Faults and Countermeasures in the Process of Aluminized Film Composite
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In recent years, due to PP oxygen permeability / PET permeable / PE ink adhesion and color migration, tensile elongation is large, and easy to wrinkle, overprinting is difficult / most PVC is toxic, such as the use of PVC high frequency Heat sealing, the film tends to be blown / PT has poor tear resistance, and shrinks at high temperatures, the strength is reduced or becomes brittle, etc. There are different defects mentioned above, and AL and aluminized film become the current Use the most frequent and stylish substrates. However, in the processing and compounding process of AL and aluminized film, there may be quality problems such as spots and white spots in the composite product. The two quality problems occur more than plastic/plastic and aluminum/plastic or aluminum/ There are many quality problems in paper composite processing, which is a headache for many flexible packaging manufacturers. A systematic introduction to the causes and solutions is now available for reference by packaging and printing colleagues.
First. Aluminized film composite products produce "spot" phenomenon
The aluminized film combines to produce distinct white or gray spots, which are most common in the full-page ink-printing compounding process. The main reasons are threefold:
1. The quality of the aluminized film itself is poor. The plating layer is easily peeled off and the aluminized film and the calendered film are not flat/especially when the adhesive is applied, and the white spots which are dense or confusing are more likely to occur after the compounding. The adhesive strength of the ink and the adhesive on the surface is different. The adhesion between the ink layer and the plating layer is low at the point where the spots are generated (the spots caused by uneven dispersion of the ink or the adhesive) make the interlayer tightness poor; no spots The coating has been transferred significantly and the tightness between the layers is good. The anti-light intensity of the aluminized layer forms white spots or gray spots, and the degree of the spots is closely related to the ink hiding power and the amount of sizing, especially the rubber leveling property. The hiding power is good, the spots are shallow; the rubber leveling is good and the coating is uniform, and the white spots are less; on the contrary, the spots are many and the white spots are serious.
2. The ink itself is not tight enough and the hiding power is poor. After the printing film is glued, the ink layer is wetted by ethyl acetate in the adhesive, and partially dissolved. After the composite, the ink layer/adhesive layer is easily infiltrated and destroyed by the solvent of the adhesive system, resulting in different shades, resulting in color Differences form so-called spots.
3. The quality of the adhesive is poor. This is not to say the adhesive itself, but the adhesive has a poor affinity for the aluminized layer. Especially the uneven adhesive is compounded in the OPP printing film and the BOPP printing film and the aluminized film. obvious. Mainly because of the high surface tension of the adhesive, poor coating performance, uneven coating of glue, causing "spot" phenomenon. At the same time, the glue generally has a high initial tack force and poor solvent release property, and the strength is not as good as the initial tackiness due to the residual solvent after the ripening. After the printing film is combined, the ink layer is wetted by the residual solvent, and speckle may occur. The above phenomenon is more pronounced when such an adhesive is used at a high speed composite on a web roll of 150 l or more. If the adhesive coating cannot be slightly soluble with the ink film of the printing ink, no white spots are visible on the surface, but the adhesion of the adhesive layer to the ink layer and even the printing film layer after the composite process cannot meet the actual requirements of the packaged product. Very easy to peel off.
There are many “spots” caused by the above three reasons, and the following methods can be used to eliminate this phenomenon:
1. The use of better hiding power is the most fundamental way to eliminate the speckle caused by the first and second causes. In addition, the printing line roller can be engraved to increase the thickness of the ink layer, but this will increase the cost. For the soft packaging manufacturer, it is not desirable, but it can be considered without other good methods.
2. The use of a suitable adhesive for aluminized film is an effective way to eliminate the speckle caused by the third cause. The adhesive for the aluminized film has a moderate molecular weight and uniformity, and the initial tack is not high, but the coating property is excellent, the solvent release property is good, and the peel strength is good after the aging. In addition, if there is no good adhesive for aluminized film, a deeper wire roller can be used, and the working concentration can be reduced, the machine speed can be slowed down, and the "spot" phenomenon can be alleviated or solved.
3. If it is caused by pigments or fillers in the ink, spots will often appear in three cases: 1 titanium dioxide and other mixing and particle size are not equal, and one of the pigments is in a flocculated state, but the density is the same, Spots will appear; 2 titanium dioxide and other particles are equal in size, and one of the pigments is in a flocculated state, but the density is different, there will be spots; 3 titanium dioxide and other particles are not equal in size, but the density is not the same, also Spots will appear. These three kinds of failures are the most "active particles" produced by flocculation or ink grinding time after the addition of white carbon black. In this case, all the dry powders should be mixed first and then put into the 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 (because most of the failure occurs at the outlets is very shallow or fundamental) Non-engraved large-area layout) to prevent the competitive adsorption between abnormal pigments and fillers -
— Glue and adhere to the plate roll and distribute it on the printing surface by scraping the blade. It is preferable to add a "CHY-1" type printing aid to eliminate spots.
Second, the general composite film white point generation and processing methods
In addition to the white point of the aluminized composite film, there are also obvious white spots on other composite films, which can be randomly distributed and uneven in size. There are two cases, one is when the machine is off, but it basically disappears after aging; the other is when it is off, it does not disappear after aging. The latter is the biggest problem affecting appearance. Such spots are most likely to appear in the effect of printing with a full white or light yellow background. In fact, it should be said that as long as such white spots appear, it is generally full version (except for equipment reasons), but the white and light yellow cover power is easy to see. There are three main reasons for the occurrence of white spots:
1. The ink particle size is large or the particle size distribution is too wide, and generally the particle size of the white ink has a large influence. Ethyl ester in the binder is a good solvent for the ink. The results of infiltration of ink particles of different particle sizes are different. The difference in chromaticity after heating or baking in an oven will make a difference, and it seems that a "white point" is produced. Generally, in this case, when the machine is off, the white point phenomenon will be alleviated and may disappear. When printing, it is best to add 1.5%-3% TM-27 coupling agent from Tianyang Chemical Factory to improve the tightness of pigment and filler in the ink system to resist the large area caused by 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 point phenomenon" of the current aluminized film, and it is also the main cause of spots on other composite films. The coating effect of the adhesive is not good, and after the printed layer is covered, the color of the different parts changes, and the same effect as before is generated, and sometimes large spots are generated.
3. Equipment process reasons. On the one hand, the workers are not aware of the special characteristics of the aluminized film composite. The aluminized film composite has its unique place. On the other hand, the equipment has different pressures on both sides of the sizing process, even in the drying and coating systems. The problem cannot be ensured that the adhesive is sufficiently uniformly coated or that the ethyl ester is not sufficiently volatilized. In addition, there are other reasons, such as the full-bottom printing screen roller web is too shallow, reducing the ink hiding power.
Take the following measures to eliminate the "white point":
1. Different batches of inks increase the fineness detection index and strictly control, especially if the particle size and fineness of the full-bottom ink are outside the standard range.
2. Use a special adhesive for aluminized film. The surface adhesive of the aluminized film composite adhesive has a low surface tension, and the coating spread effect on the surface of the aluminized layer is remarkably superior to that of the general-purpose adhesive. The use of aluminized film glue makes it easy to control the leveling of the glue and has an ideal coating condition. In terms of the adhesive coating state, the use of aluminized rubber can eliminate the occurrence of white spots.
3. The viscosity of the glue has a certain matching relationship with the number of wire roller lines. If the matching interval is too large, the coating state of the glue will be destroyed, resulting in the occurrence of "white spots" and other serious faults, but mainly on the aluminized film. It is still more interesting to produce "white spots."
4. Aluminized film coating method. The coating process usually employed is a printing film (protective layer) coating, and a special coating method is employed here to avoid the problem of uneven penetration of the ink layer by the ethyl ester, but this process has its limitations. First, it is limited to the composite of VMPET, and secondly, a certain peel strength will be sacrificed.
5. The manufacturer must adhere to the regular cleaning system of the coating roller and master the correct coating roller cleaning method. In the production of full white or light yellow printing film, it is necessary to thoroughly clean the scraper, coating roller, flattening roller, etc. before production; for the old domestic dry laminating machine, the machine speed is slower than the normal speed, ensuring drying effect.
Third, pitting
The printing on the aluminized film is often caused by the pinhole (blank point/pitting) caused by the foam in the ink. The general elimination methods are as follows: one is to adjust the composite roller; the second is to increase the amount of coating glue; the third is to add defoaming agent. Dimethyl silicone oil - 201; Fourth, try to use a straight scraper, and increase the blade edge of the blade by 1-2mm, or use a soft blade (such as a steel tape measure), and adjust the blade angle to not less than 450Angle; the fifth is to add a piece of rubber on the back of the scraper, so that the spots in the printed graphic film system can be effectively scraped due to poor dispersion or the oxidized crust in the ink fountain; the sixth is to add white charcoal to the printing ink. Black, which promotes the thickening of the printing ink film to improve the hiding power of the white ink film; the seventh is to re-print once to increase the thickness of the ink film; the eighth is to select the deep intaglio plate to improve the transfer rate of the ink; Put a stirrer in it to ensure the uniformity of the printing ink during transfer; ten is to change the high-viscosity and anti-static printing ink or slow down the printing speed, and strive to eliminate the pitting, pinhole, spot, white point failure purpose.
It has been known that both pure aluminum foil (AL), vacuum aluminum-plated film, or homogenous epitaxial growth of calendered aluminized film/surface aluminum, from the experimental production and theoretically directly prove the "deposition" The upward diffusion of the atom that the atom can climb up in growth - the quantum dot that forms a certain crystal orientation / is also the phenomenon of the growth dynamics of some aluminum products, aluminum foil, and aluminized film that we can't imagine, even closer In the past few years, China's packaging and printing industry has poor adhesion to ink ink films, spots and white spots that appear after compounding, and other technical problems that cannot be accepted. Causal relationship. We can only improve the high quality of our packaging and printing products by actually producing high-efficiency additives and new materials to make up for the shortcomings of aluminum-plated composite printing products.