Dosages of UV masterbatches

Dosages of UV masterbatches

Investigation of the effect of a NOR-HALS masterbatch on the properties of ABS/PC in automotive interior applications

Injection-molded components in the automotive industry, such as door panels, glove box components, and center consoles, are predominantly made from (ABS+PC) compounds. The reason for this is material properties such as:

  • High heat resistance, as well as high rigidity and hardness
  • High impact strength
  • Good antistatic properties
  • Poor flammability

However, the greatest challenge for such components is the long-term resistance to the UV portion (300-400nm) of sunlight, which is harmful to plastics. Inadequate or no UV stabilization would result in a deterioration of mechanical properties and/or changes in surface characteristics (e.g., fading, discoloration, or cracking). To avoid such undesirable effects, stabilizers are usually added to the polymers. Processors mix the UV active substance, which is in the form of a masterbatch, with the plastic at certain dosage levels during the molding process. The dosage (wt.-%) of the masterbatch is selected to ensure both sufficient stabilization effectiveness and cost-effectiveness. This results in specific dosage levels (usually 1.0-2.0%) of the UV additive in the final article.

Objective:

Whether and, if so, how the addition of 0.5%, 1.0%, 2.0%, and 3.0% NOR-HALS masterbatch (LV058/16SAN) affects the mechanical properties (impact strength, flexural strength, and heat resistance) of ABS/PC (Novadur Ultra 4105) was examined in detail in the current project of GODIPLAST GmbH.

Figure 1: Verwendetes Bewitterungsgerät Xenotest Beta+ von Atlas Material Testing Solutions

Procedure:

For this purpose, multipurpose test specimens of type A according to DIN EN ISO 3167 with different dosage levels of UV masterbatch were produced by injection molding. Since optimal dispersion of the NOR-HALS active substance in the base material has a significant impact on the validity of the entire study, the 5 compounds were processed on a single-screw extruder beforehand. Subsequently, ISO bars (80x10x4 mm) were cut from the 450 multipurpose test specimens by sawing off the shoulder parts. Additionally, a double-V-notch according to ISO 179-1/1fA was incorporated into 250 samples.

A total of 360 test specimens were exposed in the weathering test device Xenotest Beta+ by ATLAS MTS according to VDA 75202 ("Automotive interior materials: Colorfastness testing and aging behavior against light at high temperatures: Xenon arc light") for a duration of 220 hours.

After every 55 hours, a series was removed, and the following mechanical test procedures were conducted:

  • Charpy impact test according to DIN EN ISO 179,
  • Flexural test according to DIN EN ISO 178,
  • Heat deflection test according to DIN EN ISO 75-1, -2, -3.

Furthermore, an evaluation of the color change of all exposed samples was conducted using a gray scale according to DIN EN ISO 105-A02.

Figure 2: Mit gekerbten ISO-Stäben bestückter Warenträger zum Einsetzen in Expositionsgerät

Insights:

The results obtained from the individual test procedures allowed the determination of the optimal dosage of NOR-HALS masterbatch for each specific requirement (impact strength, flexural strength, heat resistance, and colorfastness) of the component. Additionally, it was possible to answer further questions, such as:

  1. Does the position of the weld seam relative to the aged surface of the specimen during the HDT test affect the heat deflection temperature [°C]?
  2. How does the impact strength [kJ/m2] behave when the orientation of the aged surface relative to the hammer edge is changed during impact testing?
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