Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2002-02-20
2004-09-14
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S101000, C347S096000, C347S095000
Reexamination Certificate
active
06789887
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods of inkjet printing. It more specifically relates to a method of inkjet printing which utilizes an inkjet ink which contains a thermally responsive material.
BACKGROUND OF THE INVENTION
An inkjet printer produces images on a receiving medium by ejecting ink droplets onto the receiving medium in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of inkjet printers in the marketplace.
Photographic prints made using an inkjet printer desirably have an image resolution of about 24 line pairs/mm, which corresponds to about 20 &mgr;m per line or equivalently about 1200 dots per inch. Inkjet prints must have a dynamic range of about 128 gray levels or more in order to be comparable in image quality to conventional photographic prints.
Secondary colors are formed as combinations of primary colors. The subtractive primary colors are cyan, magenta and yellow, and the secondary ones are red, green and blue. Gray can be produced by equal amounts of cyan magenta and yellow, but less fluid is deposited on the paper if the gray is produced from an ink supply containing only black dye or pigment.
Consider forming a saturated spot of a secondary color with a typical print head emitting 4 pL drops. The 4 pL droplet has a diameter of about 20 &mgr;m in the air and forms a disk of about 30 &mgr;m on the paper. Adjacent droplets are typically aimed to be placed on 21 &mgr;m centers so that adjacent disks on the paper have some overlap and thus ensure that full area coverage is obtained and that jet misdirections do not produce visible artifacts. Then, as taught in U.S. Pat. No. 6,089,692 of Anagnostopoulos, if a saturated spot of a secondary color is to be formed, at least 256 droplets (128 of each of the primary colors) have to be deposited per 84×84 &mgr;m
2
area. The amount of fluid deposited per unit area is then about 145 mL/m
2
. This is a major problem in printing photographic quality inkjet prints in that the amount of fluid deposited is at least a factor of 6 higher than the fluid holding capacity of commercial photo-grade inkjet papers.
A second problem with regards to producing photographic quality inkjet prints is that the penetration rates of ink into the image-receiving layer of presently available porous or swellable commercial receivers are too low. Consequently, the printing algorithms are written such that they do not allow a droplet to be placed on top of or adjacent to another droplet until sufficient time has elapsed. This results in slow printing time and is, therefore, unacceptable. If an attempt is made to print faster, coalescence and color bleed are observed. That is, if the second ink droplet arrives before the first droplet has been completely absorbed into the paper, the two merge or coalesce into one large droplet. This reduces the image resolution. Color bleed is essentially the same effect as coalescence, except that the two droplets that merge contain different color colorants. The result is poor image sharpness and color quality.
Inkjet print heads have been recently invented that are page wide and have nozzle spacing of finer than 300 per inch; see, for example, U.S. Pat. No. 6,079,821 of Chwalek et al. Such print heads produce 1 to 2 pL drops which are smaller than the typical droplets produced by commercial print heads. Also, because the print heads are page wide and have a large number of nozzles, they are capable of ink lay down rates substantially higher than that of scanning type conventional ink-jet printers. Unfortunately, coalescence and color bleed problems at the receiver surface may compromise the productivity of the page wide print heads. This constitutes a third problem with the printing of photographic quality inkjet prints, namely that the present receiver media seriously limit the productivity of these advanced print heads.
Several methods have been disclosed to reduce color bleed. U.S. Pat. Nos. 5,428,383 and 5,488,402 teach a method to control color bleed by using multivalent metal salts as precipitation agents in a first ink composition. The precipitation agent is designed to react with the coloring agent in a second ink composition. Other methods disclosed by U.S. Pat. Nos. 5,198,023; 5,518,534; 6,036,759; 5,181,045; and 6,281,267 are all involved in controlling color bleed by introducing precipitation reactions between inks. However, such precipitation reactions may result in non-uniformity in colorant distribution and may cause light scattering by precipitated particles. This will create negative viewing effects on image quality and are not acceptable in photographic printing.
Another method of controlling color bleed is to modify the surface of the receiving media by introducing a 3-dimensional micro-patterned structure that contains the inks within each micro-well element. Such a method has been disclosed in W099/55537 and U.S. application Ser. No. 10/046,024 filed Oct. 29, 2001. However, it will significantly add cost to the prints.
There is still needed an effective method to control color bleeding and drop coalescence in inkjet printing, especially in high speed photographic inkjet printing.
SUMMARY OF THE INVENTION
This invention provides an inkjet printing method comprising providing a liquid inkjet ink which contains a thermally responsive material and applying the liquid inkjet ink onto an inkjet recording element in an imagewise fashion, wherein the inkjet recording element has been heated to a temperature higher than the temperature of the liquid inkjet ink. In one particular embodiment this invention provides an inkjet printing method with controlled color bleed and drop coalescence comprising;
a) loading ink ejecting elements of a printer with liquid inkjet ink comprising a thermally responsive material;
b) loading the printer with an inkjet recording element;
c) heating the inkjet recording element to a temperature higher than the temperature of the inkjet ink in the ink ejecting elements; and
d) ejecting the liquid inkjet ink from the ink ejecting elements onto the heated inkjet recording element in response to digital data signals.
The method described herein minimizes the color bleed and coalescence on all receiving media without any special treatments.
DETAILED DESCRIPTION OF THE INVENTION
Color bleed and coalescence is generally caused by inter-droplet diffusion of colorants between adjacent ink drops before the drops have dried by adsorption into the media and/or evaporation of the solvents in the ink. Therefore, a longer drying time and a higher diffusion rate of the colorants will result in a more severe color bleed problem. It is well understood that the diffusion rate of colorants in inks is inversely proportional to the viscosity of the inks. In other words, the higher the ink viscosity when the ink is on the receiving media, the lower the diffusion rate of the colorants, and the less problem in color bleed and drop coalescence. However, with current inkjet ink ejecting technology, it is generally required that the inks have a viscosity below 20 centipoise and preferably below about 10 centipoise, when they are being ejected from an inkjet ejecting element.
The inkjet ink utilized in the current invention comprises a thermally responsive material, such that the viscosity of the ink increases rapidly when the ink is heated and the ink rapidly forms a non-fluidic gel at the elevated temperature. Such gelling is a direct result of the presence of the thermally responsive material and does not result merely from evaporation of the solvent. In the current invention the inkjet ink is ejected from the printhead in its liquid state, and when it comes in contact with the heated recording element (also known as a receiving element), the viscosity of ink increases. The ink itself is not generally heated prior to contact with the recording element. Preferably the ink has a viscosity of from about 0.5
Sharma Ravi
Yandila Simon
Yang Zhihao
Eastman Kodak Company
Meeks Roberts Sarah
Meier Stephen D.
Shah Manish
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