PSA D25 1413 Paint Coatings - Rubbers and Plastics Gloss Measurement

The standard “PSA D25 1413 Paint coatings - Gloss measurement of rubbers and plastics”, developed by the PSA Peugeot Citroen group, describes a method for measuring specular gloss at incidence angles of 20 degrees, 60 degrees or 85 degrees using a gloss meter (or reflectometer). This method applies to paint coatings applied to sheet metal, rubber or plastic, and to self-coloured rubber or plastic parts.

The measurement of gloss is based in principle on comparing the specular reflection factor of the test sample with a reference standard for a specific angle of incidence.

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

• Gloss refers to the directional reflectivity of a surface, which has the effect of showing more or less light reflections. Gloss is expressed in units of gloss (UB). The gloss value of black polished glass with a refractive index of 1.567 is set to 100 UB, regardless of the angle of incidence.
• The reflection factor expresses the ratio of the reflected light flux to the incident light flux.
• The specular reflection factor refers to the regular reflection factor corresponding to the fraction of the incident light flux that is reflected on a macroscopic scale according to Descartes' law.

For these tests, it is recommended to use Microgloss 20 degree, Microgloss 60 degree and Microtrigloss type gloss meters. The gloss meter consists of a housing that includes the following for a specific angle:

• A light source
• An optical system
• A receptor that is photosensitized only to visible radiation and provides information proportional to the luminous flux.

The angles and apertures of the measuring system shall meet the geometric conditions described in the annex to the standard (Annex 1). The base of the equipment shall contain a measuring window with dimensions less than 20 mm x 60 mm (for angles of 20 degrees and 60 degrees). The smallest dimension of the incident light beam read from the measuring plane shall be greater than or equal to 5 mm. A manual or automatic adjustment device shall ensure that the 0 UB value and the value of the reference standard are set.

In addition to the gloss meter, the following equipment is used in these tests: shammy leather or soft cloth or soft bristle brush, Joseph paper, pure soap (e.g. household soap) and mineralized water.

The calibration standard is an opaque black glass plate with a flat, polished surface that must be at least 5 mm thick to prevent deformation due to bending. This standard has its own brightness values ​​for 20 degrees, 60 degrees and 85 degrees, approved by organizations in Canada and Germany. Its use is limited to annual verification of secondary standards and equipment.

Secondary standards consist of opaque black glass plates with brightness values ​​evaluated against the calibration standard under various reflection angles. The calibration standard and secondary standards must be free from visible scratch marks in the areas of use. They can be wiped with a cloth and cleaned with a small amount of soapy water if necessary, then carefully dried by dabbing with Joseph paper.

The dimensions of the light trap (standard 0 UB) comply with the geometric dimensions described in the standard annex (Annex 2). The inner surfaces of the light trap are matt black (e.g. paint or broadcloth).

The measurement areas of the coating or part surface must be able to make contact with the gloss meter measurement window and meet the following conditions:

• The gloss meter window must completely cover the measuring area.
• The radius of curvature must be greater than 10 times the smallest size of the measuring window.

The gloss measurement is very sensitive to surface contamination or damage. The appearance of the surface to be measured should be visually inspected and recorded for dust marks, fingerprints, deposits, etc. The surface should be cleaned with a soft-bristled brush. In addition, the following cleaning methods should be applied to ensure that it is free from fingerprints and deposits: washing (with soapy water or a suitable product that does not affect the surface), rinsing, wiping if any, and drying. These operations should be noted in the test report. After these operations, it should be checked whether there are still some defects (streak marks, lime deposits).

Then, the brightness meter is placed in a place outside the range of direct light (sunlight, floodlight, etc.). The brightness meter should be used according to the manufacturer's instructions. The choice of illumination angle depends on the brightness value.

Gloss measurement in paint coatings is generally performed for the following purposes:

• Determining connector strength
• Determining the effect of pigment concentration
• Determining the effect of the ratio between pigment and filler
• Determining the effect of pigment type and degree
• Determining the stability of weathered coatings

The absolute value difference between two separate results obtained under repeatability conditions, defined as a probability of 95 percent, should not exceed 20 UB under a 2-degree angle and 60 UB under a 0,5-degree angle.

The absolute value difference between two separate results obtained under reproducibility conditions, defined as a probability of 95 percent, should not exceed 20 UB under a 3,3-degree angle and 60 UB under a 0,7-degree angle.

Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, it also provides certification and testing services defined in the “PSA D25 1413 Paint coatings - Rubbers and plastics gloss measurement” standard with its trained and expert staff and advanced technological equipment.