At present, aluminum foil and aluminum-plated film are the most frequently used and fashionable substrates. However, during the processing of the aluminum foil and aluminum-plated film, if they are not careful, quality problems may occur, 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 compounding aluminum foil and aluminized film.
spot
After the aluminum coating is compounded, it produces obvious white or gray spots. These spots are most common in the full-print ink printing compounding process. There are three main reasons:
1. The quality of the aluminized film itself is poor, the coating is easy to peel off and the aluminized film and the rolled film are uneven. Especially when the adhesive is applied, the flow is uneven, and after the compounding, dense white spots or irregular white spots with different sizes are more likely to occur. The adhesion of the ink and adhesive on its surface varies, and the adhesion between the ink layer and the plating layer at the spot is low (the spots caused by the uneven dispersion of ink or adhesive) make the interlayer tightness poor; without spots The coating has been transferred obviously, and the tightness between the layers is good. The intensity of the light reflection through the aluminum coating layer forms white dots or gray spots. The depth of the spots has a great relationship with the hiding power of the ink and the amount of sizing, especially the leveling of the glue. Good hiding power, shallow spots; good glue 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 glued, the ink layer is infiltrated by ethanol acetate in the adhesive and partially dissolved. After compounding, the ink layer and the glue layer are easily infiltrated and destroyed by the solvent of the adhesive system, resulting in different shades, resulting in a difference in color. , So-called spots are formed.
3. The quality of the adhesive is poor. This kind of adhesive has poor affinity to the aluminized layer, especially the uneven adhesive is compounded with OPP printed film and BOPP printed film and aluminized film, the performance of this kind of adhesive is more obvious. This is mainly due to the high surface tension of this adhesive, poor coating performance, and uneven coating of glue, resulting in a "spot" phenomenon. At the same time, this kind of glue generally has high initial adhesion and poor solvent release. After curing, due to the influence of residual solvent, the strength is not as good as the initial adhesion. After the printing film is compounded, the ink layer is infiltrated by the residual solvent, and there may be spots. The above phenomenon will be more obvious when this type of adhesive is used in high-speed compounding on a mesh roller of more than 150 lines. If the adhesive coating cannot be slightly soluble with the printing ink film, no white spots can be seen on the surface, but after the compounding process, the adhesion of the adhesive layer and the ink layer, even the printing film layer, cannot meet the actual requirements of the packaged goods. Very easy to peel.
In general, there are many "spots" phenomenon 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 the most fundamental method to eliminate the speckle phenomenon caused by the former reason. You can also engrave the printing screen roller to increase the thickness of the ink layer, but this will increase the cost.
2. Using an appropriate adhesive for aluminum coating is an effective method to eliminate the speckle caused by the third cause. This special adhesive for aluminum coating is moderate and uniform in molecular weight, and its initial adhesion is not very high, but it has excellent coating performance, good solvent release, and good peel strength after aging. In addition, if there is no better special adhesive for aluminum coating, you can use a deeper screen roller, while reducing the operating concentration, slowing down the machine speed, and can also reduce or solve the "spot" phenomenon.
3. If it is caused by pigments or fillers in the ink, spots will often appear in three cases: (1) Titanium dioxide and other particles are not equal in size when mixed, 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, will also appear spots; (3) Titanium dioxide and other particles of different sizes, but different density, also will appear spots. These three kinds of failures are most likely to be caused by the "active particles" produced by the flocculation of the white carbon black or the long grinding time of the ink. For this phenomenon, as far as possible, all dry powders are mixed and then put into dispersion, and the appropriate 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 faults appear in shallow or basic dots) Large-area plate surface without engraving) to prevent abnormal adsorption between the pigment and filler? A cluster adheres to the plate roller and is distributed on the printing surface under the pressure of a scraper. It is best to add "CHY-1" type printing auxiliary to eliminate spots.
White dot
In addition to the white spots of the aluminum composite film, there are also obvious white spots on other composite films. Such white spots can be randomly distributed with uneven sizes. One is when you get off the machine, but it basically disappears after aging; the other is when you get off the machine, and it does not disappear after aging. The latter is the biggest problem affecting performance. Such spots are most likely to appear in the printing effect of white or light yellow background. In general, as long as such white spots appear, they are usually full version (except for equipment reasons), but the difference in hiding power between white and light yellow is easy to see.
There are many reasons for the phenomenon of white spots, mainly for three reasons:
1. The particle size of the ink is large or the particle size distribution is not wide. Generally, the particle size of white ink has a greater influence. The ethyl ester in the adhesive is a good solvent for the ink. The result of infiltrating the ink particles of different particle sizes is different. The chromaticity change after heating compounding or drying in the oven will produce a difference, and it seems to produce "white spots." Generally in this case, it is obvious when getting off the machine, and the white spot phenomenon will be reduced after aging, 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 and 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 spreading on the aluminum film is poor. This is currently the "white spot phenomenon" of aluminum coatings and the main cause of spots on other composite films. The coating effect of the adhesive is not good. After the printing layer is covered, the color of the different parts will change, producing the same effect as before, and sometimes it will produce large spots.
3. Equipment process reasons. The reason for this is that on the one hand, the workers are not aware of the particularity of the aluminized film compound. The aluminized film compound has its unique features. On the other hand, the pressure on the two sides of the equipment is inconsistent during the sizing process, even in the drying, coating and other systems themselves. The problem cannot guarantee the sufficient uniform coating of the adhesive or the sufficient volatilization of the ethyl ester. There are other reasons, such as full-textured screen rollers with too shallow anilox, which reduces ink hiding power.
Take the following measures to eliminate "white spots":
1. Different batches of inks are added with fineness detection indicators and strictly controlled, especially when the particle size and fineness of full-bottom ink varieties are outside the standard range.
2. Adopt special adhesive for aluminum film. The surface tension of the special adhesive for aluminized film composite is low, and the spreading effect on the surface of the aluminized layer is obviously better than that of the general-purpose adhesive. It is very easy to control the leveling of the glue with aluminum-plated film glue, and it has a more ideal coating state. In terms of the coating state of the adhesive alone, the use of Aluminized Glue can eliminate the occurrence of white spots.
3. There is a certain matching relationship between the viscosity of the glue solution and the number of lines of the screen roller. If it exceeds the matching interval, it will damage the coating state of the glue, resulting in the occurrence of "white spots" and other serious faults. The occurrence of "white spots" is more concerning.
4. Aluminium film coating method is adopted. The commonly used coating process is to paste the printed film (protective layer). A special coating method is used here to avoid the problem of uneven penetration of the ethyl ester into the ink layer, but this process has its great limitations. First, it is limited to the compounding of VM PET, 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 method of cleaning the coating roller. There are two points to note when producing a full-white or line-yellow printed film: first, thoroughly clean the doctor blade, coating roller, flattening roller, etc. before production; secondly, for the old-style domestic dry-recovery machine, the speed ratio is normal The speed is slower to ensure the drying effect.
Pockmark
The pinholes (blank dots / pockmarks) caused by foam in the ink are often printed on the aluminum film. The general elimination methods are: first, tighten the composite roller; second, increase the amount of coating glue; third, add defoamer Dimethyl silicone oil; Fourth, use a straight scraper as much as possible, and increase the blade of the scraper by 1-2mm, or use a soft blade (such as a steel tape measure instead), and adjust the scraper angle to an angle of not less than 45 °; Fifth Add a piece of rubber on the back of the doctor blade, so that the spots in the printed graphic ink system due to poor dispersion or in the ink fountain due to oxidized skin can be effectively scraped; Sixth, add white carbon black to the printing ink to promote printing The thickening of the ink film improves the hiding power of the white ink film; the seventh is to reprint again to increase the thickness of the ink film; the eight is to select a deep engraved gravure plate to improve the transfer rate of the ink; the ninth is to put a stir in the ink fountain To ensure the uniformity of the printing ink during transfer; ten is to replace the printing ink with high viscosity and antistatic or slow down the printing speed, and strive to eliminate the pits, pinholes, spots, and white spots.
In actual production, there are only high-efficiency additives and new materials to make up for the deficiencies in its aluminized composite printed products and improve the quality of packaging and printing processes.
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