Printing – Planographic – Lithographic plate making – and processes of making or using...
Reexamination Certificate
2001-10-25
2004-02-17
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic plate making, and processes of making or using...
C347S096000
Reexamination Certificate
active
06691618
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for imaging a lithographic printing plate and more particularly to a process using an ink jet printer to imagewise apply an insolubilizing chemical to a plate coating which comprises photosensitive compounds or their reaction products.
In the art of lithographic printing it is generally required that one or more lithographic printing plates be mounted on a printing press. The lithographic printing plate is characterized by having on its printing surface oleophilic ink receiving areas in the form of the image to be printed, and hydrophilic water receiving areas corresponding to the other, non-printing areas of the surface. Because of the immiscibility of oil-based lithographic inks and water, on a well-prepared printing plate, ink will fully coat the oleophilic areas of the plate printing surface and not contaminate the hydrophilic areas. The operating press brings the inked plate surface into intimate contact with an impression cylinder or elastic transfer blanket that transfers the ink image to the media to be printed.
Traditionally, a lithographic plate is photographically imaged. The plate substrate is most commonly aluminum, from 5 to 12 mils thick, treated so that the printing surface is hydrophilic, although treated or untreated plastic or paper substrates can also be used. The substrate is coated with a solution of a photosensitive composition that is generally oleophilic. Upon drying, the coating layer thickness is commonly about 1 to 3 microns thick. A printing plate with such a photosensitive coating is called “presensitized” (PS). Both negative and positive working photosensitive compositions are used in PS lithographic plates. In a negative plate, light exposure insolubilizes the coating, so that on development the only parts of the coating that aren't removed are the light imaged areas. The reverse is the case in a positive plate. Light exposure solubilizes the coating; on development the coating is only removed in the areas that are light imaged. In an image reversal process, a positive plate is “blanket exposed” or “flood exposed”, i.e., the entire plate is light exposed without any intervening mask or other means for imaging, and imaged in a separate step which can be performed before or after the blanket exposure step. By this image reversal process, a positive plate can be negatively imaged. The aluminum substrate can be treated to make it hydrophilic either prior to the application of the photosensitive composition or at the time the non-image areas of the coating are removed in a development step. Such a process in which a pre-coated lithographic plate is prepared for press by removing exclusively either the imaged or non-imaged coating in a development step is called a subtractive process; a pre-coated plate having a coating which is at least partially removed in a development step is known as a subtractive plate.
Photosensitive compositions used in positive lithographic plates are well known. They. are comprised primarily of alkali soluble resins and o-quione diazide sulfonic acid esters or amides. In addition dyes or colored pigments, indicator dyes, plasticizers and surfactants can also be present. The ingredients are typically dissolved in organic solvents and are coated onto the substrate. Upon drying a thin film or coating is produced.
Alkali soluble resins useful in positive plates are well known and include phenol-formaldehyde resins, cresol-formaldehyde resins, styrene-maleic anhydride copolymers, alkyl vinyl ether-maleic anhydride copolymers, co-or ter-polymers that contain either acrylic or methacrylic acids and poly(vinyl phenol). U.S. Pat. No. 4,642,282 describes an alkali soluble polycondensation product that is also useful as the resin component in positive plates.
The o-quinone diazide compounds include o-benzoquinone diazides, o-naphthoquinone diazides and o-anthraquinone diazides. O-quinone diazide compounds useful in positive plates are well known and are described in detail in
Light Sensitive Systems
by J. Kosar, p.339-352. They are further described in U.S. Pat. Nos. 3,046,118; 3,046,119; 3,046,120; 3,046,121; 3,046,122; 3,046,123; 3,148,983; 3,181,461; 3,211,553; 3,635,709; 3,711,285 and 4,639,406 incorporated in entirety herein by reference.
Such positive plates are sensitive to light in the wavelength range of from about 290 to 500 nm. When used in the standard manner, photo-exposure causes the alkali insoluble o-quinone diazide of the positive plate to be converted into an alkali soluble carboxylic acid. Upon subsequent treatment with a developer, which is a dilute aqueous alkaline solution, the exposed parts of the coating are removed. The unexposed coating is alkali insoluble, because the o-quinone diazide is unaffected by the developer, and remains on the substrate.
Traditionally, lithographic plates are imaged by photographic transfer from original artwork. This process is labor-intensive and costly. Hence with the advent of the computer engendering a revolution in the graphics design process preparatory to printing, there have been extensive efforts to pattern printing plates, in particular lithographic printing plates, directly using a computer-controlled apparatus called a platesetter that is supplied with digital data corresponding to the image to be printed. A platesetter has the capability to supply an image forming agent, typically light energy or one or more chemicals, to a plate according to various patterns or images as defined by digital data, i.e., to imagewise apply an image forming agent. Specially manufactured lithographic plates may be required for certain types of platesetters. Such a combination of a computer-controlled platesetter and the proprietary plates used with them along with developer solutions and any other materials or apparatuses necessary to prepare the plates for printing is known as a computer-to-plate (CTP) system.
Heretofore, many of the new CTP systems have been large, complex, and expensive. They are designed for use by large printing companies as a means to streamline the prepress process of their printing operations and to take advantage of the rapid exchange and response to the digital information of graphic designs provided by their customers. Many of the new CTP systems use light sources, typically lasers, to directly image PS plates. But using lasers to image plates is very expensive, because the per-unit cost of the lasers is high and because they require sophisticated focusing optics and electronic controls. If because of the cost only a single laser is used, then time becomes a constraint because of the necessity of raster scanning. There remains a strong need for an economical and efficient CTP system for the many smaller printers who utilize lithographic printing.
In recent years, ink jet printers have replaced laser printers as the most popular hard copy output printers for computers. Ink jet printers have several competitive advantages over laser printers. One advantage is that it is possible to manufacture an array of 10's or even 100's of ink jet nozzles spaced very closely together in a single inexpensive print head. This nozzle array manufacturing capability enables fast printing ink jet devices to be manufactured at a much lower cost than laser printers requiring arrays of lasers. And the precision with which such a nozzle array can be manufactured and the jetting reliability of the incorporated nozzles means that these arrays can be used to print high quality images comparable to photo or laser imaging techniques. Ink jet printers also are increasingly being used for prepress proofing and other graphic arts applications requiring very high quality hard copy output.
In spite of the large and rapidly growing installed base of ink jet printers for hard copy output, ink jet printing technology is not commonly used in CTP systems. There are many challenging technical requirements facing the practitioner who would design such an ink jet based CTP system as can be seen in the prior art. A first requ
David Lawrence D.
Deutsch Albert S.
West David B.
Funk Stephen R.
Hayes & Soloway P.C.
Pisces-Print Imaging Sciences, Inc.
LandOfFree
Chemical imaging of a lithographic printing plate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chemical imaging of a lithographic printing plate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chemical imaging of a lithographic printing plate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3314446