WO2003101753A2

WO2003101753A2 - Inkjet imaging on an offset printing master

Info

Publication number: WO2003101753A2
Application number: PCT/IL2003/000451
Authority: WO
Inventors: Aharon Korem; Boaz Nitzan
Original assignee: Aprion Digital Ltd
Current assignee: Aprion Digital Ltd
Priority date: 2002-05-30
Filing date: 2003-05-29
Publication date: 2003-12-11
Anticipated expiration: 2004-11-30
Also published as: AU2003228089A1; WO2003101753A3; AU2003228089A8

Abstract

A composition for an erasing liquid able to erase a layer of conditioned jettable marking fluid from an inked imaged offset printing master to enable reuse of the offset printing master is provided. The composition comprises water, a water-soluble co-solvent, a base and a water-soluble coalescing reagent. The pH of the composition may be abov

Description

INKJET IMAGING ON AN OFFSET PRINTING MASTER

BACKGROUND OF THE INVENTION

[0001] Offset lithographic printing has been a popular method of printing for many years. The conventional method for offset printing master preparation, which involves a masking film exposed to ultraviolet light, has many drawbacks. Recently, direct imaging methods such as ink-jet recording have been used to produce the offset printing master. Ink jet recording may produce an offset printing master by placing a marking fluid on a printing plate or a printing cylinder in accordance with a predefined pattern. Direct imaging may enable relatively automated production of offset printing masters, off-press as well as on-press.

[0002] Direct imaging methods of offset printing masters are especially popular for short run printing applications, where a relatively small number of impressions is produced from the same printing master. The set-up time between printing job should be kept as short as possible in order to be cost effective. However, the operations of preparing a new blank printing plate and manual mounting of the new plate are relatively time consuming. [0003] Alternatively, a direct-to-press imaging system may be used. US Patent 5,129,321 to Fander discloses such a system including a scraper and counter-magnet for removing the whole lithographic master printing structure including its hydrophilic coating layer and the oleophilic image material from the master-image carrying cylinder. The scraping, however, damages the surface of the cylinder and shortens its life.

[0004] Reusable offset printing masters (plates) significantly reduce printing costs. There is, therefore, a need in the industry to provide an effective way of erasing the surface of an imaged offset printing master and making it ready to accept a new image.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT

INVENTION

[0005] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

[0006] Some embodiments of the present invention are directed to various compositions of a water-based erasing fluid able to erase ink-jet marking fluid from a used offset printing plate. According to some embodiments of the present invention, the erasing fluid composition comprises water as the main carrier, a water-soluble co-solvent, a water- soluble resin-coalescing reagent, and an inorganic or an organic base to provide an alkaline aqueous solution.

[0007] An imaging marking fluid (ink) is jetted from a direct imaging computer-to-press inkjet system to form an image on an offset printing master. Alternatively, the imaging marking fluid may be jetted from an off-press direct imaging computer-to-cylinder inkjet system. The cylinder may carry a replaceable substrate, either as a sleeve or as a sheet (plate) that may be replaced after printing a large number of impressions. When the imaging operation is performed off-press, the imaged cylinder or replaceable substrate is moved to an offset printing system for printing.

[0008] The printing cylinder or the replaceable substrate may comprise a hydrophilic surface, which may receive water in the printing process. Non-limiting examples of suitable surfaces include plastics, reinforced plastics, metals such as aluminum and copper, ceramics and stones, such as, for example, granite. Another suitable example is a ceramic layer, such as that manufactured by Almag of Jerusalem, Israel or Keronite, of Cambridge UK, which may be applied to a metal alloy to produce a hard ceramic layer of approximately 500 - 2500 HV (Nickers). Alternatively, the printing cylinder may carry a replaceable substrate. [0009] According to some embodiments of the present invention, the inkjet-marking fluid may be deposited in a pattern that is digitally determined to provide the information directly from a computer to the hydrophilic surface. The inkjet marking fluid may be a two-phase emulsion system having an oleophilic inner phase and a continuous, aqueous, external phase. Following the conditioning of the imaging marking fluid, the image formed on the surface becomes oleophilic. Non-limiting examples of such an inkjet marking fluid are described in International Patent Application PCT/IL00/00722, published as WO 01/34394.

[0010] A significant improvement in the resolution of the image formed by the marking fluid may be obtained by coating the surface of the printing cylinder before imaging with a pre-imaging solution. A non-limiting example of the pre-imaging coating solution may be a cationic surfactant solution as described in U.S. patent application S/N 09/822,500 (Publication No. US 2002/0139270). Another non-limiting example of the coating solution may be an aqueous and/or alcoholic solution or emulsion comprising a polyvalent metal salt and at least one of an organic swelling reagent and/or a coalescence reagent as described in U.S. patent application S/N 10/045,150 (Publication No. US 2002/0192381).

[0011] After the required number of impressions is printed during the printing process, the inked-up image may be cleaned using a conventional ink-cleaning unit. Then, according to some embodiments of the present invention, a water-based erasing solution may remove the image formed by the imaging marking fluid such that the erasable printing cylinder is ready to accept a new image. According to some embodiments of the present invention, the erasing solution may also remove the coating formed by the pre- imaging coating solution.

[0012] The operation of erasing the printed image may be performed on-press, or, alternatively, the printing cylinder may be moved to the direct imaging computer-to- cylinder inkjet system for erasing the used image and placing a new image. Alternatively, the printing cylinder may be moved to a separate erasing station for erasing the used image, and only then the erased cylinder may be moved to the inkjet imaging system to prepare the printing cylinder for reuse.

[0013] According to some embodiments of the present invention, two or more of the operations of printing, erasing and imaging may be performed generally concurrently using two or more interchangeable printing cylinders that are transported between two or more stations of a printing and imaging system.

[0014] According to some embodiments of the present invention, the water-based erasing solution to erase a water-based imaging marking fluid may be a basic (alkaline) aqueous solution comprising water, a water-soluble co-solvent, an organic or inorganic base to provide the requited pH and a water-soluble coalescing reagent to swell a polymer. The water-soluble co-solvent may act to decrease the surface tension of the erasing liquid and may enable the phase transfer of the dissolved polymer of the conditioned imaging marking fluid by lowering the polarity of the erasing liquid. The coalescing reagent may swell the polymer within the printed image and may enable the alkaline solution to dissolve the polymer.

[0015] According to some embodiments of the present invention, the erasing liquid is a basic (alkaline) aqueous solution having a pH above 1 1. According to other embodiments of the present invention, the erasing liquid is a basic (alkaline) aqueous solution having a pH above 12.

[0016] The relative amounts of the components of the erasing fluid may vary. For example, the relative amount of the co-solvent may vary between 5% weight percentage and 20% weight percentage, the relative amount of base may be 0.1 wt% - 10 wt%, and the relative amount of the coalescing reagent may be 2 wt% - 10 wt%.

[0017] According to some embodiments of the present invention, non-limiting examples of an organic base suitable for the erasing liquid may be aliphatic amines, such as, for example, methylamine, di-methylamine, tri-methylamine, ethylamine, di-ethylamine and tri-ethanolamine. According to some embodiments of the present invention, non-limiting examples of an inorganic base suitable for the erasing liquid may be sodium hydroxide, sodium bi carbonate and potassium hydroxide among others.

[0018] According to some embodiments of the present invention, non-limiting examples of a water-soluble co-solvent suitable for the erasing liquid may be an alcohol, such as, for example, propanol, isopropanol, butanol, isobutanol and hexanol.

[0019] According to some embodiments of the present invention, non-limiting examples of a water-soluble coalescing (swelling) reagent suitable for the erasing liquid may be di- ethylene glycol methyl ether, tri-propylene glycol mono-methyl ether, di-propylene glycol mono-methyl ether (DPM), 2-methyl-2-amino propanol (AMP), 2-methyl-2-amino -1,3- propanol and N-methyl pirrolidone.

[0020] The erasing solution may further comprise water-soluble surfactants to decrease the surface tension of the erasing solution. Non limiting soluble surfactants suitable for the erasing liquid may be surfactants BYK 348 and BYK 346 sold by BYK Chemie,

Wesel, Germany, Silwett L77 sold by Crompton OSi Specialties, Connecticut, USA, Tego

250 and Tego 260 sold by Tego Chemie, Essen, Germany, and sodium dodecyl sulfate

(SDS).

[0021] It should be noted that the above materials are commonly used in the industry and are relatively environmentally friendly. Non-limiting examples of some erasing fluid formulations are described herein below. The following examples of erasing solutions are now given, though by way of illustration only, to show certain aspects of some formulations according to some embodiments of the presen invention without limiting its scope.

EXAMPLES

[0022] In the following examples of erasing solutions for erasing an offset image on a printing cylinder after printing the required numbers of impressions, component designations are in weight percentages. It is noted that the following examples do not limit in any way the scope of the present invention.

[0023] Example 1

[0025] Example 3

[0027] A commercially available uncoated, post-anodized, brushed and electrochemically grained aluminum plate was first coated by immersing it into a coating solution comprising 0.1% of undecylamine sold by Aldrich , 4.9% of propylene glycol, 95% of de- ionized water and phosphoric acid which was added to provide a pH in a range between 2 to 3. The coated layer was dried at 70°C. [0028] The plate was then placed on an imaging station and imaged using a marking fluid having a viscosity of 7.8 centipoises, as described in PCT/IL00/00722 , at 600 dots per intch (dpi) resolution, using an inkjet print head manufactured by Scitex Vision Ltd, Netanya, Israel. The marking fluid used comprised 7 parts acrylic polymer emulsion sold under the trade mark Joncryl 538 by S.C. Johnson, 12 parts ethylene glycol, 1 part di- propylene glycol-monomethyl ether (DPM), 1 part black pigment sold under the trade mark Hostafme Black TS by Clariant, (or magenta Dye sold under the trade mark Byscript Magenta by BAYER) and 12 parts de-ionized water. After imaging, the plate was dried at 120°C for 1 min to create a hard image.

[0029] The same process was performed using a ceramic plate surface comprising metal alloy manufactured by Almag Company of Jerusalem, Israel or by Keronite of Cambridge, UK as the blanlc printing surface. The plates were dampened and inked using an offset ink. The offset ink was then cleaned with an offset-ink cleaner.

[0030] The imaged plates were then brushed using a soft fur brush soaked with the erasing solutions of examples 1 - 4 for approximately 15-30 seconds. The images were erased and the printing surfaces were ready for reuse.

[0031] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

[0032] What is claimed is:

1. An erasing liquid comprising: water; a water-soluble co-solvent; water-soluble base; and a water-soluble coalescing reagent, wherein said liquid has a pH above 11 and is able to erase a layer of conditioned water-based jettable marking fluid from an imaged offset printing master to enable reuse of said offset printing master.

2. The erasing liquid of claim 1, wherein said liquid is further able to erase a pre- imaging coating layer.

3. The erasing liquid of claim 1, wherein said liquid further comprises a water- soluble surfactant.

4. The erasing liquid of claim 1, wherein said base is an organic base.

5. The erasing liquid of claim 1, wherein said base is an aliphatic amine.

6. The erasing liquid of claim 5, wherein said aliphatic amine is at least one of a group consisting of methylamine, di-methylamine, tri-methylamine, ethylamine, di-ethylamine and tri-ethanolamine.

7. The erasing liquid of claim 1, wherein said base is an inorganic base.

8. The erasing liquid of claim 7, wherein said inorganic base is at least one of a group consisting of sodium hydroxide, potassium hydroxide and sodium bicarbonate.

9. The composition of claim 1, wherein the concentration of said base is 0.01 - 10 % by weight.

10. The erasing liquid of claim 1, wherein said water-soluble co-solvent is one of a group consisting of: propanol, isopropanol, butanol, isobutanol and hexanol.

11. The composition of claim 1 , wherein the concentration of said water-soluble co- solvent is 5 - 20 % by weight.

12. The composition of claim 1 , wherein the concentration of said water-soluble coalescing reagent is 2 - 8 % by weight.

13. The erasing liquid of claim 1, wherein said water-soluble coalescing reagent is diethylene glycol methyl ether.

14. The erasing liquid of claim 1, wherein said water-soluble coalescing reagent is tripopylene glycol monomethyl ether.

15. The erasing liquid of claim 1, wherein said water-soluble coalescing reagent is tripopylene glycol monomethyl ether.

16. The erasing liquid of claim 1, wherein said water-soluble coalescing reagent is 2- methyl-2-amino propanol.

17. The erasing liquid of claim 1, wherein said water-soluble coalescing reagent is 2- methyl-2-amino- 1 ,3- propanol.

18. The erasing liquid of claim 1, wherein said water-soluble coalescing reagent is N- methyl pirrolidone.

19. A method comprising : erasing a layer of conditioned water-based jettable marking fluid from an imaged offset printing master to enable reuse of said offset printing master with an erasing liquid comprising water, a wate- soluble co-solvent, water-soluble base and a water-soluble coalescing reagent.