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Innovation of flexible packaging polypropylene today and tomorrow

driven by the desire of consumers, the continuous and in-depth development of polypropylene has promoted the continuous improvement of flexible plastic packaging. In the past decade, great progress has been made in elastic and rigid films, especially in transparent cast films. The development of new easy to open, easy to handle and sterilized packaging materials has created a significant new impetus

in the past decade, the performance space and application range of flexible polypropylene film and its packaging have developed rapidly. The fundamental reason for the rapid development lies in the development of polymer design and the breakthrough of new processing technologies such as coextrusion and extrusion coating. The question now is: will this trend continue in the next decade, and has technology reached the limit of innovation? The demand of the sales chain

the unremitting efforts of the soft packaging industry to reduce costs are linked to the continuous and further development of the polymer itself and its processing and manufacturing processes. Flexible polypropylene film combines beautiful appearance, good mechanical data, and is conducive to anti-corrosion. The sensor of Jinan experimental Machinery Factory is a device or assembly that converts some physical, chemical, biological and other information it senses into information that is easy to detect and process, and has independent functions It usually consists of a sensing element and a processing circuit The former performs the sensing function, while the latter amplifies and transmits the information output by the sensing element According to different functions, sensors can be divided into temperature sensor, optical sensor, pressure sensor, magnetic sensor, gas sensor, humidity sensor, ray sensor, etc It is gradually popularized due to the characteristics of water vapor evaporation, good heat sealing and high-temperature stability. Due to changes in consumer behavior, additional new packaging features, such as easy to open (easy to tear off), light weight (reduced wall thickness), easy to recycle (ecological awareness) and the best aesthetic feeling (including printability, surface gloss, appearance and soft touch feeling) have also become more important

development of substitutes and polymers

a large share of polypropylene market growth in recent years comes from its becoming a suitable substitute for other materials. The materials to be replaced may be other polymers (such as polyvinyl chloride, polyethylene and polystyrene), or completely different materials, such as glass, aluminum, other metals, paper, or some composite material. Let's take a look at the changes in the overall properties of polypropylene flat films in the last decade. As shown in Figure 1, the improvement in mechanical properties such as elasticity/hardness and impact strength is obvious. Although the improvements in optical, fabrication, barrier and thermal insulation properties are not as good as those in mechanical properties, important progress has also been made. The development of polypropylene is a milestone. It should also be noted that the development speed of new polypropylene polymer materials as film applications is faster than one year, and the development cycle of new products is becoming shorter and shorter, as shown in Figure 2. It must be emphasized that behind the breakthrough of new polypropylene properties, the flexible chain segment of polypropylene film is often proved to be the driving force of this breakthrough

Figure 1: Polypropylene casting film performance improvement: comparison between 1990 and 2000. (measured on 50 micron film)

Figure 2: Polypropylene performance and innovation speed for film

new progress in product design and polypropylene additives has opened the door to more and more new application fields. In these areas, the requirements for special plastic materials are more than daily necessities

Figure 3 shows the relationship between optical properties and rigidity of important new polypropylene materials. The borsoft grade of flexible random polyphase has relatively good transparency, which is a very special development. They have led to a breakthrough in liquid transparent packaging bag products and have been proved to be an effective substitute for glass bottles and PVC plastic bags used in medical packaging. (Fig. 4)

Fig. 3: optical properties and stiffness of main new polypropylene products used for thin films

Fig. 4: transparent polypropylene products used for liquid therapeutic packaging (infusion bags)

in contrast, the highly crystalline bormod grade claims to combine excellent hardness, high heat resistance, good optical properties and perforation characteristics. It opens up a wide range of new applications. Typical examples are: special films for labels, food packaging materials for cheese, fast food and cakes, and glass paper for candy and pill packaging. (Fig. 5)

Fig. 5: transparent label film made of highly crystalline polypropylene homopolymer

finally, the development of new borclear c3/c4 polymer, copolymer and terpolymer has achieved a balanced combination from excellent optical characteristics and thermal insulation performance to significant hardness. This leads to great economic benefits in making flexible FFS packaging materials. When processing the packaging materials for the announced products of bread and textile Jiuli special materials on the evening of November 16, the number of cycles can be increased by 30%, and the unqualified rate is also lower

easy to open packaging

there is no doubt that any packaging that is not friendly to consumers in terms of opening and handling is lifeless. In order to comply with the above trends, Borealis has developed new peelable products: sterilized sterlipel and non sterilized borpeer. Based on the adhesive stripping system shown in Figure 6, these grades are combined with standard polypropylene grades and coextruded in very thin layers. By designing the peeling function in this way, two films of the same type (e.g. film bag) can be peeled off from each other or from a layer of polypropylene (e.g. sealing film covering the polypropylene container). The novelty of sterlipel products is that it is the first time that the peelable polypropylene grade continues to exist after being sterilized by steam at 130 ℃. Typical applications of such systems are solution packaging in food (such as ready to eat meat food or fruit salad, title picture) and medical departments (such as external packaging of medical bags)

rapid development of processing behavior

before this, polypropylene's low melt strength and poor ductility prevented it from entering more application fields, especially in the case of processing technology that requires a combination of elasticity and melt viscosity (such as blown film obtained by air cooling, coating and foaming). Due to the development of the so-called high melt strength polypropylene grade, polypropylene can penetrate the traditional low-density polyethylene part. This is a very important development. The processing behavior of polypropylene was improved by the integration of long branched chains in the pre reaction process. Rheotens measuring device is usually used to measure the maximum force and outflow velocity, and send the file to the printer for printing or ductility to obtain the viscosity of the melt

Figure 6: schematic diagram of the principle of adhesive stripping system

it can be seen from Figure 7 that although the melting strength of linear polypropylene can be significantly increased by increasing the average molecular weight, the ductility is still at a very low level. In addition to the high melt viscosity, the most important thing is that the tensile behavior (strain hardening) of the melt essentially controls the processability in the process of coating extrusion, foam extrusion and blown film extrusion. Compared with low-density polyethylene, daploy HMS, a newly developed polypropylene with high melt strength, is now possible to combine melt strength with tensile strength. In fact, this means that polypropylene (less than 100kg/cm3) which is easier to stretch and has a very low foam density is made for the first time

Figure 7: comparison of outflow velocity and stress of standard polypropylene/high melt strength polypropylene and low density polyethylene in Rheotens test (tensile viscosity measurement)

typical examples of the application of the new daploy wb130hms and wb135hms include: food packaging plates for meat and sausage, internal and external applications of many automobile extensions, and other technical applications

in addition, the application speed in the field of polypropylene coating is accelerating. Compared with the maximum use speed of standard polypropylene homopolymer of 50 m/min, the maximum use speed of daploy HMS series (we100hms and wf420hms) is 400 to 500 m/min. The development of this technology has led to the replacement of thin films/metals and aluminum sheets by more and more direct coating, and made it possible to open up new application fields, such as steam sterilized cardboard/polymer packaging materials

ongoing development

innovation of polymer technology: the potential of metallocene polypropylene technology is far from sufficient or measured research. There are great opportunities in medical and food applications. In these fields, the maximum product purity, the best transparency and the best low temperature characteristics, the maximum impact strength, high water and oxygen protection performance and excellent sensory performance are combined. These properties will take the lead in the further improvement of basic properties such as mechanical, optical and adiabatic properties

especially in the food and medical sectors, different disinfection methods play a more important role in changing the life and consumption habits of our society. People's expectations for health and medical technology are increasingly turning to ultra flexible and highly transparent elastic films, non textiles and composite materials. In the traditional food packaging sector, expectations for maximum transparency for refrigerators and freezers have been growing. For all these special uses in the future, we must gradually further improve polypropylene materials to meet the future demand as high-tech plastics and daily necessities (at a reasonable cost)

the ongoing research and development of processing and manufacturing technology plays an important role in this regard. If a highly creative polymer and application technology research and development can be economically realized on existing processing and manufacturing equipment, or if new equipment can be purchased, then this research is worth doing. Therefore, this is an effective cooperation between polymers, processing and applications that will bring the greatest benefits to all sectors involved

reprinted from; Chinese polymer

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