The introduction o f the EN16350:2014 standard, which deals with the electrostatic characteristics of protective gloves in July 2015 meant that manufacturers had to look at new ways to match the updated requirements. The use of standard carbon black and metal fibres to meet the new standard can lead to difficulties in the manufacturing process largely because of the high loading levels required and the associated complications implementing these materials into the latex material matrix. In contrast, the use of single wall carbon nanotubes (SWCNT) as a conductive additive for anti-static and ESD gloves provides an easy solution for manufacturers to comply with the new protection standard for electrostatic properties without the need to make changes to the production process. At ultra-low loadings – less than 0.05% – SWCNTs provide high electrical conductivity and retain colour brightness in gloves and don’t require any changes to be made to existing processes.
Latex-based industrial anti-static and ESD safety gloves are widely used in the electronics, automotive, pharmaceutical, biotechnology, chemical and mining industries. The commitment to ‘level up’ to the best practice currently employed within the EU has been outlined in a Framework Directive (89/391/EEC), which lays down broad guidelines for health and safety, as well as places an absolute duty “to ensure the safety and health of employees in their workplace” upon employers.
On the basis of this Framework Directive, a series of five individual directives were adopted. The Framework Directive with its general principles continues to apply in full to all the areas covered by the individual directives, but where individual directives contain more stringent and/or specific provisions, these special provisions of individual directives prevail. One of these, Directive 89/656/ EEC – use of personal protective equipment – lays down minimum requirements for personal protective equipment (PPE) including anti-static and ESD gloves, which have always been important in the European and US markets.
The EU and US markets make up more than 60% of the total worldwide consumption of antistatic and ESD gloves and for clients within these regions, ensuring the gloves’ characteristics comply with the worldwide most influential EN standard is a high priority. Products tested in accordance with the standard and which display the appropriate label for certified ESD protection are preferred by consumers. Traditionally, other countries quickly follow the EU’s lead, which suggests that worldwide adoption of the new standard for gloves’ vertical resistance level is not too far away.
Almost 80% of the more than 150 billion disposable gloves that are manufactured and used annually are produced in Malaysia and Thailand. The new EU Standard implemented by all of their main customers poses a significant challenge to manufacturers as they have to find a way to comply with the new Standard EN16350:2014 and fast.
In addition to setting minimum requirements for the surface resistivity/resistance, the EN16350:2014 standard dictates that the contact resistance of a latex glove must be less than 100 megaohms (Rv < 1.0 x 108 Ω)2. Commonly used conductive technologies do not enable manufacturers to easily comply with the new EN standard, requiring a new solution.
Challenges providing the necessary conductivity level
Anti-static agents can be either applied externally or internally. Sprayed or coated external conductive agents form a conductive layer on the surface, allowing electric charge to flow and dispel static. Although this is a low cost solution to provide latex gloves with conductivity, it is not efficient because the coating can be easily removed by rubbing or washing. Furthermore, the conductivity of the coating is highly dependent on humidity.
The new EN standard, which states the atmosphere during testing for the contact resistance must constitute an ambient temperature of 23°C (± 1°C) and have relative humidity of 25% (± 5%), makes the use of external agents even less effective.
In the past, nitrile or inorganic salts used as conductive fillers were sufficient for latex to meet the requirements of the earlier EN1149 standard for surface resistivity. However, nitrile alone provides a contact resistance level of approximately 1 × 1011 Ω, which is insufficient for the new EN16350:2014 standard that requires a contact and vertical leakage resistance of < 1.0 x 108 Ω.
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