Prepress: Establishing perfect technology is the key

The prepress process was designed to give clear guidance to print production. Everything is connected and interlocking, and no mistakes within the process are allowed to occur in every small part of the process. If something goes wrong, it will cause irreparable damage. The requirements for the production of gravure cylinders by ordinary gravure printing have been quite strict, and the requirements for the prepress production process for wired compound transfer gravure printing are more stringent. It is necessary to be cautious when formulating prepress processes.

1. Determination of raw and auxiliary materials

(1) Transfer film: PET is generally selected as the base film because PET film has a smaller stretching range than OPP film and has good stability.

(2) bottom paper: select the bottom paper to refer to the sample or according to customer requirements. It is required that the surface of the paper be smooth, smooth, and soft (paper fibers should not be too hard). In this way, it is possible to ensure that the indentation line is full and the box sheet is free of burrs during the die cutting indentation of the subsequent process.

(3) Adhesives: At present, adhesives used in composite products in China include solvent-based adhesives, water-based adhesives, and UV adhesives. Their performance varies.

Solvent-based adhesives have fast drying speed and good release properties, but they have bad odors and are not conducive to environmental protection. Moreover, composite products have a large amount of curling. After a long time of storage, the color will turn yellow, and there are cloud-like fog points (caused by large rosin content).

Water-based adhesives have no solvent evaporation problems, are non-toxic and environmentally friendly. Especially when the film is laminated with the paper, the glue liquid is a naturally flowing liquid and can quickly and fully fill the depressions on the surface of the paper. Therefore, the composite product has good smoothness and strong composite fastness, and the composite product has no warping phenomenon. , Flat and beautiful, excellent overall performance.

UV adhesives have fast drying speed, soft gel, good adhesion, high bonding strength, high temperature resistance and good freezing performance, and composite products do not burst or crisp.

In actual use, adhesives with different properties can be selected according to different equipment performances, drying methods, gluing methods, product requirements, etc. in order to achieve an ideal composite effect.

(4) Varnish: Also known as resin oil, it is used to coat the surface of gold, silver and laser paper after compounding or transfer to make it have better adsorption of ink during printing. There are currently two types of varnish available.

The first kind: oily varnish (volatile drying type), the main ingredient is synthetic resin (nitrocellulose, acrylic resin), and contains some additives. The advantage is that the coating is thick and the drying speed is fast. The disadvantage is that it is easily miscible with the resin ink of the same type in the printing process.

Second: water-based varnish, the main ingredient is acrylic emulsion, and add some defoamers and additives. The advantage is that the amount of coating is small, the varnish coating is thin, the cost can be saved, and the ink is not easily miscible with the ink during the printing process. The disadvantage is slow drying.

(5) Printing inks: At present, domestic paper gravure printing generally uses volatile drying type oily inks. The solvent is ethyl acetate, ethyl alcohol (isopropanol), butyl acetate, or even toluene, which is harmful to the human body and is not conducive to environmental protection. The environment-friendly water-based gravure ink is still immature and still under development.

The connection compound transfer gravure printing should choose benzene-free ink, its volatile drying speed is medium, the pigment particle size is 3 ~ 5μm, color concentration, color saturation, high temperature performance, strong adhesion, printing ink surface easy hot stamping The printed surface is not easily scratched. The diluent is ethyl acetate, more than 98.5% absolute ethanol or isopropanol. Slow-drying agent can use butyl ether, which is less toxic.

2. Process analysis before production

(1) Introduction to compound transfer paper technology

The steps of compounding and transferring the paper are as follows: firstly, the transfer film and the bottom paper are bonded together with an adhesive, and then the base film of the transfer film is separated from the paper so that only the adhesive layer, the aluminized layer and the coating exist on the surface of the paper. Floor.

Paper can be breathable, so it is generally used wet composite method, the first transfer film sizing, and then press it closely with the bottom paper, and finally drying.