In the field of paper packaging printing, most follow the process: the use of color printing to complete the print graphic reproduction; the use of special substrates. Ink or process to complete the print decorative decoration. Since the reform and opening up, with the abundant supply of materials and consumer products, the promotion of packaging display and enhance the value-added function is increasingly emphasized, thus greatly increasing the market demand for packaging visual effects, which also makes the decorative printing process has been developed, this paper is one of the laser embossing transfer process.
Process Principle
In terms of principle, the laser embossing transfer process is derived from the laser film molding process in the laser paper manufacturing process. The laser embossing transfer process utilizes the principle that the pattern on the surface of the laser film is revealed by a very fine bump and the characteristic that the UV varnish can be cured completely between warmth and plasticity before curing, and the UV varnish is coated with UV varnish on the surface of the print. After the UV varnish is cured, the laser pattern will be formed.
It should be noted that this process is different from the cold transfer process, which is mainly through the UV adhesive to stick the pattern layer on the surface of the laser film to the surface of the print, and its principle is completely different from the laser embossing transfer process.
Process
First, prepare the laser film. The required laser pattern is selected and made into a laser die plate, and then the laser pattern on the laser die plate is die-cast onto the surface of the rolled BOPP base film through a die press to make the laser film, which is usually done by the laser paper manufacturer.
Then, UV varnish is applied to the surface of the print, and the coating method can be flexo, screen or gravure depending on the final required embossing effect of different thicknesses, and partial or full plate coating can be selected according to the design needs.
Next, the film is unwound and pressed together with the UV varnish coated print, while the embossed laser film is wound up to be used again, and the roll of laser film can be reused more than 20 times.
Finally, the embossed print is UV cured and wound up.
Implementation method
With the demand of cigarette packet printing for the application of laser embossing transfer process, the process has been developed rapidly, and various supporting materials and equipment have become mature. At present, there are three main ways to achieve the laser embossing transfer process.
1. Fully automatic off-line production method
That is, after the printing machine has finished printing, the laser embossing transfer process is processed as a post-process production method. The fully automatic laser embossing transfer equipment is equipped with automatic material feeding, automatic material receiving, UV varnishing and laser embossing mechanism. At present, there are 2~3 domestic manufacturers who can provide such equipment, mainly located in Guangdong and Shanghai. If a printing company applies laser embossing transfer for products with larger production batches, it can consider using this production method.
2. Semi-automatic in-line production method
This kind of equipment is only equipped with a laser embossing mechanism, UV varnishing and feeding need to be completed with the help of the printing machine, the application is convenient and flexible, and can be connected with automatic screen printing machines, semi-automatic screen printing machines, single gravure machines and offset printing machines with coating units. This production method has small investment and is suitable for small and medium-sized cigarette packet printing enterprises as well as other packaging printing enterprises with many laser embossed transfer products and small batches.
3. Retrofitted in-line production method
That is, in the gravure printing machine or flexo printing machine through their own transformation, the addition of a set of laser embossing mechanism, so as to achieve the printing and laser embossing synchronous production method. This method is suitable for the gravure and flexo cigarette packet printing enterprises with single and large batch of laser embossed transfer products.
Problems to be noted in production
Problem 1: The order relationship between the laser embossing transfer process and the stamping and embossing process
If you choose to carry out the laser embossing transfer first, followed by stamping and embossing, it should be noted that the surface of the ordinary UV varnish after the curing of the laser embossing transfer is very difficult to stamping, which will easily lead to the stamping of defective images, so you need to choose the UV varnish that can be stamping
If you choose to stamping and embossing first, and then laser embossing transfer, you need to choose not easy to produce burr aluminum, in order to reduce the impact of aluminum burr on the repeated use of laser film, so as to improve the utilization of laser film.
Problem 2:Temperature and humidity control at production site
The laser embossing transfer process is sensitive to the temperature and humidity changes in the production environment, too high temperature and too low humidity can lead to serious quality problems. For example, low humidity will easily cause static electricity in the laser film, which will lead to the UV varnish on the surface of the printed products, especially the UV varnish on the surface of the electrochemical aluminum to pull back to the laser film, causing serious quality problems, and at the same time will greatly reduce the number of times the laser film is used and increase the production cost. Therefore, maintaining a good production environment is necessary to ensure product quality. Generally, it is more appropriate to keep the temperature around 25°C and humidity around 70%, which can reduce the dust level in the air and thus ensure the stable product quality.
Problem 3: Poor effect of laser embossing and transfer
The poor effect of laser embossing transfer refers to the surface of the printed products without laser effect or the position of the laser pattern drop point is not fixed, the shape changes, etc. This phenomenon is also called the discount phenomenon. The reasons for this phenomenon are mainly 3 points: one is the unstable longitudinal stretching rate of the base film of the shooting film, the second is that the film guide rollers of the laser embossing transfer equipment are not installed in place or there are problems of their own, which leads to the laser film being loose and tight when walking the film, affecting the speed of walking the film and causing the phenomenon of folding, the third is that if the printing plate or anilox roller of the coating set is uneven, it will lead to uneven UV varnish on the surface of the print, thus making the laser effect transferred to the surface of the print The laser effect to the surface of the print becomes poor.
Problem 4: Rough varnish layout
The main reason for the roughness of the print varnish page has 3 points: First, the UV light oil viscosity is too low, the second is too many times the use of the shooting film, the film surface of the network cavity is not complete, can not form a trigonal effect, resulting in a glossy varnish page, the third is the UV light oil temperature is too high or too low.
In terms of UV light oil temperature, generally control at about 50 ° C is more appropriate. In the case of low temperatures in winter, UV light oil easier to crystallize, it is necessary to use heaters to improve the temperature of UV light oil, while in the case of high temperatures in summer, UV light oil in the process of equipment operation will naturally warm up, so no heating can reach the ideal temperature.
Issue 5: Impact of paper performance
The biggest impact on the UV light oil coating paper performance is smoothness and surface absorption, which will have an impact on the leveling of UV light oil, is the key to the formation of high smoothness of the printed surface bright film. Therefore, different paper should be adjusted accordingly to the coating leveling time, curing temperature and other process parameters. It is especially worth mentioning that after stamping, embossing paper must pay attention to keep flat, otherwise it will not be able to be coated, this is because the paper and laser film lamination is not subtle will produce many bubbles, thus causing a large number of scrap.
Problem 6: Cleaning work
As the laser film is easy to produce static electricity, especially when the paper and laser film lamination is heated, it is very easy to produce strong static electricity, which will adsorb all the impurities around to the surface of the film, and then transfer to the surface of the print and produce dirty spots. Therefore, before UV varnish coating, be sure to do a good job of dust removal and cleaning of equipment in order to minimize the production downtime cleaning. Of course, the dust attached to the surface of the printing plate cylinder had to require the operator to stop cleaning general less than an hour need to clean once.
