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Very good post, I was really searching for this topic, as I wanted this topic to understand completely and it is also very rare in internet, that is why it was very difficult to understand.
Thank you for sharing this.
regards:
Husky pet preforms
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I preform a color (not transparent)
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I am working in Al Hafiz Crystoplast(Pvt)Ltd Pakistan we are using Husky injection moulding machine. we are facing problem of 45gm preforms "Stress lines on Body area.
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why is pet not used as any other thermoplastic in the industry
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Dear Sir
We would like to have your review or any comments on the IV drop rate of PET preform that related to shelf live and physical property. If we keep PET preform for than 3 months, what will IV like and what will the bottle property like?
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One simple test is to use a thermolator on the mold base control (usually a separate cooling circuit for mold bases) and run tempered waster (warm, not hot).
This acts by tempering the plastic and relieving it of stress. remember, all bottle want to return to a preform state given the chance. It is simple to do and economic.
And I agree with the comments made in regards to the preform gate quality, from my 6 years as an instructor and service tech with Husky injection Molding systems. I have see a lot of preform system set up with the incorrect and excessive hold pressure, this usually induces stress on the gate and therefore accentuate the stress cracking issue.
Fred
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SIR, I am working in ECO Pack in Pakistan.we have problem stress creaking in 500ml contour bottles.we are using A-84 grade pet resin.and blowing m/c is sbo8.is it moisture cause.
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What characterstic of PET reasin is most important for making 20 lit jar proform having weight of 730gms. Please specify accurately so that there is no scope for error as far as transparency of the preform is concerned.
Thanks
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Excessive drying temperature leads to thermal degradation and oxidative degradation of polymers.
As a result , undesirable final products containing acetaldehyde may be produced. Degradation reaction during melting acetaldehyde is larger using germanium catalysis (GeO2) than using antimony oxide (Sb2O3) catalysis.
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I am working in Ecopack limited Pakistan we r using husky injection moulding machine we r facing problem of thermal degradation in preforms
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Jorqe,
Well said I would say 80% is design of the base 15% process conditions and only 5% resin. I can prove that if the base and the process is correct then neither high IV or low IV will stress crack with 4.5vol carbonation. Providing that there is no other influences from chemical attack.
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BY: JORGE LARRA袮GA DIRECTOR OF KIMEX IN MEXICO.
The stress cracking IS RELATED IN 60% WITH THE DESIGN OF THE BOTTOM OF THE BOTTLE.
20% IS RELATED WITH THE RESIN HOMO-POLIMER OR CO-POLIMER AND THE REST IS PROCESS.
REMEMBER THE OLD BASE CUP BOTTLE WITH 2 LITERS WITH RESIN I.V. 76? NEVER SHOWS THIS PROBLEM, WHY?
NO AMORPHOUS ZONE. DESIGN OF THE BASE 100% CIRCULAR.
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I am the technology supervisor from PET in the Alcoa Latin America and the stress cracking is related with the IV and the copolymer type and level from the resin , sometimes depends on the IPA level the stress cracking could be more expressive with the higher IV , for example if the content of the IPA or DMT or CHDM is lower than the specified for some bottles so with the enviroment conditions and the type of carbonated beverage the stress can appear in the bottle base.(amorphous zone)
Rogerio Ortiz
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It could be cracked when manufactuered by the blow molder if the preform was'nt hot enough while stretching and blowing or the stretch rod is set to low. Plus the material distribution could of been incorrect and not have enough thickness to hold the pressure. Producers of carbonated drinks do burst tests to test for it. Alot of the time they find that the preform was not formed correctly in the gate area during the injection process. Theres lots of scenarios that could cause (stress cracking)
jwkinney
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It was normal some years ago to use resins with an IV of .76 for carbonated drinks. Then the problems of stress cracking raised its head and the IV was raised to .8 and now maybe .84 to combat stress cracking. What is important in my opinion is what is the IV in the raw material and what is the IV in the preform after molding. If the IV in the preform is much less than the IV of the resin then the process of molding is not correct. If you make a bad preform you can not make a good bottle. The subject of stress cracking should take into account many factors that may or may not be related to IV. The design of the base of the bottle has a very great impact on the resistance to stress cracking. Also how the filling line is working and the counter bowl pressure play a part in the precess of stress cracking. So does the chemicals that are present in the fillig area.When you have a preform with a higher IV the natural stretch ratio of that preform is significantly different to a prefrom with a lower IV. This assumes that the injection molding process is under control and the drying system is working correctly.
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How harder is the bottom of a bottle, earlier it will crack under pressure of carbonated drink inside. It'ssimple to understand it. Once a higher IV means a harder bottle, there you see a valid relationship between bottle construction, IV and Stress Cracking.
Please note that it isn't exactly higher IV a cause to Stress Cracking, but the fact that botomm of bottle is harder.
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I worked two years and a half under 90% of umidity. It was at Manaus, Amazonas, Brazil. Preforms used to get so saturated of moisture within three months of storage that a process of Stress Cracking after blow-mold bottles was almost unavoidable.
I don't have numbers or other data to show you that, beside my experience on it. Anyway, I can assure you that high umidity is very worse than aging.
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There is a distinct difference between aging and the ammount of moisture in a preform.It is possible for a preform to reach saturation of moisture in a short time under certain conditions. Where aging of preforms is determined by time.
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We would like to have your views or opinions on the moisture absorption rate of PET preforms against aging. Current studies have been performed on the moisture absorption rate of PET resins but does this have the same effect once the resin has been moulded?
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