Resource Center » What Causes the Waves That Appear in Some Plastic (Drinkware) Items?
Plastic drinkware sometimes has a wave pattern in the finished product. This is caused by the heating and cooling of the plastic material.
Plastic drinkware is created using a specific molding process. During this process, certain types of drinkware appear to have waves or darkened spots throughout the plastic. This happens to some types of cups with handles, especially coffee mugs and beer mugs, but it can also appear on plastic drinkware. In the promotional products industry, this is known as a "wave effect". The wave effect can sometimes be seen when a piece of plastic drinkware is held up to the light and different shades of the same color can be identified.
The molding process begins with a block-shaped object that is typically made of a high gauge pressure metal like steel. The design of the cup or mug is imprinted into the block, and then a second piece of similar metal is used to create another mold that lies on top of the first. This allows the manufacturer to create dozens or even thousands of cups at one time by using a machine.
The plastic material used to create the drinkware is heated to a specific temperature and poured directly into the mold. The second mold slides down on top of the first one to create the inside of the cup or mug. This is typically done using a computerized process wherein the molds move along a conveyor belt, the liquid plastic is poured in, and the second mold automatically moves into place.
Prior to pouring of the plastic, it’s first mixed to the proper consistency and tone or color. This is done in large multi-gallon drums and usually by computer, although some makers still do this step by hand. This is also known as the tinting process because various colors are mixed together to create a specific color. For example, to create a purple color, the maker mixes together red and blue dyes to create the right shade of purple. However, this mixing of colors can sometimes create the wave effect on the drinkware; there will be different shades and tones of purple when the mug is examined closely. It is possible that another purple mug created using the same process will look slightly different and even contain a different wave pattern.
The wave effect occurs when the plastic liquid is rapidly cooled after being poured into the mug. The change from the intense heat necessary to liquefy the plastic followed by the rapid cool down results in the wave effect. This effect is unique to the world of plastics and not found in other materials like glass. It doesn’t affect the strength of the finished promotional product.
The second mold used to create the drinkware is sometimes referred to as the stamp. Another machine creates a smooth surface by wiping off the excess plastic. After the plastic cools, the plastic drinkware pieces are removed and ready for the application of the design or logo. Some companies also use a release agent that’s applied directly to the mold, which makes the removal of the finished product much easier. With plastic items, this agent is typically an oil-based mixture that doesn’t impair the drying process but allows the cups to easily slide out of the mold.
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