Eliminating "white point phenomenon" of aluminized films and improving peel strength

The aluminized film is a kind of flexible aluminum packaging material with good barrier properties, which is formed by compounding aluminized film (generally VMPET, VMBOPP, VMCPP or VMPE, VMPET and VMCPP) and transparent plastic film. Has been widely used in food, construction products, pharmaceuticals, cosmetics, packaging, especially in the dry, puffed food, because of its convenient, beautiful, inexpensive and better barrier properties and obtained a wider range of applications. However, in our investigation, it has been found that the composite condition of the aluminum-coated composite film on the market is worrying. There are two problems in general: the white point phenomenon is serious and the peel strength is low. Especially in the PET / VMCPP and PET / VMPET / PE structure of the composite film products more obvious. Here I would like to introduce to friends how to produce high-quality aluminized film on a dry laminating machine and hope to communicate with friends.
First, we first talk about the causes of white point phenomenon and solutions: aluminum composite film white point phenomenon can be described, the composite product apparently has obvious white spots, this white spot can be randomly distributed, size Uneven. There are two kinds of situations, one is: When the machine is down, but it basically disappears after aging; the other is: There is a time when the machine does not disappear after curing. The latter is the biggest problem that affects appearance. Such spots are most likely to appear in printed effects with white or light yellow bottoms. In fact, it should be said that as long as such a white point appears, it is generally full version (except for equipment reasons). Only 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 too wide, and the white ink generally has a large influence on the particle size. 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 change in the color of the ink particles after drying in the oven may cause a difference, and it seems to produce a “white point”. In this kind of situation, when the machine is down, the white point phenomenon will be lessened and may disappear after curing.
2. The surface tension of the adhesive is high, and the effect of infiltration and spreading on the aluminized film is poor. This is one of the main reasons for the current "white point phenomenon" of aluminized 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 workers are not aware of the special characteristics of the aluminized film composite, and the aluminized film composite has its unique place; on the other hand, the equipment drying, coating, and the system itself cannot guarantee the full uniformity of the adhesive. Coating or can not guarantee the full volatilization of ethyl ester.
There are other reasons. For example, if the net roller of the printing roller is too shallow, the hiding power of the ink is reduced.
Take the following measures to eliminate "white spots"
1. Different batches of inks will increase the particle size detection index and be strictly controlled. In particular, the granularity and particle size of full-bottom inks will not be 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 adhesives makes it very easy to control the leveling of the glue and has a desirable coating state. From the state of adhesive coating alone, the use of aluminized adhesive eliminates the possibility of white spots.
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 "white spots" and more serious other effects, but in the aluminized film. It seems that the main cause for the "white point" is more concern.
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 the ethyl ester to the ink layer, but this process has its very big limitations. , is limited to the VMPET compound; 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 white or light yellow printing film, we must pay attention to two points, first, before the production of the scraper, coating roll, flat roll and other thorough cleaning; Second, for the old domestic dry machine, the speed ratio than the party speed Slower to ensure the drying effect.
Second, we talk about how to improve the aluminum composite film peel strength.
This phenomenon can be seen by peeling off the aluminum-plated composite film. Destruction generally occurs at the aluminized layer-PET (CPP) interface, and only when the aluminized layer undergoes most of the transfer, the peel strength is significantly reduced. For detailed discussion, please refer to "YH501S Application on PET/VMCPP Composite Film" published in "Plastic Packaging", Issue 4, 2000. This paper discusses in detail the effect of composite peeling strength of aluminum plating film. The conclusion is that the peel strength of the special composite adhesive for aluminum plating will be greatly improved. Here, I only introduce to my friends several production experiences to increase the strength of composite peeling for friends' reference.
1. Select the appropriate VMCPP, VMPET. At present, the prices of aluminized films from different manufacturers are almost the same. Well-known brand products are used, and the adhesion of plating is more assured, thus ensuring the necessary conditions for high peel strength.
2. Establish a method for the detection of coating adhesion fastness, so that the adhesion of different batches of VM film coating is very good, which can guarantee the stability of product quality in different batches. I will introduce another simple and effective detection method.
3. Reduce the temperature of the composite roll to improve the composite fastness. The negative effect is the relatively poor state of glue coating. In addition, the initial peeling strength of the machine immediately fell.
4. Using a special method, VMPET coating, the oven temperature as low as possible, increase ventilation. The negative effect is that the degree of evaporation of ethyl ester is affected. The ethyl ester residue increases. Manufacturers should consider the ventilation conditions of the equipment, compare the temperature to what extent, and whether the ethyl ester can fully evaporate.
5. For the PER/VMPET/PE (CPP) structure, the first pass will not enter the curing chamber, and the second pass will be performed after being placed in the workshop for 1-2 hours, and the composite strength will increase.
6. For the PER/VMPET/PE (CPP) structure, when the PE thickness is greater than 50μ or the thickness of the CPP is greater than 40μ, it is recommended to first perform a small test to adjust the optimal working conditions to ensure that the peel strength meets the design requirements.
7. Proper reduction in the curing dose can also increase the peel strength, generally not less than 15% of the normal amount, otherwise, there will be problems with curing of the adhesive.
In actual production, the situation is more complicated. Here I only talked about some experiences in the work and I hope to be able to help the composite production of aluminum film in the industry. (Deng Yidong) (From China Packaging News, 2001.1.8)