BMW GS 93011-7 Method for Determining Color Change in Organic Materials Caused by Elastomers (Dye Difference)

The standard “BMW GS 93011-7 Determination of elastomer properties - Method for determining color change in organic materials caused by elastomers (dye difference)”, developed by BMW, a multinational vehicle manufacturer headquartered in Germany, describes two test methods for determining color change in organic materials caused by elastomers:

• Method A: Contact discoloration and migration discoloration
• Method B: Discoloration by subtraction

Paints used in direct contact with or in close proximity to elastomers may be discolored by the elastomers due to heat, contact pressure, or weather conditions at the point of contact or on the adjacent surface. Additionally, water or water/alcohol mixtures can release components from the elastomer, causing the paint surface to discolor when these liquids come into contact with the elastomer.

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

• Contact discoloration: This refers to the discoloration of the contact surface of the organic material with the elastomer.
• Migration discoloration: This refers to the discoloration of the surface of the organic material directly adjacent to the contact surface.
• Extraction-induced discoloration: This refers to the discoloration of the surface of an organic material by water or a water/alcohol mixture (1:1) containing components released from the elastomer. The alcohols used can be rubbing alcohol or isopropyl alcohol.

The following equipment is used in the tests:

• Hot cupboard with air circulation according to DIN 50011-2 standard.
• UV radiator with filter for absorption of radiation with wavelengths shorter than 280 nm.
• 150 ml beaker (tall type)

Elastomer test pieces are rectangular, preferably 2 mm plus/minus 0,2 mm thick, and have the following minimum dimensions:

• 12 mm x 25 mm for Method A
• 25 mm x 150 mm for Method B

If test pieces are taken from finished products, they should be cleaned with a 2% aqueous solution of a non-alkaline detergent. Vulcanized test pieces should be tested no earlier than 16 hours or no later than four weeks after vulcanization. Testing on finished products should be performed no later than three months after vulcanization. If this is not possible, testing should be performed on the consumer within two months of receiving the material.

The dimensions of the paint plates (method A and method B) depend on the dimensions of the elastomer test pieces according to the test arrangement of the methods and, if necessary, the irradiation device.

Testing begins 6 plus/minus 2 hours after drying. Intermediate conditioning of the paint boards is permitted for up to 7 days at approximately -20°C.

The testing procedures are as follows:

• Method A: Determination of contact-induced discoloration and migration-induced media discoloration. Elastomer test pieces should be placed between two paint labs, at least 40 mm apart and at least 20 mm from the paint lab boundary. To ensure proper contact between the elastomer samples and the paint sheets, the entire assembly is pressed together, for example using weights, to achieve a surface contact pressure of 5 to 10 kPa.

Heat treatment: The test piece assembly is conditioned in a heating chamber with air circulation according to DIN 50011-2 at 70°C plus/minus 2°C for 24 hours plus/minus 2°C. Care must be taken to ensure that the heating chamber is free of gases or vapors that could cause discoloration.

The paint sheets are then irradiated for 1 hour under a UV radiator with a radiation intensity of 1 kW/m² ^. The paint coating is visually evaluated to determine if there is any discoloration on the contact surfaces or in the environment.

• Method B: Determination of the washing effect when exposed to water or a water/alcohol mixture. Three sections of finished parts weighing a total of 5 g were cut into 50 m³ (150cm³ beaker) are conditioned at room temperature for 24 hours in the following liquids:
  • Deionized water
  • A mixture of 50 percent alcohol by volume and 50 percent deionized water by volume, denatured according to the quality requirements of the Federal Monopoly Administration for brandy.

Immediately after removing the rubber parts, the dyed plates are placed vertically in beakers for 24 hours at room temperature. After the test period is complete, the plates are exposed to light under a quartz lamp for one hour. Discoloration assessment is performed before and after light exposure.

In the high-stakes world of automotive engineering, where precision and reliability are paramount, standards like BMW GS 93011-7 play a crucial role in ensuring the quality and safety of vehicle components. This standard is part of a broader series dedicated to elastomers, the flexible, rubber-like materials essential for seals, hoses, and vibration-damping components in modern vehicles. This standard helps manufacturers mitigate risks such as material degradation, which can lead to failures in critical systems.

The BMW GS 93011-7 standard includes rigorous test protocols to verify material properties under real-world conditions. This standard specifically addresses the determination of coloration effects or dye indifference in organic materials caused by elastomers.

The primary purpose of this standard is to evaluate how elastomers can transfer dyes or pigments to adjacent organic materials such as paint, coatings, or plastics over time. This phenomenon, known as migration-induced color change, can compromise the aesthetics and functionality of vehicle interiors and exteriors.

Our organization, with its competent and experienced team, has been understanding the needs of its customers for years, providing them with the advanced testing services they need, and assisting them in the establishment, implementation, and improvement of management systems. In this context, we also provide testing services in accordance with the "BMW GS 93011-7 Determination of Elastomer Properties - Method for Determination of Color Change in Organic Materials Caused by Elastomers (Dye Difference)" standard.