Silver lining in a coating

In businesses as diverse as direct food handling, pharmaceutical manufacture, hospital environments, leisure and animal handling, ensuring that micro-organisms are not allowed to proliferate and contaminate products or affect human health is a key requirement. Hygienic solutions need to be found that are suitable for food and drink processing facilities, abbatoirs, pharmaceutical cleanrooms and hospital wards through to swimming pools, gyms and shower areas.

All these sectors face a multiplicity of microbial problems, often specific to the particular use of the building. Food plants, for example, must constantly combat the threat of bacteria such as salmonella, campylobacter, listeria, e.coli and staphylococcus that could cause food poisoning in humans. The 2006 Food Hygiene Regulations require that the layout, design, construction and size of food premises shouldpermit not only adequate cleaning and disinfection but also protect against the accumulation of dirt, the shedding of particles into food and the formation of condensation. Wall surfaces must be easy to clean and, where necessary, easy to disinfect. Ceilings must prevent the accumulation of dirt, condensation or the growth of undesirable moulds and the shedding of particles.

In the healthcare sector, hospital acquired infections (HAI) are a major problem with HAI deaths in the UK running into several thousand per year. Undoubtedly, the one culprit grabbing the headlines is methicillin-resistant Staphylococcus aureus (MRSA). With a survival time of up to six months for MRSA bacteria, and with many hospitals identified as being contaminated with this organism, hygiene coatings that neutralise it could have a significant part to play in secondary prevention roles. Evidence is emerging that these potentially lethal bacteria can survive on the fabric of a building. It is also worth noting that ceilings in medical environments are not usually cleaned and walls are subject to less cleaning than floors.

The pharmaceutical sector faces a threat from the contamination of products and cultures from mainly airborne bacteria. Equally it would be disastrous to have any fungal or mould growth, giving rise to the potential for cross-contamination. It requires only low levels of opportunistic pathogens to cause spoilage. Examples of spoilage micro-organisms are salmonella sp, pseudonomas sp and various general gram negative bacteria or pyrogens.

A solution to many of these problems is to apply a multi-functional hygienic new surface to a building substrate. Dependant on how and where a hygiene coating system is to be used, the products that make up the system need to meet certain criteria. For example, they must be tested, certified, safe to use and apply, not contaminate the environment locally or generally, provide defined physical functions as well as decorative benefits, and be capable of use in a variety of environments and on virtually any substrate. More importantly, the film must protect itself from micro-organisms, while neutralising them in a way that will not allow resistance to develop.

A hygienic system faces further demands. It needs to cope with anything from old, possibly damp substrates, to modern synthetic surfaces. In so doing, it must allow for moisture vapour pressure, give excellent adhesion even if steam-cleaned daily, be resistant to cleaning chemicals or contamination from chemical or food splashing, and continue to provide a seamless film protected environment with no hiding places for organic matter.

Seamless film

To ensure this, the coatings must be more than primer and topcoats. They must be part of a system approach, which recognises that substrates – particularly old, previously uncoated ones – will be contaminated with micro-organisms and require sterilising before a hygiene system is applied. Following this, the in-use situation may demand that the coating can be reinforced to resist impact damage, and a fully seamless approach must be provided over joints and cracks that may already exist or can be expected to occur.

The coatings need to include elastomers and possess a rheology that allows a high enough film build to incorporate local or overall reinforcement systems. Perhaps most importantly, the coating needs to maintain long-term protection from the growth of micro-organisms. There are now also demands to resist non-visible growth (i.e., bacterial contamination and proliferation).

A further requirement is that the coating system will do this without exuding contaminating chemicals. If biocides are used to protect the film, which then leach to the surface, they will be both short-lived and potentially contaminating to the food or human environment.

There are additional specific sector requirements. Pharmaceutical industries demand cleanrooms whose surface finishes will not attract and retain dust and can be easily cleaned. Ceilings above wet food canning processes can be prone to condensation and this reinforces the point that film-protective agents must be non-leaching. Also, coatings must not contaminate the working atmosphere and must offer fast turnaround times. Only a water-borne system can offer this, allowing a resumption of processes or operations within 24 - 48 hours.

In summary, hygienic coatings need to provide:

• High build capability with a range of hardness and flexibility – and be reinforceable
• Resistance to chemicals in order to withstand frequent cleaning, including the use of steam and water
• Vapour permeability plus defined mechanical properties
• A package of systems, with associated decorative aspects
• Ease of use and application with acceptable environmental parameters
• Guarantees of 10 years plus for anti-microbial efficiency to provide cost effectiveness
• Test certification against a wide variety of micro-organisms – fungi, bacteria and yeasts

Conventional fungicidal paints are designed to give a ‘quick kill’ of micro-organisms using biocides that are in excess on the surface of the dried paint. The drawbacks are that they leach toxic chemicals into the environment, and washing cycles dilute these so that they are efficient for only a relatively short period. The paints also tend to be thin, hard, prone to flaking and can lose adhesion. They can therefore only be used on dry static substrates. Correctly formulated elastomeric hygienic coatings are designed to obviate these drawbacks.

Ceramic tiles are hard-wearing, easy to clean and impermeable. However, the grouting is the weak link with bacterial growth usually seen in that area. In addition, they can only be used on perfectly flat substrates. Hygienic coatings are seamless, take account of variation in substrate profiles and allow continuation from walls to ceiling.

Wall cladding systems are inert, but expensive and require specialist installation. They also do not provide a seamless finish and have no inherent surface protection, unlike hygienic coatings.

Antimicrobial action

Silver has long been recognised for its antimicrobial healing properties and for centuries has been used to aid the healing process and control infections. The earliest record of its use as an antimicrobial was by the Romans who stored their wine in silver urns to prevent spoilage. Silver is a naturally occurring antimicrobial with no known toxicity to humans and is used today to inhibit the growth of bacteria in healthcare equipment.

Liquid Plastics has been manufacturing high performance hygienic coatings for over 40 years and in that time has developed an unparalleled knowledge of the protective coatings market. As an innovator in the coatings market, Liquid Plastics has developed a way of incorporating silver ions into hygienic coatings. The silver ions are slowly released on demand via an ion exchange mechanism. This maintains an effective concentration of silver ions near the surface of the coating to inhibit the reproduction of the microbes. Due to the slow release mechanism, the coating remains effective for the long-term.

Rather than a single mode of action against micro-organisms, silver acts in three non-specific modes of action:

• Silver Ions inactivate critical physiological functions such as cell wall synthesis and membrane transport
• Silver Ions have a high affinity for negatively charged side groups on biological molecules. These include groups such as thiol, carboxyl, phosphate, and other charged groups distributed throughout microbial cells. This binding reaction alters the molecular structure of the macromolecule disrupting the respiration, rendering it worthless to the cell
• Silver Ions bond to nucleic acids such as RNA and DNA, preventing replication

Liquid Plastics’ Silver Ion products have undergone extensive and successful independent efficacy testing against a variety of micro-organisms, such as infectious gram positive and gram negative bacteria, including aerobic and anaerobic varieties. These tests have included bacteria with known antibiotic resistance such as MRSA and E.coli 0157, with results showing in excess of 99.9% reductions.

The above suggests that silver provides a durable, broad-spectrum antimicrobial treatment for many applications.

As well as beneficial antimicrobial properties, Liquid Plastics’ Silver Ion Technology coatings offer the following benefits:

• Impact and scratch resistance – preventing coatings from cracking and subsequently flaking due to impact from heavy or sharp objects
• Fire retardancy – effective against surface spread of flame and flame penetration
• Wide service temperature – performs across a wide range of temperatures typically from –30ºC to +80ºC
• Reduced weathering – resistance to ultra-violet light and non-yellowing
• Chemical resistance – to a wide range of reagents and cleaning products
• Physical toughness – they are strong and elastomeric in nature
• Water vapour permeable – allowing substrates to breath and, therefore, preventing coatings from blistering and subsequently cracking due to excess moisture in the substrate.