Because the light-shielding and barrier properties of aluminum-plated films are relatively close to those of aluminum foils, aluminum-plated films are particularly used in food, pharmaceuticals, health products, electronic products, clothing packaging and other fields, especially puffed foods in food. Compared with aluminum foil packaging, aluminized film is a low-cost, high-performance packaging structure. Therefore, in flexible packaging structure, aluminized material structure is a commonly used and universal packaging structure. However, after the aluminized film is compounded, there is often such a problem: the aluminized film has a poor composite strength, the aluminized film is easy to transfer, or there are many white spots and fog points.
At present, the commonly used aluminized structure composite film such as BOPP / VMPET / PE, BOPP / VMCPP, PET / VMCPP and other structures, this article focuses on the solution to the abnormal phenomenon of aluminized film composite.
I. Poor composite peel strength of aluminized film
In the production of composite VMPET or VMCPP materials, when it is cured, when we test in the laboratory, we will find that most products containing this structure are very easy to peel off on the surface compounded with the aluminized layer. There are two main types of peeling: One is the large-area transfer of aluminum plating, and the other is the easy peeling of the printed layer. Moreover, the peeling force of the two phenomena is very small, and the basic boundary is about 0.8N / 15mm. And another weird phenomenon is that some parts of the same roll of composite aluminized film are very difficult to peel off, or even cannot be peeled off, while some are very easy to peel off, and they are block-like, very easy to pull apart, resulting in aluminum plating. Transfer phenomenon.
1.In terms of raw materials
Purchasing aluminized films from large factories or manufacturers with more experience in aluminizing can ensure the uniformity and good adhesion of the aluminizing layer of the aluminizing raw materials. According to BB / T0030-2004 "Plastic packaging film deposited with aluminium" related standards, the adhesion of the aluminized film is less than or equal to 20% (represented by the area of the aluminized layer falling off), but it turns out that This standard is difficult to meet production licenses and customer requirements in production practice.
In addition, the batchability of the aluminized film should be stable. This is also a very critical factor for the selection of the aluminized substrate. The stability of the substrate is the basis for the quality of the aluminized layer. On the other hand, the thickness of aluminum plating is also one of the influencing factors. Taking VMCPP as an example, the thickness of the aluminum plating layer is about 300 ~ 600 Angstroms, and many suppliers often cut corners and cut the aluminum plating layer very thinly. It is difficult to tell with our naked eyes. At present, the common practice is to face the film to a 40W tube, and use the film to block the observation surface from the light and make a rough judgment. If the aluminum coating is relatively thin, a slight fog point will appear, similar to a kind of uneven mirror surface. The other is judging from the light transmittance. When the aluminum coating is thin, the light transmittance is relatively high. On the contrary, when the aluminum coating is thick enough, only the weak light is transmitted through the aluminum coating, and even the light is not visible. .
2. Reduce the transfer rate through production process control
In the composite aluminum plating layer, it is almost normal temperature composite, and the temperature of the hot-rolled hot roller is turned off. This kind of approach is to ensure that the aluminized layer is not damaged as much as possible, and the glue can better penetrate between the mask and the aluminized film to form a better mechanical equilibrium situation.
Generally, low temperature or normal temperature conditions are used for curing to extend the curing time. This process is a hidden means to increase the peel strength.
We passed the test. One group was cured at a high temperature of about 50 ° C for 12 hours, and the other group was cured at 35 ° C for 30 hours. Samples with the same structure and the same material were tested for curing. After the completion of the peeling, the samples in the curing group were cured at a high temperature of 50 ° C, and a large area of the aluminum plating layer was transferred; while the aluminum plating transfer area of the samples in the low temperature group was greatly reduced.
After being left at room temperature for one month, when the low temperature group was tested again, the area of aluminum plating transfer increased by more than half. After another two months of storage, the area of the aluminum coating transferred was increased compared to the original one month. A lot.
The method of using low-temperature or normal-temperature curing to reduce the aluminum plating transfer is similar to the method of reducing the rated proportion of the curing agent, and its essence is the same. When cured to a certain period, that is, when the glue cross-linking reaction is complete, the base material of the non-aluminum layer and the aluminized layer will increase to a stable state, and its force value will reach a high end. The adhesion between the aluminized layer and its aluminized substrate is higher.
3. Improve the formulation of auxiliary materials
There are two main ways to improve the formulation of excipients: one is to change to a special aluminized film glue. The aluminized film special glue can make a good mechanical distribution ratio between the aluminized layer and the substrate, and reach the two sides as much as possible. The mechanical balance between the material and the aluminized interlayer, but its essence is consistent with the practice of reducing the proportion of curing dose.
The other is production using water-based acrylic glue. When using water-based acrylic glue, it is easy to transfer the ink layer to the aluminized layer, and the corresponding ink needs to be selected.
To fundamentally solve the problem of aluminum coating transfer, most foreign countries, including some domestic soft-pack companies, have improved the raw materials and used reinforced aluminum coatings or silicon dioxide aluminum coatings. However, this will increase costs. For the current flexible packaging enterprises, which are increasing labor costs and expenditures in various aspects, this approach may not be acceptable.
To sum up all aspects, on the basis of the existing technical basis and regulations, to carry out technical transformation and auxiliary material technology improvement from the existing aluminization basis, is what the market and soft pack companies expect.
Factors and Solutions for "Composite White Spot" Phenomenon
Aluminized composite white spots are generally defined as a composite film containing an aluminized layer material. When the aluminized layer and the substrate to be plated are combined with a non-aluminum plated material, the surface distribution of the product varies, with dot-like bubble spots or white spots. For this reason, soft pack manufacturers have racked their brains to solve such problems.
The compound white point phenomenon is mainly caused by the following factors:
1. The surface tension of the glue adhesive is high, and the wetting tension spreading effect on the aluminized film is poor, which is a major factor; on the other hand, the leveling property of the glue adhesive is not good, which leads to the coating effect. Defective, after the printing film layer is covered, the color and luster of some locations will be changed, and more large spots will be generated, especially the transition position of the color ink layer, which is very easy to produce such phenomena.
The fineness and viscosity of inks from various manufacturers are different. When the ink layer particles are large, it is easy to cause the glue adhesive to spread poorly and produce white spots. Especially at the position of white ink, white spots are very easy to appear. On the other hand, the solubility of the solvent to the ink is also one of the factors that cause white spots; there is also the problem of the compatibility of the ink with the glue, that is, the problem of affinity that everyone calls.
3. Machine operation
When the machine is operated improperly, such as drying effect, glue ratio, control of various tension systems, etc., once abnormalities occur, white spots will easily occur. For example, if the drying temperature is not well controlled, or the temperature of each gradient in the oven is not well controlled, resulting in a very high solvent residue, it is very easy to appear white spots. At the same time, the insufficient amount of glue is also one of the factors affecting the white point.
1. Strengthen the inspection and testing of inks and glue adhesives. Multiple batches of comparative tests must be made for different batches. For products with aluminized film structure, effective communication with ink supplier manufacturers and technical staff of glue adhesive manufacturers, There must be corresponding adjustments in the product formulation in order to better carry out production operations;
2. Use special aluminized film compound glue. Aluminized special glue is a product that can better spread and level on the aluminized film, and can have a more ideal coating effect. When using water-based glue, we must consider the temperature resistance of the product's post-process and some factors affecting the use of the finished product.
3. Machine process operation
(1) Ensure that the step temperature of the machine is reasonably increased to ensure that the solvent residue is minimized. Generally, the drying tunnel is divided into three areas, namely the evaporation area, the hardening area, and the odor elimination area. The temperature is generally set to: 50 ° C, 60 ° C, 70 ° C, but the length of the drying tunnel is different for different materials and different machines, and the amount of air volume and wind speed are also different. Therefore, the specific setting of the step temperature must be fine-tuned , But there must be increments.
(2) Establish network cable cleaning and network cable roll capacity control management, and do a good job of the machine's instant gluing test to ensure that the gluing amount is sufficient;
(3) Pay attention to the cleanliness of the machine. For the entire production process, the cleanliness of the compound process machine is the highest. Only clean can produce good products.
(4) The use of aluminized film for gluing has major limitations. It is necessary to be very careful about VMCPP material.
(5) Adopt low temperature and long-term ripening to control the back-end process.
Third, the conclusion
There are many problems with dry composite aluminum coatings, and the scope is relatively wide. However, through the accumulation of years of process technology in the industry, the proficiency of staff operations and the precision of mechanical operations are constantly improving, coupled with the gradual improvement of raw and auxiliary materials, Some anomalies in the composite aluminum coating will gradually disappear.