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A Guide to Bonding Polyethylene With Hot Melt Adhesives

2021-09-09 11:12   Үл хөдлөх зарна   Баян-Өлгий   10 views

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From kitchenware to our vehicles, plastic products have permeated every aspect of our lives and are integral to our day-to-day activities. Plastics can be divided into two main groups: thermoplastics and thermosets. Thermoplastics, like Polyethylene, soften easily when heated. Thermosets do not. Manufacturers must be able to efficiently and permanently join plastic components into complete assemblies, such as in vehicles, and that means using hot melt glue adhesives.


Advantages of Adhesive Bonding

Adhesives have several advantages over other types of bonding, like welding, or even using screws or nails.

  • Adhesives distribute the weight between two substrates more evenly, reducing stress on joints.

  • Adhesives are invisible, which means you get a nice, clean seamless line where the materials join.

  • Adhesives form a seal, as well as a bond, which protects the joint from corrosion.

  • Other hot melt adhesives can join irregularly shaped surfaces, quickly and easily bonding the substrates.

  • Assembly line operations are much easier, as there is less need for customization in the bonding process.


History of Hot Melt Adhesives

Archeologists have found evidence of humans using adhesives over 6000 years ago. The Ancient Egyptians used a form of glue to seal the wooden caskets of the pharaohs. However, modern adhesive technology did not begin to evolve until about 100 years ago.

A scientist invented thermoplastic glue, today is known as hot melt, in 1940. The scientists wanted something that would seal cereal boxes and stop them from popping open before getting to the consumer.

Manufacturers, particularly packing companies, first began the widespread use of hot melt in the 1960s. Eventually, hot melt technology led to the invention of hot melt glue sticks, spray-on bulk hot melt products and various formulations targeting specific bonding for plastics.


What Are Hot Melt Adhesives?

Traditional hot melts are thermoplastic resins. The resins are heated and applied to the substrates. Once it cools, the glue forms a strong bond that holds well under all types of conditions.

Although manufacturers produce a variety of hot melt glue tapes, depending on the usage, the most popular and best-performing hot melt varieties are ethyl vinyl acetate (EVA), polyamide, polyolefin and reactive urethane.

Hot melts have a thermoplastic polymer base that remains solid at room temperatures. Heating and applying them in liquid form make them well-suited for industrial applications. You can apply them by hand, using an industrial spray gun, by rolling or by extruding.


Applications of Hot Melt Adhesives

Polyamide hot melt adhesive products have an extensive range of applications in a variety of industries, such as:


  • Printing

  • Bookbinding

  • Taxidermy

  • Textiles, including applique bonding

  • Shoe manufacturing

  • Wood processing

  • Automotive, including interior and exterior finishing work like cushioning, headlights, taillights and wheel covers

  • Electronics manufacturing


Hot Melt Additives

Hot melt adhesives do not contain water or solvent. The adhesive sets when it loses heat, which is why the bond forms literally within seconds after applying.

  • The polymers in the adhesives provide strength and flexibility.

  • Resins provide immediate tack needed for adhesive action. Wax in the adhesive thins it making it easy to apply.

  • Antioxidants help protect the adhesive from losing its bonding ability even at elevated temperatures.

  • Tackifiers boost bonding strength.

  • Waxes alter the surface properties and reduce the viscosity.

  • Fillers, like tackifiers, also increase bond strength, as well as increasing the melting point and viscosity.


Important Factors That Influence Hot Melt and Adhesion

Since hot melt for heat shrink adhesives lose heat while setting, you need to be careful about the temperature control. The adhesive material should be in liquid or molten form for wetting substrates and is sufficiently hot to bond the materials together. Insufficient heat can lead to the failure of the bond.

It is important when using heat shrink tubing to proceed with caution and observe basic safety measures to avoid accidents or injuries. Here’s how to use heat shrink tubing:

  1. Begin by choosing the right size tubing with the correct shrink ratio. It should comfortably cover the wire or components before it has been shrunk into place to ensure a tight fit afterwards. Remember that it will be across both its breadth and its length.

  2. If the components to be covered could change size after application, ensure that the tubing has sufficient expandability by comparing its diameter when shrunk (called the ‘recovered’ diameter) with its size before shrinking (called the ‘expanded’ diameter). Check the recommended heating temperature for the tube to avoid uneven application or melts.

  3. Cut a suitable length of tubing using standard scissors and lay or slide this over the target components. It’s now time to heat the shrink wrap. This can be done with a handheld heat gun or a heat shrink oven. The latter are specialist appliances for more precise and advanced heat applications.

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