In the offset printing laminating process, many factors will affect the quality of the film more or less, here, for your inventory of the "seven sins" affecting the quality of the process. These seven points are: Design, Paper characteristics, Ink characteristics, Laminator selection, Environmental conditions, Speed and Pressure.
At the beginning of the design of the printed matter, the film should be considered. That is to say, when designing the printed matter, the designer should take into account the processes that need to be carried out in the subsequent printing and post-printing process. Process, what paper and ink to use.
When a thermal lamination film is used for the cover of a publication such as a book or magazine, the film is often insufficient due to insufficient coating conditions, resulting in a defective cover. In the cover design, if our designer designs the color to be light or even colorless at the rolling line, so that the adhesion here excludes the interference of the ink, then there is no problem of filming. Similarly, the thermal lamination film is not suitable for metal inks, and it is prone to filming. Therefore, for the problem of film coating, first, the designer of the printed matter should know how many processing steps the printed matter needs to go through, what effect each processing process has on the film, and how to avoid such influence, thereby improving the yield. This requires designers to master the effects of printing, bronzing, local UV, rolling lines, bumps and other processes on the film during design.
2. Paper characteristics
The thermal lamination film has certain requirements on the paper, and the improper selection of the paper may also cause the printed matter after the thermal lamination film is bad. According to experience, the tensile strength of short staple paper is low, and the paper is easily broken after the thermal lamination film is applied at the rolling line or the unevenness, so that the ink on the paper is broken, causing partial separation of the film and the printed matter, especially when the direction of the rolling line is This problem is more likely to occur when the orientation of the paper is the same. In addition, the coated coated paper, especially the thick coated coated paper, has no problem after using the thermal lamination film, but if the film is rolled, the unevenness and the like are formed, the film is formed at the rolling line and the unevenness. Phenomenon, this is mainly due to the small amount of high molecular polymer added in the coating of the coated paper, and the inorganic components are many. When the external force is applied, the coating is easily powdered and peeled off. Therefore, the film is caused by the rolling line or the unevenness process. The film layer of the film is separated from the printing paper.
Another problem with paper is that the surface is too rough, and if the thermal lamination film device used does not have a flattening system, it tends to cause the surface of the offset print to be unsightly.
3. Ink characteristics
In practice, this often happens. The same thermal lamination film, the same laminating equipment, and the same laminating process conditions have the opposite two results for the two prints: one is qualified, The another is unqualified. Such results have to attract attention.
There are many types of printing inks, and the performance varies greatly. After many years of practice, it is found that the surface properties of the ink after printing have a great influence on the results of the thermal lamination film, which affects the composite fastness or bonding fastness of the thermal lamination film to the ink. The method of checking the surface wetting tension of the ink is used to determine the composite fastness of the ink and the thermal lamination film with different surface properties, and to detect the problematic film proof. When the surface energy of the ink is above 34 dyn/cm, the adhesion of the thermal film to the ink is very poor, and when the surface energy of the ink is increased to 38 dyn/cm or more, the product of the qualified film can be subjected to the rolling line and the unevenness.
When paraffin is deposited on the surface of the printing ink, silicon-based organic substances or excessive mineral oil is insufficiently dried, the surface energy after printing is lowered. The above substances are small molecular substances, and the bonding force between the surface of the ink and the ink body is very weak. Since the bonding force between the film and the ink is completed by the attraction between the molecules at a close distance, the film is The glue layer can only adsorb the material of this layer, and cannot pass through the layer and the binder in the ink, thus causing the film to not bond firmly with the printed matter.
4. Laminator selection
There are many factors to consider when actually selecting thermal lamination equipment. The main points to note are:
(1). Heating roller temperature uniformity
In the laminating process, the surface of the heating roller through which the coating product passes and the surface temperature through which the laminating product does not pass are very different, often when the coating temperature is sufficient, and when the film is rolled and uneven There is a filming phenomenon. Since the sensor that detects the heating roller is fixed to the edge of the heating roller, and the temperature seen by the operator is not the true temperature of the film, it is easy to cause confusion to the operator. Therefore, * place the induction temperature device close to the intermediate surface.
(2). Surface state of steel drum
The surface of the conventional oil-coated or water-based film is required to be as smooth as possible, so that the BOPP gloss after the film is better, but such conditions are not suitable for the thermal lamination film. When the film is precoated, the surface temperature of the roll is required to be about 110 degrees. At such a temperature, the roll-off property of the film after the film is deteriorated as the processing progresses. Therefore, the surface of the steel bar used for the thermal lamination film should be finely rough. The surface condition of the steel drum also requires no pits, drums, scratches, and the like.
(3). Uniformity of the rubber roller
The uniformity of the rubber roller mainly includes the uniformity of the outer dimensions and materials.
5. Environmental conditions
For the environment of the film, it mainly involves the temperature and humidity changes in the plant area.
In the cold winter, film and prints cannot be processed immediately after they are transferred from the outside to the inside of the room. They must be processed until the temperature of the raw materials and the ambient temperature are balanced.
After the film is completed, since the moisture cannot be volatilized from the surface of the film, it has to be moved to the edge and precipitated, so that the separation of the paper film easily occurs at the edge, and when the humidity exceeds 90%, such a problem is very prominent.
The speed of filming determines the melting time of the adhesive on the thermal lamination film on the heating roller and the contact time of the film and paper. The filming speed is slow, and the heating time of the adhesive on the BOPP film is relatively long. The film and paper are relatively long. The pressing time is long, the bonding effect is good, but the production efficiency is low. The film coating speed is fast, the adhesive on the BOPP film has a short heating time on the heating roller, the contact time between the film and the paper is short, and the bonding effect is poor. Therefore, the production speed of domestic thermal lamination film laminating equipment is generally controlled between 5-30 m/min.
In fact, the surface of the paper is not flat, and only under the proper pressure, the molten hot melt can completely cover the surface of the print. If the pressure is small, the bonding is not strong; the pressure is large, and the product is easily wrinkled, and the surface of the rubber roller is easily damaged, deformed, and the service life of the rubber roller is lowered. And as the pressure continues to increase, the contact pressure between the rubber roller and the heating roller increases, the shaft head and bearing load of the two rollers increase, the wear is intensified, and the load of the transmission system is increased, so the pressure is too large, which will affect the whole machine. Service life.
In actual production, the pressure should be adjusted according to the difference in the paper.