A moulder supplies a syrup brand with amber 100 ml bottle preforms and a hair oil brand with clear ones, from one machine. Monday is amber, Wednesday is clear, and every switch costs a purge and a mould change. That is the daily pattern of pharma and cosmetic bottle preforms: small batches, many neck finishes and several colours. A 75 t machine suits the work because shots are small and changeovers are frequent.
This article covers what changes from water preforms, which PET grades are named for these uses, how to plan colour and mould changes, and how to estimate machine hours for an order.
Key Takeaways
- Pharma and cosmetic preform work can mean small batches, many neck finishes and colours, so changeover time can cost more output than cycle time.
- Reliance names its Relpet G5801 bottle grade for containers for cosmetics, hair oil, disinfectants and pharmaceuticals.
- Running colours from light to dark, and grouping jobs by mould, cuts purge and mould-change losses.
- Changing a neck finish means retooling both the preform mould and the closure mould, so agree the finish before steel is cut.
How Do Pharma and Cosmetic Bottle Preforms Differ From Water Preforms?
They can be smaller, run in shorter batches and come in colour, with a wide spread of neck finishes and weights. Acetaldehyde affects the taste of water most, while colour match, clean handling and batch records can matter more for syrups, lotions and oils.
Amber can be specified for light-sensitive medicines, and cosmetic brands may want tinted, opaque or clear preforms. Each colour is a masterbatch dosed at the feed throat, so its letdown ratio, its drying and its effect on the melt should be settled during the trial, not on the first production day.
Neck finish is the other variable. Packaging Digest's account of the PCO 1881 change on soft drink bottles shows how much a neck matters: moving from PCO 1810 cut the neck from 5.1 g to 3.8 g, but meant retooling both preform and closure moulds. A small bottle line faces the same trade-off on every new finish.
Pharma buyers can also ask for documentation on resin, colourant and process. Confirm what your customer's quality team needs before the first order, because records are hard to rebuild after a batch has shipped.
Which PET Grades Suit Pharma and Cosmetic Bottles?
Choose a bottle grade the resin maker names for these uses. Reliance, for example, describes Relpet G5801 as a general-purpose bottle grade used in containers for cosmetics, hair oil, disinfectants and pharmaceuticals, and says the Relpet family runs from 0.76 to 0.84 dl/g intrinsic viscosity.
Intrinsic viscosity, or IV, reflects the length of the polymer chains. Higher IV suits bottles that need more strength, while lower IV suits still products that do not carry pressure. The trial moulds article in this series explains how much IV a preform can lose in moulding and how to check it.
For containers that touch food or drink, check each grade's compliance statement. The SpecialChem listing shows every Relpet grade there stating compliance with US FDA 21 CFR 177.1630. Indian food-contact rules for PET are covered in the applications article in this series.
Check chemical compatibility for each new formulation as well. Some solvents and essential oils can attack plastics, so a storage test on filled bottles, agreed with the brand owner, is worth running before the first large order.
How Many Cavities Suit Small-Batch Preform Work?
Fewer than you might expect. On short runs, a four-cavity mould that changes quickly can deliver more good preforms per week than an eight-cavity mould that sits idle during long changes. Base the count on batch size and change frequency, not on clamp alone.
Fewer cavities also cut mould cost and make inserts cheaper to swap when a buyer adds a weight. The trade-off is output per hour, which the worked example below turns into machine hours for a real order size.
Clamp is seldom the deciding check for preforms, as the applications article in this series shows. Mould width, shot against the barrel and changeover time decide the count, so bring all three to the mould design review.
How Should You Plan Colour and Mould Changes?
Group jobs by mould first and colour second, and run colours from light to dark within each mould. A clear run after amber needs a full purge, while amber after clear needs far less. Plan the week so the hardest change happens once, not daily.
Our view: on a small PET machine that runs pharma and cosmetic work, changeover discipline deserves as much attention as cycle time. Write the changeover sequence down, time it and treat it as part of the process, with its own checklist and sign-off.
Purging PET also takes care. Melt held hot for long loses IV, and the PETplanet Rapid Guide to Perfect Preforms sets melt at about 280 °C, plus or minus 10 °C, warning that excessive temperatures may degrade it. Keep purge and idle time short, and do not leave a hot barrel standing full.
Changeover types for pharma and cosmetic preform work
| Change | What it involves | Planning tip |
|---|---|---|
| Colour, same mould, light to dark | Masterbatch change and a short purge | Run in sequence at the end of a mould campaign |
| Colour, dark to light | Long purge, possibly screw and hot-runner cleaning | Avoid where you can; schedule it at a planned stop |
| Preform weight, same neck | New core and cavity inserts, or a new mould | Keep several weights on one neck so closures are shared |
| Neck finish | New neck splits or a new mould, plus a new closure | Agree the finish with the bottle buyer before tooling |
What Should You Send for a Pharma or Cosmetic Preform Job?
Send each preform's weight, neck finish, colour and annual quantity, plus the batch sizes your customers order and how often they change. With that, cavity count, changeover plan and machine hours can be estimated together. See the 75 ton PET injection moulding machine page.
Frequently Asked Questions About Pharma and Cosmetic Preforms
Can amber and clear preforms run on the same 75 t machine?
Yes. Run clear first and amber afterwards within a mould campaign, because moving from a dark colour back to clear needs a long purge and sometimes cleaning. Keep separate masterbatch dosing records for each colour, so a customer complaint can be traced back to the resin lot and the run.
Does acetaldehyde matter for cosmetic and pharma preforms?
It matters less for taste than in water, but keep it low. Acetaldehyde forms when PET degrades in the barrel, so a high level also signals a process problem such as wet resin or excess melt temperature. Ask your buyer whether they set a limit, and test trial preforms against it.
Can one mould make preforms of different weights?
It can, if the mould is built with interchangeable cores or cavity inserts on a common neck. Changing weight then means swapping parts rather than the whole mould. Confirm this with the mould maker at the design stage, because insert changes still take time and each weight needs its own settings.
Is PET suitable for hair oil and disinfectant bottles?
Resin makers name it for these uses; Reliance lists hair oil and disinfectants among the applications of one Relpet bottle grade. Still, check compatibility for each new formulation with the brand owner, because some solvents and essential oils can attack plastics. A storage test on filled bottles settles the question.
How do I keep preform colour consistent across batches?
Fix the masterbatch grade and letdown ratio during the trial, dose it by weight, and keep a retained sample preform from each batch. Compare new batches against that sample under the same light. A change of resin lot or masterbatch lot is a reason to recheck colour before full production.
Related Articles
- What PET Products Can You Make on a 75 Ton Machine?
- Running Trial Preform Moulds Before Scaling Up Production
- Starting PET Preform Production With a 75 Ton Machine
Sources & References
- SpecialChem, Reliance Industries supplier page: Relpet: plastics and elastomers supplied by Reliance Industries
- Packaging Digest, A. Steeman: Short, Shorter, the Shortest
- PETplanet Insider, R. Unterlander and O. Brandau: The Rapid Guide to Perfect Preforms (Vol. 11, No. 11/10, p. 24)
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.
Actual injection moulding machine and process requirements vary according to the component design, material, mould, production volume, machine configuration and operating conditions. The information, examples, calculations and recommendations provided should be independently evaluated and verified for the specific application before making any equipment, process or production decision. Information obtained from third-party sources remains subject to the accuracy and limitations of those sources.
Limitation of Liability: Pratishna Engineers makes no representation or warranty, express or implied, regarding the completeness, accuracy or suitability of the information for any particular application. To the extent permitted by applicable law, Pratishna Engineers shall not be liable for any loss, damage, cost or consequence arising from reliance on or use of the information contained in this document. Final machine selection, configuration and application suitability should be confirmed with Pratishna Engineers based on complete and accurate project requirements.
