What are water-based adhesives?
Supplied as pre-mixed solutions or dry solutions – which are then mixed with water before application – wet glues are applied in liquid form, with the water acting as a carrier to ensure proper coating of substrates.
Evaporation, or absorption of the water into the substrates, leaves the adhesive base behind, allowing it to form a bond. This curing process means it’s important for at least one of the substrates to be porous - allowing the water to escape or be absorbed. Because this process can take several hours, depending on the formulation, good tack is necessary to support first contact between the substrates, as well as the process potentially requiring drying ovens.
The liquid nature of the adhesive makes some wet glues more susceptible to excess moisture and water – which can negatively affect bond performance through extra curing time and reduced bond integrity. In addition, many types of wet glue have a limited shelf life, compared to other adhesive technologies.
Conversely, the wet base of the adhesive means it is easy to clean off equipment and, in some cases, supports environmental measures; for instance, by allowing labelled glass bottles that have been bonded with a water-based adhesive to be easily washed and reused as part of the move towards a circular economy.
Water-based adhesive technologies
Both synthetic polymers and natural polymers - from vegetable sources (dextrin and starch) and protein sources (casein) - can be used as the base for water-based adhesives.
Each option carries with it specific properties that influence how the product can be used, and for which applications.
- Dextrin and starch-based adhesives: popular within the paper industry, these adhesives are very durable with specific materials, but due to their vegetable base, can break down when exposed to water. They are probably the most environmentally friendly of all wet glues, being biobased, biodegradable, and compostable.
- Casein-based adhesives: provide strong bonds, but with a relatively long curing time; these adhesives are resistant to water and can be condensation water resistant (CWR) and ice water resistant (IWR), making them ideal for glass bottle labelling in the beverage industry.
- Synthetic-based adhesives: considered to be more modern; can form stronger bonds, with greater customisation, this makes synthetics suitable for more challenging applications and environments. They also tend to have a longer shelf life compared to natural-based adhesives.
Whether they be synthetic or natural-based, polymers are the backbone of the adhesive, providing both its strength and chemical resistance. Each glue also includes plasticisers to soften, and improve flexibility, whilst other ingredients help to modify the processing and bonding properties of water-based adhesives.
Advantages of water-based adhesives
Offering an economically viable option for many manufacturers, wet glues are cheaper to produce compared to most other adhesives.
Solvent-free, they can also be used in non-ventilated areas, making them a user-friendly choice, in addition to being an environmentally friendly option. Their eco-credentials are further enhanced by ambient temperature application – usually around 21°C - 25°C – which helps users to reduce energy consumption. And with many types of wet glue formulated with biobased polymers, they tick the box for companies searching for a truly eco-friendly product.
Clean-up is also quick and easy, with only water needed to wash adhesive off machinery and equipment – limiting production downtime and further boosting the bottom line.
Unless directly exposed to water or moisture, wet glues provide a strong bond. Although, as has been mentioned already, some glues, caseins specifically, can offer condensation water resistance (CWR) and ice water resistance (IWR), making them ideal for glass bottle labelling applications.
Manufacturers choosing a water-based adhesive should take into account the longer drying times and limited shelf life, and factor in the need to carefully store and transport water-based adhesives to avoid wastage.
Industrial applications of water-based adhesives
Due to the curing process that involves evaporation, or the absorption of water, the most suitable industries for wet glues involve the use of porous substrates:
- Paper applications including labelling, bookbinding, corrugated board, envelop and stamp production
- Fabrics for non-woven hygiene applications
- Flooring and interior products in the automotive and transport industries
- Woodworking and furniture applications
- Tissue and towel sectors, for example, for the manufacture of toilet roll
Water-based adhesive maintenance and housekeeping
Water-based adhesives can offer consistent processing and bonding performance. However, a common problem involves centrifugal forces during processing splashing adhesive on equipment leading to production stoppages and additional cleaning.
How to prevent this: check and adjust the viscosity or ‘thickness’ of the adhesive, if necessary, then clean or change the rollers, palettes/pads, and brushes, or adjust the roller speed.
Good housekeeping, routine application auditing and forward planning can prevent many production problems, such as adhesive splashing, from happening in the first place.
Storing 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 from the glue from becoming too hot, which can increase viscosity and limit its shelf life.
When handling adhesive, the lid should always be kept on; this reduces surface skin, avoids contamination, and reduces microbial growth.
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For further information about our water-based adhesive range, or advice on handling and maintenance, contact us using the website, or send an email to: marketing@beardowadams.com