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What are isocyanates?

Isocyanates are chemical compounds containing a specific functional group referred to as the isocyanate group. Isocyanates are highly reactive compounds and are used in various industrial applications, a common representative of which is methylene diphenyl isocyanate (MDI) in reactive PUR hot-melt adhesives.

This group consists of a nitrogen atom bonded to a carbon atom and an oxygen atom, whereby the carbon atom has a double bond to a further oxygen atom:  

R-N=C=O

Here, “R” stands for an organic residue or organic group that is bonded to the nitrogen atom.  For this reason, isocyanates are often referred to as NCO.

Production of PUR hot adhesives

Polyaddition: PUR hot-melt adhesives are polyurethane resins that are formulated by polyaddition from polyoles and polyester resins or mixtures of these, with a significant excess of diisocyanates.

The polymer chains therefore consistently have terminal, reactive isocyanate groups that are available for subsequent cross-linking/curing using atmospheric moisture. The majority of the isocyanates are bound to the polyoles / polyesters; free diisocyanate components remain (which are not polymer-bound). According to the hazardous substances regulations, their content leads to the corresponding classifications:

The gradations are as follows:

  • Classic PUR adhesives = > 1.0 < 5.0 % free diisocyanate – subject to labelling
    (H317: Can cause an allergic skin reaction; H334: Can cause allergy, asthma-like symptoms or breathing difficulties if inhaled; H351: Suspected of causing cancer; P261: Avoid breathing in dust/fumes/gas/mist/vapour/aerosol; P280: Wear protective gloves/protective clothing/eye protection).
  • LE - Low Emission = >0.1<1.0 % free diisocyanate – subject to labelling
    (H334: Can cause allergy, asthma-like symptoms or breathing difficulties if inhaled; P260: Do not breathe in dust/fumes/gas/mist/vapour/aerosol). H351 label no longer applicable (suspected of causing cancer)
  • ME – Micro Emission = <0.1 % free diisocyanate– no labelling required

  • Mandatory training when working with LE and classic PUR products

    Ensure that all employees working with reactive PUR hot-melt adhesives are appropriately trained and understand the required safety precautions.

    Since 24th August 2023, the training requirement for ME products has been lifted in accordance with REACH.

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