Smart colour solutions

Jumping out of the box is an objective every pioneering and forward-thinking coatings chemist or engineer likes to achieve.

Modern and innovative coatings are striving for an apparent break-through effect that imparts the coating system an obvious added value. This ambition is driven by the general need for creating more and more cost efficient products without turning them into commodities.

To prevail it is essential to focus on the right raw materials! One of the most innovative options is the use of “smart” materials.

A smart pigmentation is a pigmentation that is capable to respond to changes in its environment or that may also exhibit an unexpected functionality.

We would like to introduce two smart pigment technologies developed by Heubach. The first technology was designed to achieve not only a high value alternative to the toxic Chromate and Cadmium but also a group of products which offer better stability and formulation cost efficiency compared to formulations based on titanium dioxide and organic pigments which till now had been the main alternative.

The second pigment technology gives coatings the ability to reflect IR-radiation in order to reduce the potential of buildings to heat up, due to exposure to sun-light, resulting in reduced energy for air-conditioning.

Tico® – Lead chromate and Cadmium pigment replacement
In the past chrome and cadmium pigments were the preferred choice for opaque full shade coatings that called for brilliant yellow, orange, red, brown and green colours. Since the ban of these pigments, formulators have had the choice between several alternative non-toxic options.

Today’s preferred option is blends of organic and titanium white pigments. This has the disadvantage of “whitening” the brilliant chroma of the organic pigment and it is well known that in the presence of titanium white, the weather stability of these expensive colorants rapidly decreases.

Blends between high performance organic pigments and titanium yellows overcome this problem in theory, but do not develop the full potential of these two different pigment classes using today’s conventional blending methods. Such blends suffer from separation, which creates stability problems. Additionally, the high abrasion of titanium yellows often prevents the development of a shear stable colour. The result is insufficient colour development and unsatisfying dispersion properties that accounts for the limited use of rutile yellows.

For these reasons blends between titanium white or titanium yellow cannot match the excellent coloristic and processing properties of lead and cadmium based pigments, which has been an ongoing challenge since the ban of these colorants.

An essential task of this R&D challenge was the search for titanium carrier pigments, which combine lower abrasiveness with optimal gloss, opacity, chroma and UV-protection. As a second building block a process for a special pre-treatment of high performance organic color pigments had to be found that would allow this component to attach easily to the inorganic carrier. A strong link such as the one created by this new technique is needed before the two pigment components can perform as one.

This contributes considerable value in use with respect to color saturation, gloss, opacity, strength and stability and allows the users to produce shear stable final colors. Ticos® offer a better cost to performance ratio than any of the traditional options.

One unique further benefit of the Tico® technology is a significant improvement in light and weather fastness. Unlike titanium dioxide, which has been known to exhibit photocatalytic activity, accounting for weather induced degradation mechanisms, the new titanium carrier pigments of Tico® act like UV absorbers and protect the sensitive organic pigment.

High performance organic colorants and inorganic pigments differ significantly with respect to their surface characteristics and their specific gravities. This is one of the underlying reasons why inorganic pigments allow themselves to be incorporated much easier into coating systems than their organic counterparts. The difference in dispersion properties becomes even more problematic when blends of inorganic and organic pigments are incorporated into coating systems.

The new Tico® technology resolves this problem by preparing a pre-dispersed form of the two pigments which cut in half the grinding times as compared to those for pure organic pigments.

Tico® offers two further advantages compared to straight blends:

• the oil absorption can be greatly decreased, allowing for higher pigment loadings in colorant pastes,
• the tendency for dusting is significantly reduced. Tico products offer approx. a 10-fold reduction in the lung respirative fine dust particle concentration compared to handling the tested organic pigments.

These new pigments are non-toxic and environmentally friendly alternatives to cadmium and lead containing pigments.

Additionally Ticos® comply with the purity requirements for safety of toys and qualify for the requirements of nearly all demanding applications in the coatings and plastic industry.

Thermo Control – How to turn Black into Cool? Smart Complex Inorganic Colored Pigments
One of the most striving challenges of this century is a reduction in energy consumption. For example Japan’s electrical energy crisis this year is the result of excessive use of air conditioning. If we were able to reduce the heat build-up effect, the energy consumption would have been much lower.

An unexpected functionality which we therefore need is the ability to control the absorption of the solar radiation by pigments without affecting their visible colouristic properties. This is what we call a thermo controlling pigmentation.

It is well known, that a white surface remains cool, while a black one heats up. The reason for this is the interaction of the coated object with the near infrared-radiation (NIR) emitted by the sun.

The sun emits almost 50% of its energy as IR-radiation. When this NIR-radiation is absorbed light is physically converted into heat. A surface interacts not only by absorbing radiation but also by emitting in the far infrared region until the equilibrium at a certain temperature is reached. By using a conventional pigmentation this effect could result in a severe build-up of heat.

Black surfaces strongly absorb NIR- and visible light, while white surfaces are effective in reflecting NIR- and visible light. But white or pastel colours cannot always satisfy the consumer’s demands.

Differently coloured pigments exhibit different, specific electromagnetic reflection profiles.

Focusing on the IR-range (780-2500 nm) a pigment like rutile yellow exhibits the highest reflection followed by titanium dioxide. On the other hand carbon black benchmarks the lowest reflection. Compared to carbon black a considerable higher reflectance in the NIR-region of the solar spectrum can be achieved by a specifically designed IR-reflecting spinel black pigment.

These different and characteristic reflectance curves are also mirrored in different heat build-up curves. In the heat build-up experiment a coated panel is exposed to artificial NIR-light in a closed box under defined conditions. The increase of temperature is measured together with the duration of exposure.

By reflecting the NIR-radiation more efficiently, this pigmentation gives coatings the ability to significantly reduce the surface temperature.

The advantage we can get from this approach is not only a reduction of the heat build-up that can be correlated with decreased energy consumption. The benefit is also an enhanced shelf life of the coating.

Due to the significant reduction in surface temperature, thermal degradation of the polymeric matrix is reduced. In addition temperature differences between day and night, direct sunlight and shadowed areas etc. will also be levelled out. As a consequence thermal warping becomes less effective.

This aspect of the use of thermo controlling pigments is very important, because this effect can be utilised for numerous other applications – not only housing, roofing and facades.

This is the key reason, why this approach truly deserves the label SMART. Not only because it contributes to a more environmentally aware use of resources, but also because of its exceptional ability to extend the shelf life of exterior coatings or polymers.

We are looking for efficient IR-reflecting pigments offered in different colour shades, exhibiting an outstanding outdoor durability to their intended use in exterior coatings and available on large scale.

In order to select the right pigments we need to dig a little bit deeper into theory:

Comparing pigments regarding their influence on the heat build-up always depends on the polymeric matrix. As a consequence the characteristic absorption of solar radiation needs to be taken into consideration when designing an effective IR-reflecting coating formulation.

When selecting an effective IR-reflecting pigment the most important factor is the TSR value. TSR means Total Solar Reflectance and is the integral total amount of solar energy that is immediately rejected by a surface material (e.g. coating). That means that it includes UV-, visible- as well as NIR-radiation and is thus a key figure to describe the heat build-up of surfaces.

Due to the fact, that the TSR covers the entire range of radiation between UV and NIR, e.g. black pigments show systematically lower TSR values compared to e.g. white pigments. Therefore only TSR values of similar pigments should be compared.

A high TSR value indicates efficient reflection – a low TSR value indicates a strong tendency to absorb NIR-light and therefore induce significant heat build-up. It is helpful to interpret the TSR value in relation to the matrix used and/or a reference pigment (e.g. titanium dioxide).

Furthermore it should be considered, that even small amounts of impurities can negatively effect the TSR of the coating. Even fillers, which are usually added to the paint, can potentially reduce the resulting reflectance in the near infrared.

On the other hand varying the pigment load (10% to 30%) does not generally cause notably different TSR values.

An additional influence on the scattering of electromagnetic radiation is given by the particle size distribution.

The scattering of light of the wavelength is dependent from the diameter of a spherical particle and the difference between the refractive indices of the pigment and the matrix. As a consequence smaller particles selectively reflect short-wave radiation, while larger particles more efficiently reflect long-wave radiation. This effect is used to control and adjust the scattering properties of pigments.

To achieve maximum reflection of solar radiation a NIR-reflective pigmentation of exterior coatings is required, that provides a high TSR value and the highest outdoor durability. All these requirements can be fulfilled by Complex Inorganic Color Pigments (CICP), which exhibit specially designed reflectance characteristics whilst retaining their excellent weather and light fastness as well as their exceptional temperature resistance.

These novel, IR-reflecting complex inorganic colored pigments offer a wide range of color shades from yellow to black. They allow the formulation of not only architectural, building and construction coatings, tiles, plasters etc., but also automotive exterior and interior applications like dash-boards, fuel tanks, etc.
Because of the reduced surface temperature the use of these pigments extends the shelf-life of the polymeric matrix through a minimization of thermo induced degradation effects and of course substantially reduces the heat build-up.

By that they take care for the customer’s comfort as a result of reducing the heat build-up and thus his electricity bill.