CS200041B1 - Printing varnish for offset plates - Google Patents

Description

The invention relates to a printing varnish for offset plates.

One method of making an offset printing plate uses suitable varnishes as the printing element carrier. The method of this method consists of several successive operations. First, the offset printing plate (usually of surface-treated aluminum) is coated with a suitable light-sensitive substance. Thereafter, the plate is exposed in contact with the original. Illuminated spots become harder, become less soluble and, after rinsing with water, remain on the plate, while the 00 spots covered (unlit) will dissolve and wash away. The dried plate is then coated with a thin layer of printing varnish and dried. A suitable delaminating solution then washes away the areas covered with the cured light-sensitive material and the layer of printing varnish. The locations covered only by the printing varnish firmly anchored in the surface of the plate are retained and form the printing element in the final stage.

Requirements for printing varnish properties are very demanding. In particular, it must dry slowly enough to allow even spreading in a thin layer and wiping practically dry. The lacquer must resist the action of water and dampening solutions used in offset printing, however, excessive hydrophobicity would make it difficult, but not impossible, to delaminate the above coating. Furthermore, a high affinity for the inks is a condition, but it must not become soluble in each other.

Summary of the 1 other, as seen by the conflicting performance requirements

200 041

200 041 greatly restricts the choice of both solvents and lacquer resins and, as a result, often entails the choice of annoying substances (eyclohaxanone, matylcyclohexanone, etc.) or directly toxic (cyclic hydrocarbons and nitrobenzene). The narrow choice of solvents also limits the choice of lacquer resins,

These drawbacks are overcome by an ophthalmic printing varnish comprising a lacquer resin such as a maleic acid-styrene copolymer and / or a vinyl chloride-vinyl acetate copolymer and a solvent comprising 20 to 95% by weight of ethyl acetate. based on the total weight of the printing varnish.

An advantage of the invention is that ethyl acetate is a nontoxic, weak, pleasant fragrance. As a solvent, it fully complies with the technological requirements for drying speed, allows firm anchoring to the surface of the printing plate, and applies its combination of ketone and ester properties suitably when preparing the lacquer.

Example 1

A solution containing 90% ethyl acetate and 10% styrene-maleic acid copolymer was prepared in advance and dissolved in methyl violet in an amount of 0.5% by weight of the total amount of the solution. The resulting lacquer ae nanaae on the offset plate after washing the non-glazed surfaces in a conventional manner and branched off. The finished offset plate is of very good quality, is easy to process and has a long print life, lasts between 50,000 and 120,000 prints. No toxic substances are used during its preparation and the environment is favorable for workers.

Example 2

A solution of% ethyl acetate,% ethylene glycol monoethyl ether (Cellosolv) is prepared.

Ί0% vinyl chloride / vinyl acetate copolymer and dissolve methyl violet in an amount of 0,5% by weight. The lacquer was applied in the same manner as in Example 1 and was equally favorable.

Example 3

A solution of% ethyl acetate / ethyl acetate% of maleic anhydride copolymer and styrene of 5% vinyl chloride / vinyl acetate copolymer was prepared and dissolved in 0.5% by weight of methyl violet to the total amount of lacquer. The lacquer aa is applied to the offset plate after washing the non-glazed surfaces and subjected to further conventional processing. The finished offset plate can withstand up to 120,000 prints in good quality. Hygienic conditions

200,041 in the preparation of the board preferably differs from the conditions for processing the boards with previously used lacquers.

Claims (1)

Offset printing varnish consisting of a lacquer resin such as a maleic acid-styrene copolymer and / or a vinyl chloride-wool acetate copolymer and a solvent, characterized in that it contains 20 to 95% by weight of ethyl acetate as the solvent, based on the total weight of the printing varnish .