1. Field of the Invention
The present invention relates to an ink jet print head having nozzles densely arrayed therein to eject ink containing a colorant, and to an ink jet printing apparatus and an ink jet printing method to form an image using the print head. More specifically, the present invention relates to an ink jet printing apparatus and an ink jet printing method using an elongate print head which has a plurality of nozzle groups each made up of an array of nozzles arranged staggered between two parallel lines, one on an upstream side and the other on a downstream side with respect to a direction in which a print medium is moved relative to the print head. Particularly, this invention relates to an ink jet printing method, an ink jet printing apparatus and a print head suited for a so-called one-pass printing in which the elongate print head is scanned only once over a print area to complete a printed image.
This invention is applicable to all devices that print on print mediums made of paper, cloth, nonwoven fabric, OHP sheets and metal materials. Examples of applicable devices include office equipment such as printers, copying machines and facsimiles, and industrial manufacturing equipment.
2. Description of the Related Art
As information processing equipment, such as copying machines, word processors and computers, and communication equipment make technological advances, ink jet printing apparatus that print digital images by an ink jet method are becoming increasingly widespread as an image recording device for these equipment. One of the ink jet printing apparatus is known to use a print head that has a plurality of print elements (also referred to as nozzles) densely arrayed therein to increase a print speed. Further, in recent years there is a growing demand for a capability to print color images and, in response to this demand, printing apparatus that use a plurality of print heads for ejecting color inks are in common use. What is meant by a nozzle as referred to in this specification and the scope of claim is one that includes an ink ejection opening to eject ink supplied into a common ink chamber in the print head, an ink path to introduce ink supplied into the common ink chamber to the ink ejection opening, and an ejection energy generation element to eject ink supplied to the ink path from the ink ejection opening.
Generally, an ink jet printing apparatus ejects ink or recording liquid in the form of flying ink droplets onto a variety of print mediums made of such material as paper to form an image thereon. Since the ink jet printing apparatus adopts a non-contact system by which the print head does not contact the print medium, the printing can be performed with low noise. Another advantage is that the print resolution and the print speed can be increased by increasing the nozzle density. Further, the ink jet printing apparatus does not need special processing, such as development and fixing, even for such print mediums as plain paper. All these advantages allow for the printing of images at low cost and at high quality and therefore the ink jet printing apparatus is finding an ever widening range of applications. An on-demand type ink jet printing apparatus in particular has the advantages of being able to be easily upgraded to print color images and be reduced in size and simplified in construction and thus its demand is expected to expand in the future. As a demand for a capability to print color images grows, so does the need for higher print quality and faster print speed.
With a remarkable advance in recent years in the technology to form nozzles with high density, a fabrication of a high-density, elongate print head has come to be realized. An elongate print head having nozzles arrayed at high density is generally called a full-multi type elongate print head An ink jet printing apparatus using such an elongate print head has been proposed and implemented which completes a printed image in one printing scan over a wide print area corresponding to the elongate print head. This ink jet printing apparatus can meet requirements for both print speed and print quality. Because of these advantages, further efforts for development are being made on this type of printing apparatus.
However, the ink jet printing apparatus using the elongate print head with high-density nozzles has the following problems.
First, in the above system if an image in a print area is to be completed in one printing scan (one pass) or in a small number of passes, ink droplets ejected from the nozzles of print head units need to be absorbed and fixed in the print medium in a short period of time. This requires a bulky heat and dry means for the print medium or a means to reduce a volume of ink used for printing. This in turn increases cost and reduces the print density or pixel density, degrading the quality of the printed image.
Second, if the nozzles are arrayed at high density in a single line, ink droplets ejected from the adjoining nozzles may merge together on the print medium into an inappropriate shape. When an image to be printed has a high duty, the ink that failed to be absorbed in the print medium may remain on the print medium in a liquid state, degrading the print quality.
Third, ink dots formed by those nozzles in a boundary portion between the nozzle groups may produce artifacts such as streaking caused by optical density variations which shows up in the form of white or black lines, degrading a print quality.
To avoid this problem, a print head has been proposed which has nozzle groups each having two parallel lines of nozzles, one on an upstream side and one on a downstream side, so that the nozzles are staggered alternately between the upstream and downstream parallel lines. Further, in this configuration, the nozzle groups are connected longitudinally to form an elongate head for use in a full-line printer.
In an ink jet printing apparatus using the above print head having a plurality of longitudinally connected nozzle groups, however, a problem has been observed. Although white or black lines are rendered less conspicuous in an image area printed by those nozzles in one nozzle group, an image area printed by those nozzles in the boundary portion between the nozzle groups may still show white or black lines. A satisfactory image quality has yet to be obtained with this type of ink jet printing apparatus.