Water-based adhesives are one of the many bonding technologies available on the market today. They are used in many industries, but especially in paper labeling, woodworking, automotive and textiles, offering many benefits to users and the environment.
To understand the benefits of water-based adhesives and why they might be suitable for your application, it is important to see how they work, evaluate the different chemistries, and identify the best maintenance and handling practices when using these adhesives.
What are water-based adhesives?
Supplied as premixed or dry solutions – which are then mixed with water prior to application – water-based adhesives are applied in liquid form, with water acting as a carrier to ensure proper coating of substrates.
Evaporation, or the absorption of water into the substrates, leaves the base of the adhesive, allowing it to form a bond, so it is important that at least one of the substrates is porous, allowing water to escape or be absorbed. As this process can take several hours, depending on the formulation, good tack is required to support the initial contact between the substrates, in addition to the fact that the process may require drying ovens.
The liquid nature of the adhesive makes some wet glues more susceptible to moisture and excess water, which can adversely affect bonding performance through additional curing time and reduced bond integrity. In addition, many types of wet glue have a limited shelf life compared to other adhesives.
In spite of this, the wet base of the adhesive facilitates the cleaning of equipment and, in some cases, facilitates environmental measures, e.g. by allowing glass bottles labeled and bonded with a water-based adhesive to be easily washed and reused, with a view to a circular economy.
Water-based adhesive technologies
Both synthetic and natural polymers from plant (dextrin and starch) and protein (casein) sources can be used as a base for these adhesives.
Each option has specific properties that influence how the product can be used and for which applications:
- Dextrin and starch-based adhesives: popular in the paper industry, these adhesives are very strong when used with specific materials, but due to their vegetable base, they can break down when exposed to water. They are probably the most environmentally friendly of the wet glues, being biodegradable and compostable;
- Casein-based adhesives: they provide strong bonds, but with a relatively long curing time; these adhesives are water-resistant and can be resistant to condensation water (CWR) and ice water (IWR), making them ideal for labeling glass bottles in the beverage industry;
- Synthetic-based adhesives: these are considered more modern; they can form stronger bonds with greater customisation, making synthetics suitable for more demanding applications and environments. They also tend to have a longer shelf life than natural-based adhesives.
Whether synthetic or natural adhesives, polymers are the backbone of the adhesive and ensure its strength and chemical resistance. Each adhesive also contains plasticisers to soften and improve flexibility, while other ingredients contribute to the processing and bonding properties of water-based adhesives.
Advantages of water-based adhesives
Wet adhesives are cheaper to produce than most other adhesives.
Solvent-free, they can also be used in non-vented areas, making them an easy choice for the user, as well as an environmentally friendly option. Their ecological credentials are further enhanced by application at room temperature – usually around 21°C – 25°C – which helps users reduce energy consumption. Furthermore, many wet glue types are formulated with polymers of organic origin and are therefore ideal for companies looking for a truly environmentally friendly product.
Cleaning is also quick and easy: water is enough to wash the adhesive off machinery and equipment, limiting production downtime and further increasing profits.
Unless directly exposed to water or humidity, wet glues provide a strong bond. However, as mentioned above, some, particularly caseins, can offer resistance to condensation water (CWR) and ice water (IWR), making them ideal for glass bottle labeling applications.
However, manufacturers choosing a water-based adhesive must take into account the longer drying time and limited shelf life, as well as the need to carefully store and transport water-based adhesives to avoid wastage.
Industrial applications of water-based adhesives
Due to the curing process involving the evaporation or absorption of water, the industrial sectors most suitable for water-based adhesives involve the use of porous substrates:
- Paper applications, including labeling, binding, corrugated board, envelope and stamp production;
- Fabrics for hygienic fabric applications;
- Flooring and interior products in the automotive and transport industries;
- Woodworking and furniture applications;
- Textile and towel sectors, e.g. for the production of toilet rolls.
Maintenance and cleaning of water-based adhesives
Water-based adhesives can offer consistent processing and bonding performance. However, a common problem is centrifugal forces during processing that spray adhesive onto equipment, leading to production interruptions and additional cleaning.
There is a way around this: check and adjust the viscosity or ‘thickness’ of the adhesive, if necessary, then clean or change the rollers, or adjust the speed of the rollers.
Storing the adhesive at the right temperature – usually around 20°C – 25°C – should prevent it from becoming too cold, which can increase the viscosity and reduce the flexibility of the adhesive, or the adhesive from becoming too hot, which can increase the viscosity and limit its shelf life.
When handling the adhesive, always keep the lid on; this reduces the surface skin, prevents contamination and reduces microbial growth.
Ask the expert for more information on water-based adhesives.
