Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-01-27
2003-04-29
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S209000, C428S211100, C428S461000, C428S500000, C101S457000, C101S461000, C101S463100, C101S465000, C101S466000, C523S160000, C524S555000, C106S031130, C347S100000, C347S105000
Reexamination Certificate
active
06555205
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printing plate, a method of making a printing plate, and a method of printing using a printing plate to form a desired image on a medium. More particularly, the printing plate of this invention employs a substrate and a fluid composition comprising a cationic polymer and an anionic polymer, in which the ionic polymers interact and adhere to the substrate. The fluid composition is applied by ink jetting to the 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 a 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 non-image hydrophilic areas, but will contract into tiny droplets on the oleophilic 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 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 droplets of ink-jetted fluid that forms the oleophilic ink-accepting regions on the printing plate substrate. Such droplet “dot spreading” causes lower resolution of printed images 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 on the substrate 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.
U.S. Pat. No. 5,942,335 discloses the use of a polymer containing a nitrogen-containing heterocyclic group, namely a polymer of 4-vinyl pyridine, in the formulation of an ink receiving layer of an ink jet recording sheet. However, the use of such a compound in a fluid composition applied directly to a printing plate substrate to form an imaged, ink-receptive layer 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 a cationic product polymer and an anionic product polymer, in non-aqueous solvent. The ionic product polymers interact and adhere to the substrate, so that after drying, a durable printing plate is formed without chemical development.
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 below. In a preferred embodiment, the substrate is pretreated with a surfactant to provide a printing plate precursor.
In preferred embodiments, the cationic product polymer is prepared from a basic polymeric compound which is selected from the group consisting of polymers and copolymers of 2-vinylpyridine, polymers and copolymers of 4-vinylpyridine, polymers and copolymers of dimethylaminoethyl methacrylate, and mixtures or derivatives thereof. The basic polymeric compounds prepared from these monomers are made cationic by at least partially neutralizing with an acid, preferably formic acid, to create cationic conjugate acid groups from the base groups of the basic polymeric compounds.
In preferred embodiments, the anionic product polymer is prepared from an acidic polymeric compound which is selected from the group consisting of poly(acrylic acid)s, poly(methacrylic acid)s, poly(maleic acid)s, poly(maleic anhydride)s, poly(fumaric acid)s, poly(styrene-co-acrylic acid)s, poly(styrene-co-maleic acid)s, poly(styrene-co-fumaric acid)s, and mixtures or derivatives thereof. These acidic polymeric compounds are made anionic by at least partially neutralizing with base, preferably ammonia, to create anionic conjugate base groups from the acid groups of the acidic polymeric compounds.
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 with lithographic plates 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. Further, high cohesive strength of the oleophilic material helps to bind it to itself on the substrate, thus improving its adhesion. Cohesive strength of the oleophilic material is enhanced by providing a means for chemical interaction between the molecules of the oleophilic material, preferably by crosslinking.
The second way that adhesion of the oleophilic material may be controlled is by providing a substrate in which microscopic topology 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. Optionally, by pretreating the substrate sur
Aurenty Patrice M.
Grant Alexander
Lindsey Mark J.
Stone Edward
Faegre & Benson LLP
Jackson Monique R.
Kodak Polychrome Graphics LLC
Thibodeau Paul
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