Flexible Packaging

Currently, flexible packaging is the most widely used in everyday life because it is used to store and transport everyday products such as food, body care products, household cleaning products, among others. The main functionalities of flexible packaging include preservation (for food products), protection of these products, and the ease of transporting, storing, and marketing them.

This article will discuss the production process of flexible packaging, providing a deeper understanding of the production process.

Before going into detail about the processes that raw materials go through to form flexible packaging, it is necessary to talk about the types of flexible packaging that exist and are most commonly used today, as well as the most commonly used raw materials for their manufacturing.

What types of flexible packaging exist?

There are different types of flexible packaging with different characteristics, depending on their manufacturing method. The main types include:

  1. Two-seal packages: These packages seal at opposite ends and have a bottom heat seal. They are suitable for solid rectangular-shaped products, such as cereal bars or nougat tablets.
  2. Three-seal flexible packages: These are among the most commonly used and are used for non-rectangular products. They involve inserting the product into the package and sealing it at the top. Their simple and efficient structure is often used to package frozen products such as fish, vegetables, prepared meals, among other frozen foods.
  3. Four-seal packages: Similar to two-seal packages, these packages are sealed on all four sides. During production, three sides are sealed first, then the product is inserted, and finally, the top of the package is sealed. This type of flexible packaging is found in powdered products like coffee or chocolate (cocoa), as well as products such as sliced bread, pet food, industrial detergents, among others.

Based on their structure, the types of flexible packaging can be distinguished into two types: monolayer (formed by a single layer of plastic material) or multilayer (formed by several layers of different plastic materials), depending on the manufacturing method.

Production process of flexible packaging

The production process of flexible packaging involves six different processes: extrusion and coextrusion (whether monolayer or multilayer), printing, lamination, cutting and trimming, and finally, sealing. This is the complete procedure for producing flexible packaging.

Image 1. Distribution of materials after lamination [1]

Next, each of the processes will be described:

Extrusion and Coextrusion

The extrusion process involves forcing a thermoplastic material through a more or less complex and continuous orifice under pressure, in such a way that the material acquires a cross-sectional shape equal to that of the orifice. In the extrusion of thermoplastics, the process is not as simple, as during it, the polymer is melted inside a cylinder and subsequently, after obtaining its desired shape, it is allowed to cool. The objective of this extrusion process is to be used for the production of profiles, pipes, plastic films, plastic sheets, among others. In the case of flexible packaging production, it involves the extrusion of plastic films.

The extrusion of plastic films consists of the following elements: an extruder, a head or die, a cooling air ring, a stabilizing or film calibrating device, a bubble collapsing device, an upper pull roller, and a winder, as seen in the following image.

Image2. Tubular Film Extrusion Process [2]

The process of coextrusion of tubular film gains importance due to its great versatility and the variety of films that can be obtained. Among its uses is the combination of properties from two different polymers to obtain a product with the sum of their advantages in a sandwiched film, aiming for a reduced thickness and lower product cost. The basic differences between a film extrusion line and coextrusion are evident in the appearance of two or more extruders and the modification of the head.

Print

In this process, inks are applied to the packaging material in a controlled manner and according to a specific pattern. Printing can be direct or indirect. Indirect printing is a procedure in which the image is not formed directly on the piece by a cliché, screen, or rubber plate but passes to the substrate through another medium, as in offset printing, where the image goes from the plate to the blanket and from the blanket to the substrate. In contrast, in direct printing, the image or artwork goes directly onto the substrate without any intermediate surface or roller. Flexography and rotogravure are examples of direct printing methods.

The most commonly used method in this procedure is flexographic printing, which is a rotary printing method that uses plates engraved in high relief, adjustable to rollers carrying plates in variable repeat lengths. These plates are inked by another roller equipped with a doctor blade, which virtually transfers fluid inks to various substrates, resulting in high-definition images.

Image 3. Flexographic printing process [3] 

Lamination

Plastic lamination is used to enhance the appearance and barrier/technical properties of the final product. It is a process in which two or more plastic films are bonded using adhesive.

In general terms, adhesive is applied to the less absorbent substrate layer, and then the second layer is pressed against it to produce a duplex or two-layer laminate. This allows us to blend the properties of different plastic and non-plastic films, resulting in structures with medium and high barrier properties.

In the lamination process, the primary support coil is coated continuously with the adhesive solution. Without coming into contact with rollers or the other support, it enters the drying tunnel where a forced stream of hot air and powerful extraction removes the solvent included in the coating.

Cutting and Trimming

The cutting process is carried out using a rewinder where it cuts the master coil to the width of the packaging machines and also undergoes the trimming process. Trimming is known as the process in which excess material from a roll is removed to give a better appearance to a product or to improve processability conditions required by the customer.

Sealing

The sealing process involves giving a specific measurement to the film through a thermal process that melts two layers, providing a seal with resistance characteristics and defining volumetric capacity for the units produced.

It involves a tool that is heated and maintained at a constant temperature (also known as direct contact thermal sealing).

Various heated bars are used to make contact between the material and the hot interface, forming a bond. The bars, plates, and dies have different configurations and can be covered with a non-stick layer or use various interposing materials. An example of this is Teflon coating, which is used to prevent sticking to the hot tool.

Image 4. Sealing process [4]


Following all these processes, the packaging undergoes various quality controls in quality laboratories equipped with equipment and standards that allow for a wide range of tests, validations, and checks to ensure the quality of the products and processes involved. Some of these include puncture resistance, elongation force, breaking strength, sealing strength, dart impact, coefficient of friction, and vacuum tests.

Referencias

  1. “¿Qué son los envases flexibles? Tipos, usos y ventajas – Simapack”.
    Simapack. https://simapack.com/2022/06/28/envases-
    flexibles/#:~:text=En%20base%20a%20su%20estructura,varias%20capas%20de%20distint
    os%20materiales. (accedido el 11 de noviembre de 2022).
  2. “EXTRUSIÓN DE MATERIALES PLÁSTICOS”. Tecnología de los
    Plásticos. https://tecnologiadelosplasticos.blogspot.com/2011/03/extrusion-de-materiales-
    plasticos.html (accedido el 15 de noviembre de 2022).
  3. “Impresión flexográfica: características y ventajas | Esagraf”.
    Esagraf. https://www.esagraf.com/caracteristicas-impresion-flexografica/ (accedido el 15 de
    noviembre de 2022).
  4. “Termosellado”. Tecnología de los
    Plásticos. https://tecnologiadelosplasticos.blogspot.com/2013/12/termosellado.html (accedido
    el 16 de noviembre de 2022).

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