Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N1/00—Printing plates or foils; Materials therefor
  • B41N1/04—Printing plates or foils; Materials therefor metallic
  • B41N1/08—Printing plates or foils; Materials therefor metallic for lithographic printing
  • B41N1/086—Printing plates or foils; Materials therefor metallic for lithographic printing laminated on a paper or plastic base
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
  • B41C2201/06—Backcoats; Back layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M1/00—Inking and printing with a printer's forme
  • B41M1/06—Lithographic printing

Definitions

• the present invention relates to a method for making a lithographic printing plate comprising a flexible support and laminated thereto a dimensionally stable base.
• Lithographic printing is the process of printing from specially prepared surfaces, some areas of which are capable of accepting ink (oleophilic areas) whereas other areas will not accept ink (oleophobic areas).
• the oleophilic areas form the printing areas while the oleophobic areas form the background areas.
• lithographic printing plates Two basic types of lithographic printing plates are known. According to a first type, so called wet printing plates, both water or an aqueous dampening liquid and ink are applied to the plate surface that contains hydrophilic and hydrophobic areas. The hydrophilic areas will be soaked with water or the dampening liquid and are thereby rendered oleophobic while the hydrophobic areas will accept the ink.
• a second type of lithographic printing plates operate without the use of a dampening liquid and are called driographic printing plates. This type of printing plates comprise highly ink repellent areas and oleophilic areas. Generally the highly ink repellent areas are formed by a silicone layer.
• Lithographic printing plates can be prepared using a photosensitive lithographic printing plate precursor, also called imaging element.
• imaging element is exposed to electromagnetic radiation or heat in accordance with the image data and is generally developed thereafter so that a differentiation results in ink accepting properties between the exposed and unexposed areas.
• photosensitive lithographic printing plate precursors are for example: the silver salt diffusion transfer (hereinafter DTR) materials disclosed in EP-A-410500, EP-A-483415 and EP-A-423399; imaging elements having a photosensitive layer containing diazonium salts or a diazo resin as described in e.g. EP-A-450199; imaging elements having a photosensitive layer containing a photopolymerizable composition as described in e.g. EP-A-502562, EP-A-491457, EP-A-503602, EP-A-471483 or DE-A-4102173.
• DTR silver salt diffusion transfer
• a lithographic printing plate may be prepared from a heat mode recording material as a lithographic printing plate precursor.
• a heat pattern in accordance with image data and optional development the surface of such heat mode recording material may be differentiated in ink accepting and ink repellent areas.
• the heat pattern may be caused by a direct heating source such as a thermal head but may also be caused by a light source as e.g. a laser.
• the heat mode recording material will include a substance capable of converting the light into heat.
• Heat mode recording materials that can be used for making a lithographic printing plate precursor are described in e.g. EP-A-573091, DE-A-2512038, FR-A-1.473.751, Research Disclosure 19201 of April 1980 or Research Disclosure 33303 of January 1992.
• European patent application No. 97 20 1336 filed on 3 May 1997 discloses a printing plate that is laminated to a dimensionally stable base via an adhesive intermediate layer.
• a disadvantage is that a lamination under heat or under pressure is required for every new printing plate.
• re-use of the dimensionally stable base is fairly simple, there is still room for improvement.
• laminate stands for a sandwich of two or more layers adhering to each other; each layer can be a separate sheet or plate, or a continuous web.
• a lithographic printing plate obtained according to the claimed method combines the advantages of a printing plate having a flexible support without showing its disadvantages.
• An embodiment according to the present invention comprises an imaging element on a flexible support, laminated, with its side opposite to the side carrying the lithographic surface, to a dimensionally stable assembly.
• the flexible support has a low modulus of elasticity (e.g. 4 GPa, the modulus of polyethylene terephthalate), while the dimensionally stable assembly has a high modulus of elasticity (e.g. 210 GPa, the modulus of steel).
• the flexible support has a high friction coefficient with respect to the dimensionally stable assembly.
• Such a laminate behaves like a printing plate on a non-flexible support, such as an aluminium printing plate, without having the cost of such a printing plate.
• the dimensionally stable assembly comprises a dimensionally stable base.
• the dimensionally stable assembly comprises a dimensionally stable base and an intermediate layer, having a high friction coefficient with respect to the imaging element. Both embodiments will be discussed more in detail hereinafter.
• both the dimensionally stable assembly and the imaging element are separate sheets or plates.
• the dimensionally stable assembly is a separate plate and the imaging element is a continuous web.
• the dimensionally stable base is a separate plate, while the intermediate layer and the imaging element both are continuous webs.
• the dimensionally stable base is a separate plate, the intermediate layer is a continuous web and the imaging element is a separate sheet or plate.
• the dimensionally stable base is a continuous web.
• An imaging element according to the invention comprises a flexible support.
• Flexible supports suitable for use in accordance with the present invention may be opaque or transparent, e.g. a paper support, a plastic film, an aluminium foil.
• a paper support preference is given to one coated at one or both sides with an alpha-olefin polymer.
• a plastic film is used, e.g. a poly(ethylene terephthalate) film or a poly-alpha-olefin film.
• the thickness of such plastic film is preferably comprised between 0.07 and 0.35 mm.
• an aluminium foil is used, its thickness is preferably between 0.05 and 0.1 mm.
• the present invention may be used with any type of lithographic printing plate (precursor), also called an imaging element, having a flexible support and capable of laser image recording.
• lithographic printing plate also called an imaging element
• Examples are the printing plate precursors mentioned in the introduction.
• the present invention is however especially suitable for use with a lithographic printing plate precursor that is processed according to the DTR-process to obtain a lithographic printing plate.
• the present invention is also especially suitable for use with a driographic printing plate precursor.
• the present invention is also especially suitable for a heat mode recording material, particularly for a heat mode recording material comprising on a support, having an oleophilic surface, (i) a recording layer containing a light-to-heat converting substance capable of converting radiation into heat and (ii) a cured oleophobic surface layer and wherein said oleophobic surface layer and recording layer may be the same layer.
• Said printing plates are exposed, preferably by using a laser or a light emitting diode.
• the light source used is depending on the spectral sensitivity of the imaging element.
• Argon lasers, helium-neon lasers, semiconductor lasers, e.g. Nd-YAG or laser diodes can be used.
• Said imaging elements are preferably exposed in an apparatus including means for a scanning exposure such as an imagesetter, in particular one of the internal drum type.
• Such files may be generated by a raster image processor (RIP) or other suitable means.
• a RIP can accept input data in page-description language, which defines all the features required to be transferred onto the imaging element, or as a combination of page-description language and one or more image data files. From the commands formulated according to the page description language and from the image datafiles, at least one bitmap is constructed. Since image data are defined in terms of continuous tone (contone) levels, and a printing plate is a binary device, i.e. either ink or no ink can be accepted and transferred to the reproduction, a conversion from a contone image to a binary image is required. This conversion is referred to as halftoning.
• halftone dots are laid out on a periodic grid, defined by a screen angle and a screen ruling (see e.g. EP-A-0 748 109).
• the size or area of the halftone dots is in accordance with the corresponding optical density of the contone image.
• frequency modulation halftoning the number of halftone dots per unit area rather than their size is modified according to the corresponding optical density of the contone image (see e.g. EP-A-0 639 023).
• the bitmap is thus a binary representation of the image, i.e.
• the laser beam is directed along the axis of the drum and is deflected at right angles onto the imaging element by means of an optical system, preferably an optical prism, that rotates around the drum axis.
• the beam source is moved along the drum axis, thereby scanning the imaging element circumferentially, so that the image "grows" in the axial direction.
• the required relative motion between the laser beam and the imaging element is achieved by rotating the drum (and the imaging element mounted thereon) about its axis, and moving the beam source parallel to the drum axis.
• the beam source can move parallel to the drum axis and, after each pass across the imaging element, the laser beam is rotated at a small angle, either by rotating an optical system or by rotating the drum, so that the image on the imaging element "grows" line by line circumferentially.
• the beam is drawn across either axis of the imaging element, and is indexed along the other axis after each pass.
• the requisite relative motion between the beam and the imaging element may be produced by movement of the imaging element rather than (or in addition to) movement of the beam.
• the scan-wise exposed imaging material requires in most cases a development step in order to yield a lithographic printing plate.
• said development step proceeds by rubbing the exposed imaging element with e.g. a cotton pad and is then completely dry. So, there is a method for making a lithographic printing plate requiring no dampening liquid comprising the steps of:
• the development step requires the treatment of the exposed imaging element with an aqueous solution, particularly an aqueous alkaline solution.
• the development is preferably done in a developing means.
• the present invention is especially suitable for use with a lithographic printing plate precursor that is processed according to the DTR-process to obtain a lithographic printing plate.
• the precursor is scan-wise exposed e.g. by means of a laser or a LED, and is subsequently developed in an alkaline processing liquid in the presence of a developing agent and a silver halide solvent.
• the plate surface may then be neutralised with a neutralising agent.
• the image-receiving layer will bear a silver image that is capable of accepting greasy ink in a printing process using a dampening liquid.
• Suitable bases are for instance metal bases, preferably aluminium or stainless steel bases.
• a laminate according to the present invention - comprising an imaging element on a flexible support and a dimensionally stable assembly - behaves like a printing plate on a non-flexible support, such as an aluminium printing plate. This is now explained in detail.
• a laminate preferably meets the following requirements, in order to behave like a printing plate on a non-flexible support, such as an aluminium printing plate.
• a printing plate on a non-flexible support is referred to below as "an aluminium plate”.
• the friction coefficient ⁇ and the peel adhesion value P fulfil the relations (1) and (2) stated above, such that the imaging element is fixedly adhered to the dimensionally stable assembly during printing.
• "Fixedly adhered" means that the imaging element is not repositionable with respect to the dimensionally stable assembly. If the imaging element is repositionable with respect to the dimensionally stable assembly, instead of being fixedly adhered, temporary or permanent delamination of the laminate may occur. Preferably, delamination is avoided, especially in colour printing, since it may result in register errors.
• the dimensionally stable assembly comprises a dimensionally stable base.
• the imaging element is laminated with its side opposite to the lithographic surface to a side of the dimensionally stable base. Said side opposite to the lithographic surface, or said side of the dimensionally stable base, or both said sides are preferably roughened so that a high friction coefficient is obtained.
• a partly cured silicone layer as intermediate layer provides additional advantages. After printing, the imaging element is easily peeled off from the dimensionally stable assembly. The intermediate layer is then cleaned from dirt, printing ink, etc. The intermediate layer may have printing ink on its surface, if the size of the imaging element is smaller than the size of the dimensionally stable assembly (one - large - dimensionally stable assembly may be used for imaging elements having different sizes, i.e. smaller and larger sizes). After peeling off and cleaning, a new imaging element can be laminated to the dimensionally stable assembly, which is reused. A partly cured silicone layer is easily cleaned; cleaning it is easier than cleaning a cured (i.e. completely cured) silicone layer. A partly cured silicone layer is easily reused. A partly cured silicone layer moreover has a lower peel adhesion value P than a cured silicone layer, with respect to the imaging element.
• both the dimensionally stable assembly and the imaging element are a separate sheet or plate.
• the sheets or plates may have a width of 51 cm and a length of 40 cm (these are the dimensions of a plate for a Heidelberg GTO52 press).
• Lamination of the separate sheets or plates can be effected manually, by pressing the sheets or plates together, but preferably a laminating means called a laminator is used.
• a laminator preferably comprises a pair of rollers, having an adjustable pressure to each other and moving at a fixed or an adjustable speed. Lamination with a laminator is effected by bringing the two elements which have to be laminated in close contact with each other.
• the geometry of the laminated layers is the following: the dimensionally stable assembly is a separate plate and the imaging element is a continuous web.
• the printing press comprises means for providing a portion of the imaging element at the position of the dimensionally stable assembly, and means for forming a laminate of said portion and the dimensionally stable assembly. Said portion of the imaging element may cover the entire length of the dimensionally stable assembly, and it may cover the complete width or only part of the width of the dimensionally stable assembly.
• the imaging element is exposed on the press. Exposure of the imaging element may occur before or after the laminate is formed.
• US-A-5 355 795 discloses a printing press wherein the imaging element is a continuous web.
• the dimensionally stable base may be comprised in the printing cylinder of the press, or the dimensionally stable base may be a separate sheet or plate that has to be mounted on the printing cylinder.
• the printing press may comprise means for providing a portion of the intermediate layer at the position of the dimensionally stable base, e.g. an intermediate layer supply spool and an intermediate layer uptake spool.
• the intermediate layer has a high friction coefficient with respect to the imaging element. Operation may now be as follows. After printing, tension of the web-like imaging element is decreased, and tension of the web-like intermediate layer is decreased. Then, the imaging element supply roller provides a new portion of imaging element, and the intermediate layer supply roller provides a new portion of intermediate layer.
• the geometry of the laminated layers is the following: the dimensionally stable base is a separate plate, the intermediate layer is a continuous web and the imaging element is a separate sheet or plate.
• This embodiment is similar to the third embodiment described above, but now only the intermediate layer is supplied as a web, e.g. by a supply spool and an uptake spool.
• the imaging element is laminated to the intermediate layer and the dimensionally stable base, preferably by on-press lamination (on-press lamination is discussed above).
• the dimensionally stable base may be comprised in the printing cylinder of the press, or the dimensionally stable base may be a separate sheet or plate that has to be mounted on the printing cylinder.
• the dimensionally stable base may be mounted on the printing cylinder of the printing press in several ways, as known in the art.
• the dimensionally stable base may comprise register punch holes, required for mounting a lithographic printing plate on a printing press with register pins.
• the dimensionally stable base comprises several holes for attaching the dimensionally stable base onto a press pin bar.
• the dimensionally stable base comprises one or more bends for mounting it onto the printing cylinder.
• the laminate comprises an intermediate layer.
• the intermediate layer is adhered to the dimensionally stable base.
• the intermediate layer is adhered to the flexible support.
• the intermediate layer can be applied in several ways, some of which are explained already hereinbefore.
• the intermediate layer is adhered to the dimensionally stable base via a primer.
• the intermediate layer can also be applied by sputtering.

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• Printing Plates And Materials Therefor (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

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Citations (4)

• 1998
  • 1998-07-29 EP EP98202539A patent/EP0976573A1/fr not_active Withdrawn
• 1999
  • 1999-07-26 JP JP21057099A patent/JP2000043438A/ja active Pending

Patent Citations (4)

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