A bottler sends you a 1 litre water bottle and asks for a quote on preforms. Before anyone talks about cavities, check four things in order: the resin grade and food rules, the neck finish, the preform weight and wall, and the trial plan. Get those right and water bottle preforms on a 100 ton machine become a question of shot volume and cycle time, which you can calculate.
Each check below says what to ask for and why. Food-contact rules come first, because they decide which resins you can quote at all.
Key Takeaways
- Use a bottle-grade PET that its supplier lists for still water, and keep its data sheet and compliance letter on file.
- Get the neck finish drawing from the bottler before the mould is cut, because the finish fixes the closure and part of the preform weight.
- Wall thickness sets cooling time: a wall 20% thinner needs about 36% less cooling, and 20% thicker about 44% more.
- Cycle time, cavities and preform weight give the resin used each hour, which sizes the dryer.
Which Resin and Rules Apply to Water Bottle Preforms?
Packaged drinking water bottles fall under the FSSAI Packaging Regulations, 2018, which list PET to IS 12252 and require these bottles to have at least 85% transparency. Choose a bottle-grade PET that its supplier lists for still water, and hold its compliance documents before you quote.
The same regulations set an overall migration limit of 60 mg/kg, or 10 mg/dm², tested to IS 9845. Your customer will ask for the resin paperwork to support their own certificate of conformity, so request it from the resin supplier with the first order.
Reliance's data sheet for Relpet G5761 shows what a still-water grade gives you: intrinsic viscosity (IV) of 0.76 ± 0.02 dl/g, acetaldehyde of 1.0 ppm maximum, crystallinity of at least 50% and a melting point of 247 ± 3 °C. It lists the grade for still water and APET sheet.
IV is the figure to watch. The preform comes out with a lower IV than the resin went in, and the size of that drop depends on drying and melt conditions. The PET moisture and drying article in this series covers it in full.
Why Does the Neck Finish Come Before the Mould?
The neck finish fixes the closure, the thread and the support ring, and it carries a share of the preform weight. The neck is moulded to final size and is not stretched in blowing, so a later change means new neck inserts. Confirm the finish drawing with the bottler first.
Carbonated drinks show what is at stake. Packaging Digest reports that moving from the PCO 1810 finish to PCO 1881 cut neck weight from 5.1 g to 3.8 g and neck height from 21 mm to 17 mm, about 1.3 g less resin per preform, but it meant retooling both preform and closure moulds.
Water bottlers can use shorter, lighter finishes than carbonated drinks need. Which finish your customer uses is their decision. Your part is to confirm it, with tolerances and the closure supplier's drawing, before steel is cut.
A gram saved at the neck is saved on every preform. At 800 shots an hour, 1.3 g per preform is about 1 kg of resin an hour, as the worked example shows.
What Sets the Cycle for Water Bottle Preforms on a 100 Ton Machine?
Preform weight sets the shot volume each cycle. Wall thickness sets the cooling time, which made up about 85% of the cycle in one RJG trial on thick ABS bars. A thinner wall cools faster, so preform design can move output more than machine speed does.
RJG explains that wall thickness is squared in the cooling equation. A wall 20% thinner needs about 36% less cooling (0.8² = 0.64), while a wall 20% thicker needs about 44% more (1.2² = 1.44). RJG also adds about 20% to the calculated cooling time as a safety factor.
For the shot, add the preform weights across all cavities and convert to melt volume before comparing with the barrel. The 32 mm and 35 mm screw article in this series works through that step, and the products article shows why clamp is seldom the limit for narrow-neck preforms at 100 t.
Our view: quote water preforms on a cycle time from a trial or a similar running mould, never from a dry cycle figure. Cooling a thick preform wall takes time that no machine speed can recover.
What Should the First Trial Confirm?
Weigh preforms from every cavity, check the neck against the drawing, test preform IV against the resin's, and record the stable cycle. Those four results tell you whether the mould, the dryer and the cycle you quoted will hold once the job runs day and night.
Blow sample bottles from the trial preforms and check them with the bottler for clarity and fit of the closure. A preform that looks clear can still blow badly if its IV has dropped, so keep a few preforms from each cavity for the lab.
First-trial checks for a water preform mould
| Check | How | What it tells you |
|---|---|---|
| Weight per cavity | Weigh preforms from every cavity | Whether the hot runner fills all cavities evenly |
| Neck finish | Gauge against the bottler's drawing | Closure fit, before any bottles are blown |
| Preform IV against resin IV | Lab IV test on kept samples | Whether drying and melt temperature are under control |
| Stable cycle | Record once the mould is at temperature | The output figure you can quote |
| Blown bottle clarity | Blow samples with the bottler | Transparency against the 85% requirement |
What Should You Send for a Water Preform Quote?
Send the preform drawing with weight and neck finish, the bottle size, the resin grade, the cavity count and the daily output your customer needs. Shot, clamp and resin supply can then be checked together. See the 100 ton PET injection moulding machine page.
Frequently Asked Questions About Water Bottle Preforms on a 100 Ton Machine
What preform weight suits a 1 litre water bottle?
It depends on the bottle design, the neck finish and the top-load strength the bottler needs, so the bottler's drawing decides it. Lighter preforms save resin and cooling time but need thinner walls and tighter process control. Agree the weight before the mould is designed, because changing it later means new cores or cavities.
Can I add regrind to water bottle preforms?
Ask your customer before adding any. Regrind has been melted once already, so its IV is lower, and FSSAI allows recycled plastics in food contact only as it frames standards for them. Where clean in-house regrind is accepted, keep the ratio fixed and dry it exactly like virgin resin.
Why do water bottles need at least 85% transparency?
The FSSAI Packaging Regulations set that minimum for packaged drinking water bottles, so hazy bottles can fail the customer's checks. In moulding, white or hazy areas in a preform can come from slow cooling or degraded melt, so treat haze as a process signal, not a cosmetic issue.
How many cavities should my first water preform mould have?
Work back from demand. Divide the preforms you need each day by the shots per hour and the hours you will run, then round up and add a margin for rejects and downtime. Check that cavity count against the shot volume and mould width before ordering the mould.
Does a hot-fill bottle change the preform?
Yes. Hot-fill juices and isotonic drinks need a grade made for hot filling, with higher neck and body crystallinity; the products article in this series names one Indian example. The bottler will specify the finish and process, so treat hot-fill as a separate project rather than a variation of a water preform.
Related Articles
- What PET Products Can You Make on a 100 Ton Machine?
- Choosing Between the 32 mm and 35 mm Screw for PET on a 100 Ton Machine
- PET Moisture and Drying: Why It Decides Preform Quality
Sources & References
- FSSAI: Food Safety and Standards (Packaging) Regulations, 2018, compendium
- Reliance Industries: Relpet G5761 Technical Data Sheet (Aug 2022)
- Packaging Digest, A. Steeman: Short, Shorter, the Shortest
- RJG Inc.: How to Determine Injection Molding Cooling Time
Technical Disclaimer
Disclaimer: The information provided in this document is for general informational and educational purposes only. It is based on technical references and industry information available at the time of preparation and may be subject to change. It does not constitute engineering, technical, commercial or professional advice, nor does it constitute a quotation, specification, warranty or contractual commitment by Pratishna Engineers.
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