Paint Analysis

In addition to paints and varnishes, we also analyse inks, polishes, adhesives, plastics, putties and mastics.

We have particular expertise in the analysis of :-

Much of our analytical work is carried out with the aim of establishing the reason for problems connected with the manufacture and use of products. As well establishing the cause, our aim is to provide a solution to these problems.

Analysis of Substrates

Examples of this type of analysis include the identification of preservatives in treated timber, the detection of metal pre-treatments and the identification of surface contaminants giving rise to adhesion problems. The chemistry and topography of surfaces have a profound influence on the service life of coatings applied to them and for this reason we employ a variety of techniques to investigate surface properties. Fourier Transform Infrared spectroscopy (FTIR) coupled with attenuated total reflectance (ATR) techniques can provide information on the chemistry of the topmost few microns of a surface. In situations where first few monolayers of a surface are of interest then X-ray photoelectron spectroscopy (XPS) or secondary ion mass spectrometry (SIMS) may be necessary.

There are situations where a visual representation of the surface is required and here the techniques range in sensitivity from optical microscopy through scanning electron microscopy (SEM ) to atomic force microscopy (AFM). The latter technique is capable of mapping the topography of a surface virtually down to the atomic level.

None of the above techniques are applicable if you need to assess the state of blast cleaned steel prior to painting. We can supply you with test papers that will enable you to carry out a simple, rapid, on-site test for the soluble iron salts that, unless removed, will be the starting point for under-film corrosion.

Analysis of Raw Materials

The analysis of the resins, pigments, solvents and additives that are used in the manufacture of paints and inks requires the use of a variety of techniques. At the simplest, QA, level it can often suffice to use FTIR to obtain a "fingerprint" spectrum which can be compared with that of a reference material. If more detailed analysis is required, then GC-MS is an excellent method of separating and identifying the components of solvent blends. The same technique, used in conjunction with a pyrolyser, can be used to identify polymer resins and other involatile organic materials such as organic pigments.

The detailed analysis of inorganic pigments and extenders usually involves elemental analysis such as inductively coupled plasma-atomic emission spectroscopy ( ICP-AES ) or X-ray fluorescence spectrometry ( XRF ). There are some cases where the trace impurities in a sample can give useful information regarding its origin or can be used to confirm that a particular grade of material has been used. In such case we can extend elemental analysis to determine trace elements at part per million levels. In situations where even detailed elemental analysis does not provide a conclusive identification, then for crystalline materials, X-ray diffraction ( XRD ) can often provide the information required.

Analysis of Fully Formulated Coatings

We can analyse paint and inks either before or after they have been applied. One of the simplest types of analysis we carry out is a fingerprint comparison aimed at answering a question such as "Is this paint sample really Truelux Gloss?". Although paints, unlike humans, do not yield unique fingerprints, we can use a number of different analytical fingerprinting techniques (e.g. FTIR, GC-MS and elemental analysis) to show whether two samples are so similar that it is highly probable that they have a common origin.

The ultimate in the analysis of paints and inks is to identify all the components present together with their relative proportions. A full quantitative analysis of this type can be a lengthy and expensive undertaking and we generally recommend that we start with a simple qualitative analysis in order to establish the nature of the solvents, resins and pigments present. There are a number of reasons that clients require full quantitative analysis. In some cases they are trying to match a product that they sourced several years ago but now can no longer obtain. Another common reason is that they wish to match an historic paint which is no longer made. The re-painting of cherished aircraft, boats and cars and the need to match original paint on listed buildings are all examples of situations where detailed information regarding composition is requested. We always check if a full analysis is really required or whether a modern paint of the same colour would suffice. In some cases it is more appropriate for the client to use our colour matching service.

Clients, who are not paint manufacturers but intend to use our results to have a paint custom-made, are always advised to liaise with their prospective paint manufacturer before commissioning any analysis. This ensures that we provide the amount of detail required by the manufacturer.

Analysis of Multi-layer Coating Systems

A correctly applied paint system, e.g. a primer-undercoat-gloss, will have the correct components applied in the right order at the appropriate film thicknesses. We can check all of the above provided we are supplied with one or more thumbnail-sized intact flakes that include all the layers present from the topcoat down to the substrate. In some cases all that is required is to section the flake and examine it using optical microscopy. This method will enable us to determine the overall film thickness of the flake. The thickness of the individual layers can also be measured providing there are sufficient differences in colour between them.

The techniques used for the analysis of fully formulated coatings can, in principal, be applied to the identification of the individual layers of a paint flake. In practice the only limitations are the size of the flake and the ease with which it can be dissected to reveal the layer of interest. In situations where an elemental analysis is sufficient, Scanning Electron Microscopy-Energy Dispersive Spectrometry (SEM-EDS) is particularly useful since it enables the elemental composition of the individual paint layers to be determined without the need to dissect out each one.

Analysis of Fibrous and Particulate Contaminants

As a general rule, any fibre or particle larger that 15 microns will form a visible blemish if it is located on or very close to the surface of a gloss finish. Contamination can occur during the manufacture or application of paints and in some cases can be caused by the deposition of material during service. Examples of contaminants that we have identified include gelled resin particles introduced during paint manufacture, fibres from spray booth air filters deposited during motor vehicle refinishing and iron dust from a machine shop eating into the surface of paint on cars parked nearby. Those interested in more details on the subject are referred to our publication Analytical Study of Particulate Contaminants (TR-1-85). Please contact PRA Analytical Services if you would like a copy.

This is one area of analysis where success depends on a clear understanding of the circumstances that resulted in contamination. Our first task is always to obtain as many reference samples of suspect contaminants as possible. We find that the most useful techniques for identifying the contaminants, once they have been dissected from the film, are FTIR, SEM-EDS and polarised light microscopy.

Contact PRA Analytical Services for further details.