At present, aluminum foil and aluminized film are relatively frequent and fashionable substrates, but aluminum foil and aluminized films may not be noticed in the process of composite processing. Quality problems may occur, such as the more common composite products are spotted and white. Points and other quality issues. This article will focus on the failures and countermeasures in the composite process of aluminum foil and aluminized films.
The combination of aluminized films produces noticeable white or gray spots. These spots are common in the full-print printing composite process. There are three main reasons:
1. The quality of the aluminized film itself is poor, the coating is easily peeled off, and the aluminized film and the calendered film are not even. In particular, when the adhesive is coated, the unevenness occurs, and after the compounding, white spots that are dense or irregular are more easily generated. Inks and adhesives have different levels of adhesion on the surface. The adhesion between the ink layer and the coating at the spots where the spots are generated is low (due to the uneven distribution of the ink or adhesive), resulting in poor adhesion between the layers; Plating at the place has obviously shifted and the tightness between the layers is good. Reflected by the aluminum layer reflective intensity, the formation of white spots or gray spots, the degree of speckle depth and ink hiding power and the amount of sizing, especially glue leveling are very much related. Good hiding power, light spots; good leveling and uniform coating, less white spots. On the contrary, there are many spots and serious white spots.
2. The ink itself has poor tightness and poor hiding power. After the printing film is coated, the ink layer is infiltrated with the acetate alcohol in the adhesive, and some of it is dissolved. After the compounding, the ink layer and the adhesive layer are easily infiltrated and destroyed by the solvent of the adhesive system, resulting in different shades and causing different color shades. , it forms a so-called spot.
3. The adhesive quality is poor. This adhesive has a poor affinity for the aluminized layer, especially the uneven adhesive in the OPP printing film and BOPP printing film and the aluminized film compound, this glue performance is more obvious. This is mainly due to the high surface tension of the adhesive, poor coating properties, uneven coating of the glue, and â€œspottingâ€. At the same time, the glue generally has high initial tack, poor solvent release, and due to the influence of residual solvents after aging, the strength is not as good as the initial tack. After the printing film is compounded, the ink layer is infiltrated with the residual solvent, and there is also the possibility of spotting. The above phenomenon will be more obvious when such adhesives are used at a high speed on a roller with more than 150 lines. If the adhesive coating fails to produce slight solubility with the ink of the printing ink, no white spots will be visible on the surface. However, after the composite process, the adhesiveness between the adhesive layer and the ink layer or even the printing film layer cannot reach the actual requirements of the packaged product. Easily stripped.
In general, there are more â€œspotsâ€ caused by the above three reasons, but we can use the following methods to eliminate this phenomenon:
1. The use of ink with better hiding power is a more fundamental method to eliminate the phenomenon of spots caused by the former species. It is also possible to stencil the deep-printing line roller to increase the thickness of the ink layer, but this will increase the cost.
2. The use of a suitable adhesive for aluminized films is an effective way to eliminate the phenomenon of blobs caused by the third reason. The special adhesive for the aluminized film is moderate in molecular weight and uniform, and the initial adhesive force is not very high, but the coating performance is excellent, the solvent release property is good, and the peel strength is good after aging. In addition, if you do not have a good aluminum foil adhesive, you can use a deeper network roller, while reducing the operating concentration, slow down the speed, you can also reduce or solve the "spot" phenomenon.
3. If it is caused by pigments or fillers in the ink, it will often appear in three cases: (1) When the titanium dioxide, and other particle size is not equal, and one of the pigments is in the flocculation state, but the same density , There will be spots; (2) titanium dioxide and other particles of the same size, but the density is different, there will be spots; (3) the size of titanium dioxide particles are not equal, but the density is not the same, the same will appear spots. These three types of failures are more likely to occur after the addition of silica to the "active particles" resulting from excessive flocculation or ink grinding. For this phenomenon, as much as possible, all dry powders should be mixed before being put into dispersion, or the amount of white carbon black can be reduced, or the dispersant or antistatic agent can be increased, or the grinding time can be shortened (since most of the failures occur at the outlets are shallow or fundamental The large area of â€‹â€‹the plate that is not engraved) prevents the competition between the unusual colors and fillers from sticking to the plate roller and is distributed on the printing surface by a doctor blade. A "CHY-1" type printing aid is preferably added to eliminate spots.
In addition to the white point of the aluminized composite film, there are also obvious white spots on other composite films. Such white spots can be randomly distributed and have uneven sizes. One is when there is a machine, but it basically disappears after aging; the other is when it goes down and does not disappear after aging. The latter is a bigger issue that affects performance. Such spots are more likely to appear in printed effects with white or light yellow bottoms. In general, as long as such a white point occurs, it is generally full version (except for equipment reasons), but the difference between white and light yellow hiding power is easy to see. There are many reasons for the phenomenon of white spots. There are three main reasons:
1. The ink particle size is large or the particle size distribution is not wide, generally the size of the white ink has a greater influence. The ethyl ester in the adhesive is a good solvent for the ink, and the results of infiltration of ink particles with different particle sizes are different. The color change after heating or compounding in an oven may cause a difference, and it seems to produce a â€œwhite pointâ€. In this kind of situation, when the machine is down, the white point phenomenon will be lessened and may disappear after curing. When printing, it is better to add 1.5-3% of M-27 coupling agent, such as Tian Yang Chemical Factory, to increase the tightness of the pigment filler in the ink system to resist the large area caused by the solvent infiltration and destruction in the adhesive system. White spots or spots.
2. The surface tension of the adhesive is high, and the effect of infiltration and spreading on the aluminized film is poor. This is the "white spot phenomenon" of the current aluminized film, and it is also the main reason for the occurrence of spots on other composite films. The effect of the adhesive coating is not good. After the printing layer is covered, the color of the different parts will change, resulting in the same effect as before, and sometimes large spots will be produced.
3. Equipment process reasons. On the one hand, the reason for this is that the workers are not aware of the special nature of the aluminized film composite. The aluminized film compound has its unique place. On the other hand, the pressure on both sides of the equipment during the sizing process is inconsistent, even in the system itself such as drying and coating. The problem does not guarantee adequate uniform coating of the adhesive or sufficient volatilization of the ethyl ester. There are other reasons, such as full-bottom printing network roller roller mesh is too shallow, reducing the hiding power of ink and so on.
Take the following measures to eliminate "white spots":
1. Different batches of inks increase the fineness detection index and are strictly controlled. In particular, the size and fineness of full-bottom inks are not used outside the standard range.
2. Use aluminum foil special adhesive. The special adhesive for aluminized films has a lower surface tension, and the effect of coating and spreading on the surface of the aluminized layer is significantly better than that of a general-purpose adhesive. The use of aluminized film glue is very easy to control the leveling of the glue and has a better coating state. From the state of adhesive coating alone, the use of aluminized adhesive can eliminate white point phenomenon.
3. The viscosity of the glue has a certain matching relationship with the number of roller lines of the cable. Exceeding the matching range too much will destroy the coating state of the glue, causing the occurrence of â€œwhite spotsâ€ and other serious malfunctions, but it seems to appear on the aluminized film. The main reason is that the production of "white spots" is more interesting.
4. Using aluminum film coating method. The commonly used coating process is a printing film (protective layer) coating, where a special coating method is used to avoid the problem of inhomogeneous penetration of ethyl ester to the ink layer, but this process has its own limitations. First of all, it is only limited to VMPET compounding, and second, it will sacrifice a certain peel strength.
5. The manufacturer must adhere to the regular cleaning system of the coating roller and grasp the correct cleaning method of the coating roller. In the production of full white or yellow printing film, pay attention to two points: First, before the production of the scraper, coating roller, flat roll, etc. thoroughly cleaned; Second, for the old domestic dry machine, the speed ratio than normal Slower speed to ensure the drying effect.
Printed on the aluminized film often due to the foam in the ink pinhole (blank point / pit) failure, the general exclusion method: First, tighten the composite roller; second is to increase the amount of coating glue; third is to add defoamer Simethicone oil; Fourth, try to use a straight blade, and increase blade blade 1-2mm, or use a soft blade (such as steel tape instead), and the blade angle is adjusted to not less than 45 Â° angle; five is Add a piece of rubber on the back of the scraper, which can effectively scrape the spots caused by the poor dispersion in the printing and graphic ink system or caused by the oxidized skinning in the ink fountain; Sixthly, white carbon black is added to the printing ink to promote printing. The ink ink film is thickened to increase the hiding power of the white ink ink film; the seventh is to reprint again to increase the thickness of the ink film; the eighth is to select the deep gravure printing to increase the ink transfer rate; and the 9 is to put a stirring in the ink fountain. The device ensures the uniformity of the printing ink in the transfer process. Tenth, it replaces the printing ink with high viscosity and antistatic printing or slows down the printing speed, and strives to eliminate the problems of pitting, pinholes, spots and white spots.
In actual production, only high-efficiency additives and new materials are used to make up for the deficiencies in their aluminum-plated composite printing products and improve the quality of packaging and printing processes.