A guide to hot-melt adhesives for converting professionals

By Angel Harvey, senior product mgr., Avery Dennison Label and Packaging Materials

Introduction

Hot-melt adhesives have been reliable pressure-sensitive adhesives (PSAs) for converters for a wide range of applications for more than 20 years. The solution offers broad application temperatures and ultimate bond and is used for low-surface-energy (LSE) substrates and rough or difficult-to-adhere-to surfaces. Updates to the technology now provide adhesives that are kinder to the environment, provide a substantial reduction in adhesive bleed and better productivity on-press with less adhesive contamination or ooze.

Hot melts are 100% solids and based on block copolymers. They have excellent moisture resistance, cold-temperature performance and high adhesion. Once melted, the polymers are combined with tackifiers to increase the stickiness (tack). Following that change, plasticizers are added to create a softer adhesive that is more malleable. The result is a suitable bond to many surfaces in wet or cold environments from room temperature to 25° F.

Figure 1. Hot-melt adhesives ranked by application temperatures / end-use substrate

Because of the high tack, hot melts are used in various industries, including the food and beverage market for cold packaging, fresh meats, weigh scale, spreads, cheeses and labeling of paperboard boxes (see Figure 1). In addition, the adhesives are applied to glass and plastic bottles for juices/functional beverages. Table 1 shows a range of hot-melt PSAs, their minimum application temperatures and a ranking of application conditions based on six end-use substrates.

With the evolution of food packaging and the explosive growth of e-commerce, these applications should provide label converters numerous business opportunities. There are a few important considerations when choosing a hot-melt PSA solution.

Sustainability now increasingly important

Converters should seek out hot-melt adhesives that use less fossil material and energy during production and produce less solid waste after conversion. According to a 2020 study by IBM and the National Retail Federation [1], almost 70% of US and Canadian consumers feel it’s essential that a brand is eco-friendly.

Converters can take advantage of this opportunity by choosing hot-melt adhesives that offer greater sustainability. For example, some hot-melt adhesives have received BioPreferred Certification from the USDA [2]. The certification creates new opportunities for brands to promote bio-based packaging to their customers. Bio-based materials enhance sustainability by replacing petroleum-derived products with renewable agricultural resources. The USDA BioPreferred Certification program validates the bio-based content of products through third-party testing. Certified products can promote their bio-based content on product labels, providing consumers with reliable and accurate information on the sustainability of the products and packaging they are choosing.

Table 1. Hot-melt adhesive labeling finds many food-packaging applications, such as plastic-film, corrugated-paperboard, glass and plastic rigid containers.

Lower application temperature adhesives

Battling cold temperatures during application always has been a benefit with hot-melt adhesives. Too often, labels will lift, peel or fall off entirely as cold settings can alter label adhesion. In addition to freezer-temperature hot-melt adhesives, new cold-temperature adhesives have been engineered with a lower minimum application temperature of 15° F, a ten-degree improvement versus previous adhesives.

Less ooze = less clean up

One of the usual worries with hot melts is adhesive ooze. It’s an issue that creates extra printing-press cleanup and maintenance and slows down production for many label converters. Another issue for converters with hot melts is adhesive bleed through the face stock, which gives labels an oily appearance. The latest adhesives are cleaner when converting with a decrease in adhesive ooze, bleed or plasticize migration.

Surface energy and texture

Rubber-based adhesives can be used in a variety of applications. Even the most challenging surfaces, such as textured or low surface-energy substrates, can benefit from this adhesive family. It always is recommended to test your specific application, which takes into account environmental conditions as well as converting and dispensing needs.

Hot-melt adhesives have extensive applications

Selecting the suitable hot-melt adhesive generally depends on application temperature and adhesion properties, but they work best when these qualities are needed:

High initial tack
Ultimate adhesion
Use of corrugated paperboard containers
Suitable for application on rough and damp surface substrates
Excellent for low temperature (e.g.: chilled food), room temperature as well as freezer applications
Comprehensive compliance approvals to meet global regulatory requirements

The chemical characteristics of hot melts make them an excellent adhesive choice for specific applications. Here are the application conditions under which hot melts work best:

Recycled paperboard
Low surface-energy substrates, such as HDPE
Rough or difficult-to-adhere-to substrates
Chiller or freezer performance

Hot-melt PSAs are not suitable for those applications involving heat exposure above 160° F, incidental solvent exposure or UV energy exposure.

Label adhesives are expected to stay in place and remain intact regardless of the substrates and distribution & end-use conditions. This puts great demands on both the adhesive products and the label converters themselves. Relying on a label-manufacturing partner with a broad portfolio of hot-melt options to choose from can ease that burden. The label-stock laminate provider can bring industry best practices and new hot-melt adhesive selections to help solve these issues.

References

Angel Harvey, senior product mgr. at Avery Dennison Label and Packaging Materials, has 24 years of label and packaging materials experience. With a diverse background, including roles in research and development, global project management and marketing, she currently is responsible for the Prime and VI Paper product lines. Angel can be reached at http://label.averydennison.com.