Case Study: 12-Cavity IML Bubble Tea Cup Mold

Engineering trade-offs and mass-production results as cycle time moves from 8 s to 10 s

1. Project background

As the global ready-to-drink tea market expands—especially cup formats such as bubble tea—demand for high-quality, consistent, recyclable plastic cups has surged. Traditional cups often use silk screen or shrink sleeves, with drawbacks such as poor wear resistance, label peel-off, and limited recyclability.

In-mold labeling (IML) places a pre-printed label in the cavity with a robot; during injection it bonds with the melt so the label becomes part of the part. Benefits include:

Labels that do not peel off
Scratch- and water-resistant surfaces
Fully automatic high-speed production
Strong, consistent branding

This case is a H T Mould 90700 bubble tea cup (about 700 ml) in a 12-cavity IML mold for a 480T press. Nominal data:

Item	Value
Product	90700 bubble tea cup
Cavities	12
Cycle without label	8 s
Cycle with IML	10 s
Daily output (with IML)	Approx. 103,680 pcs/day
Mold size	720×1100×625 mm
Press class	480T
Barrel temperature	310℃
Cooling water temperature	18–22℃
Cooling water pressure	0.5–0.6 MPa

Without labels the cycle can reach 8 s; with IML it extends to 10 s. The 2 s gap is the main engineering trade-off analyzed below.

2. Product and mold design

2.1 Part geometry

The 90700 cup is a thin-wall cylinder, typical wall 0.45–0.55 mm, height about 170–190 mm, rim about 90 mm. Key targets:

Rim roundness ≤ 0.3 mm
Bottom concentricity ≤ 0.2 mm
Stacking step clearance 0.1–0.15 mm
Label covers about 2/3 of sidewall height, 5 mm below rim, 10 mm above base

2.2 Mold structure

Mold size 720×1100×625 mm, weight about 3.8–4.2 t. Hot runner plus valve-gated cold sub-runner layout (as built). Twelve cavities in 2×6, pitch about 145 mm, width within 1100 mm.

Design highlights:

Hot runner: 12 valve-gate nozzles, individual zones, balanced fill; adjustable pin-close delay to avoid stringing.
Cavity/core steel: S136 or H13, 48–52 HRC.
Label retention: vacuum pores (0.5–0.8 mm) and shallow mechanical pockets per cavity; six- or three-axis servo robot with ionizer and vacuum assist.
Ejection: 6–8 ejector pins around the circumference plus air; ejector plate return with limit switches and hydraulic reset to avoid interference with the robot.

Overall mold flow layout for the 12-cavity tool

2.3 Cooling

With a tight cycle (10 s including labeling), cooling is critical. Core: helical conformal channels; cavity: dual-level annular circuits.

Core: 8–10 mm spiral channels close to the inner wall.
Cavity: upper and lower annular circuits, 25 mm apart.

Quick-connect ports, 0.5–0.6 MPa water, 18–22℃.

Moldflow check: at 10 s cycle, peak part temperature at ejection about 55–65℃, no sticking risk.

Core/cavity cooling circuit analysis

Helical conformal cooling effectiveness

Fill analysis

12-cavity balanced fill simulation

3. Process and cycle breakdown

3.1 Cycle timing: no label vs IML

Phase	No label (s)	With IML (s)	Reason for difference
Mold close	1.2	1.2	Same
Inject + pack	1.8	1.8	Same
Cool (incl. part of pack)	3.5	4.5	+1.0 label thermal barrier
Mold open	0.8	0.8	Same
Eject + take-out	0.7	0.7	Same
Label placement	—	1.0	+1.0 robot pick, place, vacuum
Total	8.0	10.0	+2.0

Of the extra 2 s with IML, about 1 s is label placement and about 1 s is added cooling because the label insulates the melt from the steel.

3.2 Why 8 s is possible without a label

Without a label, PP contacts steel directly (high conductivity), heat moves quickly to the channels, and the thin wall fills fast for packing and cooling.

3.3 Why labeling needs more time

IML film (often PP or PE, 40–80 μm) has thermal conductivity only about 0.2–0.3 W/m·K—an insulation layer between melt and mold. Cooling efficiency drops roughly 30–40%.

Cooling analysis

Post-IML thermal analysis with label barrier

Part temperature field after in-mold labeling

4. Machine fit (480T)

4.1 Clamp force

Projected area per cavity (incl. runner) about 95 cm²; 12 cavities about 1140 cm². At average cavity pressure 30–40 MPa for PP:

F = 1140 × 35 / 10 ≈ 399 t

480T is adequate with margin.

4.2 Tie-bar spacing and mold thickness

Mold width 1100 mm requires tie-bar spacing ≥ 1100 mm. This project used a domestic 480T with 1200×1000 mm spacing—verified in service.

Cavity layout and structural analysis

5. Labels and IML automation

Labels: 50 μm PP film, 6-color gravure plus antistatic coating; three-axis servo robot, 12 independent vacuum cups, placement ±0.1 mm.

6. Production issues and fixes

Poor label static pickup: added ionizing bar, vacuum holes, and tack points—scrap under 1.5%.
Short shots in some cavities: per-zone hot-runner control, thermal imaging, pressure-based tuning.
Oval rim: added rim cooling, air ejection, laser roundness check.

Warpage and dimensional quality analysis

Warpage and dimensional analysis

7. Economics (at 103,680 pcs/day)

Cost item	Unit rate	Daily (USD)	Per piece (USD)
PP resin (15 g/pc)	8.5/kg	13,219	0.1276
In-mold label	0.08/pc	8,294	0.0800
Electricity (90 kW total)	0.8/kWh	1,728	0.0167
Labor (2 people, 3 shifts)	300/person/shift	1,800	0.0174
Mold depreciation (5 yr)	Mold $50,641.38	192	0.0019
Maintenance/consumables	—	500	0.0048
Total	—	25,733	0.2484

Selling price about 0.35–$0.0651/pc, gross margin about 29–45%, payback about 8–12 months.

8. Summary

The +2 s IML penalty splits into ~1 s for label handling and ~1 s for cooling through the label—an inherent cost of IML. The 1100 mm mold width needs a wide tie-bar machine. Melt 240–260℃ is often safer in production.

IML is a system: mold, robot, label feeder, and press must be commissioned together—not bolted on piecemeal.

Production video:

Click the image to open the YouTube video.

Postscript: Data anonymized from a real production case. We welcome discussion on cooling optimization, label static control, and quick mold change.