Prepress: Developing a perfect process is the key
The prepress process was developed to give a clear path to print production. Everything is connected and interlocked. The small steps in each process are not allowed to cause human or unexpected errors. Once they fail, they will cause irreparable damage. Ordinary gravure printing has strict requirements on the gravure cylinder manufacturing process, and the connection composite transfer gravure printing has stricter requirements on the prepress manufacturing process, and the prepress process needs to be cautious.
1. Determination of raw and auxiliary materials
(1) Transfer film: PET is generally used as the base film because the stretch range of the PET film is smaller than that of the OPP film and the stability is good.
(2) Backing paper: Select the bottom paper to refer to the sample or according to customer requirements. The paper surface is required to be smooth and soft, and the paper fiber is not too hard. In this way, when the die-cutting indentation of the subsequent process is performed, it is ensured that the indentation line is full and the box piece has no burrs.
(3) Adhesives: At present, the adhesives used in composite products in China include solvent-based adhesives, water-based adhesives and UV adhesives. Their performance varies.
The solvent-based adhesive has a fast drying speed and good release performance, but has an odor, is not conducive to environmental protection, and the composite product has a serious curling effect. The color will be yellow when placed for a long time, and there is a cloud-like fog point (caused by a large rosin content).
Water-based adhesives do not have solvent evaporation problems, are non-toxic and environmentally friendly. Especially when the film is laminated with paper, the glue is a naturally flowing liquid, which can quickly fill the concave portion of the paper surface quickly, so the composite product has good finish and strong composite fastness, and the product has no warpage after compounding. , smooth and beautiful, excellent overall performance.
The UV adhesive has a fast drying speed, soft gel, good adhesion, high bonding strength, high temperature resistance and good freezing performance. The composite product does not explode and is not brittle.
In actual use, different performance adhesives can be selected according to different equipment performance, drying method, gluing method, product requirements, etc., in order to achieve the desired composite effect.
(4) Varnish: Also known as resin oil, it is applied to the surface of gold, silver or laser paper jam after compounding or transfer, so that it has better adsorption to ink during printing. There are currently two varnishes to choose from.
The first type: oily varnish (volatile dry type), the main component 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 system during the printing process.
The second type: water-based varnish, the main component is acrylic emulsion, and some defoamers and additives are added. The advantage is that the coating amount 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 that the drying speed is slow.
(5) Printing ink: At present, domestic paper gravure printing generally uses volatile drying type oily ink. The solvent is ethyl acetate, ethanol (isopropyl alcohol), butyl acetate or even toluene, which is harmful to the human body and is not conducive to environmental protection. Environmentally friendly water-based gravure inks are still immature and still in the process of development.
The connection composite transfer gravure printing should choose benzene-free ink, its volatilization drying speed is medium, the pigment particle size is 3~5μm, the color density, color saturation is high, the high temperature resistance is good, the adhesion is strong, and the surface of the printing ink layer is easy to be hot stamped. The printed surface is not easily scratched. The diluent is ethyl acetate, 98.5% or more of absolute ethanol or isopropanol. The slow drying agent can use butyl ether, which is less toxic.
2. Process analysis before production
(1) Introduction of composite transfer paper process
The steps of compounding and transferring the paper are: firstly bonding the transfer film and the base paper with a binder, and then separating the base film of the transfer film from the paper, so that only the adhesive layer, the aluminum plating layer and the coating are present on the surface of the paper. Floor.