Why Do PET Bottles Turn Hazy During ISBM?

이 기사가 입증해야 할 것

Diagnose pet haze by separating moisture degradation, overheating, crystallization, cold stretching, contamination, surface scuffing and cooling effects. A defensible baseline begins with Record whether haze is uniform, near the gate, in a shoulder band, on one bottle face or only on the surface. The first verification method is Compare under controlled lighting and by cavity. From there, the article follows only checks that can materially change the answer promised by the title. Where an exact operating value depends on the resin grade, bottle drawing, mold, or delivered machine, the approved project specification controls the final setting.

Identify Where the Haze Appears

Haze location

Haze location. Record whether haze is uniform, near the gate, in a shoulder band, on one bottle face or only on the surface. Compare under controlled lighting and by cavity. The diagnostic test should show whether haze location can physically create the observed defect before a repair or parameter change is accepted. If a change improves one region but worsens another, compare the material or energy movement between haze location and haze location instead of accepting the first visual improvement. Different locations point to different mechanisms, so treating all haze as the same defect wastes time.

Decide Whether the Defect Starts in the Preform

Preform appearance

Preform appearance. Inspect the preform before stretch blowing for milkiness, bubbles, discoloration or surface scuffing. Retain cavity-matched preforms when possible. The diagnostic test should show whether preform appearance can physically create the observed defect before a repair or parameter change is accepted. Where the outcome depends on material grade or tooling geometry, confirm the approved project limit and then use preform appearance as the next cross-check. If haze is already present before blowing, stretch parameters are unlikely to be the primary cause.

Check PET Drying and Moisture Control

Drying condition

Drying condition. Review dryer performance, residence time, hopper level and material exposure after drying. Use the plant-approved moisture verification method when PET moisture is suspected. The diagnostic test should show whether drying condition can physically create the observed defect before a repair or parameter change is accepted. When the project is near a machine or material limit, require a molding trial that isolates drying condition and then challenges drying condition under the same bottle specification. Moisture-related hydrolysis can reduce melt quality even when the bottle is still transparent enough to confuse diagnosis.

Melt heat

Melt heat. Check barrel, hot-runner and residence conditions for excessive temperature or long stagnation. Look for color shift, viscosity change or black specks accompanying haze. The diagnostic test should show whether melt heat can physically create the observed defect before a repair or parameter change is accepted. The safest interpretation comes from comparing at least several stable cycles and then verifying melt heat without changing the rest of the recipe. Increasing heat to improve flow can accelerate degradation if residence is already excessive.

본 특정 업무에 대한 근로 조건

Haze location

Record whether haze is uniform, near the gate, in a shoulder band, on one bottle face or only on the surface.

Preform appearance

Inspect the preform before stretch blowing for milkiness, bubbles, discoloration or surface scuffing.

Drying condition

Review dryer performance, residence time, hopper level and material exposure after drying.

Melt heat

Check barrel, hot-runner and residence conditions for excessive temperature or long stagnation.

Check Melt and Residence Heat History

Stretch temperature

Stretch temperature. A preform stretched outside its useful orientation window can show stress whitening or poor optical quality. Map axial temperature and correlate hazy bands with local thickness and stretch. The diagnostic test should show whether stretch temperature can physically create the observed defect before a repair or parameter change is accepted. A useful production trial keeps the resin lot and cavity identification fixed while stretch temperature is changed, followed by a separate check of stretch temperature. A cold band can be over-stressed while an overly hot band may lose desired orientation or crystallize differently.

Check Preform Temperature at Stretching

Crystallization

Crystallization. Localized overheating or slow cooling can promote visible crystallinity in PET. Check whether haze follows hot tooling zones and whether it changes with controlled cooling or temperature adjustments. The diagnostic test should show whether crystallization can physically create the observed defect before a repair or parameter change is accepted. The practical value of this check is that it turns crystallization from a vague setting into evidence that can be compared with crystallization. Blindly increasing cooling can shift the problem if the true cause is upstream melt history.

이 주제에 대해서는, 원스텝 ISBM 머신 포트폴리오 이는 공정 요구사항을 통합 수지-병 플랫폼에 연결하는 데 유용한 장비 관련 정보를 제공합니다.

Separate Crystallization from Stress Whitening

Surface scuff

Surface scuff. Scratches from transfer, ejection or conveyor contact can look like haze. Inspect the surface under magnification and compare parts before and after handling. The diagnostic test should show whether surface scuff can physically create the observed defect before a repair or parameter change is accepted. Use this result to narrow the process window, not to create a new universal setpoint; the next constraint to confirm is surface scuff. Changing resin or heat settings will not fix mechanical abrasion.

Contamination

Contamination. Mixed resin, incompatible regrind, degraded material or dirty conveying can cloud the bottle. Check material identity, purge condition and whether the defect begins after a resin or color change. The diagnostic test should show whether contamination can physically create the observed defect before a repair or parameter change is accepted. The expected response should be visible in a bottle measurement, defect map, or machine trend before the team proceeds to contamination. Small contamination can spread through several cycles and be mistaken for thermal drift.

Check Mold Surface, Handling and Contamination

Mold surface

Mold surface. Condensation, residue or damaged polish can reduce surface clarity. Inspect and clean cavity surfaces using the approved method. The diagnostic test should show whether mold surface can physically create the observed defect before a repair or parameter change is accepted. Once this check is stable, the next useful question is whether mold surface changes the same bottle region or affects a different part of the process. A mold-surface issue often repeats at the same cavity and location.

Confirm the Cause with a Controlled Trial

Confirmation trial

Confirmation trial. Change one suspected cause while keeping the rest of the process stable, then compare cavity-matched samples. Use haze location, preform evidence and thickness/temperature data to confirm. The diagnostic test should show whether confirmation trial can physically create the observed defect before a repair or parameter change is accepted. This checkpoint should be evaluated before confirmation trial is altered, because otherwise two process mechanisms change at the same time. A defect that disappears after many simultaneous changes has not been diagnosed and may return.

Questions that arise specifically in Why Do PET Bottles Turn Hazy During ISBM?

실질적인 결론

The working method for Why Do PET Bottles Turn Hazy During ISBM? is evidence first: establish haze location, isolate the effect of crystallization, and use confirmation trial as the final production check. Different locations point to different mechanisms, so treating all haze as the same defect wastes time.