Rubber Journal Asia Gloves
Complying with the new standard for electrostatic properties in protective gloves The introduction of the EN16350:2014
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 1 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 10 8 Ω) 2 . Commonly used conductive technologies do not enable manufacturers to easily comply with the new EN standard, requiring a new solution.
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.
Challenges providing the necessary conductivity level nti-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.
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atex-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 4
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Rubber Journal Asia Tyre Market Gloves TEM image of SWCNT (Bar is 1 mm)
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 10 8 Ω. The new standard also makes the use of inorganic salts as a final coating unworkable due to two reasons. Firstly, Natrium Chloride only provides surface resistance and not vertical resistance, which is a requirement of the new EN standard, and secondly, the new standard’s minimum requirements for the electrostatic properties of protective gloves set a relative humidity of 25%, compared with the previous standard of 50%, a condition where the salt coating will completely evaporate. As an alternative, internal anti-static agents such as carbon black dispersions or metal fibres can be dissolved in latex. However, the concentration of these additives in latex varies from 5% to 25% per compound, which inevitably results in a requirement to make major changes to glove manufacturing processes. Up until recently, there were no conductive additives available to glove manufacturers that could both meet the new EN16350:2014 standard and which could be easily implemented in existing manufacturing processes. Laboratory tests have demonstrated the efficacy of SWCNTs, with ultra-low loadings of 0.05% or less required to achieve the necessary level of conductivity. Embedded into latex, SWCNTs with high aspect ratio are capable of forming inter-connected networks between rubber matrix and carbon nanotubes. Therefore, a lower loading of such materials can provide the required electrical conductivity and simultaneously retain the mechanical properties of the elastomeric matrix, which makes them ideal for such applications. Years of studies have proven the significant conductive capabilities of SWCNTs. However, up until recently the lack of availability of SWCNTs in large
CURRENTLY AVAILABLE
RESULTS WITH SWCNT
Specific resistivity level
107–1011 Ω*m
102–108 Ω*m
Concentration of conductive fillers
>5%
0.03–0.075
Negative impact on mechanical properties
yes
no
Colour
yes
no
quantities at a consistent quality, made mass application difficult and cost prohibitive. In 2013, global chemical company OCSiAl developed a patented technology for single wall carbon nanotube synthesis, enabling large-scale commercial use for the first time. Graphetron 1.0 is the world’s first mass-production SWCNT reactor, enabling the creation of high quality single wall carbon nanotubes that are cost-competitive with standard conductive additives for a wide range of applications. RESULTS AT A GLANCE
The enchancements in parameters of latex after the implementation of SWCNT
Electrical resistivity <106 Ω*m
When embedded directly into the latex matrix, single wall carbon nanotubes create an additional highly conductive 3D network and provide uniform vertical conductivity.
No change in manufacturing technology processes
Water-based suspensions with high-quality dispersions of carbon nanotubes and latex-friendly chemicals provide compatibility with standard processes and equipment.
Ultra-low concentrations retain colour
Effective concentrations of single wall carbon nanotubes from 0.03% to 0.05% makes it possible to maintain bright colours in the end product, unlike most alternative conductive additives.
Developed specifically for each type of latex
Different types of surfactants were added to SWCNT dispersions to more effectively introduce single wall carbon nanotubes into natural and synthetic latex matrices.
Improved mechanical properties
Single wall carbon nanotubes create a strengthened network that intertwines with the composite matrix and reinforces the latex structure without critically impacting plasto-elastic properties.
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Rubber Journal Asia Gloves OCSiAl provides single wall carbon nanotube products under the trade name TUBALL, which contain 75% or more of SWCNT. To simplify its delivery into the matrix of different types of latex, a water-based suspension called TUBALL LATEX was developed, which features high quality dispersed carbon nanotubes and latex-friendly chemicals. An ultra-low concentration of SWCNT (0.03%0.06%) means both the production technology and formulation can remain the same.
CONTROL 0.03% 0.06% 0.1% SWCNT SWCNT SWCNT Latex
Experimental data on SWCNT introduction into latex matrix n order to evaluate the effects of SWCNT as a solution to provide conductivity in latex, a series of trials on a natural rubber-based composite, which was prepared with SWCNT using the latex stage mixing method, was conducted using a natural medium modulus natural latex (CL60) formulation with the addition of SWCNT water-based suspension via a standard mixing procedure. Nanotubes were dispersed in water utilising ultra-sonication and stabilised by adding a special surfactant. Natural rubber latex, consisting of 60% dry rubber content (DRC) and 61.2% total solids content (TSC) was purchased from Thai Rubber Latex Corporation (Thailand). TUBALL SWCNTs commercially produced by OCSiAl using the catalytic CVD method 3 were used in the trials. The diameter of one tube is 1.6±0.4 nm and the length of CNT >5 microns. To ensure the uniform distribution of SWCNT in water, an ultra-sonic disperser was used. Sodium poly [(naphthalene formaldehyde) sulphonate] and Sodium dodecyl benzenesulphonate were used as dispersants. Other components of the latex formulation were commercial grade. To prepare the water-based dispersion with 0.2wt.% of SWCNT the following were used: TUBALL – 0.2 wt.%, Distilled water – 98.8 wt.%, Surfactant* – Sodium poly[(naphthalene formaldehyde)sulphonate] (or leukanol) – 0.75 wt. %, Surfactant* – Sodium dodecyl benzenesulphonate – 0.25 wt.%. A mechanical mixer with water cooling tank was used for heat absorption and pre-mixing of the SWCNTs. After mechanical mixing, Sodium dodecyl benzenesulfonate was added into suspension, dissolved and dispersed by ultra-sonication. The total power of the treatment of suspension using the ultra-sonic disperser was 2W · h/ml. The tests found that the required amount of the SWCNT-based suspension depends on the solid rubber content of latex and the final formulation. The table below (3) shows the amount of SWCNTbased 0.2% suspension that was added to the latex to prepare dipping solutions with loading levels of SWCNT from 0.03 weight % to 0.1 weight % (based
I
167.00
167.00
167.00
167.00
SWCNT Suspension 50% ZnO dispersion
–
15.00
30.00
50.00
1.00
1.00
1.00
1.00
50% ZDC dispersion
2.00
2.00
2.00
2.00
50% Sulphur dispersion
3.00
3.00
3.00
3.00
106.56
115.56
124.56
135.56
Total
Recipe of natural latex based mixtures (Table 3)
on the solid rubber content). Aqueous dispersions of ZnO, ZDC and sulphur were prepared by ball milling using ceramic balls. Latex was mixed using an overhead stirrer at a speed that ensured thorough mixing of the entire latex mass simultaneously. All chemical components were added in accordance with standard processes and mixed. The SWCNT suspension was gradually introduced into the latex at a steady speed until the uniform grey colour was achieved. The samples were laid onto petri dishes, dried and subsequently cured. The electrical conductivity of the vulcanised films was measured in accordance with EN 16350:2014 standard. Surface resistivity/resistance (Ω) was measured in ohm along the surface of the material, between two specified electrodes (resting on the test specimen) and a potential of 100±5V. Vertical resistance was measured in ohm through a material, between two electrodes placed on opposite surfaces of the test specimen and a potential of 100±5V. Measurements of electrical conductivity were made at the temperature 23°C (± 1°C) and humidity level 25% (± 5%). The size of the sample was 40 x 15 x 1.8 mm.
CONCENTRATION OF SWCNT IN NATURAL LATEX. PHR
ELECTRICAL RESISTIVITY. Ω*m
Control
>108
0.03
3.6x106
0.06
4.3x105
0.1
2.4x105
Electrical resistivity of natural latex based films with different load of SWCNT
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Rubber Journal Asia Tyre Market Gloves
+30%
property improvements by reinforcing the latex +21% +19% structure even at extremely low concentrations. As low as 0.03% to 0.06% SWCNT, depending on the type of latex, provides a vertical resistance level of 1x10 6 Ω to 1x10 4 Ω, more than sufficient to ensure compliance with the new EN16350:2014 requirements, whilst simultaneously maintaining Ultimate Tensile strength, M100, M300, colour brightness. elongation, % MPa MPa MPa Different water-based systems with dispersed nanotubes can be used for various latex formulations. Masterbatches can No CNT added be introduced into natural and synthetic latex 0.03% CNT matrices at the compound mixing stage without any Additionally, the mechanical properties of the additional procedures, making SWCNT a ‘readyvulcanised films were measured using a Shimatzu to-use’ conductive additive suitable for use in the AGS-X 2, 5 kN machine. Tests were made on a film manufacturing of anti-static and ESD gloves, such thickness of 0.18 mm. After assessing the mechanical as cleanroom, industrial and knitted latex coated, properties of medium modulus natural latex before supported and unsupported gloves. and after applying 0.03 wt. % of SWCNT to the solid content of latex, it was found that the tensile modulus TYPE OF LATEX VERTICAL M100 increased by 21%, and M300 by 30%. Tensile RESISTANCE LEVEL strength also improved by 19%, while stretching at Natural latex Film 0.03% of break remained unchanged. These results are fully 1X105 Ω•m compliant with the philosophy about the reinforcement TUBALL mechanism of SWCNT. Nitrile latex Film 0.05% of 1X104 Ω•m Performance benefits of SWCNT as the next-generation TUBALL conductive additive for latex gloves he high length-to-diameter ratio of SWCNTs Supported Nitrile Glove 0.06% 1X106 Ω•m creates an additional reinforcement net with of TUBALL nanotubes linked to macromolecules of latex and to other nanotubes. Due to the strengthened connection Vertical resistance level of latex with different amount of SWCNT within rubber matrix, SWCNT delivers exceptional The use of single wall carbon nanotubes as a chemical and mechanical properties that far outstrip conductive additive enables manufacturers to offer those provided by carbon black and other alternative high quality anti-static and ESD latex gloves that meet additives. the vertical resistance level requirements set out in The EN388 standard covers the test requirements EN16350:2014 Standard, simultaneously maintaining their for safety gloves and requires gloves to be scored mechanical properties. Producers in the Asia-Pacific region for blade cut resistance, abrasion resistance, tear have successfully conducted trials and launched pilot-scale resistance and puncture resistance. The majority production, without changing technology or formulation. of conductive additives negatively impact a product’s mechanical properties. In contrast, For more information, visit www.ocsial.com or email SWCNT suspensions provide significant physical latex@ocsial.com
+1%
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1 World Industrial gloves Market: Global Industry Analysis and Forecast to 2021 (Allied Market Research); OCSiAl. 2
Personal Protective Equipment Directive 89/656/EEC, 1989.
3
Pat. 2478572 RF: IPC B 82 Y 40/00 (2011); Pat. 8551413 B2 USA: IPC B 01 J 19/08 (2013).
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