Blown films, sometimes referred to as tubular films, are manufactured by extruding molten resin vertically through a circular die. Introducing air through the center of the die creates a bubble. The air drives the bubble upward, and slowly cools the material. Nip rollers flatten the material into a tube that can be reeled for creating bags and pouches, or slit and then reeled as a flat sheet of film. Blown films are pre-stretched by virtue of their manufacturing process.

Cast films are made by extruding melted resin horizontally through a flat die to create a sheet of material that is pinned to a highly polished chilled roller by means of an air curtain or vacuum box. Additional chill rollers quickly cool the film prior to trimming and rolling. Cast films are minimally pre-stretched allowing for improved depth of drawing for thermoforming operations. Typically, cast films have an even distribution of polyolefins due to increased gauge consistency due to the manufacturing process.

What Is An Extruder, And Does Our Company Need One?

To understand what an extruder is, we must first know what the process of extrusion is. Extrusion is when a material, usually pellets, dry powder, rubber, plastic, metal bar stock or even food is heated and pushed through a die. A die is essentially a mold that shapes the material as it is forced through the small opening to the other side. It’s one of the most common ways to produce sheets and strips of stock metal, plastic and rubber shapes.Production of cast film is a continuous process where a thermoplastic material is extruded from a slot die onto a chill roll, quenched, and wound.

The resulting film has machine direction orientation compared to a somewhat limited bidirectional orientation achieved in blown film processing. Cast film extrusion, because of the high speed and output, can be limited to dedicated applications such as lamination web, printed packaging film, and a growing market- stretch wrap.

In recent years, the ongoing move toward automatic wrapping of pallets has shown a steady increase in demand for stretch-wrap film. Due to its processing advantages, cast film today dominates the market in this sector. Equipment producers offer high-speed cast film lines for the manufacture of coextruded linear low-density PE-based films with up to nine layers. Coextrusion also allows downgauging to save raw materials costs. The processor can also manufacture a product where he determines the level and location of cling-on the inside, outside, or on both sides. Agricultural wrapping films as well as stretch film for manual wrapping applications can also be extruded on cast film lines. Another interesting market possibility is food-wrapping film, normally a blend of LDPE and LLDPE.Basic characteristics

The group is suitable for blown polyethylene (LDPE), high-density polyethylene (HDPE), and linear (LLDPE) plastic films. It is widely used in fruits and foods, clothing, textiles, strain cultivation, daily necessities, etc. package.

Design Features

The film blowing machine is mainly composed of an extruder, a die head, a die head, a cooling device, a foam stabilizer, a herringbone plate, a traction roller, a winding device and the like.

ExtruderMulti-wall paper bags are used to transport and store dry flowable bulk materials. The paper shipping sack originated over a century ago. Today billions of units are produced and filled each year. Variations of the industrial paper bag include the pasted valve bag, pinch bottom open mouth bag, self opening satchel bag, and the sewn open mouth bag.

There are two basic types of paper bag: Open Mouth and Valve. An open mouth bag is a tube of paper plies with the bottom end sealed. The bag is filled through the open mouth and then closed by stitching, adhesive, or tape. Valve bags have both ends closed (pasted) and are filled through a valve.

Multi-wall bags are made up of 2-6 layers (plies) of paper and film. Paper plies are generally kraft or extensible paper. For bags requiring moisture or grease protection, a layer of plastic film may be added to the paper plies. The paper itself can also be coated with a thin layer of film.

The following information demonstrates the basic steps in manufacturing a multi-wall paper bag.

Step 1: Printing