Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-11-16
2003-04-29
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S008000, C347S004000
Reexamination Certificate
active
06554416
ABSTRACT:
This application is based on patent application Ser. No. 2000-353491 filed Nov. 20, 2000 in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus provided with a plurality of full line heads, relative positions of which are fixed, upon a liquid droplet being ejected onto a print medium, the print medium moving by adsorption conveyance such as suction or electrostatic adsorption as medium conveyance, and more particularly relates to solving problems associated with a cockling produced on the print medium to which the liquid is applied.
2. Description of the Prior Art
A cockling occurring on a sheet of paper that is a kind of a printing medium on which liquid droplets are applied, i.e., deformation due to water imbibition by fibers is conventionally recognized as a difficulty against liquid ejection and printed image formation. The difficulty has been recognized in a serial scan type printer (hereinafter, simply referred to as a serial system) using a carriage that moves with respect to the suspended medium while placing thereon a liquid ejecting head. Japanese Patent Application Laid-open No. 6-115068 discloses a method of solving the difficulty with the prior art wherein a rib for permitting a cockling to occur on the medium is formed on a plate shaped structure for holding in contact a medium back surface called a platen.
In a system (hereinafter referred to a full-line system) where upon ejecting liquid droplets a full-line type head is employed with a ejection opening disposed over the entire width of a print medium to convey the print medium, floating of the print medium itself upon conveyance is a problem rather than the amount of displacement of the print medium caused by the foregoing cockling. In the full-line system, many inventions on how securely adsorption and conveyance are performed have been applied. For example, Japanese Patent Application Laid-open Nos. 7-53081, 7-133035, and 9-254460 disclose a fact that a print medium is adsorbed to a platen with the aid of suction or static electricity.
A main technique of the prior art concerns such a platen structure that cockling produced even in the serial system may be allowed in a print region. It is the present situation in the full-line system that even a problem of the cockling itself has not been recognized much.
SUMMARY OF THE INVENTION
The present invention is to pursue optimum print conditions by clarifying correlations among respective components of an image forming apparatus capable of realizing high image quality with the aid of ejecting of liquid droplets by achieving clarification of a cockling itself not known conventionally. The present invention is further to complete a novel system capable of achieving optimum printing for a cockling.
More specifically, it is an object of the present invention to provide a novel optimum design method capable of determining requirements of the whole of an image forming apparatus by investigating a relationship among respective components from the occurrence of cockling in the aforementioned full-line system.
It is another object of the present invention to provide an image forming apparatus capable of achieving high image quality without being affected by cockling while utilizing an optimum printing gap by setting a relationship among the respective components without being affected by characteristics (surface tension, etc.) of horizontally ejecting a liquid such as an ink and characteristics of a print medium itself such as paper, which are both dominating stages of occurrence and growth of the cockling in the full-line system.
It is a further object of the present invention to provide an optimum image forming apparatus with all of the variations of the foregoing respective elements.
The present inventors have investigated variously a change in cockling height with respect to the time elapsed since application of liquid droplets by pursuing an occurrence mechanism of the cockling in an adsorptive conveyance system with respect to a change in the cockling produced owing to a difference among kinds of ink and a difference among its invasion characteristics or a difference among its infiltrate characteristics, and further differences among fibers of the print medium used and sizing agents. It has been hereby found that if the adsorptive conveyance system is employed for a time shorter than 1 second after application of liquid droplets, any cockling is substantially not produced on any print medium or with any ink. It is considered that the reason is that the mechanism of the occurrence of the cockling is due to infiltration of water constituting the ink. It has been also found that beyond one second after the application of liquid droplets, the height of the cockling is changed in response to the characteristics of each ink and the print medium.
FIG. 2
illustrates this change, in which cockling heights H
C
(mm) are on the y axis and the time T
D
elapsed is on the x axis, which time elapsed takes the time of application of liquid droplets as the origin, i.e., “0”. Coordinates Y(1, &ggr;) indicate a reference point with &ggr;=0.05 in water ink. Such use of &ggr; is convenient to clarify applicability of the present invention, because &ggr; changes only slightly, even when other ink systems are employed or even though ink characteristics developed hereafter, if any, change in particular. In any case, a curved line indicating a change in cockling heights H
C
after the elapsed time T
D
=1 (sec) is as illustrated in FIG.
2
.
In accordance with one view of the present invention, a tangential line H
C
=&agr;T
D
+&bgr; with respect to the curved line passing through the reference point Y(1, &ggr;) passes through (1, &ggr;), from which curved line &agr;, &bgr;, and &ggr; can be in turn determined. A choice may be made as a matter of course by a maker of a print medium that provides such a curved line upon design of the print medium by the maker. It is herein preferable to take as an object a print medium that ensures a maximum cockling. If ink used is already determined, then the reference point Y(1, &ggr;) in the individual image forming apparatus is defined by itself.
For the adsorptive conveyance means there may be typically used one in electrostatic adsorption conveyance and suction conveyance described later, in which a print medium is brought into close contact with a conveyor such as a moving belt, the accuracy of which means is practically uniform.
However, even if use is made of a belt with reduced accuracy and an adsorption system with reduced cling properties in order to reduce the manufacturing cost, the present invention can complete printing in a region where the amount of occurrence of the cockling is more reduced than the prior art. There is therefore ensured an image with higher quality than the prior art image forming apparatus without disturbance of the image by “rubbing”.
The present invention discloses items where technical idea of the present invention is developed while taking such manufacturing and practical error fractions into consideration.
Referring here to
FIG. 3
, a conceptual view of a portion of the image forming apparatus illustrated in
FIG. 1
is provided, which defines a head existing region (its length L). The head existing region in the present invention is defined from a ejection opening A of a head section
13
B where printing is first performed up to an end B of a head section
13
Y (an end which is capable of making contact with the print medium) where printing is finally performed.
A practical print system according to the present invention is adapted such that an image forming apparatus comprises:
medium-conveying means for attracting and conveying a print medium having a characteristic with which cockling is produced by application of liquid droplets;
attracting means for attracting the print medium to the medium-conveying means; and
a first liquid ejecting head for first providi
Barlow John
Tran Ly T
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