Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-12-16
2001-03-13
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031690, C106S031750
Reexamination Certificate
active
06200372
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to water-based offset lithographic newspaper printing ink.
DESCRIPTION OF RELATED ART
In an attempt to eliminate volatile organic compounds (VOCs) in the pressroom, water-based alternatives are being sought for ink formulations. Water-based printing inks for use in flexographic printing processes are known in the prior art. This type of printing process utilizes printing plates wherein the printing images stand up in relief, i.e. the areas to be printed are raised above the non-printing areas. Printing by the flexographic process requires relatively low pressure while sufficient pressure is applied to transfer the ink from the face of the image carrier to the surface of the substrate. Examples of useful water-based flexographic printing inks are disclosed in U.S. Pat. No. 4,173,554 and
The Printing Ink Manual
, edited by R. H. Leach and R. J. Pierce, pages 571-576, 5th edition, (Blueprint, 1993).
Water-based inks for gravure printing are also well known. In the gravure process, the printing image is engraved into a cylinder in the form of cells which become filled with ink. Printing is achieved by passing the substrate between the gravure cylinder and impression roller under pressure. Examples of useful water-based gravure printing inks are disclosed in U.S. Pat. Nos. 4,954,556 and 5,098,478.
The offset lithographic printing process presents a unique challenge to ink formulators since such process utilizes a planographic printing plate, i.e. the image and non-image areas are in the same plane on the image carrier, and two fluids are concurrently utilized.
It is fairly simple to define an image area by raising it above the background as in the case of the flexographic printing plate or lowering it as in the case of the gravure printing plate; avoidance of ink adhering to the non-image area is not too difficult to achieve. However, when all areas are on the same level, techniques must be utilized to insure that ink adheres only to the image area, and not to the non-image area.
In conventional offset lithographic printing processes, the plate is damped before it is inked with an oil-based ink. Typically, the damping process utilizes a fountain solution such as those described in U.S. Pat. Nos. 3,877,372, 4,278,467 and 4,854,969. Water will form a film on the hydrophilic areas (i.e. the non-image areas) of the printing plate, but will contract into tiny droplets on the oleophilic areas (i.e. the image areas). When an inked roller containing the oil-based ink is passed over the damped plate, it will be unable to ink the areas covered by the water film (the non-image areas), but will emulsify the droplets on the water-repellant areas (the image areas) and these will ink up. Such process is called offset lithography because the inked image on the plate does not directly print onto the paper substrate, but is first “offset” onto a rubber blanket, and transferred therefrom onto the paper substrate.
As mentioned above, conventional offset lithographic printing processes entails the use of oil-based inks and water-based fountain solutions. The ink/water balance is critical and is quite demanding of the pressman's skills. This issue is one of the several disadvantages associated with such printing processes as compared to flexographic and gravure printing processes. Moreover, the oil-based inks and aqueous fountain solutions typically employed in conventional offset lithographic printing processes contain fairly high levels of undesirable volatile organic compounds (“VOCs”).
U.S. Pat. No. 3,356,030 discloses the use of a water-based printing ink in respect to a method of planographic printing utilizing a lithographic printing plate whose non-image areas are coated with a cured coating of a thermosetting silicone resin. However, the patented method also entails the use of a volatile hydrocarbon fountain solution which will coat the non-image areas and which is re-applied between successive printings. Of course, the use of a volatile hydrocarbon fountain solution undermines the principal purpose of the water-based ink compositions of the present invention, i.e. the avoidance of the use of volatile organic compounds (“VOCs”) during the printing process. Indeed, the water-based ink compositions of the present invention may be used for offset lithographic printing processes without any fountain solution whatsoever.
In the 1980s, a resurgence of interest occurred in respect to “waterless” lithographic printing processes. Both positive and negative waterless planographic printing plates are commercially available from Toray Industries of Japan. The image area of a waterless planographic plate is a photopolymer similar to that employed for the image area of a conventional plate. However, the non-image area is coated with a polymer such as a silicone which is ink repellant. Further information about waterless printing plates and processes may be found in U.S. Pat. Nos. 5,370,906 and 5,417,749.
The waterless printing process solved two issues: VOCs emanating from the fountain solutions and control of the ink/water balance by the pressman. However, the difference in surface energy between the image and non-image areas of the conventional offset lithographic printing plate is typically 40 dynes/cm is dramatically reduced to 20 dynes/cm in the case of the waterless printing plate. Therefore the latitude between scumming and poor print density is considerably narrowed and the issue of VOCs (emanating from the oil-based ink) still remains in respect to waterless printing.
German Offenlegungsschrift DE 41 19 348 A1 pertains to a moistureless offset printing method and a water-based printing ink. The ink described therein is one which will adhere to hydrophilic materials, but not to hydrophobic materials, and contains a dye, water, 5-50% water-soluble macromolecular binder and a hygroscopic liquid, preferably a multihydric alcohol.
It is an object of the present invention to eliminate the principal disadvantages of conventional offset lithographic printing inks, viz. high levels of VOCs emanating from the oil-based ink and the aqueous fountain solution and the difficulty in controlling the ink/water balance, while preserving the principal advantage of the conventional lithographic printing process, i.e. high surface energy differential between the image and non-image areas of the printing plate.
Such object has been achieved by means of the present invention which comprises a water-based newspaper printing ink that is to be used in offset lithographic newspaper printing processes without the need for any accompanying fountain solutions using a re-wetting agent
SUMMARY OF THE INVENTION
The invention is a water-based single fluid fountain solution free offset lithographic news ink comprising: (a) water; (b) a macromolecular resin binder comprised of: (i) resin soluble in water regardless of the pH of the water, (ii) rosin salt resin soluble in water at a pH ranging from about 7.5 to about 10, and (iii) aqueous emulsions polymer; (c) a water dispersible modified soybean oil based polymer; (d) pigment; and (e) a hydroxyethylethylene urea rewetting agent.
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Babij Hugo
Czebotar Martin Thomas
Gan Keqi
Krishnan Ramasamy
Yamat Marilyn
Klemanski Helene
Persley Sidney
Sun Chemical Corporation
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