PLASTIC SEALING MACHINES

The extensive use of plastic as a packaging material goes hand in hand with the requirement for machines which seal flexible and rigid plastics together. Plastic seals are used in particular for liquid and viscous materials, and also for free-flowing solids such as powders, grains, and groups of loose, solid items. 

What is a plastic sealing machine?  

The key function of a plastic sealing machine is to bind layers of plastic together. The sealed pack offers protection of the contents from contamination and leakage, as well as enabling efficient handling and secondary packaging.

The sealing process includes binding two sides of a flexible plastic bag or pouch, through to sealing a rigid tray with a film lid. The seals are commonly created by heating the plastic and applying pressure by means of a sealing bar. 

Alternatively, plastic and other materials can be sealed with glue and adhesives, usually with the application of heat to melt the binding agent in a process known as hot melt gluing. Adhesives are most commonly used to apply plastic films to trays. 

Rigid plastic tubs are commonly sealed by clip fitting a lid with a gasket, while packaging lines for plastic bottles and jars apply a screw cap to seal the container. Sealing machines for rigid plastic tubs, jars and bottles are known as capping machines. Find out more about all types of closing machinery here

 

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What are the different types of plastic sealing machine? 

Plastic sealing machines fall into two principal categories. They are either constant sealing machines or impulse sealing machines. As the name implies, constant sealing machines provide permanent heat, and are designed for use in continuous packaging operations. The elements in impulse machines are heated only while they are sealing a bag or pack. 

Impulse heat sealing machines start with entry level equipment capable of sealing up to 20 packs per hour. They are low cost, and use relatively low amounts of energy. However, they are generally only designed for use with lighter grade films. As such they are suitable for smaller operations such as artisan food producers and low volume retail stores using manual operation. 

Constant heat sealing machines involve greater financial outlay but deliver higher throughputs. They can also be integrated into packaging and finishing lines, and can be operated semi-automatically or fully automatically. They are also able to seal thicker gauge films and foils as well as multi-layered materials.  

See more about heat sealer machines including options for hand-held, tabletop, foot-operated, rotary and vacuum operation. For complete packaging solutions including plastic heat sealers.

 

How does a plastic sealing machine work?

To heat seal plastic, the essential requirements are heat and pressure. Whether they are impulse or constant machines, heat sealers feature one or more electrically heated elements which press against the open end of bags or the open sides of folded films. 

The heating elements are usually in the shape of a bar which spans the top of the bags or films being used. Simple impulse sealers are most likely to feature a single electrically heated bar which melts the layers of plastic at the aperture of a bag. 

To seal sheets of film, L-sealers are used. The film is folded lengthways, the product is placed within the folded film and the L-shaped sealing bar presses down on two of the open sides of the pack. As the next length of film and the next product progresses along the packing line, the L-shaped element seals two sides of the pack and at the same time seals the last open side of the preceding pack in a continuous process. 

Side sealers initially create a tube of film by sealing two sides of a double layer of film containing the product. The side sealer then seals a third side, and as the pack progresses through the packing line, the sealing element seals the fourth side and separates the following pack. Side sealing allows for products of almost any length to be packed.  

Side sealers are generally able to operate at faster speeds than L-sealers, with speeds of up to 100 packs a minute. L-sealers are the preferred option for top quality presentation packs.

 

Which plastic films are used in heat sealing?

The core property of films used with heat sealers is that they are thermoplastic – that is, they can be softened by heat and will bond with a second layer of film. They are generally either polyethylene (PE), polypropylene (PP), or polyvinyl chloride (PVC). 

Plastic bags and films can be loosely wrapped around products, but for a tight fit the film must also be shrinkable. Shrink films tighten around the product when passed through a heat tunnel. 

More advanced heat seal films are multi-layered, with a coating on the outside of the film which prevents the inner layers from melting. With a core of PE or PP, a layer of sealant with a lower melting point creates a tight and robust seal around the product. Further advances are in the use of layered films featuring polyethylene terephthalate (PET) which is recyclable.

 

How to choose a plastic sealing machine

The choice of a plastic sealing machine needs to be based on the performance required. To make an informed purchase decision it is essential to understand the packaging requirements for the products to be packed, including 

  • size of packs
  • number of units to be produced
  • hygiene levels (especially for food and pharmaceuticals) 
  • energy requirements
  • material usage
  • the environment the equipment is to be used in

The budget too will have a key bearing on the purchase, and should be factored into return on investment calculations. The life expectancy of the machinery is an important part of the decision, as is reliability and maintenance costs. Commercial options to be considered are buying second-hand equipment and leasing rather than outright purchase. 

The simpler the business, the simpler the equipment specification and the buying decision. However, larger businesses will want to consider flexibility and options for integration into existing workflows. Plastic heat sealing is well-proven in the packaging industry, and the options on available equipment are extensive. Buyers in general will be able to find machinery which is perfectly well-suited to their requirements.

 

Where to buy a plastic sealing machine

Once the case for purchasing a sealing machine is established, the next step is to source the right equipment from a trustworthy supplier. The market is competitive, and to explore the options the Automate UK is an excellent source of information. The triennial PPMA Total Show provides an opportunity to see sealing machinery in action and to meet relevant suppliers such as our exhibitors.

A further resource for equipment buyers is Machinery Finder which features a full range of suppliers with details of their products, services and contact details.