Comparison of paper printing and tinplate printing in lithography
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In the packaging industry, paper and tinplate are widely used as packaging materials, and most packaging materials require beautiful decorative patterns, which can express the contents of the contents, increase the appearance of the products, and stimulate consumers' desire to purchase. For the printing of paper and tinplate, lithography is commonly used. For these two different materials, the techniques applied have many similarities and a few differences. This article is about lithography in paper and tinplate. The application is compared from prepress processing, printing, and post processing.
1. Comparison of prepress processing
In the prepress processing stage, the technical principles used for paper printing and metal printing are basically the same. Use professional software to redesign, modify, trap, set up bleeding, color separation, etc., for the originals that are input to the computer, and then make the plates to be printed by the plate making equipment. Thanks to the development and wide application of CTP technology, the plate making process in prepress processing has been simplified by many manufacturers. After the processed electronic files are in good format, the color separation required by the CTP printing machine can be directly used. In the printing plate, the cost of manpower and material resources is much lower than that of the film making technology. The use of film-making, a relatively complex traditional plate-making technology, has been gradually eliminated in both paper printing companies and metal printing companies.
Digital proofing technology makes pre-press proofing much easier. Both paper printing and tinplate printing can use the digital inkjet printer to print the proofreading information. Paper products can even be printed on a digital press to proofread color layout information. The tinplate is affected by the metallic luster of its surface. The proof of its surface color usually needs to be confirmed by using a special lithographic proofing machine to make the iron sample. The proofing process will be more complicated than the paper proofing.
2. Comparison during the printing process
The principle of paper printing and tinplate printing using lithography is the same, using the principle of “oil-water incompatibility”. The graphic portion of the printing plate is lipophilic, and the non-image portion is hydrophilic. In the printing process, the printing plate is first watered and then inked, so that only the graphic part of the printing plate covers the ink, and then the ink is transferred to the printing material through the transfer function of the blanket to obtain the required graphic.
The fiber structure of the paper allows the ink to penetrate smoothly into the inside of the paper, and the adhesion to the ink is relatively strong. Therefore, paper printing generally uses a four-color or five-color lithographic printing machine to complete single-sided printing at one time, and naturally dry using a dusting process, and the printing speed can be up to more than 10,000 sheets per hour. Tinplate is a rigid printing material. It has no extremely soft nature of paper, no fiber structure like paper, and no absorption. Therefore, the tinplate printing process is much more complicated than paper printing. First, the surface of the tinplate has a metallic luster. Before printing, a layer of white or white ink should be coated on the coater to improve the surface whiteness. A layer of transparent base oil can be coated to reflect the metallic luster of the tinplate. After film formation, it enters the printing process. Because the surface of the tinplate is not absorbent, the adhesion of the ink on the tinplate is poor. Therefore, generally only one or two colors can be printed at a time, and it is necessary to enter the drying room and then print the remaining color sequence. Therefore, the tinplate printing machine generally uses a monochrome printing machine or a two-color printing machine, and has a matching drying room device. The magnetism of the tinplate can be used at the inlet, and the Feda can be equipped with a magnet to help separate the tinplate. The single printing unit in the printing press is similar to the paper printing machine. Due to the rigidity of the tinplate, the sheet cannot be attached to the drum like paper. The alignment of the plate cylinder, the blanket cylinder and the printing cylinder axis in the unit is in the vertical direction. It is on the same line, and the axis of the three rollers of the paper printing machine unit has a certain angle to facilitate the transfer of paper. After the tinplate is printed, a transparent varnish is applied to the surface to protect the printed layer and increase the wear resistance of the graphic. At this point, the tinplate printing process was completed. With the application of U V printing technology in tinplate printing, the tinplate printing machine color sequence unit can be increased to 4 to 5, after a color sequence printing is performed, U V light irradiation curing can be performed, and then the next color sequence can be printed. The “dry dry” printing between the inks ensures print quality and reduces the number of times of printing. It can reduce many costs for the company, which will be a trend in the future tinplate printing industry.
In the printing process, in order to ensure the quality of the product, both need to carry out online real-time detection of the printed product. When printing paper products, it is generally only necessary to proofread the color, the registration of the color sequence, the quality of the layout, and the like. Due to the characteristics of its own materials and the needs of post-press processing, tinplate needs to detect the adhesion between paint ink and tinplate, scratch resistance, stamping properties, etc., in addition to the printing quality of proofreading color and color registration. The quality of paper printing is detected in more steps.
3. Comparison of postpress processing
The finished products made of paper after printing are mainly books, boxes, decorations and so on. According to the properties required of the finished product, the paper products can be glazed, coated, bronzing, embossed and other decorative processing before molding: glazing is coated with a layer of colorless transparent paint on the surface of the printed matter, which can be protected after drying. The effect of increasing the gloss of the printed matter; the film is bonded to the surface of the printed matter by hot pressing with a transparent film, which also serves to protect and increase the gloss; the hot stamping is to press the metal foil to the surface of the printed matter to serve as a decorative effect; A relief pattern or the like is printed. After the decoration processing is completed, the processing of the book can be completed by cutting, folding, affixing, binding, encapsulating, cutting the book, etc.; the molding of the packaging box can be completed by the processes of die cutting, indentation and molding.
After the tinplate is finished printing, the products are mainly printed with iron, cans, lids, steel drums and other packaging products. Among them, there are batteries, electrical appliances and other products. The types of cans include beverage cans, food cans, aerosol cans, chemical cans, miscellaneous cans, etc. The cover has a crown cover, an easy opening cover, and a screw-open cover. Printing and coating iron products generally need to be processed through cutting, stamping, and roll forming to further process the finished product. Can products generally need to be cut, welded, capped and sealed, and then filled with contents to complete the sealing and finished the finished product. The cut and stamped cover is often used as a matching intermediate for can products.
It can be seen from the above that the paper printing and the tinplate printing using the lithographic printing technique are identical in principle, and some of the equipments are also consistent, and there are many differences in printing and finishing processing due to the difference in material properties. In the next few years, it can be seen that the paper printing and tinplate printing industry will continue to grow. The development of technology and the improvement of technology can make the production process easier, more efficient and lower cost.