Cleaning and liquid contact with solids – Processes – Oils – grease – tar – or wax removal – by dissolving
Reexamination Certificate
2000-11-29
2003-04-08
Webb, Gregory E. (Department: 1751)
Cleaning and liquid contact with solids
Processes
Oils, grease, tar, or wax removal, by dissolving
C510S170000, C510S174000, C510S238000, C510S365000, C510S417000, C510S424000, C510S505000, C510S506000
Reexamination Certificate
active
06544348
ABSTRACT:
The invention relates to a process for cleaning printing machines and printing plates to remove, in particular, printing inks—for example, oil-based or radiation-curable printing inks—from the cylinders and rollers of printing machines, especially planographic or offset printing machines, and from printing plates, during, for example, an interruption in the printing process.
For said purposes it is common to employ cleaners based on organic solvents and/or aqueous solutions. When machines are at a prolonged standstill in printing plants, or when there is a change of ink, the parts of the printing machine that have come into contact with the printing ink are freed from ink residues. Similarly, when there is an interruption in the printing process, it is necessary to clean printing plates, especially planographic printing plates, carefully in order to remove ink residues and to coat them with preserving solutions based on hydrophilic polymers in order to maintain the hydrophilicity of the nonimage areas. Cleaners containing organic solvents usually have volatile organic components (VOCs) which pollute the atmosphere and are unacceptable from an environmental and workplace health and safety standpoint. Cleaners consisting exclusively or predominantly of apolar organic solvents, furthermore, have the disadvantage that solvent residues which adhere to the parts to be cleaned, such as printing rollers, cannot be washed off with water after cleaning. A clean printing roller, however, is vital for good wetting with printing ink and for effective ink transfer. In the case of some printing plates it is also possible for the ink-carrying print stencil to undergo incipient dissolution by the cleaner and, as a result, to become damaged or even unusable.
DE-B 27 24 557 describes a cleaner for lithographic printing plates which comprises water and water-miscible organic solvents. Its cleaning action with respect to viscous oil-based printing inks is naturally limited.
GB-A 2 089 289 describes oil-in-water and water-in-oil emulsions as cleaners. A disadvantage in this case is the relatively high interfacial tension between the water phase and the oil phase, so that, for example, lipophilic, strongly hydrophobic offset printing inks, owing to their high surface energy, are taken up only slowly and minimally by the continuous water phase cleaner solution.
Similar comments apply to emulsions as described, for example, in WO-A 90/03419 or EP-A 0 498 545.
Furthermore, emulsions of this kind are stable only kinetically but not thermodynamically, so that, especially in the case of temperature fluctuations, they have a tendency to separate [creaming (settling), thickening, flocculation] and so are impaired in their usefulness.
A particularly difficult task is the removal of UV-curable offset or relief inks based on polymerizable monomeric or oligomeric acrylates. They are generally removed using esters or mixtures of esters and mineral oil.
It is an object of the present invention to provide a cleaning process and a liquid cleaner (cleaning composition) which permit the rapid and effective detachment of printing inks without polluting the local environment by vapors from volatile organic components or attacking the print stencil of printing plates.
We have found that this object is achieved by a process for cleaning printing machines or printing plates by removing the contaminants from the surface by washing with a liquid, wherein said liquid is a preferably bicontinuous microemulsion comprising water, a surfactant and, as the oil phase, a water-immiscible organic solvent.
For the purposes of the present specification a microemulsion is a liquid mixture, preferably a bicontinuous mixture, of water phase and oil phase with an extremely low interfacial tension between water phase and oil phase, i.e., an interfacial tension up to three powers of ten lower than that of a conventional water-in-oil or oil-in-water emulsion. In the case of microemulsions this interfacial tension is in the range from 10
−3
to 10
−7
N/m, preferably from 10
−4
to 10
−6
N/m, and in the case of emulsions customarily in the range from 10
−3
to 10
−2
N/m. A microemulsion in the present specification is thermodynamically stable, visually transparent and preferably of low viscosity.
Customary, conventional emulsions may comprise oil phase and water phase in very different proportions by volume. They have a continuous phase and a disperse phase which is present as very small spherules, stabilized by coating with surfactants, in the continuous phase. Depending on the nature of the continuous phase the emulsions are referred to as oil-in-water or water-in-oil emulsions. Ideally these emulsions are kinetically stable, i.e., they persist for prolonged periods although not ad infinitum. In the case of fluctuating temperatures in particular, they may tend toward phase separation by settling, creaming, thickening or flocculating.
Bicontinuous microemulsions comprise two phases, a water phase and an oil phase, in the form of extended, adjacent and interpenetrating domains at the interface between which there is an accumulation of stabilizing surfactants in a monomolecular layer. Bicontinuous microemulsions form very easily, usually spontaneously on account of the very low interfacial tension, when the individual components—water, oil and a suitable surfactant system—are mixed. Since the domains have only very small extents in at least one dimension, in the order of magnitude of nanometers, the microemulsions appear visually transparent and are stable thermodynamically, i.e., for an unlimited time, within a certain temperature range depending on the surfactant system employed.
Bicontinuous microemulsions are described, for example, in the article “Mikroemulsionen—eine wissenschaftliche und anwendungstechnische Fundgrube?” [Microemulsions—a scientific and technological treasure chest?] by H.-F. Eicke in SÖFW-Journal 118 (1992), pages 311 to 314.
In order to achieve the required low interfacial tension at the phase boundaries the microemulsions comprise certain amphiphiles, i.e., surfactants, and also often comprise, in their aqueous phase, dissolved electrolytes and, if desired, further auxiliaries. Electrolytes are added in particular when the amphiphiles are partly or exclusively ionic surfactants.
The use of microemulsions to extract organic pollutants from contaminated soils is described in WO 94/04289. The tertiary extraction of petroleum is another known field of application for microemulsions.
In addition, EP-A-0 498 545 discloses the use of microemulsions as cleaners for surfaces such as those of coated or untreated metal panels, plastics and other surfaces, in particular for the purpose of pretreatment for subsequent coatings.
The invention additionally provides a cleaning composition for conducting the process of the invention, said composition consisting of a microemulsion comprising water, a surfactant and a water-immiscible organic solvent.
The constituents of the microemulsions should be selected such that they do not alter the mechanical properties of components of equipment or sealing materials made of rubber or similar materials, such as their elasticity, flexibility, dimensional stability, etc., as a result of swelling or shrinkage (deswelling).
Water-immiscible organic solvents used are with advantage those having a boiling range above 100° C., preferably above 150° C. and, in particular, from 200 to 400° C. In general, organic solvents having flash points above 100° C. are employed. By organic solvents are meant, inter alia, fats and oils, such as colza oil, fatty acid esters, ethers, ketones, aldehydes, and hydrocarbons.
Generally suitable are esters, especially alkyl esters, of relatively long-chain fatty acids. The alkyl group of the alcohol component generally has 1 to 20, preferably 1 to 16 carbon atoms. The fatty acid component normally has 6 to 25, preferably 8 to 18 carbon atoms and can be linear or branched, saturated or unsaturated and cont
Frank Erich
Oetter Günter
Schneider Petra
Stöckigt Dieter
Wolff Erwin
BASF - Aktiengesellschaft
Webb Gregory E.
LandOfFree
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