Analysis of common problems of aluminized composite film

In flexible packaging, all kinds of composite films have their problems, and today, we will briefly introduce the common problems of aluminum plated composite films.

Aluminized composite film is an aluminized film (generally VMPET, VMBOPP, VMCPP or VMPE, of which VMPET, VMCPP are the most commonly used) and transparent plastic film composite formed with "aluminum luster" has good barrier flexible packaging material. Has been widely used in food, health care products, medicine, cosmetics packaging, especially in dry, puffed food, because of its very good metal luster, convenient, cheap and better barrier properties (than before aluminum plating) and obtained a wider range of applications.

However, in our survey, it was found that the composite condition of aluminized composite film on the market is worrying, and there are generally two problems: serious white spot phenomenon and low peeling strength. Especially in the PET/VMCPP and PET/VMPET/PE structure of the composite film products are more obvious. Here we analyze the causes and countermeasures of the above problems caused by dry compound, and also hope to communicate with friends.

Causes and solutions of white spot phenomenon:

The white spot phenomenon of composite aluminum plating film can be described in this way, and the performance of the composite product has obvious white spots, which can be randomly distributed and uneven in size. There are two cases, one is: when off the machine, but basically disappear after curing; The other is: when you get off the machine, it does not disappear after curing. The latter is the biggest problem affecting the appearance. These spots are most likely to appear on the effect of printing on a full white background or light background color. In fact, it should be said that as long as such white spots appear, they are generally full (except for equipment reasons). It's just that white and light undertones have poor covering power and are easy to see.

There are many reasons for the phenomenon of white spots, mainly for three reasons:

1, the ink grain bottom is large or the particle size distribution is too wide, the size of the general white ink has a greater impact. The ethyl ester in the adhesive is a good solvent for the ink, the infiltration results of different particle sizes of the ink particles are different, and the color change after drying in the oven will produce a difference, which looks like a "white spot". Generally, in this case, the machine is obvious, and the white spot phenomenon will be reduced after aging, and may disappear.

2. The adhesive surface tension is high, and the effect of wetting and spreading on the aluminized film is poor. This is one of the main reasons for the current "white spot phenomenon" of aluminized film. The coating effect of the adhesive is not good, and after the printing layer is covered, the color will change on different parts, resulting in the same effect as before, and sometimes large spots will be produced.

3, equipment process reasons. On the one hand, this reason is that workers do not realize the particularity of aluminized composite film composite, aluminized composite film composite has its unique place; On the other hand, the problems of equipment drying, coating, and the system itself cannot ensure that the adhesive is fully evenly coated or that the ethyl ester is fully volatilized.

4, there are other reasons, such as full bottom printing network cable roller mesh is too shallow, reduce the ink covering power.

White spots can be eliminated by:

1, different batches of ink to increase particle size detection indicators, strict control, especially the full ink variety particle size and particle size distribution outside the standard range is not used; Choose excellent and stable suppliers.

2, using aluminized composite film special adhesive. The surface tension of aluminized composite film composite adhesive is lower, and the spreading effect on the surface of aluminized composite film is better than that of general adhesive. The use of aluminized adhesive will be very easy to control the leveling of the adhesive liquid, and have an ideal coating state. From the adhesive coating state alone, the use of aluminized adhesive can eliminate the possibility of white spot phenomenon.

3, the viscosity of the glue and the number of cable rolls have a certain matching relationship, beyond the matching interval too much damage to the coating state of the glue, resulting in the production of "white spots" more concern.

4, using aluminized composite film coating method. The usually used coating process is the printing film (ink surface) coating, here the use of special coating method, to avoid the problem of uneven penetration of ethyl ester on the ink layer, to avoid the problem of uneven penetration of ethyl ester on the ink layer, while the coated adhesive can fully and evenly cover the surface of the aluminum layer, which can eliminate white spots. However, this process has its great limitations, first of all, it is limited to the composite VMPET, and other aluminized composite films will be stretched and deformed under the influence of heat in the oven; Secondly, a certain amount of peel strength will be sacrificed.

5. Flexible packaging enterprises must adhere to the regular cleaning system of coating rollers and master the correct cleaning method of coating rollers. In the production of full white or light background printing film, we should pay attention to two points, first of all, the scraper, coating roller, flattening roller, etc., thoroughly clean before production.

6. The adhesive should be thoroughly dried. Because the barrier property of aluminum plating is better, such as the adhesion in the composite film is not completely dry, then the composite film in the curing chamber, a large number of residual solvents need to be released quickly, under the barrier of aluminum plating film, is bound to form a bubble. There will even be no white spots when the machine is unloaded, and there will be white spots after maturation. Standard of composite aluminum plating film and peel strength of composite aluminum plating film

We often use ordinary tape to check the adhesion fastness of the aluminum-plated composite film before the aluminum-plated composite film. In the stripping test of the aluminum-plated film/tape, the aluminum-plated composite film will not be stripped, and the stripping strength of the aluminum-plated film/tape at this time is ≥2.0N/15mm; After the aluminized composite film is combined with other films, after aging, the peeling strength of the aluminized surface of the composite film drops sharply, and most of the aluminum plating will be completely or mostly transferred, and the peeling strength of the aluminized layer at this time is best to reach about 0.6N/15mm, generally 0.2-0.3N/15mm, or even lower. If the aluminized composite film migrates, then the vacuumized aluminized composite film packaging (such as tea packaging) will migrate over time, and large bubbles will appear; If it is a jelly cover, when it is uncovered, only the upper layer will be uncovered, and you will still not eat jelly.

Some qualified enterprises have done such a test, if the selection of imported aluminized composite film, repeat the above test, the results will be completely different, the strength of the aluminized composite film is still very high, there is no problem of aluminized layer migration.

Through the above analysis, the migration of aluminum plating layer has a great relationship with the quality of aluminum plating itself, which is because there is a big difference in quality between domestic aluminum plating composite film and imported aluminum plating composite film, imported aluminum plating film is aluminum plating film with primer, and domestic aluminum plating is generally no primer.

Due to the current situation of domestic aluminum plating film, the reality of plating migration of aluminum plating composite film in the industry is widespread, although the number of aluminum plating composite film used is huge, the production of aluminum plating composite film products has more than 20 years of history, but so far there is still no relevant general aluminum plating film and aluminum plating composite film industry standards and enterprise standards.

At present, only very individual industry standards and enterprise standards mention the peeling strength of aluminum-plated composite film, such as in YY0236-1996 "Composite film for Pharmaceutical Packaging", the composite film is classified by material combination of Ⅲ plastic, aluminum-plated film, the example structure is OPP/VMCPP, PET/VMPET/PE, in terms of strength requirements, Double layer composite ≥1.0N/15mm, inner layer and sub-inner layer ≥2.5N/15mm. It can be seen from the above standards that the strength of OPP/VMCPP is ≥1.0N/15mm, and a large part of the products on the market are still not up to the standard. The structure of PET/VMPET/PE only has the strength of the inner layer and the sub-inner layer (VMPET/PE), and does not mention the strength of the outer layer and the sub-inner layer (PET/VMPET), which is also to avoid the problem that is prevalent in the market. If the standard of aluminized composite film is formulated according to the current low level, the user cannot accept it; Such as set too high flexible packaging enterprises can not reach.

At present, when many enterprises sign contracts, in the column of implementation standards, most of them write the relevant standards of the implementation country or industry, most of them write the relevant standards of the implementation country or unemployment, and at present, this standard should be empty. It also caused the awkward situation of the implementation of no standards on both sides of the supply and demand, and also caused the problem of the acceptance and complaint of both sides.

Here, I only introduce to friends a few years to improve the strength of composite stripping production experience, for friends reference.

1, select the appropriate VMCPP, VMPET. At present, the prices of aluminized composite films from different manufacturers are almost the same, and the well-known brand products are selected, and the adhesion fastness of the coating is more guaranteed, thus ensuring the necessary conditions for high peel strength.

2, establish a set of coating adhesion fastness detection method, so that different batches of VM film coating adhesion fastness know, can ensure the stability of different batches of product quality.

3, the composite roller temperature is reduced, can improve the composite fastness. The negative effect is that the adhesive coating state is relatively poor. In addition, the initial stripping strength of the machine is worse.

4, the use of special methods, that is, VMPET glue, oven temperature as low as possible, increase ventilation. The negative effect is that the volatilization degree of ethyl ester is affected. The residual amount of ethyl ester was increased. The manufacturer should consider the ventilation condition of the equipment, compare the degree to which the temperature is reduced, and whether the ethyl ester can be fully volatilized.

5, for PET/VMPET/PE(CPP) structure, the first composite does not enter the curing chamber, the second composite is placed in the workshop 1-2 hours later, the composite strength will be improved to a certain extent.

6, for the PET/VMPET/PE(CPP) structure, when the PE thickness is greater than 50μ or CPP thickness is greater than 40μ, it is recommended to conduct a small test to adjust the best working state to ensure that the peel strength meets the design requirements.

7, the proper reduction of the curing dose can also improve the peel strength, generally not less than 15% of the normal amount, otherwise, it will produce the curing problem of the adhesive.