The Substitution of diffuseable raw materials in the UV hardening varnishes for wood furniture
Danish furniture manufacturers use lacquers that cure by means of ultraviolet radiation as the most frequent surface treatment of wooden furnitures. A shift in monomer and acrylates with a higher molecular weight means that the acute toxicity of the UV lacquers is reduced. The monomer and binder replacements could be performed without considerable technical or financial consequences for the varnish manufacturer – and further for the end user.
The substituted substance (1,6-Hexanediol diacrylate) and one of the alternative substances (1-methyl-1,2-ethanediyl)bis[oxy(methyl-2,1-ethanediyl)]diacrylate are on the hazardous Substance Database according to SUBSPORT Screening Criteria (SDSC) as skin sensitizers.
Danish furniture manufacturers use lacquers that cure by means of ultraviolet radiation as the most frequent surface treatment of wooden furnitures. UV curing primers and finishes are being applied by rollers or by spray guns, and are subsequently cured in special ovens with UV light.
When UV cured lacquers are applied, the part of the lacquer having the lowest viscosity will penetrate into the wood and become inaccessible to the UV radiation, thus remain un-cured. Additionally, the lacquer may contain monomers and binders that do not completely polymerize from the UV radiation. In this way, all these un-cured components may fairly easily emit from the wood and lacquer when the furniture is introduced at the end-user and will deteriorate the indoor climate.
The project this report refers to has shown that UV-curing furniture lacquers contain more or less un-reacted monomers after UV curing. However the varnish manufacturer can reduce such emissions by a careful choice of appropriate materials. The choice can be made by a thoroughly environmentally related study of the ingredients included in the varnish. The study should primarily focus on the monomer and binder, since they contribute most to the varnish composition. Monomers’ and binders’ content of chemical compounds was reflected in their statutory safety data sheet and were given an indication of their reactivity: Lower reactivity leads to more un-reacted compounds in the varnish and results in higher diffusion.
There were significant differences between raw materials’ tendency to diffusion after UV curing. For example, the chemical analysis showed that the lacquer manufacturer simply by changing his commercially used monomer HDDA to DPGDA (Dipropylene diacrylat – CAS 57472-68-1) or TPGDA (Tripropyleneglycol diacrylat – CAS 42978-66-5) could reduce emissions significantly. A shift from HDDA to TPGDA means at the same time a change to acrylates with a higher molecular weight, and thereby to less acute toxic acrylates. A change in primer – acrylates with much higher molecular weight at the same time means that the acute toxicity of the UV lacquers is reduced.
Even though the final formulation of the UV lacquers was not available when this project ended, all results indicates that the new formulations consists of more pure raw materials, i.e. fewer constituents in the final product. This must be regarded as an advantage, as there is not complete knowledge about the health and environmental properties of the different constituents. The monomer and binder replacements could be performed without considerable technical or financial consequences for the varnish manufacturer – and from this – at the end user.
The optimisation of monomer and binder in the lacquers will lead to less diffusion of monomers from lacquered wooden furniture, and thereby help improve the indoor environment at the end user.
Acrylates are in general regarded as causing sensitisation. Changing to other acrylates does therefore not remove this risk.
One of the alternative substances (CAS 42978-66-5) does not pass the eliminatory criteria set by SUBSPORT, therefore we recommend further search for safer alternatives. The case story is in the database despite this, due to the fact, that the workers are well protected during the application and therefore are not exposed to the substance. Moreover the alternative releases less uncured components compared to the substituted substances.
Some acrylates are embryotoxic.
Type of information supplier
Danish EPA (Miljøstyrelsen)
DK-1401 København K
Freely available at www.mst.dk
Publication or last update: 29-03-2012