Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-07-05
2004-05-04
Huff, Mark F. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S272100, C430S284100, C430S286100, C430S302000, C430S309000, C430S434000, C430S435000, C430S494000, C101S453000, C101S463100
Reexamination Certificate
active
06730457
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to imageable elements useful in lithographic printing. More particularly, this invention relates to thermally imageable elements useful as waterless lithographic printing plate precursors.
BACKGROUND OF THE INVENTION
Waterless or driographic lithographic printing, also known as dry planography, provides several advantages over conventional offset printing. Waterless lithographic printing is particularly advantageous for short run and on-press applications. It simplifies press design by eliminating the fountain solution and aqueous delivery train. Careful ink/water balance is unnecessary, thus reducing rollup time and material waste.
A waterless lithographic printing plate precursor comprises a layer of ink-repellent material over a support. During or after imaging, the ink-repellent layer is removed in the imaged regions to form an image. When the image is mounted on a press and used as a waterless lithographic printing plate, the regions in which the ink-repellent layer has been removed accept ink, which is then transferred to a suitable receiver, such as paper.
Preparation of a waterless printing plate involves the imagewise removal of the ink-repellent layer to reveal an underlying ink-accepting surface. Direct digital imaging, which obviates the need for exposure through a mask, is becoming increasingly important in the printing industry. For example, Huang, U.S. Pat. No. 5,919,600, incorporated herein by reference, discloses thermally imageable elements that comprise a substrate; a thermal imaging layer comprising a photothermal conversion material and a thermoplastic polyurethane with pendent allyl groups; and a crosslinked silicone polymer top layer. The thermal imaging layer has enhanced solubility in certain solvents when exposed to infrared radiation, but exhibits excellent adhesion to the silicone in unexposed regions so that the imaged regions can be removed with a suitable developer and the unexposed regions remain.
Despite the improvements made in thermally imageable waterless printing plate precursors, there continues to be a need for precursors with wide developer latitude and precursors that produce waterless printing plates that can be used with aggressive inks, such as ultraviolet and electron beam curable inks.
SUMMARY OF THE INVENTION
In one aspect, the invention is an imageable element useful as a waterless lithographic printing plate precursor. The element comprises, in order:
a substrate;
an underlayer; and
an ink-repellent layer;
in which:
the underlayer comprises a crosslinked allyl functional polyurethane;
the element comprises a photothermal conversion material;
the photothermal conversion material is either in the underlayer or in an absorber layer between the underlayer and the ink-repellent layer; and
the ink-repellent layer comprises an ink-repellent polymer.
In another aspect, the invention is a method for forming an image useful as a waterless lithographic printing plate by imaging and developing the imageable element of the invention. In yet another aspect, the invention is an image useful as a waterless lithographic printing plate formed by imaging and developing the imageable element of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Imageable Elements
The imageable element comprises, in order, a substrate, an underlayer, and an ink-repellent layer. A photothermal conversion material is present in the element, either in the underlayer or in a separate absorber layer between the underlayer and the ink-repellent layer. Other layers that are conventional in imageable elements useful as waterless lithographic printing plate precursors may be present.
Substrate
The substrate comprises a support, which may be any material conventionally used to prepare lithographic printing plates. The support is preferably strong, stable and flexible. It should resist dimensional change under conditions of use so that color records will register in a full-color image. Typically, it can be any self-supporting material, such as aluminum, zinc, titanium, and alloys thereof; paper; paper coated on one or both sides with an &agr;-olefin polymer such as polyethylene; films such as cellulose acetate films, polyvinyl acetal films, polystyrene films, polypropylene films, polyester films such as polyethylene terephthalate films, polyamide films, polyimide films, nitrocellulose films, polycarbonate films, and polyvinylchloride films; composite films such as polyester, polypropylene or polystyrene films coated with polyethylene films; metalized papers or films; metal/paper laminates; and the like. The surface of plastic films may be treated using the surface treatment techniques known in the art to improve adhesion between the substrate and organic coatings.
The substrate may also comprise an antihalation compound or one or more sub coatings. Examples of subbing materials are adhesion-promoting materials, such as alkoxysilanes, aminopropyltriethoxysilane, glycidoxypropyltriethoxysilane and epoxy functional polymers, as well as conventional subbing materials used on polyester base in photographic films.
A preferred support is aluminum sheet. The surface of the aluminum may be treated by metal finishing techniques known in the art including brush roughening, electrochemical roughening, chemical roughening, anodizing, and silicate sealing and the like. If the surface is roughened, the average roughness Ra is preferably in the range from 0.1 to 0.8 &mgr;m, and more preferably in the range from 0.1 to 0.4 &mgr;m. The preferred thickness of the aluminum sheet is in the range from about 0.005 inch to about 0.020 inch.
The substrate may comprise a primer layer to, for example, prevent heat loss, especially when the support is a metal sheet, regulate ink receptivity, serve as a dye acceptor, if the developed plate needs to be dyed for visual image contrast enhancement, and/or to act as an adhesion promoter. The primer layer may be a thermoplastic coating, provided the coating is not soluble in the solvents used to coat the underlayer. Examples of thermoset coatings include polyester-melamine coatings, acrylic melamine coatings, epoxy coatings, and polyisocyanate coatings. An example of a thermoplastic coating is polyvinyl alcohol. When cured by ultraviolet radiation, the primer layer may be prepared from free radical polymerizable coatings, cationic crosslinkable coatings catalyzed by a photogenerated acid, or a diazo resin with suitable binders.
The back side of the substrate (i.e., the side opposite the underlayer) may be coated with an antistatic agent and/or a slipping layer or matte layer to improve handling and “feel” of the imageable element.
Underlayer
The underlayer is between the support and the ink-repellent layer. The underlayer comprises a crosslinked allyl functional polyurethane. Other ingredients that are conventional ingredients of these layers may also be present.
“Allyl functional polyurethane” refers to a thermoplastic polyurethane containing allyl groups, which may be either pendent or terminal allyl groups. The allyl functional polyurethane, before crosslinking, preferably has a glass transition temperature (T
g
) of about 25° C. to about 130° C., more preferably about 30° C. to about 125° C., most preferably about 50° C. to about 125° C.
The allyl functional polyurethane may be prepared by reaction of a diisocyanate with an excess of an allyl functional diol to produce a solution of a thermoplastic polyurethane, followed by further reaction with a crosslinker, which reacts with the excess hydroxyl groups. The crosslinker is preferably added to the thermoplastic polyurethane solution less than about 30 minutes, preferably less than about 10 minutes, before the solution is applied to the substrate so that crosslinking does not interfere with application of the solution to the substrate. Alternatively, the allyl functional polyurethane may be prepared by reacting a diisocyanate with a carboxyl functional diol, such as dimethylol propionic acid. The carboxyl groups of the resulting polyurethane are then converted
Huang Jianbing
Pappas S. Peter
Saraiya Shashikant
Zhong Xing Fu
Gilliam Barbara
Huff Mark F.
Kodak Polychrome Graphics LLC
RatnerPrestia
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