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All manufacturers in the furniture and building components markets utilize adhesives to assemble their products. Polyurethane (PUR) hotmelt adhesives are preferred for demanding applications such as edge-banding, flat-lamination and profile wrapping, as they offer:
- Best-in-class heat resistance
- Unmatched moisture resistance
- Broad adhesion spectrum
- Low adhesive application weight
During application, PUR hotmelts are heated to molten state and cured with moisture, forming a crosslinked polymer with resistance to heat and chemicals. This versatile ‘building block’ can be used to build a near-infinite variety of polymers, which enable the adhesive to bond to different substrates (including wood, plastics, glass and most metals), compensating for their different degrees of thermal expansion and finally offering a best-in-class array of properties:
- Broad range of applications (edge banding, straight-line, soft forming, surface bonding, lamination, profile wrapping)
- High heat resistance (>150°C/>302°F) and cold flexibility
- Excellent moisture and solvent resistance
PUR hotmelt adhesives are formed from isocyanates (technically diisocyanates) and polyols. These combine to make an intermediate ‘precursor’ that will be cured at our customers’ premises to form a completely cross-linked polymer with extremely high molecular weight. This is what is known as a reactive product; such products still contain a small amount of free monomeric, highly reactive diisocyanates.
As a PUR compound is heated during application, the vapor pressure of all individual monomeric and polymeric components within it increases (as it would with any organic compound). Though monomeric diisocyanate has a low vapor pressure (0.000005mmHg at 20˚C), it is still possible for small amounts to become airborne (and the possibility of this increases in higher temperatures). As a vapor, it presents a risk to operators since inhalation or skin contact can lead to sensitization and can trigger severe asthma attack in case of further exposure.
This is where Micro Emission products – a category introduced by Henkel, containing less than 0.1% monomeric diisocyanate – come into play. Traditional polyurethane hotmelt contains as much as 2-5% monomeric diisocyanate.
Switching to Micro Emission solutions, combined with mitigation measures to control skin contact – exhaust systems, personal protective equipment (PPE), protective screens, and so on – will bring the risk to the lowest possible level. Additionally, Micro Emission products are exempt from forthcoming regulations, can be used on the same line as conventional hotmelts, and offer the same standard in the resulting product. Therefore, they are a convenient solution for businesses as well as a safe one.
This risk airborne isocyanates present is already recognized and regulated through Occupational Exposure Limits. There is currently a regulatory initiative to lower these limits – most prominently through REACH (Registration, Evaluation, Authorization and Restriction of Chemicals), a set of regulations introduced by the European Chemicals Agency. In August 2020, an update to Annex XVII of REACH came into force, introducing greater restrictions on pure diisocyanates and mixtures containing diisocyanate.
From 24 February 2022, all diisocyanate-containing products (whether supplied on their own or as part of a mixture with other products, as long as the diisocyanate concentration is over 0.1%) must show a statement on their packaging with the remark: “As from 24 August 2023 adequate training is required before industrial or professional use.” Then, from 24 August 2023, they cannot be used at all unless strict requirements are met, as explained below.
Professional users of isocyanates must meet one of two requirements. The first is that the concentration of diisocyanates is below 0.1% in all mixtures they use. The second is that all their industrial or professional users must successfully complete training on safe use of the substances, and be certificated, before they can work with them. This training will be mandatory every five years. For more information and to download training materials, see safeusediisocyanates.eu.
Henkel is a market leader in Micro Emission adhesive technologies, with well over a decade’s experience in development, production and customer service. Our Micro Emission PUR hotmelt products enable customers to meet the ‘less than 0.1% diisocyanate concentration’ requirement, thereby allowing them to safely continue with their current processes without undergoing further training.
Ultimately, it is every customer’s choice what route they follow to meet the regulations: adopting Micro Emission products or running the necessary training. Whichever they choose, we will be there to support them, with our high standard of technical support, technical service and extensive R&D operation, supported by years of experience making Micro Emission products work seamlessly and effectively in real production conditions.
More and more safe and sustainable technologies will spring up and be widely adopted. At Henkel, we are always researching more technologies that will allow our customers in many different industries to meet their goals and advance along their sustainability journeys.
The ubiquity of adhesives means we need to make them as safe and practical as possible. Switching to less or ideally non-hazardous ingredients is preferable not just from a regulatory perspective, but also for human health and the environment. Combining the latest product innovations with the ‘safety belt’ of risk management is the practice we recommend.
On a wider level, more and more customers and consumers will be requesting sustainable products and solutions. With the demand clearly there, we can develop disruptive solutions as a priority, such as bio-based or recyclable adhesives.
It’s true that adhesives only account for a minor proportion of the cradle-to-grave emissions of, say, a kitchen unit. But we are in a forward-thinking industry. Awareness is growing, and we are all embracing the need to take action on climate change. It will become a growing focus for us.