Contents
1What are Black Specks? Why so expensive
Black Specks or black spots and burnt plastic, are black-brown contaminants in transparent, translucent or light parts, from barrel-held resin heated too long until it degrades into Carbon (Carbon Deposit) Then flaking into fresh resin in the next shots
Small specks still hit quality gates and delivery, especially transparent or light parts:
- Higher Rework and Scrap Past part or buyer speck gates
- Downtime Stopping to inspect nozzle, check ring, screw or Hot Runner
- Lot-reject risk From OEM customers, especially Automotive and Medical
25 root causes of carbon
Carbon never comes from one factor. It involves resin, temperature, time, oxygen and flow-path state. Five check groups:
| Cause | Explanation | How to check |
|---|---|---|
| 1. Dead Spot | Barrel-screw dead spots resin barely flows, such as check ring, nozzle, adapter | Remove nozzle and adapter, inspect with borescope |
| 2. Wrong set temp | Actual or set temperature above resin limits | Compare datasheet, check heater and thermocouple |
| 3. Long Residence Time | Resin held in barrel too long (small Shot Size with big barrel) | Residence Time = Barrel Capacity / Shot Size x Cycle Time |
| 4. Incomplete material change | Switching resin or color with old resin still in the path | Log Color Streak traits and first-spot timing after change |
| 5. Worn screw or check ring | Worn or scratched surfaces trap resin into degrading | Check in PM schedule |
3Science: Thermal Degradation and Hang-up
Past the resin maker melt-hold time, polymer chains start Chain Scission (chain cutting) and Cross-linking With enough heat or time, carbon builds as thin layers on hot metal
Technicians call held-resin zones "Hang-up Area" Areas rotational Shear Force never reaches: screw flights (Screw Flight), behind tip (Behind Tip), check valves and nozzle lands
4Why plain-resin purging fails
Plant tradition purges new resin over old or runs cheap pellets (such as HDPE regrind). It is physically capped:
- Insufficient viscosity: Standard resin follows old tracks, creating no new shear to pull carbon
- No Cleaning Agent: Plain polymer only, no coating or residue-pulling chemistry
- Material used with no stop criteria: Volume climbs while dead-spot residue stands
- Long color-change scrap: Old-color streaks persist until flow path and root terms are handled
5How ASACLEAN removes carbon
ASACLEAN is a purpose-built Purging Compound from Asahi Kasei, Japan, on Mechanical Purge Mechanical Purge With 3 principles:
- Designed Rheology: High-melt-viscosity matrix polymer builds massive Shear sweeping residue off screw surfaces
- In-pellet Cleaning Agent: Coating and absorbing chemistry wrapping carbon against re-sticking
- Particle Action (glass-fiber grades): Glass fiber micro-sands metal surfaces inside to take hardened residue off
6Match grade to job
Wrong grades swing results, especially glass-fiber (GF) Glass-fiber (GF) Versus Glass-fiber-free (Non-GF)
| Situation | Suggested grades | Why |
|---|---|---|
| Heavy or deep carbon · no Hot Runner | newEX, RX (GF) | Glass-fiber grades for hard residue per maker terms |
| Hot Runner · no glass fiber | RU, RE, SL, PF (Non-GF) | Maker-listed for Hot Runner; verify temperature and flow path |
| Super Engineering Plastic (PEEK, PPS) | PF Or PX2 | 280–420°C span; PF glass-fiber-free with Hot Runner vs PX2 glass-fiber barred from Hot Runner |
| Frequent color change · fast purge | GL3, RU, RE | Universal Purge across wide resins |
Still unsure? Try 1-minute grade quiz Or consult CSC technicians Free
7Standard Carbon Removal Purge steps
With grade picked, heavy-carbon purging runs:
- Stop old-resin feed · run the barrel near empty
- Verify TDS range and bans of the picked grade plus old-resin limits
- Set starting amounts from shot size, barrel capacity, Hot Runner and contamination level
- Set Back Pressure and Screw Speed per SOP, tracking pressure and discharge
- Soak-step only where that grade manual allows, timed in the SOP
- Feed new (production) resin to Rinse Rinse ASACLEAN out to true resin color
- Start production — discard first shots for safety
Want technicians to design your machine steps?
Send machine model · barrel size · resins used. We calculate amounts and steps free.
8Stopping carbon return
Purging fixes the consequence. Prevention Prevention Is what leading plants run:
- Routine Purging: Schedule from defect history, resin type and stop windows. No single frequency for every line. More at Routine Purging article & Sealing
- Pre-stop Sealing: Hold ASACLEAN in the barrel instead of held resin, cutting overnight and weekend carbon
- Control Residence Time: Pick barrels not oversized vs shot size
- Inspect Dead Spots: Cover nozzle, adapter, check ring and flow path in risk-based PM
9FAQ
What causes Black Specks in injection machines?
Black Specks usually involve resin held in dead spots or hang-up areas, degraded by temperature, time or oxygen, flaking into fresh resin on release. But check material, dryer, nozzle, Hot Runner and worn parts too.
Which ASACLEAN grade removes carbon?
Pick from resin, temperature, residue level and flow path. Non-Hot-Runner systems may consider glass-fiber grades like newEX or RX. Hot Runner needs maker-listed Non-GF grades with manifold, nozzle and gate limits verified first. (RX: Not yet available in Thailand)
Does ASACLEAN attack screws?
Built for Mechanical Purging, but fitness depends on grade, temperature, equipment and steps. Follow the TDS, especially glass-fiber grades and fine flow paths. Never conclude one formula fits every system.
How often should Routine Purging run?
No single frequency fits every machine. Set from Black Speck history, resin type, residence time, stop tables and trial results, then tune cycles to real reject data.
Why order from CSC?
CSC has distributed ASACLEAN in Thailand 30+ years. Technicians trained directly by Asahi Kasei can visit sites to set up and calculate ROI free. More at Contact page