Book cover hydrosol coating quality control points

In the book cover and other printed matter surface coated with a layer of polypropylene plastic film, used to increase the surface brightness, it has moisture, anti-fouling, folding and other functions, after the film is printed bright, luxurious, greatly enhance the value of grade.

In addition, the hydrosol has excellent adhesion properties and can produce good affinity to the ink layer. No longer use organic solvents. No effect on the printed paper or ink. No wrinkling, detackification, and release. At the same time, fire hazards are eliminated at production sites and warehouses to ensure safe production. No longer use organic solvents, no volatile pollution of harmful gases, in line with national environmental protection requirements, purify the production environment and protect human health. In addition, it is possible to perform laminating processing on printed products whose ink layers have not been completely dried after printing. This saves man-hours and shortens the processing cycle. Because of its lightfastness, it does not cause bleed and discoloration of ink pigments, and does not cause yellowish discoloration due to aging. The hydrosol is cheap, the amount of coating is small, and the cost is low. The hydrosol is now basically replacing the use of hot-melt type resin.

However, due to operation and other reasons, the product after the film often appears bright or blisters, wrinkles and other phenomena. Now talk about the handling of common problems in operation.

1. temperature control

In rainy or rainy seasons, if the temperature is not adjusted properly, the film products will not shine. There is noticeable water vapor on the silicone roller, which is caused by the paper absorbing a large amount of moisture. At this time, the temperature of the hot roller can be adjusted to 40 degrees Celsius. If the temperature is too high, it will blistering. Some hydrosol laminating machines do not have a heating device. It is necessary to add a drying lamp before pressing to dry the adhesive layer and reduce foaming.

2. Pressure control

When laminating, the pressure should be adjusted according to the thickness of the paper, generally at 5Pa. If the pressure is too high, wrinkles and paper deformation will occur.

3. Glue control

The glue control is controlled by the gap size of the sizing roller and the gluing roller, and the scraping film is added. Scratch film pressure light glue, pressure heavy rubber volume. The quantity of glue should be mastered, and it can be evenly covered without producing crystal spots. If the amount of glue is too large, the product will not be shiny. During the gluing process, care must be taken to prevent the tiny particles and impurities that remain after the gel from sticking to the rubber disc. If it is stuck on the film, it will produce a white offset, causing linear foaming. Before using the machine, use alcohol solvent to clean the rubber roller and the rubber bucket. If the rubber roller is not cleaned, it will cause pinholes. The glue containing impurities can be diluted with water. After the impurities are precipitated, the diluent can be used to reduce the waste of glue.

4. Roller cleaning

When paper separation occurs, the glue will directly roll on the silicone drum, causing accumulation, easy to wrinkle the product, or affect the brightness of the product, should clean the drum frequently and keep it clean. The drum itself will wrinkle when it is not even, and it needs to be replaced.

5. Temperature and humidity control

The environmental temperature and humidity change greatly, and the paper absorbs moisture to generate “foliage”. When the film is covered, the paper is easy to wrinkle, and the balance of temperature and humidity should be maintained. The temperature of the heating roller is too high, the tight edges of the paper will wrinkle, and the temperature must be controlled as required.

6. Paper control

Paper skew will make the paper wrinkle, operation should be serious, so that the paper delivery service, the same pressure on both sides. When feeding paper, strive to stack 3mm per sheet of paper and control the amount of glue to prevent overflow. This can reduce the mutual adhesion of products after the film is covered. If the connection is wrinkled or cavitation, the pressure should be increased appropriately to maintain the temperature and humidity balance, so that the adhesion can be reduced and foaming can be reduced.

7. Film roll control

Prevent wrinkles caused by the inconsistent elasticity of the film rolls. First, select the two sides of the elastic film, and then adjust the tension on both sides of the film to make it balanced to prevent wrinkles. When using a film, try to use a film with a size larger than the open size, such as a large format, use a 44-mm wide film instead of a 460-mm wide film, which saves 4% in cost. When the 780mm wide film is used for copying, it is necessary to trim the edges to reduce the amount of glue and save the glue.

8. Printing Do not use additives to control the amount of dusting

Do not use additives as much as possible during the printing process, because it is not easy to dry, easy to blistering after coating. And also need to control the amount of dusting. Before the film is coated, special personnel should be arranged to wipe off the powder on the cover to reduce the phenomenon of blooming or blistering of the film and make the product bright.

9. Speed ​​control

During the laminating process, do not arbitrarily change the speed of the host. The speed is too fast. The adhesive cannot reach the requirements. When the speed is slightly increased, the amount of glue is too large. If the speed is adjusted too low, the amount of glue is reduced and it is easy to foam. In order to ensure that the amount of glue is basically the same, the speed of the laminating machine can be limited by the maximum speed of 60% so that each class can run at a specified speed and data management can be implemented to reduce unnecessary losses.

Source: "Printing Technology"