Colorimetric Evaluation of VW 50195 Exterior Automotive Paint Coating

The standard “VW 50195 Colorimetric evaluation of exterior automotive paint coating” developed by the Volkswagen automobile company describes the evaluation criteria for the evaluation of color deviations for body-colored paints and the measurement and evaluation conditions for the device-based determination of color differences.

For the purposes of this standard, the following definitions apply:

• Solid paint refers to the paint structure that mainly has color pigments that exhibit diffuse reflection behavior. The color impression is largely independent of lighting and observation direction.
• Effect paint refers to the paint structure containing directional reflective effects (aluminum flakes or the like) and diffuse reflective color pigments. The color impression depends largely on the selected lighting and observation direction.
• Effect angle (test angle), the effect angle is the angle measured from the angle of reflection of the incident light in the direction of the incident light beam (DIN 6175 Colour tolerances for automotive coatings - Solid and effect coatings).
• Reference refers to the reference of the brand specified by the relevant process engineering department (original color tone, standard, target value or similar).

As test apparatus, measuring devices are used to perform a color measurement according to the standard “DIN 5033-4 Colorimetry, spectrophotometric method” (spectral method) at the required test angles.

Due to the reflective behavior of solid paints, primary measurements under a single illumination and observation angle are sufficient to define color.

Suitable measuring patterns can be 45/0 or 0/45 (according to standard DIN 5033-7). The illumination pattern can be circular in the case of the 45/0 pattern, and circular in the case of the observation pattern 0/45. Effect colors should be measured at an illumination angle of 45 or vice versa under an observation angle of 5.

Calibration is carried out according to the manufacturer's specifications. Calibration is checked by means of a control measurement on a gloss colour standard. Colour differences referred to the first measurement of the colour standard are recorded for all test angles. The colour shall differ by no more than 1/6 of the specified tolerance. If this value is exceeded, the measuring system is no longer used in the context of this standard. The test equipment is monitored at regular intervals by means of control measurements on several gloss colour standards. Test standards whose surface and colour appearance remain constant are used for this purpose. If inconsistent values ​​are detected, appropriate measures are taken.

The sample surface must not be marred by surface defects (dirt, scratches, craters, polish marks, etc.). The packaging material must be selected accordingly. Samples may only be cleaned in exceptional cases. This must be recorded in the test record.

The measuring point on the sample should be as flat as possible, as the specified angular arrangement cannot be made on inclined surfaces. The measuring points should be agreed with the test experts. Colour data for a measuring location should be formed from the average of at least 5 separate measurements. Reference and sample measurements should be made at constant room temperature.

Samples that cannot be measured directly due to their shape can be checked as follows:

• Measurement of a flat test panel that has also been painted (minimum 50 mm X 100 mm) with the same substrate and structure as the component. There should be no visual colour difference between the component and the test panel. This should be used as a sample for colour measurement. Measurement should be made using suitable measuring instruments.
• The exact location of the test panels and the type and installation of measuring instruments must be agreed with the testers.

Colour changes must be calculated according to the reference defined in accordance with the DIN 6174 standard.

Due to technical factors, revisions of scaling and weighting factors may be made during the production phase. These parameters are defined by the relevant process engineering department of the brand.

The size of the scaling factors depends on the color locus. It takes into account the effect of the color locus on the visual acceptance of chromatic aberrations.

The size of the weighting factors depends on the type of connection (direct or indirect transitions).

The overall color change as a function of the scaling factors is calculated by the release procedure as follows:

• Procedure A: This procedure evaluates the maximum, angle-dependent overall color change.
• Procedure B: This procedure evaluates the overall color change determined by the angle.

Among the numerous tests, measurements, analyses and evaluation studies carried out for businesses in various sectors, our organization also provides testing services defined in the “VW 50195 Colorimetric evaluation of exterior automotive paint coating” standard with its trained and expert staff and advanced technological equipment.