Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-11-15
2003-03-11
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
Reexamination Certificate
active
06530657
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an ink jet printer with a piezo printing head for ejecting lactate ink onto an uncoated printing medium.
2. The Prior Art
The field of ink jet printers, printing heads and inks for such printing heads, as well as of ink jet printing methods, is explained in the following with respect to their suitability for large-format printing products for outdoor applications. The term “printers” comprises in the present case both so-called desk printers and plotters.
Ink jet printers are used for printing primarily on coated materials. The properties of the coating material, also referred to as the top coating, determine the imprintability of the carrier material (or substrate) and the durability (or stability) of the printed image. The coating of the material assures that the ink is absorbed as quickly as possible; that an image with sharp edges is produced; and that such an image is as resistant as possible to environmental influences and light. Furthermore, the printed image has to dry as quickly as possible, and it has to be wipe-proof. Very many different coating materials are available in the market for this purpose. The carrier material (or substrate) itself determines only the mechanical properties of the printing medium in most cases. Commonly used carrier materials for ink jet printers and plotters are papers, foils and Banner materials.
All printing media have in common that the carrier material cannot be imprinted directly because the ink fails to enter into an adequate bond with the carrier material in most cases. The coating of the carrier material with coating material is a cost-intensive process. The refining of the carrier material frequently costs multiple times the cost of the carrier material. Coated printing media are therefore less suitable for large-formatted printed products used in outdoor applications.
Ink jet printers use different printing heads. With ink jet printers equipped with thermo-printing heads, the ink is evaporated or highly expanded by heating it in a capillary, and then sprayed onto the printing medium. This procedure is not suitable for large, UV-stable color pigments. Another drawback is, furthermore, that the thermal stressing of the ink changes the colors. Some components of the ink evaporate before impinging upon the printing medium. The useful life of the printing heads is typically short because they age in a short time due to the thermal stress. Finally, the printing speed is physically limited by the cooling and heating process. Thermo-printing heads are therefore not suitable for imprinting large-format printing products used for outdoor applications.
Thermo-type jet printers with piezo printing heads eject the ink from the capillary by mechanical oscillations of the piezo crystal and spray it onto the printing medium. These printing heads are therefore suited for large, UV-stable color pigments. The colors are not impaired by the printing process. Almost all components of the ink impact the printing medium without evaporation. The ink is processed and applied at the ambient temperature and no extraordinary heating of the ink occurs. The piezo printing heads have a long and useful life. However, the printing speed is limited by the oscillation of the piezo crystal. The printing speeds achieved, however, are nonetheless sufficiently high that a few more droplets of the ink can be shot under the lee of the first droplet. These droplets unite to a large drop (variable drop size) before impacting the material. Piezo printing heads are therefore suitable for large-sized printing products for outdoors applications.
Water-based inks are the type of inks most frequently used with ink jet printers because they can be processed without problems with thermo printing heads. However, these inks can be used only on coated printing media. Because of their low stability, they are suitable for filing purposes only to a limited extent. Their water-solubility renders them unusable for applications in a humid environment mainly outdoors.
Pigmented inks can be considered as another type of ink suitable for ink jet printers, primarily for those equipped with piezo printing heads. Oil-and-water mixtures are frequently used for pigmented inks. However, such mixtures are based on water for the most part, and such inks can be only employed for coated materials. They exhibit good UV-stability and are suitable for medium-term filing purposes. To the extent such inks are water-soluble, they can be considered at best for short-term outdoor applications.
Inks containing solvents have been used for many years in the printing industry, for example for screen printing purposes. Such inks have also been employed on special ink jet or air brush printers. These inks can be used on coated printing media. They possess good UV-stability and they can be stored for a long time. Furthermore, they are not water-soluble. However, such inks require special protective measures as they are being processed because they are highly hazardous to the environment and to health in most cases. Special exhaust measures and the use of active filters are mandated by the government authorities. The disposal of the residual inks poses problems as well. Since such inks have a low flash (or ignition) point they can be transported only as hazardous material. Their storage is critical as well because it is encumbered with government regulations. Quick drying of the inks in the hose system and in the printing heads of the ink jet printer poses additional problems for the use of such inks. The ink system of the printer therefore has to rinsed time and again with solvents, which is very cost-intensive. One switch-on (or start-up) operation may cost up to 100 German marks. Such inks are less suited for producing large-format printing products in the field of outdoors applications.
Furthermore, it is known that lactate inks based on lactic acid ester, which actually belong to the family of the adhesives, can be sprayed with piezo printing heads. In the present case, lactate inks are understood to be inks generally based on lactate, and also inks comprising components with properties similar to the ones of lactate. Such inks offer the advantage that they can be directly sprayed onto uncoated printing media.
They posses good UV-stability and they are suited for use in outdoor applications because they are not soluble in water. Due to their chemical composition, they do not pose any load to the environment. A health hazard exists only if they come into direct contact with the skin or eye. They can be transported and stored without problems. Drying of such inks in the hose system and in the printing heads is relatively uncritical because it can be controlled.
Lactate inks therefore meet the long existing demand for inks that print with ink jet printers on uncoated materials in a manner as simple as possible and friendly to the environment and without health risks because immense manufacturing costs—which have been unavoidable until now—can be saved due to the omission of coating material.
It has been found that when lactate inks are used for conventional ink jet printers and with ink jet printing methods, the quality of the printing is not acceptable because of bleeding phenomena.
An jet ink printer with a printing head for ejecting commonly used printing ink onto a printing medium within the area of a surface to be imprinted is known from WO 00/24 583 A1. A preheating area for preheating the printing medium from the bottom is provided upstream of the surface to be imprinted, and an after-heating area for drying ink applied to the printing medium from below is provided downstream. The preheating and after-heating areas are formed in connection with this known printer by the jacket of a roller, which means that the pre- and after-heating processes are coupled in connection with this known printer. Because of such coupling is not possible to assure the preheating process within the temperature range required for a satisfactory printin
Collard & Roe P.C.
Gordon Raquel Yvette
TECHNOPLOT CAD Vertriebs GmbH
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