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Weathering : Color Fading and Properties
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When ABS is used for extended periods of time in outdoor locations
or under fluorescent lights, discoloration or distinctive degradation
of properties will occur. This phenomenon is known as "weathering"
and this page will describe the corresponding mechanisms.
The cause of weathering-related ABS problems is light-induced
degradation of polybutadiene, and as a result of this, the effect
of rubber in generating impact strength is eliminated. Furthermore,
this type of degradation is characterized by its restriction to
surface layers.
 Change in color
- Discoloration due to degradation
of the coloring agent or discoloration of the base plastic.
Change in luster
- Changes in the base plastic
(i.e., degeneration or cracking)
Changes in properties
- Impact strength drops as
a result of the notch effect of minute cracks caused by weathering
of the surface.
We
recommend our Dialac® product line of weatherable grades
as countermeasures for weathering.
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Severe cases of discoloration due to weathering
(accelerated aging test, sunshine weathering, no rain) |
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It is necessary to take degradation of the coloring agent as a
result of weathering into consideration, and it is important to
carefully examine the coloring agent being used. In the case of
reds, blues, yellows, greens, and other vivid colors, it is important
to choose a coloring agent with good weatherability properties
in advance. Furthermore, changes in the discoloration behavior
of the added coloring agent are monitored in terms of color changes
in the molded component.
When coloring is being ordered, it is important to indicate that
"Weatherability is a requirement."
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Degradation
of plastic surface due to photo-oxidation
(accelerated aging test, sunshine weathering, examination using a scanning electron microscope)
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| Before exposure |
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After 500 hours of exposure with no rain
Little reduction in luster, but micro-level cracking has occurred.
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After 1,000 hours of exposure with rain
Breakdown of plastic components has occurred and the surface
has a sand blasted appearance, resulting in the loss of
all luster. (This is also known as color chalking.)
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Changes in characteristics due to photo-oxidation as image. |
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The depth of the degraded layer brought about by weathering
is in the order of several hundred microns in depth. The reaction
to photo-oxidation results in the generation of a thin yellow layer
at the surface, and this layer prevents the diffusion and permeation
of oxygen, and in addition, it also blocks out light. Accordingly,
any further photo-oxidation at the interior of the component is
prevented. If it is also desired to prevent the generation of this
degraded surface layer, we recommend the use of our weatherable
grades. |
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