Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-12-28
2003-12-23
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S100000, C106S031130, C106S031600
Reexamination Certificate
active
06666553
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of selecting ink jet inks in a color set that provide images with improved inter-color gloss differences.
BACKGROUND OF THE INVENTION
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant, which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc.
Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from major deficiencies such as poor image stability against light and gases commonly contained in the air, such as ozone (O3), nitrogen oxide (NOx) and sulfur oxide (SOx), especially on receivers having porous ink receiving layers. One method of addressing these limitations is to use pigment-based inks. When designed properly, pigment based inks usually can demonstrate image stability significantly higher than the dye based inks, and more importantly, approaching the archival quality as compared to silver halide photographic prints.
A major image quality drawback of pigment-based inks is “inter-color differential gloss”, where the gloss levels of imaged areas of different colors are very different from each other. This type of image quality defect can be quite noticeable, even to ordinary observers. One possible solution to this problem is to cover the entire receiver with a protective layer through techniques such as laminating the printed image, or fusing the top fusible polymeric layer in receivers to a continuous overcoat layer, such as those disclosed in U.S. patent application, Ser. No. 09/954,779, filed on Sep. 18, 2001 of Wexler, or coating a protective layer on the imaged areas as described in EP1057646 and EP1048466. However, all these approaches involve separate steps after printing, making the entire process complex and costly.
What the art needs is a way to minimize gloss level variations among different colors in a color image when the various inks are deposited and dried on a receiver. This should be done as part of the printing process and not as a separate step after printing.
SUMMARY OF THE INVENTION
The present invention provides a method for selecting inks in a color set so that the ink set is capable of producing images wherein the gloss level variations among different colors in the color image is minimized. The gloss variation is judged after the ink is deposited and dried on a receiver, but the invention is a part of the ink selection and printing process; not a separate step after printing.
In accordance with the invention, the gloss level of each ink is predetermined, as measured from single color patches on a receiver, and the gloss level variability among different inks is calculated. By keeping the gloss variability with a certain range, the quality of the image is improved.
Hence, the present invention discloses a method of selecting inks within an inkjet ink set for color printing comprises:
a) providing at least two color inks, each ink comprising a carrier and a pigment;
b) printing the above inks onto a receiver using test images consisting of single color patches of a Dmax density (100% dot coverage);
c) measuring the gloss level of each patch at a predefined specular angle;
d) calculating the Relative Gloss Variability (RGV) values of the ink set based on the definition in Equation A; and
e) selecting inks for the color set such that the Relative Gloss Variability (RGV) among inks is less than 10% when 60° is used as the specular angle:
RGV
(
%
)
=
∑
I
=
1
N
|
(
Gloss
(
Imaged
Area
)
I
-
AG
)
|
AG
/
N
Equation
(
A
)
Where
AG
=
∑
I
=
1
N
Gloss
(
Imaged
Area
)
I
N
I is a variable which identifies a certain color patch used in the evaluation,
N is the total number of color patches used in the evaluation
Another embodiment of the invention discloses a method of selecting inks within an inkjet ink set for color printing comprises:
a) providing at least two color inks, each ink comprising a carrier and a pigment;
b) adjusting the sizes of the pigment particle of the inks to achieve the desired gloss;
c) printing the above inks onto a receiver using test images; consisting of single color patches of a Dmax density (100% dot coverage);
d) measuring the gloss level of each patch at a predefined specular angle; and
e) selecting inks for the color set such that the Relative Gloss Variability (RGV) (Equation A) among inks is less than 10% when 60° is used as the specular angle.
Yet, another embodiment of the invention discloses a method of selecting inks within an inkjet ink set for color printing comprises:
a) providing at least two color inks, each ink comprising a carrier and a pigment;
b) adding into inks non-film forming particles with particle sizes selected to achieve the desired gloss;
c) printing the above inks onto a receiver using test images; consisting of single color patches of a Dmax density (100% dot coverage);
d) measuring the gloss level of each patch at a predefined specular angle; and
e) selecting inks for the color set such that the Relative Gloss Variability (RGV) (Equation A) among inks is less than 10% when 60° is used as the specular angle.
The advantage of the invention is that it minimizes gloss difference among the different colors in a printed color image and this is done as a part of the initial printing process.
DETAILED DESCRIPTION OF THE INVENTION
Gloss Definition
Gloss, commonly referred to as specular gloss, of a surface is defined as its degree of approach to a mirror-like surface. It is a measure of the amount of energy reflected at a reflection angle equal to or near the angle of incidence. Specular gloss can be measured in terms of gloss units (gu), at several angles, e.g. 20°, 30°, 45°, 60°, 75° and 80° from the surface normal. Gloss meters are used to measure the gloss of a sample at various angles. The BYK-Gardner micro-TRI-glossmeter is an example of such an instrument. The particular instrument used in the present invention is capable of measuring gloss at three angles, 20°, 60° and 85°.
Both ink and receiver play an important role in the gloss levels of an ink jet printed image. The gloss levels of a receiver can be influenced by the receiver design, for example, the size of particles in the surface coating material and the surface roughness of the coated paper support. On the other hand, ink factors also contribute; for example, the refractive index of polymers in the inks, the film forming property of the polymers in the inks after printing, and the ink load deposit on the receiver all influence the gloss of a printed image. For particle-containing inks, such as pigment-based inks, particle size and distribution in particular have a significant impact
Chen Huijuan D.
Han-Adebekun Gang C.
Reczek James A.
Do An H.
Eastman Kodak Company
Meier Stephen D.
Wells Doreen M.
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