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 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.
- Adhesives can join irregular shaped surfaces, quickly and easily bonding the substrates.
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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 Procter & Gamble (P&G) scientist invented thermoplastic glue, today known as hot melt, in 1940. P&G 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 glue sticks, spray-on bulk hot melt products and the 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 melts, 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
Hot melt adhesive products have an extensive range of applications in a variety of industries, such as:
- Packaging
- Printing
- Book binding
- 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 the 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 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 failure of the bond.
What Is Polyethylene
The first real plastic was invented in 1869 by John Wesley Hyatt, but Polyethylene (PE), the most common type of plastic used by industries today, wasn’t discovered until almost 20 years later. In 1898, a German chemist, Hans von Pechmann, learned how to create Polyethylene. It wasn’t until the 1930s and 1940s that the industrialization of plastics began in earnest.
Chemically, Polyethylene is a synthetic resin with distinctive properties that have made it an invaluable addition to modern life. It is light weight, flexible, chemically and corrosion resistant, and very inexpensive to make.
Why Use Hotmelt for Polyethylene Bonding
Hotmelt has a number of characteristics that make it an excellent choice for use with PE:
Sets Very Quickly
One of the biggest advantages hot melt has over other adhesives is how quickly it sets. This is particularly important in assembly lines and other types of manufacturing where you need to join two parts quickly and move on to the next step in assembly.
No Mixing
You don’t need to add anything or mix any components together when using hot melt with PE. Hot melt is a stand-alone product that does its job without any additional compounds to mix in or chemical catalyst.
Non-Toxic
There is no need for extraordinary precautions when you use hot melt. Hot melt is nontoxic. You do not have to follow hazardous material disposal methods or worry about toxic fumes. The product will not harm your employees or consumers.
Bulk Purchasing
Hot melt is a very cost-effective method to use in your manufacturing or shipping operations. It sets quickly, allowing you to maximize your manufacturing and operational speeds. You can also buy it in bulk, saving you time and money.
Food Safe Adhesives and Hot Melts
The food industry uses a lot of plastic components for shipping and storing food items. These components require adhesives approved by the Food and Drug Administration (FDA), the Government Agency that regulates food handing.
The FDA determines what substances can and cannot come into contact with food. There are specific regulations regarding what sorts of adhesives you can use for food stuff. The manufacturer of the adhesives is directly responsible for complying with these rules.
The key article related to adhesives in the FDA regulations concerns adequate curing so that any hot melt or other adhesive used in food packaging can’t leach into the food stuffs. This regulation extends to the types of adhesives you can use for plastic piping that carries drinking water, coffee or other consumable liquids. There are several choices of food-grade hot melt adhesives made for bonding polyethylene used in the food processing and packaging industries.
How to Apply Hot Melt Adhesives
To ensure a successful bonding, the bonding surfaces should be dry, clean and should not have any grease, oil or dust contamination. The adhesive should be applied at the appropriate temperature. The temperature of the surrounding environment and the materials involved can affect the adhesive properties. Too high of a temperature retards setting time, while too cold of a temperature results in adhesive setting before the bonding of the materials.
Applying too much or too little can adversely affect the bond. Insufficient quantity leads to quicker cooling of the adhesive, resulting in improper bonding. Too much prevents cooling down of the bond prior to completion of compression, resulting in a weakened bond.
Types of Hot Melt Applicators to Use for Polyethylene
Industrial hot melt applicators come in a variety of dispensers. There are pneumatic systems, roll coaters, hand guns and more. The Astro Packaging SS10 Bulk Hot Melt Dispensing System has a melt rate of 8lbs per hour. The TC500 temperature controller can handle two hoses and two applicators at a time. The 10lb bulk melt tank has a cylindrical Teflon-lined drum that eliminates char build-up and helps ensure a constant pump rate.
The Astro Packaging LS10 Bulk Hot Melt Tank is the perfect hot melt stem for product assembly. Like the SS10, it has a 10lb bulk, Teflon-lined hot melt tank. Fully electric, the LS10 takes about 30-45 minutes to warm up, and again, like the SS10, has a great 8lbs-per-hour melt rate. Weighing only 45lbs, it is easy to move around. It also has a built-in safety feature that will not allow the pump motor to operate until the tank reaches safe operating temperatures.
One of the largest and most popular bulk hot melt applicators is the Astro Packaging KB30. This unit uses up to four guns and four hoses at one time with a 30lb-capacity hot melt take, and has a 40lb melt rate. The dispenser needs 200V or 240V, and single or three phase electricity
Best Hot Melt Brands for Polyethylene Bonding
Gluegun.com offers several types of hot melt products highly effective for bonding plastic substrates:
Infinity SuperTAC 500 Plastic Bonding Glue Stick
Offering great heat resistance and bonding abilities to a wide range of plastics including PP, PE, PET and PVC; the Infinity SuperTAC 500 is the ideal plastic bonding glue stick. It’s also very cost effective, making it easy on the wallet.
Infinity SuperTAC 11 Product Assembly Bulk Hot Melt
The Infinity SuperTAC 11 is a high performance APAO bulk hot melt that is regularly used in automotive manufacturing and product assembly. It’s bonding abilities are strong and flexible and offers impeccable temperature resistance at both low and high extremes. With the option of either bead or spray form dispensing and it’s flexible bond, the SuperTAC 11 will give your great impact resistance and vibration.
Henkel Technomelt PA 7804 Bulk Hot Melt Adhesive
Henkel manufactured the Pa 7804 specifically for plastics, metals, woods and leathers that would be exposed to extreme temperatures. This Henkel product has exceptionally high impact resistance at very low temperatures. It also has excellent shock resistance and carries a UL 94VO rating.
Henkel Technomelt 0437 Bulk Hot Melt Adhesive
The Henkel Technomelt 0437 is suitable for a number of substrate applications, including Polyethylene. This product is made for bulk hot melt spraying applicators. Technomelt 0437 has approximately a 2-4-week lead time for ordering.
PAM UXR 2101 Bulk Hot Melt Adhesive
The UXR 2101, with its very long open time, allows you to reposition and tweak your product before the adhesive sets permanently. A general purpose hot melt, it comes in a 35lb case.
PAM UXR 2101 Bulk Hot Melt Adhesive
The PAM UXR 2101 is best known for its low viscosity. Sprayable, you have up to nine minutes of tackiness, which makes it excellent if you need to spray large plastic surfaces. It also works well on foam, fabric, wood, cardboard and metal. A clear hot melt, the best application temperature for the UXR 2101 is between 325-375 degrees Fahrenheit.
Warren Adhesives HM 6504 Freezer Grade Bulk Hot Melt
This freezer-grade bulk hot melt has approval under Food and Drug Administration (FDA) regulations for incidental contact of the adhesive with food products. The HM 6504 will not lose its tack in freezing temperatures. Due to its aggressive tack, the HM 6504 is optimal for fast, short compression times.
Henkel Technomelt PA 7901 Bulk Hot Melt Adhesive
The PA 7901 is another great Henkel product with low viscosity, great for potting and encapsulating. It is heat and vibration resistance and bonds not only to plastics, but also to metals. Due to its fast cure rate and quick dispensing, it makes a great alternative to an epoxy or urethanes.
Henkel Technomelt PA 7804 Bulk Hot Melt Adhesive
If your plastics will be exposed to extremes of temperature, the Henkel Technomelt PA 7804 is an excellent choice. It has exceptional impact resistance at low temperatures and has a UL 94VO rating.
Ad Tech 297 Sprayable Bulk Hot Melt Adhesive
The Ad Tech 297 was made for spraying and bonding large areas made of plastic, wood, foam, metal or cardboard. It stays tacky for up to 10 minutes. You can cover up to 48 square feet without worry about the bond setting too soon.
The Future of Hot Melts and Plastic
Experts predict that hot melts ability to bond instantly with plastics, and the increased use of plastics in construction, will significantly boost the hot melt market in the near and long term. Hot melt formulations continue to improve, with companies like Henkel and other regularly introducing new products to the market.
Emerging countries like India, Vietnam, Brazil and others are heavy users of plastics in industry. Hot melt is a cost-effective and efficient method for industrial bonding applications. The market demand is likely to drive newer and even more technologically advanced formulations for polyethylene bonding.
Last Word
Hot melt adhesives function very effectively when used to bond plastics to other plastics or substrates. There are many types of formulations available for whatever needs you might have.
Ask an experienced hot melt retailor for advice and guidance as to what sort of hot melt product and applicator will work best for your operations. Paying strict attention to the surface preparation and any manufacturer recommendations will help ensure the best results possible.