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Interesting facts
...........about heat-resistant coating systems

There are many areas, e.g. in industry, in households, and in motor-vehicle operation, where higher temperatures are usual which commercially obtainable coating systems are not resistant against. When compared with other temperature-resistant materials, such as ceramics, or various metal alloys, temperature-resistant coating systems offer a number of benefits without relinquishing coating properties such as protection against corrosion, weathering, and chemicals.

It is solely due to the lack of heat stability of organic pigments that the colour selection of temperature-resistant coating systems as from  150 °C permanent load is limited.

 

Temperatures up to 80 °C

General industrial and construction coatings without any special requirements concerning resistance against higher temperatures. This sector is covered by commercially obtainable PVC or synthetic resin, 2pack, and hydro-coating systems. Examples of products for this sector included in our range are:


>> 1pack primer 1943

>> Wetterwart 1pack synthetic resin paint

 


Temperatures up to ~100-120 °C


Not an extreme temperature load as far as mechanical and anti-corrosive properties are concerned. However, synthetic resin systems in particular may show distinct changes in gloss and colour, and considerable losses of quality can even be anticipated for 1pack PVC coatings.

 


Temperatures up to 150 °C


In this temperature range, corrosion protection and mechanical properties work without any problems in 2pack systems and special synthetic resin formulations. Changes in gloss and colour are possible in 2pack systems. Examples of products from our range for this sector are:


>> priming coat SL-1022

>> 2pack acrylic paint 966

 


Temperatures from 150 - 200 °C


This is the beginning of the temperature range which requires special formulations in order to achieve good corrosion protection and a good mechanical properties profile. It is possible to formulate almost the entire RAL colour range and different gloss levels with limitations in colour and gloss stability for thermal loads. The basis for binders are baking enamel systems based on polyester melamine, 2pack epoxy resins, and modified silicone/acrylic resins. Examples of products fromour range for this sector are:


>> 2pack EP primer 837

>> 2pack Thermo°Acrylic 968 (colours acc. to RAL)

 


Temperatures from 200 - 280 °C


The products lending themselves to this temperature range are modified 2pack acrylic systems, 1pack silicone and silicone acrylic coatings with very good property profiles. In particular, black, grey, and aluminum effect colours can be formulated for this temperature range in excellent product quality. There are numerous other RAL colours which can also be represented with good colour stability. Examples of products for this sector from our range are:


>> 2pack Thermo°Pox 250

>> 1pack Thermo°Acrylic 2206

>> 2pack Thermo°Acrylic 968 BWB

>> 2pack Thermo°Acrylic 968 PROCON

 


Temperatures from 280 - 650 °C

Formulations for this high temperature range are only feasible with suitable silicone resins and selected pigments. Silicone resins are high-molecular substances containing silicon and oxygen as builder elements and which have been modified with organic groups. All organic components "burn" at high temperatures, and a silicate structure remains which binds the pigments to the surface as a tough film in a fixed coat. Additional metal pigments are often used as stabilisers for temperature ranges above 400 °C. Examples of products from our range for this sector are:


>> 1pack-Thermo°Zinc 600AL

>> 1pack Thermo°Silicon 2227

>> 1pack Heat°Resist MS 600C

>> 1pack Heat°Resist 600ESI

 


Surface Preparation

As with all other coatings, in particular for heat-resistant applications, proper preparation is vital for the functionality and durability of the coating system used.

For coatings in the temperature range up to ~200°C, the surface needs to be clean, dry, and free from rust and grease. Imperfect surfaces should, however, be blasted as oxide layers, for example, may chip off metals at high temperature loads due to the differences in thermal expansion coefficients.


Phosphated surfaces are normally ideal for coatings. However, they are unsuitable for highly heat-resistant systems as from ~200-250°C as the phosphate layer is destroyed under thermal stress and therefore, adhesion of the coating to the substrate is no longer possible.

 

For coatings which are permanently exposed to temperature loads of >200-250°C, blasting as surface preparation is mandatory in accordance with Sa 2,5 (ISO 12944) in order to achieve optimum results with regard to long-term protection and adhesion.

 

 

Drying

With classical silicone resin systems, the coated parts are dried purely physically by exposing them to air. In most cases, this is sufficient to permit both assembly and shipment. However, the film only attains its ultimate resistance in these coatings through interlacing during the coating's exposure to temperature loads. As a rule, the drying time required is between 30 and 60 minutes at object temperatures between 220 and 250 °C..

 

Modern, highly heat-resistant coating systems based on polyorganoslioxane technology, e.g. our series „Heat°Resist“ and „Silico°Therm“ products, dry out almost completely at room temperatures utilizing ambient humidity. Compared with classical silicone resin coatings, they therefore provide decisive benefits with regard to hard-drying and resistance against mechanical and chemical stresses. An additional advantage of these modern systems is that they are smoke- and odour-free, e.g. during the initial firing of stoves, barbecue equipment, furnaces, etc.

 

1pack and 2pack systems for temperature ranges up to 280°C. do not normally require any higher temperatures or special ambient conditions for drying out and hard-drying.