Plating and Sustainability
Because plating uses chemicals,
some people worry about their impact on the environment.
Today’s plating, however, has evolved into a technology
that is safe and secure for both the environment and human health.
In this chapter, we will learn about plating and sustainability.
What environmental regulations are there surrounding plating?
Since the 2000s, a succession of regulations aimed at environmental protection have been established, primarily in Europe, and companies are being pressed to respond. The following are some representative examples of such environmental regulations.
・ELV Directive
This prohibits the use of lead, mercury, cadmium and hexavalent chromium in the materials and components used on automobiles.
・RoHS Directive
In principle, it is not possible to sell any electrical or electronic components that contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ether (PBDE).
・WEEE Directive
To reduce waste, products put on sale must be made easier to recycle.
・REACH regulations
In principle, all chemical substances must be registered, evaluated, authorized and restricted by the European Chemicals Agency.
These are all regulations related to items manufactured or sold within Europe. Even if the manufacturing takes place in a different region, compliance with the rules is necessary if the products are to be exported to Europe.
Of course, plating technology must also respond to these regulations. From here, let’s look at the environmental measures taken in plating.
What is environmentally friendly plating technology?
In order to comply with the environmental directives and regulations, plating has used technological innovation to solve the issue. The main examples of this are:
- No inclusion of heavy metals
- No inclusion of hexavalent chromium
- No inclusion of formalin
- No inclusion of cyanide
- No inclusion of PFOS and PFOA
- Recycling systems for electrolytic copper plating solution
In conventional plating, these were all important and essential substances. However, technologies to replace them have been developed and the use of these new technologies is beginning. Let’s look at each one of these.
Plating that does not include heavy metals
In the electroless plating performed up until now, heavy metals (such as lead) were contained in the plating solution itself. Also, although the amount was small, there were also some heavy metals included in the plated film. When this is the case, there are problems with the environmental regulations when items are disposed of. It was therefore desirable to develop an electroless plating solution that includes no heavy metals.
The development of plating solutions progressed from 2000 onwards and technology was established to eliminate the use of all heavy metals in electroless plating except the metal to become the plated film (i.e. to have no metal except nickel when performing electroless nickel plating). In a lot of the electroless plating performed today, there is no inclusion of heavy metals in either the plating solution or the plated film.
Also, when this plating solution that does not contain heavy metals is used, it becomes easier to dispose of the plating solution after it has been used. This plating is therefore also kinder on the environment in this regard.
Environmental measures for chrome plating
Chrome (Cr) is common in the natural world and it is a substance that is often used in plating because it is has stable properties and does not easily rust. The types of chrome are trivalent chromium (Cr+3) and hexavalent chromium (Cr+6).
Hexavalent chromium is cheap and makes chrome plating easy, so it is easy plating for a manufacturing plant to handle. However, hexavalent chromium is strongly toxic and has an extremely large effect on the human body if it is inhaled or simply touched. Therefore, if hexavalent chromium is used in the manufacturing processes for the chrome plating, then it is necessary to sufficiently clean the completed surface to ensure that the processing liquid does not remain as a residue.
On the other hand, with trivalent chromium plating, the preparations and the management of the solution are difficult and it is a more expensive method, which is why it has not been used in the past. In addition to this, with trivalent chromium plating, there is sometimes hexavalent chromium formed in the solution during the work, so it is a difficult substance to perform plating with.
The development of chemicals for trivalent chromium and the adjustment of the processing conditions for the plating are proceeding so that it is now becoming easier to perform trivalent chromium plating and there are expectations for further developments in the future.
Plating that does not use formalin, cyanide, PFOS or PFOA
In addition to heavy metals and chromium, plating also uses other substances that can affect the environment and the human body. Development is also ongoing for alternative technology that does not use these substances.
Formalin
Formalin is used in many applications such as a disinfectant, insecticide, it is highly toxic and care is required in its use. In plating, it is used widely as the reducing agent for electroless copper plating, but a new electroless copper plating solution that does not contain formalin is now being developed.
Cyanide
Cyanide, which is also known as cyanogen, is used in compounds such as potassium cyanide and sodium cyanide. It is an extremely toxic substance. It is used as a complexing agent in gold plating, but in some areas, plating methods that use sulfite and other substances are already becoming the mainstream, and this is spreading throughout the entire gold plating sector.
PFOS, PFOA
PFOS is the abbreviation for perfluorooctane sulfonic acid, and PFOA for perfluorooctanoic acid. Both substances are organic compounds that contain fluorine. PFOS and PFOA have previously been in wide use as surfactants, but because they remain intact, hardly breaking down at all, in the natural environment, there are concerns about their impact on human health. As such, alternatives have now come into use.
Recycling systems for electrolytic copper plating solution
A crucial aspect of mitigating the environmental impact of plating is the reduction of the volumes of waste liquid (liquid that are discarded because they are no longer needed). Uyemura has proposed a method to prevent the discharge of waste liquid semi-permanently, by using a combined UV and ozone treatment to break down the waste additives in electrolytic copper plating solution, followed by the replenishment and adjustment of additives.
In this chapter, we have learned about plating and sustainability. Research and development is being conducted of alternatives even for substances that have been considered essential to plating until now, and progress is being made in the further mitigation of environmental impact. The evolution of plating technology will continue, for the realization of a sustainable society.