What types of flexible packaging? What are the characteristics?

There are two broad categories of flexible packaging, namely stretch wrap and various bags. The stretch wrap is constructed of a plastic film that has not yet formed a package shape by simply wrapping the film around one or more pieces of the product to be packaged and holding it in place in some form. The plastic bag is made into a certain shape before the product is loaded or when the product is loaded. The most common is to heat seal the plastic side to form this shape.

1, winding packaging

1) Stretch wrapping

One of the biggest applications of plastic film in packaging is the stretch wrapping package, which bundles the goods on the tray together to make them integrated into circulation. The most commonly used plastic film is low density polyethylene, which stretches as it is wrapped around the product and tray, usually spirally wound. After being wrapped, the film is cut and the film head is stuck to the goods, which is usually self-adhesive. After the tensile force is released, the film is retracted to its unstretched size to create a binding force that acts on the cargo and binds the cargo so that it remains motionless during transport.

In addition to the bundled feature, stretch-wrapped packaging also protects the cargo from moisture, dust and abrasion. Stretch wrap packaging also provides this protection for a single item of cargo, as well as bundles of less than one pallet load.

Although stretch wrap is conceptually simple, the structure is quite complex. For each layer of stretch wrap, the ideal result is to stick to the underlying layer, but it is undesirable for adjacent goods that may shrink the package to stick to each other or to other objects that they contact. Therefore, the stretch wrap package may have a multi-layer structure in which a binder is added to the inner layer to enhance adhesion. In addition to LLDPE, low density polyethylene, polyvinyl chloride, ethylene-vinyl acetate copolymers, and other polymers are also used as stretch-wound films.

2) Shrink packaging

Shrink wrap is an alternative to bundled stretch wrap. When the shrink wrap is exposed to a heat source, the originally aligned (orientated) molecules attempt to return to a lower energy, unstretched random coil structure, which prevents the film from returning to its unstretched dimensions, and the material acts on the product. Force the goods to be bundled.

In order to bundle the goods on the pallet, stretch wrapping is more common than shrink packaging because it requires less energy and is more economical. Shrink wrap is more commonly used as a bale wrap that bundles two or more products (same or different) instead of a full tray of goods.

Shrink wrap is often used for product protection rather than bundling, from meat to toys. It can be designed to form a tight outer casing around the entire product, which is good for preventing dirt, moisture and wear. Typically, a loose bag is formed before the film is tightly shrunk into the product in the shrink tunnel. LDPE and LLDPE are commonly used materials for shrink films. PVC and PP are used in small amounts, as are some special films.

2, bags, large bags and sealing bags

Production bags, large bags, and closure bags are two or more sides of a plastic film that are sealed together to form a cavity for the product. In most applications, the opening is then sealed in order to completely encapsulate the product from the packaging material. Sometimes, the side of the shopping bag, etc. is open.

The words "bag", "sack" and "pouch" may be confused. Some authors believe that "small bags" are larger than "bags", but both refer to the upper end of the package, and the "sealing bag" is much smaller, referring to the completely sealed package. But these definitions do not match the general use of the word, because they are often used in practice.

Common closure bags are pillow-shaped bags, three-side sealing bags and four-sided sealing bags. The pillow-shaped bag is formed by forming a plastic film into a cylinder, and then sealing the edges together, and the sealed side becomes a back seam of the finished package. The bottom end of the cylinder is clamped and sealed, the product is loaded, and then the top seam is added. The packaging of the product is shaped like a pillow – hence the name.

As the name implies, the three-side sealing bag is made by folding the film into a rectangular shape and sealing the three unfolded edges. Sometimes the fourth side is also sealed to increase strength. The four-sided sealing bag is made of two sheets of film, all of which are sealed together. Therefore, the four-sided sealing bag does not have to be rectangular. Contrary to the pillow bag and the three-side sealing bag, different plastic films can be used for the front and rear of the four-side sealing bag.

Any of the formed closure pockets can be gusseted to expand the capacity without increasing its width or height.

The closure bag can be used alone or in combination with other packages for product circulation and/or distribution. A very common packaging structure is a box-lined bag that holds the closure bag in a folded carton or corrugated box.

The material of the bag may be either a plastic film itself or a multilayer material containing paper and/or aluminum foil. Paper can be used to increase the strength, hardness, printability and apparent density of the flexible package. Aluminum foil can be added to increase its resistance to oxygen, water vapor, odor, aroma and other permeates.

Over the past few years, stand-up pouches have increasingly replaced cartons and bottles, and their designs include gussets and specially shaped bottom panels that stand upright on retailers' shelves.

3. Production of sealing bags

There are two main ways to package in bags, large bags, and sealed bags: as prefabricated bags or in form-fill-seal production. In Form-Fill-Fill (FFS) production, the substrate (usually pre-printed if applicable) is added to a horizontal or vertical FFS machine to make a bag, then the product is loaded and finally sealed. . If a prefabricated bag is used, the bag is first made, leaving a mouth to fit the product. The product is placed in a bag in another production and the bag is then sealed.

From an economic point of view, for large-scale production, there is usually an advantage of form-fill-seal. If the output is low or the material is difficult to seal and the quality control is problematic, it is generally more economical to purchase the prefabricated bag.

4, opening and resealability

One of the long-standing disadvantages of flexible packaging is that it is difficult to provide a bag that is easy to use, easy to open and reseal. In the past few years, several innovative technologies have significantly improved the above properties of packaging.

The most common way to open a product in a flexible package is to cut or tear the mouth of the bag or peel off a seam. For some products, such as cereal breakfast food in a bag-lined bag, this problem is the most complaints from consumers. Sealing is generally not easy to peel off. It is often the case that the bag is cut along the edge so that the cereal is sprinkled in the box, and it is almost impossible to seal the bag to keep the freshness of the product. Some flexible packaging now has a zip closure, often with a tear strip for easy opening. Other packages are resealable covers, usually located at the seams.

For liquid products, some packages have a threaded outlet with a standard nut. The outlets can be placed at the top and bottom of the bag, depending on the size of the product and package. In the box-lined bag packaging, the outer carton has a flap that opens and pulls the outlet out of the flap. For disposable beverage packaging, a straw is usually attached (the straw has its own packaging to prevent dirt contamination and stick to one side of the beverage bag), and a point is specified on the package to improve the packaging and facilitate the straw. penetrate.

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