the different grade of PET resin.
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| Different grades of resins are appropriate
for different end uses. Their specific qualities make them ideal for the
product that they have been designed to package. What qualities of PET
are important depends very much on the product for which the bottles are
Carbonated soft drinks (CSD)
Strength: The resins in PET bottles for carbonated soft drinks need very specific qualities. First of all the material must be strong enough to withstand the internal pressures of CO2 without distortion or expansion. It is determined to choose a resin with high I.V. and low copolymer.
In consideration of costumer's acceptance, a low level of crystallisation is needed to achieve clarity in drink containers. It is achieved by using a resin that has a low copolymer levels to add clarity and reduce the crystallization.
Although it is so important to achieve a perfect clarity as mentioned above, with soft drinks, this property is not essential because many soft drinks themselves are colored. In that case, the clear soft drinks can also be packaged in the colored PET bottle.
Sometimes the container for carbonated drinks can also be used for still water, however, some varies are still there.
Unlike carbonated drinks, the bottle filled with still water only needs enough strength to hold water and to stand against impact outside. The 0 .74~0.76 I.V. is enough in most cases.
Since clarity is one of the most important reasons why PET is used for water container, PET used in water bottles needs to be very clear and maybe even with a slight tint of blue. A resin with higher levels of copolymer adds to the clarity.
Because water is bland, having a container that keeps tasteless and odorless is imperative. Usually PET doesn't affect the taste of the product it protects. Therefore it becomes the key material for water package.
Juice -- hot fill drinks
Juices and many other drinks like tea, dairy and sport drinks or other high acid drinks are hot filled and hot pasteurized afterwards. In such cases, PET is not the right choice, as PET bottles will soften when containing water at 80 ? . With a hot fill temperature of 95 ? , PP is becoming popular in the hot fill arena, but its clarity is not comparable to that of PET. Consequently, the most common solution is mix other materials like 25% PEN into PET to increase its hot fill temperature. Alternatively, the crystallized PET neck could withstand a higher hot fill temperature. In conclusion, PET resins with a higher temperature and a faster rate of crystallization are preferred.
Strength and color & clarity
The factors of strength and color are not as important to juices as to CSD or water while the purity factor is important, as juices would be tainted by the taste of the plastic bottle that is not pure enough.
Beer is often regarded as an extension of the CSD market, however, it also requires hot fill and barrier qualities, as PET bottle allows oxygen to migrate in and carbon dioxide out, therefore oxygen will oxidize the beer composition, changing the taste of the beer and the way of overcoming this problem is resin barrier or coating barrier. Because the technologies used to make beer bottles are varied and the applications differ (cold filled or pasteurised), it is difficult to find a common trait. Making a bottle to meet the desired requirements has been the most important thing. The types of PET beer bottles typically used are: non-tunnel pasteurised, one-way tunnel pasteurised and returnable/refillable bottles.
Compared to PET used in CSD package, beer needs higher performance in both CO2 and O2 barriers. The level required depends on the type of beer, container size, distribution channels and environmental conditions (storage time, temperature and humidity levels). Improvements in barrier properties can be obtained via adding barrier coatings, creating mutli-layer bottles and scavengers.
Color, clarity and UV protection
Further than the barrier properties, most beers also need to be sheltered from UV (Ultraviolet) light. It can be obtained via colorants or UV additives added to the PET at the injection stage. Due to varied requirements for beer, resins that provide an adequate barrier, UV protection and clarity must be chosen.
Beer bottles do need strength to endure the CO2 pressure. I.V. between the 0.80~0 .84 are favorable choice. Due to its lightweight, not only the consumer benefit, also the transportation costs and energy consumption in delivery are decreased. Because PET bottles are so much lighter than alternatives, a truck can carry 60% more of the beverage and fuel saving of 40% and less air pollution.