Lacquer Layers in Automotive Industry

Automotive lacquer finishes protect vehicle bodywork against the effects of, for example, temperature, moisture or salt while also meeting decorative requirements. Coating thicknesses and the mechanical properties of the finish are decisive for their function. FISCHER offers a variety of measurement devices for the quality control of lacquer finishes, allowing you, for example, to determine the surface hardness and scratch resistance with certainty.

Lacquer layers in automotive industry

Application notes

Mechanical characterization of lacquer coatings in automotive applications

In the automotive industry paint coatings are used as protection from corrosion and external damage. These lacquers are exposed to environmental influences such as extreme temperature fluctuations or moisture and salt. In addition, automotive coatings must exhibit a certain toughness to make them resistant to stone chips and scratches, for example in car washes. This requires the right balances between hardness and elasticity. 

Car paint has to fulfill different functions and possesses therefore various properties. A quick differentiation and determination of its properties is possible with the characteristic parameters obtained from the instrumented indentation test:

The Martens hardness (HM) and the Martens hardness after creeping (HMCR) are values which specify plastic and elastic properties of the paint coating. The indentation hardness (HIT) considers only the plastic portion of the material deformation. The hardness parameters provide conclusions about aging, curing, cross-linking, embrittlement through UV radiation, hardness change through temperature influences and the degree of polymerisation of the lacquer.

Fig. 1: Weathering rack in Florida of the company Atlas with various car body parts

One of the most important advantages of the instrumented indentation test is the determination of elastic properties. Parameters like the modulus of indentation (EIT), elastic recovery (hIT), creep at maximum load (CIT 1) and creep at minimum load (CIT 2) can be detected using this method. The parameters described above allow various conclusions regarding visco-elastic properties of lacquer coatings. These in turn show the vulnerability of the lacquer against weather influences, its susceptibility to rockfall, the ability to heal in case of scratches and the reflow behaviour.

Sample

HM

[N/mm²]

hIT

[%]

C IT 1

[%]

C IT 2

[%]

E IT

[kN/mm²]

A (mean)

(standard dev.)

42.9

1.2

23.4

0.8

18.4

0.2

-10.6

0.3

1,39

0.1

B (mean)

(standard dev.)

143.0

5.6

45.7

0.4

6.1

0.1

- 9.0

0.3

3,07

0.1

Fig. 2: Martens hardness plot and plastic and elastic measurement parameters for 2K automotive repair paints; A being a soft sample and B a hard one

Using the FISCHERSCOPE® HM2000 makes the determination of material characteristics like surface hardness, crosslinking, elastic modulus and healing behaviour in case of scratches simple and easy. In this manner, several chemical process parameters can be determined quickly during manufacturing or hardening of automotive paint coatings. Your local FISCHER representative will be happy to answer further questions.

Quality control of paint coatings on car bodies using individually created inspection plans

For a variety of reasons, assessing the quality of paint coatings on car bodies is increasing in importance. Narrow tolerance limits and strong demand for smooth finishes require precise measurements of the coating thickness according to clearly defined testing procedures. In addition, the measurement results should provide clues for potential process optimizations. Therefore, consistent inspection procedures – regardless of who is doing the measuring – are also essential.

Paint finishes on car bodies must fulfill a range of criteria: Not only should they provide sufficient corrosion protection (therefore requiring at least a minimum thickness) while simultaneously containing costs (minimum material waste), the color and texture must also be even and homogeneous. To check all these criteria systematically, test measurements should always be taken at the same spots, in the same way, regardless of who is currently executing the inspection.

Fig.1: Simplified surface development of a car body with defined measuring spots

Using simplified surface development drawings, precise inspection specifications can be displayed for the examiner, showing exactly where the paint coating is to be measured. However, such sequences are often very complex and therefore susceptible to operator failure.

Fig.2: Coating measurement according to pre-defined inspection plans with DUALSCOPE® FMP100 and FISCHER DataCenter IP software.

The FISCHER DataCenter IP (Inspection Plan) software makes it possible to create process-controlled inspection plans that can be loaded onto handheld DUALSCOPE® FMP100 measuring instruments. Enhanced by images and text, the inspection plan clearly guides the user step-by-step through the measurement tasks like a navigation system. The readings can then be down-loaded directly to the PC for easy evaluation, archival and printing (with customisable templates). For this purpose a wide variety of analysis and statistic functions, as well as supporting graphical displays, are available.

The FISCHER DataCenter IP software and DUALSCOPE® FMP100 handheld instruments put powerful tools of strategic quality control directly into inspectors’ hands: Structured measurement recording and extensive evaluation options help to highlight potential improvements in production processes, while step-by-step guidance through the complete measurement cycle not only minimizes errors and increases consistency but also makes these instruments suitable for use even by non-technical staff. For more information please contact your local FISCHER representative.

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Fischer Technology Inc.
Windsor/United States

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