The ECHA is campaigning for a ban on PFAS based on REACH in the EU, which is due to come into force in 2027 for certain industry segments. There are similar efforts in the USA, which are specifically aimed at water contamination. Although a complete ban is not expected there, global supply chains will be affected, which is why Asia and South America are proactively preparing for abolition. The NOF Metal Coatings Group already offers PFAS-free coating solutions.
The NOF Metal Coatings Group, with its European headquarters in Creil, north of Paris, creates, develops and produces patented water-based coating solutions for fasteners, brake discs and chassis parts. The coatings are mainly used for corrosion protection and friction coefficient control to ensure the reliability and durability of components. With a worldwide network of more than 300 licensees, Geomet zinc flake technology is used by major OEMs in the automotive, truck, construction, agricultural and energy industries.
PFAS, poly-(or per-)fluoroalkyl substances, form a large group of over 10,000 fluorinated compounds that are known for their anti-adhesive, waterproof and heat-resistant properties and are widely used in a variety of industries and everyday products. Due to their permanent presence in the environment and their toxicity, they are increasingly viewed critically and referred to as "eternity chemicals".
Friction coefficient control
NOF Metal Coatings is working to reduce or eliminate substances with a negative impact on the environment. Apart from PTFE (polytetrafluoroethylene), a fluoropolymer that is classified by the Organization for Economic Cooperation and Development (OECD) as a "polymer of low concern" but could still be regulated, the company does not use PFAS in its products.
PTFE is specifically used in some of the company's lubricated coatings, which are applied to fasteners to control their coefficient of friction. This makes assembly conditions more reliable and guarantees a secure connection throughout the life of the end product.
The range of PFAS-free products includes Geomet 321 (silver anti-corrosion basecoat), Geomet 360 (anti-corrosion basecoat for brake discs), Geomet 430 (grey anti-corrosion basecoat), and topcoats such as Plus M (silicate-based, lubricated topcoat with coefficient of friction µ 0.12-0.18 [ISO 16047]) and non-lubricated topcoats such as Plus, Plus 10 or Geokote products (organic topcoat with excellent mechanical and chemical resistance).
Geomet zinc flake technology
Fig. 1: EDX image of a FIB-prepared thin Geomet 321 lamella (cross section) showing the precise distribution of zinc and aluminum lamellae in the mineral matrixThephysicochemical nature, morphology and microscopic organization of the zinc and aluminum lamellae (specifically designed for water-based formulations) integrated in a sol-gel matrix make it possible to obtain very thin coatings that can meet high corrosion protection requirements such as C5-M and CX (ISO12944). The galvanic and tribological properties as well as the thermal resistance of this coating are particularly in demand in the field of fastening and safety components, especially in bimetallic steel/aluminum configurations. Depending on the substrate, a 6 to 8 µm thick Geomet coating achieves a performance level of 1,000 hours of salt spray (ISO9227) with an amount of zinc that is 2 to 3 times less than 100% metallic electroplating solutions, thus conserving natural mineral resources and reducing environmental impact.
Among all industrial galvanic coatings, zinc flake coatings are unique in that they can be applied both by immersion (bulk or rack) and by spraying (electrostatic or pneumatic). This variety of application methods not only opens up the scope of application for a very wide range of parts, but also offers the advantage of being non-electrolytic. This feature is particularly valuable for parts manufacturers working with metallurgies that are sensitive to hydrogen embrittlement caused by electrolytic application processes (which also require the recycling of very large quantities of water). This is one of the reasons why this technology is attracting so much interest in the automotive and wind energy sectors. This is because screws and steels with ultra-high yield strength are being further developed to meet the growing demands for lightness and safety. Every year, Geomet coatings ensure the long-term protection of over one million tons of steel worldwide (Fig. 1).
Combination of zinc flake basecoats and topcoats
Fig. 2: EDX image of a Geomet 430 + Plus VLh Black coating under a bolt head after tightening. The right part of the image shows the area that was stressed during tighteningThezinc flake technology usually consists of two silver (Geomet 321/720/500) or two anthracite grey (Geomet 430) basecoat layers on which silicate and lubricant-based topcoats are applied (Plus products), which can be transparent, silver, black or colored. These topcoats, which have a thickness of 1 to 5 µm depending on the application, are usually formulated to modify the tribological properties of the coating in order to control the coefficient of friction of bolts or nuts according to the specifications of various industries, including the automotive market.
Controlling the coefficient of friction is an essential feature to ensure accurate tension in the components during tightening and to avoid loosening/loosening phenomena that can occur under mechanical, vibratory and thermal stress. Compared to 100% metallic coatings, the composite structure of Geomet (sol-gel + zinc flakes) has rheological properties that allow a larger contact surface between the screw and the parts to be assembled on a microscopic level.
In combination with topcoats, these coatings are better able to control the lubrication of the interfaces involved in assembly under extreme local pressure and temperature conditions. Other advantages of these topcoats in the context of controlling the coefficient of friction of bolts and nuts include non-loosening at high temperatures, multiple tightening, stick-slip prevention and tightening control on different materials such as steel or aluminum and cathodic dip coating ( Fig. 2).
Plus Topcoat, PFAS-free
Some of the Plus Topcoats on offer, such as Plus M, COF: 0.12 - 0.18 (ISO 16047), were already formulated without PFAS, but did not cover the full range of functions expected by the market. The development objectives were to offer a new range of more environmentally friendly products while guaranteeing the same tribological performance as the current Plus products.
There are three new silver-colored PFAS-free topcoats:
- Plus XL 2 Silver : COF 0.06 - 0.09 (ISO 16047)
- Plus VLh 2 Silver : COF 0.09 - 0.14 (ISO 16047)
- Plus ML 2 Silver : COF 0.10 - 0.16 (ISO 16047)
Bolting test against aluminum
On the water-based zinc flake basecoat Geomet, these PFAS-free alternatives meet or exceed OEM requirements and specifications while providing the following tribological properties:
- Multiple bolting and high-speed bolting (Fig. 3)
- Compatibility with various substrates (e.g. KTL, aluminum, zinc and steel)
- Avoidance of stick-slip
- Loosening torques (even at high temperatures - Plus VLh 2 Silver and Plus ML 2 Silver)
Fig. 3: Bolting test against aluminum (MBN 50544 )
Optimized aesthetics and identification
The aesthetics of the products in the new series have been improved by adding aluminum pigments to achieve a uniform silver color. In this way, the visual appearance of components where the fasteners are visible to customers has been improved. In addition to optimized aesthetics with aluminum pigments in the coating, all three new PFAS-free topcoats contain fluorescent pigments that enable clear identification - a new feature for topcoats that is unique to date, according to NOF Metal Coatings Group.
Meanwhile, the research & development laboratories are working on PFAS-free coatings and Geoblack systems and additional black topcoats in the PFAS-free Plus series.
The industrialization process of PFAS-free coatings is carried out in cooperation with manufacturers of fasteners, OEMs and supply chain partners.
