With spraying colours

Clay Technology magazine
16 Aug 2018

Ines Nastali looks at the latest trends in pigment engineering and how chemicals used in the industry should be surveyed for effective environmental impact control.

The clay and brick industry relies on pigments and additives to manufacture a durable product. Tim Clay, Prince Minerals’ Sales Director for Structural Ceramics, UK, talks Clay Technology through where the company’s customers are active. ‘The manufacturers generally work in both industrial and residential applications alongside the more specialist architectural sectors, which often require one-off solutions in niche applications.’ He adds, ‘Bricks for the residential sector will mainly rely on surface colours and textures whereas the industrial application bricks tend to use the through body colourings – in the main manganese or chrome to produce either browns, blues, or greys.’

When it comes to current colour trends, Clay has noticed that in 2017, the company has seen some growth in grey type colours. 

This is not the only trend in requests for characteristics of pigment used for brick manufacture. ‘We have seen growth in recent times of liquid spray colours,’ Clay says, adding that for conventional brick production, ‘This is a very flexible means by which to add simple colour designs to a brick and the current spray technology within the industry – computer controlled application – allows for a multitude of spray patterns and the utilisation of several colours at the same time. This is more predominant on extruded products.’ At the same time, soft mud production for bricks also used spray colours but to a lesser extent. 

Liquid delivery

Apart from sprayed colours, products in powder, slurry or paste form are available. The recent trend here prevails for the liquid delivery. ‘Our own product mix with reference to surface colours is typically 60/40 in favour of liquid colours at present when measured by tonnes,’ Clay said. 

The reasoning behind this balance is economics, as one tonne of liquid spray colour will make significantly more bricks than one tonne of powder colour pigment. ‘Essentially, all powder pigment is mixed with sand to produce a sand stain mixture,’ Clay said.

Additionally, considering health and safety aspects, Clay explains, ‘Liquid sprays are better in these terms as the dust levels can be reduced in factories and they provide the perfect means by which to add very controlled measures in the clay body via peristaltic pump systems’. 

‘Products are made using high shear mixing processes and carefully selected chemicals to ensure that the liquid product stays in suspension, and does not settle out’.

Environmental scrutiny

The use of pigments and chemicals makes the brick industry accountable for a wide range of environmental scrutiny. Legislation such as the EU Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) agreement, regulated by the European Chemicals Agency, demand that the supply chain of chemicals can be traced. 

Recent research by an international team of researchers applauds the EU’s chemical database, but demands more work into determining the impact of chemicals on the environment. While the scientists did not look at any specific industry, ‘but on chemicals in general and the risk they pose to the environment, the issues raised in the paper would apply to the chemicals used in the brick and ceramics industry and their impact on the environment,’ Lorraine Maltby, Professor of Environmental Biology and Deputy Vice-President Research and Innovation at the Department of Animal and Plant Sciences of the University of Sheffield, UK, and author of the paper Toward sustainable environmental quality: Priority research questions for Europe published in Environmental Toxicology and Chemistry journal, told Clay Technology.

The scientists identified 22 questions that need urgent attention and call for a wholesome approach of surveying the supply and application chain, because while most industries handling chemicals are heavily regulated, ‘our understanding of how chemicals impact the environment and human health is still poorly developed,’ the scientists state in their paper. ‘For example, most research on and regulation of chemicals considers the impacts of individual substances, yet in the real environment chemicals will co-occur with hundreds or thousands of other substances and stressors,’ they add.

Therefore, according to the researchers, ‘when analysing nano and microparticles in different matrices, it is not only the composition and concentration that will need to be determined, but also the physical and chemical properties of the particles within the sample and the chemical characteristics of any capping or functional layer on the particle surface’. 

The researchers name a range of analytical techniques, including microscopy based approaches, chromatography, centrifugation, filtration, fractionation, spectroscopic, and related techniques, and single particle inductively coupled plasma mass spectrometry, that could aid this approach. However, ‘although many of these approaches work when used in controlled laboratory-based studies, they can lack the sensitivity and specificity for application to environmental monitoring. 

Work therefore needs to continue on the development of methods that are able to measure these substances at concentrations that are expected to occur in the environment’.

Finally, the researchers call on the industry, ‘To fully exploit the wealth of data that are available will require new ways of working – researchers and the business sector need to be more transparent and open in sharing their data, improved mechanisms are needed to support data sharing, standardisation is needed in the presentation of data and metadata, and assessment approaches are needed to determine the quality of the data’.

Environment versus technology

Clay agrees that environmental regulations change the industry. ‘Reclassification of minerals and global harmonisation of health and safety is always presenting new challenges alongside REACH issues, which is presently resulting in certain minerals and materials becoming more expensive or no longer available,’ he told Clay Technology.

‘We are therefore always looking for new minerals to challenge our longstanding and normal practices, he said, adding that ‘We use all available minerals and oxides such as manganese, iron, titanium, kaolin, all in various forms. Natural and synthetic pigments – basic oxides and ceramic grade colour pigments are also used. Glass-forming minerals can be utilised as an important aspect when engineering the product. It is very important to use reliable sources with decent life expectancy’.

Clay also puts environmental issues over technical advancements, saying that ‘Very little technical developments are ongoing at present, which affect our product types’.

It is not only the brick industry that uses pigments to enhance the characteristics of their product. They are also used in concrete. Andrew Bain, who works for chemical manufacturer Altana’s sister company ECKART Effect Pigments as Marketing & Technical Support Manager, spoke to Clay Technology about using pigments in concrete.

What kind of construction projects do you deliver your aluminium powder for porous concrete to?

Typically we are supplying aluminium flakes to the lightweight concrete blocks (LWC) market. We also have some activities with mortars and construction renders. For our concretes applications, our flake pigments are primarily used as catalyst materials and offer no function to tint colours. Certainly, we have questions on tinting but in most situations, the colouration would be achieved by way of additional process, such as surface coatings, rather than integration into the concrete material itself.

What are the beneficial characteristics of this concrete?

For LWC blocks benefits are weight and insulation properties. For mortars and renders we have projects to eliminate excessive shrinkage and mildews.

Do you deliver more products in paste or powder form and which sort of project conditions would you recommend for each?

Normally the preference is paste form due to explosive risks associated with aluminium powder.  Paste does have some drawbacks too, particularly when supplied to humid regions.

Which minerals do you use to mix your pigment in general, and what are the challenges of engineering pigments?

Not so much minerals however, we manipulate surface areas of aluminium flakes to offer bespoke reactivity, which, in turn, promotes alternate
block density.

How do technical developments change the way you work?

Synthetic materials are becoming a focus, which have new challenges.

Read the full study Toward sustainable environmental quality: Priority research questions for Europe here: bit.ly/2MezuQi