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June 28, 2016 - Flexible Packaging

Not All Metallocene Hot Melts are Equal

According to the research company Markets and Markets, the hot melt adhesives market is predicted to be worth $9.64 billion by 2020. Offering versatility and good cost in use, it’s understandable why these hot melt adhesives continue to grow in popularity among manufacturers.

In a recent blog, we discussed what hot melt adhesives are, how they work and their benefits. Now, let’s focus on one type in particular: metallocene hot melts.

What are Metallocene Hot Melts?

Metallocene is actually not a polymer per se, but rather a class of catalyst used to manufacture olefinic polymers. Hot melt adhesives based on metallocene-catalyzed polymers are generically called metallocenes. Metallocene hot melts are commonly used for case and carton sealing applications in the rigid packaging market. Based on polyolefin homo-polymers and copolymers, typical benefits of metallocene hot melts include:

  • Stable viscosity as a function of time/temperature
  • Clear color
  • Not prone to charring
  • Odor free

However, it is important to note that not all metallocene hot melts are equal. Let’s take a look at various factors that can make them different:

Homo-Polymers vs. Co-Polymers

Metallocene hot melts can be manufactured using homo-polymers or co-polymers. Which one you choose depends on your end-use application. For example:

  • Homo-Polymer Metallocene Hot Melts: Homo-polymers are good for applications that require more rigidity and have lower bond performance criteria.  An example would be general purpose case and carton sealing.
  • Co-Polymer Metallocene Hot Melts: Co-polymers are recommended when an application requires more flexibility, greater temperature performance, and/or adhesion to challenging substrates.

Density Ranges

Metallocene hot melts come in a range of densities (typically .80 to .93). The density level determines the product’s mileage in terms of how much adhesive is needed. For example:

A metallocene hot melt that has low density has increased mileage than one of higher density. This contributes to a reduction in costs, as less adhesive is needed for an application.  Remember, adhesive is purchased by the pound, but is applied by volume; lower density products give you more volume of adhesive per pound.

Additionally, low density allows a metallocene hot melt to be heat sealed at a lower application temperature and are easier to remove during the paper repulping process.   This improves ease of recycling of corrugated paper products.

Hot Tack vs. Tack-Free

Metallocene hot melts can also be manufactured to have hot tack or be tack-free.

  • Hot Tack: Also called green strength, hot tack enables the adhesive to yield an instant bond when two substrates are joined together. Metallocene hot melts that have hot tack help increase production speeds, as the adhesive bond is maintained as the substrate exits the compression section until a full crystallization occurs.
  • Tack-Free: Metallocene hot melts that are tack-free are beneficial for applications that require self-winding roll goods. Tack-free means that the adhesive can be wound on sheets back-to-back and will not stick together during unwinding.

Bostik’s Metallocene Hot Melts

Bostik uses its formulation and application expertise to manufacture smart metallocene hot melts based on customer needs. Certain products include:

  • Thermogrip® H9636A: This product has high heat resistance, making it suitable for hot-filled applications. It passes the IOPP testing standard at 170° F, which makes it particularly suited for applications that are transported via railcar.
  • Thermogrip® H9675A: This product is great for lidding applications, as it enables heat sealing to occur at lower application temperatures. It also has excellent adhesion to various films and is suitable for extrusion coating application.
  • Thermogrip® H9489: This workhorse, water-white metallocene hot melt is for case forming and sealing applications. It has one of the broadest temperature performance ranges of any case and carton seal adhesive on the market.

Additionally, this product bonds to a variety of difficult to adhere substrates, including freezer-grade. H9489 can withstand prolonged exposure to application temperatures, preventing charring and adhesive discoloration.

  • H9592B: This premium product is one of the fastest setting adhesives for case and carton seal applications in the industry.   Several of our customers have been able to increase line speeds, without investing in extended compression sections, through the use of this product.

For more information about how Bostik can formulate metallocene hot melts to your needs, call 800-7-BOSTIK.

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