Hot Stamping Technology Discussion

In recent years, with the continuous improvement of product packaging requirements, hot stamping technology as a commonly used process technology in packaging design, is also rapidly developing along with it, and its process technology is increasingly perfect. However, there are still some more difficult problems in practical use. I have carried out some simple analysis of the hot stamping problems that occurred in the production process. The following personal experience will be written down to hopefully inspire the craftsmen who are engaged in the printing work.

Composite cardboard hot stamping

As we all know, hot stamping on the surface of white cardboard is relatively easy. Composite cardboard imposes higher requirements on the performance of electrochemical aluminum. Correct understanding of the relationship between them should be carefully analyzed from the following aspects:

1. Analysis of surface tension of composite paper

There are many types of composite paper, which are generally classified into several categories: PET film paper, aluminum foil paper, aluminum spray paper, transfer paper, and so on. The surface tension of the composite materials of these papers are all different. It directly affects the hot stamping effect and the normal operation of the hot stamping process. The problem of hot stamping on such papers cannot be solved by simple operations. From the analysis of the characteristics of composite paper and the performance of hot stamping foil, the surface tension of composite paper stamping can be roughly solved by the following methods:

External assistance method: According to the surface properties of the paper, the aluminum is properly selected, and the technical problem of the aluminum manufacturer is used to solve the hot stamping problem. Their main method is to solve the hot stamping problem by adjusting the hot stamping foil glue layer according to the surface properties of the composite paper.

Active attack method: The surface properties of the composite paper are processed to change its surface tension to meet the requirements of hot foil. Can be coated on the surface of the paper (all or part of the coating can be used according to the specific circumstances) a thin layer of colorless Varnish, in order to change the surface tension of the paper to meet the requirements of hot stamping foil.

Coordinating with each other: When the above two methods alone cannot solve the hot stamping problem, the external assistance method can be used in conjunction with the active attack method to solve the hot stamping problem.

2. Composite paper stamping performance analysis

The composite paper has a variety of composite materials and its physical properties are necessarily different. When solving the problem of hot stamping on such papers, it is also necessary to pay attention to the different requirements for the properties of hot stamping materials for each composite material. According to different papers using different hot stamping foils, the suitable temperature range of the hot stamping foil glue layer is also selected according to the type of composite material, so that the hot stamping can be performed under the best condition. For example, the hot stamping temperature on PET film is lower than the hot stamping on aluminum foil paper, and so on.

Printing process on hot stamping foil

In the process of designing and developing new products, the craftsman aims to highlight the product theme. A special hot stamping technique is often used, that is, the first hot stamping technique. However, this process technology often appears in the implementation process of aluminized printed ink pull back, this problem has not only seriously damaged the design effect, but also very unfavorable for printing equipment. As the anti-pulled aluminized powder quickly accumulates on the blanket, light pattern dots are missing, and heavy prints result in partial image printing. Not only that, the electro-aluminum metal powder can enter the ink roller by transferring, it will accelerate the wear of the ink roller and cause damage to the printing equipment. From the above analysis, we can see that if we want to use this kind of process scheme, we must completely eliminate the problem of back-drawing of the electrochemical aluminum in the printing process. To solve the problem of anti-galvanic aluminum pull can start from the following two aspects:

1. Bronzing quality control

The quality of bronzing is the precondition for ensuring the normal printing. How to ensure the quality of bronzing is nothing more than the following aspects.

Depending on the surface properties of the paper material, use a suitable hot stamp foil. After foil stamping, the foil effect will generally have a great contrast with the background, and its hot stamping brightness effect need not be worried. The key point is that after hot stamping, make sure that the hot stamping layer on each sheet is firmly attached to the surface of the sheet. To achieve this goal is not only to make efforts on the selection of materials, but also to strictly regulate the operating procedures of personnel in the machine.

In addition to requiring machine personnel to pay attention to controlling the stamping temperature, pressure and speed, it is especially important to test the fixing force of the stamping layer on a regular basis. Because in the hot stamping process, the fixing force of the hot stamping layer and the paper may gradually change with the increase of the number of hot stamping sheets, which requires us to correct in a timely manner. Fixing force test method: Adhesive test method. Use adhesive tape to stick to the hot stamping layer, and then pull off the tape in a smooth way. Through this method, the fixing force of the hot stamping layer is tested. In general, printing is certainly not a problem if the hot stamping layer cannot be pulled. If the hot stamping layer is pulled off by the tape, it indicates that the fixing force of the hot stamping layer is unqualified and the school pressure treatment is required immediately. When the school presses a certain number of times, the hot stamping quality tends to a stable state.

2. Control of the printing process

General offset inks have relatively high viscosities and have a greater pull on the surface of the paper during the printing process. We can alleviate this contradiction by appropriately reducing the viscosity of the ink. In addition, in the case of normal printing, the printing pressure is as small as possible.

UV Varnish on Hot Stamping

Hot stamping on UV Varnish is very rare. At present, the performance of UV varnish in hot stamping is still not mature, and hot stamping is unstable. UV Varnish resin components and additives are also not conducive to aluminum foil stamping, these issues require the ink factory to further improve the ink. In the printing industry, UV Varnish has always played a role as a high gloss oil. Its unique highlighting effect has also been recognized by a large number of printing process personnel, but UV varnish still has deficiencies in many other post-processing performance.

The following is only a brief analysis of the problems that arise during the development of the test. The problem of hot stamping on UV Varnish is mainly due to:

1, to form a high-brightness effect must be required to have a certain thickness of UV Varnish, but the thicker the printing ink ink layer is more detrimental to hot stamping. Generally, the thickness of offset printing roller type UV varnish is above 9g/m2.

2. The drying of UV varnish requires special resins and a large amount of auxiliaries, which will inevitably affect the surface properties of UV varnish that are not conducive to hot stamping.

3. At present, the affinity of the resin component in the UV varnish under the high temperature and high pressure is not good enough with the electro-aluminum hot stamping foil. Therefore, it is difficult to perform hot stamp control on UV inks.

Through the above analysis found that in the hot stamping should pay attention to the following aspects:

1. To improve the brightness of UV light oil, it is not advocated to increase the luster effect by increasing the thickness of the ink layer. Can adjust the printing process (coating roller screen angle and number of lines, etc.) and printing equipment performance (pressing pressure and printing speed, etc.) to improve the ink smooth, bright effect.

2. Reasonably choose hot stamping materials so that the glue layer has a good affinity with the UV oleoresin layer.

3. Accurately adjust the temperature and pressure of hot stamping, hot stamping speed should not be too fast. Excessive pressure and temperature can destroy the surface properties of the ink and make bronzing harder.

Hot Stamping Pattern Registration Process

The so-called bronzing pattern registration process is a process in which the metal foil pattern is first stamped on the surface of the paper and then the overprint pattern is applied thereon. During the implementation of this process, the problem of inconsistency between the printed pattern and the bronzing position often occurs. The following analysis from the following aspects:

1. Paper scalability control

Paper stretching is the most varied and difficult part to control during the printing process. It is impossible to prevent paper from stretching in the printing process, but it is entirely possible to control its stretching value in a relatively stable state. How to control its retractability is the basis for the completion of this process. The following requirements can basically meet the control requirements. After the new paper is opened, it is stored in the printing shop for 2 to 3 weeks, allowing it to expand and contract in the production environment to a stable state, and then it is wrapped with a stretchable film. The stability of the new arrival paper is generally quite poor, the reason is: First, the new factory paper is still in a very unstable state (for example, the size of the water content), to be stable must be changed over time to complete. Second, the temperature and humidity of the environment during the transportation process changes greatly, the difference between the temperature and humidity of paper manufacturers and printers, and so on. Third, in the entire process of the product needs to use a telescopic film wrapped semi-finished products to ensure the consistency of the paper telescopic deformation.

2. Hot stamping process control

Pattern-positioning hot stamping is the key to this technology, and scientific processes and statistical techniques must be used to improve this process. Try to eliminate the problems that have emerged in the bud. Hot stamping can use the following program for hot stamping control: First, film positioning method. During the hot stamping process, the film is stamped on the position, ie, the position of the hot pattern is checked by the film to ensure that the position of the pattern on the paper is correct. During the use of the method, the gauge line must be pressed at the middle edge of the paper to facilitate the stability inspection and post-processing inspection of the hot stamp. Second, the contour positioning method. The outline of the pattern to be stamped (its size can be slightly improved) is printed using a printing device to first print a light-colored outline and then hot stamped against the printed outline. This method is conducive to the machine personnel to detect whether the hot stamping position is accurate. Third, special attention should be paid during the hot stamping process to ensure the consistency of the hot stamping two regulations, otherwise the consequences would be disastrous.

3. Printing process control

If the above two major aspects are all under normal control, the printing process will be very easy. If there are problems during the control process, the following measures can be taken to remedy: First, for the products that are not properly handled by the paper, the humidity control method can be used to record the paper humidity conditioning time and the environmental status in the form of a table. Detailed records, analysis of the humidity control process records and products after a successful small batch test. Then formulate a standardized humidity treatment process plan and implement the process plan to finalize the printing process. Second, if it is during the hot stamping process because the two regulations are not stable, you can use the method of drawing lines to carry out the regulation of printing (if hot stamping two regulations too messy that the batch of products will be scrapped). When we deal with problems in the printing process, production is in a passive state, so the focus of the entire processing process is clear to everyone, and we no longer emphasize it here.

At present, although the hot stamping process technology is already a mature process technology, there are still some unexpected problems in many new application fields. These issues still require the printing process researchers to seriously summarize the issues and tirelessly study and study hard to achieve a satisfactory solution. (Wen / Zhou Hong Zhao Zhimin)