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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. See Table 1.
(2) Bottom paper: Select the base paper to refer to the sample sheet 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 to the 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 Process
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.
Adhesive can be applied by three-roller coating or anilox roller. The relevant process parameters of rubber coating are shown in Table 2. The oven temperature and printing speed determine the dry conditions of the product.
Need to control the quality indicators are: 1 composite fastness; 2 surface roughness; 3 peel integrity.
The quality of the peeling process largely depends on the coating preparation of the base film, the coating layer, and the composite effect. The peeling process itself needs to control the degree of tightness and regularity of the collected film and ensure that the surface is free of scratches. The stripped PET base film can be recoated for transfer again, greatly reducing production costs.
(2) Connection compound transfer gravure printing process
Generally, after the composite paper has undergone a maturation period of 24 hours, the PET base film can be peeled off, so that the aluminum plating layer and the coating layer are transferred onto the base paper. However, the connecting transfer rotogravure printing line has a drying path of 16m and a maximum drying temperature of 200°C. After drying, it can be immediately cooled by double cooling rollers, which can fully achieve the desired composite and transfer effect.
Coating roller: The selection of the coating roller depends on the product being processed. The amount of glue applied directly affects the product quality, composite fastness, and peeling integrity.
Printing plate: Our company's connection compound transfer gravure printing production line should adopt the hollow version according to the original design, but at present many domestic printing enterprises have no good solutions to the problems that appear during the use of the hollow version. Its main drawbacks are: relatively long plate-making time and difficulty in machining; the version axis used by the plate-making factory cannot completely coincide with the axis axis of the printing plate, resulting in serious wear and tear in the long-term use, resulting in dynamic balance oscillation of the printing plate. Beyond the specified range, greater than 0.3mm, overprinting fluctuations are likely to occur during the printing process. Therefore, although the price of the bobbin version is slightly higher, from the viewpoint of product quality and process production, the hollow version should not be used as far as possible from the yield rate of the finished product. We have used the bobbin version instead.
UV glazing: Gravure printing on-line UV glazing technology has been very mature in China, but if we want to make the post-press processing without defects, we also need to consider it carefully before printing.
Since the UV coating must be subjected to the high-temperature baking of the UV lamp, the paper is often deformed, resulting in difficult post-printing registration. Therefore, in the pre-press process layout, we must consider the impact of the die-cutting position accuracy of the product and the deformation rate of the paper on the post-press processing.
The following is a brief introduction to the fine clamshell products in cigarette packs.
The maximum printing width of the connecting compound transfer gravure printing machine used in our factory is 820mm. Due to the high precision requirements for hot stamping, embossing, and die-cutting registration in post-press processing, the clamshell box uses 18 (3×6) when punching, and two single-knife lines in the horizontal row. 4mm double-knife; vertical 6-boxes, plus 4mm double-knife between 3 and 3. This imposition can increase or decrease the size of double-knife based on the deformation rate of the paper, which greatly eases the problem of inaccurate printing due to paper deformation.
New equipment, new technologies, new processes, and re-innovation are our common goals. Only by adopting advanced and even advanced technology can China's packaging and printing technology be quickly advanced to the international level.
Connection compound transfer gravure printing process
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.