Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-01-27
2002-10-29
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S209000, C428S211100, C428S461000, C101S457000, C101S462000, C101S463100, C101S465000, C101S466000, C101S468000
Reexamination Certificate
active
06472054
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printing plate, a method of making such a printing plate, and a method of printing using such a plate to form a desired image on a medium. More particularly, the printing plate of this invention employs a fluid composition comprising an acidic polymeric compound that is base-neutralized to adhere to a substrate that has a plurality of acidic sites. The fluid composition is applied by ink jetting to a substrate, providing a printing plate that is ready-to-use on a press without having to develop it.
BACKGROUND OF THE INVENTION
The offset lithographic printing process has long used a developed planographic printing plate having oleophilic image areas and hydrophilic non-image areas. The plate is commonly dampened before or during inking with an oil-based ink composition. The dampening process utilizes an aqueous fountain solution such as those described in U.S. Pat. Nos. 3,877,372, 4,278,467 and 4,854,969. When water is applied to the plate, the water will form a film on the hydrophilic areas, which are the non-image areas of the plate, but will contract into tiny droplets on the oleophilic plate areas, which are the image areas. When a roller carrying an oil-based ink composition is passed over the dampened plate, it will not ink the non-image areas that are covered by the aqueous film, but will emulsify the water droplets on the water repellant image areas, which will then take up ink. The resulting ink image is transferred, or “offset,” onto a rubber blanket, which is then used to print onto a medium such as paper.
It has been proposed to apply “direct” ink jet printing techniques to lithographic printing. For example, European Patent Publication No. 503,621 discloses a direct method to make lithographic plates by jetting a photocurable ink onto the plate substrate, and then exposing the plate to ultraviolet radiation to harden the image area. An oil-based ink may then be transferred to the image area for printing onto a printing medium. But, neither the resolution of ink drops jetted onto the substrate, nor the durability of the lithographic printing plate with respect to printing runlength was disclosed.
It has also been proposed to apply the direct ink jet printing techniques DI) without the additional steps of chemical development of the plate. This approach advantageously results in lower production costs and a more environmentally acceptable printing process. However, in such techniques it is difficult to control the spreading of the ink-jetted fluid that forms the oleophilic ink-accepting regions on the printing plate substrate. Such “dot spreading” causes lower printing image resolution and reduced image quality. For example, European Patent Application No. 591,916 A2 discloses a water-based ink having a polymer containing anhydride groups which are thermally cross-linked with a hydroxy-functional polymer. This formulation is applied by jetting the formulation which is at room temperature onto a room temperature substrate. However, this formulation does not achieve good control of dot spreading.
U.S. Pat. No. 4,833,486 discloses the apparatus and process for imaging a plate with a “hot melt” type of ink jet printer. The image is produced by jetting at high temperature a “phase change” type of ink which solidifies when it hits the cooler substrate. The ink becomes instantaneously solid rather than remaining a liquid or gel which is thereafter cured to form a solid. However, such an ink does not provide good resistance to press run due to the wax-type nature of the ink formulation.
European Patent Publication No. 0/101,266 describes a printing plate that may be implemented by ink jet printing a non-polymerizable carboxylic acid compound to a substrate. The compound should be oleophilic and amenable to application as a thin layer on the substrate. Polyvinyl butyral and acrylic resin in toluene solution are disclosed as potential compounds for the oleophilic layer, although never used. The use of an acidic polymeric compound that is base-neutralized as the oleophilic compound to adhere to a substrate is not disclosed.
Thus, it would be advantageous to employ a printing plate capable of extended press run length which does not require chemical development.
It is one object of this invention to provide such a printing plate. It is another object of this invention to provide a method of preparing such a printing plate. It is yet another object of this invention to provide a method of using such a printing plate. The printing plate of this invention may advantageously be prepared without a chemical development step typically required. The printing plate of this invention is also capable of extended press run length.
SUMMARY OF THE INVENTION
The fluid composition of this invention is suitable for ink jetting upon a substrate and comprises an acidic polymeric compound, in which the acid groups of the polymeric compound are at least partially neutralized with a base. The fluid composition can be aqueous or non-aqueous.
The printing plate of this invention is prepared by: (a) providing a substrate; and (b) applying by ink jetting to the substrate a fluid composition as described. In preferred embodiments, acidic polymeric compounds suitable for this invention are polymers and copolymers prepared from at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fuimaric acid, fumaric anhydride, ethylenically unsaturated sulfonic acid, sulfonated styrene, and mixtures or derivatives thereof. In particularly preferred embodiments, the acidic polymeric compound is partially or fully neutralized with base, and the fluid composition is ink jetted onto the substrate.
The printing plate of this invention is capable of extended press run length and advantageously avoids the need of chemical development.
DETAILED DESCRIPTION OF THE INVENTION
To achieve extended printing runs, the oleophilic material must adhere well to the substrate. Adhesion of the oleophilic material may be controlled in at least two ways. First, the oleophilic material should have a chemical interaction with the substrate that provides a type of chemical binding and promotes adhesion. For example, the chemical composition of the oleophilic material can be varied to promote its adhesion to the substrate. Also, the composition of the substrate can be varied to increase binding of the oleophilic material. Second, the substrate should provide microscopic topology that allows the oleophilic material to interlock mechanically with the substrate when dry or hardened. Mechanical interlocking can be affected by roughening the surface of the substrate. Thus, by controlling these variables, a printing plate can be made with increased adhesion of the oleophilic material, and correspondingly longer printing run operation.
In the invention described here, the oleophilic material is placed on the substrate by ink jetting a fluid composition comprising the oleophilic material. The fluid composition can be aqueous or non-aqueous. Because the fluid composition is the vehicle to carry the oleophilic material, the wettability of the substrate by the ink-jetted droplets of fluid composition and the spreading of the ink-jetted droplets are properties that affect resolution of the printing process. Too much spreading of the ink-jetted droplets of fluid composition will reduce printing resolution. The substrates used here typically have high surface tension and allow fluids to spread completely and rapidly over their surface. While this benefits adhesion of the oleophilic material to the substrate, it disadvantageously reduces image resolution in printing. Here, the fluid composition is prepared to balance these properties, and provide good adhesion for longer press runs in conjunction with high image resolution.
The spreading of droplets is reduced in two ways by the present invention. First, the fluid composition comprising the oleophilic material is interfacially matched to the substrate, as described below. Second, by pretreatin
Aurenty Patrice M.
Grant Alexander
Keaveney William P.
Stone Edward
Baker & Botts LLP
Jackson Monique R.
Kodak Polychrome Graphics LLC
Thibodeau Paul
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