Failure Analysis of Aluminum Foil and Aluminized Film Composite Process
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At present, aluminum foil and aluminized film are the most frequently used and fashionable substrates, but aluminum foil and aluminized film may cause quality problems when processing and compounding, such as the most common composite products with spots and white. Point and other quality issues. This article will focus on the failures and countermeasures in the process of aluminum foil and aluminized film compounding.
Spot
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, the aluminized film is formed, and the rolled film is not flat. In particular, when the adhesive is applied, the flow is uneven, and after the compounding, white spots which are dense or disorderly are more likely to occur. The adhesion of inks and adhesives on the surface is different. The adhesion of the ink layer to the coating at the point where the spots are generated (the spots caused by the uneven dispersion of the ink or the adhesive) makes the interlayer tightness; The plating has been obviously transferred, 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 largely 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 glue has good flatness and uniform coating, and less white spots. On the contrary, there are many spots 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 infiltrated by the acetic acid in the binder, and partially dissolved. After the composite, the ink layer and the rubber layer are easily infiltrated and destroyed by the solvent of the adhesive system, resulting in different shades, resulting in color difference. , the formation of so-called spots.
3. The quality of the adhesive is poor. The adhesive has a poor affinity for the aluminized layer, especially the uneven adhesive in the OPP printing film and the BOPP printing film combined with the aluminized film, the glue is more 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 and a poor solvent release property, and the strength is not as good as the initial tack 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. This phenomenon is more pronounced when such adhesives are used at high speeds on 150 rolls 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.
In general, the “spot” phenomenon caused by the above three reasons is more, but we can use the following methods to eliminate this phenomenon:
1. The use of better hiding power is the most fundamental way to eliminate the speckle caused by the former reasons. It is also possible to engrave the printed screen roller to increase the thickness of the ink layer, but this will increase the cost.
2. The use of a suitable aluminized film-specific adhesive 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 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 conditions are not equal to the particle size, 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 of equal size, but different density, there will be spots; (3) titanium dioxide and other particles are not equal in size, but the density is not the same, there will also be spots. These three kinds of failures are the most "active particles" produced by the flocculation of the white carbon black or the excessive grinding time of the ink. In this case, all the dry powders should be mixed as much as possible before being put into the dispersion. 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 the failure mostly occurs at the outlets is very shallow or fundamental) The large-area plate that is not engraved) prevents the competitive adsorption between the abnormal color and the filler. Agglomeration adheres to the plate roller and is distributed on the printing surface by the doctor blade. It is preferable to add a "CHY-1" type printing aid to eliminate spots.
White dot
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. One is when there is a machine, 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 performance. Such spots are most likely to appear in the effect of printing on a full white or light yellow background. In general, as long as such white spots appear, it is generally full (except for equipment reasons), but the difference between white and light yellow opacity is easy to see.
There are many reasons for the phenomenon of white spots, mainly for three reasons:
1. The ink has a large particle size or a small particle size distribution, 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 cause a difference, and it seems that a "white point" is produced. Under normal circumstances, 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% M-27 coupling agent, such as Tianyang Chemical Factory, to improve the tightness of the pigment 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 printing layer is covered, the color of the different parts is changed, 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 pressure on the two sides of the sizing process is inconsistent, even in the drying and coating systems. The problem cannot be ensured that the adhesive is sufficiently uniformly coated or that sufficient evaporation of the ethyl ester is not guaranteed. 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. A special adhesive for aluminized film is used. 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 significantly superior to that of the general-purpose adhesive. Gluing with an aluminized film makes it easy to control the leveling of the glue and has an ideal coating condition. From the state of adhesive application, the use of aluminized rubber can eliminate white spots.
3. The viscosity of the glue has a certain matching relationship with the number of wire rollers. If the distance exceeds the matching interval, the coating state of the glue will be destroyed, resulting in the occurrence of "white spots" and other serious faults, but it seems that the aluminum film is mainly The production of "white spots" is even more interesting.
4. It is coated with aluminized film. 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 VM PET, and secondly, a certain peel strength will be sacrificed.
5. Manufacturers must adhere to the regular cleaning system of the coating roller and master the correct coating roller cleaning method. When producing a full white or yellow printed film, pay attention to two points: First, thoroughly clean the scraper, coating roller, flattening roller, etc. before production; secondly, for the old domestic dry machine, the machine speed is normal. Slower speeds ensure a drying effect.
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 method is 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. Dimethicone; the fourth is to use a straight scraper as much as possible, and increase the blade edge of the scraper by 1-2mm, or use a soft blade (such as a steel tape measure), and adjust the blade angle to an angle of not less than 45 °; Applying a rubber on the back of the scraper to effectively remove the spots in the printed graphic ink system due to poor dispersion or oxidized crust in the ink fountain; sixth, adding white carbon to the printing ink to promote printing The ink film is thickened to increase the hiding power of the white ink film; the seventh is to reprint once to increase the thickness of the ink film; the eighth is to use a deep intaglio plate to increase the transfer rate of the ink; and the other is to put a stirring in the ink fountain. To ensure the uniformity of printing ink during transfer; ten is to change the printing ink with high viscosity and anti-static or slow down the printing speed, and strive to eliminate the defects of pitting, pinhole, spot and white point.
In actual production, only high-efficiency additives and new materials can make up for the shortcomings in the aluminized composite printing products and improve the quality of the packaging printing process.