 
heat, a belt mounted on the heat source in contact therewith, the belt 
transporting the recording sheet on one surface of the belt while 
contacting the heat source at the other surface, and a drive source for 
driving the belt; and a pressure roller positioned in contact with the 
belt for rotating synchronously with the belt driven by the drive source, 
the recording sheet being transported between the belt and the pressure 
roller while being pressed against the pressure roller, the belt 
transmitting heat from the heat source to the recording sheet. The suction 
transport means preferably includes: a transport belt support for 
supporting the transport belt, the transport belt support having an outer 
wall, on which the transport belt slides to move in the transport 
direction, and an inner wall for defining a vacuum duct, the vacuum duct 
being communicated with an air suction pump, a plurality of openings being 
formed through the transport belt support from the inner wall to the outer 
wall, the suction being performed through the plurality of openings; and a 
drive source for driving the transport belt in the transport direction. 
According to another aspect, the present invention provides a method of 
recording on a recording medium using an ink jet print head, the method 
comprising the steps of: serially preheating the recording medium directly 
before recording; transporting the recording medium, after preheating, by 
a transport belt while fixed to the transport belt by vacuum suction; and 
causing an ink jet print head to jet ink droplets onto the recording 
medium while being transported by the transport belt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An ink jet printer according to a preferred embodiment of the present 
invention will be described while referring to the accompanying drawings 
wherein like parts and components are designated by the same reference 
numerals to avoid duplicating description. 
An ink jet printer of a preferred embodiment will be described with 
reference to FIG. 1. As shown in FIG. 1, the ink jet printer of the 
present embodiment mainly includes a preheating unit 2, an ink jet print 
head 1, and a vacuum suction transport device 3. The preheating unit 2 and 
the vacuum suction transport device 3 are arranged to form a transport 
path along which they transport an object to be printed (referred to as 
recording sheet 6 hereinafter). The print head 1 is positioned confronting 
the vacuum suction transport device 3 so as to face an upper surface of 
the recording sheet 6 which is being transported on the vacuum suction 
transport device 3. 
A recording sheet 6 inserted into the printer through an inlet (not shown) 
is guided by a transport guide 9 to be introduced to the preheating unit 
2. The preheating unit 2 heats and dries the recording sheet 6, while 
transporting the recording sheet in a transport direction (indicated by an 
arrow B) along the transport path. As shown in the figure, the preheating 
unit 2 is constructed from a combination of a belt-type preheater 20 and a 
pressure roller 26. The belt-type preheater 20 is for serially heating the 
recording sheet 6 while pressing the recording sheet 6 against the 
pressure roller 26. The heated recording sheet 6 is guided by another 
transport guide 9' to the vacuum suction transport device 3. The vacuum 
suction transport device 3 transports the recording sheet 6 beneath the 
print head 1, where images are recorded on the recording sheet 6. The 
vacuum suction transport device 3 transports the recording sheet 6 by a 
transport belt 34 while vacuum suctioning the recording sheet 6 to fix it 
onto the transport belt. The vacuum suction transport device 3 also 
vaporizes moisture from the recording sheet 6, and reduces the temperature 
of the recording sheet 6. The recording sheet 6 is then discharged out of 
the printer through an outlet (not shown) positioned downstream of the 
transport path in the transport direction B. 
As described above, according to the present invention, the preheating unit 
2 is constructed from a combination of the pressure roller 26 and the 
belt-type preheater 20. The belt-type preheater 20 includes a positive 
temperature coefficient (PTC) thermistor heater 19 with an 
auto-temperature control function and a predetermined Curie temperature of 
150.degree. C., for example. A belt 24 is mounted over the PTC heater 19 
and a drive roller 25. The belt 24 is driven by the drive roller 25 to 
transport the recording sheet 6 on its one surface while its another 
surface being in contact with the PTC heater 19. The pressure roller 26 is 
rotatably supported, at a position confronting the PTC heater 19. The 
pressure roller 26 is positioned in contact with the belt 24 for rotating 
synchronously with the belt driven by the drive roller. The recording 
sheet 6 is therefore transported between the belt 24 and the pressure 
roller 26 while being pressed against the pressure roller 26. Heat 
generated at the PTC heater 19 is transmitted through the belt 24 to the 
recording sheet 6 which is being transported between the endless belt 24 
and the pressure roller 26. When the Curie temperature for the PTC heater 
19 is 150.degree. C., for example, the recording sheet 6 is heated to a 
fixed temperature in a range of between 80 and 90.degree. C. Because the 
PTC thermistor heater 19 can control its temperature not to exceed its 
Curie temperature, the sheet 6 is ensurely heated to the fixed 
temperature. High heat efficiency is obtained because the sheet 6 is 
pressingly transported by the pressure roller 26. Even envelopes and the 
like can be transported and heated without being wrinkled. 
The vacuum suction transport device 3 includes a belt support 31. An uneven 
surface, with variation of about .+-.100 .mu.m between high and low areas, 
may be provided to the surface of the belt support 31. An endless belt 34 
is rotatably supported on the belt support 31 so that a portion of the 
endless belt 34 is aligned with the path of the sheet 6 as the sheet 6 
exits from the preheating unit 2 in the transport direction B. A drive 
motor 35 is provided for rotating the endless belt 34 at a speed 
synchronized with speed of the sheet 6 as transported by the preheating 
unit 2. A plurality of holes (not shown) about 0.5 mm in diameter, for 
example, are formed through the entire surface of the endless belt 34 at a 
pitch of 3 to 4 mm, for example. A plurality of suction holes 32 are 
formed through the belt support 31 at almost the same pitch. A suction 
duct 33 is formed inside the belt support 31 for fluidly connecting the 
suction holes 32 with an air suction pump (not shown). 
The ink jet print head 1 is supported to confront a sheet 6 transported on 
the endless belt 34. A suction nozzle 8 for producing a partial vacuum 
near the surface of a printed sheet 6 may be provided at the side of the 
head 1 opposite the vacuum suction transport device 3. 
A sheet 6 heated to 80 to 90.degree. C., for example, by the preheating 
unit 2 and discharged therefrom is taken up by the rotating endless belt 
34. The sheet 6 is fixed to the endless belt 34 by the suction of the 
suction device 3 as transmitted via the suction duct 33, the suction holes 
32, and the holes formed in the endless belt 34. The uneven surface of the 
belt support 31 can prevent the endless belt 34 from being overly strongly 
fixed to the belt support 31 by the suction from the suction duct 33. The 
preheated print sheet 6 is printed on by the ink jet print head 1 while 
being transported as fixed to endless belt 34. The heat of the sheet 6 
dries ink that impinges on the sheet 6 in about 0.3 to 0.4 seconds, in 
this example, after printing. Evaporate from the drying ink can be sucked 
up and exhausted via the suction nozzle 8 so it does not adhere to the 
head 1. Therefore, despite a print speed of 150 mm/sec, an image printed 
on the sheet 6 can be handled as soon as it is discharged from the vacuum 
suction transport device 3. 
The above-described structure of the present invention can ensure extremely 
fast and safe ink jet printing operation. Contrary to the above-described 
heating device which heats the sheet before the sheet is printed, 
conventional dryers for drying a printed sheet after it is printed require 
inclusion of a non-contact rapid heating device such as an infrared heater 
which is larger and not as safe. 
Any type of ink jet print head can be applied to the ink jet printer of the 
present invention, including static electric type heads, piezoelectric 
type heads, and thermal type heads, with the same good results. It is 
noted, however, that conventional thermal type heads have a printing speed 
of about 0.5 pages per minute. On the other hand, a multi-color or 
full-color ink jet print head of a large-scale, high-density thermal type 
of the present invention (which will be described later with reference to 
FIGS. 8 through 16) can attain a print speed of 100 pages per minute. 
Therefore, drying time restricts the print speed of the ink jet printer. 
Conventional methods to dry wet ink on a recording sheet include either 
heating or drying the recording sheet in a non-contacting manner or 
heating the underside of the recording sheet using a heat transmission 
device. Thermal efficiency in both of these methods is poor. In contrast, 
the preheating unit 2 according to the present invention heats the surface 
of the recording sheet, on which images will be recorded, by contact 
pressure before recording, thereby achieving optimum thermal efficiency. 
Preheating in this manner not only dries printed image within a short 
period of time but also evaporates the moisture that has been absorbed by 
recording sheets during their storage. Recording sheets transported 
underneath the print head are heated to a high temperature and dried to a 
low moisture level to almost fixed conditions. That is, recording sheets 
when transported past the print head are at ideal conditions for printing 
regardless of their storage conditions, which can attain high quality 
image printing operation. 
Also, the recording sheets transported under the print head are fixed by 
vacuum suction to the transport belt. When the recording sheet is made 
from a material that air can pass through, such as paper, the suction from 
the suction transport belt pulls ink impinged on the recording sheet in 
the thickness direction of the recording sheet. This can utilize 
high-speed drying capability of the heated and dried recording sheet in 
the thickness direction so that droplets of different colored inks 
serially impinged on the recording sheet spread and mix only slightly. 
Accordingly, especially employing the high printing speed thermal head (to 
be described later with reference to FIGS. 8-16) in the present ink jet 
printer can attain high printing speed while attaining high quality 
printing. 
Transporting the recording sheet as fixed to the transport belt by vacuum 
suction reduces to a minimal level deformation of the recording sheet 
caused by stretching during recording processes. Therefore, poor 
positioning of impinged ink droplets can be reduced to a minimum during 
full-color printing so that high-quality full-color images can be 
obtained. 
Almost the same good effects can be obtained when recording images on 
plastic sheets, such as those used in overhead projectors, through which 
air can not pass. This is because plastic sheets retain a great deal more 
heat than do paper sheets and so ink impinged thereon dries much faster. 
Two-layered recording sheets such as envelopes can be rapidly printed on, 
because the belt-type preheater heats and dries the recording sheets 
without wrinkling them. 
First through third concrete examples of the ink jet printer of the present 
invention will be described below with reference to FIGS. 2 through 7. 
These examples are directed to a full-color thermal ink jet printer. 
According to these examples, the print head 1 is a full-color line head. 
The line head 1 is fixedly mounted in the ink jet printer to extend 
perpendicularly to the transport path. The print head 1 includes four 
parallel rows of ink ejection nozzles facing the recording sheet 6. Each 
row extends for a length equivalent to the entire width of a recording 
sheet 6. The four rows are arranged along the transport direction B. One 
of the nozzle rows is for ejecting black water-based ink and the other 
three rows are for ejecting colored water-based inks such as yellow, cyan, 
and magenta inks. 
Preferably, the full-color line head 1 may be a large-scale, high-density 
thermal jet print head, the structure of which will be described later in 
greater detail with reference to FIGS. 8 through 16. The line head 1 
includes four rows of nozzles which are separated from each other by about 
1.5 mm, for example. The nozzles of each row are aligned at a density of, 
for example, 400 dpi in lines (dots per inch) in the direction 
perpendicular to the transport direction B the recording sheet 6 is 
transported. 
As shown in FIGS. 2 through 7, the ink jet printer of each of example not 
only includes the preheating unit 2, the vacuum suction transport device 
3, and the print head 1, but also includes: an orifice cap 4 for capping 
the nozzles of the print head 1; and an orifice surface cleaning unit 5 
for cleaning a surface of the orifice cap 4. These elements are described 
in detail in co-pending U.S. Pat. No. 5,670,996 filed Mar. 31, 1995 by 
Masao Mitani, the disclosure of which is hereby incorporated by reference. 
Because these elements are not directly related to the present invention, 
their detailed explanation will be omitted here. 
The first example will be described below with reference to FIGS. 2 through 
5. 
First, the belt-type preheater 20 constituting the preheating unit 2 will 
be described below with reference to FIG. 2. 
One type of a belt-type heater has been described in U.S. Pat. No. 
3,811,828 as a fixing device for a laser printer. The heater is for 
lowering power consumption of the printer while maintaining quick start 
capability of the printer. The heater includes an infrared lamp or thermal 
resistor element as a heat source, which requires an accurate temperature 
control. An endless belt employed in this heater is a two-layer structure 
formed from a polyimide resin film, that is thermal-resistant and that 
retains its stiffness even at high temperatures, covered with non-stick 
polytetrafuoroethylene (PTFE) for preventing toner off-set. 
Contrarily, in the belt-type preheater 20 of the present example, the PTC 
heater 19 is constructed from a plurality of thin positive temperature 
coefficient thermistor heater chips (which will be referred to as "PTC 
heater chips" hereinafter) 22 and a single heat-transmission plate 21. The 
PTC heater 19 is buried in a holder 23 in a position that the 
heat-transmission plate 21 is exposed to confront the pressure roller 26. 
An endless belt 24 is mounted around the holder 23 and the drive roller 
25. As the drive roller 25 rotates as indicated by an arrow in the figure, 
the endless belt 24 moves in the transport direction B where the endless 
belt 24 is sandwiched between the heat-transmission plate 21 and the 
pressure roller 26. 
About ten PTC heater chips 22 are buried in a recess formed in the holder 
23. The PTC heater chips 22 are arranged in a row extending 
perpendicularly to the transport direction B. The single heat-transmission 
plate 21 is laminated over all the PTC heater chips 22. A single electrode 
plate (not shown) is provided over the surfaces of the PTC heater chips 22 
confronting the heat-transmission plate 21. The electrode plate entirely 
covers the surfaces of the PTC heater chips 22. Two other electrode strips 
(also not shown) are provided on the other surfaces of the PTC heater 
chips 22. An electric power source (not shown) is connected between the 
electrode strips so that electric currents flow inside of the PTC heater 
chips 22 between the electrode strips and the electrode plate to generate 
heat therein. The PTC heater chip 22 serves as a self-controlled heat 
source. When the temperature of the PTC heater chip 22 rises to reach its 
own Curie temperature, resistivity of the PTC heater chip 22 rapidly 
increases to restrain heat generation. 
A PTC heater chip has a low heat transmission rate, and therefore easily 
develops internal temperature distributions, which cause its electrical 
resistance to increase. This phenomenon is known as the pinch effect. The 
decrease in current flow caused by the pinch effect restricts the amount 
of heat the PTC heater chip can produce so that the PTC heater chip cannot 
rise to the desired temperature. According to the present invention, to 
give the PTC heater chip sufficient heating capacity, the PTC heater chips 
are formed 0.9 mm thick and the electrode plate is provided entirely over 
one side of each chip that is contacted with the heat-transmission plate 
21. 
The heat-transmission plate 21 is made from zirconia-toughened alumina 
ceramics. The heat-transmission plate 21 has good heat transmission 
characteristics for transmitting heat generated in the PTC heater chips 
22, especially at the sides of the PTC heater chips 22 entirely covered 
with the electrode plate, toward the endless belt 24. The 
heat-transmission plate 21 is also for providing a smooth surface and good 
lubricity in regards to the endless belt 24. 
It is difficult to produce a single long PTC heater chip that is 
sufficiently smooth. Therefore, in the present example, the smooth 
heat-transmission plate 21 is disposed between the array of ten aligned 
PTC heater chips 22 and the endless belt 24. Because the surface of the 
heat-transmission plate 21 is smooth, the endless belt 24 will not catch 
against it and crinkle up. The heat-transmission plate 21 has small 
abrasion and friction coefficients, a high thermal transmission rate, is 
inexpensive, and has good electric insulation properties. The 
zirconia-toughened alumina ceramics (for example, "Hallocks Z" produced by 
Hitachi Chemical Co., Ltd.) is an optimal material for the 
heat-transmission plate 21. 
According to the present invention, the endless belt 24 is formed from a 
single layer of polyimide resin. One surface of the endless belt 24 is 
contacted with the heat-transmission plate 21, while the other surface 
being for transporting the recording sheet 6. The endless belt 24 
transmits heat from the one surface contacted with the heat-transmission 
plate 21 to the other surface contacted with the recording sheet 6. The 
endless belt 24 driven by the drive roller 25 slides against the 
heat-transmission plate 21 while transporting the recording sheet 6. 
The pressure roller 26 is provided in confrontation with the 
heat-transmission plate 21 via the endless belt 24 so that the transport 
path is located between the belt-type preheater 20 and the pressure roller 
26. The pressure roller 26 rotates in a direction indicated by an arrow in 
the figure as the drive roller 25 rotates as shown in the figure. The 
belt-type preheater 20 and the pressure roller 26 cooperate to transport 
the recording sheet 6 in the transport direction B in pressing contact 
with the recording sheet 6. The pressure roller 26 is made of foam silicon 
rubber with hardness of five or less on the Japan Industrial Standard A 
(JIS-A) scale, for the following reasons. When printing both sides of the 
recording sheet 6, the recording sheet 6 should be inserted into the ink 
jet printer so that the pressure roller 26 will be in pressing contact 
with the side already printed. It is therefore desirable that the pressure 
roller 26 be formed from silicon rubber, which has excellent non-stick 
properties. Assuming that the printed side of the recording sheet 6 has 
been printed using toner (toner with a low softening point of 110 to 120 
degrees C. is common) applied using a laser beam printer, silicon rubber 
has superior non-stick properties in regards to toner that does PTFE. 
Silicon rubber also has sufficient non-stick properties in regards to 
surfaces printed with liquid using ink jet printers. It is desirable that 
the combination of the heat-transmission plate 21 and the pressure roller 
26 can efficiently transmit heat to the recording sheet 6 while 
sandwiching it therebetween at its nip portion. It is also desirable that 
the endless belt 24 and the heat-transmission plate 21 produce only a 
small friction force and a small amount of abrasion when sliding against 
each other. To fill these requirements, it is necessary to decrease the 
pressure of the pressure roller 26 while increasing the width of the nip 
portion to increase the time of thermal contact. For this reason, the 
pressure roller should be made of foam silicon rubber with hardness of 
five or less on the Japan Industrial Standard A scale, so that the width 
of the nip can easily be increased to about 8 mm. 
Experiments were performed for the preheating unit 2 constructed as 
described above. 
In the experiments, a 100 V! alternating current (AC) power source was 
connected to the electrode strips provided on the PTC heater chips 22 to 
heat the PTC heater chips 22. As the drive roller 25 rotated, the endless 
belt 24 was moved and the pressure roller 26 was rotated accordingly. The 
endless belt 24 used during these experiments was 25 micrometers thick, 
the heat-transmission plate 21 was 0.3 mm thick, the PTC heater chips 22 
were 8 mm wide, the pressure roller 26 was made of foam silicon rubber to 
produce an 8 mm nip with the endless belt 24, the PTC heater chips 22 with 
Curie temperature of 170 degrees C. were selected, and the transport speed 
of the recording sheet was 50 mm/s. The temperature at the surface of the 
heat-transmission plate 21 was measured. The temperature at the surface of 
the recording sheet 6 was also measured upon its exit from the preheating 
unit 2. The results of these experiments were plotted in the graph shown 
in FIG. 3. 
As can be seen in FIG. 3, the temperature of the PTC heater chips 22 rose 
to near its Curie temperature about 5 to 10 seconds after energization of 
the PTC heater chips 22 began. That is, a recording sheet 6 introduced 
into the preheating unit 2 five seconds after start of energization (when 
the recording sheet 6 is an A4 size sheet fed length-wise at a speed of 
eight to nine pages per minute) will be heated to 100 to 110 degrees C. 
and its moisture will rapidly evaporate. When the recording sheet 6 
reaches a region beneath the full-color line head 1, it will be almost 
completely dry and have a temperature of 90 to 100 degrees C. 
It is apparent therefore that if the preheating unit 2 is to be combined 
with a high-speed print head 1 capable of printing 20 to 30 sheets per 
minute, the PTC heater chips 22 with a higher Curie temperature should be 
selected. It is noted that PTC heater chips 22 with Curie temperature of 
240 degree C. or less are readily available. 
The advantages of using PTC heater chips 22 are that they require no 
temperature detection or energization control, as follows. Because the 
room temperature recording sheet 6 becomes a heat sink for the PTC heater 
chips 22, PTC heater chips 22 in the region of the passing recording sheet 
6 are energized to return their temperature to the desired temperature. 
Even when the small recording sheet 6, such as a postcard or other sheet, 
that is narrower than the length of the PTC heater chip array is to be 
printed on, only those chips actually confronting the recording sheet are 
energized. Accordingly, the temperature over the entire length region of 
the PTC heater chip array can be continuously maintained at a uniform 
temperature, with variations being within a range of .+-.5%. It is noted 
that other types of heaters that do not have this function, such as 
infrared lamps or thermal resistor elements, are energized equally at all 
areas, whether cooled by the passing recording sheet 6 or not. As a 
result, an extremely high temperature will possibly develop at portions of 
the heaters not confronting the narrow recording sheet 6 so that the 
polyimide belt may be damaged. To prevent such damage, safety measures, 
such as temperature dependent termination of printing processes, must be 
implemented. 
Under the same conditions as those in the above-described experiments, 
other experiments were performed. In the present experiments, the drive 
roller 25 and the pressure roller 26 were continuously rotated for 200 
hours, while the PTC heater chips 22 being continuously energized. The 
rotational speed of the drive roller 25 was set so that the moving speed 
of the endless belt 24 was fixed to 50 mm/sec. The 200 hours of operation 
transported 100,000 pages of A4sized sheets in their longitudinal 
directions, which was equivalent to running 36 kms of sheets. During this 
operation, the endless belt 24 and the heat-transmission plate 21 slided 
against each other with the relative sliding speed of 50 mm/sec. 
The present experiments measured time-dependent change in coefficient of 
kinetic friction between the heat-transmission plate 21 and the endless 
belt 24. The experiments were conducted where the heat-transmission plate 
21 was made of zirconia-toughened alumina ceramics and the endless belt 24 
was the polyimide belt made from a single layer of polyimide resin. The 
present experiment were also conducted where the endless belt 24 was 
replaced with a conductive type polyimide belt made of a single layer of 
polyimide resin in which carbon particles were dispersed. In both 
experiments, any lubricant were not provided between the heat-transmission 
plate 21 and the endless belt 24. The results of these experiments are 
shown in FIG. 4. It is apparent that an extremely small friction 
coefficient was maintained both in the cases where the endless belt 24 was 
the polyimide belt and was the conductive type polyimide belt. 
During these experiments, the amount of abrasion were also measured, at the 
surfaces of the endless belt 24 and the heat-transmission plate 21. The 
amount of abrasion for both the heat-transmission plate 21 and the endless 
belt 24 was one micrometer or less. It can be concluded therefore that a 
25 micrometer thick endless belt 24 could transport about one million 
pages. Some printers need the capacity to transport several million pages. 
However, the thicker the endless belt 24, the smaller the thermal 
transmission efficiency. The endless belt 24 is therefore desirable to 
have thickness of within 50 micrometers. 
The vacuum suction transport device 3 will be described below in greater 
detail. 
The vacuum suction transport device 3 is positioned downstream of the 
preheating unit 2 in the transport direction B. The recording sheet 6 
heated by the preheating unit 2 is guided to the vacuum suction transport 
device 3 via the guide 9'. 
The vacuum suction transport device 3 includes the vacuum duct 33 
surrounded by the belt support 31 and communicated with the air suction 
pump (not shown). An upper flat portion of the belt support 31 is provided 
with a plurality of openings 32 communicated with the vacuum duct 33. The 
transport belt 34 is mounted over the belt support 31 and a drive roller 
35. As the drive roller 35 rotates in a direction indicated by an arrow in 
the figure, the part of the transport belt 34 slides over the upper flat 
part of the belt support 31 to transport the recording sheet 6 in the 
transport direction B. The speed, at which the transport belt 34 moves, is 
adjusted equal to or slightly slower than that of the endless belt 24 of 
the preheating unit 2. A tension roller 36 is provided for supplying 
appropriate tension to the transport belt 34. 
According to the present example, the openings 32 are provided highly 
densely through the belt support 31 at an area directly under the print 
head 1. Or otherwise, the openings 32 may be in the form of a plurality of 
adsorption grooves and may be formed at positions corresponding to the 
plurality of nozzle rows provided on the print head 1. For example, if 
four nozzles of four colors of ink are provided on the print head 1, four 
absorption grooves may be formed in confrontation with the four nozzles, 
respectively. Each absorption grove may have about 1 mm wide, for example. 
According to this example, the density at which the openings are formed at 
a region far from and downstream of the print head 1 in regards to the 
transport direction B is smaller than the density at which the openings 
are formed at a region confronting the print head 1. In other words, fewer 
openings 32 need be opened in the transport belt support 31 far from and 
downstream of the print head 1. This is because the openings 32 in this 
area need only provide suction sufficient for softly or gently fixing the 
recording sheet 6 to the porous transport belt 34. Also, fewer openings 
will greatly reduce the amount of vacuum suction force required from the 
suction duct 33. This also greatly contributes to reducing rotation drive 
power and amount of abrasion to the porous transport belt 34 when it 
slides against the belt support 31. 
The transport belt 34 is formed with a number of pores or small openings. 
The porous transport belt 34 is preferably made from glass cloth coated 
with polyimide or teflon (registered trademark). The glass cloth must be 
porous such as tangle weave or net-type sheets of glass cloth. 
With this structure of the vacuum suction transport device 3, the recording 
sheet 6 is absorbed by the air suction produced through the openings 32 
and the pores in the transport belt 34 from the vacuum duct 33. The entire 
surface of the recording sheet 6 is uniformly suctioned in the area 
directly beneath the print head 1. This suction both fixes the heated 
recording sheet 6 during transportation onto the transport belt 34. 
Especially when the recording sheet is made from a material that air can 
pass through, such as paper, the suction also suctions the ink in the 
thickness direction of the recording sheet 6 (downward), thereby 
completely preventing ink runs, mixing, and smudges over the entire 
surface of the heated recording sheet 6. It also greatly contributes to 
rapidly drying the ink on the recording sheet 6. 
Though the already-described experiments confirmed that the structure of 
the ink jet printer of the present invention enables to print 30 pages per 
minute of high-quality full color images, further experiments were 
performed to determine the effect on feathering during monochrome 
printing. FIG. 5A shows magnifications of images printed under different 
conditions on special non-smudging paper developed for ink jet printers. 
FIG. 5B shows magnifications of images printed under different conditions 
on plain paper for laser printers. FIG. 5C shows magnifications of images 
printed under different conditions on recycled paper. In the experiments, 
images were printed on room temperature sheets; on sheets only preheated 
to about 60 degrees C.; and on sheets both preheated to about 60 degrees 
C. and suctioned during printing. 
As can be seen, preheating has a great effect on print quality. Because 
only small amounts of ink are impinged to the sheet during monochrome 
printing, preheating the sheet only to 60 degrees C. was sufficient to 
produce the results shown. It is noted, however, that about ten times as 
much ink is ejected and impinged to sheets during full-color printing. 
Therefore, ink needs to be dried by preheating recording sheet to 100 
degrees C. or more and also suctioning in order to maintain quality. The 
same quality images can be obtained using recording sheets of plain paper 
or recycled paper as when using recording sheets of specially produced 
expensive paper made to meet special specifications. 
It is noted that no satellites (subdroblets) were observed in sheets 
printed during these experiments, because the print head used in these 
experiments was a satellite free ink jet print head described in 
co-pending U.S. patent application Ser. No. 08/387,579, the disclosure of 
which is hereby incorporated by reference. This print head eliminated 
ghosts and reduced the burden of drying excess ink. The suction vacuum 
transport is effective for super fine printing, especially between 600 and 
800 dpi. 
The present example is directed to a printer employing a line head that 
extends the entire width of a recording sheet 6. However, the present 
example could be combined with a smaller scanning-type color head with 
equally good results. 
Vacuum suction transport does not contribute to quality of images printed 
on overhead projections sheets, because air can not pass through the 
overhead projection sheets. However, the rapid drying resulted from the 
vacuum suction transport can still prevent mixing of different colored 
inks and ink running on the overheat projection sheets. 
As described above, according to the present example, because an endless 
belt made from heat-resistance hard polyimide resin is used in the 
belt-type preheater, the polyimide resin layer should be made between 20 
to 50 micrometers thick in order to effectively transfer the heat from the 
heat source to the recording sheet and considering the effects of abrasion 
produced when the endless belt slides against the zirconia-toughened 
alumina ceramics heat plate, which has excellent heat transmission, 
stiffness, slickness, and electrical insulation properties. 
Because PTC heater chips are used for the heat source for the preheater 20, 
recording sheets can be heated to a desired temperature without performing 
any temperature control. The temperature of the heat source can normally 
be set to a fixed value in correspondence with a printing speed set to the 
print head. That is, the preheater 20 should be made from only one type of 
PTC heater chips having a fixed Curie temperature so that the set 
temperature need not be changed. 
It is noted that print speed attainable by the print head changes depending 
on whether the print head is a line head or a scanning head. Therefore, 
the PTC heater chips should be chosen by their Curie temperatures, in 
correspondence with the type of the print head. It is further noted that 
the PTC heater chips with Curie point of 230 degrees C. or less (which 
translates to about 180 degrees C. or less at the surface of recording 
sheets) should be used in order to prevent overheating the recording 
sheets when trouble occurs during their transport. Accordingly, PTC heater 
chips with Curie point in the range of 120 degrees C. and 230 degrees C. 
should preferably be used. 
According to the present example, a larger vacuum suction force is applied 
by the vacuum suction transport device to the printing region than to a 
region far from and downstream of the printing region. This ensures 
suction force large enough at the first stage of introducing the recording 
sheet into the transport device. Because the transport belt is formed from 
an endless belt made from a finely porous film or a mesh sheet, the 
transport can apply a uniform vacuum suction across the entire surface of 
the recording sheet at the printing region, which contributes to obtaining 
printed images with high quality. 
Thus, according to the present example, a body to be recording on is heated 
and dried by a belt-type preheater at the region directly before the 
recording means and then transported fixed in placed by vacuum suction 
while being recorded on by the recording means. Images with equal quality 
can be recorded on recording sheets made from plain paper, recycled paper, 
or paper specially made for ink jet printers. Also, images dry rapidly, 
thereby facilitating handling of recording sheets even when full-color 
images are recorded on the recording sheets. 
The belt-type preheater that uses PTC heater chips requires no complicated 
or expensive control. Also, consecutive recording of any sized recording 
sheet can be safely performed without worry of damaging components from 
overheating. Suction produced by using a porous endless belt for the 
suction transport belt yields high-speed drying and high print quality 
across the entire surface of the recording sheet. Feathering can be 
greatly reduced by printing on high-temperature and highly dried recording 
sheets. Images can be recorded on plain paper and recycled paper with the 
same quality as expensive paper specially produced for use with ink jet 
printers. 
A second concrete example of the ink jet printer will be described below 
with reference to FIG. 6. 
According to the structure of the ink jet printer of the present invention, 
moisture is produced during the recording sheet 6 is printed with 
water-based ink while being suctioned. In the case where the recording 
sheet 6 is made from a moisture-absorbing material, such as a paper, 
moisture is produced also during the recording sheet 6 is preheated by the 
preheating unit 2. It is therefore desirable to prevent the water vapor 
from clinging to proximal components. The second example is provided for 
appropriately exhausting the water vapor in a manner that does not 
adversely effect print quality. 
A printer of the second example is the same as that of the first example, 
except that vapor exhaust slits are provided in the second example. 
According to the present example, as shown in FIG. 6, a pair of first 
exhaust slits 7 and 7' are provided at a region between the preheating 
unit 2 and the vacuum suction transport device 3 along the transport path 
so as to exhaust air from that region. The first exhaust slits 7 and 7' 
are positioned in confrontation with each other so that the transport path 
is located therebetween. The first exhaust slits 7 and 7' serve to suction 
moisture released from both sides of the recording sheet 6 preheated by 
the preheating unit 2. The first exhaust slits 7 and 7' are built with a 
length equal to the width of the recording sheet 6 and positioned so the 
length spans the width of the recording sheet 6. The guides 9' provided to 
this section insures that the recording sheet 6 is smoothly transported to 
the vacuum suction transport device 3 while suctioned by the first exhaust 
slits 7 and 7'. 
According to the present example, a second exhaust slit 8 is provided at a 
region close to and downstream of the print head 1 in the transport 
direction B for exhausting air from that region. The second exhaust slit 8 
confronts the upper surface of the belt support 31. The second exhaust 
slit 8 therefore serves to suck out moisture that is released from the 
water-based ink impinging on the recording sheet 6 and that fills the 
narrow gap between the print head 1 and the recording sheet 6. The second 
exhaust slit 8 is built with a length equal to the width of the recording 
sheet 6 and positioned so the length spans the width of the recording 
sheet 6 as are the first exhaust slits 7 and 7'. 
Similarly to the first example, according to the structure of the ink jet 
printer of the present example, the recording sheet 6 is preheated by the 
preheating unit 2 to 100 degrees C. or more, and then transported to the 
vacuum suction transport device 3. At this time the recording sheet 6 is 
heated to 100 degrees C. or more. When the recording sheet 6 is made from 
a moisture-absorbing material, moisture is rapidly released from the 
recording sheet 6 directly after it passes out of the preheating unit 2. 
The moisture is suctioned into the first exhaust slits 7 and 7' from both 
surfaces of the recording medium 6. 
The recording sheet 6, heated to 100 degrees C. or more and almost 
completely dry, is transported underneath the print head 1 as fixed to the 
transport belt 34 of the vacuum suction transport device 3 by vacuum 
suction. The print head 1 prints images on the recording medium 6 by 
serially ejecting water-based ink. The moisture in the water-based ink 
(which is 90 to 95% water) rapidly evaporates upon impinging on the 
recording sheet 6, resulting in the narrow gap (of about one to two 
millimeters) between the print head 1 and the recording sheet 6 filling 
with water vapor. The temperature of the produced water vapor is slightly 
higher than the ambient temperature. The water vapor is sucked out of the 
gap by the second exhaust slit 8 and exhausted so that the water vapor is 
not condensed on the surface of the print head. 
Experiments were conducted for the ink jet printer of the present example. 
A full-color line head 1 used in these tests had the structure of FIGS. 
12-15 (which will be described later). The line head had the width of a 
210 mm A4 sheet and included four parallel rows of ink ejection nozzles. 
Each row contained 3,360 nozzles per row aligned at 400 dpi. Rows were 
separated by about 1.6 mm. The individual nozzles were capable of firing 
at a frequency of between 0 to 15 KHZ. In other words, the full-color line 
head was capable of printing at a speed of 100 pages or more of A4 size 
paper per minute. 
Several print tests were performed for printing A4 size papers with the ink 
jet printer of the present example. 
First, print tests were performed changing the print speed within the range 
of 5 and 20 pages per minute. Evaluations of these tests revealed no 
difference in print quality when print speed was changed within this 
range. Therefore, the first exhaust slits 7 and 7' and the second exhaust 
slit 8 dried the released moisture rapidly enough for printing within this 
printing speed range. 
Further printing tests were performed by changing conditions of the suction 
by the first exhaust slits 7 and 7' and the second exhaust slit 8. 
Printing tests were performed without activating both the first exhaust 
slits 7 and 7' and the second exhaust slit 8. A great deal of moisture 
condensed in the proximity of the full-color line head 1 after printing 
was performed for only a few minutes, even at the slow print speed of five 
pages per minute. Some droplets of condensed water were observed having 
dropped on the surface of the recording medium 6. 
Next, printing was performed while exhausting air through the second 
exhaust slit 8 only. Although condensation greatly dropped, droplets of 
condensed moisture could sometimes be still observed on the recording 
sheet 6, depending on the moisture content of the recording sheet 6 and 
the printing speed. 
In contrast, no condensation or adverse effects to proximal components were 
observed when suction exhaust was appropriately performed through both the 
first exhaust slits 7 and 7' and the second exhaust slit 8. 
It is noted, however, that some ink droplets impinged at imprecise 
locations on the recording medium, resulting in poor print quality, when 
suction through the second exhaust slit 8 was too strong or when exhaust 
was irregular. 
The additional tests were then performed. First, the speed that suction 
from the second exhaust slit 8 caused air to flow from the gap between the 
print head 1 and the recording sheet 6 was measured. Print tests were then 
performed, while changing the suction from the second exhaust slit 8 and 
changing the air flow speed. According to the print tests, poor print 
quality was observed when flow in the gap between the full-color line head 
1 and the recording sheet 6 was 2 m/s or more. This poor print quality was 
probably caused by turbulence that destabilized the trajectory of the ink 
droplets. 
Then, print tests were performed by intentionally disturbing the flow speed 
distribution locally in the gap between the print head 1 and the recording 
sheet 6. The test results show that even when flow in the gap was 2 m/s or 
less, turbulence produced in the gap resulted in the poor print quality. 
In normal printing condition, the turbulence can be possibly produced at 
either edge of the full-color line head 1 or can be produced by any 
obstruction located in the gap. 
The test results further show that fairly acceptable print quality was 
obtained when variation in air flow speed were .+-.5%/cm or less locally 
and .+-.20% or less along the entire length (i.e., in the direction 
nozzles are aligned) of the head. 
These conditions are easily met by providing a flow regulator upstream from 
and on both sides of the full-color line head 1. No condensation was 
observed at a flow speed of 1.0 to 1.5 m/s even when printing at a speed 
of 20 pages per minute. 
When a scanning-type head is used instead of the line head 1, the second 
exhaust slit 8 not only must exhaust air from between the head 1 and the 
recording sheet 6 but must also exhaust air from freshly printed surfaces 
of the recording sheet 6 exposed after the print head passes by. However, 
the conditions for condensation do not change substantially from when the 
line head 1 is used. It was confirmed through printing tests using a 
scanning-type head that the proximity of the printed recording sheet 6 
must be exhausted in virtually the same manner to prevent condensation. 
As described above, in the ink jet printer of the second example, moisture 
that has been absorbed by the recording sheet during its storage 
evaporates from the surface of the recording sheet directly after 
preheating. This moisture vapor is suction vented through exhaust slits 
positioned at front and rear surfaces of the recording sheet. Therefore, 
the ambient humidity will not increase. When water-based ink is printed at 
high speeds onto a high-temperature and highly dry recording sheet, a 
great deal of moisture vapor is generated. By sucking this moisture vapor 
into the other ventilation slit positioned downstream of the print head, 
increases in ambient humidity can be suppressed. However, it is imperative 
that the ventilation suction is controlled not to disturb the trajectory 
of ejected ink droplets. 
Contrary to papers, plastic sheets for overhead projectors have low 
moisture content. Little moisture is produced during those sheets are 
preheated. Accordingly, ventilation is basically unnecessary after 
preheating those recording sheets with low moisture content. However, it 
is still necessary to ventilate moisture vapor that is released from 
water-based ink impinged on the recording sheet and coming upstream of the 
print head. 
A third example will be described below with reference to FIG. 7. 
The structure of an ink jet printer of the third example is the same as 
those of the first and second examples, except for the arrangement in the 
ink nozzles in the print head 1. 
Generally, both monochrome and full-color ink jet printers are used to 
record characters comprised mainly of black straight lines. In fact, 
full-color printing accounts for only about 20% of all printing. Even when 
several pages are printed in full color, there are often times when 
nozzles for ejecting yellow, cyan, or magenta ink do not operate. Because 
the nozzles are not capped during printing, the ink in inactive nozzles 
will dry and become more viscous. This can result in clogged nozzles. 
According to the present invention, the recording sheet 6 is preheated 
before passing next to the print head 1. The radiant heat from the thus 
preheated recording sheet 6 will possibly increase the rate at which ink 
in inactive nozzles dries. The third example is therefore provided for 
preventing viscosity of ink in inactive nozzles from increasing to prevent 
clogging of nozzles, thereby resulting in printing clear full color 
images. 
Similarly as in the first and second examples, the print head 1 is formed 
with four rows of nozzles: a black-ink row 11, and three color-ink rows 
12, 13, and 14. Each row extends perpendicularly to the transport 
direction B. According to the present example, as shown in FIG. 7, the 
four rows are arranged along the transport direction B so that the 
black-ink row 11 is positioned most upstream side in the transport 
direction B, i.e., at a position nearest to the first exhaust slits 7 and 
7'. 
In the ink jet printer according to the present example, recording medium 
to be printed on is preheated so that moisture of water based ink impinged 
thereon rapidly evaporates. This results in the narrow approximately 1 mm 
gap between the recording medium and the print head being brought to a 
moisture saturated condition. The fixed print head (line head) is oriented 
so that the row of black ink nozzles is upstream of the nozzle rows for 
other colors. With this orientation, even when most printing is in black 
ink only, the other rows of nozzles are also surrounded by moisture 
saturated air, so the ink in color nozzles will not dry. 
Print tests were conducted for evaluating the quality of the resultant 
print images and the frequency of nozzle clogging. To provide a subject of 
comparison, in one set of experiments the nozzles in the lead row were 
filled with black ink (present example) and in another set the nozzles in 
the tail row (i.e., the row nearest to the second exhaust slit 8) were 
filled with black ink. In other words, the print head of the present 
example with the lead row filled with black ink was used in one set of 
experiments, while a head of a comparative example with the tail row 
filled with black was used in the other set of experiments. The full-color 
line head used for the print head 1 for these tests was the same as that 
used in the tests in the second example and therefore had the structure 
shown in FIGS. 12 through 15. Because the frequency of ink ejections can 
be varied from 0 to 15 KHz, the head 1 was capable of full-color printing 
at a speed of 100 pages or more of A4 size recording sheets per minute. In 
these tests, the head 1 was operated to print 20 pages per minute. Sheets 
of normal printing paper for laser beam printers were used as the 
recording sheets 6 in these experiments. 
First, the preheating unit 2 was operated so that full-color printing was 
performed on recording sheets heated to 120 degrees C. Print quality and 
frequency of clogs were evaluated. Then, character printing was performed 
with black ink only, and frequency of clogs were evaluated. The frequency 
of clogs was evaluated using general relative values. 
The results of the experiments are shown in Table 1 below. 
TABLE 1 
______________________________________ 
Frequency of 
Full-color Printing 
clogging in color 
Print Clogging nozzles during 
Clarity Frequency 
black printing 
______________________________________ 
Lead Row Good 1.0 1.5 
Black 
Tail Row Fair 1.0 6.0 
Black 
______________________________________ 
As apparent from the test results for full-color printing, no difference 
could be seen in the frequency of clogging between the two sets of 
experiments. As to the print quality, images printed in black ink bled a 
relatively high amount when printing was performed with the tail row of 
nozzles filled with black ink. Print quality was somewhat inferior. This 
is because dots first printed on the hot and dry sheet showed the least 
bleeding and dots printed next were more likely to show a great deal of 
bleeding. 
When character printing was performed with black ink only, the frequency, 
at which clogging of color nozzles was observed when the head of the 
comparative example was used, is three to four times higher than that when 
the present head was used. The rating system used for clogging in these 
evaluations was roughly based on when clogging could be observed in the 
process of printing ten sheets. For example, a value of one was assigned 
when clogging was observed during printing of the tenth sheet, but a value 
of six was assigned when clogging was observed during printing of the 
first or second sheet. Observed trends were more striking when printing 
was performed with a pigment type ink because pigments type inks are 
difficult to redissolve (redisperse) once their viscosity has increased. 
To prevent clogging, pigment type inks require more care than die type 
inks. 
The above-described experiments show that using the print head with black 
ink ejected from the lead row of nozzles produced the superior results. 
However, it can be supposed that even when the print head with the lead 
row of black ink is used, nozzle clogging will still occur during normal 
printing operations. For example, nozzle clogging will possibly occur 
after long waiting time periods provided during successive printing 
operations. Nozzle clogging will occur also after almost all the nozzles 
are not fired to print an almost entirely white image. 
It is therefore preferable to dummy eject all of the nozzles at the bottom 
of each printed sheet (that is, about 0.5 to 1.0 mm, for example, from the 
bottom edge of the sheet) to improve reliability of the print head 1. The 
line produced on the recording sheet from a single dummy ejection of all 
nozzles will be at most 0.2 mm high, which is within acceptable limits. 
This dummy ejection prevents nozzle clogs produced from overly viscous 
ink. 
Though the above description is directed to a line head, the present 
example can be applied to a scanning print head. The present example can 
be applied to the scanning print heads both of unidirectional printing 
type and of reciprocal printing type. According to the scanning print head 
of unidirectional printing type, ink droplets are ejected only while the 
print head is scanned in one direction. In this type of print head, out of 
four rows of nozzles, the lead row of nozzles should be filled with black 
ink. According to the print head of reciprocal printing type, ink droplets 
are ejected twice while the print head is scanned reciprocally. In this 
type of print head, an additional fifth row of nozzles filled with black 
should be positioned at the opposite side as the first black ink row, so 
that both sides of the print head had nozzles for ejecting black ink. 
Evaluation experiments were performed using the full-color scanning type 
print head 1. The scanning head was positioned at the same place as the 
line head. Print speed was reduced to four pages per minute. Experiments 
were performed for both the unidirectional printing type head and the 
reciprocal printing type head. The unidirectional type used in these 
experiments had four rows of 128 nozzles, with the lead row of nozzles 
filled with black ink. The reciprocal type used in these experiments had 
five rows of 128 nozzles, with the lead and tail rows of nozzles filled 
with black ink. 
When all the nozzles were dummy ejected at a rate of about one dummy 
ejection for every two or three sheets of printing, no nozzle clogging was 
observed in color nozzles even during printing only with black ink. This 
result was observed in both cases that the unidirectional type head was 
used and the reciprocal type head was used. This is because the scanning 
movement of the heads brings the colored ink nozzles into the 
moisture-saturated atmosphere produced from the black ink. 
In the full-color printer, the amount of moisture vapor produced per unit 
time decreases proportionally to the amount the printing speed decreases. 
Additionally, the scanning head cartridge diffuses the ambient air so that 
the first and second exhaust slits are not necessary. This will allow 
reductions in the size and cost of the printer. 
As described above, according to the present example, all nozzles are 
surrounded by a moisture-saturated atmosphere. Therefore, ink dries more 
slowly and clogging of nozzles is reduced. 
When the print head is a line head, after each page of printing is 
completed, all nozzles, including the black ink nozzles, may preferably be 
dummy ejected at least once to refresh the ink in the nozzles. In other 
words, dummy ejections onto the bottom portion of the recording sheet are 
performed periodically to discharge overly viscous ink. This prevents the 
nozzles from clogging. Accordingly, the reliability of the printer is 
increased without decreasing the printing speed. 
Also when the print head is a scanning type head, nozzles of the lead row 
are filled black ink. The scanning motion brings the other colored rows 
into an atmosphere saturated with moisture. Especially good effects can be 
realized in a reciprocally scanning head with five rows of nozzles when 
both edge rows are for ejecting black ink. All nozzles are dummy ejection 
away from the edge of the recording medium after a predetermined number of 
scans are performed. Nozzles can be prevented from clogging by refreshing 
the ink in this way. 
In order to ensure high reliability of the head, the dummy ejections should 
be performed regardless of the printing mode. 
Following are description of an example of a thermal ink jet print head 1 
especially suited for the above-described ink jet printer of the present 
invention. This ink jet print head of a large-scale, high-density thermal 
type can attain a high print speed, for example, a print speed of 100 
pages per minute or more. Because the preheating unit 2 and the vacuum 
suction transport device 3 can dry printed ink images rapidly, the 
combination of this ink jet print head 1 and those components 2 and 3 
enables an ink jet printing of a considerably high printing speed. 
An example of the ink jet print head 1 will be described while referring to 
FIGS. 8 through 16. 
First, a basic structure of the ink jet print head 1 will be described with 
reference to FIGS. 8 through 11. 
As shown in FIGS. 8 and 9, the ink jet print head 1 of the present example 
is constructed from a mounting frame 103 and a monolithic driving section 
101 mounted thereon. The monolithic driving section 101 includes a silicon 
substrate or wafer 109 having a top side and an under side, the under side 
being attached to the mounting frame 103. The silicon substrate 109 is 
formed with a common ink channel 111, at its top side. The common ink 
channel 111 extends in a direction A indicated in FIG. 9 (which will be 
referred to as a "main scanning direction," hereinafter). The ink jet 
print head 1 is oriented in the ink jet printer of FIG. 1 so that the main 
scanning direction A extends perpendicularly to the transport direction B. 
The silicon substrate 109 is further formed with a plurality of connection 
channels 110 extending between a bottom surface of the common ink channel 
111 and the under side of the silicon substrate 109. The connection 
channels 110 are formed in the substrate 109 intermittently along the main 
scanning direction A, as shown in FIG. 9. The mounting frame 103 is formed 
with a single ink supply channel 108 extending in the main scanning 
direction A and connected to the connection channels 110. The mounting 
frame 103 is provided with an ink supply port 106 (not shown) fluidly 
connected to the ink supply channel 108 for supplying ink thereto. 
A partition member 115 is provided on the top side of the silicon substrate 
109 so as to define a plurality of ink chambers 113 which are all 
connected to the common ink channel 111. The ink chambers 113 are aligned 
in the main scanning direction A. 
A thermal resistor 116 and a pair of conductors 117 and 118 connected to 
the thermal resistor 116 are provided in each of the ink chambers 113. The 
thermal resistor 116 and the conductors 117 and 118 are provided on the 
top side of the silicon substrate 109. 
A cover member 114 provided over the partition member 115 is formed with a 
plurality of nozzles 102, each of which is connected to a corresponding 
one of the plurality of ink chambers 113. The ink jet print head 1 is 
located in the ink jet printer of FIG. 1 so that the nozzles 102 confront 
the vacuum suction transport device 3. 
Each ink chamber 113 provided with the thermal resistor 116 and the 
conductors 117 and 118 and the nozzle 102 connected to the ink chamber 113 
construct an ink droplet generator for ejecting an ink droplet from the 
nozzle 102. Accordingly, the print head 1 of this example has a plurality 
of ink droplet generators arranged in the main scanning direction A 
perpendicular to the transport direction B of FIG. 1. 
With the above structure, ink supply pathway for supplying ink toward each 
of the ink droplet generator is constructed by the ink supply channel 108, 
the plural connection holes 110, and the common ink channel 111 which are 
fluidly connected with one another. 
A single drive large scale integrated circuit (LSI circuit) 112 is formed 
on the top side of the silicon substrate 109, through a semiconductor 
process. The LSI circuit 112 is for driving the thermal resistors 116 in 
all the ink chambers 113. The thermal resistors 116 are connected to the 
drive LSI circuit 112 in such a manner that the corresponding individual 
conductors 118 are connected via through-hole connectors 120 to collector 
electrodes (not shown) provided in the drive LSI circuit 112. 
The thermal resistor 116 and the conductors 117 and 118 are a Cr--Si--SiO 
alloy thin-film resistor and nickel thin-film conductors, respectively. 
Details of the Cr--Si--SiO alloy thin-film resistor and nickel thin-film 
conductors are described in a co-pending U.S. patent application Ser. No. 
08/068,348, the disclosure of which is hereby incorporated by reference. 
For example, the thermal resistor 116 and the conductor lines 117 and 118 
are formed to a thickness of 700.ANG. and 1 .mu.m, respectively. The 
resistance of the thin-film resistor 116 is about 1,500.OMEGA.. An 
approximately 1,500 .ANG. thick Ta.sub.2 O.sub.5 anti-etching layer (not 
shown) and an approximately 2 .mu.m thick SiO.sub.2 heat insulation layer 
(not shown) are provided under the thin-film resistor 116 and the 
conductors 117 and 118 on the top side of the silicon substrate 109. 
Because the Cr--Si--SiO alloy resistor 116 and the nickel conductors 117 
and 118 are not covered by any protection layers and therefore directly 
heat ink filling in the ink chamber 113, energy required to eject an ink 
droplet is reduced to about 1 .mu.J/droplet, that is, about 1/30th the 
energy required in conventional thermal resistors with protection layers. 
Co-pending U.S. patent application Ser. No. 068,348 describes tests which 
determined the life of this protection-layerless thermal resistor is one 
billion pulses or more regardless of whether the ink ejected is water 
based or oil based. This reduction in required energy allows positioning 
the thermal resistors adjacent to and on the same silicon substrate 109 as 
the drive LSI circuit 112 for driving the thermal resistors. 
Co-pending U.S. patent application Ser. No. 08/068,348 further describes 
that the protection-layerless thermal resistor used in the print head, 
i.e. formed from the Cr--Si--SiO alloy thin film resistor 116 and nickel 
conductors 117 and 118, efficiently heats ink in the ink chamber when 
applied with an extremely short, i.e., 1 .mu.s or less, pulse of voltage. 
Accordingly, to eject an ink droplet, the drive LSI circuit 112 applies a 
short pulse, i.e., 1 .mu.s or less, of voltage to the Cr--Si--Si alloy 
thermal resistor 116 according to a print signal. The thermal pulse 
generated by the thermal resistor 116 ejects an ink droplet from the 
nozzle 102. The ejected ink droplet impinges on a sheet 6 supported on the 
transport belt 34 by a distance of between 1 to 2 mm, for example, from 
the nozzle 102, thereby forming a dot on the sheet 6. 
The following text is a concrete example of a method for forming the print 
head 1 shown in FIG. 8. First, the common ink channel 111 is photoetched 
into one side of a silicon wafer to a depth of approximately 150 .mu.m 
using either a good inorganic resist (such as SiO.sub.2 or Si.sub.3 
N.sub.4) or an organic resist (such as a polyimide). The connection ink 
holes 110 are then photoetched into the reverse side of the silicon wafer 
to form the side of the silicon substrate 109 which will confront the head 
mounting frame 103. The LSI drive circuit 112, thermal resistors 116, and 
conductors 118 and 117 are then formed on the substrate 109. A 
water-resistant cover material 115, such as a film resist or a polyimide 
with good water resistant properties, is adhered to the surface of the 
silicon wafer with the common ink channel 111 formed therein. The 
water-resistant cover material 115 is formed and positioned so as to cover 
the drive LSI device 112 and acts as a passivation layer against the water 
or oil based ink to be ejected. The cover material 115 is removed from 
areas corresponding to the common ink channel 111 and the ink chambers 113 
by exposure and development. Afterward the remaining cover material is 
hardened to form the partition member 115. An approximately 50 .mu.m thick 
PET film 114 is adhered to the partition 115 using ultraviolet hardening 
adhesive. A row of nozzles 102 are then dry etched into the PET film 114. 
The silicon wafer is then cut to a predetermined size and mounted to the 
head mounting frame 103 to form the completed head 1 shown in FIG. 8. It 
is preferable to remove photoresist and PET film where the silicon wafer 
is to be cut at the time of photoetching. 
As shown in FIG. 10, the above-described print head 1 of FIGS. 8 and 9 is 
connected to a head drive circuit 300 for driving the print head 1. The 
head drive circuit 300 includes a head drive power source 143, a signal 
generation circuit 144 for generating a binary print data signal and a 
clock signal, and a large scale integrated circuit (LSI) power source 145. 
The drive LSI circuit 112 in the print head 1 includes a shift register 
141, a driver circuit 142 and a gate circuit 147 connecting the shift 
register 141 to the driver circuit 142. Wiring 119 for connecting the head 
drive circuit 300 to the print head 1 for serially driving the thermal 
resistors 116 in all the ink chambers 113 is constructed from only five 
lines: a data line 119a, a clock line 119b, a driver circuit power source 
line 119c, a LSI device power source line 119d, and a ground line 119e. 
The data line 119a is provided for serially sending the binary print data 
from the signal generation circuit 144 to the shift register 141. The 
clock line 119b is provided for transmitting the clock signal from the 
signal generation circuit 144 to the shift register 141. The driver 
circuit power source line 119c is provided for connecting the head drive 
power source 143 to the driver 142. The LSI device power source line 119d 
is provided for connecting the LSI power source 145 to the shift register 
141. It is noted that the LSI drive circuit 112 has five pedestals or 
terminals 146a through 146e on one end of the silicon substrate 109, at 
which the five wires 119a through 119e are connected to the LSI drive 
circuit 112. 
The ink jet print head 1 having the above-described structure uses a serial 
consecutive drive. Therefore the drive LSI circuit 112 requires no latch 
circuit as do drive LSI circuits of conventional printers which use block 
drive. In a conventional thermal ink jet print head, a latch circuit is 
provided between the shift resistor and the driver. A timing generation 
circuit must also be added to the head drive circuit for the latch 
circuit. Additionally, two or three lines of wiring must be added to 
transmit signals to the head. Contrarily, according to this example, the 
print head 1 is driven by serially consecutive drive by the head drive 
circuit 300 as shown in FIG. 10. The print head 1 requires a smaller scale 
circuit, fewer lines of wiring, and can be produced at lower costs when 
compared to conventional printer head. In concrete terms, because only 
five signal wires for drive control are required per nozzle row, mounting 
costs of the head are reduced. 
The following text will describe, in greater detail, the serially 
consecutive drive method employed in the present invention, while 
referring to FIGS. 10 and 11 (a). It is noted that during this serial 
consecutive drive method, as shown in FIG. 1, the print sheet 6 is moved 
relative to the print head 1 in the transport direction (i.e., auxiliary 
scanning direction) B approximately perpendicular to the main scanning 
direction A, that is, perpendicular to the row of nozzles 102 in the head 
1. In this example, the head 1 is stationary and the print sheet 6 is 
transported continually at a set speed. 
The signal generation circuit 144 is controlled, by a CPU (not shown) 
provided in the head drive circuit 300, to serially and consecutively 
generate a series of binary print data (A.sub.i,j).sub.j=1 to 2n for 
producing each line (i-th line where i=1, 2, . . . ) extending in the main 
scanning direction A on the sheet 6. The series of print data 
(A.sub.i,j).sub.j=1 to 2n include 2n print data A.sub.i,j where j=1, 2, . 
. . , 2n. Each print data A.sub.i,j includes print information on each dot 
j of 2n dots to be printed on the corresponding i-th line, where 2n is the 
total number of the nozzles 102 formed in one row of the print head 1. The 
series of binary data (A.sub.i,j).sub.j=1 to 2n are serially and 
consecutively transmitted to the shift register 141 via the data line 
119a. 
As shown in FIG. 10, the shift register 141 has 2n register elements 
aligned in the main scanning direction A. The gate circuit 147 has 2n 
gates aligned in the main scanning direction, and the driver 142 has 2n 
portions aligned in the main scanning direction. The 2n portions of the 
driver 142 serve to respectively drive the 2n thermal resistors 116 
aligned in the main scanning direction A. Each register element (j-th 
register element) is connected via a corresponding gate (j-th gate) in the 
gate circuit 147 to a corresponding portion (j-th portion) of the driver 
142. The j-th portion of the driver 142 is for driving a corresponding 
j-th thermal resistor 116 to print a j-th dot on the corresponding i-th 
line on the sheet 6. 
The shift register 141 shifts the received print data A.sub.i,j from one 
register element to a next register element in the main scanning direction 
of FIG. 10, synchronously with the clock signals CL supplied to the shift 
register 141 from the signal generation circuit 144. Accordingly, at the 
time when a j-th clock signal CL.sub.j is inputted to the shift register 
141, a j-th print data A.sub.i,j properly reaches a corresponding j-th 
register element. 
The shift register 141 is constructed to output the print data to the gate 
circuit 147, synchronously with the received clock signals CL. The shift 
register 141 can therefore send out the print data, as located in the 
respective register elements at the time when the shift register 141 
receives the clock signals CL, toward the corresponding gates in the gate 
circuit 147. 
The gate circuit 147 is constructed so that each j-th gate is opened only 
at the time when the corresponding j-th clock signal CL.sub.j is supplied 
via the shift register 141 to the gate circuit 147. Accordingly, the gate 
circuit 147 can supply each j-th print data A.sub.i,j to the drive circuit 
142 only at the time when the j-th print data A.sub.i,j is located in the 
corresponding j-th register element in the shift register 141. Thus, the 
gate circuit 147 can send out each j-th print data A.sub.i,j properly to 
the corresponding j-th portion of the driver 142. The j-th portion of the 
driver 142 therefore properly drives the j-th thermal resistor 116 to 
print the j-th dot, in accordance with the j-th print data A.sub.i,j. 
Because the shifting operation by the shift register 141 successively 
supplies the series of print data A.sub.i,j to the corresponding j-th 
shifting elements, the gate circuit 147 can successively supply the series 
of print data A.sub.i,j to the corresponding j-th portions of the driver 
142 so as to successively drive the j-th thermal heaters 116. 
Thus, the shift register 141 and the gate circuit 147 cooperate to serially 
output the series of print data (A.sub.i,j).sub.j=1 to 2n to the 
corresponding j-th portions of the driver 142, in synchronism with the 
clock signals. When the print data A.sub.i,j is an ejection signal (i.e., 
is 1), the corresponding j-th portion of the driver 142 applies a voltage 
at a predetermined pulse width to the corresponding j-th thermal resistor 
116, thereby causing the thermal resistor 116 to heat. If print data 
A.sub.i,j is not an ejection signal (i.e., is 0), the voltage is not 
applied. When all dots j of one line i have been printed (i.e., A.sub.i,j 
for j=1 to 2n have all been processed), print drive continues for the next 
line i+1 (i.e., A.sub.i,j where j=1 to 2n). In more concrete terms, the 
signal generation circuit 144 serially outputs the next series of print 
data (A.sub.i+1,j).sub.j=1 to 2n' and the shift register 141 and the gate 
circuit 147 cooperate to serially output the print data (A.sub.i,j 
).sub.j=1 to 2n to the corresponding thermal elements 116. When all the 
signals A.sub.i,j (j=1 to 2n) for one line i are 1 to drive all the 
nozzles 102 on the print head 1 to eject ink droplets 150, the pattern of 
ink droplets produced on the sheet 6 appears as shown in FIG. 11(a). 
As described above, printing while feeding the print sheet at a continuous 
speed becomes possible with the print head of the present example. 
Continuous-speed feed of the print sheet is better suited for high-speed 
printing and is also technically easier than is step feed. 
FIGS. 12 through 15 show an overall structure of a full-color line head 1 
which has the above-described basic structure and which is especially 
suited for the ink jet printer of the present invention. In order to 
produce this line head 1, as shown in FIG. 15, the monolithic drive 
portion 101 is formed with four rows of common ink channels 111-1, 111-2, 
111-3 and 111-4 for black ink, yellow ink, cyan ink and magenta ink, 
respectively. Four sets of connection holes 110-1, 110-2, 110-3 and 110-4 
are formed to fluidly connect with the common ink channels 111-1, 111-2, 
111-3 and 111-4, respectively. Each set of the connection holes 110-1, 
110-2, 110-3 and 110-4 includes a plurality of connection holes aligned 
intermittently in the main scanning direction A, in the same manner as the 
connection holes 110 of FIGS. 8 and 9. 
Four rows of ink droplet generators are provided in connection with the 
common ink channels 111-1, 111-2, 111-3 and 111-4, respectively. Each row 
of the four rows of ink droplet generators includes a plurality of ink 
droplet generators aligned in the main scanning direction A. Similarly to 
the ink droplet generator shown in FIG. 8, each ink droplet generator 
includes an ink chamber 113, a thermal resistor 116 and conductors 117 and 
118 connected to the thermal resistor 116, and a nozzle 102. Accordingly, 
four nozzle rows 102-1, 102-2, 102-3 and 102-4 are arranged in the 
transport direction B on a surface of the monolithic drive portion 101 so 
as to confront the vacuum suction transport device 3. Four sets of drive 
LSI circuits 112-1, 112-2, 112-3 and 112-4 are provided adjacent to the 
four rows of ink droplet generators. Each of the drive LSI circuits 112-1, 
112-2, 112-3 and 112-4 is constructed as shown in FIG. 10 for performing 
the serial conductive drive. 
As apparent from the above, the structure of the monolithic driving section 
101 shown in FIG. 15 is substantially constructed from four monolithic 
driving sections 101 described with reference to FIGS. 8 and 9 that are 
arranged in the auxiliary scanning direction B. Accordingly, an enlarged 
view encircled in C. in FIG. 15 is equivalent to the view of FIG. 8. 
The above-described monolithic driving section 101 and another monolithic 
driving section 101' having the same structure of the monolithic driving 
section 101 are mounted on a single mount frame 103 so that each row of 
the four rows of nozzles 102-1, 102-2, 102-3 and 102-4 formed on the 
driving section 101 and each row of the four rows of nozzles 102'-1, 
102'-2, 102'-3 and 102'-4 formed on the driving section 101' are arranged 
in line, as shown in FIG. 12. 
As shown in FIG. 15, the mounting frame 103 is formed with a set of four 
ink supply channels 108-1, 108-2, 108-3 and 108-4 arranged in the 
auxiliary scanning direction B communicated with respective connection 
holes of the sets of connection holes 110-1, 110-2, 110-3 and 110-4 of the 
monolithic driving section 101. Therefore, a sufficient amount of ink from 
the ink supply channels 108-1 through 108-4 can be supplied to respective 
common ink channels 111-1 through 111-4 via respective connection holes 
110-1 through 110-4. The mounting frame 103 is further formed with another 
set of four ink supply channels 108'-1, 108'-2, 108'-3 and 108'-4 arranged 
in the auxiliary scanning direction B communicated with the connection 
holes 110'-1, 110'-2, 110'-3 and 110'-4 of the monolithic driving section 
101'. As shown in FIGS. 13 and 14, the mounting frame 103 is provided, at 
its reverse side, with one set of ink supply ports 106-1, 106-2, 106-3 and 
106-4 for respectively supplying ink to the set of four ink supply 
channels 108-1, 108-2, 108-3 and 108-4. The mounting frame 103 is provided 
with another set of ink supply ports 106'-1, 106'-2, 106'-3 and 106'-4 for 
respectively supplying ink to the set of four ink supply channels 108'-1, 
108'-2, 108'-3 and 108'-4. Therefore, the four colors of ink supplied from 
the ink supply ports 106 and 106' will not mix and a sufficient and 
necessary amount of ink can be supplied to each of the common ink channels 
111-1 and 111'-1 through 111-4 and 111'-4. 
When the line head as shown in FIGS. 12-15 is employed as the print head 1 
in the printer of the present invention, the print head 1 is provided as 
shown in FIG. 1 so that the nozzle rows 102-1, 102'-1, 102-2, 102'-2, 
102-3, 102'-3, 102-4, and 102'-4 confront the vacuum suction transport 
device 3. The print head 1 is oriented so that each of the rows extends 
perpendicularly to the transport direction B. 
A concrete example of the line head having the above-described structure 
will be described below. 
The two monolithic driving sections 101 and 101' are mounted centered on 
the mounting frame 103 made from Fe-42Ni alloy using die bonding 
techniques. The monolithic driving sections 101 and 101' are connected at 
a connection portion CP. The two monolithic driving sections 101 and 101' 
are formed from equal approximately 107 mm by 8 mm sections of silicon 
wafers 109 and 109'. The two monolithic driving sections 101 and 101' 
therefore have a total 214 mm length L when connected. Two monolithic 
sections 101 and 101' are necessary because a maximum length of only 140 
mm for a head can be produced from a single six inch wafer. The head 
mounting frame 103 is made from Fe-42Ni alloy because the expansion 
coefficient of Fe-42Ni alloy is substantially the same as that of silicon. 
A layer of nickel is provided to the entire surface of the print head by 
plating to give the print head good anti-corrosion properties. 
As described above, four rows of nozzles 102 are provided in the line head: 
black nozzle row 102-1 and 102'-1, yellow nozzle row 102-2 and 102'-2, 
cyan nozzle row 102-3 and 102'-3, and magenta nozzle row 102-4 and 102'-4. 
Each row of nozzles on each monolithic driving section 101 (or 101') 
contains 1,512 nozzles. Because the two monolithic sections 101 and 101' 
are connected at the connection portion CP, the distance between the 
connection portion CP and the end nozzle nearest the connection portion CP 
limits the pitch and dot density of the line head 1. The line head of this 
example has the nozzles arranged with a pitch of (1070) in the main 
scanning direction and therefore attains a dot density of 360 dots per 
inch (dpi). The line head 1 therefore contains a total of 3,024 nozzles 
for each color nozzle row which extends in a length of 210 mm. 
It is noted that the monolithic sections 101 and 101' can be connected at a 
side edge rather than the tip edge CP to eliminate this limitation to the 
pitch of the nozzles. In this case the monolithic sections 101 and 101' 
would be shifted relative to each other in the widthwise direction by the 
width of the substrate sections 101 and 101' and then would be positioned 
so as to overlapped on an edge side. 
As described already, according to the present example, five wires 119 
(shown in FIG. 8) are provided to transmit signals and power to the 1,512 
ink droplet generators in each row of each of the monolithic driving 
sections 101 and 101'. Therefore, a total of twenty wires 119 are provided 
for all four rows of ink droplet generators of each driving section 101 or 
101'. In this concrete example, the mounting frame 103 is provided, at its 
back side, with a pair of connectors 107 and 107' for supplying electric 
signals toward the drive LSI circuits 112-1, 112-2, 112-3 and 112-4 on the 
monolithic section 101 and 112'-1, 112'-2, 112'-3 and 112'-4 on the 
monolithic section 101, respectively. In the monolithic section 101, the 
drive LSI circuits 112-1, 112-2, 112-3 and 112-4 are formed with the total 
of twenty pedestals or terminals 146 on the silicon substrate 109 at its 
one end opposed to the connection portion CP. Similarly, in the monolithic 
section 101', the drive LSI circuits 112'-1, 112'2-2, 112'-3 and 112'-4 
are formed with the total of twenty pedestals or terminals 146' on the 
silicon substrate 109' at its one end opposed to the connection portion 
CP. The total of twenty wires 119 (or 119') are connected at one end to 
the twenty pedestals 146 (or 146') on the substrate 109 (or 109'), and are 
connected at other end to the connectors 107 (or 107). The twenty wires 
119 (or 119') therefore serve to send the external control signal from the 
head driving circuit 300 received at the connectors 107 (or 107') to the 
twenty pedestals 146 (or 146') of the drive LSI circuits 101 (or 101'). 
The twenty wires 119 are held in a tape carrier (not shown), and the 
twenty wires 119' are held in another tape carrier (not shown). The two 
tape carriers 119 and 119' thus provided at opposite ends of the line head 
1 are covered with press clasps 104 and 104' to be fixed to the opposite 
ends. 
The 8 mm width of each of the monolithic sections 101 and 101' allows 
connecting the twenty wires 119 and 119' to the twenty pedestals provided 
at the end of the sections 101 and 101' at a density of about 3 lines/mm. 
Connecting lines at this density is easily performed with conventional 
mounting techniques. In comparison, using conventional techniques would 
require about 6,000 wire bonding processes to connect one half of the 
head. Additionally, nozzle rows would have to be bridged with connection 
lines which is technically impossible. 
In the line head of this example, each of the drive LSI circuits 112-1, 
112-2, 112-3 and 112-4 and 112'-1, 112'-2, 112'-3 and 112'-4 of the 
monolithic driving sections 101 and 101' is constructed as shown in FIG. 
10 for performing the serial consecutive drive. All ink droplet generators 
in the line head 1 are caused to eject ink droplets to print 3,024 
dots/line in 500 .mu.s (2 kHz), for example. Therefore an entire A4sheet 
can be printed in about two seconds or about 30 A4 size sheets per minute. 
The ejection frequency can be increased to a maximum of 5 KHz, thus 
allowing a print speed of 60 ppm (page per minute). Using the pump heaters 
described in co-pending U.S. patent application Ser. No. 068,348 is also 
an effective way to increase print speed. Details of the pump heaters is 
described in the application Ser. No. 068,348, the disclosure of which is 
hereby incorporated by reference. 
If the width of the pulse of voltage applied to each thermal resistor is 1 
.mu.s, only six ink droplet generators or less are at some stage of having 
the 1 .mu.s pulse applied to the thermal resistor 116 thereof at any one 
time (3,024 dots/500 .mu.s=6 dots). When driving the head in this way, 0.5 
W/dot is required for energizing each thermal resistor to eject each ink 
droplet. Therefore, the maximum energy that will need to be applied at any 
one time is less than three watts/line (i.e., 12 watts or less/line for 
full color print). 
It is noted that when printing while driving the line head serially and 
consecutively, and feeding the sheet at a continuous speed as described 
above, each printed line on the sheet slants only one dot width, that is, 
a 60 to 70 .mu.m shift per line at 360 dpi. The shift is only 30 to 40 
.mu.m with the print head 1 described in this concrete example because the 
line head 1 is constructed by two driving sections 101 and 101'. Slanting 
of printed rows formed during serial consecutive ejection of ink can be 
corrected by slanting the head itself the same amount as the slant of the 
printed rows. This can be done by producing the head substrate with a 
slanted arrangement. Although ink droplets will deform about 1 .mu.m when 
impinged on the print sheet, this is insignificant compared to the 60 to 
70 .mu.m diameter of printed dots. 
A line head as shown in FIGS. 12 through 15 was manufactured as per the 
above description, filled with ink and used to print an image by drive 
signals transmitted via the connectors 107 and 107'. The conditions of the 
drive are shown in the Table 2. 
TABLE 2 
______________________________________ 
Aspect Drive Condition 
______________________________________ 
Applied pulse width 1 .mu.s 
Applied power 0.5 W/dot 
Ejection freguency 2 KHz 
Dot scanning speed 3 MHz .times. 2/color 
Maximum number of dots 
3 dots .times. 2 .times. 4/color 
driven simultaneously 
Maximum power consumption 
12 W or less 
Print speed 2 sec/A4 
(for full color) 
Sheet transport speed 
150 mm/sec 
(at continuous speed) 
______________________________________ 
The drive conditions shown in Table 2 are for when the monolithic driving 
sections 101 and 101' of the print head are driven separately. In this 
case, the serial continuous drive starts at the far left (as seen in FIG. 
12) ink droplet generators of both the monolithic sections 101 and 101' 
and scans across the monolithic sections 101 and 101' separately at a 
scanning speed of 3 MHz. Alternately, the two driving sections 101 and 
101' could be driven as a single driving section that is serially 
continuously driven at a scanning speed of 6 MHz from the far left hand 
ink droplet generator of monolithic section 101'. In this second method 
all drive conditions except the scanning speed are the same as shown in 
Table 2. The slant of printed rows will be an insignificant 60 to 70 
.mu.m. 
Printing while feeding the print sheet at a continuous speed is possible 
with the present invention. Continuous-speed feed of the print sheet is 
better suited for high-speed printing and is also technically easier than 
is step feed. Even if the cycle for ejecting ink is only 2 kHz, an entire 
A4 size sheet can be printed in full color in about two seconds. 
Continuous-speed feed of the print sheet allows printing of high quality 
images inexpensively. A full color image printed at high speeds using this 
print head has an appearance equivalent to a full color photograph. A 
print head according to the present invention can also be produced for 
making B4 size full color images, with using a 6 inch silicon wafer. 
Serially driving the head eliminates problems that can arise when the 3,024 
thermal resistors per line are simultaneously or block driven, problems 
such as the capacity of thin films, especially of the common wiring 
conductors, being easily exceeded or the maximum power requirement of the 
head being excessively large. For example, the maximum power requirement 
could be reduced to 1/2 or 1/3. The drive circuit can also be simplified 
to thereby reduce production costs to about 2/3. The number of wiring 
operations can be decreased from the 88 to 1,513 wirings required in 
conventional print heads to only five. 
Copending U.S. patent application Ser. No. 068,348 describes that the 
protection-layerless thermal resistor formed from the Cr--Si--SiO alloy 
thin film resistor 116 and nickel conductors 117 and 118 efficiently heats 
ink in the ink chamber when applied with an extremely short, i.e., 1 .mu.s 
or less, pulse of voltage. The energy required to eject one droplet is 
1/30th to 1/60compared to conventional thermal resistors that have 
protection layers. Even when not considering the heat removed with ejected 
ink, the temperature of the head rises 1.degree. C. or less per every A4 
size sheet printed solid with four colors. Because so little energy is 
needed for printing with the print head according to the present 
invention, the amount of heat energy removed with ejected ink is 
relatively large. Therefore, the temperature of the print head rises 
10.degree. C. or less even when 100 sheets are printed consecutively in 
full color. By adding heat fins to the heat mounting frame 103, cooling or 
other temperature control becomes unnecessary even during continuous 
high-speed operation. Conventionally it has proven difficult to perform 
continuous high-speed print because most of the 30 to 60 times more energy 
required for driving conventional heads goes mainly to heating the head. 
In the above-described full color line head 1, two monolithic driving 
sections 101 and 101' each having four rows of ink droplet generators are 
mounted on the mounting frame 103. However, such a full color line head 
can be produced by mounting, on the frame 103, two sets of four monolithic 
driving sections each having a single row of ink droplet generators and 
therefore having the structure shown in FIGS. 8 and 9. The two sets of 
monolithic driving sections are arranged on the frame 103 in the main 
scanning direction where each set having the four driving sections 
arranged in the auxiliary scanning direction. As a result, four rows of 
nozzles are obtained as shown in FIG. 12. 
In a test, a line head 1 for full color print of A4 size sheets was 
produced from eight 2 mm wide monolithic driving sections for single color 
print, i.e., eight monolithic driving sections with only a single row of 
orifices. The precision of the external dimension when cutting the 
substrates 109 for each monolithic driving section from a silicon wafer 
was kept to within .+-.3 .mu.m through full dicing operation. Thus 
obtained eight single color monolithic driving sections were arranged on 
the head mounting frame 3 and connected using die bonding techniques. It 
is noted that adhesive got in between the monolithic chips and error was 
generated in the distance between lines to produce a maximum variance of 
20 .mu.m between extreme positions in the line. By controlling the timing 
of ejections, the variance in position was sufficiently corrected to print 
an image with appearance substantially the same as that obtained from the 
four color line head 1 of the previously-described concrete example. The 
amount of correction depends on the amount of deviation caused during 
assembly and the timing of the line drive should be shifted by 7 .mu.s for 
every variance. Adjustments for correction were performed using a test 
image for such adjustments. 
The print head structure shown in FIGS. 8 and 9 may also be applied to a 
scanning type head scanningly movable in the main scanning direction 
across the width of a sheet. The scanning type head has the same structure 
as that of the line head except that it is formed so that its length is 
less than the width of a sheet to be printed on (an A4 size sheet, for 
example) and that it is mounted to a carriage movable in the main scanning 
direction. The above-described A4 length line head could be mounted to the 
carriage so as to be scanningly movable in the main scanning direction 
when an A3 size or larger sheet is to be printed on. Slanting of printed 
rows formed during serial consecutive ejection of ink can be corrected by 
slanting the main scanning direction of the print head. 
As described above, the line head of the present example can achieve an 
extremely rapid printing speed, i.e., a four color image on a sheet 
transported at a speed of 150 mm/sec with ejection frequency of 2 KHz. 
Accordingly, the line head of the present example may preferably be 
combined with the preheating unit 2 and the vacuum suction transport 
device 3 shown in FIG. 1. Thus combining these components to the line head 
can allow the printing liquid, or ink, impinged on the sheet to have 
sufficient time to dry during sheet transport. The printer provided with 
the combination of the preheating unit 2, the vacuum suction transport 
device 3, and the line head 1 of FIGS. 12-15 can obtain an image with good 
appearance while maintaining the extremely rapid printing speed and 
preventing blurring of images. 
According to the above-described print head, the monolithic driving section 
101 is provided with a large number of nozzles 102 with high density. The 
drive LSI circuit 112 serially and consecutively drives the plurality of 
ink droplet generators so as to eject ink droplets from corresponding 
nozzles 102, as shown in FIG. 11(a). Each of the plurality of ink droplet 
generators ejects an ink droplet so that the ejected ink droplet may fly 
in a direction toward the sheet 6 at an ejection speed of V (about 10 m/s, 
for example). Thus ejected ink droplet has a spherical or slightly 
elongated shape in the flying direction. The ink droplet has a length or 
dimension L (40 to 50 .mu.m, for example) in the flying direction. If the 
distance D between corresponding points, i.e., lead point and lead point 
or center and center, of ink droplets ejected from adjacent nozzles is 
substantially equal to or lower than the length L of the ink droplet, 
there is high possibility that the ink droplets may couple while flying 
toward the sheet 6, due to slight inaccuracies in their ejection or flying 
direction. Because these inaccuracies in the ejection direction become 
large after consecutive printing over a long period of time, the 
possibility of the ink-flight coupling increases after the consecutive 
long period printing operation. This ink-flight coupling may result in a 
decrease in quality of printed images. 
In order to prevent the ink droplets ejected from adjacent nozzles from 
coupling in flight, the shift register 141 may preferably be controlled to 
output the print data A.sub.i,j serially and consecutively to the drive 
circuit 142, with a phase difference T defined by an equation T=D/V having 
at least higher than L/V. That is, the phase difference T preferably 
satisfies an inequality T&gt;L/V. The drive circuit 142 serially and 
consecutively drives the plurality of ink droplet generators with the 
phase difference T. 
For example, when ink droplets have a spherical shape with a diameter L of 
about 40 to 50 .mu.m and are ejected at V of about 10 m/s, the phase 
difference should be set at least higher than 4 to 5 .mu.s to attain the 
distance D between corresponding points of ink droplets of greater than 40 
to 50 .mu.m. It is noted that ink droplets are usually slightly elongated 
in the flying direction to have a length L of about 100 .mu.m, for 
example. Accordingly, the phase difference is preferably set to 10 .mu.s 
or more which can obtain the distance D of 100 .mu.m or more, to thereby 
largely reduce the possibility of the ink-flight coupling for the ink 
droplets. To completely eliminate the risk of ink-flight coupling even 
when ink droplets are greatly elongated in flight, the phase difference 
may preferably be increased to 30 to 50 .mu.s. 
In the concrete example of the ink jet print head 1 as shown in FIG. 12, 
ejected ink droplets have a spherical shape with a diameter of between 40 
and 50 .mu.m on average. If the distance between corresponding points, 
i.e., lead point and lead point or center and center, of ink droplets 
ejected from adjacent ink droplet generators is equal to or higher than 
about 40 to 50 .mu.m, the possibility of the ink droplet coupling in 
flight increases. However, if the distance is lower than about 40 to 50 
.mu.m, the possibility decreases. It is noted that the ink droplets are 
usually slightly elongated in the flying direction to have length L of 
about between 100 .mu.m to 130 .mu.m. Accordingly, if the distance D is 
between 100 and 130 .mu.m or more, the possibility of the ink droplets 
coupling in flight is reduced to near zero. In this concrete example, an 
ink droplet ejected from the head travels at a flight speed of about 13 
m/sec. Thus, corresponding points of ink droplets ejected from adjacent 
ink droplet generators fired at a time phase difference of between 8 and 
10 .mu.s will be separated by about 100 to 130 .mu.m. Accordingly, firings 
of adjacent ink droplet generators should preferably be adjusted between 8 
and 10 .mu.s or more. To completely eliminate the risk of ink-flight 
coupling, even when ink droplets are greatly elongated in flight, the time 
phase difference between firings of adjacent ink droplet generators can be 
increased to 30 to 50 .mu.s. Consequently, quality of printed images will 
not drop even after consecutive printing over a long period of time. On 
the other hand, when the time phase difference between subsequent firings 
is less than 8 to 10 microseconds, quality of printed images can decrease 
due to in-flight coupling of droplets. 
Accordingly, in the printer head 1 of this concrete example, the ink 
droplet generators are preferably driven serially with a phase difference 
of 10 .mu.s or more. 
Alternatively, if it is necessary or desirable to serially drive the ink 
droplet generators to be driven with a phase difference of 10 .mu.s or 
less, print data A.sub.i,j for driving the ink droplet generators are 
preferably restructured so as to cause adjacent ink droplet generators to 
be fired with a phase difference of 10 .mu.s or more. 
Below will be given a concrete example of a method for reconstructing the 
print data A.sub.i,j so as to prevent the ink-flight coupling of ink 
droplets at high print speed (that is, at a small phase difference of 10 
.mu.s or more, for example). 
In this example, the alignment of print data (A.sub.i,j) transmitted to the 
head, and also the clock signal for transmitting print data according 
thereto, are transformed or changed to prevent decreases in quality of 
printed images. Driving the head with the drive method according to this 
example will cause ink droplets to be ejected in the pattern shown in FIG. 
11(b). 
This drive method will be described in greater detail, below. 
Assume that the signal generation circuit 144 of FIG. 10 is controlled, by 
the CPU provided in the head driving circuit 300, to supply the clock 
signals CL at frequency of f Hz! to the shift register 141. (It is noted 
that the data generator 144 is also controlled to input the series of 
print data A.sub.i,j to the shift register 141 at the normal speed, i.e., 
frequency f.) In this case, the shift register 141 and the gate circuit 
147 cooperate to serially or scanningly supply the series of print data 
A.sub.i,j to the corresponding ink droplet generators every 1/f seconds!. 
Accordingly, the 2n ink droplet generators can be serially or scanningly 
fired every 1/f seconds!. In other words, the time phase difference 
between firings of adjacent ink droplet generators is 1/f seconds!. If 
A.sub.i,j for each line i are all 1, the ink droplets are ejected in the 
pattern as shown in FIG. 11(a). 
When the time phase difference 1/f between subsequent firings at adjacent 
ink droplet generators is small, for example, less than 8 to 10 .mu.s, it 
becomes necessary to prevent ink-flight coupling of ink droplets. In this 
case, according to the present invention, the print data generator 144 is 
controlled by the CPU to change the frequency of the clock signals CL to 
be set at 2f Hz!. The print data generator 144 is further controlled by 
the CPU to transform one series of print data (A.sub.i,j) where j=1 to 2n 
for each line i into two series of print data (A.sub.i,2j-1, 0).sub.j=1 to 
n and (0, A.sub.i,2j).sub.j=1 to n. The set of print data (A.sub.i, 2j-1, 
0).sub.j=1 to n includes 2n print data A.sub.i,1, 0, A.sub.i,3, 0, 
A.sub.i,5, 0, . . . A.sub.i,2n-1, 0, and the other set of print data (0, 
A.sub.i,2j).sub.j=1 to n includes 2n print data 0, A.sub.i,2, 0, A.sub.i, 
4, 0, A.sub.i,6, . . . 0, and A.sub.i,2n where each print data A.sub.i,k 
(k=1 to 2n) is 0 (no ejection) or 1 (ejection). The print data generator 
144 is controlled by the CPU to transfer the set of print data (0, 
A.sub.i,2j).sub.j=1 to n immediately after completion of the transfer of 
the set of print data (A.sub.i,2j-1, 0).sub.j=1 to n. 
The above-described print data transformation is represented by the 
following formula: 
EQU (A.sub.i,j).sub.j=1 to 2n =(A.sub.i,2j-1, 0).sub.j=1 to n +(0, 
A.sub.i,2j).sub.j=1 to n, 
where 
EQU (A.sub.i,2j-1, 0).sub.j=1 to n =A.sub.i,1, 0, A.sub.i,3, 0, A.sub.i,5, 0, . 
. . A.sub.i,2n-1, 0, 
EQU (0, A.sub.i,2j).sub.j=1 to n =0, A.sub.i,2, 0, A.sub.i,4, 0, A.sub.i,6, . . 
. 0, and A.sub.i,2n 
To summarize, for every line i, 2n print data are divided between n number 
of odd and n number of even rows of data. Non-ejection data is inserted 
between each type of data to produce 2n number each of two print data 
rows. The shift register 141 and the gate circuit 147 are controlled to 
serially input the two series of print data (A.sub.i,2j-1, 0).sub.j=1 to n 
and (0, A.sub.i,2j).sub.j=1 to n to the corresponding portions of the 
driver 142 at twice normal speed, i.e., frequency 2f, so that the number 
of the lines to be formed in the auxiliary scanning direction doubles. (It 
is noted that the data generator 144 is also controlled to input the two 
series of print data (A.sub.i,2 j-1, 0).sub.j=1 to n and (0, 
A.sub.i,2j).sub.j=1 to n to the shift register 141 at twice normal speed, 
i.e., frequency 2f.) Print data can easily be changed without increasing 
costs by using a portion of a signal process circuit, that is, the CPU 
provided in the head drive circuit 300. Doubling the clock frequency will 
not tax the capacity of the shift register 141 mounted to the head. Time 
to scan one line becomes n/f seconds! and the ejection phase shift 
between adjacent ink droplets becomes: 
EQU 1/2f+2n/2f.apprxeq.n/f. 
For example, with a 64 nozzle/line serial scan type head provided with the 
structure shown in FIG. 8 operating under 640 KHz clock frequency to 
produce the droplet ejection pattern shown in FIG. 11(a), the phase shift 
between adjacent ink droplets becomes 1.56 microseconds 
(1/64.times.10.sup.4), thereby increasing the possibility of adjacent 
droplets coupling in flight. In contrast to this, the method resulting in 
the ink droplet pattern shown in FIG. 11(b) will result in a time phase 
difference between adjacent ink droplets of 50 .mu.s (1/2 
.times.10.sup.4). The distance between droplets will therefore be 650 
.mu.m (13 m/sec.times.50 .mu.s=650 .mu.m), so that decreases in quality of 
the printed image can be completely prevented. The benefits of this method 
are even more striking with a large scale line head with 100 to 1,000 
nozzles/line. 
Rather than the drive method where every other droplet generator is driven, 
which will create the ink droplet pattern shown in FIG. 11(b), every third 
droplet generator can be driven. Other ejection methods can also be used 
as long as the time phase difference between ejections of adjacent droplet 
generators is 10 .mu.s or more. Restructuring the drive signal to produce 
a phase shift of 20 microseconds or more is even more desirable. 
A line head with 128 nozzles in a single row was built including ink 
droplet generators formed as shown in FIG. 8. Every other line of a print 
sheet transported in front of the head was printed black by serially and 
consecutively applying 1 .mu.s pulses of voltage (1 W) to the thermal 
resistors of the ink droplet generators in the head. The quality of images 
printed at various ejection frequencies (in the range of 0.5 KHz to 5 KHz) 
and at various time phase differences between ejections of adjacent 
droplet generators (in the range of about 16 is to about 1.6 .mu.s). A 
drop in the quality of printed images was only occasionally observed when 
the phase shift was 7 to 8 microseconds or more and only observed after 
printing had been performed over a long period of time. On the other hand, 
quality of printed images quickly dropped when the time phase difference 
was shortened, even after cleaning the nozzle surface of the head. 
On the other hand, when the print head was driven using the drive method 
described in the concrete example of the above-described method with an 
ejection frequency of 5 KHz, good quality of printed images was maintained 
even after consecutive printing was performed for a long period of time. 
The same good printing results were observed when every third droplet 
generator was driven or when printing was performed with a large scale 
line head. 
It can therefore be understood that driving a thermal ink jet printer by 
the serial consecutive drive described above can completely prevent the 
type of drop in quality of printed images that can be generated when ink 
is ejected from nozzles aligned in a high density. Also this can be 
achieved without increasing production costs. This driving method can be 
applied to a wide variety of print heads such as a serial scan type head 
with a total of 64 droplet generators or a line head with a total of 3,024 
droplet generators (1,512.times.2). 
The above-described drive method applied to a print head with the structure 
shown in FIG. 8, that is, a top-shooting type ink jet print head where ink 
droplets are ejected in a direction perpendicular to the thermal resistor 
surface. However, the present invention can be used with a type of head 
where the ink droplets are ejected in a direction parallel to the surface 
of the thermal resistor and obtain the same effects. 
The pitch and dot density of the line head are determined by the distance 
between the connection portion CP and the end nozzles in the monolithic 
sections 101 and 101' formed nearest the connection portion CP. Therefore, 
producing the connection portion CP becomes increasingly difficult the 
greater the dot density. In order to facilitate producing the connection 
portion CP of the line head, the following modification of a line head can 
be provided. 
As shown in FIG. 16, a line head of this modification is formed similarly 
to the above-described example, except that in the line head of the 
present modification, angled nozzles 102 and 102' formed in nozzle plates 
114 and 114' of monolithic sections 101 and 101' are angled slightly 
toward the connection portion CP' at an angle .theta.. The angle .theta. 
depends on the distance separating the nozzle plates 114 and 114' and the 
sheet 6 supported in front of the surface of the nozzle plates 114 and 
114'. In the present modification, the nozzle plates 114 and 114' and the 
sheet 6 are separated by 1 mm, (1001) and therefore the angle .theta. is 
set at 3.degree.. The angle .theta. of each angled nozzle is defined 
between a line following the axis of the angled nozzle and a line 
perpendicular to the surface of its respective nozzle plate. With this 
structure, even if the space between nozzles on either side of the 
connection portion CP is slightly greater than between other adjacent 
nozzles of the line head, the dot density of an image printed by the line 
head will be uniform. Forming the areas of the monolithic sections 101 and 
101' near the connection portion CP, and aligning and assembling the 
monolithic sections 101 and 101' is easy. 
The following is a description of a concrete example for producing a 369 
dpi line head according to the present embodiment. This production method 
is similar to the concrete method described in the above-described 
example, except for production of the angled nozzles 102 and 102'. In the 
concrete example for producing the line head according to the present 
modification, a nozzle plate 114 is formed by first forming a film resist 
to a nickel plate to a thickness of 50 .mu.m. Portions of the film resist 
are selectively exposed at an angle .theta. (for example, 3.degree.) to 
form hardened column angled at the angle .theta.. The unexposed portions 
of the film resist are removed. Nickel is then plated to the nickel plate 
around the columns to a thickness of 40 to 45 .mu.m. The resist columns 
are then removed to form the nozzles 102. The nickel plate is then lifted 
off, thereby forming the nozzle plate 114. In an alternative method, the 
nozzle plate 114 could be formed by exposing a light-sensitive glass, such 
as a PEG 3 glass ceramics produced by Hoya Corporation, at the angle 
.theta.. In this case, the nozzle plate 114 can be formed to 40 to 100 
.mu.m thickness. Next, another nozzle plate 114' is formed in the same 
manner by with angled nozzles 102' formed to an angle .theta.' equal but 
opposite to angle .theta.. 
Partitions 115 and 115', and ink chambers 113 and 113', are then formed to 
substrates 109 and 109' respectively as described in the above example. 
The ink chambers 113 and 113' are formed with a width of 50 .mu.m (1050). 
To produce a dot density of 360 dpi, the partitions 115 and 115' are 
formed with a width of 20 .mu.m (1020). Connection areas 250 and 250', 
which will separate the monolithic sections 101 and 101' at the connection 
portion CP, are formed to a width of 62 .mu.m (1062). The nozzle plates 
114 and 114' are attached to partitions 115 and 115' respectively, and the 
resultant monolithic sections 101 and 101' are connected together at their 
connection surfaces to produce the connection portion CP. The connected 
monolithic sections 101 and 101' are then mounted to a mounting frame 103. 
Ink droplets ejected from the angled nozzles 102 and 102' will follow 
respective flight paths 160 to reach the sheet 6 that is positioned away 
from the surface of the nozzle plate 114 with a distance of 1 mm. As shown 
in FIG. 16, flight paths 160 follow lines aligned with the axes of the 
angled nozzles 102 and 102'. The angles .theta. and .theta.' of the angled 
nozzles 102 and 102' create a shift of 52 .mu.m (1052) between the 
position where ink droplets impinge on the sheet 6 by following the flight 
paths 160 and where a line that intersects line aligned with the axis of 
the angled nozzle and that is perpendicular to the nozzle plate surface 
intersects the sheet. This 52 .mu.m shift allows forming each of the 
connection areas 250 and 250' to a width of 62 .mu.m (52 .mu.m+10 .mu.m), 
which otherwise would need to be formed to a width of 10 .mu.m to provide 
a uniform inter-nozzle distance of 20 .mu.m (1020). The wider connection 
areas 250 and 250' facilitate cutting the edges of the monolithic sections 
101 and 101'. Also the wide connection areas 250 and 250' are more 
reliable against pressure fluctuations in respective ink chambers. 
Connection and mounting processes are also facilitated. Actually, it is 
preferable to produce the connection areas 250 and 250' to have a width of 
about 50 to 55 .mu.m and not 62 .mu.m (1062) to the prevent modification 
of adhesive from effecting the width. Because the connection areas 250 and 
250' must be formed with a minimum width of 20 .mu.m (1020) and because 
the angle .theta. should be determined dependently on the distance between 
the nozzle plate 114 and the sheet 6, the angle .theta. can be within the 
range 0.5 to 10.degree. with 3 to 6.degree. most preferable. However, an 
angle .theta. much larger than this makes producing the nozzle plate 114 
difficult. 
Although the head described in this example is a single color head with 
only one row of angle nozzles 102 and 102', the same technology could be 
used to produce an integrated color head with a plurality of rows as shown 
in FIGS. 12-15. 
Although in the head described in the present example the direction in 
which the ink is ejected is almost perpendicular to the thermal resistor 
surface, the ink ejection direction could be made parallel to the thermal 
resistor surface by using the same technology. In this case, compared to 
conventional technology where the ink chambers are provided at right 
angles to the surface of the nozzle plate, ink chambers are formed slanted 
at an appropriate angle of between 0.5 and 10.degree.. The ink chambers 
are formed in the monolithic sections 101 and 101' so that when the 
monolithic sections 101 and 101' are joined together, their nozzles will 
slant in opposing directions. A head with this form can not be made into 
an integrated type head shown in FIG. 12 with a plurality of rows of 
nozzles in a single driving section, but several driving sections each 
with a single row of nozzles can be joined to form a full color head. 
Copending U.S. patent application Ser. No. 08/068,348 describes that a 
thermal resistor made from a Ta--Si--SiO alloy thin film and a nickel thin 
film has virtually the same properties as the thermal resistor made from a 
Cr--Si--SiO alloy thin film and a nickel thin film. Details of the 
Ta--Si--SiO alloy thin film are described in Japanese Patent Publication 
Kokai No. SHO-62-167056. A line head of FIG. 12 was made, but using 
thermal resistors made from a Ta--Si--SiO alloy thin film and a nickel 
thin film. The head was evaluated under the same conditions as shown in 
Table 2. A full color image with quality the same as that produced by the 
head described in the already-described example was obtained. 
Copending U.S. patent application Ser. No. 08/068,348 describes also that 
the good anti-corrosion and anti-cavitation properties of nickel make it a 
good conductor material to use in combination with a Cr--Si--SiO or a 
Ta--Si--SiO alloy thin film. However, there are limitations to producing 
nickel films. For example, a magnetron sputtering device with an 
especially strong magnetic field is necessary to produce a nickel film by 
sputtering because nickel has a strongly magnetic character. Also, nickel 
films require a separate process line from other semiconductor processes. 
Copending U.S. patent application Ser. No. 068,348 also describes that 
tungsten also has excellent anti-corrosion properties. Tungsten may be 
used as a conductor material in the thermal resistors of the ink droplet 
generators in combination with a Cr--Si--SiO or a Ta--Si--SiO alloy thin 
film. To test the suitability of tungsten as a conductor material in the 
thermal resistors, print heads were produced with thermal resistors 
including tungsten conductors in combination with a Cr--Si--SiO or a 
Ta--Si--SiO alloy thin film. The reliability of the thermal resistor was 
tested in water. The thermal resistor successfully underwent one billion 
continuous applications of voltage in pulses to show that a tungsten thin 
film has anti-cavitation properties equivalent to those of a nickel thin 
film. Although tungsten has anti-corrosion properties slightly inferior to 
nickel, it is non-magnetic, so can be produced using a normal magnetron 
sputtering device and in the same process line as other semiconductor 
processes. Tungsten also has a lower electric resistance than nickel. 
As described above, the monolithic section 101 of FIG. 8 for an ink jet 
head 1 allow producing an extremely small head at low costs. A color print 
head 1 for printing color images can be produced by providing ink 
generators in more than one row in the head. It is preferable that ink 
droplet generators of the color print head be formed with top-shooting 
type ink droplet generators. Because the print head 1 is integratedly 
formed with driver LSI circuit 112 and the thermal resistors 116, 
connection between the head 1 and the external drive circuit 300 is 
possible even with a large number of ink generators. The serial 
consecutive drive of the print head is more effective than conventional 
block or matrix drive. Because the print head 1 is driven serially and 
consecutively, the LSI circuit 112 integrated in the print head 1 can be 
made without a latch circuit, and therefore can be made smaller, less 
expensively, and with higher yields. Because a plurality of connection 
holes 110 for connecting the common ink channel 111 with the ink supply 
channel 108 in the mounting frame 103 are formed in the substrate 109 to 
be aligned intermittently in the main scanning direction, the resultant 
substrate 109 has sufficient structural strength. If the connection holes 
110 are connected together to extend in the main scanning direction, the 
resultant substrate 109 would be structurally weak and so could easily 
break apart. 
Thus, an ink jet print head having a plurality of nozzles in a high density 
and two dimensionally aligned to a large scale can be produced. The 
resultant head has a recording speed 10 to 100 times that of conventional 
ink jet recorders. The LSI circuit for driving the droplet generators in 
the head has only a shift register circuit and a driver circuit and 
requires only a total of five signal and power lines thereby decreasing 
costs. The present invention facilitates production of a line head 
compared to conventional technology. Continuous recording with the sheet 
transported at a uniform speed is possible, thereby facilitating transport 
of the sheet, reducing consumption of electricity, and negating any 
requirement for temperature control of the head. Because ink on the 
recorded sheet can be quickly dried, recording speed can be increased. 
The print head 1 can be applied for recording all types of images 
including, but not limited to, characters, graphics, and pictures. 
The structure of the LSI circuit 112 is not limited to that as shown in 
FIG. 10. The LSI circuit 112 may have various structures for attaining the 
serial and consecutive drive method with no latch circuit provided between 
the shift register 141 and the driver circuit 142. 
The ink jet print head 1 may be provided with the structures disclosed in 
co-pending U.S. patent application Ser. Nos. 08/331,742, 08/387,579, and 
08/405,709, the disclosures of which are hereby incorporated by reference. 
As described above, in an ink jet printer of the present invention, a 
belt-type preheating unit pressingly heats a recording sheet while 
transporting the recording sheet in a transport direction on a belt. A 
suction transport device is positioned downstream of the belt-type 
preheating unit in the transport direction. The suction transport means 
transports, on its transport belt, the recording sheet heated by the 
belt-type preheating unit in the transport direction while fixing the 
recording sheet onto the transport belt by a vacuum suction. An ink jet 
print head, positioned confronting the suction transport device, records 
images by ejecting water-based ink onto the recording sheet which is being 
transported by the suction transport device. With this structure, the ink 
jet printer of the present invention can perform high quality printing 
operation at a high speed. 
While the invention has been described in detail with reference to the 
specific embodiment thereof, it would be apparent to those skilled in the 
art that various changes and modifications may be made therein without 
departing from the spirit of the invention, the scope of which is defined 
by the attached claims.