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
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/08—Damping; Neutralising or similar differentiation treatments for lithographic printing formes; Gumming or finishing solutions, fountain solutions, correction or deletion fluids, or on-press development

Definitions

• the invention relates to the dampening of printing plates. More specifically, it relates to an improved method for the preparation of a dampening water or fountain solution for moisturing lithographic printing plates, in particular presensitized lithographic printing plates (also known as "PS plates").
• PS plates presensitized lithographic printing plates
• Lithographic printing technique makes the best use of the fact, that water and oil are essentially incompatible with one another.
• the printing surface of a lithographic printing plate comprises areas which receive water and repel an oil ink and those which repel water and receive an oil ink, the former serving as non-image areas and the latter serving as image areas.
• the non-image areas become damp with dampening water used in lithographic printing to thus enhance the difference in surface chemical properties between the image areas and the non-image area and hence to increase both the ink repellency of the non-image areas and the ink receptivity of the image areas.
• the dampening water or fountain solution is generally a homogeneous mixture of organic solvents in water and in which various additives are dissolved such as acids, salts, naturally occurring polymeric materials, such as gum Arabic and/or a variety of synthetic polymers.
• IPA isopropyl alcohol
• IPA isopropyl alcohol
• U.S. 3,877,372 describes a dampening water composition that allows avoiding the use of IPA containing a mixture of ethylene glycol monobutyl ether and at least one of hexylene glycol and ethylene glycol.
• U.S. 4,278,467 discloses an IPA free dampening water composition containing at least one of n-hexoxydiethylene glycol, n-hexoxyethylene glycol, 2-ethyl-1,3-hexanediol, n-butoxyethylene glycol acetate, n-butoxydiethylene glycol acetate and 3-butoxy-2-propanol.
• EP0066176 discloses a dampening water composition containing 2-ethyl-1,3-hexanediol and at least one of completely water-soluble propylene glycol, ethylene glycol, dipropylene glycol, diethylene glycol, hexylene glycol, triethylene glycol, tetraethylene glycol, tripropane glycol and 1,5-pentanediol.
• the method for the preparation of the dampening water solution is by dissolving a dampening solution concentrate, often called a fountain etch, in water just before using it in the printing process.
• a dampening solution concentrate often called a fountain etch
• This method has as a disadvantage, that it is not very flexible because adjusting of the dampening water can only be done by increasing the amount of concentrate or water.
• the dampening concentrate tends to be unstable upon longer time storage due to the presence of significant amounts of organic solvents required for an efficient dampening, and an incorrect composition can be formed by selective evaporation of one or more of the solvents.
• a fountain etch (dampening solution concentrate) is mixed with a formula containing the ethylene glycol monobutyl ether and hexylene glycol or ethylene glycol to which finally a sufficient amount of water is added to make up the desired concentration.
• n-hexoxydiethylene glycol or n-hexoxyethylene glycol or 2-ethyl-1,3-hexanediol is mixed with a fountain etch (dampening solution concentrate) and the resulting solution was mixed with an appropriate amount of water.
• EP 0066176 does not make use of a dampening solution concentrate but rather mixes all ingredients such as gum Arabic, phosphoric acid solution, water, 2-ethyl-1,3-hexanediol and propylene glycol in one step together.
• An object, therefore, of the present invention is to provide a more easy and convenient method for making of a dampening water solution.
• a further object is to provide a more flexible method for preparing a dampening water solution.
• a further object is to prepare this dampening water solution with a reduced amount of IPA, and in which the composition of the dampening water solution can be adjusted accurately. It is a further object of this invention to have a sufficient control on the composition of the dampening water solution. It is also an objective to provide a method for making a homogeneous dampening water composition ready for use in the printing process.
• contents or amounts of the components for use in the dampening water composition described in this specification are expressed on the basis of the total weight of the dampening water composition when used in a printing process, unless otherwise specified. This is not be confused with contents or amount of components in dampening solution concentrates that prior to the actual use need to be properly diluted.
• organic solvents materials that are liquid under standard conditions and comprise carbon- and hydrogen atoms and optionally also comprise oxygen-, nitrogen- and/or sulphur atoms, and optionally also, although in this invention not preferred halogen atoms.
• a dampening solution concentrate is as such not ready for use, namely the concentrate will be dissolved in demineralised or tap water until the required concentration is obtained, subsequently the resulting solution is used in the lithographic printing process.
• the present inventors have found, that such an embodiment has serious drawbacks, because often the concentrate is unstable upon storage due to the presence of a high concentration of organic solvents in the concentrate, required for good dampening and because in this method there is only limited flexibility to adjust the composition of the dampening water solution when for example selective evaporation occurs by one or more solvents.
• the dampening solution concentrate only contains a limited amount of organic solvents or no organic solvents at all. This has the advantage, that the stability upon storage of the concentrate is increased considerably.
• this dampening solution concentrate is dissolved in water, generally demineralised water. The dissolving step is done just before printing. To this pre-dampening solution are then added the organic solvents.
• the preparation of the dampening water solution is done just before and/or during the printing process.
• the at least two organic solvents are pre-mixed before addition to the pre dampening solution, giving an organic solvent mixture. It is preferred that the at least two organic solvents have or the organic solvent mixture has a surface tension below 40 mN/m, preferably below 35 mN/m and even more preferably below 30 mN/m.
• the concentration of organic solvents in the dampening water solution is between 1 and 8 vol% and preferably between 2 and 6 vol%.
• the resulting homogeneous mixture has a lower density than the pre-dampening water solution and therefore the concentration of the IPA can be controlled by density measuring means, which upon deviations of the density automatically can be adjusted by increasing or decreasing the amount of IPA added to the pre-dampening solution.
• IPA is added to the dampening water solution to compensate for this evaporation.
• the amount to be added is determined by the difference between a preset value for the density and the measured density value by density measuring means.
• the density measuring means and density controlling means can be selected from those known to a person skilled in the art.
• the total amount of organic solvents could be reduced by 50% or more by using IPA and an organic solvent having a surface tension of less than 40 mN/m.
• the total amount of organic solvents could be reduced with 50% or more.
• one of said at least two organic solvents is iso-propyl alcohol.
• the IPA and one or more of the organic solvents mentioned above are added separately to the pre-dampening solution, where the amount of organic solvents used is between 1 and 8 vol% and preferably between 2 and 6 vol%.
• the density of the dampening water solutions formed can be controlled in the same way as done when IPA is used alone, meaning by density control.
• the amount of IPA used as a function of the total amount of used organic solvents is between 20 and 90 vol%. For ease of use, IPA amounts over 50 vol% are preferred. It was found, that one of the methods to determine the optimal amount of organic liquids used is the measurement of the surface tension.
• the surface tension of the resulting dampening water should be below 50 mN/m in order to have homogeneous and continuous moisturing of the dampening rollers and of the lithographic printing plate.
• Such a low surface tension will only be obtained upon the use of low surface tension organic solvents, some of which have been indicated above. These solvents are characterised by their surface tension being lower than 40 mN/m.
• Preferred solvents have a surface tension below 35 mN/m, and even more preferred organic solvents have a surface tension of below 30 mN/m.
• the use of these low surface tension organic solvents preferably together with IPA will give a dampening water solution with a surface tension below 50mN/m.
• the concentration of iso-propyl alcohol in said at least two organic solvents is between 20 and 90 wt%, and in a further embodiment further organic solvents of said at least two organic solvents have a surface tension below 40 mN/m, preferably below 35 mN/m and even more preferably below 30 mN/m.
• the organic solvents are premixed before addition to the pre-dampening solution.
• This method has various advantages, as only one liquid needs to be metered, which results in a stable dampening water solution, where the possibility of formation of separate phases by mixing the pre-mix of low surface tension organic solvents with the pre-dampening solution is significantly reduced.
• the mixture of organic liquids preferably contains between 20 and 90% of IPA and preferably IPA is used in amounts over 50 vol% in the organic liquid mixture.
• the density of the dampening water solutions formed can be controlled in the same way as done when IPA is used alone, meaning by density control.
• the difference in density between the pre-dampening solution and the mixture of organic solvents should be as close as possible to the difference using IPA alone.
• accuracy we have observed, that an acceptable accuracy can be obtained when the difference in density between the organic solvent mixture and the pre-dampening solution is at least 0.1 g/cm 3 , more preferably more than 0.13 g/cm 3 and most preferably more than 0.17 g/cm 3 .
• Another method of characterising the preferred densities of the organic solvent mixture is to compare this density with the density of pure IPA. For a skilled person in the art in terms of dosing accuracy the use of IPA is preferred. IPA has a density of 0.78 g/cm 3 (25°C).
• a preferred mixture of low surface tension organic solvents should than have a density as close as possible to the density of pure IPA.
• This difference is calculated by dividing the density of the mixture by the density of IPA subtracting 1 and multiplying the outcome with 100%.
• the invention concerns an organic solvent mixture suitable for mixing with a pre-dampening solution just before and/or during the lithographic printing process, wherein the solvent mixture comprises isopropyl alcohol and at least one further organic solvent having a surface tension below 40 mN/m, preferably below 35 mN/m and even more preferably below 30mN/m.
• the concentration of iso-propyl alcohol is between 20 and 90 vol %.
• the organic solvent mixture according to the invention has a density below 0.9 g/cm 3 , preferably below 0.83 g/cm 3 .
• the concentration of the organic liquids in the resulting dampening water solution in this method is between 1 and 8 vol% and preferably between 2 and 6 vol%.
• the surface tension of the dampening water solution is preferably below 50 mN/m.
• Suitable (further) organic solvents for use in the method of the invention described above and in the organic solvent mixture of the invention described above are selected from the group consisting of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monoisobutyl ether, ethylene glycol monopropyl ether, diethylene glycol monopropyl ether, triethylene glycol monopropyl ether, ethylene glycol mono-tertiary-butyl ether, diethylene glycol mono-tertiary-butyl ether, triethylene glycol mono-tertiary-butyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, triethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, tri
• the (further) organic solvents which gave the best behaviour when used in the method of the invention described above and in the organic solvent mixture of the invention described above are selected from the group consisting of propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monopropyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monoisopropyl ether, tripropylene glycol monoisopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, dipropylene glycol monoisobutyl ether, tripropylene glycol monoisobutyl ether, propylene glycol mono-tertiary-butyl ether, dipropylene glycol mono-tertiary-butyl ether, tripropylene glycol mono-tertiary-butyl ether,2- ethy
• Suitable organic liquids as replacement of IPA can be amongst others methanol, ethanol, n-propanol, in general organic liquids having a density below 0.82 g/cm 3 and which are completely mixable with water and the organic solvents mentioned above.
• the pre-dampening water concentrate can comprise amongst others
• Suitable agents can be found amongst others in EP-A-1216842 and US-A-5637444 and are included herewith as reference.
• the kit of the present invention comprises a dampening solution concentrate and a mixture of organic solvents as described above, i.e a mixture comprising at least IPA, which mixture has a surface tension of 40 mN/m, preferably 35 mN/m and more preferably of 30 mN/m or less and preferably a density of 0.90 g/cm 3 , preferably 0.83 g/cm 3 or less.
• the organic solvent mixture in the kit comprises as a further solvent at least one of the solvents mentioned above.
• kit of parts further comprises instructions how to use the components in the kit, preferably in accordance with the method as described herein above, i.e. instructions to first mix the dampening solution concentrate with a suitable amount of water to form a pre-dampening solution and then to add to this pre-dampening solution the mixture of organic solvents.
• Another embodiment of this invention is a kit of parts comprising a mixture of organic solvents comprising at least IPA, which mixture has a density of 0.90 g/cm 3 , preferably 0.83 g/cm 3 or less and a surface tension of 40 mN/m, preferably 35 mN/m and more preferably of 30 mN/m or less and instructions how to use the mixture of organic solvents, preferably in accordance with the method as described herein above, i.e. instructions to first mix a dampening solution concentrate with a suitable amount of water to form a pre-dampening solution and then to add to this pre-dampening solution the mixture of organic solvents. It is to be understood however that instructions to first mix a dampening solution concentrate with the mixture of organic solvents comprising at least IPA as defined above and then to add water to form a ready to use dampening water solution is also encompassed by this invention.
• Dampening solution concentrates that can suitably be used in this invention are commercially available.
• suitable dampening solution concentrates are Acedin 2004, Dynafount 426 from Bousfield, Dampstar 4.6/Dampstar 5.8 from Solco, Combifix and Hydrofix from Hostmann and Steinberg, Vegra Red and Blue from Vegra, and the like.
• a further aspect of the invention is the use of the organic solvent mixture as defined above or the kit of parts defined above for the preparation of a ready to use dampening water solution for use in a lithographic printing process.
• an aspect of the present invention is a dampening water solution for use in a lithographic printing process having a surface tension of less than 50 mN/m and comprising water, for a dampening water solution customary additives and 0.2-7.2 vol% iso-propylalcohol and at least one further organic solvent having a surface tension below 40 mN/m.
• the surface tension can be measured in various ways which are described in the literature for example in The Physical Chemistry of Surfaces by A. W. Adamson; John Wiley & Sons 1982 pg 4-46.
• the surface tension is measured according to the ring method which is generally named the Du Nouy ring method which is one of the most easy and fastest methods to use.
• the Du Nouy ring method measures the force required to pull a small platinum ring through the surface of the liquid.
• Dosing of the IPA and Dampstar 5.8 as pre-dampening concentrate was done by two different dosing pumps directly into the dampening water. In this process, the IPA was replaced by 3 vol% of a mixture of 75 vol% of IPA and 25vol% of propyleneglycol-n-butylether.
• Dosing of the solvent mixture was done with the dosing pump earlier used for the IPA, also directly into the dampening water, and monitored by a density measurement device from Technotrans, called Combicontrol, which kept the concentration within the required limits.
• Dissolution of the solvent mixture in the pre dampening solution went smoothly without the need for extra stirring.
• the typical "oily" droplets indicating a separate solvent phase of non-dissolved solvent on the surface where not found, indicating complete dissolution.
• the density of the mixture of 25 vol % propyleneglycol-n-nbutylether and 75 vol % of IPA is 0.81 g/cm 3 , compared to 0.78 g/cm 3 (25°C)of IPA alone. This gives an acceptable difference of 2.5%.
• the dampening roller speed had to be increased from 40 to 85 on the dial on printing press console in order to increase the dampening water transport. This resulted in an uneven dampening water distribution across the dampening rollers an excess ink emulsification, especially at the edges of the ink form roller. This resulted in an unstable ink water equilibrium and unacceptable variation of print quality from print to print.

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Citations (13)

• 2005
  • 2005-02-03 EP EP05100733A patent/EP1688266A1/fr not_active Withdrawn

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