Special film stretching process

Due to the diversification of the application market, especially the rapid development of the packaging market, special films for various specific applications have been developed. There are great differences between daily and specialty films. The former is heavily put on the market, the latter market is small, adopting custom-made features, and the price is relatively high. Single-layer films and three-layer co-extruded films in special films have entered the market, and have been widely promoted with the advancement of global packaging technology, and are expected to increase at a rate of about 7%.

Special films are used between foods and non-foods at 75% and 25%. 90% of the biaxially oriented polypropylene (BOPP) film for daily use is produced from a high-grade progressive drawing line. This production method has the characteristics of excellent investment-output ratio. In recent years, this trend has driven the speed of production lines to continue to increase and the width of work has continued to increase. At present, 10m width and 450m/min line speed are generally considered as advanced technologies. If there is no need to change the product frequently, the production capacity of the production line can reach 5500 kg/h at full speed.

On the other hand, specialty films are characterized by a small order volume. Therefore, the parameters of the production line must be changed frequently. In this case, the advantage is to increase the flexibility of the production line and to shorten the product replacement time while achieving the average production capacity. It is worth mentioning that the configuration of Bruckner's LISIM(R) synchronous draw line is extremely flexible and allows the production of a wide range of products. Therefore, it is particularly suitable for a variety of oriented specialty films. Furthermore, it is also possible to tap into the films currently produced by the double bubble production line and the film market that cannot be produced by any other process.

The development of synthetic paper synthetic paper began in the 1970s. At that time, Japan actively used synthetic paper instead of cellophane paper. However, the scale of substitution is not great. At present, a new market has been opened up and has undergone tremendous development in recent years. It is expected that it will maintain a relatively high growth rate in the future. Its application range is very extensive, ranging from advanced prints (calendar, business cards, maps, etc.) to packaging labels. The significant advantages of synthetic paper are good water resistance, printability and form stability. The particularly efficient synthetic paper production process is the co-extrusion of polypropylene successively stretching.

5-layer label film For the production of diversified specialty film products, the 5-layer process has been promoted to some extent. Combining different material layers and additives, it can achieve smooth surface, excellent optical performance and low-cost production. The main reason for reducing costs lies in the low dosage of additives and the large amount of recycled materials. Using the same equipment can also produce 3 or 5 layers of compounding materials, making it particularly suitable for label production.

Metallized Films For most packaging applications, the barrier properties of metalized BOPP are the determinants of quality. As we all know, as long as no interruption occurs, the thin aluminum layer coated by vacuum metallization ensures good barrier effect. However, the surface properties and mechanical properties of the film actually affect the uniformity of the metal coating and, therefore, also the barrier properties.

Low heat sealing temperature co-extrusion BOPP
Through a non-contact stretching process, a coextruded layer having a very low heat sealing temperature can be used. The sequential stretching method also has its limitation that it is easy to stick the rolls longitudinally due to the low temperature of the coextruded layer. However, using LISIM to avoid this problem can be avoided. PP terpolymers, polybutylenes and special LLDPE type materials can be used as the heat seal layer in order to obtain a heat sealing temperature below 80°C.

Moreover, the thickness of the heat sealing layer (usually 0.5-1 μm) can be increased, and increasing to 3-4 μm is not a problem. In this way, a heat-sealing strength of up to 7 N/15 mm can be achieved. Reduced heat sealing temperature can speed up the packaging machine, thus improving the heat seal integrity and making the final package safer.

Multi-layered high-barrier films Long ago, people began to attempt to produce transparent barrier films by one-step co-extrusion to reduce the subsequent coating process, namely: PVDC or PVOH coating. Bruckner started production trials of seven-layer barrier films in the eighties. At the time, PAN (polypropylene) was used as a barrier material and later replaced by EVOH. Using the co-extrusion process, multi-passage die, and sequential stretching with a lower draw ratio than conventional BOPP, acceptable results from mechanical, optical and shrinkage properties were obtained. In fact, the combination of the above 7-layer compounds was successful only when EVOH-type materials with an ethylene content of less than 40% were used. As a result, the 30 micron film containing the 2 micron EVOH layer has an oxygen barrier value of approximately 24 cm3/m2 d/bar.

Shrink film According to its intended use, shrink film can be divided into different categories:
* Finish shrink film;
* display type packaging film;
* Block the shrink film.

Most of the above films are now produced on a blown film line using the double bubble method. Practice has proved that these films can also be produced with LISIM(R) and can demonstrate enhanced reproducibility, improved process orientation of each process, and improved thickness tolerance. At the same time, there has been a significant increase in production capacity. The speed of the double-film bubble line is generally 300 kg/h, and that of the LISIM(R) film line can reach 3,500 kg/h.

It is well known that raw materials play a decisive role in the degree of shrinkage that shrink films can achieve. Therefore, in combination with higher tensile strength, higher shrinkage force and more balanced mechanical properties, the equilibrium shrinkage of PP homopolymer can be adjusted between 0-15%. PP random copolymer can Up to 40%, pure LLDPE shrinkage can exceed 70%.

In addition, various blends and multilayer coextruded films can also be produced to achieve particularly desirable properties. In addition, the contraction performance (determined by the contraction temperature shrinkage value) can be adjusted by the stretching parameter.

Medium Density Shrinkable Label Film As for the label film, a continuous method that replaces the PVC and paper labels that have been used so far is now available. Among them, due to its excellent price-performance ratio, polypropylene has the highest market growth rate. Due to the choice of materials, the possibilities of the co-extrusion process and the stretching process, adjustments can be made over a wide range to achieve the desired performance. There are a variety of labels on the market, including transparent, opaque, stable, and uniaxially-contracted. Products made with LISIM(R) have a shrinkage of up to 10% for a single homopolymer and do not exhibit lateral ultimate shrinkage.

It has become a fact that low-density label films produce biaxially oriented foam films for synthetic paper or insulation applications. If a chemical foaming agent and a simultaneous stretching method are used, the final film thickness can be reduced to about 0.4 g/cm3. Further development is to modify the outer layer by similar processing methods to obtain a smooth surface, improving opacity and printability. To enhance the surface effect, titanium dioxide is added to the outer layer.

There is no difficulty in producing films up to 200 microns thick. The outstanding advantages are the characteristics of large thickness, excellent bending strength, low density, and excellent printability.

The above example shows that in addition to the general film, the market opens up new opportunities for BOPP special film and synthetic paper. These films can be run on a professionally designed continuous stretching line and are now on the market. Synchronous stretching technology can also be used, can be used for a variety of special film, in the shrinking polyolefin film market is bright prospects, experiments show that PP, PE, PET, PA, PLA, PS, COC, synthetic paper, etc. can be used for synchronous pull Some methods have been officially introduced to the market.