CS254018B1 - Dampening solution for offset printing - Google Patents

Abstract

The solution relates to a dampening solution for offset printing, suitable for alcohol dampening systems. The dampening solution contains, as an additive reducing surface tension, ethyl alcohol denatured with higher aliphatic alcohols with a carbon number of 3 to 5. Ethyl alcohol is denatured with the aforementioned higher alcohols in an amount of 20 to 100 ml per liter of ethyl alcohol.

Description

The present invention relates to a wetting solution of pre-set printing.

Typically, an offset dampening solution is used in offset printing to prevent the non-pressurized areas of the print form from being picked up by the ink. The wetting solution often contains a buffer system based on organic and inorganic bases, the acid of their salts, adjusting the pH to 4.8 to 5.8, which is most preferred for the printing process. Other substances may be included, such as, for example, a hydrophilic water-soluble polymer, preservatives, surfactants and the like. A portion of the wetting solution was transferred through the printing press to the ink in which it was emulsified during printing. Therefore, offset ink is produced so that it is capable of receiving 10 to 30% of water without substantial change in its rheological and printing properties. Color-water balance occurs when the amount of water transferred to the printing ink per unit of time amounts to water. This is preferably carried out by evaporation (the water is preferably produced in comparison with the essential volatile constituents of the ink) and rolled out of the printing mold for the suppressed material in the form of an emulsion in color. The even amount of water in the ink varies greatly from external conditions, such as the temperature or relative humidity of the air, and the like. For example, by varying the outside temperature during printing, the above-mentioned equilibrium amount can be varied, which may result in a non-standard quality of the prints and printing problems that need to be eliminated by changing the color and wetting solution, i.e., color-water balance. Therefore, it is advantageous if the inking and dampening assembly on the printing machines is equipped with the possibility of thermal tempering. In practice, cooling of the wetting solution is often used at a temperature of 5-10 ° C.

The wetting solution is applied to the printing form by a roller in many printing machines, which is coated with a special hydrophilic textile fabric, providing a uniform and perfect coating. In such dampening systems, it is not necessary to use additives to reduce the surface tension of the wetting solution. The disadvantage in this case is the possibility of contamination of the printing point by fibers from the textile coatings of the wetting rollers as well as the need to wash (or replace) the textile coatings. This is associated with the increased effort exerted by the operator on the removal of the respective cylinders as well as the need to wash the coatings in toxic organic solvents. Another disadvantage of the aforementioned dampening systems is the achievement of color-water balance at the beginning of printing, which is associated with a higher consumption of maculature sheets of printing ink.

If the surface tension of the wetting solution is reduced, it is also possible to moisten it with smooth spherical rollers. The reduction of the surface area is usually achieved by the addition of 6 to 30% by volume of isopropyl alcohol (the commonly used name is also known as alcoholic wetting). Alcohol wettability brings about advantages, which include mainly a more rapid stabilization of the color balance - the result of less intense and more uniform dampening as well as a higher moisture content of the wetting solution. In the case of alcohol dampening systems, it is possible to combine the dampening roller with val-com coloring paint. We get to the combination of dampening and dyeing systems that are extremely fast to achieve color-water balance. Their best-known representative is the Dahlgren system. The advantage of using isopropyl alcohol in wetting solutions compared to other substances that reduce the surface tension of water (surfactants, etc.) appears to be in the physical-chemical properties (breathability, surface tension, miscibility with ink, etc.) that are considered ideal from the point of view of printing processes. To date, the quantitative effect of this effect has not been quantified since neither the exact cause nor the mechanism why isopropyl alcohol imparts the above-mentioned advantageous properties to the wetting solution in relation to the ink is known. Neither are there empirical values for assessing the suitability of the substances used instead. Another advantage of isopropyl alcohol in comparison with other water surface tension reducing agents is also the ease of controlling and maintaining its concentration constant by means of sensitive isometric density meters. Based on its changes, the automatic dispenser then adds isopropyl alcohol to maintain its concentration at a pre-set value. Thus, the standardization of the wetting solution composition during the load pressure is guaranteed, which is very important for the print quality standard and for the smooth running of the printing process.

Since isopropyl alcohol has toxic properties and is flammable, attempts have been made to replace it in wetting solutions with other substances or a combination of multiple agents to provide surfactants (U.S. Pat. No. 4,030,417), glycols in combination with surfactants (U.S. Pat. Nos. 3,625,715 and 3,877,372). U.S. Pat. No. 4,278,467 proposes the use of 2-ethyl-1,3-hexanediol, n-hexylcelosolv, n-hexoxydiethylene glycol, n-butoxydiethylene glycol acetate, 3-butoxy-2-propanol and the like. mixtures thereof in concentrations of 0.5 to 5% by volume. The use of 1-hexanol is also described in the literature (M. Alexander: Forga Mitteilungen No. 81,1974). All of these substances are very volatile and already at low concentrations, they reduce the surface tension of the water. For example, reducing the surface tension of the wetting solution to 35-40 mN. No. 4 (for the same reduction of surface tension, the addition of isopropyl alcohol of about 10-15% by volume is required) a concentration of 1 - hexanol of only 0.2 to 0.5% is sufficient. The same is true for most surfactants,

However, said substances have a relatively higher density than isopropanol and, if used, the isometric method for their dosage and concentration control cannot be applied. For example, 1 liter of a 10% by volume aqueous solution of isopropyl alcohol is about 20 grams per liter of pure water. However, 1 liter 0.2% vol. the aqueous solution of 1-hexanol is only about 0.5 grams per liter of pure water. It is practically impossible to maintain the constant concentration of the above-mentioned substances at the specific gravities so close to that of pure water. Another disadvantage of the above-mentioned substances is that they come into contact with the wetting solution, since the color of the water can accumulate and interfere with the damping solution because of the increased emulsification of water. Thus, the rheological and printing properties of the color may be adversely affected and the quality variations of the loaders, coloring rollers, and other difficulties may be caused.

It can be said that none of the isopropyl alcohol substitutes in the wetting solutions has found wider application to date.

However, the use of isopropyl alcohol is dangerous to humans as it has toxic properties. The aforementioned disadvantage of the considerable reduction of the dampening solution according to the invention, the principle of which is that it contains a buffer system stabilizing the pH to 4.8 to 5.8 and a surface tension reducing additive, characterized in that the surfactant reducing agent is 6 25% by volume of ethyl alcohol denatured with higher aliphatic alcohols having a carbon number of 3 to 5. The ethyl alcohol is denatured with said higher alcohols in an amount of 20 to 100 ml per 1 liter of ethyl alcohol. Higher alcohols alter the function of the denaturing agent and their presence in the wetting solution affects the interactions on the phase-color-wetting solution. Commonly used de-naturating agents (gasoline, benzene, methyl ethyl ketone, toluene, xylene ... mostly very good dissolves inks, and many of them also attack the printing element in print form. Their presence in wetting solutions) it is not desirable even in minimal concentrations.

Ethyl alcohol has much lower toxicity compared to isopropyl alcohol.

Using ethyl alcohol with denatured higher alcohols with carbon numbers of 3 to 5 may be similar to isopropyl alcohol (and in contrast to the above-mentioned substitutes) areometric dosing and concentration control methods, which is very advantageous for smooth printing process and standardization print quality.

When using dampening solutions according to the invention, a higher print quality, resulting in a higher relative contrast and a faster equilibrium-water setting, is achieved in comparison with wetting solutions containing the same amount of isopropanol, with the consequent lower consumption-cumulative sheets and ink. .

What is important is the fact that, unlike isopropyl alcohol, ethyl alcohol is not a petroleum product, but is generally obtained by the alcoholic fermentation of an organic material of a plant origin. Example 1 A wetting solution was prepared with the following composition: 1.5% v / v additive to the wetting solution T-02 (dosing according to the manufacturer's recommendations Polygraphic plants, Bra-tislava), 8% v / v ethyl alcohol denatured with n-butanol (100%) ml of n-butanol per 1000 ml of ethyl alcohol) and 90.5% by volume of aqueous water. The wetting solution thus prepared was used in a RolandMatic dampening system on a Roland 800 sheet-fed offset printing machine at 8 ° C. Kessler printing inks and double-faced enamelled paper (120 g / m2) from SCPR are used. After setting the printout, the first print of acceptable quality was obtained after 9 prints.

In a dampening solution in which the same amount of isopropyl alcohol was used in place of n-butanol-denatured ethyl alcohol (the proportion of the other components was also low, the same was true for all conditions, including temperature and relative humidity in the room), the first 15 prints of acceptable quality.

The relative print contrast value was used to evaluate print quality: relative contrast Rk = ----

Dioo

Dioo - Full Density Optical D75 - Optical Surface Density with 75% Non-Cluster Point.

When printing with a n-butanoyl-denatured ethyl alcohol-containing wetting solution, relative contrast values of between 0.02 and 0.07 higher were achieved, even when using a wetting solution with the same amount of isopropyl alcohol. Example 2 A wetting solution was prepared with the following composition: 2% v / v additive to wetting

Claims (1)

SUBJECT Offset printing wetting solution suitable for alcohol wetting systems comprising a pH stabilizing buffer and a surface tension reducing additive, characterized in that it contains 6-25% by volume of a surface tension reducing additive. of ethyl alcohol denatured by higher aliphatic alcohols with a carbon number of 3 to 5 in an amount of 20 to 100 ml per liter of ethyl alcohol.